Entry and replication of recombinant hepatitis C viruses in cell culture

et al. 2014

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106

cHepatitis C virus (HCV) predominantly infects human hepatocytes, although extrahepatic virus reservoirs are being discussed. Infection of cells is initiated via cell-free and direct cell-to-cell transmission routes. Cell type-specific determinants of HCV entry and RNA replication have been reported. Moreover, several host factors required for synthesis and secretion of lipoproteins from liver cells, in part expressed in tissue-specific fashion, have been implicated in HCV assembly. However, the minimal cell type-specific requirements for HCV assembly have remained elusive. Here we report that production of HCV trans-complemented particles (HCV TCP ) from nonliver cells depends on ectopic expression of apolipoprotein E (ApoE). For efficient virus production by full-length HCV genomes, microRNA 122 (miR-122)-mediated enhancement of RNA replication is additionally required. Typical properties of cell culture-grown HCV (HCVcc) particles from ApoE-expressing nonliver cells are comparable to those of virions derived from human hepatoma cells, although specific infectivity of virions is modestly reduced. Thus, apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTTP), and apolipoprotein C1 (ApoC1), previously implicated in HCV assembly, are dispensable for production of infectious HCV. In the absence of ApoE, release of core protein from infected cells is reduced, and production of extracellular as well as intracellular infectivity is ablated. Since envelopment of capsids was not impaired, we conclude that ApoE acts after capsid envelopment but prior to secretion of infectious HCV. Remarkably, the lack of ApoE also abrogated direct HCV cell-to-cell transmission. These findings highlight ApoE as a host factor codetermining HCV tissue tropism due to its involvement in a late assembly step and viral cell-to-cell transmission. C urrently, around 160 million people are chronically infected with hepatitis C virus (HCV) worldwide (1). A prophylactic vaccine is not available, but direct-acting antivirals (DAA) have recently been approved for treatment (2). However, the novel triple therapy including pegylated alpha interferon (PEG-IFN-␣), ribavirin, and one of two available protease inhibitors is associated with side effects and is not licensed for all viral genotypes. A detailed understanding of the viral life cycle and the roles of specific viral and host factors may reveal novel targets for antiviral therapy and thus help to improve existing therapeutic options.Chronic HCV infection is a leading cause of liver disease, including hepatitis, liver cirrhosis, and hepatocellular carcinoma (3). It is also associated with numerous extrahepatic manifestations, such as cryoglobulenimia and neuronal disorders (reviewed in reference 4). While hepatocytes are thought to be the primary site of HCV replication, a number of studies have highlighted possible extrahepatic sites of replication, including peripheral blood mononuclear cells and cells of neuronal origin (reviewed in references 5 and 6). These observations sugge...

“…HCV titers were determined as published recently (47). The 50% tissue culture infectious dose (TCID 50 ) was calculated based on the methods described by Spearman and Kärber (48,49).…”

Section: Methodsmentioning

confidence: 99%

Apolipoprotein E Codetermines Tissue Tropism of Hepatitis C Virus and Is Crucial for Viral Cell-to-Cell Transmission by Contributing to a Postenvelopment Step of Assembly

Hueging

Doepke

et al. 2014

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106

“…Authentic viruses were titrated by using a limiting-dilution assay (37). The 50% tissue culture infectious dose (TCID 50 ) was calculated based on methods described previously by Spearman and Kärber (55,56).…”

Section: Methodsmentioning

confidence: 99%

Role of Hypervariable Region 1 for the Interplay of Hepatitis C Virus with Entry Factors and Lipoproteins

Bankwitz

Hueging

et al. 2014

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Hepatitis C virus (HCV) particles associate with lipoproteins and infect cells by using at least four cell entry factors. These factors include scavenger receptor class B type I (SR-BI), CD81, claudin 1 (CLDN1), and occludin (OCLN). Little is known about specific functions of individual host factors during HCV cell entry and viral domains that mediate interactions with these factors. Hypervariable region 1 (HVR1) within viral envelope protein 2 (E2) is involved in the usage of SR-BI and conceals the viral CD81 binding site. Moreover, deletion of this domain alters the density of virions. We compared lipoprotein interaction, surface attachment, receptor usage, and cell entry between wild-type HCV and a viral mutant lacking this domain. Deletion of HVR1 did not affect CD81, CLDN1, and OCLN usage. However, unlike wild-type HCV, HVR1-deleted viruses were not neutralized by antibodies and small molecules targeting SR-BI. Nevertheless, modulation of SR-BI cell surface expression altered the infection efficiencies of both viruses to similar levels. Analysis of affinity-purified virions revealed comparable levels of apolipoprotein E (ApoE) incorporation into viruses with or without HVR1. However, ApoE incorporated into these viruses was differentially recognized by ApoE-specific antibodies. Thus, SR-BI has at least two functions during cell entry. One of them can be neutralized by SR-BI-targeting molecules, and it is critical only for wild-type HCV. The other one is important for both viruses but apparently is not inactivated by the SR-BI binding antibodies and small molecules evaluated here. In addition, HVR1 modulates the conformation and/or epitope exposure of virus particle-associated ApoE.

“…Viral supernatants were filtered through 0.45-m-pore-size membranes. Titers of infectious viruses were determined by a limiting dilution assay as described elsewhere (50% tissue culture infective dose [TCID 50 ] method [38]). …”

Section: Methodsmentioning

confidence: 99%

“…Cell supernatants were then replaced with fresh medium (100 l/well), and the cells were further incubated for 40 h before fixation. Cell fixation, immunostaining, and focus counting were performed as described elsewhere (38).…”

Section: Methodsmentioning

confidence: 99%

Subcellular Localization and Function of an Epitope-Tagged p7 Viroporin in Hepatitis C Virus-Producing Cells

Brohm

Friesland

et al. 2013

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The hepatitis C virus (HCV) viroporin p7 is crucial for production of infectious viral progeny. However, its role in the viral replication cycle remains incompletely understood, in part due to the poor availability of p7-specific antibodies. To circumvent this obstacle, we inserted two consecutive hemagglutinin (HA) epitope tags at its N terminus. HA-tagged p7 reduced peak virus titers ca. 10-fold and decreased kinetics of virus production compared to the wild-type virus. However, HA-tagged p7 rescued virus production of a mutant virus lacking p7, thus providing formal proof that the tag does not disrupt p7 function. In HCV-producing cells, p7 displayed a reticular staining pattern which colocalized with the HCV envelope glycoprotein 2 (E2) but also partially with viral nonstructural proteins 2, 3, and 5A. Using coimmunoprecipitation, we confirmed a specific interaction between p7 and NS2, whereas we did not detect a stable interaction with core, E2, or NS5A. Moreover, we did not observe p7 incorporation into affinity-purified virus particles. Consistently, there was no evidence supporting a role of p7 in viral entry, as an anti-HA antibody was not able to neutralize Jc1 virus produced from an HA-p7-tagged genome. Collectively, these findings highlight a stable interaction between p7 and NS2 which is likely crucial for production of infectious HCV particles. Use of this functional epitope-tagged p7 variant should facilitate the analysis of the final steps of the HCV replication cycle.