Protein kinase C theta cooperates with Vav1 to induce JNK activity in T-cells

Here we show that in human T-cell leukemia cells Vav1 and protein kinase C theta (PKC theta) synergize for the activation of c-Jun N-terminal kinase ( JNK) but not p38 MAP kinase. Vav1 and PKC theta also cooperated to induce t ranscription of reporter genes controlled either by AP-1 binding sites or t he CD28RE/AP composite element contained in the IL-2 promoter by stimulatin g the binding of transcription factors to these two elements. Dominant nega tive versions of Vav1 and PKC theta inhibited CD3/CD28-induced activation o f JNK revealing their relative importance for this activation pathway, Gel filtration experiments revealed the existence of constitutively associated Vav1/PKC theta heterodimers in extracts from unstimulated T-cells, whereas T-cell costimulation induced the recruitment of Vav1 into high molecular we ight, complexes. Several experimental approaches showed that Vav1 is locate d upstream from PKC theta in the control of the pathway leading to synergis tic JNK activation. Vav1-derived signals lead to the activation of JNK by a t least two different pathways. The major contribution of Vav1 for the acti vation of JNK relies on the PKC theta -mediated CA(2+)-independent synergis tic activation pathway, whereas JNK is also activated by a separate Ca2+-de pendent signaling route.