The Nuclear Corepressors NCoR and SMRT Are Key Regulators of Both Ligand- and 8-Bromo-Cyclic AMP-Dependent Transcriptional Activity of the Human Progesterone Receptor

131

Selective estrogen receptor modulators (SERMs) show differential effects upon ER␣ activation function 1 (AF-1). Tamoxifen allows strong ER␣ AF-1 activity, whereas raloxifene allows less and ICI 182,780 (ICI) allows none. Here, we show that blockade of corepressor histone deacetylase (HDAC) activity reverses the differential inhibitory effect of SERMs upon AF-1 activity in MCF-7 cells. This suggests that differential SERM repression of AF-1 involves HDAC-dependent corepressors. Consistent with this, ICI and raloxifene are more potent than tamoxifen in promoting ER␣-dependent sequestration of progesterone receptor-associated corepressors. Moreover, ICI and raloxifene are more efficient than tamoxifen in promoting ER␣ binding to the corepressor N-CoR in vivo and in vitro. An ER␣ mutation (537X) that increases N-CoR binding in the presence of all SERMs blocks AF-1 activity. An ER␣ mutation (L379R) that decreases N-CoR binding increases AF-1 activity in the presence of ICI and raloxifene and reverses the effect of the 537X mutation. The 537X and L379R mutations also alter the ligand preference of ER␣ action at AP-1 sites and C3 complement, an action that also involves AF-1. Together, our results suggest that differential SERM effects on corepressor binding can explain differences in SERM effects on ER␣ activity. We propose a model for differential effects of SERMs on N-CoR binding.Estrogen signaling is mediated by two estrogen receptors (ER␣ and ER␤), 1 which are conditional transcription factors (1-3). In the best understood pathway of ER action, the ERs bind specific estrogen response elements (EREs) in the promoter of estrogen-regulated genes and activate transcription by recruiting a large coactivator complex composed of p160 coactivators such as GRIP1 and SRC-1 and the histone acetyltransferases p300/CREB-binding protein and pCAF (4). Like other nuclear receptors, the ERs are comprised of an N-terminal domain (NTD), a central DNA-binding domain (DBD), and a C-terminal ligand-binding domain (LBD). The DBD mediates ERE recognition, and the NTD and LBD contain distinct activation functions (AF-1 and AF-2, respectively) that mediate coactivator recruitment. The ERs also modulate expression of genes with alternate estrogen response elements, such as AP-1 sites and SP-1 sites (5-7). ER␣ acts at AP-1 sites via protein-protein interactions and recruits p160s in a process that requires ER␣ AF-1 and AF-2 and their cognate binding sites within the p160s (6, 8 -10). Thus, estrogen action at classical EREs and alternate response elements involve similar coactivators.Selective estrogen receptor modulators (SERMs) are used in treatment and prevention of estrogen-dependent breast cancer (11). The SERMs inhibit ER action by blocking AF-2 activity, and the mechanism of this effect is now understood at the atomic level (2). AF-2 is composed of surface-exposed residues from LBD helices (H) 3, 5, and 12, which form a hydrophobic cleft that binds short nuclear receptor (NR) boxes (consensus Leu-X-X-Leu-Leu or LXXLL) found in each p16...

Section: Discussionmentioning

confidence: 99%

Differential SERM Effects on Corepressor Binding Dictate ERα Activity in Vivo

Webb

Nguyen

Kushner

2003

131

“…These proteins can act synergistically to enhance PR transactivation (12), may be recruited in a sequential fashion by ligand-bound PR (13), and selectively determine PR-mediated transcriptional response (14). Transcriptional co-repressors such as the structurally related proteins NCoR and the silencing mediator for retinoid and thyroid hormone receptor similarly associate with and alter the activity of PR (15). These proteins are recruited to the PR complex only when PR is bound to an antagonist, a consequence of the distinct conformations induced by agonists and antagonists on this protein.…”

mentioning

confidence: 99%

Subfertility, Uterine Hypoplasia, and Partial Progesterone Resistance in Mice Lacking the Krüppel-like Factor 9/Basic Transcription Element-binding Protein-1 (Bteb1) Gene

Simmen

Eason

McQuown³

et al. 2004

120

Progesterone receptor (PR), a ligand-activated transcription factor, is a key regulator of cellular proliferation and differentiation in reproductive tissues. The transcriptional activity of PR is influenced by co-regulatory proteins typically expressed in a tissue-and cellspecific fashion. We previously demonstrated that basic transcription element-binding protein-1 (BTEB1), a member of the Sp/Krü ppel-like family of transcription factors, functionally interacts with the two PR isoforms, PR-A and PR-B, to mediate progestin sensitivity of target genes in endometrial epithelial cells in vitro. Here we report that ablation of the Bteb1 gene in female mice results in uterine hypoplasia, reduced litter size, and increased incidence of neonatal deaths in offspring. The reduced litter size is solely a maternal genotype effect and results from fewer numbers of implantation sites, rather than defects in ovulation. In the early pregnant uterus, Bteb1 expression in stromal cells temporally coincides with PR-A isoform-dependent decidual formation at the time of implantation. Expression of two implantation-specific genes, Hoxa10 and cyclin D3, was decreased in uteri of early pregnant Bteb1-null mutants, whereas that of Bteb3, a related family member, was increased, the latter possibly compensating for the loss of Bteb1. Progesterone responsiveness of several uterine genes was altered with Bteb1-null mutation. These results identify Bteb1 as a functionally relevant PR-interacting protein and suggest its selective modulation of cellular processes that are regulated by PR-A in the uterine stroma.

“…pCI-neo-HA-ARF and pBabe-puro-hARF coding for human ARF, pCMV␤-HA2-HDM2, and pCMV␤-HDM2 were provided by W. G. Yarbrough (Yale University). Luciferase reporter vectors included PSA-Enh-Luc from M. Carey (University of California Los Angeles) (10,32), E2F1-Luc from J. R. Nevins (Duke University) (10,33) and 5XGAL4Luc3 from D. P. McDonnell (Duke University) (34,35). GAL-ARF was prepared by PCR-amplifying pCI-neo-HA-ARF using oligonucleotide primers to omit the HA tag and produce a fragment cloned into EcoR1 and BamHI sites of GAL-O.…”

Section: Methodsmentioning

confidence: 99%

Post-translational Down-regulation of Melanoma Antigen-A11 (MAGE-A11) by Human p14-ARF Tumor Suppressor

Minges

Grossman

Zhang

et al. 2015

Background: Melanoma antigen-A11 (MAGE-A11) is a primate-specific steroid receptor coregulator and proto-oncogene expressed at increased levels in castration-resistant prostate cancer. Results: Human p14-ARF tumor suppressor promotes the proteasomal degradation of MAGE-A11 independent of ubiquitination. Conclusion: MAGE-A11 is post-translationally down-regulated by the p14-ARF tumor suppressor. Significance: Increased levels of MAGE-A11 associated with low p14-ARF promote the development of castration-resistant prostate cancer.