Abstract
Cellular messenger RNA (mRNA) of higher eukaryotes and many viral RNAs are methylated at the N-7 and 2'-O positions of the 5' guanosine cap by specific nuclear and cytoplasmic methyltransferases (MTases), respectively. Whereas N-7 methylation is essential for RNA translation and stability, the function of 2'-O methylation has remained uncertain since its discovery 35 years ago. Here we show that a West Nile virus (WNV) mutant (E218A) that lacks 2'-O MTase activity was attenuated in wild-type primary cells and mice but was pathogenic in the absence of type I interferon (IFN) signalling. 2'-O methylation of viral RNA did not affect IFN induction in WNV-infected fibroblasts but instead modulated the antiviral effects of IFN-induced proteins with tetratricopeptide repeats (IFIT), which are interferon-stimulated genes (ISGs) implicated in regulation of protein translation. Poxvirus and coronavirus mutants that lacked 2'-O MTase activity similarly showed enhanced sensitivity to the antiviral actions of IFN and, specifically, IFIT proteins. Our results demonstrate that the 2'-O methylation of the 5' cap of viral RNA functions to subvert innate host antiviral responses through escape of IFIT-mediated suppression, and suggest an evolutionary explanation for 2'-O methylation of cellular mRNA: to distinguish self from non-self RNA. Differential methylation of cytoplasmic RNA probably serves as an example for pattern recognition and restriction of propagation of foreign viral RNA in host cells.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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3T3 Cells
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Adaptor Proteins, Signal Transducing
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Animals
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Apoptosis Regulatory Proteins
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cells, Cultured
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Coronavirus / enzymology
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Coronavirus / genetics
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Coronavirus / immunology
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Coronavirus / physiology
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Fibroblasts
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Gene Expression Regulation / genetics
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Gene Expression Regulation / immunology*
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Humans
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Immunity, Innate / genetics
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Immunity, Innate / immunology*
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Interferons / deficiency
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Interferons / genetics
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Interferons / immunology*
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Methylation
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Methyltransferases / metabolism
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Mice
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Mice, Inbred C57BL
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Models, Genetic
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Models, Immunological
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism
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Poxviridae / enzymology
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Poxviridae / genetics
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Poxviridae / immunology
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Poxviridae / physiology
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Protein Biosynthesis / immunology
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Proteins / genetics
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Proteins / metabolism*
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RNA Caps / genetics
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RNA Caps / immunology
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RNA Caps / metabolism*
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RNA, Viral / genetics
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RNA, Viral / immunology
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RNA, Viral / metabolism*
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RNA-Binding Proteins
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Receptor, Interferon alpha-beta / deficiency
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Receptor, Interferon alpha-beta / genetics
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Survival Rate
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Virus Replication
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West Nile virus / enzymology
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West Nile virus / genetics
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West Nile virus / immunology
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West Nile virus / physiology
Substances
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Adaptor Proteins, Signal Transducing
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Apoptosis Regulatory Proteins
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Carrier Proteins
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IFIT5 protein, human
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Ifit1 protein, mouse
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Ifit2 protein, mouse
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Ifnar1 protein, mouse
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Neoplasm Proteins
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Proteins
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RNA Caps
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RNA, Viral
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RNA-Binding Proteins
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Receptor, Interferon alpha-beta
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Interferons
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Methyltransferases