title: Cbl-c suppresses v-Src-induced transformation through ubiquitin-dependent protein degradation.
abstract: The Cbl family proteins Cbl, Cbl-b, and Cbl-c/Cbl-3 are thought to regulate signaling through protein-tyrosine kinases, positively as scaffold proteins and negatively as ubiquitin ligases. However, the precise signaling pathways and target proteins for each Cbl family member are not well understood. Here we show that Src is a preferential target of Cbl-c for degradation. Although exogenous expression of all Cbl family proteins suppressed the anchorage-independent growth of v-Src-transformed NIH3T3 cells, only Cbl-c caused reversion of the refractile morphology. The level of v-Src protein was reduced by Cbl-c, possibly through a lysosome-dependent pathway. The TKB domain and RING finger of Cbl-c were important for its antioncogenic activity. Wild-type Cbl-c promoted ubiquitination of Src in 293T cells, whereas a RING finger mutant did not. Cbl-c bound specifically to Src phosphorylated at Tyr419. Furthermore, Cbl-c together with UbcH5 induced ubiquitination of Src in vitro. Importantly, the Tyr419 nonphosphorylated form of Src was not ubiquitinated by Cbl-c. Therefore, activated Src may be a direct target of Cbl-c in vivo. Our results suggest that Cbl and Cbl-b suppress v-Src-induced transformation through mechanisms distinct from that of Cbl-c.
authors.affiliation: Division of Oncology, Department of Cancer Biology, The Institute of Medical Science, The University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Minsoo
authors.initials: M
authors.lastname: Kim
authors.forename: Tohru
authors.initials: T
authors.lastname: Tezuka
authors.forename: Keiji
authors.initials: K
authors.lastname: Tanaka
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D002455:Cell Division; D002460:Cell Line; D002461:Cell Line, Transformed; D048429:Cell Size; D002471:Cell Transformation, Neoplastic; D006801:Humans; D051379:Mice; D041681:NIH 3T3 Cells; D015688:Oncogene Protein pp60(v-src) / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism
chemical_list: D011518:Proto-Oncogene Proteins; D025801:Ubiquitin; D019000:Phosphotyrosine; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D015688:Oncogene Protein pp60(v-src); C119570:CBLC protein, human