CD28 utilizes Vav-1 to enhance TCR-proximal signaling and NF-AT activation.
The mechanism through which CD28 costimulation potentiates TCR-driven gene expression is still not clearly defined. Vav-1, an exchange factor for Rho GTPases thought to regulate, mainly through Rac-1, various signaling components leading to cytokine gene expression, is tyrosine phosphorylated upon CD28 engagement. Here, we provide evidence for a key role of Vav-1 in CD28-mediated signaling. Overexpression of Vav-1 in Jurkat cells in combination with CD28 ligation strongly reduced the concentration of staphylococcus enterotoxin E/MHC required for TCR-induced NF-AT activation. Surprisingly, upon Vav-1 overexpression CD28 ligation sufficed to activate NF-AT in the absence of TCR engagement. This effect was not mediated by overexpression of ZAP-70 nor of SLP-76 but necessitated the intracellular tail of CD28, the intactness of the TCR-proximal signaling cascade, the Src-homology domain 2 (SH2) domain of Vav-1, and SLP-76 phosphorylation, an event which was favored by Vav-1 itself. Cells overexpressing Vav-1 formed lamellipodia and microspikes reminiscent of Rac-1 and Cdc42 activation, respectively, for which the SH2 domain of Vav-1 was dispensable. Together, these data suggest that CD28 engagement activates Vav-1 to boost TCR signals through a synergistic cooperation between Vav-1 and SLP-76 and probably via cortical actin changes to facilitate the organization of a signaling zone.
Michel
F
F
Department of Immunology, Institut Pasteur, Paris, France. fmichel@pasteur.fr
Mangino
G
G
Attal-Bonnefoy
G
G
Tuosto
L
L
Alcover
A
A
Roumier
A
A
Olive
D
D
Acuto
O
O
D048868:Adaptor Proteins, Signal Transducing; D000276:Adjuvants, Immunologic / Q000378:metabolism / Q000502:physiology*; D018106:CD28 Antigens / Q000378:metabolism / Q000502:physiology*; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010750:Phosphoproteins / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051567:Proto-Oncogene Proteins c-vav; D011554:Pseudopodia / Q000276:immunology / Q000378:metabolism; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000502:physiology*; D015398:Signal Transduction / Q000276:immunology*; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D051746:ZAP-70 Protein-Tyrosine Kinase; D018909:src Homology Domains / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D000276:Adjuvants, Immunologic; D018106:CD28 Antigens; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; D016693:Receptors, Antigen, T-Cell, alpha-beta; C092947:SLP-76 signal Transducing adaptor proteins; D014157:Transcription Factors; C496618:VAV1 protein, human; D011505:Protein-Tyrosine Kinases; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human