Prompt Description

Following viral infection, interferon regulatory factor 3 (IRF3) forms transcriptional condensates via liquid-liquid phase separation (LLPS) within the nucleus to activate interferon gene expression. However, the phase separation function of IRF3 in the cytoplasm and its regulatory mechanisms remain unclear. This study reveals for the first time that after cGAS-STING pathway activation, IRF3 can form phosphorylated pre-transcriptional condensates in the cytoplasm before entering the nucleus, localizing to the Golgi region. These condensates exhibit typical liquid-like properties and serve as signal transduction centers, effectively promoting IRF3 phosphorylation. Mechanistic studies indicate that the nuclear transport protein KPNA2 plays a crucial role in this process. KPNA2 itself is a phase separation protein, with its intrinsically disordered region (IDR) mediating multivalent interactions with IRF3. In vitro and cell-based experiments demonstrate that KPNA2 significantly enhances IRF3 condensate formation through cooperative phase separation. Further investigation reveals that the nuclear import inhibitor Ivermectin (IVM) can directly inhibit KPNA2 phase separation and block IRF3 condensate formation and downstream interferon pathway activation. This study uncovers a novel mechanism of functional phase separation of IRF3 in the cytoplasm and elucidates the non-canonical function of KPNA2 as a phase separation scaffold protein in innate immune signal amplification. These findings not only deepen the understanding of interferon signal transduction but also provide new potential targets for regulating innate immune responses.