Constitutive activation of transcription and binding of coactivator by estrogen-related receptors 1 and 2

The intersection between menopause and depression: overview of research using animal models

Menopausal women may experience symptoms of depression, sometimes even progressing clinical depression requiring treatment to improve quality of life. While varying levels of estrogen in perimenopause may contribute to an increased biological vulnerability to mood disturbances, the effectiveness of estrogen replacement therapy (ERT) in the relief of depressive symptoms remains controversial. Menopausal depression has a complex, multifactorial etiology, that has limited the identification of optimal treatment strategies for the management of this psychiatric complaint. Nevertheless, clinical evidence increasingly supports the notion that estrogen exerts neuroprotective effects on brain structures related to mood regulation. Indeed, research using preclinical animal models continues to improve our understanding of menopause and the effectiveness of ERT and other substances at treating depression-like behaviors. However, questions regarding the efficacy of ERT in perimenopause have been raised. These questions may be answered by further investigation using specific animal models of reduced ovarian function. This review compares and discusses the advantages and pitfalls of different models emulating the menopausal stages and their relationship with the onset of depressive-like signs, as well as the efficacy and mechanisms of conventional and novel ERTs in treating depressive-like behavior. Ovariectomized young rats, middle-to-old aged intact rats, and females treated with reprotoxics have all been used as models of menopause, with stages ranging from surgical menopause to perimenopause. Additionally, this manuscript discusses the impact of organistic and therapeutic variables that may improve or reduce the antidepressant response of females to ERT. Findings from these models have revealed the complexity of the dynamic changes occurring in brain function during menopausal transition, reinforcing the idea that the best approach is timely intervention considering the opportunity window, in addition to the careful selection of treatment according to the presence or absence of reproductive tissue. Additionally, data from animal models has yielded evidence to support new promising estrogens that could be considered as ERTs with antidepressant properties and actions in endocrine situations in which traditional ERTs are not effective.

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.

Novel Pan-ERR Agonists Ameliorate Heart Failure Through Enhancing Cardiac Fatty Acid Metabolism and Mitochondrial Function

BACKGROUND

Cardiac metabolic dysfunction is a hallmark of heart failure (HF). Estrogen-related receptors ERRα and ERRγ are essential regulators of cardiac metabolism. Therefore, activation of ERR could be a potential therapeutic intervention for HF. However, in vivo studies demonstrating the potential usefulness of ERR agonist for HF treatment are lacking, because compounds with pharmacokinetics appropriate for in vivo use have not been available.

METHODS

Using a structure-based design approach, we designed and synthesized 2 structurally distinct pan-ERR agonists, SLU-PP-332 and SLU-PP-915. We investigated the effect of ERR agonist on cardiac function in a pressure overload-induced HF model in vivo. We conducted comprehensive functional, multi-omics (RNA sequencing and metabolomics studies), and genetic dependency studies both in vivo and in vitro to dissect the molecular mechanism, ERR isoform dependency, and target specificity.

RESULTS

Both SLU-PP-332 and SLU-PP-915 significantly improved ejection fraction, ameliorated fibrosis, and increased survival associated with pressure overload-induced HF without affecting cardiac hypertrophy. A broad spectrum of metabolic genes was transcriptionally activated by ERR agonists, particularly genes involved in fatty acid metabolism and mitochondrial function. Metabolomics analysis showed substantial normalization of metabolic profiles in fatty acid/lipid and tricarboxylic acid/oxidative phosphorylation metabolites in the mouse heart with 6-week pressure overload. ERR agonists increase mitochondria oxidative capacity and fatty acid use in vitro and in vivo. Using both in vitro and in vivo genetic dependency experiments, we show that ERRγ is the main mediator of ERR agonism-induced transcriptional regulation and cardioprotection and definitively demonstrated target specificity. ERR agonism also led to downregulation of cell cycle and development pathways, which was partially mediated by E2F1 in cardiomyocytes.

CONCLUSIONS

ERR agonists maintain oxidative metabolism, which confers cardiac protection against pressure overload-induced HF in vivo. Our results provide direct pharmacologic evidence supporting the further development of ERR agonists as novel HF therapeutics.

ERRα Attenuates Vascular Inflammation via Enhanced NFκB Degradation Pathway

We have previously reported that β-aminoisobutyric acid (BAIBA), a muscle-derived exercise mimetic, had anti-inflammatory and reactive oxygen species (ROS) scavenging effects in vascular endothelial cells through the enhanced expression of peroxisome proliferator-activated receptor gamma coactivator-1β (PGC-1β). Although BAIBA also increased the expression of estrogen-related receptor α (ERRα), the roles of ERRα in vascular endothelial cells have yet to be fully elucidated. Here, we found that human aortic endothelial cells (HAECs) infected with ERRα-expressing adenovirus had significantly decreased mRNA levels of tumor necrosis factor α-stimulated proinflammatory molecules. However, ERRα overexpression had little effect on the mRNA levels of PGC-1β, peroxisome proliferator-activated receptors, and almost all ROS scavenging molecules, except for superoxide dismutase 2. ERRα expression significantly decreased NFκB reporter activities in a dose-dependent manner with unaltered IκBα phosphorylation levels but with a significant increase in the mRNA levels of PDZ and LIM domain protein 2 (PDLIM2) and copper metabolism gene MURR1 domain-containing protein (COMMD1), which enhance the ubiquitination and degradation of NFκB. Also, PDLIM2 and COMMD1 mRNA levels were upregulated in BAIBA-treated HAECs. Finally, we identified the ERRα-response element in the COMMD1 promoter region (-283 to -29 bp). These results indicated that ERRα exerted anti-inflammatory effects in vascular endothelial cells through COMMD1-mediated attenuation of NFκB activity, which could be an atheroprotective mechanism of physical exercise.

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 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.

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.

Structural Insights into the Specificity of Ligand Binding and Coactivator Assembly by Estrogen-Related Receptor β

Estrogen-related receptor β (ERRβ) is a nuclear receptor critical for many biological processes. Despite the biological and pharmaceutical importance of ERRβ, deciphering the structure of ERRβ has been hampered by the difficulties in obtaining a pure and stable protein for structural studies. In fact, the ERRβ ligand-binding domain remains the last unsolved ERR structure and also one of only a few unknown nuclear receptor structures. Here, we report the identification of a critical single-residue mutation resulted in robust solubility and stability of an active ERRβ ligand-binding domain, thereby providing a protein tool enabling the first probe into the biochemical and structural studies of this important receptor. The crystal structure reveals key structural features that have enabled the integration of the molecular determinants of signals transduced across the ligand binding and coregulator recruitment by all three ERR subtypes, which also provides a framework for the rational design of selective and potent ligands for the treatment of various ERR-mediated diseases.

Evaluation of the Influence of Halogenation on the Binding of Bisphenol A to the Estrogen-Related Receptor γ

Halogenation of organic compounds is one the most important transformations in chemical synthesis and is used for the production of various industrial products. A variety of halogenated bisphenol analogs have recently been developed and are used as alternatives to bisphenol A (BPA), which is a raw material of polycarbonate that has adverse effects in animals. However, limited information is available on the potential toxicity of the halogenated BPA analogs. In the present study, to assess the latent toxicity of halogenated BPA analogs, we evaluated the binding and transcriptional activities of halogenated BPA analogs to the estrogen-related receptor γ (ERRγ), a nuclear receptor that contributes to the growth of nerves and sexual glands. Fluorinated BPA analogs demonstrated strong ERRγ binding potency, and inverse antagonistic activity, similar to BPA. X-ray crystallography and fragment molecular orbital (FMO) calculation revealed that a fluorine-substituted BPA analog could interact with several amino acid residues of ERRγ-LBD, strengthening the binding affinity of the analogs. The ERRγ binding affinity and transcriptional activity of the halogenated BPAs decreased with the increase in the size and number of halogen atom(s). The IC₅₀ values, determined by the competitive binding assay, correlated well with the binding energy obtained from the docking calculation, suggesting that the docking calculation could correctly estimate the ERRγ binding potency of the BPA analogs. These results confirmed that ERRγ has a ligand binding pocket that fits very well to BPA. Furthermore, this study showed that the binding affinity of the BPA analogs can be predicted by the docking calculation, indicating the importance of the calculation method in the risk assessment of halogenated compounds.

Receptor-binding affinities of bisphenol A and its next-generation analogs for human nuclear receptors

An endocrine-disrupting chemical Bisphenol A (BPA) binds specifically to a nuclear receptor (NR) named ERRγ. Although the importance of receptor-binding evaluation for human NRs is often stressed, the binding characteristics of so-called next-generation (NextGen) bisphenol compounds are still poorly understood. The ultimate objective of this investigation was to evaluate BPA and its NextGen analogs for their abilities to bind to 21 human NRs, the greatest members of NRs for which tritium-labeled specific ligands were available. After establishing the detailed assay conditions for each NR, the receptor binding affinities of total 11 bisphenols were evaluated in competitive binding assays. The results clearly revealed that BPA and the NextGen bisphenols of BPAF, BPAP, BPB, BPC, BPE, and BPZ were highly potent against one or more of NRs such as CAR, ERα, ERβ, ERRγ, and GR, with IC₅₀ values of 3.3-73 nM. These bisphenols were suggested strongly to be disruptive to these NRs. BPM and BPP also appeared to be disruptive, but less potently. BPF exhibited only weak effects and only against estrogen-related NRs. Surprisingly, most doubtful bisphenol BPS was supposed not to be disruptive. The NRs to which BPA and NextGen bisphenols did not bind were RARα, RARβ, RARγ, and VDR. PPARγ, RORα, RORβ, RORγ, RXRα, RXRβ, and RXRγ, exhibited very weak interaction with these bisphenols. The ten remaining NRs, namely, ERRγ, ERβ, ERα, CAR, GR, PXR, PR, AR, LXRβ, and LXRα, showed distinctly strong binding to some bisphenols in this order, being likely to have consequential endocrine-disruption effects.

PGC1α Inhibits Polyamine Synthesis to Suppress Prostate Cancer Aggressiveness

Although tumorigenesis is dependent on the reprogramming of cellular metabolism, the metabolic pathways engaged in the formation of metastases remain largely unknown. The transcriptional coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) plays a pleiotropic role in the control of cancer cell metabolism and has been associated with a good prognosis in prostate cancer. Here, we show that PGC1α represses the metastatic properties of prostate cancer cells via modulation of the polyamine biosynthesis pathway. Mechanistically, PGC1α inhibits the expression of c-MYC and ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme for polyamine synthesis. Analysis of in vivo metastases and clinical data from patients with prostate cancer support the proposition that the PGC1α/c-MYC/ODC1 axis regulates polyamine biosynthesis and prostate cancer aggressiveness. In conclusion, downregulation of PGC1α renders prostate cancer cells dependent on polyamine to promote metastasis. SIGNIFICANCE: These findings show that a major regulator of mitochondrial metabolism controls polyamine synthesis and prostate cancer aggressiveness, with potential applications in therapy and identification of new biomarkers.

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.

Evidence for a role of oestrogen receptor-related receptor in the regulation of male sexual behaviour in the moth Agrotis ipsilon

The oestrogen receptor-related receptors (ERRs) are orphan nuclear receptors that were originally identified on the basis of their close homology to the oestrogen receptors. The three mammalian ERR genes participate in the regulation of vital physiological processes including reproduction, development and metabolic homeostasis. Although unique ERRs have been found in insects, data on the function and regulation of these receptors remain sparse. In the present study, a 2095-bp full-length cDNA encoding an ERR, termed AiERR, was isolated from males of the moth Agrotis ipsilon and deposited in the GenBank database under the accession number KT944662. The predicted AiERR protein shared an overall identity of 47-82% with other known insect and mammalian ERR homologues. AiERR exhibited a broad tissue expression pattern with the detection of one transcript of approximately 2 kb in the primary olfactory centres, the antennal lobes (AL). In adult males, the amount of AiERR mRNA in the AL increased concomitantly with age and responses to the female-emitted sex pheromone. Moreover, AiERR knockdown induced an inhibition in the sex pheromone-orientated flight of male. Using A. ipsilon as a model, our study demonstrates that the insect ERR is critical for the performance of male sexual behaviour, probably by acting on central pheromone processing.

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.

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.

α-Helix-peptides comprising the human nuclear receptor ERRγ competitively provoke inhibition of functional homomeric dimerization

Estrogen-related receptor γ (ERRγ) is a constitutively active nuclear receptor functioning as a transcription factor. ERRγ binds to a single half site designated as ERRE that has only a single DNA-binding motif. However, with regard to the subunit structure, it remains a matter of controversy whether ERRγ binds as a monomer or dimer. Because the ligand-binding domain (LBD) of ERRγ was in a homodimer form in its X-ray crystal structure, the peptide fragments present in the dimer interfaces would perturb or destabilize the dimer structure by inhibiting the mutual interaction among ERRγ molecules. Thus, to demonstrate the essential homodimer structure of ERRγ, we utilized the peptides corresponding to the α-helix peptides 7 (H7), H9, and H10/11 in order to test such inhibitor activity. These selections were done based on a structural analysis of the X-ray crystal structures of ERRγ-LBD, which forms a head-to-head dimer structure. Peptides were evaluated by means of a luciferase reporter gene assay, in which ERRγ exhibited a high constitutive activity with no ligand. When the peptide was expressed in the HeLa cells together with ERRγ, these peptides clearly showed a concentration-dependent activity inhibition, indicating that ERRγ is indeed homodimerized as required for DNA transcription activity. The present results strongly suggest that human nuclear receptor ERRγ functions as a genuine homomeric dimer with symmetrical dimeric interface regions. © 2015 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 547-554, 2016.

Importance of the Sequence-Directed DNA Shape for Specific Binding Site Recognition by the Estrogen-Related Receptor

Most nuclear receptors (NRs) bind DNA as dimers, either as hetero- or as homodimers on DNA sequences organized as two half-sites with specific orientation and spacing. The dimerization of NRs on their cognate response elements (REs) involves specific protein-DNA and protein-protein interactions. The estrogen-related receptor (ERR) belongs to the steroid hormone nuclear receptor (SHR) family and shares strong similarity in its DNA-binding domain (DBD) with that of the estrogen receptor (ER). In vitro, ERR binds with high affinity inverted repeat REs with a 3-bps spacing (IR3), but in vivo, it preferentially binds to single half-site REs extended at the 5'-end by 3 bp [estrogen-related response element (ERREs)], thus explaining why ERR was often inferred as a purely monomeric receptor. Since its C-terminal ligand-binding domain is known to homodimerize with a strong dimer interface, we investigated the binding behavior of the isolated DBDs to different REs using electrophoretic migration, multi-angle static laser light scattering (MALLS), non-denaturing mass spectrometry, and nuclear magnetic resonance. In contrast to ER DBD, ERR DBD binds as a monomer to EREs (IR3), such as the tff1 ERE-IR3, but we identified a DNA sequence composed of an extended half-site embedded within an IR3 element (embedded ERRE/IR3), where stable dimer binding is observed. Using a series of chimera and mutant DNA sequences of ERREs and IR3 REs, we have found the key determinants for the binding of ERR DBD as a dimer. Our results suggest that the sequence-directed DNA shape is more important than the exact nucleotide sequence for the binding of ERR DBD to DNA as a dimer. Our work underlines the importance of the shape-driven DNA readout mechanisms based on minor groove recognition and electrostatic potential. These conclusions may apply not only to ERR but also to other members of the SHR family, such as androgen or glucocorticoid, for which a strong well-conserved half-site is followed by a weaker one with degenerated sequence.

The Genomic Context and Corecruitment of SP1 Affect ERRα Coactivation by PGC-1α in Muscle Cells

The peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) coordinates the transcriptional network response to promote an improved endurance capacity in skeletal muscle, eg, by coactivating the estrogen-related receptor-α (ERRα) in the regulation of oxidative substrate metabolism. Despite a close functional relationship, the interaction between these 2 proteins has not been studied on a genomic level. We now mapped the genome-wide binding of ERRα to DNA in a skeletal muscle cell line with elevated PGC-1α and linked the DNA recruitment to global PGC-1α target gene regulation. We found that, surprisingly, ERRα coactivation by PGC-1α is only observed in the minority of all PGC-1α recruitment sites. Nevertheless, a majority of PGC-1α target gene expression is dependent on ERRα. Intriguingly, the interaction between these 2 proteins is controlled by the genomic context of response elements, in particular the relative GC and CpG content, monomeric and dimeric repeat-binding site configuration for ERRα, and adjacent recruitment of the transcription factor specificity protein 1. These findings thus not only reveal a novel insight into the regulatory network underlying muscle cell plasticity but also strongly link the genomic context of DNA-response elements to control transcription factor-coregulator interactions.

Estrogen-related receptor β (ERRβ) - renaissance receptor or receptor renaissance?

Estrogen-related receptors (ERRs) are founding members of the orphan nuclear receptor (ONR) subgroup of the nuclear receptor superfamily. Twenty-seven years of study have yet to identify cognate ligands for the ERRs, though they have firmly placed ERRα and ERRγ at the intersection of cellular metabolism and oncogenesis. The pace of discovery for novel functions of ERRβ, however, has until recently been somewhat slower than that of its family members. ERRβ has also been largely ignored in summaries and perspectives of the ONR literature. Here, we provide an overview of established and emerging knowledge of ERRβ in mouse, man, and other species, highlighting unique aspects of ERRβ biology that set it apart from the other two estrogen-related receptors, with a focus on the impact of alternative splicing on the structure and function of this receptor.

Role of Nuclear Receptors in Central Nervous System Development and Associated Diseases

The nuclear hormone receptor (NHR) superfamily is composed of a wide range of receptors involved in a myriad of important biological processes, including development, growth, metabolism, and maintenance. Regulation of such wide variety of functions requires a complex system of gene regulation that includes interaction with transcription factors, chromatin-modifying complex, and the proper recognition of ligands. NHRs are able to coordinate the expression of genes in numerous pathways simultaneously. This review focuses on the role of nuclear receptors in the central nervous system and, in particular, their role in regulating the proper development and function of the brain and the eye. In addition, the review highlights the impact of mutations in NHRs on a spectrum of human diseases from autism to retinal degeneration.

Overexpression of caspase 7 is ERα dependent to affect proliferation and cell growth in breast cancer cells by targeting p21(Cip)

Caspase 7 (CASP7) expression has important function during cell cycle progression and cell growth in certain cancer cells and is also involved in the development and differentiation of dental tissues. However, the function of CASP7 in breast cancer cells is unclear. The aim of this study was to analyze the expression of CASP7 in breast carcinoma patients and determine the role of CASP7 in regulating tumorigenicity in breast cancer cells. In this study, we show that the CASP7 expression is high in breast carcinoma tissues compared with normal counterpart. The ectopic expression of CASP7 is significantly associated with ERα expression status and persistently elevated in different stages of the breast tumor grades. High level of CASP7 expression showed better prognosis in breast cancer patients with systemic endocrine therapy as observed from Kaplan–Meier analysis. S3 and S4, estrogen responsive element (ERE) in the CASP7 promoter, is important for estrogen-ERα-mediated CASP7 overexpression. Increased recruitment of p300, acetylated H3 and pol II in the ERE region of CASP7 promoter is observed after hormone stimulation. Ectopic expression of CASP7 in breast cancer cells results in cell growth and proliferation inhibition via p21^Cip reduction, whereas small interfering RNA (siRNA) mediated reduction of CASP7 rescued p21^Cip levels. We also show that pro- and active forms of CASP7 is located in the nucleus apart from cytoplasmic region of breast cancer cells. The proliferation and growth of breast cancer cells is significantly reduced by broad-spectrum peptide inhibitors and siRNA of CASP7. Taken together, our findings show that CASP7 is aberrantly expressed in breast cancer and contributes to cell growth and proliferation by downregulating p21^Cip protein, suggesting that targeting CASP7-positive breast cancer could be one of the potential therapeutic strategies.

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.

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.

Constitutive activities of estrogen-related receptors: Transcriptional regulation of metabolism by the ERR pathways in health and disease

The estrogen-related receptors (ERRs) comprise a small group of orphan nuclear receptor transcription factors. The ERRα and ERRγ isoforms play a central role in the regulation of metabolic genes and cellular energy metabolism. Although less is known about ERRβ, recent studies have revealed the importance of this isoform in the maintenance of embryonic stem cell pluripotency. Thus, ERRs are essential to many biological processes. The development of several ERR knockout and overexpression models and the application of advanced functional genomics have allowed rapid advancement of our understanding of the physiology regulated by ERR pathways. Moreover, it has enabled us to begin to delineate the distinct programs regulated by ERRα and ERRγ that have overlapping effects on metabolism and growth. The current review primarily focuses on the physiologic roles of ERR isoforms related to their metabolic regulation; therefore, the ERRα and ERRγ are discussed in the greatest detail. We emphasize findings from gain- and loss-of-function models developed to characterize ERR control of skeletal muscle, heart and musculoskeletal physiology. These models have revealed that coordinating metabolic capacity with energy demand is essential for seemingly disparate processes such as muscle differentiation and hypertrophy, innate immune function, thermogenesis, and bone remodeling. Furthermore, the models have revealed that ERRα- and ERRγ-deficiency in mice accelerates progression of pathologic processes and implicates ERRs as etiologic factors in disease. We highlight the human diseases in which ERRs and their downstream metabolic pathways are perturbed, including heart failure and diabetes. While no natural ligand has been identified for any of the ERR isoforms, the potential for using synthetic small molecules to modulate their activity has been demonstrated. Based on our current understanding of their transcriptional mechanisms and physiologic relevance, the ERRs have emerged as potential therapeutic targets for treatment of osteoporosis, muscle atrophy, insulin resistance and heart failure in humans.

ERRγ is not required for skeletal development but is a RUNX2-dependent negative regulator of postnatal bone formation in male mice

To assess the effects of the orphan nuclear Estrogen receptor-related receptor gamma (ERRγ) deficiency on skeletal development and bone turnover, we utilized an ERRγ global knockout mouse line. While we observed no gross morphological anomalies or difference in skeletal length in newborn mice, by 8 weeks of age ERRγ +/− males but not females exhibited increased trabecular bone, which was further increased by 14 weeks. The increase in trabecular bone was due to an increase in active osteoblasts on the bone surface, without detectable alterations in osteoclast number or activity. Consistent with the histomorphometric results, we observed an increase in gene expression of the bone formation markers alkaline phosphatase (Alp) and bone sialoprotein (Bsp) in bone and increase in serum ALP, but no change in the osteoclast regulators receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) or the resorption marker carboxy-terminal collagen crosslinks (CTX). More colony forming units-alkaline phosphatase and -osteoblast (CFU-ALP, CFU-O respectively) but not CFU-fibroblast (CFU-F) formed in ERRγ +/− versus ERRγ +/+ stromal cell cultures, suggesting that ERRγ negatively regulates osteoblast differentiation and matrix mineralization but not mesenchymal precursor number. By co-immunoprecipitation experiments, we found that ERRγ and RUNX2 interact in an ERRγ DNA binding domain (DBD)-dependent manner. Treatment of post-confluent differentiating bone marrow stromal cell cultures with Runx2 antisense oligonucleotides resulted in a reduction of CFU-ALP/CFU-O in ERRγ +/− but not ERRγ +/+ mice compared to their corresponding sense controls. Our data indicate that ERRγ is not required for skeletal development but is a sex-dependent negative regulator of postnatal bone formation, acting in a RUNX2- and apparently differentiation stage-dependent manner.

Cell cycle-dependent expression of Dub3, Nanog and the p160 family of nuclear receptor coactivators (NCoAs) in mouse embryonic stem cells

Pluripotency of embryonic stem cells (ESC) is tightly regulated by a network of transcription factors among which the estrogen-related receptor β (Esrrb). Esrrb contributes to the relaxation of the G1 to S-phase (G1/S) checkpoint in mouse ESCs by transcriptional control of the deubiquitylase Dub3 gene, contributing to Cdc25A persistence after DNA damage. We show that in mESCs, Dub3 gene expression is cell cycle regulated and is maximal prior G1/S transition. In addition, following UV-induced DNA damage in G1, Dub3 expression markedly increases in S-phase also suggesting a role in checkpoint recovery. Unexpectedly, we also observed cell cycle-regulation of Nanog expression, and not Oct4, reaching high levels prior to G1/S transition, finely mirroring Cyclin E1 fluctuations. Curiously, while Esrrb showed only limited cell-cycle oscillations, transcript levels of the p160 family of nuclear receptor coactivators (NCoAs) displayed strong cell cycle-dependent fluctuations. Since NCoAs function in concert with Esrrb in transcriptional activation, we focussed on NCoA1 whose levels specifically increase prior onset of Dub3 transcription. Using a reporter assay, we show that NCoA1 potentiates Esrrb-mediated transcription of Dub3 and we present evidence of protein interaction between the SRC1 splice variant NCoA1 and Esrrb. Finally, we show a differential developmental regulation of all members of the p160 family during neural conversion of mESCs. These findings suggest that in mouse ESCs, changes in the relative concentration of a coactivator at a given cell cycle phase, may contribute to modulation of the transcriptional activity of the core transcription factors of the pluripotent network and be implicated in cell fate decisions upon onset of differentiation.

Cartilage-specific overexpression of ERRγ results in Chondrodysplasia and reduced chondrocyte proliferation

While the role of estrogen receptor-related receptor alpha (ERRα) in chondrogenesis has been investigated, the involvement of ERR gamma (ERRγ) has not been determined. To assess the effect of increased ERRγ activity on cartilage development in vivo, we generated two transgenic (Tg) lines overexpressing ERRγ2 via a chondrocyte-specific promoter; the two lines exhibited ∼3 and ∼5 fold increased ERRγ2 protein expression respectively in E14.5 Tg versus wild type (WT) limbs. On postnatal day seven (P7), we observed a 4–10% reduction in the size of the craniofacial, axial and appendicular skeletons in Tg versus WT mice. The reduction in bone length was already present at birth and did not appear to involve bones that are derived via intramembranous bone formation as the bones of the calvaria, clavicle, and the mandible developed normally. Histological analysis of P7 growth plates revealed a reduction in the length of the Tg versus WT growth plate, the majority of which was attributable to a reduced proliferative zone. The reduced proliferative zone paralleled a decrease in the number of Ki67-positive proliferating cells, with no significant change in apoptosis, and was accompanied by large cell-free swaths of cartilage matrix, which extended through multiple zones of the growth plate. Using a bioinformatics approach, we identified known chondrogenesis-associated genes with at least one predicted ERR binding site in their proximal promoters, as well as cell cycle regulators known to be regulated by ERRγ. Of the genes identified, Col2al, Agg, Pth1r, and Cdkn1b (p27) were significantly upregulated, suggesting that ERRγ2 negatively regulates chondrocyte proliferation and positively regulates matrix synthesis to coordinate growth plate height and organization.

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.

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.

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.

Negative regulation of ERRα by a novel nucleolar protein

The regulation of estrogen-related receptor (ERR) transcriptional activity is poorly understood. To explore the underlying mechanism, we sought to isolate ERRα-binding protein(s). In a yeast two-hybrid screen, we identified a novel protein that has been characterized as a retinoic acid resistance factor (RaRF) (manuscript in-preparation). A specific interaction between RaRF and ERRα was confirmed in a GST pull-down assay in vitro and immunoprecipitation (IP) in mammalian cells. Further yeast two-hybrid assays and IP analyses indicated that the C-terminus of ERRα is required for RaRF binding. Consistent with our interaction data, transfection of RaRF significantly reduced the ability of ERRα, but not ERRγ, to transactivate an ERR-responsive luciferase reporter. In contrast, down-regulation of RaRF using shRNA increased ERRα activity without affecting that of ERRγ. RaRF was subsequently shown to repress the expression of the ERR target gene pS2. Further fluorescence microscopy revealed that ERRα or ERRγ is normally expressed in the nucleoplasm, with ERRα, but not ERRγ, translocating to the nucleolus when RaRF is expressed. Taken together, our data suggest that RaRF sequesters ERRα in the nucleolus through a specific interaction, thereby inhibiting its transcriptional activity.

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.

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.

Estrogen related receptors (ERRs): a new dawn in transcriptional control of mitochondrial gene networks

Mitochondrial dysfunction contributes to the etiology of numerous diseases. Consequently, improving our knowledge of how to modulate mitochondrial activity is of considerable interest. One means to achieve this goal would be to control in a global and comprehensive manner the expression of most if not all nuclear encoded mitochondrial genes. The advent of genome-wide location analysis of transcription factor occupancy coupled with functional studies in cell and animal models has recently shown that three transcription factors possess this unique attribute. Unexpectedly, these factors are orphan members of the superfamily of nuclear receptors known as estrogen-related receptors (ERRs) α, β and γ. In this review, we will integrate current knowledge gathered through several functional and physiological genomic studies to provide persuasive evidence that the ERRs are indeed master regulators of mitochondrial biogenesis and function.

TOX3 is a neuronal survival factor that induces transcription depending on the presence of CITED1 or phosphorylated CREB in the transcriptionally active complex

TOX3 is a nuclear protein containing a high mobility group (HMG)-box domain, which regulates Ca(2+)-dependent transcription in neurons through interaction with the cAMP-response-element-binding protein (CREB). TOX3 appears to be associated with breast cancer susceptibility and was previously shown to be expressed downstream of a cytoprotective cascade together with CITED1, a transcriptional regulator that does not bind directly to DNA. In the present study we show that TOX3 is predominantly expressed in the brain, forms homodimers and interacts with CITED1. TOX3 overexpression protects neuronal cells from cell death caused by endoplasmic reticulum stress or BAX overexpression through the induction of anti-apoptotic transcripts and repression of pro-apoptotic transcripts, which correlates with enhanced transcription involving isolated estrogen-responsive elements and estrogen-responsive promoters. However, both functions cannot be inhibited with the anti-estrogen fulvestrant and are only attenuated by mutation of estrogen-responsive elements. TOX3 also interacts with native CREB and induces the CREB-responsive BCL-2 promoter, which can be inhibited by coexpression of CITED1. Coexpression of CREB, by contrast, abolishes TOX3-mediated transcription from the estrogen-responsive complement C3 promoter. Our results suggest that TOX3 can enhance transcriptional activation from different cytoprotective promoters and that this is dependent on the predominance of either phosphorylated CREB or CITED1 within the transcriptionally active complex.

Regression of castrate-recurrent prostate cancer by a small-molecule inhibitor of the amino-terminus domain of the androgen receptor

Castration-recurrent prostate cancer (CRPC) is suspected to depend on androgen receptor (AR). The AF-1 region in the amino-terminal domain (NTD) of AR contains most, if not all, of the transcriptional activity. Here we identify EPI-001, a small molecule that blocked transactivation of the NTD and was specific for inhibition of AR without attenuating transcriptional activities of related steroid receptors. EPI-001 interacted with the AF-1 region, inhibited protein-protein interactions with AR, and reduced AR interaction with androgen-response elements on target genes. Importantly, EPI-001 blocked androgen-induced proliferation and caused cytoreduction of CRPC in xenografts dependent on AR for growth and survival without causing toxicity.

Double PHD fingers protein DPF2 recognizes acetylated histones and suppresses the function of estrogen-related receptor alpha through histone deacetylase 1

Estrogen-related receptor alpha (ERRalpha) is a member of the nuclear receptor superfamily and regulates many physiological functions, including mitochondrial biogenesis and lipid metabolism. ERRalpha enhances the transactivation function without endogenous ligand by associating with coactivators such as peroxisome proliferator-activated receptor gamma coactivator 1 alpha and beta (PGC-1alpha and -beta) and members of the steroid receptor coactivator family. However, the molecular mechanism by which the transactivation function of ERRalpha is converted from a repressive state to an active state is poorly understood. Here we used biochemical purification techniques to identify ERRalpha-associated proteins in HeLa cells stably expressing ERRalpha. Interestingly, we found that double PHD fingers protein DPF2/BAF45d suppressed PGC-1alpha-dependent transactivation of ERRalpha by recognizing acetylated histone H3 and associating with HDAC1. DPF2 directly bound to ERRalpha and suppressed the transactivation function of nuclear receptors such as androgen receptor. DPF2 was recruited to ERR target gene promoters in myoblast cells, and knockdown of DPF2 derepressed the level of mRNA expressed by target genes of ERRalpha. These results show that DPF2 acts as a nuclear receptor-selective co-repressor for ERRalpha by associating with both acetylated histone H3 and HDAC1.

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.

G protein pathway suppressor 2 (GPS2) is a transcriptional corepressor important for estrogen receptor alpha-mediated transcriptional regulation

We have identified G protein suppressor 2 (GPS2) as a stable component of the SMRT corepressor complexes. GPS2 potently represses basal transcription, with the repression domain mapped to the N-terminal silencing mediator of retinoic acid and thyroid hormone receptor (SMRT)-interacting domain. Knockdown of GPS2 abrogates, whereas overexpression potentiates, SMRT-mediated repression activity. The SMRT complexes are involved in 4-hydroxyl-tamoxifen (4OHT)-mediated gene repression by estrogen receptor alpha (ERalpha). We show that 4OHT recruits SMRT and GPS2 to the promoter of pS2, an ERalpha target gene, in a dynamic manner. Unexpectedly, we also found that estradiol (E2) promotes promoter recruitment of the SMRT complexes. While knockdown of GPS2 compromised 4OHT-mediated repression, it enhanced E2-induced expression of a reporter gene and several endogenous ERalpha target genes, including pS2, cyclin D1 (CCND1), progesterone receptor (PR), and c-MYC. Finally, we show that depletion of GPS2 or SMRT by siRNA promotes cell proliferation in MCF-7 breast cancer cells. Thus, we concluded that GPS2 is an integral component of the SMRT complexes, important for ligand-dependent gene regulations by ERalpha and a suppressor for MCF-7 cell proliferation.

Suppressing the activity of ERRalpha in 3T3-L1 adipocytes reduces mitochondrial biogenesis but enhances glycolysis and basal glucose uptake

Estrogen-related receptor alpha (ERRalpha) is thought to primarily regulate lipid oxidation and control the transcription of genes in the oxidative phosphorylation pathway in skeletal and cardiac muscles. However, its role in white adipose tissue is not well studied. In this study, we aimed to establish a role for ERRalpha in adipocytes by down-regulating its activity through its inverse agonist XCT-790 in differentiated 3T3-L1 adipocytes. We found that XCT-790 differentially reduced the expression of ERRalpha target genes. Specifically, XCT-790 reduced the expressions of peroxisome proliferator-activated receptor gamma co-activator-1beta (PGC-1beta), resulting in reductions of mitochondrial biogenesis, adiogenesis and lipogeneis. Through suppressing the expression of another ERRalpha target gene pyruvate dehydrogenase kinase 2 (PDK2), we found that XCT-790 not only enhanced the conversion of pyruvate to acetyl-CoA and hyper-activated the tricarboxylic acid (TCA) cycle, but also led to higher levels of mitochondrial membrane potential and reactive oxidant species (ROS) production. Additionally, XCT-790 treatment also resulted in enhanced rates of glycolysis and basal glucose uptake. Therefore, ERRalpha stands at the crossroad of glucose and fatty acid utilization and acts as a homeostatic switch to regulate the flux of TCA cycle, mitochondrial membrane potential and glycolysis to maintain a steady level of ATP production, particularly, when mitochondrial biogenesis is reduced.

Estrogen-related receptor alpha expression and function is associated with the transcriptional coregulator AIB1 in breast carcinoma

The significance of the estrogen-related receptor alpha (ERRalpha) as prognostic marker for poor clinical outcome in breast carcinoma has recently been reported. Transcriptional activity of nuclear receptors such as ERRalpha depends on coregulatory proteins. Thus, we compared the expression of different receptors, coregulators, and target genes on RNA and protein level in identical primary breast tumor samples (n = 48). We found a positive correlation between the transcripts of ERRalpha and AIB1 (amplified in breast cancer-1), a coactivator overexpressed in breast cancers and associated with resistance to antihormone treatment. These data were confirmed on protein level, studying an independent patient collection (n = 257). Expression of the estrogen-regulated gene pS2 was associated with ERRalpha only in tumors, where estrogen receptor (ERalpha) expression was low or absent. In ERalpha high expressing tumors, no correlation of ERRalpha and pS2 was observed. AIB1 interacts directly with ERRalpha as shown by fluorescence-resonance energy transfer, mammalian two-hybrid, and coimmunoprecipitation assays with endogenous proteins. It enhances ERRalpha transcriptional activity in ERalpha-negative breast cancer cell lines as shown in functional reporter gene assays. Blocking ERRalpha with an inverse agonist abolished interaction and coactivation by AIB1. Recruitment of both proteins to ERRalpha target gene promoters further supports the significance of their interaction. Our findings identify AIB1 as functionally relevant cofactor for ERRalpha in breast carcinoma. ERRalpha/AIB1 complexes may control estradiol-regulated genes in a hormone-independent manner. Accordingly, ERRalpha might be a rewarding target for treatment of endocrine-resistant tumors.

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.

Bcl3 interacts cooperatively with peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator 1alpha to coactivate nuclear receptors estrogen-related receptor alpha and PPARalpha

Estrogen-related receptors (ERRs) play critical roles in regulation of cellular energy metabolism in response to inducible coactivators such as peroxisome proliferator-activated receptor gamma (PPARgamma) coactivator 1alpha (PGC-1alpha). A yeast two-hybrid screen led to the identification of the cytokine-stimulated transcriptional regulator, Bcl3, as an ERRalpha coactivator. Bcl3 was shown to synergize with PGC-1alpha to coactivate ERRalpha. Chromatin immunoprecipitation studies demonstrated that ERRalpha, PGC-1alpha, and Bcl3 form a complex on an ERRalpha-responsive element within the pyruvate dehydrogenase kinase 4 gene promoter in cardiac myocytes. Mapping studies demonstrated that Bc13 interacts with PGC-1alpha and ERRalpha, allowing for interaction with both proteins. Transcriptional profiling demonstrated that Bcl3 activates genes involved in diverse pathways including a subset involved in cellular energy metabolism known to be regulated by PGC-1alpha, ERRalpha, and a second nuclear receptor, PPARalpha. Consistent with the gene expression profiling results, Bcl3 was shown to synergistically coactivate PPARalpha with PGC-1alpha in a manner similar to ERRalpha. We propose that the cooperativity between Bcl3 and PGC-1alpha may serve as a point of convergence on nuclear receptor targets to direct programs orchestrating inflammatory and energy metabolism responses in heart and other tissues.

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.

Estrogen-related receptor alpha is critical for the growth of estrogen receptor-negative breast cancer

Expression of estrogen-related receptor alpha (ERRalpha) has recently been shown to carry negative prognostic significance in breast and ovarian cancers. The specific role of this orphan nuclear receptor in tumor growth and progression, however, is yet to be fully understood. The significant homology between estrogen receptor alpha (ERalpha) and ERRalpha initially suggested that these receptors may have similar transcriptional targets. Using the well-characterized ERalpha-positive MCF-7 breast cancer cell line, we sought to gain a genome-wide picture of ERalpha-ERRalpha cross-talk using an unbiased microarray approach. In addition to generating a host of novel ERRalpha target genes, this study yielded the surprising result that most ERRalpha-regulated genes are unrelated to estrogen signaling. The relatively small number of genes regulated by both ERalpha and ERRalpha led us to expand our study to the more aggressive and less clinically treatable ERalpha-negative class of breast cancers. In this setting, we found that ERRalpha expression is required for the basal level of expression of many known and novel ERRalpha target genes. Introduction of a small interfering RNA directed to ERRalpha into the highly aggressive breast carcinoma MDA-MB-231 cell line dramatically reduced the migratory potential of these cells. Although stable knockdown of ERRalpha expression in MDA-MB-231 cells had no effect on in vitro cell proliferation, a significant reduction of tumor growth rate was observed when these cells were implanted as xenografts. Our results confirm a role for ERRalpha in breast cancer growth and highlight it as a potential therapeutic target for estrogen receptor-negative breast cancer.

Activation of estrogen response elements is mediated both via estrogen and muscle contractions in rat skeletal muscle myotubes

The aim of the present study was to investigate the activation of estrogen response elements (EREs) by estrogen and muscle contractions in rat myotubes in culture and to assess whether the activation is dependent on the estrogen receptors (ERs). In addition, the effect of estrogen and contraction on the mRNA levels of ERalpha and ERbeta was studied to determine the functional consequence of the transactivation. Myoblasts were isolated from rat skeletal muscle and transfected with a vector consisting of sequences of EREs coupled to the gene for luciferase. The transfected myoblasts were then differentiated into myotubes and subjected to either estrogen or electrical stimulation. Activation of the ERE sequence was determined by measurement of luciferase activity. The results show that both ERalpha and ERbeta are expressed in myotubes from rats. Both estrogen stimulation and muscle contraction increased (P < 0.05) transactivation of the ERE sequence and enhanced ERbeta mRNA, whereas ERalpha was unaffected by estrogen and attenuated (P < 0.05) by muscle contraction. Use of ER antagonists showed that, whereas the estrogen-induced transactivation is mediated via ERs, the effect of muscle contraction is ER independent. The muscle contraction-induced transactivation of ERE and increase in ERbeta mRNA were instead found to be MAP kinase (MAPK) dependent. This study demonstrates for the first time that muscle contractions have a similar functional effect as estrogen in skeletal muscle myotubes, causing ERE activation and an enhancement in ERbeta mRNA. However, in contrast to estrogen, the effect is independent of ERs and dependent on MAPK, suggesting activation via the estrogen related receptor (ERR).