Following VEGF treatment, VAV2 phosphorylation on tyrosine 172 stimulates its GEF activity for RAC1 (Garrett et al. 2007) and thus plays an important role in linking VEGFR2 to endothelial migration. VAV exists in an auto-inhibitory state, folded in such a way as to inhibit the GEF activity of its DH domain. This folding is mediated through binding of tyrosines in the acidic domain to the DH domain and through binding of the calponin homology (CH) domain to the C1 region. Activation of VAV is thought to involve three events which relieve this auto-inhibition: phosphorylation of tyrosines in the acidic domain causes them to be displaced from the DH domain; binding of a ligand to the CH domain may cause it to release the C1 domain; binding of the PI3K product PIP3 to the PH domain may alter its conformation (Aghazadeh et al. 2000). VAV is phosphorylated on a tyrosine residue (Y174 in VAV1, 172 in VAV2, 173 in VAV3) in the acidic domain. This is mediated by Src and related family tyrosine kinases (Deckert et al. 1996, Schuebel et al. 1998).