Early growth response protein 1 binds to the luteinizing hormone-beta promoter and mediates gonadotropin-releasing hormone-stimulated gene expression

The hypothalamic neuropeptide, GnRH, regulates the synthesis and secretion of LH from pituitary gonadotropes. Furthermore, it has been shown that the LH beta-subunit gene is regulated by the transcription factors steroidogeni c factor-1 (SF-1) and early growth response protein 1 (Egr1) in vitro and i n vivo. The present study investigated the roles played by Egr1 and SF-1 in regulating activity of the equine LH beta-subunit promoter in the gonadotr ope cell line, alpha T3-1, and the importance of these factors and cis-acti ng elements in regulation of the promoter by GnRH. All four members of the Egr family were found to induce activity of the equine promoter. The region responsible for induction by Egr was localized to the proximal 185 bp of t he promoter, which contained two Egr response elements. Coexpression of Egr 1 and SF-1 led to a synergistic activation of the equine (e)LH beta promote r. Mutation of any of the Egr or SF-1 response elements attenuated this syn ergism, Endogenous expression of Egr1 in alpha T3-1 cells was not detectabl e under basal conditions, but was rapidly induced after GnRH stimulation. R eexamination of the promoter constructs harboring mutant Egr or SF-1 sites indicated that these sites were required for GnRH induction. In fact, mutat ion of both Egr sites within the eLH beta promoter completely attenuated it s induction by GnRH. Thus, GnRH induces expression of Egr1, which subsequen tly activates the eLH beta promoter. Finally, GnRH not only induced express ion of Egr1, but also its corepressor, NGFI-A (Egr1) binding protein (Nab1) , which can repress Egr1- induced transcription of the eLH beta promoter.