Abstract
Recent studies show that the effects of some oncogenes, integrins, growth factors and neuropeptides are mediated by tyrosine phosphorylation of the cytosolic kinase p125 focal adhesion kinase (p125(FAK)) and the cytoskeletal protein paxillin. Recently we demonstrated that cholecystokinin (CCK) C-terminal octapeptide (CCK-8) causes tyrosine phosphorylation of p125(FAK) and paxillin in rat pancreatic acini. The present study was aimed at examining whether protein kinase C (PKC) activation, calcium mobilization, cytoskeletal organization and small G-protein p21(rho) activation play a role in mediating the stimulation of tyrosine phosphorylation by CCK-8 in acini. CCK-8-stimulated phosphorylation of p125(FAK) and paxillin reached a maximum within 2.5 min. The CCK-8 dose response for causing changes in the cytosolic calcium concentration ([Ca2+]i) was similar to that for p125(FAK) and paxillin phosphorylation, and both were to the left of that for receptor occupation and inositol phosphate production. PMA increased tyrosine phosphorylation of both proteins. The calcium ionophore A23187 caused only 25% of the maximal stimulation caused by CCK-8. GF109203X, a PKC inhibitor, completely inhibited phosphorylation with PMA but had no effect on the response to CCK-8. Depletion of [Ca2+]i by thapsigargin had no effect on CCK-8-stimulated phosphorylation. Pretreatment with both GF109203X and thapsigargin decreased CCK-8-stimulated phosphorylation of both proteins by 50%. Cytochalasin D, but not colchicine, completely inhibited CCK-8- and PMA-induced p125(FAK) and paxillin phosphorylation. Treatment with Clostridium botulinum C3 transferase, which inactivates p21(rho), caused significant inhibition of CCK-8-stimulated p125(FAK) and paxillin phosphorylation. These results demonstrate that, in pancreatic acini, CCK-8 causes rapid p125(FAK) and paxillin phosphorylation that is mediated by both phospholipase C-dependent and -independent mechanisms. For this tyrosine phosphorylation to occur, the integrity of the actin, but not the microtubule, cytoskeleton is essential as well as the activation of p21(rho).