title: The inhibitory function of CTLA-4 does not require its tyrosine phosphorylation.
abstract: CTLA-4 is a negative regulator of T cell responses. Sequence analysis of this molecule reveals the presence of two cytoplasmic tyrosine residues at positions 165 and 182 that are potential Src homology (SH)-2 domain binding sites. The role of phosphorylation of these residues in CTLA-4-mediated signaling is unknown. Here, we show that sole TCR ligation induces zeta-associated protein (ZAP)-70-dependent tyrosine phosphorylation of CTLA-4 that is important for cell surface retention of this molecule. However, CTLA-4 tyrosine phosphorylation is not required for down-regulation of T cell activation following CD3-CTLA-4 coengagement. Specifically, inhibition of extracellular signal-regulated kinase (ERK) activation and of IL-2 production by CTLA-4-mediated signaling occurs in T cells expressing mutant CTLA-4 molecules lacking the cytoplasmic tyrosine residues, and in lck-deficient or ZAP-70-deficient T cells. Therefore, CTLA-4 function involves interplay between two different levels of regulation: phosphotyrosine-dependent cell surface retention and phosphotyrosine-independent association with signaling molecules.
authors.affiliation: The John P. Robarts Research Institute, Department of Microbiology and Immunology, University of Western Ontario, London, Canada.
authors.forename: M L
authors.initials: ML
authors.lastname: Baroja
authors.forename: D
authors.initials: D
authors.lastname: Luxenberg
authors.forename: T
authors.initials: T
authors.lastname: Chau
authors.forename: V
authors.initials: V
authors.lastname: Ling
authors.forename: C A
authors.initials: CA
authors.lastname: Strathdee
authors.forename: B M
authors.initials: BM
authors.lastname: Carreno
authors.forename: J
authors.initials: J
authors.lastname: Madrenas
mesh_terms: D000069594:Abatacept; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D017252:CD3 Complex / Q000276:immunology / Q000378:metabolism; D060908:CTLA-4 Antigen; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D003593:Cytoplasm / Q000276:immunology / Q000378:metabolism; D004789:Enzyme Activation / Q000276:immunology; D006801:Humans; D018796:Immunoconjugates; D007166:Immunosuppressive Agents / Q000378:metabolism*; D007376:Interleukin-2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D019169:Jurkat Cells; D008024:Ligands; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism*; D051746:ZAP-70 Protein-Tyrosine Kinase
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D017252:CD3 Complex; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D018796:Immunoconjugates; D007166:Immunosuppressive Agents; D007376:Interleukin-2; D008024:Ligands; D014443:Tyrosine; D000069594:Abatacept; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases