TRAF4 acts as a silencer in TLR-mediated signaling through the association with TRAF6 and TRIF

Toll-like receptors (TLR) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase play an essential role in intracellular eradication of engulfed pathogens. Here, we demonstrate the physical and functional association between components of the cytosolic NADPH oxidase and TLR-mediated signaling molecules. Cytosolic components of NADPH oxidase suppressed TLR-mediated NF-kappaB activation as well as IFN-beta promoter activation. We demonstrate that TNF-associated factor (TRAF) 4 associates with p47(phox), a component of cytosolic NADPH oxidase, and physically interacts and functionally counteracts with TRAF6 and Toll-IL-1 receptor (TIR) domain-containing adaptor-inducing IFN-beta (TRIF) molecules that critically regulate TLR-mediated signaling. TRAF4 mRNA expression was elicited in RPMI 8226 cells following LPS or CpG DNA treatment. These results suggest that TRAF4 participates in the molecular mechanism underlying silencing of TLR-mediated signaling through the interaction with molecules harboring phagosome/endosome membrane.