Role of GPR30 in the mechanisms of tamoxifen resistance in breast cancer MCF-7 cells

Endocrine Resistance in Hormone Receptor Positive Breast Cancer-From Mechanism to Therapy

The importance and role of the estrogen receptor (ER) pathway has been well-documented in both breast cancer (BC) development and progression. The treatment of choice in women with metastatic breast cancer (MBC) is classically divided into a variety of endocrine therapies, 3 of the most common being: selective estrogen receptor modulators (SERM), aromatase inhibitors (AI) and selective estrogen receptor down-regulators (SERD). In a proportion of patients, resistance develops to endocrine therapy due to a sophisticated and at times redundant interference, at the molecular level between the ER and growth factor. The progression to endocrine resistance is considered to be a gradual, step-wise process. Several mechanisms have been proposed but thus far none of them can be defined as the complete explanation behind the phenomenon of endocrine resistance. Although multiple cellular, molecular and immune mechanisms have been and are being extensively studied, their individual roles are often poorly understood. In this review, we summarize current progress in our understanding of ER biology and the molecular mechanisms that predispose and determine endocrine resistance in breast cancer patients.

G-protein-coupled estrogen receptor GPER-1 expression in hormone receptor-positive breast cancer is associated with poor benefit of tamoxifen

BACKGROUND

The role of G-protein-coupled estrogen receptor 1 (GPER-1) in the development of tamoxifen resistance in breast cancer is a highly controversial issue. The aim of this study was to determine the expression of GPER-1 in the clinical routine under conditions of endocrine treatment.

PATIENTS AND METHODS

GPER-1 expression was analyzed in 442 patients with primary invasive breast cancer. GPER-1 score of > 3 was determined as positive. Expression data were correlated with clinical and pathological characteristics and patient survival.

RESULTS

GPER-1 expression was observed in 352 (80.9%) cases, and positively correlated with estrogen and progesterone receptor status (p = 0.0001). GPER-1 positivity was associated with an increased grade of differentiation (p = 0.0001) and with a low level of Ki-67 expression (p = 0.0001). High GPER-1 expression was associated with a decreased level upon systemic treatment (p = 0.011). In the whole cohort, GPER-1 expression was associated with prolonged disease-free survival (DFS). DFS between tamoxifen- and aromatase inhibitor-treated GPER-1-positive patients was similar (p = 0.090). Notably, after matching the analysis for the most important prognostic factors, DFS for tamoxifen-treated GPER-1-positive patients was 69.1%, which is a percentage that is significantly lower compared to DFS for GPER-1-positive patients treated with aromatase inhibitors (92.7%) (p = 0.005).

CONCLUSION

GPER-1 expression is a favorable prognostic factor in breast cancer patients. Its predictive role for poor benefit form tamoxifen treatment should be investigated in further studies.

Potential Mechanisms of Age Acceleration Caused by Estrogen Deprivation: Do Endocrine Therapies Carry the Same Risks?

Longer duration of endocrine therapy decreases breast cancer recurrence and mortality, but these benefits need to be weighed against potential risks to overall health. Notable side effects of endocrine therapy include cataracts, uterine cancer, thromboembolic events, osteoporosis and fracture risk, chronic musculoskeletal complaints, as well as vaginal dryness and discharge, and vasomotor symptoms. Estrogen deprivation in healthy women younger than 50 years undergoing bilateral oophorectomy has been shown to accelerate the development of diseases related to aging, including coronary artery disease, cardiac arrhythmias, stroke, dementia, and osteoporosis, raising concern that even less dramatic modulation of estrogen homeostasis may adversely affect health outcomes. Diminished available estrogen at the cellular and molecular level may facilitate mechanisms that underlie the aging process, often termed the hallmarks of aging. In this review, we describe estrogen's role in normal physiology across tissues, review the effects of estrogen deprivation on health outcomes in the setting of both surgical and natural menopause, and examine the hallmarks of aging with attention to the effects of estrogen and estrogen blockade on each molecular mechanism underlying the aging process.

Effects of isoflavones on breast tissue and the thyroid hormone system in humans: a comprehensive safety evaluation

Isoflavones are secondary plant constituents of certain foods and feeds such as soy, linseeds, and red clover. Furthermore, isoflavone-containing preparations are marketed as food supplements and so-called dietary food for special medical purposes to alleviate health complaints of peri- and postmenopausal women. Based on the bioactivity of isoflavones, especially their hormonal properties, there is an ongoing discussion regarding their potential adverse effects on human health. This review evaluates and summarises the evidence from interventional and observational studies addressing potential unintended effects of isoflavones on the female breast in healthy women as well as in breast cancer patients and on the thyroid hormone system. In addition, evidence from animal and in vitro studies considered relevant in this context was taken into account along with their strengths and limitations. Key factors influencing the biological effects of isoflavones, e.g., bioavailability, plasma and tissue concentrations, metabolism, temporality (pre- vs. postmenopausal women), and duration of isoflavone exposure, were also addressed. Final conclusions on the safety of isoflavones are guided by the aim of precautionary consumer protection.

Predictive markers of endocrine response in breast cancer

Ongoing clinical and research efforts seek to optimise the use of endocrine therapy in the treatment of breast cancer. Accurate biomarkers are needed that predict response for individual patients. The presence of the estrogen receptor (ER) as the direct (for tamoxifen and fulvestrant) or indirect (for aromatase inhibitors) target molecule for endocrine therapy remains the foremost biomarker and determinant of response. However, ER expression only poorly predicts outcome and further indicators of response or resistance are required. The development and application of molecular signature assays such as Oncotype Dx, Prosigna, Mammaprint and Endopredict have provided valuable information on prognosis and these are being used to support clinical decision making on whether endocrine therapy alone alongside surgery is sufficient for ER-positive early stage breast cancers or whether combination of endocrine with chemotherapy are also warranted. Ki67, the proliferation marker, has been widely used in the neo-adjuvant (pre-operative) setting to help predict response and long term outcome. Gene expression studies within the same setting have allowed monitoring of changes of potential predictive markers. These have identified frequent changes in estrogen-regulated and proliferation genes. Specific molecules such as mutant ER may also prove helpful biomarkers in predicting outcome and monitoring response to treatment.

Protein arginine N-methyltransferase 2 reverses tamoxifen resistance in breast cancer cells through suppression of ER-α36

Breast cancer is one of the most common malignancies in females, and 17β-estradiol (E2)/estrogen receptor α (ERα) signaling plays an important role in the initiation and progression of breast cancer. The role of the ER-α subtype and its co-regulator in the initiation of breast cancer and the occurrence of tamoxifen resistance remains to be further elucidated. In our previous studies, protein arginine N-methyltransferase 2 (PRMT2), a co-regulator of estrogen receptor-α (ER-α), was confirmed to interact with ER-α66 and has the ability to inhibit cell proliferation in breast cancer cells. In the present study, we found that tamoxifen treatment induced a decrease in PRMT2 and an increase in ER-α36 as well as ER-α36-mediated non-genomic effect in MDA-MB-231 cells, which were relatively resistant to tamoxifen by contrast to MCF-7 cells. Moreover, PRMT2 was able to interact with ER-α36 directly, suppress ER-α36 and downstream PI3K/Akt and MAPK/ERK signaling, reversing the tamoxifen resistance of breast cancer cells. The present study may be meaningful for understanding the role of PRMT2 in breast cancer progression and for developing a new endocrine therapeutic strategy for breast cancer patients with tamoxifen resistance.

Low expression of G protein-coupled oestrogen receptor 1 (GPER) is associated with adverse survival of breast cancer patients

G protein-coupled oestrogen receptor 1 (GPER), also called G protein-coupled receptor 30 (GPR30), is attracting considerable attention for its potential role in breast cancer development and progression. Activation by oestrogen (17β-oestradiol; E2) initiates short term, non-genomic, signalling events both in vitro and in vivo. Published literature on the prognostic value of GPER protein expression in breast cancer indicates that further assessment is warranted. We show, using immunohistochemistry on a large cohort of primary invasive breast cancer patients (n=1245), that low protein expression of GPER is not only significantly associated with clinicopathological and molecular features of aggressive behaviour but also significantly associated with adverse survival of breast cancer patients. Furthermore, assessment of GPER mRNA levels in the METABRIC cohort (n=1980) demonstrates that low GPER mRNA expression is significantly associated with adverse survival of breast cancer patients. Using artificial neural networks, genes associated with GPER mRNA expression were identified; these included notch-4 and jagged-1. These results support the prognostic value for determination of GPER expression in breast cancer.

GPER is involved in the functional liaison between breast tumor cells and cancer-associated fibroblasts (CAFs)

The aggressiveness of breast tumors is deeply influenced by the surrounding stroma. In this regard, the functional crosstalk between cancer cells and the tumor microenvironment has received considerable attention in recent years. Cancer-associated fibroblasts (CAFs) are active components of the tumor stroma as they play a main role in the initiation, progression, metastasis and recurrence of breast malignancy. Hence, a better understanding of the mechanisms through which host stroma may contribute to cancer development would lead to novel therapeutic approaches aimed to target both tumor cells and the adjacent microenvironment. The G protein estrogen receptor (GPER/GPR30) has been involved in estrogenic signaling in normal and malignant cells, including breast cancer. It is noteworthy that the potential of GPER to mediate stimulatory effects of estrogens has been also shown in CAFs derived from patients with breast tumors, suggesting that GPER may act at the cross-road between cancer cells and these important components of the tumor microenvironment. This review recapitulates recent findings underlying the breast tumor-promoting action of CAFs, in particular their functional liaison with breast cancer cells via GPER toward the occurrence of malignant features.

A unifying biology of sex steroid-induced apoptosis in prostate and breast cancers

Prostate and breast cancer are the two cancers with the highest incidence in men and women, respectively. Here, we focus on the known biology of acquired resistance to antihormone therapy of prostate and breast cancer and compare laboratory and clinical similarities in the evolution of the disease. Laboratory studies and clinical observations in prostate and breast cancer demonstrate that cell selection pathways occur during acquired resistance to antihormonal therapy. Following sex steroid deprivation, both prostate and breast cancer models show an initial increased acquired sensitivity to the growth potential of sex steroids. Subsequently, prostate and breast cancer cells either become dependent upon the antihormone treatment or grow spontaneously in the absence of hormones. Paradoxically, the physiologic sex steroids now kill a proportion of selected, but vulnerable, resistant tumor cells. The sex steroid receptor complex triggers apoptosis. We draw parallels between acquired resistance in prostate and breast cancer to sex steroid deprivation. Clinical observations and patient trials confirm the veracity of the laboratory studies. We consider therapeutic strategies to increase response rates in clinical trials of metastatic disease that can subsequently be applied as a preemptive salvage adjuvant therapy. The goal of future advances is to enhance response rates and deploy a safe strategy earlier in the treatment plan to save lives. The introduction of a simple evidence-based enhanced adjuvant therapy as a global healthcare strategy has the potential to control recurrence, reduce hospitalization, reduce healthcare costs and maintain a healthier population that contributes to society.

Cholesterol and Its Metabolites in Tumor Growth: Therapeutic Potential of Statins in Cancer Treatment

Cholesterol is essential for cell function and viability. It is a component of the plasma membrane and lipid rafts and is a precursor for bile acids, steroid hormones, and Vitamin D. As a ligand for estrogen-related receptor alpha (ESRRA), cholesterol becomes a signaling molecule. Furthermore, cholesterol-derived oxysterols activate liver X receptors (LXRs) or estrogen receptors (ERs). Several studies performed in cancer cells reveal that cholesterol synthesis is enhanced compared to normal cells. Additionally, high serum cholesterol levels are associated with increased risk for many cancers, but thus far, clinical trials with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) have had mixed results. Statins inhibit cholesterol synthesis within cells through the inhibition of HMG-CoA reductase, the rate-limiting enzyme in the mevalonate and cholesterol synthetic pathway. Many downstream products of mevalonate have a role in cell proliferation, since they are required for maintenance of membrane integrity; signaling, as some proteins to be active must undergo prenylation; protein synthesis, as isopentenyladenine is an essential substrate for the modification of certain tRNAs; and cell-cycle progression. In this review starting from recent acquired findings on the role that cholesterol and its metabolites fulfill in the contest of cancer cells, we discuss the results of studies focused to investigate the use of statins in order to prevent cancer growth and metastasis.

GPER promotes tamoxifen-resistance in ER+ breast cancer cells by reduced Bim proteins through MAPK/Erk-TRIM2 signaling axis

Tamoxifen resistance is a major clinical challenge in breast cancer treatment. Our previous studies find that GPER and its down-stream signaling play a pivotal role in the development of tamoxifen (TAM) resistance. cDNA array analysis indicated a set of genes associated with cell apoptosis are aberrant in GPER activated and TAM-resistant MCF-7R cells compared with TAM-sensitive MCF-7 cells. Among these genes, Bim (also named BCL2-L11), a member of the BH3-only pro-apoptotic protein family is significantly decreased, and TRIM RING finger protein TRIM2 (a ubiquitin ligase) is highly expressed in MCF-7R. To understand the mechanism of TAM-resistance in GPER activated ER+ breast cancer, the function of TRIM2 and Bim inducing cell apoptosis was studied. By using immunohistochemical and western blot analysis, there is an adverse correlation between TRIM2 and Bim in TAM-resistant breast tumor tissues and MCF-7R cells. Knockdown Bim in TAM-sensitive MCF-7 cells or overexpression of Bim in TAM-resistant MCF-7 cells significantly changed its sensibility to TAM through altering the levels of cleaved PARP and caspase-3. Activation of GPER and its downstream signaling MAPK/ERK, not PI3K/AKT, led to enhanced TRIM2 protein levels and affected the binding between TRIM2 and Bim which resulted in a reduced Bim in TAM-resistant breast cancer cells. Thus, the present study provides a novel insight to TAM-resistance in ER-positive breast cancer cells.

GPER-1/GPR30 a novel estrogen receptor sited in the cell membrane: therapeutic coupling to breast cancer

INTRODUCTION

Breast cancer is clinically classified as 'estrogen-positive' when at least 1% of cancer cells stain for the estrogen receptor alpha (ERα). However, recent research on both basic and clinical aspects of breast cancer suggests that GPER-1 (G protein-coupled estrogen receptor-1) may have an important role in breast cancer. Areas covered: This review provides a comprehensive and systematic literature search on GPER-1. We have focused on the role of GPER-1 in breast cancer and on resistance to endocrine therapy, an unsolved clinical issue still under discussion. Expert opinion: The discovery of GPER-1 as a novel estrogen receptor is unique and the signaling pathways activated by its stimulation, when compared to the classical nuclear ERα, indicate a potential role of GPER-1 in the genesis and mechanisms of drug resistance in breast cancer. Tumors expressing ERα represent the largest group of breast cancer patients indicating that more women eventually die from ERα-positive breast tumors than from other more malignant breast cancer subtypes such as HER2-positive and the triple negative groups. It is important to develop new strategies on endocrine therapy with regard to ERα and GPER-1 receptors to achieve innovative successful therapeutic tools.

GPER-novel membrane oestrogen receptor

The recent discovery of the G protein-coupled oestrogen receptor (GPER) presents new challenges and opportunities for understanding the physiology, pathophysiology and pharmacology of many diseases. This review will focus on the expression and function of GPER in hypertension, kidney disease, atherosclerosis, vascular remodelling, heart failure, reproduction, metabolic disorders, cancer, environmental health and menopause. Furthermore, this review will highlight the potential of GPER as a therapeutic target.

Cytoplasmic GPER translocation in cancer-associated fibroblasts mediates cAMP/PKA/CREB/glycolytic axis to confer tumor cells with multidrug resistance

Multiple drug resistance is a challenging issue in the clinic. There is growing evidence that the G-protein-coupled estrogen receptor (GPER) is a novel mediator in the development of multidrug resistance in both estrogen receptor (ER)-positive and -negative breast cancers, and that cancer-associated fibroblasts (CAFs) in the tumor microenvironment may be a new agent that promotes drug resistance in tumor cells. However, the role of cytoplasmic GPER of CAFs on tumor therapy remains unclear. Here we first show that the breast tumor cell-activated PI3K/AKT (phosphoinositide 3-kinase/AKT) signaling pathway induces the cytoplasmic GPER translocation of CAFs in a CRM1-dependent pattern, and leads to the activation of a novel estrogen/GPER/cAMP/PKA/CREB signaling axis that triggers the aerobic glycolysis switch in CAFs. The glycolytic CAFs feed the extra pyruvate and lactate to tumor cells for augmentation of mitochondrial activity, and this energy metabolically coupled in a 'host-parasite relationship' between catabolic CAFs and anabolic cancer cells confers the tumor cells with multiple drug resistance to several conventional clinical treatments including endocrine therapy (tamoxifen), Her-2-targeted therapy (herceptin) and chemotherapy (epirubicin). Moreover, the clinical data from 18F-fluorodeoxyglucose positron emission tomography/computed tomography further present a strong association between the GPER/cAMP/PKA/CREB pathway of stromal fibroblasts with tumor metabolic activity and clinical treatment, suggesting that targeting cytoplasmic GPER in CAFs may rescue the drug sensitivity in patients with breast cancer. Thus, our data define novel insights into the stromal GPER-mediated multiple drug resistance from the point of reprogramming of tumor energy metabolism and provide the rationale for CAFs as a promising target for clinical therapy.

Hyper-methylation of the upstream CpG island shore is a likely mechanism of GPER1 silencing in breast cancer cells

GPER1, also known as GPR30, is a novel seven-transmembrane G-protein coupled estrogen receptor that mediates both short-term (non-genomic) and long-term (genomic) effects of estrogen in target cells and tissues. A substantial body of work over the last two decades has highlighted its therapeutic or prognostic utility. However, the clinical data on the expression of GPER1 in breast tissue is ambiguous. Analysis of TCGA RNAseq data revealed significantly lower mean expression of GPER1 mRNA in primary breast tumors compared to that in normal breast tissues. This provides support to the tumor suppressor role for GPER1. However, the mechanisms underlying the reduced expression are not completely understood. We analyzed the expression levels of GPER1 mRNA variants in MCF-7 and MDA-MB-231 cells by RT-PCR, and the methylation status of two CpG islands in the GPER1 locus by modified COBRA assays and bisulfite sequencing. Our results show that MCF-7 cells express higher levels of GPER1 mRNA variants compared to MDA-MB-231 cells. Modified COBRA assays revealed differential methylation in the upstream CpG island (upCpGi) that overlaps with the first exon of two GPER1 variants (GPER1v2 and v3) but not in the downstream CpG island (dnCpGi) that overlaps with the coding region common to all variants. Bisulfite sequencing results showed that the core upCpGi was hypo-methylated in both MCF-7 and MDA-MB-231 cells. However, eight CpGs in the 3' end of the upCpGi were hyper-methylated in MDA-MB-231 cells. 5-Azacytidine, a DNA methyltransferase inhibitor, induced the expression levels of GPER1 mRNA variants in MDA-MB-231 cells. Expression-methylation correlation analysis of TCGA breast cancer data revealed that methylation of CpGs in the regions flanking the upCpGi significantly correlated negatively with GPER1 mRNA expression. Taken together, our results demonstrate the role of DNA methylation in GPER1 repression, implicate the flanking regions (shore) of the upCpGi, and suggest a potential mechanism of GPER1 silencing in breast tumors.

G-1 Inhibits Breast Cancer Cell Growth via Targeting Colchicine-Binding Site of Tubulin to Interfere with Microtubule Assembly

G-protein-coupled estrogen receptor 1 (GPER1) has been reported to play a significant role in mediating the rapid estrogen actions in a wide range of normal and cancer cells. G-1 was initially developed as a selective agonist for GPER. However, the molecular mechanisms underlying the actions of G-1 are unknown, and recent studies report inconsistent effects of G-1 on the growth of breast cancer cells. By employing high-resolution laser scanning confocal microscopy and time-lapse imaging technology, as well as biochemical analyses, in the current study, we provide convincing in vitro and in vivo evidence that G-1 is able to suppress the growth of breast cancer cells independent of the expression status of GPERs and classic estrogen receptors. Interestingly, we found that triple-negative breast cancer cells (TNBC) are very sensitive to G-1 treatment. We found that G-1 arrested the cell cycle in the prophase of mitosis, leading to caspase activation and apoptosis of breast cancer cells. Our mechanistic studies indicated that G-1, similar to colchicine and 2-methoxyestradiol, binds to colchicine binding site on tubulin, inhibiting tubulin polymerization and subsequent assembly of normal mitotic spindle apparatus during breast cancer cell mitosis. Therefore, G-1 is a novel microtubule-targeting agent and could be a promising anti-microtubule drug for breast cancer treatment, especially for TNBC treatment. Mol Cancer Ther; 16(6); 1080-91. ©2017 AACR.

Tamoxifen has a proliferative effect in endometrial carcinoma mediated via the GPER/EGFR/ERK/cyclin D1 pathway: A retrospective study and an in vitro study

Tamoxifen has been widely used to treat breast cancer as an endocrine therapy. However, tamoxifen is known to enhance the risk of developing endometrial cancer. We want to examine the effect of tamoxifen on endometrial cancer. In our retrospective study, we found that high grade, high stage, and lymph node metastasis were more common in tamoxifen users. In vitro 4-hydroxytamoxifen (OHT) induced cell proliferation and cell cycle promotion in type I and type II endometrial cancer cell lines, and this proliferation was blocked by GPER silencing. Treatment with OHT increased EGFR and ERK phosphorylation and the mRNA and protein levels of cyclin D1 and GPER. Taken together, our data demonstrate that endometrial cancer patients with tamoxifen treatment exhibit more aggressive histological subtypes and worse prognosis. OHT is a proliferation-inducing agent for endometrial cancer cells, and the GPER/EFGR/ERK/cyclin D1 pathway is involved in this process.

Estrogens, Neuroinflammation, and Neurodegeneration

Inflammatory activation of microglia is a hallmark of several disorders of the central nervous system. In addition to protecting the brain against inflammatory insults, microglia are neuroprotective and play a significant role in maintaining neuronal connectivity, but the prolongation of an inflammatory status may limit the beneficial functions of these immune cells. The finding that estrogen receptors are present in monocyte-derived cells and that estrogens prevent and control the inflammatory response raise the question of the role that this sex steroid plays in the manifestation and progression of pathologies that have a clear sex difference in prevalence, such as multiple sclerosis, Parkinson's disease, and Alzheimer's disease. The present review aims to provide a critical review of the current literature on the actions of estrogen in microglia and on the involvement of estrogen receptors in the manifestation of selected neurological disorders. This current understanding highlights a research area that should be expanded to identify appropriate replacement therapies to slow the progression of such diseases.

Function of G-Protein-Coupled Estrogen Receptor-1 in Reproductive System Tumors

The G-protein-coupled estrogen receptor-1 (GPER-1), also known as GPR30, is a novel estrogen receptor mediating estrogen receptor signaling in multiple cell types. The progress of estrogen-related cancer is promoted by GPER-1 activation through mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinase (PI3K), and phospholipase C (PLC) signaling pathways. However, this promoting effect of GPER-1 is nonclassic estrogen receptor (ER) dependent manner. In addition, clinical evidences revealed that GPER-1 is associated with estrogen resistance in estrogen-related cancer patients. These give a hint that GPER-1 may be a novel therapeutic target for the estrogen-related cancers. However, preclinical studies also found that GPER-1 activation of its special agonist G-1 inhibits cancer cell proliferation. This review aims to summarize the characteristics and complex functions of GPER-1 in cancers.

Oxidative stress and glyoxalase I activity mediate dicarbonyl toxicity in MCF-7 mamma carcinoma cells and a tamoxifen resistant derivative

BACKGROUND

Acquired tamoxifen resistance is a significant problem in estrogen receptor positive breast cancer. In a cellular model, tamoxifen resistance was associated with increased sensitivity towards toxic dicarbonyls and reduced free sulfhydryl group content. We here analyzed the role of oxidative stress and glyoxalase I activity on dicarbonyl resistance and the significance of glyoxalase I expression for survival.

METHODS

Reactive oxygen species were determined by 2,7-dihydrochlorofluorescein diacetate. Inhibitors for NADPH-oxidase (diphenyleneiodonium), p38 MAPK (SB203580) and ERK1/2 (UO126) were applied to investigate interactions of these signaling molecules. N-acetyl cysteine was used to evaluate the effect of oxidative stress on cell viability, which was assessed by the resazurin assay. Gene expression was analyzed by real time qRT-PCR. Glyoxalase activity was inhibited by the specific inhibitor CS-0683 and siRNA. The relevance of glyoxalase 1 mRNA abundance on survival of breast cancer patients was evaluated by the KM-plotter web interface.

RESULTS

α-Oxo-aldehydes caused an immediate increase in reactive oxygen species where the tamoxifen resistant cell line (TamR) responded at lower concentrations than the MCF-7 parental cell line. Inhibitor studies placed ROS production by NADPH-oxidase downstream of p38 MAPK. The antioxidant N-acetyl cysteine (NAC) increased survival, whereas glyoxalase (GLO1) inhibition increased dicarbonyl toxicity. GLO1 mRNA abundance was correlated with unfavorable prognosis of breast cancer patients.

CONCLUSIONS

Dicarbonyl toxicity was mediated by oxidative stress and GLO1 activity determines aldehyde toxicity in tamoxifen resistant cells.

GENERAL SIGNIFICANCE

Glyoxalases might be predictive biomarkers for tamoxifen resistance and a putative target for the treatment of tamoxifen resistant breast cancer patients.

GPER1-mediated IGFBP-1 induction modulates IGF-1-dependent signaling in tamoxifen-treated breast cancer cells

Tamoxifen, a selective estrogen receptor modulator, is a commonly prescribed adjuvant therapy for estrogen receptor-α (ERα)-positive breast cancer patients. To determine if extracellular factors contribute to the modulation of IGF-1 signaling after tamoxifen treatment, MCF-7 cells were treated with IGF-1 in conditioned medium (CM) obtained from 4-OHT-treated MCF-7 cells and the accumulation of phospho-Akt (S473) was measured. CM inhibited IGF-1-dependent cell signaling and suggesting the involvement of extracellular factors (ie. IGFBPs). A significant increase in IGFBP-1 mRNA and extracellular IGFBP-1 protein was observed in 4-OHT-treated MCF-7 cells. Knockdown experiments demonstrated that both GPER1 and CREB mediate IGFBP-1 induction. Furthermore, experiments showed that 4-OHT-dependent IGFBP-1 transcription is downstream of GPER1-activation in breast cancer cells. Additionally, neutralization and knockdown experiments demonstrated a role for IGFBP-1 in the observed inhibition of IGF-1 signaling. These results suggested that 4-OHT inhibits IGF-1 signaling via GPER1 and CREB mediated extracellular IGFBP-1 accumulation in breast cancer cells.

miRNAs regulated by estrogens, tamoxifen, and endocrine disruptors and their downstream gene targets

MicroRNAs (miRNAs) are short (22 nucleotides), single-stranded, non-coding RNAs that form complimentary base-pairs with the 3' untranslated region of target mRNAs within the RNA-induced silencing complex (RISC) and block translation and/or stimulate mRNA transcript degradation. The non-coding miRBase (release 21, June 2014) reports that human genome contains ∼ 2588 mature miRNAs which regulate ∼ 60% of human protein-coding mRNAs. Dysregulation of miRNA expression has been implicated in estrogen-related diseases including breast cancer and endometrial cancer. The mechanism for estrogen regulation of miRNA expression and the role of estrogen-regulated miRNAs in normal homeostasis, reproduction, lactation, and in cancer is an area of great research and clinical interest. Estrogens regulate miRNA transcription through estrogen receptors α and β in a tissue-specific and cell-dependent manner. This review focuses primarily on the regulation of miRNA expression by ligand-activated ERs and their bona fide gene targets and includes miRNA regulation by tamoxifen and endocrine disrupting chemicals (EDCs) in breast cancer and cell lines.

Estrogen-mediated inactivation of FOXO3a by the G protein-coupled estrogen receptor GPER

Background

Estrogen (17β-estradiol) promotes the survival and proliferation of breast cancer cells and its receptors represent important therapeutic targets. The cellular actions of estrogen are mediated by the nuclear estrogen receptors ERα and ERβ as well as the 7-transmembrane spanning G protein-coupled estrogen receptor (GPER). We previously reported that estrogen activates the phosphoinositide 3-kinase (PI3Kinase) pathway via GPER, resulting in phosphatidylinositol (3,4,5)-trisphosphate (PIP3) production within the nucleus of breast cancer cells; however, the mechanisms and consequences of this activity remained unclear.

Methods

MCF7 breast cancer cells were transfected with GFP-fused Forkhead box O3 (FOXO3) as a reporter to assess localization in response to estrogen stimulation. Inhibitors of PI3Kinases and EGFR were employed to determine the mechanisms of estrogen-mediated FOXO3a inactivation. Receptor knockdown with siRNA and the selective GPER agonist G-1 elucidated the estrogen receptor(s) responsible for estrogen-mediated FOXO3a inactivation. The effects of selective estrogen receptor modulators and downregulators (SERMs and SERDs) on FOXO3a in MCF7 cells were also determined. Cell survival (inhibition of apoptosis) was assessed by caspase activation.

Results

In the estrogen-responsive breast cancer cell line MCF7, FOXO3a inactivation occurs on a rapid time scale as a result of GPER, but not ERα, stimulation by estrogen, established by the GPER-selective agonist G-1 and knockdown of GPER and ERα. GPER-mediated inactivation of FOXO3a is effected by the p110α catalytic subunit of PI3Kinase as a result of transactivation of the EGFR. The SERMs tamoxifen and raloxifene, as well as the SERD ICI182,780, were active in mediating FOXO3a inactivation in a GPER-dependent manner. Additionally, estrogen-and G-1-mediated stimulation of MCF7 cells results in a decrease in caspase activation under proapoptotic conditions.

Conclusions

Our results suggest that non-genomic signaling by GPER contributes, at least in part, to the survival of breast cancer cells, particularly in the presence of ER-targeted therapies involving SERMs and SERDs. Our results further suggest that GPER expression and FOXO3a localization could be utilized as prognostic markers in breast cancer therapy and that GPER antagonists could promote apoptosis in GPER-positive breast cancers, particularly in combination with chemotherapeutic and ER-targeted drugs, by antagonizing estrogen-mediated FOXO3a inactivation.

What have we learned about GPER function in physiology and disease from knockout mice?

Estrogens, predominantly 17β-estradiol, exert diverse effects throughout the body in both normal and pathophysiology, during development and in reproductive, metabolic, endocrine, cardiovascular, nervous, musculoskeletal and immune systems. Estrogen and its receptors also play important roles in carcinogenesis and therapy, particularly for breast cancer. In addition to the classical nuclear estrogen receptors (ERα and ERβ) that traditionally mediate predominantly genomic signaling, the G protein-coupled estrogen receptor GPER has become recognized as a critical mediator of rapid signaling in response to estrogen. Mouse models, and in particular knockout (KO) mice, represent an important approach to understand the functions of receptors in normal physiology and disease. Whereas ERα KO mice display multiple significant defects in reproduction and mammary gland development, ERβ KO phenotypes are more limited, and GPER KO exhibit no reproductive deficits. However, the study of GPER KO mice over the last six years has revealed that GPER deficiency results in multiple physiological alterations including obesity, cardiovascular dysfunction, insulin resistance and glucose intolerance. In addition, the lack of estrogen-mediated effects in numerous tissues of GPER KO mice, studied in vivo or ex vivo, including those of the cardiovascular, endocrine, nervous and immune systems, reveals GPER as a genuine mediator of estrogen action. Importantly, GPER KO mice have also demonstrated roles for GPER in breast carcinogenesis and metastasis. In combination with the supporting effects of GPER-selective ligands and GPER knockdown approaches, GPER KO mice demonstrate the therapeutic potential of targeting GPER activity in diseases as diverse as obesity, diabetes, multiple sclerosis, hypertension, atherosclerosis, myocardial infarction, stroke and cancer.

Serum estrone concentration, estrone sulfate/estrone ratio and BMI are associated with human epidermal growth factor receptor 2 and progesterone receptor status in postmenopausal primary breast cancer patients suffering invasive ductal carcinoma

Background

We investigated in postmenopausal women with primary breast cancer prior to surgical intervention whether, serum levels of different steroid hormones and hormonal precursors associated with tumor tissue estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) status.

Methods

We enrolled 1,042 patients suffering invasive ductal carcinoma undergoing surgical resection in the National Institute of Oncology, Hungary between 2003 and 2011. Serum parameters were measured by RIA/IRMA assays; tumor tissue ER, PR and HER2 status was assessed histologically. Patients were classified according to tumor receptor status. Case–case analysis subjects were categorized into four subgroups based on serum hormone concentrations in ER, PR and HER2 receptor-negative cases, respectively.

Results

Serum estrone sulfate and dehydroepiandrosterone sulfate levels correlated with each other and also with serum estrone and estradiol levels. According to case–case study the odds ratios in the highest quartile were 1.517 (p = 0.0305, P_trend = 0.0394) for androstenedione, 1.495 (p = 0.0317, P_trend < 0.0105) for estrone and 0.654 (p = 0.0273, P_trend < 0.0151) for estrone sulfate/estrone ratio in PR+ vs. PR− tumors. Regarding HER2 status (HER2+ vs. HER2−), the odds ratios for estrone, estrone sulfate and estrone sulfate/estrone ratio were 0.530 (p = 0.0234, P_trend = 0.0595), 2.438 (p = 0.0042, P_trend < 0.0066) and 3.118 (p = 0.0001, P_trend < 0.0001) in the highest quartile, respectively. Of note significantly increased BMI associates with PR+ and ER +/PR+ status while significantly decreased BMI was observed in HER2+ cases.

Conclusions

Taken together, measurement of serum estrone and estrone sulfate concentrations prior to surgical intervention might support the individualization of regime in postmenopausal primary breast cancer patients.

International Union of Basic and Clinical Pharmacology. XCVII. G Protein-Coupled Estrogen Receptor and Its Pharmacologic Modulators

Estrogens are critical mediators of multiple and diverse physiologic effects throughout the body in both sexes, including the reproductive, cardiovascular, endocrine, nervous, and immune systems. As such, alterations in estrogen function play important roles in many diseases and pathophysiological conditions (including cancer), exemplified by the lower prevalence of many diseases in premenopausal women. Estrogens mediate their effects through multiple cellular receptors, including the nuclear receptor family (ERα and ERβ) and the G protein-coupled receptor (GPCR) family (GPR30/G protein-coupled estrogen receptor [GPER]). Although both receptor families can initiate rapid cell signaling and transcriptional regulation, the nuclear receptors are traditionally associated with regulating gene expression, whereas GPCRs are recognized as mediating rapid cellular signaling. Estrogen-activated pathways are not only the target of multiple therapeutic agents (e.g., tamoxifen, fulvestrant, raloxifene, and aromatase inhibitors) but are also affected by a plethora of phyto- and xeno-estrogens (e.g., genistein, coumestrol, bisphenol A, dichlorodiphenyltrichloroethane). Because of the existence of multiple estrogen receptors with overlapping ligand specificities, expression patterns, and signaling pathways, the roles of the individual receptors with respect to the diverse array of endogenous and exogenous ligands have been challenging to ascertain. The identification of GPER-selective ligands however has led to a much greater understanding of the roles of this receptor in normal physiology and disease as well as its interactions with the classic estrogen receptors ERα and ERβ and their signaling pathways. In this review, we describe the history and characterization of GPER over the past 15 years focusing on the pharmacology of steroidal and nonsteroidal compounds that have been employed to unravel the biology of this most recently recognized estrogen receptor.

Acquisition of epithelial-mesenchymal transition phenotype in the tamoxifen-resistant breast cancer cell: a new role for G protein-coupled estrogen receptor in mediating tamoxifen resistance through cancer-associated fibroblast-derived fibronectin and β1-integrin signaling pathway in tumor cells

INTRODUCTION

Acquired tamoxifen resistance remains the major obstacle to breast cancer endocrine therapy. β1-integrin was identified as one of the target genes of G protein-coupled estrogen receptor (GPER), a novel estrogen receptor recognized as an initiator of tamoxifen resistance. Here, we investigated the role of β1-integrin in GPER-mediated tamoxifen resistance in breast cancer.

METHODS

The expression of β1-integrin and biomarkers of epithelial-mesenchymal transition were evaluated immunohistochemically in 53 specimens of metastases and paired primary tumors. The function of β1-integrin was investigated in tamoxifen-resistant (MCF-7R) subclones, derived from parental MCF-7 cells, and MCF-7R β1-integrin-silenced subclones in MTT and Transwell assays. Involved signaling pathways were identified using specific inhibitors and Western blotting analysis.

RESULTS

GPER, β1-integrin and mesenchymal biomarkers (vimentin and fibronectin) expression in metastases increased compared to the corresponding primary tumors; a close expression pattern of β1-integrin and GPER were in metastases. Increased β1-integrin expression was also confirmed in MCF-7R cells compared with MCF-7 cells. This upregulation of β1-integrin was induced by agonists of GPER and blocked by both antagonist and knockdown of it in MCF-7R cells. Moreover, the epidermal growth factor receptor/extracellular regulated protein kinase (EGFR/ERK) signaling pathway was involved in this transcriptional regulation since specific inhibitors of these kinases also reduced the GPER-induced upregulation of β1-integrin. Interestingly, silencing of β1-integrin partially rescued the sensitivity of MCF-7R cells to tamoxifen and the α5β1-integrin subunit is probably responsible for this phenomenon. Importantly, the cell migration and epithelial-mesenchymal transition induced by cancer-associated fibroblasts, or the product of cancer-associated fibroblasts, fibronectin, were reduced by knockdown of β1-integrin in MCF-7R cells. In addition, the downstream kinases of β1-integrin including focal adhesion kinase, Src and AKT were activated in MCF-7R cells and may be involved in the interaction between cancer cells and cancer-associated fibroblasts.

CONCLUSIONS

GPER/EGFR/ERK signaling upregulates β1-integrin expression and activates downstream kinases, which contributes to cancer-associated fibroblast-induced cell migration and epithelial-mesenchymal transition, in MCF-7R cells. GPER probably contributes to tamoxifen resistance via interaction with the tumor microenvironment in a β1-integrin-dependent pattern. Thus, β1-integrin may be a potential target to improve anti-hormone therapy responses in breast cancer patients.

Estrogen regulates Hippo signaling via GPER in breast cancer

The G protein-coupled estrogen receptor (GPER) mediates both the genomic and nongenomic effects of estrogen and has been implicated in breast cancer development. Here, we compared GPER expression in cancerous tissue and adjacent normal tissue in patients with invasive ductal carcinoma (IDC) of the breast and determined that GPER is highly upregulated in cancerous cells. Additionally, our studies revealed that GPER stimulation activates yes-associated protein 1 (YAP) and transcriptional coactivator with a PDZ-binding domain (TAZ), 2 homologous transcription coactivators and key effectors of the Hippo tumor suppressor pathway, via the Gαq-11, PLCβ/PKC, and Rho/ROCK signaling pathways. TAZ was required for GPER-induced gene transcription, breast cancer cell proliferation and migration, and tumor growth. Moreover, TAZ expression positively correlated with GPER expression in human IDC specimens. Together, our results suggest that the Hippo/YAP/TAZ pathway is a key downstream signaling branch of GPER and plays a critical role in breast tumorigenesis.

Dense collagen-I matrices enhance pro-tumorigenic estrogen-prolactin crosstalk in MCF-7 and T47D breast cancer cells

Breast cancers that express estrogen receptor alpha (ERα+) constitute the majority of breast tumors. Estrogen is a major driver of their growth, and targeting ER-mediated signals is a largely successful primary therapeutic strategy. Nonetheless, ERα+ tumors also result in the most breast cancer mortalities. Other factors, including altered characteristics of the extracellular matrix such as density and orientation and consequences for estrogen crosstalk with other hormones such as prolactin (PRL), may contribute to these poor outcomes. Here we employed defined three dimensional low density/compliant and high density/stiff collagen-I matrices to investigate the effects on 17β-estradiol (E2) activity and PRL/E2 interactions in two well-characterized ERα+/PRLR+ luminal breast cancer cell lines in vitro. We demonstrate that matrix density modulated E2-induced transcripts, but did not alter the growth response. However, matrix density was a potent determinant of the behavioral outcomes of PRL/E2 crosstalk. High density/stiff matrices enhanced PRL/E2-induced growth mediated by increased activation of Src family kinases and insensitivity to the estrogen antagonist, 4-hydroxytamoxifen. It also permitted these hormones in combination to drive invasion and modify the alignment of collagen fibers. In contrast, low density/compliant matrices allowed modest if any cooperation between E2 and PRL to growth and did not permit hormone-induced invasion or collagen reorientation. Our studies demonstrate the power of matrix density to determine the outcomes of hormone actions and suggest that stiff matrices are potent collaborators of estrogen and PRL in progression of ERα+ breast cancer. Our evidence for bidirectional interactions between these hormones and the extracellular matrix provides novel insights into the regulation of the microenvironment of ERα+ breast cancer and suggests new therapeutic approaches.

Role of IGF1R in Breast Cancer Subtypes, Stemness, and Lineage Differentiation

Insulin-like growth factor (IGF) signaling is fundamental for growth and survival. A large body of evidence (laboratory, epidemiological, and clinical) implicates the exploitation of this pathway in cancer. Up to 50% of breast tumors express the activated form of the type 1 insulin-like growth factor receptor (IGF1R). Breast cancers are categorized into subtypes based upon hormone and ERRB2 receptor expression and/or gene expression profiling. Even though IGF1R influences tumorigenic phenotypes and drug resistance across all breast cancer subtypes, it has specific expression and function in each. In some subtypes, IGF1R levels correlate with a favorable prognosis, while in others it is associated with recurrence and poor prognosis, suggesting different actions based upon cellular and molecular contexts. In this review, we examine IGF1R expression and function as it relates to breast cancer subtype and therapy-acquired resistance. Additionally, we discuss the role of IGF1R in stem cell maintenance and lineage differentiation and how these cell fate influences may alter the differentiation potential and cellular composition of breast tumors.

Identification of gene regulation patterns underlying both oestrogen- and tamoxifen-stimulated cell growth through global gene expression profiling in breast cancer cells

PURPOSE

A c-Src inhibitor blocks oestrogen (E2)-induced stress and converts E2 responses from inducing apoptosis to growth stimulation in E2-deprived breast cancer cells. A reprogrammed cell line, MCF-7:PF, results in a functional oestrogen receptor (ER). We addressed the question of whether the selective ER modulator 4-hydroxytamoxifen (4-OHT) could target ER to prevent E2-stimulated growth in MCF-7:PF cells.

METHODS

Expression of mRNA was measured through real-time RT-PCR. Global gene expression profile was analysed through microarray. Transcriptome profiles were screened by RNA-sequencing.

RESULTS

Unexpectedly, both 4-OHT and E2 stimulated cell growth in a concentration-dependent manner. Expression profiling showed a remarkable overlap in genes regulated in the same direction by E2 and 4-OHT. Pathway enrichment analysis of the 280 genes commonly deregulated in MCF-7:PF cells by 4-OHT and E2 revealed functions mainly related to membrane, cytoplasm and metabolic processes. Further analysis of 98 genes up-regulated by both 4-OHT and E2 uncovered a significant enrichment in genes associated with membrane remodelling, cytoskeleton reorganisation, cytoplasmic adapter proteins, cytoplasm organelle proteins and related processes. 4-OHT was more potent than E2 in up-regulating some membrane remodelling molecules, such as EHD2, FHL2, HOMER3 and RHOF. In contrast, 4-OHT acted as an antagonist to inhibit expression of the majority of enriched membrane-associated genes in wild-type MCF-7 cells.

CONCLUSIONS

Long-term selection pressure has changed the cell population responses to 4-OHT. Membrane-associated signalling is critical for 4-OHT-stimulated cell growth in MCF-7:PF cells. This study provides a rationale for the further investigation of target therapy for tamoxifen resistant patients.

GPER mediates enhanced cell viability and motility via non-genomic signaling induced by 17β-estradiol in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) is an aggressive breast cancer with a generally poor prognosis. Due to lack of specific targets for its treatment, an efficient therapy is needed. G protein-coupled estrogen receptor (GPER), a novel estrogen receptor, has been reported to be expressed in TNBC tissues. In this study, we investigated the effects of blocking non-genomic signaling mediated by the estrogen/GPER pathway on cell viability and motility in the TNBC cells. GPER was strongly expressed in the TNBC cell lines MDA-MB-468 and MDA-MB-436, and the estrogen-mediated non-genomic ERK signaling activated by GPER was involved in cell viability and motility of TNBC cells. Treatment with 17β-estradiol (E2), the GPER-specific agonist G-1 and tamoxifen (TAM) led to rapid activation of p-ERK1/2, but not p-Akt. Moreover, estrogen/GPER/ERK signaling was involved in increasing cell growth, survival, and migration/invasion by upregulating expression of cyclinA, cyclinD1, Bcl-2, and c-fos associated with the cell cycle, proliferation, and apoptosis. Immunohistochemical analysis of TNBC specimens showed a significantly different staining of p-ERK1/2 between GPER-positive tissues (58/66, 87.9%) and GPER-negative tissues (13/30, 43.3%). The positivity of GPER and p-ERK1/2 displayed a strong association with large tumor size and poor clinical stage, indicating that GPER/ERK signaling might also contribute to tumor progression in TNBC patients which corresponded with in vitro experimental data. Our findings suggest that inhibition of estrogen/GPER/ERK signaling represents a novel targeted therapy in TNBC.

Interplay between estrogen and retinoid signaling in breast cancer--current and future perspectives

All-trans-retinoic acid (RA) is a promising agent for breast cancer treatment, but it induces several adverse effects and the few clinical trials performed up to now in breast cancer patients have provided disappointing results. The combination of RA and antiestrogenic compounds, such as tamoxifen, synergistically decreases the proliferation of breast cancer cells and an interplay between retinoid and estrogen signaling has begun to be unraveled, turning these combinations into an appealing strategy for breast cancer treatment. This review focus on the current knowledge regarding the interplay between retinoid and estrogen signaling in breast cancer and the combinations of RA with antiestrogens, aiming their future utilization in cancer therapy.

GPER-targeted, 99mTc-labeled, nonsteroidal ligands demonstrate selective tumor imaging and in vivo estrogen binding

Our understanding of estrogen (17β-estradiol, E2) receptor biology has evolved in recent years with the discovery and characterization of a 7-transmembrane-spanning G protein-coupled estrogen receptor (GPER/GPR30) and the development of GPER-selective functional chemical probes. GPER is highly expressed in certain breast, endometrial, and ovarian cancers, establishing the importance of noninvasive methods to evaluate GPER expression in vivo. Here, we developed (99m)Tc-labeled GPER ligands to demonstrate the in vivo status of GPER as an estrogen receptor (ER) and for GPER visualization in whole animals. A series of (99m)Tc(I)-labeled nonsteroidal tetrahydro-3H-cyclopenta[c]quinolone derivatives was synthesized utilizing pyridin-2-yl hydrazine and picolylamine chelates. Radioligand receptor binding studies revealed binding affinities in the 10 to 30 nmol/L range. Cell signaling assays previously demonstrated that derivatives retaining a ketone functionality displayed agonist properties, whereas those lacking such a hydrogen bond acceptor were antagonists. In vivo biodistribution and imaging studies performed on mice bearing human endometrial and breast cancer cell xenografts yielded significant tumor uptake (0.4-1.1%ID/g). Blocking studies revealed specific uptake in multiple organs (adrenals, uterus, and mammary tissue), as well as tumor uptake with similar levels of competition by E2 and G-1, a GPER-selective agonist. In conclusion, we synthesized and evaluated a series of first-generation (99m)Tc-labeled GPER-specific radioligands, demonstrating GPER as an estrogen-binding receptor for the first time in vivo using competitive binding principles, and establishing the utility of such ligands as tumor imaging agents. These results warrant further investigation into the role of GPER in estrogen-mediated carcinogenesis and as a target for diagnostic/therapeutic/image-guided drug delivery.

IMPLICATIONS

These studies provide a molecular basis to evaluate GPER expression and function as an ER through in vivo imaging.

Differential response to α-oxoaldehydes in tamoxifen resistant MCF-7 breast cancer cells

Tamoxifen is the standard adjuvant endocrine therapy for estrogen-receptor positive premenopausal breast cancer patients. However, tamoxifen resistance is frequently observed under therapy. A tamoxifen resistant cell line has been generated from the estrogen receptor positive mamma carcinoma cell line MCF-7 and was analyzed for putative differences in the aldehyde defence system and accumulation of advanced glycation end products (AGE). In comparison to wt MCF-7 cells, these tamoxifen resistant cells were more sensitive to the dicarbonyl compounds glyoxal and methylglyoxal and displayed increased caspase activity, p38-MAPK- and IκBα-phosphorylation. However, mRNA accumulation of the aldehyde- and AGE-defence enzymes glyoxalase-1 and -2 (GLO1, GLO2) as well as fructosamine-3-kinase (FN3K) was not significantly altered. Tamoxifen resistant cells contained less free sulfhydryl-groups (glutathione) suggesting that the increased sensitivity towards the dicarbonyls was due to a higher sensitivity towards reactive oxygen species which are associated with dicarbonyl stress. To further analyse, if these data are of more general importance, key experiments were replicated with tamoxifen resistant MCF-7 cell lines from two independent sources. These cell lines were also more sensitive to aldehydes, especially glyoxal, but were different in their cellular signalling responses to the aldehydes. In conclusion, glyoxalases and other aldehyde defence enzymes might represent a promising target for the therapy of tamoxifen resistant breast cancers.

Tamoxifen through GPER upregulates aromatase expression: a novel mechanism sustaining tamoxifen-resistant breast cancer cell growth

Tamoxifen resistance is a major clinical challenge in breast cancer treatment. Aromatase inhibitors are effective in women who progressed or recurred on tamoxifen, suggesting a role of local estrogen production by aromatase in driving tamoxifen-resistant phenotype. However, the link between aromatase activity and tamoxifen resistance has not yet been reported. We investigated whether long-term tamoxifen exposure may affect aromatase activity and/or expression, which may then sustain tamoxifen-resistant breast cancer cell growth. We employed MCF-7 breast cancer cells, tamoxifen-resistant MCF-7 cells (MCF-7 TR1 and TR2), SKBR-3 breast cancer cells, cancer-associated fibroblasts (CAFs1 and CAFs2). We used tritiated-water release assay, realtime-RT-PCR, and immunoblotting analysis for evaluating aromatase activity and expression; anchorage-independent assays for growth; reporter-gene, electrophoretic-mobility-shift, and chromatin-immunoprecipitation assays for promoter activity studies. We demonstrated an increased aromatase activity and expression, which supports proliferation in tamoxifen-resistant breast cancer cells. This is mediated by the G-protein-coupled receptor GPR30/GPER, since knocking-down GPER expression or treatment with a GPER antagonist reversed the enhanced aromatase levels induced by long-term tamoxifen exposure. The molecular mechanism was investigated in ER-negative, GPER/aromatase-positive SKBR3 cells, in which tamoxifen acts as a GPER agonist. Tamoxifen treatment increased aromatase promoter activity through an enhanced recruitment of c-fos/c-jun complex to AP-1 responsive elements located within the promoter region. As tamoxifen via GPER induced aromatase expression also in CAFs, this pathway may be involved in promoting aggressive behavior of breast tumors in response to tamoxifen treatment. Blocking estrogen production and/or GPER signaling activation may represent a valid option to overcome tamoxifen-resistance in breast cancers.

GPER functions as a tumor suppressor in triple-negative breast cancer cells

BACKGROUND

The orphan, membrane-bound estrogen receptor (GPER) is expressed at high levels in a large fraction of breast cancer patients and its expression is favorable for patients' survival.

METHODS

We investigated the role of GPER as a potential tumor suppressor in triple-negative breast cancer cells MDA-MB-231 and MDA-MB-468 using cell cycle analysis and apoptosis assay. The constitutive activity of GPER was investigated.

RESULTS

GPER-specific activation with G-1 agonist inhibited breast cancer cell growth in concentration-dependent manner via induction of the cell cycle arrest in G2/M phase, enhanced phosphorylation of histone H3 and caspase-3-mediated apoptosis. Analysis of the methylation status of the GPER promoter in the triple-negative breast cancer cells and in tissues derived from breast cancer patients revealed that GPER amount is regulated by epigenetic mechanisms and GPER expression is inactivated by promoter methylation. Furthermore, GPER expression was induced by stress factors, such as radiation, and GPER amount inversely correlated with the p53 expression level.

CONCLUSIONS

Overall, our results establish the protective role in breast cancer tumorigenesis, and the cell surface expression of GPER makes it an excellent potential therapeutic target for triple-negative breast cancer.

Lack of G protein-coupled estrogen receptor (GPER) in the plasma membrane is associated with excellent long-term prognosis in breast cancer

G protein-coupled estrogen receptor (GPER), or GPR30, is a membrane receptor reported to mediate non-genomic estrogen responses. Tamoxifen is a partial agonist at GPER in vitro. Here, we investigated if GPER expression is prognostic in primary breast cancer, if the receptor is treatment-predictive for adjuvant tamoxifen, and if receptor subcellular localization has any impact on the prognostic value. Total and plasma membrane (PM) GPER expression was analyzed by immunohistochemistry in breast tumors from 742 postmenopausal lymph node-negative patients subsequently randomized for tamoxifen treatment for 2-5 years versus no systemic treatment, regardless of estrogen receptor (ER) status, and with a median follow-up of 17 years for patients free of event. PM GPER expression was a strong independent prognostic factor for poor prognosis in breast cancer without treatment-predictive information for tamoxifen. In the tamoxifen-treated ER-positive and progesterone receptor (PgR)-positive patient subgroup, the absence of PM GPER (53 % of all ER-positive tumors) predicted 91 % 20-year distant disease-free survival, compared to 73 % in the presence of GPER (p = 0.001). Total GPER expression showed positive correlations with ER and PgR and negative correlation with histological grade, but the correlations were biphasic. On the other hand, PM GPER expression showed strong negative correlations with ER and PgR, and strong positive correlation with HER2 overexpression and high histological grade. GPER overexpression and PM localization are critical events in breast cancer progression, and lack of GPER in the PM is associated with excellent long-term prognosis in ER-positive and PgR-positive tamoxifen-treated primary breast cancer.

GPER functions as a tumor suppressor in MCF-7 and SK-BR-3 breast cancer cells

PURPOSE

The orphan, membrane-bound estrogen receptor (GPER) is expressed at high levels in a large fraction of breast cancer patients, and its expression is favorable for patients' survival. We investigated the role of GPER as a potential tumor suppressor in MCF-7 and SK-BR-3 breast cancer cells.

METHODS

The effect of GPER agonist G-1 in cell culture was used to determine whether GPER inhibit cell growth. The methylation status of GPER promoter was investigated by methylation-specific PCR.

RESULTS

GPER-specific agonist G-1 inhibited breast cancer cell proliferation in concentration-dependent manner via induction of the cell cycle arrest in M-phase, enhanced phosphorylation of histone 3 and cell apoptosis. Analysis of the methylation status of the GPER promoter in MCF-7 and SK-BR-3 cells revealed that GPER expression is regulated by epigenetic mechanisms and GPER expression is inactivated by promoter methylation. Overall, our results are consistent with our recent findings in triple-negative breast cancer cells, and the cell surface expression of GPER makes it an excellent potential therapeutic target for non-triple-negative breast cancer.

GPER-mediated proliferation and estradiol production in breast cancer-associated fibroblasts

Cancer-associated fibroblasts (CAFs) are crucial co-mediators of breast cancer progression. Estrogen is the predominant driving force in the cyclic regulation of the mammary extracellular matrix, thus potentially affecting the tumor-associated stroma. Recently, a third estrogen receptor, estrogen (G-protein-coupled) receptor (GPER), has been reported to be expressed in breast CAFs. In this study, GPER was detected by immunohistochemical analysis in stromal fibroblasts of 41.8% (59/141) of the primary breast cancer samples. GPER expression in CAFs isolated from primary breast cancer tissues was confirmed by immunostaining and RT-PCR analyses. Tamoxifen (TAM) in addition to 17β-estradiol (E₂) and the GPER agonist G1 activated GPER, resulting in transient increases in cell index, intracellular calcium, and ERK1/2 phosphorylation. Furthermore, TAM, E₂, and G1 promoted CAF proliferation and cell-cycle progression, both of which were blocked by GPER interference, the selective GPER antagonist G15, the epidermal growth factor receptor (EGFR) inhibitor AG1478, and the ERK1/2 inhibitor U0126. Importantly, TAM as well as G1 increased E₂ production in breast CAFs via GPER/EGFR/ERK signaling when the substrate of E₂, testosterone, was added to the medium. GPER-induced aromatase upregulation was probably responsible for this phenomenon, as TAM- and G1-induced CYP19A1 gene expression was reduced by GPER knockdown and G15, AG1478, and U0126 administration. Accordingly, GPER-mediated CAF-dependent estrogenic effects on the tumor-associated stroma are conceivable, and CAF is likely to contribute to breast cancer progression, especially TAM resistance, via a positive feedback loop involving GPER/EGFR/ERK signaling and E₂ production.

The G protein-coupled estrogen receptor (GPER) is expressed in two different subcellular localizations reflecting distinct tumor properties in breast cancer

INTRODUCTION

The G protein-coupled estrogen receptor (GPER) is a novel estrogen receptor that mediates proliferative effects induced by estrogen but also by tamoxifen. The aim of our study was to analyze the frequency of GPER in a large collective of primary invasive breast carcinomas, with special emphasis on the subcellular expression and to evaluate the association with clinicopathological parameters and patient overall survival.

METHODS

The tissue microarrays from formalin-fixed, paraffin embedded samples of primary invasive breast carcinomas (n = 981) were analyzed for GPER expression using immunohistochemistry. Expression data were compared to the clinicopathological parameters and overall survival. GPER localization was also analyzed in two immortalized breast cancer cell lines T47D and MCF7 by confocal immunofluorescence microscopy.

RESULTS

A predominantly cytoplasmic GPER expression was found in 189 carcinomas (19.3%), whereas a predominantly nuclear expression was observed in 529 cases (53.9%). A simultaneous comparable positive expression of both patterns was found in 32 of 981 cases (3.2%), and negative staining was detected in 295 cases (30%). Confocal microscopy confirmed the occurrence of cytoplasmic and nuclear GPER expression in T47D and MCF7. Cytoplasmic GPER expression was significantly associated with non-ductal histologic subtypes, low tumor stage, better histologic differentiation, as well as Luminal A and B subtypes. In contrast, nuclear GPER expression was significantly associated with poorly differentiated carcinomas and the triple-negative subtype. In univariate analysis, cytoplasmic GPER expression was associated with better overall survival (p = 0.012).

CONCLUSION

Our data suggest that predominantly cytoplasmic and/or nuclear GPER expression are two distinct immunohistochemical patterns in breast carcinomas and may reflect different biological features, reason why these patterns should be clearly distinguished in histological evaluations. Prospective studies will be needed to assess whether the expression status of GPER in breast carcinomas should be routinely observed by clinicians, for instance, before implementing endocrine breast cancer treatment.

GPER Function in Breast Cancer: An Overview

The G-protein-coupled estrogen receptor-1 (GPER, formerly known as GPR30) has attracted increasing interest, considering its ability to mediate estrogenic signaling in different cell types, including the hormone-sensitive tumors like breast cancer. As observed for other GPCR-mediated responses, the activation of the epidermal growth factor receptor is a fundamental integration point in the biological action triggered by GPER. A wide number of natural and synthetic compounds, including estrogens and anti-estrogens, elicit stimulatory effects in breast cancer through GPER up-regulation and activation, suggesting that GPER function is associated with breast tumor progression and tamoxifen resistance. GPER has also been proposed as a candidate biomarker in triple-negative breast cancer, opening a novel scenario for a more comprehensive assessment of breast tumor patients.

Tamoxifen improves cholinergically modulated cognitive performance in postmenopausal women

Tamoxifen (TMX) is a selective estrogen receptor modulator that is used as an estrogen receptor antagonist for the treatment and prevention of breast cancer. Whether TMX has antagonist activities in the human brain is less clear and its effects on cognitive function have not been experimentally explored. This study examined how TMX affected cognitive performance in older women using a model of anticholinergic drug-induced cognitive dysfunction. Twenty-one postmenopausal women were administered 20 mg of oral TMX or placebo for 3 months. Participants then took part in five drug challenges using the anticholinergic antinicotinic agent mecamylamine (MECA) and antimuscarinic agent scopolamine (SCOP) and were tested on a comprehensive battery including tasks of attention and psychomotor function, verbal episodic memory, and spatial navigation. After a 3-month placebo washout, participants were then crossed over to the alternate treatment and repeated the drug challenges after 3 months. Compared with placebo treatment, TMX significantly attenuated the impairment from cholinergic blockade on tasks of verbal episodic memory and spatial navigation, but effects on attentional/psychomotor tasks were more variable. Analysis by APOE genotype showed that APO ɛ4+ women showed a greater beneficial effect of TMX on reversing the cholinergic impairment than APO ɛ4- women on most tasks. This study provides evidence that TMX may act as an estrogen-like agonist to enhance cholinergic system activity and hippocampally mediated learning.

GPR30 as an initiator of tamoxifen resistance in hormone-dependent breast cancer

Introduction

Tamoxifen is widely used to treat hormone-dependent breast cancer, but its therapeutic benefit is limited by the development of drug resistance. Here, we investigated the role of estrogen G-protein coupled receptor 30 (GPR30) on Tamoxifen resistance in breast cancer.

Methods

Primary tumors (PTs) of breast cancer and corresponding metastases (MTs) were used to evaluate the expression of GPR30 and epidermal growth factor receptor (EGFR) immunohistochemically. Tamoxifen-resistant (TAM-R) subclones derived from parent MCF-7 cells were used to investigate the role of GPR30 in the development of tamoxifen resistance, using MTT assay, western blot, RT-PCR, immunofluorescence, ELISA and flow cytometry. TAM-R xenografts were established to assess anti-tumor effects of combination therapy with GPR30 antagonist G15 plus 4-hydroxytamoxifen (Tam), using tumor volume measurement and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL).

Results

In 53 human breast cancer specimens, GPR30 expression in MTs increased compared to matched PTs; in MTs, the expression patterns of GPR30 and EGFR were closely related. Compared to parent MCF-7 cells, TAM-R cells had greater growth responses to 17β-estradiol (E2), GPR30 agonist G1 and Tam, and significantly higher activation of Mitogen-activated protein (MAP) kinases; but this increased activity was abolished by G15 or AG1478. In TAM-R cells, GPR30 cell-surface translocation facilitated crosstalk with EGFR, and reduced cAMP generation, attenuating inhibition of EGFR signaling. Combination therapy both promoted apoptosis in TAM-R cells and decreased drug-resistant tumor progression.

Conclusions

Long-term endocrine treatment facilitates the translocation of GPR30 to cell surfaces, which interferes with the EGFR signaling pathway; GPR30 also attenuates the inhibition of MAP kinases. These factors contribute to tamoxifen resistance development in breast cancer. Combination therapy with GPR30 inhibitors and tamoxifen may provide a new therapeutic option for drug-resistant breast cancer.

G protein-coupled estrogen receptor-selective ligands modulate endometrial tumor growth

Endometrial carcinoma is the most common cancer of the female reproductive tract. GPER/GPR30 is a 7-transmembrane spanning G protein-coupled receptor that has been identified as the third estrogen receptor, in addition to ERα and ERβ. High GPER expression is predictive of poor survival in endometrial and ovarian cancer, but despite this, the estrogen-mediated signaling pathways and specific estrogen receptors involved in endometrial cancer remain unclear. Here, employing ERα-negative Hec50 endometrial cancer cells, we demonstrate that GPER mediates estrogen-stimulated activation of ERK and PI3K via matrix metalloproteinase activation and subsequent transactivation of the EGFR and that ER-targeted therapeutic agents (4-hydroxytamoxifen, ICI182,780/fulvestrant, and Raloxifene), the phytoestrogen genistein, and the “ERα-selective” agonist propylpyrazole triol also function as GPER agonists. Furthermore, xenograft tumors of Hec50 cells yield enhanced growth with G-1 and estrogen, the latter being inhibited by GPER-selective pharmacologic antagonism with G36. These results have important implications with respect to the use of putatively ER-selective ligands and particularly for the widespread long-term use of “ER-targeted” therapeutics. Moreover, our findings shed light on the potential mechanisms of SERM/SERD side effects reported in many clinical studies. Finally, our results provide the first demonstration that pharmacological inhibition of GPER activity in vivo prevents estrogen-mediated tumor growth.

17β-estradiol promotes the invasion and migration of nuclear estrogen receptor-negative breast cancer cells through cross-talk between GPER1 and CXCR1

G protein-coupled estrogen receptor 1 (GPER1) is widely expressed in human breast cancers correlating with increased tumor size and malignancy. Although estrogen signaling via GPER1 was extensively studied in recent years, the underlying molecular mechanism of GPER1-associated metastasis of breast cancer still remains unclear. In this study, the main aims were focused on the potential role of GPER1 in regulating migration and invasion of nuclear estrogen receptor (ER)-negative breast cancer cells upon 17β-estradiol (E2) stimulation and the involved signaling pathway. Key events in estrogen signaling were chosen for our studies, such as the activation of ERK and AKT, nuclear translocation of NF-κB and secretion of Interleukin-8 (IL-8). The migration and invasion activities upon E2 stimulation were also examined in ER-negative SKBR3 and BT-20 breast cancer cells. Compared with ER-positive MCF-7 breast cancer cells, both SKBR3 and BT-20 cells had very similar expression of GPER1, but relatively high expression of CXC receptor-1 (CXCR1), which is considered as an active regulator for cancer metastasis upon binding IL-8. Results showed that E2 facilitated the activation of ERK, AKT and NF-κB, which could be significantly attenuated by GPER1 blockage or knock-down in both SKBR3 and BT-20 cells. Moreover, increased secretion of IL-8 induced by E2 was also inhibited either by specific inhibitors for GPER1, ERK, AKT, and NF-κB, or by knock-down for GPER1. Furthermore, E2 could activate the migration and invasion of both SKBR3 and BT-20 cells, which in turn could also be inhibited by blocking GPER1, ERK, AKT, NF-κB, and CXCR1, respectively, or knock-down for GPER1 and CXCR1. In conclusion, we demonstrated that estrogen signaling via GPER1 associated with the metastasis of breast cancer, which might be through GPER1/ERK&AKT/NF-κB/IL-8/CXCR1 cascade. The cross-talk between GPER1 and CXCR1 could be another potential target for the therapy of metastatic breast cancer.

Oleuropein and hydroxytyrosol activate GPER/ GPR30-dependent pathways leading to apoptosis of ER-negative SKBR3 breast cancer cells

SCOPE

We have previously demonstrated that oleuropein (OL) and hydroxytyrosol (HT) reduce 17β-estradiol-mediated proliferation in MCF-7 breast cancer (BC) cells without affecting the classical genomic action of estrogen receptor (ER), but activating instead the ERK1/2 pathway. Here, we hypothesized that this inhibition could be mediated by a G-protein-coupled receptor named GPER/GPR30. Using the ER-negative and GPER-positive SKBR3 BC cells as experimental model, we investigated the effects of OL and HT on GPER-mediated activation of downstream pathways.

METHODS AND RESULTS

Docking simulations and ligand-binding studies evidenced that OL and HT are able to bind GPER. MTT cell proliferation assays revealed that both phenols reduced SKBR3 cell growth; this effect was abolished silencing GPER. Focusing on OL and HT GPER-mediated pathways, using Western blot analysis we showed a sustained ERK1/2 activation triggering an intrinsic apoptotic pathway.

CONCLUSION

Showing that OL and HT work as GPER inverse agonists in ER-negative and GPER-positive SKBR3 BC cells, we provide novel insights into the potential of these two molecules as tools in the therapy of this subtype of BC.