Dysregulation of innate immunity during respiratory RNA virus infections drives systemic hyperinflammation and lung injury. Here, we show that importin β4 (IPO4) has a role in inhibiting antiviral innate immunity. Transcriptomics analysis illustrated a downregulation of IPO4 in alveolar macrophages, lung ciliated epithelium, and peripheral blood mononuclear cells from severely ill patients with COVID-19 or influenza. We further identified CCAAT/enhancer-binding protein beta (CEBPB) as the transcription factor for IPO4 reduction during RNA viral infections. Loss-of-function validation demonstrated that IPO4 dampens the innate antiviral and inflammatory responses in vitro and in vivo. Mechanistically, IPO4 sequesters fatty acid synthase (FASN) to block palmitic acid production, thereby inhibiting mitochondrial antiviral signaling protein (MAVS) activation and the downstream innate immune signaling. Moreover, Adeno-associated virus (AAV)-mediated pulmonary restoration of IPO4 significantly alleviated viral pneumonia in mice. These results indicate that the CEBPB-IPO4-FASN-MAVS axis preserves innate immune homeostasis to avoid inflammatory pathology, highlighting IPO4 as a potential therapeutic target for severe viral pneumonia.
ABSTRACT Influenza A virus (IAV) poses a serious threat to public health due to its high mutability and rapid transmissibility. The viral nucleoprotein (NP), a highly conserved and essential component, has emerged as an ideal target for antiviral therapies. However, its biological function has proven challenging to modulate with conventional drugs, and no NP-targeting therapeutics have reached the market so far. Here, we report the development and application of an aptamer-based proteolysis-targeting chimera (PROTAC) for the targeted degradation of IAV NP. Utilizing the Direct-to-Biology (D2B) platform, we efficiently screened and identified NP-PROTAC#4 as a functional candidate. Subsequently, we developed a lipid nanoparticle (LNP) formulation of NP‑PROTAC#4 (LNP@NP‑PROTAC#4) for effective intracellular delivery. Importantly, LNP@NP-PROTAC#4 demonstrated potent antiviral activity both in vitro and in vivo. Mechanistically, NP-PROTAC#4 exerts its antiviral effects by targeting and degrading NP via the ubiquitin-proteasome system. In conclusion, our findings provide the first evidence that NP-targeted PROTAC degrader exhibits therapeutic effects, proposing a novel therapeutic strategy for IAV.