Conservation of mechanisms mediating gonadotrophin-releasing hormone 1 stimulation of human luteinizing hormone beta subunit transcription.
Gonadotrophin-releasing hormone (GNRH1) regulates pituitary luteinizing hormone (LH). Previous studies have delineated a mechanism for GNRH1-induced LHbeta subunit gene (Lhb) transcription, the rate-limiting step in LH production. GNRH1 induces expression of early growth response 1 (EGR1), which interacts with steroidogenic factor 1 (SF1) and paired-like homeodomain transcription factor 1 (PITX1) to regulate Lhb promoter activity. Though the cis-elements for these factors are conserved across species, regulation of human LHB transcription has not been thoroughly investigated. We therefore characterized LHB transcriptional regulation by GNRH1 using promoter-reporter analyses in LbetaT2 cells. GNRH1 stimulated LHB transcription via an extracellular signal-regulated kinase 1/2 pathway. EGR1 bound to two binding sites on the LHB promoter and this binding was increased by GNRH1. Mutation of either site or knockdown of endogenous EGR1 decreased basal and/or GNRH1-regulated promoter activity. The human LHB promoter also contains low and high affinity SF1 binding sites. Mutation of these elements or depletion of endogenous SF1 impaired basal and ligand-induced transcription. Knockdown of PITX1 or PITX2 isoforms impaired GNRH1 induction, and endogenous PITX1 bound to the candidate PITX binding site on the LHB promoter. Thus, the mechanism described for GNRH1 regulation of Lhb in other species is largely conserved for human LHB. We also uncover a previously unappreciated role for PITX2 isoforms in this process.
Fortin
Jérôme
J
Department of Pharmacology and Therapeutics, McGill University, QC, Canada.
Lamba
Pankaj
P
Wang
Ying
Y
Bernard
Daniel J
DJ
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics / Q000502:physiology; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D051766:Early Growth Response Protein 1 / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D005786:Gene Expression Regulation; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000502:physiology; D008969:Molecular Sequence Data; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D011485:Protein Binding; D012689:Sequence Homology, Nucleic Acid; D054339:Steroidogenic Factor 1 / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects* / Q000235:genetics; D000097577:Homeobox Protein PITX2
D051766:Early Growth Response Protein 1; D007987:Gonadotropin-Releasing Hormone; D018398:Homeodomain Proteins; D037101:Luteinizing Hormone, beta Subunit; D048052:Mitogen-Activated Protein Kinase 3; D051761:Paired Box Transcription Factors; D054339:Steroidogenic Factor 1; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2; C497325:EGR1 protein, human; C101485:homeobox protein PITX1