Argonaute 2 inhibits RIG-I signaling via competition for viral RNA binding.

Area of Science:

• Virology
• Immunology
• Molecular Biology

Background:

• Interferon (IFN)-dependent responses are crucial for mammalian antiviral defense.
• RNA interference (RNAi) provides an additional layer of pathogen defense.
• RIG-I-mediated signaling is a key pathway activated by RNA viruses.

Purpose of the Study:

• To investigate the role of mammalian Argonaute 2 (AGO2) in antiviral signaling.
• To determine AGO2's mechanism of action against influenza A virus.
• To understand how AGO2 modulates RIG-I-mediated responses.

Main Methods:

• Depletion of AGO2 in human cell lines.
• Analysis of IRF3 phosphorylation.
• Assessment of downstream antiviral gene activation.
• Investigation of AGO2 binding to viral RNA and RIG-I agonists.

Main Results:

• AGO2 depletion enhanced RIG-I-mediated antiviral signaling.
• Increased IRF3 phosphorylation and antiviral gene expression were observed upon AGO2 depletion.
• AGO2's negative modulation occurred independently of canonical RNA silencing.
• AGO2 binds to viral RNA with 5'-triphosphates and cytosolic RIG-I agonists.

Conclusions:

• AGO2 negatively regulates RIG-I-mediated antiviral signaling during influenza A virus infection.
• This regulation is independent of RNA silencing and involves direct binding to viral RNA.
• AGO2 plays a critical role in balancing antiviral responses to prevent excessive immune reactions.