CHARACTERIZATION OF LIGAND-BINDING, DNA-BINDING AND PHOSPHORYLATION OF PROGESTERONE-RECEPTOR BY 2 NOVEL PROGESTERONE-RECEPTOR ANTAGONIST LIGANDS

In order to gain a better understanding of the distinctive mechanisms of the various types of antiprogestins, we have characterized in vitro ligand binding, specific DNA binding and phosphorylation of progester one receptor (PR) from T47D cells after treatment of cells with proges tins (progesterone, R5020) and antiprogestins (RU486, ZK98299, Org 318 06 and Org 31710), Treatment of the cells with R5020 or PR antagonists , with the exception of ZK98299, resulted in a quantitative upshift of PR-A and PRE indicative of ligand/DNA-induced phosphorylation of PR. Treatment of cells with RU486, Org 31710 or Org 31806, but not R5020 o r ZK98299 resulted in detectable PR-progesterone response element comp lexes (PR-PREc) as assessed by gel mobility shift assay. Although trea tment of cells with ZK98299, a type I PR antagonist, did not induce ph osphorylation, the antiprogestins, Org 31806 and Org 31710, in a manne r identical to RU486, did. Our data suggest that Org 31806 and Org 317 10 affect properties of PR from T47D cells that are similar to RU486.