In order to eliminate viral infections, hundreds of interferon-stimulated genes (ISGs) are induced via type I interferons (IFNs). However, the functions and mechanisms of most ISGs are largely unclear. A tripartite motif (TRIM) protein encoding gene TRIM69 is induced by dengue virus (DENV) infection as an ISG. TRIM69 restricts DENV replication, and its RING domain, which has the E3 ubiquitin ligase activity, is critical for its antiviral activity. An in vivo study further confirmed that TRIM69 contributes to the control of DENV infection in immunocompetent mice. Unlike many other TRIM family members, TRIM69 is not involved in modulation of IFN signaling. Instead, TRIM69 interacts with DENV Nonstructural Protein 3 (NS3) directly and mediates its polyubiquitination and degradation. Finally, Lys104 of NS3 is identified as the target of TRIM69-mediated ubiquitination. Our study demonstrates that TRIM69 restricts DENV replication by specifically ubiquitinating a viral nonstructural protein.

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has spread worldwide and has infected more than 250 million people. A typical feature of COVID-19 is the lack of type I interferon (IFN-I)-mediated antiviral immunity in patients. However, the detailed molecular mechanisms by which SARS-CoV-2 evades the IFN-I-mediated antiviral response remain elusive. Here, we performed a comprehensive screening and identified a set of SARS-CoV-2 proteins that antagonize the IFN-I response. Subsequently, we characterized the mechanisms of two viral proteins antagonize IFN-I production and downstream signaling. SARS-CoV-2 membrane protein binds to importin karyopherin subunit alpha-6 (KPNA6) to inhibit interferon regulatory factor 3(IRF3) nuclear translocation. Further, the spike protein interacts with signal transducer and activator of transcription 1 (STAT1) to block its association with Janus kinase 1 (JAK1). This study increases our understanding of SARS-CoV-2 pathogenesis and suggests novel therapeutic targets for the treatment of COVID-19.

Dengue virus (DENV) is the most important vector-borne virus globally. The safe and effective vaccines are still under development and there are no antiviral drugs for DENV induced diseases. In this study, we obtained five DENV1 isolates (DENV1 A to E) from the outbreak of dengue fever in 2014 of Guangzhou, China, and analyzed their replication efficiency and virulence in vitro and in vivo. The results suggested that among the five DENV1 strains, DENV1 B has the highest replication efficiency in both human and mosquito cells in vitro, also causes the highest mortality to suckling mice. Further study suggested that nonstructural proteins from DENV1B have higher capacity to suppress host interferon signaling. In addition, the NS2B3 protease from DENV1B has higher enzymatic activity compared with that from DENV1 E. Finally, we identified that the 64th amino acid of NS2A and the 55th amino acid of NS2B were two virulence determining sites for DENV1. This study provided new evidences of the molecular mechanisms of DENV virulence.

The type I interferon (IFN‐I, IFN‐α/β)‐mediated immune response is the first line of host defense against invading viruses. IFN‐α/β binds to IFN‐α/β receptors (IFNARs) and triggers the expression of IFN‐stimulated genes (ISGs). Thus, stabilization of IFNARs is important for prolonging antiviral activity. Here, we report the induction of an RNA‐binding motif‐containing protein, RBM47, upon viral infection or interferon stimulation. Using multiple virus infection models, we demonstrate that RBM47 has broad‐spectrum antiviral activity in vitro and in vivo. RBM47 has no noticeable impact on IFN production, but significantly activates the IFN‐stimulated response element (ISRE) and enhances the expression of interferon‐stimulated genes (ISGs). Mechanistically, RBM47 binds to the 3'UTR of IFNAR1 mRNA, increases mRNA stability, and retards the degradation of IFNAR1. In summary, this study suggests that RBM47 is an interferon‐inducible RNA‐binding protein that plays an essential role in enhancing host IFN downstream signaling.

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