CD28 Utilizes Vav-1 to Enhance TCR-Proximal Signaling and NF-AT Activation

• Published in: The Journal of immunology (1950) Vol. 165; no. 7; pp. 3820 - 3829
• Main Authors: Michel, Frederique, Mangino, Giorgio, Attal-Bonnefoy, Geraldine, Tuosto, Loretta, Alcover, Andres, Roumier, Anne, Olive, Daniel, Acuto, Oreste
• Format: Journal Article
• Language: English
• Published: United States Am Assoc Immnol 01.10.2000
• Subjects: Adaptor Proteins, Signal Transducing; Adjuvants, Immunologic - metabolism; Adjuvants, Immunologic - physiology; CD28 antigen; CD28 Antigens - metabolism; CD28 Antigens - physiology; Cell Cycle Proteins; DNA-Binding Proteins - metabolism; Humans; Jurkat Cells; NF-AT protein; NFATC Transcription Factors; Nuclear Proteins; Phosphoproteins - biosynthesis; Phosphoproteins - metabolism; Phosphoproteins - physiology; Phosphorylation; Protein-Tyrosine Kinases - biosynthesis; Protein-Tyrosine Kinases - physiology; Proto-Oncogene Proteins - biosynthesis; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins - physiology; Proto-Oncogene Proteins c-vav; Pseudopodia - immunology; Pseudopodia - metabolism; Receptors, Antigen, T-Cell, alpha-beta - physiology; Signal Transduction - immunology; SLP-76 protein; src Homology Domains - immunology; Transcription Factors - metabolism; Transfection; Vav-1 protein; ZAP-70 Protein-Tyrosine Kinase
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.165.7.3820

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.