Estrogen receptor (ER) beta1 and ERbetacx/beta2 inhibit ERalpha function differently in breast cancer cell line MCF7

The different roles of ER subtypes in cancer biology and therapy

By eliciting distinct transcriptional responses, the oestrogen receptors (ERs) ERα and ERβ exert opposite effects on cellular processes that include proliferation, apoptosis and migration and that differentially influence the development and the progression of cancer. Perturbation of ER subtype-specific expression has been detected in various types of cancer, and the differences in the expression of ERs are correlated with the clinical outcome. The changes in the bioavailability of ERs in tumours, together with their specific biological functions, promote the selective restoration of their activity as one of the major therapeutic approaches for hormone-dependent cancers.

FHL1 interacts with oestrogen receptors and regulates breast cancer cell growth

Four and a half LIM protein 1 (FHL1) belongs to the Lin-1, Isl-1 and Mec-3 (LIM)-only protein family and plays important roles in muscle growth and carcinogenesis. However, the biological function of FHL1 remains largely unknown. Here, we show that FHL1 physically and functionally interacted with oestrogen receptors (ERs), which are involved in breast cancer development and progression. FHL1 bound specifically to the activation function-1 domain of ER. Physical interaction of FHL1 and ER is required for FHL1 repression of oestrogen-responsive gene transcription. FHL1 affected recruitment of ER to an oestrogen-responsive promoter and ER binding to an oestrogen-responsive element. Overexpression of FHL1 in breast cancer cells decreased expression of oestrogen-responsive proteins, whereas knockdown of endogenous FHL1 with FHL1 small interfering RNA increased the expression of these proteins. Further analysis of 46 breast cancer samples showed that FHL1 expression negatively associated with oestrogen-responsive gene expression in breast cancer cells. FHL1 inhibited anchorage-dependent and -independent breast cancer cell growth. These results suggest that FHL1 may play an important role in ER signalling as well as breast cancer cell growth regulation.

A systematic review of the relationship between polymorphic sites in the estrogen receptor-beta (ESR2) gene and breast cancer risk

The estrogen signal is mediated by the estrogen receptor (ER). The specific role of ER-beta, a second ER, in breast carcinogenesis is not known. A number of association studies have been carried out to investigate the relationship between polymorphic sites in the ESR2 gene and breast cancer risk, however, the results are inconsistent. We searched PubMed, Medline, and Web of Science database (updated to 10 January 2010) and identified 13 relevant case-control studies, and approximately 28 single-nucleotide polymorphisms (SNPs) and one micro-satellite marker were reported in the literature. The median number of study subjects was 776 (range 158-13,550). Three genetic variants [(CA)n, rs2987983, and rs4986938] showed significant overall associations with breast cancer, and rs4986938 was reported twice. Because rs4986938 and rs1256049 were the most extensively studied polymorphisms, we subsequently conducted a meta-analysis to evaluate their relationship with breast cancer risk (9 studies of 10,837 cases and 16,021 controls for rs4986938; 8 studies of 11,652 cases and 15,726 controls for rs1256049). For rs4986938, the women harboring variant allele seemed to be associated with a decreased risk either in the dominant model [pooled OR = 0.944, 95% confidence interval (95% CI) 0.897-0.993, fixed-effects] or in the co-dominant model (AG vs. GG) (OR = 0.944, 95% CI 0.895-0.997, fixed-effects). rs1256049 was not associated with breast cancer risk in any model. Five studies had investigated the effect of haplotypes in the ESR2 gene on breast cancer risk, and four of them had positive outcomes. In summary, the present systematic review suggests that SNP rs4986938 as well as haplotypes in the ESR2 gene might be associated with breast cancer. The need for additional studies examining these issues seems of vital importance.

Estrogen signaling via estrogen receptor {beta}

Estrogens act by binding to and activating two estrogen receptors (ERs), ERα and ERβ. Transcriptional regulation by ERs is controlled by a complex array of factors such as ER-ligand binding, the DNA sequence bound by ERs, ER-interacting cofactors, and chromatin context. This minireview will provide an overview of the most recent advances in the identification of ERβ-regulated target gene networks and ERβ DNA-binding sites. We also highlight the recent work establishing new roles of ERβ signaling, including protective functions in the epithelial-mesenchymal transition and in atherosclerosis, as well as regulation of cell proliferation in the colon.

Genistein aglycone: a new therapeutic approach to reduce endometrial hyperplasia

OBJECTIVE

Endometrial hyperplasia without cytological atypia is commonly treated with progestins, but other treatment regimes may be available with equivalent efficacy and low side effects.

DESIGN

A randomized double-blind, placebo and progesterone-controlled clinical trial to evaluate the effects of genistein aglycone in reducing endometrial hyperplasia.

PATIENTS

A group of 56 premenopausal women with non-atypical endometrial hyperplasia were enrolled and received: genistein aglycone (n=19; 54 mg/day); norethisterone acetate (n=19; 10 mg/day on days 16-25 of the menstrual cycle) or placebo (n=18) for 6 months.

MEASUREMENTS

Hysteroscopy was performed with biopsies and symptomology assessed at baseline, 3 and 6 months of administration. The effect on estrogen (ER) and progesterone receptors (PR) expression in uterine biopsies were assessed after 3 and 6 months. For each treatment follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), sex hormone-binding globulin (SHBG) and progesterone (PG) levels were also evaluated.

RESULTS

After 6 months, 42% of genistein aglycone-administered subjects had a significant improvement of symptoms (histologically confirmed in the 29%) compared to 47% of norethisterone acetate subjects (histologically confirmed in the 31%), but only 12% in the placebo group with 19% exhibiting worsening symptoms and increased endometrial thickness. No significant differences were noted for hormone levels for any treatment, but immunohistochemical analysis revealed significantly reduced staining for ER-alpha and PR and enhanced ER-beta1 staining in genistein-administered subjects associated with a complete regression of bleeding.

CONCLUSIONS

These results suggest that genistein aglycone might be useful for the management of endometrial hyperplasia without atypia in women that cannot be treated with progestin.

Identification of novel transcript variants of estrogen receptor α, β and progesterone receptor gene in human endometrium

The human progesterone receptor (PR) and estrogen receptor genes (ESR1 and ESR2) are known to code for a multitude of transcript variants resulting from alternative splicing. Many of them are translated into nuclear receptor proteins with altered structure and function. Expression of these alternative estrogen and progesterone receptors modulates the cellular response to sexual steroid hormones. Recent studies also suggested their significance in development of hormone-dependent diseases like gynecological cancers. We report identification of 12 new transcript variations of the PR, ESR1, and ESR2 gene in human endometrium which result from differential exon-skipping. We succeeded in cloning of four new double or triple exon-deletion transcript variants of ERα, four single, double or triple exon-skipped mRNA isoforms of ERβ, and four new transcript variations of PR gene. Sequence analysis suggested that at least four of them, ERαΔ5/6, ERαΔ5/6/7, PRΔ7, and PRΔ6/7 are translated into receptor proteins which might exert ligand-independent effects on steroid hormone signalling. Comparison of pre- and post-menopausal endometrium revealed differential expression of PRΔ6/7, ERαΔ5/6/7, ERαΔ3/4/5, and ERβΔ1-0N. We also report differential expression of the exon-skipped isoforms in a panel of human cancer cell lines derived from the breast, ovary, and endometrium. Our identification of additional transcript variations further increases the complexity of steroid hormone receptor gene expression and signalling.

Repression of estrogen receptor beta function by putative tumor suppressor DBC1

It has been well established that estrogen is involved in the pathophysiology of breast cancer. Estrogen receptor (ER) alpha appears to promote the proliferation of cancer tissues, while ERbeta can protect against the mitogenic effect of estrogen in breast tissue. The expression status of ERalpha and ERbeta may greatly influence on the development, treatment, and prognosis of breast cancer. Previous studies have indicated that the deleted in breast cancer 1 (DBC1/KIAA1967) gene product has roles in regulating functions of nuclear receptors. The gene encoding DBC1 is a candidate for tumor suppressor identified by genetic search for breast cancer. Caspase-dependent processing of DBC1 promotes apoptosis, and depletion of the endogenous DBC1 negatively regulates p53-dependent apoptosis through its specific inhibition of SIRT1. In addition, DBC1 modulates ERalpha expression and promotes breast cancer cell survival by binding to ERalpha. Here we report an ERbeta-specific repressive function of DBC1. Immunoprecipitation and immunofluorescence studies show that ERbeta and DBC1 interact in a ligand-independent manner similar to ERalpha. In vitro pull-down assays revealed a direct interaction between DBC1 amino-terminus and activation function-1/2 domain of ERbeta. Although DBC1 shows no influence on the ligand-dependent transcriptional activation function of ERalpha, the expression of DBC1 negatively regulates the ligand-dependent transcriptional activation function of ERbetain vivo, and RNA interference-mediated depletion of DBC1 stimulates the transactivation function of ERbeta. These results implicate the principal role of DBC1 in regulating ERbeta-dependent gene expressions.

Differential effects of overexpression of ERα and ERβ in MCF10A immortalised, non-transformed human breast epithelial cells

: Cellular effects of oestrogen are mediated by two intracellular receptors ERα and ERβ. However, to compare responses mediated through these two receptors, experimental models are needed where ERα and ERβ are individually stably overexpressed in the same cell type.

: We compared the effects of stable overexpression of ERα and ERβ in the MCF10A cell line, which is an immortalised but non-transformed breast epithelial cell line without high endogenous ER expression.

: Clones of MCF10A cells were characterised which stably overexpressed ERα (10A-ERα2, 10A-ERα13) or which stably overexpressed ERβ (10A-ERβ12, 10A-ERβ15). Overexpression of either ERα or ERβ allowed induction of an oestrogen-regulated ERE-LUC reporter gene by oestradiol which was not found in the untransfected cells. Oestradiol also increased proliferation of 10A-ERα13 and 10A-ERβ12 cells, but not untransfected cells, by 1.3-fold over 7 days. The phytoestrogen, genistein, which is reported to bind more strongly to ERβ than to ERα, could induce luciferase gene expression from an ERE-LUC reporter gene at concentrations of 10

: This provides a model system to compare effects of oestradiol with other oestrogenic ligands in cells stably overexpressing individually ERα or ERβ.

Microarray analysis of altered gene expression in ERbeta-overexpressing HEK293 cells

Estrogen receptors (ERs), ERalpha and ERbeta, mediate estrogen actions in a broad range of target tissues. With the introduction of microarray techniques, a significant understanding has been gained regarding the interplay between the ERalpha and ERbeta in breast cancer cell lines. To gain a more comprehensive understanding of ERbeta-dependent gene regulation independent of ERalpha, we performed microarray analysis on HEK293/mock and HEK293/ERbeta cells. A total of 332 genes was identified as ERbeta-upregulated genes and 210 identified as ERbeta-downregulated genes. ERbeta-induced and ERbeta-repressed genes were involved in cell-cell signaling, morphogenesis, and cell proliferation. The ERbeta repressive effect on genes related to proliferation was further studied by proliferation assays, where ERbeta expression resulted in a significant decrease in cell proliferation. To identify primary ERbeta target genes, we examined a number of ERbeta-regulated genes using chromatin immunoprecipitation assays for regions bound by ERbeta. Our results showed that ERbeta recruitment was significant to regions associated with 12 genes (IL1RAP, TMSB4X, COLEC12, ENPP2, KLRC1, RERG, RGS16, TNNT2, CYR61, FER1L3, FAM108A1, and CYP4X1), suggesting that these genes are likely to be ERbeta primary target genes. This study has provided novel information on the gene regulatory function of ERbeta independent of ERalpha and identified a number of ERbeta primary target genes. The results of Gene Ontology analysis and proliferation assays are consistent with an antiproliferative role of ERbeta independent of ERalpha.

Estrogen signaling pathway and its imaging in human breast cancer

Recent remarkable progress in hormonal therapy has provided great benefit to breast cancer patients, but it also evokes novel issues: how accurately can the efficacy of each hormonal therapy be predicted and how can hormonal therapy-resistant patients be treated? These clinically important issues must be closely related to the biological events in each cancer, such as the alteration of intracellular multiple estrogen signaling pathways and the estrogen-related cancer microenvironment, which has recently revealed by molecular biological studies on estrogen and its receptors. However, the estrogen signaling status in individual breast cancers has not been clarified yet. Here we present the context of these issues and introduce our study of new tools which enable the visualization of estrogen signals in individual cancers. The assessment of estrogen receptor (ER)-alpha activity in individual cancers or ER-activating ability of the cancer microenvironment in each breast cancer patient revealed several new findings and interesting observations. We hope that these approaches provide new clues about the estrogen-dependent mechanisms of breast cancer development, and will be useful to advance the diagnosis and treatment of breast cancer patients.

Selective activation of trophoblast-specific PLAC1 in breast cancer by CCAAT/enhancer-binding protein beta (C/EBPbeta) isoform 2

The trophoblast-specific gene PLAC1 (placenta-specific 1) is ectopically expressed in a wide range of human malignancies, most frequently in breast cancer, and is essentially involved in cancer cell proliferation, migration, and invasion. Here we show that basal activity of the PLAC1 promoter is selectively controlled by ubiquitous transcription factor SP1 and isoform 2 of CCAAT/enhancer-binding protein beta that we found to be selectively expressed in placental tissue and cancer cells. Binding of both factors to their respective elements within the PLAC1 promoter was essential to attain full promoter activity. Estrogen receptor alpha (ERalpha) signaling further augmented transcription and translation of PLAC1 and most likely accounts for the positive correlation between PLAC1 expression levels and the ERalpha status we observed in primary breast cancer specimens. DNA affinity precipitation and chromatin immunoprecipitation assays revealed that transactivation of the PLAC1 promoter by ligand-activated ERalpha is based on a nonclassical pathway independent of estrogen-response elements, by tethering of ERalpha to DNA-bound CCAAT/enhancer-binding protein beta-2, and SP1. Our findings provide first insight into a novel and hitherto unknown regulatory mechanism governing selective activation of trophoblast-specific gene expression in breast cancer.

Association of estrogen receptor beta gene polymorphisms with susceptibility to adolescent idiopathic scoliosis

STUDY DESIGN

A case-control study is presented.

OBJECTIVE

To investigate the association of estrogen receptor beta gene polymorphisms with susceptibility to adolescent idiopathic scoliosis.

SUMMARY OF BACKGROUND DATA

Studies have shown that idiopathic scoliosis is related to genetic factors, such as XbaI site polymorphism of the estrogen receptor alpha gene. To our knowledge, however, the relationship of estrogen receptor beta gene polymorphisms and the individual susceptibility to idiopathic scoliosis has not been studied.

METHODS

This study included 218 patients with AIS and 140 healthy controls. Height, menarche status, curve pattern, Cobb angle, and Risser sign in female patients were recorded. Blood samples were taken from each subject by venipuncture. Genomic DNA was extracted from peripheral blood leukocytes using standard phenol/chloroform extraction. PCR products from amplification of genomic DNA from all individuals were analyzed using denaturing high-performance liquid chromatography. Samples with aberrant HPLC profiles were sequenced in both the forward and the reverse directions on an ABI 3100 automated sequencer. The chi test was used to determine the significant difference in genotype distribution between patients with AIS and the controls.

RESULTS

The frequency of CC genotype of the exon ØK (in reality 5' UTR OK-1)was significantly higher in patients than that in controls (P < 0.05). The C alleles appeared to be overrepresented in patients compared with controls (P < 0.05). Furthermore, the frequencies of CC genotypes in female patients whose height was > or =160 cm and Cobb angle was > or =30 degrees were higher than those whose height was <160 cm and Cobb angle was <30 degrees (P < 0.05). CONCLUSION.: The sites of the exon ØK polymorphisms of estrogen receptor beta gene may be associated with a susceptibility of AIS. Furthermore, the sites of the exon ØK polymorphism may be associated with the height and the curve severity of patients.

Comparative study on the nuclear hormone receptor activity of various phytochemicals and their metabolites by reporter gene assays using Chinese hamster ovary cells

Phytochemicals are naturally present in a wide variety of plants, and have been suggested to exert a number of effects beneficial to human health. Several phytochemicals possess estrogenic activity through estrogen receptor alpha (ERalpha) and ERbeta, and are, therefore, termed phytoestrogens. In this study, we examined whether various phytochemicals have agonistic and/or antagonistic activity against six human nuclear receptors (ERalpha, ERbeta, androgen receptor (AR), glucocorticoid receptor (GR), thyroid hormone receptor alpha(1) (TRalpha(1)) and TRbeta(1)) by in vitro reporter gene assays using Chinese hamster ovary cells. Of the 31 phytochemicals tested, including flavonoids, isoflavonoids, coumestan, lignans, catechins and their metabolites, 20 compounds showed estrogenic activity via ERalpha and/or ERbeta, and we ranked these phytochemicals according to their estrogenic potency via ERalpha and ERbeta. As a result, coumestrol and genistein strongly activated ERalpha and ERbeta at very low concentrations of <1x10(-10) M. Most phytochemicals showing estrogenic activity also exhibited agonistic activity against ERbeta at lower concentrations than those for ERalpha, and two typical isoflavones, genistein and daidzein, in particular, showed a potent preference for ERbeta. Further, we found that baicalein has ERbeta antagonistic activity, and two compounds, enterolacton and O-desmethylangolensin, have AR antagonistic activity. Nevertheless, none of tested compounds showed AR agonistic activity together with GR, TRalpha(1) and TRbeta(1) agonistic/antagonistic activity. These results suggest that various phytochemicals or their metabolites preferentially interact with ERalpha/beta among the six nuclear hormone receptors tested, and that the ERbeta agonistic activity, in particular, of these compounds may be associated with various beneficial effects on human health.

Breast cancer cell response to genistein is conditioned by BRCA1 mutations

Soy phytoestrogens, among which genistein, seem to protect from breast cancer development. In order to study the role of the breast tumour suppressor BRCA1 in response to genistein, we used a new breast cancer cell model: the SUM1315MO2 cell line carrying the 185delAG BRCA1 mutation, which we stably transfected with a plasmid encoding wild-type BRCA1. We showed that growth of BRCA1 mutant cells was strongly inhibited by genistein whereas it only had a weak effect in cells expressing wild-type BRCA1 protein. BRCA1 mutant cells hypersensitivity could be linked to higher expression of ERbeta gene, which suggests that genistein may be an efficient inhibitor of cancer development in BRCA1 mutant breast cancer cells.

Do Estrogen Receptor beta Polymorphisms Play A Role in the Pharmacogenetics of Estrogen Signaling?

Estrogen hormones play critical roles in the regulation of many tissue functions. The effects of estrogens are primarily mediated by the estrogen receptors (ER) alpha and beta. ERs are ligand-activated transcription factors that regulate a complex array of genomic events that orchestrate cellular growth, differentiation and death. Although many factors contribute to their etiology, estrogens are thought to be the primary agents for the development and/or progression of target tissue malignancies. Many of the current modalities for the treatment of estrogen target tissue malignancies are based on agents with diverse pharmacology that alter or prevent ER functions by acting as estrogen competitors. Although these compounds have been successfully used in clinical settings, the efficacy of treatment shows variability. An increasing body of evidence implicates ERalpha polymorphisms as one of the contributory factors for differential responses to estrogen competitors. This review aims to highlight the recent findings on polymorphisms of the lately identified ERbeta in order to provide a functional perspective with potential pharmacogenomic implications.

Loss of estrogen receptor beta isoform expression and its correlation with aberrant DNA methylation of the 5'-untranslated region in human epithelial ovarian carcinoma

Evidence exists that sex steroids such as estrogens affect epithelial ovarian cancer. The expression profiles of the estrogen receptors (ER) and ERbeta in particular have not been fully described. Therefore, in our present study, we examined the methylation status of the promoters 0K and 0N, and the expression of ERbeta isoforms in human epithelial ovarian carcinoma. We then correlated methylation status with ER expression status. Twelve ovarian carcinoma cell lines, six primary cultures of ovarian surface epithelial cells (OSE), and 64 cases of ovarian carcinoma tissues were examined. Bisulfite sequencing and quantitative reverse transcription-polymerase chain reaction were used to evaluate methylation status and expression of ERbeta isoforms. The relative abundance of exon 0N, ERbeta1, ERbeta2, and ERbeta4 mRNA was significantly lower in ovarian cancer cell lines and tissues than in their corresponding normal counterparts. However, ERbeta5 mRNA level was relatively higher in the cancers, in clear cell adenocarcinoma in particular, than in the normal ovary. Bisulfite sequencing analysis demonstrated that the two promoters of the ERbeta gene exhibited distinct methylation patterns. Promoter 0N was unmethylated in OSE, rarely methylated in normal ovarian tissues, and extensively methylated in ovarian cancer cell lines and tissues (11/15 cell lines and 18/32 cancer tissues were extensively methylated). The promoter 0K was, however, unmethylated in both normal and malignant ovarian cells and tissues. A significant correlation between promoter 0N hypermethylation and the loss of exon 0N, ERbeta1, ERbeta2, and ERbeta4 mRNA expression was detected in ovarian carcinoma cells and tissues. Treatment of ovarian carcinoma cells with 5-aza-2' deoxycytidine resulted in reexpression of the ERbeta gene. The results of our present study suggest that ERbeta is inactivated mainly through aberrant DNA methylation. This process may play an important role in the pathogenesis of epithelial ovarian cancer.

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.

Intratumoral estrogens and estrogen receptors in human non-small cell lung carcinoma

PURPOSE

The possible involvement of gender-dependent factors has been suggested in human non-small cell lung carcinomas (NSCLC), but their precise roles remain largely unclear. Therefore, we examined intratumoral estradiol concentrations in NSCLC to examine local actions of estrogens in NSCLC.

EXPERIMENTAL DESIGN

Fifty-nine frozen specimens of NSCLC were available for liquid chromatography/electrospray tandem mass spectrometry to study intratumoral estradiol concentrations. In addition, A549 NSCLC cells stably expressing estrogen receptor (ER) alpha (A549 + ERalpha) or ERbeta (A549 + ERbeta) were used in vitro studies.

RESULTS

Forty-three (73%) of 59 NSCLC showed higher concentration of estradiol in carcinoma tissues than the corresponding nonneoplastic lung tissues from the same patient, and intratumoral estradiol concentrations were significantly (P = 0.0002 and 2.2-fold) higher than the corresponding nonneoplastic lungs. The intratumoral concentration of estradiol was positively correlated with aromatase expression, tumor size, and Ki-67 status in ERalpha- or ERbeta-positive cases. In in vitro studies, estradiol significantly increased cell proliferation of A549 + ERalpha or A549 + ERbeta, which was significantly suppressed by selective ER modulators, tamoxifen or raloxifene. Both A549 + ERalpha and A549 + ERbeta cells expressed aromatase. The cell proliferation level in these cells was significantly increased under treatment with testosterone, and it was inhibited by addition of the aromatase inhibitor letrozole.

CONCLUSIONS

These results suggest that estradiol is locally produced in NSCLC mainly by aromatase and plays an important role in the growth of ERalpha- or ERbeta-positive NSCLC. Therefore, use of selective ER modulators and/or aromatase inhibitors may be clinically effective in NSCLC that are positive for both ER and aromatase.

Minireview: nuclear receptors and breast cancer

Until recently, the study of nuclear receptor (NR) function in breast cancer biology has been largely limited to estrogen and progesterone receptors. The development of reliable gene expression arrays, real-time quantitative RT-PCR, and immunohistochemical techniques for studying NR superfamily members in primary human breast cancers has now revealed the presence and potential importance of several additional NRs in the biology of breast cancer. These include receptors for steroid hormones (including androgens and corticosteroids), fat-soluble vitamins A and D, fatty acids, and xenobiotic lipids derived from diet. It is now clear that after NR activation, both genomic and nongenomic NR pathways can coordinately activate growth factor signaling pathways. Advances in our understanding of both NR functional networks and epithelial cell growth factor signaling pathways have revealed a frequent interplay between NR and epithelial cell growth factor family signaling that is clinically relevant to breast cancer. Understanding how growth factor receptors and their downstream kinases are activated by NRs (and vice-versa) is a central goal for maximizing treatment opportunities in breast cancer. In addition to the estrogen receptor, it is predicted that modulating the activity of other NRs will soon provide novel prevention and treatment approaches for breast cancer patients.

Phytoestrogens and breast cancer prevention: possible mechanisms of action

OBJECTIVE

Phytoestrogens display an array of pharmacologic properties, and in recent years investigation of their potential as anticancer agents has increased dramatically. In this article we review the published literature related to phytoestrogens and breast cancer as well as suggest the possible mechanisms that may underlie the relationship between phytoestrogens and breast cancer.

DATA SOURCES

Electronic searches on phytoestrogens and breast cancer were performed on MEDLINE and EMBASE in June 2007. No date restriction was placed on the electronic search.

DATA EXTRACTION

We focused on experimental data from published studies that examined the characteristics of phytoestrogens using in vivo or in vitro models. We also include human intervention studies in this review.

DATA SYNTHESIS

We evaluated evidence regarding the possible mechanisms of phytoestrogen action. Discussions of these mechanisms were organized into those activities related to the estrogen receptor, cell growth and proliferation, tumor development, signaling pathways, and estrogen-metabolizing enzymes.

CONCLUSIONS

We suggest that despite numerous investigations, the mechanisms of phytoestrogen action in breast cancer have yet to be elucidated. It remains uncertain whether these plant compounds are chemoprotective or whether they may produce adverse outcomes related to breast carcinogenesis.

The estrogen receptor-interacting protein HPIP increases estrogen-responsive gene expression through activation of MAPK and AKT

Estrogen receptors (ERalpha and ERbeta) are estrogen-regulated transcription factors that play important roles in the development and progression of breast cancer. The biological function of ERs has been shown to be modulated by ER-interacting proteins. However, the ER-interacting proteins that not only activate MAPK and AKT, two important growth regulatory protein kinases, but also increase growth related estrogen-responsive gene expression remain unknown. Here, we report that hematopoietic PBX-interacting protein (HPIP) interacts both with ERalpha and with ERbeta, and increases ERalpha target gene expression through activation of MAPK and AKT and enhanced ERalpha phosphorylation. ERbeta inhibits ERalpha target gene expression, possibly by competition of ERbeta with ERalpha for binding to HPIP, and by a decrease in available ERalpha for HPIP binding through the interaction of ERbeta with ERalpha. Furthermore, HPIP increases breast cancer cell growth. These data suggest that HPIP may be an important regulator in ER signaling and that the relative ratio of ERbeta to ERalpha may be important for HPIP function.

Estrogen receptor beta: an overview and update

The discovery of a second estrogen receptor (ER), designated ERbeta (NR3A2), has redefined our knowledge about the mechanisms underlying cellular signaling by estrogens and has broad implications for our understanding of regulation of estrogen-responsive tissues. Highly variable and even contrasting effects of estrogens in different tissues seem to be at least partially explained by different estrogen signaling pathways, involving ERalpha (NR3A1) and/or ERbeta. To date, two key conclusions can be drawn from the significant body of work carried out on the specific roles of the two receptor subtypes in diverse estrogen target tissues. First, ERalpha and ERbeta have different biological functions, as indicated by their specific expression patterns and the distinct phenotypes observed in ERalpha and ERbeta knockout (alphaERKO and betaERKO) mice. Second, ERalpha and ERbeta appear to have overlapping but also unique sets of downstream target genes, as judged from a set of microarray experiments. Thus, ERalpha and ERbeta have different transcriptional activities in certain ligand, cell-type, and promoter contexts, which may help to explain some of the major differences in their tissue-specific biological actions. The phenotypes observed for betaERKO mice have suggested certain therapeutic areas to be further explored. The development of ERbeta-selective ligands active in animal disease models indicates new avenues for clinical exploration. ERbeta agonists are being explored and validated as drugs for a growing number of indications. Hopefully, some ERbeta targeted drugs will prove to be efficient in enhancing human health.

Quantitative structure-activity relationships for a series of selective estrogen receptor-beta modulators

The estrogen receptor-beta subtype (ERbeta) is an attractive drug target for the development of novel therapeutic agents for hormone replacement therapy. Hologram quantitative structure-activity relationships (HQSAR) were conducted on a series of 6-phenylnaphthalene and 2-phenylquinoline derivatives, employing values of ERbeta binding affinity. A training set of 65 compounds served to derive the models. The best statistical HQSAR model (q(2) = 0.73 and r(2) = 0.91) was generated using atoms, bonds, connections and donor and acceptor as fragment distinction parameters, and fragment size default (4-7) with hologram length of 199. The model was used to predict the binding affinity of an external test set of 16 compounds, and the predicted values were in good agreement with the experimental results. The final HQSAR model and the information obtained from 2D contribution maps should be useful for the design of novel ERbeta modulators having improved affinity.

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.

Rapid signaling mechanisms of estrogens in the developing cerebellum

The steroid hormone 17beta-estradiol regulates the normal function and development of the mammalian nervous system. Many of estradiol's effects are mediated via the nuclear hormone estrogen receptors ERalpha and ERbeta. In addition to regulating estrogen-responsive gene expression, estradiol also acts in an immediate and cell-specific fashion to regulate various intracellular signal transduction pathways. The goal of this review is to develop a contextual framework to understand the generalized function of estrogen during development of brain regions not known to be sexually specialized. However, it is first important to build this framework on the more well-developed foundation of estrogen's gonad-driven sex-specific actions. As a result, a discussion of known and proposed mechanisms of estrogen actions in reproductive and other tissues will be presented. Building upon this information, a review of our research group's recent in vitro and in vivo studies that have focused on elucidating the mechanisms of estrogen actions in neurons of the non-sexually specialized cerebellum will be presented. While the full spectrum of estrogen action during normal cerebellar development remains unresolved, results of recent studies have revealed a pathologic role for estrogen and estrogen receptors in medulloblastoma, common pediatric brain tumors that arise from cerebellar granule cell-like precursors. The potential use of anti-estrogen signaling agents as adjuvant therapy for medulloblastoma is proposed based on those finding.

Suppressive effects of bisphenol A on the proliferation of neural progenitor cells

Endocrine disruptors (EDs) exert adverse effects on reproductive and immune function or neurological behavior. Bisphenol A (BPA), one of the environmental EDs, is widely used in the manufacture of plastics and epoxy resins. Studies reported that BPA affects reproductive organ growth and development. However, the potential adverse effects of BPA on neuronal development have not been fully explored. In this study, the potent harmful effects of BPA were investigated on the murine-derived multipotent neural progenitor cells (NPCs). Pretreatment of BPA significantly decreased proliferation of NPCs in a concentration-dependent manner. Moreover, at a high concentration (> 400 microM), BPA was cytotoxic to NPCs. However, the low concentrations of BPA, previously shown to exert estrogenic actions, did not affect the proliferation of NPCs. BPA altered the activation of extracellular signal-regulated kinases and c-Jun-N-Kinases in a different manner without affecting activities of p38 kinases. It was also found that reactive oxygen species (ROS) were elevated in NPCs exposed to high concentrations of BPA, indicating oxidative stress-related cytotoxicity. These data show adverse effects of BPA on the nervous system and potentially on neonatal brain development.

Estrogen receptor beta increases the efficacy of antiestrogens by effects on apoptosis and cell cycling in breast cancer cells

Clinical evidence indicates that higher levels of estrogen receptor beta (ERbeta) predicts improved disease-free and overall survival in patients treated with adjuvant tamoxifen therapy. To better understand the mechanisms in which ERbeta can modulate breast cancer therapies, we introduced ERbeta under an inducible promoter into MCF-7 breast cancer cells. In these cells, induction of ERbeta expression led to a shift in the potency and an increase in the efficacy of tamoxifen to inhibit proliferation. A similar effect on breast cancer cells was observed for two other antiestrogens, raloxifene, and fulvestrant. Induced expression of ERbeta did not enhance the antiproliferative effects of small molecule inhibitors that target the epidermal growth factor receptor, insulin growth factor receptor-1 and histone deacetylase, indicating ERbeta specifically cooperates with antiestrogens. The combination of ERbeta expression, which arrests cells in G2, and tamoxifen, which arrests cells in G1, led to a potent blockade of the cell cycle. ERbeta also increased tamoxifen-induced cell death and cooperated with tamoxifen to induce expression of the pro-apoptotic gene bik. In summary, our data indicates that ERbeta increases the efficacy of antiestrogens by effects on apoptosis and on cell cycling and, together with clinical observations, suggests ERbeta could be a valuable prognostic marker and potential therapeutic target.

Genetics and pharmacogenetics of estrogen response

Estrogens are a steroid hormone group distributed widely in animals and human beings. Estrogens diffuse across cell phospholipidic membranes and interact with estrogen receptors. Their highest concentration is found in target tissues with reproductive function (breast, ovary, vagina and uterus). High estrogen levels are usually associated with tumor onset and progression, while loss of estrogen or its receptor(s) contributes to development and/or progression of various diseases (osteoporosis, neurodegenerative disease and cardiovascular disease). Despite the numerous efforts to highlight estrogen's mechanism of action, recent discoveries showed an unexpected degree of complexity of estrogenic response.

Expression of oestrogen receptor-? in apocrine carcinomas of the breast

AIMS

Apocrine carcinoma of the breast seldom expresses oestrogen receptors (ER) or progesterone receptors (PR), but frequently expresses androgen receptors (AR). Because of this unusual hormone receptor status, it has been suggested that oestrogens have a less important role in the pathogenesis of apocrine carcinoma. The ER status of apocrine carcinoma has been studied for one kind of ER, the classic receptor now named ER-alpha; however, the status of ER-beta, a secondary oestrogen receptor, has not been examined systematically in apocrine carcinoma. The aim was to study ER-beta status in apocrine carcinoma.

METHODS AND RESULTS

The expression of ER-beta was examined immunohistochemically in 48 apocrine carcinomas and compared with clinicopathological factors and ER-alpha, PR and AR status. ER-beta positivity was observed in 35 cases (73%), regardless of any clinicopathological factors or the status of other receptors. The results of ER-beta mRNA analysis supported the immunohistochemical results.

CONCLUSIONS

The significance of oestrogens in apocrine carcinoma should not be dismissed at present when the role of ER-beta remains to be determined. Studying the action of oestrogen or antioestrogen in apocrine carcinoma may reveal a role for ER-beta independent of ER-alpha and raise the potential of hormonal therapy for these tumours.

Estrogen receptor α/β isoforms, but not βcx, modulate unique patterns of gene expression and cell proliferation in Hs578T cells

The actions of 17beta-estradiol (E2) and selective estrogen receptor modulators (SERMs) have been extensively investigated regarding their ability to act through estrogen receptor-alpha (ERalpha) to perturb estrogen receptor positive (ER+) breast cancer (BC) growth. However, many BCs also express ERbeta, along with multiple estrogen receptor (ER) splice variants such as ERbetacx, an ERbeta splice variant incapable of binding ligand. To gain a more comprehensive understanding of ER action in BC cells, we stably expressed ERalpha, ERbeta, or ERbetacx under doxycycline (Dox) control in Hs578T cells. Microarrays performed on E2 or 4OH-tamoxifen (4HT) treated Hs578T ERalpha and ERbeta cells revealed distinct ligand and receptor-dependent patterns of gene regulation, while the induction of ERbetacx did not alter gene expression patterns. E2 stimulation of Hs578T ERbeta cells resulted in a 27% decrease in cellular proliferation, however, no significant change in proliferation was observed following the exposure of Hs578T ERalpha or ERbeta cells to 4HT. Expression of ERbetacx in Hs578T cells did not effect cellular proliferation. Flow cytometry assays revealed a 50% decrease in E2-stimulated Hs578T ERbeta cells entering S-phase, along with a 17% increase in G0/G1 cell-cycle arrest. We demonstrate here that ERalpha and ERbeta regulate unique gene expression patterns in Hs578T cells, and such regulation likely is responsible for the observed isoform-specific changes in cell proliferation. Hs578T ER expressing cell-lines provide a unique BC model system, permitting the comparison of ERalpha, ERbeta, and ERbetacx actions in the same cell-line.

Comparative gene expression profiling reveals partially overlapping but distinct genomic actions of different antiestrogens in human breast cancer cells

Antiestrogens used for breast cancer (BC) treatment differ among each other for the ability to affect estrogen receptor (ER) activity and thereby inhibit hormone-responsive cell functions and viability. We used high-density cDNA microarrays for a comprehensive definition of the gene pathways affected by 17beta-estradiol (E2), ICI 182,780 (ICI), 4OH-tamoxifen (Tamoxifen), and raloxifene (RAL) in ER-positive ZR-75.1 cells, a suitable model to investigate estrogen and antiestrogen actions in hormone-responsive BC. The expression of 601 genes was significantly affected by E2 in these cells; in silico analysis reveals that 86 among them include one or more potential ER binding site within or near the promoter and that the binding site signatures for E2F-1, NF-Y, and NRF-1 transcription factors are significantly enriched in the promoters of genes induced by estrogen treatment, while those for CAC-binding protein and LF-A1 in those repressed by the hormone, pointing to novel transcriptional effectors of secondary responses to estrogen in BC cells. Interestingly, expression of 176 E2-regulated mRNAs was unaffected by any of the antiestrogens tested, despite the fact that under the same conditions the transcriptional and cell cycle stimulatory activities of ER were inhibited. On the other hand, of 373 antiestrogen-responsive genes identified here, 52 were unresponsive to estrogen and 25% responded specifically to only one of the compounds tested, revealing non-overlapping and clearly distinguishable effects of the different antiestrogens in BC cells. As some of these differences reflect specificities of the mechanism of action of the antiestrogens tested, we propose to exploit this gene set for characterization of novel hormonal antagonists and selective estrogen receptor modulators (SERMs) and as a tool for testing new associations of antiestrogens, more effective against BC.

Basic research for hormone-sensitivity of breast cancer

Hormonal therapy is a rapidly progressing molecular-targeted therapy for breast cancer, using drugs such as LH-RH agonists, SERMs and aromatase inhibitors. Basic research for estrogen signaling and hormone sensitivity in breast cancer cells strongly contributes to the progression of clinical treatment of breast cancer. However, further problems remain unresolved, for example the accurate prediction of individual response to each hormonal therapy. Moreover, novel combinations with other molecular-targeted therapies might be advance the effectiveness of hormonal therapies. To address these issues, we are developing several new tools such as focused microarray and a GFP-reporter cell system. We first identified estrogen-responsive genes by comprehensive expression profiling of estrogen receptor (ER)-positive breast cancer cells, and produced a custom-made estrogen-responsive microarray of a narrowed-down subset. Using this microarray, we studied several basic issues regarding estrogen signaling and expression analysis of estrogen-responsive genes in breast cancer tissues. Furthermore, expression of several candidate genes selected from the contents of the customarray was also analyzed by real-time RT-PCR and by immunohistochemical techniques, to find new predictive factors for responsiveness to hormone therapy for primary breast cancer patients. We found that the expression of several genes such as HDAC6 significantly correlated with disease-free and overall survival of ER-positive patients. Furthermore, we are developing a new tool for analyzing the estrogen-related microenvironment on individual breast cancer patients using ERE-GFP-indicator cells. This system enables visualization of tumor-stroma interactions and the effects of aromatase inhibitors in an individual breast cancer sample. We believe that these approaches could provide not only new clues to elucidate the estrogen-dependent mechanisms of cancer, but also clinical benefits to patients by predicting individual response to hormonal therapy.

Estrogen receptor-beta: recent lessons from in vivo studies

The unexpected discovery of a second form of the estrogen receptor (ER), designated ERbeta, surprised and energized the field of estrogen research. In the 9 yr since its identification, the remarkable efforts from academic and industrial scientists of many disciplines have made significant progress in elucidating its biology. A powerful battery of tools, including knockout mice as well as a panel of receptor-selective agonists, has allowed an investigation into the role of ERbeta. To date, in vivo efficacy studies are limited to rodents. Current data indicate that ERbeta plays a minor role in mediating estrogen action in the uterus, on the hypothalamus/pituitary, the skeleton, and other classic estrogen target tissues. However, a clear role for ERbeta has been established in the ovary, cardiovascular system, and brain as well as in several animal models of inflammation including arthritis, endometriosis, inflammatory bowel disease, and sepsis. The next phase of research will focus on elucidating, at a molecular level, how ERbeta exerts these diverse effects and exploring the clinical utility of ERbeta-selective agonists.

In vivo and in vitro estrogenic and progestagenic actions of Tibolone

Estrogen and progestin combination in hormone replacement therapy (HRT) increases the incidence of breast cancer, but decreases the endometrial cancer risk of unopposed estrogen. Therefore, a SERM such as Tibolone, that delivers the beneficial, but not the adverse side effects, of steroid hormones would be clinically advantageous. However, data from the Million Women Study suggests that Tibolone increases the risk of both breast and endometrial cancer. Herein, we assessed the estrogenic and progestagenic actions of Tibolone using transvaginal sonography studies and an in vitro model of breast (ZR-75, MCF7) and endometrial cancer (Ishikawa). The known cancer associated proteins (ER, EGFR, STATS, tissue factor and Bcl-xL) were selected for study. Transvaginal sonography demonstrated that postmenopausal women treated with Tibolone displayed a thinner endometrium than in the late proliferative phase, but had a phenotype characteristic of the secretory phase, thus demonstrating the estrogenic and progestagenic actions of this SERM. In vitro, Tibolone acted as an estrogen in downregulating ER and upregulating Bcl-xL, yet as progesterone, increasing STAT5 and tissue factor in breast cancer cells. The increase in tissue factor by Tibolone correlated with its coagulative potential. Interestingly, EGFR was up-regulated by progesterone in the breast and by estrogen in endometrial cells, while Tibolone increased protein levels in both cell types. In conclusion, this study further demonstrates the estrogenic and progestagenic nature of Tibolone. The pattern of regulation of known oncogenes in cells of breast and endometrial origin dictates caution and vigilance in the prescription of Tibolone and subsequent patient monitoring.

Estrogen receptor beta, a possible tumor suppressor involved in ovarian carcinogenesis

Ovarian cancer is one of the leading causes of death from gynecological tumors in women. Several lines of evidence suggest that estrogens may play an important role in ovarian carcinogenesis, through their receptors, ERalpha and ERbeta. Interestingly, malignant ovarian tumors originating from epithelial surface constitute about 90% of ovarian cancers and expressed low levels of ERbeta, compared to normal tissues. In addition, restoration of ERbeta in ovarian cancer cells, leads to strong inhibition of their proliferation and invasion, while apoptosis is enhanced. In this manuscript, recent data suggesting a possible tumor-suppressor role for ERbeta in ovarian carcinogenesis are discussed.

Clinical significance of estrogen receptor beta in breast cancer

Ever since the estrogen receptor (ER) beta was discovered in 1996, we have been trying to determine its value as a prognostic and/or predictive factor in breast cancer and its potential as a novel target for pharmacological intervention. Recent progress in cellular experiments has shown that ERbeta works as counter partner of ERalpha through inhibition of the transactivating function of ERalpha by heterodimerization, distinct regulation on several specific promoters by ERalpha or ERbeta, and ERbeta-specific regulated genes which are probably related to its anti-proliferative properties. Accumulated data from protein studies in breast cancer tissues indicate that positive expression of ERbeta appears to correlate with a favorable prognosis. Although the number of studies is small, a positive response to tamoxifen treatment is observed in both ERalpha- and ERbeta-positive populations. The significance of ERbeta2/cx, a splicing variant of ERbeta, remains controversial and needs to be analyzed in further studies. We postulate that a combined evaluation of ERbetacx with progesterone receptor may help the stratification of ERalpha-positive breast cancer. Epidemiological studies of hormone replacement therapy and isoflavone (genistein) consumption indicate the possible contribution of ERbeta-specific signaling in breast cancer prevention. A selective estrogen receptor modulator, which works as an antagonist of ERalpha and an agonist of ERbeta, may be a promising chemo-preventive treatment.

Estrogen signaling and prediction of endocrine therapy

Estrogen plays an important role in the growth and progression of human breast cancer. Understanding the whole picture of estrogen signaling is a very important goal towards clarifying the biology of this disease. On the other hand, hormonal therapy for breast cancer has been progressing rapidly with the advent of drugs such as selective estrogen receptor (ER) modulators and aromatase inhibitors. Prediction of individual response to these hormonal therapies is becoming important for the management of breast cancer patients. To help address these basic and clinical issues, we are developing several new tools such as the focused microarray and the green fluorescent protein-reporter cell system. We first carried out expression profiling of approximately 10,000 genes in ER-positive breast cancer cells. Based on the results, estrogen-responsive genes (ERG) were selected and a custom-made cDNA microarray consisting of 200 genes from a narrowed-down subset was produced. Using this microarray, we investigated various aspects of estrogen signaling such as the effect of estrogen-antagonists on ERG expression profile and functional analysis of ERbeta and novel estrogen responsive gene EGR3. Furthermore, expression levels of several candidate genes selected from the custom-array contents were analyzed by real-time RT-PCR and immunohistochemistry using breast cancer tissues to determine novel predictive factors for responsiveness to hormone therapy in primary breast cancer patients. Expression of several genes, such as HDAC6, significantly correlated with disease-free and overall survival of patients treated with adjuvant tamoxifen therapy. We are currently developing a new tool for analyzing the effects of novel aromatase inhibitors in individual breast cancer patients using estrogen-responsive element-green fluorescent protein-indicator cells. We hope that these approaches may provide not only new clues for elucidation of estrogen-dependent growth mechanisms of cancer, but also clinical benefits to patients by assessment of individual responses to endocrine therapy.

Steroid hormone receptor signaling in tumorigenesis

Excessive activation of the hormone signaling pathways is implicated in several disorders of the target tissues, with cancer being one of the most serious fallouts. Steroid hormone receptors are key proteins through which steroid hormones convey their signals to the cells. Deregulated activity of the hormone receptors due to their altered activation; stability or sub-cellular localization is heavily implicated in the onset and progress of cancers. The role played by estrogen and its receptors in breast cancer remains the most thoroughly investigated steroid-dependent cancer system till date. Choosing it as an example, we have summarized the molecular mechanisms underlying the action of the estrogen receptors (ERs) in manifesting the effects of the estrogens in the cells. A special emphasis is placed on the molecular mechanism of their functionality, role of the coactivator proteins, and the reasons for the deregulated signaling. The therapeutic approaches resulting from the mechanistic study of the ER action and their efficacies are also discussed.

The human estrogen receptor-alpha isoform hERalpha46 antagonizes the proliferative influence of hERalpha66 in MCF7 breast cancer cells

The expression of two human estrogen receptor-alpha (hERalpha) isoforms has been characterized within estrogen receptor-alpha-positive breast cancer cell lines such as MCF7: the full-length hERalpha66 and the N terminally deleted hERalpha46, which is devoid of activation function (AF)-1. Although hERalpha66 is known to mediate the mitogenic effects that estrogens have on MCF7 cells, the exact function of hERalpha46 in these cells remains undefined. Here we show that, during MCF7 cell growth, hERalpha46 is mainly expressed in the nucleus at relatively low levels, whereas hERalpha66 accumulates in the nucleus. When cells reach confluence, the situation reverses, with hERalpha46 accumulating within the nucleus. Although hERalpha46 expression remains rather stable during an estrogen-induced cell cycle, its overexpression in proliferating MCF7 cells provokes a cell-cycle arrest in G(0)/G(1) phases. To gain further details on the influence of hERalpha46 on cell growth, we used PC12 estrogen receptor-alpha-negative cell line, in which stable transfection of hERalpha66 but not hERalpha46 allows estrogens to behave as mitogens. We next demonstrate that, in MCF7 cells, overexpression of hERalpha46 inhibits the hERalpha66-mediated estrogenic induction of all AF-1-sensitive reporters: c-fos and cyclin D1 as well as estrogen-responsive element-driven reporters. Our data indicate that this inhibition occurs likely through functional competitions between both isoforms. In summary, hERalpha46 antagonizes the proliferative action of hERalpha66 in MCF7 cells in part by inhibiting hERalpha66 AF-1 activity.

Estrogen receptors alfa (ERalpha) and beta (ERbeta) differentially regulate proliferation and apoptosis of the normal murine mammary epithelial cell line HC11

The mitogenic effect of 17beta-estradiol (E2) on the breast is mediated by estrogen receptor alfa (ERalpha), hence ERalpha antagonists are effective in the treatment of breast cancer. The possible use of estrogen receptor beta (ERbeta) as a target in treatment of breast cancer is under investigation. The mouse mammary cell line HC11 expresses both ERs and was used to study the role of the two receptors in proliferation. E2 had no effect on proliferation. The ERalpha-selective agonist 4,4',4''-(4-propyl-(1H)-pyrazole-1,3,5-triyl)trisphenol (PPT) stimulated proliferation. The ERbeta-selective agonist 2,3-bis(4-hydroxy-phenyl)-propionitrile (DPN) inhibited cell growth and induced apoptosis. PPT upregulated while DPN downregulated cyclin D1 and proliferating cell nuclear antigen (PCNA). Upon inhibition of ERalpha expression with RNA interference, E2 caused a decrease in cyclin D1 and PCNA, and increased apoptosis. When ERbeta expression was blocked, E2 induced proliferation and cells gained the capacity to grow in soft agar. In summary, in HC11 mammary epithelial cells, ERalpha drives proliferation in response to E2 while ERbeta is growth inhibitory. The lack of effect of E2 on HC11 cell growth is the result of the combined actions of ERalpha (proliferation) and ERbeta (apoptosis). We suggest that use of ERbeta agonists will be a useful addition in treatment of breast cancer, which, at present, is only aimed at inhibition of ERalpha.

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.

Tumor-stromal interaction through the estrogen-signaling pathway in human breast cancer

In postmenopausal breast cancers, locally produced estrogen by adipose stromal cells causes the progression of tumor growth. Although aromatase, a key enzyme of estrogen synthesis, is highly expressed in the adipose stromal cells, and aromatase inhibitors show greater efficacy in postmenopausal breast cancers, the mechanism of increasing aromatase activity in the stromal cells remains unclear. To analyze the estrogen signals and to detect the estrogen receptor (ER)-activating ability of adipose stromal cells for individual human breast cancers, we developed a new reporter cell system. To visualize the activation of ER, we first established a stable transformant, named E10, of human breast cancer MCF-7 cells by transfection with the estrogen-responsive element-green fluorescent protein (GFP) gene. E10 cells specifically express GFP when ER is activated by estrogen or by coculture with adipose stromal cells isolated from breast tumor tissues in the presence of testosterone, a substrate for aromatase. Treatment of adipose stromal cells with dexamethasone, a stimulator of aromatase gene expression, resulted in an increase in the expression of GFP in E10 cells in the coculture. Using this system, we characterized the adipose stromal cells of 67 human breast cancers and found that GFP expression levels vary among the cases, suggesting that the ability of adipose stromal cells to activate ERs is unique for individual breast cancers. High induction levels of GFP were observed more frequently in postmenopausal cases than in premenopausal cases, whereas they did not significantly correlate with the ER expression status. Aromatase inhibitors inhibited the induction of GFP expression in the coculture, but the sensitivities to the drugs varied among the individual cases. Aromatase gene expression levels in adipose stromal cells did not always correlate with their ability to induce GFP. These results suggest that this system to detect total ER activation based on the interaction with adipose stromal cells is a useful tool for analyzing local estrogen signals and for tumor-stromal interactions.

Increased Estrogen Receptor βcx Expression during Mammary Carcinogenesis

Identification of proteins that markedly vary during early steps of mammary carcinogenesis may help to understand its pathophysiology and to develop a prevention strategy. The expression of total estrogen receptor beta (ERbeta) protein and of its COOH-terminally spliced variant ERbetacx (or ERbeta2) was compared in 43 invasive breast cancers and in 39 adjacent normal mammary glands and 26 ductal carcinoma in situ (DCIS). Thirty-six breast cancers were ER positive by radioligand binding assay. The analysis was done by immunohistochemistry on adjacent sections of formalin-fixed, paraffin-embedded tumors using polyclonal anti-ERbeta 503 IgY and sheep polyclonal ERbetacx antibodies that were previously validated. Nuclear staining was quantified using a computerized image analyzer in selected areas of normal and cancer epithelial cells. Total ERbeta expression was high in normal glands, decreased in DCIS (P = 0.0004), and increased from DCIS to invasive tumors (P = 0.029). In contrast, the ERbetacx expression was low in normal glands, increased significantly in DCIS (P = 0.0014), and continued to increase in invasive carcinomas (P = 0.0027) in both ERalpha-positive and ERalpha-negative tumors. This is the first study showing a significant increase of the ERbetacx variant protein in DCIS and invasive breast cancer compared with adjacent normal glands. This contrasts with the decrease of the total ERbeta level in the same patients and indicates different mechanisms to explain these variations during mammary carcinogenesis. It also suggests a role of the ERbetacx variant in carcinogenesis opposite to the protective effect of the wild-type ERbeta1.

Estrogen receptor genotypes and haplotypes associated with breast cancer risk

Nearly one in eight US women will develop breast cancer in their lifetime. Most breast cancer is not associated with a hereditary syndrome, occurs in postmenopausal women, and is estrogen and progesterone receptor-positive. Estrogen exposure is an epidemiologic risk factor for breast cancer and estrogen is a potent mammary mitogen. We studied single nucleotide polymorphisms (SNPs) in estrogen receptors in 615 healthy subjects and 1011 individuals with histologically confirmed breast cancer, all from New York City. We analyzed 13 SNPs in the progesterone receptor gene (PGR), 17 SNPs in estrogen receptor 1 gene (ESR1), and 8 SNPs in the estrogen receptor 2 gene (ESR2). We observed three common haplotypes in ESR1 that were associated with a decreased risk for breast cancer [odds ratio (OR), approximately O.4; 95% confidence interval (CI), 0.2-0.8; P < 0.01]. Another haplotype was associated with an increased risk of breast cancer (OR, 2.1; 95% CI, 1.2-3.8; P < 0.05). A unique risk haplotype was present in approximately 7% of older Ashkenazi Jewish study subjects (OR, 1.7; 95% CI, 1.2-2.4; P < 0.003). We narrowed the ESR1 risk haplotypes to the promoter region and first exon. We define several other haplotypes in Ashkenazi Jews in both ESR1 and ESR2 that may elevate susceptibility to breast cancer. In contrast, we found no association between any PGR variant or haplotype and breast cancer. Genetic epidemiology study replication and functional assays of the haplotypes should permit a better understanding of the role of steroid receptor genetic variants and breast cancer risk.

Estrogens and their receptors in breast cancer progression: a dual role in cancer proliferation and invasion

Estrogens play an important role in regulating the growth and differentiation of normal, premalignant and malignant cell types, especially breast epithelial cells, through interaction with two nuclear estrogen receptors (ERalpha and ERbeta). In this review, we present a brief overview of the actions of estrogens in the different steps of breast carcinogenesis, including cancer progression to metastasis, and of their clinical consequences in the prevention, prognosis and treatment of the disease. The requirement of estrogen receptors, mainly of the alpha subtype, in normal mammary gland differentiation and growth has been evidenced by estrogen receptor deficiency in animals. The promotion of breast cancer carcinogenesis by prolonged exposure to estrogens is well-documented and this has logically led to the use of anti-estrogens as potentially chemopreventive agents. In breast cancer progression, however, the exact roles of estrogen receptors have been less well established but they may possibly be dual. Estrogens are mitogenic in ER-positive cells and anti-estrogens are an efficient adjuvant therapy for these tumors. On the other hand, the fact that estrogens and their receptors protect against cancer cell invasiveness through distinct mechanisms in experimental models may explain why the presence of ER is associated with well-differentiated and less invasive tumors.

Estrogen receptor mutations in human disease

As early as the 1800s, the actions of estrogen have been implicated in the development and progression of breast cancer. The estrogen receptor (ER) was identified in the late 1950s and purified a few years later. However, it was not until the 1980s that the first ER was molecularly cloned, and in the mid 1990s, a second ER was cloned. These two related receptors are now called ERalpha and ERbeta, respectively. Since their discovery, much research has focused on identifying alterations within the coding sequence of these receptors in clinical samples. As a result, a large number of naturally occurring splice variants of both ERalpha and ERbeta have been identified in normal epithelium and diseased or cancerous tissues. In contrast, only a few point mutations have been identified in human patient samples from a variety of disease states, including breast cancer, endometrial cancer, and psychiatric diseases. To elucidate the mechanism of action for these variant isoforms or mutant receptors, experimental mutagenesis has been used to analyze the function of distinct amino acid residues in the ERs. This review will focus on ERalpha and ERbeta alterations in breast cancer.

Prediction of hormone sensitivity by DNA microarray

Endocrine-therapy continues to be extensively developed for treatment of breast cancer, and accurate therapeutic prediction of this hormone-associated cancer is strongly desired. Moreover, the role of estrogen and its receptor on the estrogen-dependent growth of breast cancer cells has not been clarified hitherto. Thus, to develop a new diagnostic tool for endocrine-therapy, and to address the molecular mechanism of estrogen-dependent breast carcinogenesis, we investigated the gene expression profile of estrogen-responsive genes in breast cancer using DNA microarray technique. We first comprehensively analyzed the profile of estrogen responsiveness among several estrogen receptor (ER)-positive cancer cell lines by a large-scale DNA microarray. Based on the obtained information, a total of 138 genes which showed high induction or repression of the expression by estrogen stimulation were selected and provided for custom microarray. The results of the custom microarray analysis were consistent with those of large-scale microarray analysis, and revealed that they were clearly categorized into early- or late-response types. Further analysis of these genes may provide new clues in the elucidation of the estrogen-dependent growth mechanisms of cancer. Furthermore, the custom microarray analysis of ER-positive breast cancer tissues also showed similar but not identical profiles to those of cell lines, indicating the potential of this custom microarray to predict the response to endocrine-therapy in the breast cancer. Moreover, in order to discover the new predictive factors for endocrine therapy in breast cancer patients, several candidate genes were selected and their expressions in breast cancer tissues were analyzed by real-time RT-PCR and by immunohistochemical technique. These studies could provide new clues for elucidation of the estrogen-dependent mechanisms of cancer and clinical benefit for patients.