- TRIM25 is one of the most extensively studied members of the TRIM (Tripartite Motif) family of single‑chain RING finger ubiquitin ligases. It plays a central role in innate antiviral immunity, particularly through its regulation of the cytosolic RNA sensor RIG‑I, a critical component of the interferon response. TRIM25’s ability to assemble K63‑linked ubiquitin chains makes it a powerful signalling amplifier, enabling rapid and robust defence against viral infection.
- Structurally, TRIM25 contains the hallmark tripartite motif found in all TRIM proteins: an N‑terminal RING finger domain, two B‑box domains, and a coiled‑coil region that mediates dimerisation. These domains form the catalytic and structural core of the protein. The C‑terminal PRY/SPRY domain is responsible for substrate recognition and binding, giving TRIM25 its specificity for RIG‑I and other signalling proteins. This modular architecture allows TRIM25 to act as both an E3 ligase and a scaffolding protein within antiviral signalling complexes.
- The best‑characterised function of TRIM25 is its regulation of RIG‑I‑mediated interferon signalling. Upon viral RNA detection, RIG‑I undergoes conformational changes that expose its CARD domains. TRIM25 binds these CARD domains and catalyses the formation of K63‑linked polyubiquitin chains, which stabilise RIG‑I in its active state and promote downstream signalling through MAVS. This leads to the production of type I interferons and other antiviral cytokines. Without TRIM25, RIG‑I activation is severely impaired, resulting in weakened antiviral responses.
- Beyond RIG‑I, TRIM25 regulates additional pathways in innate immunity. It modulates signalling through ZAP (ZC3HAV1), a host restriction factor that targets viral RNA for degradation. TRIM25 also influences pathways involving NF‑κB, MAP kinases and cytokine production, integrating signals from multiple pattern‑recognition receptors. Its ability to assemble non‑degradative ubiquitin chains allows TRIM25 to fine‑tune signalling intensity and duration.
- TRIM25 is also involved in cellular stress responses, RNA metabolism and protein quality control. Recent studies show that TRIM25 interacts with RNA‑binding proteins and may regulate mRNA stability and translation. It also participates in the autophagic clearance of viral components, linking ubiquitination to selective autophagy.
- Clinically, TRIM25 has gained attention due to its role in viral pathogenesis. Several viruses—including influenza, Ebola, SARS‑CoV‑2 and certain flaviviruses—produce proteins that inhibit TRIM25 activity to evade immune detection. Viral antagonism of TRIM25 underscores its importance as a frontline antiviral factor. Dysregulation of TRIM25 has also been linked to cancer, autoimmune disorders and inflammatory diseases, although these roles are still being explored.
- In summary, TRIM25 is a pivotal RING finger ubiquitin ligase that orchestrates antiviral immunity through RIG‑I activation and K63‑linked ubiquitination. Its tripartite motif provides structural stability and catalytic power, while its PRY/SPRY domain ensures precise substrate recognition. As research continues to uncover new functions, TRIM25 remains a central focus in immunology, virology and therapeutic development.
