SARS-CoV-2 Uses Nonstructural Protein 16 To Evade Restriction by IFIT1 and IFIT3

Area of Science:

• Virology
• Immunology
• Drug Discovery

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) employs mechanisms to evade the host innate immune system.
• Nonstructural protein 16 (NSP16) is a key enzyme in coronaviruses, responsible for mRNA capping.
• The 2'-O-methylation activity of NSP16 is hypothesized to protect SARS-CoV-2 from host restriction factors.

Purpose of the Study:

• To investigate the role of SARS-CoV-2 NSP16 in viral infection and pathogenesis.
• To determine if NSP16's methyltransferase activity is essential for immune evasion.
• To explore NSP16 as a potential target for antiviral therapies.

Main Methods:

• Engineered a SARS-CoV-2 mutant with a disrupted active site in NSP16.
• Assessed viral attenuation in vitro and in vivo using a hamster model.
• Investigated the sensitivity of the NSP16 mutant to type I interferon (IFN-I) and the role of IFIT1/IFIT3.
• Tested the efficacy of sinefungin, a methyltransferase inhibitor, against SARS-CoV-2.

Main Results:

• The NSP16 mutant showed significant attenuation in vitro and in vivo, with reduced viral replication and disease in hamsters.
• The NSP16 mutant was more susceptible to type I interferon (IFN-I) compared to wild-type SARS-CoV-2.
• Silencing IFIT1 and IFIT3 partially restored viral fitness to the NSP16 mutant.
• Sinefungin treatment sensitized wild-type SARS-CoV-2 to IFN-I and inhibited viral replication.

Conclusions:

• SARS-CoV-2 NSP16 plays a critical role in evading host innate immunity, particularly type I interferon responses.
• Disrupting NSP16 methyltransferase activity attenuates viral replication in a type I interferon-dependent manner.
• Targeting NSP16 with inhibitors, in combination with type I interferon, presents a promising antiviral therapeutic strategy.