Sp1 mediates phorbol ester (PMA)-induced expression of membrane-bound guanylyl cyclase GC-A in human monocytic cells*

* Preliminary report: These results were presented at the 1st Congress of Polish Biochemistry, Cell Biology, Biophysics and Bioinformatics (BIO 2014), Warsaw, Poland (9–12 September, 2014).

Abstract

Cyclic guanosine monophosphate (cGMP) is synthesized by two types of enzymes: particulate (membrane-bound) guanylyl cyclases (pGCs) and soluble (cytosolic) guanylyl cyclases (sGCs). sGCs are activated primarily by binding of nitric oxide to their prosthetic heme group while pGCs are activated by binding of peptide ligands to their extracellular domains. One of them, pGC type A (GC-A) is activated by atrial and brain natriuretic peptides (ANP and BNP, respectively). Human monocytes isolated from peripheral blood mononuclear cells have been shown to have sGC expression without concomitant expression of GC-A. However, GC-A activity appears in monocytes under certain conditions but a molecular mechanism of GC‑A expression is still poorly understood. In this report we show that phorbol ester (PMA) induced transcription of the gene encoding GC-A in human monocytic THP-1 cells. Moreover, PMA-treated THP-1 cells have been found to raise cGMP content following treatment with ANP. Studies using pharmacological inhibitors of protein kinases have suggested involvement of protein kinase C (PKC), mitogen extracellular kinases (MEK1/2), and extracellular signal-regulated kinases (ERK1/2) in PMA-induced expression of the GC-A encoding gene in THP-1 cells. Finally, we show that PMA stimulated binding of Sp1 transcription factor to GC-rich DNA sequences and mithramycin A (a selective Sp1 inhibitor) inhibited expression of the GC-A mRNA in PMA-treated THP-1 cells. Taken together, our findings suggest that the PMA/PKC/MEK/ERK signaling pathway induces Sp1-mediated transcription of the GC-A encoding gene in human monocytic THP-1 cells.