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The lipid kinase phosphatidylinositol-4 kinase III alpha regulates the phosphorylation status of hepatitis C virus NS5A.

ABSTRACT: The lipid kinase phosphatidylinositol 4-kinase III alpha (PI4KIII?) is an essential host factor of hepatitis C virus (HCV) replication. PI4KIII? catalyzes the synthesis of phosphatidylinositol 4-phosphate (PI4P) accumulating in HCV replicating cells due to enzyme activation resulting from its interaction with nonstructural protein 5A (NS5A). This study describes the interaction between PI4KIII? and NS5A and its mechanistic role in viral RNA replication. We mapped the NS5A sequence involved in PI4KIII? interaction to the carboxyterminal end of domain 1 and identified a highly conserved PI4KIII? functional interaction site (PFIS) encompassing seven amino acids, which are essential for viral RNA replication. Mutations within this region were also impaired in NS5A-PI4KIII? binding, reduced PI4P levels and altered the morphology of viral replication sites, reminiscent to the phenotype observed by silencing of PI4KIII?. Interestingly, abrogation of RNA replication caused by mutations in the PFIS correlated with increased levels of hyperphosphorylated NS5A (p58), indicating that PI4KIII? affects the phosphorylation status of NS5A. RNAi-mediated knockdown of PI4KIII? or pharmacological ablation of kinase activity led to a relative increase of p58. In contrast, overexpression of enzymatically active PI4KIII? increased relative abundance of basally phosphorylated NS5A (p56). PI4KIII? therefore regulates the phosphorylation status of NS5A and viral RNA replication by favoring p56 or repressing p58 synthesis. Replication deficiencies of PFIS mutants in NS5A could not be rescued by increasing PI4P levels, but by supplying functional NS5A, supporting an essential role of PI4KIII? in HCV replication regulating NS5A phosphorylation, thereby modulating the morphology of viral replication sites. In conclusion, we demonstrate that PI4KIII? activity affects the NS5A phosphorylation status. Our results highlight the importance of PI4KIII? in the morphogenesis of viral replication sites and its regulation by facilitating p56 synthesis.

SUBMITTER: Reiss S

PROVIDER: S-EPMC3649985 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature

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The lipid kinase phosphatidylinositol-4 kinase III alpha regulates the phosphorylation status of hepatitis C virus NS5A.

Reiss Simon S Harak Christian C Romero-Brey Inés I Radujkovic Danijela D Klein Rahel R Ruggieri Alessia A Rebhan Ilka I Bartenschlager Ralf R Lohmann Volker V

PLoS pathogens 20130509 5

The lipid kinase phosphatidylinositol 4-kinase III alpha (PI4KIIIα) is an essential host factor of hepatitis C virus (HCV) replication. PI4KIIIα catalyzes the synthesis of phosphatidylinositol 4-phosphate (PI4P) accumulating in HCV replicating cells due to enzyme activation resulting from its interaction with nonstructural protein 5A (NS5A). This study describes the interaction between PI4KIIIα and NS5A and its mechanistic role in viral RNA replication. We mapped the NS5A sequence involved in PI ...[more]

PMID: 23675303

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Project description:UnlabelledThe lipid kinase phosphatidylinositol 4-kinase III alpha (PI4KIIIα) is an endoplasmic reticulum (ER)-resident enzyme that synthesizes phosphatidylinositol 4-phosphate (PI4P). PI4KIIIα is an essential host factor for hepatitis C virus (HCV) replication. Interaction with HCV nonstructural protein 5A (NS5A) leads to kinase activation and accumulation of PI4P at intracellular membranes. In this study, we investigated the structural requirements of PI4KIIIα in HCV replication and enzymatic activity. Therefore, we analyzed PI4KIIIα mutants for subcellular localization, reconstitution of HCV replication in PI4KIIIα knockdown cell lines, PI4P induction in HCV-positive cells, and lipid kinase activity in vitro. All mutants still interacted with NS5A and localized in a manner similar to that of the full-length enzyme, suggesting multiple regions of PI4KIIIα are involved in NS5A interaction and subcellular localization. Interestingly, the N-terminal 1,152 amino acids were dispensable for HCV replication, PI4P induction, and enzymatic function, whereas further N-terminal or C-terminal deletions were deleterious, thereby defining the minimal PI4KIIIα core enzyme at a size of ca. 108 kDa. Additional deletion of predicted functional motifs within the C-terminal half of PI4KIIIα also were detrimental for enzymatic activity and for the ability of PI4KIIIα to rescue HCV replication, with the exception of a proposed nuclear localization signal, suggesting that the entire C-terminal half of PI4KIIIα is involved in the formation of a minimal enzymatic core. This view was supported by structural modeling of the PI4KIIIα C terminus, suggesting a catalytic center formed by an N- and C-terminal lobe and an armadillo-fold motif, which is preceded by three distinct alpha-helical domains probably involved in regulation of enzymatic activity.ImportanceThe lipid kinase PI4KIIIα is of central importance for cellular phosphatidylinositol metabolism and is a key host cell factor of hepatitis C virus replication. However, little is known so far about the structure of this 240-kDa protein and the functional importance of specific subdomains regarding lipid kinase activity and viral replication. This work focuses on the phenotypic analysis of distinct PI4KIIIα mutants in different biochemical and cell-based assays and develops a structural model of the C-terminal enzymatic core. The results shed light on the structural and functional requirements of enzymatic activity and the determinants required for HCV replication.

Project description:Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) is a phosphoprotein that plays key, yet poorly defined, roles in both virus genome replication and virion assembly/release. It has been proposed that differential phosphorylation could act as a switch to regulate the various functions of NS5A; however, the mechanistic details of the role of this posttranslational modification in the virus life cycle remain obscure. We previously reported (D. Ross-Thriepland, J. Mankouri, and M. Harris, J Virol 89:3123-3135, 2015, doi:10.1128/JVI.02995-14) a role for phosphorylation at serine 225 (S225) of NS5A in the regulation of JFH-1 (genotype 2a) genome replication. A phosphoablatant (S225A) mutation resulted in a 10-fold reduction in replication and a perinuclear restricted distribution of NS5A, whereas the corresponding phosphomimetic mutation (S225D) had no phenotype. To determine the molecular mechanisms underpinning this phenotype we conducted a label-free proteomics approach to identify cellular NS5A interaction partners. This analysis revealed that the S225A mutation disrupted the interactions of NS5A with a number of cellular proteins, in particular the nucleosome assembly protein 1-like protein 1 (NAP1L1), bridging integrator 1 (Bin1, also known as amphiphysin II), and vesicle-associated membrane protein-associated protein A (VAP-A). These interactions were validated by immunoprecipitation/Western blotting, immunofluorescence, and proximity ligation assay. Importantly, small interfering RNA (siRNA)-mediated knockdown of NAP1L1, Bin1 or VAP-A impaired viral genome replication and recapitulated the perinuclear redistribution of NS5A seen in the S225A mutant. These results demonstrate that S225 phosphorylation regulates the interactions of NS5A with a defined subset of cellular proteins. Furthermore, these interactions regulate both HCV genome replication and the subcellular localization of replication complexes.IMPORTANCE Hepatitis C virus is an important human pathogen. The viral nonstructural 5A protein (NS5A) is the target for new antiviral drugs. NS5A has multiple functions during the virus life cycle, but the biochemical details of these roles remain obscure. NS5A is known to be phosphorylated by cellular protein kinases, and in this study, we set out to determine whether this modification is required for the binding of NS5A to other cellular proteins. We identified 3 such proteins and show that they interacted only with NS5A that was phosphorylated on a specific residue. Furthermore, these proteins were required for efficient virus replication and the ability of NS5A to spread throughout the cytoplasm of the cell. Our results help to define the function of NS5A and may contribute to an understanding of the mode of action of the highly potent antiviral drugs that are targeted to NS5A.

Dataset Information

The lipid kinase phosphatidylinositol-4 kinase III alpha regulates the phosphorylation status of hepatitis C virus NS5A.

Publications

The lipid kinase phosphatidylinositol-4 kinase III alpha regulates the phosphorylation status of hepatitis C virus NS5A.

Similar Datasets

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