Review

P2X7 receptor in normal and cancer cells in the perspective of nucleotide signaling

Damian Matyśniak1, Magdalena Oslislok2 and Paweł Pomorski1✉

1Laboratory of Molecular Basis of Cell Motility, Nencki Institute of Experimental Biology of Polish Academy of Sciences, Warsaw, Poland; 2Department of Embryology, Faculty of Biology, University of Warsaw, Warsaw, Poland

Nucleotides are the most common compounds produced constantly by living organisms. They are involved in most cellular processes like the synthesis of other nucleotides and nucleic acids, generation of energy needed for the maintenance of cells, and molecular signaling. In the 70s sir. Geoffrey Burstock discovered a new class of transmembrane proteins – nucleotide receptors responding to nucleotides and their derivatives. For historical reasons, we distinguish two main classes of nucleotide receptors: P1 – which are G protein-coupled adenosine receptors, and P2 – nucleotide receptors that respond to ATP and its derivatives. Additionally, the P2 receptors family can be divided into two subgroups: P2Y – G protein-coupled receptors and P2X cation channel receptors. This paper focuses mainly on the most researched receptor in the nucleotide receptors family – the P2X7 receptor – presenting it in the background of the nucleotide signaling landscape. Almost thirty years of extensive studies on the receptor contributed to understanding protein structure, splicing variants, and mechanism of action in somatic cells. Despite such a wide spectrum of research, the role of the receptor in cancer progression is still undetermined. In many reports, we can find information about the anti-tumorigenic role of this receptor caused by activation of the cell death mechanism after membrane pore formation. These results, however, contradict other studies in which the same receptor is known to promote cancer development through stimulation of proliferation and activation of pro-survival pathways. Ultimately, all this gathered knowledge points to two faces of the receptor in tumor progression. Therefore, we do provide a comprehensive overview of the topic. Finally, we also try to systemize previous and recent literature about the role of this receptor in somatic and cancer cells and provide access to it in the form of a convenient table.

Keywords: P2X7 receptor, nucleotide signaling, cancer, glioma, calcium signaling, cell death

Received: 07 April, 2022; revised: 06 September, 2022; accepted:
06 September, 2022; available on-line: 11 November, 2022

✉e-mail: p.pomorski@nencki.edu.pl

Acknowledgment of Financial Support: This work has been supported by National Science Centre research grant no. 2015/17/B/NZ3/03771

Abbreviations: ATPγS, Adenosine 5’-O-(3-thio)triphosphate; BBG, Brilliant Blue G (Coomassie brilliant blue); BzATP, 2’(3’)-O-(4-Benzoylbenzoyl)adenosine-­5’-triphosphate; CARD, caspase activation and recruitment domain; DAG, 1,2-diacylglycerol; EGFR, epidermal growth factor receptor; EMT, epithelial-mesenchymal transition; IP3, Inositol trisphosphate; IP3R, inositol trisphosphate receptor; LBP, lipopolysaccharide-binding protein; LPS, lipopolysaccharide; MIP-1, macrophage inflammatory protein 1; oxATP, oxidized ATP (also oATP); PIP2, phosphatidylinositol 4,5-bisphosphate; PKC, protein kinase C; PLC β, phospholipase C β; PLD, phospholipase D; PPADS, pyridoxalphosphate-6-azophenyl-2’,4’-disulfonic acid; SOCE, store-operated calcium entry; TLR4, toll-like receptor 4; TNF-R1, tumor necrosis factor receptor 1; TGF-β, transforming growth factor β; VEGF, vascular endothelial growth factor

The origin of nucleotide signaling

ATP is the most widespread source of chemical energy in metabolic processes. This nucleotide can be found in all cells of plants, animals, and microorganisms. It is constantly produced and consumed in most cellular processes, starting from the synthesis of other nucleotides by the synthesis of nucleic acids and ending with the transport of substances in and out of the cell and the generation of mechanical force. ATP molecules are also used in situations where chemical synthesis reactions require energy input or where regulatory processes require thermodynamic irreversibility of accompanying reactions. The concentration of ATP inside the cell results from a balance between the synthesis of new ATP molecules and their hydrolysis and is strongly related to the metabolic activity of the cell. Typically, in mammalian cells, this value is around 3–5 mM (Jones, 1986; Gorman et al., 2007), thus many orders of magnitude are larger than those in the extracellular space where it is 1–10 nM (Giuliani et al., 2019).

To fully understand the key role of ATP in the development of life on earth, it is necessary to go back to the beginning of the evolution of energy metabolism and the transmission of information using the genetic code. It was in these processes that the first nucleotides played an important part. Inorganic phosphates were the basic building blocks for the development of life on earth. The origin of these compounds on earth is enigmatic, some of the authors postulate even the extraterrestrial origin of phosphates, present on meteorites hitting the earth’s surface at an early stage of the planet’s development (Bryant et al., 2013). Without these compounds, it would be impossible to create RNA and DNA that still exist to this day and play a key role in the transmission of genetic information. With the development of life, the basic forms of information transmission changed. Initially, there were only long, self-replicating RNA chains in which nucleotides played both a building and energetic role (in the case of nucleic acid synthesis). However, when the first primitive cells appeared and DNA took over the main role of the carrier of the genetic code, nucleotides started to play a role as the energy carrier (Bada, 2004). Over the centuries, two such carriers have emerged: ATP and GTP. ATP participates in the vast majority of reactions while GTP is found in a limited group of them. The prevalence of ATP in living organisms may be associated with its greater free energy of last phosphate bond hydrolysis than in the case of GTP (Denton, 2009; Bazil et al., 2010). Despite the great advantages of using ATP as an energy carrier, this molecule has a serious disadvantage. Due to the chemical properties of ATP, it is not possible to carry out reactions using this molecule in an environment with a high concentration of calcium ions. Combination of calcium and ATP results in forming insoluble salts that cannot be used by living organisms. While the early earth ocean was alkaline, the concentration of calcium ions was low, similar to the present level in the cytoplasm (Plattner & Verkhratsky, 2016). This property of ATP turned out to be disadvantageous when the level of calcium ions on earth significantly increased in the pre-ocean (Kazmierczak et al., 2013). This complication led to the formation of a system of membranes protecting the inside of the cell against an unfavorable environment and a complex system of pumps and exchangers on the surface of these membranes in which ATP played a key energetic role. All these adaptations were to keep the levels of calcium ions low inside the cell. To summarize, ATP is needed to maintain a constant level of calcium in the cell so that ATP can be freely produced and hydrolyzed in it. This dependence made ATP and free calcium ions one of the most basic signaling molecules in the early stages of the evolution of living organisms (Berridge et al., 2003; Clapham, 2007).

As mentioned earlier, there is a very steep gradient of the ATP concentration between the cytoplasm and extracellular medium. Any tissue injury, cell damage, or lysis, including platelet aggregation and thrombosis, will result in a significant local release of ATP. There are also physiological mechanisms of active ATP release, such as connexin hemichannels activity (Anselmi et al., 2008), pannexin channels (Jackson, 2015), and nucleoside transporters (Dos Santos-Rodrigues et al., 2014) or vesicular release inactive synapses (Pankratov et al., 2006). Thus, the presence of extracellular nucleotides created a chance for nucleotide signaling development.

Nucleotide receptors

The first report that ATP, apart from its energetic function, can act as a neurotransmitter appeared in 1972 (Burnstock, 1972). Burnstock in his research indicated that the intestines and bladder of a guinea pig subjected to the action of extracellular ATP would contract independently of known neurotransmitters. Initially, the scientific world was skeptical about the idea of nucleotide signaling. This opinion was widespread because of earlier research that focused mainly on the intracellular processes related to the energetic functions of ATP (Gillespie, 1934; Lipmann, 1941; Meyerhof, 1951; Lo et al., 1968). The reluctance of the community was also caused by the results of ATP concentration measurements in the extracellular environment (1–10 nM outside the cell, 3-5 mM in the cytoplasm), and the size and charge of the molecule, which does not allow it to freely penetrate the cell membrane (Chaudry, 1982). In 1976, Burnstock, relying on pharmacological research, defined proteins that participated in the cell’s response to extracellular ATP calling them purinergic receptors. In the course of further pharmacological and molecular studies, he divided nucleotide receptors into two groups. Since the signaling role of adenosine was known for half of the century already (Drury & Szent-Györgyi, 1929), the first group was P1 receptors, stimulated by adenosine, and a new group, P2, was created for receptors stimulated by ATP and ADP. Further studies at Burnstock’s laboratory led to the division of the P2 family into metabotropic receptors or receptors that evoke a cascade of intracellular reactions as an effect of binding the ligand (Encyclopedia of Pain, 2013) – P2Y – and ionotropic receptors, opening membrane channels after binding the ligand (North, 2016) – P2X (Burnstock & Kennedy, 1985; Burnstock & Verkhratsky, 2012) (Fig. 1). Moreover, studies on the conversion of nucleotides after their release into the extracellular environment have resulted in the discovery of enzymes that hydrolyze nucleotides on the surface of the cell membrane. This created a more comprehensive picture of nucleotide signaling (Ziganshin et al., 1994; Lazarowski et al., 2000).

P1 family

The receptors stimulated by adenosine are members of the P1 family. They are defined as metabotropic. They belong to a diverse group of G-protein coupled receptors (GPCR). The receptors from this group are made up of seven transmembrane domains. The P1 family of receptors can be divided into four subtypes: A1, A2A, A2B, and A3. The homology between the individual subtypes is approximately 50% (Fredholm et al., 2000). The A1 receptor binds to the Gi/0 proteins and the A2A receptor to the Gs protein. Activation of the A1 receptor reduces the activity of adenylyl cyclase and stimulates the activity of phospholipase C by which there is an increase in the concentration of calcium ions in the cytoplasm (Schulte & Fredholm, 2000; Schulte & Fredholm, 2003). Activation of the A2A receptor increases the activity of adenylyl cyclase and activates signaling pathways related to MAP kinases (Baraldi et al., 2008; Chen et al., 2013). The A2B receptor binds to GsGq/11 proteins, and the A3 receptor binds to GiGq/11 proteins. Activation of A2A increases the activity of adenylyl cyclase, stimulates the activity of phospholipase C, and activates MAP kinases (Sun & Huang, 2016; Bader et al., 2017). The stimulation of the A3 receptor reduces the activity of adenylyl cyclase and activates phospholipase C, which, as in the case of the A1 receptor, increases the concentration of calcium ions in the cell. Like all the receptors mentioned above, A3 can stimulate the activity of MAP kinases (Fishman et al., 2002; Borea et al., 2015). A1 and A2A receptors can be stimulated by low adenosine concentrations, while the activation of A2B and A3 receptors is associated with the presence of high adenosine concentrations in the extracellular environment (Borea et al., 2018). P1 family receptors are widely distributed in living organisms and play an important role in maintaining cell homeostasis and are crucial for the development of pathological conditions.

P2 family

The P2 receptor family groups two completely unrelated subfamilies of nucleotide receptors: metabotropic P2Y receptors and P2X receptors acting as ion channels. The classification of these receptor subfamilies into a common P2 family is related to a historical classification based on pharmacological characteristics and not on a mechanism of action that was unknown at the time. Regarding the ligands that activate them, the P2X and P2Y receptors are similar. However, in terms of the mechanism of action, the P2Y and P2X receptors are completely different.

P2Y receptors

The P2Y family consists of metabotropic receptors activated by extracellular ATP, UTP, and their derivatives. In terms of molecular structure and mechanisms of intracellular signaling, they are GPCR receptors, similar to P1 adenosine receptors.

The P2Y receptor family is one of the most numerous groups of nucleotide receptors. So far, as many as 8 different receptor proteins have been discovered: P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, P2Y14 (Von Kügelgen & Hoffmann, 2016). There are also numerous related orphan receptors, receptors similar in sequence to the family members but without a known ligand (Murakami et al., 2008). An example of such a receptor is the P2Y14 receptor, activated by UDP-glucose, first known for its gene sequence, then characterized biochemically (Abbracchio et al., 2003). This is the most diverse group of nucleotide receptors – the difference in sequence between the individual types ranges from 21% to 57%.

The receptors from the P2Y family are composed of 7 transmembrane domains. The ligand-binding site takes place in the “pocket” formed by the domains TM3, TM6, and TM7 in the cell membrane. The nucleotide affinity for this region is related to positively charged amino acids that exhibit electrostatic interactions with phosphate residues in the nucleotides. The three-subunit (α, β, γ) G proteins are responsible for transmitting signals inside the cell. According to the phylogenetic tree based on differences in gene sequences, P2Y receptors can be divided into two distinct groups. The first includes P2Y1, P2Y2, P2Y4, P2Y6, P2Y11 receptors and the second includes P2Y12, P2Y13, P2Y14 (Schöneberg et al., 2007; Von Kügelgen & Hoffmann, 2016). The first group of receptors is bound to Gq/11 proteins. Their stimulation causes Gq signaling and activation of phospholipase C beta (PLCβ). Activation of this enzyme leads to the hydrolysis of phosphatidylinositol-(4,5)-bisphosphate (PIP2) present in the cell membrane. As a result of hydrolysis, two secondary information transmitters are formed: inositol triphosphate (IP3) and 1,2-diacylglycerol (DAG) (Wypych & Barańska, 2020). Water-soluble IP3 diffuses from the plasma membrane into the cytoplasm and then attaches to inositol trisphosphate receptors (IP3R) on the surface of the endoplasmic reticulum. The IP3 receptors play the role of ion channels that can release calcium ions from the endoplasmic reticulum. This results in an increase in the concentration of calcium in the cytoplasm, and then, as a result of a decrease in the concentration of calcium ions in the endoplasmic reticulum, voltage-independent calcium channels in the cell membrane are opened (Berridge, 1993; Taylor & Thorn, 2001). As a consequence, the concentration of free calcium ions in the cell increases through the influx of ions from the intercellular space. This process of secondary calcium influx from the extracellular space following the emptying of calcium resources in the endoplasmic reticulum is called Store Operated Calcium Entry (SOCE) (Hogan & Rao, 2015). The second of the secondary transmitters caused by PLCβ activity, DAG, remains in the plasma membrane and activates protein kinase C (PKC). Active PKC can have an inhibitory effect on the receptor itself and PLC by inhibiting PIP2 hydrolysis and reducing the strength of the calcium signal. In addition, activation of PKC leads to an increase in the activity of phospholipase D (PLD) and the MAP kinase pathway (Wypych & Barańska, 2020). In summary, the activation of P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11 receptors leads to the mobilization of calcium ions in the cell. However, it should be remembered that GPCR receptors do not show 100% specificity for the binding of the α subunits of G proteins, and so in the case of the P2Y11 receptor, alternative activation may occur related to the binding of the Gs protein, which leads to an increase in the activity of adenylyl cyclase and, consequently, an increase in the level of cAMP in the cell (Kennedy, 2017). The affinity of G proteins can also be altered after P2Y receptors complex with other membrane proteins. An example is the complex of integrin αvβ5 with the P2Y2 receptor, under these conditions the receptor can interact with the G0 protein activating signal transduction by the Rac1 protein. Moreover, the conformational change of the P2Y2 receptor by integrin αvβ5 causes signal transduction through the G12 protein and ROCK kinase (Kłopocka et al., 2020). The P2Y12, P2Y13, and P2Y14 receptors belonging to the second group reduce the level of cAMP in the cell by inhibiting the activity of adenylyl cyclase. In these receptors, intracellular signal transduction is mediated by the Gi/0 protein.

P2X family

Receptors from the P2X family are completely unrelated to P2Y receptors. P2X receptors are non-selective cation channels that open upon stimulation with ATP or its synthetic analogs (North, 2016), causing ion current flow and depolarization of the cell membrane. Such receptors are called ionotropic receptors. The ionotropic receptors are not monomers – for the receptor to function properly, a multi-molecular, oligomeric protein complex must be formed, which creates an ion channel in the cell membrane. These receptors can form both homo- and heterooligomers. A functional P2X receptor usually consists of three subunits from which the ion channel is created (Ralevic & Burnstock, 1998). The P2X receptor subunit consists of two transmembrane regions (TM1 and TM2), intracellular C- and N-terminals, and an extracellular loop that can undergo many post-transplantation modifications. The TM1 transmembrane domain is involved in the regulation of the conduction of channels, while the TM2 domain plays a key role in ion channel formation (Khakh et al., 2001). In the extracellular loop, there are localized binding sites for ATP and allosteric regulators (Garcia-Guzman et al., 1997; Clarke et al., 2000; Jiang et al., 2000a; Ennion et al., 2000). So far, seven genes encoding subunits of the P2X family of receptors have been discovered, numbered 1 to 7 (North, 2002). The similarity between the proteins in this family ranges from 30 to 50 percent depending on the receptor (Fig. 2). P2X family receptors are widely distributed in mammalian cell lines and tissues (Burnstock & Knight, 2004; Burnstock, 2007).

P2X7 receptor

The P2X7 receptor stands out from the P2X family. The first reports of this receptor’s existence date back to 1980, when Cockcroft and Gomperts observed increased histamine secretion from rat mast cells upon stimulation with high concentrations of extracellular ATP (Cockcroft & Gomperts, 1980). In 1986 Gordon put forward a theory, based on data from pharmacokinetic analyzes, of the presence of a new P2Z receptor that can be activated with low doses of synthetic agonists or high ATP concentrations compared to other nucleotide receptors (Gordon, 1986). In addition, stimulation of the P2Z receptor resulted in massive membrane depolarization and the formation of a pore in the cell membrane, permeable to molecules below 900 kDa (Ferrari et al., 1996; Coutinho-Silva et al., 1996). The identification of the new receptor took place in 1996 when the surprenant research group successfully cloned the rat P2X7 gene and reestablished its activity in human HEK293 cells (Surprenant et al., 1996). Since the publication of the above work, research on this type of receptor has begun in other species of animals. The receptor was classified into the P2X family (Rassendren et al., 1997).

Structure of the gene encoding P2X7

The gene encoding the P2X7 receptor is commonly found in all mammals and other vertebrates (Donnelly-Roberts et al., 2009). The human gene encoding the human P2X7 receptor (hP2X7) is located on chromosome 12 at locus q24. This human gene is composed of 53 733 base pairs of 13 exons, which can create 10 different variants of gene splicing (Buell et al., 1998). The structure of the receptor gene in mice shows 81% similarity to the human gene encoding this receptor. The gene encoding the mouse P2X7 receptor is located on chromosome 5 at locus 62.5 cM (Chessell et al., 1998). The gene encoding the rat P2X7 protein is located on chromosome 12 at locus q16 and shows 80% homology to the human gene (Surprenant et al., 1996). The P2X7 gene in all species studied so far consists of 13 exons.

The regulation of P2X7 gene transcription can take place with the participation of promoters and enhancers of transcription, microRNA, and long coding RNA. So far, the structure of human and mouse promoters has been studied. The promoter region of the human P2X7 gene is located between nucleotides –158 to +38 flanking the transcription initiation region (Zhou et al., 2009). Additionally, the transcription of the human P2X7 gene may be regulated by unknown transcription enhancers at the +222 – +323 and +401 – +573 sites by cytosine hypermethylation. The promoter region of the gene encoding the mouse P2X7 receptor is located between nucleotides –249 to +17 surrounding the transcription start site (García-Huerta et al., 2012). Additionally, transcription enhancers responsive to stimulation by retinol (vitamin A) have been identified in the mouse gene (Heiss et al., 2008; Hashimoto-Hill et al., 2017). Interestingly, in studies on the human P2X7 receptor, an opposite effect was observed. The administration of retinol decreased the level of the P2X7 receptor in cells of neuronal origin in humans (Wu et al., 2009; Orellano et al., 2010).

P2X7 mRNA can also be efficiently regulated by miRNA (microRNA) molecules. The miR-186 molecule can lower the P2X7 transcript level in podocytes in the kidney (Sha et al., 2015). On the other hand, the miR-150 molecule in mice lowers the level of P2X7 receptor in the lung epithelium, while regulating the level of surfactant secretion by these cells (Weng et al., 2012). Moreover, miR-150 may have a cardioprotective effect on cardiomyocytes in a mouse model of cardiac ischemia (Tang et al., 2015) by regulating the apoptosis of damaged cells. Regulation of P2X7 levels by microRNA molecules is also possible in cancer cells. The miR-150, miR-186, and miR-21 molecules that lower the P2X7 transcript are overproduced in breast, cervical, bladder, and lung cancers (Zhou et al., 2008; Huang et al., 2013; Boldrini et al., 2015). Additionally, the P2X7 receptor after stimulation can cause the release of microvesicles and exosomes from melanoma cells containing mRNA (Pegoraro et al., 2021a).

The last known possibility of regulating the transcription level of the P2X7 gene is by long-noncoding RNA (lncRNA). Small interfering RNAs complementary to lncRNA NONRATT021972 lower P2X7 receptor levels in many pathological conditions such as neuropathic pain (Liu et al., 2016), myocardial hypoxia (Zou et al., 2016; Tu et al., 2016), and under metabolic stress (Xu et al., 2016; Li et al., 2016a). siRNA complementary to lncRNA uc.48+ reduces the level of P2X7 receptors in neurons of diabetic rats (Wu et al., 2016).

The protein structure of the P2X7 receptor

A functional P2X7 receptor, like all P2X family receptors, is composed of at least three subunits encoded by the P2RX7 gene. In the structure of the subunit, two transmembrane domains, the extracellular loop (with ATP binding sites) and the intracellular N- and C-terminus, can be distinguished. N-terminus regulates the flow of calcium ions through the ion channel and is responsible for the activation of signal kinases (Amstrup & Novak, 2003; Liang et al., 2015) (Fig. 3). The C-terminus of the P2X7 receptor is significantly longer than that in other P2X family receptors. It is postulated that this part is responsible for the oligomerization of the receptor protein and pore formation (Kim et al., 2001; Smart et al., 2003; Costa-Junior et al., 2011; Kopp et al., 2019). Moreover, there is also a binding site for lipopolysaccharide at the C-terminus, which demonstrates the important role of this receptor in the regulation of inflammatory processes (Denlinger et al., 2001; Leiva-Salcedo et al., 2011). Additionally, this terminus contains domains that can interact with other proteins (Surprenant et al., 1996).

Post-translational modifications of the P2X7 receptor

The P2X7 receptor protein can undergo many post-translational modifications such as phosphorylation/dephosphorylation, N-glycosylation, palmitoylation, and ADP-ribosylation.

There are several putative sites at the C-terminus of the receptor where phosphorylation may occur (Y382-384). Studies on the phosphorylation pattern of this region in human microglia have shown a significant role of this receptor in the regulation of pain and tolerance to opioids (Leduc-Pessah et al., 2017). An interesting fact is that these modifications did not affect the ion permeability of the P2X7 receptor channel. The C-terminus of the P2X7 receptor can also be palmitoylated. This modification is associated with interactions between the receptor and the cell membrane. The targeted mutagenesis of the palmitoylation site influenced the presence of the receptor in the plasma membrane. Cells with a mutant P2X7 receptor variant incapable of palmitoylation had decreased levels of this receptor in the plasma membrane but high levels in the endoplasmic reticulum (Gonnord et al., 2009).

The region which undergoes N-glycosylation is the extracellular loop. Five places can undergo this modification: N187, N202, N213, N241, and N284. The pattern of glycosylation may vary depending on the type of tissue (Lenertz et al., 2010). N-glycosylation, in addition to affecting the level of the receptor in cells, also causes changes in signal transduction inside the cell. Site-directed mutagenesis at N187 blocked modification of this site, resulting in decreased P2X7 receptor activity (Di Virgilio et al., 2018).

The last known post-translational modification that the P2X7 receptor can undergo is ADP-ribosylation. This modification causes an alternative, permanent activation of P2X7 by mimicking the attachment of ATP in the active site. ART2.1 and ART2.2 enzymes ribosylate the P2X7 receptor at site R125, at the hypothetical ATP binding site, resulting in its constant activation and a decrease in the affinity for extracellular ATP (Adriouch et al., 2001, 2008). This modification has only been observed in rodents as the ART2.1 and ART2.2 enzymes needed for this process are not present in human tissues (Haag et al., 1994).

P2X7 protein splicing variants

So far, 10 splicing variants of the gene encoding the human P2X7 receptor have been identified (Pegoraro et al., 2021b) (Fig. 4). The variant that is responsible for the full and functional structure of the receptor subunit was named P2X7A, while the subsequent variants resulting from alternative splicing were named with the letters B to J. However, the conducted studies showed that only 3 of the truncated protein variants can form receptor subunits. These are P2X7B, P2X7H, and P2X7J (Feng et al., 2006; Adinolfi et al., 2010; Giuliani et al., 2014). The P2X7B isoform is characterized by a short carboxyl fragment compared to the P2X7A isoform. This isoform, 364 amino acids long, forms a functional ion channel which, due to the truncated carboxyl fragment, cannot form a functional pore in the cell membrane. Long-term stimulation with P2X7B does not lead to cell death and promotes the formation of pores in the cell membrane. Moreover, the presence of this isoform may intensify proliferation by stimulating the NFAT1 transcription factor with calcium ions (Adinolfi et al., 2010). Another isoform – P2XH with a length of 274 amino acids – forms a non-functional ion channel (Cheewatrakoolpong et al., 2005). The last of the receptor isoforms detected at the protein level is the P2X7J isoform. It is composed of 258 amino acids and can form, together with the P2X7A isoform, non-functional heterotrimers. Such a heterotrimer increased the resistance of cervical cancer cells to extracellular ATP without causing cell death (Feng et al., 2006).

In rodents, four splice variants were also detected for the gene encoding the P2X7 subunit (P2X7B, P2X7C, P2X7D, P2X7K) along with the canonical P2X7A isoform composed of 595 amino acids. The P2X7B and P2X7D isoforms can form heterodimers with the P2X7A isoform, reducing the activity of the P2X7 receptor constructed in this way. The P2X7K isoform, composed of 592 amino acids, after the creation of the P2X7 receptor has a greater affinity for ATP than the receptor composed of subunits of the P2X7A isoform (Schwarz et al., 2012).

This clear image is somehow obscured by the existence of nfP2X7 form, defined by the binding of the specific antibody, raised against amino acid sequence 200-216, with particular conformation present in tumor cells P2X7 receptor (Gilbert et al., 2019). However, the mechanism of the epitope presentation is unknown, and we do not know if nfP2X7 is another isoform produced in certain circumstances or some modification of the wild protein. It was shown that nfP2X7 is widely present both in cells able to open P2X7-dependent pore as well as those unable to open membrane pore, its presence was confirmed in prostate cancer cells (LNCaP, PC3, DU 145), KELLY neuroblastoma, Ramos (RA-1) lymphoma. Antibodies against nfP2X7 passed the first stage of clinical trials in basal cell carcinoma (Gilbert et al., 2017).

Activation of the P2X7 receptor

The P2X7 receptor, like all receptors in this group, is activated upon stimulation with extracellular ATP. However, compared to other P2X receptors, the ligand concentration needs to be higher, from 50 µM to 2.5 mM. The concentration that effectively activates the receptor varies from species to species (Surprenant et al., 1996; Rassendren et al., 1997; Fonfria et al., 2008; Roman et al., 2009; Bradley et al., 2011).

The P2X7 receptor can also be activated by synthetic ATP analogs such as 2(3)-O-(4-benzoylbenzoyl) ATP (BzATP) and adenosine 5-(γ-thio) triphosphate (ATPγS). BzATP has about 10 times greater affinity for the P2X7 receptor than ATP. The exception is that the P2X7 receptor derived from guinea pig (Fonfria et al., 2008). In this case, BzATP activates the P2X7 receptor only slightly stronger than ATP itself. ATPγS activates P2X7 originating from mice, rats, dogs, and humans. What is important, the level of P2X7 activation with ATPγS is significantly lower compared to the P2X7 activation with BzATP and ATP (Donnelly-Roberts et al., 2009; Spildrejorde et al., 2014) (Table 1).

An interesting and characteristic of P2X7 activation is its regulation by lipopolysaccharide from gram-negative bacteria (LPS). Inserting a genetic construct inside the cell that causes the production of LPS in the cytoplasm, stimulates caspase 11 that activates the pannexin-1 channel by cleaving. This results in increased release of ATP into the extracellular environment and activation of P2X7 (Yang et al., 2015). Moreover, it is postulated that LPS may increase the sensitivity of the P2X7 receptor to extracellular ATP by binding to the cytoplasmic LPS binding domain in this receptor and conformational changes (Denlinger et al., 2001).

Reports are indicating a positive role of cathelicidins in the regulation of P2X7 receptor activity. The antibacterial LL-37 peptide belonging to this family activated the P2X7 receptor, causing the maturation and release of IL-1β (Elssner et al., 2004). Studies by other research groups, however, indicate that LL-37 does not activate the P2X7 receptor directly but acts as an allosteric ATP sensitivity enhancer (Pochet et al., 2006; Tomasinsig et al., 2008). The activity of P2X7 can be regulated similarly by numerous substances such as tenidap (Sanz et al., 1998), polymyxin B (Ferrari et al., 2004), clemastine (Nörenberg et al., 2011), ivermectin (Nörenberg et al., 2012) and ginsenosides (Helliwell et al., 2015). The positive allosteric modulator of P2X7 was successfully employed in cancer with its ability to negatively control the growth and development of lung tumor by potentiating αPD-1 treatment (Douguet et al., 2021).

P2X7 receptor inhibition

During intensive research on the P2X7 receptor, many chemical compounds were developed that could inhibit its activity. Each of these antagonists differs in receptor affinity, mechanism of action, and species specificity.

The first generations of P2X7 inhibitors were not very specific – apart from inhibiting, P2X7 also affected the activity of other P2 family receptors (Gever et al., 2006). Examples of such inhibitors are PPADS (pyridoxalphosphate-6-azophenyl-2’,4’-disulfonic acid) (Lambrecht et al., 1992; Valera et al., 1994) and suramin (Urbanek et al., 1990), which blocked also other receptors from the family: P2X, P2Y, and P1. A much more specific inhibitor of the first generation P2X7 was oxidized adenosine triphosphate (oxATP) (Murgia et al., 1993), which binds irreversibly to the P2X7 receptor. However, further research has shown that it is not an ideal antagonist. In addition to the irreversible inhibition caused by covalent changes in the protein structure, oxATP can also inhibit the activity of P2X2 and P2X3 receptors (Evans et al., 1995).

One of the most widely used first-generation P2X7 inhibitors is Brilliant Blue G (BBG), also known as the Coomassie brilliant blue (Soltoff et al., 1989; Jiang et al., 2000b). This inhibitor has the greatest affinity for the rat P2X7 receptor, blocking it at nanomolar concentrations. It is a relatively cheap and non-toxic inhibitor; however, it should be mentioned that it is not without its drawbacks. BBG can inhibit the activity of other P2X receptors such as P2X1, P2X2, P2X3, and P2X4 (Jiang et al., 2000b). Moreover, there are reports of pannexin-1 inhibition by BBG (Qiu & Dahl, 2009; Dahl et al., 2013). It is also worth mentioning that BBG is a dye that can cause problems in some applications.

With the development of new screening methods and the understanding of the exact protein structure of the P2X7 receptor, second-generation inhibitors have emerged. Their development was a result of the growing attention in the pharmaceutical industry, which resulted from the recognition of the important role of the P2X7 receptor in the regulation of inflammation (Di Virgilio et al., 2017) and neuropathic pain (Zhang et al., 2020). The second P2X7 antagonists also had the ability to cross the blood-brain barrier, which, apart from the first-generation inhibitor – BBG – had not been possible before (Peng et al., 2009; Apolloni et al., 2021). The first-generation P2X7 inhibitors were mainly based on in vitro studies and were found to be often unsuitable for in vivo use. This was due to the rapid degradation of the inhibitor after administration to the animal and its poor pharmacokinetic parameters (Bartlett et al., 2014). New generation inhibitors, which include molecules such as CAY10593, A-839977, AACBA hydrochloride, and 1-Benzyl-5-aryltetrazoles, are characterized by increased efficiency compared to the first generation and greater bioavailability in the in vivo systems (Nelson et al., 2006; Michel et al., 2007; Broom et al., 2008; Honore et al., 2009; Letavic et al., 2013; Pupovac et al., 2013).

Alternatives to inhibitors in the form of small chemical molecules are monoclonal antibodies and single-domain antibodies (sdAb, nanobodies) directed against the P2X7 receptor. Administration of the anti-P2X7 antibody reduced inflammation in a mouse model of ulcerative colitis (Kurashima et al., 2012). On the other hand, the use of nanobodies directed against P2X7 reduced allergic contact dermatitis in an in vivo mouse model (Danquah et al., 2016). Anti-P2X7 antibodies can also bind to short or non-functional isoforms of the receptor (Barden et al., 2003). The use of the anti-P2X7 antibody decreased the activity of the P2X7 receptor in murine B16 melanoma cells resulting in a reduction in tumor size (Gilbert et al., 2017).

The inhibition of the P2X7 receptor may also be influenced by the extracellular ion concentration. A high concentration of magnesium ions Mg2+ can reduce channel activity upon ATP stimulation in rat and human cells (Rassendren et al., 1997). Further studies of this phenomenon showed the influence of other ions such as calcium, zinc and copper on the activity of P2X7. The concentration of hydrogen ions (pH) also had a significant effect on the P2X7 activity (Virginio et al., 1997).

Functions and physiology of the P2X7 receptor in normal cells

Regulation of interleukin secretion to the extracellular environment

One of the most extensively studied molecular functions of the P2X7 receptor is its participation in the development of inflammation. More specifically, P2X7 takes part in the formation of the NLPR3 inflammasome, and then in the maturation and release of interleukin 1β to the extracellular environment by macrophages and other cells of the immune system (Gudipaty et al., 2003; He et al., 2013). Interleukin 1β is one of the most studied pro-inflammatory interleukins. It takes an active part in the defense of the cell against pathogens and in many metabolic, autoimmune and cancer diseases (Dinarello, 1994, 2018; Macarthur et al., 2004).

The secretion of interleukin takes place in two stages. In the first stage, pro-interleukin 1β and components of the NLPR3 inflammasome are synthesized by stimulation of the transcription factor NF-κβ. This factor is activated when the cell is exposed to specific pathogen-associated molecular patterns (PAMP). An example of such a pattern is extracellular LPS, which by combining with lipopolysaccharide-binding protein (LBP) and CD14 protein forms complexes activating the toll-like receptor 4 – TLR4. The second stage involves inflammasome assembly, caspase 1 activation, and the release as well as the maturation of interleukin 1β. Extracellular ATP activates the P2X7 receptor located on the outer membrane of the immune system cells, acting as a non-selective ion channel and causing the penetration of calcium (Ca2+) and sodium (Na+) ions into the cell interior following the concentration gradient. At the same time, potassium (K+) ions are released from the cell following the concentration gradient, which is a key phenomenon in the production of interleukin 1β (Perregaux & Gabel, 1994; Muñoz-Planillo et al., 2013). A sudden decrease in the level of potassium in the cell causes the activation of caspase 1 (Kahlenberg & Dubyak, 2004). An adapter molecule ASC (apoptosis-associated speck-like protein containing a CARD), which has a CARD (caspase activation and recruitment domain) domain, binds to the overproduced in the first stage NLPR3 protein. This domain enables enhanced caspase 1 activation by cleavage of pro-caspase. The active caspase performs the proteolytic cleavage of the immature form of IL-1β from the 35 kDa form to the 18 kDa active form (Gross et al., 2011). The altered cytokine is released from the cell inducing inflammation.

Experiments with mice lacking the gene encoding the P2X7 receptor demonstrated its key role in the formation of the NLPR3 inflammasome (Solle et al., 2001). These mice showed decreased levels of IL-1β and IL-6 production after ATP stimulation, which may indicate the role of the P2X7 receptor in the pro-inflammatory response.

The role of the P2X7 receptor in other pro-inflammatory pathways

The P2X7 receptor is also involved in the secretion of prostaglandins into the extracellular environment. In murine macrophages, stimulation of the P2X7 receptor results in the secretion of prostaglandin E2, thromboxane B2, and leukotriene B4 (Barberà-Cremades et al., 2012). Activated P2X7 may also affect the hydrolysis of arachidonic acid, which is a substrate for the synthesis of cyclooxygenase, and prostaglandin E2, which together play an important role in inflammation, fever, and pain (El Ouaaliti et al., 2012). Moreover, P2X7 activation is observed in damaged tissues where the inflammatory infiltration begins. Extracellular ATP stimulation of murine Kupffer cells induced necrotic death of these cells and the release of large amounts of prostaglandin E2 and IL-1β (Toki et al., 2015). The above studies indicate P2X7 as an interesting target for the treatment of inflammation that could be an alternative to cyclooxygenase inhibitors (Barberà-Cremades et al., 2012).

Stimulation of the production of reactive oxygen and nitrogen species

Reactive oxygen species (ROS) are a common signaling element in a living cell. The enzymes of the respiratory chain, present in every actively metabolizing cell, while conducting oxidative phosphorylation produce large amounts of reactive oxygen and nitrogen species (Hoffman & Brookes, 2009), normally reduced by anti-oxidative systems (Bae et al., 2011). Reactive oxygen species produced by macrophages and microglia play a protective role against microbial invasion.

In many pathological conditions such as cancer or metabolic diseases, the level of free radicals is much higher than in normal cells (Liou & Storz, 2010; Alfadda & Sallam, 2012; Galadari et al., 2017). Nucleotide signaling can stimulate the production of reactive oxygen species. The P2X7 receptor in microglia and macrophage cells by influencing the phosphorylation of NADPH oxidase increases the production of reactive oxygen species. The molecular mechanism of this activation is unclear, but it is known from the literature that NADPH oxidases can be activated by many pathways related to calcium signaling, for example, protein kinase C, mitogen-activated protein kinases p38 and ERK1/2, and phosphatidylinositol 3-kinase (Guerra et al., 2007; Martel-Gallegos et al., 2013).

It has been observed that the continuous stimulation of the P2X7 receptor by low ATP concentrations does not cause cell death but increases the polarization of the mitochondrial membrane through an increased level of free calcium ions in the cytoplasm and thus also in the mitochondria. This calcium influenced oxidative phosphorylation, which stimulated cellular metabolism and influenced cell survival in conditions of extracellular glucose deprivation (Adinolfi et al., 2005; Amoroso et al., 2012).

Creating a cell membrane pore

The unique property of the P2X7 receptor, which distinguishes it from all other receptors in the P2X family, is its dual nature. In addition to the non-selective cation channel, activated P2X7 can induce the formation of a membrane pore, the opening of which leads to the penetration of large molecules (above 900 kDa) and cell death (Surprenant et al., 1996; Rassendren et al., 1997). With prolonged stimulation with P2X7 agonists, the penetration into the cell of organic cations such as N-methyl-D-glucamine increases (Jiang et al., 2005), a cation that is much larger than calcium, potassium, or sodium ions. The time of pore formation varies and depends on many factors, such as the type of cell line, the splice variant of the P2X7 receptor protein, and the agonist with which it is stimulated.

So far, two potential mechanisms of cell pore formation following stimulation of the P2X7 receptor have been presented. The first is associated with a protein that directly interacts with the P2X7 receptor - Pannexin-1. Many reasons point to the crucial role of this protein in the formation of the cell pore (Monif et al., 2009; Suadicani et al., 2012). Experiments with small interfering RNA, complementary to the gene encoding Pannexin-1, showed that lowering the level of this protein in the THP-1, 1321 N1 and J774 cell lines significantly inhibited the penetration of large fluorescent molecules after P2X7 receptor stimulation (Pelegrin & Surprenant, 2006; Locovei et al., 2007; Iglesias et al., 2008). Moreover, the credibility of this theory is confirmed by experiments using the co-immunoprecipitation technique, which showed a direct interaction of the P2X7 receptor with Pannexin-1 (Li et al., 2011; Poornima et al., 2012).

Experiments using murine macrophages with a deleted gene encoding Pannexin-1 suggest the existence of other mechanisms. These cells, despite the lack of Pannexin-1, showed no reduction in the efficiency of penetration of dyes into the cell interior (Qu et al., 2011; Lemaire et al., 2011).

Moreover, in HEK293 cells with a constant, increased level of the P2X7 receptor, penetration of only cationic dyes such as Yo-Pro-1 and ethidium bromide was observed. In murine macrophages, penetration of cationic dyes through the pore was observed while anionic dyes penetrated by diffusion (Schachter et al., 2008; Cankurtaran-Sayar et al., 2009).

Effect of P2X7 receptor activation on cell membrane reorganization

The P2X7 receptor is one of the many proteins involved in the organization of the cell membrane structure. The mechanism of this activity is poorly understood, but the stimulation of extracellular ATP in some cell types may lead to the formation of numerous vesicles and bulges in the cell membrane, shortly after the agonist administration (MacKenzie et al., 2001). Several candidates are postulated as the proteins responsible for changes in the cell membrane. The Rho-associated protein kinase 1 (ROCK1) (Morelli et al., 2003) is suspected to be a regulator behind this effect. The heat shock protein HSP90 is an inhibitor of the effects observed in the cell membrane (Adinolfi et al., 2003). The EMP2 protein interacts directly with the C-terminus of the P2X7 receptor, which may indicate a link between changes in the structure of the cell membrane and the formation of the cell pore following stimulation of the P2X7 receptor (Wilson et al., 2002). Expression of the P2X7 receptor is also observed in leukocyte cells where it is postulated to be responsible for the reorganization of the cell membrane prerequisite for cell migration through blood vessels and the extracellular matrix (Qu & Dubyak, 2009). Moreover, the appearance of vesicles in the plasma membrane following P2X7 receptor stimulation is considered to be the first step in the formation of extracellular vesicles. The activated release of microvesicles and exosomes is a result of the P2X7 stimulation with a high concentration of ATP (Lombardi et al., 2021; Vultaggio-Poma et al., 2022). The triggered release of the extracellular vesicles was not only observed in the immune and central nervous system cells but also in the melanoma cells, which indicates the pro-metastatic activity of the P2X7 receptor (Pegoraro et al., 2021a).

Regulation of cell death

It is not surprising that the P2X7 receptor is involved in the regulation of cell death since one of the receptor’s domains localized at the C-terminus is similar to the death domain in the tumor necrosis factor receptor 1 (TNF-R1), which is involved in the induction of apoptosis (Zanovello et al., 1990; Chow et al., 1997; Denlinger et al., 2001). Initially, activation of this receptor was thought to lead to necrotic cell death (Di Virgilio et al., 1989). However, further research has shown that P2X7 is involved in other types of cell death. In the literature, we can find information about the induction of pyroptosis, a form of lytic programmed cell death (Yang et al., 2015), necroptosis, a programmed form of necrosis (Dubyak, 2012), and autophagy (Young et al., 2015). There are also documented cases of characteristic markers of different types of cell death within the same cell. In ATP-stimulated mouse lymphocytes, cell shrinkage was first observed, which is characteristic of apoptotic death, and then after a few minutes, the treated cells disintegrated as in necrotic death (Taylor et al., 2008).

The ability to activate cell death depends on the splice variant of the receptor present in the affected cell. Activation of the P2X7B receptor variant did not result in cell death in transfected HEK293 cells (Adinolfi et al., 2010).

In conclusion, the great majority of the P2X7 receptor does not induce apoptotic death. The most common type of cell death when the P2X7 receptor is activated is necrosis. Moreover, receptor activation does not always lead to any cell death – it depends on the type of cells and the receptor isoform (Di Virgilio et al., 2017).

Stimulation of cell division

As mentioned in the previous section, the P2X7 receptor has long been recognized as a factor leading to cell death (Di Virgilio et al., 2017). However, intensive research using various cell lines and receptor assembly variants has shown that P2X7 may also play a completely different role. The first experiments with lymphocytes transiently transfected with P2X7 receptor showed increased proliferation of these cells upon ATP stimulation (Baricordi et al., 1999). In T cells, P2X7 receptor activation stimulated autocrine secretion of ATP and interleukin-2 into the environment. IL-2 stimulated the activation of transcription factors in T lymphocytes, which as a result increased their proliferation intensity in BALB/c mice (Yip et al., 2009). Studies on alternative receptor splicing variants have suggested that it is the shorter P2X7B isoform lacking the C-terminal fragment that increases the intensity of proliferation (Adinolfi et al., 2005, 2010). Additionally, experiments conducted with the use of microglial cells showed the significant role of the P2X7 receptor in stimulating cell proliferation. Inhibition of P2X7 activity by inhibitors or derivation of a cell line with a mutant receptor variant (G345Y) significantly decreased the intensity of microglial proliferation (Bianco et al., 2006; Monif et al., 2009; Monif et al., 2010).

Functions of P2X7 in cancer cells

The P2X7 receptor is as common in cancer cells as it is in somatic cells. Stress-related to intra-tumor hypoxia and cancer cell death as a result of chemotherapy or radiotherapy (Martins et al., 2009; Lecciso et al., 2017) may increase the release of ATP into the environment. In addition, the presence of tumor-specific proteins such as SLC29A1, SLC29A2, and SLC28A1-A3 nucleoside transporters may significantly affect the increased concentration of ATP in the tumor environment (Gray et al., 2004; Young et al., 2013). The observed effect of the increased concentration of extracellular nucleotides on cancer depends, however, on the type of tissue from which the tumor originates. Therefore, it should be described in some detail how different the P2X7 receptor response may be depending on the cancer type. The chapter is summarized in Table 2.

P2X7 in prostate cancer

Developing prostate cancer is characterized by a high expression of mRNA encoding the P2X7 receptor as compared to normal tissue (Ravenna et al., 2009). Immunohistochemical studies, using fragments of postoperative prostate tumors from 116 different cases, demonstrated a high level of the P2X7 receptor protein (Slater et al., 2004a). Moreover, the level of this protein has correlated with high expression of prostate-specific antigen (PSA) which is known and widely used as a marker of prostate cancer malignancy (Slater et al., 2005). These reports indicated that the level of the P2X7 receptor could be used as a negative prognostic factor in the development of this type of cancer. It was also noticed that the level of the P2X7 receptor protein correlates with the level of receptors supporting cell division, such as the epidermal growth factor receptor (EGFR) and the estrogen receptor alpha (ERα), which may indicate the significant roles of P2X7 in promoting a more malignant tumor (Ravenna et al., 2009). In addition, functional in vitro studies using prostate cancer cell lines showed increased aggressiveness and invasiveness of these lines after stimulation of the P2X7 receptor by extracellular ATP (Ghalali et al., 2014; Qiu et al., 2014). Moreover, in the PC-3M human prostate carcinoma cell line where functional P2X7 was highly expressed, the involvement of the receptor in ATP-promoted invasion and metastasis of cancer was inevitable (Qiu et al., 2014). What is more, in patients with metastatic prostate cancer, the genetic interactions between single-nucleotide polymorphisms (SNPs) in VEGFR-2 and P2X7 receptors were examined. This analysis indicated that a few SNPs in the VEGFR-2 and P2X7 receptor genotypes may be able to pinpoint a population of prostate cancer patients with a better prognosis of survival (Solini et al., 2015).

P2X7 in bone tumors

High levels of the P2X7 receptor have been detected in many types of tumors of the skeletal system. In osteosarcoma, Ewing’s sarcoma, and chondrosarcoma, an increased level of the P2X7 receptor was detected as compared to healthy tissues (Gartland et al., 2001; Alqallaf et al., 2009; Liu & Chen, 2010). Cell lines derived from the backbone are characterized by a wide variety of P2X7 receptor isoforms. The cells of the SaOs-2 lineage express a functional P2X7 receptor capable of forming a pore in the plasma membrane and stimulation of these cells by ATP or BzATP causes increased cell death (Gartland et al., 2001). On the other hand, in the HOS line, administration of extracellular ATP to the culture medium did not cause cell death but increased proliferation (Liu & Chen, 2010). Additionally, when it comes to the properties of the P2X7B split variant in human cancer cell lines, its expression decreased adherence and increased invasion and migration of cells, exhibiting a metastatic phenotype (Tattersall et al., 2021).

P2X7 in skin cancers

P2X7 receptor protein immunodetection in biopsy tissue material from patients suffering from skin cancer showed higher average levels of this receptor compared to normal tissues. Increased synthesis of P2X7 receptor protein has also been observed in normal keratinocyte cells surrounding the tumor (Slater et al., 2003; White et al., 2005). Increased levels of the P2X7 receptor protein can be found in both animal and human cell lines. In spontaneous murine B16 melanoma, the level of P2X7 receptor synthesis may influence the survival of tumor cells after radiotherapy. The use of a combination of radiotherapy and P2X7 receptor inhibitors significantly increased the treatment efficiency (Tanamachi et al., 2017). Many studies have shown that the administration of P2X7 receptor inhibitors alone significantly inhibited the development of tumors derived from murine B16 melanoma (Adinolfi et al., 2015; De Marchi et al., 2019; Brenet et al., 2021). Moreover, an increase in tumor-infiltrating T cells that express low levels of CD39 and CD73 is another effect of P2X7 pharmacological inhibition in B16-derived tumors (De Marchi et al., 2019). When it comes to B16 melanoma, the stimulation by extracellular ATP caused the formation of the cellular pore but it did not significantly affect cell death (Tanamachi et al., 2017). Studies of human melanoma cells contained in the NCI-60 matrix have shown that increased expression of mRNA encoding the P2X7 receptor is a characteristic feature common to all melanoma cells (Shankavaram et al., 2009; Reinhold et al., 2012). Moreover, in both the human A375 melanoma line and in the murine B16 line, the major variant of the P2X7 receptor is the one capable of pore formation in the plasma membrane (White et al., 2005).

P2X7 in pancreatic cancer

Increased expression of mRNA encoding the P2X7 receptor has been detected in patients with chronic pancreatitis and pancreatic cancer (Künzli et al., 2007). The P2X7 receptor protein has also been detected in cell lines derived from pancreatic cancer (Giannuzzo et al., 2015). Experiments using human pancreatic cancer cell lines have demonstrated the diversity of P2X7 receptor isoforms present in them. The tested lines could contain the full isoform – P2X7 A – as well as the shortened isoform – P2X7 B. The P2X7 receptors activated by extracellular nucleotides exerted a proliferative effect on human pancreatic cancer cells. The key molecules involved in P2X7 receptor-induced proliferation and cancer growth were protein kinase C (PKC), phospholiase D (PLD), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), and c-Jun N-terminal kinase (JNK). However, the suppression of inducible nitric oxide synthase (iNOS) by P2X7 receptors indicated their anti-inflammatory role in pancreatic cancer and recovery (Choi et al., 2018). The involvement of the P2X7 receptor in cancer development is also reported in another study. The receptor promotes the proliferation of pancreatic stellate cells (PSC) which are indirectly involved in the progression of pancreatic ductal adenocarcinoma (PDAC). The release of IL-6 cytokine from PSC in response to the P2X7 receptor causes STAT3 activation in pancreatic cancer cells, indicating the importance of P2X7 in the interaction between PSC and cancer cell (Magni et al., 2021). Cells treated with extracellular ATP had a lowered mitotic index (MI) and increased uptake of propidium iodide, which indicates the opening of the cellular pore leading to cell death (Giannuzzo et al., 2015). The same cells were however characterized by increased mobility and invasiveness. The same research group showed the effect of the P2X7 receptor on the invasiveness of these cells in vivo in an orthotopic pancreatic cancer model (Giannuzzo et al., 2016). The administration of the P2X7 receptor inhibitor significantly reduced the tumor volume and the tumor-related fibrotic changes in the pancreas.

P2X7 in breast cancer

The role of the P2X7 receptor activity in breast cancer is much more complex and unclear than in the cases described above. Some researchers indicate a reduced P2X7 synthesis in invasive lobular adenocarcinoma and pancreatic ductal adenocarcinoma compared to normal tissues (Li et al., 2009). Moreover, studies with the use of micro-RNA molecules (miR-150) regulating the synthesis of P2X7 protein have shown that such a reduction in the level of the P2X7 receptor may enhance the development of breast cancer. Cell lines incubated with miR-150 molecules showed increased aggressiveness and invasiveness along with a decrease in P2X7 protein levels. The same results were obtained during in vivo experiments, where administration of miR-150 inhibitors increased P2X7 protein synthesis and thus decreased the aggressiveness of tumors in an orthotopic model of breast cancer (Huang et al., 2013). Similarly, in a different study, BzATP, a P2X7 receptor agonist, significantly increased cancer cell migration and invasion in MCF-7 breast cancer, which effect could be blocked by the P2X7 receptor antagonists (Sharma et al., 2021). There are however results, standing in contradiction with the aforementioned. A study by Tan in 2015, showed increased production of the P2X7 protein in cancer cells compared to normal cells. Moreover, experiments using small interfering RNA have shown that inhibition of receptor synthesis may negatively affect the proliferation of MCF-7 cells. In addition, the downregulation of P2X7 initiated apoptosis in this line. Such studies also showed a positive correlation between the level of the P2X7 receptor and the level of the estrogen receptor (Tan et al., 2015). The observed discrepancy in the studies on the P2X7 receptor level in normal and cancer tissues may be related to variants of this protein. The use of an antibody detecting the C-terminus of a protein will not detect truncated variants of the receptor. Studies with an antibody that detects the extracellular fragment showed an increased level of the P2X7 receptor compared to normal tissues (Slater et al., 2004b). The above examples show how complex the receptor systems in cancer cells can be and how much the research should use methods detecting possible alternative variants of the assembly of transcripts encoding the P2X7 receptor.

The changed level of P2X7 receptor production does not have to be a result of cancer cells expression profile. It may also be associated with adverse environmental conditions in the tumor. The conditions of the lowered oxygen level increased the mRNA and protein of the P2X7 receptor synthesis (Tafani et al., 2010). Additionally, breast cancer patient’s response to treatment was correlated with purinergic signaling of the P2X7 receptor. In contrast to chemoresistant people, non-chemoresistant patients showed a higher level of P2X7 receptor expression CD8+ T cells. Patients with chemoresistance exhibited altered P2X7 receptor activity, which was demonstrated by a constant number of CD8+ T cells activation marker and a decreased level of IFN-γ production in the presence of ATP (Ruiz-Rodríguez et al., 2020). What is more, the application of P2X7 ability to promote cancer cell death in high ATP conditions was described in Draganov study in which the anti-cancer properties of Ivermectin were mediated by differential ATP/P2X7-dependent cytotoxicity (Draganov et al., 2021).

P2X7 in gastrointestinal cancers

In normal, healthy stomach tissue, the synthesis level of the P2X7 receptor remains at a low level. With the appearance of cancer changes, the level of this protein increases. Moreover, the level of P2X7 synthesis is correlated with the stage of tumor development. The more malignant the tumor is and a later stage of development progress, the greater the level of the P2X7 receptor. The above results suggest that the P2X7 receptor may be also a prognostic factor for the malignancy of gastric cancer and the estimated survival time of the patient (Calik et al., 2020).

A more complicated expression pattern is found in colorectal cancer. Analysis of postoperative fragments from 97 patients suffering from colorectal cancer showed a wide range of levels of P2X7 receptor synthesis compared to normal tissues. Moreover, patients with high levels of P2X7 receptor lived significantly shorter compared to patients with low levels of P2X7 receptor synthesis (Zhang et al., 2019). Several variants of the P2X7 receptor have been detected in colorectal cancer. There were functional variants that formed the cell pore as well as shorter variants that lacked this function (Barden, 2014). A similar pattern of P2X7 receptor expression occurs in cell lines. HT-29 and Colo-205 lines are characterized by the presence of shorter P2X7 receptor isoforms devoid of the ability to cell pore formation (Barden et al., 2003), while the HCT8, Caco-2, and MCA38 lines are characterized by the presence of the complete form of the P2X7 receptor which forms the functional cell pore (Coutinho-Silva et al., 2005; Künzli et al., 2011; Bian et al., 2013).

In colon cancer, patients with omental and peritoneal carcinomatosis had greater levels of P2X7 receptor with NLRP3 inflammasome in their adipocytes. The complex showed a correlation with the levels of circulating white blood cells (WBC) and the chemotactic factor MCP-1 implicated in tissue infiltration of monocyte and macrophages. These data indicate the involvement of the P2X7 receptor together with the NLRP3 inflammasome in modulating chemotaxis and spread of the metastasis in colon cancer (Solini et al., 2021).

P2X7 in lung cancer

Transcripts encoding the P2X7 receptor were found in 26 patients suffering from non-small-cell lung carcinoma. Interestingly, in the same studies, no P2X7 transcripts were detected in patients with a chronic obstructive pulmonary disease which may indicate an association of this receptor presence with the appearance of cancer in the lungs. Additionally, the highest expression of mRNA encoding P2X7 was found in metastatic cancer cells (Schmid et al., 2015). The P2X7 receptor is also present in the cancer cell lines of the non-small-cell lung carcinoma, A549, PC-9, and H-292 (Takai et al., 2012, 2014) and is completely absent from normal bronchial epithelial cells, Beas-2B (Takai et al., 2014). In other studies, both tumor and immune cells of lung adenocarcinoma were shown to express the P2X7 receptor, but only immune cells did so with a functioning receptor. The tumors with a high expression of the P2X7B split variant were less infiltrated with B and T cells and more infiltrated with myeloid cells. P2RX7B differential expression positively influenced tumor development by controlling the regulation of the quality of immune cell infiltration (Benzaquen et al., 2020). On the other hand, a small-molecule P2X7 receptor activator improves immune surveillance and stimulates anti-tumor immune responses by enabling the effector functions of adaptive immune T cells. These actions increase the effectiveness of αPD-1, an immune checkpoint inhibitor, in the treatment of non-small cell lung cancer (Douguet et al., 2021). In H-292 cells, the reduction of P2X7 receptor levels decreased actin cytoskeleton remodeling and migration evoked by transforming growth factor beta (TGF-β) (Takai et al., 2014).

P2X7 in blood cancers

P2X7 is also widely distributed in various types of leukemia but there is no uniform pattern in the function of this receptor. In mouse acute erythroleukemia cells (MEL), the P2X7 receptor may form a functional cell membrane pore which leads to cell death (Constantinescu et al., 2010). P2X7 receptor levels are also higher in childhood leukemias (Chong et al., 2010) and it has also been detected in patients with acute myeloblastic leukemia and acute lymphoblastic leukemia (Zhang et al., 2004). Moreover, in the cells of patients with acute myeloblastic leukemia (AML), the increased level of the P2X7 receptor correlated with the shorter survival time of the patients. When it comes to acute myeloid leukemia, it was determined that P2X7A and P2X7B receptor isoforms were overexpressed, demonstrating a favorable correlation between the progression of the disease and both receptor variations. In relapsing patients, the level of P2X7A and P2X7B receptors was downmodulated and upmodulated, respectively, whereas in remitting AML patients both P2X7A and P2X7B receptors expression was decreased. Daunorubicin (DNR), which is one of the primary chemotherapeutic agents for AML, changed the level of P2X7A and P2X7B receptors in AML blasts to the same as in the relapsing patients. In the presence of high ATP levels caused by DNR administration, the P2X7A receptor produced by AML blasts promoted the opening of a large nonselective pore, which allowed the intracellular absorption of anticancer drugs that caused cell death. In contrast, the increase in ATP promoted AML relapse by enabling the growth of P2X7B receptor-expressing blasts, which were unable to form the cytotoxic pore but were still able to activate the channel function of the receptor which protected cells from death caused by chemotherapy (Pegoraro et al., 2020). In a different study, AML development was effectively postponed both in vitro and in vivo by blocking ATP/P2X7 signaling with the particular antagonist. The P2X7 receptor was enhancing leukemogenesis by promoting the self-renewal and homing abilities of leukemia-initiating cells (He et al., 2021). Additionally, the P2X7 receptor accelerated the progression of AML in patients with mixed lineage leukemia (MLL) gene correlated with poor prognostics. Through the activation of the leukemia transcription factor Pbx3, the receptor promoted the proliferation of leukemia stem cells which resulted in the development of AML (Feng et al., 2021). The P2X7 receptor has also been detected in chronic lymphocytic leukemia cells in which the level of the P2X7 receptor has correlated with the severity of the disease (Adinolfi et al., 2002). Other studies related to chronic lymphocytic leukemia have shown the presence of two variants of the P2X7 receptor in these cells. In addition to the complete cell pore-forming receptor, these cells have also produced a truncated form of the P2X7 receptor that did not form the cell pore (Gu et al., 2000).

P2X7 in cervical cancer

In cervical squamous cell carcinoma (CSCC), an immunodetection study of P2X7 receptor variants that did not form the cell pore showed higher levels of this protein compared to healthy tissues (Barden, 2014). The higher risk of HPV-16 positive CSCC development was associated with inherited dysfunction in the P2X7 receptor caused by single nucleotide polymorphisms (Yang et al., 2016). Moreover, other studies showed a decreased level of the full-length variant of the P2X7 receptor, where the level of reduction correlated with the degree of tumor development (Li et al., 2007). Similarly, in the two separate human cervical cancer cell lines, the P2X7 receptor would become engaged in the anticancer activity of atractylenolide-I (Han et al., 2022). There are also reports indicating the coexistence of different P2X7 receptor isoforms in cervical cancer cells, where an alternative P2XJ receptor splicing variant may form non-functional trimers with the P2X7A variant (Feng et al., 2006).

P2X7 in ovarian cancer

The immunodetection of the P2X7 receptor protein showed a high level of this receptor in both: patients with ovarian cancer and in healthy tissue donors. The level of the receptor in healthy and pathological tissues did not differ significantly. Interestingly, in the same studies, cell lines from patients with SKOV-3 and CAOV-3 ovarian cancer showed an increased level of the P2X7 receptor and an increased intensity of proliferation after stimulation by ATP and BzATP (Vázquez-Cuevas et al., 2014). Other studies have shown that in the biopsy material from patients with ovarian cancer, the P2X7 receptor variant that forms the cell pore and shorter pore non-forming variants occur simultaneously (Gilbert et al., 2019).

P2X7 in neuroblastoma

Studies using samples from patients suffering from neuroblastoma showed a high level of P2X7 protein synthesis regardless of the stage of the disease. Neuroblastoma commercial cell lines are also characterized by the presence of the P2X7 protein (Raffaghello et al., 2006). Moreover, the stimulation of neuroblastoma cells by extracellular ATP did not cause cell death but the intensification of cell divisions and increased secretion of substance P. This may suggest that there is a shorter variant of the P2X7 receptor in neuroblastoma cells, which does not cause cell death by pore formation in the membrane (Raffaghello et al., 2006). Other studies have shown robust expression of mRNA encoding the P2X7 receptor in samples from 131 patients suffering from neuroblastoma (Amoroso et al., 2015). It has also been shown that there is a negative correlation between the high expression of the P2X7 gene and the survival time of the patients. Studies using ACN cells showed that lowering the P2X7 receptor level with small interfering mRNA decreased AKT kinase phosphorylation (in vivo and in vitro) and the level of vascularization of cancer tumors in vivo (Amoroso et al., 2015). Moreover, it was indicated that the cooperation between kinin and purinergic signaling networks is crucial for neuroblastoma to spread and metastasize to the bone marrow. The treatment with bradykinin, a pro-metastatic factor, increased the expression levels of the P2X7B isoform in comparison to the P2X7A receptor. As a result, the compound increased tumor proliferation, which P2X7 receptor antagonists greatly reduced. However, bradykinin did not increase cell death or P2X7A receptor-related pore activity, favoring the development of neuroblastoma (Ulrich et al., 2018). Additionally, alternative forms of non-functional P2X7 receptor (nfP2X7) were detected in neuroblastoma. The study indicated that the nfP2X7 receptors were necessary for the survival of the tumor cells. The expression of those receptors was stimulated by high ATP concentrations, which characterize the tumor microenvironment. High concentrations of ATP promoted a transition from P2X7 to nfP2X7. This switch allowed tumor cells to take advantage of nfP2X7 ability to promote cell survival and proliferation without suffering the consequences of large pore-mediated cell death, like in the case of P2X7 receptors (Gilbert et al., 2019).

P2X7 in glioblastoma

Glioblastomas are the most common and malignant primary brain tumors in adults. These tumors are also characterized by the highest degree of malignancy, frequent relapses, rapid growth, and destruction of tissues adjacent to the tumor. The life expectancy of a person diagnosed with glioblastoma ranges from several months to two years after diagnosis (Kleihues et al., 2002; Wen & Kesari, 2008). The high mortality is not only due to the malignancy of the tumor but also to difficult diagnostics and treatment. As tumors develop behind the blood-brain barrier, chemotherapy is limited to a few orally administered chemotherapeutic agents such as Temozolomide (Bush et al., 2017), able to cross this barrier. Radiation therapy is not always efficient either. This is due to the different resistance to ionizing radiation in patients and the highly hypoxic nature of glioblastoma which hinders the effects of radiotherapy (Amberger-Murphy, 2009). The most commonly used treatment strategy that ensures the longest disease-free time and improves the patient’s life is the surgical removal of the tumor along with the surrounding tissues (Li et al., 2016b). However, due to the cancer cells’ tendency to infiltrate surrounding tissue, it is almost impossible to remove the tumor completely and the residual tumor remnants are left behind to cause the disease to relapse soon.

The P2X7 receptor is, along with other nucleotide receptors, widely distributed in all cells that make up the brain tissue (Collo et al., 1997; Duan & Neary, 2006; Yu et al., 2008; Jimenez-Mateos et al., 2019). Not surprisingly, this receptor is also observed in many pathological conditions in the brain, including glioblastoma. The P2X7 receptor is present in almost all cell models of glioblastoma but its role in the development of this disease is unclear. Analysis of the protein level and expression of the gene encoding P2X7 showed a decreased level of the P2X7 receptor in glioma as compared to the healthy brain. The authors of the study explained this phenomenon by the strong methylation of the gene encoding P2X7 (Liu et al., 2017).

In studies using the murine glioblastoma line GL261, this receptor increases susceptibility to cell death and reduces resistance to radiotherapy. Decreasing the P2X7 receptor level using small interfering RNA did not reduce tumor size in the in vivo model. However, tumors with decreased levels of this receptor were significantly less responsive to radiation therapy (Gehring et al., 2015). Tamajusuku showed similar results indicating the positive role of the P2X7 receptor in stimulating cell death in vitro. Mouse GL261 glioma cells, stimulated by extracellular ATP, died as a result of necrosis (Tamajusuku et al., 2010). Moreover, in this cell line, the P2X7 receptor is probably functional and its activation results in a calcium signal and a cell pore formation, leading to cell death. Studies by Strong’s group showed an increase in calcium signal when stimulated by extracellular ATP. The stimulation of the receptor in a medium with a reduced content of calcium ions significantly reduced the number of responding cells. Moreover, the addition of the P2X7 receptor permanent inhibitor – oxATP – also decreased the number of responding cells (Strong et al., 2018). In conclusion, in the murine model of GL261 glioma, the P2X7 receptor functions as a receptor regulating cell death, and its stimulation by extracellular ATP may enhance the anti-tumor effect in therapy.

Studies of the function of the P2X7 receptor that occurs in rats’ glioblastoma are much more confusing. Studies using extracellularly administered apyrase, an enzyme that hydrolyzes ATP, showed that applying it to the area of the implanted C6 glioma tumor reduced its volume. Moreover, the effects of tumor inhibition were similar to those obtained in the group of animals treated with temozolomide (Morrone et al., 2006). However, the functionality of the P2X7 receptor in C6 glioma cells in vitro remains unclear. Some researchers believe that the calcium signal appearing after the administration of ATP or BzATP comes from the stimulation of the P2X7 receptor, and that stimulation of this receptor increases the aggressiveness of C6 glioma cells and the expression of this receptor itself (Wei et al., 2008). Also, other studies showed the appearance of a calcium signal after stimulation by BzATP and increased intensity of proliferation with no signs of cell death (Matyśniak et al., 2020). On the other hand, studies on the calcium signal in C6 glioma also showed the possibility of P2Y2 receptor stimulation by BzATP and the lack of cellular pore formation after P2X7 receptor stimulation (Supłat-Wypych et al., 2010). Other research groups indicate the TRPM7 ion channel (transient receptor potential cation channel, subfamily M, member 7) as a source of calcium signal after BzATP administration in C6 glioma cells (Nörenberg et al., 2016). It should be noted, however, that so far, no studies using small interfering RNA or other genetic engineering methods have been performed that could help test P2X7 activity in these cells in vitro.

In vivo studies with rat C6 glioblastoma show a clear and significant role of the P2X7 receptor in regulating tumor aggressiveness. Administration of an inhibitor of this receptor (BBG) to rats with C6 glioma led to a significant reduction in the size of tumors and the amount of infiltrating microglia in the tumor mass (Ryu et al., 2011). Moreover, the influence of the P2X7 receptor on the secretion of macrophage inflammatory protein (MIP-1α), which may promote microglia recruitment and support the aggressiveness of C6 glioma has also been demonstrated (Fang et al., 2011). However, there is also a report in the literature that the P2X7 receptor has an inhibitory effect on the development of C6 glioma. Studies by Fang et al. have shown that inhibition of the P2X7 receptor increases tumor size and increases expression of the P2Y2 receptor, hypoxia-inducible factor 1 (HIF-1α), and vascular endothelial growth factor (VEGF) (Fang et al., 2013).

The expression pattern and functional properties of the P2X7 receptor in human glioma cells are similarly complex. The P2X7 receptor is present in almost all studied lines of human glioblastoma (Ji et al., 2018; Bergamin et al., 2019; Matyśniak et al., 2020) and patient tissues (Ziberi et al., 2019). However, the functionality of this receptor differs depending on the cell line. All aforementioned research groups working on this issue clearly indicate the lack of P2X7-induced cell death in human glioblastoma cultures. However, this is where the consistency of the results ends. Ji et al. showed that stimulation of the P2X7 receptor by the agonist BzATP positively influenced the proliferation of human glioma cells. However, studies of other groups do not confirm these reports (Bergamin et al., 2019; Matyśniak et al., 2020). Inhibition of P2X7 receptor activity influenced tumor size in the in vivo model of human U-138 glioma (Bergamin et al., 2019). Also, in the human U-251 glioma model, blocking P2X7 receptor activity inhibited cell proliferation and the secretion of granulocyte-macrophage colony-stimulating factor (GM-CSF). Moreover, inhibition of cell growth following administration of a P2X7 inhibitor had the same effect in inhibiting proliferation as treatment of cells with temozolomide (Kan et al., 2020; Drill et al., 2020).

Extracellular ATP may also influence the development of spheroids in vitro as well as the share of glioblastoma stem cells in all tumor cells population. ATP administered to the culture medium decreased the level of stem cell markers and decreased the size of the spheroids of the human glioma lineage (Ledur et al., 2012). However, studies using glioblastoma stem cells isolated from patients have shown the stimulating role of the P2X7 receptor on the development of stem cells and the presence of epithelial-mesenchymal transition (EMT) markers which contribute to increased cell migration (Ziberi et al., 2019).

There are also reports of an inhibitory effect of glioblastoma P2X7 receptor on radiation-sensitive human M059J glioblastoma. Cell irradiation increased P2X7 receptor synthesis in these cells and increased the number of cells entering the cell death pathway (Gehring et al., 2012). Similarly, after cell irradiation, a shift in the P2X7 isoform expression was detected – the P2X7A and P2X7B isoforms were down- and upregulated, respectively. These emerged clones resistant to the radiation were responsible for tumor recurrence. The combination of radiotherapy with P2X7R-targeting drugs was a more effective treatment than radiation alone – treatment with P2X7 receptors antagonists during the recovery phase increased irradiation-dependent cytotoxicity and cell death in GB40 and GB48 cells (Zanoni et al., 2022).

Summarizing, a heterogeneous picture emerges from the research on the role of the P2X7 receptor. This receptor appears to be involved in many cellular functions but to fully understand its role in glioblastoma, more in-depth research is needed to reveal molecular interactions and mechanisms.

References

Abbracchio MP, Boeynaems JM, Barnard EA, Boyer JL, Kennedy C, Miras-Portugal MT, King BF, Gachet C, Jacobson KA, Weisman GA, Burnstock G (2003) Characterization of the UDP-glucose receptor (re-named here the P2Y 14 receptor) adds diversity to the P2Y receptor family. Trends Pharmacol. Sci. 24: 52–55. https://doi.org/10.1016/S0165-6147(02)00038-X

Adinolfi E, Melchiorri L, Falzoni S, Chiozzi P, Morelli A, Tieghi A, Cuneo A, Castoldi G, Di Virgilio F, Baricordi OR (2002) P2X7 receptor expression in evolutive and indolent forms of chronic B lymphocytic leukemia. Blood 99: 706–708. https://doi.org/10.1182/blood.V99.2.706

Adinolfi E, Kim M, Young MT, Di Virgilio F, Surprenant A (2003) Tyrosine phosphorylation of HSP90 within the P2X7 receptor complex negatively regulates P2X7 receptors. J. Biol. Chem. 278: 37344–37351. https://doi.org/10.1074/jbc.M301508200

Adinolfi E, Callegari MG, Ferrari D, Bolognesi C, Minelli M, Wieckowski MR, Pinton P, Rizzuto R, Di Virgilio F (2005) Basal activation of the P2X7 ATP receptor elevates mitochondrial calcium and potential, increases cellular ATP levels, and promotes serum-independent growth. Mol. Biol. Cell 16: 3260–3272. https://doi.org/10.1091/mbc.E04-11-1025

Adinolfi E, Cirillo M, Woltersdorf R, Falzoni S, Chiozzi P, Pellegatti P, Callegari MG, Sandonà D, Markwardt F, Schmalzing G, Di Virgilio F (2010) Trophic activity of a naturally occurring truncated isoform of the P2X7 receptor. FASEB J. 24: 3393–3404. https://doi.org/10.1096/fj.09-153601

Adinolfi E, Capece M, Franceschini A, Falzoni S, Giuliani AL, Rotondo A, Sarti AC, Bonora M, Syberg S, Corigliano D, Pinton P, Jorgensen NR, Abelli L, Emionite L, Raffaghello L, Pistoia V, Di Virgilio F (2015) Accelerated tumor progression in mice lacking the ATP receptor P2X7. Cancer Res. 75: 635–644. https://doi.org/10.1158/0008-5472.CAN-14-1259

Adriouch S, Ohlrogge W, Haag F, Koch-Nolte F, Seman M (2001) Rapid induction of naive T cell apoptosis by ecto-nicotinamide adenine dinucleotide: requirement for mono(ADP-ribosyl)transferase 2 and a downstream effector. J. Immunol. 167: 196–203. https://doi.org/10.4049/jimmunol.167.1.196

Adriouch S, Bannas P, Schwarz N, Fliegert R, Guse AH, Seman M, Haag F, Koch-Noke F (2008) ADP-ribosylation at R125 gates the P2X7 ion channel by presenting a covalent ligand to its nucleotide binding site. FASEB J. 22: 861–869. https://doi.org/10.1096/fj.07-9294com

Alfadda AA, Sallam RM (2012) Reactive oxygen species in health and disease. J. Biomed. Biotechnol. 2012: 936486. https://doi.org/10.1155/2012/936486

Alqallaf SM, Evans BAJ, Kidd EJ (2009) Atypical P2X 7 receptor pharmacology in two human osteoblast-like cell lines. Br. J. Pharmacol. 156: 1124–1135. https://doi.org/10.1111/j.1476-5381.2009.00119.x

Amberger-Murphy V (2009) Hypoxia helps glioma to fight therapy. Curr. Cancer Drug Targets 9: 381–390. https://doi.org/10.2174/156800909788166637

Amoroso F, Falzoni S, Adinolfi E, Ferrari D, Di Virgilio F (2012) The P2X7 receptor is a key modulator of aerobic glycolysis. Cell Death Dis. 3: e370. https://doi.org/10.1038/cddis.2012.105

Amoroso F, Capece M, Rotondo A, Cangelosi D, Ferracin M, Franceschini A, Raffaghello L, Pistoia V, Varesio L, Adinolfi E (2015) The P2X7 receptor is a key modulator of the PI3K/GSK3β/VEGF signaling network: Evidence in experimental neuroblastoma. Oncogene 34: 5240–5251. https://doi.org/10.1038/onc.2014.444

Amstrup J, Novak I (2003) P2X7 receptor activates extracellular signal-regulated kinases ERK1 and ERK2 independently of Ca2+ influx. Biochem. J. 374: 51–61. https://doi.org/10.1042/BJ20030585

Andrejew R, Oliveira-Giacomelli Á, Ribeiro DE, Glaser T, Arnaud-Sampaio VF, Lameu C, Ulrich H (2020) The P2X7 receptor: central hub of brain diseases. Front. Mol. Neurosci. 13: 124. https://doi.org/10.3389/fnmol.2020.00124

Anselmi F, Hernandez VH, Crispino G, Seydel A, Ortolanoa S, Roper SD, Kessaris N, Richardson W, Rickheit G, Filippov MA, Monyer H, Mammano F (2008) ATP release through connexin hemichannels and gap junction transfer of second messengers propagate Ca2+ signals across the inner ear. Proc. Natl. Acad. Sci. U. S. A. 105: 18770–18775. https://doi.org/10.1073/pnas.0800793105

Apolloni S, Fabbrizio P, Amadio S, Napoli G, Freschi M, Sironi F, Pevarello P, Tarroni P, Liberati C, Bendotti C, Volonté C (2021) Novel P2X7 antagonist ameliorates the early phase of ALS disease and decreases inflammation and autophagy in SOD1-G93A mouse model. Int. J. Mol. Sci. 22: 10649. https://doi.org/10.3390/IJMS221910649

Bada JL (2004) How life began on Earth: A status report. Earth Planet. Sci. Lett. 226: 1–15. https://doi.org/10.1016/j.epsl.2004.07.036

Bader A, Bintig W, Begandt D, Klett A, Siller IG, Gregor C, Schaarschmidt F, Weksler B, Romero I, Couraud PO, Hell SW, Ngezahayo A (2017) Adenosine receptors regulate gap junction coupling of the human cerebral microvascular endothelial cells hCMEC/D3 by Ca2+ influx through cyclic nucleotide-gated channels. J. Physiol. 595: 2497–2517. https://doi.org/10.1113/JP273150

Bae YS, Oh H, Rhee SG, Yoo Y Do (2011) Regulation of reactive oxygen species generation in cell signaling. Mol. Cells 32: 491–509. https://doi.org/10.1007/s10059-011-0276-3

Baraldi PG, Tabrizi MA, Gessi S, Borea PA (2008) Adenosine receptor antagonists: Translating medicinal chemistry and pharmacology into clinical utility. Chem. Rev. 108: 238–263. https://doi.org/10.1021/cr0682195

Barberà-Cremades M, Baroja-Mazo A, Gomez AI, Machado F, Di Virgilio F, Pelegrín P (2012) P2X7 receptor-stimulation causes fever via PGE2 and IL-1β release. FASEB J. 26: 2951–2962. https://doi.org/10.1096/fj.12-205765

Barden JA, Sluyter R, Gu BJ, Wiley JS (2003) Specific detection of non-functional human P2X7 receptors in HEK293 cells and B-lymphocytes. FEBS Lett. 538: 159–162. https://doi.org/10.1016/S0014-5793(03)00172-8

Barden JA (2014) Non-functional P2X7: A novel and ubiquitous target in human cancer. J. Clin. Cell. Immunol. 05. https://doi.org/10.4172/2155-9899.1000237

Baricordi OR, Melchiorri L, Adinolfi E, Falzoni S, Chiozzi P, Buell G, Di Virgilio F (1999) Increased proliferation rate of lymphoid cells transfected with the P2X7 ATP receptor. J. Biol. Chem. 274: 33206–33208. https://doi.org/10.1074/jbc.274.47.33206

Bartlett R, Stokes L, Sluyter R (2014) The p2x7 receptor channel: Recent developments and the use of p2x7 antagonists in models of disease. Pharmacol. Rev. 66: 638–675. https://doi.org/10.1124/pr.113.008003

Bazil JN, Buzzard GT, Rundell AE (2010) Modeling mitochondrial bioenergetics with integrated volume dynamics. PLoS Comput. Biol. 6: e1000632. https://doi.org/10.1371/journal.pcbi.1000632

Benzaquen J, Dit Hreich SJ, Heeke S, Juhel T, Lalvee S, Bauwens S, Saccani S, Lenormand P, Hofman V, Butori M, Leroy S, Berthet JP, Marquette CH, Hofman P, Vouret-Craviari V (2020) P2RX7B is a new theranostic marker for lung adenocarcinoma patients. Theranostics 10: 10849–10860. https://doi.org/10.7150/thno.48229

Bergamin LS, Capece M, Salaro E, Sarti AC, Falzoni S, Pereira MSL, De Bastiani MA nio, Scholl JN, Battastini AMO, Di Virgilio F (2019) Role of the P2X7 receptor in in vitro and in vivo glioma tumor growth. Oncotarget 10: 4840–4856. https://doi.org/10.18632/oncotarget.27106

Berridge MJ (1993) Inositol trisphosphate and calcium signalling. Nature 361: 315–325. https://doi.org/10.1038/361315a0

Berridge MJ, Bootman MD, Roderick HL (2003) Calcium signalling: Dynamics, homeostasis and remodelling. Nat. Rev. Mol. Cell Biol. 4: 517–529. https://doi.org/10.1038/nrm1155

Bian S, Sun X, Bai A, Zhang C, Li L, Enjyoji K, Junger WG, Robson SC, Wu Y (2013) P2X7 Integrates PI3K/AKT and AMPK-PRAS40-mTOR signaling pathways to mediate tumor cell death. PLoS One 8: e60184. https://doi.org/10.1371/journal.pone.0060184

Bianco F, Ceruti S, Colombo A, Fumagalli M, Ferrari D, Pizzirani C, Matteoli M, Di Virgilio F, Abbracchio MP, Verderio C (2006) A role for P2X 7 in microglial proliferation. J. Neurochem. 99: 745–758. https://doi.org/10.1111/j.1471-4159.2006.04101.x

Boldrini L, Giordano M, Alì G, Melfi F, Romano G, Lucchi M, Fontanini G (2015) P2x7 mrna expression in non-small cell lung cancer: MicroRNA regulation and prognostic value. Oncol. Lett. 9: 449–453. https://doi.org/10.3892/ol.2014.2620

Borea PA, Varani K, Vincenzi F, Baraldi PG, Tabrizi MA, Merighi S, Gessi S (2015) The a3 adenosine receptor: History and perspectives. Pharmacol. Rev. 67: 74–102. https://doi.org/10.1124/pr.113.008540

Borea PA, Gessi S, Merighi S, Vincenzi F, Varani K (2018) Pharmacology of adenosine receptors: The state of the art. Physiol. Rev. 98: 1591–1625. https://doi.org/10.1152/physrev.00049.2017

Bradley HJ, Browne LE, Yang W, Jiang LH (2011) Pharmacological properties of the rhesus macaque monkey P2X7 receptor. Br. J. Pharmacol. 164: 743–754. https://doi.org/10.1111/j.1476-5381.2011.01399.x

Brenet M, Martínez S, Pérez-Nuñez R, Pérez LA, Contreras P, Díaz J, Avalos AM, Schneider P, Quest AFG, Leyton L (2021) Thy-1 (CD90)-induced metastatic cancer cell migration and invasion are β3 integrin-dependent and involve a Ca2+/P2X7 receptor signaling axis. Front. Cell Dev. Biol. 8: 592442. https://doi.org/10.3389/fcell.2020.592442

Broom DC, Matson DJ, Bradshaw E, Buck ME, Meade R, Coombs S, Matchett M, Ford KK, Yu W, Yuan J, Sun SH, Ochoa R, Krause JE, Wustrow DJ, Cortright DN (2008) Characterization of N-(adamantan-1-ylmethyl)-5-[(3R-amino-pyrrolidin-1-yl) methyl]-2-chloro-benzamide, a P2X7 antagonist in animal models of pain and inflammation. J. Pharmacol. Exp. Ther. 327: 620–633. https://doi.org/10.1124/jpet.108.141853

Bryant DE, Greenfield D, Walshaw RD, Johnson BRG, Herschy B, Smith C, Pasek MA, Telford R, Scowen I, Munshi T, Edwards HGM, Cousins CR, Crawford IA, Kee TP (2013) Hydrothermal modification of the Sikhote-Alin iron meteorite under low pH geothermal environments. A plausibly prebiotic route to activated phosphorus on the early Earth. Geochim. Cosmochim. Acta 109: 90–112. https://doi.org/10.1016/j.gca.2012.12.043

Buell GN, Talabot F, Gos A, Lorenz J, Lai E, Morris MA, Antonarakis SE (1998) Gene structure and chromosomal localization of the human P2X7 receptor. Recept. Channels 5: 347–354

Burnstock G (1972) Purinergic nerves. Pharmacol. Rev. 24: 509–581

Burnstock G, Kennedy C (1985) Is there a basis for distinguishing two types of P2-purinoceptor? Gen. Pharmacol. 16: 433–440. https://doi.org/10.1016/0306-3623(85)90001-1

Burnstock G, Knight GE (2004) Cellular distribution and functions of P2 receptor subtypes in different systems. Int. Rev. Cytol. 240: 31–304. https://doi.org/10.1016/S0074-7696(04)40002-3

Burnstock G (2007) Physiology and pathophysiology of purinergic neurotransmission. Physiol. Rev. 87: 659–797. https://doi.org/10.1152/physrev.00043.2006

Burnstock G, Verkhratsky A (2012) Purinergic signalling and the nervous system. Springer-Verlag, Berlin Heidelberg. https://doi.org/10.1007/978-3-642-28863-0

Bush NAO, Chang SM, Berger MS (2017) Current and future strategies for treatment of glioma. Neurosurg. Rev. 40: 1–14. https://doi.org/10.1007/s10143-016-0709-8

Calik I, Calik M, Sarikaya B, Ozercan IH, Arslan R, Artas G, Dagli AF (2020) P2X7 receptor as an independent prognostic indicator in gastric cancer. Bosn. J. basic Med. Sci. 20: 188–196. https://doi.org/10.17305/BJBMS.2020.4620

Cankurtaran-Sayar S, Sayar K, Ugur M (2009) P2X7 receptor activates multiple selective dye-permeation pathways in RAW 264.7 and human embryonic kidney 293 cells. Mol. Pharmacol. 76: 1323–1332. https://doi.org/10.1124/mol.109.059923

Chaudry IH (1982) Does ATP cross the cell plasma membrane. Yale J. Biol. Med. 55: 1–10

Cheewatrakoolpong B, Gilchrest H, Anthes JC, Greenfeder S (2005) Identification and characterization of splice variants of the human P2X7 ATP channel. Biochem. Biophys. Res. Commun. 332: 17–27. https://doi.org/10.1016/j.bbrc.2005.04.087

Chen JF, Eltzschig HK, Fredholm BB (2013) Adenosine receptors as drug targets-what are the challenges? Nat. Rev. Drug Discov. 12: 265–286. https://doi.org/10.1038/nrd3955

Chessell IP, Simon J, Hibell AD, Michel AD, Barnard EA, Humphrey PPA (1998) Cloning and functional characterisation of the mouse P2X7 receptor. FEBS Lett. 439: 26–30. https://doi.org/10.1016/S0014-5793(98)01332-5

Choi JH, Ji YG, Ko JJ, Cho HJ, Lee DH (2018) Activating P2X7 receptors increases proliferation of human pancreatic cancer cells via ERK1/2 and JNK. Pancreas 47: 643–651. https://doi.org/10.1097/MPA.0000000000001055

Chong JH, Zheng GG, Zhu XF, Guo Y, Wang L, Ma CH, Liu SY, Xu LL, Lin YM, Wu KF (2010) Abnormal expression of P2X family receptors in Chinese pediatric acute leukemias. Biochem. Biophys. Res. Commun. 391: 498–504. https://doi.org/10.1016/j.bbrc.2009.11.087

Chow SC, Kass GEN, Orrenius S (1997) Purines and their roles in apoptosis. Neuropharmacology 36: 1149–1156. https://doi.org/10.1016/S0028-3908(97)00123-8

Clapham DE (2007) Calcium signaling. Cell 131: 1047–1058. https://doi.org/10.1016/j.cell.2007.11.028

Clarke CE, Benham CD, Bridges A, George AR, Meadows HJ (2000) Mutation of histidine 286 of the human P2X4 purinoceptor removes extracellular pH sensitivity. J. Physiol. 523: 697–703. https://doi.org/10.1111/j.1469-7793.2000.00697.x

Cockcroft S, Gomperts BD (1980) The ATP4-receptor of rat mast cells. Biochem. J. 188: 789–798. https://doi.org/10.1042/bj1880789

Collo G, Neidhart S, Kawashima E, Kosco-Vilbois M, North RA, Buell G (1997) Tissue distribution of the P2X7 receptor. Neuropharmacology 36: 1277–1283. https://doi.org/10.1016/S0028-3908(97)00140-8

Constantinescu P, Wang B, Kovacevic K, Jalilian I, Bosman GJCGM, Wiley JS, Sluyter R (2010) P2X7 receptor activation induces cell death and microparticle release in murine erythroleukemia cells. Biochim. Biophys. Acta – Biomembr. 1798: 1797–1804. https://doi.org/10.1016/j.bbamem.2010.06.002

Costa-Junior HM, Vieira FS, Coutinho-Silva R (2011) C terminus of the P2X7 receptor: Treasure hunting. Purinergic Signal. 7: 7–19. https://doi.org/10.1007/s11302-011-9215-1

Coutinho-Silva R, Alves LA, De Carvalho ACC, Savino W, Persechini PM (1996) Characterization of P2Z purinergic receptors on phagocytic cells of the thymic reticulum in culture. Biochim. Biophys. Acta – Biomembr. 1280: 217–222. https://doi.org/10.1016/0005-2736(95)00293-6

Coutinho-Silva R, Stahl L, Cheung KK, De Campos NE, De Oliveira Souza C, Ojeius DM, Burnstock G (2005) P2X and P2Y purinergic receptors on human intestinal epithelial carcinoma cells: Effects of extracellular nucleotides on apoptosis and cell proliferation. Am. J. Physiol. – Gastrointest. Liver Physiol. 288: G1024G1035. https://doi.org/10.1152/ajpgi.00211.2004

Dahl G, Qiu F, Wang J (2013) The bizarre pharmacology of the ATP release channel pannexin1. Neuropharmacology 75: 583–593. https://doi.org/10.1016/j.neuropharm.2013.02.019

Danquah W, Meyer-Schwesinger C, Rissiek B, Pinto C, Serracant-Prat A, Amadi M, Iacenda D, Knop JH, Hammel A, Bergmann P, Schwarz N, Assunção J, Rotthier W, Haag F, Tolosa E, Bannas P, Boué-Grabot E, Magnus T, Laeremans T, Stortelers C, Koch-Nolte F (2016) Nanobodies that block gating of the P2X7 ion channel ameliorate inflammation. Sci. Transl. Med. 8: 366ra162. https://doi.org/10.1126/scitranslmed.aaf8463

Denlinger LC, Fisette PL, Sommer JA, Watters JJ, Prabhu U, Dubyak GR, Proctor RA, Bertics PJ (2001) Cutting edge: The nucleotide receptor P2X 7 contains multiple protein- and lipid-interaction motifs including a potential binding site for bacterial lipopolysaccharide. J. Immunol. 167: 1871–1876. https://doi.org/10.4049/jimmunol.167.4.1871

Denton RM (2009) Regulation of mitochondrial dehydrogenases by calcium ions. Biochim. Biophys. Acta – Bioenerg. 1787: 1309–1316. https://doi.org/10.1016/j.bbabio.2009.01.005

Dinarello CA (1994) The biological properties of interleukin-1. Eur. Cytokine Netw. 5: 517–531

Dinarello CA (2018) Introduction to the interleukin-1 family of cytokines and receptors: Drivers of innate inflammation and acquired immunity. Immunol. Rev. 281: 5–7. https://doi.org/10.1111/imr.12624

Donnelly-Roberts DL, Namovic MT, Han P, Jarvis MF (2009) Mammalian P2X7 receptor pharmacology: Comparison of recombinant mouse, rat and human P2X7 receptors. Br. J. Pharmacol. 157: 1203–1214. https://doi.org/10.1111/j.1476-5381.2009.00233.x

Douguet L, Janho dit Hreich S, Benzaquen J, Seguin L, Juhel T, Dezitter X, Duranton C, Ryffel B, Kanellopoulos J, Delarasse C, Renault N, Furman C, Homerin G, Féral C, Cherfils-Vicini J, Millet R, Adriouch S, Ghinet A, Hofman P, Vouret-Craviari V (2021) A small-molecule P2RX7 activator promotes anti-tumor immune responses and sensitizes lung tumor to immunotherapy. Nat. Commun. 12: 653. https://doi.org/10.1038/s41467-021-20912-2

Draganov D, Han Z, Rana A, Bennett N, Irvine DJ, Lee PP (2021) Ivermectin converts cold tumors hot and synergizes with immune checkpoint blockade for treatment of breast cancer. npj Breast Cancer 7: 22. https://doi.org/10.1038/s41523-021-00229-5

Drill M, Powell KL, Kan LK, Jones NC, O’Brien TJ, Hamilton JA, Monif M (2020) Inhibition of purinergic P2X receptor 7 (P2X7R) decreases granulocyte-macrophage colony-stimulating factor (GM-CSF) expression in U251 glioblastoma cells. Sci. Rep. 10: 14844. https://doi.org/10.1038/s41598-020-71887-x

Drury AN, Szent-Györgyi A (1929) The physiological activity of adenine compounds with especial reference to their action upon the mammalian heart. J. Physiol. 68: 213–237. https://doi.org/10.1113/jphysiol.1929.sp002608

Duan S, Neary JT (2006) P2X7 receptors: Properties and relevance to CNS function. Glia 54: 738–746. https://doi.org/10.1002/glia.20397

Dubyak GR (2012) P2X7 receptor regulation of non-classical secretion from immune effector cells. Cell. Microbiol. 14: 1697–1706. https://doi.org/10.1111/cmi.12001

Elssner A, Duncan M, Gavrilin M, Wewers MD (2004) A novel P2X 7 receptor activator, the human cathelicidin-derived peptide LL37, induces IL-1β processing and release. J. Immunol. 172: 4987–4994. https://doi.org/10.4049/jimmunol.172.8.4987

Ennion, Hagan, Evans (2000) The role of positively charged amino acids in ATP recognition by human P2X1 receptors. J. Biol. Chem. 275: 35656

Evans RJ, Lewis C, Buell G, Valera S, North RA, Surprenant A (1995) Pharmacological characterization of heterologously expressed ATP-gated cation channels (P(2x) purinoceptors). Mol. Pharmacol. 48: 178–183

Fang J, Chen X, Zhang L, Chen J, Liang Y, Li X, Xiang J, Wang L, Guo G, Zhang B, Zhang W (2013) P2X7R suppression promotes glioma growth through epidermal growth factor receptor signal pathway. Int. J. Biochem. Cell Biol. 45: 1109–1120. https://doi.org/10.1016/j.biocel.2013.03.005

Fang KM, Wang YL, Huang MC, Sun SH, Cheng H, Tzeng SF (2011) Expression of macrophage inflammatory protein-1α and monocyte chemoattractant protein-1 in glioma-infiltrating microglia: Involvement of ATP and P2X7 receptor. J. Neurosci. Res. 89: 199–211. https://doi.org/10.1002/jnr.22538

Feng W, Yang X, Wang L, Wang R, Yang F, Wang H, Liu X, Ren Q, Zhang Y, Zhu X, Zheng G (2021) P2X7 promotes the progression of MLL-AF9-induced acute myeloid leukemia by upregulation of Pbx3. Haematologica 106: 1278–1289. https://doi.org/10.3324/haematol.2019.243360

Feng YH, Li X, Wang L, Zhou L, Gorodeski GI (2006) A truncated P2X7 receptor variant (P2X7-j) endogenously expressed in cervical cancer cells antagonizes the full-length P2X7 receptor through hetero-oligomerization. J. Biol. Chem. 281: 17228–17237. https://doi.org/10.1074/jbc.M602999200

Ferrari D, Villalba M, Chiozzi P, Falzoni S, Ricciardi-Castagnoli P, Di Virgilio F (1996) Mouse microglial cells express a plasma membrane pore gated by extracellular ATP. J. Immunol. 156: 1531–1539

Ferrari D, Pizzirani C, Adinolfi E, Forchap S, Sitta B, Turchet L, Falzoni S, Minelli M, Baricordi R, Di Virgilio F (2004) The antibiotic polymyxin B modulates P2X 7 receptor function. J. Immunol. 173: 4652–4660. https://doi.org/10.4049/jimmunol.173.7.4652

Fishman P, Bar-Yehuda S, Madi L, Cohn I (2002) A3 adenosine receptor as a target for cancer therapy. Anticancer. Drugs 13: 437–443. https://doi.org/10.1097/00001813-200206000-00001

Fonfria E, Clay WC, Levy DS, Goodwin JA, Roman S, Smith GD, Condreay JP, Michel AD (2008) Cloning and pharmacological characterization of the guinea pig P2X 7 receptor orthologue. Br. J. Pharmacol. 153: 544–556. https://doi.org/10.1038/sj.bjp.0707596

Fredholm BB, Arslan G, Halldner L, Kull B, Schulte G, Wasserman W (2000) Structure and function of adenosine receptors and their genes. Naunyn. Schmiedebergs. Arch. Pharmacol. 362: 364–374. https://doi.org/10.1007/s002100000313

Galadari S, Rahman A, Pallichankandy S, Thayyullathil F (2017) Reactive oxygen species and cancer paradox: To promote or to suppress? Free Radic. Biol. Med. 104: 144–164. https://doi.org/10.1016/j.freeradbiomed.2017.01.004

Garcia-Guzman M, Stühmer W, Soto F (1997) Molecular characterization and pharmacological properties of the human P2X3 purinoceptor. Mol. Brain Res. 47: 59–66. https://doi.org/10.1016/S0169-328X(97)00036-3

García-Huerta P, Diáz-Hernandez M, Delicado EG, Pimentel-Santillana M, Miras-Portugals MT, Goḿez-Villafuertes R (2012) The specificity protein factor Sp1 mediates transcriptional regulation of P2X7 receptors in the nervous system. J. Biol. Chem. 287: 44628–44644. https://doi.org/10.1074/jbc.M112.390971

Gartland A, Hipskind RA, Gallagher JA, Bowler WB (2001) Expression of a P2X7 receptor by a subpopulation of human osteoblasts. J. Bone Miner. Res. 16: 846–856. https://doi.org/10.1359/jbmr.2001.16.5.846

Gebhart GF, Schmidt RF eds. (2013) Encyclopedia of Pain. Springer Berlin Heidelberg, https://doi.org/10.1007/978-3-642-28753-4

Gehring MP, Pereira TCB, Zanin RF, Borges MC, Filho AB, Battastini AMO, Bogo MR, Lenz G, Campos MM, Morrone FB (2012) P2X7 receptor activation leads to increased cell death in a radiosensitive human glioma cell line. Purinergic Signal. 8: 729–739. https://doi.org/10.1007/s11302-012-9319-2

Gehring MP, Kipper F, Nicoletti NF, Sperotto ND, Zanin R, Tamajusuku ASK, Flores DG, Meurer L, Roesler R, Filho AB, Lenz G, Campos MM, Morrone FB (2015) P2X7 receptor as predictor gene for glioma radiosensitivity and median survival. Int. J. Biochem. Cell Biol. 68: 92–100. https://doi.org/10.1016/j.biocel.2015.09.001

Gever JR, Cockayne DA, Dillon MP, Burnstock G, Ford APDW (2006) Pharmacology of P2X channels. Pflugers Arch. Eur. J. Physiol. 452: 513–537. https://doi.org/10.1007/s00424-006-0070-9

Ghalali A, Wiklund F, Zheng H, Stenius U, Högberg J (2014) Atorvastatin prevents ATP-driven invasiveness via P2X7 and EHBP1 signaling in PTEN-expressing prostate cancer cells. Carcinogenesis 35: 1547–1555. https://doi.org/10.1093/carcin/bgu019

Giannuzzo A, Pedersen SF, Novak I (2015) The P2X7 receptor regulates cell survival, migration and invasion of pancreatic ductal adenocarcinoma cells. Mol. Cancer 14: 203. https://doi.org/10.1186/s12943-015-0472-4

Giannuzzo A, Saccomano M, Napp J, Ellegaard M, Alves F, Novak I (2016) Targeting of the P2X7 receptor in pancreatic cancer and stellate cells. Int. J. Cancer 139: 2540–2552. https://doi.org/10.1002/ijc.30380

Gilbert S, Oliphant C, Hassan S, Peille A, Bronsert P, Falzoni S, Di Virgilio F, McNulty S, Lara R (2019) ATP in the tumour microenvironment drives expression of nfP2X 7, a key mediator of cancer cell survival. Oncogene 38: 194–208. https://doi.org/10.1038/s41388-018-0426-6

Gilbert SM, Gidley Baird A, Glazer S, Barden JA, Glazer A, Teh LC, King J (2017) A phase I clinical trial demonstrates that nfP2X7 -targeted antibodies provide a novel, safe and tolerable topical therapy for basal cell carcinoma. Br. J. Dermatol. 177: 117–124. https://doi.org/10.1111/bjd.15364

Gillespie JH (1934) The biological significance of the linkages in adenosine triphosphoric acid. J. Physiol. 80: 345–359. https://doi.org/10.1113/jphysiol.1934.sp003095

Giuliani AL, Colognesi D, Ricco T, Roncato C, Capece M, Amoroso F, Wang QG, De Marchi E, Gartland A, Di Virgilio F, Adinolfi E (2014) Trophic activity of human P2X7 receptor isoforms A and B in osteosarcoma. PLoS One 9: e107224. https://doi.org/10.1371/ 10.1371/journal.pone.010722

Giuliani AL, Sarti AC, Di Virgilio F (2019) Extracellular nucleotides and nucleosides as signalling molecules. Immunol. Lett. 205: 16–24. https://doi.org/10.1016/j.imlet.2018.11.006

Gonnord P, Delarasse C, Auger R, Benihoud K, Prigent M, Cuif MH, Lamaze C, Kanellopoulos JM (2009) Palmitoylation of the P2X7 receptor, an ATP-gated channel, controls its expression and association with lipid rafts. FASEB J. 23: 795–805. https://doi.org/10.1096/fj.08-114637

Gordon JL (1986) Extracellular ATP: Effects, sources and fate. Biochem. J. 233: 309–319. https://doi.org/10.1042/bj2330309

Gorman MW, Feigl EO, Buffington CW (2007) Human plasma ATP concentration. Clin. Chem. 53: 318–325. https://doi.org/10.1373/clinchem.2006.076364

Gray JH, Owen RP, Giacomini KM (2004) The concentrative nucleoside transporter family, SLC28. Pflugers Arch. Eur. J. Physiol. 447: 728–734. https://doi.org/10.1007/s00424-003-1107-y

Gross O, Thomas CJ, Guarda G, Tschopp J (2011) The inflammasome: An integrated view. Immunol. Rev. 243: 136–151. https://doi.org/10.1111/j.1600-065X.2011.01046.x

Gu BJ, Zhang WY, Bendall LJ, Chessell IP, Buell GN, Wiley JS (2000) Expression of P2X7 purinoceptors on human lymphocytes and monocytes: Evidence for nonfunctional P2X7 receptors. Am. J. Physiol. – Cell Physiol. 279: C1189-C1197. https://doi.org/10.1152/ajpcell.2000.279.4.c1189

Gudipaty L, Munetz J, Verhoef PA, Dubyak GR (2003) Essential role for Ca2+ in regulation of IL-1β secretion by P2X7 nucleotide receptor in monocytes, macrophages, and HEK-293 cells. Am. J. Physiol. – Cell Physiol. 285: C286–C299. https://doi.org/10.1152/ajpcell.00070.2003

Guerra AN, Gavala ML, Chung HS, Bertics PJ (2007) Nucleotide receptor signalling and the generation of reactive oxygen species. Purinergic Signal. 3: 39–51. https://doi.org/10.1007/s11302-006-9035-x

Haag F, Koch-Nolte F, Kühl M, Lorenzen S, Thiele HG (1994) Premature stop codons inactivate the RT6 genes of the human and chimpanzee species. J. Mol. Biol. 243: 537–546. https://doi.org/10.1006/jmbi.1994.1680

Han Y, Bai C, He XM, Ren QL (2022) P2X7 receptor involved in antitumor activity of atractylenolide I in human cervical cancer cells. Purinergic Signal. 2022. https://doi.org/10.1007/s11302-022-09854-6

Hashimoto-Hill S, Friesen L, Kim M, Kim CH (2017) Contraction of intestinal effector T cells by retinoic acid-induced purinergic receptor P2X7. Mucosal Immunol. 10: 912–923. https://doi.org/10.1038/mi.2016.109

He X, Wan J, Yang X, Zhang X, Huang D, Li X, Zou Y, Chen C, Yu Z, Xie L, Zhang Y, Liu L, Li S, Zhao Y, Shao H, Yu Y, Zheng J (2021) Bone marrow niche ATP levels determine leukemia-initiating cell activity via P2X7 in leukemic models. J. Clin. Invest. 131: https://doi.org/10.1172/JCI140242

He Y, Franchi L, Núñez G (2013) TLR agonists stimulate Nlrp3-dependent il-1β production independently of the purinergic P2X7 receptor in dendritic cells and in vivo. J. Immunol. 190: 334–339. https://doi.org/10.4049/jimmunol.1202737

Heiss K, Jänner N, Mähnß B, Schumacher V, Koch-Nolte F, Haag F, Mittrücker H-W (2008) High sensitivity of intestinal CD8+ T cells to nucleotides indicates P2X7 as a regulator for intestinal T cell responses. J. Immunol. 181: 3861–3869. https://doi.org/10.4049/jimmunol.181.6.3861

Helliwell RM, Shioukhuey CO, Dhuna K, Molero JC, Ye JM, Xue CC, Stokes L (2015) Selected ginsenosides of the protopanaxdiol series are novel positive allosteric modulators of P2X7 receptors. Br. J. Pharmacol. 172: 3326–3340. https://doi.org/10.1111/bph.13123

Hoffman DL, Brookes PS (2009) Oxygen sensitivity of mitochondrial reactive oxygen species generation depends on metabolic conditions. J. Biol. Chem. 284: 16236–16245. https://doi.org/10.1074/jbc.M809512200

Hogan PG, Rao A (2015) Store-operated calcium entry: Mechanisms and modulation. Biochem. Biophys. Res. Commun. 460: 40–49. https://doi.org/10.1016/j.bbrc.2015.02.110

Honore P, Donnelly-Roberts D, Namovic M, Zhong C, Wade C, Chandran P, Zhu C, Carroll W, Perez-Medrano A, Iwakura Y, Jarvis MF (2009) The antihyperalgesic activity of a selective P2X7 receptor antagonist, A-839977, is lost in IL-1αβ knockout mice. Behav. Brain Res. 204: 77–81. https://doi.org/10.1016/j.bbr.2009.05.018

Huang S, Chen Y, Wu W, Ouyang N, Chen J, Li H, Liu X, Su F, Lin L, Yao Y (2013) MiR-150 promotes human breast cancer growth and malignant behavior by targeting the pro-apoptotic purinergic P2X7 receptor. PLoS One 8: e80707. https://doi.org/10.1371/journal.pone.0080707

Iglesias R, Locovei S, Roque A, Alberto AP, Dahl G, Spray DC, Scemes E (2008) P2X7 receptor-Pannexin1 complex: Pharmacology and signaling. Am. J. Physiol. – Cell Physiol. 295: C752–C760. https://doi.org/10.1152/ajpcell.00228.2008

Jackson MF (2015) Interdependence of ATP signalling and pannexin channels; The servant was really the master all along? Biochem. J. 472: e27–e30. https://doi.org/10.1042/BJ20151016

Ji Z, Xie Y, Guan Y, Zhang Y, Cho KS, Ji M, You Y (2018) Involvement of P2X7 receptor in proliferation and migration of human glioma cells. Biomed Res. Int. 2018: 8591397. https://doi.org/10.1155/2018/8591397

Jiang LH, Rassendren F, Surprenant A, North RA (2000a) Identification of amino acid residues contributing to the ATP-binding site of a purinergic P2X receptor. J. Biol. Chem. 275: 34190–34196. https://doi.org/10.1074/jbc.M005481200

Jiang LH, Mackenzie AB, North RA, Surprenant A (2000b) Brilliant blue G selectively blocks ATP-gated rat P2X7 receptors. Mol. Pharmacol. 58: 82–88. https://doi.org/10.1124/mol.58.1.82

Jiang LH, Rassendren F, Mackenzie A, Zhang YH, Surprenant A, North RA (2005) N-methyl-D-glucamine and propidium dyes utilize different permeation pathways at rat P2X7 receptors. Am. J. Physiol. - Cell Physiol. 289: C1295–C1302. https://doi.org/10.1152/ajpcell.00253.2005

Jimenez-Mateos EM, Smith J, Nicke A, Engel T (2019) Regulation of P2X7 receptor expression and function in the brain. Brain Res. Bull. 151: 153–163. https://doi.org/10.1016/j.brainresbull.2018.12.008

Jones DP (1986) Intracellular diffusion gradients of O2 and ATP. Am. J. Physiol. 250: C663–C675. https://doi.org/10.1152/ajpcell.1986.250.5.c663

Kahlenberg JM, Dubyak GR (2004) Mechanisms of caspase-1 activation by P2X7 receptor-mediated K+ release. Am. J. Physiol. – Cell Physiol. 286: C1100–C1108. https://doi.org/10.1152/ajpcell.00494.2003

Kan LK, Seneviratne S, Drummond KJ, Williams DA, O’Brien TJ, Monif M (2020) P2X7 receptor antagonism inhibits tumour growth in human high-grade gliomas. Purinergic Signal. 16: 327–336. https://doi.org/10.1007/s11302-020-09705-2

Kazmierczak J, Kempe S, Kremer B (2013) Calcium in the early evolution of living systems: A biohistorical approach. Curr. Org. Chem. 17: 1738–1750. https://doi.org/10.2174/13852728113179990081

Kennedy C (2017) P2Y11 receptors: Properties, distribution and functions. In: Advances in Experimental Medicine and Biology, pp 107–122. Springer New York LLC. https://doi.org/10.1007/5584_2017_89

Khakh BS, Burnstock G, Kennedy C, King BF, North RA, Séguéla P, Voigt M, Humphrey PP (2001) International union of pharmacology. XXIV. Current status of the nomenclature and properties of P2X receptors and their subunits. Pharmacol. Rev. 53: 107–118

Kim M, Jiang LH, Wilson HL, North RA, Surprenant A (2001) Proteomic and functional evidence for a P2X7 receptor signalling complex. EMBO J. 20: 6347–6358. https://doi.org/10.1093/EMBOJ/20.22.6347

Kleihues P, Louis DN, Scheithauer BW, Rorke LB, Reifenberger G, Burger PC, Cavenee WK (2002) The WHO classification of tumors of the nervous system. J. Neuropathol. Exp. Neurol. 61: 215–225. https://doi.org/10.1093/jnen/61.3.215

Kłopocka W, Korczyński J, Pomorski P (2020) Cytoskeleton and nucleotide signaling in glioma C6 cells. Adv. Exp. Med. Biol. 1202: 109–128. https://doi.org/10.1007/978-3-030-30651-9_6

Kopp R, Krautloher A, Ramírez-Fernández A, Nicke A (2019) P2X7 interactions and signaling – making head or tail of it. Front. Mol. Neurosci. 12: 183. https://doi.org/10.3389/FNMOL.2019.00183/BIBTEX

Von Kügelgen I, Hoffmann K (2016) Pharmacology and structure of P2Y receptors. Neuropharmacology 104: 50–61. https://doi.org/10.1016/j.neuropharm.2015.10.030

Künzli BM, Berberat PO, Giese T, Csizmadia E, Kaczmarek E, Baker C, Halaceli I, Büchler MW, Friess H, Robson SC (2007) Upregulation of CD39/NTPDases and P2 receptors in human pancreatic disease. Am. J. Physiol. – Gastrointest. Liver Physiol. 292: G223–G230 https://doi.org/10.1152/ajpgi.00259.2006

Künzli BM, Bernlochner MI, Rath S, Käser S, Csizmadia E, Enjyoji K, Cowan P, D’Apice A, Dwyer K, Rosenberg R, Perren A, Friess H, Maurer CA, Robson SC (2011) Impact of CD39 and purinergic signalling on the growth and metastasis of colorectal cancer. Purinergic Signal. 7: 231–241. https://doi.org/10.1007/s11302-011-9228-9

Kurashima Y, Amiya T, Nochi T, Fujisawa K, Haraguchi T, Iba H, Tsutsui H, Sato S, Nakajima S, Iijima H, Kubo M, Kunisawa J, Kiyono H (2012) Extracellular ATP mediates mast cell-dependent intestinal inflammation through P2X7 purinoceptors. Nat. Commun. 3: 1034. https://doi.org/10.1038/ncomms2023

Lambrecht G, Friebe T, Grimm U, Windscheif U, Bungardt E, Hildebrandt C, Bäumert HG, Spatz-Kümbel G, Mutschler E (1992) PPADS, a novel functionally selective antagonist of P2 purinoceptor-mediated responses. Eur. J. Pharmacol. 217: 217–219. https://doi.org/10.1016/0014-2999(92)90877-7

Lazarowski ER, Boucher RC, Harden TK (2000) Constitutive release of ATP and evidence for major contribution of ecto-nucleotide pyrophosphatase and nucleoside diphosphokinase to extracellular nucleotide concentrations. J. Biol. Chem. 275: 31061–31068. https://doi.org/10.1074/jbc.M003255200

Lecciso M, Ocadlikova D, Sangaletti S, Trabanelli S, De Marchi E, Orioli E, Pegoraro A, Portararo P, Jandus C, Bontadini A, Redavid A, Salvestrini V, Romero P, Colombo MP, Di Virgilio F, Cavo M, Adinolfi E, Curti A (2017) ATP release from chemotherapy-treated dying leukemia cells Elicits an immune suppressive effect by increasing regulatory T cells and Tolerogenic dendritic cells. Front. Immunol. 8: 1918. https://doi.org/10.3389/fimmu.2017.01918

Leduc-Pessah H, Weilinger NL, Fan CY, Burma NE, Thompson RJ, Trang T (2017) Site-specific regulation of P2X7 receptor function in microglia gates morphine analgesic tolerance. J. Neurosci. 37: 10154–10172. https://doi.org/10.1523/JNEUROSCI.0852-17.2017

Ledur PF, Villodre ES, Paulus R, Cruz LA, Flores DG, Lenz G (2012) Extracellular ATP reduces tumor sphere growth and cancer stem cell population in glioblastoma cells. Purinergic Signal. 8: 39–48. https://doi.org/10.1007/s11302-011-9252-9

Leiva-Salcedo E, Coddou C, Rodríguez FE, Penna A, Lopez X, Neira T, Fernández R, Imarai M, Rios M, Escobar J, Montoya M, Huidobro-Toro JP, Escobar A, Acuña-Castillo C (2011) Lipopolysaccharide inhibits the channel activity of the P2X7 receptor. Mediators Inflamm. 2011: 152625. https://doi.org/10.1155/2011/152625

Lemaire I, Falzoni S, Zhang B, Pellegatti P, Di Virgilio F (2011) The P2X 7 receptor and pannexin-1 are both required for the promotion of multinucleated macrophages by the inflammatory cytokine GM-CSF. J. Immunol. 187: 3878–3887. https://doi.org/10.4049/jimmunol.1002780

Lenertz LY, Wang Z, Guadarrama A, Hill LM, Gavala ML, Bertics PJ (2010) Mutation of putative N-linked glycosylation sites on the human nucleotide receptor P2X7 reveals a key residue important for receptor function. Biochemistry 49: 4611–4619. https://doi.org/10.1021/bi902083n

Letavic MA, Lord B, Bischoff F, Hawryluk NA, Pieters S, Rech JC, Sales Z, Velter AI, Ao H, Bonaventure P, Contreras V, Jiang X, Morton KL, Scott B, Wang Q, Wickenden AD, Carruthers NI, Bhattacharya A (2013) Synthesis and pharmacological characterization of two novel, brain penetrating P2X7 antagonists. ACS Med. Chem. Lett. 4: 419–422. https://doi.org/10.1021/ml400040v

Li G, Zou L, Xie W, Wen S, Xie Q, Gao Y, Xu C, Xu H, Liu S, Wang S, Xue Y, Wu B, Lv Q, Ying M, Zhang X, Liang S (2016a) The effects of NONRATT021972 lncRNA siRNA on PC12 neuronal injury mediated by P2X7 receptor after exposure to oxygen-glucose deprivation. Purinergic Signal. 12: 479–487. https://doi.org/10.1007/s11302-016-9513-8

Li S, Tomić M, Stojilkovic SS (2011) Characterization of novel Pannexin 1 isoforms from rat pituitary cells and their association with ATP-gated P2X channels. Gen. Comp. Endocrinol. 174: 202–210. https://doi.org/10.1016/j.ygcen.2011.08.019

Li X, Qi X, Zhou L, Catera D, Rote NS, Potashkin J, Abdul-Karim FW, Gorodeski GI (2007) Decreased expression of P2X7 in endometrial epithelial pre-cancerous and cancer cells. Gynecol. Oncol. 106: 233–243. https://doi.org/10.1016/j.ygyno.2007.03.032

Li X, Qi X, Zhou L, Fu W, Abdul-Karim FW, MacLennan G, Gorodeski GI (2009) P2X7 receptor expression is decreased in epithelial cancer cells of ectodermal, uro-genital sinus, and distal paramesonephric duct origin. Purinergic Signal. 5: 351–368. https://doi.org/10.1007/s11302-009-9161-3

Li YM, Suki D, Hess K, Sawaya R (2016b) The influence of maximum safe resection of glioblastoma on survival in 1229 patients: Can we do better than gross-total resection? J. Neurosurg. 124: 977–988. https://doi.org/10.3171/2015.5.JNS142087

Liang X, Samways DSK, Wolf K, Bowles EA, Richards JP, Bruno J, Dutertre S, DiPaolo RJ, Egan TM (2015) Quantifying Ca2+ current and permeability in ATP-gated P2X7 receptors. J. Biol. Chem. 290: 7930–7942. https://doi.org/10.1074/jbc.M114.627810

Liou GY, Storz P (2010) Reactive oxygen species in cancer. Free Radic. Res. 44: 479–496. https://doi.org/10.3109/10715761003667554

Lipmann F (1941) Metabolic Generation and Utilization of Phosphate Bond Energy. In Advances in Enzymology – and Related Areas of Molecular Biology, Nord FF, Werkman CH eds, pp 99–162. Wiley. https://doi.org/10.1002/9780470122464.ch4

Liu J, Li N, Sheng R, Wang R, Xu Z, Mao Y, Wang Y, Liu Y (2017) Hypermethylation downregulates P2X7 receptor expression in astrocytoma. Oncol. Lett. 14: 7699–7704. https://doi.org/10.3892/ol.2017.7241

Liu PS, Chen CY (2010) Butyl benzyl phthalate suppresses the ATP-induced cell proliferation in human osteosarcoma HOS cells. Toxicol. Appl. Pharmacol. 244: 308–314. https://doi.org/10.1016/J.TAAP.2010.01.007

Liu S, Zou L, Xie J, Xie W, Wen S, Xie Q, Gao Y, Li G, Zhang C, Xu C, Xu H, Wu B, Lv Q, Zhang X, Wang S, Xue Y, Liang S (2016) LncRNA NONRATT021972 siRNA regulates neuropathic pain behaviors in type 2 diabetic rats through the P2X7 receptor in dorsal root ganglia. Mol. Brain 9: 44. https://doi.org/10.1186/s13041-016-0226-2

Lo C, Cristofalo VJ, Morris HP, Weinhouse S (1968) Studies on respiration and glycolysis in transplanted hepatic tumors of the rat. Cancer Res. 28: 1–10

Locovei S, Scemes E, Qiu F, Spray DC, Dahl G (2007) Pannexin1 is part of the pore forming unit of the P2X7 receptor death complex. FEBS Lett. 581: 483–488. https://doi.org/10.1016/j.febslet.2006.12.056

Lombardi M, Gabrielli M, Adinolfi E, Verderio C (2021) Role of ATP in extracellular vesicle biogenesis and dynamics. Front. Pharmacol. 12: 654023. https://doi.org/10.3389/fphar.2021.654023

Macarthur M, Hold GL, El-Omar EM (2004) Inflammation and Cancer II. Role of chronic inflammation and cytokine gene polymorphisms in the pathogenesis of gastrointestinal malignancy. Am. J. Physiol. – Gastrointest. Liver Physiol. 286: G515–G520. https://doi.org/10.1152/ajpgi.00475.2003

MacKenzie A, Wilson HL, Kiss-Toth E, Dower SK, North RA, Surprenant A (2001) Rapid secretion of interleukin-1β by microvesicle shedding. Immunity 15: 825–835. https://doi.org/10.1016/S1074-7613(01)00229-1

Magni L, Bouazzi R, Olmedilla HH, Petersen PSS, Tozzi M, Novak I (2021) The P2X7 receptor stimulates IL-6 release from pancreatic stellate cells and tocilizumab prevents activation of STAT3 in pancreatic cancer cells. Cells 10: 1928. https://doi.org/10.3390/cells10081928

De Marchi E, Orioli E, Pegoraro A, Sangaletti S, Portararo P, Curti A, Colombo MP, Di Virgilio F, Adinolfi E (2019) The P2X7 receptor modulates immune cells infiltration, ectonucleotidases expression and extracellular ATP levels in the tumor microenvironment. Oncogene 38: 3636–3650. https://doi.org/10.1038/s41388-019-0684-y

Martel-Gallegos G, Casas-Pruneda G, Ortega-Ortega F, Sánchez-Armass S, Olivares-Reyes JA, Diebold B, Pérez-Cornejo P, Arreola J (2013) Oxidative stress induced by P2X7 receptor stimulation in murine macrophages is mediated by c-Src/Pyk2 and ERK1/2. Biochim. Biophys. Acta - Gen. Subj. 1830: 4650–4659. https://doi.org/10.1016/j.bbagen.2013.05.023

Martins I, Tesniere A, Kepp O, Michaud M, Schlemmer F, Senovilla L, Séror C, Métivier D, Perfettini JL, Zitvogel L, Kroemer G (2009) Chemotherapy induces ATP release from tumor cells. Cell Cycle 8: 3723–3728. https://doi.org/10.4161/cc.8.22.10026

Matyśniak D, Nowak N, Chumak V, Pomorski P (2020) P2X7 receptor activity landscape in rat and human glioma cell lines. Acta Biochim. Pol. 67: 7–14. https://doi.org/10.18388/ABP.2020_2848

Meyerhof O (1951) Mechanisms of glycolysis and fermentation. Can. J. Med. Sci. 29: 63–77. https://doi.org/10.1139/cjms51-008

Michel AD, Chambers LJ, Clay WC, Condreay JP, Walter DS, Chessell IP (2007) Direct labelling of the human P2X 7 receptor and identification of positive and negative cooperativity of binding. Br. J. Pharmacol. 151: 84–95. https://doi.org/10.1038/sj.bjp.0707196

Monif M, Reid CA, Powell KL, Smart ML, Williams DA (2009) The P2X7 receptor drives microglial activation and proliferation: A trophic role for P2X7R pore. J. Neurosci. 29: 3781–3791. https://doi.org/10.1523/JNEUROSCI.5512-08.2009

Monif M, Burnstock G, Williams DA (2010) Microglia: Proliferation and activation driven by the P2X7 receptor. Int. J. Biochem. Cell Biol. 42: 1753–1756. https://doi.org/10.1016/j.biocel.2010.06.021

Morelli A, Chiozzi P, Chiesa A, Ferrari D, Sanz JM, Falzoni S, Pinton P, Rizzuto R, Olson MF, Di Virgilio F (2003) Extracellular ATP causes ROCK I-dependent Bleb formation in P2X7-transfected HEK293 cells. Mol. Biol. Cell 14: 2655–2664. https://doi.org/10.1091/mbc.02-04-0061

Morrone FB, Oliveira DL, Gamermann P, Stella J, Wofchuk S, Wink MR, Meurer L, Edelweiss MIA, Lenz G, Battastini AMO (2006) In vivo glioblastoma growth is reduced by apyrase activity in a rat glioma model. BMC Cancer 6: 226. https://doi.org/10.1186/1471-2407-6-226

Muñoz-Planillo R, Kuffa P, Martínez-Colón G, Smith BL, Rajendiran TM, Núñez G (2013) K+ Efflux is the common trigger of NLRP3 inflammasome activation by bacterial toxins and particulate matter. Immunity 38: 1142–1153. https://doi.org/10.1016/j.immuni.2013.05.016

Murakami M, Shiraishi A, Tabata K, Fujita N (2008) Identification of the orphan GPCR, P2Y10 receptor as the sphingosine-1-phosphate and lysophosphatidic acid receptor. Biochem. Biophys. Res. Commun. 371: 707–712. https://doi.org/10.1016/j.bbrc.2008.04.145

Murgia M, Hanau S, Pizzo P, Rippa M, Di Virgilio F (1993) Oxidized ATP. An irreversible inhibitor of the macrophage purinergic P(2Z) receptor. J. Biol. Chem. 268: 8199–8203. https://doi.org/10.1016/s0021-9258(18)53082-9

Nelson DW, Gregg RJ, Kort ME, Perez-Medrano A, Voight EA, Wang Y, Grayson G, Namovic MT, Donnelly-Roberts DL, Niforatos W, Honore P, Jarvis MF, Faltynek CR, Carroll WA (2006) Structure-activity relationship studies on a series of novel, substituted 1-benzyl-5-phenyltetrazole P2X7 antagonists. J. Med. Chem. 49: 3659–3666. https://doi.org/10.1021/jm051202e

Nörenberg W, Hempel C, Urban N, Sobottka H, Illes P, Schaefer M (2011) Clemastine potentiates the human P2X7 receptor by sensitizing it to lower ATP concentrations. J. Biol. Chem. 286: 11067–11081. https://doi.org/10.1074/jbc.M110.198879

Nörenberg W, Sobottka H, Hempel C, Plötz T, Fischer W, Schmalzing G, Schaefer M (2012) Positive allosteric modulation by ivermectin of human but not murine P2X7 receptors. Br. J. Pharmacol. 167: 48–66. https://doi.org/10.1111/j.1476-5381.2012.01987.x

Nörenberg W, Plötz T, Sobottka H, Chubanov V, Mittermeier L, Kalwa H, Aigner A, Schaefer M (2016) TRPM7 is a molecular substrate of ATP-evoked P2X7-like currents in tumor cells. J. Gen. Physiol. 147: 467–483. https://doi.org/10.1085/jgp.201611595

North RA, Surprenant A (2000) Pharmacology of cloned P2X receptors. Annu. Rev. Pharmacol. Toxicol. 40: 563–580. https://doi.org/10.1146/annurev.pharmtox.40.1.563

North RA (2002) Molecular physiology of P2X receptors. Physiol. Rev. 82: 1013–1067. https://doi.org/10.1152/physrev.00015.2002

North RA (2016) P2X receptors. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 371: 20150427. https://doi.org/10.1098/rstb.2015.0427

Orellano EA, Rivera OJ, Chevres M, Chorna NE, González FA (2010) Inhibition of neuronal cell death after retinoic acid-induced down-regulation of P2X7 nucleotide receptor expression. Mol. Cell. Biochem. 337: 83–99. https://doi.org/10.1007/s11010-009-0288-x

El Ouaaliti M, Seil M, Dehaye JP (2012) Activation of calcium-insensitive phospholipase A2 (iPLA 2) by P2X7 receptors in murine peritoneal macrophages. Prostaglandins Other Lipid Mediat. 99: 116–123. https://doi.org/10.1016/j.prostaglandins.2012.09.005

Pankratov Y, Lalo U, Verkhratsky A, North RA (2006) Vesicular release of ATP at central synapses. Pflugers Arch. Eur. J. Physiol. 452: 589–597. https://doi.org/10.1007/s00424-006-0061-x

Pegoraro A, Orioli E, De Marchi E, Salvestrini V, Milani A, Di Virgilio F, Curti A, Adinolfi E (2020) Differential sensitivity of acute myeloid leukemia cells to daunorubicin depends on P2X7A versus P2X7B receptor expression. Cell Death Dis. 11: 876. https://doi.org/10.1038/s41419-020-03058-9

Pegoraro A, De Marchi E, Ferracin M, Orioli E, Zanoni M, Bassi C, Tesei A, Capece M, Dika E, Negrini M, Di Virgilio F, Adinolfi E (2021a) P2X7 promotes metastatic spreading and triggers release of miRNA-containing exosomes and microvesicles from melanoma cells. Cell Death Dis. 12: 1–12. https://doi.org/10.1038/s41419-021-04378-0

Pegoraro A, De Marchi E, Adinolfi E (2021b) P2X7 Variants in Oncogenesis. Cells 10: 1–16. https://doi.org/10.3390/CELLS10010189

Pelegrin P, Surprenant A (2006) Pannexin-1 mediates large pore formation and interleukin-1β release by the ATP-gated P2X7 receptor. EMBO J. 25: 5071–5082. https://doi.org/10.1038/sj.emboj.7601378

Peng W, Cotrina ML, Han X, Yu H, Bekar L, Blum L, Takano T, Tian GF, Goldman SA, Nedergaard M (2009) Systemic administration of an antagonist of the ATP-sensitive receptor P2X7 improves recovery after spinal cord injury. Proc. Natl. Acad. Sci. U. S. A. 106: 12489–12493. https://doi.org/10.1073/pnas.0902531106

Perregaux D, Gabel CA (1994) Interleukin-1 beta maturation and release in response to ATP and nigericin. Evidence that potassium depletion mediated by these agents is a necessary and common feature of their activity. J. Biol. Chem. 269: 15195–15203

Plattner H, Verkhratsky A (2016) Inseparable tandem: Evolution chooses atp and Ca2+ to control life, death and cellular signalling. Philos. Trans. R. Soc. B Biol. Sci. 371: 20150419. https://doi.org/10.1098/rstb.2015.0419

Pochet S, Tandel S, Querriére S, Tre-Hardy M, Garcia-Marcos M, De Lorenzi M, Vandenbranden M, Marino A, Devleeschouwer M, Dehaye JP (2006) Modulation by LL-37 of the responses of salivary glands to purinergic agonists. Mol. Pharmacol. 69: 2037–2046. https://doi.org/10.1124/mol.105.021444

Poornima V, Madhupriya M, Kootar S, Sujatha G, Kumar A, Bera AK (2012) P2X 7 receptor-pannexin 1 hemichannel association: Effect of extracellular calcium on membrane permeabilization. J. Mol. Neurosci. 46: 585–594. https://doi.org/10.1007/s12031-011-9646-8

Pupovac A, Stokes L, Sluyter R (2013) CAY10593 inhibits the human P2X7 receptor independently of phospholipase D1 stimulation. Purinergic Signal. 9: 609–619. https://doi.org/10.1007/s11302-013-9371-6

Qiu F, Dahl G (2009) A permeant regulating its permeation pore: Inhibition of pannexin 1 channels by ATP. Am. J. Physiol. – Cell Physiol. 296: C250–C255. https://doi.org/10.1152/ajpcell.00433.2008

Qiu Y, Li WH, Zhang HQ, Liu Y, Tian XX, Fang WG (2014) P2X7 mediates ATP-driven invasiveness in prostate cancer cells. PLoS One 9: e114371. https://doi.org/10.1371/journal.pone.0114371

Qu Y, Dubyak GR (2009) P2X7 receptors regulate multiple types of membrane trafficking responses and non-classical secretion pathways. Purinergic Signal. 5: 163–173. https://doi.org/10.1007/s11302-009-9132-8

Qu Y, Misaghi S, Newton K, Gilmour LL, Louie S, Cupp JE, Dubyak GR, Hackos D, Dixit VM (2011) Pannexin-1 is required for ATP release during apoptosis but not for inflammasome activation. J. Immunol. 186: 6553–6561. https://doi.org/10.4049/jimmunol.1100478

Raffaghello L, Chiozzi P, Falzoni S, Di Virgilio F, Pistoia V (2006) The P2X7 receptor sustains the growth of human neuroblastoma cells through a substance P-dependent mechanism. Cancer Res. 66: 907–914. https://doi.org/10.1158/0008-5472.CAN-05-3185

Ralevic V, Burnstock G (1998) Receptors for purines and pyrimidines. Pharmacol. Rev. 50: 413–492

Rassendren F, Buell GN, Virginio C, Collo G, North RA, Surprenant A (1997) The permeabilizing ATP receptor, P2X7. Cloning and expression of a human cDNA. J. Biol. Chem. 272: 5482–5486. https://doi.org/10.1074/jbc.272.9.5482

Ravenna L, Sale P, Di Vito M, Russo A, Salvatori L, Tafani M, Mari E, Sentinelli S, Petrangeli E, Gallucci M, Di Silverio F, Russo MA (2009) Up-regulation of the inflammatory-reparative phenotype in human prostate carcinoma. Prostate 69: 1245–1255. https://doi.org/10.1002/pros.20966

Reinhold WC, Sunshine M, Liu H, Varma S, Kohn KW, Morris J, Doroshow J, Pommier Y (2012) CellMiner: A web-based suite of genomic and pharmacologic tools to explore transcript and drug patterns in the NCI-60 cell line set. Cancer Res. 72: 3499–3511. https://doi.org/10.1158/0008-5472.CAN-12-1370

Roman S, Cusdin FS, Fonfria E, Goodwin JA, Reeves J, Lappin SC, Chambers L, Walter DS, Clay WC, Michel AD (2009) Cloning and pharmacological characterization of the dog P2X7 receptor. Br. J. Pharmacol. 158: 1513–1526. https://doi.org/10.1111/j.1476-5381.2009.00425.x

Ruiz-Rodríguez VM, Turiján-Espinoza E, Guel-Pañola JA, García-Hernández MH, Zermeño-Nava J de J, López-López N, Bernal-Silva S, Layseca-Espinosa E, Fuentes-Pananá EM, Estrada-Sánchez AM, Portales-Pérez DP (2020) Chemoresistance in breast cancer patients associated with changes in P2X7 and A2A purinergic receptors in CD8+ T lymphocytes. Front. Pharmacol. 11: 576955. https://doi.org/10.3389/fphar.2020.576955

Ryu JK, Jantaratnotai N, Serrano-Perez MC, McGeer PL, McLarnon JG (2011) Block of purinergic P2X7R inhibits tumor growth in a c6 glioma brain tumor animal model. J. Neuropathol. Exp. Neurol. 70: 13–22. https://doi.org/10.1097/NEN.0b013e318201d4d4

Dos Santos-Rodrigues A, Grañé-Boladeras N, Bicket A, Coe IR (2014) Nucleoside transporters in the purinome. Neurochem. Int. 73: 229–237. https://doi.org/10.1016/j.neuint.2014.03.014

Sanz JM, Chiozzi P, Di Virgilio F (1998) Tenidap enhances P2Z/P2X7 receptor signalling in macrophages. Eur. J. Pharmacol. 355: 235–244. https://doi.org/10.1016/S0014-2999(98)00482-8

Schachter J, Motta AP, Zamorano A de S, da Silva-Souza HA, Guimarães MZP, Persechini PM (2008) ATP-induced P2X7-associated uptake of large molecules involves distinct mechanisms for cations and anions in macrophages. J. Cell Sci. 121: 3261–3270. https://doi.org/10.1242/jcs.029991

Schmid S, Kübler M, Korcan Ayata C, Lazar Z, Haager B, Hoßfeld M, Meyer A, Cicko S, Elze M, Wiesemann S, Zissel G, Passlick B, Idzko M (2015) Altered purinergic signaling in the tumor associated immunologic microenvironment in metastasized non-small-cell lung cancer. Lung Cancer 90: 516–521. https://doi.org/10.1016/j.lungcan.2015.10.005

Schöneberg T, Hermsdorf T, Engemaier E, Engel K, Liebscher I, Thor D, Zierau K, Römpler H, Schulz A (2007) Structural and functional evolution of the P2Y12-like receptor group. Purinergic Signal. 3: 255–268. https://doi.org/10.1007/s11302-007-9064-0

Schulte G, Fredholm BB (2000) Human adenosine A(1), A(2A), A(2B), and A(3) receptors expressed in Chinese hamster ovary cells all mediate the phosphorylation of extracellular-regulated kinase 1/2. Mol. Pharmacol. 58: 477–482

Schulte G, Fredholm BB (2003) Signalling from adenosine receptors to mitogen-activated protein kinases. Cell. Signal. 15: 813–827. https://doi.org/10.1016/S0898-6568(03)00058-5

Schwarz N, Drouot L, Nicke A, Fliegert R, Boyer O, Guse AH, Haag F, Adriouch S, Koch-Nolte F (2012) Alternative splicing of the N-terminal cytosolic and transmembrane domains of P2X7 controls gating of the ion channel by ADP-ribosylation. PLoS One 7: e41269. https://doi.org/10.1371/journal.pone.0041269

Sha W gang, Shen L, Zhou L, Xu D yu, Lu G yuan (2015) Down-regulation of miR-186 contributes to podocytes apoptosis in membranous nephropathy. Biomed. Pharmacother. 75: 179–184. https://doi.org/10.1016/j.biopha.2015.07.021

Shankavaram UT, Varma S, Kane D, Sunshine M, Chary KK, Reinhold WC, Pommier Y, Weinstein JN (2009) CellMiner: A relational database and query tool for the NCI-60 cancer cell lines. BMC Genomics 10: 277. https://doi.org/10.1186/1471-2164-10-277

Sharma S, Kalra H, Akundi RS (2021) Extracellular ATP mediates cancer cell migration and invasion through increased expression of cyclooxygenase 2. Front. Pharmacol. 11: 617211. https://doi.org/10.3389/fphar.2020.617211

Slater M, Scolyer RA, Gidley-Baird A, Thompson JF, Barden JA (2003) Increased expression of apoptotic markers in melanoma. Melanoma Res. 13: 137–145. https://doi.org/10.1097/00008390-200304000-00005

Slater M, Danieletto S, Gidley-Baird A, Teh LC, Barden JA (2004a) Early prostate cancer detected using expression of non-functional cytolytic P2X7 receptors. Histopathology 44: 206–215. https://doi.org/10.1111/j.0309-0167.2004.01798.x

Slater M, Danieletto S, Pooley M, Teh LC, Gidley-Baird A, Barden JA (2004b) Differentiation between cancerous and normal hyperplastic lobules in breast lesions. Breast Cancer Res. Treat. 83: 1–10. https://doi.org/10.1023/B:BREA.0000010670.85915.0f

Slater M, Danieletto S, Barden JA (2005) Expression of the apoptotic calcium channel P2X7 in the glandular epithelium is a marker for early prostate cancer and correlates with increasing PSA levels. J. Mol. Histol. 36: 159–165. https://doi.org/10.1007/s10735-004-6166-7

Smart ML, Gu B, Panchal RG, Wiley J, Cromer B, Williams DA, Petrou S (2003) P2X7 receptor cell surface expression and cytolytic pore formation are regulated by a distal C-terminal region. J. Biol. Chem. 278: 8853–8860. https://doi.org/10.1074/jbc.M211094200

Solini A, Simeon V, Derosa L, Orlandi P, Rossi C, Fontana A, Galli L, Di Desidero T, Fioravanti A, Lucchesi S, Coltelli L, Ginocchi L, Allegrini G, Danesi R, Falcone A, Bocci G (2015) Genetic interaction of P2X7 receptor and VEGFR-2 polymorphisms identifies a favorable prognostic profile in prostate cancer patients. Oncotarget 6: 28743–28754. https://doi.org/10.18632/ONCOTARGET.4926

Solini A, Cobuccio L, Rossi C, Parolini F, Biancalana E, Cosio S, Chiarugi M, Gadducci A (2021) Molecular characterization of peritoneal involvement in primary colon and ovary neoplasm: the possible clinical meaning of the P2X7 receptor-inflammasome complex. Eur. Surg. Res. 63: 114–122. https://doi.org/10.1159/000519690

Solle M, Labasi J, Perregaux DG, Stam E, Petrushova N, Koller BH, Griffiths RJ, Gabel CA (2001) Altered cytokine production in mice lacking P2X7 receptors. J. Biol. Chem. 276: 125–132. https://doi.org/10.1074/jbc.M006781200

Soltoff SP, McMillian MK, Talamo BR (1989) Coomassie Brilliant Blue G is a more potent antagonist of P2 purinergic responses than Reactive Blue 2 (Cibacron Blue 3GA) in rat parotid acinar cells. Biochem. Biophys. Res. Commun. 165: 1279–1285. https://doi.org/10.1016/0006-291X(89)92741-1

Spildrejorde M, Bartlett R, Stokes L, Jalilian I, Peranec M, Sluyter V, Curtis BL, Skarratt KK, Skora A, Bakhsh T, Seavers A, McArthur JD, Dowton M, Sluyter R (2014) R270C polymorphism leads to loss of function of the canine P2X7 receptor. Physiol. Genomics 46: 512–522. https://doi.org/10.1152/physiolgenomics.00195.2013

Strong AD, Indart MC, Hill NR, Daniels RL (2018) GL261 glioma tumor cells respond to ATP with an intracellular calcium rise and glutamate release. Mol. Cell. Biochem. 446: 53–62. https://doi.org/10.1007/s11010-018-3272-5

Suadicani SO, Iglesias R, Wang J, Dahl G, Spray DC, Scemes E (2012) ATP signaling is deficient in cultured pannexin1-null mouse astrocytes. Glia 60: 1106–1116. https://doi.org/10.1002/glia.22338

Sun Y, Huang P (2016) Adenosine A2B receptor: From cell biology to human diseases. Front. Chem. 4: 37. https://doi.org/10.3389/fchem.2016.00037

Supłat-Wypych D, Dygas A, Barańska J (2010) 2′, 3′-O-(4-benzoylbenzoyl)-ATP-mediated calcium signaling in rat glioma C6 cells: Role of the P2Y2 nucleotide receptor. Purinergic Signal. 6: 317–325. https://doi.org/10.1007/s11302-010-9194-7

Surprenant A, Rassendren F, Kawashima E, North RA, Buell G (1996) The cytolytic P2Z receptor for extracellular ATP identified as a P2X receptor (P2X7). Science (80-.). 272: 735–738. https://doi.org/10.1126/science.272.5262.735

Tafani M, Russo A, Di Vito M, Sale P, Pellegrini L, Schito L, Gentileschi S, Bracaglia R, Marandino F, Garaci E, Russo MA (2010) Up-regulation of pro-inflammatory genes as adaptation to hypoxia in MCF-7 cells and in human mammary invasive carcinoma microenvironment. Cancer Sci. 101: 1014–1023. https://doi.org/10.1111/j.1349-7006.2010.01493.x

Takai E, Tsukimoto M, Harada H, Sawada K, Moriyama Y, Kojima S (2012) Autocrine regulation of TGF-β1-induced cell migration by exocytosis of ATP and activation of P2 receptors in human lung cancer cells. J. Cell Sci. 125: 5051–5060. https://doi.org/10.1242/jcs.104976

Takai E, Tsukimoto M, Harada H, Kojima S (2014) Autocrine signaling via release of ATP and activation of P2X7 receptor influences motile activity of human lung cancer cells. Purinergic Signal. 10: 487–497. https://doi.org/10.1007/s11302-014-9411-x

Tamajusuku ASK, Villodre ES, Paulus R, Coutinho-Silva R, Battasstini AMO, Wink MR, Lenz G (2010) Characterization of ATP-induced cell death in the GL261 mouse glioma. J. Cell. Biochem. 109: 983–991. https://doi.org/10.1002/jcb.22478

Tan C, Han L, Zou L, Luo C, Liu A, Sheng X, Xi D (2015) Expression of P2X7R in breast cancer tissue and the induction of apoptosis by the gene-specific shRNA in MCF-7 cells. Exp. Ther. Med. 10: 1472–1478. https://doi.org/10.3892/etm.2015.2705

Tanamachi K, Nishino K, Mori N, Suzuki T, Tanuma SI, Abe R, Tsukimoto M (2017) Radiosensitizing effect of P2X7 receptor antagonist on melanoma in vitro and in vivo. Biol. Pharm. Bull. 40: 878–887. https://doi.org/10.1248/bpb.b17-00083

Tang Y, Wang Y, Park KM, Hu Q, Teoh JP, Broskova Z, Ranganathan P, Jayakumar C, Li J, Su H, Tang Y, Ramesh G, Kim IM (2015) MicroRNA-150 protects the mouse heart from ischaemic injury by regulating cell death. Cardiovasc. Res. 106: 387–397. https://doi.org/10.1093/cvr/cvv121

Tattersall L, Shah KM, Lath DL, Singh A, Down JM, De Marchi E, Williamson A, Di Virgilio F, Heymann D, Adinolfi E, Fraser WD, Green D, Lawson MA, Gartland A (2021) The P2RX7B splice variant modulates osteosarcoma cell behaviour and metastatic properties. J. Bone Oncol. 31: 100398. https://doi.org/10.1016/j.jbo.2021.100398

Taylor CW, Thorn P (2001) Calcium signalling: IP3 rises again... and again. Curr. Biol. 11: R352–R355. https://doi.org/10.1016/S0960-9822(01)00192-0

Taylor SRJ, Gonzalez-Begne M, Dewhurst S, Chimini G, Higgins CF, Melvin JE, Elliott JI (2008) Sequential shrinkage and swelling underlie P2X 7-stimulated lymphocyte phosphatidylserine exposure and death. J. Immunol. 180: 300–308. https://doi.org/10.4049/jimmunol.180.1.300

Toki Y, Takenouchi T, Harada H, Tanuma SI, Kitani H, Kojima S, Tsukimoto M (2015) Extracellular ATP induces P2X7 receptor activation in mouse Kupffer cells, leading to release of IL-1β, HMGB1, and PGE2, decreased MHC class I expression and necrotic cell death. Biochem. Biophys. Res. Commun. 458: 771–776. https://doi.org/10.1016/j.bbrc.2015.02.011

Tomasinsig L, Pizzirani C, Skerlavaj B, Pellegatti P, Gulinelli S, Tossi A, Di Virgilio F, Zanetti M (2008) The human cathelicidin LL-37 modulates the activities of the P2X 7 receptor in a structure-dependent manner. J. Biol. Chem. 283: 30471–30481. https://doi.org/10.1074/jbc.M802185200

Tu G, Zou L, Liu S, Wu B, Lv Q, Wang S, Xue Y, Zhang C, Yi Z, Zhang X, Li G, Liang S (2016) Long noncoding NONRATT021972 siRNA normalized abnormal sympathetic activity mediated by the upregulation of P2X7 receptor in superior cervical ganglia after myocardial ischemia. Purinergic Signal. 12: 521–535. https://doi.org/10.1007/s11302-016-9518-3

Ulrich H, Ratajczak MZ, Schneider G, Adinolfi E, Orioli E, Ferrazoli EG, Glaser T, Corrêa-Velloso J, Martins PCM, Coutinho F, Santos APJ, Pillat MM, Sack U, Lameu C (2018) Kinin and purine signaling contributes to neuroblastoma metastasis. Front. Pharmacol. 9: 500. https://doi.org/10.3389/fphar.2018.00500

Urbanek E, Nickel P, Schlicker E (1990) Antagonistic properties of four suramin-related compounds at vascular purine P2X receptors in the pithed rat. Eur. J. Pharmacol. 175: 207–210. https://doi.org/10.1016/0014-2999(90)90232-U

Valera S, Hussy N, Evans RJ, Adami N, North RA, Surprenant A, Buell G (1994) A new class of ligand-gated ion channel defined by P2X receptor for extracellular ATP. Nature 371: 516–519. https://doi.org/10.1038/371516a0

Vázquez-Cuevas FG, Martínez-Ramírez AS, Robles-Martínez L, Garay E, García-Carrancá A, Pérez-Montiel D, Castañeda-García C, Arellano RO (2014) Paracrine stimulation of P2X7 receptor by ATP activates a proliferative pathway in ovarian carcinoma cells. J. Cell. Biochem. 115: 1955–1966. https://doi.org/10.1002/jcb.24867

Di Virgilio F, Bronte V, Collavo D, Zanovello P (1989) Responses of mouse lymphocytes to extracellular adenosine 5’-triphosphate (ATP). Lymphocytes with cytotoxic activity are resistant to the permeabilizing effects of ATP. J. Immunol. 143: 1955–1960

Di Virgilio F, Dal Ben D, Sarti AC, Giuliani AL, Falzoni S (2017) The P2X7 receptor in infection and inflammation. Immunity 47: 15–31. https://doi.org/10.1016/j.immuni.2017.06.020

Di Virgilio F, Schmalzing G, Markwardt F (2018) The elusive P2X7 macropore. Trends Cell Biol. 28: 392–404. https://doi.org/10.1016/j.tcb.2018.01.005

Virginio C, Church D, North RA, Surprenant A (1997) Effects of divalent cations, protons and calmidazolium at the rat P2X7 receptor. Neuropharmacology 36: 1285–1294. https://doi.org/10.1016/S0028-3908(97)00141-X

Vultaggio-Poma V, Falzoni S, Chiozzi P, Sarti AC, Adinolfi E, Giuliani AL, Sánchez-Melgar A, Boldrini P, Zanoni M, Tesei A, Pinton P, Di Virgilio F (2022) Extracellular ATP is increased by release of ATP-loaded microparticles triggered by nutrient deprivation. Theranostics 12: 859–874. https://doi.org/10.7150/thno.66274

Wei L, Caseley E, Li D, Jiang LH (2016) ATP-induced P2X receptor-dependent large pore formation: How much do we know? Front. Pharmacol. 7: 5. https://doi.org/10.3389/fphar.2016.00005

Wen PY, Kesari S (2008) Malignant gliomas in adults. N. Engl. J. Med. 359: 492–507. https://doi.org/10.1056/nejmra0708126

Weng T, Mishra A, Guo Y, Wang Y, Su L, Huang C, Zhao C, Xiao X, Liu L (2012) Regulation of lung surfactant secretion by microRNA-150. Biochem. Biophys. Res. Commun. 422: 586–589. https://doi.org/10.1016/j.bbrc.2012.05.030

White N, Butler PEM, Burnstock G (2005) Human melanomas express functional P2X7 receptors. Cell Tissue Res. 321: 411–418. https://doi.org/10.1007/s00441-005-1149-x

Wilson HL, Wilson SA, Surprenant A, Alan North R (2002) Epithelial membrane proteins induce membrane blebbing and interact with the P2X7 receptor C terminus. J. Biol. Chem. 277: 34017–34023. https://doi.org/10.1074/jbc.M205120200

Wu B, Zhang C, Zou L, Ma Y, Huang K, Lv Q, Zhang X, Wang S, Xue Y, Yi Z, Jia T, Zhao S, Liu S, Xu H, Li G, Liang S (2016) LncRNA uc.48+ siRNA improved diabetic sympathetic neuropathy in type 2 diabetic rats mediated by P2X7 receptor in SCG. Auton. Neurosci. Basic Clin. 197: 14–18. https://doi.org/10.1016/j.autneu.2016.04.001

Wu PY, Lin YC, Chang CL, Lu HT, Chin CH, Hsu TT, Chu D, Sun SH (2009) Functional decreases in P2X7 receptors are associated with retinoic acid-induced neuronal differentiation of Neuro-2a neuroblastoma cells. Cell. Signal. 21: 881–891. https://doi.org/10.1016/j.cellsig.2009.01.036

Wypych D, Barańska J (2020) Cross-talk in nucleotide signaling in glioma C6 cells. In: Advances in Experimental Medicine and Biology, pp 35–65. Springer,. https://doi.org/10.1007/978-3-030-30651-9_3

Xu H, He L, Liu C, Tang L, Xu Y, Xiong M, Yang M, Fan Y, Hu F, Liu X, Ding L, Gao Y, Xu C, Li G, Liu S, Wu B, Zou L, Liang S (2016) LncRNA NONRATT021972 siRNA attenuates P2X7 receptor expression and inflammatory cytokine production induced by combined high glucose and free fatty acids in PC12 cells. Purinergic Signal. 12: 259–268. https://doi.org/10.1007/s11302-016-9500-0

Yang D, He Y, Muñoz-Planillo R, Liu Q, Núñez G (2015) Caspase-11 requires the pannexin-1 channel and the purinergic P2X7 pore to mediate pyroptosis and endotoxic shock. Immunity 43: 923–932. https://doi.org/10.1016/j.immuni.2015.10.009

Yang YC, Chang TY, Chen TC, Lin WS, Chang SC, Lee YJ (2016) Functional variant of the P2X7 receptor gene is associated with human papillomavirus-16 positive cervical squamous cell carcinoma. Oncotarget 7: 82798–82803. https://doi.org/10.18632/oncotarget.12636

Yip L, Woehrle T, Corriden R, Hirsh M, Chen Y, Inoue Y, Ferrari V, Insel PA, Junger WG (2009) Autocrine regulation of T-cell activation by ATP release and P2X 7 receptors. FASEB J. 23: 1685–1693. https://doi.org/10.1096/fj.08-126458

Young CNJ, Sinadinos A, Lefebvre A, Chan P, Arkle S, Vaudry D, Gorecki DC (2015) A novel mechanism of autophagic cell death in dystrophic muscle regulated by P2RX7 receptor large-pore formation and HSP90. Autophagy 11: 113–130. https://doi.org/10.4161/15548627.2014.994402

Young JD, Yao SYM, Baldwin JM, Cass CE, Baldwin SA (2013) The human concentrative and equilibrative nucleoside transporter families, SLC28 and SLC29. Mol. Aspects Med. 34: 529–547. https://doi.org/10.1016/j.mam.2012.05.007

Yu Y, Ugawa S, Ueda T, Ishida Y, Inoue K, Kyaw Nyunt A, Umemura A, Mase M, Yamada K, Shimada S (2008) Cellular localization of P2X7 receptor mRNA in the rat brain. Brain Res. 1194: 45–55. https://doi.org/10.1016/j.brainres.2007.11.064

Zanoni M, Sarti AC, Zamagni A, Cortesi M, Pignatta S, Arienti C, Tebaldi M, Sarnelli A, Romeo A, Bartolini D, Tosatto L, Adinolfi E, Tesei A, Di Virgilio F (2022) Irradiation causes senescence, ATP release, and P2X7 receptor isoform switch in glioblastoma. Cell Death Dis. 13: 80. https://doi.org/10.1038/s41419-022-04526-0

Zanovello P, Bronte V, Rosato A, Pizzo P, Di Virgilio F (1990) Responses of mouse lymphocytes to extracellular ATP. II. Extracellular ATP causes cell type-dependent lysis and DNA fragmentation. J. Immunol. 145: 1545–1550

Zhang W jun, Zhu Z ming, Liu Z xu (2020) The role and pharmacological properties of the P2X7 receptor in neuropathic pain. Brain Res. Bull. 155: 19–28. https://doi.org/10.1016/j.brainresbull.2019.11.006

Zhang XJ, Zheng GG, Ma XT, Yang YH, Li G, Rao Q, Nie K, Wu KF (2004) Expression of P2X7 in human hematopoietic cell lines and leukemia patients. Leuk. Res. 28: 1313–1322. https://doi.org/10.1016/j.leukres.2004.04.001

Zhang Y, Ding J, Wang L (2019) The role of P2X7 receptor in prognosis and metastasis of colorectal cancer. Adv. Med. Sci. 64: 388–394. https://doi.org/10.1016/j.advms.2019.05.002

Zhou L, Qi X, Potashkin JA, Abdul-Karim FW, Gorodeski GI (2008) MicroRNAs miR-186 and miR-150 down-regulate expression of the pro-apoptotic purinergic P2X7 receptor by activation of instability sites at the 3′-untranslated region of the gene that decrease steady-state levels of the transcript. J. Biol. Chem. 283: 28274–28286. https://doi.org/10.1074/jbc.M802663200

Zhou L, Luo L, Qi X, Li X, Gorodeski GI (2009) Regulation of P2X7 gene transcription. Purinergic Signal. 5: 409–426. https://doi.org/10.1007/s11302-009-9167-x

Ziberi S, Zuccarini M, Carluccio M, Giuliani P, Ricci-Vitiani L, Pallini R, Caciagli F, Di Iorio P, Ciccarelli R (2019) Upregulation of epithelial-to-mesenchymal transition markers and P2X7 receptors is associated to increased invasiveness caused by P2X7 receptor stimulation in human glioblastoma stem cells. Cells 9: 85. https://doi.org/10.3390/cells9010085

Ziganshin AU, Hoyle CHV, Burnstock G (1994) Ecto-enzymes and metabolism of extracellular ATP. Drug Dev. Res. 32: 134–146. https://doi.org/10.1002/ddr.430320303

Zou L, Tu G, Xie W, Wen S, Xie Q, Liu S, Li G, Gao Y, Xu H, Wang S, Xue Y, Wu B, Lv Q, Ying M, Zhang X, Liang S (2016) LncRNA NONRATT021972 involved the pathophysiologic processes mediated by P2X7 receptors in stellate ganglia after myocardial ischemic injury. Purinergic Signal. 12: 127–137. https://doi.org/10.1007/s11302-015-9486-z