Intracellular viral RNAs are recognized by the RIG-I–like receptors (RLRs), which signal through the mitochondrial antiviral signaling protein MAVS. MAVS recruits and activates TBK1 kinase, which further phosphorylates and activates the transcription factor IRF3, leading to the induction of type I IFN and downstream antiviral genes. We identified human nucleus accumbens–associated 1 (NAC1), a member of the BTB/POZ family, as a bridge for MAVS and TBK1 that positively regulates the RLR-mediated induction of type I IFN. Overexpression or knockdown of NAC1 could, respectively, enhance or impair Sendai virus–triggered activation of TBK1 and IRF3, as well as induction of IFN-β. NAC1 also significantly boosted host antiviral responses against multiple RNA viruses. NAC1 was able to interact with MAVS and TBK1 upon viral infection. The BTB/POZ domain (aa 1–133) of NAC1 interacted with MAVS, and the remainder of NAC1 bound to TBK1. Furthermore, NAC1 could promote the recruitment of TBK1 to MAVS. In contrast, knockdown of NAC1 attenuated the interaction between TBK1 and MAVS. Collectively, our study characterizes NAC1 as an important component of RLR-mediated innate immune responses and uncovers a previously unrecognized function of the BTB/POZ family proteins.

The IL family of cytokines participates in immune response and regulation. We previously found that soluble IL-6 receptor plays an important role in the host antiviral response. In this study, we detected the IL-6–IL-27 complex in serum and throat swab samples from patients infected with influenza A virus. A plasmid expressing the IL-6–IL-27 complex was constructed to explore its biological function. The results indicated that the IL-6–IL-27 complex has a stronger antiviral effect than the individual subunits of IL-6, IL-27A, and EBV-induced gene 3. Furthermore, the activity of the IL-6–IL-27 complex is mainly mediated by the IL-27A subunit and the IL-27 receptor α. The IL-6–IL-27 complex can positively regulate virus-triggered expression of IFN and IFN-stimulated genes by interacting with adaptor protein mitochondrial antiviral signaling protein, potentiating the ubiquitination of TNF receptor-associated factors 3 and 6 and NF-κB nuclear translocation. The secreted IL-6–IL-27 complex can induce the phosphorylation of STAT1 and STAT3 and shows antiviral activity. Our results demonstrate a previously unrecognized mechanism by which IL-6, IL-27A, and EBV-induced gene 3 form a large complex both intracellularly and extracellularly, and this complex acts in the host antiviral response.

The antiviral innate immune responses are crucial steps during host defense and must be strictly regulated, but the molecular mechanisms of control remain unclear. In this study, we report increased expression of human ATPase Na+/K+ transporting subunit β 1(ATP1B1) after DNA and RNA virus infections. We found that the expression of ATP1B1 can inhibit viral replication and increase the levels of IFNs, IFN-stimulated genes, and inflammatory cytokines. Knockdown of ATP1B1 by specific short hairpin RNA had the opposite effects. Upon viral infection, ATP1B1 was induced, interacted with TRAF3 and TRAF6, and potentiated the ubiquitination of these proteins, leading to increased phosphorylation of downstream molecules, including TGF-β–activated kinase 1 (TAK1) and TANK-binding kinase 1 (TBK1). These results reveal a previously unrecognized role of ATP1B1 in antiviral innate immunity and suggest a novel mechanism for the induction of IFNs and proinflammatory cytokines during viral infection.