Gonadotropin-releasing hormone receptor initiates multiple signaling pathways by exclusively coupling to G(q/11) proteins.
The agonist-bound gonadotropin-releasing hormone (GnRH) receptor engages several distinct signaling cascades, and it has recently been proposed that coupling of a single type of receptor to multiple G proteins (G(q), G(s), and G(i)) is responsible for this behavior. GnRH-dependent signaling was studied in gonadotropic alphaT3-1 cells endogenously expressing the murine receptor and in CHO-K1 (CHO#3) and COS-7 cells transfected with the human GnRH receptor cDNA. In all cell systems studied, GnRH-induced phospholipase C activation and Ca(2+) mobilization was pertussis toxin-insensitive, as was GnRH-mediated extracellular signal-regulated kinase activation. Whereas the G(i)-coupled m2 muscarinic receptor interacted with a chimeric G(s) protein (G(s)i5) containing the C-terminal five amino acids of Galpha(i2), the human GnRH receptor was unable to activate the G protein chimera. GnRH challenge of alphaT3-1, CHO#3 and of GnRH receptor-expressing COS-7 cells did not result in agonist-dependent cAMP formation. GnRH challenge of CHO#3 cells expressing a cAMP-responsive element-driven firefly luciferase did not result in increased reporter gene expression. However, coexpression of the human GnRH receptor and adenylyl cyclase I in COS-7 cells led to clearly discernible GnRH-dependent cAMP formation subsequent to GnRH-elicited rises in [Ca(2+)](i). In alphaT3-1 and CHO#3 cell membranes, addition of [alpha-(32)P]GTP azidoanilide resulted in GnRH receptor-dependent labeling of Galpha(q/11) but not of Galpha(i), Galpha(s) or Galpha(12/13) proteins. Thus, the murine and human GnRH receptors exclusively couple to G proteins of the G(q/11) family. Multiple GnRH-dependent signaling pathways are therefore initiated downstream of the receptor/G protein interface and are not indicative of a multiple G protein coupling potential of the GnRH receptor.
Grosse
R
R
Institut für Pharmakologie, Freie Universität Berlin, Thielallee 69-73, D-14195 Berlin, Germany.
Schmid
A
A
Schöneberg
T
T
Herrlich
A
A
Muhn
P
P
Schultz
G
G
Gudermann
T
T
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002147:Calmodulin / Q000378:metabolism; D006224:Cricetinae; D000242:Cyclic AMP / Q000096:biosynthesis; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D016296:Mutagenesis; D011485:Protein Binding; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D002147:Calmodulin; D011966:Receptors, LHRH; D011993:Recombinant Fusion Proteins; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases