Differential Activation of p42ERK2 and p125FAK by Cholecystokinin and Bombesin in the Secretion and Proliferation of the Pancreatic Amphicrine Cell Line AR42J

Abstract

Background: AR42J rat pancreatic acinar carcinoma cells have retained the potential to secrete digestive enzymes in addition to their ability to proliferate upon stimulation with regulatory peptides. We investigated the involvement of p42^ERK2 and p125^FAK (extracellular signal-regulated protein kinase and focal adhesion protein kinase, respectively) by cholecystokinin and bombesin stimulation with regard to secretion and mitogenesis. Methods: The p42^ERK2 activity was measured by kinase assay and the activation of p125^FAK by antiphosphotyrosine Western blot analysis of p125^FAK immunoprecipitates. The expression of both kinases was determined by Western blot analysis, the amylase secretion by colorimetry, and the DNA synthesis by [³H]thymidine incorporation. Results: p42^ERK2 and p125^FAK were activated by cholecystokinin and bombesin with maximum stimulation at concentrations above 10 nM. Bombesin was a weaker activator of p42^ERK2 and p125^FAK, causing only half of the kinase activity induced by stimulation with cholecystokinin. PD98059 was shown to inhibit p42^ERK2, while tyrphostin 25 blocked p125^FAK tyrosine phosphorylation. Preincubation of AR42J cells with PD98059 or tyrphostin 25 was without influence on cholecystokinin- or bombesin-stimulated secretion in normal or 72-hour dexamethasone-pretreated cells. In contrast, inhibition of both protein kinases leads to reduced cholecystokinin-stimulated [³H]thymidine incorporation rates. Conclusions: Cholecystokinin induced proliferation of AR42J cells by strong activation of p42^ERK2 and p125^FAK. Bombesin failed to stimulate DNA synthesis, probably due to its reduced potency to stimulate these kinases. Both protein kinases are not implicated in the process of enzyme secretion.