Negative regulation of estrogen signaling by ERβ and RIP140 in ovarian cancer cells

Abstract

In hormone-dependent tissues such as breast and ovary, tumorigenesis is associated with an altered expression ratio between the two estrogen receptor (ER) subtypes. In this study, we investigated the effects of ERα ectopic expression on 17α-estradiol (E2)-induced transactivation and cell proliferation in ERβ-positive BG1 ovarian cancer cells. As expected, ERα expression strongly decreased the mitogenic effect of E2, significantly reduced E2-dependent transcriptional responses (both on a stably integrated estrogen response element [ERE] reporter gene and on E2-induced mRNAs), and strongly enhanced the formation of ER heterodimers as evidenced by chromatin immunoprecipitation analysis. Inhibition by the ERβ-selective ligand propyl pyrazole triol was less marked than with the pan-agonist (E2) or the ERα-selective (8α-vinyl-estradiol) ligands, indicating that ERα activation reinforced the inhibitory effects of ERα. Interestingly, in E2-stimulated BG1 cells, ERα was more efficient than ERβ to regulate the expression of receptorinteracting protein 140 (RIP140), a major ERβ transcriptional corepressor. In addition, we found that the RIP140 protein interacted better with ERα than with ERβ (both in vitro and in intact cells by fluorescence cross-correlation spectroscopy). Moreover, RIP140 recruitment on the stably integrated reporter ERE was increased upon ERα overexpression, and ERα activity was more sensitive to repression by RIP140. Finally, small interfering RNA-mediated knockdown of RIP140 expression abolished the repressive effect exerted by activated ERα on the regulation of ERE-controlled transcription by estrogens. Altogether, these data demonstrate the inhibitory effects of ERα on estrogen signaling in ovarian cancer cells and the key role that RIP140 plays in this phenomenon. © 2013 by The Endocrine Society.