title: HERC5 is an IFN-induced HECT-type E3 protein ligase that mediates type I IFN-induced ISGylation of protein targets.
abstract: Type I IFNs induce the expression of IFN-stimulated gene 15 (ISG15) and its conjugation to cellular targets. ISGylation is a multistep process involving IFN-inducible Ube1L, UbcH8, and a yet-to-be identified E3 ligase. Here we report the identification of an IFN-induced HECT-type E3 protein ligase, HERC5/Ceb1, which mediates ISGylation. We also defined a number of proteins modified by ISG15 after IFN triggering or HERC5 overexpression. A reduction in endogenous HERC5 by small interfering RNA inhibition blocks the IFN-induced ISG15 conjugation. Conversely, HERC5 coexpression with Ube1L and UbcH8 induces the ISG15 conjugation in vivo independent of IFN stimulation. A targeted substitution of Cys-994 to Ala in the HECT domain of HERC5 completely abrogates its E3 protein ligase activity. Therefore, this study demonstrates that HERC5/Ceb1 is involved in the conjugation of ISG15 to cellular proteins.
authors.affiliation: Immunology and Virology Laboratory and Proteomics Laboratory, Genome Institute of Singapore, 60 Biopolis Street, #02-01 Genome, Singapore.
authors.forename: Joyce Jing Yi
authors.initials: JJ
authors.lastname: Wong
authors.forename: Yuh Fen
authors.initials: YF
authors.lastname: Pung
authors.forename: Newman Siu-Kwan
authors.initials: NS
authors.lastname: Sze
authors.forename: Keh-Chuang
authors.initials: KC
authors.lastname: Chin
mesh_terms: D002460:Cell Line; D016207:Cytokines / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007370:Interferon Type I / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D011506:Proteins / Q000378:metabolism*; D034622:RNA Interference; D044767:Ubiquitin-Protein Ligases / Q000502:physiology*; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D016207:Cytokines; C402395:HERC5 protein, human; D007370:Interferon Type I; D047908:Intracellular Signaling Peptides and Proteins; D011506:Proteins; D014452:Ubiquitins; C074034:ISG15 protein, human; D044767:Ubiquitin-Protein Ligases