Vav1 is a hematopoietic-specific Rho GDP/GTP exchange factor and signaling adaptor. Although these activities are known to be stimulated by direct Vav1 phosphorylation, little information still exists regarding the regulatory layers that influence the overall Vav1 activation cycle. Using a collection of cell models and activation-mimetic Vav1 mutants, we show here that the dephosphorylated state of Vav1 in nonstimulated T cells requires the presence of a noncatalytic, phospholipase Cγ1–Slp76-mediated inhibitory pathway. Upon T cell stimulation, Vav1 becomes rapidly phosphorylated via the engagement of Lck and, to a much lesser extent, other Src family kinases and Zap70. In this process, Lck, Zap70 and the adaptor protein Lat contribute differently to the dynamics and amplitude of the Vav1 phosphorylated pool. Consistent with a multiphosphosite activation mechanism, the optimal stimulation of Vav1 can only be recapitulated by the combination of several activation-mimetic phosphosite mutants. The analysis of these mutants has also unveiled the presence of different Vav1 signaling competent states that are influenced by phosphosites present in the N- and C-terminal domains of the protein.

Vav1 是一种造血特异性 Rho GDP/GTP 交换因子和信号转接器。尽管已知这些活动受到直接 Vav1 磷酸化的刺激，但关于影响整个 Vav1 激活周期的调节层的信息仍然很少。使用一系列细胞模型和激活模拟 Vav1 突变体，我们在此显示未刺激的 T 细胞中 Vav1 的去磷酸化状态需要存在非催化的磷脂酶 Cγ1-Slp76 介导的抑制途径。在 T 细胞刺激后，Vav1 通过 Lck 的参与迅速磷酸化，并且在较小程度上，其他 Src 家族激酶和 Zap70。在这个过程中，Lck、Zap70 和接头蛋白 Lat 对 Vav1 磷酸化池的动力学和幅度的贡献不同。与多磷酸位点激活机制一致，Vav1 的最佳刺激只能通过几种模拟激活的磷酸位点突变体的组合来概括。对这些突变体的分析还揭示了不同 Vav1 信号传导能力状态的存在，这些状态受蛋白质 N 和 C 末端结构域中存在的磷酸位点的影响。