Estrogen Receptor β2 Negatively Regulates the Transactivation of Estrogen Receptor α in Human Breast Cancer Cells

Abstract

Estrogens, by binding to and activating two estrogen receptors (ERA and ERB), are critically involved in the development of the mammary gland and breast cancer. An isoform of ERB, ERB2 (also called ERBcx), with an altered COOH-terminal region, is coexpressed with ERA in many human breast cancers. In this study, we generated a stable cell line from MCF7 breast cancer cells expressing an inducible version of ERB2, along with endogenous ERA, and examined the effects of ERB2 on the ERA protein levels and function. We showed that ERB2 inhibited ERA-mediated transactivation via estrogen response element and activator protein-1 sites of reporter constructs as well as the endogenous genes pS2 and MMP-1. Chromatin immunoprecipitation assays revealed that ERB2 expression caused a significant reduction in the recruitment of ERA to both the pS2 and MMP-1 promoters. Furthermore, ERB2 expression induced proteasome-dependent degradation of ERA. The inhibitory effects of ERB2 on ERA activity were further confirmed in HEK293 cells that lack functional endogenous ERs. We also showed that ERB2 can interact with ERA both in vitro and in mammalian cells, which is compatible with a model where ERB2/ERA heterodimers are targeted to the proteasome. Finally, in human breast cancer samples, we observed that expression of ERB2 significantly correlated with ERA-negative phenotype. Our data suggest that ERB2 could influence ERA-mediated effects relevant for breast cancer development, including hormone responsiveness. [Cancer Res 2007;67(8):3955-62]

AP-1 Is a Key Regulator of Proinflammatory Cytokine TNFα-mediated Triple-negative Breast Cancer Progression

“…qPCR-Total RNA was extracted, reverse transcribed, and subjected to real-time qPCR using gene-specific primers, as previously described (18). The expression of genes was normalized to the expression of ␤-glucuronidase and 36B4.…”

“…ChIP and ChIP-Seq-ChIP and ChIP-Seq were performed as previously described (18,19). The antibodies used were as follows: anti-c-Jun (H-79) and normal rabbit IgG from Santa Cruz Biotechnology, anti-p65 (ab7970) and anti-p50 (ab7971) from Abcam.…”

The genome landscape of ERα- and ERβ-binding DNA regions

“…MCF-7 tet-off ER␤ cells were seeded in 150-mm tissue culture plates and grown in the presence (ϩTet; ϪER␤) or absence (ϪTet; ϩER␤) of tetracycline, respectively, for 18 h. The total cell extracts were prepared as described in ref. 22. Aliquots corresponding to 100 g of protein were separated by SDS/PAGE.…”

“…Total cell extracts from MCF7 tet-off ER␤ cells were incubated with AP1A, AP2A, and LBD antibodies, followed by immunoprecipitation as described in ref. 22. Precipitated fractions and supernatant were transferred to nitrocellulose membrane and visualized by using the anti-Flag M5 monoclonal antibody (Sigma) or the anti-ER␤ chicken polyclonal antibody Ab14021 (Abcam, Cambridge MA).…”

Membrane-Initiated Estradiol Signaling of Epithelial-Mesenchymal Transition-Associated Mechanisms Through Regulation of Tight Junctions in Human Breast Cancer Cells

“…The potential role of ER beta remains unknown. It has been clearly demonstrated that two ER beta isoforms (splice variants ER beta 1 and ER beta 2) have anti-proliferative functions when introduced into ER alpha-positive breast cancer cells, and ER beta 2 negatively regulates the transactivation of estrogen receptor alpha in MCF-7 cancer cells [40]. This is either by inducing proteasome-dependent degradation of ER alpha or repressing ER alpha-mediated transcriptional activity when co-expressed with ER alpha [22].…”