Estrogen-mediated Regulation of Igf1 Transcription and Uterine Growth Involves Direct Binding of Estrogen Receptor to Estrogen-responsive Elements
ABSTRACT 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.
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ABSTRACT: ERΔ3 transgenic mice expressing a dominant negative estrogen receptor α (ERα) variant lacking the second zinc finger in the DNA binding domain were developed to examine its potential to inhibit estrogen action in vivo. To investigate if ERΔ3 expression influences uterine carcinogenesis, ERΔ3 transgenic mice were exposed to diethylstilbestrol (DES) on post-natal days 1-5. Neonatal DES treatment induced uterine adenocarcinomas in 81% of 8-month-old ERΔ3 mice compared to 49% of wild-type females (p<0.016). ERΔ3 did not inhibit the expression of the estrogen-responsive progesterone receptor and lactoferrin genes in the presence of ERα or modify their expression in ERα knockout (αERKO) mice. Higher circulating 17β-estradiol levels and non-classical signaling by ERΔ3 may be related to the earlier incidence of uterine cancer. These findings indicate that expression of this ERα variant can influence determining events in uterine cancer development and its natural occurrence in the human uterus would unlikely be protective.Reproductive Toxicology 08/2012; 34(4):512-521. DOI:10.1016/j.reprotox.2012.08.005 · 2.77 Impact Factor
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ABSTRACT: Endocrine-disrupting chemicals (EDCs) are widely found in the environment. Estrogen-like activity is attributed to EDCs, such as bisphenol A (BPA), bisphenol AF (BPAF), and zearalenone (Zea), but mechanisms of action and diversity of effects are poorly understood. We used in vitro models to evaluate the mechanistic actions of BPA, BPAF, and Zea on estrogen receptor (ER) α and ERβ. We used three human cell lines (Ishikawa, HeLa, and HepG2) representing three cell types to evaluate the estrogen promoter activity of BPA, BPAF, and Zea on ERα and ERβ. Ishikawa/ERα stable cells were used to determine changes in estrogen response element (ERE)-mediated target gene expression or rapid action-mediated effects. The three EDCs showed strong estrogenic activity as agonists for ERα in a dose-dependent manner. At lower concentrations, BPA acted as an antagonist for ERα in Ishikawa cells and BPAF acted as an antagonist for ERβ in HeLa cells, whereas Zea was only a partial antagonist for ERα. ERE-mediated activation by BPA and BPAF was via the AF-2 function of ERα, but Zea activated via both the AF-1 and AF-2 functions. Endogenous ERα target genes and rapid signaling via the p44/42 MAPK pathway were activated by BPA, BPAF, and Zea. BPA and BPAF can function as EDCs by acting as cell type-specific agonists (≥ 10 nM) or antagonists (≤ 10 nM) for ERα and ERβ. Zea had strong estrogenic activity and activated both the AF-1 and AF-2 functions of ERα. In addition, all three compounds induced the rapid action-mediated response for ERα.Environmental Health Perspectives 04/2012; 120(7):1029-35. DOI:10.1289/ehp.1104689 · 7.03 Impact Factor
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ABSTRACT: Obesity increases the risk of female reproductive tract cancers, but the underlying mechanistic link between the two is ill-defined. Thus, the objective of the current study was to identify obesity-dependent changes in the expression of immediate early (IE) genes that contribute to cell proliferation and differentiation, and epithelial-mesenchymal transition (EMT) genes that promote cell migration. When HeLa cells were treated for 0-48 hr with IGF-1, leptin, TNFα, or IL-6, each individual adipocytokine altered the abundance of IE (cJUN, cFOS, and cMYC) and EMT (SNAI1, SNAI2, and TWIST1) mRNA abundance. For example, IGF-1 increased cJUN and cFOS and decreased cMYC; leptin increased cFOS; IL-6 increased cFOS and cMYC; and TNFα increased cJUN and cFOS mRNA abundance. Likewise, EMT gene expression was altered by IGF-1, TNFα, and IL-6. SNAI1 was increased by IGF-1 and IL-6; SNAI2 was increased by IGF-1 and TNFα; and TWIST1 was increased by TNFα and IL-6. Chronic exposure to adipocytokines also altered EMT gene expression in the whole uterus of obese compared to normal-weight mice. Specifically, there was no difference in cJun, cFos, or cMyc mRNA abundance between normal-weight and obese animals. Snai1, Snai2, and Twist1 mRNA abundance, however, was increased in the uterus of obese females and correlated with increased circulating IGF-1 levels. These data indicate that obesity-dependent alterations in adipocytokine levels regulate the expression of genes associated with cell proliferation and migration, and therefore may provide a plausible mechanism for obesity-dependent increases in cancers of the female reproductive tract.Molecular Reproduction and Development 02/2012; 79(2):128-37. DOI:10.1002/mrd.22006 · 2.68 Impact Factor