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

Abstract

IntroductionThe 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.MethodsER-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.ResultsIn 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.ConclusionsCollectively, 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.

High Estrogen Receptor β Expression Is Prognostic among Adjuvant Chemotherapy–Treated Patients—Results from a Population-Based Breast Cancer Cohort

“…Previous results from this cohort suggested that the prognostic role of AR in breast cancer was dependent on the ERa status of the tumor (20). Similar hypotheses have been proposed for ERb (10), and an in vitro study suggested ERb to be the link between AR and ERa interactions (28). However, in the current study, unlike AR, ERb1 75 þ was prognostically beneficial irrespective of ERa expression.…”

Age at first childbirth and oral contraceptive use are associated with risk of androgen receptor-negative breast cancer: the Malmö Diet and Cancer Cohort

“…The AR acts as a transcription factor and has been shown to bind to ER-regulated genes to inhibit ERdependent cell proliferation (6). Recently, in vitro studies have suggested that activated AR up-regulates estrogen receptor beta gene expression, which inhibits breast cancer cell growth (13). AR has also been suggested to interact with cell cycle checkpoint protein p21, which is involved in epidermal growth factor signaling (14).…”

Androgen receptor signaling pathways as a target for breast cancer treatment

“…ERβ exerts a growth and invasion inhibitory action on ERα-positive BC cells through ERβ inhibition of selective ERα gene expression (Rizza et al 2014). ARE is a short sequence of DNA located in the human ERβ gene promoter and thus AR binding to ARE upregulates these receptors; and (5) AR induces apoptosis through direct downregulation of cyclin D1 gene expression (Lanzino et al 2010).…”