TRIM25 RING-finger E3 ubiquitin ligase is essential for RIG-I-mediated antiviral activity

Department of Microbiology and Molecular Genetics and Tumor Virology Division, New England Primate Research Center, Harvard Medical School, 1 Pine Hill Drive, Southborough, Massachusetts 01772, USA.
Nature (Impact Factor: 41.46). 05/2007; 446(7138):916-920. DOI: 10.1038/nature05732
Source: PubMed


Retinoic-acid-inducible gene-I (RIG-I; also called DDX58) is a cytosolic viral RNA receptor that interacts with MAVS (also called VISA, IPS-1 or Cardif) to induce type I interferon-mediated host protective innate immunity against viral infection. Furthermore, members of the tripartite motif (TRIM) protein family, which contain a cluster of a RING-finger domain, a B box/coiled-coil domain and a SPRY domain, are involved in various cellular processes, including cell proliferation and antiviral activity. Here we report that the amino-terminal caspase recruitment domains (CARDs) of RIG-I undergo robust ubiquitination induced by TRIM25 in mammalian cells. The carboxy-terminal SPRY domain of TRIM25 interacts with the N-terminal CARDs of RIG-I; this interaction effectively delivers the Lys 63-linked ubiquitin moiety to the N-terminal CARDs of RIG-I, resulting in a marked increase in RIG-I downstream signalling activity. The Lys 172 residue of RIG-I is critical for efficient TRIM25-mediated ubiquitination and for MAVS binding, as well as the ability of RIG-I to induce antiviral signal transduction. Furthermore, gene targeting demonstrates that TRIM25 is essential not only for RIG-I ubiquitination but also for RIG-I-mediated interferon- production and antiviral activity in response to RNA virus infection. Thus, we demonstrate that TRIM25 E3 ubiquitin ligase induces the Lys 63-linked ubiquitination of RIG-I, which is crucial for the cytosolic RIG-I signalling pathway to elicit host antiviral innate immunity.

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    • "Considering the key role of K63-linked polyubiquitin in RIG-I antiviral signaling, we next studied the potential function of K63- linked ubiquitination in regulating the interaction of Npl4 with RIG-I CARDs. It is well established that the E3 ubiquitin ligase TRIM25 activates RIG-I by generation of K63-linked polyubiquitin chains covalently attached to K172 of RIG-I (Gack et al, 2007). Meanwhile, separated K63-linked polyubiquitin chains can bind to RIG-I noncovalently for synergistic activation (Zeng et al, 2010). "
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    • "The potential role of other E2s in the antiretroviral function of TRIM5a cannot be ascertained from these data because of possible functional redundancy of different E2 enzymes. As the key role of K63-linked polyubiquitin synthesis in the function of several other TRIM family members has been described in previous studies (Gack et al., 2007; McEwan et al., 2013; Zeng et al., 2010), we focused here on the Ubc13-mediated E3 activity of TRIM5a. For the structural and mechanistic studies described below, we expressed and purified recombinant TRIM5a RING 1–93 ; untagged ubiquitin; and E2 proteins UbcH5c, Ubc13, and Mms2 using bacterial expression vectors. "
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    • "The RLR family consists of RIG-I, MDA5, and a third truncated member, LGP2 (laboratory of genetics and physiology 2), which consist of N-terminal tandem caspase activation and recruitment domains (CARDs), adenosine triphosphatase (ATPase) activity, and a C-terminal RNA binding domain (Loo and Gale, 2011). While LGP2 lacks CARD domains, engagement of RIG-I or MDA5 is thought to result in multimerization and assembly of a large complex at the mitochondria membrane that is mediated by K63 ubiquitin chains and polymerization of the mitochondrial antiviral-signaling protein MAVS (also called IPS-I, Cardif, and VISA) (Gack et al., 2007; Hou et al., 2011; Jiang et al., 2012). Complex assembly is responsible for the activation of the IKK and IKK-like kinases, which activate necrosis factor (NF)-kB and IRF3/7, respectively, resulting in the formation of the interferon beta (IFN-B) enhanceosome (Loo and Gale, 2011). "
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