Hypoxia inducible factors regulate hepatitis B virus replication by activating the basal core promoter

Hypoxic reactivation of Kaposi's sarcoma associated herpesvirus

Hypoxic reactivation of Kaposi's sarcoma-associated herpesvirus (KSHV) refers to the phenomenon under low oxygen where the virus goes from latent to lytic replication. Typically, healthy cells generally cease cell division and DNA replication under hypoxic conditions due to limited resources, and the presence of physiological inhibitors. This restricted replication under hypoxic conditions is considered an employed strategy of the cell to minimize energy consumption. However, cancerous cells continuously replicate and divide in hypoxic conditions by reprogramming several aspects of their cell physiology, including but not limited to metabolism, cell cycle, DNA replication, transcription, translation, and the epigenome. KSHV infection, similar to cancerous cells, is known to bypass hypoxia-induced restrictions and undergo reactivation to produce progeny viruses. In previous studies we have mapped several aspects of cell physiology that are manipulated by KSHV through its latent antigens during hypoxic conditions, which allows for a permissive environment for its replication. We discuss the major strategies utilized by KSHV to bypass hypoxia-induced repression. We also describe the KSHV-encoded antigens responsible for modulating these cellular processes important for successful viral replication and persistence in hypoxia.

Hepatitis B virus enhancer 1 activates preS1 and preS2 promoters of integrated HBV DNA impairing HBsAg secretion

Background & Aims

The expression of HBsAg from integrated HBV DNA limits the achievement of functional cure for chronic hepatitis B. Thus, characterising the unique expression and secretion of HBsAg derived from integrated HBV DNA is of clinical significance.

Methods

A total of 563 treatment-naive patients and 62 functionally cured patients were enrolled, and HBsAg and HBcAg immunohistochemistry of their liver biopsy tissues was conducted followed by semi-quantitative analysis. Then, based on stratified analysis of HBeAg-positive and -negative patients, long-read RNA sequencing analysis, as well as an in vitro HBV integration model, we explored the HBsAg secretion characteristics of integrated HBV DNA and underlying mechanisms.

Results

In contrast to the significantly lower serum HBsAg levels, no significant decrease of intrahepatic HBsAg protein was observed in HBeAg-negative patients, as compared with HBeAg-positive patients. The results of long-read RNA sequencing of liver tissues from patients with chronic HBV infection and in vitro studies using integrated HBV DNA mimicking dslDNA plasmid revealed that, the lower HBsAg secretion efficiency seen in HBeAg-negative patients might be attributed to an increased proportion of preS1 mRNA derived from integrated HBV DNA instead of covalently closed circular DNA. The latter resulted in an increased L-HBsAg proportion and impaired HBsAg secretion. Enhancer 1 (EnhI) in integrated HBV DNA could retarget preS1 (SP1) and preS2 (SP2) promoters to disrupt their transcriptional activity balance.

Conclusions

The secretion of HBsAg originating from integrated HBV DNA was impaired. Mechanistically, functional deficiency of core promoter leads to retargeting of EnhI and thus uneven activation of the SP1 over the SP2 promoter, resulting in an increase in the proportion of L-HBsAg.

Impact and implications

Integrated hepatitis B virus (HBV) DNA can serve as an important reservoir for HBV surface antigen (HBsAg) expression, and this limits the achievement of a functional cure. This study revealed that secretion efficiency is lower for HBsAg derived from integrated HBV DNA than HBsAg derived from covalently closed circular DNA, as determined by the unique sequence features of integrated HBV DNA. This study can broaden our understanding of the role of HBV integration and shed new light on antiviral strategies to facilitate a functional cure. We believe our results are of great general interest to a broad audience, including patients and patient organisations, the medical community, academia, the life science industry and the public.

Harnessing CD8+ T cell dynamics in hepatitis B virus-associated liver diseases: Insights, therapies and future directions

Hepatitis B virus (HBV) infection playsa significant role in the etiology and progression of liver-relatedpathologies, encompassing chronic hepatitis, fibrosis, cirrhosis, and eventual hepatocellularcarcinoma (HCC). Notably, HBV infection stands as the primary etiologicalfactor driving the development of HCC. Given the significant contribution ofHBV infection to liver diseases, a comprehensive understanding of immunedynamics in the liver microenvironment, spanning chronic HBV infection,fibrosis, cirrhosis, and HCC, is essential. In this review, we focused on thefunctional alterations of CD8+ T cells within the pathogenic livermicroenvironment from HBV infection to HCC. We thoroughly reviewed the roles ofhypoxia, acidic pH, metabolic reprogramming, amino acid deficiency, inhibitory checkpointmolecules, immunosuppressive cytokines, and the gut-liver communication in shapingthe dysfunction of CD8+ T cells in the liver microenvironment. Thesefactors significantly impact the clinical prognosis. Furthermore, we comprehensivelyreviewed CD8+ T cell-based therapy strategies for liver diseases,encompassing HBV infection, fibrosis, cirrhosis, and HCC. Strategies includeimmune checkpoint blockades, metabolic T-cell targeting therapy, therapeuticT-cell vaccination, and adoptive transfer of genetically engineered CD8+ T cells, along with the combined usage of programmed cell death protein-1/programmeddeath ligand-1 (PD-1/PD-L1) inhibitors with mitochondria-targeted antioxidants.Given that targeting CD8+ T cells at various stages of hepatitis Bvirus-induced hepatocellular carcinoma (HBV + HCC) shows promise, we reviewedthe ongoing need for research to elucidate the complex interplay between CD8+ T cells and the liver microenvironment in the progression of HBV infection toHCC. We also discussed personalized treatment regimens, combining therapeuticstrategies and harnessing gut microbiota modulation, which holds potential forenhanced clinical benefits. In conclusion, this review delves into the immunedynamics of CD8+ T cells, microenvironment changes, and therapeuticstrategies within the liver during chronic HBV infection, HCC progression, andrelated liver diseases.

HIV coinfection exacerbates HBV-induced liver fibrogenesis through a HIF-1α- and TGF-β1-dependent pathway

BACKGROUND & AIMS

Persons with chronic HBV infection coinfected with HIV experience accelerated progression of liver fibrosis compared to those with HBV monoinfection. We aimed to determine whether HIV and its proteins promote HBV-induced liver fibrosis in HIV/HBV-coinfected cell culture models through HIF-1α and TGF-β1 signaling.

METHODS

The HBV-positive supernatant, purified HBV viral particles, HIV-positive supernatant, or HIV viral particles were directly incubated with cell lines or primary hepatocytes, hepatic stellate cells, and macrophages in mono or 3D spheroid coculture models. Cells were incubated with recombinant cytokines and HIV proteins including gp120. HBV sub-genomic constructs were transfected into NTCP-HepG2 cells. We also evaluated the effects of inhibitor of HIF-1α and HIV gp120 in a HBV carrier mouse model that was generated via hydrodynamic injection of the pAAV/HBV1.2 plasmid into the tail vein of wild-type C57BL/6 mice.

RESULTS

We found that HIV and HIV gp120, through engagement with CCR5 and CXCR4 coreceptors, activate AKT and ERK signaling and subsequently upregulate hypoxia-inducible factor-1α (HIF-1α) to increase HBV-induced transforming growth factor-β1 (TGF-β1) and profibrogenic gene expression in hepatocytes and hepatic stellate cells. HIV gp120 exacerbates HBV X protein-mediated HIF-1α expression and liver fibrogenesis, which can be alleviated by inhibiting HIF-1α. Conversely, TGF-β1 upregulates HIF-1α expression and HBV-induced liver fibrogenesis through the SMAD signaling pathway. HIF-1α small-interfering RNA transfection or the HIF-1α inhibitor (acriflavine) blocked HIV-, HBV-, and TGF-β1-induced fibrogenesis.

CONCLUSIONS

Our findings suggest that HIV coinfection exacerbates HBV-induced liver fibrogenesis through enhancement of the positive feedback between HIF-1α and TGF-β1 via CCR5/CXCR4. HIF-1α represents a novel target for antifibrotic therapeutic development in HBV/HIV coinfection.

IMPACT AND IMPLICATIONS

HIV coinfection accelerates the progression of liver fibrosis compared to HBV monoinfection, even among patients with successful suppression of viral load, and there is no sufficient treatment for this disease process. In this study, we found that HIV viral particles and specifically HIV gp120 promote HBV-induced hepatic fibrogenesis via enhancement of the positive feedback between HIF-1α and TGF-β1, which can be ameliorated by inhibition of HIF-1α. These findings suggest that targeting the HIF-1α pathway can reduce liver fibrogenesis in patients with HIV and HBV coinfection.

Oxygen-dependent histone lysine demethylase 4 restricts hepatitis B virus replication

Mammalian cells have evolved strategies to regulate gene expression when oxygen is limited. Hypoxia-inducible factors (HIF) are the major transcriptional regulators of host gene expression. We previously reported that HIFs bind and activate hepatitis B virus (HBV) DNA transcription under low oxygen conditions; however, the global cellular response to low oxygen is mediated by a family of oxygenases that work in concert with HIFs. Recent studies have identified a role for chromatin modifiers in sensing cellular oxygen and orchestrating transcriptional responses, but their role in the HBV life cycle is as yet undefined. We demonstrated that histone lysine demethylase 4 (KDM4) can restrict HBV, and pharmacological or oxygen-mediated inhibition of the demethylase increases viral RNAs derived from both episomal and integrated copies of the viral genome. Sequencing studies demonstrated that KDM4 is a major regulator of the hepatic transcriptome, which defines hepatocellular permissivity to HBV infection. We propose a model where HBV exploits cellular oxygen sensors to replicate and persist in the liver. Understanding oxygen-dependent pathways that regulate HBV infection will facilitate the development of physiologically relevant cell-based models that support efficient HBV replication.

The effect and mechanism of Qingre Huashi formula in the treatment of chronic hepatitis B with Gan-dan-shi-Re syndrome: An integrated transcriptomic and targeted metabolomic analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Qingre Huashi (QRHS) formula is an empirical prescription for the treatment of Gan-Dan-Shi-Re syndrome (GDSR) syndrome in traditional Chinese medicine (TCM). GDSR is one of the typical TCM syndromes in chronic hepatitis B (CHB). However, little is known about the mechanism of the QRHS formula in treating CHB patients with GDSR. The biological basis of GDSR also remains largely unknown.

AIM OF THE STUDY

GDSR mostly occurs in the acute and early stages of chronic liver disease. Effectively alleviating GDSR stalls disease development and benefits patients. The purpose of this study was to explore the molecular basis of GDSR in CHB and then study the mechanism of the QRHS formula treating GDSR using transcriptomics and metabolomics.

MATERIALS AND METHODS

The transcriptome and metabolome of CHB patients with GDSR syndrome were detected using RNA microarray combined with ultra-high performance liquid chromatography/mass spectrometry and information mining. The potential biomarkers were identified from differentially expressed genes and metabolites, and the metabolic pathway was analyzed. We also investigated the callback of metabolic biomarkers after treatment with the QRHS formula, an empirical prescription for the treatment of GDSR syndrome. RT-PCR analysis was carried out in an independent patient cohort of CHB for validation.

RESULTS

Four candidate genes-GPT2, HK2, DDIT3, and HIF1A-and 14 candidate metabolic biomarkers, including L-alpha-aminobutyric acid, selenomethionine, and fructose 1,6-bisphosphate, were identified and validated. All four transcripts of GPT2, HK2, DDIT3, and HIF1A were significantly differentially expressed between the GDSR and non-GDSR groups through independent microarray data and RT-PCR. After treatment with the QRHS formula, the clinical indexes and TCM syndrome were significantly improved, and the 14 disturbed biomarkers were obviously corrected. Three metabolic pathways were confirmed to be perturbed in CHB GDSR patients: alanine, aspartate, and glutamate metabolism, arginine biosynthesis, and aminoacyl-tRNA biosynthesis.

CONCLUSION

Using integrated transcriptomic and targeted metabolomic methods, we identified the potential biomarkers and dysregulated metabolic pathways in CHB patients with GDSR syndrome, which was alleviated by the QRHS formula treatment. These results may provide the mechanism of metabolic dysregulation in GDSR syndrome as well as that underlying the curative effect of the QRHS formula.

A bibliometric analysis of m6A methylation in viral infection from 2000 to 2022

BACKGROUND

N6-methyladenosine (m6A) methylation has become an active research area in viral infection, while little bibliometric analysis has been performed. In this study, we aim to visualize hotspots and trends using bibliometric analysis to provide a comprehensive and objective overview of the current research dynamics in this field.

METHODS

The data related to m6A methylation in viral infection were obtained through the Web of Science Core Collection form 2000 to 2022. To reduce bias, the literature search was conducted on December 1, 2022. Bibliometric and visual analyzes were performed using CiteSpace and Bibliometrix package. After screening, 319 qualified records were retrieved.

RESULTS

These publications mainly came from 28 countries led by China and the United States (the US), with the US ranking highest in terms of total link strength.The most common keywords were m6A, COVID-19, epitranscriptomics, METTL3, hepatitis B virus, innate immunity and human immunodeficiency virus 1. The thematic map showed that METTL3, plant viruses, cancer progression and type I interferon (IFN-I) reflected a good development trend and might become a research hotspot in the future, while post-transcriptional modification, as an emerging or declining theme, might not develop well.

CONCLUSIONS

In conclusion, m6A methylation in viral infection is an increasingly important topic in articles. METTL3, plant viruses, cancer progression and IFN-I may still be research hotspots and trends in the future.

The N6-methyladenosine demethylase ALKBH5 regulates the hypoxic HBV transcriptome

Chronic hepatitis B is a global health problem and current treatments only suppress hepatitis B virus (HBV) infection, highlighting the need for new curative treatments. Oxygen levels influence HBV replication and we previously reported that hypoxia inducible factors (HIFs) activate the basal core promoter (BCP). Here we show that the hypoxic-dependent increase in BCP-derived transcripts is dependent on N6-methyladenosine (m6A) modifications in the 5' stem loop that regulate RNA half-life. Application of a probe-enriched long-read sequencing method to accurately map the HBV transcriptome showed an increased abundance of pre-genomic RNA under hypoxic conditions. Mapping the transcription start sites of BCP-RNAs identified a role for hypoxia to regulate pre-genomic RNA splicing that is dependent on m6A modification. Bioinformatic analysis of published single cell RNA-seq of murine liver showed an increased expression of the RNA demethylase ALKBH5 in the peri-central low oxygen region. In vitro studies with a human hepatocyte derived HepG2-NTCP cell line showed increased ALKBH5 gene expression under hypoxic conditions and a concomitant reduction in m6A-modified HBV BCP-RNA and host RNAs. Silencing the demethylase reduced the level of BCP-RNAs and host gene (CA9, NDRG1, VEGFA, BNIP3, FUT11, GAP and P4HA1) transcripts and this was mediated via reduced HIFα expression. In summary, our study highlights a previously unrecognized role for ALKBH5 in orchestrating viral and cellular transcriptional responses to low oxygen.

A small molecule iCDM-34 identified by in silico screening suppresses HBV DNA through activation of aryl hydrocarbon receptor

IFN-alpha have been reported to suppress hepatitis B virus (HBV) cccDNA via APOBEC3 cytidine deaminase activity through interferon signaling. To develop a novel anti-HBV drug for a functional cure, we performed in silico screening of the binding compounds fitting the steric structure of the IFN-alpha-binding pocket in IFNAR2. We identified 37 compounds and named them in silico cccDNA modulator (iCDM)-1-37. We found that iCDM-34, a new small molecule with a pyrazole moiety, showed anti-HCV and anti-HBV activities. We measured the anti-HBV activity of iCDM-34 dependent on or independent of entecavir (ETV). iCDM-34 suppressed HBV DNA, pgRNA, HBsAg, and HBeAg, and also clearly exhibited additive inhibitory effects on the suppression of HBV DNA with ETV. We confirmed metabolic stability of iCDM-34 was stable in human liver microsomal fraction. Furthermore, anti-HBV activity in human hepatocyte-chimeric mice revealed that iCDM-34 was not effective as a single reagent, but when combined with ETV, it suppressed HBV DNA compared to ETV alone. Phosphoproteome and Western blotting analysis showed that iCDM-34 did not activate IFN-signaling. The transcriptome analysis of interferon-stimulated genes revealed no increase in expression, whereas downstream factors of aryl hydrocarbon receptor (AhR) showed increased levels of the expression. CDK1/2 and phospho-SAMHD1 levels decreased under iCDM-34 treatment. In addition, AhR knockdown inhibited anti-HCV activity of iCDM-34 in HCV replicon cells. These results suggest that iCDM-34 decreases the phosphorylation of SAMHD1 through CDK1/2, and suppresses HCV replicon RNA, HBV DNA, and pgRNA formation.

The N6-methyladenosine demethylase ALKBH5 regulates the hypoxic HBV transcriptome

Chronic hepatitis B is a global health problem and current treatments only suppress hepatitis B virus (HBV) infection, highlighting the need for new curative treatments. Oxygen levels influence HBV replication and we previously reported that hypoxia inducible factors (HIFs) activate the basal core promoter to transcribe pre-genomic RNA. Application of a probe-enriched long-read sequencing method to map the HBV transcriptome showed an increased abundance of all viral RNAs under low oxygen or hypoxic conditions. Importantly, the hypoxic-associated increase in HBV transcripts was dependent on N6-methyladenosine (m6A) modifications and an m6A DRACH motif in the 5' stem loop of pre-genomic RNA defined transcript half-life under hypoxic conditions. Given the essential role of m6A modifications in the viral transcriptome we assessed the oxygen-dependent expression of RNA demethylases and bioinformatic analysis of published single cell RNA-seq of murine liver showed an increased expression of the RNA demethylase ALKBH5 in the peri-central low oxygen region. In vitro studies with a human hepatocyte derived HepG2 cell line showed increased ALKBH5 gene expression under hypoxic conditions. Silencing the demethylase reduced the levels of HBV pre-genomic RNA and host gene (CA9, NDRG1, VEGFA, BNIP3, FUT11, GAP and P4HA1) transcripts and this was mediated via reduced HIFα expression. In summary, our study highlights a previously unrecognized role for ALKBH5 in orchestrating viral and cellular transcriptional responses to low oxygen.

Hypoxia dampens innate immune signalling at early time points and increases Zika virus RNA levels in iPSC-derived macrophages

Type I interferons (IFNs) are the major host defence against viral infection and are induced following activation of cell surface or intracellular pattern recognition receptors, including retinoic-acid-inducible gene I (RIG-I)-like receptors (RLRs). All cellular processes are shaped by the microenvironment and one important factor is the local oxygen tension. The majority of published studies on IFN signalling are conducted under laboratory conditions of 18% oxygen (O2), that do not reflect the oxygen levels in most organs (1-5 % O2). We studied the effect of low oxygen on IFN induction and signalling in induced Pluripotent Stem Cell (iPSC)-derived macrophages as a model for tissue-resident macrophages and assessed the consequence for Zika virus (ZIKV) infection. Hypoxic conditions dampened the expression of interferon-stimulated genes (ISGs) following RLR stimulation or IFN treatment at early time points. RNA-sequencing and bio-informatic analysis uncovered several pathways including changes in transcription factor availability, the presence of HIF binding sites in promoter regions, and CpG content that may contribute to the reduced ISG expression. Hypoxic conditions increased the abundance of ZIKV RNA highlighting the importance of understanding how low oxygen conditions in the local microenvironment affect pathogen sensing and host defences.

Hypoxia alters the immune response in mouse peritoneal macrophages infected with influenza a virus with truncated NS1 protein

Macrophages are the most abundant cells in infected tissue and are involved in the clearing infection, and immunomodulation of the innate and adaptive immune response. NS80 virus of influenza A virus, which encodes only the first 80 aa of the NS1 protein, suppresses the immune host response and is associated with enhanced pathogenicity. Hypoxia promotes infiltration of peritoneal macrophages into the adipose tissue and production of cytokines. To understand the role of hypoxia in the regulation of immune response, macrophages were infected with A/WSN/33 (WSN) and NS80 virus, and transcriptional profiles of the RIG-I-like receptor signalling pathway and expression of cytokines were evaluated in normoxia and hypoxia. Hypoxia inhibited the proliferation of IC-21 cells, downregulated the RIG-I-like receptor signalling pathway, and inhibited transcriptional activity of IFN-α, IFN-β, IFN-ε, and IFN-λ mRNA in infected macrophages. While transcription of IL-1β and Casp-1 mRNAs were increased in infected macrophages in normoxia, hypoxia resulted in decreased transcription activity of IL-1β and Casp-1 mRNAs. Hypoxia significantly affected expression of the translation factors IRF4, IFN-γ, and CXCL10 involved in regulation of immune response and polarization of the macrophages. The expression of pro-inflammatory cytokines such as sICAM-1, IL-1α, TNF-α, CCL2, CCL3, CXCL12, and M-CSF was to a large extent affected in uninfected and infected macrophages cultivated in hypoxia. The NS80 virus increased the expression of M-CSF, IL-16, CCL2, CCL3, and CXCL12, especially under hypoxia. The results show that hypoxia may play an important role in peritoneal macrophage activation, regulates the innate and adaptive immune response, changes production of pro-inflammatory cytokines, promotes macrophage polarization, and could affect the function of other immune cells.

Mitochondrial HIGD1A inhibits hepatitis B virus transcription and replication through the cellular PNKD-NF-κB-NR2F1 nexus

Hepatitis B Virus (HBV) replication has been reported to be restricted by the intrahepatic host restriction factors and antiviral signaling pathways. The intracellular mechanisms underlying the significant viremia difference among different phases of the natural history chronic HBV infection remain elusive. We herein report that the hypoxia-induced gene domain protein-1a (HIGD1A) was highly expressed in the liver of inactive HBV carriers with low viremia. Ectopic expression of HIGD1A in hepatocyte-derived cells significantly inhibited HBV transcription and replication in a dose-dependent manner, while silence of HIGD1A promoted HBV gene expression and replication. Similar results were also observed in both de novo HBV-infected cell culture model and HBV persistence mouse model. Mechanistically, HIGD1A is located on the mitochondrial inner membrane and activates nuclear factor kappa B (NF-κB) signaling pathway through binding to paroxysmal nonkinesigenic dyskinesia (PNKD), which further enhances the expression of a transcription factor NR2F1 to inhibit HBV transcription and replication. Consistently, knockdown of PNKD or NR2F1 and blockage of NF-κB signaling pathway abrogated the inhibitory effect of HIGD1A on HBV replication. Mitochondrial HIGD1A exploits the PNKD-NF-κB-NR2F1 nexus to act as a host restriction factor of HBV infection. Our study thus shed new lights on the regulation of HBV by hypoxia-related genes and related antiviral strategies.

High HBV-DNA serum levels are associated with type 2 diabetes in adults with positive HBsAg: An observational study

BACKGROUND

The prevalence of diabetes is higher in hepatitis B virus (HBV)-infected population. We aimed to examine the relationship between different serum HBV-DNA levels and type 2 diabetes in adults with positive HBV surface antigen (HBsAg).

METHODS

We conducted cross-sectional analyses of data obtaining from the Clinical Database System of Wuhan Union Hospital. Diabetes was defined by self-report of type 2 diabetes, fasting plasma glucose (FPG) ≥7mmol/L, or glycated hemoglobin (HbA1c) ≥6.5%. Binary logistic regression analyses were performed to investigate the factors associated with diabetes.

RESULTS

Among 12,527 HBsAg-positive adults, 2,144 (17.1%) were diabetic. Patients with serum HBV-DNA <100, 100-2000, 2000-20000 and ≥20000 IU/mL accounted for 42.2% (N=5,285), 22.6% (N=2,826), 13.3% (N=1,665) and 22.0% (N=2,751), respectively. The risk of type 2 diabetes, FPG ≥7mmol/L and HbA1c ≥6.5% in individuals with highly elevated serum HBV-DNA level (≥20000 IU/mL) were 1.38 (95% confidence interval [CI]: 1.16 to 1.65), 1.40 (95% CI: 1.16 to 1.68) and 1.78 (95% CI: 1.31 to 2.42) times relative to those with negative or lowly elevated serum HBV-DNA (<100 IU/mL). However, the analyses showed no association of moderately (2000-20000 IU/mL) to slightly (100-2000 IU/mL) raised serum HBV-DNA levels with type 2 diabetes (OR=0.88, P=0.221; OR=1.08, P=0.323), FPG ≥7mmol/L (OR=1.00, P=0.993; OR=1.11, P=0.250) and HbA1c ≥6.5% (OR=1.24, P=0.239; OR=1.17, P=0.300).

CONCLUSION

In HBsAg-positive adults, highly elevated level rather than moderately to slightly raised levels of serum HBV-DNA is independently associated with an increased risk of type 2 diabetes.

Generation and Utilization of a Monoclonal Antibody against Hepatitis B Virus Core Protein for a Comprehensive Interactome Analysis

Hepatitis B virus (HBV) core antigen (HBc) is a structural protein that forms the viral nucleocapsid and is involved in various steps of the viral replication cycle, but its role in the pathogenesis of HBV infection is still elusive. In this study, we generated a mouse monoclonal antibody (mAb) against HBc and used it in antibody-based in situ biotinylation analysis in order to identify host proteins that interact with HBc. HBc antigen was produced with a wheat germ cell-free protein synthesis system and used to immunize mice. Among the established hybridoma clones, a single clone (mAb #7) was selected and further characterized for its ability in the antibody-based in situ biotinylation analysis to collect host proteins that are in the vicinity of HBc. Using mass spectrometry, we identified 215 HBc-interacting host proteins, three of which bind HBc most significantly under hypoxic conditions. Our results indicate that mAb #7 can be used to systematically identify host proteins that interact with HBc under pathophysiological conditions, and thus may be useful to explore the molecular pathways involved in HBV-induced cytopathogenesis.

Hypoxia signaling in human health and diseases: implications and prospects for therapeutics

Molecular oxygen (O₂) is essential for most biological reactions in mammalian cells. When the intracellular oxygen content decreases, it is called hypoxia. The process of hypoxia is linked to several biological processes, including pathogenic microbe infection, metabolic adaptation, cancer, acute and chronic diseases, and other stress responses. The mechanism underlying cells respond to oxygen changes to mediate subsequent signal response is the central question during hypoxia. Hypoxia-inducible factors (HIFs) sense hypoxia to regulate the expressions of a series of downstream genes expression, which participate in multiple processes including cell metabolism, cell growth/death, cell proliferation, glycolysis, immune response, microbe infection, tumorigenesis, and metastasis. Importantly, hypoxia signaling also interacts with other cellular pathways, such as phosphoinositide 3-kinase (PI3K)-mammalian target of rapamycin (mTOR) signaling, nuclear factor kappa-B (NF-κB) pathway, extracellular signal-regulated kinases (ERK) signaling, and endoplasmic reticulum (ER) stress. This paper systematically reviews the mechanisms of hypoxia signaling activation, the control of HIF signaling, and the function of HIF signaling in human health and diseases. In addition, the therapeutic targets involved in HIF signaling to balance health and diseases are summarized and highlighted, which would provide novel strategies for the design and development of therapeutic drugs.

The role of cell-penetrating peptides in potential anti-cancer therapy

Due to the complex physiological structure, microenvironment and multiple physiological barriers, traditional anti-cancer drugs are severely restricted from reaching the tumour site. Cell-penetrating peptides (CPPs) are typically made up of 5-30 amino acids, and can be utilised as molecular transporters to facilitate the passage of therapeutic drugs across physiological barriers. Up to now, CPPs have widely been used in many anti-cancer treatment strategies, serving as an excellent potential choice for oncology treatment. However, their drawbacks, such as the lack of cell specificity, short duration of action, poor stability in vivo, compatibility problems (i.e. immunogenicity), poor therapeutic efficacy and formation of unwanted metabolites, have limited their further application in cancer treatment. The cellular uptake mechanisms of CPPs involve mainly endocytosis and direct penetration, but still remain highly controversial in academia. The CPPs-based drug delivery strategy could be improved by clever design or chemical modifications to develop the next-generation CPPs with enhanced cell penetration capability, stability and selectivity. In addition, some recent advances in targeted cell penetration that involve CPPs provide some new ideas to optimise CPPs.

Inflammatory Gene Expression Associates with Hepatitis B Virus cccDNA- but Not Integrant-Derived Transcripts in HBeAg Negative Disease

Chronic hepatitis B virus (HBV) infection is a global health problem that presents as a spectrum of liver disease, reflecting an interplay between the virus and the host immune system. HBV genomes exist as episomal covalently closed circular DNA (cccDNA) or chromosomal integrants. The relative contribution of these genomes to the viral transcriptome in chronic hepatitis B (CHB) is not well-understood. We developed a qPCR method to estimate the abundance of HBV cccDNA- and integrant-derived viral transcripts and applied this to a cohort of patients diagnosed with CHB in the HBe antigen negative phase of disease. We noted a variable pattern of HBV transcripts from both DNA templates, with preS1/S2 mRNAs predominating and a significant association between increasing age and the expression of integrant-derived mRNAs, but not with inflammatory status. In contrast, cccDNA-derived transcripts were associated with markers of liver inflammation. Analysis of the inflammatory hepatic transcriptome identified 24 genes significantly associated with cccDNA transcriptional activity. Our study uncovers an immune gene signature that associates with HBV cccDNA transcription and increases our understanding of viral persistence.

Stanniocalcin 1 is a serum biomarker and potential therapeutic target for HBV-associated liver fibrosis

Stanniocalcin 1 (STC1), a secreted protein, is upregulated in human cancers including hepatocellular carcinoma (HCC). While most HCCs develop from chronic liver disease which involves progressive parenchymal injury and fibrosis, the role of STC1 in this pre-neoplastic stage remains poorly understood. In this study, we investigated the clinical relevance and functional significance of secreted STC1 in liver fibrosis. To this end, STC1 level was determined in the serum samples of chronic hepatitis B patients and correlated with the degree of liver fibrosis. Diagnostic performance of STC1 was analysed by area under receiver operating characteristic curve (AUROC), sensitivity, specificity, positive predictive value, and negative predictive value. The results were compared with other well-characterised serum biomarkers for liver fibrosis, aspartate transaminase to Platelet Ratio Index (APRI) and Fibrosis-4 (FIB-4). The functional role of STC1 was interrogated by in vitro experiments using cell line models. Expression of fibrogenic markers was quantified by RT-qPCR and western blotting. Our results showed that serum STC1 level in chronic hepatitis B patients was positively correlated with the degree of liver fibrosis and showed a stepwise increase in accordance with the severity of fibrosis. The AUROCs for detecting significant fibrosis (>9.0 kPa) and cirrhosis (>12.0 kPa) was 0.911 and 0.880, respectively. STC1 demonstrated a superior specificity and positive predictive value when compared to APRI and FIB-4. Consistent with this, STC1 was elevated in the liver tissues and sera of CCl₄ -treated mice showing marked liver fibrosis. In vitro, STC1 was secreted by the human hepatic stellate cell line LX2. Human recombinant STC1 (rhSTC1) induced expression of fibrogenic markers in LX2 cells. The pro-fibrogenic phenotype conferred by rhSTC1 or TGF-β1 in LX2 cells could be attenuated using anti-STC1 antibody. Taken together, STC1 is a specific serum biomarker for HBV-associated liver fibrosis. STC1 functionally promotes liver fibrogenesis and is a potential actionable target. This article is protected by copyright. All rights reserved.

Host-cell interactions in HBV infection and pathogenesis: the emerging role of m6A modification

Hepatitis B virus (HBV) is a DNA virus with a complex life cycle that includes a reverse transcription step. HBV is poorly sensed by the immune system and frequently establishes persistent infection that can cause chronic infection, the leading cause of liver cancer and cirrhosis worldwide. Recent mounting evidence has indicated the growing importance of RNA methylation (m6A modification) in viral replication, immune escape, and carcinogenesis. The value of m6A RNA modification for the prediction and clinical management of chronic HBV infection remains to be assessed. However, a number of studies indicate the important role of m6A-marked transcripts and factors of m6A machinery in managing HBV-related pathologies. In this review, we discuss the fundamental and potential clinical impact of m6A modifications on HBV infection and pathogenesis, as well as highlight the important molecular techniques and tools that can be used for studying RNA m6A methylome.

Hepatitis B x antigen (HBx) is an important therapeutic target in the pathogenesis of hepatocellular carcinoma

Hepatitis B virus (HBV) is a human pathogen that has infected an estimated two billion people worldwide. Despite the availability of highly efficacious vaccines, universal screening of the blood supply for virus, and potent direct acting anti-viral drugs, there are more than 250 million carriers of HBV who are at risk for the sequential development of hepatitis, fibrosis, cirrhosis and hepatocellular carcinoma (HCC). More than 800,000 deaths per year are attributed to chronic hepatitis B. Many different therapeutic approaches have been developed to block virus replication, and although effective, none are curative. These treatments have little or no impact upon the portions of integrated HBV DNA, which often encode the virus regulatory protein, HBx. Although given little attention, HBx is an important therapeutic target because it contributes importantly to (a) HBV replication, (b) in protecting infected cells from immune mediated destruction during chronic infection, and (c) in the development of HCC. Thus, the development of therapies targeting HBx, combined with other established therapies, will provide a functional cure that will target virus replication and further reduce or eliminate both the morbidity and mortality associated with chronic liver disease and HCC. Simultaneous targeting of all these characteristics underscores the importance of developing therapies against HBx.

The immunological and metabolic landscape in primary and metastatic liver cancer

The liver is the sixth most common site of primary cancer in humans, and generally arises in a background of cirrhosis and inflammation. Moreover, the liver is frequently colonized by metastases from cancers of other organs (particularly the colon) because of its anatomical location and organization, as well as its unique metabolic and immunosuppressive environment. In this Review, we discuss how the hepatic microenvironment adapts to pathologies characterized by chronic inflammation and metabolic alterations. We illustrate how these immunological or metabolic changes alter immunosurveillance and thus hinder or promote the development of primary liver cancer. In addition, we describe how inflammatory and metabolic niches affect the spreading of cancer metastases into or within the liver. Finally, we review the current therapeutic options in this context and the resulting challenges that must be surmounted.

Rapid and Robust Continuous Purification of High-Titer Hepatitis B Virus for In Vitro and In Vivo Applications

Available treatments for hepatitis B can control the virus but are rarely curative. This led to a global initiative to design new curative therapies for the 257 million patients affected. Discovery and development of these new therapies is contingent upon functional in vitro and in vivo hepatitis B virus (HBV) infection models. However, low titer and impurity of conventional HBV stocks reduce significance of in vitro infections and moreover limit challenge doses in current in vivo models. Therefore, there is a critical need for a robust, simple and reproducible protocol to generate high-purity and high-titer infectious HBV stocks. Here, we outline a three-step protocol for continuous production of high-quality HBV stocks from supernatants of HBV-replicating cell lines. This purification process takes less than 6 h, yields to high-titer stocks (up to 1 × 10¹¹ enveloped, DNA-containing HBV particles/mL each week), and is with minimal equipment easily adaptable to most laboratory settings.