Hepatitis C virus (HCV) infection is a leading cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma worldwide. Our research focuses on the viral and cellular determinants required for the formation of a functional HCV replication complex, the investigation of structural and functional properties of the viral proteins, and analyses of interactions of these proteins with cellular proteins and functional pathways.
The topology of HCV structural and nonstructural proteins at the endoplasmic reticulum membrane is shown schematically. HCV RNA replication occurs in a specific membrane alteration, the membranous web. Note that IRES-mediated translation and polyprotein processing as well as membranous web formation and RNA replication, illustrated here as separate steps for simplicity, may occur in a tightly coupled fashion (from Moradpour D. et al. Nat. Rev. Microbiol. 2007;5:453-463.). A video describing the viral life cycle of HCV is available at the University of Lyon.
Formation of a replication complex, composed of viral proteins, replicating viral RNA, and altered cellular membranes, is a hallmark of all positive-strand RNA viruses. In this context, we have identified a specific membrane alteration, designated as membranous web, that harbors the HCV replication complex and have developed tools allowing the visualization of functional replication complexes in live cells. In addition, we have identified and characterized the determinants for membrane association of the HCV nonstructural proteins involved in viral RNA replication. Our recent structural and functional data indicate that these segments represent highly specialized structures that are involved in specific protein-protein or protein-membrane interactions essential for the formation of a functional replication complex. Such interactions as well as other viral and cellular determinants involved in the formation of a functional replication complex are currently being investigated by biochemical, cell biological, genetic and advanced imaging techniques. Progress in this direction should enhance our understanding of the functional architecture of the HCV replication complex and may contribute to our understanding of the mechanisms leading to viral persistence.
HCV has evolved various strategies to counteract the host immune response and to establish persistent infection. Previous work has identified the HCV NS3-4A serine protease as a key viral protein blocking innate immune sensing pathways. NS3-4A cleaves and inactivates the essential adaptor molecule MAVS in the RIG-I viral RNA-sensing pathway, thereby blocking interferon production. More recently, we have pursued a quantitative proteomics-based approach to identify novel cellular targets of the HCV NS3-4A protease. These studies revealed novel host targets that are currently being characterized for their role in the viral life cycle as well as in the pathogenesis of hepatitis C.
Hepatitis E virus (HEV) infection is believed to be the most common cause of acute hepatitis and jaundice in the world. Until recently, HEV infection has been considered to affect only highly endemic regions in developing countries. Recent evidence, however, clearly indicates that foodborne zoonotic transmission of HEV genotypes 3 and 4 represents a challenge to the industrialized world. In addition, chronic hepatitis E has now been recognized as a cause of progressive liver disease in immunosuppressed patients.
HEV is a non-enveloped positive-strand RNA virus belonging to the Hepeviridae family. Its 7.2-kb RNA genome harbors 3 open reading frames (ORF) that are translated into (i) the ORF1 protein, comprising the RNA-dependent RNA polymerase and other replicase components, (ii) ORF2, the viral capsid, and (iii) ORF3, a small phosphoprotein.
Our ongoing research on the molecular virology of hepatitis E focuses on the functional organization of the HEV replicase, the structure and function of the ORF3 protein, and the investigation of antiviral drugs which may be used for the treatment of immunocompromised patients with chronic hepatitis E. Our research efforts on HEV are embedded in an multidisciplinary effort covering epidemiological, clinical, diagnostic and basic aspects of hepatitis E.