title: RET(MEN 2B) is active in the endoplasmic reticulum before reaching the cell surface.
abstract: MEN 2B (multiple endocrine neoplasia type 2B) is an autosomal dominant cancer syndrome caused by an oncogenic form of the receptor tyrosine kinase REarranged during transfection (RET). The MEN 2B syndrome is associated with an abnormal autophosphorylation of the mutated receptor even without ligand-stimulation. Here, we characterize the activation of a RET(MEN 2B) variant carrying the point mutation Met918Thr, and show that the 150 kDa precursor of RET(MEN 2B) becomes phosphorylated already during synthesis in the endoplasmic reticulum (ER). At least three different tyrosine residues (Tyr905, Tyr1062, Tyr1096) of the RET(MEN 2B) precursor are phosphorylated before the oncogenic receptor reaches the cell surface. We also demonstrate that the precursor of RET(MEN 2B) interacts with both growth factor receptor-bound protein and Src homology 2 domain-containing already in the ER, and that this interaction is dependent on the kinase activity of RET. With the aid of two RET mutants (RET(MEN 2B/S32L) and RET(MEN 2B/F393L)), which accumulate in the ER, we show that the oncogenic precursor of the receptor has the capacity to activate AKT, extracellular signal-regulated kinase and signal transducer and activator of transcription 3 from the ER. Taken together, our data demonstrate that the oncogenic precursor of RET(MEN 2B) is phosphorylated, interacts with adapter proteins and induces downstream signalling from the ER.
authors.affiliation: Institute of Biotechnology, Viikki Biocenter, University of Helsinki, Helsinki, Finland. pia.runeberg@helsinki.fi
authors.forename: P
authors.initials: P
authors.lastname: Runeberg-Roos
authors.forename: H
authors.initials: H
authors.lastname: Virtanen
authors.forename: M
authors.initials: M
authors.lastname: Saarma
mesh_terms: D020126:Brefeldin A / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D018814:Multiple Endocrine Neoplasia Type 2b / Q000235:genetics; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051096:Proto-Oncogene Proteins c-ret / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D050796:STAT3 Transcription Factor / Q000378:metabolism
chemical_list: D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D020126:Brefeldin A; D051096:Proto-Oncogene Proteins c-ret; C099282:RET protein, human; D051057:Proto-Oncogene Proteins c-akt