Regulation of CCK-induced ERK1/2 activation by PKC epsilon in rat pancreatic acinar cells

Abstract

The extracellular signal-regulated kinase ERK1/2 is activated in pancreatic acinar cells by cholecystokinin (CCK) and other secretagogues with this activation mediated primarily by protein kinase C (PKC). To identify the responsible PKC isoform, we utilized chemical inhibitors, cell permeant inhibitory peptides and overexpression of individual PKC dominant negative variants by means of adenoviral vectors. While the broad-spectrum PKC inhibitor GF109203X strongly inhibited ERK1/2 activation induced by 100 pM CCK, Go6976 which inhibits the classical PKC isoforms (alpha, beta and gamma), as well as Rottlerin, a specific PKC delta inhibitor, had no inhibitory effect. To test the role of PKC epsilon, we used specific cell permeant peptide inhibitors which block PKC interaction with their intracellular receptors or RACKs. Only PP93 (PKC epsilon peptide inhibitor) inhibited CCK-induced ERK1/2 activation, while PP95, PP101 and PP98, which are PKC alpha, delta and zeta peptide inhibitors respectively, had no effect. We also utilized adenovirus to express dominant negative PKC isoforms in pancreatic acini. Only PKC epsilon dominant negative inhibited CCK-induced ERK1/2 activation. Dominant negative PKC epsilon expression similarly blocked the effect of carbachol and bombesin to activate ERK1/2. Immunoprecipitation results demonstrated that CCK can induce an interaction of c-Raf-1 and PKC epsilon, but not that of other isoforms of Raf or PKC. We conclude that PKC epsilon is the isoform of PKC primarily involved with CCK-induced ERK1/2 activation in pancreatic acinar cells.