Activation of βγ subunits of Gi2 and Gi3 proteins by basic secretagogues induces exocytosis through phospholipase Cβ and arachidonate release through phospholipase Cγ in mast cells

Mast cells are activated by Ag-induced clustering of IgE bound to Fc epsilon RI receptors or by basic secretagogues that stimulate pertussis toxin-sensitive heterotrimeric G proteins. The cell response includes the secretion of stored molecules, such as histamine, through exocytosis and of de novo synthesized mediators, such as arachidonate metabolites. The respective roles of G proteins alpha and beta gamma subunits as well as various types of phospholipase C (PLC) in the signaling pathways elicited by basic secretagogues remain unknown. We show that a specific Ab produced against the C-terminus of G alpha (i3) and an anti-recombinant G alpha (i2) Ab inhibited, with additive effects, both exocytosis and arachidonate release from permeabilized rat peritoneal mast cells elicited by the basic secretagogues mastoparan and spermine. A specific Ab directed against G beta gamma dimers prevented both secretions. Anti-PLC beta Abs selectively prevented exocytosis. The selective phosphatidylinositol 3-kinase inhibitor LY 294002 prevented arachidonate release without modifying exocytosis. G beta gamma coimmunoprecipitated with PLC beta and phosphatidylinositol 3-kinase. The anti-PLC gamma1 and anti-phospholipase A, Abs selectively blocked arachidonate release. Protein tyrosine phosphorylation was inhibited by anti-G beta gamma Abs, LY294002, and anti PLC gamma1 Abs. These data show that the early step of basic secretagogue transduction is common to both signaling pathways, involving Jay subunits of G(i2) and G(i3) proteins. Activated G beta gamma interacts, on one hand, with PLC beta to elicit exocytosis and, on the other hand, with phosphatidylinositol 3-kinase to initiate the sequential activation of PLC gamma1, tyrosine kinases, and phospholipase A(2), leading to arachidonate release.