Hepatitis C Virus p7 Protein Is Crucial for Assembly and Release of Infectious Virions

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Abstract
Hepatitis C virus (HCV) infection is associated with chronic liver disease and currently affects about 3% of the world population. Although much has been learned about the function of individual viral proteins, the role of the HCV p7 protein in virus replication is not known. Recent data, however, suggest that it forms ion channels that may be targeted by antiviral compounds. Moreover, this protein was shown to be essential for infectivity in chimpanzee. Employing the novel HCV infection system and using a genetic approach to investigate the function of p7 in the viral replication cycle, we find that this protein is essential for efficient assembly and release of infectious virions across divergent virus strains. We show that p7 promotes virus particle production in a genotype-specific manner most likely due to interactions with other viral factors. Virus entry, on the other hand, is largely independent of p7, as the specific infectivity of released virions with a defect in p7 was not affected. Together, these observations indicate that p7 is primarily involved in the late phase of the HCV replication cycle. Finally, we note that p7 variants from different isolates deviate substantially in their capacity to promote virus production, suggesting that p7 is an important virulence factor that may modulate fitness and in turn virus persistence and pathogenesis. The hepatitis C virus (HCV), a major human pathogen associated with severe liver disease, encodes a small membrane protein designated p7. Although recent reports indicated that p7 forms channels conducting ions across membranes and is essential for HCV infection, its exact role in the viral life cycle remained elusive. In this study, we illustrate that HCV relies on p7 function for efficient assembly and release of infectious progeny virions from liver cells. Conversely, entry of HCV particles into new host cells is independent of p7. This new evidence supports the recent proposal to include p7 into the family of viroporins that comprises proteins from diverse viruses, for instance, HIV-1 and influenza A virus. Members of this group of functionally related proteins form membrane pores that promote virus release and in some cases also virus entry. Moreover, we identify several conserved p7 residues crucial for functioning of this protein. These amino acids possibly stabilize the structure of p7 or directly participate in channelling of ions. Interestingly, p7 variants from divergent patient isolates differ with regard to their ability to promote virus production, suggesting that p7 modulates viral fitness. Together these observations shed new light on fundamental aspects of the HCV replication strategy.