Gi-mediated activation of the p42/p44 mitogen-activated protein kinases by receptor mimetic basic secretagogues is abrogated by inhibitors of endocytosis.

摘要

Exocytosis in mast cells, effector cells of allergic and inflammatory reactions, can be activated, in a receptor-independent manner, by a family of polycationic molecules (e.g. the Basic Secretagogues of mast cells) that activate directly heterotrimeric G-proteins that control exocytosis. We have recently shown that pertussis toxin (Ptx)-sensitive Gi-protein(s), activated directly by Basic Secretagogues, also stimulate protein tyrosine phosphorylation and activation of the p42/p44 MAP kinases, via a mechanism that involves protein kinase C (PKC), phosphatidylinositol-3-kinase and Ca2+ as intermediates (J. Pharmacol. Exp. Ther. 289 (1999) 1654). In this paper, we have investigated the role of endocytosis in this receptor-independent, G-protein-mediated signaling. Using mechanistically distinct inhibitors of clathrin-mediated endocytosis, we demonstrate that protein tyrosine phosphorylation and activation of p42/p44 MAP kinases are endocytosis-dependent. In contrast, Gi-stimulated exocytosis is unaffected. We show further that Gi activation results in recruitment of clathrin from the cytosol to the plasma membrane. Taken together, our results indicate that signal transduction between G-proteins and the components of the MAP kinase activation cascade is dependent on clathrin-mediated endocytosis and can occur independently of a 7 TM cell surface receptor.