Induction of mPer1 expression by GnRH in pituitary gonadotrope cells involves EGR-1.

Academic Article

Abstract

  • We reported earlier that gonadotropin-releasing hormone (GnRH) activates period1 (mPer1) gene expression in immortalized gonadotropes through protein kinase C and p42/44 mitogen-activated protein kinase pathways. GnRH stimulation also leads to the upregulation of early growth response protein 1 (EGR-1), a critical transcription factor for GnRH-induced luteinizing hormone beta (LHbeta) synthesis. The parallels between the GnRH-LHbeta and the GnRH-mPer1 pathways led us to explore whether EGR-1 is involved in the regulation of mPer1 expression in gonadotropes. Of particular interest was the presence of an EGR-1 binding site in the proximal promoter of the mPer1 gene. Stimulation of LbetaT2 gonadotrope cells with a GnRH agonist caused the rapid induction of Egr-1 mRNA, which was rapidly followed by mPer1 expression. Chromatin immunoprecipitation revealed that the mPer1 promoter can bind EGR-1, while site-directed mutagenesis experiments confirmed the involvement of Egr-1 sequences in maintaining basal and allowing GnRH-stimulated mPer1 transcription. By means of RNA interference experiments, it could also be demonstrated that silencing of Egr-1 expression resulted in markedly lower mPer1 transcript levels. This silencing effect of the Egr-1 siRNA could be rescued by transfecting the cells with an EGR-1 overexpression vector. In summary, these results all point to a role for the EGR-1 protein in transactivating both the LHbeta as well as the mPer1 gene in pituitary gonadotrope cells.

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    Keywords

  • Animals, Buserelin, CLOCK Proteins, Chromatin Immunoprecipitation, Early Growth Response Protein 1, Flavonoids, Gene Expression Regulation, Gene Silencing, Genes, Reporter, Gonadotrophs, Gonadotropin-Releasing Hormone, Luciferases, Mice, Mitogen-Activated Protein Kinase 1, Mutagenesis, Site-Directed, Period Circadian Proteins, RNA, Messenger, RNA, Small Interfering, Time Factors

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    Author List

  • Resuehr HES; Resuehr D; Olcese J

    • Start Page

  • 120

    • End Page

  • 125

    • Volume

  • 311

    • Issue

  • 1-2