Cholecystokinin activates PYK2/CAK beta by a phospholipase C-dependent mechanism and its association with the mitogen-activated protein kinase signaling pathway in pancreatic acinar cells

PYK2/CAK beta is a recently described cytoplasmic tyrosine kinase related t o p125 focal adhesion kinase (p125(FAK)) that can be activated by a number of stimuli including growth factors, lipids, and some G protein-coupled rec eptors. Studies suggest PYK2/CAK beta 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 ac tivate both phospholipase C-dependent 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! activ ation of PYK2/CAK beta by both activation of high affinity and low affinity CCKA receptor states. Blockage of CCK-stimulated increases in protein kina se C activity or CCK-stimulated increases in [Ca2+](i), inhibited by 40-50% PYK2/CAK beta but not p125FAK tyrosine phosphorylation. Simultaneous block age of both phospholipase C cascades inhibited PYK2/CAK beta tyrosine phosp horylation completely and p125(FAK) tyrosine phosphorylation by 50%. CCK-8 stimulated a rapid increase in PYK2/CAK beta kinase activity assessed by bo th an in vitro kinase assay and autophosphorylation. Total PYK2/CAK beta un der basal conditions was largely localized (77 +/- 7%) in the membrane frac tion, whereas total p125(FAK) was largely localized (86 +/- 3%) in the cyto solic fraction. With CCK stimulation, both p125(FAK) and PYK2/CAK beta tran slocated to the plasma membrane. Moreover CCK stimulation causes a rapid fo rmation of both PYK2/CAK beta-Grb2 and PYK2/CAK beta-Crk complexes. These r esults demonstrate that PYK2/CAK beta and p125(FAK) are regulated different ly by CCKA receptor stimulation and that PYK2/CAK beta is probably an impor tant mediator of downstream signals by CCK-8, especially in its ability to activate the MAPK signaling pathway, which possibly mediates CCK growth eff ects in normal and neoplastic tissues.