Basic secretagogues activate protein tyrosine phosphorylation and release of arachidonic acid in mast cells via a novel protein kinase C and phosphatidylinositol 3-kinase-dependent mechanism.

Mast cells play a central role in inflammatory and immediate-type allergic reactions. These granulated cells release by a process of regulated exocytosis a variety of biologically active substances which are either preformed (e.g. histamine), or synthesized de novo following activation [e. g. metabolites of arachidonic acid (AA) and multifunctional cytokines]. Exocytosis in mast cells is activated either in response to aggregation of the receptors for immunoglobulin E (FcepsilonRI) or by the direct activation of pertussis toxin-sensitive G-proteins by a class of receptor mimetic agents, collectively known as basic secretagogues of mast cells. In the present study we show that compound 48/80 (c48/80), a synthetic member of the class of basic secretagogues, stimulates protein tyrosine phosphorylation of a number of as yet unidentified cellular substrates. These phosphorylations were inhibited by the tyrphostin AG-18, by the phosphatidylinositol 3-kinase inhibitor wortmannin and by the protein kinase C inhibitors K252a and GF1 09203X. These inhibitors also inhibited the release of AA induced by c48/80 but had no effect on exocytosis. Taken together, our findings suggest that basic secretagogues induce protein tyrosine phosphorylation as part of their parallel multiple signaling pathways which are presumably mediated by more than one G-protein. Both protein kinase C and phosphatidylinositol 3-kinase serve as intermediates in this signaling pathway. The protein tyrosine kinase signaling pathway, which mediates the activation of AA release, does not contribute to secretion of the preformed mediators such as histamine, but it might largely contribute to the de novo production of inflammatory mediators like leukotrienes and prostaglandins.