New insights into estrogen receptor function in human breast cancer

Roles of estrogen receptors during sexual reversal in Pelodiscus sinensis

BACKGROUND

The Chinese soft-shelled turtle, Pelodiscus sinensis, exhibits distinct sexual dimorphism, with the males growing faster and larger than the females. During breeding, all-male offspring can be obtained using 17β-estradiol (E2). However, the molecular mechanisms underlying E2-induced sexual reversal have not yet been elucidated. Previous studies have investigated the molecular sequence and expression characteristics of estrogen receptors (ERs).

METHODS AND RESULTS

In this study, primary liver cells and embryos of P. sinensis were treated with ER agonists or inhibitors. Cell incubation experiments revealed that nuclear ERs (nERs) were the main pathway for the transmission of estrogen signals. Our results showed that ERα agonist (ERα-ag) upregulated the expression of Rspo1, whereas ERα inhibitor (ERα-Inh) downregulated its expression. The expression of Dmrt1 was enhanced after ERα-Inh + G-ag treatment, indicating that the regulation of male genes may not act through a single estrogen receptor, but a combination of ERs. In embryos, only the ERα-ag remarkably promoted the expression levels of Rspo1, Wnt4, and β-catenin, whereas the ERα-Inh had a suppressive effect. Additionally, Dmrt1, Amh, and Sox9 expression levels were downregulated after ERβ inhibitor (ERβ-Inh) treatment. GPER agonist (G-ag) has a significant promotion effect on Rspo1, Wnt4, and β-catenin, while the inhibitor G-Inh does not affect male-related genes.

CONCLUSIONS

Overall, these results suggest that ERs play different roles during sexual reversal in P. sinensis and ERα may be the main carrier of estrogen-induced sexual reversal in P. sinensis. Further studies need to be performed to analyze the mechanism of ER action.

Mechanisms of endocrine therapy resistance in breast cancer

The most commonly diagnosed breast cancer (BC) subtype is characterized by estrogen receptor (ER) expression. Treatment of this BC subtype typically involves modalities that either suppress the production of estrogen or impede the binding of estrgen to its receptors, constituting the basis for endocrine therapy. While many patients have benefitted from endocrine therapy with clear reduction in mortality and cancer recurrence, one of the clinical hurdles that remain involves overcoming intrinsic (de novo) or acquired resistance to endocrine therapy driven by diverse and complex changes occurring in the tumor microenvironment. Moreover, such resistance may persist even after progression through additional antiestrogen therapies thus demonstrating the importance of further investigation of mechanisms of ER modulation. Here, we discuss a number of advances that provide a better understanding of the complex mechanistic basis for resistance to endocrine therapy as well as future therapeutic maneuvers that may break this resistance.

A Closer Look at Estrogen Receptor Mutations in Breast Cancer and Their Implications for Estrogen and Antiestrogen Responses

Breast cancer (BC) is the most common cancer among women worldwide. More than 70% of BC cases express estrogen receptor alpha (ERα), a central transcription factor that stimulates the proliferation of breast cancer cells, usually in the presence of estrogen. While most cases of ER-positive BC initially respond to antiestrogen therapies, a high percentage of cases develop resistance to treatment over time. The recent discovery of mutated forms of ERα that result in constitutively active forms of the receptor in the metastatic-resistance stage of BC has provided a strong rationale for the development of new antiestrogens. These molecules targeting clinically relevant ERα mutants and a combination with other pharmacological inhibitors of specific pathways may constitute alternative treatments to improve clinical practice in the fight against metastatic-resistant ER-positive BC. In this review, we summarize the latest advances regarding the particular involvement of point mutations of ERα in endocrine resistance. We also discuss the involvement of synonymous ERα mutations with respect to co-translational folding of the receptor and ribosome biogenesis in breast carcinogenesis.

The feasibility of 18F-FES and 18F-FDG microPET/CT for early monitoring the effect of fulvestrant on sensitizing docetaxel by downregulating ERα in ERα+ breast cancer

OBJECTIVE

Our study aimed to investigate the feasibility of PET/CT for monitoring the influence of fulvestrant on sensitizing docetaxel by downregulating ERα in ERα+ breast cancer.

METHODS

Docetaxel-insensitive ERα+ breast cancer cells (DIS-ZR751) were established, identified and cultured. ERα expression, toxicity and viability of DIS-ZR751 were analyzed before and after treatment in vitro. DIS-ZR751-bearing nude mice were randomly divided into four groups according to different treatments: blank (DIS-ZR751), docetaxel (DIS-ZR751+DOC), fulvestrant (DIS-ZR751+FUL), and combination treatment (DIS-ZR751+DOC+FUL). ¹⁸F-FES and ¹⁸F-FDG microPECT/CT scans were performed before and 7, 14 days after treatment. Absolute %ID/g_max was calculated.

RESULTS

ERα expression level and growth rate of DIS-ZR751 were higher than control group and decreased dramatically after docetaxel and fulvestrant combination treatment. ¹⁸F-FES and ¹⁸F-FDG PET/CT imaging in vivo revealed that ERα expression in DIS-ZR751 treated with fulvestrant, and tumor activity in DIS-ZR751 treated with combination drugs decreased as early as 7 days after treatment.

CONCLUSIONS

¹⁸F-FES and ¹⁸F-FDG PET/CT were feasible for early monitoring the effect of fulvestrant on sensitizing docetaxel by downregulation of ERα in ERα+ breast cancer noninvasively.

Effects of lifelong exercise training on mammary tumorigenesis induced by MNU in female Sprague-Dawley rats

Breast cancer is the most common malignancy in women worldwide. Several studies have suggested that exercise training may decrease the risk of breast cancer development. This study aimed to evaluate the effects of long-term exercise training on mammary tumorigenesis in an animal model of mammary cancer. Fifty female Sprague-Dawley rats were randomly divided into four groups: MNU sedentary, MNU exercised, control sedentary and control exercised. Animals from MNU groups received an intraperitoneal administration of N-methyl-N-nitrosourea (MNU). Animals were exercised on a treadmill during 35 weeks. When animals were killed, blood samples were collected to determine the hematocrit and to perform the biochemical analysis. Mammary tumors were collected and histologically evaluated; the expression of ERs α and β was evaluated in tumor sections by immunohistochemistry. All survived animals from both MNU groups developed mammary tumors. The number of mammary tumors (p > 0.05) and lesions (p = 0.056) was lower in MNU exercised than in MNU sedentary animals. MNU exercised animals showed lower number of malignant lesions than MNU sedentary animals (p = 0.020). C-reactive protein serum concentration was lower in exercised animals; however, the levels of 17-β estradiol were higher in exercised animals. Tumors from exercised animals exhibited higher expression of ER α than tumors from sedentary animals (p < 0.05). This study analyzes the impact of the longest exercise training protocol on mammary tumorigenesis ever performed. We concluded that the lifelong endurance training has beneficial effects on mammary tumorigenesis in female rats (reduced the inflammation, the number of mammary tumors and lesions, and histological grade of malignancy). Additionally, the mammary tumors from MNU exercised group exhibited higher immunoexpression of ER α that is an indicator of well-differentiated tumors and better response to hormone therapy.

Obesity Suppresses Estrogen Receptor Beta Expression in Breast Cancer Cells via a HER2-Mediated Pathway

Obesity is associated with a worse breast cancer prognosis, while greater breast tumor estrogen receptor beta (ERβ) expression is correlated with improved therapy response and survival. The objective of this study was to determine the impact of obesity on breast cancer cell ERβ expression, which is currently unknown. We utilized an in vitro model of obesity in which breast cancer cells were exposed to patient serum pooled by body mass index category (obese (OB): ≥30 kg/m2; normal weight (N): 18.5-24.9 kg/m2). Four human mammary tumor cell lines representing the major breast cancer subtypes (SKBR3, MCF-7, ZR75, MDA-MB-231) and mammary tumor cells from MMTV-neu mice were used. ERβ expression, assessed by qPCR and western blotting, was suppressed in the two HER2-overexpressing cell lines (SKBR3, MMTV-neu) following OB versus N sera exposure, but did not vary in the other cell lines. Expression of Bcl-2 and cyclin D1, two genes negatively regulated by ERβ, was elevated in SKBR3 cells following exposure to OB versus N sera, but this difference was eliminated when the ERβ gene was silenced with siRNA. Herceptin, a HER2 antagonist, and siRNA to HER2 were used to evaluate the role of HER2 in sera-induced ERβ modulation. SKBR3 cell treatment with OB sera plus Herceptin increased ERβ expression three-fold. Similar results were obtained when HER2 expression was silenced with siRNA. OB sera also promoted greater SKBR3 cell viability and growth, but this variance was not present when ERβ was silenced or the cells were modified to overexpress ERβ. Based on this data, we conclude that obesity-associated systemic factors suppress ERβ expression in breast cancer cells via a HER2-mediated pathway, leading to greater cell viability and growth. Elucidation of the mechanism(s) mediating this effect could provide important insights into how ERβ expression is regulated as well as how obesity promotes a more aggressive disease.

Endocrine resistance in breast cancer--An overview and update

Tumors that express detectable levels of the product of the ESR1 gene (estrogen receptor-α; ERα) represent the single largest molecular subtype of breast cancer. More women eventually die from ERα+ breast cancer than from either HER2+ disease (almost half of which also express ERα) and/or from triple negative breast cancer (ERα-negative, progesterone receptor-negative, and HER2-negative). Antiestrogens and aromatase inhibitors are largely indistinguishable from each other in their abilities to improve overall survival and almost 50% of ERα+ breast cancers will eventually fail one or more of these endocrine interventions. The precise reasons why these therapies fail in ERα+ breast cancer remain largely unknown. Pharmacogenetic explanations for Tamoxifen resistance are controversial. The role of ERα mutations in endocrine resistance remains unclear. Targeting the growth factors and oncogenes most strongly correlated with endocrine resistance has proven mostly disappointing in their abilities to improve overall survival substantially, particularly in the metastatic setting. Nonetheless, there are new concepts in endocrine resistance that integrate molecular signaling, cellular metabolism, and stress responses including endoplasmic reticulum stress and the unfolded protein response (UPR) that provide novel insights and suggest innovative therapeutic targets. Encouraging evidence that drug combinations with CDK4/CDK6 inhibitors can extend recurrence free survival may yet translate to improvements in overall survival. Whether the improvements seen with immunotherapy in other cancers can be achieved in breast cancer remains to be determined, particularly for ERα+ breast cancers. This review explores the basic mechanisms of resistance to endocrine therapies, concluding with some new insights from systems biology approaches further implicating autophagy and the UPR in detail, and a brief discussion of exciting new avenues and future prospects.

Prognostic significance of interactions between ER alpha and ER beta and lymph node status in breast cancer cases

OBJECTIVE

Both estrogen receptors, ER alpha (ERα) and ER beta (ERβ), are expressed in 50-70% of breast cancer cases. The role of ERα as a prognostic marker in breast cancer has been well established as its expression is negative correlated with tumor size and lymph node metastasis. ERβ is also a favorable prognostic predictor although this is less well documented than for ERα.

MATERIALS AND METHODS

To explore whether ERs independently or together might influence clinical outcome in breast cancer, the correlation between the ERs with the clinicopathological features was analyzed in 84 patients.

RESULTS

ERα expression negatively correlated with tumor stage (r=-0.246, p=0.028) and tended to be negatively correlated with lymph node status (r=-0.156, p=0.168) and tumor size (r=-0.246, p=0.099). Also, ERβ was negatively correlated with nodal status (r=-0.243, p=0.028), as was coexpression of ERα and ERβ (p=0.043, OR=0.194, 95% CI= 0.040- 0.953).

CONCLUSION

Coexpression of ERs might serve as an indicator of good prognosis in breast cancer patients.

A bi-faceted role of estrogen receptor β in breast cancer

Despite over 15 years of research, the exact role, if any, played by estrogen receptor β (ERβ) in human breast cancer remains elusive. A large body of data both in vitro and in vivo supports its role as an antiproliferative, pro-apoptotic factor especially when co-expressed with ERα. However, there is a smaller body of data associating ERβ with growth and survival in breast cancer. In clinical studies and most often in cell culture studies, the pro-growth and pro-survival activity of ERβ occurs in ERα-negative breast cancer tissue and cells. This bi-faceted role of ERβ is discussed in this review.

Expression of both estrogen receptor-beta 1 (ER-β1) and its co-regulator steroid receptor RNA activator protein (SRAP) are predictive for benefit from tamoxifen therapy in patients with estrogen receptor-alpha (ER-α)-negative early breast cancer (EBC)

BACKGROUND

Roles of Estrogen Receptor-beta 1 (ER-β1) and its co-regulator Steroid Receptor RNA Activator Protein (SRAP) in breast cancer remain unclear. Previously, ER-β1 and SRAP expression were found positively correlated in breast cancer and, therefore, expression of these two molecules could characterize cancers with a distinct clinical outcome.

PATIENTS AND METHODS

ER-β1 and SRAP expression was determined by immunohistochemistry (IHC) in tissue microarrays from a randomized, placebo-controlled trial (NCIC-CTG-MA12), designed to determine the benefit of tamoxifen following chemotherapy in premenopausal early breast cancer (EBC). Expression was dichotomized into low and high using median IHC scores. Relationships with survival used Cox modeling.

RESULTS

In the whole cohort, ER-β1 and SRAP were not prognostic. However, high ER-β1 and SRAP significantly predicted tamoxifen responsiveness [overall survival, interaction test, P = 0.03; relapse-free survival (RFS), interaction test, P = 0.01]. Stratification by ER-α-status found predictive benefit only in ER-α-negative cases. The difference in RFS between tamoxifen and placebo was greater in patients whose tumors expressed both high SRAP and ER-β1[hazard ratio = 0.07; 95% confidence interval (CI) 0.01-0.41; P = 0.003] versus those with low SRAP or ER-β1 (interaction test, P = 0.02). The interaction test was not significant in ER-α-positive cohorts.

CONCLUSIONS

This study provides evidence that both ER-β1 and SRAP could be predictive biomarkers of tamoxifen benefit in ER-α-negative premenopausal EBC.

Progressive increase of glucose transporter-3 (GLUT-3) expression in estrogen-induced breast carcinogenesis

INTRODUCTION

Increased glucose uptake and glycolysis are main metabolic characteristics of malignant cells. A family of glucose transporters (GLUTs) facilitates glucose movement across the plasma membranes in a tumor-specific manner. Glucose transporter-1 (GLUT-1), GLUT-3 and recently GLUT-12, have been previously shown in breast cancer cells and are found to be associated with poor prognosis. In addition, it has been shown that estrogen plays critical roles in GLUT regulation, however, the stage-specific GLUT regulation of mammary carcinogenesis is unclear.

METHODS

GLUT expression patterns were investigated in an in vitro-in vivo progressive, estrogen-induced, mammary carcinogenesis model which consisted of four cell lines, with same genetic background. In this model, different stages of tumor initiation and progression are represented, MCF-10F being the normal stage, E2 cells the transformed stage by estrogen, C5 cells, the invasive stage, and T4 cells the tumorigenic stage. In addition, loss of ductulogenesis and solid mass formation in collagen matrix and invasiveness of the cells were counted.

RESULTS

Real time PCR showed that GLUT1 expression was downregulated in MCF10F after treatment with 17β-estradiol (E2), and in the invasive cell type (C5), but not in the tumor cells (T4), which had no changes compared to MCF10F. C5 and T4 cells showed the highest rate of GLUT-3 expression. These cells were also found to be associated with loss of ductulogenesis, solid mass formation and higher invasive capacity, whereas, GLUT-12 was downregulated in C5 and T4 cells.

CONCLUSION

Estrogen-induced malignant transformation is associated with remarkable and progressive GLUT-3 expression, GLUT-1 re-expression at further stages, as well as GLUT-12 downregulation.

Estrogen receptor-beta and breast cancer: translating biology into clinical practice

Estrogen receptor (ER) β was discovered over a decade ago. The design of most studies on this receptor was based on knowledge of its predecessor, ERα. Although breast cancer (BCa) has been a main focus of ERβ research, its precise roles in breast carcinogenesis remain elusive. Data from in vitro models have not always matched those from observational or clinical studies. Several inherent factors may contribute to these discrepancies: (a) several ERβ spliced variants are expressed at the protein level, and isoform-specific antibodies are unavailable for some variants; (b) post-translational modifications of the receptor regulate receptor functions; (c) the role of the receptor differs significantly depending on the type of ligands, cis-elements, and co-regulators that interact with the receptor; and (d) the diversity of distribution of the receptor among intracellular organelles of BCa cells. This review addresses the gaps in knowledge in ERβ research as it pertains to BCa regarding the following questions: (1) is ERβ a tumor suppressor in BCa?; (2) do ERβ isoforms play differential roles in breast carcinogenesis?; (3) do nuclear signaling and extranuclear ERβ signaling differ in BCa?; (4) what are the consequences of post-translational modifications of ERβ in BCa?; (5) how do co-regulators and interacting proteins increase functional diversity of ERβ?; and (6) how do the types of ligand and regulatory cis-elements affect the action of ERβ in BCa?. Insights gained from these key questions in ERβ research should help in prevention, diagnosis/prognosis, and treatment of BCa.

Fulvestrant (ICI 182,780) sensitizes breast cancer cells expressing estrogen receptor alpha to vinblastine and vinorelbine

Cumulative data suggest that some chemotherapeutic agents may be less effective in estrogen receptor alpha positive (ER+) breast tumors than ER negative (ER-) tumors, which has raised a clinically relevant question as to how to reverse this ER-mediated chemoresistance in ER+ breast tumors. This study is to investigate the possible influence of estrogen receptor alpha (ERalpha) on the therapeutic effects of vinblastine and vinorelbine on breast cancer cells and explore whether combination of anti-estrogen agent fulvestrant (ICI 182, 780) may enhance the sensitivity of ERalpha+ cells to these chemotherapeutic agents. Through comparing ER+ with ER- human breast tumor cells or through stable transfection of an ERalpha expression vector into ER negative human breast cancer BCap37 cells, a series of assays were applied to determine the sensitivity of ER+ and ER- breast tumor cells to vinblastine and vinorelbine in the presence or absence of 17-beta-estradiol and/or fulvestrant. 17-beta-Estradiol showed no effect on the sensitivity of ER- MDA-MB-468 and BCap37 cells to the treatment of vincristine or vinblastine, but it significantly reduced the sensitivity of ER+ T47D cells and BCap37 cells expressing ERalpha to the two drugs mentioned. Further analyses show that ERalpha has little effect on vinca alkaloids-induced mitotic arrest, but dramatically affects their ability to induce tumor cell apoptosis. Moreover, through a series of assays, we also demonstrated that the combination of fulvestrant, a selective ER down-regulator, could reverse the resistance of ER+ breast tumor cells to vinca alkaloids and even produce synergistic effects. The findings obtained from this study have provided important evidence that expression and subsequent activation of ERalpha are associated with resistance of breast cancer cells to vinca alkaloids. This study also suggested that the combination of anti-estrogen agents, such as fulvestrant, might be a novel strategy to reverse ER-mediated chemoresistance or sensitize ER+ breast tumors to vinca alkaloids and possibly other chemotherapeutic agents.

Estrogen receptor beta exerts growth-inhibitory effects on human mammary epithelial cells

Estrogen receptor beta (ERbeta) is widely expressed in mammary epithelium. ERbeta expression is reported to decline during carcinogenesis of the breast and other tissues. In this study, we examined the consequences of a loss of ERbeta expression in mammary epithelial cells. We knocked down ERbeta transcript levels in human mammary epithelial MCF-10A cells and in MCF-7 breast cancer cells by means of stable transfection with a specific shRNA plasmid. ERbeta knockdown resulted in a significant growth increase of both cell types in a ligand-independent manner. This effect was accompanied by elevated cyclin A2 expression in MCF-10A cells and by decreased expression of growth-inhibitory p21/WAF and epithelial cell marker cytokeratine 8 in both cell lines. Transfection of ERbeta shRNA did not alter the absent proliferative estrogen response of MCF-10A cells, but conferred sensitivity to selective estrogen receptor modulator tamoxifen to this cell line. In contrast, ERbeta knockdown diminished estrogen responsiveness of MCF-7 breast cancer cells and also weakened the effect of tamoxifen on this cell line. These ligand-dependent effects only observed in MCF-7 cells exhibiting a high ERalpha/beta ratio were accompanied by smaller estrogenic repression of p21/WAF expression, an impaired tamoxifen-triggered induction of this gene and by relative downregulation of ERalpha and cyclin A2 transcript levels. Our data suggest that ERbeta exerts antiproliferative effects both on MCF-10A and MCF-7 cells in a ligand- and ERalpha-independent manner by regulation of p21/WAF or cyclin A2 gene expression. Knockdown of ERbeta in both cell types was sufficient to significantly decrease transcript levels of epithelial cell marker cytokeratin 8. The results of this study support the hypothesis that ERbeta acts as a tumor suppressor in mammary epithelium.

ERbeta in breast cancer--onlooker, passive player, or active protector?

The role of estrogen exposure in breast cancer risk is well-documented, and both estrogen synthesis and actions through the estrogen receptor (ER) have been targeted by therapies to control hormone-dependent breast cancer. The discovery of a second ER form and its therapeutic implications sparked great interest. Both the original ERalpha and the more recently identified ERbeta subtypes bind and respond similarly to many physiological and pharmacological ligands. However, differences in phytoestrogen binding have been noted, and subtype-specific ligands have been developed. Cell-based assays show that ERbeta and its variants are generally less active on gene transcription than ERalpha, and may influence ERalpha activity; however, both gene- and cell-specific responses occur, and nongenomic activities are less well explored. Specific ligands, and methods to disrupt or eliminate receptor subtype expression in animal and cell models, demonstrate that the ERs have both overlapping and distinct biological functions. Overall, in cell-based studies, ERalpha appears to play a predominant role in cell proliferation, and ERbeta is suggested to be antiproliferative. The potential for distinct populations of breast tumors to be identified based on ER subtype expression, and to exhibit distinct clinical behaviors, is of greatest interest. Several studies suggest that the majority of ER-positive tumors contain both subtypes, but that some tumors contain only ERbeta and may have distinct clinical behaviors and responses. Expression of ERbeta together with ERalpha favors positive responses to endocrine therapy in most studies, and additional studies to determine if the addition of ERbeta to ERalpha as a tumor marker is of clinical benefit are warranted. In contrast, the positive association between ERbeta and HER2 expression in high-grade ERalpha-negative breast cancer does not favor positive responses to endocrine therapy. Expression of ERbeta in specific clinical subpopulations, and the potential for therapies targeting ERbeta specifically, is discussed.

Estrogen receptor alpha negative breast cancer patients: estrogen receptor beta as a therapeutic target

Clinical management of breast cancer is increasingly guided by assessment of tumor phenotypic parameters. One of these is estrogen receptor (ER) status, currently defined by ERalpha expression. However with the discovery of a second ER, ERbeta and its variant isoforms, the definition of ER status is potentially more complex. In breast tumors there are two ERbeta expression cohorts. One where ERbeta is co-expressed with ERalpha and the other expressing ERbeta alone. In the latter subgroup of currently defined ER negative patients ERbeta has the potential to be a therapeutic target. Characterization of the nature and role of ERbeta in ERalpha negative tumors is essentially unexplored but available data suggest that the role of ERbeta may be different when co-expressed with ERalpha and when expressed alone. This review summarizes available data and explores the possibility that ERbeta signaling may be a therapeutic target in these tumors. Evidence so far supports the idea that the role of ERbeta in breast cancer is different in ERalpha negative compared to ERalpha positive tumors. However, cohort size and numbers of independent studies are small to date, and more studies are needed with better standardization of antibodies and protocols. Also, the ability to determine the role of ERbeta in ERalpha negative breast cancer and therefore assess ERbeta signaling pathways as therapeutic targets would be greatly facilitated by identification of specific downstream markers of ERbeta activity in breast cancer.

Effects of exon-deleted estrogen receptor β transcript variants on growth, apoptosis and gene expression of human breast cancer cell lines

Estrogen receptor beta gene codes for a variety of transcript isoforms resulting from alternative splicing, which are expressed both in mammary gland and in breast cancer cells. We studied the function of two exon-deleted ERbeta isoforms recently identified by our group in comparison to ERbeta1 in regulation of growth, apoptosis and gene expression of two breast cancer cell lines with different ERalpha status. Overexpression of ERbeta1, but not of the exon-deleted variants exerted strong antitumoral effects both on ERalpha-positive MCF-7 and ERalpha-negative SK-BR-3 cells. ERbeta1 overexpression slowed growth of MCF-7 and SK-BR-3 cells in the absence of E2 and also inhibited E2-triggered growth stimulation of MCF-7 cells, but overexpression of the exon-skipped variants did not affect cell growth. Whereas overexpression of ERbeta1 triggered an increased basal and tamoxifen-induced apoptosis of MCF-7 and SK-BR-3 cells, the isoforms ERbetadelta125 or ERbetadelta1256 did not affect cellular tamoxifen response. The observed lack of function of the exon-deleted variants in terms of regulation of proliferation was accompanied both by their inability to affect expression of cyclins D1 and A2, p21 (WAF1) and PR and their disability to modulate estrogen response element (ERE) activation. In contrast, our results demonstrating antitumoral effects of ERbeta1 on breast cancer cells with different ERalpha-status support the hypothesis that ERbeta is able to exert antitumoral actions both on ERalpha-positive and -negative breast cancer cells.

Estrogen receptor-beta: why may it influence clinical outcome in estrogen receptor-alpha positive breast cancer?

In the previous issue of the journal, Lin and coworkers present data demonstrate that increased expression of estrogen receptor (ER)-β in ER-α-positive breast cancer cells antagonizes a defined group of ER-α/estrogen stimulated genes that are involved in cell cycle regulation and DNA replication. Similar expression patterns for these genes were found human ER-α positive breast tumors expressing higher levels or ER-β, and this correlated with better clinical outcome. The implications for these data, which suggest that ER-β is a positive actor and diagnostic marker for therapeutic outcome, are discussed.

Estrogen receptor alpha mediates breast cancer cell resistance to paclitaxel through inhibition of apoptotic cell death

Estrogen receptors (ER) are expressed in approximately 65% of human breast cancer. Cumulative data from clinical trials and retrospective analyses suggest that some chemotherapeutic agents may be less effective in patients with ER-positive (ER+) tumors than those with ER-negative (ER-) tumors. Paclitaxel is an active agent used in breast cancer chemotherapy. To investigate the possible influence of ER on the therapeutic efficacy of paclitaxel and its underlying mechanism, we established several isogenic ER+ cell lines by stable transfection of ERalpha expression vectors into ER- breast cancer BCap37 cells. We showed that 17-beta estradiol significantly reduces the overall cytotoxicity of paclitaxel in BCap37-expressing ERalpha but has no influence on the ER- parental cells. Further analyses indicate that expression of ERalpha in BCap37 cells mainly interferes with paclitaxel-induced apoptotic cell death, without affecting paclitaxel-induced microtubule bundling and mitotic arrest. Moreover, we found that the addition of ICI 182,780 (Fulvestrant), a selective ER down-regulator, could completely reverse the resistance of ER+ BCap37 cells to paclitaxel. These findings showed that ERalpha-mediated breast tumor cell resistance to paclitaxel was through selective inhibition of paclitaxel-induced tumor cell apoptosis. Additionally, the combination of ICI 182,780 also sensitizes MCF-7 and T47D cell lines to the treatment of paclitaxel, which further confirmed the correlation between ERalpha and drug resistance in ER+ tumor cells. The results obtained from this study provide useful information for understanding ER-mediated resistance to paclitaxel and possibly other antineoplastic agents.

ERbeta shifts from mitochondria to nucleus during estrogen-induced neoplastic transformation of human breast epithelial cells and is involved in estrogen-induced synthesis of mitochondrial respiratory chain proteins

Both estrogen receptors (ER) alpha (ERalpha) and beta (ERbeta) are localized in the nucleus, plasma membrane, and mitochondria, where they mediate the different physiological effects of estrogens. It has been observed that the relative subcellular localization of ERs is altered in several cancer cells. We have demonstrated that MCF-10F cells, the immortal and non-tumorigenic human breast epithelial cells (HBEC) that are ERalpha-negative and ERbeta-positive, are transformed in vitro by 17beta-estradiol (E(2)), generating highly invasive cells that are tumorigenic in severe combined immunodeficient mice. E(2)-transformed MCF-10F (trMCF) cells exhibit progressive loss of ductulogenesis, invasive (bsMCF) and tumorigenic (caMCF) phenotypes. Immunolocalization of ERbeta by confocal fluorescent microscopy and electron microscopy revealed that ERbeta is predominantly localized in mitochondria of MCF-10F and trMCF cells. Silencing ERbeta expression with ERbeta-specific small interference RNA (siRNA-ERbeta) markedly diminishes both nuclear and mitochondrial ERbeta in MCF-10F cells. The ERbeta shifts from its predominant localization in the mitochondria of MCF-10F and trMCF cells to the nucleus of bsMCF cells, becoming predominantly nuclear in caMCF cells. Furthermore, we demonstrated that the mitochondrial ERbeta in MCF-10F cells is involved in E(2)-induced expression of mitochondrial DNA (mtDNA)-encoded respiratory chain (MRC) proteins. This is the first report of an association of changes in the subcellular localization of ERbeta with various stages of E(2)-induced transformation of HBEC and a functional role of mitochondrial ERbeta in mediating E(2)-induced MRC protein synthesis. Our findings provide a new insight into one of the potential roles of ERbeta in human breast cancer.

Estrogen receptor-beta regulates psoriasin (S100A7) in human breast cancer

We have previously observed a paradoxical relationship of the psoriasin/S100A7 gene with estrogen response in-vitro in ERalpha positive cells but its association with ERalpha negative status in-vivo raising the possibility that S100A7 might be regulated by ERbeta in breast cancer. Using doxycycline-inducible ERbeta and ERalpha expressing MCF-7 cells the hypothesis that psoriasin/S100A7 is ERbeta regulated was investigated To explore the relationship between psoriasin/S100A7 and ERbeta expression in-vivo, we also assessed a cohort of 233 ERalpha negative breast tumors using tissue microarrays and immunohistochemistry. Psoriasin/S100A7 was increased by 17beta-estradiol (E2) following ERbeta induction, in several clones of ERbeta over-expressing but not in the original MCF-7 cells, nor clones over-expressing ERalpha. The effect of E2 on psoriasin/S100A7 was inhibited by 4-hydroxytamoxifen and ICI 182780 but not with a selective ERalpha antagonist. An ERbeta selective-agonist but not an ERalpha selective-agonist, induced psoriasin/S100A7. This induction still occurred after stable down-regulation of ERalpha using siRNA in ERbeta inducible cells. E2 increased psoriasin/S100A7 mRNA but cycloheximide treatment inhibited this effect. A relationship between ERbeta and psoriasin/S100A7 was observed in the p53 immunohistochemically negative subset of invasive breast tumors in-vivo (r = 0.225, p = 0.046, n = 79). In conclusion we demonstrate that E2 induction of psoriasin/S100A7 can be specifically regulated through ERbeta in-vitro and associated with ERbeta in-vivo. These data support the hypothesis that psoriasin/S100A7 is specifically regulated by ERbeta activity and could be useful to guide future therapies targeting ERbeta in certain phenotypic subsets of breast cancers in-vivo.

Expression of oestrogen receptor-beta in oestrogen receptor-alpha negative human breast tumours

To analyse the phenotype of breast tumours that express oestrogen receptor-β (ERβ) alone tissue microarrays were used to investigate if ERβ isoforms are associated with specific prognostic markers and gene expression phenotypes in ERα-negative tumours. ERα-negative tumours were positive for ERβ1 in 58% of cases (n=122/210), total ERβ in 60% (n=115/192) and ERβ2/cx in 57% of cases (n=114/199). Oestrogen receptor-β1 and total ERβ were significantly correlated with Ki67 (r=0.28, P<0.0001, n=209; r=0.29, P<0.0001, n=191) and with CK5/6, a marker of the basal phenotype (r=0.20, P=0.0106, n=170; r=0.18, P=0.0223, n=158). ERβ2/cx was strongly associated with p-c-Jun and NF-κBp65 (r=0.53, P<0.0001, n=93; r=0.35, P<0.0001, n=176). This study shows that a range of ERβ isoform expression occurs in ERα-negative breast tumours. While expression of ERβ1, total and ERβ2/cx are correlated, individual forms show associations with certain phenotypes that suggest different roles in subsets of ERα-negative cancers. Based on our in vivo observations, ERβ may have the potential to become a therapeutic target in the specific subcohort of ERα-negative breast cancers.

Assessment of multiple different estrogen receptor-beta antibodies for their ability to immunoprecipitate under chromatin immunoprecipitation conditions

Several different antibodies to total estrogen receptor (ER)beta, ERbeta1 and ERbeta2/cx have been tested and compared for their ability to immunoprecipitate ERbeta specific isoforms under chromatin immunoprecipitation conditions (ChIP). The rabbit polyclonal antibodies AP-ERbeta1 and AP-ERbeta2/cx, specific for ERbeta1 and ERbeta2/cx isoforms, respectively, were the most efficient for ChIP. The monoclonal antibody MCA1974/PPG5/10 was also able to ChIP ERbeta1, but less efficiently than AP-ERbeta1. All other antibodies tested were not suitable for ChIP analyses although most antibodies tested immunoprecipitated the appropriate ERbeta isoforms under standard conditions. To identify antibodies that can also be used to verify in-vivo expression profiles, a comparison of the antibodies to detect ERbeta isoforms by western blotting and immunohistochemistry was also undertaken. Under the tissue processing and autostaining conditions used at the Manitoba Breast Tumor Bank 385P/GC17, MCA1974/PPG5/10, Ab288/14C8 and MCA2279S/57/3 were found to be the best for IHC of ERbeta isoforms in human breast tissue biopsy sections, while Ab14021, AP-ERbeta1 and AP-ERbeta2/cx were best for western blot detection of ERbeta isoforms.

Estrogen receptor alpha and beta are prognostic factors in non-small cell lung cancer

PURPOSE

Estrogen receptor-alpha (ER-alpha) and -beta (ER-beta) play important roles in the carcinogenesis of breast tumors. Similarly, there have been several reports of ER expression in lung cancers, but the results have not been consistent, and the receptors' prognostic value remains unclear. Our goal was to investigate ER expression in non-small cell lung cancer (NSCLC) and to assess whether their expression correlates with prognosis.

EXPERIMENTAL DESIGN

ER expression was examined using immunohistochemical methods with sections from 132 resected NSCLC specimens. Kaplan-Meier survival curves were analyzed to determine the significance of ER expression in the prognosis of NSCLC patients.

RESULTS

ER-alpha was detected in the cytoplasm of 73% of the specimens analyzed, whereas ER-beta was detected in the nucleus of 51%. ER-alpha expression correlated with poorer overall survival (P < 0.001), as did the absence of ER-beta expression (P = 0.048). Likewise, at histopathologic stage I, ER-alpha expression (P = 0.028) or the absence of ER-beta (P = 0.037) correlated with a poorer prognosis, and ER-alpha(+)ER-beta(-) patients had a significantly worse prognosis than ER-alpha(-)ER-beta(+) patients (P = 0.00007). Multivariate Cox regression analysis revealed the absence of ER-beta to be an independent factor predictive of poor disease outcome (hazard ratio, 1.9; 95% confidence interval, 1.1-3.4; P = 0.0264).

CONCLUSIONS

ER-alpha expression and the absence of ER-beta expression are associated with a poorer prognosis among NSCLC patients. In particular, the absence of ER-beta could serve as a marker identifying patients at high risk even at an early clinical stage.

Expression of the Brn-3b Transcription Factor Correlates with Expression of HSP-27 in Breast Cancer Biopsies and Is Required for Maximal Activation of the HSP-27 Promoter

In breast cancer, overexpression of the small heat shock protein, HSP-27, is associated with increased anchorage-independent growth, increased invasiveness, and resistance to chemotherapeutic drugs and is associated with poor prognosis and reduced disease-free survival. Therefore, factors that increase the expression of HSP-27 in breast cancer are likely to affect the prognosis and outcome of treatment. In this study, we show a strong correlation between elevated levels of the Brn-3b POU transcription factor and high levels of HSP-27 protein in manipulated MCF-7 breast cancer cells as well as in human breast biopsies. Conversely, HSP-27 is decreased on loss of Brn-3b. In cotransfection assays, Brn-3b can strongly transactivate the HSP-27 promoter, supporting a role for direct regulation of HSP-27 expression. Brn-3b also cooperates with the estrogen receptor (ER) to facilitate maximal stimulation of the HSP-27 promoter, with significantly enhanced activity of this promoter observed on coexpression of Brn-3b and ER compared with either alone. RNA interference and site-directed mutagenesis support the requirement for the Brn-3b binding site on the HSP-27 promoter, which facilitates maximal transactivation either alone or on interaction with the ER. Chromatin immunoprecipitation provides evidence for association of Brn-3b with the HSP-27 promoter in the intact cell. Thus, Brn-3b can, directly and indirectly (via interaction with the ER), activate HSP-27 expression, and this may represent one mechanism by which Brn-3b mediates its effects in breast cancer cells.

Expression of BP1, a novel homeobox gene, correlates with breast cancer progression and invasion

BACKGROUND

Our previous studies revealed that the mRNA encoded by BP1, a member of the homeobox gene superfamily of transcription factors, was expressed in leukemia and infiltrating breast ductal carcinoma (IDC). This study investigated the immunohistochemical profile of BP1, to determine whether the expression of BP1 protein correlated with breast tumor progression and invasion and whether BP1 was co-localized with erbB2.

DESIGN

Paraffin sections from normal reduction mammoplasties (n = 34) and a variety of in situ and invasive breast cancers (n = 270) were either singly immunostained for BP1, or doubly immunostained for BP1 plus either erbB2 or Ki-67.

RESULTS

The prevalence of BP1 positive cells and the intensity of BP1 immunoreactivity increased with the extent of ductal proliferation and carcinogenesis. BP1 expression was barely detectable in normal reduction mammoplasties compared to distinct staining in 21, 46, and 81% of hyperplastic, in situ, and infiltrating lesions, respectively. In cases with co-existing normal, hyperplastic, in situ, and invasive lesions, the tumor cells of the invasive lesions consistently showed the highest frequency and the highest intensity of BP1 immunostaining, followed by in situ tumor cells. Double immunostaining revealed that BP1 co-localized with a subset of erbB2 positive cells in all 15 in situ and IDC tumors examined, and that BP1 positive cells had a substantially higher proliferation rate than morphologically similar cells without BP1 expression.

CONCLUSION

These findings suggest that BP1 is an important upstream factor in an oncogenic pathway, and that expression of BP1 may reliably reflect or directly contribute to tumor progression and/or invasion.

Polymorphisms in ER-α Gene Interact with Estrogen Receptor Status in Breast Cancer Survival

Purpose: The effects of estrogens are mediated primarily through estrogen receptor (ER) in breast tissue, and polymorphisms in the ER genes may alter the functions of these receptors. Polymorphisms in the ER-α gene have been reported to be associated with breast cancer risk. However, to our knowledge, no study has been published on the relation between ER-α gene polymorphisms and breast cancer survival.

Experimental Design: To determine whether three common polymorphisms in the ER-α gene, PvuII, XbaI, and GT dinucleotide repeats are associated with breast cancer survival, we evaluated data from a cohort of 1,069 breast cancer patients who participated in the Shanghai Breast Cancer Study between 1996 and 1998. The median follow-up time for this cohort of women was 5.2 years.

Results: No overall association was observed between ER gene polymorphisms and breast cancer survival. The genotype associations, however, were modified by ER status in breast cancer tissues. Comparing those with the PP genotype to the pp genotype of the PvuII polymorphism, the hazard ratios (HR) of dying were 3.30 [95% confidence interval (95% CI), 1.42-7.69] and 0.54 (95% CI, 0.24-1.23), respectively, for participants with ER-negative breast cancer and ER-positive breast cancer. Similarly, compared with those with no (GT)23 alleles, carrying one or two (GT)23 alleles of the GT repeat polymorphism was related to a HR of 1.48 (95% CI, 0.77-2.87) for ER-negative breast cancer and a HR of 0.25 (95% CI, 0.09-0.69) for ER-positive cancer. The effect of ER on breast cancer survival was also modified by genotypes of ER-α gene. Tests for multiplicative interaction were highly significant.

Conclusions: These data suggest that the ER-α gene polymorphisms and ER status may have an interactive effect on breast cancer survival.

Steroid hormone receptor expression and proliferation in rat mammary gland carcinomas induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mammary gland carcinogen present in the human diet. Herein, the expression of estrogen receptor alpha (ERalpha), estrogen receptor beta (ER beta) and progesterone receptor (PR) was examined in mammary gland carcinomas induced by PhIP in female Sprague-Dawley rats. Quantitative real-time polymerase chain reaction demonstrated that ER alpha, ER beta and PR were statistically elevated by 3-, 4- and 8-fold in carcinomas compared with normal mammary glands. By immunohistochemistry, carcinomas showed statistically higher nuclear expression of all three steroid receptors with the majority of carcinomas showing at least 10% of epithelial cells stained for ER alpha (49/55, 89%), ER beta (41/55, 75%) and PR (48/55, 87%). Furthermore, the level of expression of the three steroid hormone receptors was positively correlated with each other across the bank of carcinomas (Spearman analysis, P < 0.05). The expression of ER alpha in carcinomas was associated with tumor grade, extent of nuclear pleomorphism and cellular proliferation as measured by proliferating cell nuclear antigen (PCNA) and phospho-Rb immunostaining (Spearman analysis, P < 0.05). Confocal microscopy was used to measure the percentage of epithelial cells showing nuclear colocalization of receptors, PCNA, and cyclin D1. Colocalization of the receptors, and the colocalization of the receptors with PCNA and cyclin D1 was strikingly higher in carcinomas than in the normal mammary gland. In carcinoma cells, 37% of ER alpha positive epithelial cells were colocalized with PCNA in contrast to just 0.25% of cells in the normal mammary gland. The findings from this study indicate that ER alpha, ER beta and PR were co-upregulated and nuclear localized in epithelial cells from rat mammary carcinomas compared with normal mammary glands, and that the co-upregulation was positively correlated with proliferation and cell cycle progression in carcinomas.

Phosphorylation of progesterone receptor serine 400 mediates ligand-independent transcriptional activity in response to activation of cyclin-dependent protein kinase 2

Human progesterone receptors (PR) are phosphorylated by cyclin-dependent protein kinase 2 (CDK2) at multiple sites, including Ser400. Herein, we have addressed the significance of phosphorylation of this residue. PR phospho-Ser400-specific antibodies revealed regulated phosphorylation of Ser400 in response to progestins and mitogens, and this correlated with increased CDK2 levels and activity. Expression of cyclin E elevated CDK2 activity and downregulated PR independently of ligand. Similarly, overexpression of activated mutant CDK2 increased PR transcriptional activity in the absence and presence of progestin. Mutation of PR Ser400 to alanine (S400A) blocked CDK2-induced PR activity in the absence, but not in the presence, of progestin. PR was unresponsive to activated CDK2 in breast cancer cells with elevated p27, and RNA interference knock-down of p27 partially restored CDK2-induced ligand-independent PR activation. Similarly, in p27(-/-) mouse embryonic fibroblasts, elevated CDK2 activity increased wild-type (wt) but not S400A PR transcriptional activity in the absence of progestin. CDK2 induced nuclear localization of unliganded wt but not S400A PR; liganded S400A PR exhibited delayed nuclear accumulation. These studies demonstrate that CDK2 regulates PR in the absence of progestins via phosphorylation of Ser400, thus revealing a novel mechanism for upregulated PR transcriptional activity in human breast cancer cells expressing altered cell cycle regulatory molecules.

Involvement of Ras Activation in Human Breast Cancer Cell Signaling, Invasion, and Anoikis

Although mutated forms of ras are not associated with the majority of breast cancers (<5%), there is considerable experimental evidence that hyperactive Ras can promote breast cancer growth and development. Therefore, we determined whether Ras and Ras-responsive signaling pathways were activated persistently in nine widely studied human breast cancer cell lines. Although only two of the lines harbor mutationally activated ras, we found that five of nine breast cancer cell lines showed elevated active Ras-GTP levels that may be due, in part, to HER2 activation. Unexpectedly, activation of two key Ras effector pathways, the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinase and phosphatidylinositol 3'-kinase/AKT signaling pathways, was not always associated with Ras activation. Ras activation also did not correlate with invasion or the expression of proteins associated with tumor cell invasion (estrogen receptor alpha and cyclooxygenase 2). We then examined the role of Ras signaling in mediating resistance to matrix deprivation-induced apoptosis (anoikis). Surprisingly, we found that ERK and phosphatidylinositol 3'-kinase/AKT activation did not have significant roles in conferring anoikis resistance. Taken together, these observations show that Ras signaling exhibits significant cell context variations and that other effector pathways may be important for Ras-mediated oncogenesis, as well as for anoikis resistance, in breast cancer. Additionally, because ERK and AKT activation are not strictly associated with Ras activation, pharmacological inhibitors of these two signaling pathways may not be the best approach for inhibition of aberrant Ras function in breast cancer treatment.