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 alle rgic reactions. These granulated cells release by a process of regulat ed exocytosis a variety of biologically active substances which are ei ther preformed (e.g. histamine), or synthesized de novo following acti vation [e.g. metabolites of arachidonic acid (AA) and multifunctional cytokines]. Exocytosis in mast cells is activated either in response t o aggregation of the receptors for immunoglobulin E (Fc epsilon RI) or by the direct activation of pertussis toxin-sensitive G-proteins by a class of receptor mimetic agents, collectively known as basic secreta gogues of mast cells. In the present study we show that compound 48/80 (c48/80), a synthetic member of the class of basic secretagogues, sti mulates protein tyrosine phosphorylation of a number of as yet unident ified cellular substrates. These phosphorylations were inhibited by th e tyrphostin AG-18, by the phosphatidylinositol 3-kinase inhibitor wor tmannin and by the protein kinase C inhibitors K252a and GF109203X. Th ese 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 o f their parallel multiple signaling pathways which are presumably medi ated by move than one G-protein. Both protein kinase C and phosphatidy linositol 3-kinase serve as intermediates in this signaling pathway. T he protein tyrosine kinase signaling pathway, which mediates the activ ation of AA release, does not contribute to secretion of the preformed mediators such as histamine, but it might largely contribute to the d e novo production of inflammatory mediators like leukotrienes and pros taglandins.