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

Abstract

Oncogenic activation of the Ron tyrosine kinase (Macrophage Stimulating Protein receptor) relies on substitutions of two highly conserved residues in the catalytic domain (D1232V and M1254T), which result in ligand-independent activation of the receptor, in vivo tumorigenesis and metastasis. We show here that the Y/F conversion of the Y¹³¹⁷ residue in the kinase domain impairs tumorigenic and metastatic properties of Ron activated by the MEN2B-like mutation (Ron^M1254T), but not by other two oncogenic substitutions. Furthermore, Ron^M1254T lacking the multifunctional docking site retains transforming and metastatic activity. These data reveal that the transforming activity of Ron^M1254T mutant is dependent on Y¹³¹⁷ phosphorylation, suggesting a shift in intramolecular substrate specificity. Consistently, a shift of Ron^M1254T kinase substrate specificity was observed by in vitro peptide phosphorylation assays and in vivo receptor auto-phosphorylation. The Y¹³¹⁷ 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 Y¹³¹⁷ residue in the tyrosine kinase domain.