Activation of m3 Muscarinic Receptors Induces Rapid Tyrosine Phosphorylation of p125FAK, p130cas, and Paxillin in Rat Pancreatic Acini

Abstract

Tyrosine phosphorylation plays a key role in transmembrane and cytoplasmic signal transduction mechanisms stimulated by oncogenes, integrins, growth factors, neuropeptides, and bioactive lipids. Moreover, recent studies show that stimulation of odd-numbered muscarinic receptors increases the tyrosine phosphorylation of several proteins in different cellular types. The present study was aimed at examining whether activation of m3 muscarinic receptors in rat pancreatic acini evokes tyrosine phosphorylation of p125FAK, and its substrates, p130cas and paxillin. Results show that stimulation of pancreatic acini with carbachol resulted in a rapid and transient increase in tyrosine phosphorylation of p125FAK, p130cas, and paxillin. Tyrosine phosphorylation of these proteins occurred in a time- and concentration-dependent manner. Simultaneous blockage of both PKC activation and increases in [Ca2+]i partially decreased p125FAK, p130cas, and paxillin tyrosine phosphorylation stimulated by carbachol. Pretreatment of pancreatic acini with Clostridium botulinum C3 transferase, which specifically inactivates p21rho, partially inhibited carbachol-induced p125FAK, p130cas, and paxillin tyrosine phosphorylation. In contrast, this treatment had no effect on amylase release stimulated by carbachol. Cytochalasin D, which disrupts actin microfilaments network, completely inhibited carbachol stimulated tyrosine phosphorylation of these proteins without having significant effects in carbachol-stimulated amylase secretion. These results dissociate tyrosine phosphorylation of p125FAK, p130cas, and paxillin from amylase secretion after m3 muscarinic receptors occupation in rat pancreatic acini. Taken together, these data suggest that (a) activation of m3 muscarinic receptors in rat pancreatic acini increases tyrosine phosphorylation of p125FAK and its substrates, p130cas and paxillin by diacylglycerol-activated PKC- and calcium- dependent, and independent pathways, (b) these responses require activation of p21rho and an intact actin cytoskeleton, and (c) p125FAK, p130cas, and paxillin are unlikely related to secretion in rat pancreatic acinar cells.