GnRH pulsality and the differential activation of the rat luteinizing hormone subunit genes in the anterior pituitary gland.

: Detailed studies have been focused on the mechanisms by which the rat alpha and LHbeta genes are differentially regulated by GnRH and indicate that differential sensitivity to the second messenger exists in a physiological context. Differential signaling from the GnRH receptor may be a mechanism for preferential regulation of luteinizing hormone subunit gene transcription; however which of these genes are specifically regulated by PKC or calcium and how GnRH pulsatility could preferentially activate individual pathways of second messengers within gonadotrope cells remain unclear. Several transcription factors that have profound effects on basal and/or GnRH-stimulated LHbeta gene promoter activity have been identified: SF-1, Egr-1, Sp-1. A model explaining possible interactions among them in mediating GnRH responsiveness of the LHbeta gene has been proposed: Sp1, SF-1 and Egr-1 form a tripartite GnRH response element which is sensitive to the spacing changes between the upstream Sp1 binding sites and the downstream SF-1/Egr-1 binding elements and SF-1 plays a critical role in integrating the effects of Sp1 and Egr-1. GnRH responsive element located on LHbeta gene promoter in position between -495 to -342 has been identified. At 3'-end of the promoter three Sp-1 binding sites have been identified: position -416, sequence: GGGGGCTGGG and two sites almost completely overlapping, position -403, sequence; GGGGCGGCGCCCA while at the 5'region of the promoter one Sp-1 binding site exists: position -450, sequence: ACCACACCCATTTTTGG. The 5'Sp1 site overlaps a CArG box (at -443 to -434, sequence: CCATTTTTGG) which seems to be essential in LHbeta gene sensitivity for pulsatile GnRH stimulation.