Environmental estrogens induce transcriptionally active estrogen receptor dimers in yeast: Activity potentiated by the coactivator RIP140

We used three yeast genetic systems to investigate the estrogen-like activi ty of octylphenol (OP), bisphenol-A (BPA), o,p'-DDT, and o,p'-DDE to induce human estrogen receptor (hER) dimerization and transcriptional activation. We have demonstrated that OF, BPA, and o,p'-DDT can induce hER ligand-depe ndent dimerization using a yeast two-hybrid assay. All three xenoestrogens, plus estradiol, enhanced estrogen response element (ERE)-dependent transcr iptional activation of hER. In the presence of receptor interacting protein 140 (RIP140), ERE-dependent activity was dramatically amplified by 100-fol d for estradiol, OF, BPA, and o,p'-DDT. A yeast whole-cell [H-3]estradiol b inding assay was developed to determine the site of interaction on the hER. We determined nonspecific binding by parallel incubations run in the prese nce of 5 mu M unlabelled estradiol in PCY2 yeast. At the concentrations tes ted, unlabeled estradiol, OF, and BPA displaced [H-3]estradiol in this bind ing assay, whereas the concentrations of o,p'-DDT and o,p'-DDE tested were insufficient to inhibit binding, incubating yeast in the presence of increa sing concentrations of estradiol and OP (1 mu M) or BPA (1 mu M) neither bl ocked nor altered the effect of estradiol on hER activity, We observed no a gonistic activity of o,p'-DDE in any of the yeast models used. These result s suggest that OP, BPA, and o,p'-DDT exert their estrogen-like activity thr ough the ER in a manner similar to that of estradiol, and the coactivator R IP140 markedly potentiates this activity.