Our results demonstrate that miR-1 acts as a positive regulator of HBV replication and transcription through regulating the cellular gene expression. MiR-1 has been shown to play an important role in many cellular and biological functions of the cardiovascular system. The presence of miR-1 in liver tissues and hepatoma cells has been reported.21, 29 By real-time PCR, we confirmed the expression of miR-1 in primary hepatocytes and hepatoma cell lines (Supporting Information Fig. 9), indicating that miR-1 may play a role in the regulation of hepatic

gene expression, as well as HBV replication. It is has been suggested that miRNAs may not only regulate gene expression at the posttranscriptional level, but that they are also capable of modifying chromatin.30 Because HBV covalently closed circular DNA (cccDNA) forms a viral minichromosome in infected hepatocytes as a template for the transcription of viral mRNAs, epigenetic modifications of the HBV cccDNA, AUY-922 purchase such as the deacetylation of cccDNA-bound histones by HDACs, might regulate the transcription of viral chromatin and thereby viral replication.31 A recent study revealed that HBV replication is regulated by the acetylation status of H3/H4 histones bound to the HBV cccDNA, both in cell-based replication systems

and in the liver of HBV chronically infected patients.23 We confirmed that HDAC4 expression is down-regulated by miR-1. Silencing of HDAC4 by siRNA or histone deacetylase inhibitors selleck inhibitor TSA treatment led to the enhancement of HBV replication. Our results are consistent with previous findings and suggest selleck chemicals llc the significance of epigenetic modifications for HBV replication. A direct link from miR-1 action to HBV replication is the

regulation of HBV core promoter activity by augmenting FXRA expression. Several studies have described the essential role of FXRA/RXRA in the HBV life cycle in detail. FXRA forms a heterodimer with RXRA and binds to the regulatory sequences in the HBV core promoter. Activation of the FXR/RXR pathway by bile acids can enhance HBV transcription and replication.24, 32 Ectopic expression of FXRA/RXRA can establish HBV replication in nonhepatoma cells.15 In our study, FXRA was significantly up-regulated by miR-1. Furthermore, the FXRA antagonist GGS and FXRA-specific siRNA partially attenuated the miR-1 effect on HBV replication. Our results strongly suggested that FXRA may contribute to the modulation of HBV core promoter activity and subsequently to the level of viral replication by miR-1 expression. However, the mechanism of miR-1 regulation in FXRA expression remains to be clarified. The ability of miRNAs to regulate the expression of multiple target genes implies the influence of miRNAs on global biological processes in cells. As shown previously, miR-1 expression was reduced in primary human hepatocellular carcinomas compared with matching normal liver tissue.