TBK1-targeted suppression of TRIF-dependent signaling pathway of Toll-like receptors by helenalin

Abstract

Aims: The purpose of this study was to evaluate the therapeutic potential of the helenalin in Toll-like receptor (TLR) signaling pathways. Main methods: RAW264.7 cells were transfected with a NF-kappa B, IFN beta PRDIII-I, or IP-10 luciferase plasmid and then luciferase enzyme activities were determined by luciferase assay. The expression of iNOS, COX-2, and IF-ID and phosphorylation of IRF3 were determined by Western blotting. The levels of IP-10 were determined with culture medium by using IP-10 ELISA kit. TBK1 kinase activity was determined by MBP assay kit. Key findings: Helenalin inhibited transcription factor NF-kappa B and IRF3 activation, which was induced by TLR agonists as well as its target genes, such as COX-2, iNOS, and IP-10. Helenalin attenuated ligand-independent activation of NF-kappa B induced by MyD88, IKK beta, and p65, and IRF3 induced by TRIF, TBK1, or IRF3. Furthermore, helenalin inhibited TBK1 kinase activity in vitro. Significance: TLRs are primary sensors that detect a wide variety of microbial components and play an important role in the induction of innate immune. To evaluate the therapeutic potential of helenalin, we examined its effect on signal transduction via the TLR signaling pathways. Our results suggest that beneficial effects of helenalin on chronic inflammatory diseases are mediated through modulation of TLR signaling pathways by targeting TBK1. (C) 2013 Elsevier Inc. All rights reserved.