title: Riplet/RNF135, a RING finger protein, ubiquitinates RIG-I to promote interferon-beta induction during the early phase of viral infection.
abstract: RIG-I (retinoic acid-inducible gene-I), a cytoplasmic RNA helicase, interacts with IPS-1/MAVS/Cardif/VISA, a protein on the outer membrane of mitochondria, to signal the presence of virus-derived RNA and induce type I interferon production. Activation of RIG-I requires the ubiquitin ligase, TRIM25, which mediates lysine 63-linked polyubiquitination of the RIG-I N-terminal CARD-like region. However, how this modification proceeds for activation of IPS-1 by RIG-I remains unclear. Here we identify an alternative factor, Riplet/RNF135, that promotes RIG-I activation independent of TRIM25. The Riplet/RNF135 protein consists of an N-terminal RING finger domain, C-terminal SPRY and PRY motifs, and shows sequence similarity to TRIM25. Immunoprecipitation analyses demonstrated that the C-terminal helicase and repressor domains of RIG-I interact with the Riplet/RNF135 C-terminal region, whereas the CARD-like region of RIG-I is dispensable for this interaction. Riplet/RNF135 promotes lysine 63-linked polyubiquitination of the C-terminal region of RIG-I, modification of which differs from the N-terminal ubiquitination by TRIM25. Overexpression and knockdown analyses revealed that Riplet/RNF135 promotes RIG-I-mediated interferon-beta promoter activation and inhibits propagation of the negative-strand RNA virus, vesicular stomatitis virus. Our data suggest that Riplet/RNF135 is a novel factor of the RIG-I pathway that is involved in the evoking of human innate immunity against RNA virus infection, and activates RIG-I through ubiquitination of its C-terminal region. We infer that a variety of RIG-I-ubiquitinating molecular complexes sustain RIG-I activation to modulate RNA virus replication in the cytoplasm.
authors.affiliation: Department of Microbiology and Immunology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oshiumi
authors.forename: Misako
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Shigetsugu
authors.initials: S
authors.lastname: Hatakeyama
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Seya
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D002522:Chlorocebus aethiops; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016899:Interferon-beta / Q000096:biosynthesis*; D011485:Protein Binding; D011971:Receptors, Immunologic; D015398:Signal Transduction; D013997:Time Factors; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination; D018116:Vesiculovirus / Q000502:physiology*; D016335:Zinc Fingers
chemical_list: D002352:Carrier Proteins; D011971:Receptors, Immunologic; D016899:Interferon-beta; C522809:RNF135 protein, human; D044767:Ubiquitin-Protein Ligases; C452820:RIGI protein, human; D000071457:DEAD Box Protein 58; D053487:DEAD-box RNA Helicases