Inhibition of Antiviral Innate Immunity by Avibirnavirus VP3 via Blocking TBK1-TRAF3 Complex Formation and IRF3 Activation

Abstract

The host innate immune system develops various strategies to antagonize virus infection, and the pathogen subverts or evades host innate immunity for self-replication. In the present study, we discovered that Avibirnavirus infectious bursal disease virus (IBDV) VP3 protein significantly inhibits MDA5-induced beta interferon (IFN-β) expression by blocking IRF3 activation. Binding domain mapping showed that the CC1 domain of VP3 and the residue lysine-155 of tumor necrosis factor receptor-associated factor 3 (TRAF3) are essential for the interaction. Furthermore, we found that the CC1 domain was required for VP3 to downregulate MDA5-mediated IFN-β production. A ubiquitination assay showed that lysine-155 of TRAF3 was the critical residue for K33-linked polyubiquitination, which contributes to the formation of a TRAF3-TBK1 complex. Subsequently, we revealed that VP3 blocked TRAF3-TBK1 complex formation through reducing K33-linked polyubiquitination of lysine-155 on TRAF3. Taken together, our data reveal that VP3 inhibits MDA5-dependent IRF3-mediated signaling via blocking TRAF3-TBK1 complex formation, which improves our understanding of the interplay between RNA virus infection and the innate host antiviral immune response. IMPORTANCE Type I interferon plays a critical role in the host response against virus infection, including Avibirnavirus. However, many viruses have developed multiple strategies to antagonize the innate host antiviral immune response during coevolution with the host. In this study, we first identified that K33-linked polyubiquitination of lysine-155 of TRAF3 enhances the interaction with TBK1, which positively regulates the host IFN immune response. Meanwhile, we discovered that the interaction of the CC1 domain of the Avibirnavirus VP3 protein and the residue lysine-155 of TRAF3 reduced the K33-linked polyubiquitination of TRAF3 and blocked the formation of the TRAF3-TBK1 complex, which contributed to the downregulation of host IFN signaling, supporting viral replication.

DeSUMOylation of Apoptosis Inhibitor 5 by Avibirnavirus VP3 Supports Virus Replication

“…Beta interferon (IFN-β) was reported to play a critical role in inhibiting viral replication ( 49 ). IBDV dsRNA could be sensed by MDA5 (cytoplasmic RIG-I-like receptor melanoma differentiation gene 5) to induce IFN‐β expression ( 44 , 50 , 51 ). Therefore, we speculated that API5 might play an important role in regulating MDA5-induced IFN-β production.…”

FBXO11 amplifies type I interferon signaling to exert antiviral effects by facilitating the assemble of TRAF3–TBK1–IRF3 complex

“…Among these, TRAF3 is identified as the crucial adaptor protein for bridging TBK1 to upstream or downstream signaling complexes. 37,38 Binding of viral RNA or DNA to these receptors initiates downstream TRAF3-TBK1-IRF3 signal transduction, thus ultimately resulting in the production of IFN-I, and finally eliminating the virus infection. 26,31 The K63-linked polyubiquitination of TRAF3-TBK1 on several sites (such as K429/K436, Cys56, or Cys124) promotes an antiviral response, 39,40 but TRAF3 is also involved in DTX4-mediated K48-linked ubiquitination of TBK1 on K372, thereby promoting degradation of TBK1.…”

“…Among these, TRAF3 is identified as the crucial adaptor protein for bridging TBK1 to upstream or downstream signaling complexes 37,38 . Binding of viral RNA or DNA to these receptors initiates downstream TRAF3–TBK1–IRF3 signal transduction, thus ultimately resulting in the production of IFN‐I, and finally eliminating the virus infection 26,31 .…”

Advances on Innate Immune Evasion by Avian Immunosuppressive Viruses

“…In addition to intervening the recognition of viral dsRNA genome by chMDA5, IBDV also employs other strategies to escape the innate immune response. It was reported that VP3 blocked the formation of TRAF3-TBK1 complex by reducing K33-linked poly-ubiquitination of Lysine-155 on TRAF3, inhibiting the production of IFN-I and facilitating viral replication ( 51 ). Interestingly, our previous study indicated that VP3 could interact with chicken Ribosomal Protein L18 (chRPL18) and chicken double-stranded RNA-activated protein kinase (chPKR), which enhanced IFN-I expression and inhibited viral replication ( 52 ).…”