title: Stimulation of CD28 triggers an association between CD28 and phosphatidylinositol 3-kinase in Jurkat T cells.
abstract: The T cell surface molecule CD28 can provide costimulatory signals that permit the full activation of T cells. Here we demonstrate that stimulation of CD28, either by B7, its natural ligand, or by the anti-CD28 monoclonal antibody 9.3, induces an association between CD28 and phosphatidylinositol 3-kinase (PI3-K) in Jurkat T cells, raising the possibility that an interaction with PI3-K contributes to CD28-mediated signaling. To examine the mechanism of the association, we synthesized tyrosine-phosphorylated oligopeptides corresponding to each of the four tyrosines in the CD28 cytoplasmic domain. When added to lysates of B7-stimulated Jurkat cells, the oligopeptide corresponding to Tyr 173 inhibits the coimmunoprecipitation of PI3-K with CD28; the other oligopeptides have no effect. Tyr 173 is contained within the sequence YMNM, a motif that is also found in the platelet-derived growth factor receptor and that, when phosphorylated, forms a high affinity binding site for the p85 subunit of PI3-K. These observations suggest that phosphorylation of Tyr 173 may mediate the interaction between CD28 and PI3-K. However, because CD28 is not known to be phosphorylated, it remains possible that CD28 interacts with PI3-K through a mechanism independent of tyrosine phosphorylation.
authors.affiliation: Department of Medicine, San Francisco Veterans Affairs Medical Center, California.
authors.forename: K E
authors.initials: KE
authors.lastname: Truitt
authors.forename: C M
authors.initials: CM
authors.lastname: Hicks
authors.forename: J B
authors.initials: JB
authors.lastname: Imboden
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D018106:CD28 Antigens / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D007700:Kinetics; D012515:Mast-Cell Sarcoma; D051379:Mice; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases; D010748:Phosphopeptides / Q000138:chemical synthesis / Q000494:pharmacology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000302:isolation & purification / Q000378:metabolism*; D019000:Phosphotyrosine; D011485:Protein Binding; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000031:analogs & derivatives
chemical_list: D015703:Antigens, CD; D018106:CD28 Antigens; D009842:Oligopeptides; D010748:Phosphopeptides; D019000:Phosphotyrosine; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor)