SARS-CoV-2 main protease suppresses type I interferon production by preventing nuclear translocation of...

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Highly pathogenic human coronaviruses, including SARS-CoV and SARS-CoV-2, suppress the type I interferon (IFN) response.
• These viruses encode multiple IFN antagonists to achieve immune evasion.
• Understanding these mechanisms is crucial for developing antiviral strategies.

Purpose of the Study:

• To investigate the role of SARS-CoV-2 main protease NSP5 in IFN antagonism.
• To elucidate the mechanism by which NSP5 interferes with the IFN signaling pathway.
• To assess the IFN-antagonizing activity of common NSP5 variants.

Main Methods:

• Assessed the ability of SARS-CoV and SARS-CoV-2 NSP5 to counteract Sendai virus-induced IFN production.
• Evaluated the effect of NSP5 on IFN-β gene transcription induced by key signaling molecules (RIG-I, MAVS, TBK1, IKKϵ).
• Examined the impact of NSP5 on IRF3 phosphorylation and nuclear translocation in infected cells.

Main Results:

• NSP5 proteins from both SARS-CoV and SARS-CoV-2 effectively inhibited Sendai virus-induced IFN production.
• Commonly circulating SARS-CoV-2 NSP5 variants (G15S, K90R) retained significant IFN-antagonizing activity.
• NSP5 suppressed IFN-β transcription and, crucially, blocked the nuclear translocation of phosphorylated IRF3.

Conclusions:

• SARS-CoV-2 NSP5 antagonizes the type I IFN response by preventing phosphorylated IRF3 from entering the nucleus.
• This mechanism, involving cytoplasmic retention of IRF3, represents a novel viral immune evasion strategy.
• The findings provide insights for designing targeted antiviral therapies against SARS-CoV-2.