The impact of HBx protein on mitochondrial dynamics and associated signaling pathways strongly depends on the hepatitis B virus genotype.

Chronic hepatitis B virus (HBV) infections are strongly associated with liver cirrhosis, inflammation, and hepatocellular carcinoma. In this context, the viral HBx protein is considered as a major factor influencing HBV-associated pathogenesis through deregulation of multiple cellular signaling pathways and is therefore a potential target for prognostic and therapeutic applications. However, HBV-associated pathogenesis differs significantly between genotypes, with the relevant factors and in particular the contribution of the genetic diversity of HBx being largely unknown. To address this question, we studied the specific genotype-dependent impact of HBx on cellular signaling pathways, focusing in particular on morphological and functional parameters of mitochondria. To exclusively investigate the impact of HBx of different genotypes on integrity and function of mitochondria in the absence of additional viral factors, we overexpressed HBx in Huh7 or HepG2 cells. Key signaling pathways were profiled by kinome analysis and correlated with expression levels of mitochondrial and pathogenic markers. Conclusively, HBx of genotypes A and G caused strong disruption of mitochondrial morphology alongside an induction of PTEN-induced putative kinase 1/Parkin-mediated mitophagy. These effects were only moderately dysregulated by genotypes B and E, whereas genotypes C and D exhibit an intermediate effect in this regard. Accordingly, changes in mitochondrial membrane potential and elevated reactive oxygen species production were associated with the HBx-mediated dysfunction among different genotypes. Also, genotype-related differences in mitophagy induction were identified and indicated that HBx-mediated changes in the mitochondria morphology and function strongly depend on the genotype. This indicates a relevant role of HBx in the process of genotype-dependent liver pathogenesis of HBV infections and reveals underlying mechanisms.IMPORTANCEThe hepatitis B virus is the main cause of chronic liver disease worldwide and differs in terms of pathogenesis and clinical outcome among the different genotypes. Furthermore, the viral HBx protein is a known factor in the progression of liver injury by inducing aberrant mitochondrial structures and functions. Consequently, the selective removal of dysfunctional mitochondria is essential to maintain overall cellular homeostasis and cell survival. Consistent with the intergenotypic difference of HBV, our data reveal significant differences regarding the impact of HBx of different genotypes on mitochondrial dynamic and function and thereby on radical oxygen stress levels within the cell. We subsequently observed that the induction of mitophagy differs significantly across the heterogenetic HBx proteins. Therefore, this study provides evidence that HBx-mediated changes in the mitochondria dynamics and functionality strongly depend on the genotype of HBx. This highlights an important contribution of HBx in the process of genotype-dependent liver pathogenesis.

SIAH2 suppresses c-JUN pathway by promoting the polyubiquitination and degradation of HBx in hepatocellular carcinoma.

As an important protein encoded by hepatitis B virus (HBV), HBV X protein (HBx) plays an important role in the development of hepatocellular carcinoma (HCC). It has been shown that seven in absentia homologue 1 (SIAH1) could regulates the degradation of HBx through the ubiquitin-proteasome pathway. However, as a member of SIAH family, the regulatory effects of SIAH2 on HBx remain unclear. In this study, we first confirmed that SIAH2 could reduce the protein levels of HBx depending on its E3 ligase activity. Moreover, SIAH2 interacted with HBx and induced its K48-linked polyubiquitination and proteasomal degradation. Furthermore, we provided evidence that SIAH2 inhibits HBx-associated HCC cells proliferation by regulating HBx. In conclusion, our study identified a novel role for SIAH2 in promoting HBx degradation and SIAH2 exerts an inhibitory effect in the proliferation of HBx-associated HCC through inducing the degradation of HBx. Our study provides a new idea for the targeted degradation of HBx and may have great huge significance into providing novel evidence for the targeted therapy of HBV-infected HCC.

Oxidative stress sensor Keap1 recognizes HBx protein to activate the Nrf2/ARE signaling pathway, thereby inhibiting hepatitis B virus replication.

IMPORTANCE: The Kelch-like ECH-associated protein 1 (Keap1)/NF-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling pathway is one of the most important defense mechanisms against oxidative stress. We previously reported that a cellular hydrogen peroxide scavenger protein, peroxiredoxin 1, a target gene of transcription factor Nrf2, acts as a novel HBV X protein (HBx)-interacting protein and negatively regulates hepatitis B virus (HBV) propagation through degradation of HBV RNA. This study further demonstrates that the Nrf2/ARE signaling pathway is activated during HBV infection, eventually leading to the suppression of HBV replication. We provide evidence suggesting that Keap1 interacts with HBx, leading to Nrf2 activation and inhibition of HBV replication via suppression of HBV core promoter activity. This study raises the possibility that activation of the Nrf2/ARE signaling pathway is a potential therapeutic strategy against HBV. Our findings may contribute to an improved understanding of the negative regulation of HBV replication by the antioxidant response.

Mitochondrial Glycerol-3-Phosphate Dehydrogenase Restricts HBV Replication via the TRIM28-Mediated Degradation of HBx.

Hepatitis B virus (HBV) infection affects hepatic metabolism. Serum metabolomics studies have suggested that HBV possibly hijacks the glycerol-3-phosphate (G3P) shuttle. In this study, the two glycerol-3-phosphate dehydrogenases (GPD1 and GPD2) in the G3P shuttle were analyzed for determining their role in HBV replication and the findings revealed that GPD2 and not GPD1 inhibited HBV replication. The knockdown of GPD2 expression upregulated HBV replication, while GPD2 overexpression reduced HBV replication. Moreover, the overexpression of GPD2 significantly reduced HBV replication in hydrodynamic injection-based mouse models. Mechanistically, this inhibitory effect is related to the GPD2-mediated degradation of HBx protein by recruiting the E3 ubiquitin ligase TRIM28 and not to the alterations in G3P metabolism. In conclusion, this study revealed GPD2, a key enzyme in the G3P shuttle, as a host restriction factor in HBV replication. IMPORTANCE The glycerol-3-phosphate (G3P) shuttle is important for the delivery of cytosolic reducing equivalents into mitochondria for oxidative phosphorylation. The study analyzed two key components of the G3P shuttle and identified GPD2 as a restriction factor in HBV replication. The findings revealed a novel mechanism of GPD2-mediated inhibition of HBV replication via the recruitment of TRIM28 for degrading HBx, and the HBx-GPD2 interaction could be another potential therapeutic target for anti-HBV drug development.

The ubiquitin specific protease 7 stabilizes HPV16E7 to promote HPV-mediated carcinogenesis.

Human papillomavirus (HPV) encoded E7 oncoprotein plays an important role in supporting the viral productive cycle and inducing cancer phenotypes. The ability of E7 to exercise these functions, partly, depends upon its steady-state level. HPV manipulates the host de-ubiquitination pathway to maintain the stability of its viral proteins. In this study, we uncovered that HPV interacts with the host ubiquitin specific protease 7 (USP7), a universal de-ubiquitinating enzyme, leading to the stabilization of E7 oncoprotein. We observed that HPV16E7 complexes with USP7 via the E7-CR3 domain, and this E7-USP7 complex exists predominantly in the nucleus. Our results showed that USP7 stabilizes and prolongs the half-life of HPV16E7 by antagonizing ubiquitination and proteasomal degradation. Consistently, when we inhibited USP7 activity using HBX 19818, HPV16E7 protein level was reduced and its turnover was increased. We also provide evidence that HBX 19818-induced USP7 inhibition can halt HPV-mediated carcinogenesis, including cell proliferation, invasion, migration and transformation. These findings indicate that USP7 plays an essential role in stabilizing E7. The specific and potent inhibitory effects of HBX 19818 on HPV-induced carcinogenesis provide a molecular insight, suggesting the potential of targeting USP7 as a new therapeutic approach for the treatment of HPV-associated cancers.

Transcriptome wide functional analysis of HBx expressing human hepatocytes stimulated with endothelial cell cross-talk.

Identification of genes dysregulated during the hepatitis B virus (HBV)-host cell interaction adds to the understanding of underlying molecular mechanisms and aids in discovering effective therapies to improve prognosis in hepatitis B virus (HBV)-infected individuals. Through bioinformatics analyses of transcriptomics data, this study aimed to identify potential genes involved in the cross-talk of human hepatocytes expressing the HBV viral protein HBx with endothelial cells. Transient transfection of HBV viral gene X (HBx) was performed in THLE2 cells using pcDNA3 constructs. Through mRNA Sequencing (RNA Seq) analysis, differentially expressed genes (DEGs) were identified. THLE2 cells transfected with HBx (THLE2x) were further treated with conditioned medium from cultured human umbilical vein derived endothelial cells (HUVEC-CM). Gene Ontology (GO) enrichment analysis revealed that interferon and cytokine signaling pathways were primarily enriched for the downregulated DEGs in THLE2x cells treated with HUVEC-CM. One significant module was selected following protein-protein interaction (PPI) network generation, and thirteen hub genes were identified from the module. The prognostic values of the hub genes were evaluated using Kaplan-Meier (KM) plotter, and three genes (IRF7, IFIT1, and IFITM1) correlated with poor disease specific survival (DSS) in HCC patients with chronic hepatitis. A comparison of the DEGs identified in HUVEC-stimulated THLE2x cells with four publicly available HBV-related HCC microarray datasets revealed that PLAC8 was consistently downregulated in all four HCC datasets as well as in HUVEC-CM treated THLE2x cells. KM plots revealed that PLAC8 correlated with worse relapse free survival and progression free survival in HCC patients with hepatitis B virus infection. This study provided molecular insights which may help develop a deeper understanding of HBV-host stromal cell interaction and open avenues for future research.

HBx promotes glomerular podocyte-induced immune cell responses.

BACKGROUND: Podocytes, as intrinsic renal cells, can also express MHC-II and costimulatory molecules under inflammatory conditions, suggesting that they may act as antigen-presenting cells (APCs) to activate immune cell responses and then lead to immune-mediated renal injury. They are already recognized as main targets in the pathogenic mechanism of hepatitis B virus (HBV)-associated glomerulonephritis (HBV-GN). Previous studies also have indicated that inflammatory cells infiltration and immune-mediated tissue injury are evident in the kidney samples of patients with HBV-GN. However, the role of podocytes immune disorder in the pathogenic mechanism of HBV-GN remains unclear. METHODS: Renal function and inflammatory cells infiltration were measured in HBV transgenic (HBV-Tg) mice. In vitro, podocytes/CD4+ T cells or macrophages co-culture system was established. Then, the expression of HBx, CD4, and CD68 was determined by immunohistochemistry, while the expression of MHC-II, CD40, and CD40L was determined by immunofluorescence. Co-stimulatory molecules expression was examined by flow cytometry. The levels of inflammatory factors were detected by ELISA. RESULTS: In vivo, renal function was obviously impaired in HBV-Tg mice. HBx was significantly upregulated and immune cells infiltrated in the glomerulus of HBV-Tg mice. Expression of MHC-II and costimulatory molecule CD40 increased in the podocytes of HBV-Tg mice; CD4+ T cells exhibited increased CD40L expression in glomerulus. In vitro, CD40 expression was markedly elevated in HBx-podocytes. In co-culture systems, HBx-podocytes stimulated CD4+ T cells activation and caused the imbalance between IFN-γ and IL-4. HBx-podocytes also enhanced the adhesion ability of macrophages and induced the release of proinflammatory mediators. CONCLUSION: Taken together, these podocyte-related immune disorder may be involved in the pathogenic mechanism of HBV-GN.

Reactive Oxygen Species Induction by Hepatitis B Virus: Implications for Viral Replication in p53-Positive Human Hepatoma Cells.

Hepatitis B virus (HBV) infects approximately 300 million people worldwide, causing chronic infections. The HBV X protein (HBx) is crucial for viral replication and induces reactive oxygen species (ROS), leading to cellular damage. This study explores the relationship between HBx-induced ROS, p53 activation, and HBV replication. Using HepG2 and Hep3B cell lines that express the HBV receptor NTCP, we compared ROS generation and HBV replication relative to p53 status. Results indicated that HBV infection significantly increased ROS levels in p53-positive HepG2-NTCP cells compared to p53-deficient Hep3B-NTCP cells. Knockdown of p53 reduced ROS levels and enhanced HBV replication in HepG2-NTCP cells, whereas p53 overexpression increased ROS and inhibited HBV replication in Hep3B-NTCP cells. The ROS scavenger N-acetyl-L-cysteine (NAC) reversed these effects. The study also found that ROS-induced degradation of the HBx is mediated by the E3 ligase Siah-1, which is activated by p53. Mutations in p53 or inhibition of its transcriptional activity prevented ROS-mediated HBx degradation and HBV inhibition. These findings reveal a p53-dependent negative feedback loop where HBx-induced ROS increases p53 levels, leading to Siah-1-mediated HBx degradation and HBV replication inhibition. This study offers insights into the molecular mechanisms of HBV replication and identifies potential therapeutic targets involving ROS and p53 pathways.

Hepatitis B Virus (HBV) Upregulates TRAIL-R3 Expression in Hepatocytes Resulting in Escape From Both Cell Apoptosis and Suppression of HBV Replication by TRAIL.

BACKGROUND: Hepatitis B virus (HBV) evades host immunity by regulating intracellular signals. To clarify this immune tolerance mechanism, we performed gene expression analysis using HBV-infected humanized mouse livers. METHODS: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 3 (TRAIL-R3) was significantly upregulated in livers of HBV-infected human hepatocyte transplanted mice by cDNA microarray and next-generation sequencing. We analyzed the significance of TRAIL-R3 upregulation in HBV infection using human hepatocyte transplanted mice and HepG2 cell lines. RESULTS: TRAIL-R3 induction by HBV infection was verified by in vitro and in vivo HBV replication models, and induction was inhibited by antiviral nucleot(s)ide analogue treatment. TRAIL-R3 transcription was regulated by the TRAIL-R3 promoter at -969 to -479 nucleotides upstream from the transcription start site, and by hepatitis B x (HBx) via activation of nuclear factor-κB (NF-κB) signal. TRAIL not only induced cell apoptosis but also inhibited HBV replication. TRAIL-R3 upregulation could inhibit both TRAIL-dependent apoptosis in HBV-infected hepatocytes and TRAIL-mediated suppression of HBV replication. CONCLUSIONS: These results suggest a mechanism by which HBV persists by escaping host immunity through upregulation of TRAIL-R3. Development of novel drugs to inhibit this escape system might lead to complete HBV elimination from human hepatocytes.

Hepatitis B Virus X Protein Expression Is Tightly Regulated by N6-Methyladenosine Modification of Its mRNA.

Hepatitis B virus (HBV) encodes a regulatory protein, termed HBx, that has been intensely studied in the past and shown to play a key role(s) in viral transcription and replication. In addition, a huge body of work exists in the literature related to signal transduction and possible mechanism(s) leading to hepatocarcinogenesis associated with infection. We have previously reported that HBV transcripts are modified by N6-methyladenosine (m6A) at the single consensus DRACH motif at nucleotides (nt) 1905 to 1909 in the epsilon structural element, and this m6A modification affects the HBV life cycle. In this study, we present evidence that additional variants of m6A (DRACH) motifs located within nt 1606 to 1809 correspond to the coding region of HBx mRNA and 3' untranslated region (UTR) of other viral mRNAs. Using the mutants of additional m6A sites in nt 1606 to 1809 and a depletion strategy of m6A methyltransferases (METTL3/14) and reader proteins (YTHDFs), we show that m6A modification at nt 1616, located in the HBx coding region, regulates HBx protein expression. The HBx RNA and protein expression levels were notably increased by the silencing of m6A reader YTHDF2 and methyltransferases as well as the mutation of m6A sites in the HBx coding region. However, other viral protein expression levels were not affected by the m6A modification at nt 1616. Thus, m6A modifications in the HBx open reading frame (ORF) downregulate HBx protein expression, commonly seen during HBV transfections, transgenic mice, and natural infections of human hepatocytes. These studies identify the functional role of m6A modification in the subtle regulation of HBx protein expression consistent with its possible role in establishing chronic hepatitis. IMPORTANCE N6-methyladenosien (m6A) modifications recently have been implicated in the HBV life cycle. Previously, we observed that m6A modification occurs in the adenosine at nt 1907 of the HBV genome, and this modification regulates the viral life cycle. Here, we identified an additional m6A site located in nt 1616 of the HBV genome. This modification negatively affects HBx RNA and protein expression. In the absence of m6A methyltransferases (METTL3/14) and reader protein (YTHDF2), the HBx RNA and protein expression were increased. Using HBV mutants that lack m6A in the HBx coding region, we present the unique positional effects of m6A in the regulation of HBx protein expression.

Hepatitis B Virus X Protein Is Stabilized by the Deubiquitinating Enzyme VCPIP1 in a Ubiquitin-Independent Manner by Recruiting the 26S Proteasome Subunit PSMC3.

Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide, and the viral X protein (HBx) is an etiological factor in HCC development. HBx is a high-turnover protein, but knowledge of the role of deubiquitinating enzymes (DUBs) in maintaining HBx homeostasis is very limited. We used a 74-DUB library-based yeast two-hybrid assay and determined that a novel DUB, valosin-containing protein-interacting protein 1 (VCPIP1), interacted with HBx. VCPIP1 and its C-terminal amino acids 863 to 1221 upregulated the HBx protein expression, with or without HBV infection. Mechanistically, VCPIP1 stabilized HBx protein through a ubiquitin-independent pathway, which was validated by the HBx ubiquitination site mutant plasmid. Coimmunoprecipitation assays demonstrated the potency of VCPIP1 in recruiting 26S proteasome regulatory subunit 6A (PSMC3) and forming a ternary complex with HBx through mutual interaction. In vitro, purified His-tagged PSMC3 protein rescued HBx degradation induced by the 20S proteasome, and in vivo VCPIP1 synergized the mechanism. Functionally, HBx specifically binding to VCPIP1 significantly enhanced the transcriptional transactivation of HBx by activating NF-κB, AP-1, and SP-1 and inhibited hepatoma cell clonogenicity in Huh7 and HepG2 cells. Moreover, we further demonstrated that overexpression of VCPIP1 significantly affected the HBV covalently closed circular DNA (cccDNA) transcription in HBV-infected HepG2-NTCP cells. Altogether, our results indicate a novel mechanism by which VCPIP1 recruits PSMC3 to bind with HBx, stabilizing it in a ubiquitin-independent manner, which might be critical for developing DUB inhibitors in the future. IMPORTANCE HBx is a multifunctional viral oncoprotein that plays an essential role in the viral life cycle and hepatocarcinogenesis. HBx degradation occurs through the ubiquitin-proteasome system (UPS). However, whether novel compartments of the DUBs in the UPS also act in regulating HBx stability is not fully understood. Here, for the first time, we defined VCPIP1 as a novel DUB for preventing HBx degradation by the 20S proteasome in a ubiquitin-independent manner. PSMC3, encoding the 26S proteasome regulatory subunit, directly stabilized HBx through physical binding instead of a common approach in protein degradation, serving as the key downstream effector of VCPIP1 on HBx. Therefore, the ternary binding pattern between VCPIP1, HBx, and PSMC3 is initiated for the first time, which eventually promotes HBx stability and its functions. Our findings provide novel insights into host-virus cross talk by targeting DUBs in the UPS.

Sphondin efficiently blocks HBsAg production and cccDNA transcription through promoting HBx degradation.

Hepatitis B surface antigen (HBsAg) loss and seroconversion, which is considered as functional cure of chronic Hepatitis B virus (HBV) infection, is rarely achieved even after long-term antiviral treatments. Therefore, new antiviral strategies interfering with other HBV replication steps are required, especially those that could efficiently inhibit HBsAg production. Here, we identified novel anti-HBV compounds that could potently block HBsAg expression from cccDNA by screening a natural compound library derived from Chinese traditional medical plants by a novel screening strategy. The combination of ELISA assay detecting the HBsAg and real-time PCR detecting HBV RNAs as indicator for cccDNA transcriptional activity were used. The antiviral activity of a candidate compound and underlying mechanism were evaluated in HBV-infected cells and a humanized liver mouse model. Herein, we selected a highly effective low-cytotoxic compound sphondin, which could effectively inhibit both intracellular HBsAg production and HBV RNAs levels. Moreover, we found that sphondin markedly inhibited cccDNA transcriptional activity without affecting cccDNA level. Mechanistic study found sphondin preferentially bound to HBx protein by residue Arg72, which led to increased 26S proteasome-mediated degradation of HBx. Sphondin treatment significantly reduced the recruitment of HBx to cccDNA, which subsequently led to inhibition of cccDNA transcription and HBsAg expression. The absence of HBx or R72A mutation potently abrogated the antiviral effect induced by sphondin in HBV-infected cells. Collectively, sphondin may be considered as a novel and natural antiviral agent directly targeting HBx protein, which effectively inhibited cccDNA transcription and HBsAg expression.

HBV confers innate immune evasion through triggering HAT1/acetylation of H4K5/H4K12/miR-181a-5p or KPNA2/cGAS-STING/IFN-I signaling.

Viral immune evasion is crucial to the pathogenesis of hepatitis B virus (HBV) infection. However, the role of HBV in the modulation of innate immune evasion is poorly understood. A liver-specific histone acetyltransferase 1 (Hat1) knockout (KO) mouse model and HAT1 KO cell line were established. Immunohistochemistry staining, Western blot analysis, Southern blot analysis, Northern blot analysis, immunofluorescence assays, enzyme-linked immunosorbent assay, reverse transcription-quantitative polymerase chain reaction, and chromatin immunoprecipitation assays were performed in the livers of mouse models, primary human hepatocytes, HepG2-NTCP, and Huh7 and HepG2 cell lines. HBV-elevated HAT1 increased the expression of miR-181a-5p targeting cyclic GMP-AMP synthase (cGAS) messenger RNA 3' untranslated regions through modulating acetylation of H4K5 and H4K12 in vitro and in vivo, leading to the inability of cGAS-stimulator of interferon genes (STING) pathway and type I interferon (IFN-I) signaling. Additionally, HBV-elevated HAT1 promoted the expression of KPNA2 through modulating acetylation of H4K5 and H4K12 in the system, resulting in nuclear translocation of cGAS, HBx was responsible for the events by HAT1, suggesting that HBV-elevated HAT1 controls the cGAS-STING pathway and IFN-I signaling to modulate viral innate immune evasion. HBV confers innate immune evasion through triggering HAT1/acetylation of H4K5/H4K12/miR-181a-5p or KPNA2/cGAS-STING/IFN-I signaling. Our finding provides new insights into the mechanism by which HBV drives viral innate immune evasion.

Integrated analysis of intratumoral biomarker and tumor-associated macrophage to improve the prognosis prediction in cancer patients.

BACKGROUND: The lack of effective and accurate predictive indicators remains a major bottleneck for the improvement of the prognosis of patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). Hepatitis B virus X (HBx) has been widely suggested as a critical pathogenic protein for HBV-driven liver carcinogenesis, while tumor-associated macrophage (TAM) infiltration is also closely related to the tumorigenesis and progression of HCC. However, few studies have determined whether combining HBx expression with TAM populations could increase the accuracy of prognostic prediction for HBV-related HCC. METHODS: The study cohort enrolling 251 patients with HBV-related HCC was randomly split into a training and a validation group (ratio 1:1). The expression levels of HBx and TAM marker CD68 in HCC samples were detected by immunohistochemistry. Kaplan-Meier curves, Cox regression and Harrell's concordance index (C-index) analysis were conducted to evaluate the prognostic significance of these indicators alone or in combination. RESULTS: The expression level of HBx was strongly correlated with CD68+ TAM infiltration in HCC tissues. Elevated HBx or CD68 expression indicated poorer overall survival (OS) and progression-free survival (PFS) after hepatectomy, and both of them were independent risk factors for postoperative survival. Meanwhile, patients with both high HBx and CD68 levels had worst clinical outcomes. Moreover, integrating HBx and CD68 expression with clinical indicators (tumor size and micro-vascular invasion) showed the best prognostic potential with highest C-index value for survival predictivity, and this proposed model also performed better than several conventional classifications of HCC. CONCLUSION: Combining the expression of intratumoral HBx, CD68+ TAM population and clinical variables could enable better prognostication for HBV-related HCC after hepatectomy, thus providing novel insights into developing more effective clinical prediction model based on both molecular phenotypes and tumor-immune microenvironment.

rt269L-Type hepatitis B virus (HBV) in genotype C infection leads to improved mitochondrial dynamics via the PERK-eIF2α-ATF4 axis in an HBx protein-dependent manner.

BACKGROUND: In our previous report, the rt269I type versus the rt269L type in genotype C2 infection led to poor clinical outcomes and enhanced mitochondrial stress in infected hepatocytes. Here, we sought to investigate differences between the rt269L and rt269I types in mitochondrial functionality in hepatitis B virus (HBV) genotype C2 infection, mainly focusing on endoplasmic reticulum (ER) stress-mediated autophagy induction as an upstream signal. METHODS: Mitochondrial functionality, ER stress signaling, autophagy induction, and apoptotic cell death between rt269L-type and rt269I-type groups were investigated via in vitro and in vivo experiments. Serum samples were collected from 187 chronic hepatitis patients who visited Konkuk or Seoul National University Hospital. RESULTS: Our data revealed that genotype C rt269L versus rt269I infection led to improved mitochondrial dynamics and enhanced autophagic flux, mainly due to the activation of the PERK-eIF2α-ATF4 axis. Furthermore, we demonstrated that the traits found in genotype C rt269L infection were mainly due to increased stability of the HBx protein after deubiquitination. In addition, clinical data using patient sera from two independent Korean cohorts showed that, compared with rt269I, rt269L in infection led to lower 8-OHdG levels, further supporting its improved mitochondrial quality control. CONCLUSION: Our data showed that, compared with the rt269I type, the rt269L type, which presented exclusively in HBV genotype C infection, leads to improved mitochondrial dynamics or bioenergetics, mainly due to autophagy induction via activation of the PERK-eIF2α-ATF4 axis in an HBx protein-dependent manner. This suggests that HBx stability and cellular quality control in the rt269L type predominating in genotype C endemic areas could at least partly contribute to some distinctive traits of genotype C infection, such as higher infectivity or longer duration of the hepatitis B e antigen (HBeAg) positive stage.

Biological Roles of Hepatitis B Viral X Protein in the Viral Replication and Hepatocarcinogenesis.

Hepatitis B virus is a pathogenic virus that infects 300 million people worldwide and causes chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Hepatitis B virus encodes four proteins. Among them, the HBx protein plays a central role in the HBV pathogenesis. Because the HBx protein is considered to play a central role in the induction of viral replication and hepatocarcinogenesis, the regulation of its function could be a key factor in the development of new interventions against hepatitis B. In this review, HBx protein-related viral replication and hepatocarcinogenesis mechanisms are described, with a focus on the recently reported viral replication mechanisms related to degradation of the Smc5/6 protein complex. We also discuss our recent discovery of a compound that inhibits HBx protein-induced degradation of the Smc5/6 protein complex, and that exerts inhibitory effects on both viral replication and hepatocarcinogenesis. Finally, prospects for future research on the HBx protein are described.

HBx-induced PLA2R overexpression mediates podocyte pyroptosis through the ROS-NLRP3 signaling pathway.

INTRODUCTION: Hepatitis B virus-associated glomerulonephritis (HBV-GN) is one of the main types of secondary glomerular diseases, and podocyte injury is an important pathogenic mechanism of HBV-GN, participating in the occurrence and development of HBV-GN. However, the specific mechanism of podocyte injury remains to be studied. METHODS: Human renal podocytes cultured in vitro were divided into six groups. The podocyte morphology was observed under a transmission electron microscope, and the expression of M-type phospholipase A2 receptor (M-PLA2R) on the podocyte membrane was observed by indirect immunofluorescence staining under a fluorescence microscope. The pyroptosis rate and reactive oxygen species (ROS) of podocytes were assessed by FLICA/PI double staining and flow cytometry. Western blot (WB) and quantitative real-time PCR (qPCR) were used to determine the expression of PLA2R, nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein containing card (ASC), caspase-1, IL-1ß, and IL-18. RESULTS: Hepatitis B virus X (HBx) transfected into human renal podocytes in vitro induced the overexpression of PLA2R. Moreover, the overexpressed PLA2R combined with secretory phospholipase A2 group IB (sPLA2-IB) aggravated podocyte injury and increased the pyroptosis rate. In addition, the expression of ROS, the NLRP3 inflammasome and downstream inflammatory factors was increased. In contrast, after inhibiting the expression of PLA2R and ROS, podocyte damage was alleviated, and the pyroptosis rate and the expression of genes related to the ROS-NLRP3 signaling pathway were decreased. CONCLUSION: HBx-induced PLA2R overexpression on the podocyte membrane can significantly upregulate the ROS-NLRP3 signaling pathway, thereby mediating podocyte pyroptosis.

Relevance of HBx for Hepatitis B Virus-Associated Pathogenesis.

The hepatitis B virus (HBV) counts as a major global health problem, as it presents a significant causative factor for liver-related morbidity and mortality. The development of hepatocellular carcinomas (HCC) as a characteristic of a persistent, chronic infection could be caused, among others, by the pleiotropic function of the viral regulatory protein HBx. The latter is known to modulate an onset of cellular and viral signaling processes with emerging influence in liver pathogenesis. However, the flexible and multifunctional nature of HBx impedes the fundamental understanding of related mechanisms and the development of associated diseases, and has even led to partial controversial results in the past. Based on the cellular distribution of HBx-nuclear-, cytoplasmic- or mitochondria-associated-this review encompasses the current knowledge and previous investigations of HBx in context of cellular signaling pathways and HBV-associated pathogenesis. In addition, particular focus is set on the clinical relevance and potential novel therapeutic applications in the context of HBx.

Hydrogen Peroxide Inhibits Hepatitis B Virus Replication by Downregulating HBx Levels via Siah-1-Mediated Proteasomal Degradation in Human Hepatoma Cells.

The hepatitis B virus (HBV) is constantly exposed to significant oxidative stress characterized by elevated levels of reactive oxygen species (ROS), such as H2O2, during infection in hepatocytes of patients. In this study, we demonstrated that H2O2 inhibits HBV replication in a p53-dependent fashion in human hepatoma cell lines expressing sodium taurocholate cotransporting polypeptide. Interestingly, H2O2 failed to inhibit the replication of an HBV X protein (HBx)-null HBV mutant, but this defect was successfully complemented by ectopic expression of HBx. Additionally, H2O2 upregulated p53 levels, leading to increased expression of seven in absentia homolog 1 (Siah-1) levels. Siah-1, an E3 ligase, induced the ubiquitination-dependent proteasomal degradation of HBx. The inhibitory effect of H2O2 was nearly abolished not only by treatment with a representative antioxidant, N-acetyl-L-cysteine but also by knockdown of either p53 or Siah-1 using specific short hairpin RNA, confirming the role of p53 and Siah-1 in the inhibition of HBV replication by H2O2. The present study provides insights into the mechanism that regulates HBV replication under conditions of oxidative stress in patients.

C-Terminal Truncated HBx Facilitates Oncogenesis by Modulating Cell Cycle and Glucose Metabolism in FXR-Deficient Hepatocellular Carcinoma.

Farnesoid X receptor (FXR) is a nuclear receptor known to play protective roles in anti-hepatocarcinogenesis and regulation of the basal metabolism of glucose, lipids, and bile acids. FXR expression is low or absent in HBV-associated hepatocarcinogenesis. Full-length HBx and HBx C-terminal truncation are frequently found in clinical HCC samples and play distinct roles in hepatocarcinogenesis by interacting with FXR or FXR signaling. However, the impact of C-terminal truncated HBx on the progression of hepatocarcinogenesis in the absence of FXR is unclear. In this study, we found that one known FXR binding protein, a C-terminal truncated X protein (HBx C40) enhanced obviously and promoted tumor cell proliferation and migration by altering cell cycle distribution and inducing apoptosis in the absence of FXR. HBx C40 enhanced the growth of FXR-deficient tumors in vivo. In addition, RNA-sequencing analysis showed that HBx C40 overexpression could affect energy metabolism. Overexpressed HSPB8 aggravated the metabolic reprogramming induced by down-regulating glucose metabolism-associated hexokinase 2 genes in HBx C40-induced hepatocarcinogenesis. Overall, our study suggests that C-terminal truncated HBx C40 synergizes with FXR deficiency by altering cell cycle distribution as well as disturbing glucose metabolism to promote HCC development.