Epitranscriptomic cytidine methylation of the Hepatitis B viral RNA encapsidation signal ensure the reverse transcription of viral RNA [PA-m6A-seq]
Epitranscriptomic RNA modifications have emerged as important regulators of the fate and function of both cellular and viral RNAs. One prominent modification, the cytidine methylation 5-methylcytidine (m5C), is found on the RNA of HIV-1, where m5C enhances the translation and splicing of HIV-1 RNA. However, whether m5C functionally enhances the RNA of other pathogenic viruses remain elusive. Here, we report that the RNA of hepatitis B virus (HBV) is enriched with a high level of m5C, mediated mainly through the cellular methyltransferase NSUN2. Intrigingly, the most prominent cluster of NSUN2-deposited m5C is found on the epsilon hairpin, an RNA element required for viral RNA encapsidation and reverse transcription. Loss of m5C from HBV RNA due to depletion of NSUN2 resulted in a modest decrease in viral capsid protein (HBc) translation, yet this is accompaneied by a near-complete loss of the reverse transcribed viral DNA. Similarly, mutations introduced to remove the methylated cytidines resulted in a translation decrease and block of reverse transcription. Furthermore, pharmacological disruption of m5C deposition with a nucleoside analogue led to a significant decrease in HBV replication. Thus, our data indicates m5C methylations is a critical enhancer of the epsilon element in HBV reverse transcription. Our study suggests the theraputic potential of targeting the m5C methyltransfer process on the HBV 5'epsilon as an alternative antiviral stratagy. Overall design: PA-m6A-seq: Photoactivated UV crosslinking of m56Aantibody to m6A+ RNA, followed by immunoprecipitation and sequencing. RNA from HuH-7 cells, WT or NSUN2 knockout cells, transfected with or without HBV replicon plasmid.