The neuropeptides VIP and PACAP inhibit IL-2 transcription by decreasing c-Jun and increasing JunB expression in T cells.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) act as macrophage and T-cell deactivators. Previously we established that VIP/PACAP limit T-cell activation directly, by inhibiting interleukin 2 (IL-2), and indirectly, by reducing the macrophage costimulatory functions. The nature of the IL-2 transcriptional factors affected by VIP/PACAP has not been elucidated. Here we investigate the effect of VIP on the AP-l complexes bound to several regulatory sites. VIP/PACAP downregulate c-Jun, and upregulate JunB mRNA and protein. The reduction in c-Jun correlates with the inhibition of the c-Jun N-terminal kinase (JNK). The effects of VIP/PACAP on c-Jun and JunB expression lead to changes in the composition of the AP-l complexes, from c-Jun/Fos to JunB/Fos dimers, with a subsequent decrease in DNA binding and loss of transactivating activity.