The RNA Helicase DHX16 Provides Specific Viral RNA for RIG-I to Trigger Innate Antiviral Immunity

Type-I interferon (IFN-I) is essential to establish antiviral innate immunity. Unanchored (or free) polyubiquitin (poly-Ub) has been shown to regulate IFN-I responses, however few unanchored poly-Ub interactors are known. To identify factors regulated by unanchored poly-Ub in a physiological setting, we developed an approach to isolate unanchored poly-Ub from lung tissue and identified the DEAH-box RNA helicase DHX16 as a factor that enhances IFN-I production. Silencing of DHX16 in cells and in vivo diminished IFN-I responses against influenza virus. DHX16-dependent IFN-I production requires RIG-I and unanchored K48-poly-Ub synthesized by the E3 Ub ligase TRIM6. DHX16 recognizes a signal in influenza segments that undergo splicing and requires its intact RNA helicase motif for direct, high-affinity interactions with specific viral RNAs. Our study establishes DHX16 as a potentiator of RIG-I-mediated IFN-I production and recognizes a mechanism for activation of antiviral immunity requiring unanchored poly-Ub and the viral RNA recognition activity of DHX16 Next Generation Sequencing of human A549 lung cells treated with either non-targeting control or DHX16 targeting siRNA and either mock or influenza A virus infected (MOI=1) for 24 hours.