title: Co-stimulation of IL-2 production by CD28 is independent of tyrosine-based signaling motifs in a murine T cell hybridoma.
abstract: In addition to the antigen-specific stimulus delivered by the TCR, T cells under most circumstances require a co-stimulatory signal for complete activation. CD28 can provide this signal, and the importance of CD28-mediated co-stimulation has been well documented both in vitro and in vivo, but the intracellular pathways downstream of CD28 are less well characterized. So far, maximal co-stimulation of IL-2 production has been attributed to tyrosine-based signaling motifs, either including the first cytoplasmic tyrosine residue that binds phosphatidylinositol 3'-kinase (PI3-K), or the third tyrosine residue. Here we describe results of the expression of murine CD28 receptor mutants in a CD28-deficient murine T cell hybridoma, A1.1. We show that in A1.1 cells co-stimulation of IL-2 production is independent of CD28 cytoplasmic tyrosine residues, since a mutant lacking all four cytoplasmic tyrosines is still able to induce a full co-stimulatory response. Using truncation mutants, this activity can be attributed to amino acids 183 to 194, a sequence containing a conserved diproline motif that may recruit SH3 domains of other signaling molecules like Grb2. Thus we have identified a novel pathway for CD28-mediated co-stimulation of IL-2 production that is independent of PI3-K activity and phosphotyrosine-based signaling motifs.
authors.affiliation: Department of Medicine III and Institute for Clinical Immunology and Rheumatology, Friedrich-Alexander-University Erlangen-Nuremberg, Nuremberg, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Nagel
authors.forename: J R
authors.initials: JR
authors.lastname: Kalden
authors.forename: B
authors.initials: B
authors.lastname: Manger
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids; D000818:Animals; D018106:CD28 Antigens / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D015870:Gene Expression; D006825:Hybridomas; D007376:Interleukin-2 / Q000096:biosynthesis*; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010835:Phytohemagglutinins / Q000494:pharmacology; D021382:Protein Sorting Signals / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D018106:CD28 Antigens; D007376:Interleukin-2; D010835:Phytohemagglutinins; D021382:Protein Sorting Signals; D014443:Tyrosine; D015759:Ionomycin; D019869:Phosphatidylinositol 3-Kinases