Haploinsufficiency of the corepressor of estrogen receptor activity (REA) enhances estrogen receptor function in the mammary gland

Abstract

Estrogen receptor (ER)-mediated gene expression plays an essential role in mammary gland morphogenesis, function, and carcinogenesis. The repressor of ER activity (REA) is an ER-interactive protein that counterbalances estrogen-induced ER transcriptional activity. Our previous study showed that genetic deletion of both REA alleles resulted in embryonic lethality. This study demonstrates that REA and ER␣ are coexpressed in mammary epithelial cells. REA heterozygous (REA ؉͞؊ ) mutant mice exhibit faster mammary ductal elongation in virgin animals, increased lobuloalveolar development during pregnancy, and delayed mammary gland involution after weaning. These morphological phenotypes of REA ؉͞؊ mice are associated with significantly increased cell proliferation and ER transcriptional activities, as indicated by the estrogen response element (ERE)-luciferase reporter in the WT͞ ERE-Luc and REA ؉͞؊ ͞ERE-Luc bigenic mice and by the higher expression levels of estrogen-responsive genes such as progesterone receptor and cyclin D1 in the mammary gland. Our analysis also revealed that REA is an important repressor of ER transcriptional activity in the mammary gland under natural, as well as ovariectomized and estrogen-replaced, hormonal conditions. Our results indicate that REA is a physiological modulator of ER function in the mammary gland and that its correct gene dosage is required for maintenance of normal ER activity and normal mammary gland development. Consequently, a reduction or loss of REA function may cause overactivation of ER and increase breast cancer risk in humans.prohibitin 2 ͉ nuclear receptor ͉ coregulator ͉ breast ͉ gene expression T he mammary gland is a dynamic tissue in which morphogenesis, epithelial differentiation, and physiological function are tightly regulated by estrogen and progesterone in accordance with pubertal development and reproductive cycles (1). Estrogen regulates mammary gland development and function through binding to the estrogen receptor ␣ (ER␣) and inducing the expression of ER␣ target genes such as progesterone receptor (PR) and cyclin D1. The phenotype of ER knockout mice has clearly shown that ER␣ plays a mandatory role in promoting mammary epithelial proliferation and mammary ductal growth after birth (2). Recent studies have demonstrated that the transcriptional activity of nuclear receptors, including ER␣ and PR, is determined not only by hormone binding but also by relative activities of nuclear receptor-associated coactivators and corepressors (3-5). Repressor of ER activity (REA) is a recently identified corepressor that interacts with select nuclear receptors such as ER (6, 7) and the orphan nuclear receptors chicken ovalbumin upstream promoter transcription factors I and II (COUP-TFI and II) (8). Unlike most other known corepressors that are recruited to nuclear receptors mainly in the absence of ligand or in the presence of antagonists, REA belongs to a subclass of corepressors that interacts dynamically with both agonist-and antagonist-occupied ER (6). REA and ot...

Skp2B Stimulates Mammary Gland Development by Inhibiting REA, the Repressor of the Estrogen Receptor

“…The relevance of the interaction between Skp2B and REA is strongly supported by the observations first that the transcriptional activity of the ER is increased in MCF-7-Skp2B cells and second that the expression of Skp2B in the mammary glands of transgenic mice mimics the phenotype observed for the REA heterozygous mice (15). As the 50% reduction in REA levels observed for Skp2B transgenic mice is equivalent to that observed for REA heterozygous mice and that this level of reduction was shown to be sufficient to induce the activity of the ER in vivo (15), the decrease of REA level observed for MMTV-Skp2B mice is likely to participate in the phenotype observed.…”

“…The best-characterized function of the ER is as a transcriptional factor, which is highly regulated by binding to coactivators and corepressors. Among the corepressors, the repressor of ER activity (REA) was recently shown to have a profound effect on the development of the mammary gland (14,15). REA heterozygote mice display accelerated invasion of the fat pad and development of the mammary gland during pregnancy, which is associated with an increase in the ER activity (15).…”

“…Skp2B induces precocious invasion of the fat pad and side branching in the mammary glands of mice during early puberty. The 50% reduction in REA levels observed for REA heterozygote mice has been reported to lead to an accelerated invasion of the fat pad during puberty (15). To determine the effect of MMTV-Skp2B expression on the early mammary gland development, we analyzed whole-mount preparations of mammary glands from age-matched virgin transgenic and nontransgenic littermates.…”

Genetic Ablation of the Amplified-in-Breast Cancer 1 Inhibits Spontaneous Prostate Cancer Progression in Mice

“…The reverse primer specific to SV40 T mRNA was 5 ¶-ctgctcccattcatcagttcc-3 ¶. As an epithelial RNA loading control, the relative mRNA concentration of the keratin 18 epithelial marker was also analyzed by real-time RT-PCR as previously described (30).…”

Changes in expression of steroid receptors, their downstream target genes and their associated co-regulators during the sequential acquisition of tamoxifen resistance in vitro

“…However, since REA requires an intact F region, within the AF-2 domain (51) it is unlikely that altered expression would induce TAMr if AF-2 activity is compromised. Recent data from animal models have shown that REA is required for maintenance of ER activity and normal mammary gland development (52).…”