The steroid receptor coactivator SRC-3 (p/CIP/RAC3/AIB1/ACTR/TRAM-1) is required for normal growth, puberty, female reproductive function, and mammary gland development

NCOA3 coactivator is a transcriptional target of XBP1 and regulates PERK-eIF2α-ATF4 signalling in breast cancer

XBP1 is a multitasking transcription factor and a key component of the unfolded protein response (UPR). Despite the wealth of knowledge about the role of XBP1 in luminal/ER-positive breast cancer, not much is known about the effectors of XBP1 in this context. Here we show that NCOA3 is a transcriptional target of XBP1. We observed increased expression of NCOA3 during conditions of UPR and oestrogen (E2) stimulation. Further investigations revealed a role for the IRE1–XBP1 axis in the induction of NCOA3 during UPR and oestrogen signalling. We identify a novel role for NCOA3 in activation of PERK–ATF4 axis during UPR where knockdown of NCOA3 compromised the optimal activation of the PERK–ATF4 pathway. We found that NCOA3 is required for induction of XBP1 during E2 stimulation and uncover a positive feedback regulatory loop that maintains high levels of NCOA3 and XBP1 in breast cancer. Furthermore, upregulated NCOA3 was required for XBP1-mediated resistance to antihormonal agents. Increased expression of NCOA3 was associated with poor prognosis and higher levels of XBP1-S in breast cancer tissues. Our results uncover a novel steroid hormone-independent role for NCOA3 in UPR signalling. Further we identify a positive feedback regulatory loop consisting of XBP1 and NCOA3 that maintains high levels of NCOA3 and XBP1 expression in breast cancer tissues. Taken together our data identify XBP1–NCOA3 axis that regulates cell fate decisions in ER-positive breast cancer cells.

Interaction of steroid receptor coactivators and estrogen receptors in the human placenta

Female sex steroid hormones such as estrogen and progesterone have a pivotal role in maintaining pregnancy in human and animals. Especially, estrogen exerts specific effects on the cardiovascular system and angiogenesis, and thus affects significantly on placentation. Although the functions of estrogen have been emphasized during pregnancy, their signaling pathways in the placenta have not been fully understood. In this study, estrogen signaling was evaluated according to gestational age. Human placenta samples were collected and divided into early preterm (n=10), late preterm (n=18), and term (n=20) groups. First, serum estrogen concentration and corticotropin-releasing hormone (CRH) mRNA expression, which is known as gestation clock gene, were increased following gestation age in our experimental condition, as we expected. Next, the expression of estrogen receptors (ERs) and steroid receptor coactivators (SRCs) in the placenta was evaluated. ERα (ESR1) and ERβ (ESR2) were expressed highly at term period compared with early preterm. In addition, SRC family including SRC1, SRC2, and SRC3 was expressed in the human placenta, and the levels of SRC1, SRC2, and SRC3 were increased in the placenta at the late stage of gestation. The interaction of ERs with SRCs was also examined, which was significantly enhanced at term period. In the immunostaining results, it was indicated that ERs and SRCs were all dominantly expressed in syncytiotrophoblast cells. These results suggested that SRC1, SRC2, and SRC3 were expressed and interact with ERs highly at the late stage of gestation, and may amplify the signaling of estrogen in the placenta to maintain pregnancy.

Role of co-regulators in metabolic and transcriptional actions of thyroid hormone

Thyroid hormone (TH) controls a wide range of physiological processes through TH receptor (TR) isoforms. Classically, TRs are proposed to function as tri-iodothyronine (T3)-dependent transcription factors: on positively regulated target genes, unliganded TRs mediate transcriptional repression through recruitment of co-repressor complexes, while T3 binding leads to dismissal of co-repressors and recruitment of co-activators to activate transcription. Co-repressors and co-activators were proposed to play opposite roles in the regulation of negative T3 target genes and hypothalamic-pituitary-thyroid axis, but exact mechanisms of the negative regulation by TH have remained elusive. Important insights into the roles of co-repressors and co-activators in different physiological processes have been obtained using animal models with disrupted co-regulator function. At the same time, recent studies interrogating genome-wide TR binding have generated compelling new data regarding effects of T3, local chromatin structure, and specific response element configuration on TR recruitment and function leading to the proposal of new models of transcriptional regulation by TRs. This review discusses data obtained in various mouse models with manipulated function of nuclear receptor co-repressor (NCoR or NCOR1) and silencing mediator of retinoic acid receptor and thyroid hormone receptor (SMRT or NCOR2), and family of steroid receptor co-activators (SRCs also known as NCOAs) in the context of TH action, as well as insights into the function of co-regulators that may emerge from the genome-wide TR recruitment analysis.

HER2 Signaling Drives DNA Anabolism and Proliferation through SRC-3 Phosphorylation and E2F1-Regulated Genes

Approximately 20% of early-stage breast cancers display amplification or overexpression of the ErbB2/HER2 oncogene, conferring poor prognosis and resistance to endocrine therapy. Targeting HER2(+) tumors with trastuzumab or the receptor tyrosine kinase (RTK) inhibitor lapatinib significantly improves survival, yet tumor resistance and progression of metastatic disease still develop over time. Although the mechanisms of cytosolic HER2 signaling are well studied, nuclear signaling components and gene regulatory networks that bestow therapeutic resistance and limitless proliferative potential are incompletely understood. Here, we use biochemical and bioinformatic approaches to identify effectors and targets of HER2 transcriptional signaling in human breast cancer. Phosphorylation and activity of the Steroid Receptor Coactivator-3 (SRC-3) is reduced upon HER2 inhibition, and recruitment of SRC-3 to regulatory elements of endogenous genes is impaired. Transcripts regulated by HER2 signaling are highly enriched with E2F1 binding sites and define a gene signature associated with proliferative breast tumor subtypes, cell-cycle progression, and DNA replication. We show that HER2 signaling promotes breast cancer cell proliferation through regulation of E2F1-driven DNA metabolism and replication genes together with phosphorylation and activity of the transcriptional coactivator SRC-3. Furthermore, our analyses identified a cyclin-dependent kinase (CDK) signaling node that, when targeted using the CDK4/6 inhibitor palbociclib, defines overlap and divergence of adjuvant pharmacologic targeting. Importantly, lapatinib and palbociclib strictly block de novo synthesis of DNA, mostly through disruption of E2F1 and its target genes. These results have implications for rational discovery of pharmacologic combinations in preclinical models of adjuvant treatment and therapeutic resistance.

The influence of adiponectin on the transcriptomic profile of porcine luteal cells

Reproductive functions are closely related to nutritional status. Recent studies suggest that adiponectin may be a hormonal link between them. Adiponectin is an adipocytokine, abundantly expressed in adipose tissues. It plays a dominant role in lipid and carbohydrate metabolism by stimulating fatty acid oxidation, decreasing plasma triglycerides, and increasing cells' sensitivity to insulin and has direct antiatherosclerotic effects. The hormone is also postulated to play a modulatory role in the regulation of the reproductive system. The aim of this study was to identify differentially expressed genes (DE-genes) in response to adiponectin treatment of porcine luteal ovarian cells. The global expression of genes in the porcine ovary was investigated using the Porcine (V2) Two-color gene expression microarray, 4 × 44 (Agilent, USA). Analysis of the microarray data showed that 701 genes were differentially expressed and 389 genes showed a fold change greater than 1.2 (p < 0.05). Among this number, 186 genes were up-regulated and 203 were down-regulated. The list of DE-genes was used for gene ontology analyses. The biological process list was generated from up-regulated and down-regulated DE-genes. We found that up-regulated products of DE-genes take part in 30 biological processes and down-regulated products in 9. Analysis of the interaction network among DE-genes showed that adiponectin interacts with genes involved in important processes in luteal cells. These results provide a basis for future work describing the detailed interactions and relationships explaining local regulation of adiponectin actions in the ovary of pigs.

Steroid receptor coactivators as therapeutic targets in the female reproductive system

The steroid receptor coactivators (SRCs/p160/NCOA) are a family of three transcriptional coregulators initially discovered to transactivate the transcriptional potency of steroid hormone receptors. Even though SRCs were also found to modulate the activity of multiple other transcription factors, their function is still strongly associated with regulation of steroid hormone action and many studies have found that they are critical for the regulation of reproductive biology. In the case of the female reproductive tract, SRCs have been found to play crucial roles in its physiology, ranging from ovulation, implantation, to parturition. Not surprisingly, SRCs' action has been linked to numerous abnormalities and debilitating disorders of female reproductive tissues, including infertility, cancer, and endometriosis. Many of these pathologies are still in critical need of therapeutic intervention and "proof-of-principle" studies have found that SRCs are excellent targets in pathological states. Therefore, small molecule modulators of SRCs' activity could be applied in the future in the treatment of many diseases of the female reproductive system.

Reprint of "Steroid receptor coactivators as therapeutic targets in the female reproductive system"

The steroid receptor coactivators (SRCs/p160/NCOA) are a family of three transcriptional coregulators initially discovered to transactivate the transcriptional potency of steroid hormone receptors. Even though SRCs were also found to modulate the activity of multiple other transcription factors, their function is still strongly associated with regulation of steroid hormone action and many studies have found that they are critical for the regulation of reproductive biology. In the case of the female reproductive tract, SRCs have been found to play crucial roles in its physiology, ranging from ovulation, implantation, to parturition. Not surprisingly, SRCs' action has been linked to numerous abnormalities and debilitating disorders of female reproductive tissues, including infertility, cancer, and endometriosis. Many of these pathologies are still in critical need of therapeutic intervention and "proof-of-principle" studies have found that SRCs are excellent targets in pathological states. Therefore, small molecule modulators of SRCs' activity could be applied in the future in the treatment of many diseases of the female reproductive system.

Knockout of SRC-1 and SRC-3 in Mice Decreases Cardiomyocyte Proliferation and Causes a Noncompaction Cardiomyopathy Phenotype

Noncompaction cardiomyopathy (NCC) is a congenital heart disease that causes ventricular dysfunction and high mortality rate in children. The mechanisms responsible for NCC are still unknown. The steroid receptor coactivator-1 (SRC-1) and SRC-3 are transcriptional coactivators for nuclear hormone receptors and certain other transcription factors that regulate many genes in development and organ function. However, the roles of SRC-1/3 in heart morphogenesis, function and NCC occurrence are unknown. This study aims to examine the spatial and temporal expression patterns of SRC-1/3 in the heart and investigate the specific roles of SRC-1/3 in heart development, function and NCC occurrence. Immunochemical analysis detected SRC-1/3 expressions in the proliferating cardiomyocytes of mouse heart at prenatal and neonatal stages, while these expressions disappeared within two weeks after birth. Through generating and characterizing mouse lines with global or cardiomyocyte-specific knockouts of SRC-1/3, we found ablation of SRC-1/3 in the myocardial lineage resulted in prominent trabeculae, deep intertrabecular recesses and thin ventricular wall and septum. These developmental defects caused a failure of trabecular compaction, decreased internal ventricular dimension, reduced cardiac ejection fraction and output and led to a high rate of postnatal mortality. Collectively, these structural and functional abnormalities closely simulate the phenotype of NCC patients. Further molecular analysis of cardiomyocytes in vivo and in vitro revealed that SRC-1/3 directly up-regulate cyclin E2, cyclin B1 and myocardin to promote cardiomyocyte proliferation and differentiation. In conclusion, SRC-1/3 are required for cardiomyocyte proliferation and differentiation at earlier developmental stages, and their dysfunction causes NCC-like abnormalities in the hearts of newborn and adult mice.

Hormone-sensing mammary epithelial progenitors: emerging identity and hormonal regulation

The hormone-sensing mammary epithelial cell (HS-MEC-expressing oestrogen receptor-alpha (ERα) and progesterone receptor (PGR)) is often represented as being terminally differentiated and lacking significant progenitor activity after puberty. Therefore while able to profoundly influence the proliferation and function of other MEC populations, HS-MECs are purported not to respond to sex hormone signals by engaging in significant cell proliferation during adulthood. This is a convenient and practical simplification that overshadows the sublime, and potentially critical, phenotypic plasticity found within the adult HS-MEC population. This concept is exemplified by the large proportion (~80 %) of human breast cancers expressing PGR and/or ERα, demonstrating that HS-MECs clearly proliferate in the context of breast cancer. Understanding how HS-MEC proliferation and differentiation is driven could be key to unraveling the mechanisms behind uncontrolled HS-MEC proliferation associated with ERα- and/or PGR-positive breast cancers. Herein we review evidence for the existence of a HS-MEC progenitor and the emerging plasticity of the HS-MEC population in general. This is followed by an analysis of hormones other than oestrogen and progesterone that are able to influence HS-MEC proliferation and differentiation: androgens, prolactin and transforming growth factor-beta1.

Minireview: nuclear receptor coregulators of the p160 family: insights into inflammation and metabolism

Nuclear receptor coactivators (NCOAs) are multifunctional transcriptional coregulators for a growing number of signal-activated transcription factors. The members of the p160 family (NCOA1/2/3) are increasingly recognized as essential and nonredundant players in a number of physiological processes. In particular, accumulating evidence points to the pivotal roles that these coregulators play in inflammatory and metabolic pathways, both under homeostasis and in disease. Given that chronic inflammation of metabolic tissues ("metainflammation") is a driving force for the widespread epidemic of obesity, insulin resistance, cardiovascular disease, and associated comorbidities, deciphering the role of NCOAs in "normal" vs "pathological" inflammation and in metabolic processes is indeed a subject of extreme biomedical importance. Here, we review the evolving and, at times, contradictory, literature on the pleiotropic functions of NCOA1/2/3 in inflammation and metabolism as related to nuclear receptor actions and beyond. We then briefly discuss the potential utility of NCOAs as predictive markers for disease and/or possible therapeutic targets once a better understanding of their molecular and physiological actions is achieved.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

A meta-analysis of genome-wide association studies identifies novel variants associated with osteoarthritis of the hip

OBJECTIVES

Osteoarthritis (OA) is the most common form of arthritis with a clear genetic component. To identify novel loci associated with hip OA we performed a meta-analysis of genome-wide association studies (GWAS) on European subjects.

METHODS

We performed a two-stage meta-analysis on more than 78,000 participants. In stage 1, we synthesised data from eight GWAS whereas data from 10 centres were used for 'in silico' or 'de novo' replication. Besides the main analysis, a stratified by sex analysis was performed to detect possible sex-specific signals. Meta-analysis was performed using inverse-variance fixed effects models. A random effects approach was also used.

RESULTS

We accumulated 11,277 cases of radiographic and symptomatic hip OA. We prioritised eight single nucleotide polymorphism (SNPs) for follow-up in the discovery stage (4349 OA cases); five from the combined analysis, two male specific and one female specific. One locus, at 20q13, represented by rs6094710 (minor allele frequency (MAF) 4%) near the NCOA3 (nuclear receptor coactivator 3) gene, reached genome-wide significance level with p=7.9×10(-9) and OR=1.28 (95% CI 1.18 to 1.39) in the combined analysis of discovery (p=5.6×10(-8)) and follow-up studies (p=7.3×10(-4)). We showed that this gene is expressed in articular cartilage and its expression was significantly reduced in OA-affected cartilage. Moreover, two loci remained suggestive associated; rs5009270 at 7q31 (MAF 30%, p=9.9×10(-7), OR=1.10) and rs3757837 at 7p13 (MAF 6%, p=2.2×10(-6), OR=1.27 in male specific analysis).

CONCLUSIONS

Novel genetic loci for hip OA were found in this meta-analysis of GWAS.

Lysine residues 639 and 673 of mouse Ncoa3 are ubiquitination sites for the regulation of its stability

Ncoa3 is a transcriptional coactivator involved in a wide range of biological processes. Regulation of Ncoa3 protein stability is important to control its activity precisely. Here, we found that deleting amino acid residues 614-740 of Ncoa3 enhances the protein expression level. Replacing two lysine residues, K639 and K673, within this region by arginine, increases the stability of the luciferase fusion protein as well as Ncoa3 protein. When these two lysine residues are mutated to arginine, the overall ubiquitination level of Ncoa3 decreases, indicating that lysine 639 and 673 are its ubiquitination sites. Taken together, we identified two ubiquitination sites at lysine 639 and 673 of Ncoa3. Ubiquitination of these two lysine residues leads to proteasomal degradation of Ncoa3.

Osteoarthritis year in review 2014: genetics and genomics

Recent developments in genetics/genomics of osteoarthritis (OA) are discussed to improve our understanding of OA pathophysiology. The discovery of a novel variant near the NCOA3 (nuclear receptor coactivator 3) gene associated with hip OA and the regulation of GDF5 gene by four transcription factors via the OA susceptibility locus rs143383 are among important findings in OA genetics. Several microarray-based gene expression studies were published for different tissues of the joint. In OA synovium elevation of collagens and cross-linking enzymes (COL1A1, COL5A1, PLOD2, LOX and TIMP1) responsive to TGF-β was found as well as differential expression pattern between different areas of the osteoarthritic synovial membrane. In OA peripheral blood the role of apoptotic genes was highlighted, while whole genome expression profiling in OA subchondral bone and cartilage revealed common genes in cartilage and bone to be involved in OA development. In epigenetics, several microRNAs (miRNAs) were found to regulate genes' expression in chondrocytes, among which miR-125, miR-127b miR-21, miR-148a and their use as potential drug targets was highlighted. Future studies must focus on the integration of genetics, genomics and epigenetics for the identification of signaling pathways and regulatory networks responsible for OA development.

Nuclear receptor modulation--role of coregulators in selective estrogen receptor modulator (SERM) actions

Selective estrogen receptor modulators (SERMs) are a class of small-molecule chemical compounds that bind to estrogen receptor (ER) ligand binding domain (LBD) with high affinity and selectively modulate ER transcriptional activity in a cell- and tissue-dependent manner. The prototype of SERMs is tamoxifen, which has agonist activity in bone, but has antagonist activity in breast. Tamoxifen can reduce the risk of breast cancer and, at same time, prevent osteoporosis in postmenopausal women. Tamoxifen is widely prescribed for treatment and prevention of breast cancer. Mechanistically the activity of SERMs is determined by the selective recruitment of coactivators and corepressors in different cell types and tissues. Therefore, understanding the coregulator function is the key to understanding the tissue selective activity of SERMs.

The p160/steroid receptor coactivator family: potent arbiters of uterine physiology and dysfunction

The p160/steroid receptor coactivator (SRC) family comprises three pleiotropic coregulators (SRC-1, SRC-2, and SRC-3; otherwise known as NCOA1, NCOA2, and NCOA3, respectively), which modulate a wide spectrum of physiological responses and clinicopathologies. Such pleiotropy is achieved through their inherent structural complexity, which allows this coregulator class to control both nuclear receptor and non-nuclear receptor signaling. As observed in other physiologic systems, members of the SRC family have recently been shown to play pivotal roles in uterine biology and pathobiology. In the murine uterus, SRC-1 is required to launch a full steroid hormone response, without which endometrial decidualization is markedly attenuated. From "dovetailing" clinical and mouse studies, an isoform of SRC-1 was recently identified which promotes endometriosis by reprogramming endometrial cells to evade apoptosis and to colonize as endometriotic lesions within the peritoneal cavity. The endometrium fails to decidualize without SRC-2, which accounts for the infertility phenotype exhibited by mice devoid of this coregulator. In related studies on human endometrial stromal cells, SRC-2 was shown to act as a molecular "pacemaker" of the glycolytic flux. This finding is significant because acceleration of the glycolytic flux provides the necessary bioenergy and biomolecules for endometrial stromal cells to switch from quiescence to a proliferative phenotype, a critical underpinning in the decidual progression program. Although studies on uterine SRC-3 function are in their early stages, clinical studies provide tantalizing support for the proposal that SRC-3 is causally linked to endometrial hyperplasia as well as with endometrial pathologies in patients diagnosed with polycystic ovary syndrome. This proposal is now driving the development and application of innovative technologies, particularly in the mouse, to further understand the functional role of this elusive uterine coregulator in normal and abnormal physiologic contexts. Because dysregulation of this coregulator triad potentially presents a triple threat for increased risk of subfecundity, infertility, or endometrial disease, a clearer understanding of the individual and combinatorial roles of these coregulators in uterine function is urgently required. This minireview summarizes our current understanding of uterine SRC function, with a particular emphasis on the next critical questions that need to be addressed to ensure significant expansion of our knowledge of this underexplored field of uterine biology.

The steroid receptor coactivator-3 is required for developing neuroendocrine tumor in the mouse prostate

Neuroendocrine tumor cells (NETCs) are commonly observed in prostate cancer. Their presence is associated with castration resistance, metastasis and poor prognosis. Cellular and molecular mechanisms for NETC initiation and growth are unknown. TRAMP mice develop heterogeneous adenocarcinomas induced by expression of the SV40-T/t oncogene in prostate epithelial cells. Here, we demonstrate prostate tumors in TRAMP mice with a mixed genetic background are characterized mostly by atypical hyperplasia (AH) containing steroid receptor coactiator-3-positive, androgen receptor-positive and synaptophysin-negative (SRC-3+/AR+/Syp-) cells. Few SRC-3+/AR-/Syp+ NETCs are present in their prostates. We generated TRAMP mice in which SRC-3 was specifically ablated in AR+/Syp- prostatic epithelial cells (termed PE3KOT mice). In these animals, we observed a substantial reduction in SRC-3-/AR+/Syp- AH tumor growth. There was a corresponding increase in SRC-3-/AR+/Syp- phyllodes lesions, suggesting SRC-3 knockout can convert aggressive AH tumors with mostly epithelial tumor cells into less aggressive phyllodes lesions with mostly stromal tissue. Surprisingly, PE3KOT mice developed many more SRC-3+/AR-/Syp+ NETCs versus control TRAMP mice, indicating SRC-3 expression was retained in NETCs. In contrast, TRAMP mice with global SRC-3 knockout did not develop any NETC, indicating SRC-3 is required for developing NETC. Analysis of cell-differentiating markers revealed that these NETCs might not be derived from the mature AR-/Syp+ neuroendocrine cells or the AR+/Syp- luminal epithelial tumor cells. Instead, these NETCs might originate from the SV40-T/t-transformed intermediate/progenitor epithelial cells. In summary, SRC-3 is required for both AR+/Syp- AH tumor growth and AR-/Syp+ NETC development, suggesting SRC-3 is a target for inhibiting aggressive prostate cancer containing NETCs.

Physiological functions of peroxisome proliferator-activated receptor β

The peroxisome proliferator-activated receptors, PPARα, PPARβ, and PPARγ, are a family of transcription factors activated by a diversity of molecules including fatty acids and fatty acid metabolites. PPARs regulate the transcription of a large variety of genes implicated in metabolism, inflammation, proliferation, and differentiation in different cell types. These transcriptional regulations involve both direct transactivation and interaction with other transcriptional regulatory pathways. The functions of PPARα and PPARγ have been extensively documented mainly because these isoforms are activated by molecules clinically used as hypolipidemic and antidiabetic compounds. The physiological functions of PPARβ remained for a while less investigated, but the finding that specific synthetic agonists exert beneficial actions in obese subjects uplifted the studies aimed to elucidate the roles of this PPAR isoform. Intensive work based on pharmacological and genetic approaches and on the use of both in vitro and in vivo models has considerably improved our knowledge on the physiological roles of PPARβ in various cell types. This review will summarize the accumulated evidence for the implication of PPARβ in the regulation of development, metabolism, and inflammation in several tissues, including skeletal muscle, heart, skin, and intestine. Some of these findings indicate that pharmacological activation of PPARβ could be envisioned as a therapeutic option for the correction of metabolic disorders and a variety of inflammatory conditions. However, other experimental data suggesting that activation of PPARβ could result in serious adverse effects, such as carcinogenesis and psoriasis, raise concerns about the clinical use of potent PPARβ agonists.

Estrogen receptor coregulators and pioneer factors: the orchestrators of mammary gland cell fate and development

The steroid hormone, 17β-estradiol (E2), plays critical role in various cellular processes such as cell proliferation, differentiation, migration and apoptosis, and is essential for reproduction and mammary gland development. E2 actions are mediated by two classical nuclear hormone receptors, estrogen receptor α and β (ERs). The activity of ERs depends on the coordinated activity of ligand binding, post-translational modifications (PTMs), and importantly the interaction with their partner proteins called “coregulators.” Because coregulators are proved to be crucial for ER transcriptional activity, and majority of breast cancers are ERα positive, an increased interest in the field has led to the identification of a large number of coregulators. In the last decade, gene knockout studies using mouse models provided impetus to our further understanding of the role of these coregulators in mammary gland development. Several coregulators appear to be critical for terminal end bud (TEB) formation, ductal branching and alveologenesis during mammary gland development. The emerging studies support that, coregulators along with the other ER partner proteins called “pioneer factors” together contribute significantly to E2 signaling and mammary cell fate. This review discusses emerging themes in coregulator and pioneer factor mediated action on ER functions, in particular their role in mammary gland cell fate and development.

Steroid receptor coactivators: servants and masters for control of systems metabolism

Coregulator recruitment to nuclear receptors (NRs) and other transcription factors is essential for proper metabolic gene regulation, with coactivators enhancing and corepressors attenuating gene transcription. The steroid receptor coactivator (SRC) family is composed of three homologous members (SRC-1, SRC-2, and SRC-3), which are uniquely important for mediating steroid hormone and mitogenic actions. An accumulating body of work highlights the diverse array of metabolic functions regulated by the SRCs, including systemic metabolite homeostasis, inflammation, and energy regulation. We discuss here the cooperative and unique functions among the SRCs to provide a comprehensive atlas of systemic SRC metabolic regulation. Deciphering the fractional and synergistic contributions of the SRCs to metabolic homeostasis is crucial to understanding fully the networks underlying metabolic transcriptional regulation.

Hormonal regulation of the immune microenvironment in the mammary gland

It is well established that the development and homeostasis of the mammary gland are highly dependent upon the actions of ovarian hormones progesterone and estrogen, as well as the availability of prolactin for the pregnant and lactating gland. More recently it has become apparent that immune system cells and cytokines play essential roles in both mammary gland development as well as breast cancer. Here, we review hormonal effects on mammary gland biology during puberty, menstrual cycling, pregnancy, lactation and involution, and dissect how hormonal control of the immune system may contribute to mammary development at each stage via cytokine secretion and recruitment of macrophages, eosinophils, mast cells and lymphocytes. Collectively, these alterations may create an immunotolerant or inflammatory immune environment at specific developmental stages or phases of the menstrual cycle. Of particular interest for further research is investigation of the combinatorial actions of progesterone and estrogen during the luteal phase of the menstrual cycle and key developmental points where the immune system may play an active role both in mammary development as well as in the creation of an immunotolerant environment, thereby affecting breast cancer risk.

Perturbing the cellular levels of steroid receptor coactivator-2 impairs murine endometrial function

As pleiotropic coregulators, members of the p160/steroid receptor coactivator (SRC) family control a broad spectrum of transcriptional responses that underpin a diverse array of physiological and pathophysiological processes. Because of their potent coregulator properties, strict controls on SRC expression levels are required to maintain normal tissue functionality. Accordingly, an unwarranted increase in the cellular levels of SRC members has been causally linked to the initiation and/or progression of a number of clinical disorders. Although knockout mouse models have underscored the critical non-redundant roles for each SRC member in vivo, there are surprisingly few mouse models that have been engineered to overexpress SRCs. This deficiency is significant since SRC involvement in many of these disorders is based on unscheduled increases in the levels (rather than the absence) of SRC expression. To address this deficiency, we used recent mouse technology that allows for the targeted expression of human SRC-2 in cells which express the progesterone receptor. Through cre-loxP recombination driven by the endogenous progesterone receptor promoter, a marked elevation in expression levels of human SRC-2 was achieved in endometrial cells that are positive for the progesterone receptor. As a result of this increase in coregulator expression, female mice are severely subfertile due to a dysfunctional uterus, which exhibits a hypersensitivity to estrogen exposure. Our findings strongly support the proposal from clinical observations that increased levels of SRC-2 are causal for a number of endometrial disorders which compromise fertility. Future studies will use this mouse model to decipher the molecular mechanisms that underpin the endometrial defect. We believe such mechanistic insight may provide new molecular descriptors for diagnosis, prognosis, and/or therapy in the clinical management of female infertility.

Steroid receptor coactivator-2 is a dual regulator of cardiac transcription factor function

We have previously demonstrated the potential role of steroid receptor coactivator-2 (SRC-2) as a co-regulator in the transcription of critical molecules modulating cardiac function and metabolism in normal and stressed hearts. The present study seeks to extend the previous information by demonstrating SRC-2 fulfills this role by serving as a critical coactivator for the transcription and activity of critical transcription factors known to control cardiac growth and metabolism as well as in their downstream signaling. This knowledge broadens our understanding of the mechanism by which SRC-2 acts in normal and stressed hearts and allows further investigation of the transcriptional modifications mediating different types and degrees of cardiac stress. Moreover, the genetic manipulation of SRC-2 in this study is specific for the heart and thereby eliminating potential indirect effects of SRC-2 deletion in other organs. We have shown that SRC-2 is critical to transcriptional control modulated by MEF2, GATA-4, and Tbx5, thereby enhancing gene expression associated with cardiac growth. Additionally, we describe SRC-2 as a novel regulator of PPARα expression, thus controlling critical steps in metabolic gene expression. We conclude that through regulation of cardiac transcription factor expression and activity, SRC-2 is a critical transcriptional regulator of genes important for cardiac growth, structure, and metabolism, three of the main pathways altered during the cardiac stress response.

Crafting the brain - role of histone acetyltransferases in neural development and disease

The human brain is a highly specialized organ containing nearly 170 billion cells with specific functions. Development of the brain requires adequate proliferation, proper cell migration, differentiation and maturation of progenitors. This is in turn dependent on spatial and temporal coordination of gene transcription, which requires the integration of both cell intrinsic and environmental factors. Histone acetyltransferases (HATs) are one family of proteins that modulate expression levels of genes in a space- and time-dependent manner. HATs and their molecular complexes are able to integrate multiple molecular inputs and mediate transcriptional levels by acetylating histone proteins. In mammals, 19 HATs have been described and are separated into five families (p300/CBP, MYST, GNAT, NCOA and transcription-related HATs). During embryogenesis, individual HATs are expressed or activated at specific times and locations to coordinate proper development. Not surprisingly, mutations in HATs lead to severe developmental abnormalities in the nervous system and increased neurodegeneration. This review focuses on our current understanding of HATs and their biological roles during neural development.

The levels of RAC3 expression are up regulated by TNF in the inflammatory response

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The inflammatory response increases the expression of RAC3 in vitro and in vivo.

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TNF induces the increase of RAC3 at transcriptional level through NF-κB activation.

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Glucocorticoids also induce the increase of RAC3 expression levels.

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RAC3 appears to be essential for NF-κB- and GR-mediated transcription.

RAC3 is a coactivator of glucocorticoid receptor and nuclear factor-κB (NF-κB) that is usually over-expressed in tumors and which also has important functions in the immune system. We investigated the role of the inflammatory response in the control of RAC3 expression levels in vivo and in vitro. We found that inflammation regulates RAC3 levels. In mice, sub-lethal doses of lipopolysaccharide induce the increase of RAC3 in spleen and the administration of the synthetic anti-inflammatory glucocorticoid dexamethasone has a similar effect. However, the simultaneous treatment with both stimuli is mutually antagonistic. In vitro stimulation of the HEK293 cell line with tumor necrosis factor (TNF), one of the cytokines induced by lipopolysaccharide, also increases the levels of RAC3 mRNA and protein, which correlates with an enhanced transcription dependent on the RAC3 gene promoter. We found that binding of the transcription factor NF-κB to the RAC3 gene promoter could be responsible for these effects. Our results suggest that increase of RAC3 during the inflammatory response could be a molecular mechanism involved in the control of sensitivity to both pro- and anti-inflammatory stimuli in order to maintain the normal healthy course of the immune response.

Increased radiosensitivity and radiation-induced apoptosis in SRC-3 knockout mice

Steroid receptor coactivator-3 (SRC-3), a multifunctional transcriptional coactivator, plays an important role in regulation of cell apoptosis in chemoresistant cancer cells. However, its role in radiation-induced apoptosis in hematopoietic cells is still unclear. In this study, we used SRC-3 knockout (SRC-3(-/-)) mice to assess the role of SRC-3 in radiation-induced hematopoietic injury in vivo. After a range of doses of irradiation, SRC-3(-/-) mice exhibited lower counts of peripheral blood cells and bone marrow (BM) mononuclear cells and excessive BM depression, which resulted in a significantly higher mortality compared with wildtype mice. Moreover, BM mononuclear cells obtained from SRC-3(-/-) mice showed a remarkable increase in radiation-induced apoptosis. Collectively, our data demonstrate that SRC-3 plays a role in radiation-induced apoptosis of BM hematopoietic cells. Regulation of SRC-3 might influence the radiosensitivity of hematopoietic cells, which highlights a potential therapeutic target for radiation-induced hematopoietic injury.

NCOA1 Directly Targets M-CSF1 Expression to Promote Breast Cancer Metastasis

In breast cancer, overexpression of the nuclear coactivator NCOA1 (SRC-1) is associated with disease recurrence and resistance to endocrine therapy. To examine the impact of NCOA1 overexpression on morphogenesis and carcinogenesis in the mammary gland (MG), we generated MMTV-hNCOA1 transgenic [Tg(NCOA1)] mice. In the context of two distinct transgenic models of breast cancer, NCOA1 overexpression did not affect the morphology or tumor-forming capability of MG epithelial cells. However, NCOA1 overexpression increased the number of circulating breast cancer cells and the efficiency of lung metastasis. Mechanistic investigations showed that NCOA1 and c-Fos were recruited to a functional AP-1 site in the macrophage attractant CSF1 promoter, directly upregulating colony-simulating factor 1 (CSF1) expression to enhance macrophage recruitment and metastasis. Conversely, silencing NCOA1 reduced CSF1 expression and decreased macrophage recruitment and breast cancer cell metastasis. In a cohort of 453 human breast tumors, NCOA1 and CSF1 levels correlated positively with disease recurrence, higher tumor grade, and poor prognosis. Together, our results define an NCOA1/AP-1/CSF1 regulatory axis that promotes breast cancer metastasis, offering a novel therapeutic target for impeding this process.

Deficiency in steroid receptor coactivator 3 enhances cytokine production in IgE-stimulated mast cells and passive systemic anaphylaxis in mice

Background

Steroid receptor coactivator 3 (SRC-3) is a multifunctional protein that plays an important role in malignancy of several cancers and in regulation of bacterial LPS-induced inflammation. However, the involvement of SRC-3 in allergic response remains unclear. Herein we used passive systemic anaphylaxis (PSA) and passive cutaneous anaphylaxis (PCA) mouse models to assess the role of SRC-3 in allergic response.

Results

SRC-3-deficient mice exhibited more severe allergic response as demonstrated by a significant drop in body temperature and a delayed recovery period compared to wild-type mice in PSA mouse model, whereas no significant difference was observed between two kinds of mice in PCA mouse models. Mast cells play a pivotal role in IgE-mediated allergic response. Antigen-induced aggregation of IgE receptor (FcϵRI) on the surface of mast cell activates a cascade of signaling events leading to the degranulation and cytokine production in mast cells. SRC-3-deficient bone marrow derived mast cells (BMMCs) developed normally but secreted more proinflammatory cytokines such as TNF-α and IL-6 than wild-type cells after antigen stimulation, whereas there was no significant difference in degranulation between two kinds of mast cells. Further studies showed that SRC-3 inhibited the activation of nuclear factor NF-κB pathway and MAPKs including extracellular signal-regulated kinase (ERK), c-jun N-terminal kinase (JNK), and p38 in antigen-stimulated mast cells.

Conclusions

Our data demonstrate that SRC-3 suppresses cytokine production in antigen-stimulated mast cells as well as PSA in mice at least in part through inhibiting NF-κB and MAPK signaling pathways. Therefore, SRC-3 plays a protective role in PSA and it may become a drug target for anaphylactic diseases.

LXXLL peptide converts transportan 10 to a potent inducer of apoptosis in breast cancer cells

Degenerate expression of transcription coregulator proteins is observed in most human cancers. Therefore, in targeted anti-cancer therapy development, intervention at the level of cancer-specific transcription is of high interest. The steroid receptor coactivator-1 (SRC-1) is highly expressed in breast, endometrial, and prostate cancer. It is present in various transcription complexes, including those containing nuclear hormone receptors. We examined the effects of a peptide that contains the LXXLL-motif of the human SRC-1 nuclear receptor box 1 linked to the cell-penetrating transportan 10 (TP10), hereafter referred to as TP10-SRC1_LXXLL, on proliferation and estrogen-mediated transcription of breast cancer cells in vitro. Our data show that TP10-SRC1_LXXLL induced dose-dependent cell death of breast cancer cells, and that this effect was not affected by estrogen receptor (ER) status. Surprisingly TP10-SRC1_LXXLL severely reduced the viability and proliferation of hormone-unresponsive breast cancer MDA-MB-231 cells. In addition, the regulation of the endogenous ERα direct target gene pS2 was not affected by TP10-SRC1_LXXLL in estrogen-stimulated MCF-7 cells. Dermal fibroblasts were similarly affected by treatment with higher concentrations of TP10-SRC1_LXXLL and this effect was significantly delayed. These results suggest that the TP10-SRC1_LXXLL peptide may be an effective drug candidate in the treatment of cancers with minimal therapeutic options, for example ER-negative tumors.

Impaired hematopoiesis and delayed thrombopoietic recovery following sublethal irradiation in SRC‑3 knockout mice

The objective of the present study was to investigate the role of the steroid receptor coactivator-3 (SRC-3) in hematopoiesis of mouse bone marrow (BM) following total body irradiation (TBI). SRC-3^−/− mice and wild-type (WT) mice were exposed to 4.5 Gy γ rays. Immunoblotting analysis revealed that the SRC-3 protein (p160) levels in normal BM-nucleated cells in WT were higher than in SRC-3^−/− mice. Furthermore, peripheral blood cell counts, BM cellularity and colony-forming unit (CFU) assays were performed following irradiation. The results showed that peripheral blood cells were significantly lower in number and recovered less rapidly in irradiated SRC-3^−/− mice as compared with control animals. BM-nucleated cell and CFU counts were significantly decreased in SRC-3^−/− mice on the 7th and 14th day. Of note, the recovery of platelet (PLT) and megakaryocytic lineage were more depressed than the granulocytic and erythroid lineage in SRC-3^−/− mice. In conclusion, the present study demonstrated that the hematopoietic ability in SRC-3 knockout mice is severely impaired following a sublethal dose of irradiation.

Nuclear receptor coactivators: master regulators of human health and disease

Transcriptional coregulators (coactivators and corepressors) have emerged as the principal modulators of the functions of nuclear receptors and other transcription factors. During the decade since the discovery of steroid receptor coactivator-1 (SRC-1), the first authentic coregulator, more than 400 coregulators have been identified and characterized, and deciphering their function has contributed significantly to our understanding of their role in human physiology. Deregulated expression of coregulators has been implicated in diverse disease states and related pathologies. The advancement of molecular technologies has enabled us to better characterize the molecular associations of the SRC family of coactivators with other protein complexes in the context of gene regulation. These continuing discoveries not only expand our knowledge of the roles of coactivators in various human diseases but allow us to discover novel coactivator-targeting strategies for therapeutic intervention in these diseases.

Research resource: loss of the steroid receptor coactivators confers neurobehavioral consequences

Steroid receptor coactivators (SRCs) are important transcriptional modulators that regulate nuclear receptor and transcription factor activity to adjust transcriptional output to cellular demands. Highlighting their pleiotropic effects, dysfunction of the SRCs has been found in numerous pathologies including cancer, inflammation, and metabolic disorders. The SRC family is expressed strongly in the brain including the hippocampus, cortex, and hypothalamus. Studies focusing on the effect of SRC loss using congenic SRC knockout mice (SRC(-/-)) are limited in number, yet strongly indicate that the SRCs play important roles in regulating reproductive behavior, development, and motor coordination. To better understand the unique functions of the SRCs, we performed a neurobehavioral test battery focusing on anxiety and exploratory behaviors, motor coordination, sensorimotor gating, and nociception in both male and female null mice and compared them with their wild-type (WT) littermates. Results from the test battery reveal a role for SRC1 in motor coordination. Additionally, we found that SRC1 regulates anxiety responses in SRC1(-/-) male and female mice, and nociception sensitivity in SRC1(-/-) male but not female mice. By comparison, SRC2 regulates anxiety response with SRC2(-/-) females showing decreased anxiety in novel environments, as well as increased exploratory behavior in the open field compared with WT littermates. Additionally, SRC2(-/-) males were shown to have deficits in sensorimotor gating. Loss of SRC3 also shows sex differences in anxiety and exploratory behaviors. In particular, SRC3(-/-) female mice have increased anxiety and reduced exploratory activity and impairments in prepulse inhibition, whereas SRC3(-/-) male mice show no significant behavioral differences. In both genders, ablation of SRC3 decreases nocifensive behaviors. Collectively, these resource data suggest that loss of the SRCs results in behavioral phenotypes, underscoring the importance of understanding both the general and gender-based activity of SRCs in the brain.

Driving pluripotency and reprogramming: nuclear receptors at the helm

The identity of a cell is determined by the concerted interplay of multiple molecular modulators such as transcription factors, chromatin modifiers and signalling mediators. Among these, the transcriptional circuitry holds great influence on the specification and maintenance of a cellular state, and its perturbation can trigger a transition to another cell state. This is particularly striking in the field of pluripotency, where tempering the expression levels of one or few transcription factors is sufficient to induce the loss or acquisition of the pluripotent state. Recently, nuclear receptors, a class of transcription factors, have emerged as major players in the molecular network governing pluripotency. In this review, we discuss the importance of nuclear receptors in embryonic stem cell self-renewal, differentiation and cellular reprogramming, highlighting recent discoveries as well as providing an outlook in stem cell and nuclear receptor research.

Inducible knockout of Twist1 in young and adult mice prolongs hair growth cycle and has mild effects on general health, supporting Twist1 as a preferential cancer target

Twist1 promotes epithelial-mesenchymal transition, invasion, metastasis, stemness, and chemotherapy resistance in cancer cells and thus is a potential target for cancer therapy. However, Twist1-null mice are embryonic lethal, and people with one Twist1 germline mutant allele develop Saethre-Chotzen syndrome; it is questionable whether Twist1 can be targeted in patients without severe adverse effects. We found that Twist1 is expressed in several tissues, including fibroblasts of the mammary glands and dermal papilla cells of the hair follicles. We developed a tamoxifen-inducible Twist1 knockout mouse model; Twist1 knockout in 6-week-old female mice did not affect mammary gland morphogenesis and function during pregnancy and lactation. In both males and females, the knockout did not influence body weight gain, heart rate, or total lean and fat components. The knockout also did not alter blood pressure in males, although it slightly reduced blood pressure in females. Although Twist1 is not cyclically expressed in dermal papilla cells, knockout of Twist1 at postnatal day 13 (when hair follicles have developed) drastically extended the anagen phase and accelerated hair growth. These results indicate that Twist1 is not essential for maintaining an overall healthy condition in young and adult mice and that loss of function facilitates hair growth in adulthood, supporting Twist1 as a preferential target for cancer therapy.

Advances in osteoarthritis genetics

Osteoarthritis (OA), the most common form of arthritis, is a highly debilitating disease of the joints and can lead to severe pain and disability. There is no cure for OA. Current treatments often fail to alleviate its symptoms leading to an increased demand for joint replacement surgery. Previous epidemiological and genetic research has established that OA is a multifactorial disease with both environmental and genetic components. Over the past 6 years, a candidate gene study and several genome-wide association scans (GWAS) in populations of Asian and European descent have collectively established 15 loci associated with knee or hip OA that have been replicated with genome-wide significance, shedding some light on the aetiogenesis of the disease. All OA associated variants to date are common in frequency and appear to confer moderate to small effect sizes. Some of the associated variants are found within or near genes with clear roles in OA pathogenesis, whereas others point to unsuspected, less characterised pathways. These studies have also provided further evidence in support of the existence of ethnic, sex, and joint specific effects in OA and have highlighted the importance of expanded and more homogeneous phenotype definitions in genetic studies of OA.

Integrative genomics of gene and metabolic regulation by estrogen receptors α and β, and their coregulators

The closely related transcription factors (TFs), estrogen receptors ERα and ERβ, regulate divergent gene expression programs and proliferative outcomes in breast cancer. Utilizing breast cancer cells with ERα, ERβ, or both receptors as a model system to define the basis for differing response specification by related TFs, we show that these TFs and their key coregulators, SRC3 and RIP140, generate overlapping as well as unique chromatin-binding and transcription-regulating modules. Cistrome and transcriptome analyses and the use of clustering algorithms delineated 11 clusters representing different chromatin-bound receptor and coregulator assemblies that could be functionally associated through enrichment analysis with distinct patterns of gene regulation and preferential coregulator usage, RIP140 with ERβ and SRC3 with ERα. The receptors modified each other's transcriptional effect, and ERβ countered the proliferative drive of ERα through several novel mechanisms associated with specific binding-site clusters. Our findings delineate distinct TF-coregulator assemblies that function as control nodes, specifying precise patterns of gene regulation, proliferation, and metabolism, as exemplified by two of the most important nuclear hormone receptors in human breast cancer.

Insulin-like growth factor 1 mRNA expression in the uterus of streptozotocin-treated diabetic mice

Reproductive functions decline with the onset of diabetes in female mice. Diabetic mice have smaller uteri with an underdeveloped endometrium, suggesting diminished estrogen-induced growth. We aimed to clarify the changes in the estrous cycle and in insulin-like growth factor 1 (IGF1) expression in the uteri of streptozotocin (STZ)-treated diabetic mice, because IGF1 is one of the main growth factors involved in estrogen-induced uterine growth. ICR female mice were intraperitoneally administered STZ (10 mg/100 g BW), and blood glucose levels were determined. Mice with blood glucose levels > 200 mg/dl were classified as diabetic mice. The onset of diabetes was associated with acyclic estrous cycles. Diabetes was also induced with STZ in ovariectomized mice. Uterine Igf1 mRNA levels were reduced in ovariectomized STZ-treated diabetic mice. Estrogen is known to stimulate Igf1 mRNA expression in the uterus, but estrogen action was abolished in the uteri of STZ-treated diabetic mice. mRNA expressions of estrogen receptor α (ERα) and steroid hormone receptor coactivators (SRC-1/Ncoa1, SRC-2/Ncoa2, SRC-3/Ncoa3 and CBP/p300/Crebbp) were reduced in the uteri of ovariectomized STZ-treated diabetic mice. The present study demonstrates that diabetes induces a decline in female reproductive functions in mice. Igf1 expression in ovariectomized diabetic female mice was decreased, and decreased responsiveness to estrogen in the uteri of diabetic mice is probably associated with a reduction in ERα and steroid receptor coactivator mRNA expression.

Oestrogen receptor co-activator AIB1 is a marker of tamoxifen benefit in postmenopausal breast cancer

Background

The oestrogen receptor (ER) co-activator amplified in breast cancer 1 (AIB1) has been suggested as a treatment predictive and prognostic marker in breast cancer. Studies have however not been unanimous.

Patients and methods

AIB1 protein expression was analysed by immunohistochemistry on tissue micro-arrays with tumour samples from 910 postmenopausal women randomised to tamoxifen treatment or no adjuvant treatment. Associations between AIB1 expression, clinical outcome in the two arms and other clinicopathological variables were examined.

Results

In patients with ER-positive breast cancer expressing low tumour levels of AIB1 (<75%), we found no significant difference in recurrence-free survival (RFS) or breast cancer-specific survival (BCS) between tamoxifen treated and untreated patients. In patients with high AIB1 expression (>75%), there was a significant decrease in recurrence rate (HR 0.40, 95% CI 0.26–0.61, P < 0.001) and breast cancer mortality rate (HR 0.38, 95% CI 0.21–0.69, P = 0.0015) with tamoxifen treatment. In the untreated arm, we found high expression of AIB1 to be significantly associated with lower RFS (HR 1.74, 95% CI 1.20–2.53, P = 0.0038).

Conclusion

Our results suggest that high AIB1 is a predictive marker of good response to tamoxifen treatment in postmenopausal women and a prognostic marker of decreased RFS in systemically untreated patients.

The steroid receptor coactivator-3 is required for the development of castration-resistant prostate cancer

The transcriptional coactivator SRC-3 plays a key role in enhancing prostate cancer cell proliferation. Although SRC-3 is highly expressed in advanced prostate cancer, its role in castration-resistant prostate cancer (CRPC) driven by PTEN mutation is unknown. We documented elevated SRC-3 in human CRPC and in PTEN-negative human prostate cancer. Patients with high SRC-3 and undetectable PTEN exhibited decreased recurrence-free survival. To explore the causal relationship in these observations, we generated mice in which both Pten and SRC-3 were inactivated in prostate epithelial cells (Pten3CKO mice), comparing them with mice in which only Pten was inactivated in these cells (PtenCKO mice). SRC-3 deletion impaired cellular proliferation and reduced tumor size. Notably, while castration of PtenCKO control mice increased the aggressiveness of prostate tumors relative to noncastrated counterparts, deletion of SRC-3 in Pten3CKO mice reversed all these changes. In support of this finding, castrated Pten3CKO mice also exhibited decreased levels of phospho-Akt, S6 kinase (RPS6KB1), and phosphorylated S6 protein (RPS6), all of which mediate cell growth and proliferation. Moreover, these tumors appeared to be more differentiated as evidenced by higher levels of Fkbp5, an AR-responsive gene that inhibits Akt signaling. Lastly, these tumors also displayed lower levels of certain androgen-repressed genes such as cyclin E2 and MMP10. Together, our results show that SRC-3 drives CRPC formation and offer preclinical proof of concept for a transcriptional coactivator as a therapeutic target to abrogate CRPC progression.

AIB1 predicts bladder cancer outcome and promotes bladder cancer cell proliferation through AKT and E2F1

Background:

We previously demonstrated that AIB1 overexpression is an independent molecular marker for shortened survival of bladder cancer (BC) patients. In this study, we characterised the role and molecular mechanisms of AIB1 in BC tumorigenicity.

Methods:

AIB1 expression was measured by immunohistochemistry in non-muscle-invasive BC tissue and adjacent normal bladder tissue. In addition, the tumorigenicity of AIB1 was assessed with in vitro and in vivo functional assays.

Results:

Overexpression of AIB1 was observed in tissues from 46 out of 146 patients with non-muscle-invasive BC and was an independent predictor for poor progression-free survival. Lentivirus-mediated AIB1 knockdown inhibited cell proliferation both in vitro and in vivo, whereas AIB1 overexpression promoted cell proliferation in vitro. The growth-inhibitory effect induced by AIB1 knockdown was mediated by G1 arrest, which was caused by reduced expression of key cell-cycle regulatory proteins through the AKT pathway and E2F1.

Conclusion:

Our results suggest that AIB1 promotes BC cell proliferation through the AKT pathway and E2F1. Furthermore, AIB1 overexpression predicts tumour progression in patients with non-muscle-invasive BC.

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.

The expression of AIB1 correlates with cellular proliferation in human prolactinomas

Estrogens as well as certain growth factors strongly influence the development and growth of prolactinomas. However, the molecular mechanisms by which extracellular factors trigger prolactinomas are not well known. Amplified in breast cancer 1 (AIB1), also known as steroid receptor co-activator 3 (SRC-3), belongs to the p160/SRC family of nuclear receptor co-activators and is a major co-activator of the estrogen receptor. Here, we report that the estrogen receptor coactivator AIB1 is overexpressed in human prolactinomas and correlates with the detection of aromatase and estrogen receptor α (ERα). Of the 87 pituitary tumors evaluated in women, 56%, corresponding to hyperoprolactinemic women, contained an enriched population of prolactin-positive cells and hence were further classified as prolactinomas. All prolactinomas stained positive for both ERα and AIB1. Moreover, AIB1 sub-cellular distribution was indicative of the cell-cycle status of tumors; the nuclear expression of AIB1 was correlated with proliferative markers whereas the cytoplasmic localization of AIB1 coincided with active caspase-3. Thus, our results demonstrate for the first time that AIB1 is expressed in prolactinomas and suggest its participation in the regulation of proliferation and apoptosis of tumoral cells. Because aromatase expression is also enhanced in these prolactinomas and it is involved in the local production of estradiol, both mechanisms, ER-AIB1 and aromatase could be related.

Research resource: tissue- and pathway-specific metabolomic profiles of the steroid receptor coactivator (SRC) family

The rapidly growing family of transcriptional coregulators includes coactivators that promote transcription and corepressors that harbor the opposing function. In recent years, coregulators have emerged as important regulators of metabolic homeostasis, including the p160 steroid receptor coactivator (SRC) family. Members of the SRC family have been ascribed important roles in control of gluconeogenesis, fat absorption and storage in the liver, and fatty acid oxidation in skeletal muscle. To provide a deeper and more granular understanding of the metabolic impact of the SRC family members, we performed targeted metabolomic analyses of key metabolic byproducts of glucose, fatty acid, and amino acid metabolism in mice with global knockouts (KOs) of SRC-1, SRC-2, or SRC-3. We measured amino acids, acyl carnitines, and organic acids in five tissues with key metabolic functions (liver, heart, skeletal muscle, brain, plasma) isolated from SRC-1, -2, or -3 KO mice and their wild-type littermates under fed and fasted conditions, thereby unveiling unique metabolic functions of each SRC. Specifically, SRC-1 ablation revealed the most significant impact on hepatic metabolism, whereas SRC-2 appeared to impact cardiac metabolism. Conversely, ablation of SRC-3 primarily affected brain and skeletal muscle metabolism. Surprisingly, we identified very few metabolites that changed universally across the three SRC KO models. The findings of this Research Resource demonstrate that coactivator function has very limited metabolic redundancy even within the homologous SRC family. Furthermore, this work also demonstrates the use of metabolomics as a means for identifying novel metabolic regulatory functions of transcriptional coregulators.

Cytoplasmic localization of alteration/deficiency in activation 3 (ADA3) predicts poor clinical outcome in breast cancer patients

Transcriptional activation by estrogen receptor (ER) is a key step to breast oncogenesis. Given previous findings that ADA3 is a critical component of HAT complexes that regulate ER function and evidence that overexpression of other ER coactivators such as SRC-3 is associated with clinical outcomes in breast cancer, the current study was designed to assess the potential significance of ADA3 expression/localization in human breast cancer patients. In this study, we analyzed ADA3 expression in breast cancer tissue specimens and assessed the correlation of ADA3 staining with cancer progression and patient outcome. Tissue microarrays prepared from large series of breast cancer patients with long-term follow-ups were stained with anti-ADA3 monoclonal antibody using immunohistochemistry. Samples were analyzed for ADA3 expression followed by correlation with various clinicopathological parameters and patients’ outcomes. We report that breast cancer specimens show predominant nuclear, cytoplasmic, or mixed nuclear + cytoplasmic ADA3 staining patterns. Predominant nuclear ADA3 staining correlated with ER+ status. While predominant cytoplasmic ADA3 staining negatively correlated with ER+ status, but positively correlated with ErbB2, EGFR, and Ki67. Furthermore, a positive correlation of cytoplasmic ADA3 was observed with higher histological grade, mitotic counts, Nottingham Prognostic Index, and positive vascular invasion. Patients with nuclear ADA3 and ER positivity have better breast cancer specific survival and distant metastasis free survival. Significantly, cytoplasmic expression of ADA3 showed a strong positive association with reduced BCSS and DMFS in ErbB2+/EGFR+ patients. Although in multivariate analyses ADA3 expression was not an independent marker of survival, predominant nuclear ADA3 staining in breast cancer tissues correlates with ER+ expression and together serves as a marker of good prognosis, whereas predominant cytoplasmic ADA3 expression correlates with ErbB2+/EGFR+ expression and together is a marker of poor prognosis. Thus, ADA3 cytoplasmic localization together with ErbB2+/EGFR+ status may serve as better prognostic marker than individual proteins to predict survival of patients.

Physiological and molecular determinants of embryo implantation

Embryo implantation involves the intimate interaction between an implantation-competent blastocyst and a receptive uterus, which occurs in a limited time period known as the window of implantation. Emerging evidence shows that defects originating during embryo implantation induce ripple effects with adverse consequences on later gestation events, highlighting the significance of this event for pregnancy success. Although a multitude of cellular events and molecular pathways involved in embryo-uterine crosstalk during implantation have been identified through gene expression studies and genetically engineered mouse models, a comprehensive understanding of the nature of embryo implantation is still missing. This review focuses on recent progress with particular attention to physiological and molecular determinants of blastocyst activation, uterine receptivity, blastocyst attachment and uterine decidualization. A better understanding of underlying mechanisms governing embryo implantation should generate new strategies to rectify implantation failure and improve pregnancy rates in women.