title: A mouse with a loss-of-function mutation in the c-Cbl TKB domain shows perturbed thymocyte signaling without enhancing the activity of the ZAP-70 tyrosine kinase.
abstract: The unique tyrosine kinase binding (TKB) domain of Cbl targets phosphorylated tyrosines on activated protein tyrosine kinases (PTKs); this targeting is considered essential for Cbl proteins to negatively regulate PTKs. Here, a loss-of-function mutation (G304E) in the c-Cbl TKB domain, first identified in Caenorhabditis elegans, was introduced into a mouse and its effects in thymocytes and T cells were studied. In marked contrast to the c-Cbl knockout mouse, we found no evidence of enhanced activity of the ZAP-70 PTK in thymocytes from the TKB domain mutant mouse. This finding contradicts the accepted mechanism of c-Cbl-mediated negative regulation, which requires TKB domain targeting of phosphotyrosine 292 in ZAP-70. However, the TKB domain mutant mouse does show aspects of enhanced signaling that parallel those of the c-Cbl knockout mouse, but these involve the constitutive activation of Rac and not enhanced PTK activity. Furthermore, the enhanced signaling in CD4(+)CD8(+) double positive thymocytes appears to be compensated by the selective down-regulation of CD3 on mature thymocytes and peripheral T cells from both strains of mutant c-Cbl mice.
authors.affiliation: Department of Pathology, University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Christine B F
authors.initials: CB
authors.lastname: Thien
authors.forename: Robin M
authors.initials: RM
authors.lastname: Scaife
authors.forename: John M
authors.initials: JM
authors.lastname: Papadimitriou
authors.forename: Maria A
authors.initials: MA
authors.lastname: Murphy
authors.forename: David D L
authors.initials: DD
authors.lastname: Bowtell
authors.forename: Wallace Y
authors.initials: WY
authors.lastname: Langdon
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis; D001665:Binding Sites; D017252:CD3 Complex / Q000032:analysis; D018956:CD5 Antigens / Q000032:analysis; D029742:Caenorhabditis elegans Proteins; D066246:ErbB Receptors / Q000502:physiology; D005260:Female; D015801:Helminth Proteins / Q000502:physiology; D037181:Lectins, C-Type; D008297:Male; D008565:Membrane Proteins / Q000032:analysis; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D050721:Proto-Oncogene Proteins c-cbl; D011948:Receptors, Antigen, T-Cell / Q000032:analysis; D013601:T-Lymphocytes / Q000502:physiology*; D013950:Thymus Gland / Q000201:enzymology; D044767:Ubiquitin-Protein Ligases; D051746:ZAP-70 Protein-Tyrosine Kinase; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D018909:src Homology Domains; D000099192:CD69 Antigens
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D017252:CD3 Complex; D018956:CD5 Antigens; D029742:Caenorhabditis elegans Proteins; D066246:ErbB Receptors; D015801:Helminth Proteins; D037181:Lectins, C-Type; D008565:Membrane Proteins; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D050721:Proto-Oncogene Proteins c-cbl; D011948:Receptors, Antigen, T-Cell; D044767:Ubiquitin-Protein Ligases; D051746:ZAP-70 Protein-Tyrosine Kinase; D020744:rac GTP-Binding Proteins; D000099192:CD69 Antigens; C054979:antigen T cell receptor, zeta chain; C085873:let-23 protein, C elegans; C497262:Zap70 protein, mouse; C493849:Cbl protein, mouse