Mitogenic CD28 signals require the exchange factor Vav1 to enhance TCR signaling at the SLP-76-Vav-Itk signalosome.
Almost all physiological T cell responses require costimulation-engagement of the clonotypic TCR with MHC/Ag and CD28 by its ligands CD80/86. Whether CD28 provides signals that are qualitatively unique or quantitatively amplify TCR signaling is poorly understood. In this study, we use superagonistic CD28 Abs, which induce T cell proliferation without TCR coligation, to determine how CD28 contributes to mitogenic responses. We show that mitogenic CD28 signals require but do not activate the proximal TCR components TCRzeta and Zap-70 kinase. In cell lines lacking proximal TCR signaling, an early defect in the CD28 pathway is in phosphorylation of the adaptor molecule SLP-76, which we show is essential for recruitment of the exchange factor Vav leading to Ca(2+) flux and IL-2 production. Point mutations in CD28 that result in diminished Vav phosphorylation also result in defective Ca(2+) flux, IL-2 production, and Tec-kinase phosphorylation. Using Vav1-deficient mice, we further demonstrate the importance of Vav1 for efficient proliferation, IL-2 production, and Ca(2+) flux. Our results indicate that CD28 signals feed into the TCR signaling pathway at the level of the SLP-76 signalosome.
Dennehy
Kevin M
KM
Institute of Virology and Immunobiology, University of Würzburg, Würzburg, Germany.
Elias
Fernando
F
Na
Shin-Young
SY
Fischer
Klaus-Dieter
KD
Hünig
Thomas
T
Lühder
Fred
F
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D018106:CD28 Antigens / Q000502:physiology*; D049109:Cell Proliferation; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D046912:Multiprotein Complexes; D010750:Phosphoproteins / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav / Q000378:metabolism / Q000502:physiology*; D051381:Rats; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000166:cytology
D048868:Adaptor Proteins, Signal Transducing; D018106:CD28 Antigens; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D051567:Proto-Oncogene Proteins c-vav; D011948:Receptors, Antigen, T-Cell; C092947:SLP-76 signal Transducing adaptor proteins; C496618:VAV1 protein, human; C496619:Vav1 protein, mouse; D011505:Protein-Tyrosine Kinases; C080813:emt protein-tyrosine kinase