Oestrogen receptor-related receptor alpha (ERRalpha) and oestrogen receptors (ERalpha and ERbeta) exhibit different gene expression in human colorectal tumour progression

Production and characterization of monoclonal antibodies to estrogen-related receptor alpha (ERRα) and use in immunoaffinity chromatography

Estrogen-related receptor alpha (ERRα) is an orphan nuclear receptor whose elevated expression is thought to contribute to breast, colon, and ovarian cancers. In order to investigate the role of ERRα in human disease, there is a need for immunological reagents suitable for detection and purification of ERRα. We expressed recombinant human ERRα in Escherichia coli, purified the protein, and used it to generate monoclonal antibodies (mAbs) to ERRα. Nine high-affinity mAbs were chosen for their abilities to detect overexpressed ERRα in enzyme-linked immunosorbent assays (ELISAs) and Western blots, after which isotyping and preliminary epitope mapping was performed. The mAbs were all IgG subtypes and reacted with several different regions of full-length ERRα. A majority of the mAbs were found to be useful for immunoprecipitation of ERRα, and several could detect DNA-bound ERRα in electrophoretic mobility supershift assays (EMSAs) and chromatin immunoprecipitation (ChIP). The suitability of mAbs to detect ERRα in immunofluorescence assays was assessed. One mAb in particular, 2ERR10, could specifically detect endogenous ERRα in mammary carcinoma cells. Finally, we performed assays to screen for mAbs that gently release ERRα in the presence of a low-molecular-weight polyhydroxylated compound (polyol) and nonchaotropic salt. Using gentle immunoaffinity chromatography, we were able to isolate ERRα from mammalian cells by eluting with a polyol-salt solution. Our characterization studies show that these monoclonal antibodies perform well in a variety of biochemical assays. We anticipate that these novel reagents will prove useful for the detection and purification of ERRα in research and clinical applications.

The estrogen-related receptor alpha upregulates secretin expressions in response to hypertonicity and angiotensin II stimulation

Osmoregulation via maintenance of water and salt homeostasis is a vital process. In the brain, a functional secretin (SCT) and secretin receptor (SCTR) axis has recently been shown to mediate central actions of angiotensin II (ANGII), including initiation of water intake and stimulation of vasopressin (VP) expression and release. In this report, we provide evidence that estrogen-related receptor α (ERRα, NR3B1), a transcription factor mainly involved in metabolism, acts as an upstream activator of the SCT gene. In vitro studies using mouse hypothalamic cell line N-42 show that ERRα upregulates SCT promoter and gene expression. More importantly, knockdown of endogenous ERRα abolishes SCT promoter activation in response to hypertonic and ANGII stimulations. In mouse brain, ERRα coexpresses with SCT in various osmoregulatory brain regions, including the lamina terminalis and the paraventricular nucleus of the hypothalamus, and its expression is induced by hyperosmotic and ANGII treatments. Based on our data, we propose that both the upregulation of ERRα and/or the increased binding of ERRα to the mouse SCT promoter are two possible mechanisms for the elevated SCT expression upon hyperosmolality and central ANGII stimulation.

The estrogen-related receptors: orphans orchestrating myriad functions

Coordinated and tight regulation of gene expression in metazoans is essential for cellular homeostasis and functions. Tissue- and cell-specific regulatory factors are indispensable and a wide variety of them exist to regulate genes. A family of transcriptional factors was identified in the past two decades through gene cloning studies and was informally referred as "orphan receptors", as appropriate endogenous ligands for such receptors were unknown. One of the subclasses of such receptors is known as the estrogen-related receptors (ERRs), which include three isoforms, namely ERRα, ERRβ and ERRγ. Over the past one decade, unprecedented knowledge about the ERRs biology has been generated, indicating their vital roles in various metabolic and physiological activities in animals. The ERRs cellular action is largely attributed to its interaction with a wide variety of other nuclear receptors, including some orphan nuclear receptors, and thereby can modulate diverse array of genes involved in metabolism and animal physiology. Studies using genome-wide location analyses, microarray and functional genomics, including ERR-specific null mice have revealed a number of pathways controlled by the ERRs. In this context, new and recent information on the biological functions of ERRs are being reviewed.

The cannabinoid receptor inverse agonist AM251 regulates the expression of the EGF receptor and its ligands via destabilization of oestrogen-related receptor α protein

BACKGROUND AND PURPOSE

AM251 is an inverse agonist of the cannabinoid 1 receptor (CB(1)R) that can exert 'off-target' effects in vitro and in CB(1)R knock-out mice. AM251 is also potent at modulating tumour cell growth, suggesting that growth factor-mediated oncogenic signalling could be regulated by AM251. Since dysregulation of the EGF receptor has been associated with carcinogenesis, we examined AM251 regulation of EGF receptor (EGFR) expression and function.

EXPERIMENTAL APPROACH

The various biological functions of AM251 were measured in CB(1)R-negative human cancer cells. Pharmacological and genetic approaches were used to validate the data.

KEY RESULTS

The mRNA levels for EGFR and its associated ligands, including HB-EGF, were induced several fold in PANC-1 and HCT116 cells in response to AM251. This event was associated with enhanced expression of EGFR on the cell surface with concomitant increase in EGF-induced cellular responses in AM251-treated cells. Exposure to XCT790, a synthetic inverse agonist of the orphan nuclear oestrogen-related receptor α (ERRα), also induced EGFR and HB-EGF expression to the same extent as AM251, whereas pretreatment with the ERRα-selective agonist, biochanin A, blunted AM251 actions. AM251 promoted the degradation of ERRα protein without loss of the corresponding mRNA. Knock-down of ERRα by siRNA-based approach led to constitutive induction of EGFR and HB-EGF levels, and eliminated the biological responses of AM251 and XCT790. Finally, AM251 displaced diethylstilbestrol prebound to the ligand-binding domain of ERRα.

CONCLUSIONS AND IMPLICATIONS

AM251 up-regulates EGFR expression and signalling via a novel non-CB(1)R-mediated pathway involving destabilization of ERRα protein in selected cancer cell lines.

Dual function of ERRα in breast cancer and bone metastasis formation: implication of VEGF and osteoprotegerin

Bone metastasis is a complication occurring in up to 70% of advanced breast cancer patients. The estrogen receptor-related receptor alpha (ERRα) has been implicated in breast cancer and bone development, prompting us to examine whether ERRα may function in promoting the osteolytic growth of breast cancer cells in bone. In a mouse xenograft model of metastatic human breast cancer, overexpression of wild-type ERRα reduced metastasis, whereas overexpression of a dominant negative mutant promoted metastasis. Osteoclasts were directly affected and ERRα upregulated the osteoclastogenesis inhibitor, osteoprotegerin (OPG), providing a direct mechanistic basis for understanding how ERRα reduced breast cancer cell growth in bone. In contrast, ERRα overexpression increased breast cancer cell growth in the mammary gland. ERRα-overexpressing primary tumors were highly vascularized, consistent with an observed upregulation of angiogenic growth factor, the VEGF. In support of these findings, we documented that elevated expression of ERRα mRNA in breast carcinomas was associated with high expression of OPG and VEGF and with disease progression. In conclusion, our results show that ERRα plays a dual role in breast cancer progression in promoting the local growth of tumor cells, but decreasing metastatic growth of osteolytic lesions in bone.

Estrogen-related receptor α expression and function are associated with vascular endothelial growth factor in human cervical cancer

INTRODUCTION

Estrogen-related receptor α (ERRα), one of orphan nuclear receptors with an unknown ligand, is expressed in various types of cancer. Increased ERRα levels are associated with a higher risk of recurrence and poor clinical outcome in breast cancer, suggesting that ERRα could be a negative prognostic factor. Recently, it has been suggested that vascular endothelial growth factor (VEGF) could be one of the transcriptional targets of ERRα in breast cancer. Here, we examined the expression of ERRα and the association of ERRα with VEGF in uterine cervical cancer cells and tissues.

METHODS

We evaluated the expression of ERRα and VEGF by immunohistologic analysis using specimens from 40 patients with invasive cervical cancer. We also evaluated the VEGF promoter activity of ERRα in cervical cancer cell lines by transfection and luciferase assay. We overexpressed or knocked down ERRα and examined VEGF expression by real-time polymerase chain reaction. Finally, cell proliferation assay was performed to examine whether ERRα affects tumor growth in cervical cancer.

RESULTS

Immunohistologic analysis demonstrated that ERRα expression in cervical cancer tissues was higher than that in noncancerous tissues and that there was a positive association between ERRα and VEGF expression in cancer tissues (P < 0.05). We showed that ERRα stimulated the VEGF promoter activity in cervical cancer cell lines. We further showed the overexpression and knockdown of ERRα-regulated VEGF expression level by real-time polymerase chain reaction. Moreover, we showed that ERRα and VEGF knockdown by small interfering RNA or an inverse agonist of ERRα, XCT 790, could suppress cell growth compared with control cells in cervical cancer.

CONCLUSIONS

We have provided compelling evidence that ERRα affects VEGF expression and tumor growth in cervical cancer. These results justify further investigation into the use of ERRα as a therapeutic target for patients with uterine cervical cancer.

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.

Oestrogen-related receptor alpha inverse agonist XCT-790 arrests A549 lung cancer cell population growth by inducing mitochondrial reactive oxygen species production

OBJECTIVE

Although oestrogen-related receptor alpha (ERRalpha) is primarily thought to regulate energy homeostasis, it also serves as a prognostic marker for cancer. The aim of this study was to investigate any connection between ERRalpha activity and cell population growth.

MATERIALS AND METHODS

XCT-790, an ERRa specific inverse agonist, was employed to suppress ERRa activity in human non-small cell lung cancer cells (NSCLC) A549. Gene expressions were detected using quantitative real-time PCR and Western blot analysis. Mitochondrial mass, membrane potential and reactive oxygen species (ROS) production were measured by staining with Mitotracker green, JC-1 and CM-H(2)DCFDA dyes respectively. Rate of progression through the tricarboxylic acid (TCA) cycle was analysed by measuring activities of citrate synthase and succinate dehydrogenase. Cell cycle analysis was performed by using flow cytometry.

RESULTS

We found that XCT-790 treatment reduced mitochondrial mass but enhanced mitochondrial ROS production by increasing rate through the TCA cycle, elevating mitochondrial membrane potential (DeltaPsi(m)) and down-regulating expression of superoxide dismutase. It was further demonstrated that XCT-790-induced ROS modulated p53 and Rb signalling pathways and suppressed cell replication.

CONCLUSIONS

ERRalpha affects cell cycle mechanisms through modulating mitochondrial mass and function. Dysregulation of this essential pathway leads to elevation in mitochondrial ROS production, which in turn modulates activities of tumour suppressors, resulting in cell cycle arrest.

Relevance of serum estradiol and estrogen receptor beta expression from a high-incidence area for esophageal squamous cell carcinoma in China

The striking 3-4:1 male predominance of esophageal squamous cell carcinoma (ESCC) has not yet been well explained. Our hypothesis is that the changes in level of estrogen and/or subtype of estrogen receptor (ER) may exert a protective factor in esophageal carcinogenesis and prognosis of ESCC. Radioimmunoassay (RIA) was used to determine the serum level of estradiol in healthy cohort from high-incidence area (HIA) and low-incidence area (LIA) for esophageal cancer as well as patients with ESCC from HIA in Henan, northern China. The ERβ expression profiling during the multi-stage progression of ESCC pathogenesis was evaluated by immunohistochemistry (IHC). Both males and females from HIA had significant decreases of serum estradiol in high-risk subjects predisposing for ESCC compared to healthy counterparts from LIA (P < 0.01). Furthermore, patients with ESCC from HIA developed the lowest level of estradiol (P < 0.01). ERβ expressed in precursor lesions of ESCC and changed quantitatively and qualitatively with disease progression during the multi-stages process of esophageal carcinogenesis. High frequency of ERβ expression was correlated with less aggressive potential of clinical behavior (P = 0.012, 0.015 for lymph node metastasis and tumor stage, respectively). This study indicates that lower serum level of estradiol may represent higher predisposition for development of ESCC, and ERβ expression and/or nuclear location may predict better outcome for patients with ESCC. The present results provide clues to explain the striking gender difference for ESCC, which warrants further investigations on potential applications of estrogen or analogs in prevention of ESCC.

Differential expression of estrogen-related receptors beta and gamma (ERRbeta and ERRgamma) and their clinical significance in human prostate cancer

Estrogen-related receptor (ERR) is a nuclear receptor that modulates the estrogen-signaling pathway. Here, we investigated the expression of both ERRbeta and ERRgamma in human prostate tissues. Using original rabbit polyclonal anti-ERRbeta and anti-ERRgamma antibodies, the expression of ERRbeta and ERRgamma was evaluated by immunohistochemical analysis of cancerous lesions (n = 107) and benign foci (n = 92), obtained by radical prostatectomy. Stained slides were evaluated for the proportion of immunoreactive cells and their staining intensity. Total immunoreactivity scores (IR scores; range, 0-8) were calculated as the sum of the proportion and intensity scores. The relationship between the clinicopathological characteristics of the patients and the expression of the three ERRs (ERRalpha, ERR beta, and ERR gamma) was evaluated. IR scores for ERRbeta and ERRgamma were significantly lower in cancerous lesions than that in benign foci (P < 0.0001, for both). Clinicopathological analyses revealed that the patients with low ERRgamma IR scores ( Collapse

Key Words Collapse

MESH Headings

• Aged
• Humans
• Immunohistochemistry
• Male
• Middle Aged
• Prognosis
• Prostatic Neoplasms/chemistry
• Prostatic Neoplasms/mortality
• Receptors, Estrogen/analysis

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Grants Collapse

Affiliation(s)

Tetsuya Fujimura Department of Urology, Faculty of Medicine, The University of Tokyo, Tokyo, Japan
Satoru Takahashi
Tomohiko Urano
Nobuhiro Ijichi
Kazuhiro Ikeda
Jinpei Kumagai
Taro Murata
Kenichi Takayama
Kuniko Horie-Inoue
Yasuyoshi Ouchi
Masami Muramatsu
Yukio Homma
Satoshi Inoue

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Probing the link between oestrogen receptors and oesophageal cancer

BACKGROUND

Human oesophageal carcinoma is considered to be one of the most aggressive malignancies and has a very poor prognosis. The incidence of oesophageal cancer shows a gender bias and is higher in males compared with females, the ratio between males and females varying from 3:1 to 7:1. This sex ratio is not entirely attributable to differences in the prevalence of known risk factors between the sexes. The potential role of oestrogen receptors (ER) in oesophageal cancer has been debated for several years but the significance of the receptors in this cancer remains unknown. Most of the work has been based on immunohistochemistry and has not been validated with other available techniques. The inconsistencies in the published literature on the link between ER expression and oesophageal cancer warrant a thorough evaluation of the potential role of ERs in this malignancy. Even the expression of the two ER isoforms, ERalpha and ERbeta, and its implications for outcome of treatments in histological subtypes of oesophageal tumours is ill defined. The aim of this article is to provide updated information from the available literature on the current status of ER expression in oesophageal cancer and to discuss its potential therapeutic role.

METHODS AND RESULTS

We performed a comprehensive literature search and analysed the results regarding ER expression in oesophageal tumours with special emphasis on expression of different oestrogen receptors and the role of sex hormones in oesophageal cancer. This article also focuses on the significance of the two main ER subtypes and mechanisms underlying the presumed male predominance of this disease.

CONCLUSION

We postulate that differential oestrogen receptor status may be considered a biomarker of poor clinical outcome based on tissue dedifferentiation or advanced stage of the disease. Further, if we can establish the importance of oestrogen and its receptors in the context of oesophageal cancer, then this may lead to a new future direction in the management of this malignancy.

Estrogen-related receptor alpha and PGC-1-related coactivator constitute a novel complex mediating the biogenesis of functional mitochondria

Mitochondrial biogenesis, which depends on nuclear as well as mitochondrial genes, occurs in response to increased cellular ATP demand. The nuclear transcriptional factors, estrogen-related receptor alpha (ERRalpha) and nuclear respiratory factors 1 and 2, are associated with the coordination of the transcriptional machinery governing mitochondrial biogenesis, whereas coactivators of the peroxisome proliferator-activated receptor gamma coactivator-1 (PGC-1) family serve as mediators between the environment and this machinery. In the context of proliferating cells, PGC-1-related coactivator (PRC) is a member of the PGC-1 family, which is known to act in partnership with nuclear respiratory factors, but no functional interference between PRC and ERRalpha has been described so far. We explored three thyroid cell lines, FTC-133, XTC.UC1 and RO 82 W-1, each characterized by a different mitochondrial content, and studied their behavior towards PRC and ERRalpha in terms of respiratory efficiency. Overexpression of PRC and ERRalpha led to increased respiratory chain capacity and mitochondrial mass. The inhibition of ERRalpha decreased cell growth and respiratory chain capacity in all three cell lines. However, the inhibition of PRC and ERRalpha produced a greater effect in the oxidative cell model, decreasing the mitochondrial mass and the phosphorylating respiration, whereas the nonphosphorylating respiration remained unchanged. We therefore hypothesize that the ERRalpha-PRC complex plays a role in arresting the cell cycle through the regulation of oxidative phosphorylation in oxidative cells, and through some other pathway in glycolytic cells.

Estrogen-related receptor alpha (ERRalpha) inverse agonist XCT-790 induces cell death in chemotherapeutic resistant cancer cells

Estrogen-related receptor alpha (ERRalpha) is primarily thought to regulate energy homeostasis through interacting with peroxisome proliferator-activated receptor gamma coactivator-1alpha and -1beta (PGC-1alpha and -1beta). They coordinately control the transcription of genes in the oxidative phosphorylation pathway. In addition to its role in energy metabolism, ERRalpha has also been implicated as a prognostic marker for breast, ovarian, colon and prostate cancers. In this study, we found that an ERRalpha inverse agonist XCT-790 induced cell death in HepG2 hepatocarcinoma and its multi-drug resistance (MDR) sub-line R-HepG2. Using a dye Mitotracker Green which stains mitochondrion independent of mitochondrial membrane potential (DeltaPsi(m)), we found that XCT-790 dose-dependently decreased mitochondrial mass. Intriguingly, XCT-790 increased DeltaPsi(m) upon short term treatment but decreased DeltaPsi(m) upon longer term treatment. The changes of DeltaPsi(m) in turn promoted the production of reactive oxygen species (ROS) and led to ROS-mediated caspases 3/7, 8, 9 activation and cell death. Importantly, we established that an anti-oxidative compound Mn(III) Tetra(4-benzoic acid) porphyrin chloride (MnTBAP) blocked the caspases activities and cell death increased by XCT-790 treatment. Finally, we found that XCT-790 synergized with paclitaxel to induce cell death in multi-drug resistance sub-line R-HepG2. Our results provide a conceptual framework for further developing chemotherapeutics based on suppressing ERRalpha activity.

Modulating estrogen receptor-related receptor-alpha activity inhibits cell proliferation

High expression of the estrogen receptor-related receptor (ERR)-alpha in human tumors is correlated to a poor prognosis, suggesting an involvement of the receptor in cell proliferation. In this study, we show that a synthetic compound (XCT790) that modulates the activity of ERRalpha reduces the proliferation of various cell lines and blocks the G(1)/S transition of the cell cycle in an ERRalpha-dependent manner. XCT790 induces, in a p53-independent manner, the expression of the cell cycle inhibitor p21(waf/cip)(1) at the protein, mRNA, and promoter level, leading to an accumulation of hypophosphorylated Rb. Finally, XCT790 reduces cell tumorigenicity in Nude mice.

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.

The orphan receptor ERRalpha interferes with steroid signaling

The estrogen receptor-related receptor alpha (ERRalpha) is an orphan member of the nuclear receptor superfamily that has been shown to interfere with the estrogen-signaling pathway. In this report, we demonstrate that ERRalpha also cross-talks with signaling driven by other steroid hormones. Treatment of human prostatic cells with a specific ERRalpha inverse agonist reduces the expression of several androgen-responsive genes, in a manner that does not involve perturbation of androgen receptor expression or activity. Furthermore, ERRalpha activates the expression of androgen response elements (ARE)-containing promoters, such as that of the prostate cancer marker PSA, in an ARE-dependent manner. In addition, promoters containing a steroid response element can be activated by all members of the ERR orphan receptor subfamily, and this, even in the presence of antisteroid compounds.

Estrogen receptor (ER) and ER-related receptor expression in normal and atrophic human vagina

OBJECTIVES

The estrogen level decline in menopausal status is involved in physiological alterations of different human tissues including vaginal mucosa. In this study, we have evaluated the estrogen receptor (ER) and estrogen receptor-related receptor (ERR) expression in tissue samples of posterior vaginal wall obtained from pre- and post-menopausal women.

METHODS

The nuclear receptor expression was determined by quantitative real-time PCR (qPCR).

RESULTS

The qPCR results showed the presence of the three isoforms of the ERR family (ERRalpha, ERRbeta and ERRgamma) that were coexpressed with ERs in all vaginal tissue samples examined. The ERRalpha and ERRgamma mRNA levels decreased from normal vagina of the pre-menopausal women to atrophic vaginal tissue in post-menopausal women. This trend was also observed for the ERbeta subtype.

CONCLUSIONS

The ERRs, such as ERs, are present in human vagina at the mRNA level and the cessation of ovarian estrogen secretion, that is the key event during the post-menopause, may be linked to ERbeta, ERRalpha and ERRgamma mRNA decline in human vaginal mucosa. These findings may provide a biological rationale for the clinical susceptibility of the post-menopausal vagina to local estrogen treatment.

Estrogen induces estrogen-related receptor alpha gene expression and chromatin structural changes in estrogen receptor (ER)-positive and ER-negative breast cancer cells

Estrogen-related receptor alpha (ERRalpha), a member of the nuclear receptor superfamily, is closely related to the estrogen receptors (ERalpha and ERbeta). The ERRalpha gene is estrogen-responsive in several mouse tissues and cell lines, and a multiple hormone-response element (MHRE) in the promoter is an important regulatory region for estrogen-induced ERRalpha gene expression. ERRalpha was recently shown to be a negative prognostic factor for breast cancer survival, with its expression being highest in cancer cells lacking functional ERalpha. The contribution of ERRalpha in breast cancer progression remains unknown but may have important clinical implications. In this study, we investigated ERRalpha gene expression and chromatin structural changes under the influence of 17beta-estradiol in both ER-positive MCF-7 and ER-negative SKBR3 breast cancer cells. We mapped the nucleosome positions of the ERRalpha promoter around the MHRE region and found that the MHRE resides within a single nucleosome. Local chromatin structure of the MHRE exhibited increased restriction enzyme hypersensitivity and enhanced histone H3 and H4 acetylation upon estrogen treatment. Interestingly, estrogen-induced chromatin structural changes could be repressed by estrogen antagonist ICI 182 780 in MCF-7 cells yet were enhanced in SKBR3 cells. We demonstrated, using chromatin immunoprecipitation assays, that 17beta-estradiol induces ERRalpha gene expression in MCF-7 cells through active recruitment of co-activators and release of co-repressors when ERRalpha and AP1 bind and ERalpha is tethered to the MHRE. We also found that this estrogen effect requires the MAPK signaling pathway in both cell lines.

The NR3B subgroup: an ovERRview

Members of the NR3B group of the nuclear receptor superfamily, known as the estrogen-related receptors (ERRs), were the first orphan receptors to be identified two decades ago. Despite the fact that a natural ligand has yet to be associated with the ERRs, considerable knowledge about their mode of action and biological functions has emerged through extensive biochemical, genetic and functional genomics studies. This review describes our current understanding of how the ERRs work as transcription factors and as such, how they control diverse developmental and physiological programs.

Potentiation of ICI182,780 (Fulvestrant)-induced estrogen receptor-alpha degradation by the estrogen receptor-related receptor-alpha inverse agonist XCT790

ICI182,780 (Fulvestrant) is a pure anti-estrogen used in adjuvant therapies of breast cancer. This compound not only inhibits the transcriptional activities of the estrogen receptor-alpha (ER alpha) but also induces its proteasome-dependent degradation. The latter activity is believed to be required for the antiproliferative effects of ICI182,780. Estrogen receptor-related receptor-alpha (ERR alpha) is an orphan member of the nuclear receptor superfamily that is expressed in a wide range of tissues including breast tumors, in which its high expression correlates with poor prognosis. Although not regulated by any natural ligand, ERR alpha can be deactivated by the synthetic molecule XCT790. Here we demonstrate that this compound also induces a proteasome degradation of ERR alpha. We also show that although it does not act directly on the steady-state level of ER alpha, XCT790 potentiates the ICI182,780-induced ER alpha degradation. We suggest that treatment with XCT790 could thus enhance the efficacy of ICI182,780 in ER alpha-dependent pathologies such as breast cancer.

Significance of immunohistochemical expression of estrogen receptors alpha and beta in squamous cell carcinoma of the esophagus

PURPOSE

Possible significance of sex hormone estrogen as an antitumor therapeutic arm toward esophageal squamous cell carcinoma (ESCC) cells has been suggested. The aim of the current study was to clarify the clinicopathologic significance of an immunohistochemical expression of estrogen receptors alpha and beta (ER alpha and ER beta) in ESCC.

EXPERIMENTAL DESIGN

Expression of ER alpha and ER beta were examined using an immunohistochemical methods in 73 paraffin-embedded sections collected from patients with ESCC who had been subjected to esophageal resection and digestive reconstruction without any preoperative induction therapy.

RESULTS

Forty-seven (64.4%) ESCCs had a positive cytoplasmic expression of ER alpha and 21 (28.8%) ESCCs had a positive nuclear expression of ER beta. Univariate analysis showed that both positive ER alpha expression (P=0.0001) and negative ER beta expression (P=0.026) were unfavorable prognostic indicators in ESCC. Moreover, multivariate analysis showed that ER alpha-positive/ER beta-negative expression (P=0.003) and progression of tumor stage (P=0.014) were found to be independent unfavorable prognostic indicators in ESCCs.

CONCLUSIONS

Immunohistochemical expression of ER alpha and ER beta were found to be observed in ESCC. Positive expression of ER alpha in addition to negative expression of ER beta proved to be an unfavorable independent prognostic indicator in ESCC.

Increased expression of estrogen-related receptor alpha (ERRalpha) is a negative prognostic predictor in human prostate cancer

The nuclear receptor ERRalpha (estrogen-related receptor alpha) is known to modulate the estrogen-signaling pathway, but the biological significance of ERRalpha in the prostate remains unclear. We investigated the expression of ERRalpha in human prostate tissues and cancer cell lines to evaluate the potential roles of the receptor in prostate cancer (PC). Western blot analysis of ERRalpha was performed in three cell lines of human PC (LNCaP, DU145 and PC-3). The expressions of ERRalpha in cancerous lesions (n = 106) and benign foci (n = 99) of 106 surgically obtained prostate specimens were evaluated by immunohistochemistry. The relationships between the ERRalpha expression and clinicopathological features were evaluated. Western blot analysis using the polyclonal anti-ERRalpha antibody detected a 52 kD band in all three PC cell lines. Positive immunostaining of ERRalpha in the nuclei was found in 73 (69%) cancerous and 47 (47.5%) benign epithelium, whereas the stromal tissues were negative for ERRalpha. The mean immunoreactivity score (IR score) of the cancerous lesions (3.5 +/- 2.6) was significantly higher than that of the benign foci (1.8 +/- 2.1) (p < 0.0001). The IR score of the cancerous lesions significantly correlated with the Gleason score (p = 0.0135). Univariate and multivariate hazard analyses revealed significant correlations between elevated ERRalpha expression and poor cancer-specific survival (p = 0.0141 and 0.0367, respectively). The enhanced expression of ERRalpha might play a role in the development of human PC and serve as a significant prognostic factor for the disease.

Definition of the molecular basis for estrogen receptor-related receptor-alpha-cofactor interactions

Estrogen receptor-related receptor-alpha (ERRalpha) is an orphan nuclear receptor that does not appear to require a classical small molecule ligand to facilitate its interaction with coactivators and/or hormone response elements within target genes. Instead, the apo-receptor is capable of interacting in a constitutive manner with coactivators that stimulate transcription by acting as protein ligands. We have screened combinatorial phage libraries for peptides that selectively interact with ERRalpha to probe the architecture of the ERRalpha-coactivator pocket. In this manner, we have uncovered a fundamental difference in the mechanism by which this receptor interacts with peroxisome proliferator-activated receptor-gamma coactivator-1alpha, as compared with members of the steroid receptor coactivator subfamily of coactivators. Our findings suggest that it may be possible to develop ERRalpha ligands that exhibit different pharmacological activities as a consequence of their ability to differentially regulate coactivator recruitment. In addition, these findings have implications beyond ERRalpha because they suggest that subtle alterations in the structure of the activation function-2 pocket within any nuclear receptor may enable differential recruitment of coactivators, an observation of notable pharmaceutical importance.

Studying non-mammalian models? Not a fool's ERRand!

Through studies in mammalian model systems, the estrogen-receptor-related receptor (ERR) alpha, an orphan nuclear receptor, has been shown to interfere with estrogen signaling and might therefore be an interesting pharmaceutical target in estrogen-related diseases. ERRalpha is also involved in energy storage and consumption, and its modulation might be of relevance in the treatment of obesity and diabetes. Recent data have also been published on the effects of this receptor, as well as other members of the ERR family, in non-mammalian animal model systems. Besides indications concerning their mechanisms of action, this analysis demonstrated a role for ERRalpha in controlling cellular movements, and suggested that ERRs might be implicated in a more subtle range of processes than originally envisioned.