title: Differential gonadotropin-releasing hormone stimulation of rat luteinizing hormone subunit gene transcription by calcium influx and mitogen-activated protein kinase-signaling pathways.
abstract: Gonadotropin secretion and gene expression are differentially regulated by hypothalamic GnRH pulses by unknown mechanisms. GnRH stimulates calcium influx through L-type voltage-gated channels and activates phospholipase C, leading to increased protein kinase C (PKC) and mitogen-activated protein kinase activity. We found differential contributions of these pathways to GnRH-stimulated rat LH subunit transcription in pituitary gonadotropes and cell lines. Endogenous transcription of the alpha- and LHbeta-subunits in rat pituitary cells was stimulated by GnRH. Independent PKC activation by phorbol myristate acid stimulated only the alpha-subunit gene. In contrast, an L-channel antagonist (nimodipine) inhibited only LHbeta stimulation by GnRH, and an L-channel agonist (BayK 8644) stimulated only basal LHbeta transcription. GnRH induction of a rat alpha-subunit promoter construct in alphaT3 cells was unaffected by nimodipine or elimination of external calcium, while both treatments eliminated the LHbeta response. Application of a mitogen-activated kinase kinase (MEK) inhibitor (PD098059) decreased basal and GnRH-stimulated alpha-subunit promoter activity and had no effect on LHbeta promoter activity. In pituitary cells from mice bearing an LHbeta promoter-luciferase reporter transgene, GnRH stimulation was inhibited by nimodipine but not by PD098059. Thus, GnRH induction and basal control of the alpha-subunit gene seem to occur through the PKC/mitogen-activated protein kinase pathway, while induction of the LHbeta gene is dependent on calcium influx. Differential signaling from the same receptor may be a mechanism for preferential regulation of transcription.
authors.affiliation: Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville 22908, USA.
authors.forename: J
authors.initials: J
authors.lastname: Weck
authors.forename: P C
authors.initials: PC
authors.lastname: Fallest
authors.forename: L K
authors.initials: LK
authors.lastname: Pitt
authors.forename: M A
authors.initials: MA
authors.lastname: Shupnik
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002460:Cell Line; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism* / Q000494:pharmacology; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D007986:Luteinizing Hormone / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D010902:Pituitary Gland / Q000502:physiology; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D015398:Signal Transduction; D014158:Transcription, Genetic; D014162:Transfection; D019076:Transgenes
chemical_list: D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D008156:Luciferases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium