title: Elk-1, CREB, and MKP-1 regulate Egr-1 expression in gonadotropin-releasing hormone stimulated gonadotrophs.
abstract: Stimulation of gonadotropin-releasing hormone (GnRH) receptors with the GnRH analogue buserelin enhances expression of the zinc finger transcription factor Egr-1 in a pituitary gonadotroph cell line. The signaling cascade is blocked by overexpression of MAP kinase phosphatase-1 that dephosphorylates extracellular signal-regulated protein kinase in the nucleus. Chromatin immunoprecipitation experiments revealed that the phosphorylated form of Elk-1, a key regulator of gene transcription driven by serum response element (SRE), binds to the 5'-upstream region of the Egr-1 gene in buserelin-stimulated gonadotrophs. Expression of a dominant-negative mutant of Elk-1 completely blocked Egr-1 expression, indicating that Elk-1 connects the intracellular signaling cascade elicited by activation of GnRH receptors with transcription of the Egr-1 gene. GnRH receptor activation additionally induced the phosphorylation of CREB, which in its phosphorylated form bound to the Egr-1 gene. Expression of a dominant-negative mutant of CREB reduced GnRH receptor-induced upregulation of Egr-1 expression, indicating that CREB plays a role in the signaling pathway that regulates Egr-1 expression in gonadotrophs. We further identified the genes encoding basic fibroblast growth factor, tumor necrosis factor alpha, and transforming growth factor beta as bona fide target genes of Egr-1 in gonadotrophs. The analysis of gonadotroph cells that express--in addition to GnRH receptors--muscarinic M(3) acetylcholine receptors revealed that the nuclear events connecting GnRH receptors and muscarinic M(3) acetylcholine receptors with the Egr-1 gene are indistinguishable.
authors.affiliation: Department of Medical Biochemistry and Molecular Biology, University of Saarland Medical Center, D-66421 Homburg, Germany.
authors.forename: Sabine I
authors.initials: SI
authors.lastname: Mayer
authors.forename: Gary B
authors.initials: GB
authors.lastname: Willars
authors.forename: Eisuke
authors.initials: E
authors.lastname: Nishida
authors.forename: Gerald
authors.initials: G
authors.lastname: Thiel
mesh_terms: D000818:Animals; D001665:Binding Sites; D002217:Carbachol / Q000494:pharmacology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D054638:Dual Specificity Phosphatase 1 / Q000378:metabolism*; D051766:Early Growth Response Protein 1 / Q000096:biosynthesis / Q000235:genetics*; D052681:Gonadotrophs / Q000187:drug effects / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D051379:Mice; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D015854:Up-Regulation; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism*
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D051766:Early Growth Response Protein 1; D014409:Tumor Necrosis Factor-alpha; D050807:ets-Domain Protein Elk-1; D007987:Gonadotropin-Releasing Hormone; D002217:Carbachol; D054638:Dual Specificity Phosphatase 1