Interaction of Hepatitis C Virus Nonstructural Protein 5A with Core Protein Is Critical for the Production of Infectious Virus Particles

Department of Virology II, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan.
Journal of Virology (Impact Factor: 4.44). 08/2008; 82(16):7964-76. DOI: 10.1128/JVI.00826-08
Source: PubMed


Nonstructural protein 5A (NS5A) of the hepatitis C virus (HCV) possesses multiple and diverse functions in RNA replication, interferon resistance, and viral pathogenesis. Recent studies suggest that NS5A is involved in the assembly and maturation of infectious viral particles; however, precisely how NS5A participates in virus production has not been fully elucidated. In the present study, we demonstrate that NS5A is a prerequisite for HCV particle production as a result of its interaction with the viral capsid protein (core protein). The efficiency of virus production correlated well with the levels of interaction between NS5A and the core protein. Alanine substitutions for the C-terminal serine cluster in domain III of NS5A (amino acids 2428, 2430, and 2433) impaired NS5A basal phosphorylation, leading to a marked decrease in NS5A-core interaction, disturbance of the subcellular localization of NS5A, and disruption of virion production. Replacing the same serine cluster with glutamic acid, which mimics the presence of phosphoserines, partially preserved the NS5A-core interaction and virion production, suggesting that phosphorylation of these serine residues is important for virion production. In addition, we found that the alanine substitutions in the serine cluster suppressed the association of the core protein with viral genome RNA, possibly resulting in the inhibition of nucleocapsid assembly. These results suggest that NS5A plays a key role in regulating the early phase of HCV particle formation by interacting with core protein and that its C-terminal serine cluster is a determinant of the NS5A-core interaction.

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    • "NS5A, in addition to its roles in viral RNA replication, is also necessary for viral assembly [8]. HCV assembly requires cellular lipid droplets as a platform [9] and interactions between NS5A and the core protein [10]. Assembled particles bud into the ER and traffic through the secretory pathway. "
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    • "Yet, low levels of hyperphosphorylated NS5A seem to be essential for viral replication since viral replication is inhibited upon its complete loss (Appel et al., 2005a; Fridell et al., 2011). The increase in viral replication caused by reduced levels of the NS5A hyperphosphorylated form inversely correlates with viral production, leading to the notion that the hyperphosphorylated form of NS5A has adverse effects on viral replication but is required for viral assembly (Masaki et al., 2008; Miyanari et al., 2007; Pietschmann et al., 2009; Tellinghuisen et al., 2008a). It was also proposed to regulate the interface between replication and assembly (Tellinghuisen et al., 2008a). "
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