The hepatitis E virus ORF3 protein regulates the expression of liver-specific genes by modulating localization of hepatocyte nuclear factor 4

Characteristics and Functions of HEV Proteins

Hepatitis E virus (HEV) is a non-enveloped virus containing a single-stranded, positive-sense RNA genome of 7.2 kb, which consists of a 5' non-coding region, three open reading frames (ORFs), and a 3' non-coding region. ORF1 is diverse between genotypes and encodes the nonstructural proteins, which include the enzymes needed for virus replication. In addition to its role in virus replication, the function of ORF1 is relevant to viral adaption in culture and may also relate to virus infection and HEV pathogenicity. ORF2 protein is the capsid protein, which is about 660 amino acids in length. It not only protects the integrity of the viral genome, but is also involved in many important physiological activities, such as virus assembly, infection, host interaction, and innate immune response. The main immune epitopes, especially neutralizing epitopes, are located on ORF2 protein, which is a candidate antigen for vaccine development. ORF3 protein is a phosphoprotein of 113 or 114 amino acids with a molecular weight of 13 kDa with multiple functions that can also induce strong immune reactivity. A novel ORF4 has been identified only in genotype 1 HEV and its translation promotes viral replication.

Development of 68Ga-Labeled Hepatitis E Virus Nanoparticles for Targeted Drug Delivery and Diagnostics with PET

Targeted delivery of diagnostics and therapeutics offers essential advantages over nontargeted systemic delivery. These include the reduction of toxicity, the ability to reach sites beyond biological barriers, and the delivery of higher cargo concentrations to diseased sites. Virus-like particles (VLPs) can efficiently be used for targeted delivery purposes. VLPs are derived from the coat proteins of viral capsids. They are self-assembled, biodegradable, and homogeneously distributed. In this study, hepatitis E virus (HEV) VLP derivatives, hepatitis E virus nanoparticles (HEVNPs), were radiolabeled with gallium-68, and consequently, the biodistribution of the labeled [⁶⁸Ga]Ga-DOTA-HEVNPs was studied in mice. The results indicated that [⁶⁸Ga]Ga-DOTA-HEVNPs can be considered as promising theranostic nanocarriers, especially for hepatocyte-targeting therapies.

Uncoupling protein 2 and aldolase B impact insulin release by modulating mitochondrial function and Ca2+ release from the ER

Uncoupling protein 2 (UCP2), a mitochondrial protein, is known to be upregulated in pancreatic islets of patients with type 2 diabetes (T2DM); however, the pathological significance of this increase in UCP2 expression is unclear. In this study, we highlight the molecular link between the increase in UCP2 expression in β-cells and β-cell failure by using genetically engineered mice and human islets. β-cell-specific UCP2-overexpressing transgenic mice (βUCP2Tg) exhibited glucose intolerance and a reduction in insulin secretion. Decreased mitochondrial function and increased aldolase B (AldB) expression through oxidative-stress-mediated pathway were observed in βUCP2Tg islets. AldB, a glycolytic enzyme, was associated with reduced insulin secretion via mitochondrial dysfunction and impaired calcium release from the endoplasmic reticulum (ER). Taken together, our findings provide a new mechanism of β-cell dysfunction by UCP2 and AldB. Targeting the UCP2/AldB axis is a promising approach for the recovery of β-cell function.

Long-Term Dietary Taurine Lowers Plasma Levels of Cholesterol and Bile Acids

Cholesterol is an essential lipid in vertebrates, but excess blood cholesterol promotes atherosclerosis. In the liver, cholesterol is metabolized to bile acids by cytochrome P450, family 7, subfamily a, polypeptide 1 (CYP7A1), the transcription of which is negatively regulated by the ERK pathway. Fibroblast growth factor 21 (FGF21), a hepatokine, induces ERK phosphorylation and suppresses Cyp7a1 transcription. Taurine, a sulfur-containing amino acid, reportedly promotes cholesterol metabolism and lowers blood and hepatic cholesterol levels. However, the influence of long-term feeding of taurine on cholesterol levels and metabolism remains unclear. Here, to evaluate the more chronic effects of taurine on cholesterol levels, we analyzed mice fed a taurine-rich diet for 14-16 weeks. Long-term feeding of taurine lowered plasma cholesterol and bile acids without significantly changing other metabolic parameters, but hardly affected these levels in the liver. Moreover, taurine upregulated Cyp7a1 levels, while downregulated phosphorylated ERK and Fgf21 levels in the liver. Likewise, taurine-treated Hepa1-6 cells, a mouse hepatocyte line, exhibited downregulated Fgf21 levels and upregulated promoter activity of Cyp7a1. These results indicate that taurine promotes cholesterol metabolism by suppressing the FGF21/ERK pathway followed by upregulating Cyp7a1 expression. Collectively, this study shows that long-term feeding of taurine lowers both plasma cholesterol and bile acids, reinforcing that taurine effectively prevents hypercholesterolemia.

Structural aspects of hepatitis E virus

Hepatitis E virus (HEV) is a leading cause of acute hepatitis worldwide. Hepatitis E is an enterically transmitted zoonotic disease that causes large waterborne epidemic outbreaks in developing countries and has become an increasing public-health concern in industrialized countries. In this setting, the infection is usually acute and self-limiting in immunocompetent individuals, although chronic cases in immunocompromised patients have been reported, frequently associated with several extrahepatic manifestations. Moreover, extrahepatic manifestations have also been reported in immunocompetent individuals with acute HEV infection. HEV belongs to the alphavirus-like supergroup III of single-stranded positive-sense RNA viruses, and its genome contains three partially overlapping open reading frames (ORFs). ORF1 encodes a nonstructural protein with eight domains, most of which have not been extensively characterized: methyltransferase, Y domain, papain-like cysteine protease, hypervariable region, proline-rich region, X domain, Hel domain, and RNA-dependent RNA polymerase. ORF2 and ORF3 encode the capsid protein and a multifunctional protein believed to be involved in virion release, respectively. The novel ORF4 is only expressed in HEV genotype 1 under endoplasmic reticulum stress conditions, and its exact function has not yet been elucidated. Despite important advances in recent years, the biological and molecular processes underlying HEV replication remain poorly understood, primarily due to a lack of detailed information about the functions of the viral proteins and the mechanisms involved in host-pathogen interactions. This review summarizes the current knowledge concerning HEV proteins and their biological properties, providing updated detailed data describing their function and focusing in detail on their structural characteristics. Furthermore, we review some unclear aspects of the four proteins encoded by the ORFs, highlighting the current key information gaps and discussing potential novel experimental strategies for shedding light on those issues.

Akt plays differential roles during the life cycles of acute and persistent murine norovirus strains in macrophages

Akt (Protein kinase B) is a key signaling protein in eukaryotic cells that controls many cellular processes such as glucose metabolism and cell proliferation for survival. As obligate intracellular pathogens, viruses modulate host cellular processes, including Akt signaling, for optimal replication. The mechanisms by which viruses modulate Akt and the resulting effects on the infectious cycle differ widely depending on the virus. In this study, we explored the effect of Akt serine 473 phosphorylation (p-Akt) during murine norovirus (MNV) infection. p-Akt increased during infection of murine macrophages with acute MNV-1 and persistent CR3 and CR6 strains. Inhibition of Akt with MK2206, an inhibitor of all three isoforms of Akt (Akt1/2/3), reduced infectious virus progeny of all three virus strains. This reduction was due to decreased viral genome replication (CR3), defective virus assembly (MNV-1), or diminished cellular egress (CR3 and CR6) in a virus strain-dependent manner. Collectively, our data demonstrate that Akt activation increases in macrophages during the later stages of the MNV infectious cycle, which may enhance viral infection in unique ways for different virus strains. The data, for the first time, indicate a role for Akt signaling in viral assembly and highlight additional phenotypic differences between closely related MNV strains. Importance Human noroviruses (HNoV) are a leading cause of viral gastroenteritis, resulting in high annual economic burden and morbidity; yet there are no small animal models supporting productive HNoV infection, or robust culture systems producing cell culture-derived virus stocks. As a result, research on drug discovery and vaccine development against norovirus infection has been challenging, and no targeted antivirals or vaccines against HNoV are approved. On the other hand, murine norovirus (MNV) replicates to high titers in cell culture and is a convenient and widespread model in norovirus research. Our data demonstrate the importance of Akt signaling during the late stage of the MNV life cycle. Notably, the effect of Akt signaling on genome replication, virus assembly and cellular egress is virus strain specific, highlighting the diversity of biological phenotypes despite small genetic variability among norovirus strains. This study is the first to demonstrate a role for Akt in viral assembly.

Cellular Organelles Involved in Hepatitis E Virus Infection

Hepatitis E virus (HEV), a major cause of acute hepatitis worldwide, infects approximately 20 million individuals annually. HEV can infect a wide range of mammalian and avian species, and cause frequent zoonotic spillover, increasingly raising public health concerns. To establish a successful infection, HEV needs to usurp host machineries to accomplish its life cycle from initial attachment to egress. However, relatively little is known about the HEV life cycle, especially the functional role(s) of cellular organelles and their associated proteins at different stages of HEV infection. Here, we summarize current knowledge regarding the relation of HEV with the different cell organelles during HEV infection. Furthermore, we discuss the underlying mechanisms by which HEV infection is precisely regulated in infected cells and the modification of host cell organelles and their associated proteins upon HEV infection.

Lipid overload impairs hepatic VLDL secretion via oxidative stress-mediated PKCδ-HNF4α-MTP pathway in large yellow croaker (Larimichthys crocea)

Lipid overload-induced hepatic steatosis is a major public health problem worldwide. However, the potential molecular mechanism is not completely understood. Herein, we found that high-fat diet (HFD) or oleic acid (OA) treatment induced oxidative stress which prevented the entry of hepatocyte nuclear factor 4 alpha (HNF4α) into the nucleus by activating protein kinase C delta (PKCδ) in vivo and in vitro in large yellow croaker (Larimichthys crocea). This reduced the level of microsomal triglyceride transfer protein (MTP) transcription, resulting in the impaired secretion of very-low-density lipoprotein (VLDL) and the abnormal accumulation of triglyceride (TG) in hepatocytes. Meanwhile, the detrimental effects induced by lipid overload could be partly alleviated by pretreating hepatocytes with Go6983 (PKCδ inhibitor) or N-acetylcysteine (NAC, reactive oxygen species (ROS) scavenger). In conclusion, for the first time, we revealed that lipid overload impaired hepatic VLDL secretion via oxidative stress-mediated PKCδ-HNF4α-MTP pathway in fish. This study may provide critical insights into potential intervention strategies against lipid overload-induced hepatic steatosis of fish and human beings.

Progesterone-Mediated Enhancement of Hepatitis E Virus Replication in Human Liver Cells

Progesterone is crucial for the maintenance of pregnancy. During pregnancy hepatitis E virus (HEV) infection is associated with increased fulminant hepatic failure and mortality rates. In this study, we determined whether progesterone modulates HEV replication and HEV-induced innate cytokine response in Huh7-S10-3 human liver cells. We first demonstrated that Huh7-S10-3 liver cells expressed SH3-domain-containing progesterone receptor membrane component (PGRMC)1/2 receptors involved in the progesterone nonclassical signaling pathway, while the classical progesterone receptor isoforms progesterone receptor-A and -B protein levels were undetectable. We showed that the genotype 3 HEV (strain P6) induced mRNA expression of type III interferon (IFN-λ1), but not other innate cytokines in Huh7-S10-3 cells. Pretreatment with progesterone at concentrations of 80 nM, 160 nM, or 480 nM, which are the physiological concentrations typically seen in the first- to third-trimester during pregnancy, significantly increased HEV replication in Huh7-S10-3 cells. However, pretreatment of cells with progesterone (80 nM) did not affect the level of HEV-induced IFN-λ1 mRNA expression. We further showed that loss of PGRMC1/2 receptors by small interfering RNA (siRNA) knockdown leads to an increase in HEV-induced IFN-λ1 expression levels at early time points via the extracellular signal-regulated kinase pathway and thus resulted in a reduced level of HEV replication. Collectively, the results indicated that progesterone-mediated modulation of HEV replication in human liver cells is plausibly through SH3-domain containing proteins such as PGRMC1/2, but not likely through immunomodulation of HEV-induced interferon response in liver cells. The results have important implications in understanding the underlying mechanisms of high mortality and fulminant hepatitis in HEV-infected pregnant women.

Open reading frame 3 protein of hepatitis E virus: Multi-function protein with endless potential

Hepatitis E virus (HEV), a fecal-orally transmitted foodborne viral pathogen, causes acute hepatitis in humans and is responsible for hepatitis E outbreaks worldwide. Since the identification of HEV as a zoonotic agent, this virus has been isolated from a variety of hosts with an ever-expanding host range. HEV-open reading frame (ORF) 3, the smallest ORF in HEV genomes, initially had been perceived as an unremarkable HEV accessory protein. However, as novel HEV-ORF3 function has been discovered that is related to the existence of a putative third virion structural form, referred to as “quasi-enveloped” HEV particles, HEV is challenging the conventional virion structure-based classification scheme, which assigns all viruses to two groups, “enveloped” or “non-enveloped”. In this review, we systematically describe recent progress that has identified multiple pathogenic roles of HEV-ORF3, including roles in HEV virion release, biogenesis of quasi-enveloped virus, regulation of the host innate immune response, and interference with host signaling pathways. In addition, implications of HEV-ORF3-associated quasi-enveloped virions are discussed to guide future development of improved vaccines against zoonotic HEV infection.

Review of Hepatitis E Virus in Rats: Evident Risk of Species Orthohepevirus C to Human Zoonotic Infection and Disease

Hepatitis E virus (HEV) (family Hepeviridae) is one of the most common human pathogens, causing acute hepatitis and an increasingly recognized etiological agent in chronic hepatitis and extrahepatic manifestations. Recent studies reported that not only are the classical members of the species Orthohepevirus A (HEV-A) pathogenic to humans but a genetically highly divergent rat origin hepevirus (HEV-C1) in species Orthohepevirus C (HEV-C) is also able to cause zoonotic infection and symptomatic disease (hepatitis) in humans. This review summarizes the current knowledge of hepeviruses in rodents with special focus of rat origin HEV-C1. Cross-species transmission and genetic diversity of HEV-C1 and confirmation of HEV-C1 infections and symptomatic disease in humans re-opened the long-lasting and full of surprises story of HEV in human. This novel knowledge has a consequence to the epidemiology, clinical aspects, laboratory diagnosis, and prevention of HEV infection in humans.

Role of hepatocyte nuclear factor 4-alpha in gastrointestinal and liver diseases

Hepatocyte nuclear factor 4-alpha (HNF4α) is a highly conserved member of nuclear receptor superfamily of ligand-dependent transcription factors that is expressed in liver and gastrointestinal organs (pancreas, stomach, and intestine). In liver, HNF4α is best known for its role as a master regulator of liver-specific gene expression and essential for adult and fetal liver function. Dysregulation of HNF4α expression has been associated with many human diseases such as ulcerative colitis, colon cancer, maturity-onset diabetes of the young, liver cirrhosis, and hepatocellular carcinoma. However, the precise role of HNF4α in the etiology of these human pathogenesis is not well understood. Limited information is known about the role of HNF4α isoforms in liver and gastrointestinal disease progression. There is, therefore, a critical need to know how disruption of the expression of these isoforms may impact on disease progression and phenotypes. In this review, we will update our current understanding on the role of HNF4α in human liver and gastrointestinal diseases. We further provide additional information on possible use of HNF4α as a target for potential therapeutic approaches.

Steroid receptor coactivator 3 inhibits hepatitis B virus gene expression through activating Akt signaling to prevent HNF4α nuclear translocation

Background

Chronic hepatitis B virus (HBV) infection is one of the most serious global public health problems. The role of steroid receptor coactivator 3 (SRC-3) in HBV biosynthesis is unknown. The aim of this study is to investigate the function of SRC-3 in regulating HBV biosynthesis both in vitro and in vivo and to identify the underlying mechanism.

Results

In this study, we found that knockdown of SRC-3 could increase the levels of HBV mRNA and HBV proteins HBsAg and HBeAg in human liver cancer cell line HepG2 transfected with pHBV1.3 plasmids. In contrast, enforced expression of SRC-3 in SRC-3-knockdown HepG2 cells reduced the levels of HBV mRNA and HBV proteins HBsAg and HBeAg. Knockdown of SRC-3 dampened the Akt signaling, which has been shown to play a negative role in HBV transcription. Ectopic expression of constitutively activated Akt impaired the enhancement of HBV transcription by SRC-3 knockdown, indicating that SRC-3 inhibits HBV transcription by enhancing Akt signaling. Both SRC-3 and constitutively activated Akt could inhibit hepatocyte nuclear factor 4α (HNF4α)-mediated upregulation of HBV core promoter activity by preventing HNF4α nuclear translocation. Consistent with the in vitro results, in an in vivo chronic HBV replication mouse model developed by hydrodynamic injection of pHBV1.3 plasmids into mouse tail vein, enforced expression of SRC-3 in mouse liver reduced the levels of HBV mRNA in the liver and HBV antigens in serum, whereas knockout of SRC-3 in mouse increased the levels of HBV mRNA in the liver and HBV antigens in the serum.

Conclusion

Our study suggests that SRC-3 inhibits HBV gene expression by activating Akt signaling to prevent HNF4α nuclear translocation.

Electronic supplementary material

The online version of this article (10.1186/s13578-019-0328-5) contains supplementary material, which is available to authorized users.

HEV ORF3 downregulatesCD14 and CD64 to impair macrophages phagocytosis through inhibiting JAK/STAT pathway

Hepatitis E virus (HEV) could induce chronic hepatitis and liver failure with high mortality through unknown mechanisms. The previous study showed that the HEV open reading frames 3 (ORF3) could inhibit macrophages inflammatory response. Impaired macrophages phagocytosis was also found in patients infected with HEV and its nucleic acids could be detected in macrophages. To elucidate the role of HEV ORF3 on phagocytosis, the phagocytosis activation was measured by phagocytosis test, flow cytometry, and phalloidin staining. Meanwhile, the expression of key phagocytic receptors and the activation of transduction pathway were investigated by using reverse transcription real-time quantitative polymerase chain reaction (RT-qPCR) and Western blot analysis. Results of phagocytosis test showed that the HEV ORF3 could significantly impair the absorption capacity of latex beads. Furthermore, results of RT-qPCR and Western blot analysis showed that the expression of CD14 and CD64 decreased. Afterward, the present study showed that the activation of Janus kinase-signal transducer and activator of transcription (JAK/STAT) signaling pathway was inhibited by HEV ORF3 and downregulation of CD14 and CD64 could be reversed by interferon γ, one activator of the JAK1/STAT1 signaling pathway. In conclusion, HEV ORF3 could significantly impair the phagocytosis of macrophage by downregulating expression of CD14 and CD64, which may function by inhibiting the activation of the JAK1/STAT1 signaling pathway.

HEV ORF3 downregulates TLR7 to inhibit the generation of type I interferon via impairment of multiple signaling pathways

Hepatitis E is the most common type of acute hepatitis prevalent worldwide. The open reading frame 3 protein of HEV (HEV ORF3) is proposed to create a favorable environment for viral replication and pathogenesis. However, the mechanisms by which HEV overcomes the effects of host immunity, particularly the role of ORF3, remain to be established. Expression of IFNα and IFNβ in supernatant and cell samples was examined via ELISA and quantitative RT-PCR. The protein levels of specific signaling factors in cells overexpressing HEV ORF3 were examined via western blot. Analyses of cells transfected with vectors expressing ORF3 demonstrated that HEV ORF3 significantly impairs the generation of endogenous type I interferon through downregulating TLR3 and TLR7 as well as their corresponding downstream signaling pathways. Moreover, inhibition of NFκB, JAK/STAT and JNK/MAPK signaling pathways contributed significantly to suppression of increased levels of TLR7. Levels of p-P65, p-STAT1 and p-JNK were markedly impaired in ORF3-expressing cells, even upon treatment with the respective agonists. HEV ORF3 inhibits the production of endogenous type I interferon through downregulation of TLR3 and TLR7. Furthermore, suppression of TLR7 is achieved through impairment of multiple signaling pathways, including NFκB, JAK/STAT and JNK/MAPK.

Inhibition of Hepatitis E Virus Spread by the Natural Compound Silvestrol

Every year, there are about 20 Mio hepatitis E virus (HEV) infections and 60,000 deaths that are associated with HEV worldwide. At the present, there exists no specific therapy for HEV. The natural compound silvestrol has a potent antiviral effect against the (-)-strand RNA-virus Ebola virus, and also against the (+)-strand RNA viruses Corona-, Picorna-, and Zika virus. The inhibitory effect on virus spread is due to an inhibition of the DEAD-box RNA helicase eIF4A, which is required to unwind structured 5'-untranslated regions (UTRs). This leads to an impaired translation of viral RNA. The HEV (+)-strand RNA genome contains a 5'-capped, short 5'-UTR. This study aims to analyze the impact of silvestrol on the HEV life cycle. Persistently infected A549 cells were instrumental. This study identifies silvestrol as a potent inhibitor of the release of HEV infectious viral particles. This goes along with a strongly reduced HEV capsid protein translation, retention of viral RNA inside the cytoplasm, and without major cytotoxic effects. Interestingly, in parallel silvestrol affects the activity of the antiviral major vault protein (MVP) by translocation from the cytoplasm to the perinuclear membrane. These data further characterize the complex antiviral activity of silvestrol and show silvestrol's broad spectrum of function, since HEV is a virus without complex secondary structures in its genome, but it is still affected.

Hepatitis E virus: advances and challenges

At least 20 million hepatitis E virus (HEV) infections occur annually, with >3 million symptomatic cases and ∼60,000 fatalities. Hepatitis E is generally self-limiting, with a case fatality rate of 0.5-3% in young adults. However, it can cause up to 30% mortality in pregnant women in the third trimester and can become chronic in immunocompromised individuals, such as those receiving organ transplants or chemotherapy and individuals with HIV infection. HEV is transmitted primarily via the faecal-oral route and was previously thought to be a public health concern only in developing countries. It is now also being frequently reported in industrialized countries, where it is transmitted zoonotically or through organ transplantation or blood transfusions. Although a vaccine for HEV has been developed, it is only licensed in China. Additionally, no effective, non-teratogenic and specific treatments against HEV infections are currently available. Although progress has been made in characterizing HEV biology, the scarcity of adequate experimental platforms has hampered further research. In this Review, we focus on providing an update on the HEV life cycle. We will further discuss existing cell culture and animal models and highlight platforms that have proven to be useful and/or are emerging for studying other hepatotropic (viral) pathogens.

Molecular Biology and Infection of Hepatitis E Virus

Hepatitis E virus (HEV) is a viral pathogen transmitted primarily via fecal-oral route. In humans, HEV mainly causes acute hepatitis and is responsible for large outbreaks of hepatitis across the world. The case fatality rate of HEV-induced hepatitis ranges from 0.5 to 3% in young adults and up to 30% in infected pregnant women. HEV strains infecting humans are classified into four genotypes. HEV strains from genotypes 3 and 4 are zoonotic, whereas those from genotypes 1 and 2 have no known animal reservoirs. Recently, notable progress has been accomplished for better understanding of HEV biology and infection, such as chronic HEV infection, in vitro cell culture system, quasi-enveloped HEV virions, functions of the HEV proteins, mechanism of HEV antagonizing host innate immunity, HEV pathogenesis and vaccine development. However, further investigation on the cross-species HEV infection, host tropism, vaccine efficacy, and HEV-specific antiviral strategy is still needed. This review mainly focuses on molecular biology and infection of HEV and offers perspective new insight of this enigmatic virus.

Distinct Entry Mechanisms for Nonenveloped and Quasi-Enveloped Hepatitis E Viruses

The hepatitis E virus (HEV) sheds into feces as nonenveloped virions but circulates in the blood in a membrane-associated, quasi-enveloped form (eHEV). Since the eHEV virions lack viral proteins on the surface, we investigated the entry mechanism for eHEV. We found that compared to nonenveloped HEV virions, eHEV attachment to the cell was much less efficient, requiring a longer inoculation time to reach its maximal infectivity. A survey of cellular internalization pathways identified clathrin-mediated endocytosis as the main route for eHEV entry. Unlike nonenveloped HEV virions, eHEV entry requires Rab5 and Rab7, small GTPases involved in endosomal trafficking, and blocking endosomal acidification abrogated eHEV infectivity. However, low pH alone was not sufficient for eHEV uncoating, suggesting that additional steps are required for entry. Supporting this concept, eHEV infectivity was substantially reduced in cells depleted of Niemann-Pick disease type C1, a lysosomal protein required for cholesterol extraction from lipid, or in cells treated with an inhibitor of lysosomal acid lipase. These data support a model in which the quasi-envelope is degraded within the lysosome prior to virus uncoating, a potentially novel mechanism for virus entry.

IMPORTANCE

The recent discovery of quasi-enveloped viruses has shifted the paradigm of virus-host interactions. The impact of quasi-envelopment in the virus life cycle and pathogenesis is largely unknown. HEV is a highly relevant model to study these questions. HEV circulates as quasi-enveloped virions in the blood that are hidden from neutralizing antibodies. eHEV particles most likely are responsible for the cell-to-cell spread of the virus. Given the increasing concerns about persistent HEV infection and its potential for transmission via the blood supply, understanding how eHEV infects cells is important for understanding its pathogenesis and developing therapies. Our data provide evidence that eHEV uses a potentially novel mechanism for cellular entry. Several steps critical to eHEV entry were identified and may provide a basis for developing treatments for hepatitis E. Because quasi-enveloped viruses resemble exosomes, these data also may provide insights into the exosome-mediated intercellular communications.

A Novel Astrovirus-Like RNA Virus Detected in Human Stool

Several novel clades of astroviruses have recently been identified in human faecal samples. Here, we describe a novel astrovirus-like RNA virus detected in human stools, which we have tentatively named bastrovirus. The genome of this novel virus consists of 6,300 nucleotides organized in three open reading frames. Several sequence divergent strains were detected sharing 67–93 per cent nucleotide identity. Bastrovirus encodes a putative structural protein that is homologous to the capsid protein found in members of the Astroviridae family (45% amino acid identity). The virus also encodes a putative non-structural protein that is genetically distant from astroviruses but shares some homology to the non-structural protein encoded by members of the Hepeviridae family (28% amino acid identity). This novel bastrovirus is present in 8.7 per cent (35/400) of faecal samples collected from 300 HIV-1-positive and 100 HIV-1-negative individuals suggesting common occurrence of the virus. However, whether the source of the virus is infected human cells or other, for example, dietary, remains to be determined.

Characteristics and Functions of HEV Proteins

Hepatitis E virus (HEV) is a non-enveloped virus containing a single-stranded, positive-sense RNA genome of 7.2 kb, which consists of a 5' noncoding region, three open reading frames (ORFs), and a 3' noncoding region. ORF1 is diverse between genotypes and encodes the nonstructural proteins, which include the enzymes needed for virus replication. In addition to its role in virus replication, the function of ORF1 is relevant to viral adaption in cultured cells and may also relate to virus infection and HEV pathogenicity. ORF2 protein is the capsid protein, which is about 660 amino acids in length. It not only protects the integrity of the viral genome but is also involved in many important physiological activities, such as virus assembly, infection, and host interaction. The main immune epitopes, especially neutralizing epitopes, are located on ORF2 protein, which is a candidate antigen for vaccine development. ORF3 protein is a phosphoprotein of 113 or 114 amino acids with a molecular weight of 13 kDa with multiple functions that can also induce strong immune reactivity.

Hepatitis E virus enters liver cells through a dynamin-2, clathrin and membrane cholesterol-dependent pathway

The hepatitis E virus (HEV) causes large outbreaks and sporadic cases of acute viral hepatitis in developing countries. In the developed world, HEV occurrence has increased as a result of zoonotic transmission from swine. The cellular aspects of HEV infection, especially the determinants of entry, are poorly understood. In the absence of a robust in vitro culture system for HEV, it is not possible to produce high titre infectious virus that can be labeled for tracking its internalization. We have therefore used an Escherichia coli expressed HEV-like particle (HEV-LP) to study HEV entry. Following internalization, the HEV-LP initially trafficks to Rab5-positive compartments en route to acidic lysosomal compartments where it is degraded. Using pharmacological inhibitors, dominant negative and constitutively active mutants, and siRNA-mediated perturbations, we show that HEV entry requires dynamin-2, clathrin, membrane cholesterol and actin, but is independent of factors associated with macropinocytosis. The HEV-LP results were further validated through infection of liver cells with virus from the stool of an infected patient. The comparative analysis also showed involvement of the phosphatidylinositol-3-kinase/Akt pathway in an early post-entry step of viral replication. This report provides a detailed description of endocytic processes associated with HEV infection.

Thyroid-Stimulating Hormone Increases HNF-4α Phosphorylation via cAMP/PKA Pathway in the Liver

Hepatocyte nuclear factor-4 alpha (HNF-4α) is an orphan nuclear receptor with important roles in hepatic metabolism. Protein phosphorylation plays a functional role in its nuclear localization, DNA binding, and transactivation. Thyroid-stimulating hormone (TSH) is a hormone produced by the anterior pituitary gland, whose direct effect on the metabolic pathway has been observed. Our previous study demonstrated that TSH significantly decreases hepatic nuclear HNF-4α expression. However, whether TSH can influence HNF-4α phosphorylation is unclear. Here, we discovered that TSH can increase HNF-4α phosphorylation and modulate its subcellularlocalization. When HepG2 cells were treated with TSH, the phosphorylation of HNF-4α increased and its nuclear localization was interrupted. Cytoplasmic HNF-4α increased, while nuclear HNF-4α decreased. When the cAMP/PKA pathway was inhibited by the PKA inhibitor H89 and the adenylate cyclase (AC) inhibitor SQ22536, the TSH-mediated phosphorylation of HNF-4α was disrupted. When Tshr was silenced in mice, the phosphorylation of HNF-4α decreased, and cytoplasmic HNF-4α decreased while nuclear HNF-4α increased. In conclusion, our study revealed a novel mechanism by which TSH regulated the hepatic HNF-4α subcellular localization, suggesting the possibility that one of the effects of TSH is to reduce the expression of HNF-4α target genes.

Molecular detection of hepatitis E virus in sheep from southern Xinjiang, China

Hepatitis E virus (HEV) is a causative agent of infectious hepatitis in animals and humans both in developing and developed countries. Here, we collected 500 sheep sera and 75 raw sheep liver samples from a slaughterhouse in the southern part of the Xinjiang region, China, along with 26 sera of butchers from the same slaughterhouse. All serum samples were tested for anti-HEV antibody by enzyme-linked immunosorbent assay. Both serum and liver samples were evaluated for the presence of HEV RNA by nested polymerase chain reaction targeting partial nucleotide sequences of open reading frame 2 (ORF2). The results indicate that sheep seroprevalence was 35.20 % (176/500) and that four of the 75 (5.3 %) sheep livers showed detectable amounts of HEV RNA. The seroprevalence of the butchers was 57.7 % (15/26). The four amplicons shared 97.8-100 % nucleotide sequence identity and had pairwise sequence identities of 81.6-85.3 %, 84.2-85.3 %, 82.1-85.3 % and 84.7-97.9 % with the corresponding regions of genotypes 1, 2, 3 and 4 of HEV, respectively. A phylogenetic tree was constructed based on alignments of an amplified 186-bp ORF2 sequence and corresponding reference strains. The analysis showed that the four sheep strains detected in our study formed a lineage within a genotype 4 cluster that contains hb-3, bjsw1, T1, swCH189 and swCH25, all of which belong to genotype 4, subtype 4d. The results indicated a high level of seroconversion in sheep and suggested that sheep liver may be a source of foodborne HEV infection in humans.

New insights into hepatitis E virus virus–host interaction: interplay with host interferon induction

ABSTRACT 

Hepatitis E virus (HEV) is a fecal–oral-transmitted viral pathogen causing several large outbreaks of hepatitis across the world. HEV-mediated hepatitis has a mortality rate from 0.5 to 3% in young adults but is up to 30% in pregnant women. HEV is also a zoonotic pathogen as it has been isolated from different mammalian hosts including the pig, rabbit, rat, ferret, bat and deer. As an invading pathogen, HEV needs to overcome the host innate immune response to establish infection. Notable progress has been recently made in HEV mechanisms of antagonizing the host innate immune responses. In this review, we elaborate on the HEV interplay with host interferon induction while briefly summarizing the major aspects of HEV biology and host interferon induction to assist the understanding of the virus–host interaction.

Bridging cell surface receptor with nuclear receptors in control of bile acid homeostasis

Bile acids (BAs) are traditionally considered as "physiological detergents" for emulsifying hydrophobic lipids and vitamins due to their amphipathic nature. But accumulating clinical and experimental evidence shows an association between disrupted BA homeostasis and various liver disease conditions including hepatitis infection, diabetes and cancer. Consequently, BA homeostasis regulation has become a field of heavy interest and investigation. After identification of the Farnesoid X Receptor (FXR) as an endogenous receptor for BAs, several nuclear receptors (SHP, HNF4α, and LRH-1) were also found to be important in regulation of BA homeostasis. Some post-translational modifications of these nuclear receptors have been demonstrated, but their physiological significance is still elusive. Gut secrets FGF15/19 that can activate hepatic FGFR4 and its downstream signaling cascade, leading to repressed hepatic BA biosynthesis. However, the link between the activated kinases and these nuclear receptors is not fully elucidated. Here, we review the recent literature on signal crosstalk in BA homeostasis.

The hepatitis B virus (HBV) HBx protein activates AKT to simultaneously regulate HBV replication and hepatocyte survival

Chronic infection with hepatitis B virus (HBV) is a risk factor for developing liver diseases such as hepatocellular carcinoma (HCC). HBx is a multifunctional protein encoded by the HBV genome; HBx stimulates HBV replication and is thought to play an important role in the development of HBV-associated HCC. HBx can activate the phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway in some cell lines; however, whether HBx regulates PI3K/AKT signaling in normal hepatocytes has not been evaluated. In studies described here, we assessed HBx activation of PI3K/AKT signaling in an ex vivo model of cultured primary hepatocytes and determined how this HBx activity affects HBV replication. We report that HBx activates AKT in primary hepatocytes and that the activation of AKT decreases HBV replication and HBV mRNA and core protein levels. We show that the transcription factor hepatocyte nuclear factor 4α (HNF4α) is a target of HBx-regulated AKT, and we link HNF4α to HBx-regulated AKT modulation of HBV transcription and replication. Although we and others have shown that HBx stimulates and is likely required for HBV replication, we now report that HBx also activates signals that can diminish the overall level of HBV replication. While this may seem counterintuitive, we show that an important effect of HBx activation of AKT is inhibition of apoptosis. Consequently, our studies suggest that HBx balances HBV replication and cell survival by stimulating signaling pathways that enhance hepatocyte survival at the expense of higher levels of HBV replication.

IMPORTANCE

Chronic hepatitis B virus (HBV) infection is a common cause of the development of liver cancer. Regulation of cell signaling pathways by the HBV HBx protein is thought to influence the development of HBV-associated liver cancer. HBx stimulates, and may be essential for, HBV replication. We show that HBx activates AKT in hepatocytes to reduce HBV replication. While this seems contradictory to an essential role of HBx during HBV replication, HBx activation of AKT inhibits hepatocyte apoptosis, and this may facilitate persistent, noncytopathic HBV replication. AKT regulates HBV replication by reducing the activity of the transcription factor hepatocyte nuclear factor 4α (HNF4α). HBx activation of AKT may contribute to the development of liver cancer by facilitating persistent HBV replication, augmenting the dedifferentiation of hepatocytes by inhibiting HNF4α functions, and activating AKT-regulated oncogenic pathways. AKT-regulated factors may provide therapeutic targets for inhibiting HBV replication and the development of HBV-associated liver cancer.

Quantitative proteomics identifies host factors modulated during acute hepatitis E virus infection in the swine model

Hepatitis E virus (HEV) causes acute enterically transmitted hepatitis. In industrialized countries, it is a zoonotic disease, with swine being the major reservoir of human HEV contamination. The occurrence and severity of the disease are variable, with clinical symptoms ranging from asymptomatic to self-limiting acute hepatitis, chronic infection, or fulminant hepatitis. In the absence of a robust cell culture system or small-animal models, the HEV life cycle and pathological process remain unclear. To characterize HEV pathogenesis and virulence mechanisms, a quantitative proteomic analysis was carried out to identify cellular factors and pathways modulated during acute infection of swine. Three groups of pigs were inoculated with three different strains of swine HEV to evaluate the possible role of viral determinants in pathogenesis. Liver samples were analyzed by a differential proteomic approach, two-dimensional difference in gel electrophoresis, and 61 modulated proteins were identified by mass spectroscopy. The results obtained show that the three HEV strains replicate similarly in swine and that they modulate several cellular pathways, suggesting that HEV impairs several cellular processes, which can account for the various types of disease expression. Several proteins, such as heterogeneous nuclear ribonucleoprotein K, apolipoprotein E, and prohibitin, known to be involved in other viral life cycles, were upregulated in HEV-infected livers. Some differences were observed between the three strains, suggesting that HEV's genetic variability may induce variations in pathogenesis. This comparative analysis of the liver proteome modulated during infection with three different strains of HEV genotype 3 provides an important basis for further investigations on the factors involved in HEV replication and the mechanism of HEV pathogenesis.

IMPORTANCE

Hepatitis E virus (HEV) is responsible for acute hepatitis, with clinical symptoms ranging from asymptomatic to self-limiting acute hepatitis, chronic infection, or fulminant hepatitis. In industrialized countries, HEV is considered an emerging zoonotic disease, with swine being the principal reservoir for human contamination. The viral and cellular factors involved in the replication and/or pathogenesis of HEV are still not fully known. Here we report that several cellular pathways involved in cholesterol and lipid metabolism or cell survival were modulated during HEV infection in the swine model. Moreover, we observed a difference between the different swine strains, suggesting that HEV's genetic variability could play a role in pathogenesis. We also identified some proteins known to be involved in other viral cycles. Our study provides insight into the mechanisms modulated during HEV infection and constitutes a useful reference for future work on HEV pathogenesis and virulence.

Hepatitis E genotype 4 virus from feces of monkeys infected experimentally can be cultured in PLC/PRF/5 cells and upregulate host interferon-inducible genes

The understanding of the interaction between hepatitis E virus (HEV) and its host cells has been impeded greatly by the absence of a cell culture system. In this study, an efficient cultivation method was developed in PLC/PRF/5 cells for HEV genotype 4 from the feces of monkeys infected experimentally. Compared to minimal essential medium (MEM), mixed Dulbecco's Modified Eagle's Medium (DMEM)/M199 improved the infection efficiency of HEV in PLC/PRF/5 cells. The incubation time and temperature were set at 6 hr and 40°C, respectively. Compared to a 100% ELISA positive ratio (EPR) of 1 × 10(6)  copies/ml HEV inoculated flasks, the ELISA positive ratio was 100%, 75%, 37.5%, and 100% for flasks inoculated with HEV incubated for 30 min under the conditions of pH 3.0, pH 11.0, 56°C and delipidation treatment, respectively. Gene expression profiles of HEV inoculated and control PLC/PRF/5 cells were assayed using a microarray. Four interferon-inducible genes, IFI27, IFI6, Mx1, and CMPK2, were up-regulated during HEV-infection. Furthermore, the replication of HEV was inhibited at 3-14 days after treatment with 500 IU/ml IFN-α2b.

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.

Hepatitis E: an emerging disease

Currently, the infection with the hepatitis E virus represents the most frequent cause for acute hepatitis and jaundice in the world. According to WHO estimations, around two billion people, representing one third of the world's population, live in endemic areas for HEV and, therefore, are at risk of infection. In developed countries, the circulation of the virus in both human and animal (swine, boar, deer) sewage has been confirmed; however, the incidence rate is low compared to that of developing countries where outbreaks of acute hepatitis transmitted via the fecal-oral route are originated, more frequently in the flooding season or after natural disasters, combined with deficient sanitary conditions. There are currently 4 known genotypes of HEV. Genotypes 1 and 2 are isolated in all human epidemic outbreaks in developing countries, while genotypes 3 and 4 are isolated not only in humans but also in animals, in both developing and industrialized countries. These data support genotypes 3 and 4 having zoonotic nature. The diagnosis of this disease is based in the detection of anti-HEV IgG and IgM in blood serum using enzyme-linked immunosorbent methods. However, the method that best confirms the diagnosis is the RT-PCR, which detects HEV RNA in blood serum and also provides the genotype. The clinical course is generally that of an acute hepatitis which in some cases may require hospitalization and that, in transplant patients or HIV infected individuals can become a chronic hepatitis. Furthermore, the virus constitutes an important risk for pregnant women. The hepatitis E can present a wide range of symptoms, from a subclinical case to chronic liver disease with extrahepatic manifestations. For this reason, the diagnostic is challenging if no differential diagnosis is included. There is no specific antiviral drug for hepatitis E, but satisfactory results have been observed in some patients treated with pegylated interferon alfa2a and/or ribavirin. This revision is an update of all the molecular, epidemiological, clinic and preventive knowledge on this emergent disease up to date.

Hepatocyte nuclear factor 4-alpha involvement in liver and intestinal inflammatory networks

Hepatocyte nuclear factor 4-alpha (HNF4-α) is a nuclear receptor regulating metabolism, cell junctions, differentiation and proliferation in liver and intestinal epithelial cells. Mutations within the HNF4A gene are associated with human diseases such as maturity-onset diabetes of the young. Recently, HNF4A has also been described as a susceptibility gene for ulcerative colitis in genome-wide association studies. In addition, specific HNF4A genetic variants have been identified in pediatric cohorts of Crohn’s disease. Results obtained from knockout mice supported that HNF4-α can protect the intestinal mucosae against inflammation. However, the exact molecular links behind HNF4-α and inflammatory bowel diseases remains elusive. In this review, we will summarize the current knowledge about the role of HNF4-α and its isoforms in inflammation. Specific nature of HNF4-α P1 and P2 classes of isoforms will be summarized. HNF4-α role as a hepatocyte mediator for cytokines relays during liver inflammation will be integrated based on documented examples of the literature. Conclusions that can be made from these earlier liver studies will serve as a basis to extrapolate correlations and divergences applicable to intestinal inflammation. Finally, potential functional roles for HNF4-α isoforms in protecting the intestinal mucosae from chronic and pathological inflammation will be presented.

Development of a fluorescent microbead-based immunoassay for the detection of hepatitis E virus IgG antibodies in pigs and comparison to an enzyme-linked immunoassay

Swine hepatitis E virus (HEV) is a zoonotic virus and pigs are considered as an important reservoir. Swine HEV infection is widespread and most pig herds are infected. Humans can be infected with swine HEV via consumption of undercooked pork or through direct contact with infected pigs. To minimize the risk of zoonotic transmission, sensitive tools to assess the HEV infection status of pigs and pork products are needed. The objective of this study was to develop a fluorescent microbead-based immunoassay (FMIA) for the detection of IgG antibodies against swine HEV and compare it to an in-house enzyme-linked immunoassay (ELISA). Three sets of samples were utilized: (A) samples from pigs infected experimentally with different strains of HEV (positive controls, n=72), (B) samples from known HEV-negative pigs (negative controls, n=62) and (C) samples from pigs of unknown HEV infection status (n=182). All samples were tested by both ELISA and FMIA. The results on the experimental samples with known HEV exposure indicate that both assays have a specificity of 100% while the sensitivity ranges from 84.6% (ELISA) to 92.3% (FMIA). The overall prevalence of HEV IgG antibodies in field samples from pigs with unknown HEV exposure was 21.9% (40/182) for the ELISA and 21.4% (39/182) for the FMIA. The two assays had an almost perfect overall agreement (Kappa=0.92).

Hepatitis E virus seroprevalence of domestic pigs in Germany determined by a novel in-house and two reference ELISAs

Autochthonous hepatitis E virus (HEV) infections by zoonotic transmission of genotype 3 (GT3) have been reported increasingly from industrialized countries. In this paper the development and validation of an IgG ELISA for the detection of HEV-specific antibodies in domestic pigs is described. Comparison of the diagnostic value of Escherichia coli-expressed HEV-GT3 capsid protein (CP) derivatives revealed a carboxy-terminal derivative as most suitable. Validation of the in-house assay using a commercially available IgG ELISA revealed a high diagnostic specificity and sensitivity. The average HEV seroprevalence of domestic pigs from Germany and the federal state Baden-Wuerttemberg determined by the in-house test was 42.7% and 50.3%, respectively. The seroprevalence in different districts of Baden-Wuerttemberg ranged from 34.9% to 60%, but from 0% to 100% between different herds. These data were compared to those achieved by two commercially available ELISA kits and an in-house ratHEV-based ELISA. In conclusion, the CP-based in-house test proved sensitive and specific, indicating that the ORF3-encoded protein might be dispensable for diagnostics. The novel assay also allowed a parallel analysis by a homologous ratHEV-derived antigen. Thus, the novel IgG ELISA represents a useful tool for future standardized seroprevalence studies in domestic pigs from Germany and other regions of Europe.

Molecular biology and replication of hepatitis E virus

Hepatitis E virus (HEV), a single-stranded, positive-sense RNA virus, is responsible for acute hepatitis E epidemics in many developing countries, and the virus is also endemic in some industrialized countries. Hepatitis E is a recognized zoonotic disease, and several animal species, including pigs, are potential reservoirs for HEV. The genome of HEV contains three open reading frames (ORFs). ORF1 encodes the nonstructural proteins, ORF2 encodes the capsid protein, and ORF3 encodes a small multifunctional protein. The ORF2 and ORF3 proteins are translated from a single, bicistronic mRNA. The coding sequences for these two ORFs overlap each other, but neither overlaps with ORF1. Whereas the mechanisms underlying HEV replication are poorly understood, the construction of infectious viral clones, the identification of cell lines that support HEV replication, and the development of small animal models have allowed for more detailed study of the virus. As result of these advances, recently, our understanding of viral entry, genomic replication and viral egress has improved. Furthermore, the determination of the T=1 and T=3 structure of HEV virus-like particles has furthered our understanding of the replication of HEV. This article reviews the latest developments in the molecular biology of HEV with an emphasis on the genomic organization, the expression and function of genes, and the structure and replication of HEV.