Establishment of stable HeLa cell lines expressing enzymatically active hepatitis C virus RNA polymerase

Hepatitis C virus and its protein NS4B activate the cancer-related STAT3 pathway via the endoplasmic reticulum overload response

Oxidative stress induces the activation of signal transducer and activator of transcription 3 (STAT3), which plays an important role in hepatocellular carcinoma (HCC). We have previously reported that hepatitis C virus (HCV) and its protein NS4B induce the production of reactive oxygen species (ROS) via the endoplasmic reticulum overload response (EOR) in human hepatocytes. Here, we found that NS4B and HCV induce STAT3 activation and stimulate the expression of cancer-related STAT3 target genes, including VEGF, c-myc, MMP-9 and Mcl-1, by EOR in human hepatocytes. Moreover, the cancer-related STAT3 pathway activated by NS4B and HCV via EOR were found to promote human hepatocyte viability. Taken together, these findings revealed that HCV NS4B might contribute to HCC by activating the EOR-mediated cancer-related STAT3 pathway, and this could provide novel insights into HCV-induced HCC.

Hepatitis C virus (HCV) NS2 protein up-regulates HCV IRES-dependent translation and down-regulates NS5B RdRp activity

Chronic hepatitis C virus (HCV) infection often leads to liver cancer. The HCV NS2 protein is a hydrophobic transmembrane protein that associates with several cellular proteins in mammalian cells. In this report, we investigated the function of NS2 protein on HCV replication and translation by using a transient cell-based expression system. Cells co-transfected with pcDNA3.1 (-)-NS2 and the dual-luciferase reporter construct containing the HCV IRES were used to detect the effect of NS2 protein on HCV translation. Cells co-transfected with pcDNA3.1(-)-NS2, pcDNA-NS5B and a reporter plasmid were used to detect the effect of NS2 protein on HCV replication. The results showed that HCV NS2 protein up-regulated HCV IRES-dependent translation in a specific and dose-dependent manner in Huh7 cells but not in HeLa and HepG2 cells, and NS2 protein inhibited NS5B RdRp activity in a dose-independent manner in all three cell lines. These findings may suggest a novel mechanism by which HCV modulates its NS5B replication and IRES-dependent translation and facilitates virus persistence.

Inhibition of HCV RNA-dependent RNA polymerase activity by aqueous extract from Fructus Ligustri Lucidi

The development of effective antiviral drugs against hepatitis C virus (HCV) continues to be needed, since neither vaccines nor broadly effective therapeutic agents are available. HCV RNA-dependent RNA polymerase (NS5B) is strictly required for viral replication and thus represents an attractive target. Here, aqueous extracts from five traditional Chinese medicines were tested for their ability to inhibit NS5B activity by reporter assays using cell-based NS5B activity detecting systems. Among them, aqueous extract from Fructus Ligustri Lucidi exhibited a promising result, dose-dependent inhibition of the luciferase activity, an indicator of intracellular NS5B activity (p<0.001), in the absence of cytotoxicity. Further Quantitative RT-PCR assays and Western blot analysis showed aqueous extract from Fructus Ligustri Lucidi inhibited intracellular NS5B-catalyzed RNA synthesis dose-dependently (p<0.001) without affecting intracellular NS5B expression. Subsequent in vitro NS5B assays revealed that this extract could directly inhibit NS5B activity. Taken together, these results indicated that Fructus Ligustri Lucidi might offer a promising source of antiviral drugs against HCV NS5B. Purification of the active compound(s) and antiviral effect are clearly required in the future.

Binding-site identification and genotypic profiling of hepatitis C virus polymerase inhibitors

The search for hepatitis C virus polymerase inhibitors has resulted in the identification of several nonnucleoside binding pockets. The shape and nature of these binding sites differ across and even within diverse hepatitis C virus genotypes. These differences confront antiviral drug discovery with the challenge of finding compounds that are capable of inhibition in variable binding pockets. To address this, we have established a hepatitis C virus mutant and genotypic recombinant polymerase panel as a means of guiding medicinal chemistry through the elucidation of the site of action of novel inhibitors and profiling against genotypes. Using a genotype 1b backbone, we demonstrate that the recombinant P495L, M423T, M414T, and S282T mutant enzymes can be used to identify the binding site of an acyl pyrrolidine analog. We assess the inhibitory activity of this analog and other nonnucleoside inhibitors with our panel of enzyme isolates generated from clinical sera representing genotypes 1a, 1b, 2a, 2b, 3a, 4a, 5a, and 6a.