Vav2 Activates c-fos Serum Response Element and CD69 Expression but Negatively Regulates Nuclear Factor of Activated T Cells and Interleukin-2 Gene Activation in T Lymphocyte

Abstract

Vav1 and Vav2 are members of the Dbl family of guanine nucleotide exchange factors for the Rho family of small GTPases. Although the role of Vav1 during lymphocyte development and activation is well characterized, the function of Vav2 is still unclear. In this study, we compared the signaling pathways regulated by Vav1 and Vav2 following engagement of the T cell receptor (TCR). We show that Vav2 is tyrosine-phosphorylated upon TCR stimulation and by co-expressed Src and Syk family kinases. Using glutathione S-transferase fusion proteins, we observed that the Src homology 2 domain of Vav2 binds tyrosine-phosphorylated proteins from TCR-stimulated Jurkat T cell lysates, including c-Cbl and SLP-76. Like Vav1, Vav2 cooperated with TCR stimulation to increase extracellular signal-regulated kinase activation and to promote c-fos serum response element transcriptional activity. Moreover, both proteins displayed a similar action in increasing the expression of the early activation marker CD69 in Jurkat T cells. However, in contrast to Vav1, Vav2 dramatically suppressed TCR signals leading to nuclear factor of activated T cells (NF-AT)-dependent transcription and induction of the interleukin-2 promoter. Vav2 appears to act upstream of the phosphatase calcineurin because a constitutively active form of calcineurin rescued the effect of Vav2 by restoring TCR-induced NF-AT activation. Interestingly, the Dbl homology and Src homology 2 domains of Vav2 were necessary for its inhibitory effect on NF-AT activation and for induction of serum response element transcriptional activity. Taken together, our results indicate that Vav1 and Vav2 exert overlapping but nonidentical functions in T cells. The negative regulatory pathway elicited by Vav2 might play an important role in regulating lymphocyte activation processes.