UC San Diego

Chronic hepatitis B virus (HBV) infections are one of the leading causes of cirrhosis and hepatocellular carcinoma. N6-methyladenosine (m6A) modification of cellular and viral RNAs is the most prevalent internal modification that occurs cotranscriptionally. Previously, we reported the dual functional role of m6A modification of HBV transcripts in the viral life cycle. Here, we show that viral HBV X (HBx) protein is responsible for the m6A modifications of viral transcripts. HBV genomes defective in HBx failed to induce m6A modifications of HBV RNAs during infection/transfection, while ectopic expression of HBx restores m6A modifications of the viral RNAs but not the mutant HBx carrying the nuclear export signal. Using chromatin immunoprecipitation assays, we provide evidence that HBx and m6A methyltransferase complexes are localized on the HBV minichromosome to achieve cotranscriptional m6A modification of viral RNAs. HBx interacts with METTL3 and 14 to carry out methylation activity and also modestly stimulates their nuclear import. This role of HBx in mediating m6A modification also extends to host phosphatase and tensin homolog (PTEN) mRNA. This study provides insight into how a viral protein recruits RNA methylation machinery to m6A-modify RNAs.