Estrogen receptor beta as a novel target of androgen receptor action in breast cancer cell lines

• Published in: Breast cancer research : BCR 2014-02, Vol.16 (1), p.R21-R21, Article R21
• Main Authors: Rizza, Pietro, Barone, Ines, Zito, Domenico, Giordano, Francesca, Lanzino, Marilena, De Amicis, Francesca, Mauro, Loredana, Sisci, Diego, Catalano, Stefania, Dahlman Wright, Karin, Gustafsson, Jan-Ake, Andò, Sebastiano
• Format: Article
• Language: English
• Subjects: Analysis; Breast Neoplasms - pathology; Cell Line, Tumor; Cell Proliferation - genetics; Chromatin; Cyclin D1 - biosynthesis; Enzyme Activation; Estrogen Receptor alpha - metabolism; Estrogen Receptor beta - biosynthesis; Estrogen Receptor beta - genetics; Estrogen Receptor beta - metabolism; Female; Genes; Humans; MCF-7 Cells; Medicin och hälsovetenskap; Mutagenesis, Site-Directed; Nandrolone - analogs & derivatives; Nandrolone - pharmacology; Physiological aspects; Promoter Regions, Genetic - drug effects; Protein Binding; Receptors, Androgen - metabolism; rho GTP-Binding Proteins - biosynthesis; RNA Interference; RNA Polymerase II - genetics; RNA, Messenger - biosynthesis; RNA, Small Interfering; Testosterone Congeners - pharmacology; Up-Regulation
• ISSN: 1465-542X; 1465-5411; 1465-542X
• DOI: 10.1186/bcr3619

The two isoforms of estrogen receptor (ER) alpha and beta play opposite roles in regulating proliferation and differentiation of breast cancers, with ER-alpha mediating mitogenic effects and ER-beta acting as a tumor suppressor. Emerging data have reported that androgen receptor (AR) activation inhibits ER-positive breast cancer progression mainly by antagonizing ER-alpha signaling. However, to date no studies have specifically evaluated a potential involvement of ER-beta in the inhibitory effects of androgens. ER-beta expression was examined in human breast cancer cell lines using real-time PCR, Western blotting and small interfering RNA (siRNA) assays. Mutagenesis studies, electromobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) analysis were performed to assess the effects of mibolerone/AR on ER-beta promoter activity and binding. In this study, we demonstrate that mibolerone, a synthetic androgen ligand, up-regulates ER-beta mRNA and protein levels in ER-positive breast cancer cells. Transient transfection experiments, using a vector containing the human ER-beta promoter region, show that mibolerone increases basal ER-beta promoter activity. Site-directed mutagenesis and deletion analysis reveal that an androgen response element (ARE), TGTTCT motif located at positions -383 and -377, is critical for mibolerone-induced ER-beta up-regulation in breast cancer cells. This occurs through an increased recruitment of AR to the ARE site within the ER-beta promoter region, along with an enhanced occupancy of RNA polymerase II. Finally, silencing of ER-beta gene expression by RNA interference is able to partially reverse the effects of mibolerone on cell proliferation, p21 and cyclin D1 expression. Collectively, these data provide evidence for a novel mechanism by which activated AR, through an up-regulation of ER-beta gene expression, inhibits breast cancer cell growth.