Stimulation of mitogen-activated protein kinase by gonadotropin-releasing hormone in human granulosa-luteal cells.
The present study investigated the activation of mitogen-activated protein kinases (MAPKs) by a GnRH agonist (GnRHa) in human granulosa-luteal cells (hGLCs). The phosphorylation state of p44 and p42 MAPK was examined using antibodies that distinguish phospho-p44/42 MAPK (Thr(202)/Tyr(204)) from total p44/42 MAPK (activated plus inactivated). Activation of MAPK by GnRHa was observed within 5 min and was sustained for 60 min after treatment. GnRHa stimulated MAPK activation in a dose-dependent manner, with maximum stimulation (6.7-fold over basal levels) at 10(-7) M. Pretreatment with a protein kinase C (PKC) inhibitor, GF109203X, completely blocked GnRHa-induced MAPK activation. In addition, pretreatment with a PKC activator, phorbol-12-myristate 13-acetate, potentiated GnRH-induced MAPK activation. These results indicate that GnRHa stimulates MAPK activation through a PKC-dependent pathway in hGLCs, possibly coupled to G(q)alpha protein. MAPK activation was also observed in response to 8-bromo-cAMP or cholera toxin, but not pertussis toxin. Forskolin (50 microM) substantially stimulated a rapid cAMP accumulation, whereas GnRHa (10(-7) M) or pertussis toxin (100 mg/ml) did not affect basal intracellular cAMP levels. Cotreatment of GnRHa (10(-7) M) did not attenuate forskolin- or hCG-stimulated cAMP accumulation. These results suggest that the GnRH receptor is probably not coupled to G(s)alpha or G(i)alpha in hGLCs. Finally, GnRHa (10(-7) M) stimulated a significant increase in Elk-1 phosphorylation and c-fos messenger RNA expression, as revealed by an in vitro kinase assay and Northern blot analysis, respectively. These results clearly demonstrate that GnRH activates the MAPK cascade through a PKC-dependent pathway in the human ovary.
Kang
S K
SK
Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, British Columbia, Canada V6H 3V5.
Tai
C J
CJ
Nathwani
P S
PS
Choi
K C
KC
Leung
P C
PC
D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D003338:Corpus Luteum / Q000166:cytology / Q000201:enzymology*; D000242:Cyclic AMP / Q000378:metabolism; D004268:DNA-Binding Proteins; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists / Q000494:pharmacology*; D006107:Granulosa Cells / Q000201:enzymology*; D006727:Hormone Antagonists / Q000494:pharmacology; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D037342:Pertussis Toxin; D010766:Phosphorylation / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D050807:ets-Domain Protein Elk-1
D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; D004791:Enzyme Inhibitors; D006727:Hormone Antagonists; D009842:Oligopeptides; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D014157:Transcription Factors; D010566:Virulence Factors, Bordetella; D050807:ets-Domain Protein Elk-1; D005576:Colforsin; D007987:Gonadotropin-Releasing Hormone; D002772:Cholera Toxin; C057022:iturelix; D000242:Cyclic AMP; D037342:Pertussis Toxin; D020928:Mitogen-Activated Protein Kinases; D013755:Tetradecanoylphorbol Acetate