Abstract
Coronaviruses (CoV) have recently emerged as potentially serious pathogens that can cause significant human morbidity and death. The severe acute respiratory syndrome (SARS)-CoV was identified as the etiologic agent of the 2002-2003 international SARS outbreak. Yet, how SARS evades innate immune responses to cause human disease remains poorly understood. In this study, we show that a protein encoded by SARS-CoV designated as open reading frame-9b (ORF-9b) localizes to mitochondria and causes mitochondrial elongation by triggering ubiquitination and proteasomal degradation of dynamin-like protein 1, a host protein involved in mitochondrial fission. Also, acting on mitochondria, ORF-9b targets the mitochondrial-associated adaptor molecule MAVS signalosome by usurping PCBP2 and the HECT domain E3 ligase AIP4 to trigger the degradation of MAVS, TRAF3, and TRAF 6. This severely limits host cell IFN responses. Reducing either PCBP2 or AIP4 expression substantially reversed the ORF-9b-mediated reduction of MAVS and the suppression of antiviral transcriptional responses. Finally, transient ORF-9b expression led to a strong induction of autophagy in cells. The induction of autophagy depended upon ATG5, a critical autophagy regulator, but the inhibition of MAVS signaling did not. These results indicate that SARS-CoV ORF-9b manipulates host cell mitochondria and mitochondrial function to help evade host innate immunity. This study has uncovered an important clue to the pathogenesis of SARS-CoV infection and illustrates the havoc that a small ORF can cause in cells.
Publication types
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Research Support, N.I.H., Intramural
MeSH terms
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Adaptor Proteins, Signal Transducing / metabolism*
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Autophagy / genetics
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Autophagy-Related Protein 5
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Cell Line
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Dynamins
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GTP Phosphohydrolases / genetics
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GTP Phosphohydrolases / metabolism
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Green Fluorescent Proteins
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HEK293 Cells
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Humans
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Immune Evasion
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Immunity, Innate / genetics*
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Microtubule-Associated Proteins / biosynthesis
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Microtubule-Associated Proteins / genetics
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Microtubule-Associated Proteins / metabolism
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Mitochondria / genetics
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Mitochondria / immunology*
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Mitochondria / virology
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Mitochondrial Proteins / genetics
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Mitochondrial Proteins / metabolism
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Open Reading Frames / genetics
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Open Reading Frames / immunology
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RNA Interference
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RNA, Small Interfering
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RNA-Binding Proteins / biosynthesis
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RNA-Binding Proteins / genetics
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Repressor Proteins / biosynthesis
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Repressor Proteins / genetics
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Severe Acute Respiratory Syndrome / immunology
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Severe Acute Respiratory Syndrome / virology
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Severe acute respiratory syndrome-related coronavirus / genetics
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Severe acute respiratory syndrome-related coronavirus / immunology*
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TNF Receptor-Associated Factor 3 / metabolism
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TNF Receptor-Associated Factor 6 / metabolism
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Ubiquitin-Protein Ligases / biosynthesis
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Ubiquitin-Protein Ligases / genetics
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Ubiquitination
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Viral Proteins / genetics
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Viral Proteins / immunology*
Substances
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ATG5 protein, human
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Adaptor Proteins, Signal Transducing
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Autophagy-Related Protein 5
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MAVS protein, human
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Microtubule-Associated Proteins
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Mitochondrial Proteins
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ORF-9b protein, SARS coronavirus
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PCBP2 protein, human
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RNA, Small Interfering
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RNA-Binding Proteins
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Repressor Proteins
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TNF Receptor-Associated Factor 3
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TNF Receptor-Associated Factor 6
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TRAF3 protein, human
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Viral Proteins
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Green Fluorescent Proteins
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ITCH protein, human
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Ubiquitin-Protein Ligases
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GTP Phosphohydrolases
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DNM1L protein, human
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Dynamins