Studies on the Role of SARS-CoV-2 Nucleocapsid as an Interferon Antagonist

ABSTRACT

Introduction: The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2), responsible for the coronavirus disease 2019 (COVID-19) pandemic, has resulted in significantly disruptive global impacts. Cytokine storm syndrome (CSS) can accompany SARSCoV2 infection, and involves the excessive release of pro-inflammatory cytokines that lead to acute respiratory distress syndrome (ARDS) in infected patients. Given the correlation between ARDS and poor patient prognosis, inflammatory pathways (e.g., interferon-1 (IFN-1)) would be a target area for antiviral development. Our preliminary results have demonstrated a direct correlation between the SARS-CoV-2 nucleocapsid (N) protein and host intracellular IFN-1 pathway components IRF3 and STAT1. Methods: A549 cells were transfected with pCMV-GFP vectors expressing N protein and harvested. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western Blotting were performed. The membranes were then incubated with STAT-1, p-STAT1 and IRF3 antibodies and visualised. Protein content was quantified using ImageJ software. Results: Transfection with SARS-CoV-2 N was correlated with a decrease in intracellular IRF3 and reduced phosphorylation of STAT1, suggesting the involvement of N protein in the delayed IFN-1 response commonly observed in SARS-CoV-2 patients. These findings suggest that IRF3 and STAT1 may be part of the innate immune response affected by SARS-CoV-2 infection. Conclusion: Our results show that IRF3 and STAT1 are responsible for stimulating transcription of interferon signalling genes (ISGs). Future studies on SARS-CoV-2 N and its downstream effectors could provide further insight into the IFN-1 response during infection, and assist in future antiviral development strategies.