Inhibitory action of aurintricarboxylic acid and rifamycin AF/013 at the polynucleotide domain of 1,25-dihydroxyvitamin D3-receptor complexes.

The binding of 1,25-dihydroxyvitamin D3-receptor complexes from chicken intestine to DNA-cellulose and isolated intestinal nuclei is inhibited in a dose-dependent manner by aurintricarboxylic acid and rifamycin AF/013. Since both nuclear- and cytoplasmic-associated receptors have been identified, some experiments were carried out on both populations of receptors. Concentrations resulting in 50% displacement of cytoplasmic receptor complexes were 3.2 X 10(-6) M and 1.2 X 10(-4) M for aurintricarboxylic acid and rifamycin AF/013 respectively. Moreover, rifamycin AF/013 was approximately nine times more potent at inhibiting nuclear receptor binding to DNA-cellulose compared to cytoplasmic receptors. Contrary to these findings, rifampicin, which does not inhibit eukaryotic RNA or DNA polymerases, did not cause a loss of receptor complex binding to DNA-cellulose at the doses tested. Neither aurintricarboxylic acid, rifampicin, nor rifamycin AF/013 resulted in any significant loss of sterol binding. Inhibition of receptor binding to DNA-cellulose by these polymerase inhibitors was not due to alteration of the DNA and was reversed by dialysis. Incubation of receptor complexes with aurintricarboxylic acid or rifamycin AF/013 inhibited binding to Cibacron blue-agarose and phosphocellulose. Furthermore, these polymerase inhibitors were utilized specifically to desorb receptor complexes from Cibacron blue-agarose columns. Sucrose density gradient analysis of inhibitor treated and untreated receptor revealed that rifamycin AF/013 treatment resulted in the appearance of a broadened 3.7 S sedimenting receptor in addition to specific bound 1,25-dihydroxyvitamin D3 in the 6.0 S region and in the pellet of the gradient.