The HCV life cycle begins with the HCV low-affinity binding to two host receptors on the surface of a hepatocyte: low density lipoprotein receptor (LDLr) and heparin sulfate proteoglycans (HSPGs). This initial interaction triggers the HCV outer E1/E2 heterodimer membrane protein to bind to the scavenger receptor B1 (SRB1) and the tetraspanin protein CD81. The interactions between these proteins create a wave in the lipid membrane, propelling the HCV particle to a tight junction between hepatocytes.
6 References
Agnello V, Abel G, Elfahal M, Knight GB, Zhang QX. Hepatitis C virus and other flaviviridae viruses enter cells via low density lipoprotein receptor. Proc Natl Acad Sci U S A. 1999;96:12766-71.
Boo I, teWierik K, Douam F, Lavillette D, Poumbourios P, Drummer HE. Distinct roles in folding, CD81 receptor binding and viral entry for conserved histidine residues of hepatitis C virus glycoprotein E1 and E2. Biochem J. 2012;443:85-94.
As HCV reaches the tight junction, CD81 interacts with claudin-1 (CLDN1), initiating inward folding of the viral particle and hepatocyte cell membrane into a pit-like region covered by clathrin. This process generates an internal endosome comprised of a viral particle coated by the host cell membrane; the entire endosome is surrounded by a clathrin cage.
5 References
Blanchard E, Belouzard S, Goueslain L, et al. Hepatitis C virus entry depends on clathrin-mediated endocytosis. J Virol. 2006;80:6964-72.
Upon viral entry into the cell, the clathrin cage surrounding the endosome disperses, leaving the endosomal vesicle free within the cytosol. The acidic pH within the endosome triggers fusion between the viral and host membranes, in a process referred to as endosomal fusion. This event permits uncoating of the capsid shell and the release of the HCV RNA into the cytosol for translation and replication.
6 References
Koutsoudakis G, Kaul A, Steinmann E, et al. Characterization of the early steps of hepatitis C virus infection by using luciferase reporter viruses. J Virol. 2006;80:5308-20.
Sharma NR, Mateu G, Dreux M, Grakoui A, Cosset FL, Melikyan GB. Hepatitis C virus is primed by CD81 protein for low pH-dependent fusion. J Biol Chem. 2011;286:30361-76.
Tscherne DM, Jones CT, Evans MJ, Lindenbach BD, McKeating JA, Rice CM. Time- and temperature-dependent activation of hepatitis C virus for low-pH-triggered entry. J Virol. 2006;80:1734-41.
The process of HCV polyprotein translation is initiated when ribosomal subunits bind to HCV RNA in the rough endoplasmic reticulum. Subsequently, the ribosome-RNA complex attaches to the endoplasmic reticulum membrane and HCV polyprotein translation is completed. The translation process generates a single polyprotein that is approximately 3,000 amino acids long.
3 References
Fraser CS, Doudna JA. Structural and mechanistic insights into hepatitis C viral translation initiation. Nat Rev Microbiol. 2006;5:29-38.
Niepmann M, Shalamova LA, Gerresheim GK, Rossbach O. Signals Involved in Regulation of Hepatitis C Virus RNA Genome Translation and Replication. Front Microbiol. 2018;9:395.
Viral proteolytic processing occurs within the rough endoplasmic reticulum. First, cellular proteases cleave the core, E1, E2, and p7 proteins. Next, the NS2 cysteine protease, in conjunction with the N-terminal end of the NS3 protein, cleaves NS2 from NS3. Last, NS3, assisted by the membrane bound NS4A, forms an NS3-4A protease complex that cleaves the remaining proteins (NS3, NS4A, NS4B, NS5A, NS5B). The final result is 10 mature HCV proteins, including structural and nonstructural proteins.
4 References
Bartenschlager R, Ahlborn-Laake L, Mous J, Jacobsen H. Kinetic and structural analyses of hepatitis C virus polyprotein processing. J Virol. 1994;68:5045-55.
Carrère-Kremer S, Montpellier C, Lorenzo L, et al. Regulation of hepatitis C virus polyprotein processing by signal peptidase involves structural determinants at the p7 sequence junctions. J Biol Chem. 2004;279:41384-92.
Several HCV proteins, likely in conjunction with host factors, induce rearrangement of the host cell membranes to form the membranous web—an aggregate of double-membrane vesicles. In the membranous web, the NS5B RNA-dependent RNA polymerase catalyzes the synthesis of a negative-sense RNA intermediate (template) that is used to create numerous copies of positive-sense progeny HCV RNA. These newly synthesized HCV RNAs are either incorporated into nucleocapsid particles or used for RNA translation and replication. The RNA replication process is supported by multiple HCV nonstructural proteins (replication complex).
6 References
Appleby TC, Perry JK, Murakami E, et al. Viral replication. Structural basis for RNA replication by the hepatitis C virus polymerase. Science. 2015;347:771-5.
Kazakov T, Yang F, Ramanathan HN, Kohlway A, Diamond MS, Lindenbach BD. Hepatitis C virus RNA replication depends on specific cis- and trans-acting activities of viral nonstructural proteins. PLoS Pathog. 2015;11:e1004817.
Romero-Brey I, Merz A, Chiramel A, et al. Three-dimensional architecture and biogenesis of membrane structures associated with hepatitis C virus replication. PLoS Pathog. 2012;8:e1003056.
HCV particles assemble near cytosolic lipid droplets (cLDLs) and with the assistance of the host diacylglycerol acetyltransferase-1 (DGAT1) enzyme form the nucleocapsid that consists of core proteins surrounding HCV RNA. During assembly the core proteins use the HCV RNA as a scaffold as the proteins form a protective shell around the HCV RNA. Once the core is formed, the immature HCV particle fuses with a luminal lipid droplet (LuLD) that is loaded with ApoE proteins to create a high-density HCV precursor. Simultaneously, the ER synthesizes pre-very-low-density proteins (pre-VLDLs); the high-density HCV precursor and the pre-VLDL transit to the Golgi where they mature prior to being packaged and released.
7 References
Bartenschlager R, Penin F, Lohmann V, André P. Assembly of infectious hepatitis C virus particles. Trends Microbiol. 2011;19:95-103.
Crouchet E, Baumert TF, Schuster C. Hepatitis C virus-apolipoprotein interactions: molecular mechanisms and clinical impact. Expert Rev Proteomics. 2017;14:593-606.
Lee JY, Acosta EG, Stoeck IK, et al. Apolipoprotein E likely contributes to a maturation step of infectious hepatitis C virus particles and interacts with viral envelope glycoproteins. J Virol. 2014;88:12422-37.
Stewart H, Bingham RJ, White SJ, et al. Identification of novel RNA secondary structures within the hepatitis C virus genome reveals a cooperative involvement in genome packaging. Sci Rep. 2016;6:22952.
Zayas M, Long G, Madan V, Bartenschlager R. Coordination of Hepatitis C Virus Assembly by Distinct Regulatory Regions in Nonstructural Protein 5A. PLoS Pathog. 2016;12:e1005376.
In the Golgi, the pre-VLDLs are believed to fuse with large triacylglycerol (TG)-rich lipid droplets to form VLDLs. The VLDLs then fuse with the high-density HCV precursors to form the HCV lipoviral particle. This low-density HCV lipoviral particle leaves the trans-Golgi network (TGN) in specialized transport vesicles known as multivesicular bodies. The cellular secretory machinery transports the multivesicular bodies to the cell surface. The endosomal-sorting complex required for transport (ESCRT) pathway plays a key role in multivesicular body formation and in other post-assembly steps that lead to transport to the cell surface and release of the lipoviral particle.
7 References
Coller KE, Heaton NS, Berger KL, Cooper JD, Saunders JL, Randall G. Molecular determinants and dynamics of hepatitis C virus secretion. PLoS Pathog. 2012;8:e1002466.
Syed GH, Khan M, Yang S, Siddiqui A. Hepatitis C Virus Lipoviroparticles Assemble in the Endoplasmic Reticulum (ER) and Bud off from the ER to the Golgi Compartment in COPII Vesicles. J Virol. 2017;91. pii: e00499-17.
Syed GH, Khan M, Yang S, Siddiqui A. Hepatitis C Virus Lipoviroparticles Assemble in the Endoplasmic Reticulum (ER) and Bud off from the ER to the Golgi Compartment in COPII Vesicles. J Virol. 2017;91(15).pii: e00499-17.
Following transport of the multivesicular bodies that contain the HCV lipoviral particles to the cell surface, the vesicles fuse with the hepatocyte cell membrane. The generation of the HCV lipoviral particle is coupled to the cellular VLDL pathway and during this process both HCV lipoviral particles and VLDL particles are released into the extracellular compartments.
5 References
Coller KE, Heaton NS, Berger KL, Cooper JD, Saunders JL, Randall G. Molecular determinants and dynamics of hepatitis C virus secretion. PLoS Pathog. 2012;8:e1002466.
Corless L, Crump CM, Griffin SD, Harris M. Vps4 and the ESCRT-III complex are required for the release of infectious hepatitis C virus particles. J Gen Virol. 2010;91:362-72.
Bartenschlager R, Lohmann V, Penin F. The molecular and structural basis of advanced antiviral therapy for hepatitis C virus infection. Nat Rev Microbiol. 2013;11:482-96.
Bukh J. The history of hepatitis C virus (HCV): Basic research reveals unique features in phylogeny, evolution and the viral life cycle with new perspectives for epidemic control. J Hepatol. 2016;65:S2-S21.
Grassi G, Di Caprio G, Fimia GM, Ippolito G, Tripodi M, Alonzi T. Hepatitis C virus relies on lipoproteins for its life cycle. World J Gastroenterol. 2016;22:1953-65.
Agnello V, Abel G, Elfahal M, Knight GB, Zhang QX. Hepatitis C virus and other flaviviridae viruses enter cells via low density lipoprotein receptor. Proc Natl Acad Sci U S A. 1999;96:12766-71.
Boo I, teWierik K, Douam F, Lavillette D, Poumbourios P, Drummer HE. Distinct roles in folding, CD81 receptor binding and viral entry for conserved histidine residues of hepatitis C virus glycoprotein E1 and E2. Biochem J. 2012;443:85-94.
Koutsoudakis G, Kaul A, Steinmann E, et al. Characterization of the early steps of hepatitis C virus infection by using luciferase reporter viruses. J Virol. 2006;80:5308-20.
Sharma NR, Mateu G, Dreux M, Grakoui A, Cosset FL, Melikyan GB. Hepatitis C virus is primed by CD81 protein for low pH-dependent fusion. J Biol Chem. 2011;286:30361-76.
Tscherne DM, Jones CT, Evans MJ, Lindenbach BD, McKeating JA, Rice CM. Time- and temperature-dependent activation of hepatitis C virus for low-pH-triggered entry. J Virol. 2006;80:1734-41.
Niepmann M, Shalamova LA, Gerresheim GK, Rossbach O. Signals Involved in Regulation of Hepatitis C Virus RNA Genome Translation and Replication. Front Microbiol. 2018;9:395.
Carrère-Kremer S, Montpellier C, Lorenzo L, et al. Regulation of hepatitis C virus polyprotein processing by signal peptidase involves structural determinants at the p7 sequence junctions. J Biol Chem. 2004;279:41384-92.
Appleby TC, Perry JK, Murakami E, et al. Viral replication. Structural basis for RNA replication by the hepatitis C virus polymerase. Science. 2015;347:771-5.
Kazakov T, Yang F, Ramanathan HN, Kohlway A, Diamond MS, Lindenbach BD. Hepatitis C virus RNA replication depends on specific cis- and trans-acting activities of viral nonstructural proteins. PLoS Pathog. 2015;11:e1004817.
Romero-Brey I, Merz A, Chiramel A, et al. Three-dimensional architecture and biogenesis of membrane structures associated with hepatitis C virus replication. PLoS Pathog. 2012;8:e1003056.
Crouchet E, Baumert TF, Schuster C. Hepatitis C virus-apolipoprotein interactions: molecular mechanisms and clinical impact. Expert Rev Proteomics. 2017;14:593-606.
Lee JY, Acosta EG, Stoeck IK, et al. Apolipoprotein E likely contributes to a maturation step of infectious hepatitis C virus particles and interacts with viral envelope glycoproteins. J Virol. 2014;88:12422-37.
Stewart H, Bingham RJ, White SJ, et al. Identification of novel RNA secondary structures within the hepatitis C virus genome reveals a cooperative involvement in genome packaging. Sci Rep. 2016;6:22952.
Zayas M, Long G, Madan V, Bartenschlager R. Coordination of Hepatitis C Virus Assembly by Distinct Regulatory Regions in Nonstructural Protein 5A. PLoS Pathog. 2016;12:e1005376.
Coller KE, Heaton NS, Berger KL, Cooper JD, Saunders JL, Randall G. Molecular determinants and dynamics of hepatitis C virus secretion. PLoS Pathog. 2012;8:e1002466.
Syed GH, Khan M, Yang S, Siddiqui A. Hepatitis C Virus Lipoviroparticles Assemble in the Endoplasmic Reticulum (ER) and Bud off from the ER to the Golgi Compartment in COPII Vesicles. J Virol. 2017;91. pii: e00499-17.
Syed GH, Khan M, Yang S, Siddiqui A. Hepatitis C Virus Lipoviroparticles Assemble in the Endoplasmic Reticulum (ER) and Bud off from the ER to the Golgi Compartment in COPII Vesicles. J Virol. 2017;91(15).pii: e00499-17.
Coller KE, Heaton NS, Berger KL, Cooper JD, Saunders JL, Randall G. Molecular determinants and dynamics of hepatitis C virus secretion. PLoS Pathog. 2012;8:e1002466.
Corless L, Crump CM, Griffin SD, Harris M. Vps4 and the ESCRT-III complex are required for the release of infectious hepatitis C virus particles. J Gen Virol. 2010;91:362-72.
The hepatitis C virus (HCV) biology page provides a highly visual learning format to explore basic concepts related to the biology of HCV. Conceptually, it is important to understand that translation of the HCV RNA results in the production of structural and non-structural proteins and these non-structural proteins are found only inside of hepatocytes. Click on any of the links above to learn more about HCV structure, proteins, or life cycle.
Editors
David H. Spach, MD
H. Nina Kim, MD
Illustrators
Jared Travnicek, CMI, Cognition Studio
David Ehlert, CMI, Cognition Studio
Reviewers
Shyamasundaran Kottilil, PhD
Stephen J. Polyak, PhD