ABSTRACT
Middle East respiratory syndrome coronavirus (MERS-CoV) belongs to the beta coronavirus subfamily and causes severe morbidity and mortality in humans especially when infected patients have underlying diseases such chronic obstructive pulmonary disease (COPD). Previously, we demonstrated that MERS-CoV-encoded ORF8b strongly inhibits MDA5- and RIG-I-mediated induction of the interferon beta (IFN-ß) promoter activities. Here, we report that ORF8b seem to regulate MDA5 or RIG-I differentially as protein levels of MDA5 were significantly down-regulated while those of RIG-I were largely unperturbed. In addition, ORF8b seemed to efficiently suppress phosphorylation of IRF3 at the residues of 386 and 396 in cells transfected with RIG-I while total endogenous levels of IRF3 remained largely unchanged. Furthermore, ORF8b was able to inhibit all forms of RIG-I; full-length, RIG-I-1-734, and RIG-I-1-228, last of which contains only the CARD domains. Taken together, it is tempting to postulate that ORF8b may interfere with the CARD-CARD interactions between RIG-I and MAVS. Further detailed analysis is required to delineate the mechanisms of how ORF8b inhibits the MDA5/RIG-I receptor signaling pathway.
Subject(s)
DEAD Box Protein 58/drug effects , DEAD Box Protein 58/metabolism , Middle East Respiratory Syndrome Coronavirus/genetics , Middle East Respiratory Syndrome Coronavirus/metabolism , Viral Proteins/antagonists & inhibitors , Viral Proteins/genetics , Caspase Activation and Recruitment Domain/drug effects , Down-Regulation , Genes, Viral/genetics , HEK293 Cells , Host-Pathogen Interactions/physiology , Humans , Interferon Regulatory Factor-3/metabolism , Interferon-Induced Helicase, IFIH1/drug effects , Interferon-Induced Helicase, IFIH1/metabolism , Interferon-beta/metabolism , Phosphorylation , Receptors, Immunologic , Signal TransductionABSTRACT
Hepatitis E virus (HEV) is a causative agent of acute hepatitis and jaundice. The number of human infections is approximated to be over 20 million cases per year. The transmission is mainly via the fecal-oral route and contaminated water and food are considered to be a major source of infection. As a mouse model is not available, a recent development of a cell culture-adapted HEV strain (47832c) is considered as a very important tools for molecular analysis of HEV pathogenesis in cells. Previously, we demonstrated that HEV-encoded methyltransferase (MeT) encoded by the 47832c strain inhibits MDA5- and RIG-I-mediated activation of interferon ß (IFN-ß) promoter. Here, we report that MeT impairs the phosphorylation and activation of interferon regulatory factor 3 and the p65 subunit of NF-κB in a dose-dependent manner. In addition, the MeT encoded by the 47832c, but not that of HEV clinical or field isolates (SAR-55, Mex-14, KC-1, and ZJ-1), displays the inhibitory effect. A deeper understanding of MeTmediated suppression of IFN-ß expression would provide basis of the cell culture adaptation of HEV.
Subject(s)
Hepatitis E virus/physiology , Interferon-Induced Helicase, IFIH1/drug effects , Interferon-Induced Helicase, IFIH1/metabolism , Methyltransferases/antagonists & inhibitors , Methyltransferases/metabolism , Signal Transduction/physiology , Animals , Cell Culture Techniques , DEAD Box Protein 58/drug effects , DEAD Box Protein 58/metabolism , Disease Models, Animal , HEK293 Cells , Hepatitis E/virology , Hepatitis E virus/enzymology , Hepatitis E virus/pathogenicity , Humans , Interferon Regulatory Factor-3/metabolism , Interferon-beta/metabolism , Mice , NF-kappa B/metabolism , Phosphorylation , Receptors, ImmunologicABSTRACT
BACKGROUND: Anti-MDA-5 antibody is closely associated with interstitial lung disease (ILD) in amyopathic dermatomyositis (ADM). Patients with ADM with anti-MDA-5 antibody sometimes develop fatal ILD in spite of intensive immunosuppressive therapy. However, an initial decrease after treatment in anti-MDA-5 antibody titers may not be predictive of subsequent better survival of the disease. METHODS: To clarify immunoregulatory features of deadly ILD in ADM with the anti-MDA-5 antibody, we retrospectively examined clinical records of consecutive patients with anti-MDA-5 antibody positive ADM-ILD with preserved serum since 2000. Serum cytokine/growth factor (GF) protein concentration was measured using a cytokine panel analysis. We compared concentrations of each cytokine/GF between survivors and non-survivors and further examined changes in cytokines/GF levels during treatment in some patients. RESULTS: Twenty-six patients were enrolled in the study. Nine out of 26 patients did not respond to intensive immunosuppressive therapy and died due to respiratory failure. We compared cytokine/GF concentrations and found that serum IL-15 before treatment was significantly elevated in non-survivors than in survivors (pâ¯<â¯0.05). 11 out of 17 responders and 6 of 9 dead patients had preserved serum taken more than one time. We then calculated rates of change per day (slopes) in each cytokine/GF concentration. Comparison of slopes of cytokine/GF protein over the treatment duration showed that the slopes in non-survivors were significantly increased in IL-10 and IL-15 (pâ¯<â¯0.01). CONCLUSIONS: IL-15, as well as IL-10, may play a key role in the progression of the patients with ADM-ILD with anti-MDA-5 antibody positive.
