Regulation of Lhb and Egr1 gene expression by GNRH pulses in rat pituitaries is both c-Jun N-terminal kinase (JNK)- and extracellular signal-regulated kinase (ERK)-dependent.
Pulsatile GNRH regulates the gonadotropin subunit genes in a differential manner, with faster frequencies favoring Lhb gene expression and slower frequencies favoring Fshb. Early growth response 1 (EGR1) is critical for Lhb gene transcription. We examined GNRH regulation of EGR1 and its two corepressors, Ngfi-A-binding proteins 1 and 2 (NAB1 and NAB2), both in vivo and in cultured rat pituitary cells. In rats, fast GNRH pulses (every 30 min) stably induced Egr1 primary transcript (PT) and mRNA 2-fold (P < 0.05) for 1-24 h. In contrast, slow GNRH pulses (every 240 min) increased Egr1 PT at 24 h (6-fold; P < 0.05) but increased Egr1 mRNA 4- to 5-fold between 4 and 24 h. Both GNRH pulse frequencies increased EGR1 protein 3- to 4-fold. In cultured rat pituitary cells, GNRH pulses (every 60 min) increased Egr1 (PT, 2.5- to 3-fold; mRNA, 1.5- to 2-fold; P < 0.05). GNRH pulses had little effect on Nab1/2 PT/mRNAs either in vivo or in vitro. We also examined specific intracellular signaling cascades activated by GNRH. Inhibitors of mitogen-activated protein kinase 8/9 (MAPK8/9 [also known as JNK]; SP600125) and MAP Kinase Kinase 1 (MAP2K1 [also known as MEK1]; PD98059) either blunted or totally suppressed the GNRH induction of Lhb PT and Egr1 PT/mRNA, whereas the MAPK14 (also known as p38) inhibitor SB203580 did not. In summary, pulsatile GNRH stimulates Egr1 gene expression and protein in vivo but not in a frequency-dependent manner. Additionally, GNRH-induced Egr1 gene expression is mediated by MAPK8/9 and MAPK1/3, and both are critical for Lhb gene transcription.
Burger
Laura L
LL
Division of Endocrinology and Metabolism, Department of Medicine, and the Center for Research in Reproduction, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA. llb3k@virginia.edu
Haisenleder
Daniel J
DJ
Aylor
Kevin W
KW
Marshall
John C
JC
D000704:Analysis of Variance; D000818:Animals; D000873:Anthracenes / Q000494:pharmacology; D015153:Blotting, Western; D002478:Cells, Cultured; D051766:Early Growth Response Protein 1 / Q000235:genetics* / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D037101:Luteinizing Hormone, beta Subunit / Q000235:genetics* / Q000378:metabolism; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D008297:Male; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
D000873:Anthracenes; D051766:Early Growth Response Protein 1; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007093:Imidazoles; D037101:Luteinizing Hormone, beta Subunit; D009363:Neoplasm Proteins; D011725:Pyridines; D012333:RNA, Messenger; D012097:Repressor Proteins; C432165:pyrazolanthrone; D007987:Gonadotropin-Releasing Hormone; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one