The Ron oncogenic activity induced by the MEN2B-like substitution overcomes the requirement for the multifunctional docking site

Oncogenic activation of the Ron tyrosine kinase (Macrophage Stimulating Pro tein receptor) relies on substitutions of two highly conserved residues in the catalytic domain (D1232V and M1254T), which result in ligand-independen t activation of the receptor, in vivo tumorigenesis and metastasis. We show here that the Y/F conversion of the Y-1317 residue in the kinase domain im pairs tumorigenic and metastatic properties of Ron activated by the MEN2B-l ike mutation (Ron(M1254T)), but not by other two oncogenic substitutions, F urthermore, Ron(M1254T) lacking the multifunctional docking site retains tr ansforming and metastatic activity, These data reveal that the transforming activity of Ron(M1254T) mutant is dependent on Y-1317 phosphorylation, sug gesting a shift in intramolecular substrate specificity. Consistently, a sh ift of Ron(M1254T) kinase substrate specificity was observed by in vitro pe ptide phosphorylation assays and in vitro receptor autophosphorylation, The Y-1317 phosphorylation elicits by itself activation of PI-3K/Akt and MAPK signalling pathways, Our data indicate that the accomplishment of the full oncogenic phenotype of Ron(M1254T) requires the phosphorylation both of the canonical C-terminal docking site and of the unique Y-1317 residue in the tyrosine kinase domain.