Actinomycin D specifically inhibits the interaction between transcription factor Sp1 and its binding site.

Abstract

The mode of action of many anticancer drugs involves DNA interactions. We here examine the ability of actinomycin D to alter the specific binding of transcription factors Spl and NFkappaB to their DNA sequences. Employing an electrophoretic mobility shift assay, it is shown that actinomycin D inhibits complex formation between nuclear proteins present in the extracts from stimulated human umbilical vein endothelial cells and the Sp1-binding site. Actinomycin D is also able to induce disruption of preformed DNA-protein complexes, pointing to the importance of an equilibrium of three components: actinomycin D, protein and DNA for drug action. The effect of actinomycin D is sequence-specific, since no inhibition is observed for interaction of nuclear proteins with the NFkappaB binding site. The results support the view that DNA-binding drugs displaying high sequence-selectivity can exhibit distinct effects on the interaction between DNA and different DNA-binding proteins.