title: Analysis of interferon signaling by infectious hepatitis C virus clones with substitutions of core amino acids 70 and 91.
abstract: Substitution of amino acids 70 and 91 in the hepatitis C virus (HCV) core region is a significant predictor of poor responses to peginterferon-plus-ribavirin therapy, while their molecular mechanisms remain unclear. Here we investigated these differences in the response to alpha interferon (IFN) by using HCV cell culture with R70Q, R70H, and L91M substitutions. IFN treatment of cells transfected or infected with the wild type or the mutant HCV clones showed that the R70Q, R70H, and L91M core mutants were significantly more resistant than the wild type. Among HCV-transfected cells, intracellular HCV RNA levels were significantly higher for the core mutants than for the wild type, while HCV RNA in culture supernatant was significantly lower for these mutants than for the wild type. IFN-induced phosphorylation of STAT1 and STAT2 and expression of the interferon-inducible genes were significantly lower for the core mutants than for the wild type, suggesting cellular unresponsiveness to IFN. The expression level of an interferon signal attenuator, SOCS3, was significantly higher for the R70Q, R70H, and L91M mutants than for the wild type. Interleukin 6 (IL-6), which upregulates SOCS3, was significantly higher for the R70Q, R70H, and L91M mutants than for the wild type, suggesting interferon resistance, possibly through IL-6-induced, SOCS3-mediated suppression of interferon signaling. Expression levels of endoplasmic reticulum (ER) stress proteins were significantly higher in cells transfected with a core mutant than in those transfected with the wild type. In conclusion, HCV R70 and L91 core mutants were resistant to interferon in vitro, and the resistance may be induced by IL-6-induced upregulation of SOCS3. Those mechanisms may explain clinical interferon resistance of HCV core mutants.
authors.affiliation: Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Funaoka
authors.forename: Naoya
authors.initials: N
authors.lastname: Sakamoto
authors.forename: Goki
authors.initials: G
authors.lastname: Suda
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Itsui
authors.forename: Mina
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Sei
authors.initials: S
authors.lastname: Kakinuma
authors.forename: Takako
authors.initials: T
authors.lastname: Watanabe
authors.forename: Kako
authors.initials: K
authors.lastname: Mishima
authors.forename: Mayumi
authors.initials: M
authors.lastname: Ueyama
authors.forename: Izumi
authors.initials: I
authors.lastname: Onozuka
authors.forename: Sayuri
authors.initials: S
authors.lastname: Nitta
authors.forename: Akiko
authors.initials: A
authors.lastname: Kitazume
authors.forename: Kei
authors.initials: K
authors.lastname: Kiyohashi
authors.forename: Miyako
authors.initials: M
authors.lastname: Murakawa
authors.forename: Seishin
authors.initials: S
authors.lastname: Azuma
authors.forename: Kiichiro
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Mamoru
authors.initials: M
authors.lastname: Watanabe
mesh_terms: D019943:Amino Acid Substitution; D000998:Antiviral Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D024882:Drug Resistance, Viral; D016174:Hepacivirus / Q000187:drug effects* / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D006801:Humans; D000077190:Interferon alpha-2; D016898:Interferon-alpha / Q000494:pharmacology*; D015850:Interleukin-6 / Q000378:metabolism; D011994:Recombinant Proteins; D015398:Signal Transduction; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins / Q000378:metabolism; D015854:Up-Regulation; D014758:Viral Core Proteins / Q000235:genetics*; D014779:Virus Replication
chemical_list: D000998:Antiviral Agents; D000077190:Interferon alpha-2; D016898:Interferon-alpha; D015850:Interleukin-6; D011994:Recombinant Proteins; C106644:SOCS3 protein, human; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D014758:Viral Core Proteins