Title : SARS-CoV-2 omicron nucleocapsid effectively suppresses interferon beta expression via interaction with host HSPA4
Abstract:
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can dysregulate host antiviral responses, including interferon production, to facilitate viral replication and spread via interacting with their hosts; however, the impact of the SARS-CoV-2 Omicron nucleocapsid protein on the innate immune response remains unclear. In this study, FLAG-tagged nucleocapsids of SARS-CoV-2 were first overexpressed in HEK293T cells, after which anti-FLAG immunoprecipitation and Western blotting assays were performed. Nucleocapsid-associated protein complexes in human cells were identified using co-immunoprecipitation and were combined with in-gel digestion and ultra-high-pressure liquid chromatography coupled to tandem mass spectrometry. We discovered that the nucleocapsid of SARS-CoV-2 could specifically interact with cellular heat shock protein family A member 4 (HSPA4) in the cytoplasm. The nucleocapsid of the SARS-CoV-2 Omicron variant exhibited a heightened interaction with HSPA4 compared to other variants. Downregulation of HSPA4 expression in A549-ACE2-TMPRSS2 cells decreased the innate immune responses and significantly increased the viral titers, suggesting that HSPA4 was an antiviral regulator in the SARS-CoV-2 life cycle. We further demonstrated that the nucleocapsid inhibited the phosphorylated-interferon regulatory factor 3 protein, interferon beta mRNA, and interferon-stimulated genes; however, HSPA4 overexpression could recover them. Moreover, HSPA4 is involved in the upregulation of innate antiviral immunity. Our data suggests a novel mechanism by which the SARS-CoV-2 nucleocapsid hijacks cellular HSPA4 to suppress the host innate immune response and facilitate viral replication.
