Hepatitis C virus glycoproteins mediate low pH-dependent membrane fusion with liposomes.
It has been suggested that the hepatitis C virus (HCV) infects host cells through a pH-dependent internalization mechanism, but the steps leading from virus attachment to the fusion of viral and cellular membranes remain uncharacterized. Here we studied the mechanism underlying the HCV fusion process in vitro using liposomes and our recently described HCV pseudoparticles (pp) bearing functional E1E2 envelope glycoproteins. The fusion of HCVpp with liposomes was monitored with fluorescent probes incorporated into either the HCVpp or the liposomes. To validate these assays, pseudoparticles bearing either the hemagglutinin of the influenza virus or the amphotropic glycoprotein of murine leukemia virus were used as models for pH-dependent and pH-independent entry, respectively. The use of assays based either on fusion-induced dequenching of fluorescent probes or on reporter systems, which produce fluorescence when the virus and liposome contents are mixed, allowed us to demonstrate that HCVpp mediated a complete fusion process, leading to the merging of both membrane leaflets and to the mixing of the internal contents of pseudoparticle and liposome. This HCVpp-mediated fusion was dependent on low pH, with a threshold of 6.3 and an optimum at about 5.5. Fusion was temperature-dependent and did not require any protein or receptor at the surface of the target liposomes. Most interestingly, fusion was facilitated by the presence of cholesterol in the target membrane. These findings clearly indicate that HCV infection is mediated by a pH-dependent membrane fusion process. This paves the way for future studies of the mechanisms underlying HCV membrane fusion.
Lavillette
Dimitri
D
IFR128 Biosciences Lyon Gerland, Institut de Biologie et Chimie des Protéines, UMR 5086 CNRS-Université Claude Bernard de Lyon.
Bartosch
Birke
B
Nourrisson
Delphine
D
Verney
Géraldine
G
Cosset
François-Loïc
FL
Penin
François
F
Pécheur
Eve-Isabelle
EI
D002784:Cholesterol / Q000502:physiology; D016174:Hepacivirus / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D008561:Membrane Fusion; D013696:Temperature; D014759:Viral Envelope Proteins / Q000502:physiology*; D014771:Virion / Q000502:physiology
C087035:E1 protein, Hepatitis C virus; D008081:Liposomes; D014759:Viral Envelope Proteins; C091015:glycoprotein E2, Hepatitis C virus; D002784:Cholesterol