GSE136139
N6-methyladenosine is a molecular signature for discrimination of self and non-self RNA by cytoplasmic RNA sensor RIG-I
Internal N6-methyladenosine (m6A) modification of RNA is one of the most common and abundant modifications in eukaryotic cells as well as in viruses. However, the biological role(s) of RNA m6A in virus-host interaction remains elusive. Using human metapneumovirus (hMPV), a medically important non-segmented negative-sense RNA virus as a model, we demonstrate that m6A serves as a molecular marker for innate immune discrimination self and nonself RNAs. We show that hMPV RNAs are m6A methylated and that viral m6A methylation promotes hMPV replication and gene expression. HMPV infection leads to differential expression of interferon-related genes involved in innate immune signaling pathways. Inactivating these m6A sites with synonymous mutations resulted in m6A deficient recombinant hMPVs that induced significantly higher expression of type I interferon that restricted viral replication. Notably, the induction of type I interferons by m6A-deficient rhMPVs and virion RNA was dependent on the cytoplasmic RNA sensor RIG-I, not MDA5. Mechanistically, m6A-deficient virion RNA induces higher expression of RIG-I, enhances its binding affinity to RIG-I, and facilitates the conformational change of RIG-I, leading to enhanced induction of type I IFN expression. The replication of m6A-deficient rhMPVs was attenuated in wild type A459 cells but was restored in cells knocked out for RIG-I and MAVS. Furthermore, m6A-deficient rhMPVs triggered higher type I interferon in vivo and were significantly attenuated in the lower respiratory tract yet retained high immunogenicity in cotton rats. Collectively, our results highlight that (i) virus acquires m6A in their RNAs as a means of mimicking cellular RNA to avoid the detection by innate immunity; and (ii) viral m6A RNA can serve as a novel target to attenuate hMPV for vaccine purposes. Overall design: HMPV virions were purified from supernatants of hMPV-infected Hela and A549 cell lines. Virus derived mRNA as well as host mRNA were purified from total RNA, which were extracted from hMPV infected cells.