title: Regulation of cytotoxic T lymphocyte-associated molecule-4 by Src kinases.
abstract: Cytotoxic T lymphocyte-associated molecule-4 (CTLA-4) is a cell surface receptor expressed on activated T cells that can inhibit T cell responses induced by activation of the TCR and CD28. Studies with phosphorylated peptides based on the CTLA-4 intracellular domain have suggested that tyrosine phosphorylation of CTLA-4 may regulate its interactions with cytoplasmic proteins that could determine its intracellular trafficking and/or signal transduction. However, the kinase(s) that phosphorylate CTLA-4 remain uncharacterized. In this report, we show that CTLA-4 can associate with the Src kinases Fyn and Lck and that transfection of Fyn or Lck, but not the unrelated kinase ZAP70, can induce tyrosine phosphorylation of CTLA-4 on residues Y201 and Y218. A similar pattern of tyrosine phosphorylation was found in pervanadate-treated Jurkat T cells stably expressing CTLA-4. Phosphorylation of CTLA-4 Y201 in Jurkat cells correlated with cell surface accumulation of CTLA-4. CTLA-4 phosphorylation induced the association of CTLA-4 with the tyrosine phosphatase SHP-2, but not with phosphatidylinositol 3-kinase. In contrast, Lck-induced phosphorylation of CD28 resulted in the recruitment of phosphatidylinositol 3-kinase, but not SHP-2. These findings suggest that phosphorylation of CD28 and CTLA-4 by Lck activates distinct intracellular signaling pathways. The association of CTLA-4 with Src kinases and with SHP-2 results in the formation of a CTLA-4 complex with the potential to regulate T cell activation.
authors.affiliation: Gwen Knapp Center for Lupus and Immunology Research, Department of Medicine, University of Chicago, Chicago, IL 60637, USA.
authors.forename: E
authors.initials: E
authors.lastname: Chuang
authors.forename: K M
authors.initials: KM
authors.lastname: Lee
authors.forename: M D
authors.initials: MD
authors.lastname: Robbins
authors.forename: J M
authors.initials: JM
authors.lastname: Duerr
authors.forename: M L
authors.initials: ML
authors.lastname: Alegre
authors.forename: J E
authors.initials: JE
authors.lastname: Hambor
authors.forename: M J
authors.initials: MJ
authors.lastname: Neveu
authors.forename: J A
authors.initials: JA
authors.lastname: Bluestone
authors.forename: C B
authors.initials: CB
authors.lastname: Thompson
mesh_terms: D000069594:Abatacept; D000595:Amino Acid Sequence; D015703:Antigens, CD; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D060908:CTLA-4 Antigen; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D006801:Humans; D018796:Immunoconjugates; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000201:enzymology* / Q000276:immunology*; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism*