Figure 2.

REA enhances the potency of antiestrogens and dominant negative ER as suppressors of ER activity, but has no affect on the potency of antiprogestin as a progesterone receptor antagonist. In A– C, CHO cells were transfected with an expression vector for the wild-type ER (5 ng) and the reporter construct (ERE)₂-TATA-CAT in the absence or presence of an expression vector for REA (10 ng). In A, cells were cotransfected with increasing amounts of an expression vector for the dominant negative L540Q ER and were treated with 10⁻⁸ M E₂ for 24 h. In B and C, cells were treated with 10⁻⁸ M E₂ along with increasing concentrations of the antiestrogen TOT (B) or ICI182,780 (ICI) (C) for 24 h. (D) The effect of REA on the repressive action of antiprogestin on R5020-mediated activation of the PR also was tested. CHO cells were transfected with an expression vector for human PR-B (5 ng), the PR responsive reporter construct MMTV-CAT in the absence or presence of REA expression vector (10 ng), and were treated with 10⁻⁸ M progestin R5020 plus increasing concentrations of the antiprogestin RU486 for 24 h. All cells in A– D also were transfected with a β-galactosidase internal control reporter to correct for transfection efficiency. Cell extract CAT activity values, normalized for β-galactosidase activity, are the means ± SD from three separate experiments.