The Rho family guanine nucleotide exchange factor Vav-2 regulates the development of cell-mediated cytotoxicity

Previous pharmacologic and genetic studies have demonstrated a critical rol e for the low molecular weight GTP-binding protein RhoA in the regulation o f cell-mediated killing by cytotoxic lymphocytes. However, a specific Rho f amily guanine nucleotide exchange factor (GEF) that activates this critical regulator of cellular cytotoxicity has not been identified. in this study, we provide evidence that the Rho family GEF, Vav-2, is present in cytotoxi c lymphocytes, and becomes tyrosine phosphorylated after the cross-linking of activating receptors on cytotoxic lymphocytes and during the generation of cell-mediated killing. In addition, we show that overexpression of Vav-2 in cytotoxic lymphocytes enhances cellular cytotoxicity, and this enhancem ent requires a functional Dbl homology and Src homology 2 domain. Interesti ngly, the pleckstrin homology domain of Vav-2 was found to be required for enhancement of killing through some, but not all activating receptors on cy totoxic lymphocytes. Lastly, although Vav and Vav-2 share significant struc tural homology, only Vav is able to enhance nuclear factor of activated T c ells-activator protein 1-mediated gene transcription downstream of the T ce ll receptor. receptor. These data demonstrate that Vav-2, a Rho family GEF, differs from Vav in the control of certain lymphocyte functions and partic ipates in the control of cell-mediated killing by cytotoxic lymphocytes.