SOCS3 Drives Proteasomal Degradation of TBK1 and Negatively Regulates Antiviral Innate Immunity

TANK-binding kinase 1 (TBK1)-mediated induction of type I interferon (IFN) plays a critical role in host antiviral responses and immune homeostasis. The negative regulation of TBK1 activity is largely unknown.We report that suppressor of cytokine sig-naling 3 (SOCS3) inhibits the IFN- signaling pathway by promoting proteasomal degradation of TBK1. Overexpression and knockdown experiments indicated that SOCS3 is a negative regulator of IFN regulatory factor 3 (IRF3) phosphorylation and IFN- transcription. Moreover, SOCS3 directly associates with TBK1, and they colocalize in the cytoplasm. SOCS3 catalyzes K48-linked polyubiquitination of TBK1 at Lys341 and Lys344 and promotes subsequent TBK1 degradation. On the contrary, SOCS3 knockdownmarkedly increases the abundance of TBK1. Interestingly, both the BOX domain of SOCS3 and Ser172 phos-phorylation of TBK1 are indispensable for the processes of ubiquitination and degradation. Ectopic expression of SOCS3 signifi-cantly inhibits vesicular stomatitis virus (VSV) and influenza A virus strain A/WSN/33 (WSN)-induced IRF3 phosphorylation and facilitates the replication ofWSN virus by detecting the transcription of its viral RNA (vRNA). Knockdown of SOCS3 re-pressesWSN replication. Collectively, these results demonstrate that SOCS3 acts as a negative regulator of IFN- signal by ubiq-uitinating and degrading TBK1, shed light on the understanding of antiviral innate immunity, and provide a potential target for developing antiviral agents