title: CD28 delivers costimulatory signals independently of its association with phosphatidylinositol 3-kinase.
abstract: CD28, a cell-surface molecule expressed by T cells, delivers costimulatory signals during the activation of T cells by Ag. Stimulation of CD28 induces its association with phosphatidylinositol 3'-kinase (PI3-K), raising the possibility that PI3-K plays a critical role in CD28 signaling. We find, however, that wortmannin, a potent inhibitor of PI3-K, does not block CD28-mediated costimulation of Jurkat (a human T cell line) or of murine CD4+ T cells. To address further the role of PI3-K in CD28-mediated signaling, we expressed mutant murine CD28 molecules in Jurkat cells. Mutation of Tyr 170 of murine CD28 to Phe abrogates the association of murine CD28 with PI3-K but does not affect the ability of murine CD28 to augment IL-2 production by Jurkat cells in response to the combination of ionomycin and PMA. Conversely, a mutant of murine CD28 that has a Tyr at position 170 but has Phe substitutions at the remaining three cytoplasmic tyrosines retains the ability to associate with PI3-K and has an impaired ability to deliver a costimulus that augments IL-2 production. CD28, therefore, can deliver costimulatory signals independently of its interaction with PI3-K, and association with PI3-K is insufficient to mediate the full effector function of CD28. Optimal signaling by CD28 requires the integrity of one or more of the carboxyl-terminal three Tyr residues.
authors.affiliation: Department of Medicine, Veterans Affairs Medical Center, San Francisco, CA, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Truitt
authors.forename: J
authors.initials: J
authors.lastname: Shi
authors.forename: S
authors.initials: S
authors.lastname: Gibson
authors.forename: L G
authors.initials: LG
authors.lastname: Segal
authors.forename: G B
authors.initials: GB
authors.lastname: Mills
authors.forename: J B
authors.initials: JB
authors.lastname: Imboden
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D018106:CD28 Antigens / Q000235:genetics / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis*; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D015290:Second Messenger Systems; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D018106:CD28 Antigens; D007376:Interleukin-2; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D000077191:Wortmannin