Cellular nucleic acid-binding protein restricts SARS-CoV-2 by regulating interferon and disrupting RNA-protein condensates.

A detailed understanding of the innate immune mechanisms involved in restricting SARS-CoV-2 infection and how the virus disrupts these processes could reveal new strategies to boost antiviral mechanisms and develop therapeutics for COVID-19. Here, we identify cellular nucleic acid-binding protein (CNBP) as a key host factor controlling SARS-CoV-2 infection. In response to RNA-sensing pathways, CNBP is phosphorylated and translocates from the cytosol to the nucleus where it binds to the interferon-β enhancer to initiate transcription. Because SARS-CoV-2 evades immune detection by the host's RNA-sensing pathways, CNBP is largely retained in the cytosol where it restricts SARS-CoV-2 directly, leading to a battle between the host and SARS-CoV-2 that extends beyond antiviral immune signaling pathways. We further demonstrated that CNBP binds SARS-CoV-2 viral RNA directly and competes with the viral nucleocapsid protein to prevent viral RNA and nucleocapsid protein from forming liquid-liquid phase separation (LLPS) condensates critical for viral replication. Consequently, cells and animals lacking CNBP have higher viral loads, and CNBP-deficient mice succumb rapidly to infection. Altogether, these findings identify CNBP as a key antiviral factor for SARS-CoV-2, functioning both as a regulator of antiviral IFN gene expression and a cell-intrinsic restriction factor that disrupts LLPS to limit viral replication and spread. In addition, our studies also highlight viral condensates as important targets and strategies for the development of drugs to combat COVID-19.