SARS-CoV-2 Orf6 hijacks Nup98 to block STAT nuclear import and antagonize interferon signaling

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes the COVID-19 pandemic.
• Viruses often evade host antiviral responses, like interferon (IFN) signaling, for replication.
• Understanding viral evasion mechanisms is crucial for developing countermeasures.

Purpose of the Study:

• To investigate how SARS-CoV-2 antagonizes IFN-mediated antiviral signaling.
• To identify the specific viral protein responsible for this antagonism.
• To elucidate the molecular mechanism of viral interference with host antiviral pathways.

Main Methods:

• Cell-based assays to monitor STAT1 and STAT2 nuclear translocation.
• Localization studies of SARS-CoV-2 Orf6 protein.
• Co-immunoprecipitation to assess protein-protein interactions.
• Mutagenesis studies to evaluate the role of specific Orf6 residues.

Main Results:

• SARS-CoV-2 efficiently blocks STAT1 and STAT2 nuclear import, impairing interferon-stimulated gene (ISG) induction.
• The viral accessory protein Orf6 is responsible for this anti-IFN activity.
• Orf6 localizes to the nuclear pore complex (NPC) and interacts with Nup98-Rae1.
• This interaction disrupts the nuclear import of essential cellular components.
• A specific mutation (M58R) in Orf6 abolishes its interaction with Nup98-Rae1 and its IFN antagonistic function.

Conclusions:

• SARS-CoV-2 Orf6 protein directly interferes with the host's nuclear import machinery.
• The virus hijacks the Nup98-Rae1 complex at the NPC to block antiviral signaling.
• This mechanism highlights a novel viral strategy to overcome IFN-mediated immunity.