Vav-Rac1-mediated activation of the c-Jun N-terminal kinase/c-Jun/AP-1 pathway plays a major role in stimulation of the distal NFAT site in the interleukin-2 gene promoter

Vav, a hematopoiesis-specific signaling protein, plays an important role in T cell development and activation. Vav upregulates the expression of the i nterleukin-2 (IL 2) gene, primarily via activation of the distal NFAT site in the IL-2 gene promoter (NFAT-IL-2). However, since this site cooperative ly binds NFAT and AP-1, the relative contribution of Vav to NFAT versus AP- 1 activation has not been determined, Here, we studied the respective roles of the AP-1 and NFAT pathways in the T-cell receptor (TCR) mediated, Vav-d ependent activation of NFAT-IL-2. Although Vav stimulated the transcription al activity of an NFAT-IL-2 reporter gene, it failed to stimulate the trans criptional or DNA-binding activities of an AP-1-independent NFAT site deriv ed from the human gamma interferon gene promoter. Vav also did not stimulat e detectable Ca2+ mobilization and nuclear translocation of NFATc or NFATp. On the other hand, Vav induced the activation of Rac1 or Cdc42 and c-Jun N -terminal kinase (JNK), enhanced the transcriptional and DNA-binding activi ties of AP-1, and induced increased phosphorylation of c-Jun, Dominant-nega tive Vav and/or Rac1 mutants blocked the TCR-mediated stimulation of these events, demonstrating the physiological relevance of these effects. Vav als o associated with Rac1 or Cdc42 in T cells, and anti-CD3 antibody stimulati on enhanced this association. These findings indicate that a Rac1-dependent JNK/c-Jun/AP-1 pathway, rather than the Ca2+/NFAT pathway, plays the predo minant role in NFAT-IL-2 activation by Vav.