Involvement of G(s) and G(i) proteins in dual coupling of the luteinizing hormone receptor to adenylyl cyclase and phospholipase C

Binding of lutropin/choriogonadotropin to its cognate receptor results in the activation of adenylyl cyclase and phospholipase C, The mechanism underlying the generation of this bifurcating signal is presently not known. To analyze the coupling mechanism of the LH receptor, activated G proteins were labeled with [alpha-P-32]GTP azidoanilide and identified by selective immunoprecipitation, In membranes of bovine corpora lutea and of L cells stably expressing the murine LH receptor (LHR cells), human chorionic gonadotropin (hCG) led to incorporation of the label into alpha(s) and alpha(i2). Stimulation of LHR cells or of L cells expressing the M(5) muscarinic receptor (LM5 cells) with the respective agonist resulted in activation of phospholipase C in both cell lines, However, alpha(q) and alpha(11) were only labeled upon stimulation of the Ms muscarinic receptor, Agonist-induced Ca2+ mobilization and inositol phosphate accumulation were partially sensitive to pertussis toxin, and the expression of the beta gamma-stimulable phospholipase C isoforms beta 2 and beta 3 could be demonstrated in LHR cells, Overexpression of phospholipase C-beta 2 led to increased hCG-stimulated inositol phosphate accumulation, and expression of a beta-ARK1 C-terminal polypeptide effectively suppressed hCG-mediated phosphatidylinositol hydrolysis, Thus, the LH receptor couples to both G(s) and G(i), and beta gamma-subunits released from either G protein contribute to the stimulation of phospholipase C-beta isoforms.