Vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide inhibit the MEKK1/MEK4/JNK signaling pathway in LPS-stimulated macrophages.

The vasoactive intestinal peptide (VIP) and the pituitary adenylate cyclase activating polypeptide (PACAP), two immunomodulatory neuropeptides that affect both innate and acquired immunity, downregulate TNFalpha expression in LPS-stimulated peritoneal macrophages and Raw 264.7 cells. We showed previously that VIP/PACAP change the composition of the CRE-binding complex in the TNFalpha promoter from highc-Jun/(low)CREB, characteristic for LPS-stimulated macrophages, to lowc-Jun/(high)CREB, characteristic for the unstimulated cells. In the present study we examined the effects of VIP/PACAP on the MEKK1/MEK4/JNK transduction pathway, and on the subsequent changes in Jun family members. Our studies indicate that VIP/PACAP inhibit MEKK1 activity, and the subsequent phosphorylation of MEK4, JNK, and c-Jun. Treatment with VIP or PACAP results in a decrease in AP-1 binding, and a marked change in the composition of the AP-1 complexes from c-Jun/c-Fos to JunB/c-Fos. Western blots confirm that VIP stimulates JunB production in LPS-stimulated macrophages. Both the inhibition of the MEKK1/MEK4/JNK pathway, leading to the reduction in phosphorylated c-Jun, and the stimulation of JunB, are mediated through the specific VPAC1 receptor and the cAMP/PKA pathway. The VIP/PACAP interference with the stress-induced SAPK/JNK pathway in stimulated macrophages may represent a significant element in the regulation of the inflammatory response by the endogenous neuropeptides.