Steroid Receptor Coregulators Research Articles

Steroid Receptor Coregulators Can Modulate the Action of Progesterone Receptor during the Estrous Cycle in Cow Endometrium.

Simple SummaryProper functioning of the endometrium is necessary for the implantation of the embryo after fertilization and its development throughout pregnancy. The key role in this process plays appropriate action of progesterone through the nuclear receptor isoforms. The action of the receptor is regulated by the attachment of receptor modulators called coregulators which include coactivators and corepressors. Their improper expression in humans causes a malfunction of progesterone receptors and leads to disorders of pregnancy. However, in farm animals, such disorders may be one of the reasons leading up to early embryonic lethality, which in cows reaches up to 40%. Obtained results indicate the important role of the studied coregulators in regulating progesterone activity in endometrial cells, especially during the preimplantation period. Therefore, they can be helpful in better understanding the regulation and expression of the coactivators and corepressors in cow endometrium during the estrous cycle and can contribute to reducing this problem. They can also be of significant practical importance, making for the increased efficiency of breeding these animals.Nuclear receptor coregulators include coactivators and corepressors which associate with the progesterone receptor (PGR) during its activation. Fluctuations in the transcription levels of their respective genes and subsequent protein production as well as in related activities for histone acetyltransferase (HAT) and histone deacetylase (HDAC) can affect PGR function and thus change the action of progesterone (P4) in bovine endometrium during the estrous cycle. Endometrial tissue on days 2–5, 6–10, 11–16, and 17–20 of the estrous cycle was used for determination of the mRNA expression levels of coactivators P300, CREB, and SRC-1 along with corepressor NCOR-2 using Real-Time PCR, with protein levels by Western blot. Coregulators cellular localizations were assessed by immunohistochemistry whereas the activities of HAT and HDAC by using EIA. The highest levels of mRNA and proteins for all of the investigated coregulators, as well as the highest levels of activity for HAT and HDAC, were detected over days 2–16 of the estrous cycle. All of the tested coregulatory proteins were localized in the nuclei of endometrial cells. This research indicates the important role of coregulators of the PGR receptor in regulating P4 activity in endometrial cells, especially during the pre-implantation period.

SUN-028 Role of Estrogen Receptor Alpha (ERa) Acetylation in Estrogen-Dependent Gene Regulation in Breast Cancers

Estrogens, such as 17β- estradiol (E2), act through estrogen receptor alpha (ERα), a ligand-regulated transcription factor that binds across the genome to promote enhancer formation and regulate gene expression. ERα is expressed in approximately 70% of breast cancers, where it regulates the transcription of genes involved in mitogenic and inflammatory pathways. We are exploring the acetylation of ERα on lysines (K) 266 and 268, modifications that we previously showed enhance the DNA binding and transcriptional activities of ERα in biochemical and cell-based assays. ERα acetylation is catalyzed by the lysine acetyltransferases p300 and CBP in an E2- and steroid receptor coregulator (SRC)-dependent manner. Acetylation-dependent activation of ERα has potential implications in breast cancers associated with enhanced coregulator interactions, such as SRC-3/Amplified in Breast (AIB1) gene amplifications and gain-of-function ERα mutations in endocrine resistant metastatic tumors, such as Y537S and D538G. Notably, the constitutively-activated Y537S mutant exhibits E2-independent K266/268 acetylation and further enhanced acetylation with E2 stimulation when expressed in breast cancer cells. Enhanced ERα acetylation may promote the gain-of-function ERα activity in this context. Our hypothesis is that acetylation of ERα alters its function by increasing E2-responsive gene transcription and signaling in breast cancers. We are using the ER-positive MCF-7 breast cancer cell line with a knockdown/re-expression strategy with biochemical mimics of acetylated (K266/268Q) or unacetylated (K266/268R) ERα. Genomic ERα binding profiles using chromatin immunoprecipitation-sequencing (ChIP-seq) has defined both overlapping and unique sets of transcriptional targets and recruitment kinetics for the ERα mutants. Collectively, our results suggest that the transcriptional activities of the ERα acetylation mutants share a common altered mechanism of recruitment to chromatin with potential implications on enhancer activation. Our current efforts are focused on investigating the role of ERα acetylation on chromatin accessibility, enhancer activity, and target gene transcription.

OR34-1 Regulation of Breast Cancer Stem Cells by Nuclear Receptor Co-Regulatory Proteins

Despite highly effective treatments for breast cancer (BC), recurrence remains a significant risk among node-positive patients. Breast cancer stem or stem-like progenitor cells (BCSCs herein) are non-proliferative, evade first-line therapies in resistant breast tumors, and account for high mortality among patients with advanced disease. Our objective is to define the signaling pathways that drive cell fate transitions associated with endocrine resistance and the survival and expansion of BCSCs, with the goal of blocking these pathways to impact breast cancer survival. Filling this knowledge gap will pave the way for interventions that increase endocrine therapy duration and specifically target BCSC populations within heterogeneous luminal tumors. We recently defined the steroid receptor (SR) co-regulator, PELP1, as a mediator of BCSC expansion. Utilizing mass spectrometry, we identified steroid receptor coactivator-3, SRC-3, as a novel and preferential interactor with cytoplasmic PELP1. Notably, cytoplasmic PELP1 elevated SRC-3 activation, as measured by SRC-3 phosphorylation at Thr24 and Ser857. SRC-3 knockdown blocked cytoplasmic PELP1-induced BCSC expansion measured using tumorsphere assays, suggesting an essential role for PELP1/SRC-3 complexes in BCSC outgrowth. To better understand PELP1-regulated pathways we performed RNA-seq on MCF7 models grown in tumorsphere conditions to enrich for BCSC populations. We found that cells expressing cytoplasmic PELP1 have a dramatically different global gene profile relative to cells expressing wt-PELP1 (i.e. nuclear). Stem cell biology, metabolic, and hypoxic gene signatures were differentially upregulated, including members of the bi-functional kinase/phosphatase family (PFKFBs). Seahorse metabolic phenotype tests demonstrate that cytoplasmic PELP1 expression influences cellular metabolism by increasing both glycolysis and mitochondrial respiration. Recent studies have implicated pSer857 SRC-3 as a key substrate of PFKFB4 in lung and breast cancer metastases. Furthermore, we found that cytoplasmic PELP1 interacts with PFKFB3 and PFKFB4, and inhibition of PFKFB3 kinase activity blocks PELP1-induced tumorsphere formation. Together, our data suggests that PELP1, SRC-3, and PFKFBs form cytoplasmic signaling complexes that reprogram cellular metabolism to promote BCSC expansion. Our work will lead to the development of targeted therapies against BCSCs that can be used in combination with current treatments to overcome endocrine therapy resistance.

Abstract P5-05-16: Role of estrogen receptor alpha acetylation in estrogen-dependent gene regulation in breast cancers

Abstract Estrogens, such as 17β-estradiol (E2), act through estrogen receptor alpha (ERα), a ligand-regulated transcription factor that binds across the genome to promote enhancer formation and regulate gene expression. ERα is expressed in approximately 70% of breast cancers, where it regulates the transcription of genes involved in mitogenic and inflammatory pathways. We are exploring the the acetylation of ERα on lysines 266 and 268, a modification that enhances the DNA binding and transcriptional activities of ERα. ERα acetylation is catalyzed by the lysine acetyltransferases p300 and CBP in an E2- and steroid receptor coregulator (SRC)-dependent manner. Acetylation-dependent activation of ERα has potential implications in breast cancers associated with enhanced coregulator interactions, such as SRC-3/Amplified in Breast (AIB1) gene amplifications and gain-of-function ERα mutations in endocrine resistant metastatic tumors, such as Y537S and D538G. Increased association of ERα with SRCs and p300/CBP leading to enhanced ERα acetylation may promote gain-of-function ERα activity. Our hypothesis is that acetylation of ERα alters its function by increasing E2-responsive gene transcription and signaling in breast cancers. Our current efforts are focused on investigating the role of ERα acetylation on chromatin binding and accessibility, enhancer activity, and target gene transcription. We are using the ER-positive MCF-7 breast cancer cell line with a knockdown/re-expression strategy with biochemical mimics of acetylated (K266/268Q) or unacetylated (K266/268R) ERα. Genomic ERα binding profiles using chromatin immunoprecipitation-sequencing (ChIP-seq) has defined overlapping, but unique, sets of transcriptional targets and recruitment kinetics for the ERα mutants. Current efforts are focused on defining global transcriptional responses associated with the unique binding activities using precision run-on sequencing (PRO-seq). Ultimately, our goal is to define how acetylation affects the binding of ERα to chromatin and its effect on the transcriptional activity of E2-target genes in breast cancers in the context of gain-of-function ERα mutations and coregulator amplifications. Supported in part by a postdoctoral fellowship from the Lalor Foundation to YMV, and grants from the NIDDK, NICHD, and CPRIT to WLK, as well as support from the Cecil H. and Ida Green Center for Reproductive Biology Sciences Endowment. Citation Format: Vasquez YM, Setlem R, Murakami S, Kraus WL. Role of estrogen receptor alpha acetylation in estrogen-dependent gene regulation in breast cancers [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-05-16.

Genetic variations in MAGE-A11 predict the risk and survival of renal cell cancer.

Melanoma antigen-A11 (MAGE-A11) is a low-abundance, primate-specific steroid receptor coregulator in normal tissues of the human reproductive tract, which plays an important role in tumorigenesis. Single-nucleotide polymorphisms (SNPs) have been shown to contribute to cancer risk and prognosis. However, the role of SNPs of MAGE-A11 in renal cell carcinoma (RCC) has not been established. Two intronic SNPs (rs6641352 and rs6540341) of MAGE-A11 have been screened to assess their associations with RCC risk and prognosis in a case control study. We found that rs6641352 was associated with RCC susceptibility in the dominant model (TC/CC vs. TT, adjusted odds ratio = 1.315, 95% confidence interval [CI] = 1.089-1.588) and with survival of RCC in the recessive model (CC vs. TT/TC, adjusted hazard ratio = 3.526, 95% CI = 1.072-11.595). For the SNP rs6540341, individuals with the T allele could have a critically increased risk of RCC (adjusted odds ratio = 1.301, 95% CI = 1.081-1.564, P = 0.005 in the dominant model). However, there was no significant association between rs6540341 and RCC survival. Hence, rs6641352 in MAGE-A11 may contribute to the genetic susceptibility and prognosis for RCC and act as a biomarker for RCC occurrence and prognosis.

Dynamic assembly and activation of estrogen receptor α enhancers through coregulator switching.

Although many features of active transcriptional enhancers have been defined by genomic assays, we lack a clear understanding of the order of events leading to enhancer formation and activation as well as the dynamics of coregulator interactions within the enhancer complex. Here, we used selective loss- or gain-of-function mutants of estrogen receptor α (ERα) to define two distinct phases of ligand-dependent enhancer formation. In the first phase (0-20 min), p300 is recruited to ERα by Mediator as well as p300's acetylhistone-binding bromodomain to promote initial enhancer formation, which is not competent for sustained activation. In the second phase (20-45 min), p300 is recruited to ERα by steroid receptor coregulators (SRCs) for enhancer maturation and maintenance. Successful transition between these two phases ("coregulator switching") is required for proper enhancer function. Failure to recruit p300 during either phase leads to abortive enhancer formation and a lack of target gene expression. Our results reveal an ordered and cooperative assembly of ERα enhancers requiring functional interplay among p300, Mediator, and SRCs, which has implications for hormone-dependent gene regulation in breast cancers. More broadly, our results demonstrate the unexpectedly dynamic nature of coregulator interactions within enhancer complexes, which are likely to be a defining feature of all enhancers.

Androgen Triggers the Pro-Migratory CXCL12/CXCR4 Axis in AR-Positive Breast Cancer Cell Lines: Underlying Mechanism and Possible Implications for the Use of Aromatase Inhibitors in Breast Cancer

Background/Aims: Reports regarding the role of androgen in breast cancer (BC) are conflicting. Some studies suggest that androgen could lead to undesirable responses in the presence of certain BC tumor characteristics. We have shown that androgen induces C-X-C motif chemokine 12 (CXCL12) in BC cell lines. Our aim was to identify the mechanisms regulating the phenotypic effects of androgen-induced CXCL12 on Androgen Receptor (AR) positive BC cell lines. Methods: We analyzed the expression of CXCL12 and its receptors with qPCR and ELISA and the role of Nuclear Receptor Coactivator 1 (NCOA1) in this effect. AR effects on the CXCL12 promoter was studied via Chromatin-immunoprecipitation. We also analyzed publically available data from The Cancer Genome Atlas to verify AR-CXCL12 interactions and to identify the effect or Aromatase Inhibitors (AI) therapy on CXCL12 expression and disease progression in AR positive cases. Results: CXCL12 induction occurs only in AR-positive BC cell lines, possibly via an Androgen Response Element, upstream of the CXCL12 promoter. The steroid receptor co-regulator NCOA1 is critical for this effect. Androgen only induced the motility of p53-mutant BC cells T47D cells via upregulation of CXCR4 expression while they had no effect on wild-type p53 MCF-7 cells. Loss of CXCR4 expression and depletion of CXCL12 abolished the effect of androgen in T47D cells while inhibition of p53 expression in MCF-7 cells made them responsive to androgen and increased their motility in the presence to androgen. Patients with estrogen receptor positive (ER+)/AR+ BC treated with AIs were at increased risk of disease progression compared to ER+/AR+ non-AI treated and ER+/AR- AI treated cases. Conclusion: AIs may lead to unfavorable responses in some ER/AR positive BC cases, especially in patients with AR+, p53 mutant tumors.

Neonatal exposure to low doses of endosulfan induces implantation failure and disrupts uterine functional differentiation at the pre-implantation period in rats

We investigated whether neonatal exposure to low doses of endosulfan affects fertility and uterine functional differentiation at pre-implantation in rats. Newborn female rats received the vehicle, 0.2 µg/kg/d of diethylstilbestrol (DES), 6 µg/kg/d of endosulfan (Endo6) or 600 µg/kg/d of endosulfan (Endo600) on postnatal days (PND) 1, 3, 5, and 7. On PND90, the rats were mated to evaluate their reproductive performance on gestational day (GD) 19 and their ovarian steroid serum levels, endometrial proliferation and implantation-associated proteins on GD5. DES and endosulfan decreased the pregnancy rate and the number of implantation sites. On GD5, DES and endosulfan did not change the serum levels of 17β-estradiol (E2) and progesterone (P); the endometrial proliferation decreased, which was associated with silencing of Hoxa10 in the Endo600-treated rats. Both doses of endosulfan increased the progesterone receptor (PR) expression, whereas the higher dose led additionally to an increase in estrogen receptor alpha (ERα). In the Endo600-treated rats, the down-regulation of Hoxa10 was associated with a deregulation of the steroid receptor coregulators. Alterations in endometrial proliferation and the endocrine pathway of Hoxa10/steroid receptors/coregulators might be the mechanism of endosulfan-induced implantation failure.

Effects of levonorgestrel-releasing intrauterine system on the expression of steroid receptor coregulators TIF-2, AIB-1 and ncor in adenomyosis

In the present study, the expressions of steroid receptor coregulators, transcriptional intermediary factor-2 (TIF-2), amplified in breast cancer-1 (AIB-1) and nuclear receptor corepressor (NCoR) in endometrial tissues from control group, untreated adenomyosis group and levonorgestrel-releasing intrauterine system (LNG-IUS)-treated adenomyosis group are immunohistochemically evaluated.

Proto-oncogene Activity of Melanoma Antigen-A11 (MAGE-A11) Regulates Retinoblastoma-related p107 and E2F1 Proteins

Melanoma antigen-A11 (MAGE-A11) is a low-abundance, primate-specific steroid receptor coregulator in normal tissues of the human reproductive tract that is expressed at higher levels in prostate cancer. Increased expression of MAGE-A11 enhances androgen receptor transcriptional activity and promotes prostate cancer cell growth. Further investigation into the mechanisms of MAGE-A11 function in prostate cancer demonstrated interactions with the retinoblastoma-related protein p107 and Rb tumor suppressor but no interaction with p130 of the Rb family. MAGE-A11 interaction with p107 was associated with transcriptional repression in cells with low MAGE-A11 and transcriptional activation in cells with higher MAGE-A11. Selective interaction of MAGE-A11 with retinoblastoma family members suggested the regulation of E2F transcription factors. MAGE-A11 stabilized p107 by inhibition of ubiquitination and linked p107 to hypophosphorylated E2F1 in association with the stabilization and activation of E2F1. The androgen receptor and MAGE-A11 modulated endogenous expression of the E2F1-regulated cyclin-dependent kinase inhibitor p27(Kip1). The ability of MAGE-A11 to increase E2F1 transcriptional activity was similar to the activity of adenovirus early oncoprotein E1A and depended on MAGE-A11 interactions with p107 and p300. The immunoreactivity of p107 and MAGE-A11 was greater in advanced prostate cancer than in benign prostate, and knockdown with small inhibitory RNA showed that p107 is a transcriptional activator in prostate cancer cells. These results suggest that MAGE-A11 is a proto-oncogene whose increased expression in prostate cancer reverses retinoblastoma-related protein p107 from a transcriptional repressor to a transcriptional activator of the androgen receptor and E2F1.

The Coregulator, Repressor of Estrogen Receptor Activity (REA), Is a Crucial Regulator of the Timing and Magnitude of Uterine Decidualization

Successful implantation and maintenance of pregnancy require the transformation of uterine endometrial stromal cells into distinct decidualized cells. Although estrogen and progesterone (P4) receptors are known to be essential for decidualization, the roles of steroid receptor coregulators in this process remain largely unknown. In this study, we have established a key role for the coregulator, repressor of estrogen receptor activity (REA), in the decidualization of human endometrial stromal cells (hESCs) in vitro and of the mouse uterus in vivo. Our studies revealed that the level of REA normally decreases to half as hESC decidualization proceeds and that uterine reduction of REA in transgenic heterozygous knockout mice or small interfering RNA knockdown of REA in hESC temporally accelerated and strongly enhanced the differentiation process, as indicated by changes in cell morphology and increased expression of biomarkers of decidualization, including P4 receptor. Findings in hESC cultured in vitro with estradiol, P4, and 8-bromo-cAMP over a 10-day period mirrored observations of enhanced decidualization response in transgenic mice with heterozygous deletion of REA. Importantly, gene expression and immunohistochemical analyses revealed changes in multiple components of the Janus kinase/signal transducer and activator of transcription pathway, including marked up-regulation of signal transducer and activator of transcription 3 and IL-11, master regulators of decidualization, and the down-regulation of several suppressor of cytokine signaling family members, upon reduction of REA. The findings highlight that REA physiologically restrains endometrial stromal cell decidualization, controlling the timing and magnitude of decidualization to enable proper coordination of uterine differentiation with concurrent embryo development that is essential for implantation and optimal fertility.

Melanoma Antigen-A11 (MAGE-A11) Enhances Transcriptional Activity by Linking Androgen Receptor Dimers

Prostate cancer growth and progression depend on androgen receptor (AR) signaling through transcriptional mechanisms that require interactions with coregulatory proteins, one of which is the primate-specific steroid receptor coregulator melanoma antigen-A11 (MAGE-A11). In this report, we provide evidence how increased expression of MAGE-A11 during prostate cancer progression enhances AR signaling and prostate cancer growth. MAGE-A11 protein levels were highest in castration-recurrent prostate cancer. The cyclic AMP-induced increase in androgen-dependent and androgen-independent AR transcriptional activity correlated with an increase in MAGE-A11 and was inhibited by silencing MAGE-A11 expression. MAGE-A11 mediated synergistic AR transcriptional activity in LAPC-4 prostate cancer cells. The ability of MAGE-A11 to rescue transcriptional activity of complementary inactive AR mutants and promote coimmunoprecipitation between unlike forms of AR suggests that MAGE-A11 links transcriptionally active AR dimers. A model for the AR·MAGE-A11 multidimeric complex is proposed in which one AR FXXLF motif of the AR dimer engages in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction, whereas the second FXXLF motif region of the AR dimer interacts with dimeric MAGE-A11. The AR·MAGE-A11 multidimeric complex accounts for the dual functions of the AR FXXLF motif in the androgen-dependent AR NH(2)- and carboxyl-terminal interaction and binding MAGE-A11 and for synergy between reported AR splice variants and full-length AR. We conclude that the increased expression of MAGE-A11 in castration-recurrent prostate cancer, which is enhanced by cyclic AMP signaling, increases AR-dependent growth of prostate cancer by MAGE-A11 forming a molecular bridge between transcriptionally active AR dimers.

The roles of SRA1 gene in breast cancer

The Steroid receptor RNA activator (SRA) gene has been implicated in estrogen receptor signaling pathw ay. First identified as a RNA coregulator, SRA had been shown to increase steroid receptor activity. SRA RNA exp ression is altered during breast tumorigenesis and its molecul ar role in underscoring these events has been sugge sted. The subsequent identification of molecules capable of b inding SRA, including RNA helicase p68, SRA stem-loop interacting RNA binding protein (SLIRP), and steroi dogenic factor 1 (SF1) indicates SRA function is no t exclusively limited to modulate steroid receptor activity. A re cent genome-wide expression analysis by depleting SRA in cancer cells has further expanded our understanding of a b roader biological role played by SRA. In addition, several RNA isoforms have been found to encode an endogenous protein (SRAP), which is well conserved among Chordata. Interestingly, SRAP also modulates steroid receptor activity and functions as a co-regulator in estrog en receptor signaling. The recent observation that a higher exp ression of SRAP protein is associated with poorer s urvival in breast cancer patients treated with tamoxifen, highlights the potential relevance of this protein in cancer. Together, the SRA1 gene encodes both functional RNA and protein (SRAP) products, making it a unique member amongst the growing population of steroid receptor co-regulators.

Consensus PP1 Binding Motifs Regulate Transcriptional Corepression and Alternative RNA Splicing Activities of the Steroid Receptor Coregulators, p54nrb and PSF

Originally identified as essential pre-mRNA splicing factors, non-POU-domain-containing, octamer binding protein (p54nrb) and PTB-associated RNA splicing factor (PSF) are also steroid receptor corepressors. The mechanisms by which p54nrb and PSF regulate gene transcription remain unclear. Both p54nrb and PSF contain protein phosphatase 1 (PP1) consensus binding RVxF motifs, suggesting that PP1 may regulate phosphorylation status of p54nrb and PSF and thus their function in gene transcription. In this report, we demonstrated that PP1 forms a protein complex with both p54nrb and PSF. PP1 interacts directly with the RVxF motif only in p54nrb, but not in PSF. Association with PP1 results in dephosphorylation of both p54nrb and PSF in vivo and the loss of their transcriptional corepressor activities. Using the CD44 minigene as a reporter, we showed that PP1 regulates p54nrb and PSF alternative splicing activities that determine exon skipping vs. inclusion in the final mature RNA for translation. In addition, changes in transcriptional corepression and RNA splicing activities of p54nrb and PSF are correlated with alterations in protein interactions of p54nrb and PSF with transcriptional corepressors such as Sin3A and histone deacetylase 1, and RNA splicing factors such as U1A and U2AF. Furthermore, we demonstrated a novel function of the RVxF motif within PSF that enhances its corepression and RNA splicing activities independent of PP1. We conclude that the RVxF motifs play an important role in controlling the multifunctional properties of p54nrb and PSF in the regulation of gene transcription.

Small Molecule Inhibitors as Probes for Estrogen and Androgen Receptor Action

Because activated estrogen (ER) and androgen (AR) receptors stimulate cell proliferation in breast and prostate cancer, inhibiting their actions represents a major therapeutic goal. Most efforts to modulate ER and AR activity have focused on inhibiting the synthesis of estrogens or androgens or on the identification of small molecules that act by competing with agonist hormones for binding in the ligand-binding pocket of the receptor. An alternative approach is to implement screens for small molecule inhibitors that target other sites in the pathway of steroid receptor action. Many of these second-site inhibitors directly target ER or AR; others have still unknown sites of action. Small molecule inhibitors that target second sites represent new leads with clinical potential; they serve as novel modulators of receptor action; and they can reveal new and as yet unidentified interactions and pathways that modulate ER and AR action.

Behavioral implications of rapid changes in steroid production action in the brain [Commentary on Pradhan D.S., Newman A.E.M., Wacker D.W., Wingfield J.C., Schlinger B.A. and Soma K.K.: Aggressive interactions rapidly increase androgen synthesis in the brain during the non-breeding season. Hormones and Behavior, 2010

Not so long ago, most behavioral neuroendocrinologists probably believed that the steps of steroid action located up-stream from the binding of the hormone to its intracellular receptor had been largely elucidated so that research could now concentrate on the identification of genes transcribed under the control of steroids and their role in cellular function including activation of behavior. During the last 10–15 years, several important discoveries have clearly forced us to re-evaluate this notion. For example, a second nuclear estrogen receptor was identified first in humans (Kuiper et al., 1996) and then in a variety of other vertebrates (e.g., Foidart et al., 1999; Mosselman et al., 1996; Tremblay et al., 1997). A new family of proteins regulating steroid-dependent gene transcription, the steroid receptor co-regulators, was also discovered and now includes approximately 300 members (McKenna et al., 1999; Tetel et al., 2009).

Impairment in protein expression profile of testicular steroid receptor coregulators in male rat offspring perinatally exposed to Bisphenol A

Aims Steroid hormones and steroid receptors (SRs) play a crucial role in spermatogenesis. Steroid receptor coregulators are the major determinants of SR functioning, and any alteration in their expression is known to be associated with impaired spermatogenesis. Since Bisphenol A (BPA) exposure leads to an impairment of spermatogenesis, we hypothesized that this effect could be associated with the altered expression of steroid receptors and their coregulators in the testes. The present study describes the effect of perinatal exposure of rats to BPA on the expression profile of testicular steroid receptor coregulators in the F 1 generation. These effects were further studied in the F 2 and F 3 generations to determine vertical transmission. Main methods Pregnant female rats (F 0) were gavaged daily with BPA (1.2 and 2.4 μg/kg bw) (or vehicles for controls) from gestation day 12 through postnatal day (PND) 21 to obtain the F 1 and subsequent F 2 and F 3 generations. Immunohistochemical localization of steroid receptor coactivator-1 (SRC-1), G-receptor integrating protein-1 (GRIP-1), p300/CBP/cointegrator-associated protein (p/CIP) and nuclear corepressor (NCoR) was carried out in the testes of F 1, F 2 and F 3 generation adult rats. Key findings A significant reduction in the expression of SRC-1 and NCoR, with a parallel increase in the expression of p/CIP and GRIP-1, was observed in the testes of rats exposed perinatally to BPA. Surprisingly, a similar pattern was observed in the testes of F 2 and F 3 rats. Significance Perinatal exposure of male rats to BPA leads to transgenerational perturbations in the expression profile of testicular steroid receptor coregulators.

Prognostic significance of steroid receptor co-regulators in breast cancer: co-repressor NCOR2/SMRT is an independent indicator of poor outcome

Background Advances in understanding the molecular basis of breast cancer has necessitated a definition of improved indicators of prognosis that are central to the underlying cancer biology and that reflect the heterogeneous nature of the disease. This study investigates the pattern of expression of the steroid receptor co-regulators NCOA1/SRC1, NCOA3/RAC3, NCOR2/SMRT, and CBP/ p300 in breast cancer. The aims were to identify whether their expression was related to patient outcome, their relationships to known prognostic factors and to provide a basis for further research into the mechanistic significance of such associations. Methods The protein levels of steroid receptor co-regulators were assessed by immunohistochemistry in a large well-characterised series of breast carcinomas prepared as tissue microarrays. Relationships between these targets, other clinicopathological variables and patients’ outcome were examined. Results NCOR2/SMRT was an independent prognostic indicator of overall patient survival (OS) and disease free interval (DFI) and was significantly correlated with distant metastases and local recurrence whereas tumours expressing NCOA1/SRC1 had a significantly longer OS and DFI. There were also significant correlations between co-regulator expression of NCOA1/SRC1, CBP/p300 and NCOA3/ RAC3, which were associated with lower tumour grade. NCOA1/SRC1 was also correlated with smaller tumour size. Furthermore, the co-activators had a significant association with steroid receptors, particularly ERa. Conclusions NCOR2/SMRT is associated with poor patient outcome, independent of other prognostic factors. In contrast, steroid receptor co-activator expression is generally associated with a good prognosis. Further investigations are needed to establish the mechanisms of these links between the steroid receptor co-regulator system and patient outcome.

The prognostic significance of steroid receptor co-regulators in breast cancer: co-repressor NCOR2/SMRT is an independent indicator of poor outcome

Advances in understanding the molecular basis of breast cancer has necessitated a definition of improved indicators of prognosis that are central to the underlying cancer biology and that reflect the heterogeneous nature of the disease. This study investigates the pattern of expression of the steroid receptor co-regulators NCOA1/SRC1, NCOA3/RAC3, NCOR2/SMRT, and CBP/p300 in breast cancer. The aims were to identify whether their expression was related to patient outcome, their relationships to known prognostic factors and to provide a basis for further research into the mechanistic significance of such associations. The protein levels of steroid receptor co-regulators were assessed by immunohistochemistry in a large well-characterised series of breast carcinomas prepared as tissue microarrays. Relationships between these targets, other clinicopathological variables and patients' outcome were examined. NCOR2/SMRT was an independent prognostic indicator of overall patient survival (OS) and disease free interval (DFI) and was significantly correlated with distant metastases and local recurrence whereas tumours expressing NCOA1/SRC1 had a significantly longer OS and DFI. There were also significant correlations between co-regulator expression of NCOA1/SRC1, CBP/p300 and NCOA3/RAC3, which were associated with lower tumour grade. NCOA1/SRC1 was also correlated with smaller tumour size. Furthermore, the co-activators had a significant association with steroid receptors, particularly ERalpha. NCOR2/SMRT is associated with poor patient outcome, independent of other prognostic factors. In contrast, steroid receptor co-activator expression is generally associated with a good prognosis. Further investigations are needed to establish the mechanisms of these links between the steroid receptor co-regulator system and patient outcome.

Steroid receptor coregulator diversity: What can it mean for the stressed brain?

Glucocorticoid hormones modulate brain function and as such are crucial for responding and adjusting to physical and psychological stressors. Their effects are mediated via mineralo- and glucocorticoid receptors, which in large measure act as transcription factors to modulate transcription of target genes, in a receptor-, cell-, and state-specific manner. The nature and magnitude of these transcriptional effects depend on the presence and activity of downstream proteins, such as steroid receptor coactivators and corepressors (together: coregulators), many of which are expressed in the brain. We address the role of coregulators for mineralo- and glucocorticoid receptor-mediated modulation of gene transcription. We first address evidence from cell lines for the importance of coregulator stoichiometry for steroid signaling. The in vivo importance of coregulators—when possible specifically for glucocorticoid signaling in the brain—is discussed based on knockout mice, transient knockdown of steroid receptor coactivators, and distribution and regulation of coactivator expression in the brain. We conclude that for a better understanding of modulation of brain function by glucocorticoids, it is necessary to take into account the role of coregulators, and to assess their importance relative to changes in hormone levels and receptor expression.