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 Sp1 and NFκB 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 NFκB 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.
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