Abstract
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.
Publication types
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Adaptor Proteins, Signal Transducing
-
Adjuvants, Immunologic / metabolism
-
Adjuvants, Immunologic / physiology*
-
CD28 Antigens / metabolism
-
CD28 Antigens / physiology*
-
Cell Cycle Proteins*
-
DNA-Binding Proteins / metabolism*
-
Humans
-
Jurkat Cells
-
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*
-
Transcription Factors / metabolism*
-
Transfection
-
ZAP-70 Protein-Tyrosine Kinase
-
src Homology Domains / immunology
Substances
-
Adaptor Proteins, Signal Transducing
-
Adjuvants, Immunologic
-
CD28 Antigens
-
Cell Cycle Proteins
-
DNA-Binding Proteins
-
NFATC Transcription Factors
-
Nuclear Proteins
-
Phosphoproteins
-
Proto-Oncogene Proteins
-
Proto-Oncogene Proteins c-vav
-
Receptors, Antigen, T-Cell, alpha-beta
-
SLP-76 signal Transducing adaptor proteins
-
Transcription Factors
-
VAV1 protein, human
-
Protein-Tyrosine Kinases
-
ZAP-70 Protein-Tyrosine Kinase
-
ZAP70 protein, human