EARLY SIGNALING MECHANISM IN COLONIC EPITHELIAL-CELL RESPONSE TO GASTRIN

The hormone gastrin exerts a growth-promoting effect on gastrointestin al cells. The molecular mechanisms by which colonic epithelial cells r espond to gastrin are still poorly understood. In this study, we demon strate a novel feature of the action of gastrin on normal colonic cell s, namely the rapid phosphorylation on tyrosine of phospholipase C(gam ma(1)) (PLC gamma(1)). Tyrosine phosphorylation of PLC gamma(1), elici ted by gastrin, was transient, concentration-dependent, and was abroga ted by pretreating the colonic cells with the gastrin-receptor antagon ist proglumide, the tyrosine kinase inhibitor genistein, and by remova l of the tyrosine phosphatase inhibitor orthovanadate from the isolati on buffer. Tyrosine phosphorylation of PLC gamma(1) correlated with th e time- and concentration-dependent decrease in the mass of membrane p hosphatidylinositol 4,5-bisphosphate (PIP2) and the increase in the ep ithelial concentration of inositol 1,4,5-trisphosphate (IP3). Likewise , the stimulated increase in IP3 was also prevented by proglumide and genistein. Gastrin induced a definite but transient increase in the in tracellular concentration of free Ca2+ [Ca2+](i), and increased membra ne-translocation of immunoreactive alpha-and beta-protein kinase C. Th e data thus indicate that gastrin elicits at least one signalling casc ade, through rapid tyrosine phosphorylation of PLC gamma(1), leading t o the activation of a PIP2-specific PLC pathway.