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A Novel Activating Mutation in the RET Tyrosine Kinase Domain Mediates Neoplastic Transformation

Cambridge Institute for Medical Research and Cancer Research UK Department of Oncology (A.C., S.M., Y.H., J.L., B.A.J.P.), University of Cambridge, Cambridge CB2 2XY, United Kingdom; Department of Experimental Oncology (C.C., P.M., M.P., I.B.), Istituto Nazionale per lo Studio e la Cura dei Tumori, 20133 Milan, Italy; and Division of Medical and Molecular Genetics (S.H.) and Department of Nuclear Medicine (S.C.), Guys’ Hospital, London SE1 9RT, United Kingdom

Address all correspondence and requests for reprints to: Aaron Cranston, Cambridge Institute for Medical Research and Cancer Research UK Department of Oncology, University of Cambridge, Hills Road, Cambridge CB2 2XY, United Kingdom. E-mail: aaron.cranston{at}ntlworld.com.

We report the finding of a novel missense mutation at codon 833 in the tyrosine kinase of the RET proto-oncogene in a patient with a carcinoma of the thyroid. In vitro experiments demonstrate that the R833C mutation induces transformed foci only when present in the long 3' splice isoform and, in keeping with a model in which the receptor has to dimerize to be completely activated, glial cell line-derived neurotrophic factor stimulation leads the RET^R833C receptor to a higher level of activation. Tyrosine kinase assays show that the RET^R833C long isoform has weak intrinsic kinase activity and phosphorylation of an exogenous substrate is not elevated even in the presence of glial cell line-derived neurotrophic factor. Furthermore, the R833C mutation is capable of sustaining the transformed phenotype in vivo but does not confer upon the transformed cells the ability to degrade the basement membrane in a manner analogous to metastasis. Our functional characterization of the R833C substitution suggests that, like the V804M and S891A mutations, this tyrosine kinase mutation confers a weak activating potential upon RET. This is the first report demonstrating that the introduction of an intracellular cysteine can activate RET. However, this does not occur via dimerization in a manner analogous to the extracellular cysteine mutants.