DNA binding by estrogen receptor-alpha is essential for the transcriptional response to estrogen in the liver and the uterus

Estrogen receptor (ER)α-regulated lipocalin 2 expression in adipose tissue links obesity with breast cancer progression

Obesity is associated with increased breast cancer (BrCA) incidence. Considering that inactivation of estrogen receptor (ER)α promotes obesity and metabolic dysfunction in women and female mice, understanding the mechanisms and tissue-specific sites of ERα action to combat metabolic-related disease, including BrCA, is of clinical importance. To study the role of ERα in adipose tissue we generated fat-specific ERα knock-out (FERKO) mice. Herein we show that ERα deletion increased adipocyte size, fat pad weight, and tissue expression and circulating levels of the secreted glycoprotein, lipocalin 2 (Lcn2), an adipokine previously associated with BrCA development. Chromatin immunoprecipitation and luciferase reporter studies showed that ERα binds the Lcn2 promoter to repress its expression. Because adipocytes constitute an important cell type of the breast microenvironment, we examined the impact of adipocyte ERα deletion on cancer cell behavior. Conditioned medium from ERα-null adipocytes and medium containing pure Lcn2 increased proliferation and migration of a subset of BrCA cells in culture. The proliferative and promigratory effects of ERα-deficient adipocyte-conditioned medium on BrCA cells was reversed by Lcn2 deletion. BrCA cell responsiveness to exogenous Lcn2 was heightened in cell types where endogenous Lcn2 expression was minimal, but components of the Lcn2 signaling pathway were enriched, i.e. SLC22A17 and 3-hydroxybutyrate dehydrogenase (BDH2). In breast tumor biopsies from women diagnosed with BrCA we found that BDH2 expression was positively associated with adiposity and circulating Lcn2 levels. Collectively these data suggest that reduction of ERα expression in adipose tissue promotes adiposity and is linked with the progression and severity of BrCA via increased adipocyte-specific Lcn2 production and enhanced tumor cell Lcn2 sensitivity.

The role of genetics in estrogen responses: a critical piece of an intricate puzzle

The estrogens are female sex hormones that are involved in a variety of physiological processes, including reproductive development and function, wound healing, and bone growth. They are mainly known for their roles in reproductive tissues--specifically, 17β-estradiol (E2), the primary estrogen, which is secreted by the ovaries and induces cellular proliferation and growth of the uterus and mammary glands. In addition to the role of estrogens in promoting tissue growth and development during normal physiological states, they have a well-established role in determining susceptibility to disease, particularly cancer, in reproductive tissues. The responsiveness of various tissues to estrogen is genetically controlled, with marked quantitative variation observed across multiple species, including humans. This variation presents both researchers and clinicians with a veritable physiological puzzle, the pieces of which--many of them unknown--are complex and difficult to fit together. Although genetics is known to play a major role in determining sensitivity to estrogens, there are other factors, including parent of origin and the maternal environment, that are intimately linked to heritable phenotypes but do not represent genotype, per se. The objectives of this review article were to summarize the current knowledge of the role of genotype, and uterine and neonatal environments, in phenotypic variation in the response to estrogens; to discuss recent findings and the potential mechanisms involved; and to highlight exciting research opportunities for the future.

Association of PvuII and XbaI polymorphisms in estrogen receptor alpha gene with the risk of hepatitis B virus infection in the Guangxi Zhuang population

BACKGROUND AND OBJECTIVE

Available evidence has suggested that estrogen receptor alpha (ESR1) is implicated in the pathogenic process of hepatitis B infection. Therefore, we evaluated the association of PvuII (rs2234693) and XbaI (rs9340799) in ESR1 and HBV infection in Guangxi Zhuang populations.

METHODS

A total of 389 subjects were divided into four groups: 112 patients with chronic hepatitis B (CHB), 65 patients with hepatitis B virus (HBV)-related liver cirrhosis (LC), 107 patients with HBV-related hepatocellular carcinoma (HCC), and 105 healthy controls. The polymerase chain reaction-restriction fragment length polymorphism strategy was used to detect ESR1 gene PvuII and XbaI polymorphisms.

RESULTS

Compared with healthy controls, binary logistic regression analyses show that the CC genotype of PvuII was associated with a significantly increased susceptibility to CHB compared with the TT genotype (OR=1.760, 95% CI 1.316-2.831; p=0.044). The PvuII CC genotype was also associated with significantly increased risk of HBV-related LC (OR=1.921, 95% CI 1.342-2.478; p=0.043). Similarly, the subjects bearing the homozygous CC genotype of PvuII polymorphism also had more than a 1.7-fold increased risk for development of HCC (OR=1.748, 95% CI 1.313-2.787; p=0.010) compared with those bearing the TT genotype. Furthermore, the AC haplotype was associated with a significantly increased risk of HCC with an OR of 1.456 (p=0.003). In contrast, there were no significant differences in the genotype and allele of XbaI polymorphisms in the ESR1 gene between the groups of patients and healthy controls. In addition, ESR1 polymorphisms were not significantly associated with susceptibility to HBV-related HCC when using CHB and LC patients as references.

CONCLUSION

We conclude that the CC genotype of PvuII in ESR1 is associated with an increased risk of CHB, HBV-related LC and HCC in Guangxi Zhuang populations.

Research resource: Aorta- and liver-specific ERα-binding patterns and gene regulation by estrogen

Estrogen has vascular protective effects in premenopausal women and in women younger than 60 years who are receiving hormone replacement therapy. However, estrogen also increases the risks of breast and uterine cancers and of venous thromboses linked to up-regulation of coagulation factors in the liver. In mouse models, the vasculoprotective effects of estrogen are mediated by the estrogen receptor α (ERα) transcription factor. Here, through next-generation sequencing approaches, we show that almost all of the genes regulated by 17β-estradiol (E2) differ between mouse aorta and mouse liver, ex vivo, and that this difference is associated with a distinct genomewide distribution of ERα on chromatin. Bioinformatic analysis of E2-regulated promoters and ERα binding site sequences identify several transcription factors that may determine the tissue specificity of ERα binding and E2-regulated genes, including the enrichment of NF-κB, AML1, and AP1 sites in the promoters of E2 down-regulated inflammatory genes in aorta but not liver. The possible vascular-specific functions of these factors suggest ways in which the protective effects of estrogen could be promoted in the vasculature without incurring negative effects in other tissues.

Novel DNA motif binding activity observed in vivo with an estrogen receptor α mutant mouse

Estrogen receptor α (ERα) interacts with DNA directly or indirectly via other transcription factors, referred to as "tethering." Evidence for tethering is based on in vitro studies and a widely used "KIKO" mouse model containing mutations that prevent direct estrogen response element DNA- binding. KIKO mice are infertile, due in part to the inability of estradiol (E2) to induce uterine epithelial proliferation. To elucidate the molecular events that prevent KIKO uterine growth, regulation of the pro-proliferative E2 target gene Klf4 and of Klf15, a progesterone (P4) target gene that opposes the pro-proliferative activity of KLF4, was evaluated. Klf4 induction was impaired in KIKO uteri; however, Klf15 was induced by E2 rather than by P4. Whole uterine chromatin immunoprecipitation-sequencing revealed enrichment of KIKO ERα binding to hormone response elements (HREs) motifs. KIKO binding to HRE motifs was verified using reporter gene and DNA-binding assays. Because the KIKO ERα has HRE DNA-binding activity, we evaluated the "EAAE" ERα, which has more severe DNA-binding domain mutations, and demonstrated a lack of estrogen response element or HRE reporter gene induction or DNA-binding. The EAAE mouse has an ERα null-like phenotype, with impaired uterine growth and transcriptional activity. Our findings demonstrate that the KIKO mouse model, which has been used by numerous investigators, cannot be used to establish biological functions for ERα tethering, because KIKO ERα effectively stimulates transcription using HRE motifs. The EAAE-ERα DNA-binding domain mutant mouse demonstrates that ERα DNA-binding is crucial for biological and transcriptional processes in reproductive tissues and that ERα tethering may not contribute to estrogen responsiveness in vivo.

Estrogen hormone physiology: reproductive findings from estrogen receptor mutant mice

Estrogen receptors (ERs) play a crucial role in reproduction and normal physiology. The two sub-types of ER (ERα and β) are expressed in various levels in different tissues and selective cell types. Gene targeting technology allowed us to produce lines of mice with disrupted ERα (αERKO) and ERβ genes (βERKO) as well as a compound αβERKO in the whole body. Male and female αERKO mice are infertile. Estrogen, EGF and IGF-1 treatments failed to induce uterine growth and DNA synthesis in αERKO uteri. αERKO females are infertile due to hypoplastic uteri and hyperemic ovaries with no corpora lutea due to persistent LH stimulation from loss of negative feedback. αERKO males are infertile, with testicular atrophy and seminiferous tubule dysmorphogenesis producing decreased spermatogenesis and inactive sperm. βERKO females show arrested folliculogenesis and subfertility. Ovarian analyses indicate differential gene expression related to ovulatory stimulation deficits including lack of LH, PR, Cyp19 and Cox2 expression. A unique ovarian phenotype is found only in αβERKO females showing transdifferentiation of granulosa cells to Sertoli cells. We describe here several novel mouse models which possess ERα gene modification. To understand ERα function in uterine endometrial epithelial cells, we generated a tissue selective ERα gene disrupted mouse model, the uterine epithelial-specific ERα knockout (UtEpiαERKO). To understand the physiological role of ERα functional domains, we generated a mouse model with a mutation in the ligand dependent transcription activation domain of ERα (AF2ERKI). Findings from the ERα mutant mice suggest that the absence of functional ERα is not lethal and results in significant endocrine effects and altered physiological processes.

The AF-1 activation function of estrogen receptor α is necessary and sufficient for uterine epithelial cell proliferation in vivo

Estrogen receptor-α (ERα) regulates gene transcription through the 2 activation functions (AFs) AF-1 and AF-2. The crucial role of ERαAF-2 was previously demonstrated for endometrial proliferative action of 17β-estradiol (E2). Here, we investigated the role of ERαAF-1 in the regulation of gene transcription and cell proliferation in the uterus. We show that acute treatment with E2 or tamoxifen, which selectively activates ERαAF-1, similarly regulate the expression of a uterine set of estrogen-dependent genes as well as epithelial cell proliferation in the uterus of wild-type mice. These effects were abrogated in mice lacking ERαAF-1 (ERαAF-1(0)). Four weeks of E2 treatment led to uterine hypertrophy and sustained luminal epithelial and stromal cell proliferation in wild-type mice, but not in ERαAF-1(0) mice. However, ERαAF-1(0) mice still presented a moderate uterine hypertrophy essentially due to a stromal edema, potentially due to the persistence of Vegf-a induction. Epithelial apoptosis is largely decreased in these ERαAF-1(0) uteri, and response to progesterone is also altered. Finally, E2-induced proliferation of an ERα-positive epithelial cancer cell line was also inhibited by overexpression of an inducible ERα isoform lacking AF-1. Altogether, these data highlight the crucial role of ERαAF-1 in the E2-induced proliferative response in vitro and in vivo. Because ERαAF-1 was previously reported to be dispensable for several E2 extrareproductive protective effects, an optimal ERα modulation could be obtained using molecules activating ERα with a minimal ERαAF-1 action.

Pharmacological estrogen administration causes a FSH-independent osteo-anabolic effect requiring ER alpha in osteoblasts

Postmenopausal osteoporosis is characterized by declining estrogen levels, and estrogen replacement therapy has been proven beneficial for preventing bone loss in affected women. While the physiological functions of estrogen in bone, primarily the inhibition of bone resorption, have been studied extensively, the effects of pharmacological estrogen administration are still poorly characterized. Since elevated levels of follicle-stimulating hormone (FSH) have been suggested to be involved in postmenopausal bone loss, we investigated whether the skeletal response to pharmacological estrogen administration is mediated in a FSH-dependent manner. Therefore, we treated wildtype and FSHβ-deficicent (Fshb^−/−) mice with estrogen for 4 weeks and subsequently analyzed their skeletal phenotype. Here we observed that estrogen treatment resulted in a significant increase of trabecular and cortical bone mass in both, wildtype and Fshb^−/− mice. Unexpectedly, this FSH-independent pharmacological effect of estrogen was not caused by influencing bone resorption, but primarily by increasing bone formation. To understand the cellular and molecular nature of this osteo-anabolic effect we next administered estrogen to mouse models carrying cell specific mutant alleles of the estrogen receptor alpha (ERα). Here we found that the response to pharmacological estrogen administration was not affected by ERα inactivation in osteoclasts, while it was blunted in mice lacking the ERα in osteoblasts or in mice carrying a mutant ERα incapable of DNA binding. Taken together, our findings reveal a previously unknown osteo-anabolic effect of pharmacological estrogen administration, which is independent of FSH and requires DNA-binding of ERα in osteoblasts.

Estrogen receptor alpha gene polymorphisms and risk of HBV-related acute liver failure in the Chinese population

BACKGROUND

The sexual dimorphism of hepatitis B virus (HBV) -related liver diseases is related with estrogen and its receptors. Recent reports indicate that abnormal expression of estrogen receptor alpha (ESR1) may be a hallmark for the progression of liver disease and HBV carriers presenting variant ESR1 have an extremely aggressive clinical course. Here we examine whether the ESR1 polymorphisms or its haplotypes are related to HBV-related acute liver failure (ALF) risk among chronic HBV carriers in a Chinese population.

METHODS

A total of 1216 unrelated Han Chinese HBV carriers were recruited in this hospital-based case-control study, including 359 HBV surface antigen (HBsAg) carriers affected with ALF and 857 asymptomatic HBsAg carriers. Two ESR1 haplotype tagging polymorphisms, c.30 T > C (rs2077647) and c.453-397 T > C (rs2234693), were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay.

RESULTS

We observed a significantly increased susceptibility to HBV-ALF associated with the c.30 C allele (P = 8.65 × 10-4), c.453-397 C allele (5.37 × 10-4) and [c.30 C; c.453-397 C] haplotype (Dominant model, P =0.0004, odds ratio = 1.53, 95% CI 1.23 ~ 1.96) compared with the T alleles and [c.30 T; c.453-397 T] haplotype of c.30 T > C and c.453-397 T > C polymorphisms, respectively.

CONCLUSIONS

Our study suggests that [c.30 C; c.453-397 C] haplotype may be a risk factor for genetic susceptibility to HBV-related ALF in the Chinese population. It also emphasizes the importance of ESR1 in the pathophysiology of HBV-related ALF on the population level.

Estradiol release kinetics determine tissue response in ovariectomized rats

Estrogen replacement is an effective therapy of postmenopausal symptoms such as hot flushes, bone loss, and vaginal dryness. Undesired estrogen effects are the stimulation of uterine and mammary gland epithelial cell proliferation as well as hepatic estrogenicity. In this study, we examined the influence of different estradiol release kinetics on tissue responsivity in ovariectomized (OVX) rats. Pulsed release kinetics was achieved by ip or sc administration of estradiol dissolved in physiological saline containing 10% ethanol (EtOH/NaCl) whereas continuous release kinetics was achieved by sc injection of estradiol dissolved in benzylbenzoate/ricinus oil (1+4, vol/vol). Initial 3-d experiments in OVX rats showed that pulsed ip estradiol administration had profoundly reduced stimulatory effects on the uterus and the liver compared with continuous release kinetics. On the other hand, both administration forms prevented severe vaginal atrophy. Based on these results, we compared the effects of pulsed (sc in EtOH/NaCl) vs. continuous (sc in benzylbenzoate/ricinus oil) estradiol release kinetics on bone, uterus, mammary gland, and liver in a 4-month study in OVX rats. Ovariectomy-induced bone loss was prevented by both administration regimes. However, pulsed estradiol resulted in lower uterine weight, reduced induction of hepatic gene expression, and reduced mammary epithelial hyperplasia relative to continuous estradiol exposure. We conclude that organ responsivity is influenced by different hormone release kinetics, a fact that might be exploited to reduce undesired estradiol effects in postmenopausal women.

Phosphorylation of serine 212 confers novel activity to human estrogen receptor α

Estrogen receptor α (ERα) can be phosphorylated at various residues, one of which is serine 212 in the DNA binding domain. The majority of human nuclear receptors conserves, as a motif, this serine residue within their DNA binding domain. Among these nuclear receptors, phosphorylation of the corresponding threonine 38 in the nuclear receptor CAR is essential for determining its activity [9]. Here, we have investigated the role of phosphorylated serine 212 in the regulation of ERα activity by comparing it with serine 236, another potential phosphorylation site within the DNA binding domain, and demonstrated that phosphorylation of serine 212 confers upon ERα a distinct activity regulating gene expression in Huh-7 cells. In Western blot analysis, wild type ERα and mutants ERα S212A, ERα S212D, ERα S236A and ERα S236D were equally expressed in the nucleus, thus indicating that phosphorylation does not determine nuclear localization of ERα. ERα S212D, but not ERα S236D, retained its capability of activating an ERE-reporter gene in luciferase assays. Similar results were also obtained for human ERβ; the ERβ S176D mutant retained its trans-activation activity, but the ERβ S200D mutant did not. cDNA microarray and Ingenuity Pathway Analysis, employed on Huh-7 cells ectopically expressing either ERα S212A or ERα S212D, revealed that phosphorylation of serine 212 enabled ERα to regulate a unique set of genes and cellular functions.

A cis-acting regulatory variation of the estrogen receptor α (ESR1) gene is associated with hepatitis B virus-related liver cirrhosis

The hepatic fibrogenesis and sexual dimorphism of hepatitis B virus-related liver cirrhosis (HBV-LC) are related to estrogen and its receptors. Abnormal expression of estrogen receptor α (ESR1) is implicated in the development of cirrhosis in both animal models and humans. Here, we examine whether the ESR1 polymorphisms are related to HBV-LC risk among chronic HBV carriers, and we investigate the functional significance of positively associated polymorphisms. A total of 2,404 unrelated Chinese HBV carriers were recruited to conduct the two-stage designed case-control study. Two ESR1 haplotype tagging polymorphisms, c.30T>C (rs2077647) and c.453-397T>C (rs2234693), were genotyped in 1,285 patients with HBV-LC and in 1,119 asymptomatic HBV carriers. We observed a significantly increased susceptibility to HBV-LC associated with the c.30C allele (P = 4.2 × 10(-8) ), c.453-397C allele (P = 2.0 × 10(-8) ), and [c.30C; c.453-397C] haplotype (Dominant model, P = 8.85 × 10(-10) , odds ratio = 1.50, 95% CI 1.32∼1.71) compared with the T alleles and (c.30T; c.453-397T) haplotype of c.30T>C and c.453-397T>C polymorphisms, respectively. Functional analyses were conducted to verify the biological functions of the associated genetic variations and showed that the c.453-397T>C polymorphism is a novel c.453-397C allele-specific and c-myb-dependent enhancer-like cis-acting regulatory variation and could be part of the genetic variations underlying the susceptibility of individuals to HBV-LC.

Estrogen-like effects of cadmium in vivo do not appear to be mediated via the classical estrogen receptor transcriptional pathway

BACKGROUND

Cadmium (Cd), a ubiquitous food contaminant, has been proposed to be an endocrine disruptor by inducing estrogenic responses in vivo. Several in vitro studies suggested that these effects are mediated via estrogen receptors (ERs).

OBJECTIVE

We performed this study to clarify whether Cd-induced effects in vivo are mediated via classical ER signaling through estrogen responsive element (ERE)-regulated genes or if other signaling pathways are involved.

METHODS

We investigated the estrogenic effects of cadmium chloride (CdCl2) exposure in vivo by applying the Organisation for Economic Co-operation and Development (OECD) rodent uterotrophic bioassay to transgenic ERE-luciferase reporter mice. Immature female mice were injected subcutaneously with CdCl2 (5, 50, or 500 µg/kg body weight) or with 17α-ethinylestradiol (EE2) on 3 consecutive days. We examined uterine weight and histology, vaginal opening, body and organ weights, Cd tissue retention, activation of mitogen-activated protein kinase (MAPK) pathways, and ERE-dependent luciferase expression.

RESULTS

CdCl2 increased the height of the uterine luminal epithelium in a dose-dependent manner without increasing the uterine wet weight, altering the timing of vaginal opening, or affecting the luciferase activity in reproductive or nonreproductive organs. However, we observed changes in the phosphorylation of mouse double minute 2 oncoprotein (Mdm2) and extracellular signal-regulated kinase (Erk1/2) in the liver after CdCl2 exposure. As we expected, EE2 advanced vaginal opening and increased uterine epithelial height, uterine wet weight, and luciferase activity in various tissues.

CONCLUSION

Our data suggest that Cd exposure induces a limited spectrum of estrogenic responses in vivo and that, in certain targets, effects of Cd might not be mediated via classical ER signaling through ERE-regulated genes.

17α-Ethinylestradiol rapidly alters transcript levels of murine coagulation genes via estrogen receptor α

BACKGROUND

 Oral estrogen use is associated with changes in plasma levels of many coagulation proteins.

OBJECTIVE

 To gain more insight into the underlying mechanism of estrogen-induced changes in coagulation.

METHODS

 Ovariectomized female mice were used to study the impact of oral 17α-ethinylestradiol (EE) on plasma coagulation, hepatic coagulation gene transcript levels, and dependence on estrogen receptor (ER) α and ERβ.

RESULTS

 Ten days of oral EE treatment resulted in significantly reduced plasma activity levels of factor (F)VIII, FXII, combined FII/FVII/FX and antithrombin, whereas FIX activity significantly increased. Regarding hepatic transcript levels, oral EE caused significant decreases in fibrinogen-γ, FII, FV, FVII, FX, FXII, antithrombin, protein C, protein Z, protein Z inhibitor and heparin cofactor II mRNA levels, whereas FXI levels significantly increased and transcript levels of FVIII, FIX, protein S and α(2) -antiplasmin remained unaffected. All EE-induced coagulation-related changes were neutralized by coadministration of the non-specific ER antagonist ICI182780. In addition, ERα-deficient mice lacked the EE-induced changes in plasma coagulation and hepatic transcript profile, whereas ERβ-deficient mice responded similarly to non-deficient littermate controls. A crucial role for the ER was further demonstrated by its rapid effects on transcription, within 2.5-5 h after EE administration, suggesting a short chain of events leading to its final effects.

CONCLUSIONS

 Oral EE administration has a broad impact on the mouse coagulation profile at the level of both plasma and hepatic mRNA levels. The effects on transcription are rapidly induced, mostly downregulatory, and principally mediated by ERα.

Estrogen-mediated regulation of Igf1 transcription and uterine growth involves direct binding of estrogen receptor alpha to estrogen-responsive elements

Estrogen enables uterine proliferation, which depends on synthesis of the IGF1 growth factor. This proliferation and IGF1 synthesis requires the estrogen receptor (ER), which binds directly to target DNA sequences (estrogen-responsive elements or EREs), or interacts with other transcription factors, such as AP1, to impact transcription. We observe neither uterine growth nor an increase in Igf1 transcript in a mouse with a DNA-binding mutated ER alpha (KIKO), indicating that both Igf1 regulation and uterine proliferation require the DNA binding function of the ER. We identified several potential EREs in the Igf1 gene, and chromatin immunoprecipitation analysis revealed ER alpha binding to these EREs in wild type but not KIKO chromatin. STAT5 is also reported to regulate Igf1; uterine Stat5a transcript is increased by estradiol (E(2)), but not in KIKO or alpha ERKO uteri, indicating ER alpha- and ERE-dependent regulation. ER alpha binds to a potential Stat5a ERE. We hypothesize that E(2) increases Stat5a transcript through ERE binding; that ER alpha, either alone or together with STAT5, then acts to increase Igf1 transcription; and that the resulting lack of IGF1 impairs KIKO uterine growth. Treatment with exogenous IGF1, alone or in combination with E(2), induces proliferation in wild type but not KIKO uteri, indicating that IGF1 replacement does not rescue the KIKO proliferative response. Together, these observations suggest in contrast to previous in vitro studies of IGF-1 regulation involving AP1 motifs that direct ER alpha-DNA interaction is required to increase Igf1 transcription. Additionally, full ER alpha function is needed to mediate other cellular signals of the growth factor for uterine growth.