TRIM25 and DEAD-Box RNA Helicase DDX3X Cooperate to Regulate RIG-I-Mediated Antiviral Immunity

Area of Science:

• Immunology
• Virology
• Molecular Biology

Background:

• Retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs) are crucial for detecting RNA viruses and initiating antiviral responses, including interferon (IFN) production.
• Tripartite motif protein 25 (TRIM25) is an E3 ligase involved in RLR signaling, with both ubiquitination-dependent and -independent roles in IFN induction.
• Understanding the regulation of RLR signaling is vital for developing effective antiviral strategies.

Purpose of the Study:

• To investigate the novel interactions and regulatory roles of TRIM25 within the RLR signaling pathway.
• To elucidate the functional relationship between TRIM25 and DEAD-box helicase 3X (DDX3X) in type I IFN induction.
• To uncover the mechanism by which influenza A virus NS1 protein interferes with host antiviral responses.

Main Methods:

• In vitro biochemical assays to determine TRIM25 ubiquitination of DDX3X.
• Knockdown studies to assess the roles of TRIM25 and DDX3X in IFN-β (IFNB1) induction.
• Analysis of the interaction between TRIM25, DDX3X, and influenza A virus NS1 protein.

Main Results:

• TRIM25 directly ubiquitinates DDX3X at lysine 55 (K55).
• TRIM25 and DDX3X cooperatively enhance IFNB1 induction upon RIG-I activation, a function of DDX3X independent of TRIM25's catalytic activity.
• Influenza A virus NS1 protein disrupts the TRIM25:DDX3X interaction, inhibiting DDX3X ubiquitination and IFNB1 promoter activation.

Conclusions:

• A novel interaction between TRIM25 and DDX3X enhances IFN-β production, highlighting a new regulatory mechanism in RLR signaling.
• Influenza A virus NS1 employs a distinct mechanism to suppress host antiviral immunity by targeting the TRIM25-DDX3X complex.
• These findings provide insights into host-pathogen interactions and potential targets for antiviral therapies.