Abstract
The replication and infectivity of the lipotropic hepatitis C virus (HCV) are regulated by cellular lipid status. Among differentially expressed microRNAs (miRNAs), we found that miR-27a was preferentially expressed in HCV-infected liver over hepatitis B virus (HBV)-infected liver. Gene expression profiling of Huh-7.5 cells showed that miR-27a regulates lipid metabolism by targeting the lipid synthetic transcription factor RXRα and the lipid transporter ATP-binding cassette subfamily A member 1. In addition, miR-27a repressed the expression of many lipid metabolism-related genes, including FASN, SREBP1, SREBP2, PPARα, and PPARγ, as well as ApoA1, ApoB100, and ApoE3, which are essential for the production of infectious viral particles. miR-27a repression increased the cellular lipid content, decreased the buoyant density of HCV particles from 1.13 to 1.08 g/cm(3), and increased viral replication and infectivity. miR-27a overexpression substantially decreased viral infectivity. Furthermore, miR-27a enhanced in vitro interferon (IFN) signaling, and patients who expressed high levels of miR-27a in the liver showed a more favorable response to pegylated IFN and ribavirin combination therapy. Interestingly, the expression of miR-27a was upregulated by HCV infection and lipid overload through the adipocyte differentiation transcription factor C/EBPα. In turn, upregulated miR-27a repressed HCV infection and lipid storage in cells. Thus, this negative feedback mechanism might contribute to the maintenance of a low viral load and would be beneficial to the virus by allowing it to escape host immune surveillance and establish a persistent chronic HCV infection.