CD28-mediated costimulation in the absence of phosphatidylinositol 3-kinase association and activation.
T-cell activation involves two distinct signal transduction pathways. Antigen-specific signaling events are initiated by T-cell receptor recognition of cognate peptide presented by major histocompatibility complex molecules. Costimulatory signals, which are required for optimal T-cell activation and for overcoming the induction of anergy, can be provided by the homodimeric T-cell glycoprotein CD28 through its interaction with the counterreceptors B7-1 and B7-2 on antigen-presenting cells. Ligation of CD28 results in its phosphorylation on tyrosines and the subsequent recruitment and activation of phosphatidylinositol 3-kinase (PI 3-kinase). It has been suggested that the induced association of CD28 and PI 3-kinase is required for costimulation. We report here that ligation of CD19, a heterologous B-cell receptor that also associates with and activates PI 3-kinase upon ligation, failed to costimulate interleukin-2 production. Moreover, pharmacological inhibition of PI 3-kinase activity failed to block costimulation mediated by CD28. By mutational analysis, we demonstrate that disruption of PI 3-kinase association with CD28 also did not abrogate costimulation. These results argue that PI 3-kinase association with CD28 is neither necessary nor sufficient for costimulation of interleukin-2 production. Finally, we identify specific amino acid residues required for CD28-mediated costimulatory activity.
Crooks
M E
ME
Department of Microbiology and Immunology, University of California, San Francisco 94143, USA.
Littman
D R
DR
Carter
R H
RH
Fearon
D T
DT
Weiss
A
A
Stein
P H
PH
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D018941:Antigens, CD19 / Q000502:physiology; D018106:CD28 Antigens / Q000096:biosynthesis / Q000502:physiology*; D002460:Cell Line; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis*; D008156:Luciferases / Q000096:biosynthesis; D008213:Lymphocyte Activation; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000096:biosynthesis / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D018941:Antigens, CD19; D018106:CD28 Antigens; D004791:Enzyme Inhibitors; D007376:Interleukin-2; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D008156:Luciferases; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D000077191:Wortmannin