Different forms of phospholipase A2, together with pertussis toxin-sensitive G-proteins, [Ca2+]i (intracellular Ca2+ concentration), protein kinase C, calmodulin, protein tyrosine kinases, mitogen-activated protein kinases and Ca2+/calmodulin-dependent protein kinase appear to play a role in agonist-mediated release of arachidonic acid. Here we report that fibroblasts from 14-day-old mouse embryos with inactivated Gi2α (α-subunit of the heterotrimeric G-protein Gi2) gene display a marked decrease in the ability of lysophosphatidic acid, thrombin and Ca2+ ionophores to release arachidonic acid compared with their normal counterparts. The requirement for Gi2α in the release of arachidonic acid following increased [Ca2+]i may be explained by the incomplete translocation of cytosolic phospholipase A2 observed in Gi2α-deficient cells. Paradoxically, inactivation of the Gi2α gene resulted in up-regulation of bradykinin receptors and their coupling to increased arachidonic acid release, phospholipase C activity and [Ca2+]i. A concomitant increase in basal phospholipase C activity was also observed in the Gi2α-deficient cells. These observations establish a pleiotropic and essential role for Gi2α in receptor-phospholipase coupling that contrasts with its less obligatory participation in agonist-mediated inhibition of adenylate cyclase.
In memory of Dr. M. Leonardo Satz (deceased 10 October 1997).
Present address and address for correspondence: Rammelkamp Center for Education and Research, MetroHealth Medical Center, 2500 MetroHealth Drive, Cleveland, OH 44109, U.S.A. (e-mail email@example.com).