Distinct effects on the conformation of estrogen receptor alpha and beta by both the antiestrogens ICI 164,384 and ICI 182,780 leading to opposite effects on receptor stability

Tissue-specific effects of 17 beta-estradiol (E-2) and synthetic estrogen r eceptor (ER) ligands on target gene regulation might, at least partly, be e xplained by a selective ligand-induced conformational change of their recep tors (ER alpha and ER beta). In this study, the effects of E-2 and the synt hetic ER ligands tamoxifen (TAM), ICI 164,384, and ICI 182,780 on the confo rmation of ER alpha and ER beta were examined using limited proteolytic dig estion analysis. We found that E-2 induced a conformational change of ER al pha resulting in the protection of a 30-kDa product, whereas TAM protected a 28-kDa fragment. Strikingly, the ER alpha conformational change induced b y both ICI 164,384 and ICI 182,780 did not result in protection but rather seems to induce a ligand concentration-dependent increase in proteolytic de gradation of the 30- and 28-kDa products. Incubation of ER beta with E-2 re sulted in an increased protection of a 30-kDa fragment, whereas with TAM pr otection of a 29-kDa fragment was observed. In contrast to the situation wi th ER alpha, ICI 164,384 and ICI 182,780 incubation induced the protection in a manner similar to 30-kDa fragment E-2. In addition, the ICI compounds also induced in a dose-dependent manner the preservation of a 32-kDa fragme nt. Our observations demonstrate that ICI 164,384 and ICI 182,780 have dist inct effects on the conformation of ER alpha and ERP, resulting in receptor subtype-selective opposite effects on receptor stability in vitro. (C) 199 9 Academic Press.