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

Abstract

Mast cells are activated by Ag-induced clustering of IgE bound to FcεRI 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 α and βγ 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 Gαi3 and an anti-recombinant Gαi2 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 Gβγ dimers prevented both secretions. Anti-PLCβ Abs selectively prevented exocytosis. The selective phosphatidylinositol 3-kinase inhibitor LY 294002 prevented arachidonate release without modifying exocytosis. Gβγ coimmunoprecipitated with PLCβ and phosphatidylinositol 3-kinase. The anti-PLCγ1 and anti-phospholipase A2 Abs selectively blocked arachidonate release. Protein tyrosine phosphorylation was inhibited by anti-Gβγ Abs, LY294002, and anti PLCγ1 Abs. These data show that the early step of basic secretagogue transduction is common to both signaling pathways, involving βγ subunits of Gi2 and Gi3 proteins. Activated Gβγ interacts, on one hand, with PLCβ to elicit exocytosis and, on the other hand, with phosphatidylinositol 3-kinase to initiate the sequential activation of PLCγ1, tyrosine kinases, and phospholipase A2, leading to arachidonate release.

Substance P can stimulate prostaglandin D2 and leukotriene C4 generation without granule exocytosis in murine mast cells

“…that phospholipase-h and -g are in control of mast cell stimulation by basic secretagogues leading to granule exocytosis and arachidonate release, respectively (Ferry et al, 2001). Taken together, these findings support a differential regulation of the respective signal transduction pathways leading to exocytosis and lipid mediator production in mast cells.…”

“…These findings point to an involvement of protein phosphorylation by protein tyrosine kinase(s) and protein kinase C in the substance P-stimulated production of lipid mediators by mast cells. A role for these enzymes has been suggested earlier for stimulation of mast cells by basic secretagogues (Shefler and Sagi-Eisenberg, 2001;Ferry et al, 2001).…”

“…In a recent study, we showed that stimulation of mast cells grown interleukin-3 with substance P is independent of the neurokinin-1 receptor (Van der Kleij et al, 2003) and likely through direct interaction with G proteins (Shefler et al, 1998;Ferry et al, 2001). Our study shows that substance Pinduced lipid mediator production in mouse bone marrowderived mast cells is completely blocked with a specific tyrosine kinase inhibitor, implicating activation of protein tyrosine phosphorylation in arachidonic acid metabolite production.…”

Mast cell activation is differentially affected by heat shock

“…Previous data demonstrated differential regulation of the respective signal transduction pathways leading to exocytosis and lipid mediator production in mast cells [32,33]. Our present findings suggest that heat shock has differential and relatively specific effects on signaling pathways leading to mast cell activation and the release of mast cell mediators.…”

Altered Endothelin-1 Signaling in Production of Thromboxane A2 in Kupffer Cells from Bile Duct Ligated Rats

“…In addition to Gq/G11, it is well documented the  dimer of Gi proteins stimulate the activation of PLC (57,(67)(68)(69)(70)(71). PLC activated by the  dimer of Gi proteins has been demonstrated to mediate the activation of cPLA 2 and release of AA in response to ET-1 (57, 71).…”