Cholecystokinin rapidly stimulates CrkII function in vivo in rat pancreatic acini

Abstract

Crk belongs to a family of adapter proteins whose structure allows interaction with tyrosine-phosphorylated proteins and is therefore an important modulator of downstream signals, representing a convergence of the actions of numerous stimuli. Recently, it was demonstrated that cholecystokinin (CCK) induced tyrosine phosphorylation of proteins related to fiber stress formation in rat pancreatic acini. Here, we investigated whether CCK receptor activation signals through CrkII and forms complexes with tyrosine-phosphorylated proteins in rat pancreatic acini. We demonstrated that CCK promoted the transient formation of CrkII-paxillin and CrkII-p130Cas complexes with maximal effect at 1 min. Additionally, CCK decreased the electrophoretic mobility of CrkII. This decrease was time-and concentration-dependent and inversely related with its function. Carbachol and bombesin also decreased CrkII electrophoretic mobility, whereas epidermal growth factor, vasoactive intestinal peptide, secretin or pituitary adenylate cyclase-activating polypeptide had no effect. CCK-induced CrkII electrophoretic shift was dependent on the Src family of tyrosine kinases and occurred in the intact animal, suggesting a physiological role of CrkII mediating CCK actions in the exocrine pancreas in vivo.

The Src kinase Yes is activated in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters, but not pancreatic growth factors, which stimulate its association with numerous other signaling molecules

“…However, the relative importance of activation of the high and low affinity CCK 1 receptor state differs among these proteins. In contrast to these results, CCK-mediated activation in pancreatic acini of phospholipase D or PI3K requires activation of only the high affinity receptor state [49], whereas in the case of PKC-δ [6] or CRK-II [50] only the low affinity CCK 1 receptor state is required for activation. Also, in contrast to our results with Yes activation, a previous study [3] reported CCK-stimulated SFK activity is mediated almost entirely by activation of the low CCK 1 receptor state in pancreatic acini.…”

Gastrointestinal hormones/neurotransmitters and growth factors can activate P21 activated kinase 2 in pancreatic acinar cells by novel mechanisms

“…Our results with PAK2 activation are similar to the CCK-induced activation of the Src kinases(Lyn, Yes)[41,78], the focal adhesion kinases (p125FAK, PYK2)[34,39], paxillin[34,40] and PKD[54] in pancreatic acini[78], that are all mediated by activation of both high- and low-affinity receptor-states, although with differences in their relative importance. In contrast to these results, CCK-mediated activation in pancreatic acini of phospholipase D or PI3K requires activation of only the high-affinity receptor-state[97], whereas in the case of PKC-δ [32] or CRK-II[98], only the low-affinity CCK 1 receptor-state is required for activation. Also, a previous study[99] reported CCK-stimulated SFK activity is mediated almost entirely by activation of the low-CCK 1 receptor state in pancreatic acini.…”

PKCθ activation in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors is needed for stimulation of numerous important cellular signaling cascades

“…Activation of the high affinity CCK A receptor state is responsible for only 20% of the maximal activation of PKCmu (PKD1) [18] and PYK2/CAKβ [17], whereas it mediates 50% of the maximal stimulation of p125 FAK and paxillin phosphorylation [65] and mediates 60% of Lyn activation [64]. These results with PKCθ activation differ from results seen with CCK activation in pancreatic acinar cells of the novel PKC, PKCδ [14] or stimulation of phosphorylation of the adaptor protein, CrKII, [66] where are mediated only through activation of the low affinity CCK A receptor state. In contrast, CCK-mediated activation of PI-3 kinase and phospholipase D in pancreatic acinar cells is mediated entirely by the activation of the high affinity receptor state [67].…”