Identification of Host Factors Required for Hepatitis C Virus Infection
Hepatitis C virus (HCV), a positive-strand RNA virus, infects more than 170 million people and is the leading cause of liver failure worldwide. A protective vaccine is not yet available. Current interferon-based therapies are only effective in a fraction of patients. Thus, there is an urgent need to develop better therapeutic strategies. However, the intrinsic low fidelity of HCV replication makes it more difficult to develop drugs targeting viral proteins since HCV could quickly generate drug-resistant strains. In this context, drugs targeting host factors that control HCV infection may be more effective therapies in that the potency of drugs is not affected by viral mutations. For this purpose, more knowledge regarding host factors involved in HCV infection is needed. HCV is known to replicate on intracellular membrane vesicles. In searching for host proteins localized in membrane vesicles containing HCV replication complex, a magnetic immuno-isolation procedure was employed. This study identified that Apolipoprotein B, Microsomal Triglyceride Transfer Protein, and Apolipoprotein E, three proteins participated in the assembly of very low-density lipoprotein (VLDL) were enriched in membrane vesicles. It was demonstrated that agents inhibiting VLDL assembly also inhibit the secretion of HCV. These studies raise the possibility for treating HCV infection with agents blocking VLDL secretion. HCV infection is also known to produce reactive oxygen species (ROS), which initiate lipid peroxidation. We found that when HCV-infected cells were exposed to polyunsaturated fatty acids (PUFAs) in the absence of lipid-soluble antioxidants, a dramatic increase in lipid peroxidation caused a reduction in HCV RNA. Because peroxidation of PUFAs only occurs in HCV-infected cells that produce ROS, PUFAs could be used to suppress HCV replication in patients without intolerable toxicity. Different in vitro model systems have been used to study the HCV lifecycle. However, the genotype1 HCV, which is the most difficult strain to treat in clinic, still can not be grown in cultured cells. We found a cell line named HCV Replication Permissive 1 (HRP1) that supports the replication of genotype 1 HCV. Interestingly, HRP1 cells appear to have normal interferon response, suggesting a novel innate antiviral pathway may be disrupted in these cells.