The life cycle of hepatitis C virus (HCV) is highly dependent on host cellular proteins for virus propagation. In order to identify the cellular factors involved in HCV propagation, we performed protein microarray assay using the HCV nonstructural 5A (NS5A) protein as a probe. Of ϳ9,000 human cellular proteins immobilized in a microarray, approximately 90 cellular proteins were identified as NS5A interactors. Of these candidates, Pim1, a member of serine/threonine kinase family composed of three different isoforms (Pim1, Pim2, and Pim3), was selected for further study. Pim kinases share a consensus sequence which overlaps with kinase activity. Pim kinase activity has been implicated in tumorigenesis. In the present study, we verified the physical interaction between NS5A and Pim1 by both in vitro pulldown and coimmunoprecipitation assays. Pim1 interacted with NS5A through amino acid residues 141 to 180 of Pim1. We demonstrated that protein stability of Pim1 was increased by NS5A protein and this increase was mediated by protein interplay. Small interfering RNA (siRNA)-mediated knockdown or pharmacological inhibition of Pim kinase abrogated HCV propagation. By employing HCV pseudoparticle entry and single-cycle HCV infection assays, we further demonstrated that Pim kinase was involved in HCV entry at a postbinding step. These data suggest that Pim kinase may represent a new host factor for HCV entry. IMPORTANCEPim1 is an oncogenic serine/threonine kinase. HCV NS5A protein physically interacts with Pim1 and contributes to Pim1 protein stability. Since Pim1 protein expression level is upregulated in many cancers, NS5A-mediated protein stability may be associated with HCV pathogenesis. Either gene silencing or chemical inhibition of Pim kinase abrogated HCV propagation in HCVinfected cells. We further showed that Pim kinase was specifically required at an early entry step of the HCV life cycle. Thus, we have identified Pim kinase not only as an HCV cell entry factor but also as a new anti-HCV therapeutic target.

Hepatitis C virus (HCV) is highly dependent on host proteins for its own propagation. By transcriptome sequencing (RNA-Seq) analysis, we identified 30 host genes that were significantly differentially expressed in cell culture-grown HCV (HCVcc)-infected cells. Of these candidate genes, we selected and characterized ankyrin repeat domain 1 (ANKRD1). Here, we showed that protein expression of ANKRD1 was up-regulated in HCVcc-infected cells. We further showed that protein expression level of ANKRD1 was increased by nonstructural 5A (NS5A) protein. ANKRD1 specifically interacted with NS5A both in vitro and coimmunoprecipitation assays. Protein interaction was mediated through the domain II of NS5A and the C-terminal region of ANKRD1. Promoter activity of ANKRD1 was also increased by NS5A protein. Moreover, up-regulation of ANKRD1 expression was mediated through alteration in intracellular calcium homeostasis and ER stress in HCVcc-infected cells. We showed that silencing of ANKRD1 impaired HCV propagation without affecting HCV replication. By using HCV-like infectious particle (HCV-LP), we demonstrated that HCV single-cycle infection was drastically impaired in ANKRD1 knockdown cells. Finally, we verified that ANKRD1 was required for HCV entry. These data suggest that HCV coopts ANKRD1 for its own propagation and up-regulation of ANKRD1 may contribute to HCV-mediated liver pathogenesis.

Hepatitis C virus (HCV) infection often causes chronic hepatitis, liver cirrhosis, and ultimately hepatocellular carcinoma. However, the mechanisms underlying HCV-induced liver pathogenesis are still not fully understood. By transcriptome sequencing (RNA-Seq) analysis, we recently identified host genes that were significantly differentially expressed in cell culture-grown HCV (HCVcc)-infected cells. Of these, tribbles homolog 3 (TRIB3) was selected for further characterization. TRIB3 was initially identified as a binding partner of protein kinase B (also known as Akt). TRIB3 blocks the phosphorylation of Akt and induces apoptosis under endoplasmic reticulum (ER) stress conditions. HCV has been shown to enhance Akt phosphorylation for its own propagation. In the present study, we demonstrated that both mRNA and protein levels of TRIB3 were increased in the context of HCV replication. We further showed that promoter activity of TRIB3 was increased by HCV-induced ER stress. Silencing of TRIB3 resulted in increased RNA and protein levels of HCV, whereas overexpression of TRIB3 decreased HCV replication. By employing an HCV pseudoparticle entry assay, we further showed that TRIB3 was a negative host factor involved in HCV entry. Both in vitro binding and immunoprecipitation assays demonstrated that HCV NS3 specifically interacted with TRIB3. Consequently, the association of TRIB3 and Akt was disrupted by HCV NS3, and thus, TRIB3-Akt signaling was impaired in HCVinfected cells. Moreover, HCV modulated TRIB3 to promote extracellular signal-regulated kinase (ERK) phosphorylation, activator protein 1 (AP-1) activity, and cell migration. Collectively, these data indicate that HCV exploits the TRIB3-Akt signaling pathway to promote persistent viral infection and may contribute to HCV-mediated pathogenesis. IMPORTANCETRIB3 is a pseudokinase protein that acts as an adaptor in signaling pathways for important cellular processes. So far, the functional involvement of TRIB3 in virus-infected cells has not yet been demonstrated. We showed that both mRNA and protein expression levels of TRIB3 were increased in the context of HCV RNA replication. Gene silencing of TRIB3 increased HCV RNA and protein levels, and thus, overexpression of TRIB3 decreased HCV replication. TRIB3 is known to promote apoptosis by negatively regulating the Akt signaling pathway under ER stress conditions. Most importantly, we demonstrated that the TRIB3-Akt signaling pathway was disrupted by NS3 in HCV-infected cells. These data provide evidence that HCV modulates the TRIB3-Akt signaling pathway to establish persistent viral infection.

a b s t r a c tTo identify the novel genes involved in lipid metabolism and lipid droplet formation that may play important roles in Hepatitis C virus (HCV) propagation, we have screened the small interfering RNA library using cell culture derived HCV (HCVcc)-infected cells. We selected and characterized the gene encoding farnesyl-diphosphate farnesyltransferase 1 (FDFT1). siRNA-mediated knockdown of FDFT1 impaired HCV replication in both subgenomic replicon and HCVcc infected cells. Moreover, YM-53601, an inhibitor of FDFT1 enzyme activity, abrogated HCV propagation. HCV infection increased FDFT1 protein level but not FDFT1 mRNA level. These results suggest that HCV may modulate FDFT1 protein level to facilitate its own propagation.

Hepatitis C virus (HCV) is a major cause of chronic liver disease and is highly dependent on cellular proteins for virus propagation. To identify the cellular factors involved in HCV propagation, we recently performed protein microarray assays using the HCV nonstructural 5A (NS5A) protein as a probe. Of 90 cellular protein candidates, we selected the soluble resistance-related calcium-binding protein (sorcin) for further characterization. Sorcin is a calcium-binding protein and is highly expressed in certain cancer cells. We verified that NS5A interacted with sorcin through domain I of NS5A, and phosphorylation of the threonine residue 155 of sorcin played a crucial role in protein interaction. Small interfering RNA (siRNA)-mediated knockdown of sorcin impaired HCV propagation. Silencing of sorcin expression resulted in a decrease of HCV assembly without affecting HCV RNA and protein levels. We further demonstrated that polo-like kinase 1 (PLK1)-mediated phosphorylation of sorcin was increased by NS5A. We showed that both phosphorylation and calcium-binding activity of sorcin were required for HCV propagation. These data indicate that HCV modulates sorcin activity via NS5A protein for its own propagation. IMPORTANCESorcin is a calcium-binding protein and regulates intracellular calcium homeostasis. HCV NS5A interacts with sorcin, and phosphorylation of sorcin is required for protein interaction. Gene silencing of sorcin impaired HCV propagation at the assembly step of the HCV life cycle. Sorcin is phosphorylated by PLK1 via protein interaction. We showed that sorcin interacted with both NS5A and PLK1, and PLK1-mediated phosphorylation of sorcin was increased by NS5A. Moreover, calcium-binding activity of sorcin played a crucial role in HCV propagation. These data provide evidence that HCV regulates host calcium metabolism for virus propagation, and thus manipulation of sorcin activity may represent a novel therapeutic target for HCV. Hepatitis C virus (HCV) is a major causative agent of non-A, non-B hepatitis. HCV infection often leads to chronic hepatitis, liver cirrhosis, and ultimately hepatocellular carcinoma (HCC) (1). HCV belongs to the member of the Hepacivirus genus within the Flaviviridae family. HCV is an enveloped virus with a positive-sense, single-stranded RNA genome of ϳ9.6 kb. Its genome encodes a single polyprotein precursor of more than 3,000 amino acids, which is cleaved by both host and viral proteases at the endoplasmic reticulum (ER), yielding structural (core, E1, and E2) and nonstructural (p7 and NS2 to NS5B) proteins (2). The nonstructural 5A (NS5A) protein is a phosphoprotein consisting of 447 amino acid residues. NS5A exists in two forms of polypeptide, p56 and p58, which are phosphorylated at serine residues by cellular kinase (3), and phosphorylation regulates the HCV life cycle (4). NS5A protein forms a part of the HCV RNA replication complex (5) and is involved in liver pathogenesis (6). NS5A is a multifunctional protein that regulates RNA replication, interferon (IFN) resis...

Hepatitis C virus (HCV) exploits cellular proteins to facilitate viral propagation. To identify the cellular factors involved in HCV life cycle, we previously performed protein microarray assays using either HCV nonstructural 5A (NS5A) protein or core protein as a probe. Interestingly, cellular cortactin strongly interacted with both NS5A and core. Cortactin is an actin-binding protein critically involved in tumor progression by regulating migration and invasion of cancerous cells. Protein interaction between cortactin and NS5A or core was confirmed by coimmunoprecipitation and immunofluorescence assays. We showed that cortactin interacted with NS5A and core via N-terminal acidic domain of cortactin. Cortactin expression levels were not altered by HCV infection. siRNA-mediated knockdown of cortactin dramatically decreased HCV protein expression and infectivity levels, whereas overexpression of cortactin increased viral propagation. Ectopic expression of the siRNA-resistant cortactin recovered the viral infectivity, suggesting that cortactin was specifically required for HCV propagation. We further showed that cortactin was involved in assembly step without affecting viral entry, HCV IRES-mediated translation, and replication steps of the HCV life cycle. Of note, silencing of cortactin markedly reduced both NS5A and core protein levels on the lipid droplets (LDs) and this effect was reversed by the overexpression of cortactin. Importantly, NS5A and core promoted cell migration by activating phosphorylation of cortactin at tyrosine residue 421 and 466. Taken together, these data suggest that cortactin is not only involved in HCV assembly but also plays an important role in the cell migration. IMPORTANCE Cortactin is a cytoskeletal protein that regulates cell migration in response to a number of extracellular stimuli. The functional involvement of cortactin in virus life cycle has not yet been fully understood. The most significant finding is that cortactin strongly interacted with both HCV core and NS5A. Cortactin is involved in HCV assembly by tethering core and NS5A on the LDs with no effect on LD biogenesis. It was noteworthy that HCV NS5A and core activated cortactin by phosphorylation at tyrosine 421 and 466 to regulate cell migration. Collectively, our study shows that cortactin is a novel host factor involved in viral production and HCV-associated pathogenesis.

Hepatitis C virus (HCV) is the major causative agent of chronic liver diseases, including liver cirrhosis and hepatocellular carcinoma. The recent development of highly effective direct-acting antivirals (DAAs) has revolutionized the treatment of HCV patients. However, these DAAs are exorbitantly expensive for the majority of HCV patients worldwide. Moreover, these drugs still show genotypic difference in cure rate and have some resistant-associated variants. Tylophorine, a natural compound derived from Tylophora indica plants, is known to have anti-inflammatory and anti-cancerous growth activities. In the present study, we showed that two tylophorine intermediates, 5-Oxo-1-[(2,3,6,7-tetramethoxy-9-phenanthrenyl) methyl]-L-proline (O859585) and 2,3,6,7-tetramethoxy-9-phenanthrenecarboxylic acid (T298875), displayed anti-HCV activity with an EC 50 of 38.25 µM for T298875 and 29.11~35.3 µM for O859585 in various HCV genotypes. We demonstrated that O859585 efficiently blocked HCV attachment by neutralizing free viral particles without affecting other stages of the HCV life cycle and interferon stimulation. O859585 interrupted binding between HCV E2 and CD81. Of note, co-treatment of O859585 with either interferon alpha (IFNα) or sofosbuvir exerted either an additive or synergistic antiviral activity in HCV-infected cells with no measurable effect on cell viability. Most importantly, O859585 in combination with IFNα and sofosbuvir exhibited synergistic effects on anti-HCV activity in primary human hepatocytes. Collectively, these data suggest that O859585 may be a novel antiviral agent for HCV therapy.

The life cycle of hepatitis C virus (HCV) is tightly coupled to the lipid metabolism of host cells. In order to identify host factors involved in HCV propagation, we have previously screened a small interfering RNA (siRNA) library targeting host genes that control lipid metabolism and lipid droplet (LD) formation using cell culture-grown HCV (HCVcc)-infected cells. In this study, we selected and characterized the gene encoding ADP-ribosylation factor-related protein 1 (ARFRP1). ARFRP1 is essential for LD growth and is involved in the regulation of lipolysis. siRNA-mediated knockdown of ARFRP1 significantly inhibited HCV replication in both subgenomic replicon cells and HCVcc-infected cells. ARFRP1 interacted with NS5A and NS5A partially colocalized with LD. Silencing of ARFRP1 abrogated HCV-induced LD growth and viral protein expressions. Moreover, ARFRP1 recruited synaptosomal-associated protein 23 (SNAP23) to sites in close proximity to LDs in HCV-infected cells. Silencing of ARFRP1 ablated relocalization of SNAP23 to LD. These data indicate that HCV regulates ARFRP1 for LD growth to facilitate viral propagation and thus ARFRP1 may be a potential target for antiviral therapy.