title: Direct binding of Cbl to Tyr568 and Tyr936 of the stem cell factor receptor/c-Kit is required for ligand-induced ubiquitination, internalization and degradation.
abstract: The ubiquitin E3 ligase Cbl has been shown to negatively regulate tyrosine kinase receptors, including the stem cell factor receptor/c-Kit. Impaired recruitment of Cbl to c-Kit results in a deregulated positive signalling that eventually can contribute to carcinogenesis. Here, we present results showing that Cbl is activated by the SFKs (Src family kinases) and recruited to c-Kit in order to trigger receptor ubiquitination. We demonstrate that phosphorylated Tyr568 and Tyr936 in c-Kit are involved in direct binding and activation of Cbl and that binding of the TKB domain (tyrosine kinase binding domain) of Cbl to c-Kit is specified by the presence of an isoleucine or leucine residue in position +3 to the phosphorylated tyrosine residue on c-Kit. Apart from the direct association between Cbl and c-Kit, we show that phosphorylation of Cbl by SFK members is required for activation of Cbl to occur. Moreover, we demonstrate that Cbl mediates monoubiquitination of c-Kit and that the receptor is subsequently targeted for lysosomal degradation. Taken together, our findings reveal novel insights into the mechanisms by which Cbl negatively regulates c-Kit-mediated signalling.
authors.affiliation: Experimental Clinical Chemistry, Department of Laboratory Medicine, Lund University, Malmö University Hospital, SE-205 02 Malmö, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Masson
authors.forename: Elke
authors.initials: E
authors.lastname: Heiss
authors.forename: Hamid
authors.initials: H
authors.lastname: Band
authors.forename: Lars
authors.initials: L
authors.lastname: Rönnstrand
mesh_terms: D000818:Animals; D002460:Cell Line; D004705:Endocytosis; D006801:Humans; D008024:Ligands; D051379:Mice; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism*; D019009:Proto-Oncogene Proteins c-kit / Q000737:chemistry* / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D015398:Signal Transduction; D013552:Swine; D014443:Tyrosine / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D008024:Ligands; D025801:Ubiquitin; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D019009:Proto-Oncogene Proteins c-kit; D016392:Proto-Oncogene Proteins pp60(c-src)