Project description:Numerous mammalian proto-oncogene and other growth-regulatory transcripts are upregulated in malignancy due to abnormal mRNA stabilization. In hepatoma cells expressing a hepatitis C virus (HCV) subgenomic replicon, we found that the viral nonstructural protein 5A (NS5A), a protein known to bind to viral RNA, also bound specifically to human cellular transcripts that encode regulators of cell growth and apoptosis, and this binding correlated with transcript stabilization. An important subset of human NS5A-target transcripts contained GU-rich elements, sequences known to destabilize mRNA. We found that NS5A bound to GU-rich elements in vitro and in cells. Mutation of the NS5A zinc finger abrogated its GU-rich element-binding and mRNA stabilizing activities. Overall, we identified a molecular mechanism whereby HCV manipulates host gene expression by stabilizing host transcripts in a manner that would promote growth and prevent death of virus-infected cells, allowing the virus to establish chronic infection and lead to the development of hepatocellular carcinoma.
Project description:Chronic hepatitis C virus (HCV) infection is a leading cause of liver cancer. HCV propagation and oncogenicity depend in part on the phosphorylation states of its non-structural protein 5A (NS5A); however, little is known about how hypo- or hyper-phosphorylated NS5A functions. Here, we segregated hypo- from hyper-phosphorylated NS5A in HCV-infected Huh7.5.1 cells with two custom-made specific antibodies and differentiated their interacting proteins with dimethyl labeling-based quantitative proteomics. Bioinformatics analysis revealed that hyper-phosphorylated NS5A preferentially binds the polymerase II-associated factor 1 complex known to alter host gene expression involved in cancer progression. In contrast, hypo-phosphorylated NS5A binds proteins involved in host antiviral response. Moreover, we found that the hypo-phosphorylated NS5A binds DNA-dependent protein kinase catalytic subunit (DNA-PKcs) predicted to phosphorylate NS5A at serine 232, a key amino acid that governs NS5A transition from hypo- to hyper-phosphorylation state. Inhibition of DNA-PKcs with an inhibitor or via gene-specific knockdown significantly reduced serine 232 phosphorylation and NS5A hyper-phosphorylation. Collectively, we have identified a protein kinase that regulates a delicate balance of NS5A between hypo- and hyper-phosphorylation states respectively involved in host antiviral responses and liver cancer progression.
Project description:In order to infer the inverse expression relationships between microRNAs and mRNAs during HCV infection, we profiled both microRNA and mRNA expressions in HCV positive (HCV+) and HCV negative (HCV-) human liver biopsy tissue samples. This series includes all microRNA profiles.
Project description:The RNA-dependent RNA polymerase (NS5B) of hepatitis C virus (HCV) is an unusually attractive target for drug discovery since it contains five distinct drugable sites. The success of novel antiviral therapies will require nonnucleoside inhibitors to be active in at least patients infected with HCV of subtypes 1a and 1b. Therefore, the genotypic assessment of these agents against clinical isolates derived from genotype 1-infected patients is an important prerequisite for the selection of suitable candidates for clinical development. Here we report the 1a/1b subtype profiling of polymerase inhibitors that bind at each of the four known nonnucleoside binding sites. We show that inhibition of all of the clinical isolates tested is maintained, except for inhibitors that bind at the palm-1 binding site. Subtype coverage varies across chemotypes within this class of inhibitors, and inhibition of genotype 1a improves when hydrophobic contact with the polymerase is increased. We investigated if the polymorphism of the palm-1 binding site is the sole cause of the reduced susceptibility of subtype 1a to inhibition by 1,5-benzodiazepines by using reverse genetics, X-ray crystallography, and surface plasmon resonance studies. We showed Y415F to be a key determinant in conferring resistance on subtype 1a, with this effect being mediated through an inhibitor- and enzyme-bound water molecule. Binding studies revealed that the mechanism of subtype 1a resistance is faster dissociation of the inhibitor from the enzyme.
Project description:Hepatitis C virus uniquely requires the liver specific microRNA-122 for replication, yet global effects on endogenous miRNA targets during infection are unexplored. Here, high-throughput sequencing and crosslinking immunoprecipitation (HITS-CLIP) experiments of human Argonaute (Ago) during HCV infection showed robust Ago binding on the HCV 5’UTR, at known and predicted miR-122 sites. On the human transcriptome, we observed reduced Ago binding and functional mRNA de-repression of miR-122 targets during virus infection. This miR-122 “sponge” effect could be relieved and redirected to miR-15 targets by swapping the miRNA tropism of the virus. Single-cell expression data from reporters containing miR-122 sites showed significant de-repression during HCV infection depending on expression level and number of sites. We describe a quantitative mathematical model of HCV induced miR-122 sequestration and propose that such miR-122 inhibition by HCV RNA may result in global de-repression of host miR-122 targets, providing an environment fertile for the long-term oncogenic potential of HCV.
Project description:Despite the introduction of effective treatments for hepatitis C in clinics, issues remain regarding the liver diseases induced by chronic hepatitis C virus (HCV) infection. HCV is known to disturb the metabolism of infected cells, especially lipid metabolism and redox balance, but the mechanisms leading to HCV-induced pathogenesis are still poorly understood. In an APEX2-based proximity biotinylation screen, we identified ACBD5, a peroxisome membrane protein, as located in the vicinity of HCV replication complexes. Confocal microscopy confirmed the relocation of peroxisomes near HCV replication complexes and indicated that their morphology and number are altered in approximately 30% of infected Huh-7 cells. Peroxisomes are small versatile organelles involved among other functions in lipid metabolism and ROS regulation. To determine their importance in the HCV life cycle, we generated Huh-7 cells devoid of peroxisomes by inactivating the PEX5 and PEX3 genes using CRISPR/Cas9 and found that the absence of peroxisomes had no impact on replication kinetics or infectious titers of HCV strains JFH1 and DBN3a. The impact of HCV on peroxisomal functions was assessed using sub-genomic replicons. An increase of ROS was measured in peroxisomes of replicon-containing cells, and this increase was more pronounced than in mitochondria or the cytosol, suggesting that the redox balance of peroxisomes is specifically impaired in cells replicating HCV. Our study provides evidence that peroxisome function and morphology are altered in HCV-infected cells.
Project description:Hepatitis C virus uniquely requires the liver specific microRNA-122 for replication, yet global effects on endogenous miRNA targets during infection are unexplored. Here, high-throughput sequencing and crosslinking immunoprecipitation (HITS-CLIP) experiments of human Argonaute (Ago) during HCV infection showed robust Ago binding on the HCV 5’UTR, at known and predicted miR-122 sites. On the human transcriptome, we observed reduced Ago binding and functional mRNA de-repression of miR-122 targets during virus infection. This miR-122 “sponge” effect could be relieved and redirected to miR-15 targets by swapping the miRNA tropism of the virus. Single-cell expression data from reporters containing miR-122 sites showed significant de-repression during HCV infection depending on expression level and number of sites. We describe a quantitative mathematical model of HCV induced miR-122 sequestration and propose that such miR-122 inhibition by HCV RNA may result in global de-repression of host miR-122 targets, providing an environment fertile for the long-term oncogenic potential of HCV. mRNA-seq libraries were generated from mock or J6/JFH1 Clone2 infected Huh7.5 cells. Cells were infected at an MOI of 1-2 and harvested at 72 hours and 96 hours post-infection for CLIP. Libraries were generated using Illumina Truseq technology.