title: Herc5, an interferon-induced HECT E3 enzyme, is required for conjugation of ISG15 in human cells.
abstract: ISG15 is an interferon (IFN)-alpha/beta-induced ubiquitin-like protein that is conjugated to cellular proteins during innate immune responses to viral and bacterial infections. A recent proteomics study identified 158 human proteins targeted for ISG15 conjugation, including the ISG15 E1 and E2 enzymes (Ube1L and UbcH8, respectively) and a HECT E3 enzyme, Herc5. Like the genes encoding Ube1L and UbcH8, expression of Herc5 was also induced by IFN-beta, suggesting that Herc5 might be a component of the ISG15 conjugation system. Consistent with this, small interfering RNAs targeting Herc5 had a dramatic effect on overall ISG15 conjugation in human cells, abrogating conjugation to the vast majority of ISG15 target proteins in vivo. In addition, co-transfection of plasmids expressing ISG15, Ube1L, UbcH8, and Herc5 resulted in robust ISG15 conjugation in non-IFN-treated cells, while the active-site cysteine mutant of Herc5 or a mutant lacking the RCC1 repeat region did not support ISG15 conjugation. These results demonstrate that Herc5 is required for conjugation of ISG15 to a broad spectrum of target proteins in human cells.
authors.affiliation: Institute for Cellular and Molecular Biology, Section of Molecular Genetics and Microbiology, The University of Texas at Austin, 78712, USA.
authors.forename: Anahita
authors.initials: A
authors.lastname: Dastur
authors.forename: Sylvie
authors.initials: S
authors.lastname: Beaudenon
authors.forename: Melissa
authors.initials: M
authors.lastname: Kelley
authors.forename: Robert M
authors.initials: RM
authors.lastname: Krug
authors.forename: Jon M
authors.initials: JM
authors.lastname: Huibregtse
mesh_terms: D016207:Cytokines / Q000378:metabolism*; D006801:Humans; D016899:Interferon-beta / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D016207:Cytokines; C402395:HERC5 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D034741:RNA, Small Interfering; D014452:Ubiquitins; C074034:ISG15 protein, human; D016899:Interferon-beta