Intracellular accumulation of subviral HBsAg particles and diminished Nrf2 activation in HBV genotype G expressing cells lead to an increased ROI level

Impaired HBsAg release and antiproliferative/antioxidant cell regulation by HBeAg-negative patient isolates reflects an evolutionary process

BACKGROUND

The hepatitis B e antigen (HBeAg)-negative infection Phase 3 is characterized by no or minimal signs of hepatic inflammation and the absence of hepatic fibrosis. However, underlying molecular mechanisms leading to this benign phenotype are poorly understood.

METHODS

Genotype A, B and D HBeAg-negative patient isolates with precore mutation G1896A from Phase 3 were analysed in comparison with respective HBeAg-positive rescue mutant and HBeAg-positive wild-type reference genomes regarding differences in viral replication, morphogenesis, infectivity and impact on NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE)-dependent gene expression and cellular kinome.

RESULTS

In comparison with reference genomes, the patient isolates are characterized by a lower intra- and extracellular hepatitis B surface antigen (HBsAg)-amount, and HBsAg-retention in the endoplasmic reticulum. Rescue of HBeAg expression increased HBsAg-amount but not its release. Expression of the isolated genomes is associated with a higher Nrf2/ARE-dependent gene expression as compared to reference genomes independent of HBeAg expression. Kinome analyses revealed a decreased activity of receptors involved in regulation of proliferative pathways for all patient isolates compared to the reference genomes. No specific conserved mutations could be found between all genomes from Phase 3.

CONCLUSIONS

HBeAg-negative genomes from Phase 3 exhibit distinct molecular characteristics leading to lower HBsAg synthesis and release, enhanced oxidative stress protection and decreased activity of key kinases, triggering an antiproliferative stage, which might contribute to the lower probability of hepatocellular carcinoma. The observed differences cannot be associated with loss of HBeAg or specific mutations common to all analysed isolates, indicating the phenotype of Phase 3 derived genomes to be the result of a multifactorial process likely reflecting a conserved natural selection process.

Inhibition of Pim kinases triggers a broad antiviral activity by affecting innate immunity and via the PI3K-Akt-mTOR axis the endolysosomal system

Zoonoses such as ZIKV and SARS-CoV-2 pose a severe risk to global health. There is urgent need for broad antiviral strategies based on host-targets filling gaps between pathogen emergence and availability of therapeutic or preventive strategies. Significant reduction of pathogen titers decreases spread of infections and thereby ensures health systems not being overloaded and public life to continue. Based on previously observed interference with FGFR1/2-signaling dependent impact on interferon stimulated gene (ISG)-expression, we identified Pim kinases as promising druggable cellular target. We therefore focused on analyzing the potential of pan-Pim kinase inhibition to trigger a broad antiviral response. The pan-Pim kinase inhibitor AZD1208 exerted an extraordinarily high antiviral effect against various ZIKV isolates, SARS-CoV-2 and HBV. This was reflected by strong reduction in viral RNA, proteins and released infectious particles. Especially in case of SARS-CoV-2, AZD1208 led to a complete removal of viral traces in cells. Kinome-analysis revealed vast changes in kinase landscape upon AZD1208 treatment, especially for inflammation and the PI3K/Akt-pathway. For ZIKV, a clear correlation between antiviral effect and increase in ISG-expression was observed. Based on a cell culture model with impaired ISG-induction, activation of the PI3K-Akt-mTOR axis, leading to major changes in the endolysosomal equilibrium, was identified as second pillar of the antiviral effect triggered by AZD1208-dependent Pim kinase inhibition, also against HBV. We identified Pim-kinases as cellular target for a broad antiviral activity. The antiviral effect exerted by inhibition of Pim kinases is based on at least two pillars: innate immunity and modulation of the endolysosomal system.

A state-of-the-art review on the NRF2 in Hepatitis virus-associated liver cancer

According to a paper released and submitted to WHO by IARC scientists, there would be 905,700 new cases of liver cancer diagnosed globally in 2020, with 830,200 deaths expected as a direct result. Hepatitis B virus (HBV) hepatitis C virus (HCV), and hepatitis D virus (HDV) all play critical roles in the pathogenesis of hepatocellular carcinoma (HCC), despite the rising prevalence of HCC due to non-infectious causes. Liver cirrhosis and HCC are devastating consequences of HBV and HCV infections, which are widespread worldwide. Associated with a high mortality rate, these infections cause about 1.3 million deaths annually and are the primary cause of HCC globally. In addition to causing insertional mutations due to viral gene integration, epigenetic alterations and inducing chronic immunological dysfunction are all methods by which these viruses turn hepatocytes into cancerous ones. While expanding our knowledge of the illness, identifying these pathways also give possibilities for novel diagnostic and treatment methods. Nuclear factor erythroid 2-related factor 2 (NRF2) activation is gaining popularity as a treatment option for oxidative stress (OS), inflammation, and metabolic abnormalities. Numerous studies have shown that elevated Nrf2 expression is linked to HCC, providing more evidence that Nrf2 is a critical factor in HCC. This aberrant Nrf2 signaling drives cell proliferation, initiates angiogenesis and invasion, and imparts drug resistance. As a result, this master regulator may be a promising treatment target for HCC. In addition, the activation of Nrf2 is a common viral effect that contributes to the pathogenesis, development, and chronicity of virus infection. However, certain viruses suppress Nrf2 activity, which is helpful to the virus in maintaining cellular homeostasis. In this paper, we discussed the influence of Nrf2 deregulation on the viral life cycle and the pathogenesis associated with HBV and HCV. We summed up the mechanisms for the modulation of Nrf2 that are deregulated by these viruses. Moreover, we describe the molecular mechanism by which Nrf2 is modulated in liver cancer, liver cancer stem cells (LCSCs), and liver cancer caused by HBV and HCV. Video Abstract.

Hepatocellular carcinoma: The virus or the liver?

Hepatocellular carcinoma (HCC) represents a major public health problem being one of the most common causes of cancer-related deaths worldwide. Hepatitis B (HBV) and C viruses have been classified as oncoviruses and are responsible for the majority of HCC cases, while the role of hepatitis D virus (HDV) in liver carcinogenesis has not been elucidated. HDV/HBV coinfection is related to more severe liver damage than HBV mono-infection and recent studies suggest that HDV/HBV patients are at increased risk of developing HCC compared to HBV mono-infected patients. HBV is known to promote hepatocarcinogenesis via DNA integration into host DNA, disruption of molecular pathways by regulatory HBV x (HBx) protein and excessive oxidative stress. Recently, several molecular mechanisms have been proposed to clarify the pathogenesis of HDV-related HCC including activation of signalling pathways by specific HDV antigens, epigenetic dysregulation and altered gene expression. Alongside, ongoing chronic inflammation and impaired immune responses have also been suggested to facilitate carcinogenesis. Finally, cellular senescence seems to play an important role in chronic viral infection and inflammation leading to hepatocarcinogenesis. In this review, we summarize the current literature on the impact of HDV in HCC development and discuss the potential interplay between HBV, HDV and neighbouring liver tissue in liver carcinogenesis.

The role of hepatitis B virus genome variations in HBV-related HCC: effects on host signaling pathways

Hepatocellular carcinoma (HCC) is a significant global health issue, with a high prevalence in many regions. There are variations in the etiology of HCC in different regions, but most cases are due to long-term infection with viral hepatitis. Hepatitis B virus (HBV) is responsible for more than 50% of virus-related HCC, which highlights the importance of HBV in pathogenesis of the disease. The development and progression of HBV-related HCC is a complex multistep process that can involve host, viral, and environmental factors. Several studies have suggested that some HBV genome mutations as well as HBV proteins can dysregulate cell signaling pathways involved in the development of HCC. Furthermore, it seems that the pathogenicity, progression of liver diseases, response to treatment and also viral replication are different among HBV mutants. Understanding the relationship between HBV genome variations and host signaling pathway alteration will improve our understanding of the molecular pathogenesis of HBV-related HCC. Furthermore, investigating commonly dysregulated pathways in HBV-related HCC is necessary to discover more specific therapeutic targets and develop more effective strategies for HCC treatment. The objective of this review is to address the role of HBV in the HCC progression and primarily focus on the impacts of HBV genome variations on HCC-related signaling pathways.

An RNA-based system to study hepatitis B virus replication and evaluate antivirals

Hepatitis B virus (HBV) chronically infects an estimated 300 million people, and standard treatments are rarely curative. Infection increases the risk of liver cirrhosis and hepatocellular carcinoma, and consequently, nearly 1 million people die each year from chronic hepatitis B. Tools and approaches that bring insights into HBV biology and facilitate the discovery and evaluation of antiviral drugs are in demand. Here, we describe a method to initiate the replication of HBV, a DNA virus, using synthetic RNA. This approach eliminates contaminating background signals from input virus or plasmid DNA that plagues existing systems and can be used to study multiple stages of HBV replication. We further demonstrate that this method can be uniquely applied to identify sequence variants that confer resistance to antiviral drugs.

Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatitis B virus (HBV) is DNA-based virus, member of the Hepadnaviridae family, which can cause liver disease and increased risk of hepatocellular carcinoma (HCC) in infected individuals, replicating within the hepatocytes and interacting with several cellular proteins. Chronic hepatitis B can progressively lead to liver cirrhosis, which is an independent risk factor for HCC. Complications as liver decompensation or HCC impact the survival of HBV patients and concurrent HDV infection worsens the disease. The available data provide evidence that HBV infection is associated with the risk of developing HCC with or without an underlying liver cirrhosis, due to various direct and indirect mechanisms promoting hepatocarcinogenesis. The molecular profile of HBV-HCC is extensively and continuously under study, and it is the result of altered molecular pathways, which modify the microenvironment and lead to DNA damage. HBV produces the protein HBx, which has a central role in the oncogenetic process. Furthermore, the molecular profile of HBV-HCC was recently discerned from that of HDV-HCC, despite the obligatory dependence of HDV on HBV. Proper management of the underlying HBV-related liver disease is fundamental, including HCC surveillance, viral suppression, and application of adequate predictive models. When HBV-HCC occurs, liver function and HCC characteristics guide the physician among treatment strategies but always considering the viral etiology in the treatment choice.

Hepatitis B Virus Genotype G: The Odd Cousin of the Family

With a widespread distribution but low prevalence worldwide, the hepatitis B virus (HBV) genotype G (HBV/G) is a recently described genotype for which the origin and biology are poorly understood. Some unique features make HBV/G the most peculiar of all genotypes. In this review, we reflect on the major milestones in HBV/G research, highlighting the main aspects of its discovery, molecular epidemiology, and virological and clinical characteristics. We also illustrate common pitfalls in the routine detection, which may lead to underestimated rates of HBV/G infection. Large-scale analysis of data from dozens of articles was further performed, with the aim of gaining comprehensive insights into the epidemiological aspects of HBV/G. Finally, we point out recent findings on HBV/G origins and discuss new perspectives regarding the evolutionary history of HBV/G and the plausibility of an African geographic re-emergence of this genotype.

Influenza A virus uses PSMA2 for downregulation of NRF2-mediated oxidative stress response

Influenza A virus (IAV), an obligatory intracellular parasite, uses host cellular molecules to complete its replication cycle and suppress immune responses. Proteasome subunit alpha type 2 (PSMA2) is a cellular protein highly expressed in IAV-infected human lung epithelial A549 cells. PSMA2 is part of the 20S proteasome complex that degrades or recycles defective proteins and involves proteolytic modification of many cellular regulatory proteins. However, the role of PSMA2 in IAV replication is not well understood. In this study, PSMA2 knockdown (KD) in A549 cells caused a significant reduction in extracellular progeny IAV, but intracellular viral protein translation and viral RNA transcription were not affected. This indicates that PSMA2 is a critical host factor for IAV maturation. To better understand the interplay between PSMA2 KD and IAV infection at the proteomic level, we used the SomaScan 1.3K version, which measures 1,307 proteins to analyze alterations induced by these treatments. We found seven cellular signaling pathways, including phospholipase C signaling, Pak signaling, and nuclear factor erythroid 2p45-related factor 2 (NRF2)-mediated oxidative stress response signaling, that were inhibited by IAV infection but significantly activated by PSMA2 KD. Further analysis of NRF2-mediated oxidative stress response signaling indicated IAV inhibits accumulation of reactive oxygen species (ROS), but ROS levels significantly increased during IAV infection in PSMA2 KD cells. However, IAV infection caused significantly higher NFR2 nuclear translocation that was inhibited in PSMA2 KD cells. This indicates that PSMA2 is required for NRF2-mediated ROS neutralization and that IAV uses PSMA2 to escape viral clearance via the NRF2-mediated cellular oxidative response.

IMPORTANCE Influenza A virus (IAV) remains one of the most significant infectious agents, responsible for 3 million to 5 million illnesses each year and more than 50 million deaths during the 20th century. The cellular processes that promote and inhibit IAV infection and pathogenesis remain only partially understood. PSMA2 is a critical component of the 20S proteasome and ubiquitin-proteasome system, which is important in the replication of numerous viruses. This study examined host protein responses to IAV infection alone, PSMA2 knockdown alone, and IAV infection in the presence of PSMA2 knockdown and determined that interfering with PSMA2 function affected IAV maturation. These results help us better understand the importance of PSMA2 in IAV replication and may pave the way for designing additional IAV antivirals targeting PSMA2 or the host proteasome for the treatment of seasonal flu.

Emodin resists to Cyprinid herpesvirus 3 replication via the pathways of Nrf2/Keap1-ARE and NF-κB in the ornamental koi carp (Cyprinus carpio haematopterus)

Cyprinid herpesvirus 3 (CyHV-3) causes high mortality in carp. Emodin has been shown of the effects of antioxidant, anti-inflammatory and antiviral. In present study, we investigated the preventive effects and mechanism of emodin on CyHV-3 infection. The ornamental koi carp (Cyprinus carpio haematopterus) were intraperitoneally injected with emodin (10 mg/kg, 20 mg/kg, or 40 mg/kg). 72 h later, an intraperitoneal injection of CyHV-3 was administered, and collected the samples one week later to detect the antioxidant parameters, antioxidant genes, inflammatory genes and to perform histopathology assays. The results showed that emodin significantly suppressed CyHV-3 replication (P < 0.05), improved the koi survival rate and slowed the damage caused by CyHV-3. Emodin treatment increased the antioxidant activity and decreased the lipid peroxidation level of the koi. Compared to the CyHV-3 group, emodin treatment resulted in the same antioxidant parameters after CyHV-3 infection. Emodin treatment activated the Nuclear factorery throid 2-related factor 2/Kelch-like ECH-associated protein 1-antioxidatant response element (Nrf2/Keap1-ARE) pathway and upregulated the expression of heme oxygenase 1 (HO-1), superoxide dismutase (SOD), and catalase (CAT) in the hepatopancreas after CyHV-3 infection. Emodin activated the nuclear factor kappa-B (NF-κB) pathway and decreased the expression of interleukin-6 (IL-6), interleukin-8 (IL-8), and tumour necrosis factor-α (TNF-α) in the koi induced by CyHV-3. In conclusion, emodin treatment can suppress CyHV-3 replication and reduce the mortality of koi caused by CyHV-3. Emodin improves antioxidant function, relieves oxidative stress and inflammation cytokines via Nrf2/Keap1-ARE and NF-κB pathways, and protects against the adverse effects induced by CyHV-3.

Not uncommon: HBV genotype G co-infections among healthy European HBV carriers with genotype A and E infection

BACKGROUND & AIMS

HBV genotype G (HBV/G) is mainly found in co-infections with other HBV genotypes and was identified as an independent risk factor for liver fibrosis. This study aimed to analyse the prevalence of HBV/G co-infections in healthy European HBV carriers and to characterize the crosstalk of HBV/G with other genotypes.

METHODS

A total of 560 European HBV carriers were tested via HBV/G-specific PCR for HBV/G co-infections. Quasispecies distribution was analysed via deep sequencing, and the clinical phenotype was characterized regarding qHBsAg-/HBV-DNA levels and frequent mutations. Replicative capacity and expression of HBsAg/core was studied in hepatoma cells co-expressing HBV/G with either HBV/A, HBV/D or HBV/E using bicistronic vectors.

RESULTS

Although no HBV/G co-infection was found by routine genotyping PCR, HBV/G was detected by specific PCR in 4%-8% of patients infected with either HBV/A or HBV/E but only infrequently in other genotypes. In contrast to HBV/E, HBV/G was found as the quasispecies major variant in co-infections with HBV/A. No differences in the clinical phenotype were observed for HBV/G co-infections. In vitro RNA and DNA levels were comparable among all genotypes, but expression and release of HBsAg was reduced in co-expression of HBV/G with HBV/E. In co-expression with HBV/A and HBV/E expression of HBV/G-specific core was enhanced while core expression from the corresponding genotype was markedly diminished.

CONCLUSIONS

HBV/G co-infections are common in European inactive carriers with HBV/A and HBV/E infection, but sufficient detection depends strongly on the assay. HBV/G regulated core expression might play a critical role for survival of HBV/G in co-infections.

Changes in Glutathione Content in Liver Diseases: An Update

Glutathione (GSH), a tripeptide particularly concentrated in the liver, is the most important thiol reducing agent involved in the modulation of redox processes. It has also been demonstrated that GSH cannot be considered only as a mere free radical scavenger but that it takes part in the network governing the choice between survival, necrosis and apoptosis as well as in altering the function of signal transduction and transcription factor molecules. The purpose of the present review is to provide an overview on the molecular biology of the GSH system; therefore, GSH synthesis, metabolism and regulation will be reviewed. The multiple GSH functions will be described, as well as the importance of GSH compartmentalization into distinct subcellular pools and inter-organ transfer. Furthermore, we will highlight the close relationship existing between GSH content and the pathogenesis of liver disease, such as non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease (ALD), chronic cholestatic injury, ischemia/reperfusion damage, hepatitis C virus (HCV), hepatitis B virus (HBV) and hepatocellular carcinoma. Finally, the potential therapeutic benefits of GSH and GSH-related medications, will be described for each liver disorder taken into account.

Mutations and methods of analysis of mutations in Hepatitis B virus

Immunization programmes against hepatitis-B are being carried out since more than three decades but still HBV is a major public health problem. Hepatitis B virus (HBV) genome consists of circular and partial double stranded DNA. Due to partial double stranded DNA, it uses an RNA intermediate during replication. This replicative strategy of HBV and lack of polymerase proofreading activity give rise to error occurrences comparable to retroviruses. The low fidelity of polymerase, overlapping reading frames and high replication rate produces many non-identical variants at every cycle of replication. Therefore, HBV spreads with mutations and variations. The mutations have been reported both in non-structural as well as structural genes of HBV genome. Recent advances in molecular biology have made easier to analyse these mutations. Hepatitis B antiviral therapy and immunization are all influenced by genetic variability. The analysis and understanding of these mutations are important for therapy against hepatitis B and updating of diagnostic tools. The present review discusses about mutations occurring in whole HBV genome. The mutation occurring both in structural and non-structural genes and non-coding regions have been described in details. It is much more informative because most of literature available, covers only individual gene or DNA regions of HBV.

Mutual antagonism between indoleamine 2,3-dioxygenase 1 and nuclear factor E2-related factor 2 regulates the maturation status of DCs in liver fibrosis

Liver fibrosis can develop into liver cirrhosis and hepatocellular carcinoma substantially without effective available treatment currently due to rarely characterized molecular pathogenesis. Indoleamine 2,3-dioxygenase 1(IDO1) can be detected on antigen-presenting cells (APCs) and modulates various immune responses. However, the role of IDO1 in the regulation of dendritic cells (DCs) during liver fibrosis is rarely reported. Here, we found that hepatic IDO1 was up-regulated during CCL4-induced liver fibrosis, which accompanied by a significant decrease in the frequencies of CD11c⁺CD80⁺, CD11c⁺CD86⁺, CD11c⁺CD40⁺ and CD11c⁺MHCII⁺ cells and a reduction in the subsequent T cell proliferation rate, whereas these changes were reversed significantly in IDO1^-/- mice. Overexpressing IDO1 by adeno-associated viral vector serotype 9 (AAV9) significantly inhibited the maturation status of DCs, worsened fibrosis. In vitro studies showed that significantly elevated CD80, CD86, CD40 and MHCII expression were observed in BMDCs derived from IDO1^-/- mice. Moreover, the maturation of BMDCs derived from WT mice were significantly increased after stimulated with IDO1 inhibitor (1-methyl- D -tryptophan). Nuclear factor E2-related factor 2 (Nrf2), a key regulator of the cellular adaptive response to oxidative insults and inflammation, exhibited a markedly decrease in the liver of WT fibrotic mice, nevertheless, knockout of IDO1 enhanced the protein level of Nrf2. Moreover, the expression of IDO1 and Nrf2 exhibited inverse colocalization pattern suggesting that ectopically expressed IDO1 down-regulated Nrf2. Additionally, up-regulation of IDO1 was also observed in the livers of Nrf2^-/- fibrotic mice. Taken together, these data uncovered mutual antagonism between IDO1 and Nrf2 on the maturation status of DCs during hepatic fibrosis.

Quadruple mutation GCAC1809-1812TTCT acts as a biomarker in healthy European HBV carriers

Many mutation analyses of the HBV genome have been performed in the search for new prognostic markers. However, the Kozak sequence preceding precore was covered only infrequently in these analyses. In this study, the HBV core promoter/precore region was sequenced in serum samples from European inactive HBV carriers. Quadruple mutation GCAC1809-1812TTCT was found with a high prevalence of 42% in the Kozak sequence preceding precore among all HBV genotypes. GCAC1809-1812TTCT was strongly associated with coexistence of basal core promoter (BCP) double mutation A1762T/G1764A and lower HBV DNA levels. In vitro GCAC1809-1812TTCT lead to drastically diminished synthesis of pregenomic RNA (pgRNA), precore mRNA, core, HBsAg, and HBeAg. Calculation of the pgRNA secondary structure suggests a destabilization of the pgRNA structure by A1762T/G1764A that was compensated by GCAC1809-1812TTCT. In 125 patients with HBV-related cirrhosis, GCAC1809-1812TTCT was not detected. While a strong association of GCAC1809-1812TTCT with inactive carrier status was observed, BCP double mutation was strongly correlated with cirrhosis, but this was only observed in absence of GCAC1809-1812TTCT. In conclusion, our data reveal that GCAC1809-1812TTCT is highly prevalent in inactive carriers and acts as a compensatory mutation for BCP double mutation. GCAC1809-1812TTCT seems to be a biomarker of good prognosis in HBV infection.

HBV core promoter/precore region was sequenced in serum samples of European inactive HBV carriers, revealing that GCAC1809-1812TTCT mutation is highly prevalent in inactive carriers.

Molecular mechanisms of viral hepatitis induced hepatocellular carcinoma

Chronic infection with viral hepatitis affects half a billion individuals worldwide and can lead to cirrhosis, cancer, and liver failure. Liver cancer is the third leading cause of cancer-associated mortality, of which hepatocellular carcinoma (HCC) represents 90% of all primary liver cancers. Solid tumors like HCC are complex and have heterogeneous tumor genomic profiles contributing to complexity in diagnosis and management. Chronic infection with hepatitis B virus (HBV), hepatitis delta virus (HDV), and hepatitis C virus (HCV) are the greatest etiological risk factors for HCC. Due to the significant role of chronic viral infection in HCC development, it is important to investigate direct (viral associated) and indirect (immune-associated) mechanisms involved in the pathogenesis of HCC. Common mechanisms used by HBV, HCV, and HDV that drive hepatocarcinogenesis include persistent liver inflammation with an impaired antiviral immune response, immune and viral protein-mediated oxidative stress, and deregulation of cellular signaling pathways by viral proteins. DNA integration to promote genome instability is a feature of HBV infection, and metabolic reprogramming leading to steatosis is driven by HCV infection. The current review aims to provide a brief overview of HBV, HCV and HDV molecular biology, and highlight specific viral-associated oncogenic mechanisms and common molecular pathways deregulated in HCC, and current as well as emerging treatments for HCC.

Phosphorylation of the Arginine-Rich C-Terminal Domains of the Hepatitis B Virus (HBV) Core Protein as a Fine Regulator of the Interaction between HBc and Nucleic Acid

The morphogenesis of Hepatitis B Virus (HBV) viral particles is nucleated by the oligomerization of HBc protein molecules, resulting in the formation of an icosahedral capsid shell containing the replication-competent nucleoprotein complex made of the viral polymerase and the pre-genomic RNA (pgRNA). HBc is a phospho-protein containing two distinct domains acting together throughout the viral replication cycle. The N-terminal domain, (residues 1–140), shown to self-assemble, is linked by a short flexible domain to the basic C-terminal domain (residues 150–183) that interacts with nucleic acids (NAs). In addition, the C-terminal domain contains a series of phospho-acceptor residues that undergo partial phosphorylation and de-phosphorylation during virus replication. This highly dynamic process governs the homeostatic charge that is essential for capsid stability, pgRNA packaging and to expose the C-terminal domain at the surface of the particles for cell trafficking. In this review, we discuss the roles of the N-terminal and C-terminal domains of HBc protein during HBV morphogenesis, focusing on how the C-terminal domain phosphorylation dynamics regulate its interaction with nucleic acids throughout the assembly and maturation of HBV particles.

Progressive Rotavirus Infection Downregulates Redox-Sensitive Transcription Factor Nrf2 and Nrf2-Driven Transcription Units

Eukaryotic cells adopt highly tuned stress response physiology under threats of exogenous stressors including viruses to maintain cellular homeostasis. Not surprisingly, avoidance of cellular stress response pathways is an essential facet of virus-induced obligatory host reprogramming to invoke a cellular environment conducive to viral perpetuation. Adaptive cellular responses to oxidative and electrophilic stress are usually taken care of by an antioxidant defense system, core to which lies the redox-responsive transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2-driven transcriptional cascade. Deregulation of host redox balance and redox stress-sensitive Nrf2 antioxidant defense have been reported for many viruses. In the current study, we aimed to study the modulation of the Nrf2-based host cellular redox defense system in response to Rotavirus (RV) infection in vitro. Interestingly, we found that Nrf2 protein levels decline sharply with progression of RV infection beyond an initial upsurge. Moreover, Nrf2 decrease as a whole was found to be accompanied by active nuclear vacuity of Nrf2, resulting in lowered expression of stress-responsive Nrf2 target genes heme oxygenase-1 (HO-1), NAD(P)H quinone dehydrogenase 1, and superoxide dismutase 1 both in the presence and absence of Nrf2-driven transcriptional inducers. Initial induction of Nrf2 concurred with RV-induced early burst of oxidative stress and therefore was sensitive to treatments with antioxidants. Reduction of Nrf2 levels beyond initial hours, however, was found to be independent of the cellular redox status. Furthermore, increasing the half-life of Nrf2 through inhibition of the Kelch-like erythroid cell-derived protein with CNC homology- (ECH-) associated protein 1/Cullin3-RING Box1-based canonical Nrf2 turnover pathway could not restore Nrf2 levels post RV-SA11 infection. Depletion of the Nrf2/HO-1 axis was subsequently found to be sensitive to proteasome inhibition with concurrent observation of increased K48-linked ubiquitination associated with Nrf2. Together, the present study describes robust downregulation of Nrf2-dependent cellular redox defense beyond initial hours of RV infection, justifying our previous observation of potent antirotaviral implications of Nrf2 agonists.

Formation of semi-enveloped particles as a unique feature of a hepatitis B virus PreS1 deletion mutant

BACKGROUND

Naturally occurring variants with deletions or mutations in the C-terminal PreS1 domain from hepatitis B virus (HBV) chronically infected patients have been shown to promote HBsAg retention, inhibit HBsAg secretion and change the extracellular appearance of PreS1-containing HBV particles (filaments and virions).

AIMS

To study the impact of N-terminal deletion in preS1 domain on viral secretion and morphogenesis.

METHODS

An HBV mutant with 15 amino acids (aa 25-39) deletion in N-terminal preS1 was isolated. Intracellular and extracellular HBsAg were quantified by Western blot. Subcellular HBsAg distribution was analysed by confocal laser scanning microscopy. The viral morphology was characterised by sucrose density gradient ultracentrifugation, Western blot, electron microscopy, HBV mixed ELISA and HBV particle gel essay.

RESULTS

Expression of this mutant genome released higher amounts of HBsAg in the form of shorter filaments. A significant fraction of semi-enveloped virions was observed in the supernatant that has been unprecedented so far. Stepwise insertion of aa 25-31, aa 32-39 and aa 25-39 increased the length of filaments. The rescue of aa 25-31 and aa 25-39 drastically reduced the amounts of extracellular HBsAg and semi-enveloped virions, while such effects could not be observed after insertion of aa 32-39, arguing against a simple spacer function of this region. The deletion and rescued mutants do not differ in subcellular HBsAg distribution and colocalisation with ER, Golgi and multivesicular bodies markers arguing against differences in release pathways.

CONCLUSION

N-terminal PreS1-domain (aa 25-31) determines HBsAg secretion and triggers proper assembly of PreS1-containing particles.

Effect of Hepatitis Viruses on the Nrf2/Keap1-Signaling Pathway and Its Impact on Viral Replication and Pathogenesis

With respect to their genome and their structure, the human hepatitis B virus (HBV) and hepatitis C virus (HCV) are complete different viruses. However, both viruses can cause an acute and chronic infection of the liver that is associated with liver inflammation (hepatitis). For both viruses chronic infection can lead to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Reactive oxygen species (ROS) play a central role in a variety of chronic inflammatory diseases. In light of this, this review summarizes the impact of both viruses on ROS-generating and ROS-inactivating mechanisms. The focus is on the effect of both viruses on the transcription factor Nrf2 (nuclear factor erythroid 2 (NF-E2)-related factor 2). By binding to its target sequence, the antioxidant response element (ARE), Nrf2 triggers the expression of a variety of cytoprotective genes including ROS-detoxifying enzymes. The review summarizes the literature about the pathways for the modulation of Nrf2 that are deregulated by HBV and HCV and describes the impact of Nrf2 deregulation on the viral life cycle of the respective viruses and the virus-associated pathogenesis.

Structure-Guided Approach to Identify Potential Inhibitors of Large Envelope Protein to Prevent Hepatitis B Virus Infection

Hepatitis B virus (HBV) infection is one of the major causes of liver diseases, which can lead to hepatocellular carcinoma. The role of HBV envelope proteins is crucial in viral morphogenesis, infection, and propagation. Thus, blocking the pleiotropic functions of these proteins especially the PreS1 and PreS2 domains of the large surface protein (LHBs) is a promising strategy for designing efficient antivirals against HBV infection. Unfortunately, the structure of the LHBs protein has not been elucidated yet, and it seems that any structure-based drug discovery is critically dependent on this. To find effective inhibitors of LHBs, we have modeled and validated its three-dimensional structure and subsequently performed a virtual high-throughput screening against the ZINC database using RASPD and ParDOCK tools. We have identified four compounds, ZINC11882026, ZINC19741044, ZINC00653293, and ZINC15000762, showing appreciable binding affinity with the LHBs protein. The drug likeness was further validated using ADME screening and toxicity analysis. Interestingly, three of the four compounds showed the formation of hydrogen bonds with amino acid residues lying in the capsid binding region of the PreS1 domain of LHBs, suggesting the possibility of inhibiting the viral assembly and maturation process. The identification of potential lead molecules will help to discover more potent inhibitors with significant antiviral activities.

Therapeutic Modulation of Virus-Induced Oxidative Stress via the Nrf2-Dependent Antioxidative Pathway

Virus-induced oxidative stress plays a critical role in the viral life cycle as well as the pathogenesis of viral diseases. In response to reactive oxygen species (ROS) generation by a virus, a host cell activates an antioxidative defense system for its own protection. Particularly, a nuclear factor erythroid 2p45-related factor 2 (Nrf2) pathway works in a front-line for cytoprotection and detoxification. Recently, a series of studies suggested that a group of clinically relevant viruses have the capacity for positive and negative regulations of the Nrf2 pathway. This virus-induced modulation of the host antioxidative response turned out to be a crucial determinant for the progression of several viral diseases. In this review, virus-specific examples of positive and negative modulations of the Nrf2 pathway will be summarized first. Then a number of successful genetic and pharmacological manipulations of the Nrf2 pathway for suppression of the viral replication and the pathogenesis-associated oxidative damage will be discussed later. Understanding of the interplay between virus-induced oxidative stress and antioxidative host response will aid in the discovery of potential antiviral supplements for better management of viral diseases.

Liver - master and servant of serum proteome

Hepatocytes synthesise the majority of serum proteins. This production occurs in the endoplasmic reticulum (ER) and is adjusted by complex local and systemic regulatory mechanisms. Accordingly, serum levels of hepatocyte-made proteins constitute important biomarkers that reflect both systemic processes and the status of the liver. For example, C-reactive protein is an established marker of inflammatory reaction, whereas transferrin emerges as a liver stress marker and an attractive mortality predictor. The high protein flow through the ER poses a continuous challenge that is handled by a complex proteostatic network consisting of ER folding machinery, ER stress response, ER-associated degradation and autophagy. Various disorders disrupt this delicate balance and result in protein accumulation in the ER. These include chronic hepatitis B infection with overproduction of hepatitis B surface antigen or inherited alpha1-antitrypsin deficiency that give rise to ground glass hepatocytes and alpha1-antitrypsin aggregates, respectively. We review these ER storage disorders and their downstream consequences. The interaction between proteotoxic stress and other ER challenges such as lipotoxicity is also discussed. Collectively, this article aims to sharpen our view of liver hepatocytes as the central hubs of protein metabolism.

Impact of HBV genotype and mutations on HBV DNA and qHBsAg levels in patients with HBeAg-negative chronic HBV infection

BACKGROUND

HBV DNA and quantitative (q)HBsAg levels as prognostic markers for HBV-related disease are mostly validated in Asia and their significance in Western populations is uncertain.

AIM

To analyse the impact of the HBV genotype and frequent mutations in precore (PC), basal core promoter (BCP) and preS on HBV DNA and qHBsAg levels.

METHODS

HBV DNA and qHBsAg serum levels of 465 patients with HBeAg-negative chronic HBV infection were correlated with the HBV genotype and mutations in PC, BCP and preS. For a detailed analysis of the molecular virology, genotype A2 genomes harbouring these mutations were analysed for replication efficacy and HBsAg release in cell culture.

RESULTS

While no impact of the HBV genotype on HBV DNA levels was observed, qHBsAg levels differed up to 1.4 log among the genotypes (P < 0.001), reflected by large differences regarding the 1000 IU/mL HBsAg cut-off. While PC mutations were associated with higher (P < 0.001), BCP mutations were associated with lower HBV DNA levels (P < 0.001). Higher qHBsAg levels were associated with preS and lower levels with PC mutations (P < 0.001 and P = 0.001, respectively). The cell culture experiments revealed a higher HBsAg release and shorter filaments in case of a HBV genome harbouring a preS deletion. In contrast, a perinuclear HBsAg accumulation was detected for the PC and BCP-variants, reflecting an impaired HBsAg release.

CONCLUSIONS

qHBsAg serum levels depend on the HBV genotype and together with HBV DNA levels on frequent mutations in PC, BCP and preS in HBeAg-negative patients. qHBsAg cut-offs when used as prognostic markers require genotype-dependent validation.

Cisplatin Enhances Hepatitis B Virus Replication and PGC-1α Expression through Endoplasmic Reticulum Stress

Chronic hepatitis B infection remains a serious public health issue worldwide. Hepatitis B virus (HBV) reactivation is commonly reported in patients receiving anticancer therapy, immunosuppressive therapy, or organ and tissue transplantation. However, the precise mechanisms underlying chemotherapeutic agent-related HBV reactivation remain unclear. Here, we report that peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) plays a central role in cisplatin-induced HBV transcription and replication. First, cisplatin treatment upregulated the expression levels of PGC-1α and hepatocyte nuclear factor 4 alpha (HNF-4α) in both HBV-replicating cells and an HBV-transgenic mouse model. PGC-1α coactivates with HNF-4α, which interacts with a core promoter and enhancer II region of HBV genome, thereby promoting HBV production. In contrast, knockdown of PGC-1α and HNF-4α by RNA interference in hepatoma cells reversed HBV activation in response to cisplatin. Additionally, PGC-1α upregulation depended on cisplatin-mediated endoplasmic reticulum (ER) stress. We further observed that the recruitment of cyclic AMP-responsive element-binding protein plays a crucial role for PGC-1α transcriptional activation in cisplatin-treated cells. Finally, pharmacologic inhibition of ER stress impaired PGC-1α upregulation and HBV production induced by cisplatin treatment. These findings demonstrate novel molecular mechanisms indicating that ER stress-PGC1α signaling pathway plays a critical role in cisplatin-evoked HBV reactivation.

Oxidative stress, a trigger of hepatitis C and B virus-induced liver carcinogenesis

Virally induced liver cancer usually evolves over long periods of time in the context of a strongly oxidative microenvironment, characterized by chronic liver inflammation and regeneration processes. They ultimately lead to oncogenic mutations in many cellular signaling cascades that drive cell growth and proliferation. Oxidative stress, induced by hepatitis viruses, therefore is one of the factors that drives the neoplastic transformation process in the liver. This review summarizes current knowledge on oxidative stress and oxidative stress responses induced by human hepatitis B and C viruses. It focuses on the molecular mechanisms by which these viruses activate cellular enzymes/systems that generate or scavenge reactive oxygen species (ROS) and control cellular redox homeostasis. The impact of an altered cellular redox homeostasis on the initiation and establishment of chronic viral infection, as well as on the course and outcome of liver fibrosis and hepatocarcinogenesis will be discussed The review neither discusses reactive nitrogen species, although their metabolism is interferes with that of ROS, nor antioxidants as potential therapeutic remedies against viral infections, both subjects meriting an independent review.

Hepatitis B virus X protein inhibits apoptosis by modulating endoplasmic reticulum stress response

Chronic Hepatitis B virus (HBV) infection is a major risk of hepatocellular carcinoma (HCC) worldwide. Hepatitis B virus X protein (HBx) is encoded by one of the four open reading frames of HBV, and is well known as an important coactivator for HBV replication and HBV-associated hepatocellular carcinogenesis. However, its role in keeping cells from apoptosis to promote HCC proliferation remains controversial. Here, we used HBx expressing HCC cells as a model, to investigate the mechanism of HBx-mediated cellular response to endoplasmic reticulum (ER) stress. We found that HBx protein was localized in ER lumen and interacted with GRP78 directly. This interaction resulted in suppression of eIF2α phosphorylation, inhibited expression of ATF4/CHOP/Bcl-2, and reduced cleavage of poly ADP-ribose polymerase (PARP) and level of γH2AX, thus preventing HCC cells from cell death and negatively regulating DNA repair. This study reveals a novel mechanism of the HBx-mediated oncogenesis and provides a basis for potential HBx-targeted therapeutic intervention of HCC.

Heterogeneous recombination among Hepatitis B virus genotypes

The rapid evolution of Hepatitis B virus (HBV) through both evolutionary forces, mutation and recombination, allows this virus to generate a large variety of adapted variants at both intra and inter-host levels. It can, for instance, generate drug resistance or the diverse viral genotypes that currently exist in the HBV epidemics. Concerning the latter, it is known that recombination played a major role in the emergence and genetic diversification of novel genotypes. In this regard, the quantification of viral recombination in each genotype can provide relevant information to devise expectations about the evolutionary trends of the epidemic. Here we measured the amount of this evolutionary force by estimating global and local recombination rates in >4700 HBV complete genome sequences corresponding to nine (A to I) HBV genotypes. Counterintuitively, we found that genotype E presents extremely high levels of recombination, followed by genotypes B and C. On the other hand, genotype G presents the lowest level, where recombination is almost negligible. We discuss these findings in the light of known characteristics of these genotypes. Additionally, we present a phylogenetic network to depict the evolutionary history of the studied HBV genotypes. This network clearly classified all genotypes into specific groups and indicated that diverse pairs of genotypes are derived from a common ancestor (i.e., C-I, D-E and, F-H) although still the origin of this virus presented large uncertainty. Altogether we conclude that the amount of observed recombination is heterogeneous among HBV genotypes and that this heterogeneity can influence on the future expansion of the epidemic.

Comparative characterization of hepatitis B virus surface antigen derived from different hepatitis B virus genotypes

For human hepatitis B virus eight distinct and two candidate genotypes are described. These genotypes differ with respect to geographic distribution, molecular virology and virus-associated pathogenesis. Comparative analysis of HBV genotypes revealed, with exception of HBV/G that shows impaired HBsAg release, that no fundamental disparities between genotypes exist regarding glycosylation, subcellular distribution, release of HBsAg and formation of subviral particles. However, there are distinctions regarding the proportion of L to M to S HBs proteins detected intra- and extracellularly for different genotypes. 2D electrophoresis revealed different posttranslational modification patterns for LHBs. In light of the relevance of HBsAg as diagnostic marker, detectability of purified recombinant HBsAg of various genotypes by HBsAg-specific detection systems licensed in Europe was investigated, showing similar sensitivities for genotypes included in this analysis. These data indicate that recombinant HBsAg reproducibly purified following a defined protocol might be used as an alternative to reference materials currently established.

Subviral Hepatitis B Virus Filaments, like Infectious Viral Particles, Are Released via Multivesicular Bodies

In addition to infectious viral particles, hepatitis B virus-replicating cells secrete large amounts of subviral particles assembled by the surface proteins, but lacking any capsid and genome. Subviral particles form spheres (22-nm particles) and filaments. Filaments contain a much larger amount of the large surface protein (LHBs) compared to spheres. Spheres are released via the constitutive secretory pathway, while viral particles are ESCRT-dependently released via multivesicular bodies (MVBs). The interaction of virions with the ESCRT machinery is mediated by α-taxilin that connects the viral surface protein LHBs with the ESCRT component tsg101. Since filaments in contrast to spheres contain a significant amount of LHBs, it is unclear whether filaments are released like spheres or like virions. To study the release of subviral particles in the absence of virion formation, a core-deficient HBV mutant was generated. Confocal microscopy, immune electron microscopy of ultrathin sections and isolation of MVBs revealed that filaments enter MVBs. Inhibition of MVB biogenesis by the small-molecule inhibitor U18666A or inhibition of ESCRT functionality by coexpression of transdominant negative mutants (Vps4A, Vps4B, and CHMP3) abolishes the release of filaments while the secretion of spheres is not affected. These data indicate that in contrast to spheres which are secreted via the secretory pathway, filaments are released via ESCRT/MVB pathway like infectious viral particles.

IMPORTANCE

This study revises the current model describing the release of subviral particles by showing that in contrast to spheres, which are secreted via the secretory pathway, filaments are released via the ESCRT/MVB pathway like infectious viral particles. These data significantly contribute to a better understanding of the viral morphogenesis and might be helpful for the design of novel antiviral strategies.

Hepatitis C virus comes for dinner: How the hepatitis C virus interferes with autophagy

Autophagy is a highly-regulated, conserved cellular process for the degradation of intracellular components in lysosomes to maintain the energetic balance of the cell. It is a pro-survival mechanism that plays an important role during development, differentiation, apoptosis, ageing and innate and adaptive immune response. Besides, autophagy has been described to be involved in the development of various human diseases, e.g., chronic liver diseases and the development of hepatocellular carcinoma. The hepatitis C virus (HCV) is a major cause of chronic liver diseases. It has recently been described that HCV, like other RNA viruses, hijacks the autophagic machinery to improve its replication. However, the mechanisms underlying its activation are conflicting. HCV replication and assembly occurs at the so-called membranous web that consists of lipid droplets and rearranged endoplasmic reticulum-derived membranes including single-, double- and multi-membrane vesicles. The double-membrane vesicles have been identified to contain NS3, NS5A, viral RNA and the autophagosomal marker microtubule-associated protein 1 light chain 3, corroborating the involvement of the autophagic pathway in the HCV life-cycle. In this review, we will highlight the crosstalk of the autophagosomal compartment with different steps of the HCV life-cycle and address its implications on favoring the survival of infected hepatocytes.