PROTEIN-TYROSINE PHOSPHORYLATION IN PANCREATIC ACINI - DIFFERENTIAL-EFFECTS OF VIP AND CCK

Cholecystokinin (CCK) and vasoactive intestinal peptide (VIP) stimulat e enzyme secretion from pancreatic acini by binding to heptahelical re ceptors without intrinsic tyrosine kinase activity. Signal transductio n by the CCK receptor involves activation of phospholipase C by G(q) p roteins and activation of tyrosine kinases, whereas occupation of VIP receptors stimulates adenylyl cyclase through binding to G(s) proteins . Here, we use electrophoretic separation of cellular proteins and ant iphosphotyrosine immunoblotting to demonstrate a VIP-stimulated rapid and dose-dependent increase in tyrosine phosphorylation of proteins mi grating at 130, 115, and 93 kDa in freshly isolated rat pancreatic aci ni. Phosphorylation of these proteins was increased after direct stimu lation of adenylyl cyclase or the adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase with forskolin or dibutyryl cAMP and was inhibited by the tyrosine kinase inhibitors genistein or tyrphosti n 23. Compared with VIP, CCK stimulated tyrosine phosphorylation of ad ditional proteins migrating at 60, 66, and 72/78 kDa. Using two-dimens ional electrophoretic separation or immunoprecipitation, the 72/78-kDa phosphoprotein was identified as paxillin. We propose that paxillin m ight be involved in CCK-but not in VIP;induced exocytosis.