title: Full activation of MEN2B mutant RET by an additional MEN2A mutation or by ligand GDNF stimulation.
abstract: Germline mutations of RET gene, encoding a receptor tyrosine kinase, have been associated with the MEN2A and MEN2B inherited cancer syndromes. In MEN2A mutations affecting cysteine residues in the extracellular domain of the receptor cause constitutive activation of the tyrosine kinase by the formation of disulfide-bonded homodimers. In MEN2B a single mutation in the tyrosine kinase domain (Met918Thr) has been identified. This mutation does not lead to dimer formation, but has been shown (both biologically and biochemically) to cause ligand-independent activation of the Ret protein, but to a lesser extent than MEN2A mutations. Intramolecular activation by cis-autophosphorylation of RetMEN2B monomers has been proposed as a model for activation, although alternative mechanisms can be envisaged. Here we show that the activity of RetMEN2B can be increased by stable dimerization of the receptor. Dimerization was achieved experimentally by constructing a double mutant receptor with a MEN2A mutation (Cys634Arg) in addition to the MEN2B mutation, and by chronic exposure of RetMEN2B-expressing cells to the Ret ligand GDNF. In both cases full activation of RetMEN2B, measured by 'in vitro' transfection assays and biochemical parameters, was seen. These results indicate that the MEN2B phenotype could be influenced by the tissue distribution or concentration of Ret ligand(s).
authors.affiliation: Division of Experimental Oncology A, Istituto Nazionale Tumori, Milan, Italy.
authors.forename: I
authors.initials: I
authors.lastname: Bongarzone
authors.forename: E
authors.initials: E
authors.lastname: Vigano
authors.forename: L
authors.initials: L
authors.lastname: Alberti
authors.forename: M G
authors.initials: MG
authors.lastname: Borrello
authors.forename: B
authors.initials: B
authors.lastname: Pasini
authors.forename: A
authors.initials: A
authors.lastname: Greco
authors.forename: P
authors.initials: P
authors.lastname: Mondellini
authors.forename: D P
authors.initials: DP
authors.lastname: Smith
authors.forename: B A
authors.initials: BA
authors.lastname: Ponder
authors.forename: G
authors.initials: G
authors.lastname: Romeo
authors.forename: M A
authors.initials: MA
authors.lastname: Pierotti
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019281:Dimerization; D029721:Drosophila Proteins; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D006801:Humans; D008024:Ligands; D051379:Mice; D018813:Multiple Endocrine Neoplasia Type 2a / Q000235:genetics*; D018814:Multiple Endocrine Neoplasia Type 2b / Q000235:genetics*; D009154:Mutation; D009414:Nerve Growth Factors / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics*; D011994:Recombinant Proteins; D014162:Transfection
chemical_list: D029721:Drosophila Proteins; C495039:GDNF protein, human; C495040:Gdnf protein, mouse; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008024:Ligands; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C494999:Ret protein, mouse