Anti-TRAF3 polyclonal antibody

The mechanisms that enable Seneca Valley Virus (SVV) to escape the host innate immune response are not well known. Previous studies demonstrated that SW 305(pro) suppresses innate immune responses by cleavage of host proteins and degradation of IRF3 and IRF7 protein expression. Here, we showed that SVV 3C protease (3CP(pro)) has deubiquitinating activity. Overexpressed 3CP(pro) inhibits the ubiquitination of cellular substrates, acting on both lysine-48-and lysine-63-linked polyubiquitin chains. SVV infection also possessed deubiquitinating activity. The ubiquitin-proteasome system was significantly involved in SVV replication. Furthermore, 3CP(pro) inhibited the ubiquitination of retinoic acid-inducible gene I (RIG-I), TANK-binding kinase 1 (TBK1), and TNF receptor-associated factor 3 (TRAF3), thereby blocking the expression of interferon (IFN)-beta and IFN stimulated gene 54 (ISG54) mRNAs. A detailed analysis revealed that mutations (H48A, C160A, or H48A/C160A) that ablate the Cys and His residues of 3CP(pro) abrogated its deubiquitinating activity and the ability of 3CP(pro) to block IFN-beta induction. Together, our results demonstrate a novel mechanism developed by SVV 3C(pro) to promote viral replication, and may also provide a novel strategy for improving ubiquitination-based therapy.

The virus-induced signaling adaptor (VISA) complex plays a critical role in the innate immune response to RNA viruses. However, the mechanism of VISA complex formation remains unclear. Here, we demonstrate that thioredoxin 2 (TRX2) interacts with VISA at mitochondria both in vivo and in vitro. Knockdown and knockout of TRX2 enhanced the formation of the VISA-associated complex, as well as virus-triggered activation of interferon regulatory factor 3 (IRF3) and transcription of the interferon beta 1 (IFNB1) gene. TRX2 inhibits the formation of VISA aggregates by repressing reactive oxygen species (ROS) production, thereby disrupting the assembly of the VISA complex. Furthermore, our data suggest that the C93 residue of TRX2 is essential for inhibition of VISA aggregation, whereas the C283 residue of VISA is required for VISA aggregation. Collectively, these findings uncover a novel mechanism of TRX2 that negatively regulates VISA complex formation. IMPORTANCE The VISA-associated complex plays pivotal roles in inducing type I interferons (IFNs) and eliciting the innate antiviral response. Many host proteins are identified as VISA-associated-complex proteins, but how VISA complex formation is regulated by host proteins remains enigmatic. We identified the TRX2 protein as an important regulator of VISA complex formation. Knockout of TRX2 increases virus- or poly(I.C)-triggered induction of type I IFNs at the VISA level. Mechanistically, TRX2 inhibits the production of ROS at its C93 site, which impairs VISA aggregates at its C283 site, and subsequently impedes the assembly of the VISA complex. Our findings suggest that TRX2 plays an important role in the regulation of VISA complex assembly.