Kavain inhibition of LPS-induced TNF-α via ERK/LITAF
Kavain, an extract from the shrub Piper methysticum, was recently reported to modulate TNF-α expression in both human and mouse cells via regulation of LPS-Induced TNF-Alpha Factor (LITAF). The purpose of the present study was to define the molecular pathway(s) associated with Kavain′s effects on TNF modulation. In vitro studies using WT mouse primary macrophages showed that Kavain significantly reduced E. coli LPS-induced TNF-α production but this effect was almost abrogated in LITAF−/− and ERK2−/− cells. Therefore we reintroduced the ERK2 gene in ERK2−/− cells and partially restored E. coli LPS-induced LITAF-mediated TNF-α production. The translocation of LITAF into to nucleus was found to be dependent on ERK2 S206 residue. Kavain inhibits LITAF/TNF-α expression via dephosphorylation of ERK2 in response to E. coli LPS. Finally, in vivo, Kavain had a significant anti-inflammatory effect on wild type mice that developed Collagen Antibody Induced Arthritis (CAIA), but only a minor effect in ERK2−/− mice also affected by CAIA. Based on these findings, we concluded that ERK2 may be the kinase upstream for LITAF being a crucial factor for Kavain-mediated regulation of LPS-induced TNF-α.