Estrogen-mediated Regulation of Igf1 Transcription and Uterine Growth Involves Direct Binding of Estrogen Receptor α 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␣ (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␣ 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 ␣ERKO uteri, indicating ER␣-and ERE-dependent regulation. ER␣ binds to a potential Stat5a ERE. We hypothesize that E 2 increases Stat5a transcript through ERE binding; that ER␣, 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␣-DNA interaction is required to increase Igf1 transcription. Additionally, full ER␣ function is needed to mediate other cellular signals of the growth factor for uterine growth.

Dispersed Chromosomal Stat5b-binding Elements Mediate Growth Hormone-activated Insulin-like Growth Factor-I Gene Transcription

“…The two Stat5s may serve distinct physiological functions largely because of different tissuelimited patterns of expression (2) but also may potentially interact with unique modifying factors, possibly through their more divergent COOH-terminal transcriptional activation domains (2). The majority of studies examining the roles of Stat5 in GH actions, particularly in vivo, have focused on effects in the liver, where Stat5b predominates over Stat5a (2), and loss of Stat5b alone leads to severe systemic growth defects in both humans and mice (22,25), although a recent report has implicated Stat5a as a potential mediator of IGF-I gene transcription in the uterus (45). Although it has not been determined if Stat5a and Stat5b always recognize the same DNA sites in chromatin, it is likely that they usually do, because in vitro protein-DNA binding studies have yielded identical optimal sequence profiles (7).…”

“…Promoter 1 (P1) is active in all tissues in which IGF-I is expressed, whereas P2 is more restricted in its distribution, functioning primarily in liver, kidney, heart, uterus, and testes (42,44,45). We next looked at the effects of different Stat5b domains on each IGF-I promoter in reconstitution studies in COS-7 cells.…”

Identifying growth hormone-regulated enhancers in the Igf1 locus

“…More broadly, perhaps each individual Stat5b-binding domain in the Igf1 locus differs in its activation dynamics or kinetics and/or responds independently to varying hormone doses or exposures, but collectively the cohort of elements function as a high-content GH dose-dependent rheostat. We can now test these and other hypotheses in our experimental system and subsequently in animal models and begin to elucidate the complex regulatory mechanisms by which GH or other factors (20,32,33,36,44,51) control IGF-I gene expression.…”

Estrogen modulates mesenchyme-epidermis interactions in the adult nipple

“…Upon reviewing the growth factor pathways differentially represented in the KrP fibroblasts as determined by the GO analysis, we found that several of them can be regulated by estrogen in non-nipple tissues (Hewitt et al, 2010;Knabbe et al, 1987;Yokota et al, 2008). Among these is the TGFβ pathway, which has been shown to be inhibited by estrogen signaling components at multiple levels (Cherlet and Murphy, 2007;Colletta et al, 1990), including repression of ligand secretion (Knabbe et al, 1987).…”