Vav is a regulator of cytoskeletal reorganization mediated by the T-cell receptor

Abstract

Background: Vav is a guanine-nucleotide exchange factor for the Rho-like small GTPases RhoA, Rac1 and Cdc42, which regulate cytoskeletal reorganization and activation of stress-activated protein kinases (SAPK/JNKs). Vav is expressed in hematopoietic cells and is phosphorylated in T and B cells following activation of various growth factor or antigen receptors. Vav interacts with several signaling molecules in T cells, but the functional relevance of these interactions is established only for Slp 76: they cooperate to induce activity of the transcription factor NF-AT and interleukin-2 expression. We have investigated the role of Vav in T cells by generating vav^−/− mice. Results: Mice deficient for vav were viable and healthy, but had impaired T-cell development. In vav^−/− T cells, in response to activation of the T-cell receptor (TCR), cell cycle progression, induction of NF-ATc1 activity, downregulation of the cell-cycle inhibitor p27^Kip1, interleukin-2 production, actin polymerization and the clustering of TCRs into patches and caps – a cytoskeletal reorganization process – were defective. TCR-mediated activation of mitogen-activated protein kinase and SAPK/JNK was unaffected. Ca²⁺ mobilization was impaired in vav^−/− thymocytes and T cells. In wild-type cells, Vav constitutively associated with the cytoskeletal membrane anchors talin and vinculin. In the absence of Vav, phosphorylation of Slp76, Slp76–talin interactions, and recruitment of the actin cytoskeleton to the CD3ζ chain of the TCR co-receptor were impaired. Conclusions: Vav is a crucial regulator of TCR-mediated Ca²⁺ flux, cytoskeletal reorganization and TCR clustering, and these are required for T-cell maturation, interleukin-2 production and cell cycle progression.