Tyrosine Phosphorylation of the vav Proto-Oncogene Product in Activated B Cells

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Abstract
Activation of B lymphocytes by engagement of their immunoglobulin M antigen receptors results in phosphorylation of a number of proteins on tyrosine residues. One such protein is p95 vav , the product of the vav proto-oncogene. Tyrosine phosphorylation of p95 vav occurred within seconds of immunoglobulin M cross-linking and was independent of other events induced during stimulation of B cells, such as protein kinase C activation, guanosine triphosphate-binding protein signaling, and calcium mobilization. Moreover, engagement of antigen receptors induced the rapid (∼5 seconds) and transient (∼60 seconds) association of p95 vav with a 70-kilodalton tyrosine-phosphorylated protein, Vap-1, an interaction mediated by the Src homology 2 domain of p95 vav . These results suggest that the vav proto-oncogene participates in the signaling processes that mediate the antigen-induced activation of B lymphocytes.