Gi protein activation of gonadotropin-releasing hormone-mediated protein dephosphorylation in human endometrial carcinoma.
OBJECTIVE
Gonadotropin-releasing hormone receptor is demonstrated in uterine endometrial carcinomas. This study was performed to determine gonadotropin-releasing hormone receptor-mediated membrane events and to identify the guanosine triphosphate binding protein (G protein) subtypes linked to gonadotropin-releasing hormone receptor in the tumors.


METHODS
Endometrial carcinomas surgically removed had been screened for gonadotropin-releasing hormone receptor expression before plasma membrane isolation. The phosphoprotein level was observed in the phosphorus 32-labeled incorporation from [gamma-32P]adenosine triphosphate into the isolated plasma membranes. The Gi (alpha subunit) protein was detected by immunoblotting and pertussis toxin-catalyzed adenosine diphosphate ribosylation.


RESULTS
Incubation of phosphorus 32-labeled membranes with a gonadotropin-releasing hormone analog in the presence of guanosine thiotriphosphate caused a remarkable loss of phosphoprotein from 35 kd protein. This dephosphorylation action was dose dependent of the gonadotropin-releasing hormone analog, and the maximal effect (90% loss) occurred at 100 nmol/L. Pertussis toxin brought about adenosine diphosphate ribosylation of an immunodetected G alpha i. Gonadotropin-releasing hormone analog alone or guanosine thiotriphosphate alone had no effect. Pretreatment of the membrane with the pertussis toxin completely inhibited gonadotropin-releasing hormone-mediated dephosphorylation of the 35 kd protein.


CONCLUSIONS
These data demonstrate the coupling of gonadotropin-releasing hormone receptor to protein dephosphorylation through Gi, raising the possibility that the antimitogenic action of gonadotropin-releasing hormone may occur by release of the action of protein phosphorylation to promote cell growth.
Imai
A
A
Department of Obstetrics and Gynecology, Gifu University School of Medicine, Japan.
Horibe
S
S
Takagi
A
A
Tamaya
T
T
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D002064:Buserelin / Q000494:pharmacology; D002277:Carcinoma / Q000378:metabolism*; D016889:Endometrial Neoplasms / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D019204:GTP-Binding Proteins / Q000187:drug effects / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D037342:Pertussis Toxin; D010766:Phosphorylation; D011966:Receptors, LHRH / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
C057003:1-(2-nitro)phenylethyl-P(3)-guanosine 5'-O-(3-thio)triphosphate; D018931:Antineoplastic Agents, Hormonal; D011966:Receptors, LHRH; D010566:Virulence Factors, Bordetella; D000246:Adenosine Diphosphate Ribose; D007987:Gonadotropin-Releasing Hormone; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D002064:Buserelin