Functional Dichotomy in Natural Killer Cell Signaling: Vav1-Dependent and -Independent Mechanisms

The product of the protooncogene Vav1 participates in multiple signaling pathways and is a critical regulator of antigen–receptor signaling in B and T lymphocytes, but its role during in vivo natural killer (NK) cell differentiation is not known. Here we have studied NK cell development in Vav1^−/− mice and found that, in contrast to T and NK-T cells, the absolute numbers of phenotypically mature NK cells were not reduced. Vav1^−/− mice produced normal amounts of interferon (IFN)-γ in response to Listeria monocytogenes and controlled early infection but showed reduced tumor clearance in vivo. In vitro stimulation of surface receptors in Vav1^−/− NK cells resulted in normal IFN-γ production but reduced tumor cell lysis. Vav1 was found to control activation of extracellular signal-regulated kinases and exocytosis of cytotoxic granules. In contrast, conjugate formation appeared to be only mildly affected, and calcium mobilization was normal in Vav1^−/− NK cells. These results highlight fundamental differences between proximal signaling events in T and NK cells and suggest a functional dichotomy for Vav1 in NK cells: a role in cytotoxicity but not for IFN-γ production.