Tyrosine-phosphorylated Vav1 as a point of integration for T-cell receptor- and CD28-mediated activation of JNK, p38, and interleukin-2 transcription

In this study Re identified tyrosine-phosphorylated Vav1 as an early point of integration between the signaling routes triggered by the T-cell recepto r and CD28 in human T-cell leukemia cells. Costimulation resulted in a prol onged and sustained phosphorylation and membrane localization of Vav1 in co mparison to T-cell receptor activation alone. T-cell stimulation induced th e recruitment of Vav1 to an inducible multiprotein T-cell activation signal ing complex at the plasma membrane. Vav1 activated the mitogen-activated pr otein kinases JNK and p38. The Vav1-mediated activation of JNK employed a p athway involving Rac, HPK1, MLK3, and MKK7. The costimulation-induced activ ation of p38 was inhibited by dominant negative forms of Vav1, Pac, and MKK 6. Here we show that Vav1 also induces transcription factors that bind to t he CD28RE/AP element contained in the interleukin-2 promoter. A detailed mu tational analysis of Vav1 revealed a series of constitutively active and no nfunctional forms of Vav1. Almost all inactive versions were mutated in the ir Dbl homology domain and behaved as dominant negative mutants that impair ed costimulation-induced activation of JNK, p38, and CD28RE/AP-dependent tr anscription. In contrast to NF-AT-dependent transcription, Vav1-mediated tr anscriptional induction of the CD28RE/AP element in the interleukin-a promo ter could only partially be inhibited by cyclosporin A, suggesting a dual r ole of Vav1 for controlling Ca2+-dependent and -independent events.