The variability of the hepatitis C virus (HCV), which likely contributes to immune escape, is most pronounced in hypervariable region 1 (HVR1) of viral envelope protein 2. This domain is the target for neutralizing antibodies, and its deletion attenuates replication in vivo. Here we characterized the relevance of HVR1 for virus replication in vitro using cell culture-derived HCV. We show that HVR1 is dispensable for RNA replication. However, viruses lacking HVR1 (⌬HVR1) are less infectious, and separation by density gradients revealed that the population of ⌬HVR1 virions comprises fewer particles with low density. Strikingly, ⌬HVR1 particles with intermediate density (1.12 g/ml) are as infectious as wild-type virions, while those with low density (1.02 to 1.08 g/ml) are poorly infectious, despite quantities of RNA and core similar to those in wild-type particles. Moreover, ⌬HVR1 particles exhibited impaired fusion, a defect that was partially restored by an E1 mutation (I347L), which also rescues infectivity and which was selected during long-term culture. Finally, ⌬HVR1 particles were no longer neutralized by SR-B1-specific immunoglobulins but were more prone to neutralization and precipitation by soluble CD81, E2-specific monoclonal antibodies, and patient sera. These results suggest that HVR1 influences the biophysical properties of released viruses and that this domain is particularly important for infectivity of low-density particles. Moreover, they indicate that HVR1 obstructs the viral CD81 binding site and conserved neutralizing epitopes. These functions likely optimize virus replication, facilitate immune escape, and thus foster establishment and maintenance of a chronic infection.Hepatitis C virus (HCV) is a single-stranded positive-sense RNA virus of the family Flaviviridae that has infected an estimated 130 million people worldwide (1). Acute HCV infection is mostly asymptomatic; however, virus persistence can lead to severe liver disease, and within 20 years ca. 20% of chronically infected adults develop cirrhosis (46). In fact, morbidity associated with chronic HCV infection is the most common indication for orthotopic liver transplantation (7). The mechanisms that permit the virus to establish chronic infection in ca. 55 to 85% of cases (24) despite vigorous immune responses are incompletely understood.A number of studies have highlighted the pivotal role of strong, multispecific, and sustained T-cell responses for control of HCV infection (summarized in reference 53). Although resolution of acute HCV infection can occur in the absence of antibodies (47), mounting evidence indicates that neutralizing antibodies also contribute to protective immunity (summarized in reference 62). Nevertheless, HCV often successfully evades cellular and humoral immune pressure likely at least in part via the constant generation of variants created by an error-prone RNA replication machinery. In line with this notion, a high degree of HCV sequence evolution is associated with chronic disease, while a comparatively st...

Hepatitis C virus (HCV) naturally infects only humans and chimpanzees. The determinants responsible for this narrow species tropism are not well defined. Virus cell entry involves human scavenger receptor class B type I (SR-BI), CD81, claudin-1 and occludin. Among these, at least CD81 and occludin are utilized in a highly species-specific fashion, thus contributing to the narrow host range of HCV. We adapted HCV to mouse CD81 and identified three envelope glycoprotein mutations which together enhance infection of cells with mouse or other rodent receptors approximately 100-fold. These mutations enhanced interaction with human CD81 and increased exposure of the binding site for CD81 on the surface of virus particles. These changes were accompanied by augmented susceptibility of adapted HCV to neutralization by E2-specific antibodies indicative of major conformational changes of virus-resident E1/E2-complexes. Neutralization with CD81, SR-BI- and claudin-1-specific antibodies and knock down of occludin expression by siRNAs indicate that the adapted virus remains dependent on these host factors but apparently utilizes CD81, SR-BI and occludin with increased efficiency. Importantly, adapted E1/E2 complexes mediate HCV cell entry into mouse cells in the absence of human entry factors. These results further our knowledge of HCV receptor interactions and indicate that three glycoprotein mutations are sufficient to overcome the species-specific restriction of HCV cell entry into mouse cells. Moreover, these findings should contribute to the development of an immunocompetent small animal model fully permissive to HCV.

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...

Hepatitis C virus (HCV) has infected around 160 million individuals. Current therapies have limited efficacy and are fraught with side effects. To identify cellular HCV dependency factors, possible therapeutic targets, we manipulated signaling cascades with pathway-specific inhibitors. Using this approach we identified the MAPK/ERK regulated, cytosolic, calcium-dependent, group IVA phospholipase A2 (PLA2G4A) as a novel HCV dependency factor. Inhibition of PLA2G4A activity reduced core protein abundance at lipid droplets, core envelopment and secretion of particles. Moreover, released particles displayed aberrant protein composition and were 100-fold less infectious. Exogenous addition of arachidonic acid, the cleavage product of PLA2G4A-catalyzed lipolysis, but not other related poly-unsaturated fatty acids restored infectivity. Strikingly, production of infectious Dengue virus, a relative of HCV, was also dependent on PLA2G4A. These results highlight previously unrecognized parallels in the assembly pathways of these human pathogens, and define PLA2G4A-dependent lipolysis as crucial prerequisite for production of highly infectious viral progeny.

Turmeric curcumin inhibits HCV entry independently of the genotype and in primary human hepatocytes by affecting membrane fluidity thereby impairing virus binding and fusion.

Scavenger receptor class B type I (SR-BI) is a high-density lipoprotein (HDL) receptor highly expressed in the liver and modulating HDL metabolism. Hepatitis C virus (HCV) is able to directly interact with SR-BI and requires this receptor to efficiently enter into hepatocytes to establish productive infection. A complex interplay between lipoproteins, SR-BI and HCV envelope glycoproteins has been reported to take place during this process. SR-BI has been demonstrated to act during binding and postbinding steps of HCV entry. Although the SR-BI determinants involved in HCV binding have been partially characterized, the postbinding function of SR-BI remains largely unknown. To uncover the mechanistic role of SR-BI in viral initiation and dissemination, we generated a novel class of anti-SR-BI monoclonal antibodies that interfere with postbinding steps during the HCV entry process without interfering with HCV particle binding to the target cell surface. Using the novel class of antibodies and cell lines expressing murine and human SR-BI, we demonstrate that the postbinding function of SR-BI is of key impact for both initiation of HCV infection and viral dissemination. Interestingly, this postbinding function of SR-BI appears to be unrelated to HDL interaction but to be directly linked to its lipid transfer function. Conclusion: Taken together, our results uncover a crucial role of the SR-BI postbinding function for initiation and maintenance of viral HCV infection that does not require receptor-E2/HDL interactions. The dissection of the molecular mechanisms of SR-BI-mediated HCV entry opens a novel perspective for the design of entry inhibitors interfering specifically with the proviral function of SR-BI. (HEPATOLOGY 2013;57:492-504) H epatitis C virus (HCV) is a major cause of liver cirrhosis and hepatocellular carcinoma. Preventive modalities are nonexistent, and the current antiviral treatment is limited by resistance, toxicity, and high cost. 1 Viral entry is required for initiation, spread, and maintenance of infection, and thus is a promising target for antiviral therapy. HCV binding and entry into hepatocytes is a complex process involving the viral envelope glycoproteins E1 and E2, as well as several host factors,

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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.