Vav1 Regulates Phospholipase Cγ Activation and Calcium Responses in Mast Cells

ABSTRACT The hematopoietic cell-specific protein Vav1 is a substrate of tyrosine kinases activated following engagement of many receptors, including FcɛRI. Vav1-deficient mice contain normal numbers of mast cells but respond more weakly than their normal counterparts to a passive systemic anaphylaxis challenge. Vav1-deficient bone marrow-derived mast cells also exhibited reduced degranulation and cytokine production, although tyrosine phosphorylation of FcɛRI, Syk, and LAT (linker for activation of T cells) was normal. In contrast, tyrosine phosphorylation of phospholipase Cγ1 (PLCγ1) and PLCγ2 and calcium mobilization were markedly inhibited. Reconstitution of deficient mast cells with Vav1 restored normal tyrosine phosphorylation of PLCγ1 and PLCγ2 and calcium responses. Thus, Vav1 is essential to FcɛRI-mediated activation of PLCγ and calcium mobilization in mast cells. In addition to its known role as an activator of Rac1 GTPases, these findings demonstrate a novel function for Vav1 as a regulator of PLCγ-activated calcium signals.