Regulation of Virus-triggered Signaling by OTUB1- and OTUB2-mediated Deubiquitination of TRAF3 and TRAF6

Abstract

Ubiquitination and deubiquitination have emerged as critical post-translational regulatory mechanisms for activation or attenuation of the virus-triggered type I interferon (IFN) 2 induction pathways. In this study, we identified two deubiquitinating enzymes, OTUB1 and OTUB2, as negative regulators of virus-triggered type I IFN induction. Overexpression of OTUB1 and OTUB2 inhibited virus-induced activation of IRF3 and NF-B, transcription of the IFNB1 gene as well as cellular antiviral response, whereas knockdown of OTUB1 and OTUB2 had opposite effects. Coimmunoprecipitations indicated OTUB1 and -2 interacted with TRAF3 and TRAF6, two E3 ubiquitin ligases required for virus-triggered IRF3 and NF-B activation, respectively. Furthermore, we found that OTUB1 and OTUB2 mediated virus-triggered deubiquitination of TRAF3 and -6. These findings suggest that OTUB1 and OTUB2 negatively regulate virus-triggered type I IFN induction and cellular antiviral response by deubiquitinating TRAF3 and -6. Viral infections triggered a series of signaling events that lead to induction of type I interferons (IFNs). Type I IFNs then activate the JAK-STAT signal transduction pathways, leading to transcriptional induction of a wide range of downstream antiviral genes and subsequent innate antiviral response (1-4). Transcriptional induction of type I IFN genes requires the coordinate activation of multiple transcription factors and their cooperative assembly into transcriptional enhancer complexes in vivo. For example, the IFNB1 gene promoter contains conserved enhancer elements recognized by NF-B (B site) and phosphorylated IRF3 (ISRE site, also known as PRDIII or IRF-E). It has been shown that transcriptional activation of the IFNB1 gene requires coordinate and cooperative assembly of an enhanceosome that contains all of these transcription factors (2, 5, 6).The innate immune system has developed at least two types of pathogen recognition receptors for the recognition of viral RNAs (7).One is mediated by membrane-bound Toll-like receptors (TLRs) such as TLR3. Engagement of TLR3 by double-stranded RNA triggers TRIF-mediated signaling pathways, leading to IRF3 and NF-B activation (8). The second one involves the cytosolic RIG-I-like receptor family members RIG-I, MDA5, and Lgp2. Both RIG-I and MDA5 contain two CARD modules at their N terminus and a DexD/H-box RNA helicase domain at their C terminus (9, 10). Upon viral infection, the RNA helicase domains of RIG-I and MDA5 serve as intracellular viral RNA receptors, whereas their CARD modules are associated with the downstream CARD-containing adapter protein VISA (also known as MAVS, IPS-1, and Cardif) (11-15). The essential roles of VISA in antiviral innate immune response were demonstrated by the observations that VISAdeficient mice failed to mount a proper IFN response to viral infections (14,16). Various studies have demonstrated that VISA plays a central role in assembling a complex that activates distinct signaling pathways leading to NF-B and IRF3 activation, respectively. VISA is as...

WDR82 Negatively Regulates Cellular Antiviral Response by Mediating TRAF3 Polyubiquitination in Multiple Cell Lines

“…TRAF3 is a key molecule in the cascade of RIG-I signaling pathway, and its K63-linked polyubiquitination is required for TBK1 recruitment and downstream events; additionally, the regulation of different forms of polyubiquitination chains emerged as critical to the regulation of innate immunity pathways (14,(27)(28)(29)(30)(31). To further elucidate the biochemical mechanisms, we investigate the impact of WDR82 in regulating TRAF3 polyubiquitination.…”

MIP-T3 Is a Negative Regulator of Innate Type I IFN Response

“…TRAF3 is a ubiquitin ligase, and several negative regulators of TRAF3 have been shown to modulate K63-or K48-linked polyubiquitination of TRAF3 (8,10,12). In view of this, we next investigated whether the interaction of MIP-T3 with TRAF3 might also influence TRAF3 ubiquitination.…”

“…TRAF3 acts as a ubiquitin ligase for itself and other substrates (6)(7)(8). In response to different upstream signals, it also undergoes K48-and K63-linked ubiquitination that is modulated by other ubiquitin ligases and deubiquitinases (8)(9)(10)(11)(12). In line with its positive regulatory role in antiviral response, TRAF3 signaling complexes are targeted by various viral proteins as countermeasures to inhibit IFN production (13)(14)(15); however, it is not fully understood how the adaptor function of TRAF3 in innate IFN response is achieved and regulated in the cell.…”

Ubiquitin-Specific Protease 13 Regulates IFN Signaling by Stabilizing STAT1

“…Thus, A20 inhibits NF-kB activation upstream of IkB kinase by removing K63-linked polyubiquitin chains and promoting K48-linked polyubiquitination and degradation of receptor-interacting protein 1 (23)(24)(25). Additionally, ovarian tumor (OTU) B1 and OTUB2 inhibit virus-triggered IFN-b expression by deubiquitinating TRAF3 and TRAF6 (26). Furthermore, ubiquitin-specific protease (USP) 17 (also called DUB3) positively regulates virusinduced type I IFN signaling through interaction and deubiquitination of RIG-I and MDA5 (27).…”