Viral deISGylase activity antagonizes the host innate immune response and enhances coronavirus pathogenesis in a murine model of coronavirus infection 4265

Abstract Description Coronaviruses have evolved a breadth of mechanisms to antagonize host innate immune responses. One widely studied mechanism is the ability to deconjugate ISG15 from target proteins in a process called deISGylation, which is catalyzed by the papain-like protease (PLP) domain of viral non-structural protein 3. Since PLP activity is required for viral replication, it has been challenging to generate an infectious virus with a PLP that maintains protease activity but has lost deISGylase activity. In this study, we generated a chimeric MHV-A59 with its PLP2 domain replaced with that of the human coronavirus HKU1, which has been documented to have minimal deISGylase activity in vitro. We determined that the deISGylase-deficient chimera (MHV-HP2) replicates to high titers in IFN-deficient cells but is significantly attenuated in IFN-competent BMDMs compared to WT MHV-A59. We also determined that MHV-HP2 induces a more robust IFN response in BMDMs compared to MHV-A59. Importantly, we report that MHV-HP2 is highly attenuated in vivoand is more rapidly cleared from infected mice compared to MHV-A59. Accordingly, we found that at earlier stages of infection, MHV-HP2 induces a higher IFN response in the liver, providing a potential mechanism for the rapid clearance of the deISGylase-deficient coronavirus. These results document the critical role of viral deISGylase activity as a key contributor to innate immune evasion during coronavirus infection. Funding Sources Supported by R01 AI159945 and R37 AI087846 Topic Categories Viral Immunology (VIR)