The F-domain of estrogen receptor-alpha inhibits ligand induced receptor dimerization

Somatic estrogen receptor α mutations that induce dimerization promote receptor activity and breast cancer proliferation

Physiologic activation of estrogen receptor α (ERα) is mediated by estradiol (E2) binding in the ligand-binding pocket of the receptor, repositioning helix 12 (H12) to facilitate binding of coactivator proteins in the unoccupied coactivator binding groove. In breast cancer, activation of ERα is often observed through point mutations that lead to the same H12 repositioning in the absence of E2. Through expanded genetic sequencing of breast cancer patients, we identified a collection of mutations located far from H12 but nonetheless capable of promoting E2-independent transcription and breast cancer cell growth. Using machine learning and computational structure analyses, this set of mutants was inferred to act distinctly from the H12-repositioning mutants and instead was associated with conformational changes across the ERα dimer interface. Through both in vitro and in-cell assays of full-length ERα protein and isolated ligand-binding domain, we found that these mutants promoted ERα dimerization, stability, and nuclear localization. Point mutations that selectively disrupted dimerization abrogated E2-independent transcriptional activity of these dimer-promoting mutants. The results reveal a distinct mechanism for activation of ERα function through enforced receptor dimerization and suggest dimer disruption as a potential therapeutic strategy to treat ER-dependent cancers.

Computer-Aided Ligand Discovery for Estrogen Receptor Alpha

Breast cancer (BCa) is one of the most predominantly diagnosed cancers in women. Notably, 70% of BCa diagnoses are Estrogen Receptor α positive (ERα+) making it a critical therapeutic target. With that, the two subtypes of ER, ERα and ERβ, have contrasting effects on BCa cells. While ERα promotes cancerous activities, ERβ isoform exhibits inhibitory effects on the same. ER-directed small molecule drug discovery for BCa has provided the FDA approved drugs tamoxifen, toremifene, raloxifene and fulvestrant that all bind to the estrogen binding site of the receptor. These ER-directed inhibitors are non-selective in nature and may eventually induce resistance in BCa cells as well as increase the risk of endometrial cancer development. Thus, there is an urgent need to develop novel drugs with alternative ERα targeting mechanisms that can overcome the limitations of conventional anti-ERα therapies. Several functional sites on ERα, such as Activation Function-2 (AF2), DNA binding domain (DBD), and F-domain, have been recently considered as potential targets in the context of drug research and discovery. In this review, we summarize methods of computer-aided drug design (CADD) that have been employed to analyze and explore potential targetable sites on ERα, discuss recent advancement of ERα inhibitor development, and highlight the potential opportunities and challenges of future ERα-directed drug discovery.

Detecting the Ligand-binding Domain Dimerization Activity of Estrogen Receptor Alpha Using the Mammalian Two-Hybrid Assay

Estrogen receptor alpha (ERα) is an estrogenic ligand-dependent transcription regulator. The sequence of ERα protein is highly conserved among species. It has been thought that the function of human and mouse ERαs is identical. We demonstrate the differential 4-hydroxy-tamoxifen (4OHT) effect on mouse and human ERα ligand-binding domain (LBD) dimerization activity using the mammalian two-hybrid (M2H) assay. The M2H assay can demonstrate the efficiency of LBD homodimerization activity in mammalian cells, utilizing the transfection of two protein expression plasmids (GAL4 DNA-binding domain [DBD] fusion LBD and VP16 transactivation domain [VP16AD] fusion LBD) and a GAL4-responsive element (GAL4RE) fused luciferase reporter plasmid. When the GAL4DBD fusion LBD and the VP16AD fusion LBD make a dimer in the cells, this protein complex binds to the GAL4RE and, then, activates a luciferase gene expression through the VP16AD dependent transcription activity. The 4OHT-mediated luciferase activation is higher in the HepG2 cells that were transfected with the mouse ERα LBD fusion protein expression plasmids than in the human ERα LBD fusion protein expression plasmid transfected cells. This result suggests that the efficacy of the 4OHT-dependent mouse ERα LBD homodimerization activity is higher than human ERα LBD. In general, the utilization of the M2H assay is not ideal for the evaluation of nuclear receptor LBD dimerization activity, because agonistic ligands enhance the basal level of the LBD activity and that impedes the detection of LBD dimerization activity. We found that 4OHT does not enhance ERα LBD basal activity. That is a key factor for being able to determine and detect the 4OHT-dependent LBD dimerization activity for successfully using the M2H assay. ERα LBD-based M2H assays may be applied to study the partial agonist activity of selective estrogen receptor modulators (e.g., 4OHT) in various mammalian cell types.

A comparative review on estrogen receptors in the reproductive male tract of non mammalian vertebrates

Estrogen receptors alpha (ERα) and beta (ERβ) are transcription factors known to be involved in the regulation of many complex physiological processes in mammals. They are expressed primarily in the reproductive tract of all vertebrates females, thus indicating important and conserved functions in female reproductive success. ERs are also present in physiological different tissues as bone, brain, liver, skin and adipose tissues, in both females and males. In the latter, ERs have been found also in the genital tract, supporting the findings of a complex role for estrogen in spermatogenesis and, more generally, in male reproduction. This review provides an overview and update on ERα and ERβ expression and synthesis in male reproductive tract of non-mammalian vertebrates, with focus on their role in germ cells proliferation, maturation and survival. Data from studies on fish, amphibians, reptiles and birds were collated and common or species-specific distribution highlighted. The widespread distribution of estrogen receptors in testicular cells and ducts of all vertebrates so far investigated suggests that whatever are the roles that estrogens may exert on these structures, they are phylogenetically conserved and are possibly related to the physiological support given to achieve male reproductive success.

Structural underpinnings of oestrogen receptor mutations in endocrine therapy resistance

Oestrogen receptor-α (ERα), a key driver of breast cancer, normally requires oestrogen for activation. Mutations that constitutively activate ERα without the need for hormone binding are frequently found in endocrine-therapy-resistant breast cancer metastases and are associated with poor patient outcomes. The location of these mutations in the ER ligand-binding domain and their impact on receptor conformation suggest that they subvert distinct mechanisms that normally maintain the low basal state of wild-type ERα in the absence of hormone. Such mutations provide opportunities to probe fundamental issues underlying ligand-mediated control of ERα activity. Instructive contrasts between these ERα mutations and those that arise in the androgen receptor (AR) during anti-androgen treatment of prostate cancer highlight differences in how activation functions in ERs and AR control receptor activity, how hormonal pressures (deprivation versus antagonism) drive the selection of phenotypically different mutants, how altered protein conformations can reduce antagonist potency and how altered ligand-receptor contacts can invert the response that a receptor has to an agonist ligand versus an antagonist ligand. A deeper understanding of how ligand regulation of receptor conformation is linked to receptor function offers a conceptual framework for developing new anti-oestrogens that might be more effective in preventing and treating breast cancer.

The F domain of estrogen receptor α is involved in species-specific, tamoxifen-mediated transactivation

Estrogen receptor α (ERα) is a major transducer of estrogen-mediated physiological signals. ERα is a member of the nuclear receptor superfamily, which encompasses ligand-dependent transcription factors. The C terminus of nuclear receptors, termed the F domain, is the least homologous region among the members of this family. The ERα F domain possesses 45 amino acids; however, its function remains unclear. We noticed that the homology of the F domains between mouse and human ERαs is remarkably lower (75.6% similarity) than that between the entire proteins (94.7% similarity). To assess the functionality of the ERα F domains, here we generated chimeric ERα expression constructs with mouse-human-exchanged F domains. Using cell-based in vitro assays, we analyzed the transcriptional coactivator interaction and ligand-binding domain dimerization activities of these mouse-human F domain-swapped ERαs. We found that the transcriptional activity of the mouse WT ERα is more potent than that of the human WT ERα in the human hepatoma cell line HepG2. 4-Hydroxytamoxifen (4OHT)-mediated transcriptional activity of mouse-human F domain-swapped ERαs was the inverse of the WT ERα activities but not estradiol-mediated transcriptional activities. Further experiments with constructs containing deletion or point mutations of a predicted β-strand region within the F domain suggested that this region governs the species-specific 4OHT-mediated transcriptional activity of ERα. We conclude that the ERα F domain has a species-specific function in 4OHT-mediated receptor transactivation and that mouse-human F domain-swapped ERα mutants enable key insights into ERα F domain structure and function.

Raptor localization predicts prognosis and tamoxifen response in estrogen receptor-positive breast cancer

Purpose

Deregulated PI3K/mTOR signals can promote the growth of breast cancer and contribute to endocrine treatment resistance. This report aims to investigate raptor and its intracellular localization to further understand its role in ER-positive breast cancer.

Methods

Raptor protein expression was evaluated by immunohistochemistry in 756 primary breast tumors from postmenopausal patients randomized to tamoxifen or no tamoxifen. In vitro, the MCF7 breast cancer cell line and tamoxifen-resistant MCF7 cells were studied to track the raptor signaling changes upon resistance, and raptor localization in ERα-positive cell lines was compared with that in ERα-negative cell lines.

Results

Raptor protein expression in the nucleus was high in ER/PgR-positive and HER2-negative tumors with low grade, features associated with the luminal A subtype. Presence of raptor in the nucleus was connected with ERα signaling, here shown by a coupled increase of ERα phosphorylation at S167 and S305 with accumulation of nuclear raptor. In addition, the expression of ERα-activated gene products correlated with nuclear raptor. Similarly, in vitro we observed raptor in the nucleus of ERα-positive, but not of ER-negative cells. Interestingly, raptor localized to the nucleus could still be seen in tamoxifen-resistant MCF7 cells. The clinical benefit from tamoxifen was inversely associated with an increase of nuclear raptor. High cytoplasmic raptor expression indicated worse prognosis on long-term follow-up.

Conclusion

We present a connection between raptor localization to the nucleus and ERα-positive breast cancer, suggesting raptor as a player in stimulating the growth of the luminal A subtype and a possible target along with endocrine treatment.

Electronic supplementary material

The online version of this article (10.1007/s10549-017-4508-x) contains supplementary material, which is available to authorized users.

The complex nature of oestrogen signalling in breast cancer: enemy or ally?

The pleiotropic nature of oestradiol, the main oestrogen found in women, has been well described in the literature. Oestradiol is positioned to play a unique role since it can respond to environmental, genetic and non-genetic cues to affect genetic expression and cellular signalling. In breast cancer, oestradiol signalling has a dual effect, promoting or inhibiting cancer growth. The potential impact of oestradiol on tumorigenesis depends on the molecular and cellular characteristics of the breast cancer cell. In this review, we provide a broad survey discussing the cellular and molecular consequences of oestrogen signalling in breast cancer. First, we review the structure of the classical oestrogen receptors and resultant transcriptional (genomic) and non-transcriptional (non-genomic) signalling. We then discuss the nature of oestradiol signalling in breast cancer including the specific receptors that initiate these signalling cascades as well as potential outcomes, such as cancer growth, proliferation and angiogenesis. Finally, we examine cellular and molecular mechanisms underlying the dimorphic effect of oestrogen signalling in breast cancer.

What's new in estrogen receptor action in the female reproductive tract

Estrogen receptor alpha (ERα) is a critical player in development and function of the female reproductive system. Perturbations in ERα response can affect wide-ranging aspects of health in humans as well as in livestock and wildlife. Because of its long-known and broad impact, ERα mechanisms of action continue to be the focus on cutting-edge research efforts. Consequently, novel insights have greatly advanced understanding of every aspect of estrogen signaling. In this review, we attempt to briefly outline the current understanding of ERα mediated mechanisms in the context of the female reproductive system.

Modulation of nuclear receptor activity by the F domain

The F domain located at the C-terminus of proteins is one of the least conserved regions of the estrogen receptors alpha and beta, members of the nuclear hormone receptor superfamily. Indeed, many members of the superfamily lack the F domain. However, when present, removing the F domain entirely or mutating it alters transactivation, dimerization, and the responses to agonist and antagonist ligands. This review focuses on the functions of the F domain of the estrogen receptors, particularly in relation to other members of the superfamily.

The molecular, cellular and clinical consequences of targeting the estrogen receptor following estrogen deprivation therapy

During the past 20 years our understanding of the control of breast tumor development, growth and survival has changed dramatically. The once long forgotten application of high dose synthetic estrogen therapy as the first chemical therapy to treat any cancer has been resurrected, refined and reinvented as the new biology of estrogen-induced apoptosis. High dose estrogen therapy was cast aside once tamoxifen, from its origins as a failed "morning after pill", was reinvented as the first targeted therapy to treat any cancer. The current understanding of the mechanism of estrogen-induced apoptosis is described as a consequence of acquired resistance to long term antihormone therapy in estrogen receptor (ER) positive breast cancer. The ER signal transduction pathway remains a target for therapy in breast cancer despite "antiestrogen" resistance, but becomes a regulator of resistance. Multiple mechanisms of resistance come into play: Selective ER modulator (SERM) stimulated growth, growth factor/ER crosstalk, estrogen-induced apoptosis and mutations of ER. But it is with the science of estrogen-induced apoptosis that the next innovation in women's health will be developed. Recent evidence suggests that the glucocorticoid properties of medroxyprogesterone acetate blunt estrogen-induced apoptosis in estrogen deprived breast cancer cell populations. As a result breast cancer develops during long-term hormone replacement therapy (HRT). A new synthetic progestin with estrogen-like properties, such as the 19 nortestosterone derivatives used in oral contraceptives, will continue to protect the uterus from unopposed estrogen stimulation but at the same time, reinforce apoptosis in vulnerable populations of nascent breast cancer cells.

Aberrant Splicing of Estrogen Receptor, HER2, and CD44 Genes in Breast Cancer

Breast cancer (BC) is the most common cause of cancer-related death among women under the age of 50 years. Established biomarkers, such as hormone receptors (estrogen receptor [ER]/progesterone receptor) and human epidermal growth factor receptor 2 (HER2), play significant roles in the selection of patients for endocrine and trastuzumab therapies. However, the initial treatment response is often followed by tumor relapse with intrinsic resistance to the first-line therapy, so it has been expected to identify novel molecular markers to improve the survival and quality of life of patients. Alternative splicing of pre-messenger RNAs is a ubiquitous and flexible mechanism for the control of gene expression in mammalian cells. It provides cells with the opportunity to create protein isoforms with different, even opposing, functions from a single genomic locus. Aberrant alternative splicing is very common in cancer where emerging tumor cells take advantage of this flexibility to produce proteins that promote cell growth and survival. While a number of splicing alterations have been reported in human cancers, we focus on aberrant splicing of ER, HER2, and CD44 genes from the viewpoint of BC development. ERα36, a splice variant from the ER1 locus, governs nongenomic membrane signaling pathways triggered by estrogen and confers 4-hydroxytamoxifen resistance in BC therapy. The alternative spliced isoform of HER2 lacking exon 20 (Δ16HER2) has been reported in human BC; this isoform is associated with transforming ability than the wild-type HER2 and recapitulates the phenotypes of endocrine therapy-resistant BC. Although both CD44 splice isoforms (CD44s, CD44v) play essential roles in BC development, CD44v is more associated with those with favorable prognosis, such as luminal A subtype, while CD44s is linked to those with poor prognosis, such as HER2 or basal cell subtypes that are often metastatic. Hence, the detection of splice variants from these loci will provide keys to understand the pathogenesis, predict the prognosis, and choose specific therapies for BC.

Estrogen receptor mutations found in breast cancer metastases integrated with the molecular pharmacology of selective ER modulators

The consistent reports of mutations at Asp538 and Tyr537 in helix 12 of the ligand-binding domain (LBD) of estrogen receptors (ERs) from antihormone-resistant breast cancer metastases constitute an important advance. The mutant amino acids interact with an anchor amino acid, Asp351, to close the LBD, thereby creating a ligand-free constitutively activated ER. Amino acids Asp 538, Tyr 537, and Asp 351 are known to play a role in either the turnover of ER, the antiestrogenic activity of the ER complex, or the estrogen-like actions of selective ER modulators. A unifying mechanism of action for these amino acids to enhance ER gene activation and growth response is presented. There is a range of mutations described in metastases vs low to zero in primary disease, so the new knowledge is of clinical relevance, thereby confirming an additional mechanism of acquired resistance to antihormone therapy through cell population selection pressure and enrichment during treatment. Circulating tumor cells containing ER mutations can be cultured ex vivo, and tumor tissues can be grown as patient-derived xenografts to add a new dimension for testing drug susceptibility for future drug discovery.

Intrinsically disordered proteins and multicellular organisms

Intrinsically disordered proteins (IDPs) and IDP regions lack stable tertiary structure yet carry out numerous biological functions, especially those associated with signaling, transcription regulation, DNA condensation, cell division, and cellular differentiation. Both post-translational modifications (PTMs) and alternative splicing (AS) expand the functional repertoire of IDPs. Here we propose that an "IDP-based developmental toolkit," which is comprised of IDP regions, PTMs, especially multiple PTMs, within these IDP regions, and AS events within segments of pre-mRNA that code for these same IDP regions, allows functional diversification and environmental responsiveness for molecules that direct the development of complex metazoans.

Selective estrogen receptor modulators: tissue specificity and clinical utility

Selective estrogen receptor modulators (SERMs) are a diverse group of nonsteroidal compounds that function as agonists or antagonists for estrogen receptors (ERs) in a target gene-specific and tissue-specific fashion. SERM specificity involves tissue-specific expression of ER subtypes, differential expression of co-regulatory proteins in various tissues, and varying ER conformational changes induced by ligand binding. To date, the major clinical applications of SERMs are their use in the prevention and treatment of breast cancer, the prevention of osteoporosis, and the maintenance of beneficial serum lipid profiles in postmenopausal women. However, SERMs have also been found to promote adverse effects, including thromboembolic events and, in some cases, carcinogenesis, that have proven to be obstacles in their clinical utility. In this review, we discuss the mechanisms of SERM tissue specificity and highlight the therapeutic application of well-known and emergent SERMs.

Association of genetic variants in estrogen receptor α with HCV infection susceptibility and viral clearance in a high-risk Chinese population

The purpose of this study was to test the hypothesis that genetic variants of estrogen receptor α (ERα) are associated with the outcomes of hepatitis C virus (HCV) infection. We genotyped the seven single nucleotide polymorphisms (SNPs) (rs2077647, rs9340799, rs2234693, rs1801132, rs9322354, rs2228480 and rs3798577) of ERα and conducted a case-control study in a high-risk Chinese population, including 429 HCV spontaneous clearance cases, 880 persistent infection cases and 1,174 uninfected controls. The C allele of rs2234693 was significantly associated with increased susceptibility to HCV infection [dominant model: adjusted odds ratio (OR) = 1.377, 95% confidence interval (CI) =1.126-1.778], and the risk effect remained significant among the younger (≤55 years) and hemodialysis subjects (all P < 0.007). The other three SNPs variant genotypes also showed significant correlation with elevated risk of HCV infection in different strata (rs2077647 in males; rs9340799 in blood donors; rs1801132 in younger subjects; all P < 0.007). It was also discovered that carriage of rs2228480 A allele was more prone to develop persistent HCV infection (dominant model: adjusted OR = 1.203, 95% CI = 1.154-1.552), and the risk effect was more evident in females and blood donors (all P < 0.007). Haplotype analyses (rs2077647, rs9340799 and rs2234693) showed that, compared with the most frequent haplotype TAT, CAC played a risk effect in subgroups of younger (P = 3.24 × 10(-3)) and male (P = 5.51 × 10(-4)), whereas CAT expressed a protective effect in females (P = 2.27 × 10(-4)) for HCV infection susceptibility. We first report that these SNPs (rs2077647, rs9340799, rs2234693, rs1801132 and rs2228480) in ERα can influence the outcomes of HCV infection in a high-risk Chinese population.

Interaction of 14-3-3 proteins with the estrogen receptor alpha F domain provides a drug target interface

Estrogen receptor alpha (ERα) is involved in numerous physiological and pathological processes, including breast cancer. Breast cancer therapy is therefore currently directed at inhibiting the transcriptional potency of ERα, either by blocking estrogen production through aromatase inhibitors or antiestrogens that compete for hormone binding. Due to resistance, new treatment modalities are needed and as ERα dimerization is essential for its activity, interference with receptor dimerization offers a new opportunity to exploit in drug design. Here we describe a unique mechanism of how ERα dimerization is negatively controlled by interaction with 14-3-3 proteins at the extreme C terminus of the receptor. Moreover, the small-molecule fusicoccin (FC) stabilizes this ERα/14-3-3 interaction. Cocrystallization of the trimeric ERα/14-3-3/FC complex provides the structural basis for this stabilization and shows the importance of phosphorylation of the penultimate Threonine (ERα-T(594)) for high-affinity interaction. We confirm that T(594) is a distinct ERα phosphorylation site in the breast cancer cell line MCF-7 using a phospho-T(594)-specific antibody and by mass spectrometry. In line with its ERα/14-3-3 interaction stabilizing effect, fusicoccin reduces the estradiol-stimulated ERα dimerization, inhibits ERα/chromatin interactions and downstream gene expression, resulting in decreased cell proliferation. Herewith, a unique functional phosphosite and an alternative regulation mechanism of ERα are provided, together with a small molecule that selectively targets this ERα/14-3-3 interface.

Characterisation of human oestrogen receptor beta (ERβ) splice variants in neuronal cells

Oestrogen receptor (ER)α and ERβ are members of the ligand-activated superfamily of nuclear receptors and mediate most facets of oestrogen signalling. Several naturally occurring splice variants of each ER have been identified in the human brain, yet the biological significance of these splice variants in the brain remains unknown. In the present study, we exploit the unique structural differences of the human ERβ splice variants to determine the functional significance of individual ER domains in the brain. We previously established that full-length rodent ERβ (i.e. rERβ1) has constitutive transcriptional activity in neuronal cells in the absence of ligand. By contrast to the rodent splice variants, the human ERβ splice variants used in the present study contain varying length truncations of exon 8, which encodes for the E/F domains. Our results reveal that, in neuronal cells, each human-specific ERβ splice variant constitutively activated promoters mediated by a canonical oestrogen response element and repressed promoters mediated by activator protein-1 sites via p38 activity. From these data, we conclude that the C-terminus, encoding the AF-2 region and F domain, is not essential for the constitutive properties of human ERβ. Taken together, these studies show that human-specific ERβ variants are constitutively active and also provide novel insight into the contributions of the functional domains of ERβ towards mediating constitutive transcription at various promoters in neuronal cells.

The dynamic structure of the estrogen receptor

The estrogen receptor (ER) mediates most of the biological effects of estrogens at the level of gene regulation by interacting through its site-specific DNA and with other coregulatory proteins. In recent years, new information regarding the dynamic structural nature of ER has emerged. The physiological effects of estrogen are manifested through ER's two isoforms, ER_α and ER_β. These two isoforms (ER_α and ER_β) display distinct regions of sequence homology. The three-dimensional structures of the DNA-binding domain (DBD) and ligand-binding domain (LBD) have been solved, whereas no three-dimensional natively folded structure for the ER N-terminal domain (NTD) is available to date. However, insights about the structural and functional correlations regarding the ER NTD have recently emerged. In this paper, we discuss the knowledge about the structural characteristics of the ER in general and how the structural features of the two isoforms differ, and its subsequent role in gene regulation.

Selectively targeting estrogen receptors for cancer treatment

Estrogens regulate growth and development through the action of two distinct estrogen receptors (ERs), ERα and ERβ, which mediate proliferation and differentiation of cells. For decades, ERα mediated estrogen signaling has been therapeutically targeted to treat breast cancer, most notably with the selective estrogen receptor modulator (SERM) tamoxifen. Selectively targeting ERs occurs at two levels: tissue selectivity and receptor subtype selectivity. SERMs have been developed with emphasis on tissue selectivity to target ER signaling for breast cancer treatment. Additionally, new approaches to selectively target the action of ERα going beyond ligand-dependent activity are under current investigation. As evidence of the anti-proliferative role of ERβ accumulates, selectively targeting ERβ is an attractive approach for designing new cancer therapies with the emphasis shifted to designing ligands with subtype selectivity. This review will present the mechanistic and structural features of ERs that determine tissue and subtype selectivity with an emphasis on current approaches to selectively target ERα and ERβ for cancer treatment.

Glucocorticoid receptor cofactors as therapeutic targets

Numerous transcriptional cofactors (e.g. coactivators, corepressors, and comodulators) are known to alter the maximal transcriptional activity (A(max)) in gene induction and repression by steroid receptors in general and glucocorticoid receptors (GRs) in particular. However, recent data advance the earlier reports that these same factors also modify other parameters of glucocorticoid receptor transcriptional activity: the potency of agonists (or EC₅₀ and the partial agonist activity of antisteroids (or PAA). In several instances, factors modulate the EC₅₀ and/or PAA without changing A(max). Thus, studies of all three parameters reveal new factors acting at various stages of receptor action, thereby increasing the potential therapeutic targets for adjusting GR actions in pathological situations.

Estrogen receptor alpha polymorphisms and the risk of malignancies

Estrogens represent risk factors for endocrine-related cancers and play also an important role in the development and progression of other malignancies. In order to analyze the associations between estrogen receptor gene alpha polymorphisms and cancers susceptibility, we genotyped six single nucleotide polymorphisms (SNPs) in 163 Caucasian cancer patients--103 breast cancers and 60 other malignancies (colorectal, bladder, hepatocellular carcinoma and acute myeloid leukemia)--and 114 healthy controls using hybridization probes. We performed Armitage`s association trend-test to evaluate the risk. Linkage disequilibrium (LD) was assessed for each pair of markers. The genotypes CC and CT of rs3798577 were significantly associated with the cancers risk (p-trend breast = 4 × 10(-5); p-trend cancers = 1 × 10(-5)); in discrepancy with breast cancer where the C-allele represented the risk allele, for bladder, hepatocellular carcinomas and leukemia, the T allele seems to confer susceptibility. The minor G allele of rs1801132 was protective in our cases (p = 1 × 10(-4)); for rs2228480, the heterozygous frequency was higher for cancer groups (p = 0.03); the SNP pairs rs2228480&rs3798577 and rs2234693&rs9340799 were in low LD; the haplotypes T-A of rs2234693&rs9340799 and G-C of rs2228480&rs3798577 showed a trend to be higher represented in breast cancers; T allele of rs2234693 was higher expressed in breast, colon cancers and leukemia; rs2077647 was associated with colon (p = 0.008, C-risk allele) and bladder (p = 0.01, T-risk allele) cancers. We concluded that ESR1 polymorphisms may have distinct impact in carcinogenesis and further genotyping will establish whether these findings remain significant in larger cohorts.

Estrogen and progesterone receptors: from molecular structures to clinical targets

Research involving estrogen and progesterone receptors (ER and PR) have greatly contributed to our understanding of cell signaling and transcriptional regulation. In addition to the classical ER and PR nuclear actions, new signaling pathways have recently been identified due to ER and PR association with cell membranes and signal transduction proteins. Bio-informatics has unveiled how ER and PR recognize their ligands, selective modulators and co-factors, which has helped to implement them as key targets in the treatment of benign and malignant tumors. Knowledge regarding ER and PR is vast and complex; therefore, this review will focus on their isoforms, signaling pathways, co-activators and co-repressors, which lead to target gene regulation. Moreover it will highlight ER and PR involvement in benign and malignant diseases as well as pharmacological substances influencing cell signaling and provide established and new structural insights into the mechanism of activation and inhibition of these receptors.