N⁶-methyladenosine modification enables viral RNA to escape recognition by RNA sensor RIG-I

Area of Science:

• Virology
• Immunology
• RNA Biology

Background:

• N⁶-methyladenosine (m⁶A) is a prevalent RNA modification, but its role in viral RNA biology is largely unknown.
• Innate immune sensors, such as RIG-I, distinguish self from non-self RNA to initiate antiviral responses.

Purpose of the Study:

• To investigate the role of m⁶A modification in human metapneumovirus (HMPV) RNA.
• To determine if viral RNA m⁶A influences innate immune recognition and viral replication.
• To explore the potential of targeting viral RNA m⁶A for vaccine development.

Main Methods:

• Generation of m⁶A-deficient HMPV using synonymous mutations or demethylase treatment.
• Analysis of type I interferon induction in response to m⁶A-deficient HMPV and its RNA.
• Assessment of RIG-I and MDA5 activation by m⁶A-deficient viral RNA.
• In vivo studies in cotton rats to evaluate viral attenuation and immunogenicity.

Main Results:

• HMPV RNAs are methylated by m⁶A, which promotes viral replication and gene expression.
• m⁶A-deficient HMPV and its RNA induced significantly increased type I interferon expression, dependent on RIG-I.
• m⁶A-deficient viral RNA enhanced RIG-I binding and activation, leading to greater interferon production.
• m⁶A-deficient HMPV showed attenuation in vivo while retaining high immunogenicity.

Conclusions:

• Viruses utilize RNA m⁶A modification to mimic cellular RNA and evade innate immune detection.
• Viral RNA m⁶A is a critical factor in HMPV's interaction with the host immune system.
• Targeting viral RNA m⁶A presents a promising strategy for developing attenuated HMPV vaccines.