Cholecystokinin Activates PYK2/CAKbeta by a Phospholipase C-dependent Mechanism and Its Association with the Mitogen-activated Protein Kinase Signaling Pathway in Pancreatic Acinar Cells (original) (raw)

PYK2/CAK␤ is a recently described cytoplasmic tyrosine kinase related to p125 focal adhesion kinase (p125 FAK) that can be activated by a number of stimuli including growth factors, lipids, and some G proteincoupled receptors. Studies suggest PYK2/CAK␤ may be important for coupling various G protein-coupled receptors to the mitogen-activated protein kinase (MAPK) cascade. The hormone neurotransmitter cholecystokinin (CCK) is known to activate both phospholipase Cdependent cascades and MAPK signaling pathways; however, the relationship between these remain unclear. In rat pancreatic acini, CCK-8 (10 nM) rapidly stimulated tyrosine phosphorylation and activation of PYK2/CAK␤ by both activation of high affinity and low affinity CCK A receptor states. Blockage of CCK-stimulated increases in protein kinase C activity or CCKstimulated increases in [Ca 2؉ ] i , inhibited by 40-50% PYK2/CAK␤ but not p125 FAK tyrosine phosphorylation. Simultaneous blockage of both phospholipase C cascades inhibited PYK2/CAK␤ tyrosine phosphorylation completely and p125 FAK tyrosine phosphorylation by 50%. CCK-8 stimulated a rapid increase in PYK2/CAK␤ kinase activity assessed by both an in vitro kinase assay and autophosphorylation. Total PYK2/CAK␤ under basal conditions was largely localized (77 ؎ 7%) in the membrane fraction, whereas total p125 FAK was largely localized (86 ؎ 3%) in the cytosolic fraction. With CCK stimulation, both p125 FAK and PYK2/CAK␤ translocated to the plasma membrane. Moreover CCK stimulation causes a rapid formation of both PYK2/CAK␤-Grb2 and PYK2/CAK␤-Crk complexes. These results demonstrate that PYK2/CAK␤ and p125 FAK are regulated differently by CCK A receptor stimulation and that PYK2/CAK␤ is probably an important mediator of downstream signals by CCK-8, especially in its ability to activate the MAPK signaling pathway, which possibly mediates CCK growth effects in normal and neoplastic tissues.