Using a construct containing the human estrogen receptor cDNA with a yeast PGK promoter, Metzger et al. (1988) demonstrated that the human estrogen receptor can be expressed in yeast. Initiation of transcription in the system operated in a strictly hormone-dependent manner, documenting an extraordinarily high level of conservation of this activation mechanism.
Issa et al. (1994) reported that CpG island methylation, an epigenetic modification of DNA known to correlate closely with silencing of gene transcription, appears in the ESR gene in a subpopulation of cells that increases as a direct function of age in human colonic mucosa. They found that the same methylation change characterized almost all cells in the 45 colorectal tumors examined, including the earliest stages of tumor formation. ESR gene expression is diminished or absent in colorectal tumors, and introduction of an exogenous ESR gene in cultured colon carcinoma cells was found to result in marked growth suppression. Issa et al. (1994) concluded that methylation-associated inactivation of the ESR gene in aging colorectal mucosa may be one of the earliest events that predispose to sporadic colorectal tumorigenesis.
One mechanism suggested to play a role in the progression of human breast cancer from hormone dependence to independence is the expression or altered expression of mutant and/or variant forms of the estrogen receptor. Murphy et al. (1996) stated that 2 major types of variant ESR mRNA had been reported in human breast biopsy samples so far: truncated transcripts and exon-deleted transcripts. Murphy et al. (1996) provided data on a novel type of abnormal ESR mRNA. They found larger-than-wildtype ESR mRNA RT-PCR products in 9.4% of 212 human breast tumors analyzed. Cloning and sequencing of these larger RT-PCR products showed 3 different types: complete duplication of exon 6 in 7.5%; complete duplication of exons 3 and 4 in 1 tumor; and a 69-bp insertion between exons 5 and 6 in 3 tumors. While it is unknown if these novel ESR-like mRNAs are stably translated in vivo, any resulting protein would be structurally altered, possibly resulting in altered function.
Two isoforms of the human ESR, ESRA and ESR-beta (ESR2; 601663), occur, each with distinct tissue and cell patterns of expression. Additional ESR isoforms, generated by alternative mRNA splicing, have been defined in several tissues and are postulated to play a role in tumorigenesis or in modulating the estrogen response. By RT-PCR and hybridization blotting analysis, Shupnik et al. (1998) examined 71 human pituitary adenomas of varying phenotypes and 6 normal pituitary specimens for ESR mRNA isoforms. All 14 prolactinomas contained ESRA, and 5 of 14 contained ESRB mRNA. In comparison, 6 tumors that expressed prolactin (176760) and growth hormone (GH; 139250) expressed ESRB (4 of 6) more frequently than ESRA (3 of 6). ESRB mRNA was also found more frequently in null cell (8 of 24 ESRA and 14 of 24 ESRB) and gonadotrope (13 of 21 ESRA and 18 of 21 ESRB) tumors. Additionally, ESRB was found in 4 of 6 tumors that contained only GH, although ESRA was not observed in this tumor type. Expression of the 2 ESR isoforms within a tumor type was overlapping, but some tumors contained only 1 isoform. Expression of ESRA mRNA splice variants also varied with cell type. All normal pituitaries contained ESRA deletions of exon 4, 5, and 7, whereas only 2 of 6 samples contained the exon 2 deletion variant. Although the same ESRA mRNA variants were observed among the various tumor types, the proportion of specific splice variants expressed varied. The authors concluded that expression of the ESR isoforms, as well as of the mRNA splice variants, may influence the biologic properties of these tumors and affect their ability to respond to estrogen and antiestrogen therapies.
Vaults are large ribonucleoprotein particles composed largely of MVP (605088). Abbondanza et al. (1998) found that MVP coprecipitated with ER from nuclear extracts of MCF-7 human breast cancer cells and that ER associated with intact vaults. Mutation analysis showed that a central region of ER containing nuclear localization signals was involved in the interaction. A limited amount of ER molecules in the nuclear extract appeared to be associated with MVP. Physiologic concentrations of estradiol increased the amount of MVP present in MCF-7 nuclear extracts and coimmunoprecipitated with ER. The hormone-dependent interaction of vaults with ER was reproduced in vitro.
Lawson et al. (1999) studied ESR1 expression in normal breast tissue biopsies obtained by open surgical and core biopsy of benign lesions of the breast from 74 white Australian women and 92 Japanese women. Among Australians, the median of the percentage of ESR1-positive cells is about 12% for women younger than 50 years and 17% among women 50 years or older. Among Japanese, the overall median is about 9% and does not vary substantially with age. The authors concluded that their results are compatible with the hypothesis that the expression of estrogen receptors in normal breast tissue increases the risk of breast cancer and explains the 5-fold contrast of breast cancer incidence between white and Asian women. The difference in estrogen receptor expression as well as in breast cancer incidence between white and Japanese is more evident among older women.
Primary transcripts of the human ESR and progesterone receptor (PGR; 607311) genes undergo a number of alternative-splicing events that result in a range of variant mRNA isoforms in receptor-positive tissues. Despite in vitro demonstrations of a possible role for some of these isoforms in hormonal sensitivity, the clinical significance of this process is uncertain. By RT-PCR and Southern blot analysis, Balleine et al. (1999) documented the coexpression of variant ESR and PGR transcripts in a series of receptor-positive breast tumors. In 35 ESR-positive tumors, a common profile of variant ESR transcripts was present, with all tumors containing the exon 2-deleted and exon 7-deleted ESR variants, 94% containing the exon 4-deleted ESR variant, and 83% containing the exon 5-deleted ESR variant. In 25 of these cases, which were also PGR positive, the most highly expressed PGR variants, the exon 4-deleted PGR, exon 6-deleted PGR, and delta-4/2PGR, a transcript from which a 126-bp portion of PGR exon 4 was deleted, were detected in more than 90% of the cases. The alternatively spliced ESR isoforms were expressed at higher relative levels than the PGR isoforms, which had mean levels of expression less than 10% that of wildtype PGR. The most abundant isoform was the exon 7-deleted ESR, which was present at levels ranging from 29 to 83% of the wildtype. Balleine et al. (1999) concluded that the common profile of alternatively spliced ESR and PGR transcripts seen in breast tumors precludes its use as a discriminator of hormone responsiveness or other clinical end points. Furthermore, the low level of expression of the majority of variant isoforms called into question their potential for impacting significantly on receptor function.
Chaidarun and Alexander (1998) examined the effects of a human ESR1 isoform on estrogen-mediated gene activation in U2-OS osteosarcoma cells. ESR1-5, an ESR1 variant generated by an alternate splice event that omits exon 5 and alters the reading frame of the resulting mRNA, was coexpressed with normal ESR1 in several estrogen-responsive neoplastic tissues. ESR1-5 encodes the hormone-independent trans-activating function (AF-1), as well as the constitutive receptor dimerization and DNA-binding domains. The ESR1-5 protein is prematurely truncated and lacks the majority of the hormone-binding and activating function-2 (AF-2) domains. When ESR1-5 was cotransfected with normal ESR1, both basal and estrogen-stimulated reporter activation were increased approximately 500% over the levels observed when cells were transfected with ESR1 alone. Electromobility shift/supershift assays using nuclear extracts of U2-OS cells stably transfected with ESR1 and ESR1-5 confirmed the constitutive binding of ESR1-5 and ESR1 protein to the estrogen-response element (ERE) sequence independent of estrogen, and also showed an increase in ESR1-5/ESR1-ERE complexes with estrogen treatment. These data were considered to be consistent with the interactive effects of normal ESR1 and ESR1-5 on transcription from classic ERE gene promoters. Chaidarun and Alexander (1998) concluded that ESR1-5 acts as a dominant-positive receptor that increases both basal and estrogen-stimulated gene transactivation of normal ESR1.
Ye et al. (2000) investigated the expression of ESR1 in prostate cancer cell lines and unexpectedly found a FASN/ESR1 fusion transcript. Using semi-nested RT-PCR analysis of ESR1 and its variants, Ye et al. (2000) found that the N-terminal coding region of FASN containing domain 1 was fused to the C-terminal coding region of the ESR1 ligand binding domain. Nested RT-PCR also detected the fusion transcript in breast, cervical, and bladder cancer cell lines.
Using transient transfection assays, Fan et al. (1999) demonstrated that BRCA1 inhibits signaling by the ligand-activated estrogen receptor ESR-alpha through the estrogen-responsive enhancer element and blocks the C-terminal transcriptional activation function AF2 of ESR-alpha. These results suggested that wildtype BRCA1 protein may function, in part, to suppress estrogen-dependent mammary epithelial proliferation by inhibiting ESR-alpha-mediated transcriptional pathways related to cell proliferation, and that loss of this ability may contribute to tumorigenesis.
Esmaeli et al. (2000) found immunohistochemical evidence that estrogen receptors are present in the meibomian glands of the upper eyelid. Unlike sebaceous glands elsewhere on the skin, the meibomian glands lack androgen receptors. Esmaeli et al. (2000) suggested that these eyelid estrogen receptors may play a role in modulation of the tear film lipid layer. They concluded that estrogen receptor activity may be linked to meibomian gland dysfunction and dry eye syndrome.
ESR1 is downregulated in the presence of its cognate ligand, estradiol, through the ubiquitin proteasome pathway. Lonard et al. (2000) showed that ubiquitin proteasome function is required for ESR1 to serve as a transcriptional activator. Deletion of the last 61 amino acids of ESR1, including residues that form helix 12, abolished ligand-mediated downregulation of the receptor, as did point mutations in the ligand-binding domain that impaired coactivator binding. In addition, the authors found that coactivators also are subject to degradation by the 26S proteasome, but their intrinsic transcriptional activity is not affected. These data provided evidence that protein interactions with ESR1 coactivator binding surfaces are important for ligand-mediated receptor downregulation and suggested that receptor and coactivator turnover contributes to ESR1 transcriptional activity.
Zhao et al. (2003) noted that the crystal structure of the ER-alpha ligand-binding domain suggests that leu536 may be involved in hydrophobic interactions at the start of helix 12. They found that certain mutations of leu536 increased the ligand-independent activity of ER-alpha and reduced or eliminated the agonist activity of 17-beta-estradiol and 4-hydroxytamoxifen in a reporter assay. Zhao et al. (2003) concluded that leu536 is critical in coupling the binding of ligand to changes in the conformation and transcriptional activity of ER-alpha.
Simoncini et al. (2000) showed that the estrogen receptor isoform ESR-alpha binds in a ligand-dependent manner to the p85-alpha (171833) regulatory subunit of the phosphatidylinositol-3-hydroxy kinase (PI3K). Stimulation with estrogen increases ESR-alpha-associated PI3K activity, leading to the activation of protein kinase B/AKT (164730) and endothelial nitric oxide synthase (eNOS; 163729). Recruitment and activation of PI3K by ligand-bound ESR-alpha are independent of gene transcription, do not involve phosphotyrosine adaptor molecules or src homology domains of p85-alpha, and extend to other steroid hormone receptors. Mice treated with estrogen showed increased eNOS activity and decreased vascular leukocyte accumulation after ischemia and reperfusion injury. This vascular protective effect of estrogen was abolished in the presence of PI3K or eNOS inhibitors. Simoncini et al. (2000) concluded that their findings defined a physiologically important nonnuclear estrogen-signaling pathway involving the direct interaction of ESR-alpha with PI3K.
Li et al. (2003) showed that the ESR46 isoform more efficiently modulates membrane-initiated estrogen actions, including activation of eNOS, than full-length ESR66. Conversely, ESR66 more efficiently mediates estrogen response element reporter-gene transactivation than ESR46.
Pelletier and El-Alfy (2000) studied the immunocytochemical localization of ESRA and ESRB in human reproductive tissues. In the ovary, ESRB immunoreactivity was found in nuclei of granulosa cells of growing follicles at all stages from primary to mature follicles, interstitial gland, and germinal epithelium cells. Nuclear staining for ESRA occurred in thecal, interstitial gland, and germinal epithelium cells. In the uterus, strong ESRA immunoreactivity was detected in nuclei of epithelial, stromal, and muscle cells. Similar localization was obtained for ESRB, although the staining was much weaker. In the vagina, only ESRA could be detected; a nuclear reaction was observed in deep layers of the stratified epithelium as well as in stromal and muscle cells. In the mammary gland, both ESR subtypes were observed in epithelial and stromal cells. In the testis, ESRB was detected in the nuclei of Sertoli and Leydig cells, whereas ESRA immunoreactivity was only observed in Leydig cells, with no tubular labeling. In the efferent ducts, only ESRB could be detected, whereas neither ESRB nor ESRA could be found in the epididymis. In the prostate, ESRB nuclear immunolabeling was observed in both basal and secretory cells in alveoli as well as in stromal cells, whereas ESRA could not be detected. The authors concluded that there is a cell-specific localization for each of the ESR subtypes in the majority of the reproductive organs studied.
Chiang et al. (2000) examined the regulation of ESRA and ESRB expression by human chorionic gonadotropin (CG; see 118850) in human granulosa-luteal cells. CG treatment significantly attenuated the ESRA (45%) and ESRB (40%) mRNA levels. The CG-induced decrease in ESRA and ESRB expression was mimicked by 8-bromo-cAMP and forskolin treatment. Next, the effect of gonadotropin-releasing hormone (GNRH; 152760) on estrogen receptor expression was studied. Sixty-eight percent and 60% decreases in ESRA and ESRB mRNA levels, respectively, were observed after treatment with GNRH agonist. Pretreatment of the cells with a protein kinase C (PKC; see 176960) inhibitor completely reversed the GNRH agonist-induced downregulation of ESRA and ESRB expression, suggesting the involvement of PKC in GNRH signal transduction in granulosa-luteal cells. Chiang et al. (2000) observed a differential expression of ESRA and ESRB mRNA in granulosa-luteal cells in vitro. The authors concluded that the demonstration of CG- and GNRH agonist-induced downregulation of ESRA and ESRB gene expression suggests that CG and GNRH may contribute to the control of granulosa-luteal cell function. Furthermore, they inferred that the effects of CG and GNRH on ESRA and ESRB expression in granulosa-luteal cells are mediated in part by activation of PKA (see 176911) and PKC signaling pathways, respectively.
Bord et al. (2001) examined the expression of ESR1 and ESR2 in neonatal human rib bone. ESR1 and ESR2 immunoreactivity was seen in proliferative and prehypertrophic chondrocytes in the growth plate, with lower levels of expression in the late hypertrophic zone. Different patterns of expression of the 2 estrogen receptors were seen in bone. In cortical bone, intense staining for ESR1 was observed in osteoblasts and osteocytes adjacent to the periosteal-forming surface and in osteoclasts on the opposing resorbing surface. In cancellous bone, ESR2 was strongly expressed in both osteoblasts and osteocytes, whereas only low expression of ESR1 was seen in these areas. Nuclear and cytoplasmic staining for ESR2 was apparent in osteoclasts. The authors concluded that these observations demonstrate distinct patterns of expression for the 2 ER subtypes in developing human bone and indicate functions in both the growth plate and mineralized bone. In the latter, ESR1 is predominantly expressed in cortical bone, whereas ESR2 shows higher levels of expression in cancellous bone.
Takeyama et al. (2001) examined the expression and cellular localization of ESR1 and ESR2 in various human fetal tissues by semiquantitative RT-PCR (13 and 20 gestational weeks) and immunohistochemistry (13, 20, and 38 gestational weeks), respectively, to study the possible effects of estrogens on human fetal tissues during development. Relatively high levels of ESR2 expression were detected in various human fetal tissues, whereas those tissues expressing ESR2 had markedly lower levels of ESR1 expression. ESR2 mRNA expression was especially high in the adrenal gland. ESR2-immunoreactive protein was localized to the definitive zone, but not in the fetal zone, of the adrenal cortex. Although low levels of ESR2 mRNA were present in the brain, heart, lung, and kidney, ESR2 immunoreactivity was not detected in these tissues. These results suggested that the effects of estrogens in these tissues are predominantly mediated through ESR2. ESR2 immunoreactivity was detected in Sertoli cells and spermatogonia in the male reproductive tract and in germ cells in the fetal testis and epididymis. In the female reproductive tract, both ESR1 and ESR2 were immunopositive in the epithelium of the oviduct. These results demonstrated the possible sites for estrogenic action in the human fetus and suggested that the effects of estrogen via ESR2 may play important roles in human fetal development, especially in the definitive zone of the adrenal cortex and in the reproductive tissues of the developing fetus.
The therapeutic effectiveness of selective estrogen receptor modulators such as tamoxifen and raloxifene in breast cancer depends on their antiestrogenic activity. In the uterus, however, tamoxifen is estrogenic. Shang and Brown (2002) showed that both tamoxifen and raloxifene induce the recruitment of corepressors to target gene promoters in mammary cells. In endometrial cells, tamoxifen, but not raloxifene, acts like estrogen by stimulating the recruitment of coactivators to a subset of genes. The estrogen-like activity of tamoxifen in the uterus requires a high level of steroid receptor coactivator-1 (SRC1; 602691) expression. Thus, Shang and Brown (2002) concluded that cell type- and promoter-specific differences in coregulator recruitment determine the cellular response to selective estrogen receptor modulators.
Kumar et al. (2002) identified a naturally occurring short form of MTA1 (603526), which they called MTA1s, that contains a theretofore unknown sequence of 33 amino acids with an estrogen receptor-binding motif, leu-arg-ile-leu-leu (LRILL). MTA1s localizes in the cytoplasm, sequesters estrogen receptor in the cytoplasm, and enhances nongenomic responses of estrogen receptor. Deletion of the LRILL motif in MTA1s abolished its corepressor function and its interaction with estrogen receptor, and restored nuclear localization of estrogen receptor. Dysregulation of human epidermal growth factor receptor-2 (ERBB2; 164870) in breast cancer cells enhanced the expression of MTA1s and the cytoplasmic sequestration of estrogen receptor. Expression of MTA1s in breast cancer cells prevented ligand-induced nuclear translocation of estrogen receptor and stimulated malignant phenotypes. MTA1s expression is increased in human breast tumors with no or low nuclear estrogen receptor. The regulation of the cellular localization of estrogen receptor by MTA1s represents a mechanism for redirecting nuclear receptor signaling by nuclear exclusion.
Auboeuf et al. (2002) examined the impact of transcription mediated by steroid receptors, including progesterone and estrogen receptors, on RNA processing using reporter genes subject to alternative splicing driven by steroid-sensitive promoters. Steroid hormones affected the processing of pre-mRNA synthesized from steroid-sensitive promoters, but not from steroid unresponsive promoters, in a steroid receptor-dependent and receptor-selective manner. Several nuclear receptor coregulators showed differential splicing effects, suggesting that steroid hormone receptors may simultaneously control gene transcription activity and exon content of the product mRNA by recruiting coregulators involved in both processes.
Flouriot et al. (2000) showed that the 46-kD isoform of ESR1 can heterodimerize with the 66-kD isoform and can competitively inhibit the ligand-independent transactivation function of the larger receptor.
Kos et al. (2002) noted that the various ESR1 promoters are utilized in a tissue-specific manner to control the levels of mRNA variants in individual tissues. They looked specifically at the effect of upstream AUGs on the translation of major ESR1 variants. The 5-prime untranslated region of 1 mRNA species significantly suppressed the translation of a reporter gene in transient transfection assays. The 5-prime untranslated region of 3 others showed moderate negative effects. Toeprinting analysis revealed that leaky scanning occurs with mRNAs bearing the most inhibitory 5-prime untranslated regions. Kos et al. (2002) concluded that short upstream open reading frames in the 5-prime untranslated regions of ESR1 mRNAs can regulate receptor expression.
Reid et al. (2003) established the ubiquitination status and subnuclear distribution of ESR, its mobility, the kinetics of transcriptional activation, and the cyclic recruitment of E3 ligases and the 19S regulatory component of the proteasome. They demonstrated that proteasome-mediated degradation and ESR-mediated transactivation are linked and act to turn over ESR continuously on responsive promoters, and concluded that the cyclic turnover of ESR permits continuous responses to changes in the concentration of estradiol.
A heterodimer of the dioxin receptor (AHR; 600253) and ARNT (126110), which are basic helix-loop-helix/PAS family transcription factors, mediates most of the toxic effects of dioxins. Ohtake et al. (2003) demonstrated that the agonist-activated AHR/ARNT heterodimer directly associates with the estrogen receptors ESR-alpha and ESR-beta. They showed that this association results in the recruitment of unliganded estrogen receptor and the coactivator p300 (602700) to estrogen-responsive gene promoters, leading to activation of transcription and estrogenic effects. The function of liganded estrogen receptor was found to be attenuated. Estrogenic actions of AHR agonists were detected in wildtype ovariectomized mouse uteri, but were absent in Ahr -/- or Er-alpha -/- ovariectomized mice. Ohtake et al. (2003) concluded that their findings suggest a novel mechanism by which estrogen receptor-mediated estrogen signaling is modulated by a coregulatory-like function of activated AHR/ARNT, giving rise to adverse estrogen-related actions of dioxin-type environmental contaminants.
Garcia-Morales et al. (1994) found that cadmium is a potent stimulator of the estrogen receptor independent of estradiol. Stoica et al. (2000) found that cadmium activates ESR1 at concentrations as low as 10(-11) M. Cadmium was found to block the binding of estradiol to ESR1 in a noncompetitive manner, suggesting that the heavy metal interacts with the hormone-binding domain of the receptor. Stoica et al. (2000) showed that cadmium activates ESR1 through an interaction with the hormone-binding domain of the receptor. Transfection and binding assays with ESR1 mutants identified cys381, cys447, glu523, his524, and asp538 as possible interaction sites of cadmium with the hormone-binding domain of ER-alpha. Johnson et al. (2003) showed that cadmium has a potent estrogen-like activity in vivo. Female rats were ovariectomized on postnatal day 28 and allowed to recover for 3 weeks. Rats were then given a single intraperitoneal dose of cadmium (5 microgram/per kg body weight or approximately 27 nmol/kg). This exposure to cadmium increased uterine weight, promoted growth and development of mammary glands, and induced hormone-regulated genes in ovariectomized animals. In the uterus, the increase in wet weight was accompanied by proliferation of the endometrium and induction of progesterone receptor (Pgr; 607311), and complement component C3 (120700). In the mammary gland, cadmium promoted an increase in the formation of side branches and alveolar buds and the induction of casein, whey acidic protein, Pgr, and C3. In utero exposure to the metal also mimicked the effects of estrogens. Female offspring experienced an earlier onset of puberty and an increase in the epithelial area and the number of terminal end buds in the mammary gland.
Using chromatin immunoprecipitation assays, Metivier et al. (2003) identified protein complexes recruited by ESR1 to the pS2 (TFF1; 113710) promoter in a breast carcinoma cell line following estradiol treatment, and they determined the order in which the complexes were recruited.
By immunoprecipitation of human breast cancer cell lines and protein pull-down assays with in vitro translated proteins, Wada-Hiraike et al. (2005) demonstrated that ESR1 interacted with MSH2 (609309) in a ligand-dependent manner, whereas ESR2 (601663) and MSH2 interacted in a ligand-independent manner. Both receptors bound MSH2 through its MSH3 (600887)/MSH6 (600678)-interaction domain. In a transient expression assay, MSH2 potentiated the transactivation function of ligand-activated ESR1 but not ESR2. Wada-Hiraike et al. (2005) concluded that MSH2 may be a coactivator of ESR1-dependent gene expression.
Wei et al. (2006) found that the MUC1 (158340) C-terminal subunit associated with ESR1 and that the interaction was stimulated by 17-beta-estradiol in human breast carcinoma cell lines. MUC1 bound directly to the ESR1 DNA-binding domain and stabilized ESR1 by blocking its ubiquitination and degradation. Chromatin immunoprecipitation assays demonstrated that MUC1 associated with ESR1 complexes on estrogen-responsive promoters, enhanced ESR1 promoter occupancy, and increased recruitment of p160 (PELP1; 609455) coactivators SRC1 and GRIP1 (604597). MUC1 stimulated ESR1-mediated transcription and contributed to estradiol-mediate d growth and survival of breast cancer cells.
Perillo et al. (2008) analyzed how H3 histone methylation and demethylation control expression of estrogen-responsive genes and showed that a DNA-bound estrogen receptor directs transcription by participating in bending chromatin to contact the RNA polymerase II (see 180660) recruited to the promoter. This process is driven by receptor-targeted demethylation of H3K9 (see 601128) at both enhancer and promoter sites and is achieved by activation of resident LSD1 (AOF2; 609132) demethylase. Localized demethylation produces hydrogen peroxide, which modifies the surrounding DNA and recruits 8-oxoguanine-DNA glycosylase-1 (601982) and topoisomerase II-beta (126431), triggering chromatin and DNA conformational changes that are essential for estrogen-induced transcription. Perillo et al. (2008) concluded that their data showed a strategy that uses controlled DNA damage and repair to guide productive transcription.
Nunez et al. (2008) found that, in addition to interactions between multiple ER-alpha-binding sites within the same chromosome, estrogen induced interactions between loci on different chromosomes in human breast cancer cells and normal epithelial cells. These interchromosomal interactions occurred rapidly and depended upon recruitment of a subset of ER-alpha coactivators and components of chromatin-remodeling complexes, including nuclear dynein light chain-1 (DYNLL1; 601562), and dynamic assembly of nuclear motors made up of G-actin (see ACTB; 102630), nuclear myosin-1 (MYO1C; 606538), and actin-associated proteins involved in branching (e.g., ARP2; 604221). The interchromosomal interaction hubs exhibited LSD1-dependent interactions with interchromatin granules, or nuclear speckles, harboring factors for transcriptional elongation and pre-mRNA splicing. Nunez et al. (2008) concluded that these interchromosomal interactions enhance transcription of specific ER target genes.
Hurtado et al. (2008) showed that estrogen-estrogen receptor (ER) and tamoxifen-ER complexes directly repress ERBB2 (164870) transcription by means of a cis-regulatory element within the ERBB2 gene in human cell lines. Hurtado et al. (2008) implicated the paired box-2 gene product (PAX2; 167409) in a previously unrecognized role, as a crucial mediator of ER repression of ERBB2 by the anticancer drug tamoxifen. Hurtado et al. (2008) showed that PAX2 and the ER coactivator AIB1/SRC3 (601937) compete for binding and regulation of ERBB2 transcription, the outcome of which determines tamoxifen response in breast cancer cells. The repression of ERBB2 by ER-PAX2 links these 2 breast cancer subtypes and suggests that aggressive ERBB2-positive tumors can originate from ER-positive luminal tumors by circumventing this repressive mechanism. Hurtado et al. (2008) concluded that their data provided mechanistic insight into the molecular basis of endocrine resistance in breast cancer.
Fullwood et al. (2009) described the development of a new strategy, which they called chromatin interaction analysis by paired-end tag sequencing (ChIA-PET), for the de novo detection of global chromatin interactions, with which they comprehensively mapped the chromatin interaction network bound by estrogen receptor-alpha (ER-alpha) in the human genome. Fullwood et al. (2009) found that most high-confidence remote ER-alpha-binding sites are anchored at gene promoters through long-range chromatin interactions, suggesting that ER-alpha functions by extensive chromatin looping to bring genes together for coordinated transcriptional regulation. Fullwood et al. (2009) proposed that chromatin interactions constitute a primary mechanism for regulating transcription in mammalian genomes.
Crystal Structure
Shiau et al. (1998) reported the crystal structure of the human ESRA ligand-binding domain (LBD) bound to both the agonist diethylstilbestrol (DES) and a peptide derived from the nuclear receptor (NR) box II region of the coactivator GRIP1 (601993) as well as the crystal structure of the ESRA-LBD bound to the selective antagonist 4-hydroxytamoxifen (OHT). In the DES-LBD-peptide complex, the peptide binds as a short alpha helix to a hydrophobic groove on the surface of the LBD. In the OHT-LBD complex, helix 12 occludes the coactivator recognition groove by mimicking the interactions of the NR box peptide with the LBD.
Ponglikitmongkol et al. (1988) showed that the human ESR gene is more than 140 kb long. It contains 8 exons, and the position of its introns has been highly conserved, being, for example, remarkably similar to those of one of the chicken thyroid hormone receptor genes.
Kos et al. (2001) reviewed the organization of the ESR1 gene. They described promoters used in the generation of ESR1 transcripts in human and other species and suggested a consistent nomenclature. The possible role of multiple promoters in the differential expression of ESR1 in tissues and during development was also discussed.
Walter et al. (1985) determined that the human ESR gene maps to chromosome 6. By in situ hybridization, using a cDNA probe containing the coding sequence for the estrogen receptor, Gosden et al. (1986) assigned the gene to 6q24-q27. Zuppan et al. (1989) reported linkage data between the ESR locus and MYB (189990) and TCP10 (187020) on chromosome 6q. The estimated recombination fractions were 0.19 between ESR and MYB and 0.14 between ESR and TCP10, assuming equal male and female recombination fractions. To localize ESR more precisely, Menasce et al. (1993) isolated a YAC containing the gene and mapped it to 6q25.1 by fluorescence in situ hybridization (FISH) and a new simple method of post-FISH chromosome banding. Using a single interspecific backcross, Justice et al. (1990) demonstrated the genetic location of the Esr gene in relation to other loci on mouse chromosome 10.
Association with Breast Cancer
Zuppan et al. (1991) reported a lod score of 1.85 for linkage of ESR at zero recombination with late-onset breast cancer in 1 extended family with 8 affected members. Simulation of this pedigree assuming independent inheritance of breast cancer and ESR genotypes led to a lod score equal to or greater than 1.85 only once in 2,000 replicates. Zuppan et al. (1991) suggested testing linkage in other breast cancer families of the late-onset type.
McGuire et al. (1991) used the screening techniques of chemical mismatch cleavage, single-strand conformation polymorphism (SSCP), and gel retardation to discover a number of estrogen receptor mRNA variants in tissues from breast cancers. They identified basepair insertions, transitions, and deletions as well as alternative splicing, yielding deletions of exon 3, 5, or 7. Using a yeast transactivation assay, they discovered receptors with 'outlaw' function, including both a dominant-positive receptor which was transcriptionally active in the absence of estrogen, and a dominant-negative receptor, which was itself transcriptionally inactive but prevented the action of normal estrogen receptor. McGuire et al. (1991) concluded that these variants could have clinical significance, helping to explain differences in the behavior of breast tumors and patient outcome.
Ponglikitmongkol et al. (1988) found that the ESR isolated from a human breast cancer cell line contained a gly400-to-val mutation in the hormone-binding domain. A highly conserved 66-amino acid region of the estrogen and glucocorticoid receptors, which corresponds to part of the receptor DNA-binding domain (region C), determines the specificity of target gene recognition. This region contains 2 subregions (CI and CII), encoded by 2 separate exons that are analogous to 'zinc fingers.' By the study of chimeric estrogen receptor, Mader et al. (1989) showed that 3 amino acids located on the C-terminal side of the CI finger play a key role in the specificity.
It is accepted that the presence of estrogen receptor identifies those breast cancer patients with a lower risk of relapse and better overall survival (Clark and McGuire, 1988), and the measurement of ESR has become a standard assay in the clinical management of breast cancer. Receptor status also provides a guideline for those tumors that may be responsive to hormonal intervention. But only about half of ESR-positive patients respond to various hormonal therapies and of those who do respond initially, most will eventually develop hormonally unresponsive disease following a period of treatment even though ESR is often still present. Sluyser and Mester (1985) hypothesized that the loss of hormone dependence of certain breast tumors may be due to the presence of mutated or truncated steroid receptors that activate transcription even in the absence of hormone. Fuqua et al. (1993) reviewed ESR mutations that may be important in breast cancer progression. Scott et al. (1991), for example, had found truncated forms of DNA-binding ESR in human breast cancer. To better understand structure-activity relationships of the human estrogen receptor, Weis et al. (1996) examined the role of tyrosine-537 in transcriptional response of the receptor. This residue is close to a region of the hormone-binding domain shown previously to be important in hormone-dependent transcriptional activity; it also has been proposed to be a tyrosine kinase phosphorylation site important in ESR activity. Weis et al. (1996) substituted 5 amino acids at this position (alanine, phenylalanine, glutamic acid, lysine, or serine) and screened these mutants for their biologic activities in the presence and absence of estradiol. Two of the ESR mutants, tyr537 to ala and tyr537 to ser, displayed estrogen-independent constitutive activity that was approximately 20% or 100%, respectively, of the activity of the wildtype receptor with estradiol. In some circumstances, the tyr537-to-glu and tyr537-to-lys proteins also exhibited some low level of constitutive activity. Their findings indicated that tyrosine-537 is in a region important in the ligand regulation of ESR transcriptional activity and that certain amino acid substitutions at this position can shift ESR into a conformation that is active even without ligand.
Sluyser (1995) reviewed the somatically generated mutations in ESR that had been found at the mRNA/cDNA level in human breast cancer biopsies and in established breast cancer cell lines. Aberrantly spliced ESR mRNA causes the appearance of truncated or internally deleted ESR protein forms. Studies on the functional activity of ESR variants in expression systems demonstrated dominant-positive receptors that are transcriptionally active in the absence of estrogen, and dominant-negative receptors that are themselves transcriptionally inactive but that prevent the action of the normal receptor. The ESR variants are believed to confer resistance to endocrine therapy in breast cancer patients. Abnormally spliced forms of ESR, similar to those in breast cancer, were reported by McGuire et al. (1992) and by others. In all, 19 somatic mutations were tabulated and mapped on a diagram of the structural organization of the ESR gene.
Andersen et al. (1997) studied leukocyte DNA from 143 patients with familial clustering of breast and/or ovarian cancer and tumor DNA from 96 breast carcinomas for base mutations in the ESR gene. Three patients with a family history of cancer were carrying a gly160-to-cys germline substitution, which they concluded represents a polymorphism because it was detected in 4 females and 4 males of 729 controls, split about equally between males and females. However, in the 229 female controls in whom family history of cancer was known, 1 of 2 who had a sister with breast cancer was carrying the variant allele; hence, a possible clinical significance of the gly160-to-cys change should be further investigated. Somatic mutations were not detected in any of the tumors studied, and the data did not provide support for somatic ESR base mutations as an important mechanism for hormonal therapy resistance in estrogen receptor-positive breast carcinomas.
Using an Affymetrix 10K SNP array to screen for gene copy number changes in breast cancer, Holst et al. (2007) detected a single-gene amplification of the ESR1 gene. A subsequent tissue microarray analysis of more than 2,000 clinical breast cancer samples showed ESR1 amplification in 20.6% of breast cancers. In 99% of tumors with ESR1 amplification, overexpression of estrogen receptor protein was demonstrated, compared with 66.6% of cancers without ESR1 amplification. In 175 women who had received adjuvant tamoxifen monotherapy, survival was significantly longer for women with cancer with ESR1 amplification than for women with estrogen receptor-expressing cancers without ESR1 amplification (P = 0.023). Notably, they also found ESR1 amplification in benign and precancerous breast diseases, suggesting that ESR1 amplification may be a common mechanism in proliferative breast disease and a very early genetic alteration in a large subset of breast cancers.
In correspondences, Brown et al. (2008), Horlings et al. (2008), Vincent-Salomon et al. (2008), and Reis-Filho et al. (2008) reported attempts to replicate the finding of Holst et al. (2007) of a high frequency of ESR1 amplification in breast cancer. No group was able to replicate the results of Holst et al. (2007), using a variety of methods including array comparative genomic hybridization (CGH), FISH, and quantitative PCR. Amplification was found at a frequency of approximately 10% or less (Albertson, 2008). In a discussion of the findings of all of these groups, Albertson (2008) noted that although Holst et al. (2007) reported to have followed the standard procedure for scoring FISH, i.e., to count closely spaced signals as 1 signal, in their reply to the contesting groups Holst et al. (2008) emphasized the importance of scoring clusters of signals. Holst et al. (2008) stated, 'In our laboratory, most ESR1-amplified tumors have small gene clusters that could be considered as one signal if 'ERBB criteria' were applied....We therefore feel that estimating the ESR1 gene copy number may--given the currently available reagents--enable a more reliable identification of amplified cancers than classical counting.' Albertson (2008) concluded that this and other discrepancies, including that involving the clinical significance concerning prognosis, indicated that 'the jury is still out on the question of ESR1 amplification and its clinical significance.'
Certain malignant breast tumors (see 114480) are characterized by a high prediction uncertainty ('low-confidence') with respect to ESR status. Kun et al. (2003) analyzed these 'low-confidence' tumors and determined that their uncertain prediction status arose as a result of widespread perturbations in multiple genes whose expression is important for ESR-subtype discrimination. Patients with 'low-confidence' ESR-positive tumors exhibited a significantly worse overall survival (p = 0.03) and shorter time to distant metastasis (p = 0.004) compared with their 'high-confidence' ESR-positive counterparts. Elevated expression of ERBB2 (164870) was significantly correlated with a breast tumor exhibiting a 'low-confidence' prediction. Although ERBB2 signaling has been proposed to inhibit the transcriptional activity of ESR1, a large proportion of the perturbed genes in the 'low-confidence'/ERBB2-positive samples are not known to be estrogen responsive. Kun et al. (2003) proposed that a significant portion of the effect of ERBB2 on ESR-positive breast tumors may involve ESR-independent mechanisms of gene activation, which may contribute to the clinically aggressive behavior of the 'low-confidence' breast tumor subtype.
Association with Bone Mineral Density Variation
Lorentzon et al. (1999) investigated the influence of ESRA gene polymorphism and estradiol on height and bone density during and after puberty in males. Using the restriction enzymes XbaI and PvuII, the allelic variants XX, Xx, xx, PP, Pp, and pp were identified in 90 Caucasian boys. In a multivariate analysis including pubertal development, physical activity, and body weight, the XbaI genotype independently predicted total body BMD, head BMD, and spine volumetric BMD (P less than 0.05). The PvuII genotype independently predicted spine volumetric BMD (pp greater than PP; P of 0.01). The 20 boys with the PP allelic variant were found to have a greater body height than the other 70 boys (182 cm vs 179 cm; P of 0.03). At a 2-year follow-up, the XbaI genotype was still independently related to total body BMD, head BMD, and spine volumetric BMD. The authors concluded that ESRA polymorphism is related to bone density and height during late puberty and at attainment of peak bone density in young men.
Bone mineral density, the major determinant of osteoporotic fracture risk, has a strong genetic component. The discovery that inactivation of ESR1 is associated with low BMD indicated ESR1 as a candidate gene for osteoporosis (166710). Becherini et al. (2000) genotyped 610 postmenopausal women for 3 ESR1 gene polymorphisms (intron 1 RFLPs PvuII and XbaI, and a (TA)n repeat 5-prime upstream of exon 1). Although no significant relationship between intron 1 RFLPs and BMD was observed, a statistically significant correlation between (TA)n-repeat allelic variants and lumbar BMD was observed (P = 0.04, ANCOVA), with subjects having a low number of repeats (TA less than 15) showing the lowest BMD values. The authors observed a statistically significant difference in the mean +/- SD number of (TA)n repeats between 73 analyzed women with a vertebral fracture and the nonfracture group, equivalent to a 2.9-fold increased fracture risk in women with a low number of repeats. The authors concluded that in their large sample the (TA)n polymorphism in ESR1 accounts for part of the heritable component of BMD and may prove useful in the prediction of vertebral fracture risk in postmenopausal osteoporosis.
Colin et al. (2003) studied the combined influence of polymorphisms in the ESR1 and the VDR (601769) genes on the susceptibility to osteoporotic vertebral fractures in 634 women aged 55 years and older. Three VDR haplotypes (1, 2, and 3) of the BsmI, ApaI, and TaqI restriction fragment length polymorphisms and 3 ESR1 haplotypes (1, 2, and 3) of the PvuII and XbaI RFLPs were identified. ESR1 haplotype 1 was dose-dependently associated with increased vertebral fracture risk corresponding to an odds ratio of 1.9 (95% confidence interval, 0.9-4.1) per copy of the risk allele. VDR haplotype 1 was overrepresented in vertebral fracture cases. There was a significant interaction (P = 0.01) between ESR1 haplotype 1 and VDR haplotype 1 in determining vertebral fracture risk. The association of ESR1 haplotype 1 with vertebral fracture risk was present only in homozygous carriers of VDR haplotype 1. The risk of fracture was 2.5 for heterozygous and 10.3 for homozygous carriers of ESR1 haplotype 1. These associations were independent of BMD. The authors concluded that interaction between ESR1 and VDR gene polymorphisms leads to increased risk of osteoporotic vertebral fractures in women, largely independent of BMD.
Van Meurs et al. (2003) investigated the influence of genetic variation in ESR1 on several bone parameters in 2,042 individuals of the Rotterdam Study, a prospective population-based cohort study of elderly individuals. They analyzed 3 polymorphic sites in the 5-prime region of the ESR1 gene: a (TA)n repeat in the promoter region, molecular haplotypes of the PvuII and XbaI RFLPs in intron 1, and inferred long-range haplotypes thereof. Linkage disequilibrium (LD) analysis between the PvuII-XbaI haplotype and the (TA)n repeat showed strong LD between the 2 sites. Reconstruction of long-range haplotypes over the entire 5-prime region revealed 6 frequent long-range haplotypes. In women only, there was an allele dose effect of haplotype 'px' (p = 0.003) and a low number of (TA)n repeats (p = 0.008) with decreased lumbar spine BMD and decreased vertebral bone area (p = 0.016). There was also an increased vertebral fracture risk with evidence for an allele dose effect with an odds ratio of 2.2 (95% CI, 1.3-3.5) for haplotype 'px' and an odds ratio of 2.0 (95% CI, 1.5-3.2) for a low number of (TA)n repeats. The ESR1 genotype-dependent fracture risk was largely independent of BMD and bone area. Van Meurs et al. (2003) concluded that ESR1 polymorphisms in the 5-prime promoter region are associated with vertebral fracture risk, lumbar spine BMD, and vertebral bone area in postmenopausal women, but not in men.
Khosla et al. (2004) studied relationships between polymorphisms of the ESRA and ESRB genes, BMD, and rates of bone loss in an age-stratified random sample of 283 Rochester, Minnesota, men aged 22 to 90 years. DNA was analyzed for the XbaI and PvuII ESRA and AluI ESRB polymorphisms. The X/P and x/p alleles of the ESRA gene were in strong linkage disequilibrium. BMD at multiple sites did not differ as a function of either the ESRA or ESRB genotype. However, the ESRA (but not ESRB) genotypes did modulate the relationship between BMD or rates of bone loss and bioavailable estradiol levels in these men. The authors concluded that the ESRA genotype may modulate the relationship between BMD or rates of bone loss and estrogen levels in men and that bone mass in men with the X or P alleles may be more susceptible to the consequences of estrogen deficiency (and conversely, benefit most from estrogen sufficiency) than in men with the xx or pp genotypes.
Sowers et al. (2004) conducted a 10-year prospective study of peak bone mass and its change in 604 women, aged 24 to 44 years at study initiation, and related changes in bone mineral density (BMD) and osteocalcin (OCN; 112260) concentrations to ESR1 gene polymorphisms (the XbaI and PvuII RFLPs) in 442 of these women. The authors concluded that while ESR1 genotype associations were statistically significant in explaining the rate of perimenopausal bone loss and its turnover, baseline BMI or becoming postmenopausal contributed more to the magnitude of the difference in bone change.
In 945 postmenopausal Scottish women who had not received hormone replacement therapy (non-HRT), Albagha et al. (2005) found that annual rates of femoral neck bone loss were 14% higher in subjects who carried 1 copy of the 'px' allele and 22% higher in those who carried 2 copies compared to those who did not carry the px haplotype (p = 0.009). The px haplotype was associated with lower femoral neck BMD in non-HRT postmenopausal women (p = 0.02), and with reduced calcaneal broadband ultrasound attenuation in the whole study population of 3,054 Scottish women (p = 0.005). Albagha et al. (2005) concluded that the ESR1 px haplotype is associated with reduced femoral neck BMD and increased rates of femoral neck bone loss in non-HRT postmenopausal women, and suggested that the association with broadband ultrasound attenuation may explain the fact that ESR1 intron 1 alleles predict osteoporotic fractures by a mechanism partly independent of differences in BMD.
Tobias et al. (2007) investigated whether the gain in area-adjusted bone mineral content (ABMC) in girls occurs in late puberty and examined whether the magnitude of this gain is related to ESR1 polymorphisms. For rs2234693 (PvuII) and rs9340799 (XbaI) polymorphisms, differences in spinal ABMC in late puberty were 2-fold greater in girls who were homozygous for the C and G alleles, respectively (P = 0.001). For rs7757956, the difference in total body less head ABMC in late puberty was 50% less in individuals homozygous or heterozygous for the A allele (P = 0.006). Tobias et al. (2007) concluded that gains in ABMC in late pubertal girls are strongly associated with ESR1 polymorphisms, suggesting that estrogen contributes to this process via an estrogen receptor-alpha-dependent pathway.
In a case-control study of 70 osteoporotic Mexican women and 70 nonosteoporotic female controls, Gomez et al. (2007) analyzed the (TA)n repeat and 2014G-A polymorphisms of the ESR1 gene and found that, with correction for population stratification, the 2014G allele was associated with osteoporosis (OR, 4.34; p = 0.006) in the Mexican population, whereas the TA repeat polymorphism was not.
In a genomewide association study to find common sequence variants that influence bone mineral density and low-trauma fractures in 3 populations of European descent, Styrkarsdottir et al. (2008) identified a complex pattern of association in the 6q25 region (see BMND11, 612114). SNPs in this region showed an association with BMD of both hip and spine, although no single SNP could fully explain the association. At least 3 SNPs were required to account for the overall association; one of these was in an intron of an ESR1 splice variant, and the other 2 were in the nearby C6ORF97 gene.
Other Associations
Weel et al. (1999) investigated whether genetic variation in the ESR gene contributes to the variability in the onset of menopause in 900 postmenopausal women, 55 to 80 years of age, of the Rotterdam Study, a population-based cohort study in the Netherlands. Gynecologic information was obtained, and if women reported surgical menopause, validation of type and indication of surgery was accomplished by checking medical records. The ESR genotypes (PP, Pp, and pp) were assessed by PCR using the PvuII endonuclease to detect an anonymous intronic RFLP. Compared with women carrying the pp genotype, homozygous PP women had a 1.1 year (P less than 0.02) earlier onset of menopause. Furthermore, an allele dose effect was observed, corresponding to a 0.5 year (P less than 0.02) earlier onset of menopause per copy of the P allele. The risk of surgical menopause was 2.4 (95% confidence interval, 1.5 to 3.8) times higher for women carrying the PP genotype compared to those in the pp group, with the most prominent effect in women who underwent hysterectomy due to fibroids or menorrhagia. The authors concluded that genetic variations of the ESR gene are related to the onset of natural menopause and the risk of surgical menopause, especially hysterectomy.
In a study of 309 postmenopausal women with coronary artery disease, Herrington et al. (2002) found that women who were of a particular genotype at the ESR1 locus had an augmented response of HDL cholesterol to hormone replacement therapy (see 133430.0004).
Bergink et al. (2003) studied the association between ESRA haplotypes as defined by the RFLPs PvuII and XbaI and radiographic osteoarthritis of the knee (see 165720) in a large population-based cohort of 1,483 individuals aged 55 years and older from the Rotterdam Study. Three different haplotype alleles, px, PX and Px, were identified. The PX allele was associated with an increased prevalence of radiographic knee osteoarthritis with an adjusted odds ratio of 1.3 for heterozygotes and 2.2 for homozygotes. Separate analyses for men and women showed similar risk estimates.
In a study of 2,238 Japanese individuals, Okura et al. (2003) found that middle-aged women (40-59 years old) with the AG or GG genotype of the XbaI polymorphism had significantly greater BMI, fat mass, percentage of fat mass, and waist-to-hip ratio than those with the AA genotype. Conversely, waist size and fat mass were smaller in older women with the GG genotype. Okura et al. (2003) concluded that the XbaI polymorphism, particularly the GG genotype, may contribute to the development of abdominal obesity (see 609830) in middle-aged women, but may decrease the whole-body and abdominal fat tissue of older women.
In a study of 2,617 men and 3,791 postmenopausal women, aged 55 years and older, followed up over a period of 7 years or more, Schuit et al. (2004) found that postmenopausal women who carried the ESR1 haplotype 1 had an increased risk of myocardial infarction (MI) and ischemic heart disease, independent of known cardiovascular risk factors. In men, no association was observed. Haplotype 1 is comprise of 2 polymorphisms located in the first intron of the ESR1 gene, 397 bp (PvuII; rs2234693) and 351 bp (XbaI; rs9340799) upstream of exon 2.
Taguchi (2004) raised the question of whether the connection between ESR1 and MI might not be direct. Since Mattila et al. (1989) reported an association between poor dental health and acute MI in men, several studies had shown such an association in women as well (Emingil et al., 2000); Taguchi et al. (2001) reported a significant association between ESR1 polymorphisms and tooth loss in postmenopausal women. Thus, the association between ESR1 polymorphisms and MI in postmenopausal women could actually be due to an association between ESR1 polymorphisms and tooth loss. Another possibility that Taguchi (2004) raised was that endothelial dysfunction that may lead to MI contributes to periodontitis and subsequent tooth loss in postmenopausal women. A third possibility was that the association between ESR1 polymorphisms and tooth loss and between ESR1 polymorphisms and MI are both real, so that the association between tooth loss and MI in postmenopausal women in previous studies is spurious and actually due to the ESR1 polymorphisms.
Shearman et al. (2005) tested for interaction between smoking and ESR1 variation in association with plasma concentration of atherogenic small, low density lipoprotein (LDL) particles and LDL particle size. Among 1,727 unrelated subjects from the population-based Framingham Heart Study, women who smoked and had the common ESR1 rs2234693 TT genotype had more than 1.7-fold higher levels of small LDL particles than women with the alternative genotypes (P-value for smoking-genotype interaction = 0.001). Similar results were obtained for 3 other ESR1 variants including rs9340799, in the same linkage disequilibrium block. A similar substantial gender-specific result was also evident with a 975C-G variant, in a separate linkage disequilibrium block, in exon 4 (P = 0.003). Women who smoked and had specific, common ESR1 genotypes had a substantially higher plasma concentration of atherogenic small LDL particles. Significant results revealed a dose-dependent effect of smoking and were evident in both pre- and postmenopausal women. The reported association has the potential to explain the risks associated with estrogen use in certain women and an association between the ESR1 haplotype 1 (rs2234693 T allele and rs9340799 A allele) with increased MI and ischemic heart disease, independent of the standard, established cardiovascular risk factors.
In a prospective, population-based study of 4,571 individuals aged 55 and older (the Rotterdam study) with a mean follow-up time of 7 years, Boekhoorn et al. (2007) found that ESR1 PvuII-XbaI haplotype 1 was a risk factor for late age-related macular degeneration (ARMD; see 603075). The 2 single nucleotide polymorphisms (SNPs) of haplotype 1 are the adjacent PvuII (rs2234693), a T-to-C transition in intron 1, and XbaI (rs9340799), a G-to-A transition located 46 bp downstream of the PvuII polymorphism. Persons with 2 copies of haplotype 1 were at 3.2 times higher risk for late ARMD than noncarriers of haplotype 1, after adjustment for age and gender. This increase was more pronounced for wet ARMD (hazard ratio 4.3) after adjustment for age, gender, smoking, and complement factor H genotype. Correction for hormone replacement therapy, blood pressure, and body mass index did not essentially alter the findings.
Korach (1994) investigated hormone responsiveness in genetic mutant mice without a functional estrogen receptor, created through gene knockout techniques. Both sexes of these mutant animals were infertile and showed a variety of phenotypic changes associated with the gonads, mammary glands, reproductive tracts, and skeletal tissues.
To clarify the role of estrogen signaling in reproductive tract development and function, Couse et al. (1999) generated mice lacking ESRA and ESRB by targeted disruption. ESRA/ESRB knockout males were infertile but possessed a grossly normal reproductive tract. They exhibited various stages of spermatogenesis, but the numbers and motility of epididymal sperm were reduced significantly. ESRA/ESRB knockout females exhibited proper differentiation of the mullerian-derived structures of the uterus, cervix, and upper vagina, but these structures were severely hypoplastic in adults. Similar uterine hypoplasia was observed in ESRA, but not in ESRB, knockout mice. The ovaries of adult ESRA/ESRB knockout females exhibited morphologic phenotypes that were clearly distinct from those of the prepubertal ESRA/ESRB knockout females and the individual estrogen receptor knockout mice. The double-knockout female ovaries had structures resembling seminiferous tubules of the testis. Within the lumen of the tubule-like structures were degenerating granulosa cells and cells resembling Sertoli cells of the testis. Couse et al. (1999) argued that certain characteristics of the adult ESRA/ESRB knockout ovary indicated redifferentiation of varying components rather than a developmental phenomenon: the absence of similar structures in prepubertal ESRA/ESRB knockout ovaries; the consistent spherical shape of the tubules, suggesting origination from a once healthy follicle; and age-related increases in the area of transdifferentiation. The ovaries of adult ESRA/ESRB knockout females expressed mullerian-inhibiting substance (600957), sulfated glycoprotein-2 (185430), and Sox9 (608160). Couse et al. (1999) concluded that the loss of both receptors leads to an ovarian phenotype that is distinct from that of the individual estrogen receptor knockout mutants, which indicates that both receptors are required for the maintenance of germ and somatic cells in the postnatal ovary.
Heine et al. (2000) found that male and female Esr1 knockout mice had hyperplasia and hypertrophy of adipocytes, insulin resistance, and glucose intolerance. The results provided evidence that estrogen/ESR1 signaling is critical in female and male white adipose tissue; obesity in the knockout males involved a mechanism of reduced energy expenditure rather than increased energy intake. Similar results were obtained by Jones et al. (2000) studying aromatase (CYP19; 107910) knockout mice, which cannot synthesize endogenous estrogens. Both male and female aromatase knockout mice progressively accumulated significantly more intraabdominal adipose tissue than their wildtype littermates and had elevated circulating levels of leptin and cholesterol, as well as elevated insulin levels and a striking accumulation of lipid droplets in the livers.
Davis et al. (2002) noted that studies in humans and rodent models had suggested that estrogen may provide protection against age-related cataracts. The presence of estrogen receptors in the eye indicates that estrogen protection may result from direct interactions with its receptors in the eye, instead of being an indirect consequence from effects on another tissue. Davis et al. (2002) validated the concept that estrogen is beneficial for the eye. In transgenic mice expressing ESR-delta-3, a natural variant of ESR1 with an in-frame deletion of exon 3 resulting from alternative splicing, they found that cortical cataracts spontaneously formed in females after puberty and progressed with age. ESR-delta-3 is a dominant-negative form of ESR-alpha that inhibits ESR-alpha function. Cataract formation could be prevented if the females were ovariectomized before, but not after, sexual maturity. Both male and female ESR-delta-3 mice developed cataracts after neonatal treatment with the potent estrogen DES. The incidence of spontaneous and DES-induced cataracts in ESR-delta-3 mice was 100%, whereas such cataracts were absent from wildtype mice. The data suggested that repression of estrogen action induces cortical cataract formation because estrogen is required to activate the ESR-delta-3 repressor. Evidence of DES-induced cataracts in the ESR-delta-3 males as well as the females suggested that estrogen is important in lens physiology in both sexes.
Using mice lacking functional Esr1, Lee et al. (2003) showed that bone in vivo undergoes an adaptive response to loading that is less effective in the absence of Esr1 and that osteoblast-like cells require Esr1 to proliferate in response to mechanical strain in vitro. Lee et al. (2003) speculated that as ESR1 expression in osteoblasts and osteocytes depends on estrogen concentration, a failure to maintain bone strength after menopause might be due to reduction in the activity of ESR1 in bone cells, thereby limiting their anabolic response to mechanical loading and allowing a loss of bone tissue comparable to that associated with disuse.
Nakamura et al. (2007) selectively ablated Esr1 in differentiated mouse osteoclasts and found that females, but not males, exhibited trabecular bone loss, similar to the osteoporotic bone phenotype in postmenopausal women. Furthermore, estrogen induced apoptosis and upregulation of Fas ligand (FASL, or TNFSF6; 134638) in osteoclasts of trabecular bones of wildtype mice, but not mutant mice. Expression of Esr1 was also required for induction of apoptosis by tamoxifen and estrogen in cultured osteoclasts. Nakamura et al. (2007) concluded that estrogen regulates the life span of mature osteoclasts via induction of the FAS (TNFRSF6; 134637)/FASL system.
Garey et al. (2003) identified a generalized arousal component in the behavior of mice. Analyzed by mathematical/statistical approaches across experiments, investigators, and mouse populations, it accounted for approximately one-third of the variance in arousal-related measures. Knockout of the Esr1 gene greatly reduced arousal responses. In contrast, disrupting the Esr2 gene (601663), a likely gene duplication product which encodes ER-beta, did not have these effects.
In mice, ovariectomy accelerates the progression of the end-stage renal disease glomerulosclerosis. In women, the incidence of this disorder increases after menopause, and estrogen alters its progression. Polymorphisms in the ESR1 gene may constitute a genetic predisposition for lupus nephritis (Liu et al., 2002). Shim et al. (2004) showed that by 1 year of age, mice lacking ER-alpha, but not those lacking ER-beta, exhibited immune complex-type glomerulonephritis, proteinuria, and destruction of tubular cells. The mice also showed spontaneous formation of germinal centers in the spleen in the absence of antigen challenge and infiltration of plasma cells in the kidney and spleen. The results indicated that ER-alpha has indispensable functions in the kidney and in germinal centers, and that defective ER-alpha signaling results in glomerulonephritis.
In female mice and rats, Musatov et al. (2007) used RNAi to focally silence ER-alpha in the ventromedial nucleus of the hypothalamus and observed development of a phenotype characteristic of metabolic syndrome, marked by obesity, hyperphagia, impaired glucose tolerance, and reduced energy expenditure; this phenotype persisted despite normal ER-alpha levels elsewhere in the brain. Although an increase in food intake preceded weight gain, the authors stated that their data suggested that a leading factor of obesity in this model was likely a decline in energy expenditure with all 3 major constituents being affected, including voluntary activity, basal metabolic rate, and diet-induced thermogenesis. Musatov et al. (2007) concluded that ER-alpha in the ventromedial nucleus of the hypothalamus neurons plays an essential role in the control of energy balance and maintenance of normal body weight.
(Selected Examples)
NotesSee allelic variants in tabular display
.0001 ESTROGEN RECEPTOR MUTANT, TEMPERATURE-SENSITIVE [ESR1, CYS447ALA]
Reese and Katzenellenbogen (1991) identified an estrogen receptor mutant that had a similar binding affinity for estradiol as wildtype ESR but displayed a dose-response shift for estradiol in transactivation studies. The mutant contained an alanine substitution for cysteine at amino acid 447 in the hormone binding domain of the receptor. Reese and Katzenellenbogen (1992) showed by hormone binding studies that the C447A receptor is a temperature-sensitive mutant, whose instability is only apparent at elevated temperatures, and that ligand can stabilize the mutant receptor. The mutant also showed a temperature-sensitive loss in the DNA binding ability of the receptor. (The mutant was one of several created by Reese and Katzenellenbogen (1991) by in vitro oligonucleotide site-directed mutagenesis of human ESR cDNA. Function of the mutant forms was tested in Chinese hamster ovary (CHO) cells, an estrogen receptor-deficient cell line.)
.0002 ESTROGEN RESISTANCE [ESR1, ARG157TER] dbSNP:rs104893956
Smith et al. (1994) described a 28-year-old man with estrogen resistance. He was 204 cm tall and had incomplete epiphyseal closure, with a history of continued linear growth into adulthood despite otherwise normal pubertal development. He was normally masculinized and had bilateral axillary acanthosis nigricans. Serum estradiol and estrone concentrations were elevated, and serum testosterone concentrations were normal. Serum follicle-stimulating hormone and luteinizing hormone concentrations were increased. Glucose tolerance was impaired and hyperinsulinemia was present. Bone mineral density of the lumbar spine was 3.1 SD below the mean for age-matched normal women; there was no biochemical evidence of increased bone turnover. Administration of estrogen had no detectable effect. Single-strand conformation polymorphism analysis of the ESR gene revealed a variant banding pattern in exon 2. Direct sequencing of exon 2 demonstrated a cytosine-to-thymine transition at codon 157 of both alleles, resulting in a change from CGA (arg) to TGA (stop). Both parents were heterozygous carriers of the R157X mutation, and pedigree analysis showed that they were related as second cousins. Three sisters were also heterozygous. Thus, estrogen is important for bone maturation and mineralization in men as well as in women.
Sudhir et al. (1997) presented further clinical and laboratory findings from this man at the age of 31 years. By use of electron-beam CT scanning, they found evidence of early atherosclerosis in the left anterior descending coronary artery. Abnormal serum lipid concentrations were thought to reflect estrogen insensitivity. The authors concluded that the absence of functional estrogen receptors may be a novel risk factor for coronary artery disease in men.
Smith et al. (2008) performed a follow-up of the propositus with a homozygous R157X mutation in ESR1 originally reported by Smith et al. (1994) combined with an assessment of the effect of heterozygosity on spine density and adult height in members of his extended kindred. The authors concluded that homozygous ESR1 disruption markedly affects bone growth, mineral content, and structure, but not periosteal circumference. ESR1 heterozygosity appeared to not impair areal spine BMD.
.0003 ESTROGEN RESISTANCE [ESR1, VAL364GLU]
McInerney et al. (1996) characterized a human ESR mutant, val364 to glu, which has a single amino acid substitution in its hormone-binding domain. While this mutant is fully active or even superactive at saturating levels of estradiol it also acts as a strong dominant-negative inhibitor of the wildtype ESR and it is able to repress ESR-mediated transcription when the mutant and wildtype ESR are present together in cells, even without DNA binding. It is probable that altered interactions with proteins important in ESR-mediated transcription play a key role in the repression of transcription by val364 to glu.
.0004 HDL CHOLESTEROL, AUGMENTED RESPONSE OF, TO HORMONE REPLACEMENT [ESR1, IVS1, T-C, -401]
ATHEROSCLEROSIS, SUSCEPTIBILITY TO, INCLUDED, MYOCARDIAL INFARCTION, SUSCEPTIBILITY TO, INCLUDED
Herrington et al. (2002) characterized 309 women with coronary artery disease with respect to 8 previously described and 2 novel ESR1 polymorphisms, and examined the association between these polymorphisms and the response of HDL cholesterol and other lipids to treatment with estrogen alone or estrogen plus progestin. They found that postmenopausal women who had the ESR1 C/C genotype at the -401 position in intron 1, or several other closely related genotypes, had an augmented response of HDL cholesterol to hormone replacement therapy.
Lehtimaki et al. (2002) examined coronary artery specimens from 300 Finnish white men aged 33 to 69 years included in the Helsinki Sudden Death Study and determined the ESR1 IVS1 -401T/C (or PvuII) genotype. After adjusting for age and BMI, men aged 53 years or over with C/T and C/C genotypes had areas of complicated lesions on average 2- and 5-fold larger, respectively, than subjects with the T/T genotype. The age and BMI-adjusted odds ratios for coronary thrombosis were 6.2 for C/T and 10.6 for C/C compared to men with the T/T genotype. After additional adjustment for diabetes and hypertension, ESR1 genotype persisted as an independent predictor of complicated lesions and coronary thrombosis. Lehtimaki et al. (2002) concluded that the ESR1 gene is a potential candidate behind the pathogenesis of acute coronary events.
In a study of atherosclerotic cardiovascular events in 1,739 unrelated men and women from the Framingham Heart Study, Shearman et al. (2003) found that after adjustment for covariates, the ESR1 C/C genotype was significantly associated with major atherosclerotic cardiovascular disease and myocardial infarction (odds ratios of 2.0 and 3.0, respectively, compared to individuals with the C/T or T/T genotypes). The results remained significant when analyses were restricted to men; too few women had events to study them separately. Shearman et al. (2003) concluded that individuals with the common ESR1 C/C genotype have a substantial increase in risk of myocardial infarction.
.0005 MIGRAINE, SUSCEPTIBILITY TO [ESR1, 594G-A]
Migraine (157300) is a painful and debilitating disorder with a significant genetic component. Steroid hormones, in particular estrogen, have long been considered to play a role in migraine, as variations in hormone levels are associated with migraine onset in many individuals with the disorder. Steroid hormones mediate their activity via hormone receptors, which have a wide tissue distribution. Estrogen receptors have been localized to the brain in regions considered to be involved in migraine pathogenesis. Colson et al. (2004) examined the ESR1 gene for a potential role in migraine pathogenesis and susceptibility. A population-based cohort of 224 patients with migraine and 224 matched controls were genotyped for the 594G-A polymorphism located in exon 8 of the ESR1 gene. Statistical analysis indicated a significant difference between patients with migraine and those without migraine in both the allele frequencies (P = 0.003) and genotype distributions (P = 0.008). An independent follow-up study using this marker in an additional population-based cohort of 260 patients with migraine and 260 matched controls resulted in a significant association between the 2 groups with regard to allele frequencies and genotype distributions. The findings supported the hypothesis that genetic variation in hormone receptors, in particular the ESR1 gene, may play a role in migraines.
