The Tyrosine Kinase Encoded by the MET Proto-Oncogene Is Activated by Autophosphorylation

Luigi Naldini, Elisa Vigna, Riccardo Ferracini, Paola Longati, Lucia Gandino, Maria Prat, Paolo M. Comoglio

Research output: Contribution to journalArticlepeer-review


Protein tyrosine kinases are crucially involved in the control of cell proliferation. Therefore, the regulation of their activity in both normal and neoplastic cells has been under intense scrutiny. The product of the MET oncogene is a transmembrane receptorlike tyrosine kinase with a unique disulfide-linked heterodimeric structure. Here we show that the tyrosine kinase activity of the MET-encoded protein is powerfully activated by tyrosine autophosphorylation. The enhancement of activity was quantitated with a phosphorylation assay of exogenous substrates. It involved an increase in the Vmax of the enzyme-catalyzed phosphotransfer reaction. No change was observed in the Km (substrate). A causal relationship between tyrosine autophosphorylation and activation of the kinase activity was proved by (i) the kinetic agreement between autophorylation and kinase activation, (ii) the overlapping dose-response relationship for ATP, (iii) the specificity for ATP of the activation process, (iv) the phosphorylation of tyrosine residues only, in the Met protein, in the activation step, (v) the linear dependence of the activation from the input of enzyme assayed, and (vi) the reversal of the active state by phosphatase treatment. Autophosphorylation occurred predominantly on a single tryptic peptide, most likely via an intermolecular reaction. The structural features responsible for this positive modulation of kinase activity were all contained in the 45-kDa intracellular moiety of the Met protein.

Original languageEnglish
Pages (from-to)1793-1803
Number of pages11
JournalMolecular and Cellular Biology
Issue number4
Publication statusPublished - Apr 1991

ASJC Scopus subject areas

  • Cell Biology
  • Genetics
  • Molecular Biology


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