title: Consecutive Inhibition of ISG15 Expression and ISGylation by Cytomegalovirus Regulators.
abstract: Interferon-stimulated gene 15 (ISG15) encodes an ubiquitin-like protein that covalently conjugates protein. Protein modification by ISG15 (ISGylation) is known to inhibit the replication of many viruses. However, studies on the viral targets and viral strategies to regulate ISGylation-mediated antiviral responses are limited. In this study, we show that human cytomegalovirus (HCMV) replication is inhibited by ISGylation, but the virus has evolved multiple countermeasures. HCMV-induced ISG15 expression was mitigated by IE1, a viral inhibitor of interferon signaling, however, ISGylation was still strongly upregulated during virus infection. RNA interference of UBE1L (E1), UbcH8 (E2), Herc5 (E3), and UBP43 (ISG15 protease) revealed that ISGylation inhibits HCMV growth by downregulating viral gene expression and virion release in a manner that is more prominent at low multiplicity of infection. A viral regulator pUL26 was found to interact with ISG15, UBE1L, and Herc5, and be ISGylated. ISGylation of pUL26 regulated its stability and inhibited its activities to suppress NF-κB signaling and complement the growth of UL26-null mutant virus. Moreover, pUL26 reciprocally suppressed virus-induced ISGylation independent of its own ISGylation. Consistently, ISGylation was more pronounced in infections with the UL26-deleted mutant virus, whose growth was more sensitive to IFNβ treatment than that of the wild-type virus. Therefore, pUL26 is a viral ISG15 target that also counteracts ISGylation. Our results demonstrate that ISGylation inhibits HCMV growth at multiple steps and that HCMV has evolved countermeasures to suppress ISG15 transcription and protein ISGylation, highlighting the importance of the interplay between virus and ISGylation in productive viral infection.
authors: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.
authors: Ye Ji
authors: YJ
authors: Kim
authors: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.
authors: Eui Tae
authors: ET
authors: Kim
authors: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.
authors: Young-Eui
authors: YE
authors: Kim
authors: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.
authors: Myoung Kyu
authors: MK
authors: Lee
authors: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.
authors: Ki Mun
authors: KM
authors: Kwon
authors: Department of Biological Sciences, Sookmyung Women's University, Seoul, Republic of Korea.
authors: Keun Il
authors: KI
authors: Kim
authors: Institute for Clinical and Molecular Virology, University of Erlangen-Nuremberg, Schlossgarten, Erlangen, Germany.
authors: Thomas
authors: T
authors: Stamminger
authors: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, Republic of Korea.
authors: Jin-Hyun
authors: JH
authors: Ahn
mesh_terms: D002460:Cell Line; D016207:Cytokines / Q000276:immunology / Q000378:metabolism*; D003587:Cytomegalovirus / Q000276:immunology / Q000378:metabolism; D003586:Cytomegalovirus Infections / Q000276:immunology* / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015967:Gene Expression Regulation, Viral / Q000502:physiology*; D006790:Host-Parasite Interactions / Q000502:physiology*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D016133:Polymerase Chain Reaction; D014162:Transfection; D020798:Two-Hybrid System Techniques; D014452:Ubiquitins / Q000276:immunology / Q000378:metabolism*; D014764:Viral Proteins / Q000276:immunology / Q000378:metabolism*
chemical_list: D016207:Cytokines; D014452:Ubiquitins; D014764:Viral Proteins; C074034:ISG15 protein, human