RNF213 Is an Interferon-Stimulated Gene That Targets Influenza A Virus NP and Activates MDA5 to Restrict Infection

Influenza A virus (IAV) infection induces a type I interferon (IFN) response in host cells, which exerts antiviral effects by upregulating interferon-stimulated genes (ISGs). However, the ISG response to IAV remains incompletely understood. Here, we systematically identify antiviral ISGs in A549 cells following type I and type II IFN treatment. We demonstrate that ring finger protein 213 (RNF213) strongly inhibits IAV replication in vitro. Notably, RNF213 knockout (KO) mice exhibit heightened susceptibility to IAV infection, with exacerbated disease severity. Mechanistically, RNF213, which is induced by both IFN signaling and IAV infection, amplifies IFN production by enhancing melanoma-differentiation-associated gene 5 (MDA5) signaling. We further show that RNF213 interacts with MDA5 via its AAA+ ATPase and E3 ligase domains, promoting K63-linked polyubiquitination of MDA5 at Lys137 and Lys743. Additionally, RNF213 mediates K48-linked polyubiquitination of viral nucleoprotein (NP), targeting it for proteasomal degradation. Our findings identify RNF213 as a critical antiviral ISG that bridges innate immune activation and direct viral restriction. Our study reveals a dual mechanism of RNF213 in antiviral immunity, highlighting its potential as a therapeutic target against influenza.