Cellular Binding and Entry of Hepatitis C Virus Pseudotypes and Virus-like Particles Requires a Different Set of Cellular Co-receptors

ABSTRACT Recently, complete replication of hepatitis C virus (HCV) in tissue culture was established using the JFH1 isolate. To analyze determinants of HCV genome packaging and virion assembly, we developed a system that supports particle production based on trans-packaging of subgenomic viral RNAs. Using JFH1 helper viruses, we show that subgenomic JFH1 replicons lacking the entire core to NS2 coding region are efficiently encapsidated into infectious virus-like particles. Similarly, chimeric helper viruses with heterologous structural proteins trans-package subgenomic JFH1 replicons. Like authentic cell culture-produced HCV (HCVcc) particles, these trans-complemented HCV particles (HCVTCP) penetrate target cells in a CD81 receptor-dependent fashion. Since HCVTCP production was limited by competition between the helper and subgenomic RNA and to avoid contamination of HCVTCP stocks with helper viruses, we created HCV packaging cells. These cells encapsidate various HCV replicons with high efficiency, reaching infectivity titers up to 106 tissue culture infectious doses 50 per milliliter. The produced particles display a buoyant density comparable to HCVcc particles and can be propagated in the packaging cell line but support only a single-round infection in naïve cells. Together, this work demonstrates that subgenomic HCV replicons are assembly competent, thus excluding cis-acting RNA elements in the core-to-NS2 genomic region essential for RNA packaging. The experimental system described here should be helpful to decipher the mechanisms of HCV assembly and to identify RNA elements and viral proteins involved in particle formation. Similar to other vector systems of plus-strand RNA viruses, HCVTCP may prove valuable for gene delivery or vaccination approaches.

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Analysis of Antigenicity and Topology of E2 Glycoprotein Present on Recombinant Hepatitis C Virus-Like Particles

Journal of Virology ◽

10.1128/jvi.76.15.7672-7682.2002 ◽

2002 ◽

Vol 76 (15) ◽

pp. 7672-7682 ◽

Cited By ~ 110

Author(s):

Reginald F. Clayton ◽

Ania Owsianka ◽

Jim Aitken ◽

Susan Graham ◽

David Bhella ◽

...

Keyword(s):

Hepatitis C Virus ◽

Hepatitis C ◽

Mammalian Cells ◽

Function Analysis ◽

Recombinant Baculovirus ◽

Microscopic Analysis ◽

Surface Topology ◽

Viral Glycoprotein ◽

Electron Microscopic ◽

Virus Like Particles

ABSTRACT Purification of hepatitis C virus (HCV) from sera of infected patients has proven elusive, hampering efforts to perform structure-function analysis of the viral components. Recombinant forms of the viral glycoproteins have been used instead for functional studies, but uncertainty exists as to whether they closely mimic the virion proteins. Here, we used HCV virus-like particles (VLPs) generated in insect cells infected with a recombinant baculovirus expressing viral structural proteins. Electron microscopic analysis revealed a population of pleomorphic VLPs that were at least partially enveloped with bilayer membranes and had viral glycoprotein spikes protruding from the surface. Immunogold labeling using specific monoclonal antibodies (MAbs) demonstrated these protrusions to be the E1 and E2 glycoproteins. A panel of anti-E2 MAbs was used to probe the surface topology of E2 on the VLPs and to compare the antigenicity of the VLPs with that of truncated E2 (E2660) or the full-length (FL) E1E2 complex expressed in mammalian cells. While most MAbs bound to all forms of antigen, a number of others showed striking differences in their abilities to recognize the various E2 forms. All MAbs directed against hypervariable region 1 (HVR-1) recognized both native and denatured E2660 with comparable affinities, but most bound either weakly or not at all to the FL E1E2 complex or to VLPs. HVR-1 on VLPs was accessible to these MAbs only after denaturation. Importantly, a subset of MAbs specific for amino acids 464 to 475 and 524 to 535 recognized E2660 but not VLPs or FL E1E2 complex. The antigenic differences between E2660, FL E1E2, and VLPs strongly point to the existence of structural differences, which may have functional relevance. Trypsin treatment of VLPs removed the N-terminal part of E2, resulting in a 42-kDa fragment. In the presence of detergent, this was further reduced to a trypsin-resistant 25-kDa fragment, which could be useful for structural studies.

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