title: Selective inactivation of USP18 isopeptidase activity in vivo enhances ISG15 conjugation and viral resistance.
abstract: Protein modification by the ubiquitin-like protein ISG15 is an interferon (IFN) effector system, which plays a major role in antiviral defense. ISG15 modification is counteracted by the isopeptidase USP18, a major negative regulator of IFN signaling, which was also shown to exert its regulatory function in an isopeptidase-independent manner. To dissect enzymatic and nonenzymatic functions of USP18 in vivo, we generated knock-in mice (USP18(C61A/C61A)) expressing enzymatically inactive USP18. USP18(C61A/C61A) mice displayed increased levels of ISG15 conjugates, validating that USP18 is a major ISG15 isopeptidase in vivo. Unlike USP18(-/-) mice, USP18(C61A/C61A) animals did not exhibit morphological abnormalities, fatal IFN hypersensitivity, or increased lethality, clearly showing that major USP18 functions are unrelated to its protease activity. Strikingly, elevated ISGylation in USP18(C61A/C61A) mice was accompanied by increased viral resistance against vaccinia virus and influenza B virus infections. Enhanced resistance upon influenza B infection in USP18(C61A/C61A) mice was completely reversed in USP18(C61A/C61A) mice, which additionally lack ISG15, providing evidence that the observed reduction in viral titers is ISG15 dependent. These results suggest that increasing ISGylation by specific inhibition of USP18 protease activity could constitute a promising antiviral strategy with only a minimal risk of severe adverse effects.
authors.affiliation: Institute of Neuropathology, University of Freiburg, 79106 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany;
authors.forename: Lars
authors.initials: L
authors.lastname: Ketscher
authors.affiliation: Department of General, Visceral, Vascular and Thoracic Surgery, Division of Molecular Biology, Charité-Universitätsmedizin Berlin, 10117 Berlin, Germany; Fachbereich Biologie, Chemie, Pharmazie, Free University Berlin, 14195 Berlin, Germany;
authors.forename: Ronny
authors.initials: R
authors.lastname: Hannß
authors.affiliation: Department of Medicine and Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110;
authors.forename: David J
authors.initials: DJ
authors.lastname: Morales
authors.affiliation: Institute of Neuropathology, University of Freiburg, 79106 Freiburg, Germany; Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany;
authors.forename: Anja
authors.initials: A
authors.lastname: Basters
authors.affiliation: Department of Preventive Medicine, Public Health and Microbiology, Universidad Autónoma Madrid, 28029 Madrid, Spain;
authors.forename: Susana
authors.initials: S
authors.lastname: Guerra
authors.affiliation: Institute of Neuropathology, University of Freiburg, 79106 Freiburg, Germany;
authors.forename: Tobias
authors.initials: T
authors.lastname: Goldmann
authors.affiliation: Institute of Neuropathology, University of Freiburg, 79106 Freiburg, Germany;
authors.forename: Annika
authors.initials: A
authors.lastname: Hausmann
authors.affiliation: Institute of Neuropathology, University of Freiburg, 79106 Freiburg, Germany; Centre of Biological Signalling Studies (BIOSS), University of Freiburg, 79106 Freiburg, Germany;
authors.forename: Marco
authors.initials: M
authors.lastname: Prinz
authors.affiliation: Max Planck Institute of Molecular Cell Biology and Genetics, Transgenic Core Facility, 01307 Dresden, Germany;
authors.forename: Ronald
authors.initials: R
authors.lastname: Naumann
authors.affiliation: W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205;
authors.forename: Andrew
authors.initials: A
authors.lastname: Pekosz
authors.affiliation: Institute for Medical Microbiology, Immunology and Hygiene, Medical Center, University of Cologne, 50935 Cologne, Germany; and Center for Molecular Medicine Cologne, University of Cologne, 50931 Cologne, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Utermöhlen
authors.affiliation: Department of Medicine and Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110;
authors.forename: Deborah J
authors.initials: DJ
authors.lastname: Lenschow
authors.affiliation: Institute of Neuropathology, University of Freiburg, 79106 Freiburg, Germany; klaus-peter.knobeloch@uniklinik-freiburg.de.
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Knobeloch
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D024882:Drug Resistance, Viral; D009981:Influenza B virus / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D043222:Ubiquitin Thiolesterase / Q000037:antagonists & inhibitors*; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D016207:Cytokines; C489550:G1p2 protein, mouse; D014452:Ubiquitins; C118306:Usp18 protein, mouse; D043222:Ubiquitin Thiolesterase
keywords: ISG15; UBP43; influenza; interferon; ubiquitin isopeptidase