DDX3 directly facilitates IKKα activation and regulates downstream signalling pathways

Area of Science:

• Immunology
• Molecular Biology
• Virology

Background:

• DDX3 (DEAD-box RNA helicase) is known to regulate antiviral immune signaling, particularly type I interferon (IFN) induction, by interacting with IKKε (IκB kinase ε).
• However, the Toll-like receptor 7/9 (TLR7/9)-mediated pathway, crucial for IFN induction in plasmacytoid dendritic cells sensing viral nucleic acids, operates independently of IKKε and TBK1 (TANK-binding kinase 1), relying instead on NIK (NF-κB-inducing kinase) and IKKα.

Purpose of the Study:

• To investigate the role of DDX3 in the NIK/IKKα-mediated pathway of type I interferon induction.
• To determine if DDX3 also influences alternative NF-κB activation regulated by NIK and IKKα.

Main Methods:

• Investigated DDX3 interaction with IKKα using co-immunoprecipitation assays.
• Assessed the effect of DDX3 modulation on IKKα autophosphorylation and activation.
• Analyzed DDX3's impact on NIK/IKKα-mediated IRF7 phosphorylation and type I interferon induction.
• Examined the effect of DDX3 knockdown on alternative NF-κB activation.

Main Results:

• DDX3 directly interacts with IKKα, enhancing its autophosphorylation and activation.
• Modulation of DDX3 expression significantly affected NIK/IKKα-mediated IRF7 phosphorylation and subsequent type I interferon induction.
• DDX3 knockdown led to down-regulation of alternative NF-κB activation, a pathway also regulated by NIK and IKKα.

Conclusions:

• DDX3 plays a significant role in innate immune signaling beyond the TBK1/IKKε pathway, extending its function to the NIK/IKKα-mediated induction of type I interferons and alternative NF-κB activation.
• These findings broaden the understanding of DDX3's involvement in antiviral responses.
• DDX3 emerges as a potential therapeutic target for diseases involving dysregulation of these innate immune pathways.