Analysis of Estrogen Receptor Interaction with a Repressor of Estrogen Receptor Activity (REA) and the Regulation of Estrogen Receptor Transcriptional Activity by REA

Abstract

The transcriptional activity of nuclear hormone receptors is known to be modulated by coregulator proteins. We found that the repressor of estrogen receptor activity (REA), a protein recruited to the hormone-occupied estrogen receptor (ER), decreased the transcriptional activity of ER, both when ER was acting directly through DNA response elements as well as when it was tethered to other transcription factors. Administration of antisense REA resulted in a 2-4-fold increase in ER transactivation, implying that endogenous REA normally dampens the stimulatory response to estradiol. To define the interaction regions between ER and REA, we used glutathione S-transferase pull-down assays. We found that REA bound to the ligand-binding domain (E domain) of ER, but not to other regions of ER, and that REA interaction with ER involved a region in the Cterminal half of REA. REA and the coactivator SRC-1 were involved in a functional competition for regulation of ER transcriptional activity, which we show results from competition between these two coregulators for interaction with ER. REA contains an LXXLL motif near its N terminus, but this motif was not involved in its binding to ER. Rather, this sequence was required for the competitive binding of REA and SRC-1 to ER and thus for optimal repression of ER activity. Our findings show that the regions of REA required for its interaction with ER and for its repression of ER activity are different.Nuclear hormone receptors comprise a large superfamily of transcription factors whose activity is under hormonal control (1-3). These receptors are characterized by a central DNAbinding domain, which interacts with specific hormone response elements located near the target gene promoter, and by two distinct activation function (AF) 1 domains that contribute to the transcriptional activity of these receptors. The first activation function, AF-1, is located within the amino-terminal portion of the receptor, whereas the second, hormone-dependent activation function, AF-2, is located in the carboxyl-terminal half of the molecule, overlapping the ligand-binding domain. AF-1 and AF-2 function in a synergistic manner and are required for full transcriptional activity in most cell contexts (4, 5).In addition to having their activities regulated by specific hormones, the activity of these nuclear receptors is also dramatically affected by their interaction with coregulator proteins that function either to enhance (coactivators) or repress (corepressors) transcriptional activity (6 -9). These coregulator proteins are believed to be interposed between the receptor and the basal transcriptional complex. This tripartite action of nuclear hormone receptors, involving the receptor and its ligands and coregulator proteins (10), allows for the precise regulation of the biological effects of these hormones on gene expression.In the case of the estrogen receptor (ER), which mediates the biological effects of estrogens in a variety of target tissues and in breast cancer, most of its identified coregula...

The Role of the Prohibitin Gene in Apoptosis of Breast Cancer Cells

“…Prohibitin was found complcxed %vith either Rb or E2FI in diHerent cell types including Ramos cells without overexpression of any component, as detected by immunofS^uf o"~^"*^™ '''°t experiments (Wane et al, 1999a,b) Because the Rb binding domain and the E2F binding domain on prohibitin are distinct (amino acids /4-I16 versus 184-214. respectively), the three P'"°*^'"s could potentially associate together at the Oncogene same time. Our results on a transcriptional regulatory role for prohibitin are further supported by the studies showing that a highly related protein, Phb2/BAP37/ REA mediates the repression of estrogen receptors (Delage-Mourroux et al, 2000; Collectively, these observations suggest that while prohibitin might have other functions in the cell (Nijtmans et al, , 2002 its mitochondrial functions, if any, are distinct from' its ability to bring about transcriptional repression or powth suppression.…”

CARL lncRNA inhibits anoxia-induced mitochondrial fission and apoptosis in cardiomyocytes by impairing miR-539-dependent PHB2 downregulation

“…Furthermore, in other cell types, PHB2 has also been suggested to be localized in the nucleus and modulate transcriptional activity by interacting with transcription factors, including nuclear receptors, either directly or indirectly 12,[29][30][31][32] . PHB2 has been shown to interact with and inhibit the transcriptional activity of the ER in breast cancer 12 .…”

Unliganded estrogen receptor-α activates transcription of the mammary gland Na+/I− symporter gene

“…However, a growing body of evidence indicates that this model is too simple and not adequate to explain the dynamic pattern of transcriptional regulation [20]. It has previously been shown that liganded ERa is able to interact with a selective repressor protein illustrating an unpredictable mode of action for liganded receptors [21]. On the other hand, in a recent report, the activator function of apo-ERa was also demonstrated [7].…”