Cellular Basis Of Action Of Gastrointestinal Peptides

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Recent studies show that gastrointestinal hormones, similar to many growth factors, may stimulate cell growth by stimulating intracellular tyrosine phosphorylation signaling cascades. However at present little is known about the ability of these G-protein-coupled receptors to activate these cascades. During the year we have investigated the ability of the hormone/neurotransmitter, cholecystokinin (CCK) to activate these cascades. CCKA-R activation causes rapid tyrosine phosphorylation of p125FAK, paxillin, p130Cas, PYK2 and PKC delta. Our recent studies show PKC delta activation is independent of changes in [Ca2+]i or PI3K but is regulated by activation of PKC-alpha. Focal adhesion kinases (p125FAK,PYK) are important intracellular signals mediating effects of integrins, growth factors, oncogenes, bioactive lipids and some G protein-coupled receptors on growth, adhesion, cellular motility and cytoskeletal changes. Little is known on the ability of GPCR such as the CCKA-R to alter these kinases. We demonstrated CCK can stimulate tyrosine phosphorylation at three p125FAK sites (Y397,Y577,Y925) and PYK2 sites (pY402,Y580,Y881), however, they differ in kinetics, magnitude, participation of the different receptor states, PKC and changes in cytosolic calcium. These results show that phosphorylation of these different sites is differentially regulated and involves different intracellular mechanisms in the same cell. These results suggest that differences in the phosphorylation and regulation of these different kinases likely contribute to their different cellular effects in normal and neoplastic diseases after activation.