Protease-activated receptor-2 increases exocytosis via multiple signal transduction pathways in pancreatic duct epithelial cells.

Protease-activated receptor-2 (PAR-2) is activated when trypsin cleaves its NH(2) terminus to expose a tethered ligand. We previously demonstrated that PAR-2 activates ion channels in pancreatic duct epithelial cells (PDEC). Using real-time optical fluorescent probes, cyan fluorescence protein-Epac1-yellow fluorescence protein for cAMP, PH(PLC-delta1)-enhanced green fluorescent protein for phosphatidylinositol 4,5-bisphosphate, and protein kinase Cgamma (PKCgamma)-C1-yellow fluorescence protein for diacylglycerol, we now define the signaling pathways mediating PAR-2 effect in dog PDEC. Although PAR-2 activation does not stimulate a cAMP increase, it induces phospholipase C to hydrolyze phosphatidylinositol 4,5-bisphosphate into inositol 1,4,5-trisphosphate and diacylglycerol. Intracellular Ca(2+) mobilization from inositol 1,4,5-trisphosphate-sensitive Ca(2+) stores and a subsequent Ca(2+) influx through store-operated Ca(2+) channels cause a biphasic increase in intracellular Ca(2+) concentration (Ca(2+)), measured with Indo-1 dye. Single-cell amperometry demonstrated that this increase in Ca(2+) in turn causes a biphasic increase in exocytosis. A protein kinase assay revealed that trypsin also activates PKC isozymes to stimulate additional exocytosis. Paralleling the increased exocytosis, mucin secretion from PDEC was also induced by trypsin or the PAR-2 activating peptide. Consistent with the serosal localization of PAR-2, 1 microm luminal trypsin did not induce exocytosis in polarized PDEC monolayers; on the other hand, 10 microm trypsin at 37 degrees C damaged the epithelial barrier sufficiently so that it could reach and activate the serosal PAR-2 to stimulate exocytosis. Thus, in PDEC, PAR-2 activation increases Ca(2+) and activates PKC to stimulate exocytosis and mucin secretion. These functions may mediate the reported protective role of PAR-2 in different models of pancreatitis.