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

Estrogen-Related Receptor α: A Key Transcription Factor in the Regulation of Energy Metabolism at an Organismic Level and a Target of the ABA/LANCL Hormone Receptor System

The orphan nuclear receptor ERRα is the most extensively researched member of the estrogen-related receptor family and holds a pivotal role in various functions associated with energy metabolism, especially in tissues characterized by high energy requirements, such as the heart, skeletal muscle, adipose tissue, kidney, and brain. Abscisic acid (ABA), traditionally acknowledged as a plant stress hormone, is detected and actively functions in organisms beyond the land plant kingdom, encompassing cyanobacteria, fungi, algae, protozoan parasites, lower Metazoa, and mammals. Its ancient, cross-kingdom role enables ABA and its signaling pathway to regulate cell responses to environmental stimuli in various organisms, such as marine sponges, higher plants, and humans. Recent advancements in understanding the physiological function of ABA and its mammalian receptors in governing energy metabolism and mitochondrial function in myocytes, adipocytes, and neuronal cells suggest potential therapeutic applications for ABA in pre-diabetes, diabetes, and cardio-/neuroprotection. The ABA/LANCL1-2 hormone/receptor system emerges as a novel regulator of ERRα expression levels and transcriptional activity, mediated through the AMPK/SIRT1/PGC-1α axis. There exists a reciprocal feed-forward transcriptional relationship between the LANCL proteins and transcriptional coactivators ERRα/PGC-1α, which may be leveraged using natural or synthetic LANCL agonists to enhance mitochondrial function across various clinical contexts.

ERRα: unraveling its role as a key player in cell migration

Cell migration is essential throughout the life of multicellular organisms, and largely depends on the spatial and temporal regulation of cytoskeletal dynamics, cell adhesion and signal transduction. Interestingly, Estrogen-related receptor alpha (ERRα) has been identified as a major regulator of cell migration in both physiological and pathological conditions. ERRα is an orphan member of the nuclear hormone receptor superfamily of transcription factors and displays many biological functions. ERRα is a global regulator of energy metabolism, and it is also highly involved in bone homeostasis, development, differentiation, immunity and cancer progression. Importantly, in some instances, the regulation of these biological processes relies on the ability to orchestrate cell movements. Therefore, this review describes how ERRα-mediated cell migration contributes not only to tissue homeostasis but also to tumorigenesis and metastasis, and highlights the molecular and cellular mechanisms by which ERRα finely controls the cell migratory potential.

LOX, but not LOXL2, promotes bone metastasis formation and bone destruction in triple-negative breast cancer

The primary function of the lysyl oxidase (LOX) family, including LOX and its paralogue LOX-like (LOXL)-2, is to catalyze the covalent crosslinking of collagen and elastin in the extracellular matrix. LOX and LOXL2 are also facilitating breast cancer invasion and metastatic spread to visceral organs (lungs, liver) in vivo. Conversely, the contribution of LOX and LOXL2 to breast cancer bone metastasis remains scant. Here, using gene overexpression or silencing strategies, we investigated the role of LOX and LOXL2 on the formation of metastatic osteolytic lesions in animal models of triple negative breast cancer. In vivo, the extent of radiographic metastatic osteolytic lesions in animals injected with LOX-overexpressing [LOX(+)] tumor cells was 3-fold higher than that observed in animals bearing tumors silenced for LOX [LOX(-)]. By contrast, the extent of osteolytic lesions between LOXL2(+) and LOXL2(-) tumor-bearing animals did not differ, and was comparable to that observed with LOX(-) tumor-bearing animals. In situ, TRAP staining of bone tissue sections from the hind limbs of LOX(+) tumor-bearing animals was substantially increased compared to LOX(-), LOXL2(+) and LOXL2(-)-tumor-bearing animals, which was indicative of enhanced active-osteoclast resorption. In vitro, tumor-secreted LOX increased osteoclast differentiation induced by RANKL, whereas LOXL2 seemed to counteract LOX's pro-osteoclastic activity. Furthermore, LOX (but not LOXL2) overexpression in tumor cells induced a robust production of IL-6, the latter being a pro-osteoclastic cytokine. Based on these findings, we propose a model in which LOX and IL-6 secreted from tumor cells act in concert to enhance osteoclast-mediated bone resorption that, in turn, promotes metastatic bone destruction in vivo.

Distinguished biomimetic dECM system facilitates early detection of metastatic breast cancer cells

Breast cancer is the most prevalent malignant tumor affecting women's health. Bone is the most common distant metastatic organ, worsening the quality of life and increasing the mortality of patients. Early detection of breast cancer bone metastasis is urgent for halting disease progression and improving tumor prognosis. Recently, extracellular matrix (ECM) with biomimetic tissue niches opened a new avenue for tumor models in vitro. Here, we developed a biomimetic decellularized ECM (dECM) system to recapitulate bone niches at different situations, bone mimetic dECM from osteoblasts (BM-ECM) and bone tumor mimetic dECM from osteosarcoma cells (OS-ECM). The two kinds of dECMs exhibited distinct morphology, protein composition, and distribution. Interestingly, highly metastatic breast cancer cells tended to adhere and migrate on BM-ECM, while lowly metastatic breast cancer cells preferred the OS-ECM niche. Epithelial-to-mesenchymal transition was a potential mechanism to initiate the breast cancer cell migration on different biomimetic dECMs. Importantly, in the nude mice model, the dECM system captured metastatic breast cancer cells as early as 10 days after orthotopic transplantation in mammary gland pads, with higher signal on BM-ECM than that on OS-ECM. Collectively, the biomimetic dECM system might be a promising tumor model to distinguish the metastatic ability of breast cancer cells in vitro and to facilitate early detection of metastatic breast cancer cells in vivo, contributing to the diagnosis of breast cancer bone metastasis.

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

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

Role of HIF-1α/ERRα in Enhancing Cancer Cell Metabolism and Promoting Resistance of Endometrial Cancer Cells to Pyroptosis

Oxygen is critical to energy metabolism, and tumors are often characterized by a hypoxic microenvironment. Owing to the high metabolic energy demand of malignant tumor cells, their survival is promoted by metabolic reprogramming in the hypoxic microenvironment, which can confer tumor cell resistance to pyroptosis. Pyroptosis resistance can inhibit anti-tumor immunity and promote the development of malignant tumors. Hypoxia inducible factor-1α (HIF-1α) is a key regulator of metabolic reprogramming in tumor cells, and estrogen-related receptor α (ERRα) plays a key role in regulating cellular energy metabolism. Therefore, the close interaction between HIF-1α and ERRα influences the metabolic and functional changes in cancer cells. In this review, we summarize the reprogramming of tumor metabolism involving HIF-1α/ERRα. We review our understanding of the role of HIF-1α/ERRα in promoting tumor growth adaptation and pyroptosis resistance, emphasize its key role in energy homeostasis, and explore the regulation of HIF-1α/ERRα in preventing and/or treating endometrial carcinoma patients. This review provides a new perspective for the study of the molecular mechanisms of metabolic changes in tumor progression.

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

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

Effects of Estrogens on Osteoimmunology: A Role in Bone Metastasis

Bone loss associated with estrogen deficiency indicates a fundamental role of these hormones in skeletal growth and bone remodeling. In the last decades, growing recent evidence demonstrated that estrogens can also affect the immune compartment of the bone. In this review, we summarize the impacts of estrogens on bone immune cells and their consequences on bone homeostasis, metastasis settlement into the bone and tumor progression. We also addressed the role of an orphan nuclear receptor ERRalpha (“Estrogen-receptor Related Receptor alpha”) on macrophages and T lymphocytes, and as an immunomodulator in bone metastases. Hence, this review links estrogens to bone immune cells in osteo-oncology.

Emerging Roles of COX7RP and Mitochondrial Oxidative Phosphorylation in Breast Cancer

Metabolic alterations are critical events in cancers, which often contribute to tumor pathophysiology. While aerobic glycolysis is a known characteristic of cancer-related metabolism, recent studies have shed light on mitochondria-related metabolic pathways in cancer biology, including oxidative phosphorylation (OXPHOS), amino acid and lipid metabolism, nucleic acid metabolism, and redox regulation. Breast cancer is the most common cancer in women; thus, elucidation of breast cancer-related metabolic alteration will help to develop cancer drugs for many patients. We here aim to define the contribution of mitochondrial metabolism to breast cancer biology. The relevance of OXPHOS in breast cancer has been recently defined by the discovery of COX7RP, which promotes mitochondrial respiratory supercomplex assembly and glutamine metabolism: the latter is also shown to promote nucleic acid and fatty acid biosynthesis as well as ROS defense regulation. In this context, the estrogen-related receptor (ERR) family nuclear receptors and collaborating coactivators peroxisome proliferator-activated receptor-γ coactivator-1 (PGC-1) are essential transcriptional regulators for both energy production and cancer-related metabolism. Summarizing recent findings of mitochondrial metabolism in breast cancer, this review will aim to provide a clue for the development of alternative clinical management by modulating the activities of responsible molecules involved in disease-specific metabolic alterations.

miR-137/ERRα axis mediates chemoresistance of nasopharyngeal carcinoma cells

Nasopharyngeal carcinoma (NPC) is the most common malignant tumor of the head and neck region and is characterized by an increased risk of developing chemoresistance after treatment. The present study demonstrated that estrogen-related receptor α (ERRα) was upregulated in cisplatin- and fluorouracil-resistant NPC cells. In addition, ERRα knockdown or treatment of cells with the ERRα inverse agonist XCT-790 attenuated the chemoresistance of NPC cells. Mechanistically, the increased expression of ERRα in chemoresistant cells was associated with enhanced mRNA stability. Bioinformatics analysis for screening microRNAs (miRs) regulating the expression of ERRα revealed that miR-137 was downregulated in chemoresistant NPC cells. Additionally, transfection of cells with miR-137 mimics reduced ERRα mRNA stability and increased the chemosensitivity of NPC cells. Furthermore, ERRα knockdown reduced glucose consumption, and lactate and ATP production rates in chemoresistant cells. The aforementioned findings suggested that the miR-137/ERRα-mediated metabolic programming could be involved in the chemoresistance of NPC cells.

Quantitative analysis of bone microvasculature in a mouse model using the monogenic signal phase asymmetry and marker-controlled watershed

Thethree-dimensional (3D) imaging and quantitative analysis of bone microvasculature are important to describe angiogenesis involvement in bone metastatic processes. Here, we propose an algorithm based on marker-controlled watershed for the 3D segmentation of vessels and bone in mouse bone imaged with a contrast agent using synchrotron radiation micro-computed tomography (SR-μCT). Markers were generated using hysteresis thresholding and morphological filters, and the control surface was constructed using the monogenic signal phase asymmetry. The accuracy and robustness of the proposed method were evaluated on a series of synthetic volumes generated to mimic the vessel, bone and background structures. Different contrast between different structures, as well as different noise levels were considered. A series of multi-class synthetic volumes were segmented using the proposed method, and the overall segmentation quality was evaluated using the Matthews correlation coefficient (MCC) by comparing to the ground truth. Additionally, we evaluated the segmentation of thin structures under various levels of Gaussian noise. The simulation study indicated that the algorithm was performant in multi-class segmentation with different contrast, noise, and thickness. The algorithm was applied to images of bone from a mouse model of breast cancer bone metastasis acquired using SR-μCT. The segmentation quality was evaluated using the Dice coefficient and the MCC by comparing to manual segmentation. The proposed method performed better than hysteresis thresholding and marker-controlled watershed using the magnitude of the gradient as control surface. Several quantitative parameters on bone and vessels were extracted, including bone volume fraction (BV/TV), vessel volume fraction (VV/TV) and the mean vessel thickness (VTh). The bone volume fraction (BV/TV) was significantly lower in the metastatic group compared to the healthy group. This demonstrated the effectiveness of the algorithm for the study of bone and vessel microstructures in mouse model.

Estrogen-related receptors: novel potential regulators of osteoarthritis pathogenesis

Osteoarthritis (OA) is a chronic inflammatory disease that is associated with articular cartilage destruction, subchondral bone alterations, synovitis, and even joint deformity and the loss of joint function. Although current basic research on the pathogenesis of OA has made remarkable progress, our understanding of this disease still needs to be further improved. Recent studies have shown that the estrogen-related receptor (ERR) family members ERRα and ERRγ may play significant roles in the pathogenesis of OA. In this review, we refer to the latest research on ERRs and the pathogenesis of OA, elucidate the structure and physiopathological functions of the ERR orphan nuclear receptor family, and systematically examine the relationship between ERRs and OA at the molecular level. Moreover, we also discuss and predict the capacity of ERRs as potential targets in the clinical treatment of OA.

Bone metastasis: mechanisms, therapies, and biomarkers

Skeletal metastases are frequent complications of many cancers, causing bone complications (fractures, bone pain, disability) that negatively affect the patient's quality of life. Here, we first discuss the burden of skeletal complications in cancer bone metastasis. We then describe the pathophysiology of bone metastasis. Bone metastasis is a multistage process: long before the development of clinically detectable metastases, circulating tumor cells settle and enter a dormant state in normal vascular and endosteal niches present in the bone marrow, which provide immediate attachment and shelter, and only become active years later as they proliferate and alter the functions of bone-resorbing (osteoclasts) and bone-forming (osteoblasts) cells, promoting skeletal destruction. The molecular mechanisms involved in mediating each of these steps are described, and we also explain how tumor cells interact with a myriad of interconnected cell populations in the bone marrow, including a rich vascular network, immune cells, adipocytes, and nerves. We discuss metabolic programs that tumor cells could engage with to specifically grow in bone. We also describe the progress and future directions of existing bone-targeted agents and report emerging therapies that have arisen from recent advances in our understanding of the pathophysiology of bone metastases. Finally, we discuss the value of bone turnover biomarkers in detection and monitoring of progression and therapeutic effects in patients with bone metastasis.

Cholesterol as an Endogenous Ligand of ERRα Promotes ERRα-Mediated Cellular Proliferation and Metabolic Target Gene Expression in Breast Cancer Cells

Breast cancer is the 2nd leading cause of cancer-related death among women. Increased risk of breast cancer has been associated with high dietary cholesterol intake. However, the underlying mechanisms are not known. The nuclear receptor, estrogen-related receptor alpha (ERRα), plays an important role in breast cancer cell metabolism, and its overexpression has been linked to poor survival. Here we identified cholesterol as an endogenous ligand of ERRα by purification from human pregnancy serum using a GST-ERRα affinity column and liquid chromatography-tandem mass spectrometry (LC-MS/MS). We show that cholesterol interacts with ERRα and induces its transcriptional activity in estrogen receptor positive (ER+) and triple negative breast cancer (TNBC) cells. In addition, we show that cholesterol enhances ERRα-PGC-1α interaction, induces ERRα expression itself, augments several metabolic target genes of ERRα, and increases cell proliferation and migration in both ER+ and TNBC cells. Furthermore, the stimulatory effect of cholesterol on metabolic gene expression, cell proliferation, and migration requires the ERRα pathway. These findings provide a mechanistic explanation for the increased breast cancer risk associated with high dietary cholesterol and possibly the pro-survival effect of statins in breast cancer patients, highlighting the clinical relevance of lowering cholesterol levels in breast cancer patients overexpressing ERRα.

ERRα Expression in Bone Metastases Leads to an Exacerbated Antitumor Immune Response

Bone is the most common metastatic site for breast cancer. Although the estrogen-related receptor alpha (ERRα) has been implicated in breast cancer cell dissemination to the bone from the primary tumor, its role after tumor cell anchorage in the bone microenvironment remains elusive. Here, we reveal that ERRα inhibits the progression of bone metastases of breast cancer cells by increasing the immune activity of the bone microenvironment. Overexpression of ERRα in breast cancer bone metastases induced expression of chemokines CCL17 and CCL20 and repressed production of TGFβ3. Subsequently, CD8+ T lymphocytes recruited to bone metastases escaped TGFβ signaling control and were endowed with exacerbated cytotoxic features, resulting in significant reduction in metastases. The clinical relevance of our findings in mice was confirmed in over 240 patients with breast cancer. Thus, this study reveals that ERRα regulates immune properties in the bone microenvironment that contributes to decreasing metastatic growth. SIGNIFICANCE: This study places ERRα at the interplay between the immune response and bone metastases of breast cancer, highlighting a potential target for intervention in advanced disease.

The enhanced expression of estrogen-related receptor α in human bladder cancer tissues and the effects of estrogen-related receptor α knockdown on bladder cancer cells

Estrogen-related receptor α (ERRα) belongs to the superfamily of nuclear orphan receptors. However, the role of ERRα in bladder cancer remains unknown. This study examined the expression of ERRα in bladder cancer tissues and explored the molecular mechanisms of ERRα in bladder cancer progression. The expression of ERRα in bladder cancer tissues from 61 patients was determined by immunohistochemistry. We performed quantitative real-time polymerase chain reaction assay to detect the gene expression levels and carried out Western blot assay to measure protein levels. In vitro functional assays, including colony formation, Cell Counting Kit-8, Transwell invasion, and migration assays, were performed to detect bladder cancer cell growth, proliferation, invasion, and migration, respectively. Flow cytometry was used to determine the cell apoptotic rate of bladder cancer cells. Among the 61 detected bladder cancer tissues, 39 bladder cancer tissues showed positive ERRα immunoreactivity. Higher ERRα immunoreactivity score was significantly associated with TNM stage, tumor grade, distant metastasis, and poor survival in patients with bladder cancer. Univariate and multivariate analyses showed that ERRα immunoreactivity was an independent prognostic factor for overall survival in patients with bladder cancer. ERRα was found to be upregulated in bladder cancer cell lines, and knockdown of ERRα suppressed bladder cancer cell growth, proliferation, invasion, and migration; promoted bladder cancer cell apoptosis; and inhibited the epithelial-mesenchymal transition of bladder cancer cells. On the other hand, bladder cancer cell proliferation, invasion, and migration were significantly enhanced after cells were transfected with an ERRα-overexpressing vector. In vivo tumor growth and metastasis assays showed that ERRα knockdown resulted in remarkable inhibition of tumor growth and tumor metastasis in nude mice. Collectively, our results suggest that the enhanced expression of ERRα may play a key role in the development and progression of bladder cancer and ERRα may serve as an important prognostic factor for bladder cancer.

Regulatory mechanisms leading to differential Acyl-CoA synthetase 4 expression in breast cancer cells

Acyl-CoA synthetase 4 (ACSL4) overexpression plays a causal role in the aggressiveness of triple negative breast cancer. In turn, a negative correlation has been established between ACSL4 and estrogen receptor alpha (ERα) expression. However, the upstream regulatory mechanisms leading to differential ACSL4 expression between triple negative breast cancer and ERα-positive cells remained unknown. We performed the characterization of the human ACSL4 promoter and the identification of transcription factors involved. Deletional analysis demonstrated the proximal 43 base pairs of the promoter are involved in overexpression. By site directed mutagenesis we describe that retinoid-related orphan receptor alpha (RORα), Sp1 and E2F elements are involved in the promoter activity. We established for the first time that estrogen-related receptor alpha (ERRα) is a transcription factor involved in the higher activation of the human ACSL4 promoter in breast cancer cells. Furthermore, a combination of inhibitors of ACSL4 and ERRα produced a synergistic decrease in MDA-MB-231 cell proliferation. We also demonstrated that ERα restoration in triple negative breast cancer cells downregulates ACSL4 expression. The results presented in this manuscript demonstrated transcriptional mechanism is involved in the different expression of ACSL4 in human breast cancer cell lines of different aggressiveness.

Identification of Compounds That Inhibit Estrogen-Related Receptor Alpha Signaling Using High-Throughput Screening Assays

The nuclear receptor, estrogen-related receptor alpha (ERRα; NR3B1), plays a pivotal role in energy homeostasis. Its expression fluctuates with the demands of energy production in various tissues. When paired with the peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), the PGC/ERR pathway regulates a host of genes that participate in metabolic signaling networks and in mitochondrial oxidative respiration. Unregulated overexpression of ERRα is found in many cancer cells, implicating a role in cancer progression and other metabolism-related diseases. Using high throughput screening assays, we screened the Tox21 10K compound library in stably transfected HEK293 cells containing either the ERRα-reporter or the reporter plus PGC-1α expression plasmid. We identified two groups of antagonists that were potent inhibitors of ERRα activity and/or the PGC/ERR pathway: nine antineoplastic agents and thirteen pesticides. Results were confirmed using gene expression studies. These findings suggest a novel mechanism of action on bioenergetics for five of the nine antineoplastic drugs. Nine of the thirteen pesticides, which have not been investigated previously for ERRα disrupting activity, were classified as such. In conclusion, we demonstrated that high-throughput screening assays can be used to reveal new biological properties of therapeutic and environmental chemicals, broadening our understanding of their modes of action.

ERRα promotes breast cancer cell dissemination to bone by increasing RANK expression in primary breast tumors

Bone is the most common metastatic site for breast cancer. Estrogen-related-receptor alpha (ERRα) has been implicated in cancer cell invasiveness. Here, we established that ERRα promotes spontaneous metastatic dissemination of breast cancer cells from primary mammary tumors to the skeleton. We carried out cohort studies, pharmacological inhibition, gain-of-function analyses in vivo and cellular and molecular studies in vitro to identify new biomarkers in breast cancer metastases. Meta-analysis of human primary breast tumors revealed that high ERRα expression levels were associated with bone but not lung metastases. ERRα expression was also detected in circulating tumor cells from metastatic breast cancer patients. ERRα overexpression in murine 4T1 breast cancer cells promoted spontaneous bone micro-metastases formation when tumor cells were inoculated orthotopically, whereas lung metastases occurred irrespective of ERRα expression level. In vivo, Rank was identified as a target for ERRα. That was confirmed in vitro in Rankl stimulated tumor cell invasion, in mTOR/pS6K phosphorylation, by transactivation assay, ChIP and bioinformatics analyses. Moreover, pharmacological inhibition of ERRα reduced primary tumor growth, bone micro-metastases formation and Rank expression in vitro and in vivo. Transcriptomic studies and meta-analysis confirmed a positive association between metastases and ERRα/RANK in breast cancer patients and also revealed a positive correlation between ERRα and BRCA1mut carriers. Taken together, our results reveal a novel ERRα/RANK axis by which ERRα in primary breast cancer promotes early dissemination of cancer cells to bone. These findings suggest that ERRα may be a useful therapeutic target to prevent bone metastases.

Receptor activator of nuclear factor kB ligand, osteoprotegerin, and risk of death following a breast cancer diagnosis: results from the EPIC cohort

BACKGROUND

Receptor activator of nuclear factor kappa-B (RANK)-signaling is involved in tumor growth and spread in experimental models. Binding of RANK ligand (RANKL) to RANK activates signaling, which is inhibited by osteoprotegerin (OPG). We have previously shown that circulating soluble RANKL (sRANKL) and OPG are associated with breast cancer risk. Here we extend these findings to provide the first data on pre-diagnosis concentrations of sRANKL and OPG and risk of breast cancer-specific and overall mortality after a breast cancer diagnosis.

METHODS

Two thousand six pre- and postmenopausal women with incident invasive breast cancer (1620 (81%) with ER+ disease) participating in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort were followed-up for mortality. Pre-diagnosis concentrations of sRANKL and OPG were quantified in baseline serum samples using an enzyme-linked immunosorbent assay and electrochemiluminescent assay, respectively. Hazard ratios (HRs) and 95% confidence intervals (CIs) for breast cancer-specific and overall mortality were calculated using Cox proportional hazards regression models.

RESULTS

Especially in women with ER+ disease, higher circulating OPG concentrations were associated with higher risk of breast cancer-specific (quintile 5 vs 1 HR 1.77 [CI 1.03, 3.04]; ptrend 0.10) and overall mortality (q5 vs 1 HR 1.39 [CI 0.94, 2.05]; ptrend 0.02). sRANKL and the sRANKL/OPG ratio were not associated with mortality following a breast cancer diagnosis.

CONCLUSIONS

High pre-diagnosis endogenous concentrations of OPG, the decoy receptor for RANKL, were associated with increased risk of death after a breast cancer diagnosis, especially in those with ER+ disease. These results need to be confirmed in well-characterized patient cohorts.

Breast Cancer Metastasis: Are Cytokines Important Players During Its Development and Progression?

In breast cancer, an uncontrolled cell proliferation leads to tumor formation and development of a multifactorial disease. Metastasis is a complex process that involves tumor spread to distant parts of the body from its original site. Metastatic dissemination represents the main physiopathology of cancer. Inter- and intracellular communication in all systems in vertebrates is mediated by cytokines, which are highly inducible, secretory proteins, produced not only by immune system cells, but also by endocrine and nervous system cells. It has become clear in recent years that cytokines, as well as their receptors are produced in the organisms under physiological and pathological conditions; recently, they have been closely related to breast cancer metastasis. The exact initiation process of breast cancer metastasis is unknown, although several hypotheses have emerged. In this study, we thoroughly reviewed the role of several cytokines in breast cancer metastasis. Data reviewed suggest that cytokines and growth factors are key players in the breast cancer metastasis induction. This knowledge must be considered with the aim to development of new therapeutic approaches to counter breast cancer metastasis.

A novel fatty acid-binding protein 5-estrogen-related receptor α signaling pathway promotes cell growth and energy metabolism in prostate cancer cells

Epidermal or cutaneous fatty acid-binding protein is an intracellular lipid-binding protein, also known as FABP5, and its expression level is closely related to cancer cell proliferation and metastatic activities in various types of carcinoma. However, the molecular mechanisms of FABP5 in cancer cell proliferation and its other functions have remained unclear. In the present study, we have clearly revealed that FABP5 activated expression of metabolic genes (ATP5B, LCHAD, ACO2, FH and MFN2) via a novel signaling pathway in an ERRα (estrogen-related receptor α)-dependent manner in prostate cancer cell lines. To clarify the novel function of FABP5, we examined the activation mechanisms of the ERRα target genes via FABP5. A direct protein-protein interaction between FABP5 and ERRα was demonstrated by immunoprecipitation and GST pull-down assays. We have clearly revealed that FABP5 interacted directly with transcriptional complex containing ERRα and its co-activator PGC-1β to increase expression of the ERRα target genes. In addition, we have shown that FABP5 knockdown induced high energy stress leading to induction of apoptosis and cell cycle arrest via AMPK-FOXO3A signaling pathway in prostate cancer cells, suggesting that FABP5 plays an important role in cellular energy status directing metabolic adaptation to support cellular proliferation and survival.

miRNA-30 Family Members Inhibit Breast Cancer Invasion, Osteomimicry, and Bone Destruction by Directly Targeting Multiple Bone Metastasis-Associated Genes

miRNAs are master regulators of gene expression that play key roles in cancer metastasis. During bone metastasis, metastatic tumor cells must rewire their biology and express genes that are normally expressed by bone cells (a process called osteomimicry), which endow tumor cells with full competence for outgrowth in the bone marrow. Here, we establish miR-30 family members miR-30a, miR-30b, miR-30c, miR-30d, and miR-30e as suppressors of breast cancer bone metastasis that regulate multiple pathways, including osteomimicry. Low expression of miR-30 in primary tumors from patients with breast cancer were associated with poor relapse-free survival. In addition, estrogen receptor (ER)-negative/progesterone receptor (PR)-negative breast cancer cells expressed lower miR-30 levels than their ER/PR-positive counterparts. Overexpression of miR-30 in ER/PR-negative breast cancer cells resulted in the reduction of bone metastasis burden in vivoIn vitro, miR-30 did not affect tumor cell proliferation, but did inhibit tumor cell invasion. Furthermore, overexpression of miR-30 restored bone homeostasis by reversing the effects of tumor cell-conditioned medium on osteoclastogenesis and osteoblastogenesis. A number of genes associated with osteoclastogenesis stimulation (IL8, IL11), osteoblastogenesis inhibition (DKK-1), tumor cell osteomimicry (RUNX2, CDH11), and invasiveness (CTGF, ITGA5, ITGB3) were identified as targets for repression by miR-30. Among these genes, silencing CDH11 or ITGA5 in ER-/PR-negative breast cancer cells recapitulated inhibitory effects of miR-30 on skeletal tumor burden in vivo Overall, our findings provide evidence that miR-30 family members employ multiple mechanisms to impede breast cancer bone metastasis and may represent attractive targets for therapeutic intervention.Significance: These findings suggest miR-30 family members may serve as an effective means to therapeutically attenuate metastasis in triple-negative breast cancer. Cancer Res; 78(18); 5259-73. ©2018 AACR.

LSD1-ERRα complex requires NRF1 to positively regulate transcription and cell invasion

Lysine-specific demethylase 1 (LSD1) exerts dual effects on histone H3, promoting transcriptional repression via Lys4 (H3K4) demethylation or transcriptional activation through Lys9 (H3K9) demethylation. These activities are often exerted at transcriptional start sites (TSSs) and depend on the type of enhancer-bound transcription factor (TFs) with which LSD1 interacts. In particular, the Estrogen-Receptor Related α (ERRα) TF interacts with LSD1 and switches its activities toward H3K9 demethylation, resulting in transcriptional activation of a set of common target genes. However, how are the LSD1-TF and, in particular LSD1-ERRα, complexes determined to act at TSSs is not understood. Here we show that promoter-bound nuclear respiratory factor 1 (NRF1), but not ERRα, is essential to LSD1 recruitment at the TSSs of positive LSD1-ERRα targets. In contrast to ERRα, NRF1 does not impact on the nature of LSD1 enzymatic activity. We propose a three factor model, in which the LSD1 histone modifier requires a TSS tethering factor (NRF1) as well as an activity inducer (ERRα) to transcriptionally activate common targets. The relevance of this common network is illustrated by functional data, showing that all three factors are required for cell invasion in an MMP1 (Matrix MetalloProtease 1)-dependent manner, the expression of which is regulated by NRF1/LSD1/ERRα-mediated H3K9me2 demethylation.

Estrogen-related receptors alpha, beta and gamma expression and function is associated with transcriptional repressor EZH2 in breast carcinoma

BACKGROUND

Orphan nuclear receptors ERRα, ERRβ and ERRγ that belong to NR3B or type IV nuclear receptor family are well studied for their role in breast cancer pathophysiology. Their homology with the canonical estrogen receptor dictates their possible contributing role in mammary gland development and disease. Although function and regulation of ERRα, ERRγ and less about ERRβ is reported, role of histone methylation in their altered expression in cancer cells is not studied. Transcriptional activity of nuclear receptors depends on co-regulatory proteins. The present study for the first time gives an insight into regulation of estrogen-related receptors by histone methylation specifically through methyltransferase EZH2 in breast cancer.

METHODS

Expression of ERRα, ERRβ, ERRγ and EZH2 was assessed by immunohistochemistry in four identical tissue array slides that were prepared as per the protocol. The array slides were stained with ERRα, ERRβ, ERRγ and EZH2 simultaneously. Array data was correlated with expression in MERAV expression dataset. Pearson correlation coeficient r was calculated from the partial matrix expression values available at MERAV database to study the strength of association between EZH2 and three orphan nuclear receptors under study. By western blot and real time PCR, their correlated expression was studied in breast cancer cell lines MCF-7, MDA-MB-231, T47D and MDA-MB-453 including normal breast epithelial MCF-10A cells at both protein and RNA level. Regulation of ERRα, ERRβ, ERRγ by EZH2 was further investigated upon overexpression and silencing of EZH2. The interaction between ERRs and EZH2 was validated in vivo by CHIP-qPCR.

RESULTS

We found a negative correlation between estrogen-related receptors and Enhancer of Zeste Homolog 2, a global repressor gene. Immunohistochemistry in primary breast tumors of different grades showed a correlated expression of estrogen-related receptors and EZH2. Their correlated expression was further validated using online MERAV expression dataset where a negative correlation of variable strengths was observed in breast cancer. Ectopic expression of EZH2 in low EZH2-expressing normal breast epithelial cells abrogated their expression and at the same time, its silencing enhanced the expression of estrogen-related receptors in cancerous cells. Global occupancy of EZH2 on ERRα and ERRβ was observed in-vivo.

CONCLUSION

Our findings identify EZH2 as a relevant coregulator for estrogen-related receptors in breast carcinoma.

Estrogen and Androgen Blockade for Advanced Prostate Cancer in the Era of Precision Medicine

Androgen deprivation therapy (ADT) has been widely prescribed for patients with advanced prostate cancer (PC) to control key signaling pathways via androgen receptor (AR) and AR-collaborative transcriptional factors; however, PC gradually acquires a lethal phenotype and results in castration-resistant PC (CRPC) during ADT. Therefore, new therapeutic strategies are required in clinical practice. In addition, ARs; estrogen receptors (ERs; ERα and ERβ); and estrogen-related receptors (ERRs; ERRα, ERRβ, and ERRγ) have been reported to be involved in the development or regulation of PC. Recent investigations have revealed the role of associated molecules, such as KLF5, FOXO1, PDGFA, VEGF-A, WNT5A, TGFβ1, and micro-RNA 135a of PC, via ERs and ERRs. Selective ER modulators (SERMs) have been developed. Recently, estrogen and androgen blockade (EAB) using a combination of toremifene and ADT has been demonstrated to improve biochemical recurrence rate in treatment-naïve bone metastatic PC. In the future, the suitability of ADT alone or EAB for individuals may be evaluated by making clinical decisions on the basis of information obtained from RT-PCR, gene-panel, or liquid biopsy to create a “personalized medicine” or “precision medicine”. In this review, we summarize ER and ERR signaling pathways, molecular diagnosis, and SERMs as candidates for advanced PC treatment.

IL-8 Is Involved in Estrogen-Related Receptor α-Regulated Proliferation and Migration of Colorectal Cancer Cells

BACKGROUND AND AIMS

Studies revealed that estrogenic signals were involved in the development of colorectal cancer (CRC), while the roles of estrogen related receptor (ERR) on the progression of CRC have not been well illustrated. Its roles on the development of CRC were investigated.

METHODS

The expression of ERRα/β/γ in CRC cells were measured. The effects of ERRα on cell proliferation, migration and expression of cytokines were investigated accordingly.

RESULTS

Our data revealed that the expression of ERRα, while not ERRβ or ERRγ, was significantly increased in CRC cells and clinical CRC tissues. Both the inverse agonist of ERRα (XCT-790) and si-ERRα can inhibit the proliferation of CRC cells. XCT-790 treatment can also suppress the wound healing and in vitro migration of CRC cells. Cytokine assays showed that XCT-790 can significantly decrease the expression of interleukin-8 (IL-8), while not IL-4, IL-6, IL-8, IL-9, IL-10, IL-18, IFN-γ, or TGF-β, in CRC cells. Over expression of ERRα increased the expression of IL-8. Luciferase assay showed XCT-790 decreased the promoter activity of IL-8. XCT-790 can increase the decay of IL-8 mRNA in SW480 cells. The recombinant IL-8 (rIL-8) can rescue XCT-790 induced suppression of proliferation and migration of CRC cells. XCT-790 can decrease the phosphorylation of ERK1/2 and STAT3, two downstream signal molecules of IL-8, in CRC cells. While rIL-8 can markedly attenuate XCT-790 induced dephosphorylation of ERK1/2 and STAT3.

CONCLUSION

Our data showed that ERRα can trigger the proliferation and migration of CRC cells via up regulation of IL-8. Therefor targeted inhibition of ERRα/IL-8 might be a potential approach for CRC treatment and drug development.

Estrogen-related receptor α participates transforming growth factor-β (TGF-β) induced epithelial-mesenchymal transition of osteosarcoma cells

Osteosarcoma patients often exhibit pulmonary metastasis, which results in high patient mortality. Understanding the mechanisms of advanced metastasis in osteosarcoma cell is important for the targeted treatment and drug development. Our present study revealed that transforming growth factor-β (TGF-β) treatment can significantly promote the in vitro migration and invasion of human osteosarcoma MG-63 and HOS cells. The loss of epithelial characteristics E-cadherin (E-Cad) and up regulation of mesenchymal markers Vimentin (Vim) suggested TGF-β induced epithelial-mesenchymal transition (EMT) of osteosarcoma cells. TGF-β treatment obviously increased the expression of Snail, a key EMT-related transcription factor, in both MG-63 and HOS cells. Silencing of Snail markedly attenuated TGF-β induced down regulation of E-cad and up regulation of Vim. TGF-β treatment also significantly increased the expression and nuclear translocation of estrogen-related receptors α (ERRα), while had no obvious effect on the expression of ERα, ERβ, or ERRγ. Knock down of ERRα or its inhibitor XCT-790 significantly attenuated TFG-β induced EMT and transcription of Snail in osteosarcoma cells. Collectively, our present study revealed that TGF-β treatment can trigger the EMT of osteosarcoma cells via ERRα/Snail pathways. Our data suggested that ERRα/Snail pathways might be potential therapeutic targets of metastasis of osteosarcoma cells.

ERRα negatively regulates type I interferon induction by inhibiting TBK1-IRF3 interaction

Estrogen-related receptor α (ERRα) is a member of the nuclear receptor superfamily controlling energy homeostasis; however, its precise role in regulating antiviral innate immunity remains to be clarified. Here, we showed that ERRα deficiency conferred resistance to viral infection both in vivo and in vitro. Mechanistically, ERRα inhibited the production of type-I interferon (IFN-I) and the expression of multiple interferon-stimulated genes (ISGs). Furthermore, we found that viral infection induced TBK1-dependent ERRα stabilization, which in turn associated with TBK1 and IRF3 to impede the formation of TBK1-IRF3, IRF3 phosphorylation, IRF3 dimerization, and the DNA binding affinity of IRF3. The effect of ERRα on IFN-I production was independent of its transcriptional activity and PCG-1α. Notably, ERRα chemical inhibitor XCT790 has broad antiviral potency. This work not only identifies ERRα as a critical negative regulator of antiviral signaling, but also provides a potential target for future antiviral therapy.

ERRα induces H3K9 demethylation by LSD1 to promote cell invasion

Lysine Specific Demethylase 1 (LSD1) removes mono- and dimethyl groups from lysine 4 of histone H3 (H3K4) or H3K9, resulting in repressive or activating (respectively) transcriptional histone marks. The mechanisms that control the balance between these two antagonist activities are not understood. We here show that LSD1 and the orphan nuclear receptor estrogen-related receptor α (ERRα) display commonly activated genes. Transcriptional activation by LSD1 and ERRα involves H3K9 demethylation at the transcriptional start site (TSS). Strikingly, ERRα is sufficient to induce LSD1 to demethylate H3K9 in vitro. The relevance of this mechanism is highlighted by functional data. LSD1 and ERRα coregulate several target genes involved in cell migration, including the MMP1 matrix metallo-protease, also activated through H3K9 demethylation at the TSS. Depletion of LSD1 or ERRα reduces the cellular capacity to invade the extracellular matrix, a phenomenon that is rescued by MMP1 reexpression. Altogether our results identify a regulatory network involving a direct switch in the biochemical activities of a histone demethylase, leading to increased cell invasion.

Osteoprotegerin and breast cancer risk by hormone receptor subtype: a nested case-control study in the EPIC cohort

BACKGROUND

Circulating osteoprotegerin (OPG), a member of the receptor activator of nuclear factor kappa-B (RANK) axis, may influence breast cancer risk via its role as the decoy receptor for both the RANK ligand (RANKL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Circulating OPG and breast cancer risk has been examined in only one prior study.

METHODS

A case-control study was nested in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. A total of 2008 incident invasive breast cancer cases (estrogen receptor (ER)+, n = 1622; ER-, n = 386), matched 1:1 to controls, were included in the analysis. Women were predominantly postmenopausal at blood collection (77%); postmenopausal women included users and non-users of postmenopausal hormone therapy (HT). Serum OPG was quantified with an electrochemiluminescence assay. Relative risks (RRs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression.

RESULTS

The associations between OPG and ER+ and ER- breast cancer differed significantly. Higher concentrations of OPG were associated with increased risk of ER- breast cancer (top vs. bottom tertile RR = 1.93 [95% CI 1.24-3.02]; p trend = 0.03). We observed a suggestive inverse association for ER+ disease overall and among women premenopausal at blood collection. Results for ER- disease did not differ by menopausal status at blood collection (p het = 0.97), and we observed no heterogeneity by HT use at blood collection (p het ≥ 0.43) or age at breast cancer diagnosis (p het ≥ 0.30).

CONCLUSIONS

This study provides the first prospective data on OPG and breast cancer risk by hormone receptor subtype. High circulating OPG may represent a novel risk factor for ER- breast cancer.

Key Factors in Breast Cancer Dissemination and Establishment at the Bone: Past, Present and Future Perspectives

Bone metastases associated with breast cancer remain a clinical challenge due to their associated morbidity, limited therapeutic intervention and lack of prognostic markers. With a continually evolving understanding of bone biology and its dynamic microenvironment, many potential new targets have been proposed. In this chapter, we discuss the roles of well-established bone markers and how their targeting, in addition to tumour-targeted therapies, might help in the prevention and treatment of bone metastases. There are a vast number of bone markers, of which one of the best-known families is the bone morphogenetic proteins (BMPs). This chapter focuses on their role in breast cancer-associated bone metastases, associated signalling pathways and the possibilities for potential therapeutic intervention. In addition, this chapter provides an update on the role receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) play on breast cancer development and their subsequent influence during the homing and establishment of breast cancer-associated bone metastases. Beyond the well-established bone molecules, this chapter also explores the role of other potential factors such as activated leukocyte cell adhesion molecule (ALCAM) and its potential impact on breast cancer cells' affinity for the bone environment, which implies that ALCAM could be a promising therapeutic target.

Estrogen related receptor alpha in castration-resistant prostate cancer cells promotes tumor progression in bone

Bone metastases are one of the main complications of prostate cancer and they are incurable. We investigated whether and how estrogen receptor-related receptor alpha (ERRα) is involved in bone tumor progression associated with advanced prostate cancer. By meta-analysis, we first found that ERRα expression is correlated with castration-resistant prostate cancer (CRPC), the hallmark of progressive disease. We then analyzed tumor cell progression and the associated signaling pathways in gain-of-function/loss-of-function CRPC models in vivo and in vitro. Increased levels of ERRα in tumor cells led to rapid tumor progression, with both bone destruction and formation, and direct impacts on osteoclasts and osteoblasts. VEGF-A, WNT5A and TGFβ1 were upregulated by ERRα in tumor cells and all of these factors also significantly and positively correlated withERRα expression in CRPC patient specimens. Finally, high levels of ERRα in tumor cells stimulated the pro-metastatic factor periostin expression in the stroma, suggesting that ERRα regulates the tumor stromal cell microenvironment to enhance tumor progression. Taken together, our data demonstrate that ERRα is a regulator of CRPC cell progression in bone. Therefore, inhibiting ERRα may constitute a new therapeutic strategy for prostate cancer skeletal-related events.

Hydroxytyrosol decreases the oxidative and nitrosative stress levels and promotes angiogenesis through HIF-1 independent mechanisms in renal hypoxic cells

In the kidney, tissue oxygen tension is comparatively low and this renders this organ more prone to hypoxic injury. In fact, hypoxia has a central role in the development and progression of renal disease. The recovery from this situation is dependent on the degree to which sublethally damaged cells restore normal function. The master regulator of the hypoxic response is hypoxia-inducible factor-1 (HIF-1). HIF-1 activity depends on the HIF-1α subunit level which is regulated by oxygen, nitric oxide (NO), reactive oxygen species and mTOR. Given the antioxidant and antinitrosative properties ascribed to hydroxytyrosol (HT), this study evaluates the impact of this olive oil polyphenol on the response to hypoxia in kidney cells. For this purpose, the human embryonic kidney HEK293T cell line was treated with HT and cultured under sublethal hypoxic conditions. Our results demonstrate that HT treatment decreases both, post-hypoxic reactive oxygen species and NO levels and, consequently, HIF-1α accumulation. However, HT does not affect mTOR activation or the factor inhibiting HIF level but promotes the expression of angiogenic proteins, suggesting that HT activates an adaptive response to hypoxia in a HIF-1α-independent pathway. In fact, this effect could be ascribed to the up-regulation of estrogen-related receptor α. In conclusion, our results suggest that in renal hypoxia, HT treatment might act as an effective preventive therapeutic approach to decrease stress and to improve the adaptive response to this pathological situation.

MicroRNA-497 downregulation contributes to cell proliferation, migration, and invasion of estrogen receptor alpha negative breast cancer by targeting estrogen-related receptor alpha

Metastasis has become the main challenge for treatment of estrogen receptor alpha (ERα) negative breast cancer. Here, we found a negative correlation between miR-497 and estrogen-related receptor alpha (ERRα), a nuclear receptor overexpressed in ERα negative breast cancer. Targeted inhibition of ERRα by si-RNA increased miR-497 expression while overexpression of ERRα inhibited miR-497 expression. Further investigation showed that miR-497 targeted ERRα by binding to the 3'UTR region of ERRα. Luciferase assay and ChIP assay confirmed that ERα directly regulated the transcription of miR-497, suggesting that loss of ERα lowered miR-497 level in ERα negative breast cancer. Further, overexpression of miR-497 not only inhibited ERRα expression but also reduced MIF level and MMP9 activity, which led to significant decreases in cell proliferation, migration, and invasion of ERα negative breast cancer. Taken together, our findings suggested that, in ERα negative breast cancer, the low level of ERα reduced miR-497 expression, which promoted ERRα expression that enhanced cell proliferation, migration, and invasion by increasing MIF expression and MMP9 activity.

The estrogen-related receptors (ERRs): potential targets against bone loss

Bone loss and the resulting skeletal fragility is induced by several pathological or natural conditions, the most prominent of which being aging as well as the decreased levels of circulating estrogens in post-menopause females. To date, most treatments against bone loss aim at preventing excess bone resorption. We here summarize data indicating that the estrogen-related receptors (ERRs) α and γ prevent bone formation. Inhibiting these receptors may thus constitute an anabolic approach by increasing bone formation.

The PLA2R1-JAK2 pathway upregulates ERRα and its mitochondrial program to exert tumor-suppressive action

Little is known about the biological role of the phospholipase A2 receptor (PLA2R1) transmembrane protein. In recent years, PLA2R1 has been shown to have an important role in regulating tumor-suppressive responses via JAK2 activation, but the underlying mechanisms are largely undeciphered. In this study, we observed that PLA2R1 increases the mitochondrial content, judged by increased levels of numerous mitochondrial proteins, of the mitochondrial structural component cardiolipin, of the mitochondrial DNA content, and of the mitochondrial DNA replication and transcription factor TFAM. This effect of PLA2R1 relies on a transcriptional program controlled by the estrogen-related receptor alpha1 (ERRα) mitochondrial master regulator. Expression of ERRα and of its nucleus-encoded mitochondrial targets is upregulated upon PLA2R1 ectopic expression, and this effect is mediated by JAK2. Conversely, downregulation of PLA2R1 decreases the level of ERRα and of its nucleus-encoded mitochondrial targets. Finally, blocking the ERRα-controlled mitochondrial program largely inhibits the PLA2R1-induced tumor-suppressive response. Together, our data document ERRα and its mitochondrial program as downstream effectors of the PLA2R1-JAK2 pathway leading to oncosuppression.

Estrogen-Related Receptors and the control of bone cell fate

Bone loss is naturally occurring in aging males and females and exacerbated in the latter after menopause, altogether leading to cumulative skeleton fragility and increased fracture risk. Two types of therapeutic strategies can be envisioned to counteract age- or menopause-associated bone loss, aiming at either reducing bone resorption exerted by osteoclasts or, alternatively, promoting bone formation by osteoblasts. We here summarize data suggesting that inhibition of the Estrogen-Related Receptors α and/or γ could promote bone formation and compensate for bone loss induced by ageing or estrogen-deficiency.

The emerging roles of orphan nuclear receptors in prostate cancer

Orphan nuclear receptors are members of the nuclear receptor (NR) superfamily and are so named because their endogenous physiological ligands are either unknown or may not exist. Because of their important regulatory roles in many key physiological processes, dysregulation of signalings controlled by these receptors is associated with many diseases including cancer. Over years, studies of orphan NRs have become an area of great interest because their specific physiological and pathological roles have not been well-defined, and some of them are promising drug targets for diseases. The recently identified synthetic small molecule ligands, acting as agonists or antagonists, to these orphan NRs not only help to understand better their functional roles but also highlight that the signalings mediated by these ligand-independent NRs in diseases could be therapeutically intervened. This review is a summary of the recent advances in elucidating the emerging functional roles of orphan NRs in cancers, especially prostate cancer. In particular, some orphan NRs, RORγ, TR2, TR4, COUP-IFII, ERRα, DAX1 and SHP, exhibit crosstalk or interference with androgen receptor (AR) signaling in either normal or malignant prostatic cells, highlighting their involvement in prostate cancer progression as androgen and AR signaling pathway play critical roles in this process. We also propose that a better understanding of the mechanism of actions of these orphan NRs in prostate gland or prostate cancer could help to evaluate their potential value as therapeutic targets for prostate cancer.

miR-135a Inhibits the Invasion of Cancer Cells via Suppression of ERRα

MicroRNA-135a (miR-135a) down-modulates parameters of cancer progression and its expression is decreased in metastatic breast cancers (as compared to non-metastatic tumors) as well as in prostate tumors relative to normal tissue. These expression and activity patterns are opposite to those of the Estrogen-Related Receptor α (ERRα), an orphan member of the nuclear receptor family. Indeed high expression of ERRα correlates with poor prognosis in breast and prostate cancers, and the receptor promotes various traits of cancer aggressiveness including cell invasion. Here we show that miR-135a down-regulates the expression of ERRα through specific sequences of its 3'UTR. As a consequence miR-135a also reduces the expression of downstream targets of ERRα. miR-135a also decreases cell invasive potential in an ERRα-dependent manner. Our results suggest that the decreased expression of miR-135a in metastatic tumors leads to elevated ERRα expression, resulting in increased cell invasion capacities.

The role of osteoclasts in breast cancer bone metastasis

Breast cancer frequently metastasises to the skeleton, interfering with the normal bone remodelling process and inducing bone degradation. Bone degradation is caused by osteoclasts, the normal bone-resorbing cells. Osteoclast-mediated bone degradation subsequently leads to the release of bone-derived factors that promote skeletal tumour growth. Osteoclasts themselves stimulate tumour growth. This Review describes the molecular mechanisms through which osteoclasts and breast cancer cells collaborate with each other, triggering the formation of osteolytic bone metastasis.

Research progress on the reproductive and non-reproductive endocrine tumors by estrogen-related receptors

Oncologists have traditionally considered that tumorigenesis are closely related to classical nuclear estrogen receptors (ERs), such as estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ), through the ligands binding and target gene transcription induction. Estrogen-related receptors (ERRs) have similar structures with ERs, which are also gradually thought to be relevant to reproductive endocrine tumor diseases, even non-reproductive endocrine tumors. In this review, different subtypes of ERRs and their structures firstly will be introduced, then the expression patterns in gynecological oncology (i.e., breast cancer, endometrial cancer, and ovarian cancer), male genitourinary system malignancy especially prostatic cancer along with other non-reproductive endocrine tumors (i.e., lung cancer, colorectal cancer, and liver cancer) will be described, and simultaneously the role of tumorigenesis related to ERRs will be discussed. Therefore, the review is benefit to explore the way of tumor prevention and treatment.

Downregulation of ERRα inhibits angiogenesis in human umbilical vein endothelial cells through regulating VEGF production and PI3K/Akt/STAT3 signaling pathway

The human estrogen related receptor α (ERRα) is a pivotal regulator involved in energy homeostasis and mitochondrial biogenesis. It has been demonstrated that activation of ERRα in various breast cancer cells results in a significant increase of vascular endothelial growth factor (VEGF) mRNA and protein secretion. However, little is known about the relationship between ERRα and angiogenesis. Thus, the present study is aimed to investigate the effects and mechanism of ERRα suppression on the angiogenesis in human umbilical vein endothelial cells (HUVECs). Here we show that ERRα suppression powerfully inhibits proliferation, migration and capillary-like structures formation of HUVECs. Importantly, we demonstrate that these inhibitory effects are associated with the significantly reduced expression and production of VEGF. Results from further experiments using western blot and luciferase reporter assay exhibit that ERRα suppression inhibits hypoxia-inducible factor 1α (HIF-1α) expression, and phosphorylation of protein kinase B (Akt) and signal transducer and activator of transcription (STAT3) which up-regulated VEGF expression. In summary, we show that ERRα suppression inhibits angiogenesis in HUVECs and deserves further studies for application of rationale therapeutic target for patient with diseases related with aberrant angiogenesis.

Skeletal metastases from breast cancer: pathogenesis of bone tropism and treatment strategy

Breast cancer (BC) is the most common female cancer worldwide with approximately 10 % of new cases metastatic at diagnosis and 20-50 % of patients with early BC who will eventually develop metastatic disease. Bone is the most frequent site of colonisation and the development of skeletal metastases depends on a complex multistep process, from dissemination and survival of malignant cells into circulation to the actual homing and metastases formation inside bone. Disseminated tumor cells (DTCs) can be detected in bone marrow in approximately 30 % of BC patients, likely reflecting the presence of minimal residual disease that would eventually account for subsequent metastatic disease. Patients with bone marrow DTCs have poorer overall survival compared with patients without them. Although bone-only metastatic disease seems to have a rather indolent behavior compared to visceral disease, bone metastases can cause severe and debilitating effects, including pain, spinal cord compression, hypercalcemia and pathologic fractures. Delivering an appropriate treatment is therefore paramount and ideally it should require interdisciplinary care. Multiple options are currently available, from bisphosphonates to new drugs targeting RANK ligand and radiotherapy. In this review we describe the mechanisms underlying bone colonization and provide an update on existing systemic and locoregional treatments for bone metastases.

Estrogen-related receptor alpha and cancer: axis of evil

Cancer is perhaps the fastest growing non-communicable disease in the human population worldwide. Although the molecular mechanism of cancer initiation and progression is known to some extent, however, the majority of pathways responsible for its onset, development and progression are largely unknown. Many members of the nuclear receptors (NRs) superfamily of transcriptional factors have key roles in cancer. Estrogen-related receptor alpha (ERRα) is one of the members of the NR superfamily and studies have linked it with a wide variety of cancers. In endocrine-related cancers such as breast cancer, ERRα regulates a number of target genes directing cell proliferation and growth independent of estrogen receptor alpha (ERα). Knockdown of ERRα in a number of cancer tissues and cell lines significantly reduced tumor growth and malignancy indicating dependence on ERRα activity. The pro-angiogenesis factor vascular endothelial growth factor expression has been shown to be regulated by ERRα and has implications in several types of cancer. The effect of ERRα on cancers seems to be multipronged via regulation of cell cycle regulators, osteopontin, hypoxia inducible factor-1 as well as several energy metabolism genes that are part of glycolysis, TCA cycle, lipogenesis, etc., providing a metabolic twist to cancer. In this article, the action of ERRα on various types of cancers including new developments in this field shall be reviewed.

Inhibition of ERRα suppresses epithelial mesenchymal transition of triple negative breast cancer cells by directly targeting fibronectin

Triple-negative breast cancer (TNBC) patients have poor prognosis due to the aggressive metastatic behaviors. Our study reveals that expression of estrogen related receptor α (ERRα) is significantly (p < 0.01) positively associated with high grade tumors and lymph node metastasis, while negatively correlated with overall survival (OS), in 138 TNBC patients. Targeted inhibition of ERRα by its inverse agonist XCT-790 or si-RNA obviously inhibits in vitro motility of TNBC cells. While over expression of ERRα triggers the invasion and migration of TNBC cells. Further, si-ERRα and XCT-790 inhibit the epithelial mesenchymal transition (EMT) of TNBC cells with increasing the expression of E-cadherin and decreasing fibronectin (FN) and vimentin. While XCT-790 has no effect on the expression of EMT related transcription factors such as Snail or Slug. Further, inhibitors of MAPK, PI3K/Akt, NF-κB signal molecules, which are activated by XCT-790, can not attenuate the suppression effects of XCT-790 on EMT. Alternatively, luciferase reporter gene assays and ChIP analysis indicate that ERRα can directly bind with FN promoter at ERR response element-3 (ERRE-1), ERRE-3, and ERRE-4, while XCT-790 reduces this bond. In vivo data show that ERRα expression is significantly (p < 0.05) correlated with FN in clinical TNBC patients. In MDA-MB-231 tumor xenograft models, XCT-790 decreases the expression of FN, inhibits the growth and lung metastasis, and suppresses the EMT. Our results demonstrate that ERRα functions as a metastasis stimulator and its targeted inhibition may be a new therapeutic strategy for TNBC treatment.

Osteoprotegerin in breast cancer: beyond bone remodeling

Osteoprotegerin (OPG) is a secreted protein and member of the Tumor Necrosis Factor (TNF) Receptor superfamily. OPG has been well characterized as a regulator of bone metabolism which acts by blocking osteoclast maturation and preventing bone breakdown. Given this role, early studies on OPG in breast cancer focused on the administration of OPG in order to prevent the osteolysis observed with bone metastases. However OPG is also produced by the breast tumor cells themselves. Research focusing on OPG produced by breast tumor cells has revealed actions of OPG which promote tumor progression. In vitro studies into the role of OPG produced by breast tumor cells have demonstrated that OPG can block TNF-related apoptosis inducing ligand (TRAIL)-mediated apoptosis. Furthermore, in vivo studies show that OPG expression by breast tumors can promote tumor growth and metastasis. In addition it has been shown that OPG stimulates endothelial cell survival and tube formation thus it may indirectly promote breast tumor progression through impacting angiogenesis. This article will present a summary of the data concerning the tumor-promoting effects of OPG in breast cancer.

ITGBL1 Is a Runx2 Transcriptional Target and Promotes Breast Cancer Bone Metastasis by Activating the TGFβ Signaling Pathway

Bone metastasis affects more than 70% of advanced breast cancer patients, but the molecular mechanisms of this process remain unclear. Here, we present clinical and experimental evidence to clarify the role of the integrin β-like 1 (ITGBL1) as a key contributor to bone metastasis of breast cancer. In an in vivo model system and in vitro experiments, ITGBL1 expression promoted formation of osteomimetic breast cancers, facilitating recruitment, residence, and growth of cancer cells in bone microenvironment along with osteoclast maturation there to form osteolytic lesions. Mechanistic investigations identified the TGFβ signaling pathway as a downstream effector of ITGBL1 and the transcription factor Runx2 as an upstream activator of ITGBL1 expression. In support of these findings, we also found that ITGBL1 was an essential mediator of Runx2-induced bone metastasis of breast cancer. Overall, our results illuminate how bone metastasis occurs in breast cancer, and they provide functional evidence for new candidate biomarkers and therapeutic targets to identify risk, to prevent, and to treat this dismal feature of advanced breast cancer.