Estrogen receptor-related receptor alpha 1 interacts with coactivator and constitutively activates the estrogen response elements of the human lactoferrin gene

SIRT1 mediates breast cancer development and tumorigenesis controlled by estrogen-related receptor β

Silent mating type information regulation 2 homolog 1 (SIRT1) is a class III histone deacetylase (HDAC) that is NAD + dependent and essential for metabolism, senescence, and cell survival. SIRT1 is overexpressed in several cancers, including breast cancer. SIRT1 is a well-known target gene of the estrogen receptor alpha (ER alpha) and is closely related to ER alpha deacetylation. Transcription factor Estrogen-related receptors (ERRs) share sequence homology with ERs in the DNA-binding domain, therefore, the possibility of sharing target genes between them is high. Our current research aims to gain insight into the function of ERRβ in regulating the activity of SIRT1 during the progression of breast cancer. ER-positive (ER + ve) breast cancer cells and tissues had considerably enhanced SIRT1 expression. Six potential ERRE sites were identified by analysis of the 5' upstream region of SIRT1, and both in vitro and in vivo experiments supported their presence. We found SIRT1 to be up-regulated in ERRβ overexpressed ER + ve breast cancer cells. Furthermore, our findings suggested that ectopic production of ERR and PCAF would increase SIRT1 activity. Our findings also indicated that ectopic production of ERRβ and PCAF increased SIRT1 activity. With sufficient evidence demonstrating the substantial involvement of SIRT1 in cell proliferation, migration, and colony formation capability, we were also able to illustrate the tumorigenic role of SIRT1. Overall, our findings highlight SIRT1's tumorigenic influence on breast cancer and suggest that SIRT1 inhibitors might serve as potential therapeutic drugs for the treatment of breast cancer.

Asymmetric dimerization in a transcription factor superfamily is promoted by allosteric interactions with DNA

Transcription factors, such as nuclear receptors achieve precise transcriptional regulation by means of a tight and reciprocal communication with DNA, where cooperativity gained by receptor dimerization is added to binding site sequence specificity to expand the range of DNA target gene sequences. To unravel the evolutionary steps in the emergence of DNA selection by steroid receptors (SRs) from monomeric to dimeric palindromic binding sites, we carried out crystallographic, biophysical and phylogenetic studies, focusing on the estrogen-related receptors (ERRs, NR3B) that represent closest relatives of SRs. Our results, showing the structure of the ERR DNA-binding domain bound to a palindromic response element (RE), unveil the molecular mechanisms of ERR dimerization which are imprinted in the protein itself with DNA acting as an allosteric driver by allowing the formation of a novel extended asymmetric dimerization region (KR-box). Phylogenetic analyses suggest that this dimerization asymmetry is an ancestral feature necessary for establishing a strong overall dimerization interface, which was progressively modified in other SRs in the course of evolution.

The Role of the Estrogen-Related Receptor Alpha (ERRa) in Hypoxia and Its Implications for Cancer Metabolism

Under low oxygen conditions (hypoxia), cells activate survival mechanisms including metabolic changes and angiogenesis, which are regulated by HIF-1. The estrogen-related receptor alpha (ERRα) is a transcription factor with important roles in the regulation of cellular metabolism that is overexpressed in hypoxia, suggesting that it plays a role in cell survival in this condition. This review enumerates and analyses the recent evidence that points to the role of ERRα as a regulator of hypoxic genes, both in cooperation with HIF-1 and through HIF-1- independent mechanisms, in invertebrate and vertebrate models and in physiological and pathological scenarios. ERRα's functions during hypoxia include two mechanisms: (1) direct ERRα/HIF-1 interaction, which enhances HIF-1's transcriptional activity; and (2) transcriptional activation by ERRα of genes that are classical HIF-1 targets, such as VEGF or glycolytic enzymes. ERRα is thus gaining recognition for its prominent role in the hypoxia response, both in the presence and absence of HIF-1. In some models, ERRα prepares cells for hypoxia, with important clinical/therapeutic implications.

ERRγ Ligand Regulates Adult Neurogenesis and Depression-like Behavior in a LRRK2-G2019S-associated Young Female Mouse Model of Parkinson's Disease

Adult neurogenesis, a process controlling the proliferation to maturation of newly generated neurons in the post-developmental brain, is associated with various brain functions and pathogenesis of neuropsychological diseases, such as Parkinson's disease (PD) and depression. Because orphan nuclear receptor estrogen-related receptor γ (ERRγ) plays a role in the differentiation of neuronal cells, we investigated whether an ERRγ ligand enhances adult neurogenesis and regulates depressive behavior in a LRRK2-G2019S-associated mouse model of PD. Young female LRRK2-G2019S mice (7-9 weeks old) showed depression-like behavior without dopaminergic neuronal loss in the nigrostriatal pathway nor motor dysfunction. A significant decrease in adult hippocampal neurogenesis was detected in young female LRRK2-G2019S mice, but not in comparable male mice. A synthetic ERRγ ligand, (E)-4-hydroxy-N'-(4-(phenylethynyl)benzylidene)benzohydrazide (HPB2), ameliorated depression-like behavior in young female LRRK2-G2019S mice and enhanced neurogenesis in the hippocampus, as evidenced by increases in the number of bromodeoxyuridine/neuronal nuclei-positive cells and in the intensity and number of doublecortin-positive cells in the hippocampal dentate gyrus (DG). Moreover, HPB2 significantly increased the number of spines and the number and length of dendrites in the DG of young female LRRK2-G2019S mice. Furthermore, HPB2 upregulated brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling, one of the important factors regulating neurogenesis, as well as phosphorylated cAMP-response element binding protein-positive cells in the DG of young female LRRK2-G2019S mice. Together, these results suggest ERRγ as a novel therapeutic target for PD-associated depression by modulating adult neurogenesis and BDNF/TrkB signaling.

Estrogen-Related Receptor α: A Significant Regulator and Promising Target in Bone Homeostasis and Bone Metastasis

Bone homeostasis is maintained with the balance between bone formation and bone resorption, which is involved in the functional performance of osteoblast and osteoclast. Disruption of this equilibrium usually causes bone disorders including osteoporosis, osteoarthritis, and osteosclerosis. In addition, aberrant activity of bone also contributes to the bone metastasis that frequently occurs in the late stage of aggressive cancers. Orphan nuclear receptor estrogen-related receptor (ERRα) has been demonstrated to control the bone cell fate and the progression of tumor cells in bone through crosstalk with various molecules and signaling pathways. However, the defined function of this receptor in bone is inconsistent and controversial. Therefore, we summarized the latest research and conducted an overview to reveal the regulatory effect of ERRα on bone homeostasis and bone metastasis, this review may broaden the present understanding of the cellular and molecular model of ERRα and highlight its potential implication in clinical therapy.

Estrogen-Related Receptors Gene Expression and Copy Number Alteration Association With the Clinicopathologic Characteristics of Breast Cancer

Purpose:

It has been suggested that dysregulation of transcription factors expression or activity plays significant roles in breast cancer (BC) severity and poor prognosis. Therefore, our study aims to thoroughly evaluate the estrogen-related receptor isoforms (ESRRs) expression and copy number alteration (CNA) status and their association with clinicopathologic characteristics in BC.

Methods:

A METABRIC dataset consist of 2509 BC patients’ samples was obtained from the cBioPortal public domain. The gene expression, putative CNA, and relevant tumor information of ESRRs were retrieved. ESRRs messenger RNA (mRNA) expression in BC cell lines was obtained from the Cancer Cell Line Encyclopedia (CCLE). Association and correlation analysis of ESRRs expression with BC clinicopathologic characteristics and molecular subtype were performed. Kaplan–Meier survival analysis was conducted to evaluate the prognostic value of ESRRs expression on patient survival.

Results:

ESRRα expression correlated negatively with patients’ age and overall survival, whereas positively correlated with tumor size, the number of positive lymph nodes, and Nottingham prognostic index (NPI). Conversely, ESRRγ expression was positively correlated with patients’ age and negatively correlated with NPI. ESRRα and ESRRγ expression were significantly associated with tumor grade, expression of hormone receptors, human epidermal growth factor receptor 2 (HER2), and molecular subtype, whereas ESRRβ was only associated with tumor stage. A significant and distinct association of each of ESRRs CNA with various clinicopathologic and prognostic factors was also observed. Kaplan–Meier survival analysis demonstrated no significant difference for survival curves among BC patients with high or low expression of ESRRα, β, or γ. On stratification, high ESRRα expression significantly reduced survival among premenopausal patients, patients with grade I/II, and early-stage disease. In BC cell lines, only ESRRα expression was significantly higher in HER2-positive cells. No significant association was observed between ESRRβ expression and any of the clinicopathologic characteristics examined.

Conclusions:

In this clinical dataset, ESRRα and ESRRγ mRNA expression and CNA show a significant correlation and association with distinct clinicopathologic and prognostic parameters known to influence treatment outcomes; however, ESRRβ failed to show a robust role in BC pathogenesis. ESRRα and ESRRγ can be employed as therapeutic targets in BC-targeted therapy. However, the role of ESRRβ in BC pathogenesis remains unclear.

Small-molecule profiling for steroid receptor activity using a universal steroid receptor reporter assay

A critical step in the development of novel drug candidates for the treatment of steroid related diseases is ensuring the absence of crosstalk with steroid receptors (SRs). Establishing this SR cross-reactivity profile requires multiple reporter assays as each SR associates with its unique enhancer region, a labor intensive and time-consuming approach. To overcome this need for multi-reporter assays, we established a steroid receptor inducible luciferase reporter assay (SRi-Luc) that allows side-by-side examination of agonistic and antagonistic properties of small-molecules on all steroid receptors. This state-of-the-art SRi-Luc consists of a unique alteration of four distinct keto-steroid- and estrogen response elements. As proof of principle, the SRi-Luc assay was used to profile a set of novel designed steroidal 1,2,3-triazoles. These triazolized steroidal compounds were developed via our in-house triazolization methodology, in which an enolizable ketone is converted into a triazolo-fused or -linked analog by treatment with a primary amine or ammonium salt in the presence of 4-nitrophenyl azide. From these designed steroidal 1,2,3-triazoles, six successfully reduced androgen receptor activity by 40 %. Although opted as antiandrogens, their cross-reactivity with other SRs was apparent in our SRi-Luc assay and rendered them unsuited for further antagonist development and clinical use. Overall, the SRi-Luc overcomes the need of multi-reporter assays for the profiling of small-molecules on all SRs. This not only reduces the risk of introducing biases, it as well accelerates early-stage drug discovery when designing particular SR selective (ant)agonists or characterizing off-target effects of lead molecules acting on any drug target.

Molecular dynamics of estrogen-related receptors and their regulatory proteins: roles in transcriptional control for endocrine and metabolic signaling

Estrogen-related receptor (ERR) is a member of the nuclear receptor (NR) superfamily and has three subtypes α, β, and γ. Despite their strong homology with estrogen receptor (ER) α, ERRs cannot accommodate endogenous hormones. However, they are able to regulate gene expression without ligand binding. ERRα and ERRγ orchestrate the expression of genes involved in bioenergetic pathways, while ERRβ controls placental development and stem cell maintenance. Evidence from recent studies, including clinical research, has also demonstrated close associations of ERRs with the pathophysiology of hormone-related cancers and metabolic disorders including type 2 diabetes mellitus. This review summarizes the basic knowledge and recent advances in ERRs and their associated proteins, focusing on the subcellular dynamics involved in transcriptional regulation. Fluorescent protein labeling enabled monitoring of ERRs in living cells and revealed previously unrecognized characteristics. Using this technique, we demonstrated a role of ERRβ in controlling estrogen signaling by regulating the subnuclear dynamics of ligand-activated ERα. Visualization of ERRs and related proteins and subsequent analyses also revealed a function of ERRγ in promoting liver lactate metabolism in association with LRPGC1, a recently identified lactic acid-responsive protein. These findings suggest that ERRs activate unique transregulation mechanisms in response to extracellular stimuli such as hormones and metabolic signals, implying an adaptive system behind the cellular homeostatic regulation by orphan NRs. Control of subcellular ERR dynamics will contribute toward the development of therapeutic approaches to treat various diseases including hormone-related cancers and metabolic disorders associated with abnormal ERR signaling pathways.

Subcellular dynamics of estrogen-related receptors involved in transrepression through interactions with scaffold attachment factor B1

Estrogen-related receptor (ERR), a member of the nuclear receptor superfamily, consists of three subtypes (α, β, γ) and has strong homology with estrogen receptor. No endogenous ligands have been identified for ERRs, but they play key roles in metabolic, hormonal, and developmental processes as transcription factors without ligand binding. Although subnuclear dynamics are essential for nuclear events including nuclear receptor-mediated transcriptional regulation, the dynamics of ERRs are poorly understood. Here, we report that ERRs show subcellular kinetic changes in response to diethylstilbestrol (DES), a synthetic estrogen that represses the transactivity of all three ERR subtypes, using live-cell imaging with fluorescent protein labeling. Upon DES treatment, all ERR subtypes formed discrete clusters in the nucleus, with ERRγ also displaying nuclear export. Fluorescence recovery after photobleaching analyses revealed significant reductions in the intranuclear mobility of DES-bound ERRα and ERRβ, and a slight reduction in the intranuclear mobility of DES-bound ERRγ. After DES treatment, colocalization of all ERR subtypes with scaffold attachment factor B1 (SAFB1), a nuclear matrix-associated protein, was observed in dot-like subnuclear clusters, suggesting interactions of the ERRs with the nuclear matrix. Consistently, co-immunoprecipitation analyses confirmed enhanced interactions between ERRs and SAFB1 in the presence of DES. SAFB1 was clarified to repress the transactivity of all ERR subtypes through the ERR-response element. These results demonstrate ligand-dependent cluster formation of ERRs in the nucleus that is closely associated with SAFB1-mediated transrepression. Taken together, the present findings provide a new understanding of the pathophysiology regulated by ERR/SAFB1 signaling pathways and their subcellular dynamics.

FBXL10 promotes ERRα protein stability and proliferation of breast cancer cells by enhancing the mono-ubiquitylation of ERRα

The underlying mechanism of orphan nuclear receptor estrogen-related receptor α (ERRα) in breast cancer was investigated by identifying its interaction partners using mass spectrometry. F-box and leucine-rich repeat protein 10 (FBXL10), which modulates various physiological processes, may interact with ERRα in breast cancer. Here, we investigated the interaction between FBXL10 and ERRα, and their protein expression and correlation in breast cancer. Mechanical studies revealed that FBXL10 stabilized ERRα protein levels by reducing its poly-ubiquitylation and promoting its mono-ubiquitylation. The reporter gene assay and examination of ERRα target genes validated the increased transcriptional activity of ERRα due to its increased protein levels by FBXL10. FBXL10 also increased ERRα enrichment at the promoter region of its target genes. Functionally, FBXL10 facilitated the ERRα/peroxisome proliferator-activated receptor gamma coactivator 1 β (PGC1β)-mediated proliferation and tumorigenesis of breast cancer cells in vitro and in vivo. Our results uncovered a molecular mechanism linking the mono-ubiquitylation and protein stability of ERRα to functional interaction with FBXL10. Moreover, a novel regulatory axis of FBXL10 and ERRα regulating the proliferation and tumorigenesis of breast cancer cells was established.

The emerging role of estrogen related receptorα in complications of non-small cell lung cancers

Approximately 85% of lung cancer cases are recognized as non-small cell lung cancer (NSCLC) with a perilous (13–17%) 5-year survival in Europe and the USA. Although tobacco smoking has consistently emerged as the leading cause of NSCLC complications, its consequences are distinctly manifest with respect to sex bias, due to differential gene and sex hormone expression. Estrogen related receptor α (ERRα), a member of the nuclear orphan receptor superfamily is normally expressed in the lungs, and activates various nuclear genes without binding to the ligands, such as estrogens. In NSCLC ERRα expression is significantly higher compared with healthy individuals. It is well established ERα and ERβ‚ have 93% and 60% identity in the DNA and ligand binding domains, respectively. ERα and ERRα have 69% (70% with ERRα-1) and 34% (35% with ERRα-1) identity, respectively; ERRα and ERRβ‚ have 92 and 61% identity, respectively. However, whether there is distinctive ERRα interaction with mammalian estrogens or concurrent involvement in non-ER signalling pathway activation is not known. Relevant to NSCLC, ERRα promotes proliferation, invasion and migration by silencing the tumor suppressor proteins p53 and pRB, and accelerates G₂-M transition during cell division. Epithelial to mesenchymal transition (EMT) and activation of Slug (an EMT associated transcription factor) are the prominent mechanisms by which ERRα activates NSCLC metastasis. Based on these observations, the present article focuses on the feasibility of antiERRα therapy alone and in combination with antiER as a therapeutic strategy for NSCLC complications.

Insights into the interaction mechanisms of estrogen-related receptor alpha (ERRα) with ligands via molecular dynamics simulations

Estrogen-related receptor alpha (ERRα), a member of nuclear receptors (NRs), participates in energy metabolism. Recent experiments identified that several agonists to increase the activity of ERRα, which have a therapeutic effect in improving insulin sensitivity and lowering blood glucose levels. However, the detailed molecular mechanism about how the ligands affect the structure of ERRα remains elusive. To better understand the conformational change of ERRα complexed with agonists and inverse agonists, unbiased molecular dynamics (MD) simulations were performed on the ligand binding domain of ERRα (ERRα-LBD) bound with different ligands. According to the results, the ERRα-agonist interactions were more stable in the presence of the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α). More importantly, we observed that the binding of inverse agonists would decrease the stability of helix 12 (H12) of ERRα. Moreover, we suggested that Phe232 and Phe414 should be key residues in the interaction pathway from ligands to H12, which provided a possible explanation about how ligands impact the structure of ERRα. These results would provide insights into the design of novel and efficient agonists of ERRα to treat metabolic diabetes.Communicated by Ramaswamy H. Sarma.

Computational insights into the interaction mechanisms of estrogen-related receptor alpha with endogenous ligand cholesterol

Estrogen-related receptor alpha (ERRα) has attracted increasing concerns. ERRα, orphan nuclear receptor, plays important roles in energy metabolism. Therefore, small molecule agonists of ERRα could be a potential therapeutic strategy in the treatment of metabolic diseases such as diabetes. Recently, Wei et al. identified cholesterol as the endogenous agonist of ERRα. However, the detailed molecular mechanism of cholesterol bound with ERRα remains ambiguous. Thus, in this study molecular docking and molecular dynamics (MD) simulations were performed to characterize how cholesterol affects the behavior of ERRα. Based on the results, we found that a proven residue Phe232 and others including Leu228, Glu235, Arg276, and Phe399 were key residues to ligand binding. A hydrogen-bonding interaction between cholesterol and Glu235 ensured the orientation of the ligand in the binding pocket, while hydrophobic interactions between cholesterol and the above-mentioned residues promoted the stability of ERRα-cholesterol complex. In the presence of the proliferator-activated receptor γ coactivator 1α (PGC-1α), the cholesterol-ERRα interaction became more stable. Interestingly, we observed that cholesterol facilitated the binding of ERRα with its coactivator PGC-1α via stabilizing the conformation of helix 12 and the interaction surface of ERRα/PGC-1α. Overall, these findings would be valuable for the future rational design of novel ERRα agonists.

ERRα as a Bridge Between Transcription and Function: Role in Liver Metabolism and Disease

As transcriptional factors, nuclear receptors (NRs) function as major regulators of gene expression. In particular, dysregulation of NR activity has been shown to significantly alter metabolic homeostasis in various contexts leading to metabolic disorders and cancers. The orphan estrogen-related receptor (ERR) subfamily of NRs, comprised of ERRα, ERRβ, and ERRγ, for which a natural ligand has yet to be identified, are known as central regulators of energy metabolism. If AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) can be viewed as sensors of the metabolic needs of a cell and responding acutely via post-translational control of proteins, then the ERRs can be regarded as downstream effectors of metabolism via transcriptional regulation of genes for a long-term and sustained adaptive response. In this review, we will focus on recent findings centered on the transcriptional roles played by ERRα in hepatocytes. Modulation of ERRα activity in both in vitro and in vivo models via genetic or pharmacological manipulation coupled with chromatin-immunoprecipitation (ChIP)-on-chip and ChIP-sequencing (ChIP-seq) studies have been fundamental in delineating the direct roles of ERRα in the control of hepatic gene expression. These studies have identified crucial roles for ERRα in lipid and carbohydrate metabolism as well as in mitochondrial function under both physiological and pathological conditions. The regulation of ERRα expression and activity via ligand-independent modes of action including coregulator binding, post-translational modifications (PTMs) and control of protein stability will be discussed in the context that may serve as valuable tools to modulate ERRα function as new therapeutic avenues for the treatment of hepatic metabolic dysfunction and related diseases.

Oestrogen-related receptor reduces vitellogenin expression by crosstalk with the ecdysone receptor pathway in female silkworm, Bombyx mori

Oestrogen-related receptor (ERR) is involved in oestrogen receptor (ER) signalling pathways owing to its similarity to ER in terms of domain structure and co-activator and response elements. Although insects lack ER, they harbour an ERR gene that is thought to modulate metabolism and energy conversion via an unknown mechanism. The present study investigated the function of ERR in insects using female silkworm (Bombyx mori, Bm). We found that the expression of B. mori vitellogenin (BmVg) and B. mori ERR (BmERR) in the fat bodies of female silkworms at different stages of development exhibited alternating patterns, and RNA interference of BmERR in females induced BmVg transcription, resulting in an increase in egg weight relative to the control. Furthermore, BmERR was found to be involved in regulating the transcription of BmVg through an oestrogen-related receptor response element (ERRE) in the promoter of the BmVg gene, as demonstrated by electrophoretic mobility shift assay, cell transfection assay and chromatin immunoprecipitation. In summary, our results indicate that BmERR bound to the ERRE motif in the BmVg promoter reducing the expression of BmVg in the fat body of the female silkworm. To our surprise, the ERRE also showed the ability to bind the ecdysone receptor (BmEcR) and ultraspiracle complex. Thus, we surmise that ERR participates in steroid hormone signalling by engaging in crosstalk with the ER pathway in vertebrates and with the EcR pathway in insects.

Avian genomics lends insights into endocrine function in birds

The genomics era has brought along the completed sequencing of a large number of bird genomes that cover a broad range of the avian phylogenetic tree (>30 orders), leading to major novel insights into avian biology and evolution. Among recent findings, the discovery that birds lack a large number of protein coding genes that are organized in highly conserved syntenic clusters in other vertebrates is very intriguing, given the physiological importance of many of these genes. A considerable number of them play prominent endocrine roles, suggesting that birds evolved compensatory genetic or physiological mechanisms that allowed them to survive and thrive in spite of these losses. While further studies are needed to establish the exact extent of avian gene losses, these findings point to birds as potentially highly relevant model organisms for exploring the genetic basis and possible therapeutic approaches for a wide range of endocrine functions and disorders.

Establishment of primary mixed cell cultures from spontaneous canine mammary tumors: Characterization of classic and new cancer-associated molecules

There are many factors which make canine cancer like cancer in humans. The occurrence of spontaneous mammary tumors in pet dogs, tumor genetics, molecular targets and exposure to the same environmental risk factors are among these factors. Therefore, the study of canine cancer can provide useful information to the oncology field. This study aimed to establish and characterize a panel of primary mixed cell cultures obtained from spontaneous canine mammary tumors. Eight established cell cultures obtained from one normal mammary gland, one complex adenoma, one mixed adenoma, two complex carcinomas and two mixed carcinomas were analyzed. The gene expression levels of classic molecular cancer players such as fibroblast growth factor receptor (FGFR) 2, breast cancer (BRCA) 1, BRCA2 and estrogen receptor (ESR) 1 were evaluated. For the first time, three orphan nuclear receptors, estrogen-related receptors (ERRs) α, β and γ were studied in canine mammary cancer. The highest expression level of ERRα was observed in complex carcinoma-derived cell culture, while the highest levels of ERRβ and γ were observed in cells derived from a mixed carcinoma. Meanwhile, complex carcinomas presented the highest levels of expression of ESR1, BRCA1 and FGFR2 among all samples. BRCA2 was found exclusively in complex adenoma. The transcription factor GATA3 had its highest levels in mixed carcinoma samples and its lowest levels in complex adenoma. Proliferation assays were also performed to evaluate the mixed cell cultures response to ER ligands, genistein and DES, both in normoxia and hypoxic conditions. Our results demonstrate that morphological and functional studies of primary mixed cell cultures derived from spontaneous canine mammary tumors are possible and provide valuable tool for the study of various stages of mammary cancer development.

Chlorinated biphenyls effect on estrogen-related receptor expression, steroid secretion, mitochondria ultrastructure but not on mitochondrial membrane potential in Leydig cells

To characterize polychlorinated biphenyls (PCBs) action on Leydig cells, PCBs congeners, low-chlorinated (delor 103; d103) and high-chlorinated ones (delor 106; d106) were selected. The cells were treated according to PCBs dose (d103 or d106 0.2 ng/ml in low doses:, or 2 ng/ml in high doses) and type (d103 + d106 in low doses or 103 + 106 in high doses). After 24 h treatment with PCBs, a distinct increase in estrogen-related receptors (ERRs type α, β and γ) expression was revealed. However, the dose- and type-dependent PCBs effect was mostly exerted on ERRα expression. A similar increase in ERRs expression was demonstrated by estradiol but not testosterone, which was without an effect on ERRs. PCBs caused no decrease in the membrane potential status of Leydig cells (either in dose or type schedule) but had severe effects on the mitochondria number and structure. Moreover, PCBs markedly increased calcium (Ca2+) concentration and sex steroid secretion (both androgens and estrogens were elevated). These findings suggest a similar estrogenic action of PCBs congeners (d103 and d106) on Leydig cell function. We report dose- and type-specific effects of PCBs only on Leydig cell ERRs expression. Both delors showed common effects on the mitochondria ultrastructural and functional status. Based on our results, ERRα seems to be the most sensitive to hormonal modulation. The increases in Ca2+ and sex steroid secretion may be due to the activation of ERRs by PCBs binding and/or direct effect of PCBs on ERRs mRNA/protein expression. Nevertheless, to confirm the existence of possible relationships between ERRs signaling (including PCBs as ligands) and mitochondria function in Leydig cells, further intensive studies are needed.

Development of Novel Cell Lines for High-Throughput Screening to Detect Estrogen-Related Receptor Alpha Modulators

Estrogen-related receptor alpha (ERRα), the first orphan nuclear receptor discovered, is crucial for the control of cellular energy metabolism. ERRα and its coactivator, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), are required for rapid energy production in response to environmental challenges. They have been implicated in the etiology of metabolic disorders such as type 2 diabetes and metabolic syndrome. ERRα also plays a role in the pathogenesis of breast cancer. Identification of compounds that modulate ERRα signaling may elucidate environmental factors associated with these diseases. Therefore, we developed stable cell lines containing an intact ERRα signaling pathway, with and without the coactivator PGC-1α, to use as high-throughput screening tools to detect ERRα modulators. The lentiviral PGC-1α expression constructs and ERRα multiple hormone response element (MHRE) reporters were introduced into HEK293T cells that express endogenous ERRα. A cell line expressing the reporter alone was designated "ERR." A second cell line expressing both reporter and PGC-1α was named "PGC/ERR." Initial screenings of the Library of Pharmacologically Active Compounds (LOPAC) identified 33 ERR and 22 PGC/ERR agonists, and 54 ERR and 15 PGC/ERR antagonists. Several potent ERRα agonists were dietary plant compounds (e.g., genistein). In conclusion, these cell lines are suitable for high-throughput screens to identify environmental chemicals affecting metabolic pathways and breast cancer progression.

Modulation of estrogen related receptor alpha activity by the kinesin KIF17

Estrogen-related receptor alpha (ERR1) is an orphan nuclear receptor that can bind transcriptional co-activators constitutively. ERR1 expression correlates with poor patient outcomes in breast cancer, heightening interest in this nuclear receptor as a therapeutic target. Because ERR1 has no known regulatory ligand, a major challenge in targeting its activity is to find cellular or synthetic modulators of its function. We identified an interaction between ERR1 and KIF17, a kinesin-2 family microtubule motor, in a yeast-2-hybrid screen. We confirmed the interaction using in vitro biochemical assays and determined that binding is mediated by the ERR1 ligand-binding/AF2 domain and the KIF17 C-terminal tail. Expression of KIF17 tail domain in either ER-negative or ER-positive breast cancer epithelial cells attenuated nuclear accumulation of newly synthesized ERR1 and inhibited ERR1 transcriptional activity. Conversely, ERR1 transcriptional activity was elevated significantly in KIF17 knock-out cells. Sequence analysis of the KIF17 tail domain revealed it contains a nuclear receptor box with a conserved LXXLL motif found in transcriptional co-activators. Expression of a 12 amino-acid peptide containing this motif was sufficient to inhibit ERR1 transcriptional activity and cell invasion, while deletion of this region from the KIF17 tail resulted in increased ERR1 activity. Together, these data suggest KIF17 modifies ERR1 function by two possible, non-exclusive mechanisms: (i) by regulating nuclear-cytoplasmic distribution or (ii) by competing with transcriptional co-activators for binding to ERR1. Thus targeting the ERR1-KIF17 interaction has potential as a novel strategy for treating breast cancer.

Characterization of a selective inverse agonist for estrogen related receptor α as a potential agent for breast cancer

The estrogen-related receptor α (ERRα) is an orphan nuclear receptor that plays a primary role in the regulation of cellular energy homeostasis and osteogenesis. It is reported that ERRα is widely expressed in a range of tissues and accumulating evidence has supported that the high expression of ERRα correlates with poor prognosis of various human malignancies, including breast, endometrium, colon, prostate and ovary cancers. Herein is described the discovery of a novel selective inverse agonist (HSP1604) of ERRα, but not of ERRβ and ERRγ, as determined using transient transfection luciferase reporter assay and a time-resolved fluorescence resonance energy transfer (TR-FRET) co-activator assay. HSP1604 potently inhibits ERRα transcriptional activity with IC50=1.47±0.17μM in cell-based luciferase reporter assay and also decreases the protein level of ERRα and the mRNA levels of its downstream target genes such as pyruvate dehydrogenase kinase 4 (PDK4), pS2 and osteopontin. HSP1604 has also suppressed the proliferation of different human cancer cell lines and the migration of breast cancer cells with high expression of ERRα. Representative in vivo results show that HSP1604 suppresses the growth of human breast cancer xenograft in nude mice as doses at 30mg/kg or 100mg/kg administered every other day during 28-day period. HSP1604 thus has the potential both as a new agent to inhibit the growth of tumors and as a chemical probe of ERRα biology.

Molecular cloning, expression, and stress response of the estrogen-related receptor gene (AccERR) from Apis cerana cerana

Estrogen-related receptor (ERR), which belongs to the nuclear receptor superfamily, has been implicated in diverse physiological processes involving the estrogen signaling pathway. However, little information is available on ERR in Apis cerana cerana. In this report, we isolated the ERR gene and investigated its involvement in antioxidant defense. Quantitative real-time polymerase chain reaction (qPCR) revealed that the highest mRNA expression occurred in eggs during different developmental stages. The expression levels of AccERR were highest in the muscle, followed by the rectum. The predicted transcription factor binding sites in the promoter of AccERR suggested that AccERR potentially functions in early development and in environmental stress responses. The expression of AccERR was induced by cold (4 °C), heat (42 °C), ultraviolet light (UV), HgCl2, and various types of pesticides (phoxim, deltamethrin, triadimefon, and cyhalothrin). Western blot was used to measure the expression levels of AccERR protein. These data suggested that AccERR might play a vital role in abiotic stress responses.

In silico selection of an aptamer to estrogen receptor alpha using computational docking employing estrogen response elements as aptamer-alike molecules

Aptamers, the chemical-antibody substitute to conventional antibodies, are primarily discovered through SELEX technology involving multi-round selections and enrichment. Circumventing conventional methodology, here we report an in silico selection of aptamers to estrogen receptor alpha (ERα) using RNA analogs of human estrogen response elements (EREs). The inverted repeat nature of ERE and the ability to form stable hairpins were used as criteria to obtain aptamer-alike sequences. Near-native RNA analogs of selected single stranded EREs were modelled and their likelihood to emerge as ERα aptamer was examined using AutoDock Vina, HADDOCK and PatchDock docking. These in silico predictions were validated by measuring the thermodynamic parameters of ERα -RNA interactions using isothermal titration calorimetry. Based on the in silico and in vitro results, we selected a candidate RNA (ERaptR4; 5′-GGGGUCAAGGUGACCCC-3′) having a binding constant (Ka) of 1.02 ± 0.1 × 10⁸M⁻¹ as an ERα-aptamer. Target-specificity of the selected ERaptR4 aptamer was confirmed through cytochemistry and solid-phase immunoassays. Furthermore, stability analyses identified ERaptR4 resistant to serum and RNase A degradation in presence of ERα. Taken together, an efficient ERα-RNA aptamer is identified using a non-SELEX procedure of aptamer selection. The high-affinity and specificity can be utilized in detection of ERα in breast cancer and related diseases.

Gene expression underlying enhanced, steroid-dependent auditory sensitivity of hair cell epithelium in a vocal fish

BACKGROUND

Successful animal communication depends on a receiver's ability to detect a sender's signal. Exemplars of adaptive sender-receiver coupling include acoustic communication, often important in the context of seasonal reproduction. During the reproductive summer season, both male and female midshipman fish (Porichthys notatus) exhibit similar increases in the steroid-dependent frequency sensitivity of the saccule, the main auditory division of the inner ear. This form of auditory plasticity enhances detection of the higher frequency components of the multi-harmonic, long-duration advertisement calls produced repetitively by males during summer nights of peak vocal and spawning activity. The molecular basis of this seasonal auditory plasticity has not been fully resolved. Here, we utilize an unbiased transcriptomic RNA sequencing approach to identify differentially expressed transcripts within the saccule's hair cell epithelium of reproductive summer and non-reproductive winter fish.

RESULTS

We assembled 74,027 unique transcripts from our saccular epithelial sequence reads. Of these, 6.4 % and 3.0 % were upregulated in the reproductive and non-reproductive saccular epithelium, respectively. Gene ontology (GO) term enrichment analyses of the differentially expressed transcripts showed that the reproductive saccular epithelium was transcriptionally, translationally, and metabolically more active than the non-reproductive epithelium. Furthermore, the expression of a specific suite of candidate genes, including ion channels and components of steroid-signaling pathways, was upregulated in the reproductive compared to the non-reproductive saccular epithelium. We found reported auditory functions for 14 candidate genes upregulated in the reproductive midshipman saccular epithelium, 8 of which are enriched in mouse hair cells, validating their hair cell-specific functions across vertebrates.

CONCLUSIONS

We identified a suite of differentially expressed genes belonging to neurotransmission and steroid-signaling pathways, consistent with previous work showing the importance of these characters in regulating hair cell auditory sensitivity in midshipman fish and, more broadly, vertebrates. The results were also consistent with auditory hair cells being generally more physiologically active when animals are in a reproductive state, a time of enhanced sensory-motor coupling between the auditory periphery and the upper harmonics of vocalizations. Together with several new candidate genes, our results identify discrete patterns of gene expression linked to frequency- and steroid-dependent plasticity of hair cell auditory sensitivity.

Sex steroid signaling: implications for lung diseases

There is increasing recognition that sex hormones (estrogen, progesterone, and testosterone) have biological and pathophysiological actions in peripheral, non-reproductive organs, including the lung. Clinically, sex differences in the incidence, morbidity and mortality of lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), pulmonary fibrosis, lung cancer and pulmonary hypertension have been noted, although intrinsic sex differences vs. the roles of sex steroids are still not well-understood. Accordingly, it becomes important to ask the following questions: 1) Which sex steroids are involved? 2) How do they affect different components of the lung under normal circumstances? 3) How does sex steroid signaling change in or contribute to lung disease, and in this regard, are sex steroids detrimental or beneficial? As our understanding of sex steroid signaling in the lung improves, it is important to consider whether such information can be used to develop new therapeutic strategies to target lung diseases, perhaps in both sexes or in a sex-specific manner. In this review, we focus on the basics of sex steroid signaling, and the current state of knowledge regarding how they influence structure and function of specific lung components across the life span and in the context of some important lung diseases. We then summarize the potential for sex steroids as useful biomarkers and therapeutic targets in these lung diseases as a basis for future translational research in the area of gender and individualized medicine.

Identification of estrogen-responsive genes based on the DNA binding properties of estrogen receptors using high-throughput sequencing technology

Estrogens are important endocrine hormones that control physiological functions in reproductive organs, and play a pivotal role in the generation and progression of breast cancer. Therapeutic drugs including anti-estrogen and aromatase inhibitors are used to treat patients with breast cancer. The estrogen receptors, ERα and ERβ, function as hormone-dependent transcription factors that directly regulate the expression of their target genes. Therefore, a better understanding of the function and regulation of estrogen-responsive genes provides insight into the gene regulation network associated with breast cancer. Recent technological developments in high-throughput sequencing have enabled the genome-wide identification of estrogen-responsive genes. Further elucidating the estrogen gene cascade is critical for advancements in the diagnosis and treatment of breast cancer.

Road to exercise mimetics: targeting nuclear receptors in skeletal muscle

Skeletal muscle is the largest organ in the human body and is the major site for energy expenditure. It exhibits remarkable plasticity in response to physiological stimuli such as exercise. Physical exercise remodels skeletal muscle and enhances its capability to burn calories, which has been shown to be beneficial for many clinical conditions including the metabolic syndrome and cancer. Nuclear receptors (NRs) comprise a class of transcription factors found only in metazoans that regulate major biological processes such as reproduction, development, and metabolism. Recent studies have demonstrated crucial roles for NRs and their co-regulators in the regulation of skeletal muscle energy metabolism and exercise-induced muscle remodeling. While nothing can fully replace exercise, development of exercise mimetics that enhance or even substitute for the beneficial effects of physical exercise would be of great benefit. The unique property of NRs that allows modulation by endogenous or synthetic ligands makes them bona fide therapeutic targets. In this review, we present an overview of the current understanding of the role of NRs and their co-regulators in skeletal muscle oxidative metabolism and summarize recent progress in the development of exercise mimetics that target NRs and their co-regulators.

An energetic orphan in an endocrine tissue: a revised perspective of the function of estrogen receptor-related receptor alpha in bone and cartilage

Estrogen receptor-related receptor alpha (ERRα) is an orphan nuclear receptor with sequence homology to the estrogen receptors, ERα/β, but it does not bind estrogen. ERRα not only plays a functional role in osteoblasts but also in osteoclasts and chondrocytes. In addition, the ERRs, including ERRα, can be activated by coactivators such as peroxisome proliferator-activated receptor-gamma coactivator-1 (PGC1α and β) and are implicated in adipogenesis, fatty acid oxidation, and oxidative stress defense, suggesting that ERRα-through its activity in bone resorption and adipogenesis--may regulate the insulin and leptin pathways and contribute to aging-related changes in bone and cartilage. In this review, we discuss data on ERRα and its cellular and molecular modes of action, which have broad implications for considering the potential role of this orphan receptor in cartilage and bone endocrine function, on whole-organism physiology, and in the bone aging process.

The biarylpyrazole compound AM251 alters mitochondrial physiology via proteolytic degradation of ERRα

The orphan nuclear receptor estrogen-related receptor alpha (ERRα) directs the transcription of nuclear genes involved in energy homeostasis control and the regulation of mitochondrial mass and function. A crucial role for controlling ERRα-mediated target gene expression has been ascribed to the biarylpyrazole compound 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251) through direct binding to and destabilization of ERRα protein. Here, we provide evidence that structurally related AM251 analogs also have negative impacts on ERRα protein levels in a cell-type-dependent manner while having no deleterious actions on ERRγ. We show that these off-target cellular effects of AM251 are mediated by proteasomal degradation of nuclear ERRα. Cell treatment with the nuclear export inhibitor leptomycin B did not prevent AM251-induced destabilization of ERRα protein, whereas proteasome inhibition with MG132 stabilized and maintained its DNA-binding function, indicative of ERRα being a target of nuclear proteasomal complexes. NativePAGE analysis revealed that ERRα formed a ∼220-kDa multiprotein nuclear complex that was devoid of ERRγ and the coregulator peroxisome proliferator-activated receptor γ coactivator-1. AM251 induced SUMO-2,3 incorporation in ERRα in conjunction with increased protein kinase C activity, whose activation by phorbol ester also promoted ERRα protein loss. Down-regulation of ERRα by AM251 or small interfering RNA led to increased mitochondria biogenesis while negatively impacting mitochondrial membrane potential. These results reveal a novel molecular mechanism by which AM251 and related compounds alter mitochondrial physiology through destabilization of ERRα.

Oestrogen-related receptors in breast cancer: control of cellular metabolism and beyond

Oestrogen-related receptors (ERRs) are orphan nuclear receptors that were initially investigated in breast cancer because of their structural relationship to oestrogen receptors. Recent data have shown that the ERRs control vast gene networks that are involved in glycolysis, glutaminolysis, oxidative phosphorylation, nutrient sensing and biosynthesis pathways. In the context of breast cancer, the ERRs affect cellular metabolism in a manner that promotes a Warburg-like phenotype. The ERRs also modulate breast cancer cell metabolism, growth and proliferation through the regulation of key oncoproteins. We discuss the value but also the implications of the complexity of targeting the ERRs for the development of cancer therapeutics.

Ncoa3 functions as an essential Esrrb coactivator to sustain embryonic stem cell self-renewal and reprogramming

Embryonic stem cell (ESC) pluripotency depends on a well-characterized gene regulatory network centered on Oct4, Sox2, and Nanog. In contrast, little is known about the identity of the key coregulators and the mechanisms by which they may potentiate transcription in ESCs. Alongside core transcription factors, the orphan nuclear receptor Esrrb (estrogen-related receptor β) is vital for the maintenance of ESC identity and furthermore is uniquely associated with the basal transcription machinery. Here, we show that Ncoa3, an essential coactivator, is required to mediate Esrrb function in ESCs. Ncoa3 interacts with Esrrb via its ligand-binding domain and bridges Esrrb to RNA polymerase II complexes. Functionally, Ncoa3 is critical for both the induction and maintenance of pluripotency. Through chromatin immunoprecipitation (ChIP) sequencing and microarray experiments, we further demonstrate that Ncoa3 shares overlapping gene regulatory functions with Esrrb and cooperates genome-wide with the Oct4-Sox2-Nanog circuitry at active enhancers to up-regulate genes involved in self-renewal and pluripotency. We propose an integrated model of transcriptional and coactivator control, mediated by Ncoa3, for the maintenance of ESC self-renewal and somatic cell reprogramming.

Transcriptional activation of breast cancer-associated gene 2 by estrogen receptor

RNF115, or Breast Cancer-Associated Gene 2 (BCA2), encodes a RING-finger ubiquitin E3 ligase, expression of which was associated with estrogen receptor (ER)-positive status in human breast tumors. Although the BCA2 promoter contains several estrogen response element (ERE) half-sites, the role of ER in the regulation of BCA2 transcription has not been reported. The aim of this study is to investigate the molecular mechanism by which estrogen regulates BCA2 transcription. BCA2 mRNA and protein levels were examined by RT-PCR and Western blot analysis, respectively, and localization was assessed by immunofluorescence. BCA2 promoter activity in response to E(2) was tested by a dual luciferase reporter assay and ER binding to the BCA2 promoter was examined by chromatin immunoprecipitation assay. We found that BCA2 mRNA and protein levels are regulated by estrogen in ER-positive MCF7 breast cancer cells and MDA MB 231 cells stably transfected with ER. Estrogen treatment in hormonal depleted MCF7 and MDA MB 231/ER stably transfected cells resulted in increased nuclear ER and cytoplasmic and nuclear BCA2 staining. Cycloheximide is not able to inhibit BCA2 mRNA levels, suggesting potential BCA2 regulation at the transcriptional level. Anti-estrogens like tamoxifen and ICI 182 178 counteracted E(2)-induced BCA2 protein and knockdown of ER by ER siRNA resulted in a significant decrease in BCA2 protein and a lower nuclear expression pattern. Estrogen treatment lead to a significant increase in BCA2 promoter response, associated with increased binding of ER to the ERE region of the BCA2 promoter. BCA2 is therefore a newly identified transcriptional target of estrogen receptor.

Estrogen-related receptor alpha: an orphan finds a family

Identification of molecules and their effectors has led to new therapies designed to specifically inhibit pathways in molecularly defined breast cancer subtypes. An orphan nuclear receptor, estrogen-related receptor alpha, has been shown to be a downstream target of two tyrosine kinase growth factor receptors: human epidermal growth factor receptor 2 and the type I insulin-like growth factor receptor. Identifying the mechanistic actions of orphan nuclear receptors could lead to new biomarkers and molecular targets in malignancy.

Estrogen-related receptor α regulates osteoblast differentiation via Wnt/β-catenin signaling

Based on its homology to the estrogen receptor and its roles in osteoblast and chondrocyte differentiation, the orphan nuclear receptor estrogen-related receptor α (ERRα (ESRRA)) is an intriguing therapeutic target for osteoporosis and other bone diseases. The objective of this study was to better characterize the molecular mechanisms by which ERRα modulates osteoblastogenesis. Experiments from multiple systems demonstrated that ERRα modulates Wnt signaling, a crucial pathway for proper regulation of bone development. This was validated using a Wnt-luciferase reporter, where ERRα showed co-activator-dependent (peroxisome proliferator-activated receptor gamma co-activator 1α, PGC-1α) stimulatory effects. Interestingly, knockdown of ERRα expression also enhanced WNT signaling. In combination, these data indicated that ERRα could serve to either activate or repress Wnt signaling depending on the presence or absence of its co-activator PGC-1α. The observed Wnt pathway modulation was cell intrinsic and did not alter β-catenin nuclear translocation but was dependent on DNA binding of ERRα. We also found that expression of active ERRα correlated with Wnt pathway effects on osteoblastic differentiation in two cell types, consistent with a role for ERRα in modulating the Wnt pathway. In conclusion, this work identifies ERRα, in conjunction with co-activators such as PGC-1α, as a new regulator of the Wnt-signaling pathway during osteoblast differentiation, through a cell-intrinsic mechanism not affecting β-catenin nuclear translocation.

Binding of the ERα and ARNT1 AF2 domains to exon 21 of the SRC1 isoform SRC1e is essential for estrogen- and dioxin-related transcription

Steroid receptor co-activator 1 (SRC1) is a transcriptional co-activator of numerous transcription factors involving nuclear receptors. Aryl hydrocarbon receptor nuclear translocator 1 (ARNT1) is an obligatory transcriptional partner of the aryl hydrocarbon receptor (AhR) and hypoxia inducible factor-1α (HIF-1α), as well as a co-activator of estrogen receptors (ERs). To initiate transcription, the activation function 2 (AF2) domains of estrogen-activated ERs interact with LxxLL motifs in the nuclear receptor interaction domain (NID) of SRC1. Here we describe an estrogen and LxxLL domain-independent ERα AF2 binding to SRC1e exon 21. In addition, we found an AF2 domain in exon 16 of ARNT1 that also binds to SRC1e exon 21. Surprisingly, the interaction between SRC1e exon 21 and the AF2 domain of ERα functions as a crucial enhancer of estrogen-induced transcription. The binding of ARNT1 AF2 to SRC1e exon 21 enhances the transcriptional response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), but the upregulation essentially depends on two cyclin destruction boxes (D-boxes), which are also located on exon 16 of ARNT1. Our findings reveal that a binding site for ERα and ARNT1 AF2 domains in the C-terminus of SRC1e upregulates estrogen- and TCDD-related responses in mammalian cells.

Underlying mechanisms for LTF inactivation and its functional analysis in nasopharyngeal carcinoma cell lines

The lactoferrin (LTF) gene, located at 3p21.3, behaves like a tumor suppressor gene in diverse tumors. To elucidate the exact role of LTF in NPC, we first detected its expression level in seven NPC cell lines by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The results showed the mRNA level of LTF was nearly undetectable in all the seven NPC cell lines, while it could be detected in chronic nasopharyngitis tissues. Subsequently, we used methylation-specific PCR (MSP), microsatellite assay, PCR-single-strand conformation polymorphism (PCR-SSCP) and sequencing methods to examine the promoter methylation, loss of heterozygosity (LOH) and gene mutation of LTF in NPC cell lines respectively. Consequently, we found that 100% (7 of 7) of NPC cell lines were methylated in LTF promoter, only one cell line (14%, 1 of 7) had LOH and gene mutation of LTF, respectively, while LTF exhibited re-expression in all cell lines after 5-aza-dC treatment, indicating promoter methylation should be the key mechanism causing LTF downregulation in NPC cell lines. Furthermore, patched methylation assay confirmed that promoter methylation could down-regulate LTF gene expression in NPC cells. Finally, we investigated the function of LTF in NPC cell lines by gene transfection. Restoration of LTF expression in NPC cells resulted in blockage of cell cycle progression, significant inhibition of cell growth and a reduced colony-formation capacity in vitro and obviously weaker tumor formation potential in vivo. In conclusion, our data indicate LTF may participate in NPC carcinogenesis as a negative effector, that is, a tumor suppressor gene.

Estrogens and prostate cancer: etiology, mediators, prevention, and management

The mainstay targets for hormonal prostate cancer (PCa) therapies are based on negating androgen action. Recent epidemiologic and experimental data have pinpointed the key roles of estrogens in PCa development and progression. Racial and geographic differences, as well as age-associated changes, in estrogen synthesis and metabolism contribute significantly to the etiology. This article summarizes how different estrogens/antiestrogens/estrogen mimics contribute to prostate carcinogenesis, the roles of the different mediators of estrogen in the process, and the potentials of new estrogenic/antiestrogenic compounds for prevention and treatment of PCa.

Expanding the paradigm for estrogen receptor binding and transcriptional activation

Estrogen receptor (ER) binds to a spectrum of functional estrogen response elements (ERE) within the human genome, including ERE half-sites (HERE), inverted and direct repeats. This has been confounding, because ER has been reported to bind weakly, if at all, to these sites in vitro. We show that ER binds strongly to these nonconventional EREs, and the binding is enhanced by the presence of high-mobility group protein B1 (HMGB1). Collectively, these and previous findings reinforce the notion of the plasticity of strong ER/ERE interactions, consistent with their broader range of observed binding specificity. In addition, transient transfection studies using luciferase reporter gene assays show that these EREs drive luciferase activity, and HMGB1 enhances transcriptional activity. Furthermore, HMGB1 gene expression knockdown results in a precipitous drop in luciferase activity, suggesting a prominent role for HMGB1 in activation of estrogen/ER-responsive genes. Therefore, these data advocate that the minimal target site for ER is a cHERE (consensus HERE) that occurs in many different contexts and that HMGB1 enhances both the binding affinity and transcriptional activity. This challenges the current paradigm for ER binding affinity and functional activity and suggests that the paradigm requires significant reevaluation and modification. These findings also suggest a possible mechanism for a cross talk between genes regulated by ER and class II nuclear receptors.

Estrogen receptor-related receptor alpha mediates up-regulation of aromatase expression by prostaglandin E2 in prostate stromal cells

Estrogen receptor-related receptor alpha (ERRalpha) is an orphan member of the nuclear receptor superfamily of transcription factors. ERRalpha is highly expressed in the prostate, especially in prostate stromal cells. However, little is known about the regulation and function of ERRalpha, which may contribute to the progression of prostatic diseases. We previously found that prostaglandin E2 (PGE2) up-regulated the expression of aromatase in prostate stromal cells. Here we show that PGE2 also up-regulates the expression of ERRalpha, which, as a transcription factor, further mediates the regulatory effects of PGE2 on the expression of aromatase. ERRalpha expression was up-regulated by PGE2 in prostate stromal cell line WPMY-1, which was mediated mainly through the protein kinase A signaling pathway by PGE2 receptor EP2. Suppression of ERRalpha activity by chlordane (an antagonist of ERRalpha) or small interfering RNA knockdown of ERRalpha blocked the increase of expression and promoter activity of aromatase induced by PGE2. Overexpression of ERRalpha significantly increased aromatase expression and promoter activity, which were further augmented by PGE2. Chromatin immunoprecipitation assay demonstrated that ERRalpha directly bound to the aromatase promoter in vivo, and PGE2 enhanced the recruitment of ERRalpha and promoted transcriptional regulatory effects on aromatase expression in WPMY-1. 17Beta-estradiol concentration in WPMY-1 medium was up-regulated by ERRalpha expression, and that was further increased by PGE2. Our results provided evidence that ERRalpha contributed to local estrogen production by up-regulating aromatase expression in response to PGE2 and provided further insights into the potential role of ERRalpha in estrogen-related prostatic diseases.

Regulation of ERRalpha gene expression by estrogen receptor agonists and antagonists in SKBR3 breast cancer cells: differential molecular mechanisms mediated by g protein-coupled receptor GPR30/GPER-1

In selected tissues and cell lines, 17beta-estradiol (E2) regulates the expression of estrogen-related receptor alpha (ERRalpha), a member of the orphan nuclear receptor family. This effect is thought to be mediated by the estrogen receptor alpha (ERalpha). However in the ERalpha- and ERbeta-negative SKBR3 breast cancer cell line, physiological levels of E2 also stimulate ERRalpha expression. Here, we explored the molecular mechanism that mediates estrogen action in ER-negative breast cancer cells. We observed that E2, the ERalpha agonist, as well as the ERalpha antagonists ICI 182,780 and tamoxifen (TAM), a selective ER modulator, stimulate the transcriptional activity of the ERRalpha gene and increase the production of ERRalpha protein in SKBR3 cells. Moreover, the ERRalpha downstream target genes expression and cellular proliferation are also increased. We show further that the G protein-coupled receptor GPR30/GPER-1 (GPER-1) mediates these effects. The GPER-1 specific ligand G-1 mimics the actions of E2, ICI 182,780, and TAM on ERRalpha expression, and changing the levels of GPER-1 mRNA by overexpression or small interfering RNA knockdown affected the expression of ERRalpha accordingly. Utilizing inhibitors, we delineate a different downstream pathway for ER agonist and ER antagonist-triggered signaling through GPER-1. We also find differential histone acetylation and transcription factor recruitment at distinct nucleosomes of the ERRalpha promoter, depending on whether the cells are activated with E2 or with ER antagonists. These findings provide insight into the molecular mechanisms of GPER-1/ERRalpha-mediated signaling and may be relevant to what happens in breast cancer cells escaping inhibitory control by TAM.

cAMP enhances estrogen-related receptor alpha (ERRalpha) transcriptional activity at the SP-A promoter by increasing its interaction with protein kinase A and steroid receptor coactivator 2 (SRC-2)

Estrogen-related receptor (ERRalpha) plays a critical role in basal and cAMP-induced expression of the human surfactant protein-A (SP-A) gene in lung type II cells through direct binding to an ERR response element (ERRE, 5'-TGACCTTA-3') within its 5'-flanking region. Furthermore, protein kinase A (PKA) up-regulates ERRalpha activation of the hSP-A promoter. In the present study, using cultured human fetal lung type II cells, we observed that cAMP enhanced ERRalpha phosphorylation and nuclear expression levels. cAMP/PKA stimulation of ERRalpha activation of the SP-A promoter was blocked by the PKA inhibitor, H89, whereas the MAPK P38 inhibitor, SB203580, and the MAPK kinase inhibitor, PD98059, had negligible to modest effects. This suggests that cAMP acts selectively through PKA to increase ERRalpha transcriptional activity. Of several coactivators tested, steroid receptor coactivator 2 (SRC-2) had the most pronounced effect to increase ERRalpha transcriptional activity at the SP-A promoter; this was enhanced by cotransfection with PKA catalytic subunit (PKAcat). Interestingly, SRC-2, ERRalpha, and PKAcat in type II cell nuclear extracts interacted at the ERRE; this was enhanced by cAMP and inhibited by H89. cAMP increased in vivo binding of PKAcat and SRC-2 to the ERRE genomic region in lung type II cells. In mutagenesis studies, three serines (S87, S114, and S277) were found to be critical for PKA and SRC-2 induction of ERRalpha transcriptional activity. Collectively, these findings indicate that cAMP/PKA signaling enhances ERRalpha phosphorylation and nuclear localization, recruitment to the SP-A promoter, and interaction with PKAcat and SRC-2, resulting in the up-regulation of SP-A gene transcription.

Characterization of a novel small molecule subtype specific estrogen-related receptor alpha antagonist in MCF-7 breast cancer cells

BACKGROUND

The orphan nuclear receptor estrogen-related receptor alpha (ERRalpha) is a member of the nuclear receptor superfamily. It was identified through a search for genes encoding proteins related to estrogen receptor alpha (ERalpha). An endogenous ligand has not been found. Novel ERRalpha antagonists that are highly specific for binding to the ligand binding domain (LBD) of ERRalpha have been recently reported. Research suggests that ERRalpha may be a novel drug target to treat breast cancer and/or metabolic disorders and this has led to an effort to characterize the mechanisms of action of N-[(2Z)-3-(4,5-dihydro-1,3-thiazol-2-yl)-1,3-thiazolidin-2-yl idene]-5H dibenzo[a,d][7]annulen-5-amine, a novel ERRalpha specific antagonist.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrate this ERRalpha ligand inhibits ERRalpha transcriptional activity in MCF-7 cells by luciferase assay but does not affect mRNA levels measured by real-time RT-PCR. Also, ERalpha (ESR1) mRNA levels were not affected upon treatment with the ERRalpha antagonist, but other ERRalpha (ESRRA) target genes such as pS2 (TFF1), osteopontin (SPP1), and aromatase (CYP19A1) mRNA levels decreased. In vitro, the ERRalpha antagonist prevents the constitutive interaction between ERRalpha and nuclear receptor coactivators. Furthermore, we use Western blots to demonstrate ERRalpha protein degradation via the ubiquitin proteasome pathway is increased by the ERRalpha-subtype specific antagonist. We demonstrate by chromatin immunoprecipitation (ChIP) that the interaction between ACADM, ESRRA, and TFF1 endogenous gene promoters and ERRalpha protein is decreased when cells are treated with the ligand. Knocking-down ERRalpha (shRNA) led to similar genomic effects seen when MCF-7 cells were treated with our ERRalpha antagonist.

CONCLUSIONS/SIGNIFICANCE

We report the mechanism of action of a novel ERRalpha specific antagonist that inhibits transcriptional activity of ERRalpha, disrupts the constitutive interaction between ERRalpha and nuclear coactivators, and induces proteasome-dependent ERRalpha protein degradation. Additionally, we confirmed that knocking-down ERRalpha lead to similar genomic effects demonstrated in vitro when treated with the ERRalpha specific antagonist.

Estrogen-related receptor-alpha antagonist inhibits both estrogen receptor-positive and estrogen receptor-negative breast tumor growth in mouse xenografts

Estrogen-related receptors (ERR) are orphan members of the nuclear receptor superfamily most closely related to estrogen receptors (ER). Although ERalpha is a successful target for treating breast cancer, there remains an unmet medical need especially for estrogen-independent breast cancer. Although estradiol is not an ERR ligand, ER and ERR share many commonalities and overlapping signaling pathways. An endogenous ERR ligand has not been identified; however, novel synthetic ERRalpha subtype-specific antagonists have started to emerge. In particular, we recently identified a novel compound, N-[(2Z)-3-(4,5-dihydro-1,3-thiazol-2-yl)-1,3-thiazolidin-2-yl idene]-5H dibenzo[a,d][7]annulen-5-amine (termed compound A) that acts specifically as an ERRalpha antagonist. Here, we show that compound A inhibited cell proliferation in ERalpha-positive (MCF-7 and T47D) and ERalpha-negative (BT-20 and MDA-MD-231) breast cancer cell lines. Furthermore, we report the differential expression of 83 genes involved in ERRalpha signaling in MCF-7 and BT-20 breast cancer cell lines. We show that compound A slowed tumor growth in MCF-7 and BT-20 mouse xenograft models, and displayed antagonistic effects on the uterus. Furthermore, a subset of genes involved in ERRalpha signaling in vitro were evaluated and confirmed in vivo by studying uterine gene expression profiles from xenograft mice. These results suggest for the first time that inhibition of ERRalpha signaling via a subtype-specific antagonist may be an effective therapeutic strategy for ER-positive and ER-negative breast cancers.

The significance of the expression of ERRalpha as a potential biomarker in breast cancer

It was shown the functional crosstalk between ERRalpha and ERalpha in breast cancer, however, the biological significance of estrogen-related receptor alpha (ERRalpha) remains largely unclear. Therefore, we examined the expression of ERRalpha in 39 primary human breast cancer tissues and 19 matched normal tissues using RT-PCR and immunohistochemistry in the context of the aromatase, ERalpha and proliferation markers (c-myc, Ki-67) expression. Compared to the normal breast tissue, breast cancer tissues showed a slightly higher expression level of ERRalpha mRNA (mean 46.2+/-S.D.42.0, 57.7+/-S.D.58.7, respectively). However, ERRalpha mRNA levels in breast cancer tissues showed greater diversity than in normal tissues. Immunohistochemical analysis of breast cancers revealed perinuclear and cytoplasmic localization of ERRalpha. Our study shows that there is no correlation between ERRalpha and ERalpha expression. We demonstrated a positive correlation between ERRalpha and c-myc at the transcriptional level and statistically significant positive correlation between aromatase and the ERRalpha at protein level. It seems that ERRalpha could play an important role in the alternative pathway to classical estrogen receptors-dependent pathway in cell signaling. Development and use of ERRs modulators might lead in the future to design new well-tolerated and individualized therapeutic agents.

PGC-1alpha induces dynamic protein interactions on the ERRalpha gene multi-hormone response element nucleosome in kidney cells

ERR (oestrogen-related receptor)-alpha modulates the oestrogen signalling pathway and regulates genes participating in the physiological energy balance programme. Oestrogen and PGC-1alpha (peroxisome proliferator-activated receptor-gamma coactivator-1alpha), the master regulator of the energy homoeostasis programme, both regulate the expression of ERRalpha through the MHRE (multi-hormone response element) of the ERRalpha gene. Although the molecular mechanism of oestrogen action on ERRalpha regulation is well characterized, the mechanism of PGC-1alpha induction is unclear. In this study, we examine chromatin structural changes and protein interactions at the MHRE nucleosome in response to PGC-1alpha expression in HK2 human kidney cells. We mapped the nucleosome positions of the ERRalpha gene promoter and examined the changes of histone acetylation in response to PGC-1alpha expression. The interactions of DNA-binding proteins, ERRalpha and ERRgamma, co-activators {CBP [CREB (cAMP-response-element-binding protein)-binding protein], p300, PCAF (p300/CBP-associated factor)}, co-repressor [RIP140 (receptor-interacting protein of 140 kDa)] and RNA polymerase II at the MHRE nucleosome region were investigated over time before and after PGC-1alpha expression in the HK2 cells. We found a dynamic cyclic interaction of these proteins shortly after PGC-1alpha expression and a slower cycling interaction, with fewer proteins involved, 20 h later. By using the siRNA (small interfering RNA) knockdown approach, we discovered that ERRgamma was involved in the initial phase, but not in the later phase, of PGC-1alpha-induced ERRalpha expression.