DDX50 Is a Viral Restriction Factor That Enhances IRF3 Activation

Area of Science:

• Immunology
• Virology
• Molecular Biology

Background:

• Interferon regulatory factor 3 (IRF3) and Nuclear Factor kappa B (NF-κB) are key transcription factors in innate immune responses against pathogens.
• Mechanisms activating IRF3 and NF-κB, particularly in response to viral RNA, are not fully understood.
• While RIG-I, MDA5, TLR3, and DExD-Box RNA helicases like DDX1 are known sensors, other factors may contribute to IRF3 activation.

Purpose of the Study:

• To identify and characterize novel factors involved in IRF3 signaling pathway activation upon viral RNA detection.
• To elucidate the role of DDX50 in innate immune responses against viral infections.
• To determine if DDX50 acts as a viral restriction factor.

Main Methods:

• Utilized gene deletion in mouse and human cells to assess DDX50 function.
• Investigated IRF3 phosphorylation, gene expression, and cytokine/chemokine production.
• Performed co-immunoprecipitation to study protein interactions (DDX50 and TRIF).
• Assessed viral replication and dissemination in DDX50-deficient cells using various viruses (vaccinia, herpes simplex, Zika).

Main Results:

• DDX50 deletion impaired IRF3 phosphorylation and downstream gene expression and cytokine/chemokine production in response to dsRNA and viral infections.
• DDX50 co-immunoprecipitated with TRIF but acted independently of DDX1 in IRF3 activation.
• DDX1 was found to be dispensable for signaling during RNA virus infection.
• Loss of DDX50 significantly increased replication and dissemination of vaccinia virus, herpes simplex virus, and Zika virus.

Conclusions:

• DDX50 is a non-redundant factor crucial for activating the IRF3 signaling pathway in response to viral RNA and infection.
• DDX50 functions independently of DDX1, suggesting parallel pathways for viral RNA sensing and IRF3 activation.
• DDX50 acts as a broad-spectrum viral restriction factor, limiting the replication and spread of diverse viruses.