Egr-1 binds the GnRH promoter to mediate the increase in gene expression by insulin

Abstract

SUMMARYInsulin increases gonadotropin-releasing hormone (GnRH) gene expression in in vitro models of GnRH neurons. Early growth response-1 (Egr-1) is a transcription factor that mediates the effect of insulin on target genes. In the GN11 cell line-an immortalized GnRH-secreting neuronal cell line -insulin maximally increases Egr-1 mRNA after 30 minutes of treatment and Egr-1 protein and GnRH mRNA after 60 minutes of treatment. Egr-1 small interfering RNA blocks the insulin-induced increase in GnRH promoter activity, measured as luciferase expression. Chromatin immunoprecipitation using Egr-1 antibody precipitates DNA in a proximal region of the GnRH promoter but not DNA in a distal region. Mutagenesis of a putative Egr-1 binding site within the proximal region blocks the insulin-induced increase in GnRH promoter activity. Thus, Egr-1 binds the GnRH promoter at a site between −67 and −76 bp from the transcriptional start site to mediate the insulin induced increase in GnRH gene transcription.

Divergent roles of growth factors in the GnRH regulation of puberty in mice

“…The NIRKO mice exhibited obesity with associated metabolic derangements including insulin and leptin resistance and hypertriglyceridemia, raising the possibility that the infertility was secondary to the dysregulated hormonal milieu rather than the loss of IRs in neurons. In vitro, low concentrations of insulin that do not activate the IGF-1R have been shown to increase GnRH gene expression (14) in GnRH-secreting immortalized cell lines. Insulin also increases GnRH pulsatile secretion (16), suggesting that insulin pathways can be activated in the GnRH neuron.…”

“…GnRH neurons contain both insulin receptors (IRs) and IGF-1 receptors (IGF-1Rs) (11)(12)(13). In vitro stimulation of GnRH neurons with insulin increases GnRH expression and release (11,(14)(15)(16). IGF-1 stimulation also increases GnRH expression (17,18) and release (19) in vitro.…”

An Arf-Egr-C/EBPβ Pathway Linked to Ras-Induced Senescence and Cancer

“…pWZL(hygro)-H-Ras V12 was obtained from K. Vousden. pSuperRetro-(puro)-shEgr1 (where shEgr1 is short hairpin RNA [shRNA] targeting Egr1) was constructed using the short hairpin sequences described by DiVall et al (16); pSirenRetroQ(puro)-shEgr2 was kindly provided by J. M. Friedman. Oligonucleotides encoding short hairpin transcripts targeting Egr3 and Egr4 were inserted between the BamHI and EcoRI sites of pSirenRetroQ(puro) (Clontech).…”

Regulation of gonadotropin-releasing hormone-1 gene transcription by members of the purine-rich element-binding protein family

“…In the mouse, the neuron-specific expression of GnRH1 was found to be highly dependent on the proximal promoter region (Ϫ356 to Ϫ249 bp), where two Otx2 binding sites were found (47). The MAP kinase pathway (46) and another proximal promoter region (Ϫ75 to Ϫ67 bp) binding protein, early growth response gene (17), were found to be responsible for insulin-induced mouse GnRH1 expression. In contrast, chicken ovalbumin upstream promoter-TFI or C/EBP␤ may be involved in the melatoninmediated repression of rat GnRH1 gene expression (29).…”