Two distinct regions of the CD28 intracytoplasmic domain are involved in the tyrosine phosphorylation of Vav and GTPase activating protein-associated p62 protein.
The T cell-associated CD28 molecule plays a key role in T cell co-stimulation. Its ligation induces the tyrosine phosphorylation of numerous proteins including CD28 itself as well as a restricted set of substrates of 97 and 62-68 kDa which are poorly phosphorylated by the tyrosine kinases induced by CD3-TCR triggering. In this study, we identify these substrates as the product of the vav proto-oncogene and as a 62 kDa protein that could correspond at least in part to p62dok, the 62 kDa adaptor molecule associated to p120 Ras-GTPase activating protein. Both p97vav and p62 are tyrosine phosphorylated upon CD28 ligation by mAb or by its counter-receptor B7-1/CD80. Using CD28 mutants, we also show that Vav and p62 tyrosine phosphorylation is regulated by distinct domains within the CD28 cytoplasmic tail: residues 173-181 for Vav and residues 182-202 for p62. Finally, the phosphorylation of Vav and p62 does not require an intact binding site for Grb-2 or p85 SH2 domains. We thus demonstrate that the CD28 cytoplasmic domain contains at least three functionally independent regions involved in CD28-induced signal transduction, since in addition to the Grb-2 and p85 SH2 domain binding site (Tyr173), residues 173-181 and 182-202 are associated with Vav and p62 tyrosine phosphorylation respectively.
Klasen
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INSERM U119, Marseille, France.
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Peyron
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Cantrell
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Olive
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D000818:Animals; D001665:Binding Sites; D018106:CD28 Antigens / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D016601:RNA-Binding Proteins / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism*
D018106:CD28 Antigens; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C489560:DOK1 protein, human; C489561:Dok1 protein, mouse; C074561:GAP-associated protein p62; C000715470:MAS1 protein, human; D010750:Phosphoproteins; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D016601:RNA-Binding Proteins; C496618:VAV1 protein, human; C496619:Vav1 protein, mouse; D014443:Tyrosine