REGULATORY ROLE OF MAJOR TYROSINE AUTOPHOSPHORYLATION SITE OF KINASE DOMAIN OF C-MET RECEPTOR (SCATTER FACTOR HEPATOCYTE GROWTH-FACTOR RECEPTOR)/

Ligand-induced tyrosine kinase activation of the scatter factor/hepato cyte growth factor receptor (c-Met) is thought to be essential for the biological responses of target cells. To assess the regulatory role o f the major tyrosine autophosphorylation site (tyrosine 1233) of the m ouse c-Met receptor in the tyrosine kinase activation of the receptor, we constructed a mutant receptor in which the tyrosine residue was re placed with phenylalanine. When the cells expressing the mutant recept or were incubated with the ligand, no biological responses were observ ed, and the level of tyrosine phosphorylation of the receptor was very low compared with that of the wild-type receptor. The in vitro kinase activity of the mutant receptor toward an exogenous substrate and the receptor itself was also low. Furthermore, tyrosine phosphorylation o f the cellular proteins by ligand stimulation was not detected in inta ct cells expressing the mutant receptor. The low level of kinase activ ity and the lack of biological activity of the mutant receptor indicat e that the major autophosphorylation site positively regulates the tyr osine kinase of the c-Met receptor and phosphorylation of cellular sub strates in the scatter factor/hepatocyte growth factor signaling pathw ay.