G Protein Pathway Suppressor 2 (GPS2) Is a Transcriptional Corepressor Important for Estrogen Receptor α-mediated Transcriptional Regulation

Abstract

We have identified G protein suppressor 2 (GPS2) as a stable component of the SMRT corepressor complexes. GPS2 potently represses basal transcription, with the repression domain mapped to the N-terminal silencing mediator of retinoic acid and thyroid hormone receptor (SMRT)-interacting domain. Knockdown of GPS2 abrogates, whereas overexpression potentiates, SMRT-mediated repression activity. The SMRT complexes are involved in 4-hydroxyl-tamoxifen (4OHT)-mediated gene repression by estrogen receptor ␣ (ER␣). We show that 4OHT recruits SMRT and GPS2 to the promoter of pS2, an ER␣ target gene, in a dynamic manner. Unexpectedly, we also found that estradiol (E2) promotes promoter recruitment of the SMRT complexes. While knockdown of GPS2 compromised 4OHT-mediated repression, it enhanced E2-induced expression of a reporter gene and several endogenous ER␣ target genes, including pS2, cyclin D1 (CCND1), progesterone receptor (PR), and c-MYC. Finally, we show that depletion of GPS2 or SMRT by siRNA promotes cell proliferation in MCF-7 breast cancer cells. Thus, we concluded that GPS2 is an integral component of the SMRT complexes, important for ligand-dependent gene regulations by ER␣ and a suppressor for MCF-7 cell proliferation. Transcriptional regulation by estrogen receptor ␣ (ER␣)2 is mediated by transcriptional coactivators and corepressors. SMRT and N-CoR are two closely related transcriptional corepressors that mediate transcriptional repression by many nuclear hormone receptors including ER␣ (1-5). Both SMRT and N-CoR are large nuclear proteins that contain multiple functional domains, including four repression domains (RDs) (2, 4, 6, 7). Transcriptional repression by SMRT or N-CoR is manifested through their recruitment of a histone deacetylase (HDAC) complex containing mSin3A and HDAC1 (6 -8). In addition, SMRT and N-CoR also interact with HDAC3 (9 -11) and with class II HDACs including HDAC4, -5, and -7 (12, 13). TBL1 and TBRL1 are also common stable components of the SMRT and N-CoR complexes (9,14). Despite this long list, SMRT and N-CoR are large proteins, and other components of their complexes undoubtedly exist but have not yet been identified.GPS2 (G protein suppressor 2) was first identified as a suppressor of G protein-activated MAPK signaling in both yeast and mammalian cells (16,17). GPS2 is also involved in transcription regulation through its association with the papillomavirus E2 and E6 proteins (18,19), the human T-cell lymphotrophic viral oncoprotein Tax (20), p53 and p300 (18,19,21), and regulatory factor X4 variant transcript 3 (RFX4_v3) (22). GPS2 was also found in the N-CoR corepressor complex and is capable of repressing basal transcription when forcibly bound to a promoter (23). Besides transcription regulation, previous studies suggested that GPS2 is involved in cell cycle regulation, DNA repair, cytoskeleton architecture, brain development, and metabolism (22, 24 -29). These data indicate that GPS2 is involved in multiple cellular pathways.To better understand the mechanisms by which SM...

The Actin-binding Protein, Actinin Alpha 4 (ACTN4), Is a Nuclear Receptor Coactivator that Promotes Proliferation of MCF-7 Breast Cancer Cells

“…Chromatin Immunoprecipitation Assays-MCF-7 cells were treated with 100 nM E2, and ChIP assays were performed according to our published protocol (18) except that ␣-HDAC7, ␣-ACTN4, and ␣-ER␣ antibodies were used.…”

SpliceArray Profiling of Breast Cancer Reveals a Novel Variant of NCOR2/SMRT That Is Associated with Tamoxifen Resistance and Control of ERα Transcriptional Activity

“…Using the ERE-TK-Luc reporter, NCOR2 acted as a corepressor for ERa-mediated transcription (21,22), whereas on the ERE-E1b-Luc reporter, it was shown that NCOR2 was required for full ERa transcriptional activity (20). We therefore used both luciferase reporters in turn to test the modulation of BQ323636.1 on ERa-mediated transcription activation (Fig.…”

The Optimal Corepressor Function of Nuclear Receptor Corepressor (NCoR) for Peroxisome Proliferator-activated Receptor γ Requires G Protein Pathway Suppressor 2

“…2A). Both NCoR and SMRT form complexes with histone deacetylase 3 (HDAC3), transducin ␤-like protein 1 (TBL1)/TBL1-related protein 1 (TBLR1), and G protein pathway suppressor 2 (GPS2) (22)(23)(24)(25). HDAC3 interacts with the N-terminal SWI3/ADA2/NCoR/ TFIIIB-like domain along with a short upstream sequence.…”