A crucial role for Galphaq/11, but not Galphai/o or Galphas, in gonadotropin-releasing hormone receptor-mediated cell growth inhibition.
GnRH acts on its cognate receptor in pituitary gonadotropes to regulate the biosynthesis and secretion of gonadotropins. It may also have direct extrapituitary actions, including inhibition of cell growth in reproductive malignancies, in which GnRH activation of the MAPK cascades is thought to play a pivotal role. In extrapituitary tissues, GnRH receptor signaling has been postulated to involve coupling of the receptor to different G proteins. We examined the ability of the GnRH receptor to couple directly to Galpha(q/11), Galpha(i/o), and Galpha(s), their roles in the activation of the MAPK cascades, and the subsequent cellular effects. We show that in Galpha(q/11)-negative cells stably expressing the GnRH receptor, GnRH did not induce activation of ERK, jun-N-terminal kinase, or P38 MAPK. In contrast to Galpha(i) or chimeric Galpha(qi5), transfection of Galpha(q) cDNA enabled GnRH to induce phosphorylation of ERK, jun-N-terminal kinase, and P38. Furthermore, no GnRH-mediated cAMP response or inhibition of isoproterenol-induced cAMP accumulation was observed. In another cellular background, [35S]GTPgammaS binding assays confirmed that the GnRH receptor was unable to directly couple to Galpha(i) but could directly interact with Galpha(q/11). Interestingly, GnRH stimulated a marked reduction in cell growth only in cells expressing Galpha(q), and this inhibition could be significantly rescued by blocking ERK activation. We therefore provide direct evidence, in multiple cellular backgrounds, that coupling of the GnRH receptor to Galpha(q/11), but not to Galpha(i/o) or Galpha(s), and consequent activation of ERK plays a crucial role in GnRH-mediated cell death.
White
Colin D
CD
The Medical Research Council Human Reproductive Sciences Unit, The Queen's Medical Research Institute, 47 Little France Crescent, Edinburgh EH16 4TJ, United Kingdom.
Coetsee
Marla
M
Morgan
Kevin
K
Flanagan
Colleen A
CA
Millar
Robert P
RP
Lu
Zhi-Liang
ZL
D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D000242:Cyclic AMP / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D011966:Receptors, LHRH; D011994:Recombinant Proteins; D000242:Cyclic AMP; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs