MAVS activates TBK1 and IKKε through TRAFs in NEMO dependent and independent manner

Mitochondrial antiviral-signaling protein (MAVS) transmits signals from RIG-I-like receptors after RNA virus infections. However, the mechanism by which MAVS activates downstream components, such as TBK1 and IKK alpha/beta, is unclear, although previous work suggests the involvement of NEMO or TBK1-binding proteins TANK, NAP1, and SINTBAD. Here, we report that MAVS-mediated innate immune activation is dependent on TRAFs, partially on NEMO, but not on TBK1-binding proteins. MAVS recruited TBK1/IKK epsilon by TRAFs that were pre-associated with TBK1/IKK epsilon via direct interaction between the coiled-coil domain of TRAFs and the SDD domain of TBK1/IKK epsilon. TRAF(2-/-)3(-/-)5(-/-)6(-/-) cells completely lost RNA virus responses. TRAFs' E3 ligase activity was required for NEMO activation by synthesizing ubiquitin chains that bound to NEMO for NF-kappa B and TBK1/IKK epsilon activation. NEMO-activated IKK alpha/beta were important for TBK1/IKK epsilon activation through IKK alpha/beta-mediated TBK1/IKK epsilon phosphorylation. Moreover, individual TRAFs differently mediated TBK1/IKK epsilon activation and thus fine-tuned antiviral immunity under physiological conditions.