title: TCR subunit specificity of CTLA-4-mediated signaling.
abstract: Cytotoxic T-lymphocyte-associated antigen (CTLA)-4 is an activation-induced receptor that down-regulates T cell responses by antagonizing B7-dependent costimulation and/or by transducing a negative signal. The mechanism of CTLA-4-mediated negative signaling is unknown. Recently, it has been postulated that CTLA-4 inhibits T cell activation by causing specific dephosphorylation of the T cell receptor (TCR)-zeta chain of the antigen-receptor complex through an lck-dependent recruitment of the Src homology-2-containing tyrosine phosphatase-2. To test this hypothesis, we generated stably transfected T cell clones expressing doxycycline-inducible CTLA-4 with CD25:TCR-zeta (CD25-zeta) or CD25:CD3-epsilon (CD25-epsilon) fusion proteins. In these clones, ligation of CD25-zeta or of CD25-epsilon with antibodies against CD25 induced full T cell activation, as illustrated by extracellular signal-regulated kinase (ERK) activation and interleukin (IL)-2 production. More importantly, coligation of CTLA-4 with CD25-zeta or of CTLA-4 with CD25-epsilon in the respectively transfected clones inhibited ERK activation and IL-2 production, demonstrating that CTLA-4 does not specifically inhibit signals from TCR-zeta but can also inhibit signals from CD3-epsilon. Our results suggest that the target specificity of CTLA-4 is determined by its coligation with any given transmembrane receptor rather than by its intracellular mediators.
authors.affiliation: The FOCIS Centre for Clinical Immunology and Immunotherapeutics, Robarts Research Institute, London, Ontario, Canada N6A 5K8.
authors.forename: Eric
authors.initials: E
authors.lastname: Siu
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: Carreno
authors.forename: Joaquín
authors.initials: J
authors.lastname: Madrenas
mesh_terms: D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D017252:CD3 Complex / Q000378:metabolism; D060908:CTLA-4 Antigen; D015536:Down-Regulation; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000378:metabolism*; D015375:Receptors, Interleukin-2 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D017252:CD3 Complex; D060908:CTLA-4 Antigen; C556706:CTLA4 protein, human; D007376:Interleukin-2; D008565:Membrane Proteins; D011948:Receptors, Antigen, T-Cell; D015375:Receptors, Interleukin-2; C054979:antigen T cell receptor, zeta chain; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D020928:Mitogen-Activated Protein Kinases; D054648:Protein Phosphatase 2; D017027:Protein Tyrosine Phosphatases