Involvement of g protein betagamma-subunits in diverse signaling induced by Gi/o-coupled receptors: Study using the Xenopus oocyte expression system

• Published in: American Journal of Physiology: Cell Physiology Vol. 56; no. 4; p. C885
• Main Authors: Uezono, Yasuhito, Kaibara, Muneshige, Murasaki, Osamu, Taniyama, Kohtaro
• Format: Journal Article
• Language: English
• Published: Bethesda American Physiological Society 01.10.2004
• Subjects: Cells; Cystic fibrosis; Genes; Proteins; Reproductive system
• ISSN: 0363-6143; 1522-1563

We studied the functions of [beta][gamma]-subunits of Gi/o protein using the Xenopus oocyte expression system. Isoproterenol (ISO) elicited cAMP production and slowly activating Cl- currents in oocytes expressing beta2-adrenoceptor and the protein kinase A-dependent Cl- channel encoded by the cystic fibrosis transmembrane conductance regulator (CFTR) gene. 5-Hydroxytryptamine (5-HT), [D-Ala2, D-Leu5]-enkephalin (DADLE), and baclofen enhanced ISO-induced cAMP levels and CFTR currents in oocytes expressing beta2-adrenoceptor-CFTR and 5-HT1A receptor (5-HT1AR), delta-opioid receptor, or GABAB receptor, respectively. 5-HT also enhanced pituitary adenylate cyclase activating peptide (PACAP) 38-induced cAMP levels and CFTR currents in oocytes expressing PACAP receptor, CFTR and 5-HT1AR. The 5-HT-induced enhancement of Gs-coupled receptor-mediated currents was abrogated by pretreatment with pertussis toxin (PTX) and coexpression of G transducin alpha(Gt[alpha]). The 5-HT-induced enhancement was further augmented by coexpression of the G-activated form of adenylate cyclase (AC) type II but not AC type III. Thus [beta][gamma]-subunits of Gi/o protein contribute to the enhancement of Gs-coupled receptor-mediated responses. 5-HT and DADLE did not elicit any currents in oocytes expressing 5-HT1AR or delta-opioid receptor alone. They elicited Ca2+-activated Cl- currents in oocytes coexpressing these receptors with the G-activated form of phospholipase C (PLC)-beta2 but not with PLC-beta1. These currents were inhibited by pretreatment with PTX and coexpression of Gt, suggesting that [beta][gamma]-subunits of Gi/o protein activate PLC-beta2 and then cause intracellular Ca2+ mobilization. Our results indicate that [beta][gamma]-subunits of Gi/o protein participate in diverse intracellular signals, enhancement of Gs-coupled receptor-mediated responses, and intracellular Ca2+ mobilization. [PUBLICATION ABSTRACT]