ACTINOMYCIN-D SPECIFICALLY INHIBITS THE INTERACTION BETWEEN TRANSCRIPTION FACTOR SP1 AND ITS BINDING-SITE

The mode of action of many anticancer drugs involves DNA interactions. We here examine the ability of actinomycin D to alter the specific bi nding of transcription factors Sp1 and NF kappa B to their DNA sequenc es. Employing an electrophoretic mobility shift assay, it is shown tha t actinomycin D inhibits complex formation between nuclear proteins pr esent 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 importa nce 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 w ith the NF kappa B binding site. The results support the view that DNA -binding drugs displaying high sequence-selectivity can exhibit distin ct effects on the interaction between DNA and different DNA-binding pr oteins.