DHX9 regulates production of hepatitis B virus-derived circular RNA and viral protein levels

Abstract

// Kazuma Sekiba 1 , Motoyuki Otsuka 1 , Motoko Ohno 1 , Takahiro Kishikawa 1 , Mari Yamagami 1 , Tatsunori Suzuki 1 , Rei Ishibashi 1 , Takahiro Seimiya 1 , Eri Tanaka 1 and Kazuhiko Koike 1 1 Department of Gastroenterology, Graduate School of Medicine, The University of Tokyo, Tokyo 113-8655, Japan Correspondence to: Motoyuki Otsuka, email: otsukamo-tky@umin.ac.jp Keywords: HBV; cccDNA; minicircle; primary hepatocytes; digital PCR; Immunology Received: February 28, 2018      Accepted: March 24, 2018      Published: April 20, 2018 ABSTRACT Hepatitis B virus (HBV) infection, which is a major health concern worldwide, can lead to liver cirrhosis and hepatocellular carcinoma. Although current nucleos(t)ide analogs efficiently inhibit viral reverse transcription and viral DNA load clinically, episomal viral covalently closed circular DNA (cccDNA) minichromosomes and transcripts from cccDNA continue to be expressed over the long term. We hypothesized that, under these conditions, viral transcripts may have biological functions involved in pathogenesis. Here, we show that the host protein DExH-box helicase 9 (DXH9) is associated with viral RNAs. We also show that viral-derived circular RNA is produced during HBV replication, and the amount is increased by knockdown of the DHX9 protein, which, in turn, results in decreased viral protein levels but does not affect the levels of HBV DNA. These phenomena were observed in the HBV-producing cell culture model and HBV mini-circle model mimicking HBV cccDNA, as well as in human primary hepatocytes infected with HBV. Based on these results, we conclude that, in HBV infection, the RNA binding factor DHX9 is a novel regulator of viral circular RNA and viral protein levels.