title: Negative regulation of Rap1 activation by the Cbl E3 ubiquitin ligase.
abstract: Cbl functions as an adaptor protein by interacting with other signalling molecules to form multimolecular complexes. Previous studies have proposed that Cbl is also a positive regulator of CrkL-C3G signalling, which leads to Rap1 activation. However, there is a lack of genetic evidence for a physiological function of Cbl in regulating this pathway. Here, we show that Cbl deficiency results in enhanced activation of Rap1. Cbl was shown to promote the ubiquitylation of CrkL without any apparent effect on its stability. Remarkably, the membrane translocation of C3G, its association with CrkL, and the guanine-nucleotide exchange activity of C3G were all increased in Cbl(-/-) thymocytes. Consistent with a function of Rap1 in integrin activation, enhanced integrin-mediated cell adhesion was also seen in Cbl(-/-) thymocytes. Thus, Cbl negatively regulates Rap1 activation, probably through a proteolysis-independent E3-ubiquitin-ligase activity of Cbl that modulates protein-protein interactions.
authors.affiliation: Division of Cell Biology, La Jolla Institute for Allergy and Immunology, San Diego, California 92121, USA.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Shao
authors.forename: Chris
authors.initials: C
authors.lastname: Elly
authors.forename: Yun-Cai
authors.initials: YC
authors.lastname: Liu
mesh_terms: D000818:Animals; D002448:Cell Adhesion; D002460:Cell Line; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D008025:Ligases / Q000235:genetics*; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D050722:Oncogene Protein v-cbl; D011994:Recombinant Proteins / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology / Q000502:physiology; D014162:Transfection; D044767:Ubiquitin-Protein Ligases; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
chemical_list: D050722:Oncogene Protein v-cbl; D011994:Recombinant Proteins; D015682:Retroviridae Proteins, Oncogenic; D044767:Ubiquitin-Protein Ligases; D019204:GTP-Binding Proteins; D020827:rap1 GTP-Binding Proteins; D008025:Ligases