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

Abstract

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.

Characterization of Hepatitis C Virus Interaction with Heparan Sulfate Proteoglycans

“…These results are in line with those recently reported by Bankwitz et al (48). In addition, these authors also showed that HVR1 deletion does not affect the content of apoE associated with the virion (48). Furthermore, in line with the results of Jiang et al (29), the findings of our kinetic analysis of HCV entry in the presence of anti-apoE antibody and the capacity of the anti-apoE antibody to inhibit virion binding to cells are other arguments supporting the role of apoE in binding to HS.…”

“…Although JFH1-⌬HVR1 was more sensitive to neutralization by the anti-apoE polyclonal antibody, no difference was observed with two different MAbs. These results are in line with those recently reported by Bankwitz et al (48). In addition, these authors also showed that HVR1 deletion does not affect the content of apoE associated with the virion (48).…”

“…This could potentially be due to the presence of noninfectious particles and/or exosomes which might not have the same properties as infectious virus for their interaction with HS. Similar observations have previously been reported when the results of an assay of neutralization by antiapoE antibodies were compared with those of a binding assay (48). These data suggest that HVR1 of E2 is not involved in virus binding to HS.…”

“…Furthermore, in line with the results of Jiang et al (29), the findings of our kinetic analysis of HCV entry in the presence of anti-apoE antibody and the capacity of the anti-apoE antibody to inhibit virion binding to cells are other arguments supporting the role of apoE in binding to HS. The difference in the sensitivity of JFH1-⌬HVR1 to heparin and polyclonal anti-apoE antibody suggests that deletion of HVR1 affects the conformation of virion-associated apoE, as recently shown (48). A role for apoE in the interaction with HS is also supported by the abundance of this apolipoprotein on the virion, in contrast to the low number of HCV envelope proteins found on the viral particle (11,12).…”

“…Indeed, deletion of HVR1 does not reduce the binding capacity of the virion. JFH1-⌬HVR1 even showed an increased sensitivity to inhibition by heparin, but this difference could be due to a global change in the HCV particle after HVR1 deletion (48), which could modulate virion binding to HS. Concerning the functional studies, previous observations were first made with the help of pseudoparticles (26,27).…”