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Hepatitis C virus (HCV) or HCV-low-density lipoprotein (LDL) complexes interact with the LDL receptor (LDLr) and the HCV envelope glycoprotein E2 interacts with CD81 in vitro. However, E2 interactions with LDLr and HCV interactions with CD81 have not been clearly described. Using sucrose gradient-purified low-density particles (1.03 to 1.07 g/cm 3 ), intermediate-density particles (1.12 to 1.18 g/cm 3 ), recombinant E2 protein, or control proteins, we assessed binding to MOLT-4 cells, foreskin fibroblasts, or LDLr-deficient foreskin fibroblasts at 4°C by flow cytometry and confocal microscopy. Viral entry was determined by measuring the coentry of ␣-sarcin, a protein synthesis inhibitor. We found that low-density HCV particles, but not intermediate-density HCV or controls bound to MOLT-4 cells and fibroblasts expressing the LDLr. Binding correlated with the extent of cellular LDLr expression and was inhibited by LDL but not by soluble CD81. In contrast, E2 binding was independent of LDLr expression and was inhibited by human soluble CD81 but not mouse soluble CD81 or LDL. Based on confocal microscopy, we found that low-density HCV particles and LDL colocalized on the cell surface. The addition of low-density HCV but not intermediate-density HCV particles to MOLT-4 cells allowed coentry of ␣-sarcin, indicating viral entry. The amount of viral entry also correlated with LDLr expression and was independent of the CD81 expression. Using a solid-phase immunoassay, recombinant E2 protein did not interact with LDL. Our data indicate that E2 binds CD81; however, virus particles utilize LDLr for binding and entry. The specific mechanism by which HCV particles interact with LDL or the LDLr remains unclear.Hepatitis C virus (HCV) infection is a major cause of chronic liver disease worldwide. Approximately 85% of people infected with HCV remain persistently viremic, and approximately 20% to 50% of these individuals ultimately develop cirrhosis (12,21,50). Of those with HCV-related cirrhosis, approximately 5% develop hepatocellular carcinoma (21, 50). In the United States, an estimated 4 million people are infected, and HCV is the leading cause of liver transplantation (21). Extrahepatic manifestations, including cryoglobulinemia and B-lymphocyte proliferative disorders, which are characterized by polyclonal B-cell activation and autoantibody production, are also associated with HCV infection (3,13,14,39). Hepatocytes represent the primary site of HCV replication in vivo. Although explanted peripheral blood mononuclear cells (PBMCs) contain HCV RNA (4, 30, 40), it is unclear if HCV replication occurs in PBMCs in vivo (1,16,23,52). No efficient cell culture system has been described for HCV, but in vitro studies have shown that several human cells including primary PBMC cultures (10) and cell lines of hepatocyte and lymphoid origin (42-45) are permissive for HCV replication.Currently, the mechanism of HCV cell entry is not clear. Two cell surface receptors interact with HCV or HCV E2 protein in vitro, leading to speculation t...

MicroRNAs (miRNAs) are small RNAs that regulate gene expression pathways. Previous studies have shown interactions between hepatitis C virus (HCV) and host miRNAs. We measured miR-122 and miR-21 levels in HCV-infected human liver biopsies relative to uninfected human livers and correlated these with clinical patient data. miR-122 is required for HCV replication in vitro, and miR-21 is involved in cellular proliferation and tumorigenesis. We found that miR-21 expression correlated with viral load, fibrosis and serum liver transaminase levels. miR-122 expression inversely correlated with fibrosis, liver transaminase levels and patient age. miR-21 was induced Btwofold, and miR-122 was downregulated on infection of cultured cells with the HCV J6/JFH infectious clone, thus establishing a link to HCV. To further examine the relationship between fibrosis and the levels of miR-21 and miR-122, we measured their expression levels in a mouse carbon tetrachloride fibrosis model. As in the HCV-infected patient samples, fibrotic stage positively correlated with miR-21 and negatively correlated with miR-122 levels. Transforming growth factor b (TGF-b) is a critical mediator of fibrogenesis. We identified SMAD7 as a novel miR-21 target. SMAD7 is a negative regulator of TGF-b signaling, and its expression is induced by TGF-b. To confirm the relationship between miR-21 and the TGF-b signaling pathway, we measured the effect of miR-21 on a TGF-b-responsive reporter. We found that miR-21 enhanced TGF-b signaling, further supporting a relationship between miR-21 and fibrosis. We suggest a model in which miR-21 targeting of SMAD7 could increase TGF-b signaling, leading to increased fibrogenesis.

GB virus C (GBV-C or hepatitis G virus) is a recently described flavivirus which frequently leads to chronic viremia in humans. Although GBV-C is associated with acute posttransfusion hepatitis, it is not clear if the virus is pathogenic for humans. We constructed a full-length cDNA from the plasma of a person with chronic GBV-C viremia. Peripheral blood mononuclear cells (PBMCs) transfected with full-length RNA transcripts from this GBV-C clone resulted in viral replication. This was demonstrated by serial passage of virus from cell culture supernatants, detection of increasing concentrations of positive-and negative-sense GBV-C RNA over time, and the detection of the GBV-C E2 antigen by confocal microscopy. In addition, two types of GBV-C particles were identified in cell lysates; these particles had buoyant densities of 1.06 and 1.12 to 1.17 g/ml in sucrose gradients. PBMCs sorted for expression of CD4 contained 100-fold-more GBV-C RNA than CD4-negative cells. Taken together, these data demonstrate that RNA transcripts from GBV-C full-length cDNA are infectious in primary CD4-positive T cells. In contrast, RNA transcripts from an infectious hepatitis C virus clone did not replicate in the same cell culture system. Infectious RNA transcripts from GBV-C cDNA should prove useful for studying viral replication and may allow identification of differences between GBV-C and hepatitis C virus cultivation in vitro.