The phosphatidylserine receptor TIM1 promotes infection of enveloped hepatitis E virus

The hepatitis E virus (HEV) is an underestimated RNA virus of which the viral life cycle and pathogenicity remain partially understood and for which specific antivirals are lacking. The virus exists in two forms: nonenveloped HEV that is shed in feces and transmits between hosts; and membrane-associated, quasi-enveloped HEV that circulates in the blood. It is suggested that both forms employ different mechanisms for cellular entry and internalization but little is known about the exact mechanisms. Interestingly, the membrane of enveloped HEV is enriched with phosphatidylserine, a natural ligand for the T-cell immunoglobulin and mucin domain-containing protein 1 (TIM1) during apoptosis and involved in 'apoptotic mimicry', a process by which viruses hijack the apoptosis pathway to promote infection. We here investigated the role of TIM1 in the entry process of HEV. We determined that HEV infection with particles derived from culture supernatant, which are cloaked by host-derived membranes (eHEV), was significantly impaired after knockout of TIM1, whereas infection with intracellular HEV particles (iHEV) was unaffected. eHEV infection was restored upon TIM1 expression; and enhanced after ectopic TIM1 expression. The significance of TIM1 during entry was further confirmed by viral binding assay, and point mutations of the PS-binding pocket diminished eHEV infection. In addition, Annexin V, a PS-binding molecule also significantly reduced infection. Taken together, our findings support a role for TIM1 in eHEV-mediated cell entry, facilitated by the PS present on the viral membrane, a strategy HEV may use to promote viral spread throughout the infected body.

Identification of Plant Peptides as Novel Inhibitors of Orthohepevirus A (HEV) Capsid Protein by Virtual Screening

Hepatitis E virus (HEV) is the notable causative agent of acute and chronic hepatic, renal, pancreatic, neurological, and hematopoietic blood cell infections with high risk in immunocompromised patients. Hepatic failure is mostly documented among adults, pregnant women, and patients with preexisting liver disease. HEV is a positive sense RNA virus of 7.2 kb genome size with typically three open reading frames (ORFs) which play essential roles in viral replication, genome assembly, and transcription. The mutational substitution in the viral RNA genome makes more it difficult to understand the actual relationship in the host–virus association. ORFs of HEV encode different structural and non-structural proteins and one of them is the capsid protein which is coded by ORF2. The capsid protein mediates the encapsulation of the viral genome as well as being involved in virion assembly. In the current study, the ligand-based docking approach was employed to inhibit the active amino acids of the viral capsid protein. Depending upon S-score, ADMET profiling, and drug scanning, the top ten tetrapeptides were selected as potential drug candidates with no toxicity counter to HEV receptor protein. The S-score or docking score is a mathematical function which predicts the binding affinities of docked complexes. The binding affinity of the predicted drug–target complexes helps in the selectivity of the desired compound as a potential drug. The best two selected peptides (i.e., TDGH with S-score of −8.5 and EGDE with S-score of −8.0) interacted with the active site amino acids of the capsid protein (i.e., Arg399, Gln420, and Asp444). The molecular dynamics simulations of RMSD trajectories of TDGH–capsid protein and EDGE–capsid protein have revealed that both docked complexes were structurally stable. The study revealed that these tetrapeptides would serve as strong potential inhibitors and a starting point for the development of new drug molecules against the HEV capsid protein. In future, in vivo studies are needed to explore selected peptides as potential drug candidates.

Integrative Multiomics and Regulatory Network Analyses Uncovers the Role of OAS3, TRAFD1, miR-222-3p, and miR-125b-5p in Hepatitis E Virus Infection

The hepatitis E virus (HEV) is a long-ignored virus that has spread globally with time. It ranked 6th among the top risk-ranking viruses with high zoonotic spillover potential; thus, considering its viral threats is a pressing priority. The molecular pathophysiology of HEV infection or the underlying cause is limited. Therefore, we incorporated an unbiased, systematic methodology to get insights into the biological heterogeneity associated with the HEV. Our study fetched 93 and 2016 differentially expressed genes (DEGs) from chronic HEV (CHEV) infection in kidney-transplant patients, followed by hub module selection from a weighted gene co-expression network (WGCN). Most of the hub genes identified in this study were associated with interferon (IFN) signaling pathways. Amongst the genes induced by IFNs, the 2'-5'-oligoadenylate synthase 3 (OAS3) protein was upregulated. Protein-protein interaction (PPI) modular, functional enrichment, and feed-forward loop (FFL) analyses led to the identification of two key miRNAs, i.e., miR-222-3p and miR-125b-5p, which showed a strong association with the OAS3 gene and TRAF-type zinc finger domain containing 1 (TRAFD1) transcription factor (TF) based on essential centrality measures. Further experimental studies are required to substantiate the significance of these FFL-associated genes and miRNAs with their respective functions in CHEV. To our knowledge, it is the first time that miR-222-3p has been described as a reference miRNA for use in CHEV sample analyses. In conclusion, our study has enlightened a few budding targets of HEV, which might help us understand the cellular and molecular pathways dysregulated in HEV through various factors. Thus, providing a novel insight into its pathophysiology and progression dynamics.

A tightly clustered hepatitis E virus genotype 1a is associated with endemic and outbreak infections in Bangladesh

BACKGROUND

Hepatitis E virus (HEV) infection is endemic in Bangladesh and there are occasional outbreaks. The molecular characteristics and pathogenesis of endemic and outbreak HEV strains are poorly understood. We compared the genetic relatedness and virulence associated mutations of endemic HEV strains with outbreak strains.

METHODS

We analyzed systematically collected serum samples from HEV immunoglobulin M (IgM) positive patients attended at Bangabandhu Sheikh Mujib Medical University, Dhaka from August 2013 to June 2015. HEV RNA positive samples were subjected to whole genome sequencing. Genotype and subtype of the strains were determined by phylogenetic analysis. Virulence associated mutations e.g. acute viral hepatitis (AVH), fulminant hepatic failure (FHF), chronic hepatitis, ribavirin treatment failure (RTF), B and T cell neutralization epitopes were determined.

RESULTS

92 HEV immunoglobulin M (IgM) antibody positive plasma samples (43 in 2013-2014 and 49 in 2014-2015) were studied. 77.1% (70/92) of the samples were HEV RNA positive. A 279 bp open reading frame (ORF) 2 and ORF 3 sequence was obtained from 54.2% (38/70) of the strains. Of these 38 strains, whole genome sequence (WGS) was obtained from 21 strains. In phylogenetic analysis of 38 (279 bp) sequence all HEV sequences belonged to genotype 1 and subtype 1a. Further phylogenetic analysis of 21 HEV WGS, Bangladeshi HEV sequences clustered with genotype 1a sequences from neighboring countries. Within genotype 1a cluster, Bangladesh HEV strains formed a separate cluster with the 2010 HEV outbreak strains from northern Bangladesh. 80.9 to 100% of the strains had A317T, T735I, L1120I, L1110F, P259S, V1479I, G1634K mutations associates AVH, FHF and RTF. Mutations in T cell recognition epitope T3, T5, T7 was observed in 76.1%, 100% and 100% of the strains respectively.

CONCLUSION

Strains of HEV genotype 1a are dominant in Bangladesh and are associated with endemic and outbreak of HEV infection. HEV isolates in Bangladesh have high prevalence of virulence associated mutations and mutation which alters antigenicity to B and T cell epitopes.

A plant-based transient expression system for the rapid production of highly immunogenic Hepatitis E virus-like particles

OBJECTIVE

Hepatitis E virus (HEV) infection is a major cause of acute hepatitis worldwide. The aim of the study is the development of plant expression system for the production of virus-like particles formed by HEV capsid and the characterization of their immunogenicity.

RESULTS

Open reading frame (ORF) 2 encodes the viral capsid protein and possesses candidate for vaccine production. In this study, we used truncated genotype 3 HEV ORF 2 consisting of aa residues 110 to 610. The recombinant protein was expressed in Nicotiana benthamiana plants using the self-replicating potato virus X-based vector pEff up to 10% of the soluble protein fraction. The yield of HEV 110-610 after purification was 150-200 µg per 1 g of green leaf biomass. The recombinant protein formed nanosized virus-like particles. The immunization of mice with plant-produced HEV 110-610 protein induced high levels of HEV-specific serum antibodies.

CONCLUSIONS

HEV ORF 2 (110-610 aa) can be used as candidate for the development of a plant-produced vaccine against Hepatitis E.

Zinc: A Potential Antiviral Against Hepatitis E Virus Infection?

Hepatitis E virus (HEV) is a major cause of viral hepatitis worldwide. Owing to its feco oral transmission route, sporadic as well as epidemic outbreaks recurrently occur. No specific antiviral therapy is available against the disease caused by HEV. Broad spectrum antivirals such as ribavirin and interferon alfa are prescribed in severe and chronic HEV cases. However, the side effects, cost, and limitations of usage render the available treatment unsuitable for several categories of patients. We recently reported the ability of zinc to inhibit viral replication in mammalian cell culture models of HEV infection. Zinc will be a safe and economical antiviral therapy option if it inhibits HEV replication during the natural course of infection. This essay discusses the putative mechanism(s) by which zinc inhibits HEV replication and provides an overview of the possible therapeutic potential of zinc in HEV patients.

Detection of Serum Antibodies to Hepatitis E Virus Based on HEV Genotype 3 ORF2 Capsid Protein Expressed in Nicotiana benthamiana

BACKGROUND

Hepatitis E virus (HEV) causes epidemics in developing countries and is primarily transmitted through the fecal-oral route. There have been recent reports on the zoonotic spread of the virus, and several animal species, primarily pigs, have been recognized as reservoirs of HEV. Because of its possible spread, there is an urgent need of a method for the cost-effective production of HEV proteins that can be used as diagnostic antigens for the serological detection of anti-HEV antibodies.

METHODS

The HEV open reading frame (ORF)2 protein was purified from plant tissue by using immobilized metal-anion chromatography (IMAC). The recombinant protein was used to develop an in-house ELISA for testing anti-HEV antibodies in both human and swine sera. Thirty-six serum samples collected from patients with serologically proven HEV infection with commercial kits were tested for anti-HEV IgG antibodies by using the plant-expressed protein. Forty-five serum samples collected from apparently healthy pigs in Bulgarian farms were also tested.

RESULTS

We confirmed the transient expression and purification of a truncated version of the HEV genotype 3 capsid protein in Nicotiana benthamiana and its usefulness as a diagnostic antigen. ELISA showed the presence of anti-HEV IgG antibodies in 29 of the 36 human samples. The in-house ELISA showed anti-HEV IgG antibodies in 34 of the 45 pigs.

CONCLUSIONS

We describe a method for the production of HEV ORF2 protein in N. benthamiana and the usefulness of this protein for the serological detection of anti-HEV antibodies in both humans and swine.

[Preparation and Characterization of Recombinant HEV RNA-loaded MS2 Bacteriophage Capsid by Armored RNA Technology]

The purpose of this study was to develop an effective control to be applied in hepatitis E virus(HEV)nucleic acid detection.Construction of an MS2/HEV gene was performed based on an "Armored RNA technology" protocol. The gene included a partial MS2 phage genome including the 5’UTR,the maturation protein, capsid protein and initiation site of the replicase and a partially conserved sequence derived from the HEV ORF2.The target genes were synthesized and amplified by PCR, and the purified target gene products subcloned into the pET-28 b prokaryotic expression vector to obtain the pET-28b-MS2/HEV recombinant plasmid. SDS-PAGE was used for expression analysis in E. coli BL21(DE3)cells harboring the pET-28b-MS2/HEV plasmid. Centrifugal ultrafiltration was adopted for the purification and concentration of recombinant HEV RNA-loaded MS2 Bacteriophage Capsid (rHEPC). The morphological identification of the particles was subsequently performed by scanning electron microscopy. Stability of the rHEPC particles were evaluated by challenging with different concentrations of DNase I and RNase A, and also evaluated for long-term storage based on RT-PCR verification. SDS-PAGE results showed that the target MS2/HEV gene could express efficiently in recombinant E. coli BL21(DE3)and RT-PCR results revealed that the designed HEV conserved gene sequence was successfully packaged into MS2phage-like or rHEPC particles. Stability evaluation showed that the prepared rHEPC particles exhibited strong resistance to degradation by DNase I and RNase A and long-lasting protection of coated HEV RNA for at least seven months when stored at-20℃.The prepared rHEPC particles in the present study meet the basic requirements to be used as a quality control material for routine HEV nucleic acid detection.

[Construction of Recombinant Full-length Hepatitis E Virus Fused with EGFP and Assessment of Infectivity]

The purpose of this study was to construct recombinant full-length hepatitis E virus(HEV)fused with enhanced green fluorescent protein(EGFP),and assess its infectivity in A549 cells. Two fragments from the full-length HEV genome and the EGFP gene were amplified by PCR. The EGFP gene was inserted downstream of the HEV ORF2 and then cloned into the pGEM® -7Zf(+)vector containing the T7 and SP6RNA polymerase promoters, producing pGEM-HEV-EGFP. The construction of the pGEM-HEV-EGFP recombinant plasmid was confirmed by restriction enzyme digest and sequencing. The pGEM-HEV-EGFP recombinant plasmid was transfected into A549 cells to assess infectivity using Lipofectamine. EGFP expression was observed at 24hpost-transfection,and expression of the HEV ORF2 was detected by immunofluorescence, confirming the presence of the HEV ORF2 and EGFP fusion protein. Cytopathic effects were observed at day seven post-transfection. The infectivity of pGEM-HEV-EGFP was confirmed by the presence of fluorescence after three continuous passages. The recombinant pGEM-HEV-EGFP vector was successfully constructed and effectively infected A549 cells, which will facilitate future studies on the mechanisms of HEV infection and pathogenesis.

Hepatitis E virus ORF1 encoded macro domain protein interacts with light chain subunit of human ferritin and inhibits its secretion

Hepatitis E Virus (HEV) is the major causative agent of acute hepatitis in developing countries. Its genome has three open reading frames (ORFs)-called as ORF1, ORF2, and ORF3. ORF1 encodes nonstructural polyprotein having multiple domains, namely: Methyltransferase, Y domain, Protease, Macro domain, Helicase, and RNA-dependent RNA polymerase. In the present study, we show that HEV-macro domain specifically interacts with light chain subunit of human ferritin (FTL). In cultured hepatoma cells, HEV-macro domain reduces secretion of ferritin without causing any change in the expression levels of FTL. This inhibitory effect was further enhanced upon Brefeldin-A treatment. The levels of transferrin Receptor 1 or ferroportin, two important proteins in iron metabolism, remained unchanged in HEV-macro domain expressing cells. Similarly, there were no alterations in the levels of cellular labile iron pool and reactive oxygen species, indicating that HEV-macro domain does not influence cellular iron homeostasis/metabolism. As ferritin is an acute-phase protein, secreted in higher level in infected persons and HEV-macro domain has the property of reducing synthesis of inflammatory cytokines, we propose that by directly binding to FTL, macro domain prevents ferritin from entering into circulation and helps in further attenuation of the host immune response.

Hepatitis E Virus Produced from Cell Culture Has a Lipid Envelope

The absence of a productive cell culture system hampered detailed analysis of the structure and protein composition of the hepatitis E virion. In this study, hepatitis E virus from a robust HEV cell culture system and from the feces of infected monkeys at the peak of virus excretion was purified by ultra-centrifugation. The common feature of the two samples after ultracentrifugation was that the ORF2 protein mainly remained in the top fractions. The ORF2 protein from cell culture system was glycosylated, with an apparent molecular weight of 88 kDa, and was not infectious in PLC/PRF/5 cells. The ORF2 protein in this fraction can bind to and protect HEV RNA from digestion by RNase A. The RNA-ORF2 product has a similar sedimentation coefficient to the virus from feces. The viral RNA in the cell culture supernatant was mainly in the fraction of 1.15 g/cm3 but that from the feces was mainly in the fraction of 1.21 g/cm3. Both were infectious in PLC/PRF/5 cells. And the fraction in the middle of the gradient (1.06 g/cm3) from the cell culture supernatant,but not that from the feces, also has ORF2 protein and HEV RNA but was not infectious in PLC/PRF/5.The infectious RNA-rich fraction from the cell culture contained ORF3 protein and lipid but the corresponding fraction from feces had no lipid and little ORF3 protein. The lipid on the surface of the virus has no effect on its binding to cells but the ORF3 protein interferes with binding. The result suggests that most of the secreted ORF2 protein is not associated with HEV RNA and that hepatitis E virus produced in cell culture differs in structure from the virus found in feces in that it has a lipid envelope.

[Construction and investigation of a recombinant eukaryotic expression vector for expressing the ORF3 protein of hepatitis E virus in BHK-21 fibroblasts]

OBJECTIVE

To construct a eukaryotic expression vector to express the hepatitis E virus protein open reading frame 3 (ORF3) and investigate the intracellular location of the expressed protein using the baby hamster kidney (BHK-21) fibroblast cell line.

METHODS

The ORF3 gene was amplified by RT-PCR, cloned into the HindIII and EcoRI sites in the multicloning site of the pDsRed-Monomer-N1mammalian expression vector that encodes a red fluorescent protein (DsRed), and confirmed by restriction enzyme digestion and sequencing. The recombinant plasmid was then transfected into BHK-21 cells via the Lipofectamine 2000 reagent; the subsequent ORF3 gene overexpression was confirmed by RT-PCR and the protein expression and location was detected by Western blotting and immunofluorescence assay.Results TThe pDsRed-Monomer-N1-ORF3 recombinant plasmid was successfully constructed. After transfection into BHK-21 ceils, the ORF3 gene was transcribed and expressed, and the ORF3 protein was mainly located in the cytoplasm, where it could react with a specific antibody.

CONCLUSION

The ORF3-DsRed fusion protein was mainly located in the cytoplasm of BHK-21 fibroblasts, and may represent a useful tool for research on the role of this protein in HEV infection.

RNA-seq based transcriptome analysis of hepatitis E virus (HEV) and hepatitis B virus (HBV) replicon transfected Huh-7 cells

Pathogenesis of hepatitis B virus (HBV) and hepatitis E virus (HEV) infection is as varied as they appear similar; while HBV causes an acute and/or chronic liver disease and hepatocellular carcinoma, HEV mostly causes an acute self-limiting disease. In both infections, host responses are crucial in disease establishment and/or virus clearance. In the wake of worsening prognosis described during HEV super-infection over chronic HBV hepatitis, we investigated the host responses by studying alterations in gene expression in liver cells (Huh-7 cell line) by transfection with HEV replicon only (HEV-only), HBV replicon only (HBV-only) and both HBV and HEV replicons (HBV+HEV). Virus replication was validated by strand-specific real-time RT-PCR for HEV and HBsAg ELISA of the culture supernatants for HBV. Indirect immunofluorescence for the respective viral proteins confirmed infection. Transcription profiling was carried out by RNA Sequencing (RNA-Seq) analysis of the poly-A enriched RNA from the transfected cells. Averages of 600 million bases within 5.6 million reads were sequenced in each sample and ∼15,800 genes were mapped with at least one or more reads. A total of 461 genes in HBV+HEV, 408 in HBV-only and 306 in HEV-only groups were differentially expressed as compared to mock transfection control by two folds (p<0.05) or more. Majority of the significant genes with altered expression clustered into immune-associated, signal transduction, and metabolic process categories. Differential gene expression of functionally important genes in these categories was also validated by real-time RT-PCR based relative gene-expression analysis. To our knowledge, this is the first report of in vitro replicon transfected RNA-Seq based transcriptome analysis to understand the host responses against HEV and HBV.

Virus host protein interaction network analysis reveals that the HEV ORF3 protein may interrupt the blood coagulation process

Hepatitis E virus (HEV) is endemic worldwide and a major cause of acute liver disease in developing countries. However, the molecular mechanisms of liver pathology and clinical disease are not well understood for HEV infection. Open reading frame 3 (ORF3) of HEV encodes a small phosphoprotein, which is assumed to be involved in liver pathology and clinical disease. In this study, the interactions between the HEV ORF3 protein and human proteins were investigated using a stringent, high-throughput yeast two-hybrid (Y2H) analysis. Thirty two proteins were shown to interact with genotype 1 ORF3, 28 of which have not been reported previously. These novel interactions were evaluated by coimmunoprecipitation of protein complexes from transfected cells. We found also that the ORF3 proteins of genotype 4 and rabbit HEV interacted with all of the human proteins identified by the genotype 1 ORF3 protein. However, the putative ORF3 protein derived from avian HEV did not interact with the majority of these human proteins. The identified proteins were used to infer an overall interaction map linking the ORF3 protein with components of the host cellular networks. Analysis of this interaction map, based on functional annotation with the Gene Ontology features and KEGG pathways, revealed an enrichment of host proteins involved in complement coagulation, cellular iron ion homeostasis and oxidative stress. Additional canonical pathway analysis highlighted the enriched biological pathways relevant to blood coagulation and hemostasis. Consideration of the clinical manifestations of hepatitis E reported previously and the results of biological analysis from this study suggests that the ORF3 protein is likely to lead to an imbalance of coagulation and fibrinolysis by interacting with host proteins and triggering the corresponding pathological processes. These results suggest critical approaches to further study of the pathogenesis of the HEV ORF3 protein.

Clinical features and risk factors of acute hepatitis E with severe jaundice

AIM: To compares the clinical features of patients infected with hepatitis E virus (HEV) with or without severe jaundice. In addition, the risk factors for HEV infection with severe jaundice were investigated.

METHODS: We enrolled 235 patients with HEV into a cross-sectional study using multi-stage sampling to select the study group. Patients with possible acute hepatitis E showing elevated liver enzyme levels were screened for HEV infection using serologic and molecular tools.HEV infection was documented by HEV antibodies and by the detection of HEV-RNA in serum. We used χ² analysis, Fisher’s exact test, and Student’s t test where appropriate in this study. Significant predictors in the univariate analysis were then included in a forward, stepwise multiple logistic regression model.

RESULTS: No significant differences in symptoms, alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, or hepatitis B virus surface antigen between the two groups were observed. HEV infected patients with severe jaundice had significantly lower peak serum levels of γ-glutamyl-transpeptidase (GGT) (median: 170.31 U/L vs 237.96 U/L, P = 0.007), significantly lower ALB levels (33.84 g/L vs 36.89 g/L, P = 0.000), significantly lower acetylcholine esterase (CHE) levels (4500.93 U/L vs 5815.28 U/L, P = 0.000) and significantly higher total bile acid (TBA) levels (275.56 μmol/L vs 147.03 μmol/L, P = 0.000) than those without severe jaundice. The median of the lowest point time tended to be lower in patients with severe jaundice (81.64% vs 96.12%, P = 0.000). HEV infected patients with severe jaundice had a significantly higher viral load (median: 134 vs 112, P = 0.025) than those without severe jaundice. HEV infected patients with severe jaundice showed a trend toward longer median hospital stay (38.17 d vs 18.36 d, P = 0.073). Multivariate logistic regression indicated that there were significant differences in age, sex, viral load, GGT, albumin, TBA, CHE, prothrombin index, alcohol overconsumption, and duration of admission between patients infected with acute hepatitis E with and without severe jaundice.

CONCLUSION: Acute hepatitis E patients may naturally present with severe jaundice.

Rabbit as a novel animal model for hepatitis E virus infection and vaccine evaluation

Background

The identification of hepatitis E virus (HEV) from rabbits motivated us to assess the possibility of using rabbits as a non-human primate animal model for HEV infection and vaccine evaluation.

Methodology/Principal Findings

First, 75 rabbits were inoculated with seven strains of genotypes 1, 3, 4, and rabbit HEV, to determine the appropriate strain, administrative route and viral dosage. Second, 15 rabbits were randomly divided into three groups and vaccinated with 0 µg (placebo), 10 µg and 20 µg of HEV candidate vaccine, HEV p179, respectively. After three doses of the vaccination, the rabbits were challenged with 3.3×10⁵ genome equivalents of genotype 4 HEV strain H4-NJ703. The strain of genotype 1 HEV was not found to be infectious for rabbits. However, approximately 80% of the animals were infected by two rabbit HEV strains. All rabbits inoculated with a genotype 3 strain were seroconverted but did not show viremia or fecal viral shedding. Although two genotype 4 strains, H4-NJ153 and H4-NJ112, only resulted in part of rabbits infected, another strain of genotype 4, H4-NJ703, had an infection rate of 100% (five out of five) when administrated intravenously. However, only two out of fifteen rabbits showed virus excretion and seroconversion when inoculated orally with H4-NJ703 of three different dosages. In the vaccine evaluation study, rabbits vaccinated with 20 µg of the HEV p179 produced anti-HEV with titers of 1∶10⁴–1∶10⁵ and were completely protected from infection. Rabbits vaccinated with 10 µg produced anti-HEV with titers of 1∶10³–1∶10⁴ and were protected from hepatitis, but two out of the five rabbits showed virus shedding.

Conclusions/Significance

Rabbits may be served as an alternative to the non-human primate models for HEV infection and vaccine evaluation when certain virus strains, appropriate viral dosages, and the intravenous route of inoculation are selected.

Hepatitis E virus ORF2 protein activates the pro-apoptotic gene CHOP and anti-apoptotic heat shock proteins

Background

Hepatitis E virus (HEV) is a non-enveloped plus-strand RNA virus that causes acute hepatitis. The capsid protein open reading frame 2 (ORF2) is known to induce endoplasmic reticulum stress in ORF2 expressing cells.

Methodology/Principal Findings

In this study we found that HEV ORF2 activates the expression of the pro-apoptotic gene C/EBP homologous protein (CHOP). ORF2 stimulates the CHOP promoter mainly through AARE (amino acid response elements) and to a minor extent the ERSE (endoplasmic reticulum stress response elements). Activating transcription factor 4 (ATF4) protein binds and activates the AARE regulatory sites of the CHOP promoter. ORF2 expression also leads to increased phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α) that in turn initiates the translation of ATF4 mRNA. The pro-apoptotic gene CHOP is an important trigger to initiate endoplasmic reticulum stress induced apoptosis. However, the activation of CHOP by ORF2 in this study did not induce apoptosis, nor did BCL2-associated X protein (Bax) translocate to mitochondria. Microarray analysis revealed an ORF2 specific increased expression of chaperones Hsp72, Hsp70B', and co-chaperone Hsp40. Co-immunoprecipitation (Co-IP) and in silico molecular docking analysis suggests that HEV ORF2 interacts with Hsp72. In addition, Hsp72 shows nuclear accumulation in ORF2 expressing cells.

Conclusions/Significance

These data provide new insight into simultaneously occurring counter-acting effects of HEV ORF2 that may be part of a strategy to prevent host suicide before completion of the viral replication cycle.

RNA interference induces effective inhibition of mRNA accumulation and protein expression of SHEV ORF3 gene in vitro

RNA interference (RNAi) provides a powerful promising approach to inhibit viral infection specifically. To explore the possibility of using RNAi as a strategy against HEV infection, which is a serious public health problem in developing countries of Asia, Middle East, Africa, and in Mexico, after the fusion protein expression plasmids pEGFP-ORF3 which contain the EGFP reporter gene and SHEV ORF3 as silencing target, were constructed; EGFP-ORF3 fusion protein expressing HEK 293 cell lines were established; and four siRNAs targeting ORF3 gene were designed, synthesized, and used to transfect the stable cell lines. At 24, 48, and 72 h after transfection, flow cytometry, real-time quantitative PCR, and Western blot were used to assess the expression level of ORF3. The results demonstrated that specific siRNAs which are sequence dependant effectively inhibited mRNA accumulation and protein expression of SHEV ORF3 in HEK 293 cells. These findings provide useful information for the development of RNAi-based prophylaxis and therapy for SHEV infection.

Intergenotypic chimeric hepatitis E viruses (HEVs) with the genotype 4 human HEV capsid gene in the backbone of genotype 3 swine HEV are infectious in pigs

Genotypes 1 and 2 hepatitis E virus (HEV) infect only humans whereas genotypes 3 and 4 HEV infect both humans and pigs. To evaluate the mechanism of cross-species HEV infection between humans and swine, in this study we constructed five intergenotypic chimeric viruses and tested for their infectivity in vitro and in pigs. We demonstrated that chimeric viruses containing the ORF2 capsid gene either alone or in combination with its adjacent 5' junction region (JR) and 3' noncoding region (NCR) from a genotype 4 human HEV in the backbone of a genotype 3 swine HEV are replication-competent in Huh7 cells and infectious in HepG2/C3A cells and in pigs, and thus supporting the hypothesis that genotypes 3 and 4 human HEV are of swine origin. However, chimeric viruses containing the JR+ORF2+3' NCR of genotypes 3 or 4 HEV in the backbone of genotype 1 human HEV failed to infect pigs, suggesting that other genomic regions such as 5' NCR and ORF1 may also be involved in HEV cross-species infection. The results from this study provide the first experimental evidence of the exchangeability of the capsid gene between genotype 3 swine HEV and genotype 4 human HEV, and have important implications for understanding the mechanism of HEV cross-species infection.

Hepatitis E virus infection: a general review with a focus on hemodialysis and kidney transplant patients

BACKGROUND

Hepatitis E virus (HEV) infection is a self-limited viral disease that causes acute hepatitis epidemics in developing countries. The common route of transmission for HEV is supposedly fecal-oral. Serological evidence may be unexpectedly found in hemodialysis (HD) patients and kidney transplant recipients. Although the route of HEV transmission is not usually determined in HD subjects, this virus seems to be transmitted either directly through HD or nosocomially. In this study, we gathered the published information on HEV infection in HD patients and kidney transplant recipients.

METHODS

For this review, we collected the relevant articles by searching through Medline and Google Scholar from January 1980 up to September 2009.

RESULTS

Some variables including older age, low education, living in rural versus urban areas and the duration of HD seem to be risk factors for HEV infection in HD patients. Compared with non-HD subjects, HEV infection may be specifically associated with poor outcome in HD patients. Specific considerations seem to be required to prevent transmission of HEV to HD patients.

CONCLUSION

More extensive investigations are required to determine the disease burden of HEV infection in HD subjects in countries which experience outbreaks of HEV infection.

Virulence factor activity relationships for hepatitis E and Cryptosporidium

The hepatitis E virus and Cryptosporidium are waterborne pathogens, each consisting of distinct taxa, genotypes and isolates that infect humans, nonhuman animal species or both. Some are associated with disease, others are not. Factors contributing to disease are extremely complicated, possibly involving differences in one or more traits associated with an organism's taxon, genotype or isolate and its infectious dose, and age or condition, as well as the host's physiology and immune status. Potential virulence factors have not yet been identified for HEV. Putative virulence factors for Cryptosporidium might be found in recently recognized genes involved in processes such as excystation, adherence to host cells, invasion, intracellular maintenance and host cell destruction.

[HEV capsid protein interacts with CYP 2A6 and decreases its coumarin 7-hydroxylation activity]

E2 is a recombinant hepatitis E virus capsid protein including its main antigenic determinants but lacking of the particle assembling domain. P239 was the C-terminal extending protein of E2 and could self-assemble to form virus like particles, which might serve as mimicry of virions both structurally and antigenically. We previously used yeast two-hybrid system to screen proteins interacting with E2 based on a human hepatocyte cDNA library. One candidate was identified as the segment (aa388-437) of cytochrome P450 2A6 protein, which is predominantly expressed in liver and important for metabolization. Some studies have demonstrated that hepatitis virus infection may altered cell metabolic clearance of coumrarin which were rapidly matebolised by CYP2A6. In this research, we demonstrated that the protein interaction between HEV capsid proteins and CYP2A6 by pull-down and co-immunoprecipitation. It was also found that their interaction could decrease the CYP2A6 catalytic activity when p239 was incubated within the CYP2A6-transfected Huh7 cells. These results suggested that CYP2A6 might be related to the pathological process when HEV invaded host cells.

[Identification of a novel antigenic epitope on GST fusion-expressed and ORF2-encoded proteins of hepatitis E virus]

AIM

To investigate the effect of a GST tag on the antigenic structure of GST fusion-expressed and ORF2-encoded recombinant proteins of hepatitis E virus (HEV).

METHODS

The monoclonal antibodies (mAb) were prepared with a GST fusion protein, p166Chn-GST, which was derived from a Chinese HEV strain. Then they were tested by indirect ELISA, competition ELISA and Western blot with different GST fusion, His fusion or non-fusion recombinant proteins derived from HEV reference strains of all 4 genotypes and other non-HEV recombinant proteins.

RESULTS

Three mAb named 1A8, 9B4 and 8H10 were obtained. All of them reacted to p166Chn-GST but did not react to GST. mAb 1A8 and 9B4 reacted to 4 p166-GST proteins of different HEV genotypes and 2 N- or C-terminal truncated p166Chn-GST proteins named p146Chn-GST and p137Chn-GST, but they did not react to 4 p166-His proteins of different HEV genotypes and a non-fusion p179Chn protein. No detectable signals were found when 1A8 and 9B4 were subjected to HEV antigen competition ELISA or Western blot after SDS-PAGE. No cross reaction was observed between the two mAb and HEV-irrelevant GST fusion proteins, either.

CONCLUSION

A novel antigenic epitope recognized by mAb 1A8 and 9B4 appears on the GST fusion-expressed and ORF2-encoded HEV recombinant proteins and it is dependent on the conformational folding of both GST and HEV sequences.

[Recombinant HEV caspid protein p239 specifically attached on HepG2 cells and blocked the infection of wild-type HEV on liver cells]

By using Western blot and immunofluorescence assays, the recombinant HEV capsid protein p239 was found specifically attached to the HepG2 cell surface and entered to the cytoplasm with the increase of incubation temperature. Pre-mixture of wild-type HEV with p239 blocked the infectivity of the virus on primary cultured human hepatocytes and HepG2 cells, indicating that p239 and HEV competed the same targeting site on these cells. These data provide evidence that p239 has a similar cell surface structure with wild-type HEV.

Evaluation of human (genotype 1) and swine (genotype 4)-ORF2-based ELISAs for anti-HEV IgM and IgG detection in an endemic country and search for type 4 human HEV infections

Open reading frame 2 proteins (ORF2) from swine (genotype 4, S-ORF2) and human (genotype 1, H-ORF2) hepatitis E virus (HEV) having 91.4% identity at amino acid level were expressed using baculovirus expression system. Comparison of ELISAs based on the two proteins yielded identical results when sequential serum samples from monkeys and pigs experimentally infected with genotypes 1 and 4 HEV, respectively, were tested. Samples from patients (n = 258) suffering from non-A, non-B hepatitis during outbreaks of the disease and 180 sera from apparently healthy children were screened by H-ORF2-, S-ORF2-based ELISAs and Genelabs ELISA, a widely used commercial test for HEV diagnosis. Specificity of all three tests in detecting IgM and IgG antibodies in healthy children was comparable. Excellent correlation was noted in detecting both IgM (98.7% concordance) and IgG (97.7% concordance) anti-HEV antibodies when H-ORF2 and S-ORF2 ELISAs were compared. When compared with Genelabs ELISA, both H-ORF2 and S-ORF2 ELISAs identified 34 and 18 additional positives, respectively, in IgM and IgG anti-HEV tests showing comparatively less sensitivity of the commercial assay. The concordance of Genelabs ELISA in IgM detection was 86.4% and 85.6%, respectively, with H-ORF2 and S-ORF2 ELISAs. The concordance between Genelabs ELISA and H-ORF2 decreased further to 73.6% when 129 human samples from recent HEV epidemics (2002-2004) were tested for IgM. Similar results were obtained when sequential samples from 11 hepatitis E patients were examined. Screening of serum samples from 137 sporadic non-A, non-B hepatitis cases further confirmed the superiority of the H-ORF2 and S-ORF2 ELISAs. All 36/137 HEV-RNA-positive samples from sporadic cases belonged to genotype 1 confirming absence/rarity of type 4 human infections. H-ORF2 and S-ORF2 antigens were swappable in ELISAs for detecting both genotypes 1 and 4 HEV infections.

The hepatitis E virus Orf3 protein protects cells from mitochondrial depolarization and death

The biology and pathogenesis of hepatitis E virus are poorly understood due to the lack of an in vitro culture or infection models. The viral Orf3 protein activates the cellular mitogen-activated protein kinase pathway and is likely to modulate the host cell environment for efficient viral replication. We screened for cellular genes whose transcription was differentially up-regulated in an Orf3-expressing stable cell line (ORF3/4). The gene for mitochondrial voltage-dependent anion channel (VDAC) was one such candidate. The up-regulation of VDAC in ORF3/4 cells was confirmed by Northern and Western blotting in various cell lines. Transfection of ORF3/4 cells with an ORF3-specific small interfering RNA led to a reduction in VDAC protein levels. VDAC is a critical mitochondrial outer membrane protein, and its overexpression results in apoptosis. Surprisingly, Orf3-expressing cells were protected against staurosporine-induced cell death by preservation of mitochondrial potential and membrane integrity. A small interfering RNA-mediated reduction in Orf3 and VDAC levels also made cells sensitive to staurosporine. Chemical cross-linking showed Orf3-expressing cells to contain higher levels of oligomeric VDAC. These cells also contained higher levels of hexokinase I that directly interacted with VDAC. This interaction is known to preserve mitochondrial potential and prevent cytochrome c release. We report here the first instance of a viral protein promoting cell survival through such a mechanism.

[Detection of the virus of hepatitis E isolates and elucidation of the possibility of their replication in vitro]

Blood serum samples collected from patients with acute hepatitis symptoms admitted to Infectious Disease Hospitals of Novosibirsk, Barnaul, and Irkutsk were studied. The serum samples were tested for the IgM and IgG antibodies to HEV using ELISA. Seropositive samples were tested using RT-PCR for HEV RNA. Two HEV strains were isolated, and thus HEV infection was identified for West Siberia. One of this strains is classified as HEV genotype I; the other, as genotype III. Cell culturing of these strains in green monkey kidney (4647) cells showed an ability of HEV genotype I strain to cause persistent infection.

[Expression of ORF2 protein of HEV genotype IV in Hansenula polymorpha]

Hepatitis E, an acute infectious disease transmitted via the fecal-oral route, is caused by hepatitis E virus. However, no effective treatment currently exists for hepatitis E, and the only epidemic control approach is vaccination. But so for there are no commercial vaccine for hepatitis E available in the world. To find a new expression system to develop recombinant hepatitis E vaccine, in this study the expression system of methylotrophic yeast Hansenula polymorpha was used to express the gene encoding amino acid 112 - 607 of the open reading frame 2 (ORF2) of hepatitis E virus (HEV) genotype IV. In order to achieve high expression level, the coding sequence was optimized according to codon usage bias of Hansenula polymorpha and synthesized through overlapping PCR. Subsequently the gene was subcloned into the multi-copy expression vectors of Hansenula polymorpha, which include pDGXHP1.0 (MOX promotor), pDGXHP2.0 (MOX promotor) and pDGXHP2.1 ( FMD promotor). The series of one-copy and multi-copy recombinant plasmids were transformed into ATCC26012(Ura3-) by electroporation. The transformants were cultured in selection media MDL and screened for the existence of foreign gene by PCR. Then the strains were induced in MM media and the expression products were detected by SDS-PAGE, ELISA and Western blot assays to select the high-level expression strains. The result of SDS-PAGE showed that the HEV ORF2 expression product was accumulated up to 12% of total cellular protein and its molecular weight is 56kD. The expression product showed high immunoreactivity detected by ELISA and the highest titer is 1:2048. The result of Western blot demonstrated that the expression product could be specifically recognized by the polyclonal antibody against HEV. The successful expression of HEV ORF2 protein in Hansenula polymorpha provides foundation for the further development of recombinant subunit vaccine against hepatitis E.

Detection of HEV antigen as a novel marker for the diagnosis of hepatitis E

Infection with hepatitis E virus (HEV) may be diagnosed by the presence of HEV RNA or anti-HEV antibodies. An enzyme immunoassay (EIA) was developed for the detection of antigen. Twenty-four monoclonal antibodies (mAbs) were produced. An indirect sandwich EIA was developed to detect HEV antigen using a combination of three mAbs as coating antibodies. Approximately 44.6% (33/74), 28.6% (50/175), and none (0/27) of sera positive for anti-HEV IgM alone, both anti-HEV IgM and IgG, and anti-HEV IgG alone also were positive for HEV antigen using this EIA. Forty-two HEV antibody-positive sera were tested for HEV RNA and antigen in parallel and the concordance was 81.0% (34/42). All PCR products were found to belong to HEV genotype 4. In order to evaluate the temporal relationship between HEV antigen positivity and HEV RNA, anti-HEV IgG and IgM, and ALT concentrations, macaques were infected with HEV genotypes 1 and 4 and serial samples were collected. The results showed that the antigen EIA can detect the capsid proteins of both genotypes. HEV antigen was detectable prior to ALT elevation and the appearance of anti-HEV antibodies in the infected monkeys and lasted for several weeks in all cases. HEV antigen became detectable in the serum at almost the same time as HEV RNA in feces but persisted for 4 weeks less than HEV RNA. This assay should be valuable for the diagnosis of acute hepatitis E, particularly in the window period prior to seroconversion to anti-HEV.

Structural and functional basis for ADP-ribose and poly(ADP-ribose) binding by viral macro domains

Macro domains constitute a protein module family found associated with specific histones and proteins involved in chromatin metabolism. In addition, a small number of animal RNA viruses, such as corona- and toroviruses, alphaviruses, and hepatitis E virus, encode macro domains for which, however, structural and functional information is extremely limited. Here, we characterized the macro domains from hepatitis E virus, Semliki Forest virus, and severe acute respiratory syndrome coronavirus (SARS-CoV). The crystal structure of the SARS-CoV macro domain was determined at 1.8-Angstroms resolution in complex with ADP-ribose. Information derived from structural, mutational, and sequence analyses suggests a close phylogenetic and, most probably, functional relationship between viral and cellular macro domain homologs. The data revealed that viral macro domains have relatively poor ADP-ribose 1"-phosphohydrolase activities (which were previously proposed to be their biologically relevant function) but bind efficiently free and poly(ADP-ribose) polymerase 1-bound poly(ADP-ribose) in vitro. Collectively, these results suggest to further evaluate the role of viral macro domains in host response to viral infection.

Expression and processing of the Hepatitis E virus ORF1 nonstructural polyprotein

Background

The ORF1 of hepatitis E virus (HEV) encodes a nonstructural polyprotein of ~186 kDa that has putative domains for four enzymes: a methyltransferase, a papain-like cysteine protease, a RNA helicase and a RNA dependent RNA polymerase. In the absence of a culture system for HEV, the ORF1 expressed using bacterial and mammalian expression systems has shown an ~186 kDa protein, but no processing of the polyprotein has been observed. Based on these observations, it was proposed that the ORF1 polyprotein does not undergo processing into functional units. We have studied ORF1 polyprotein expression and processing through a baculovirus expression vector system because of the high level expression and post-translational modification abilities of this system.

Results

The baculovirus expressed ORF1 polyprotein was processed into smaller fragments that could be detected using antibodies directed against tags engineered at both ends. Processing of this ~192 kDa tagged ORF1 polyprotein and accumulation of lower molecular weight species took place in a time-dependent manner. This processing was inhibited by E-64d, a cell-permeable cysteine protease inhibitor. MALDI-TOF analysis of a 35 kDa processed fragment revealed 9 peptide sequences that matched the HEV methyltransferase (MeT), the first putative domain of the ORF1 polyprotein. Antibodies to the MeT region also revealed an ORF1 processing pattern identical to that observed for the N-terminal tag.

Conclusion

When expressed through baculovirus, the ORF1 polyprotein of HEV was processed into smaller proteins that correlated with their proposed functional domains. Though the involvement of non-cysteine protease(s) could not be be ruled out, this processing mainly depended upon a cysteine protease.

[Expression, purification and immunogenicity of a novel hepatitis E virus-like particle]

AIM

To express and characterize a novel hepatitis E virus (HEV) recombinant protein which contains HEV neutralization epitope(s).

METHODS

The gene fragment encoding for amino acid 452-617 of HEV open reading frame 2 protein (pORF2) was inserted into the plasmid pET28a(+). The recombinant plasmid was used to transform the E. coli BL21(DE3) strain. The recombinant protein was expressed by IPTG induction, purified by Ni-NTA chromatography and analyzed by SDS-PAGE, Western blot and electronmicroscopy. Immune responses to the recombinant protein were determined by the immunization of mice.

RESULTS

The expressed HEV recombinant protein was in a naturally-soluble form with a molecular weight of 22,000. The protein assembled into a virus like particle (VLP) with a diameter of approximate 20 nanometers. Moreover, this novel protein was reactive to serum samples obtained from the patients with HEV infection. After the mice were immunized with the protein, they developed anti-HEV antibodies which could neutralize HEV infection in cell culture.

CONCLUSION

An E. coli-expressed recombinant protein containing 166 amino acid of HEV pORF2 can form VLP with good immunogenicity and antigenicity. This novel HEV VLP is valuable for the development of HEV vaccine and new diagnostic kit.

[Effects of different vectors and gene fragments on antigen expression of hepatitis E virus DNA immunization]

AIM

To investigate the effects of different vectors and gene fragments on antigen expression of hepatitis E virus (HEV) DNA immunization.

METHODS

Gene fragments encoding p166 and p179, which contain the neutralization antigenic epitopes of a Chinese strain of HEV genotype IV, were cloned into two different eukaryotic expression vectors (pTR421 and pCDNA3.1), respectively. The in vitro expression level of p166 and p179 in HepG2 cells transfected by each of the recombinant plasmids with lipofectamine2000 was examined by means of immunofluorescence and Western blot. Meanwhile, the in vivo expression level in muscles of mice was examined with immunohistochemistry staining.

RESULTS

Four recombinant plasmids, pTR421-166, pTR421-179, pCDNA3.1-166 and pCDNA3.1-179, were constructed successfully and confirmed correct with restriction endonuclease analysis and nucleotide sequencing. The antigen expression was only detected in HepG2 cells transfected by pTR421-179 and in myocytes of the mice injected with pTR421-179. Neither in vitro nor in vivo antigen expression was detected with pTR421-166 although p166 was only 13 amino acids shorter than p179 at N terminus. Neither pCDNA3.1-166 nor pCDNA3.1-179 was expressed in vitro and in vivo.

CONCLUSION

Selection of the vectors and gene fragments is critical to HEV gene expression and HEV DNA vaccine.

The 41-amino-acid C-terminal region of the hepatitis E virus ORF3 protein interacts with bikunin, a kunitz-type serine protease inhibitor

Hepatitis E virus (HEV), a human plus-stranded RNA virus, contains three open reading frames (ORF). Of these, ORF1 encodes the viral nonstructural polyprotein, ORF2 encodes the major capsid protein, and ORF3 codes for a phosphoprotein of undefined function. Recently, using the yeast two-hybrid system to screen a human cDNA liver library, we have isolated and characterized AMBP (alpha1-microglobulin/bikunin precursor), which specifically interacts with the ORF3 protein of HEV. The ORF3 protein expedites the processing and secretion of alpha1-microglobulin. When checked individually for interaction, the second processed protein from AMBP, bikunin, strongly interacted with the full-length ORF3 protein. This protein-protein interaction has been validated by immunoprecipitation in both COS-1 and Huh7 cells and by His6 pull-down assays. In dual-labeling immunofluorescent staining, followed by fluorescence microscopy of transfected human liver cells, ORF3 colocalized with endogenously expressed bikunin. Finally, a 41-amino-acid C-terminal region of ORF3 has been found to be responsible for interacting with bikunin. The importance of this virus-host protein-protein interaction, with reference to the viral life cycle, has been discussed.

Analysis of hepatitis E virus neutralization sites using monoclonal antibodies directed against a virus capsid protein

The dimeric form of the recombinant peptide (E2), comprising amino acid 394-606 of the capsid protein of hepatitis E virus (HEV), is strongly recognized by HEV reactive human serum, and when used as a vaccine, it protects rhesus monkeys against experimental HEV infection. In this work, the relationship of E2 to HEV has been probed using three murine monoclonal antibodies, 8C11, 13D8 and 8H3, all of which react predominantly against the E2 dimer, and can effect immune capture of the virus as well. 8C11 and 8H3 were further found to neutralize HEV infectivity in animals. Cross-blocking patterns between these antibodies discerned two spatially separate antigenic domains, one identified by 8C11 and 13D8, and the other, by 8H3. Kinetic studies using BIAcore biosensor suggest that the epitope to which 8H3 is directed is partially masked, and thus has limited access by the native antibody. However, this is not the case with the smaller Fab. Access to the 8H3 epitope was enhanced by the binding of 8C11, and inhibited by the binding of 13D8 to a distal site on the peptide. Similar to the effects of binding 8H3 to E2, 8C11 was found to enhance immune capture by 8H3, while 13D8 was inhibitory. Moreover, 8C11 and 8H3 act synergistically to neutralize HEV infectivity. The parallel cross-reaction patterns that these antibodies exhibit against the peptide and the virus, respectively, implicate two interacting conformationally dependent neutralization sites on the HEV particle. These sites might cooperate in the adsorption and penetration of the HEV virus.

Replication of a recombinant hepatitis E virus genome tagged with reporter genes and generation of a short-term cell line producing viral RNA and proteins

Hepatitis E virus (HEV) replication has been demonstrated in HepG2 cells transfected with full-length in vitro transcripts of an infectious cDNA clone. This cDNA clone was modified to generate several subgenomic HEV replicons with fused reporter genes. In vitro-transcribed capped RNAs generated from these were transfected into HepG2 cells. Negative-strand RNA was detected, indicating the occurrence of replication. The replicon containing an in-frame fusion of HEV ORF2 with enhanced green fluorescent protein (EGFP) was positive for fluorescence, whereas no signal was observed when the replicase domain was deleted. An HEV ORF3-EGFP in-frame fusion did not yield fluorescence. Deletions introduced into ORF2 did not affect the replication competency of the viral RNA. To explore the possibility of using a reporter-gene assay to monitor the synthesis of plus- and minus-strand RNA, the EGFP gene fused to the encephalomyocarditis virus internal ribosome entry site (IRES) was inserted into partially deleted ORF2 of HEV, in both the sense [HEV-IRES-EGFP(+)] and antisense [HEV-IRES-EGFP(-)] orientations. HepG2 cells transfected with HEV-IRES-EGFP(+) and HEV-IRES-EGFP(-) vectors were positive for EGFP fluorescence. To quantify HEV replication, EGFP was replaced with Renilla luciferase (RLuc). HEV-IRES-RLuc(+) showed approximately 10-fold higher luminescence than HEV-IRES-RLuc(-). There was complete loss of activity when the helicase-replicase domain in HEV-IRES-RLuc(-) was deleted. A short-term HepG2 cell line containing the full-length viral genome in the pcDNA3 vector was established. Viral RNA and proteins (RdRp, pORF2 and pORF3) could be detected in the geneticin-resistant cells, even after the seventh passage. In the absence of a reliable cell-culture system to study HEV biology, these reporter replicons, as well as the cell line, bestow immense utility.

Mutational analysis of essential interactions involved in the assembly of hepatitis E virus capsid

The hepatitis E virus (HEV) capsid consists of a single structural protein, a portion of which is engaged in isosahedral contact to form a basal shell, and another portion in dimeric contact to form the homodimers protruding from the shell. Previous studies revealed that homodimers of the truncated HEV capsid proteins, E2 (amino acids 394-606) and p239 (amino acids 368-606), model dominant antigenic determinants of HEV. Immunization with these proteins protected rhesus monkeys against the virus, and three monoclonal antibodies against the homodimers could neutralize HEV infectivity and/or immune-capture of the virus. Furthermore, homodimers of p239 further interact to form particles of 23 nm diameter, rendering it an efficacious candidate vaccine. In light of this we postulate that the interactions involved in the formation of the homodimers and particles might be similar to those involved in assembly of the virus capsid. Presently, mutational analysis was carried out to identify these sites of interactions. The site of dimeric interactions was located to a cluster of six hydrophobic amino acids residues, Ala597, Val598, Ala599, Leu601, and Ala602; furthermore, the site involved in particle formation was located at amino acids 368-394. The possibility that these sites are also involved in assembly of the virus capsid is supported by the fact that they are located at two major and highly conserved hydrophobic regions of the HEV structural protein.

[Construction and expression of single-chain antibody of neutralizing monoclonal antibody 13D8 against hepatitis E virus]

AIM

To weaken the immunogenicity of the neutralizing monoclonal antibody (mAb) 13D8 against hepatitis E virus and express its scFv.

METHODS

The V(L) and V(H) genes were cloned by RT-PCR from hybridoma cells producing mouse mAb. And then V(H)-linker-V(L) fragment (scFv) was constructed and cloned into vector pTO-T7. The scFv protein was expressed in E.coli. The activity of expressed scFv was detected by ELISA and Western blot.

RESULTS

SDS-PAGE analysis showed that the scFv was highly expressed mostly in the form of inclusion body in E.coli, and the yield was up to 26.8% of the total bacteria protein. The results of indirect ELISA and Western blot showed that the expressed scFv could bind specifically to a recombinant protein in OFR2 region of HEV (NE2). The result of competitive ELISA demonstrated that the epitope recognized by the scFv was the same as that by mAb 13D8.

CONCLUSION

The scFv constructed from V(H) and V(L) genes of mAb 13D8 with immunological activity was successfully expressed.

The ORF3 protein of hepatitis E virus interacts with liver-specific alpha1-microglobulin and its precursor alpha1-microglobulin/bikunin precursor (AMBP) and expedites their export from the hepatocyte

Hepatitis E virus (HEV), a plus-stranded RNA virus contains three open reading frames. Of these, ORF1 encodes the viral nonstructural polyprotein; ORF2 encodes the major capsid protein and ORF3 codes for a phosphoprotein of undefined function. Using the yeast two-hybrid system to screen a human cDNA liver library we have isolated, an N-terminal deleted protein, alpha(1) -microglobulin/bikunin precursor (AMBP) that specifically interacts with the ORF3 protein of HEV. Independently cloned, full-length AMBP was obtained and tested positive for interaction with ORF3 using a variety of in vivo and in vitro techniques. AMBP, a liver-specific precursor protein codes for two different unrelated proteins alpha(1)-microglobulin (alpha(1)m) and bikunin. alpha(1) m individually interacted with ORF3. The above findings were validated by COS-1 cell immunoprecipitation, His(6) pull-down experiments, and co-localization experiments followed by fluorescence resonance energy transfer analysis. Human liver cells showing co-localization of ORF3 with endogenously expressing alpha(1) m showed a distinct disappearance of the protein from the Golgi compartment, suggesting that ORF3 enhances the secretion of alpha(1)m out of the hepatocyte. Using drugs to block the secretory pathway, we showed that alpha m was not degraded in the presence of ORF3. Finally, (1)pulse labeling of alpha(1)m showed that its secretion was expedited out of the liver cell at faster rates in the presence of the ORF3 protein. Hence, ORF3 has a direct biological role in enhancing alpha(1)m export from the hepatocyte.

The ORF2 protein of hepatitis E virus binds the 5' region of viral RNA

Hepatitis E virus (HEV) is a major human pathogen in much of the developing world. It is a plus-strand RNA virus with a 7.2-kb polyadenylated genome consisting of three open reading frames, ORF1, ORF2, and ORF3. Of these, ORF2 encodes the major capsid protein of the virus and ORF3 encodes a small protein of unknown function. Using the yeast three-hybrid system and traditional biochemical techniques, we have studied the RNA binding activities of ORF2 and ORF3, two proteins encoded in the 3' structural part of the genome. Since the genomic RNA from HEV has been postulated to contain secondary structures at the 5' and 3' ends, we used these two terminal regions, besides other regions within the genome, in this study. Experiments were designed to test for interactions between the genomic RNA fusion constructs with ORF2 and ORF3 hybrid proteins in a yeast cellular environment. We show here that the ORF2 protein contains RNA binding activity. The ORF2 protein specifically bound the 5' end of the HEV genome. Deletion analysis of this protein showed that its RNA binding activity was lost when deletions were made beyond the N-terminal 111 amino acids. Finer mapping of the interacting RNA revealed that a 76-nucleotide (nt) region at the 5' end of the HEV genome was responsible for binding the ORF2 protein. This 76-nt region included the 51-nt HEV sequence, conserved across alphaviruses. Our results support the requirement of this conserved sequence for interaction with ORF2 and also indicate an increase in the strength of the RNA-protein interaction when an additional 44 bases downstream of this 76-nt region were included. Secondary-structure predictions and the location of the ORF2 binding region within the HEV genome indicate that this interaction may play a role in viral encapsidation.

[Selection of a peptide mimic the neutralization epitope of hepatitis E virus with phage peptide display technology]

Hepatitis E is an acute hepatitis casused by hepatitis E virus (HEV) in developing countries, where it occurs as cases sporadic and in epidemics form. The causative agent, hepatitis E virus, is transmitted primarily by the fecal-oral route. HEV is icosahedron non-enveloped virus, and its genome is a single-stranded, positive-sense, 3'-polyadenylated RNA about 7.5 kb in length. It contains three open reading frames (ORFs). Of which ORF1 codes for a polyprotein of 1693 amino acids and contain domains homologous to a viral methyltransferase, a papainlike cysteine protease, an RNA helicasre, and an RNA-dependent RNA polymerase, besides the most hypervariable region of the HEV genome. And ORF3 codes for a 123-amino-acide-long polypeptide with unknown function. While the major viral capsid protein (pORF2, ORF2 codes) of 660 amino acid was showed to contain the protective epitope. The bacterially expressed polypeptide disignated as NE2 has been proved to be a protective antige. And the anti-NE2 monoclonal antibodies (mAb) was screend, two of these mAbs 8C11 and 8H3 were showed to be against separate conformational neutralization epitope of hepatitis E virus (HEV). And these two mAb were used to screen for binding peptides from a 7-peptides phage display library. After four rounds of panning, tweenty-one positive monoclonal phages (11 for 8C11, and 10 for 8H3) were selected and the inserted fragments were sequenced. The DNA sequence coding for the obtained dominant peptide 8C11 (N'-His-Pro-Thr-Leu-Leu-Arg-Ile-C', named 8C11A) and 8H3 (N'-Ser-Ile-Leu-Pro-Tyr-Pro-Tyr-C', named 8H3A) were then synthesized and cloned to insert between amino acid 78 to 83 of hepatitis B core antigen (HBcAg), then expressed in E. coli. The recombinant proteins aggregate into homodimer or polymer on SDS-PAGE, and could bind with mAb 8C11 and 8H3 in Western blotting. Respectively, the recombinant protein C8C11A showed to be dimer mainly, which can bind with mAb 8C11. The monomer and dimer of C8H3A are in the same amount on SDS-PAGE, but only the dimer could bind with mAb 8H3 on Western blotting. The renatured recombinant proteins were all showed to aggregate into virus like particles which were similar as HBcAg on transmission electron micrograph. The dominant peptide 8H3A (N'-Ser-Ile-Leu-Pro-Tyr-ProTyr-C') that selected out by mAb 8H3 was further chemo-synthesized, and its binding activity was confirmed by BIAcore biosensor. The result showed that this 7-peptide can bind with mAb 8H3 in a big Ka and Kd form, which means the binding is not stable. These results implicated that conformational dependent neutralization epitope could be partially modeled by short peptide, which provided a feasible route for subunit vaccine development.

Virus-specific mRNA capping enzyme encoded by hepatitis E virus

Hepatitis E virus (HEV), a positive-strand RNA virus, is an important causative agent of waterborne hepatitis. Expression of cDNA (encoding amino acids 1 to 979 of HEV nonstructural open reading frame 1) in insect cells resulted in synthesis of a 110-kDa protein (P110), a fraction of which was proteolytically processed to an 80-kDa protein. P110 was tightly bound to cytoplasmic membranes, from which it could be released by detergents. Immunopurified P110 catalyzed transfer of a methyl group from S-adenosylmethionine (AdoMet) to GTP and GDP to yield m(7)GTP or m(7)GDP. GMP, GpppG, and GpppA were poor substrates for the P110 methyltransferase. There was no evidence for further methylation of m(7)GTP when it was used as a substrate for the methyltransferase. P110 was also a guanylyltransferase, which formed a covalent complex, P110-m(7)GMP, in the presence of AdoMet and GTP, because radioactivity from both [alpha-(32)P]GTP and [(3)H-methyl]AdoMet was found in the covalent guanylate complex. Since both methyltransferase and guanylyltransferase reactions are strictly virus specific, they should offer optimal targets for development of antiviral drugs. Cap analogs such as m(7)GTP, m(7)GDP, et(2)m(7)GMP, and m(2)et(7)GMP inhibited the methyltransferase reaction. HEV P110 capping enzyme has similar properties to the methyltransferase and guanylyltransferase of alphavirus nsP1, tobacco mosaic virus P126, brome mosaic virus replicase protein 1a, and bamboo mosaic virus (a potexvirus) nonstructural protein, indicating there is a common evolutionary origin of these distantly related plant and animal virus families.

The 3' end of hepatitis E virus (HEV) genome binds specifically to the viral RNA-dependent RNA polymerase (RdRp)

Hepatitis E virus (HEV) is the major cause of acute epidemic and sporadic hepatitis in the developing world. It is a positive-strand RNA virus with a genome length of about 7.2 kb. The replication mechanism of this virus is virtually unexplored. Identification of the regulatory elements involved in initiation of replication may help in designing specific inhibitors for therapy. In the positive-stranded RNA viruses the initiation of replication requires interaction of the 3' end of genome with its RNA-dependent RNA polymerase (RdRp) and possibly host-derived cofactors for synthesis of the minus-strand replicative intermediate. Secondary structure prediction of the conserved 3' end of the infectious HEV genome was carried out to identify possible stem-loop structures necessary for RNA-protein interaction and the model was confirmed by structure probing experiments. Electrophoretic mobility-shift assays showed specific binding of purified and refolded recombinant HEV RdRp protein to the 3' end of its RNA genome containing the poly(A) stretch. Mutations at the 3' end, in which the stem-loop structures were partially or completely destroyed or recreated revealed that the two stem-loop structures SL1 and SL2 at the 3' end and the poly(A) stretch are necessary for this binding. The interacting nucleotides in such an interaction were further identified by generating footprints of the complex by Pb(II)-induced hydrolysis. This specific binding of viral RdRp to the 3' end of HEV RNA directs the synthesis of complementary-strand RNA and thus such a binding domain might assume the role of a possible cis-acting element as a potential site for the initiation of replication.

Self-association and mapping of the interaction domain of hepatitis E virus ORF3 protein

Hepatitis E virus (HEV) is a major human pathogen in the developing world. In the absence of an in vitro culture system, very little information on the basic biology of the virus exists. A small protein (approximately 13.5 kDa) of unknown function, pORF3, is encoded by the third open reading frame of HEV. The N-terminal region of pORF3 is associated with the cytoskeleton using one of its hydrophobic domains. The C-terminal half of pORF3 is rich in proline residues and contains a putative src homology 3 (SH3) binding domain and a mitogen-activated protein kinase phosphorylation site. In this study, we demonstrate that pORF3 can homodimerize in vivo, using the yeast two-hybrid system. We have isolated a 43-amino-acid interaction domain of pORF3 which is capable of self-association in vivo and in vitro. The overlap of the dimerization domain with the SH3 binding and phosphorylation domains suggests that pORF3 may have a dimerization-dependent regulatory role to play in the signal transduction pathway.

Cloning, sequencing, and expression of the hepatitis E virus (HEV) nonstructural open reading frame 1 (ORF1)

Hepatitis E virus (HEV) causes enterically transmitted epidemic and sporadic viral hepatitis affecting millions of people in the developing world. Different geographical isolates of HEV show a high degree of homology at the nucleotide and amino acid levels. The approximately 7.2 kb RNA genome has three open reading frames of which ORF1 is predicted to code for the viral nonstructural polyprotein. The expression, processing and properties of the nonstructural ORF1 polyprotein have not been reported so far. In this study, the complete HEV ORF1 was reconstructed from overlapping fragments amplified by polymerase chain reaction (PCR) of total RNA isolated from the bile fluid of a rhesus monkey experimentally infected with HEV isolate from an epidemic. The complete assembled ORF1 was sequenced using HEV specific primers. The ORF1 polyprotein was expressed in E. coli, in a cell free translation system and in HepG2 cells, and was characterized by western blotting and immunoprecipitation using acute phase patient serum as well as polyclonal antibodies raised against defined parts of the ORF1 polyprotein. The nonstructural polyprotein of HEV was expressed as a 186 kDa protein. No processing was observed into discrete units, either in-vitro based on a kinetic analysis, or in HepG2 cells based on immunoprecipitation.

Mutational analysis of glycosylation, membrane translocation, and cell surface expression of the hepatitis E virus ORF2 protein

Hepatitis E virus (HEV) is the etiological agent for viral hepatitis type E, which is a major problem in the developing world. Because HEV cannot be cultured in vitro, very little information exists on the mechanisms of HEV gene expression and genome replication. HEV is a positive-strand RNA virus with three potential open reading frames (ORFs), one of which (ORF2) is postulated to encode the major viral capsid protein (pORF2). We earlier showed (S. Jameel, M. Zafrullah, M. H. Ozdener, and S. K. Panda, J. Virol. 70:207-216, 1996) pORF2 to be a approximately 88-kDa glycoprotein, carrying N-linked glycans and a potential endoplasmic reticulum (ER)-directing signal at its N terminus. Treatment with the drugs brefeldin A and monensin suggest that the protein may accumulate within the ER. Based on mutational analysis, we demonstrate Asn-310 to be the major site of N-glycan addition. In COS-1 cell expression and in vitro translation experiments, we confirm the ER-translocating nature of the pORF2 N-terminal hydrophobic sequence and show that the protein is cotranslationally, but not posttranslationally, translocated across the ER membrane. Earlier, we had also demonstrated cell surface localization of a fraction of the COS-1 cell-expressed pORF2. Using glycosylation- and translocation-defective mutants of pORF2, we now show that while transit of pORF2 into the ER is necessary for its cell surface expression, glycosylation of the protein is not required for such localization. These results may offer clues to the mechanisms of gene expression and capsid assembly in HEV.

Only the non-glycosylated fraction of hepatitis E virus capsid (open reading frame 2) protein is stable in mammalian cells

Hepatitis E virus (HEV) is a non-enveloped, positive-strand RNA virus, with the genome encoding three open reading frames (ORFs) of which ORF 2 directs translation of the capsid protein, PORF2. Following pulse-labelling and cell fractionation of PORF2 expressed in mammalian cells using the Semliki Forest virus replicon, the capsid protein was detected as three major species of 78 (PORF2), 82 and 86 kDa, with P82 and P86 being N-glycosylated (gPORF2 and ggPORF2, respectively). Although gPORF2 and ggPORF2 species represented 79% of total PORF2 after 20 min metabolic labelling and were largely membrane-associated, the glycosylated PORF2 species were much less stable than non-glycosylated PORF2, which was present in the cytosol and represented the major product accumulated in the cell. In the absence of detectable surface expression or export of PORF2, this suggests that glycosylated ORF 2 proteins may not be intermediates in HEV capsid assembly.

A high hepatitis E virus (HEV) seroprevalence among unpaid blood donors and haemodialysis patients in Egypt

BACKGROUND/AIMS

The aim of this study was to determine the frequency of hepatitis E virus (HEV) infection among unpaid blood donors and haemodialysis patients in Egypt and to find out any possible relationship between HEV and HCV.

METHODS

Serum samples collected from 95 unpaid blood donors and 96 haemodialysis patients were screened for HEV and HCV antibodies by enzyme immunoassay techniques.

RESULTS

The prevalence of anti-HEV IgG was 45.2% (43/95) in blood donors and 39.6% (38/96) in haemodialysis patients. Anti-HEV IgG was found in 69.2% (18/26) and 28.6% (20/70) in haemodialysis patients positive and negative for HCV, respectively.

CONCLUSION

This study emphasizes that HEV is endemic in Egypt and tends to accumulate in certain groups showing evidence of hepatitis C virus infection as in haemodialysis patients suggesting either shared parenteral risk or increased sensitivity to HEV coinfection; that is to say a possibility of combined route of transmission for HEV.

The ORF3 protein of hepatitis E virus is a phosphoprotein that associates with the cytoskeleton

Hepatitis E virus (HEV) is a major human pathogen in the developing world. In the absence of an in vitro culture system, very little information exists on the basic biology of the virus. A small protein (approximately 13.5 kDa) of unknown function, pORF3, is encoded by the third open reading frame of HEV. We expressed pORF3 in transiently transfected COS-1 and Huh-7 cells and showed that it is a phosphoprotein which is modified at a serine residue(s). Deletion and site-directed mutants were created to establish Ser-80 as the phosphorylation site. This residue is present within a conserved primary sequence that showed consensus sites for phosphorylation by p34cdc2 kinase (cdc2K) and mitogen-activated protein kinase (MAPK). In vitro experiments with hexahistidine-tagged pORF3 expressed either in Escherichia coli or in COS-1 cells showed efficient phosphorylation with exogenously added MAPK. The pORF3 mutants also exhibited an in vitro phosphorylation profile with MAPK which was identical to that observed in vivo. In its primary sequence, pORF3 possesses two highly hydrophobic N-terminal domains. On subcellular fractionation, pORF3 was found to partition with the cytoskeletal fraction, and this association with the cytoskeleton was lost on deletion of hydrophobic domain I (amino acid residues 1 to 32). These results suggest that HEV pORF3 is a cytoskeleton-associated phosphoprotein and are discussed in terms of a possible function for pORF3 within the HEV replicative cycle.