title: Identification of c-Cbl as a new ligase for insulin-like growth factor-I receptor with distinct roles from Mdm2 in receptor ubiquitination and endocytosis.
abstract: The insulin-like growth factor receptor (IGF-IR) plays several pivotal roles in cancer. Although most studies on the function of the IGF-IR have been attributed to kinase-dependent signaling, recent findings by our group and others have implicated biological roles mediated by ubiquitination of the receptor. As previously reported, the E3 ligases Mdm2 and Nedd4 mediate IGF-IR ubiquitination. Here we show that c-Cbl is a novel E3 ligase for IGF-IR. On ligand stimulation, both Mdm2 and c-Cbl associate with IGF-IR and mediate receptor polyubiquitination. Whereas Mdm2 catalyzed lysine 63 (K63) chain ubiquitination, c-Cbl modified IGF-IR through K48 chains. Mdm2-mediated ubiquitination occurred when cells were stimulated with a low concentration (5 ng/mL) of IGF-I, whereas c-Cbl required high concentrations (50-100 ng/mL). Mdm2-ubiquitinated IGF-IR was internalized through the clathrin endocytic pathway whereas c-Cbl-ubiquitinated receptors were endocytosed via the caveolin route. Taken together, our results show that c-Cbl constitutes a new ligase responsible for the ubiquitination of IGF-IR and that it complements the action of Mdm2 on ubiquitin lysine residue specificity, responsiveness to IGF-I, and type of endocytic pathway used. The actions and interactions of Mdm2 and c-Cbl in the ubiquitination and endocytosis of IGF-IR may have implications in cancer. In addition, identification and functional characterization of new E3 ligases are important in itself because therapeutic targeting of substrate-specific E3 ligases is likely to represent a critical strategy in future cancer treatment.
authors.affiliation: Department of Oncology and Pathology, Karolinska Institutet, Cancer Center Karolinska, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Bita
authors.initials: B
authors.lastname: Sehat
authors.forename: Sandra
authors.initials: S
authors.lastname: Andersson
authors.forename: Leonard
authors.initials: L
authors.lastname: Girnita
authors.forename: Olle
authors.initials: O
authors.lastname: Larsson
mesh_terms: D045744:Cell Line, Tumor; D004705:Endocytosis; D056827:Endosomal Sorting Complexes Required for Transport; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D018613:Microscopy, Confocal; D008954:Models, Biological; D000075702:Nedd4 Ubiquitin Protein Ligases; D009369:Neoplasms / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism / Q000502:physiology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D025801:Ubiquitin; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C497206:MDM2 protein, human; D050721:Proto-Oncogene Proteins c-cbl; D051736:Proto-Oncogene Proteins c-mdm2; D044767:Ubiquitin-Protein Ligases; D017526:Receptor, IGF Type 1