The Interaction of Mandarin Fish DDX41 with STING Evokes type I Interferon Responses Inhibiting Ranavirus Replication

Area of Science:

• Immunology
• Molecular Biology
• Aquaculture

Background:

• DDX41 acts as an intracellular DNA sensor, activating type I interferon (IFN-I) production through the STING adaptor to mediate innate immune responses against viral infections.
• The regulatory mechanisms of the DDX41-STING pathway in teleost fish, particularly in commercially important species like mandarin fish (Siniperca chuatsi), are not well understood.
• Viral diseases pose a significant threat to intensive aquaculture of mandarin fish, necessitating research into their immune defense mechanisms.

Purpose of the Study:

• To investigate the role of mandarin fish DDX41 (scDDX41) and its functional domains (DEAD and HELIC) in the antiviral innate immune response.
• To elucidate the molecular mechanisms by which scDDX41 interacts with STING to activate the IFN-I signaling pathway.
• To assess the potential of scDDX41 in enhancing antiviral immunity and inhibiting viral replication in mandarin fish.

Main Methods:

• Gene expression analysis (qRT-PCR) to measure scDDX41, IFN-I, ISGs, and cytokine levels following stimulation with poly(dA:dT) or Mandarin fish ranavirus (MRV).
• Overexpression studies to evaluate the impact of scDDX41 on IFN-I and ISG expression.
• Co-immunoprecipitation and pull-down assays to determine the interaction between scDDX41 domains and STING, and DNA binding.
• Viral replication assays to assess the antiviral efficacy of scDDX41 against MRV.

Main Results:

• scDDX41 expression was upregulated by poly(dA:dT) and MRV, indicating its involvement in fish innate immunity.
• Overexpression of scDDX41 significantly boosted the expression of IFN-I, interferon-stimulated genes (ISGs), and pro-inflammatory cytokines.
• The DEAD domain of scDDX41 recognized IFN-stimulatory DNA and interacted with STING, activating the IFN-I pathway. The HELIC domain directly bound to the N-terminus of STING, inducing IFN-I and ISG expression.
• scDDX41 enhanced STING-mediated IFN-I immune responses and significantly inhibited MRV replication.

Conclusions:

• Mandarin fish DDX41 (scDDX41) plays a critical role in the antiviral innate immune response by sensing viral DNA and activating the STING-dependent IFN-I signaling pathway.
• Both the DEAD and HELIC domains of scDDX41 are essential for its function, mediating DNA recognition, STING interaction, and subsequent immune activation.
• scDDX41 enhances antiviral immunity against ranavirus in mandarin fish, offering potential applications for aquaculture disease resistance.