MRC National Institute for Medical Research, London
Science for Health
Victor Tybulewicz group project:
Vav1
Vav1 is a guanine nucleotide exchange factor (GEF) for members of the Rho-family of small GTPases, including Rac1, Cdc42 and RhoA. This activity is activated by tyrosine phosphorylation. Using gene targeting we have shown that Vav1 plays a critical role in T cell development. Vav1-deficient mice show a partial block in thymic development at the pre-TCR checkpoint which monitors for successful rearrangement of the TCRβ genes, as well as stronger blocks in positive and negative selection of double positive thymocytes into the peripheral T cell pool (Tarakhovsky et al, 1995; Turner et al, 1997).
Analysis of TCR signalling in these mice showed that Vav1 was required for TCR-induced calcium flux, ERK and NF-κB activation (Costello et al, 1999). Furthermore we showed that the calcium defect was due to defective activation of phospholipase Cγ1 probably because of a failure to activate phophatidylinositide-3-kinase (PI3K) and the Tec-family kinases Itk and Tec (Reynolds et al, 2002).
Using knock-in gene targeting, we have generated mice expressing an enzymatically inactive Vav1. This showed that the GEF activity of Vav1 was important for some, but not all of its functions (Saveliev et al, 2009). In particular, Vav1’s GEF activity is required to transduce signals leading to PI3K activation and actin polymerization, but not to calcium flux, ERK activation or T cell polarization. The latter pathways are dependent on a GEF-independent function of Vav1, which is currently under investigation.
In collaboration with Katrin Rittinger (Molecular Structure, NIMR) we have analysed the structure of the catalytically active part of Vav1. This showed that the PH and C1 domains of the protein play a critical role in supporting catalysis by the DH domain (Rapley et al, 2008). The structure suggested a possible allosteric regulation of Vav1.
Structure of Vav1 and Rac1
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Diagram showing structure of Vav1 and Rac1. Ribbon diagram of the DH, PH and C1 domains of Vav1 (grey) in complex with Rac1 (gold) (Rapley et al., 2008). Amino acids Leu 334 and Lys 335 (red) were mutated to generate an enzymatically inactive Vav1 (see Saveliev et al.).
Selected publications
- Tarakhovsky, A., M. Turner, S. Schaal, P.J. Mee, L.P. Duddy, K. Rajewsky, and V.L.J. Tybulewicz. (1995)
Defective antigen receptor-mediated proliferation of B and T cells in the absence of Vav.
Nature 374, 467-470 PubMed abstract - Turner, M., P.J. Mee, A. Walters, M.E. Quinn, A.L. Mellor, R. Zamoyska, and V.L.J. Tybulewicz. (1997)
A requirement for the Rho-family GTP exchange factor Vav in positive and negative selection of thymocytes.
Immunity 7, 451-460 PubMed abstract - Reynolds, L.F., L.A. Smyth, T. Norton, N. Freshney, J. Downward, D. Kioussis, and V.L.J. Tybulewicz. (2002)
Vav1 transduces T cell receptor signals to the activation of phospholipase C-g1 via phosphoinositide 3-kinase-dependent and -independent pathways.
Journal of Experimental Medicine 195, 1103-1114 PubMed abstract - Prisco, A; Vanes, L; Ruf, S; Trigueros, C and Tybulewicz, VL (2005)
Lineage-specific requirement for the PH domain of Vav1 in the activation of CD4+ but not CD8+ T cells
Immunity 23, 263-274 PubMed abstract - Rapley, J; Tybulewicz, VLJ and Rittinger, K (2008)
Crucial structural role for the PH and C1 domains of the Vav1 exchange factor.
EMBO Reports 9, 655-661 PubMed abstract - Saveliev, A; Vanes, L; Ksionda, O; Rapley, J; Smerdon, SJ; Rittinger, K and Tybulewicz, VLJ (2009)
Function of the nucleotide exchange activity of Vav1 in T cell development and activation.
Science Signaling 2, ra83 PubMed abstract
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