RIG-I and MDA-5 Detection of Viral RNA-dependent RNA Polymerase Activity Restricts Positive-Strand RNA Virus Replication (original) (raw)
Type I interferons (IFN) are important for antiviral responses. Melanoma differentiation-associated gene 5 (MDA-5) and retinoic acid-induced gene I (RIG-I) proteins detect cytosolic double-stranded RNA (dsRNA) or 59-triphosphate (59-ppp) RNA and mediate IFN production. Cytosolic 59-ppp RNA and dsRNA are generated during viral RNA replication and transcription by viral RNA replicases [RNA-dependent RNA polymerases (RdRp)]. Here, we show that the Semliki Forest virus (SFV) RNA replicase can induce IFN-b independently of viral RNA replication and transcription. The SFV replicase converts host cell RNA into 59-ppp dsRNA and induces IFN-b through the RIG-I and MDA-5 pathways. Inactivation of the SFV replicase RdRp activity prevents IFN-b induction. These IFN-inducing modified host cell RNAs are abundantly produced during both wild-type SFV and its non-pathogenic mutant infection. Furthermore, in contrast to the wild-type SFV replicase a non-pathogenic mutant replicase triggers increased IFN-b production, which leads to a shutdown of virus replication. These results suggest that host cells can restrict RNA virus replication by detecting the products of unspecific viral replicase RdRp activity.
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