ERα In Mice Research Articles

Immunoprecipitation Analyses of Estrogen Receptor α Phosphorylated at Serine 216 in the Mouse Liver.

Estrogen receptor α (ERα) conserves a phosphorylation motif at Serine 216. This site constitutes a protein kinase C phosphorylation motif located within the DNA binding domain (DBD) of ERα. The liver plays a critical role in the regulation of metabolism of various xenobiotics, fatty acids, and cholesterol or endogenous compounds. Moreover, numerous metabolizing enzymes are mainly expressed in the liver. In this chapter, we describe several practical experimental procedures confirming that mouse ERα is phosphorylated at serine 216 in livers upon phenobarbital (PB) treatment. Also, this phosphorylation regulates the expression of estrogen sulfotransferase gene (SULT1E1) which has an important role to sulfate and inactivate estrogen. In response to PB, the conserved motif within the DBD activates the Sult1e1 gene. When this motif was mutated, the activation of Sult1e1 was suppressed significantly. This chapter also describes the use of a phospho-peptide antibody (αP-S216) in the chromatin immunoprecipitation (ChIP) assay, and the co-immunoprecipitation (Co-IP) assay visualized by Western blot analysis.

Detection and Functional Analysis of Estrogen Receptor α Phosphorylated at Serine 216 in Mouse Neutrophils.

Serine 216 constitutes a protein kinase C phosphorylation motif located within the DNA binding domain of estrogen receptor α (ERα). In this chapter, we present experimental procedures confirming that mouse ERα is phosphorylated at serine 216 in peripheral blood neutrophils and in neutrophils that infiltrate the uterus, as well as the role of phosphoserine 216 in neutrophil migration. A phospho-peptide antibody (αP-S216) was utilized in Western blot, immunohistochemistry, and double immunofluorescence staining to detect this phosphorylation of an endogenous ERα. Both immunohistochemistry (with αP-S216 or neutrophil marker Ly6G antibody) and double immunofluorescence staining of mouse uterine sections prepared from C3H/HeNCrIBR females revealed that phosphorylated ERα was expressed in all infiltrating neutrophils during hormonal cycles but not in any other of the other uterine cells. Neutrophils infiltrate the uterus from the bloodstream. White blood cells (WBC) were prepared from peripheral blood of C3H/HeNCrIBR females or males and double immunostained. Blood neutrophils also expressed phosphorylated ERα but in only about 20% of cells in both sexes. Only the neutrophils expressing phosphorylated ERα spontaneously migrated in in vitro Transwell migration assays and infiltrated the uterus in mice.

Effects of ERα gene overexpression on bone mineral density and calcium and phosphorus metabolism inovariectomized osteoporosis mice

Objective: To investigate the effects of estrogen receptor α (ERα) gene overexpression on bone metabolism and calcium and phosphorus metabolism in ovariectomized osteoporosis mice, and to provide experimental basis for targeted gene therapy of osteoporosis. Methods: Thirty SPF female mice were randomly divided into sham operation group, model group and ERα overexpression group with 10 mice in each group. After the model was established, the ERα overexpression group was transfected with recombinant adenovirus vector carrying mouse ERα gene by intraspinal injection. The model group was transfected with empty virus, and the sham operation group was not treated. The expression of ERα gene in bone tissue of mice was detected by quantitative Real-time PCR (qRT-PCR). Bone mineral density (BMD) of mouse femur was measured after modeling. Trabecular number (Tb.N), trabecular thickness (Tb.Th), trabecular segregation (Tb.Sp), bone volume fraction (BV/TV) and biomechanical strength of femur were measured by micro-CT scanning. Serum levels of calcium (Ca), phosphorus (P), osteocalcin (BGP) and alkaline phosphatase (ALP) were measured by automatic biochemical analyzer. The expressions of tissue inhibitor of metalloproteinases 1 (TIMP-1) and monocyte chemotactic protein 1 (MCP-1) in bone homogenate were detected by Immunohistochemistry. Results: Compared with sham operation group, the expression level of ERα gene in bone tissue of model group was decreased significantly, the levels of BMD, BV/TV, Tb. Th, maximum load, rigidity coefficient, Ca and P were decreased, while the levels of Tb. Sp, BGP and ALP were increased significantly (P＜0.05). Compared with the sham operation group, the expression level of TIMP-1 protein in the bone tissue of the model group was significantly decreased, while that of MCP-1 protein was increased, while that of the ERα overexpression group was increased while that of MCP-1 was decreased (P＜0.05).The levels of ERα gene expression, BMD, BV/TV, TB. Th, maximum load, rigidity coefficient, Ca and P in the ERα overexpression group were significantly higher than those in the model group, while Tb. Sp, BGP and ALP were significantly lower (P＜0.05). Compared with the sham operation group, mean optical density of TIMP-1 in the bone tissue of the model group was significantly decreased, while that of MCP-1 was significantly increased, and that of the ERα overexpression group was significantly increased while that of MCP-1 was significantly decreased (P＜0.05). Conclusion: ERα gene overexpression can improve osteoporosis by regulating bone mineral density, bone parameters, bone metabolism, calcium and phosphorus metabolic indicators and the expression levels of TIMP-1 and MCP-1 in tissues.

Impaired Female Reproductive Function in A Novel Estrogen Receptor Alpha Hypomorphic Mouse Model

IntroductionEstrogen signaling plays an important role in the regulation of both energy homeostasis and reproductive function. Human and animal studies indicate that the metabolic actions of estrogen signaling are primarily mediated by estrogen receptor alpha (ERα). Both human and mouse ERα genes show remarkable heterogeneity due to complicated alternative splicing, which results in a wide variety of variant transcripts with different protein products or a common protein. However, functional significance of this ERα genomic complexity has not been well documented. Here we generated a novel mouse model in which ERα expression was differentially affected in various tissues, and examined their body weight change and reproduction.MethodUsing CRISPR/Cas9 technology, we introduced a loxP‐flanked sequence containing En2 splice acceptor, a green fluorescent marker with mitochondrial localization signal and DNA translation stop signals before the first coding exon of mouse ERα gene for the potential restoration of the ERα expression.ResultsERα protein expressions were significantly reduced in pituitary (~37%) and ovary (~67%), but not in brain, of the homozygous mutant female compared to those of controls, indicating that unknown elements important for ERα tissue‐specific expression were affected. In contrast to body weight gain observed in previous studies of ERα knockout female mice, our hypomorphic mutant females did not show significant body weight gain. On the other hand, virginal smears from the mutant females rarely showed typical estrus stage. Uterine wet weight was significantly lower in the mutant female mice compared to the controls, indicating abnormal reproductive system. Continuous mating study further confirmed delayed pregnancy and inability to have alive newborns in the mutant female mice.ConclusionEstrogen receptor alpha protein expression varies among tissues in terms of the level and pattern of splicing variants. Splicing variant‐specific ERα functions are not fully elucidated. Our results suggest that a particular variant affected in our mouse model is less critical for proper functioning of systems involved in estrogen‐regulated energy metabolism, but indispensable for some aspects of female reproductive function.

Estrogen receptor inhibition enhances cold-induced adipocyte beiging and glucose tolerance.

Background Low estrogen states, exemplified by postmenopausal women, are associated with increased adiposity and metabolic dysfunction. We recently reported a paradox, in which a conditional estrogen receptor-alpha (ERα) mutant mouse shows a hyper-metabolic phenotype with enhanced brown/beige cell formation (“browning/beiging”).Hypothesis These observations led us to consider that although systemic deficiency of estrogen or ERα in mice results in obesity and glucose intolerance at room temperature, cold exposure might induce enhanced browning/beiging and improve glucose metabolism.Methods and results Remarkably, studying cold-exposure in mouse models of inhibited estrogen signaling - ERαKO mice, ovariectomy, and treatment with the ERα antagonist Fulvestrant - supported this notion. ERα/estrogen-deficient mice demonstrated enhanced cold-induced beiging, reduced adiposity and improved glucose tolerance. Fulvestrant was also effective in diet-induced obesity settings. Mechanistically, ERα inhibition sensitized cell-autonomous beige cell differentiation and stimulation, including β3-adrenoreceptor-dependent adipocyte beiging.Conclusion Taken together, our findings highlight a therapeutic potential for obese/diabetic postmenopausal patients; cold exposure is therefore predicted to metabolically benefit those patients.

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

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

Determine the Role of FSH Receptor Binding Inhibitor in Regulating Ovarian Follicles Development and Expression of FSHR and ERα in Mice.

Mice of FRBI-1, FRBI-2, and FRBI-3 groups were intramuscularly injected with 20, 30, and 40mg/kg, respectively, for five consecutive days. Ovarian weights of three FRBI groups were reduced in comparison with FSH group. Ovarian cortex thicknesses (OCT) of the FRBI-3 group were less than that of the FSH group (P<0.05). As compared to FSH group, there were fewer numbers of secondary follicles (SFs) and mature follicles (MF) on the ovaries of FRBI-treated mice numbers of primary follicles (PFs) and SFs also decreased. In FRBI-3 mice, we found that the primordial follicles (POF) were scarcer, the follicles developed poorly, and granulosa cells became apoptosis. SF numbers of FRBI-2 and FRBI-3 groups were less than that of the FSH group on day 20 (P<0.05). Maximum longitudinal diameter (MLD) and transverse diameter (MTD) of three FRBI groups became decreased during the experiment. MLD and MTD of the FRBI-3 group were smaller than FSH group. Levels of FSHR mRNA and protein were less than that of CG and FSH group (P<0.05). ERα protein levels of FRBI group and serum concentrations of FSH and estradiol (E2) in the FRBI-treated mice were decreased when compared to CG and FSH group. In conclusion, FSH treatment could increase the numbers of SF and MF, enhance follicle development, reduce the numbers of SF and MF, and depress the follicular development of mice. Furthermore, FRBI declined the mRNA and protein levels of ERα and FSHR in the ovaries and dropped serum concentrations of FSH and E2 of mice.

Environmental Xenoestrogens Super-Activate a Variant Murine ER Beta in Cholangiocytes.

High systemic levels of oestrogens are cholestatic and primary biliary cholangitis (PBC)—which is characterized by hepatic ductular inflammation—is thought to be triggered by exposure to xenobiotics such as those around landfill sites. Xenoestrogens may be a component of this chemical trigger. We therefore hypothesized that xenoestrogens are present at higher levels in the proximity of landfill sites. To test this hypothesis, soil samples were collected, extracts prepared and biological oestrogenic activity examined using cell-based reporter gene assays. Extracts from several sample sites around a landfill site contained a chemical(s) which activated the human ERα in a dose-dependent manner. Extracts from 3 separate control sampling sites were absent of any detectable activity. The mouse ERα and 2 variant mouse ERβ cDNAs were cloned and extracts from sample sites around a landfill site also activated these receptors. One variant murine ERβ was constitutively active when expressed in cholangiocytes, was readily inactivated by ICI182780 and activated in a dose-responsive, ICI182780-inhibitable manner by oestrogen. However, when this receptor was activated by extracts from landfill site soils, ICI182780 failed to antagonize activation. ERβ was readily detectable in murine cholangiocytes and exposing mice acutely to a pooled ER activating soil extracts also gave rise to a mild cholestatic injury. These data indicate that the environment around landfill sites may contain higher levels of xenoestrogens; that these chemicals have “super-activating” characteristics with a variant ERβ and therefore these chemicals could be a component of a xenobiotic insult that triggers PBC.

Detection and Functional Analysis of Estrogen Receptor α Phosphorylated at Serine 216 in Mouse Neutrophils.

Serine 216 constitutes a protein kinase C phosphorylation motif located within the DNA binding domain of estrogen receptor α (ERα). In this chapter we present experimental procedures confirming that mouse ERα is phosphorylated at serine 216 in peripheral blood neutrophils and in neutrophils that infiltrate the uterus, as well as the role of phosphoserine 216 in neutrophil migration. A phospho-peptide antibody (αP-S216) was utilized in Western blot, immunohistochemistry, and double immunofluorescence staining to detect this phosphorylation of an endogenous ERα. Both immunohistochemistry (with αP-S216 or neutrophil marker Ly6G antibody) and double immunofluorescence staining of mouse uterine sections prepared from C3H/HeNCrIBR females revealed that phosphorylated ERα was expressed in all infiltrating neutrophils during hormonal cycles but not in any other of the other uterine cells. Neutrophils infiltrate the uterus from the blood stream. White blood cells (WBC) were prepared from peripheral blood of C3H/HeNCrIBR females or males and double immunostained. Blood neutrophils also expressed phosphorylated ERα but in only about 20 % of cells in both sexes. Only the neutrophils expressing phosphorylated ERα spontaneously migrated in in vitro Transwell migration assays and infiltrated the uterus in mice.

Sequence to structure approach of estrogen receptor alpha and ligand interactions.

Estrogen receptors (ERs) are steroid receptors located in the cytoplasm and on the nuclear membrane. The sequence similarities of human ERα, mouse ERα, rat ERα, dog ERα, and cat ERα are above 90%, but structures of ERα may different among species. Estrogen can be agonist and antagonist depending on its target organs. This hormone play roles in several diseases including breast cancer. There are variety of the relative binding affinity (RBA) of ER and estrogen species in comparison to 17β-estradiol (E2), which is a natural ligand of both ERα and ERβ. The RBA of the estrogen species are as following: diethyl stilbestrol (DES)>hexestrol>dienestrol>17β-estradiol (E2)>17-estradiol>moxestrol>estriol (E3)>4-OH estradiol>estrone-3-sulfate. Estrogen mimetic drugs, selective estrogen receptor modulators (SERMs), have been used as hormonal therapy for ER positive breast cancer and postmenopausal osteoporosis. In the postgenomic era, in silico models have become effective tools for modern drug discovery. These provide three dimensional structures of many transmembrane receptors and enzymes, which are important targets of de novo drug development. The estimated inhibition constants (Ki) from computational model have been used as a screening procedure before in vitro and in vivo studies.

Progression of mouse skin carcinogenesis is associated with increased ERα levels and is repressed by a dominant negative form of ERα.

Estrogen receptors (ER), namely ERα and ERβ, are hormone-activated transcription factors with an important role in carcinogenesis. In the present study, we aimed at elucidating the implication of ERα in skin cancer, using chemically-induced mouse skin tumours, as well as cell lines representing distinct stages of mouse skin oncogenesis. First, using immunohistochemical staining we showed that ERα is markedly increased in aggressive mouse skin tumours in vivo as compared to the papilloma tumours, whereas ERβ levels are low and become even lower in the aggressive spindle tumours of carcinogen-treated mice. Then, using the multistage mouse skin carcinogenesis model, we showed that ERα gradually increases during promotion and progression stages of mouse skin carcinogenesis, peaking at the most aggressive stage, whereas ERβ levels only slightly change throughout skin carcinogenesis. Stable transfection of the aggressive, spindle CarB cells with a dominant negative form of ERα (dnERα) resulted in reduced ERα levels and reduced binding to estrogen responsive elements (ERE)-containing sequences. We characterized two highly conserved EREs on the mouse ERα promoter through which dnERα decreased endogenous ERα levels. The dnERα-transfected CarB cells presented altered protein levels of cytoskeletal and cell adhesion molecules, slower growth rate and impaired anchorage-independent growth in vitro, whereas they gave smaller tumours with extended latency period of tumour onset in vivo. Our findings suggest an implication of ERα in the aggressiveness of spindle mouse skin cancer cells, possibly through regulation of genes affecting cell shape and adhesion, and they also provide hints for the effective targeting of spindle cancer cells by dnERα.

1583 LOSS OF EPITHELIAL OESTROGEN RECEPTOR α INHIBITS OESTROGEN-STIMULATED PROSTATE PROLIFERATION AND SQUAMOUS METAPLASIA VIA IN VIVO TISSUE SELECTIVE KNOCKOUT MODELS

Squamous metaplasia (SQM) is a specific phenotype in response to oestrogen in the prostate and oestrogen receptor (ER) α is required to mediate this response. Previous studies utilizing tissue recombination with seminal vesicle (SV) mesenchyme and prostatic ductal tips from wild type and ERαKO mice suggested that both epithelial and stromal ERα are necessary for SQM. However, tissue recombination is conducted in the renal capsule of immune-deficient mice, in which the microenvironment is different from normal prostate microenvironment in the intact mice. Furthermore, whether the requirement of stromal ERα in the SV for developing SQM is the same as in the prostate is unknown. Therefore, there is a clear need to evaluate the respective roles of ERα in prostate epithelial versus stromal compartments in the intact mouse. Here we generated a mouse model that has selectively lost ERα in either stromal (FSP-ERαKO) or epithelial prostate cells (pes-ERαKO) to determine the requirements of ERα for oestrogen-stimulated prostate proliferation and SQM. Our results indicated that FSP-ERαKO prostates develop full and uniform SQM, which suggests that loss of the majority (∼65%) of stromal ERα will not influence oestrogen-mediated SQM. In contrast, loss of epithelial ERα inhibits oestrogen-mediated prostate growth and SQM evidenced by decreasing cytokertin 10 positive squamous cell stratification and differentiation, by reduced ERα protein expression in SQM compared to wild type mice ERα, and by the presence of normal proliferative activities in the oestrogen-treated pes-ERαKO prostates. These in vivo results suggest that epithelial ERα is required for oestrogen-mediated proliferative response and could be an appropriate target for preventing aberrant oestrogen signalling in the prostate. Copyright  2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The Predominant Proteins that React to the MC-20 Estrogen Receptor Alpha Antibody Differ in Molecular Weight between the Mammary Gland and Uterus in the Mouse and Rat

There are many estrogen receptor α(ERα) antibodies available but few of them target a rodent ERα. Using the MC-20 antibody raised against the C-terminus of mouse ERα, we show in this communication that in the mammary gland of female mice and rats, the wild type (wt) ERα was detected on immunoblots as a dominant protein only during lactation, and the protein was lactating specific as it migrated slightly faster than the 67-kD wt ERα in the uterus, likely due to a different phosphorylation status. In contrast, in the nulliparous, pregnant, involuting and involuted mammary glands, the dominant protein recognized by MC-20 was about 61-kD, which is dubbed herein as "MC-20 reactive protein" or MC20RP in abbreviation as its identity is unknown. Our results showed that it was not derived from proteolysis or de-phosphorylation of the 67-kD ERα and was unlikely to be translated from an ERα mRNA variant. Ovariectomy decreased the lactating specific wt ERα but increased the 61-kD MC20RP in the mammary tumors from MMTV-c-myc transgenic mice but these two proteins in the uterus were unaffected. The 61-kD MC20RP was decreased in the mammary tumors, compared with proliferating mammary glands, in estrogen-treated ACI rats. These results suggest that while the lactating specific wt ERα alone or together with the MC20RP may sustain lactation, the MC20RP may support proliferation of the mammary gland and some mammary tumors.

Loss of epithelial oestrogen receptor α inhibits oestrogen‐stimulated prostate proliferation and squamous metaplasia via in vivo tissue selective knockout models

Squamous metaplasia (SQM) is a specific phenotype in response to oestrogen in the prostate and oestrogen receptor (ER) α is required to mediate this response. Previous studies utilizing tissue recombination with seminal vesicle (SV) mesenchyme and prostatic ductal tips from wild type and ERαKO mice suggested that both epithelial and stromal ERα are necessary for SQM. However, tissue recombination is conducted in the renal capsule of immune-deficient mice, in which the microenvironment is different from normal prostate microenvironment in the intact mice. Furthermore, whether the requirement of stromal ERα in the SV for developing SQM is the same as in the prostate is unknown. Therefore, there is a clear need to evaluate the respective roles of ERα in prostate epithelial versus stromal compartments in the intact mouse. Here we generated a mouse model that has selectively lost ERα in either stromal (FSP-ERαKO) or epithelial prostate cells (pes-ERαKO) to determine the requirements of ERα for oestrogen-stimulated prostate proliferation and SQM. Our results indicated that FSP-ERαKO prostates develop full and uniform SQM, which suggests that loss of the majority (~65%) of stromal ERα will not influence oestrogen-mediated SQM. In contrast, loss of epithelial ERα inhibits oestrogen-mediated prostate growth and SQM evidenced by decreasing cytokertin 10 positive squamous cell stratification and differentiation, by reduced ERα protein expression in SQM compared to wild type mice ERα, and by the presence of normal proliferative activities in the oestrogen-treated pes-ERαKO prostates. These in vivo results suggest that epithelial ERα is required for oestrogen-mediated proliferative response and could be an appropriate target for preventing aberrant oestrogen signalling in the prostate.

Estrogen receptor activation reduces lipid synthesis in pancreatic islets and prevents β cell failure in rodent models of type 2 diabetes

The failure of pancreatic β cells to adapt to an increasing demand for insulin is the major mechanism by which patients progress from insulin resistance to type 2 diabetes (T2D) and is thought to be related to dysfunctional lipid homeostasis within those cells. In multiple animal models of diabetes, females demonstrate relative protection from β cell failure. We previously found that the hormone 17β-estradiol (E2) in part mediates this benefit. Here, we show that treating male Zucker diabetic fatty (ZDF) rats with E2 suppressed synthesis and accumulation of fatty acids and glycerolipids in islets and protected against β cell failure. The antilipogenic actions of E2 were recapitulated by pharmacological activation of estrogen receptor α (ERα) or ERβ in a rat β cell line and in cultured ZDF rat, mouse, and human islets. Pancreas-specific null deletion of ERα in mice (PERα-/-) prevented reduction of lipid synthesis by E2 via a direct action in islets, and PERα-/- mice were predisposed to islet lipid accumulation and β cell dysfunction in response to feeding with a high-fat diet. ER activation inhibited β cell lipid synthesis by suppressing the expression (and activity) of fatty acid synthase via a nonclassical pathway dependent on activated Stat3. Accordingly, pancreas-specific deletion of Stat3 in mice curtailed ER-mediated suppression of lipid synthesis. These data suggest that extranuclear ERs may be promising therapeutic targets to prevent β cell failure in T2D.

Complex organization of the 5′-untranslated region of the mouse estrogen receptor α gene: Identification of numerous mRNA transcripts with distinct 5′-ends

The 5′-untranslated region (5′-UTR) of the estrogen receptor α (ERα) gene plays an important role in determining its tissue-specific expression. We examined the 5′-UTRs of the mouse ERα mRNA variants in depth using the Basic Local Alignment Search Tool (BLAST), rapid amplification of 5′-cDNA ends (5′-RACE) and RT-PCR. We demonstrated the presence of multiple variants containing unique 5′-UTRs. We mapped the cDNA sequences onto the mouse genome, and found that both alternative splicing from four different leader exons (A, C, F1, and H) to exon 1, and combinations of 12 internal exons (X1, X2, X3, X4, F2/X5, X6, X7, X8, X9, X10, X11, and B) generate multiple ERα transcripts. Mouse exon B, that has homologies with human exon B and rat exon 0T, was used as an internal exon, not as a leader exon. RT-PCR analysis revealed distinct expression patterns of the variants, suggesting that the alternative promoter usage and alternative splicing are regulated in a tissue-specific manner. Our results indicate that the genomic organization of the mouse ERα gene is complicated as previously shown in the rat ERα gene. In addition, both alternative promoter usage and alternative splicing contribute to the remarkable mRNA diversity of the mouse ERα gene.

Identification of C-terminally and N-terminally truncated estrogen receptor α variants in the mouse

We re-examined mouse ERα mRNA variants using rapid amplification of cDNA ends (RACE) and RT-PCR. Our analysis showed the presence of several mRNA variants containing unique 5′- or 3′-nucleotide sequences. We mapped the cDNA sequences on the mouse genome, and identified four novel 3′-terminal and 5′-leader exons in the intronic region between exons 4 and 5. RT-PCR analysis revealed that the expression patterns of the C-terminally truncated ERα products (CTERPs) were similar to that of Wild-type ERα and that the N-terminally truncated ERα products (NTERPs) appeared to have different expression profiles. Moreover, we constructed expression vectors and analyzed the subcellular localization and the transcriptional activation abilities of the variant proteins in transfected HEK293 cells using immunocytochemistry and luciferase reporter assay. The CTERP variants localized in the nuclei and constitutively activated estrogen response element (ERE)-driven promoters, while the NTERP variant was located in the extra-nuclear regions and had no ability to activate the ERE promoters in the presence or absence of 10 nM estradiol. Our results indicate that the mouse ERα gene is more complex than previously thought in terms of genomic organization and that alternative splicing and alternative usage of intronic promoters contribute to the remarkable diversity of ERα mRNAs and proteins.

Estrogen receptor subtypes selectively mediate female mouse reproductive abnormalities induced by neonatal exposure to estrogenic chemicals

Perinatal exposure to estrogens such as diethylstilbestrol (DES), and to estrogenic chemicals, induces persistent anovulation caused by alteration of hypothalamic–pituitary–gonadal (HPG) axis, polyovular follicles, uterine abnormalities and persistent vaginal changes in mice. Most activities of estrogenic chemicals are mediated through estrogen receptor α (ERα) and/or ERβ. However, little was known about the relative contribution of the individual ER subtypes in induction of abnormalities. We tested the effects of neonatal exposure to ER selective ligands and DES on female mice. Transactivation assays using mouse ERα and ERβ showed that 10 −10 M DES activated both ER subtypes and that the ERα agonist (propyl pyrazole triol, PPT) and the ERβ agonist (diarylpropionitrile, DPN) selectively activated their respective ERs at 10 −9 M. Neonatal female mice were injected subcutaneously with DES, PPT or DPN and the animals were examined at 13 and 15 weeks of age, respectively. Persistent estrous smears and anovulation were induced in all mice by 0.025–2.5 μg DES and 2.5–25 μg PPT, but not by DPN, suggesting that the observed anovulation was primarily mediated through ERα. Disorganization of uterine musculature and ovary-independent vaginal epithelial cell proliferation accompanied by persistent expression of EGF-related genes and interleukin-1-related genes were also mediated through ERα. In contrast, polyovular follicles were induced by neonatal treatment with both ERα and ERβ ligands, suggesting that ovarian abnormalities are mediated through both ER subtypes.

Identification of the Estrogen Receptor Alpha Gene as a Potential Target of the Transcription Factor FoxL2.

The estrogen receptor alpha (ERα) gene is known to be regulated by the forkhead transcription factors FoxM1 and FoxO3a in breast carcinoma cells. At least eight consensus forkhead response elements (FHREs) have been identified in the human ERα promoter. In this study, we aim to determine if the forkhead transcription factor FoxL2 functions to regulate the ERα gene. FoxL2 is critical to ovarian function during follicullogenesis and has also been shown to play an important role in sex determination. FoxL2 is expressed in granulosa cells during follicular development. Therefore, the KK1 mouse granulosa cell line was chosen as a model system for these studies. We have performed promoter analysis of a 1.5 kB sequence representing the mouse ERα gene promoter to identify putative FoxL2 binding sites (ACAACA). Two such sequences were identified 411 and 449 base pairs upstream of the TATA element. We have also used Real Time RT PCR to determine the effect of FoxL2 over-expression on ERα gene expression. To perform this study, KK1 cells were transiently transfected for 24 hours with either a FoxL2 expression vector or the empty vector pcDNA3.1 as a control. Cells were harvested and total RNA was purified. Real-Time RT PCR was performed using Applied Biosystems (AB) Taqman Assays on the AB 7200 System. AB RQ software was used to determine changes in levels of FoxL2 and ERα mRNA. Upon comparing levels of mRNA in cells over-expressing FoxL2 to the control cells expressing normal levels of FoxL2, we found that the level of FoxL2 mRNA increased upon introduction of the expression vector as expected. However, we were surprised to find that the level of ERα mRNA increased as a result of FoxL2 over-expression. These results suggest that FoxL2 is an activator of ERα gene expression in the KK1 granulosa cell line.

Estradiol regulates alternative splicing of estrogen receptor-α mRNA in differentiated NG108-15 neuronal cells

The biological actions of estrogen are mostly conveyed through interaction with two different types of estrogen receptor (ER), ER-α and ER-β. With regard to ER-α, an alternatively spliced form and its translated product, truncated estrogen receptor product-1 (TERP-1), have been identified in the rat pituitary. TERP-1 has the ability to inhibit the ER binding to DNA response element by forming hetero-dimers with the wild-type ER. Furthermore, TERP-1 expression increased concurrently with serum estrogen levels. Although estrogen also plays important roles in the central nervous system, the existence and regulatory mechanism of alternatively spliced ER-α mRNA expression has remained unclear. The present study evaluated the expression of the alternatively spliced form of the ER-α gene, and examined the influence of a representative ER ligand, 17β-estradiol (E 2), on the expression in differentiated NG108-15 neuronal cells. A real-time RT-PCR analysis using primer sets designed to amplify from exons 3 to 4, exons 4 to 5, exons 5 to 6, exons 6 to 7, and exons 7 to 8 of the mouse ER-α gene revealed the existence of alternatively spliced ER-α mRNA and its putative transcription initiation site, located between exon 4 and exon 5. Although E 2 had no apparent effect on the overall expression of ER-α mRNA, it reduced the incidence of the alternatively spliced form of ER-α. The down-regulation by E 2 predominantly arose via binding to nuclear ERs. The present study demonstrated that alternatively spliced ER-α mRNA is expressed in differentiated NG108-15 neuronal cells, and provides evidence for the functional up-regulation of ER-α via the ligand-binding activation of ERs.