Hepatitis C virus (HCV) NS2 protein up-regulates HCV IRES-dependent translation and down-regulates NS5B RdRp activity. Arch Virol. 2008;153:1991-1997. [PMID: 18853100 DOI: 10.1007/s00705-008-0198-3]

PKM2 Facilitates Classical Swine Fever Virus Replication by Enhancing NS5B Polymerase Function

Host metabolic reprogramming is a critical strategy employed by many viruses to support their replication, and the key metabolic enzyme plays important roles in virus infection. This study investigates the role of pyruvate kinase M2 (PKM2), a glycolytic enzyme with non-canonical functions, in the replication of classical swine fever virus (CSFV). Using PK-15 cells and piglet models, we demonstrate that CSFV infection upregulates PKM2 expression both in vitro and in vivo, creating a proviral environment. knockdown of PKM2 by siRNA reduced CSFV proliferation, while PKM2 overexpression significantly increased virus propagation, which was evaluated by viral protein synthesis, genome replication, and progeny virion production. A direct interaction between PKM2 and CSFV NS5B protein was identified by co-immunoprecipitation and GST-pulldown assays, and PKM2 affected NS5B polymerase activity in a dual-luciferase reporter assay, with PKM2 depletion reducing RdRp function by 50%. Temporal analysis of the first viral replication cycle confirmed PKM2-dependent enhancement of CSFV RNA synthesis. These findings establish PKM2 as a proviral host factor that directly binds NS5B to potentiate RdRp activity, thereby bridging metabolic adaptation and viral genome replication. This study provides new evidence of a glycolytic enzyme physically interacting and enhancing viral polymerase function, offering new information about CSFV-host interaction.

MEAN inhibits hepatitis C virus replication by interfering with a polypyrimidine tract-binding protein

MEAN (6‐methoxyethylamino‐numonafide) is a small molecule compound, and here, we report that it effectively inhibits hepatitis C virus (HCV) infection in an HCV cell culture system using a JC1‐Luc chimeric virus, with a 50% effective concentration (EC50) of 2.36 ± 0.29 μM. Drug combination usage analyses demonstrated that MEAN was synergistic with interferon α, ITX5061 and ribavirin. In addition, MEAN effectively inhibits N415D mutant virus and G451R mutant viral infections. Mechanistic studies show that the treatment of HCV‐infected hepatocytes with MEAN inhibits HCV replication but not translation. Furthermore, treatment with MEAN significantly reduces polypyrimidine tract‐binding protein (PTB) levels and blocks the cytoplasmic redistribution of PTB upon infection. In the host cytoplasm, PTB is directly associated with HCV replication, and the inhibition of HCV replication by MEAN can result in the sequestration of PTB in treated nuclei. Taken together, these results indicate that MEAN is a potential therapeutic candidate for HCV infection, and the targeting of the nucleo‐cytoplasmic translocation of the host PTB protein could be a novel strategy to interrupt HCV replication.

Establishment of chronic hepatitis C virus infection: Translational evasion of oxidative defence

Hepatitis C virus (HCV) causes a clinically important disease affecting 3% of the world population. HCV is a single-stranded, positive-sense RNA virus belonging to the genus Hepacivirus within the Flaviviridae family. The virus establishes a chronic infection in the face of an active host oxidative defence, thus adaptation to oxidative stress is key to virus survival. Being a small RNA virus with a limited genomic capacity, we speculate that HCV deploys a different strategy to evade host oxidative defence. Instead of counteracting oxidative stress, it utilizes oxidative stress to facilitate its own survival. Translation is the first step in the replication of a plus strand RNA virus so it would make sense if the virus can exploit the host oxidative defence in facilitating this very first step. This is particularly true when HCV utilizes an internal ribosome entry site element in translation, which is distinctive from that of cap-dependent translation of the vast majority of cellular genes, thus allowing selective translation of genes under conditions when global protein synthesis is compromised. Indeed, we were the first to show that HCV translation was stimulated by an important pro-oxidant-hydrogen peroxide in hepatocytes, suggesting that HCV is able to adapt to and utilize the host anti-viral response to facilitate its own translation thus allowing the virus to thrive under oxidative stress condition to establish chronicity. Understanding how HCV translation is regulated under oxidative stress condition will advance our knowledge on how HCV establishes chronicity. As chronicity is the initiator step in disease progression this will eventually lead to a better understanding of pathogenicity, which is particularly relevant to the development of anti-virals and improved treatments of HCV patients using anti-oxidants.

DNA methyltransferases 1 and 3B are required for hepatitis C virus infection in cell culture

DNA methyltransferases (DNMTs) are responsible for establishing and maintaining DNA methylation, which are dysregulated in hepatitis C virus (HCV)-associated hepatocellular carcinoma (HCC). In this report, using lentivirus-mediated shRNA interference technology, we identified DNMT1 and DNMT3B as host factors involved in HCV propagation. Our results demonstrated that down-regulation of DNMT1 or DNMT3B expression in Huh7.5.1 cells severely impaired cell culture-produced HCV (HCVcc) infection. Furthermore, knockdown of DNMT1 or DNMT3B did not affect HCV entry and internal ribosome entry site (IRES)-directed translation but did inhibit subgenomic replication. In contrast, knockdown of DNMT3A had no significant effect on HCV infection, entry, translation, or replication, which suggested that DNMT3A did not play a significant role in HCV life cycle. Moreover, we showed that DNMT inhibitors 5-Aza-C and 5-Aza-dC significantly suppressed HCVcc infection, viral RNA replication, and protein expression. These results suggest that DNMTs are critical for HCV replication and may represent potent targets for the treatment of HCV infection.

Serum cystatin C correlates negatively with viral load in treatment-naïve children with chronic hepatitis C

OBJECTIVES

Hepatitis C virus (HCV) infection is a serious health problem that causes chronic infection in up to 85% of cases. HCV nonstructural (NS) cysteine protease, NS2/3, is required for viral replication in vivo. Cystatin C is a naturally occurring cysteine protease inhibitor in human cells. We aimed to investigate the relation between serum levels of cystatin C and HCV viremia in treatment-naïve children with chronic hepatitis C.

METHODS

Serum cystatin C levels were measured in 27 children with chronic hepatitis C and determined their relation with liver functions, histopathological parameters, and hepatitis C viral load. Serum cystatin C was compared with that of 25 age- and sex-matched healthy controls.

RESULTS

Cystatin C was significantly higher in patients than in controls (1.4 ± 0.47 vs 0.99 ± 0.49; P = 0.006), and in those with low viremia than in those with moderate viremia (1.55 ± 0.41 vs 0.99 ± 0.43; P = 0.013). Cystatin C was not correlated with histopathological findings in liver biopsy (P > 0.05 for all). In addition, there was no significant difference of cystatin C levels in patients with normal versus those with elevated transaminases (P > 0.05). Of importance, cystatin C correlated negatively with viral load (P < 0.0001).

CONCLUSIONS

Cystatin C levels correlated negatively with HCV viremia. This finding may reflect an inhibitory effect of cystatin C on HCV replication through inhibiting its NS2/3 and tempting for further studies for cystatin C as a possible adjuvant therapy for HCV infection.

Novel nucleotide and amino acid covariation between the 5'UTR and the NS2/NS3 proteins of hepatitis C virus: bioinformatic and functional analyses

Molecular covariation of highly polymorphic viruses is thought to have crucial effects on viral replication and fitness. This study employs association rule data mining of hepatitis C virus (HCV) sequences to search for specific evolutionary covariation and then tests functional relevance on HCV replication. Data mining is performed between nucleotides in the untranslated regions 5′ and 3′UTR, and the amino acid residues in the non-structural proteins NS2, NS3 and NS5B. Results indicate covariance of the 243^rd nucleotide of the 5′UTR with the 14^th, 41^st, 76^th, 110^th, 211^th and 212^th residues of NS2 and with the 71^st, 175^th and 621^st residues of NS3. Real-time experiments using an HCV subgenomic system to quantify viral replication confirm replication regulation for each covariant pair between 5′UTR₂₄₃ and NS2-41, -76, -110, -211, and NS3-71, -175. The HCV subgenomic system with/without the NS2 region shows that regulatory effects vanish without NS2, so replicative modulation mediated by HCV 5′UTR₂₄₃ depends on NS2. Strong binding of the NS2 variants to HCV RNA correlates with reduced HCV replication whereas weak binding correlates with restoration of HCV replication efficiency, as determined by RNA-protein immunoprecipitation assay band intensity. The dominant haplotype 5′UTR₂₄₃-NS2-41-76-110-211-NS3-71-175 differs according to the HCV genotype: G-Ile-Ile-Ile-Gly-Ile-Met for genotype 1b and A-Leu-Val-Leu-Ser-Val-Leu for genotypes 1a, 2a and 2b. In conclusion, 5′UTR₂₄₃ co-varies with specific NS2/3 protein amino acid residues, which may have significant structural and functional consequences for HCV replication. This unreported mechanism involving HCV replication possibly can be exploited in the development of advanced anti-HCV medication.

Hepatitis C virus NS2/3 protease regulates HCV IRES-dependent translation and NS5B RdRp activity

Chronic hepatitis C virus (HCV) infection often leads to liver cancer. NS2/3 protease is the first of two virally encoded proteases required for HCV polyprotein processing. In this report, we investigated the function of NS2/3 protease on HCV replication and translation. Cells transfected with plasmids encoding wild-type or mutant NS2/3 and a dual-luciferase reporter construct containing an HCV internal ribosome entry site (IRES) were used to examine the effect of NS2/3 protease on translation of HCV RNA. Cells transfected with plasmids encoding wild-type or mutant NS2/3, pcDNA-NS5B and a reporter plasmid were used to examine the effect of NS2/3 protease on HCV replication. The results showed that both autocleavage processing and the uncleaved form of NS2/3 protease specifically decrease HCV IRES-directed translation, while the uncleaved form of NS2/3 protease decreases HCV NS5B RdRp activity (replication), indicating that autoregulation by NS2/3 protease of HCV replication and translation may play an important role in persistent HCV infection.