The SARS-CoV-2 papain-like protease suppresses type I interferon responses by deubiquitinating STING

The SARS-CoV-2 papain-like protease (PLpro), which has deubiquitinating activity, suppresses the type I inter-feron (IFN-I) antiviral response. We investigated the mechanism by which PLpro antagonizes cellular antiviral responses. In HEK392T cells, PLpro removed K63-linked polyubiquitin chains from Lys289 of the stimulator of interferon genes (STING). PLpro-mediated deubiquitination of STING disrupted the STING-IKK epsilon-IRF3 complex that induces the production of IFN-beta and IFN-stimulated cytokines and chemokines. In human airway cells in-fected with SARS-CoV-2, the combined treatment with the STING agonist diABZi and the PLpro inhibitor GRL0617 resulted in the synergistic inhibition of SARS-CoV-2 replication and increased IFN-I responses. The PLpros of seven human coronaviruses (SARS-CoV-2, SARS-CoV, MERS-CoV, HCoV-229E, HCoV-HKU1, HCoV-OC43, and HCoV-NL63) and four SARS-CoV-2 variants of concern (alpha, beta, gamma, and delta) all bound to STING and sup-pressed STING-stimulated IFN-I responses in HEK293T cells. These findings reveal how SARS-CoV-2 PLpro inhib-its IFN-I signaling through STING deubiquitination and a general mechanism used by seven human coronaviral PLpros to dysregulate STING and to facilitate viral innate immune evasion. We also identified simultaneous phar-macological STING activation and PLpro inhibition as a potentially effective strategy for antiviral therapy against SARS-CoV-2.