Hepatitis B virus X protein induces cell death by causing loss of mitochondrial membrane potential

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.

The influence of male HBV infection on sperm quality, embryonic development, and assisted reproductive outcomes

STUDY QUESTION

What is the impact of male hepatitis B virus (HBV) infection on sperm quality, embryonic development, and assisted reproductive outcomes?

SUMMARY ANSWER

Male HBV infection did not affect assisted reproductive outcomes, but HBV is capable of impairing human sperm and embryo formation in the early stages following fertilization.

WHAT IS KNOWN ALREADY

HBV is found in germ cells and early embryos of patients with HBV. HBV may impair human sperm function via increasing reactive oxygen species.

STUDY DESIGN, SIZE, DURATION

We conducted a retrospective cohort study of 1581 infertile couples, including 496 male patients clinically confirmed to have hepatitis B infection, and a laboratory study of effects of HBV proteins on early embryos, using human embryonic stem cells (hESCs), human sperm, and golden hamster oocytes.

PARTICIPANTS/MATERIALS, SETTING, METHODS

In total, 1581 infertile couples (24-40 years of age) who were admitted to a reproductive medicine center to undergo ART for the first time from January 2019 to November 2021 were selected as the study subjects. The case group was composed of 469 couples with hepatitis B surface antigen (HBsAg)-seropositive men and seronegative women (368 for IVF and 101 for ICSI treatment). The negative control group was composed of 1112 couples where both men and women were seronegative for hepatitis B antigen. We divided these couples into three comparison groups (IVF/ICSI, IVF, and ICSI). IVF of human sperm and hamster oocytes was used to evaluate the influence of the HBV HBs protein on formation of 2-cell embryos. Mitochondrial membrane potential (MMP) of hESCs was assayed via a fluorescence intensity system. Immunofluorescence staining of the phosphorylated histone H2A.X was applied to identify DNA damage to hESCs caused by the HBV X (HBx) protein.

MAIN RESULTS AND THE ROLE OF CHANCE

Sperm concentration, total sperm number, and sperm with normal morphology were decreased in the couples with HBV-infected males in couples who were undergoing IVF/ICSI (male HBV(+) vs control: 469 vs 1112 individuals; sperm number, P < 0.01; normal sperm morphology, P < 0.01), IVF (368 vs 792; sperm number, P < 0.01; normal sperm morphology, P ≤ 0.05), and ICSI (101 vs 306; sperm number, P < 0.01; normal sperm morphology, P < 0.001). There was no significant difference in the number of embryo cleavages, blastocyst formation, biochemical pregnancy rate, clinical pregnancy rate, and live-birth rate between case and control groups. The 2PN fertilization rate in IVF/ICSI (P < 0.01) and ICSI (P < 0.05) couples, and the number of 2PN-fertilized oocytes in IVF (P < 0.001) couples were lower in couples with male HBV infection compared to control couples. HBV HBs protein reduced the MMP of human sperm and decreased 2-cell embryo formation in IVF of human sperm and zona-free-hamster oocyte. A reduction in fluorescence intensity and immunofluorescence staining of phosphorylated histone H2A.X indicated that HBx caused MMP impairment and DNA damage in human early embryonic cells, respectively.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

HBV can be examined in samples of sperm or discarded IVF early embryos from HBsAg-seropositive men and seronegative women. The hESC model in vitro may not fully mimic the natural embryos in vivo.

WIDER IMPLICATIONS OF THE FINDINGS

This study furthers our understanding of the influence of male HBV infection on embryonic development. Our results suggest that a semen-washing process may be necessary for male patients with HBV undergoing ART to minimize the potential negative effects of HBV infection on the early embryo.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by grants from the National Natural Science Foundation of China, grant numbers 81870432 and 81570567 to X.Z., 81571994 to P.S., and 81950410640, the Natural Science Foundation of Guangdong Province, China (No. 2023A1515010660 to X.Z.), and the Li Ka Shing Shantou University Foundation (Grant No. L11112008). The authors have no conflicts of interest.

Hepatitis B doubly spliced protein (HBDSP) promotes hepatocellular carcinoma cell apoptosis via ETS1/GATA2/YY1-mediated p53 transcription

IMPORTANCE

Hepatitis B virus (HBV) spliced variants are associated with viral persistence or pathogenicity. Hepatitis B doubly spliced protein (HBDSP), which has been previously reported as a pleiotropic transactivator protein, can potentially serve as an HBV virulence factor. However, the underlying mechanisms of HBDSP in HBV-associated liver diseases remain to be elucidated. In this study, we revealed that HBDSP promotes cellular apoptosis and induces wt-p53-dependent apoptotic signaling pathway in wt-p53 hepatocellular cells by transactivating p53 transcription, and increases the release of HBV progeny. Therefore, HBDSP may promote the HBV particles release through wt-p53-dependent hepatocellular apoptosis. Our findings suggest that blocking HBDSP-induced wt-p53-dependent apoptosis might have therapeutic values for chronic hepatitis B.

Mitochondrial stress in advanced fibrosis and cirrhosis associated with chronic hepatitis B, chronic hepatitis C, or nonalcoholic steatohepatitis

BACKGROUND AND AIMS

Hepatitis B virus (HBV) infection causes oxidative stress (OS) and alters mitochondria in experimental models. Our goal was to investigate whether HBV might alter liver mitochondria also in humans, and the resulting mitochondrial stress might account for the progression of fibrosis in chronic hepatitis B (CHB).

APPROACH AND RESULTS

The study included 146 treatment-naïve CHB mono-infected patients. Patients with CHB and advanced fibrosis (AF) or cirrhosis (F3-F4) were compared to patients with no/mild-moderate fibrosis (F0-F2). Patients with CHB were further compared to patients with chronic hepatitis C (CHC; n = 33), nonalcoholic steatohepatatis (NASH; n = 12), and healthy controls ( n = 24). We detected oxidative damage to mitochondrial DNA (mtDNA), including mtDNA strand beaks, and identified multiple mtDNA deletions in patients with F3-F4 as compared to patients with F0-F2. Alterations in mitochondrial function, mitochondrial unfolded protein response, biogenesis, mitophagy, and liver inflammation were observed in patients with AF or cirrhosis associated with CHB, CHC, and NASH. In vitro , significant increases of the mitochondrial formation of superoxide and peroxynitrite as well as mtDNA damage, nitration of the mitochondrial respiratory chain complexes, and impairment of complex I occurred in HepG2 cells replicating HBV or transiently expressing hepatitits B virus X protein. mtDNA damage and complex I impairment were prevented with the superoxide-scavenging Mito-Tempo or with inducible nitric oxide synthase (iNOS)-specific inhibitor 1400 W.

CONCLUSIONS

Our results emphasized the importance of mitochondrial OS, mtDNA damage, and associated alterations in mitochondrial function and dynamics in AF or cirrhosis in CHB and NASH. Mitochondria might be a target in drug development to stop fibrosis progression.

The Abnormal Proliferation of Hepatocytes is Associated with MC-LR and C-Terminal Truncated HBX Synergistic Disturbance of the Redox Balance

Background

Microcystin-LR (MC-LR) and hepatitis B virus (HBV) are associated with hepatocellular carcinoma (HCC). However, the concentrations of MC-LR in drinking water and the synergistic effect of MC-LR and HBV on hepatocellular carcinogenesis through their disturbance of redox balance have not been fully elucidated.

Methods

We measured the MC-LR concentrations in 168 drinking water samples of areas with a high incidence of HCC. The relationships between MC-LR and both redox status and liver diseases in 177 local residents were analyzed. The hepatoma cell line HepG2 transfected with C-terminal truncated hepatitis B virus X gene (Ct-HBX) were treated with MC-LR. Reactive oxygen species (ROS), superoxide dismutase (SOD), glutathione (GSH) and malondialdehyde (MDA) were measured. Cell proliferation, migration, invasion, and apoptosis were assessed with cell activity assays, scratch and transwell assays, and flow cytometry, respectively. The mRNA and protein expression-related redox status genes were analyzed with qPCR and Western blotting.

Results

The average concentration of MC-LR in well water, river water and reservoir water were 57.55 ng/L, 76.74 ng/L and 132.86 ng/L respectively, and the differences were statistically significant (P < 0.05). The MC-LR levels in drinking water were correlated with liver health status, including hepatitis, clonorchiasis, glutamic pyruvic transaminase abnormalities and hepatitis B surface antigen carriage (all P values < 0.05). The serum MDA increased in subjects who drank reservoir water and were infected with HBV (P < 0.05). In the cell experiment, ROS increased when Ct-HBX-transfected HepG2 cells were treated with MC-LR, followed by a decrease in SOD and GSH and an increase in MDA. MC-LR combined with Ct-HBX promoted the proliferation, migration and invasion of HepG2 cells, upregulated the mRNA and protein expression of MAOA gene, and downregulated UCP2 and GPX1 genes.

Conclusion

MC-LR and HBV may synergistically affect redox status and play an important role in hepatocarcinoma genesis.

Genome-Wide Association Study for Chronic Hepatitis B Infection in the Thai Population

To identify novel host genetic variants that predispose to hepatitis B virus (HBV) persistence, we performed the first genome-wide association study in the Thai population involving 318 cases of chronic hepatitis B and 309 healthy controls after quality control measures. We detected the genome-wide significant association of the HLA class II region (HLA-DPA1/DPB1, rs7770370, p-value = 7.71 × 10⁻¹⁰, OR = 0.49) with HBV chronicity. Subsequent HLA allele imputation revealed HLA-DPA1*01:03 (Pc = 1.21 × 10⁻⁶, OR = 0.53), HLA-DPB1*02:01 (Pc = 2.17 × 10⁻³, OR = 0.50), and HLA-DQB1*06:09 (Pc = 2.17 × 10⁻², OR = 0.07) as protective alleles, and HLA-DPA1*02:02 (Pc = 6.32 × 10⁻⁵, OR = 1.63), HLA-DPB1*05:01 (Pc = 1.13 × 10⁻⁴, OR = 1.72), HLA-DPB1*13:01 (Pc = 4.68 × 10⁻², OR = 1.60), and HLA-DQB1*03:03 (Pc = 1.11 × 10⁻³, OR = 1.84) as risk alleles for HBV persistence. We also detected suggestive associations in the PLSCR1 (rs35766154), PDLIM5 (rs62321986), SGPL1 (rs144998273), and MGST1 (rs1828682) loci. Among single-nucleotide polymorphisms in the PLSCR1 locus, rs1061307 was identified as the primary functional variant by in silico/in vitro functional analysis. In addition to replicating the association of the HLA class II region, we detected novel candidate loci that provide new insights into the pathophysiology of chronic hepatitis B.

Inhibition of Protease Activated Receptor 2 Attenuates HBx-Induced Inflammation and Mitochondria Oxidative Stress

BACKGROUND

Hepatitis B virus (HBV) infection is one of the global public problems. Among the known infection cases, HBV X protein (HBx) is one of the key inducements of viral replication and host infection. This study was aimed to uncover the role of protease activated receptor 2 (PAR2) on HBx-induced liver injury.

METHODS

A PAR2-KO mouse model expressing HBx was constructed using hydrodynamics-based in vivo gene transfection method. In addition, pcDNA3.1-HBx was used to over-express HBx in LO2 cells. The effects of HBx overexpression on inflammation and mitochondria oxidative stress were evaluated.

RESULTS

We found that PAR2 protein level was increased by HBx overexpression. The enforced HBx inhibited LO2 cells apoptosis. Meanwhile, HBx induced inflammation reactions through promoting the secretion of pro-inflammatory cytokines such as TNF-α, IL-6, and CXCL-2. Overexpressed HBx also resulted in mitochondria oxidative stress by upregulation of ROS level and downregulation of MMP and ATP. However, in FSLLRY-NH2 (PAR2 antagonist) treated LO2 cells or PAR2-KO mice, PAR2 blockade reversed the above adverse effects of HBx on liver cells or tissues.

CONCLUSION

Inhibition of PAR2 may suppress inflammation and mitochondria oxidative stress caused by HBx, pointing out the potential application values of PAR2 antagonist on the treatment of HBV infection in clinic.

The association between hepatocarcinogenesis and intracellular alterations due to hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is a worldwide health problem leading to severe liver dysfunction, including liver cirrhosis and hepatocellular carcinoma. Although current antiviral therapies for chronic HBV infection have been improved and can lead to a strong suppression of viral replication, it is difficult to completely eliminate the virus with these therapies once chronic HBV infection is established in the host. Furthermore, chronic HBV infection alters intracellular metabolism and signalling pathways, resulting in the activation of carcinogenesis in the liver. HBV produces four viral proteins: hepatitis B surface-, hepatitis B core-, hepatitis B x protein, and polymerase; each plays an important role in HBV replication and the intracellular signalling pathways associated with hepatocarcinogenesis. In vitro and in vivo experimental models for analyzing HBV infection and replication have been established, and gene expression analyses using microarrays or next-generation sequencing have also been developed. Thus, it is possible to clarify the molecular mechanisms for intracellular alterations, such as endoplasmic reticulum stress, oxidative stress, and epigenetic modifications. In this review, the impact of HBV viral proteins and intracellular alterations in HBV-associated hepatocarcinogenesis are discussed.

Mitochondrial dysfunction and liver disease: role, relevance, and potential for therapeutic modulation

Mitochondria are key organelles involved in energy production as well as numerous metabolic processes. There is a growing interest in the role of mitochondrial dysfunction in the pathogenesis of common chronic diseases as well as in cancer development. This review will examine the role mitochondria play in the pathophysiology of common liver diseases, including alcohol-related liver disease, non-alcoholic fatty liver disease, chronic hepatitis B and hepatocellular carcinoma. Mitochondrial dysfunction is described widely in the literature in studies examining patient tissue and in disease models. Despite significant differences in pathophysiology between chronic liver diseases, common mitochondrial defects are described, including increased mitochondrial reactive oxygen species production and impaired oxidative phosphorylation. We review the current literature on mitochondrial-targeted therapies, which have the potential to open new therapeutic avenues in the management of patients with chronic liver disease.

Signal Activation of Hepatitis B Virus-Related Hepatocarcinogenesis by Up-regulation of SUV39h1

BACKGROUND

Hepatitis B virus (HBV) X (HBx) protein is associated with hepatocellular carcinogenesis via the induction of malignant transformation and mitochondrial dysfunction. However, the association between HBx and histone methyltransferase in carcinogenesis has not been fully clarified. In the current study, we analyzed the association between HBx and the histone methyltransferase suppressor of variegation 3-9 homolog 1 (SUV39h1) using HBV replication models.

METHODS

We constructed several HBx and SUV39h1 expression plasmids and analyzed the association between HBx and SUV39h1 with respect to HBV replication and hepatocarcinogenesis.

RESULTS

SUV39h1 up-regulation was observed in HBV-infected humanized mouse livers and clinical HBV-related hepatocellular carcinoma tissues, indicating that SUV39h1 expression might be regulated by HBV infection. Through in vitro analysis, we determined that the coactivator domain of HBx interacts with the PSET (PostSET) and SET (Su(var)3-9, Enhancer-of-zeste, Trithorax) domains of SUV39h1. The expression levels of 4 genes, activating transcription factor 6, α-fetoprotein, growth arrest and DNA damage-inducible 45a, and dual-specificity phosphatase 1, known to induce carcinogenesis via HBx expression, were up-regulated by HBx and further up-regulated in the presence of both HBx and SUV39h1. Furthermore, histone methyltransferase activity, the main function of SUV39h1, was enhanced in the presence of HBx.

CONCLUSIONS

We demonstrated that SUV39h1 and HBx enhance each other's activity, leading to HBx-mediated hepatocarcinogenesis. We propose that regulation of this interaction could help suppress development of hepatocellular carcinoma.

Phosphorylation of Phylogenetically Conserved Amino Acid Residues Confines HBx within Different Cell Compartments of Human Hepatocarcinoma Cells

Hepatitis B virus (HBV) is a circular, and partially double-stranded DNA virus. Upon infection, the viral genome is translocated into the cell nucleus, generating the covalently closed circular DNA (cccDNA) intermediate, and forming a mini chromosome. HBV HBx is a small protein displaying multiple roles in HBV-infected cells, and in different subcellular locations. In the nucleus, the HBx protein is required to initiate and maintain viral transcription from the viral mini chromosome. In contrast, HBx also functions in the cytoplasm, where it is able to alter multiple cellular functions such as mitochondria metabolism, apoptosis and signal transduction pathways. It has been reported that in cultured cells, at low expression levels, the HBx protein is localized in the nucleus, whereas at high expression levels, it accumulates in the cytoplasm. This dynamic subcellular distribution of HBx might be essential to exert its multiple roles during viral infection. However, the mechanism that regulates different subcellular localizations of the HBx protein is unknown. We have previously taken a bioinformatics approach to investigate whether HBx might be regulated via post-translational modification, and we have proposed that the multiple nucleocytoplasmic functions of HBx might be regulated by an evolutionarily conserved mechanism via phosphorylation. In the current study, phylogenetically conserved amino acids of HBx with a high potential of phosphorylation were targeted for site-directed mutagenesis. Two conserved serine (Ser25 and Ser41), and one conserved threonine (Thr81) amino acids were replaced by either alanine or aspartic acid residues to simulate an unphosphorylated or phosphorylated state, respectively. Human hepatoma cells were transfected with increasing amounts of the HBx DNA constructs, and the cells were analyzed by fluorescence microscopy. Together, our results show that the nucleocytoplasmic distribution of the HBx protein could be regulated by phosphorylation since some of the modified proteins were mainly confined to distinct subcellular compartments. Remarkably, both HBx Ser41A, and HBx Thr81D proteins were predominantly localized within the nuclear compartment throughout the different expression levels of HBx mutants.

Transcriptome analysis of hepatoma cells transfected with Basal Core Promoter (BCP) and Pre-Core (PC) mutant hepatitis B virus full genome construct

Infections with Basal Core Promoter (BCP) (A1762T/G1764A) and Pre-Core (PC) (G1896A) hepatitis B virus HBeAg mutants are associated with severe liver injury. We analysed host cell responses in HepG2/C3A, hepatoma cells transfected with infectious clones developed from genotype D wild type (WT) and BCP/PC mutant (MT) viruses isolated from an acute resolved and an acute liver failure hepatitis B case respectively. Cells transfected with MT virus construct showed ~55 % apoptosis and with WT ~30 % apoptosis at 72 h. To determine possible roles of HBe and HBx proteins in apoptosis, we cloned these genes and co-transfected cells with WT+HBe/HBx or MT+HBe/HBx constructs. Co-expression of HBe protein improved cell viability significantly in both WT and MT virus constructs, indicating an important role of HBe in protecting cells. RNA sequencing analysis carried out at 12 and 72 h post-transfection with WT virus construct showed enrichment of innate/adaptive immune response-activating signal transduction, cell survival and amino acid/nucleic acid biosynthetic pathways at 12 and 72 h. By contrast, MT virus construct showed enrichment in host defence pathways and some biosynthetic pathways at the early time point (12 h), and inflammatory response, secretary granule, regulation of membrane potential and stress response regulatory pathways at the late time point (72 h). There was a significant down-regulation of genes involved in endoplasmic reticulum and mitochondrial functions and metabolism with MT construct and this possibly led to induction of apoptosis in cells. Considering rapid apoptotic changes in cells transfected with MT construct, it can be speculated that HBeAg plays a crucial role in cell survival. It enhances induction of metabolic and synthetic pathways and facilitates management of cellular stress that is induced due to hepatitis B virus infection/replication.

Cell Death and Liver Disease

Cell death is now reclassified into several types based on the mechanisms and morphologic phenotype. Understanding of such classifications offers insights into the pathogenesis of liver disease, as well as diagnostic or therapeutic implications. Apoptosis is recognized relatively easily due to its unique morphology, but lytic cell death may occur in the form of accidental necrosis, mitochondria permeability transition-driven necrosis, necroptosis, pyroptosis, ferroptosis, and parthanatos. The cell may be engulfed by neighboring cells due to a loss of integrin signaling or cancer cell competition by entosis, a type of cell death. The classification also includes mechanistically termed cell death such as autophagy-dependent cell death and lysosome-dependent cell death. These different types of cell death may occur uniquely in certain liver diseases but may coexist in the evolution of the disease. They occur in parenchymal and non-parenchymal liver cells, as well as inflammatory cells, causing distinct pathologic consequences. This review briefly covers the recently revised classifications of cell death and discusses their relevance to liver diseases of different etiologies.

TIMM29 interacts with hepatitis B virus preS1 to modulate the HBV life cycle

Hepatitis B virus (HBV), a major global health problem, can cause chronic hepatitis, liver cirrhosis, and hepatocellular carcinomas in chronically infected patients. However, before HBV infection can be adequately controlled, many mysteries about the HBV life cycle must be solved. In this study, TIMM29, an inner mitochondrial membrane protein, was identified as an interaction partner of the preS1 region of the HBV large S protein. The interaction was verified by both an immunoprecipitation with preS1 peptides and a GST-pulldown assay. Immunofluorescence studies also showed colocalization of preS1 and TIMM29. Moreover, it was determined that the preS1 bound with amino acids 92-189 of the TIMM29 protein. Infection of HBV in TIMM29-overexpressing NTCP/G2 cells resulted in a significant decrease of HBeAg and both extracellular particle-associated and core particle-associated HBV DNA without affecting cccDNA formation. Comparable results were obtained with TIMM29-overexpressing HB611 cells, which constitutively produce HBV. In contrast, knockout of TIMM29 in NTCP/G2 cells led to a higher production of HBV including HBeAg expression, as did knockout of TIMM29 in HB611. Collectively, these results suggested that TIMM29 interacts with the preS1 region of the HBV large S protein and modulates HBV amplification.

VDAC1 at the Intersection of Cell Metabolism, Apoptosis, and Diseases

The voltage-dependent anion channel 1 (VDAC1) protein, is an important regulator of mitochondrial function, and serves as a mitochondrial gatekeeper, with responsibility for cellular fate. In addition to control over energy sources and metabolism, the protein also regulates epigenomic elements and apoptosis via mediating the release of apoptotic proteins from the mitochondria. Apoptotic and pathological conditions, as well as certain viruses, induce cell death by inducing VDAC1 overexpression leading to oligomerization, and the formation of a large channel within the VDAC1 homo-oligomer. This then permits the release of pro-apoptotic proteins from the mitochondria and subsequent apoptosis. Mitochondrial DNA can also be released through this channel, which triggers type-Ι interferon responses. VDAC1 also participates in endoplasmic reticulum (ER)-mitochondria cross-talk, and in the regulation of autophagy, and inflammation. Its location in the outer mitochondrial membrane, makes VDAC1 ideally placed to interact with over 100 proteins, and to orchestrate the interaction of mitochondrial and cellular activities through a number of signaling pathways. Here, we provide insights into the multiple functions of VDAC1 and describe its involvement in several diseases, which demonstrate the potential of this protein as a druggable target in a wide variety of pathologies, including cancer.

Effect of HBx on inflammation and mitochondrial oxidative stress in mouse hepatocytes

Hepatitis B virus × protein (HBx) serves an important role in the pathogenesis of the hepatitis B virus infection. Previous studies have reported that the interaction between HBx and hepatocyte mitochondria is an important factor leading to liver cell injury and apoptosis, ultimately inducing the formation of liver cancer. In the present study, a mouse model expressing HBx was constructed using hydrodynamic in vivo transfection based on the interaction between HBx and cytochrome c oxidase (COX) subunit III. The specific mechanism of HBx-induced oxidative stress in mouse hepatocytes and the subsequent effect on mitochondrial function and inflammatory injury was assessed. The results demonstrated that HBx reduced the activity of COX and the expression of superoxide dismutase and upregulated the expression of malondialdehyde, NF-κB and phospho-AKT, thus increasing oxidative stress. In addition, HBx induced an increase in interleukin (IL)-6, IL-1β and IL-18 expression levels, which created an inflammatory microenvironment in the liver, further promoting hepatocyte inflammatory injury. Therefore, it was proposed that HBx may affect hepatocyte mitochondrial respiration by reducing the activity of cytochrome c oxidase, leading to mitochondrial dysfunction and inducing hepatocyte inflammation and injury.

Impact of the Interaction of Hepatitis B Virus with Mitochondria and Associated Proteins

Around 350 million people are living with hepatitis B virus (HBV), which can lead to death due to liver cirrhosis and hepatocellular carcinoma (HCC). Various antiviral drugs/nucleot(s)ide analogues are currently used to reduce or arrest the replication of this virus. However, many studies have reported that nucleot(s)ide analogue-resistant HBV is circulating. Cellular signaling pathways could be one of the targets against the viral replication. Several studies reported that viral proteins interacted with mitochondrial proteins and localized in the mitochondria, the powerhouse of the cell. And a recent study showed that mitochondrial turnover induced by thyroid hormones protected hepatocytes from hepatocarcinogenesis mediated by HBV. Strong downregulation of numerous cellular signaling pathways has also been reported to be accompanied by profound mitochondrial alteration, as confirmed by transcriptome profiling of HBV-specific CD8 T cells from chronic and acute HBV patients. In this review, we summarize the ongoing research into mitochondrial proteins and/or signaling involved with HBV proteins, which will continue to provide insight into the relationship between mitochondria and HBV and ultimately lead to advances in viral pathobiology and mitochondria-targeted antiviral therapy.

SpBcl2 promotes WSSV infection by suppressing apoptotic activity of hemocytes in mud crab, Scylla paramamosain

White spot syndrome virus (WSSV) is one of the most virulent and widespread pathogens that infect almost all marine crustaceans and therefore cause huge economic losses in aquaculture. The Bcl2 protein plays a key role in the mitochondrial apoptosis pathway, which is a crucial immune response in invertebrates. However, the role of Bcl2 in apoptosis and immunoregulation in mud crab, Scylla paramamosain, is poorly understood. Here, the Bcl2 homolog (SpBcl2) in S. paramamosain was cloned and its role in WSSV infection explored. The expression of SpBcl2 increased at both the transcriptional level and post-transcriptional level after WSSV infection, while the hemocytes apoptosis decreased significantly. Furthermore, there was increase in the level of cytochrome c coupled with an upregulation in the expression of SpBcl2. These results indicated that SpBcl2 suppressed apoptosis by preventing the release of cytochrome c from mitochondria, thereby promoting WSSV replication in mud crab. The findings here therefore provide novel insight into the immune response of mud crabs to WSSV infection.

LncRNA H19/microRNA-675/PPARα axis regulates liver cell injury and energy metabolism remodelling induced by hepatitis B X protein via Akt/mTOR signalling

Emerging evidence indicates that the lncRNAs/microRNA/mRNA axis plays important roles in a variety of diseases. This study was aimed to investigate the potential roles and underlying molecular mechanisms of lncRNA H19 and H19-derived miR-675 in regulating hepatitis B virus (HBV)-associated liver injury. mRNA and miR-675 levels were determined by quantitative real-time PCR (qRT-PCR), protein levels were determined by western blot, cell viability was measured by the MTT assay, cell apoptosis was measured by flow cytometry, inflammatory cytokine production was determined by ELISA, oxidative stress and energy metabolism were assessed by commercial kits, and the target relationship between PPARα and miR-675 was confirmed by the dual-luciferase reporter assay. The results showed that the expression of lncRNA H19 and miR-675 was up-regulated in patients with chronic hepatitis B (n = 20). Inhibition of lncRNA H19 or miR-675 in L02 cells increased cell viability, suppressed hepatitis B X protein (HBx)-induced cell apoptosis, inflammatory cytokine production, and oxidative stress, and remodelled energy metabolism. Furthermore, PPARα was found to be a target gene of miR-675. The expression of PPARα was down-regulated in patients with chronic hepatitis B, and there was a negative correlation between the expression of lncRNA H19 and PPARα, or between miR-675 and PPARα. Moreover, by knocking down the expression of PPARα, the actions (apoptosis, inflammatory factors, oxidative stress, and energy metabolism) of lncRNA H19 or miR-675 inhibition in HBx-induced L02 cells were at least partially reversed. In addition, HBx-induced elevated levels of p-Akt^Ser473, p-Akt^Thr308 and p-mTOR^Ser2448 were down-regulated by lncRNA H19 or miR-675 inhibition. Furthermore, PPARα knockdown partly reversed the down-regulated effects of H19 or miR-675 inhibition. Taken together, these data indicate that the lncRNA H19/miR-675/PPARα axis regulates liver cell injury and energy metabolism remodelling induced by HBx, which may be related to the modulation of Akt/mTOR signalling.

Mitochondria Redistribution in Enterovirus A71 Infected Cells and Its Effect on Virus Replication

Enterovirus A71 (EV-A71) is one of the main causative agents of hand, foot and mouth disease (HFMD) and it also causes severe neurologic complications in infected children. The interactions between some viruses and the host mitochondria are crucial for virus replication and pathogenicity. In this study, it was observed that EV-A71 infection resulted in a perinuclear redistribution of the mitochondria. The mitochondria rearrangement was found to require the microtubule network, the dynein complex and a low cytosolic calcium concentration. Subsequently, the EV-A71 non-structural protein 2BC was identified as the viral protein capable of inducing mitochondria clustering. The protein was found localized on mitochondria and interacted with the mitochondrial Rho GTPase 1 (RHOT1) that is a key protein required for attachment between the mitochondria and the motor proteins, which are responsible for the control of mitochondria movement. Additionally, suppressing mitochondria clustering by treating cells with nocodazole, EHNA, thapsigargin or A23187 consistently inhibited EV-A71 replication, indicating that mitochondria recruitment played a crucial role in the EV-A71 life cycle. This study identified a novel function of the EV-A71 2BC protein and provided a potential model for the regulation of mitochondrial motility in EV-A71 infection.

Contribution of hepatitis B virus X protein-induced aberrant microRNA expression to hepatocellular carcinoma pathogenesis

The hepatitis B virus-encoded X (HBX) protein plays important roles in Hepatocellular carcinoma (HCC). Previous studies have demonstrated that HBX can induce alterations in the expression of numerous microRNAs (miRNAs) involved in the carcinogenesis of various tumors. However, the global profile of liver miRNA changes induced by HBX has not been characterized. In this study, we conducted a miRNA microarray analysis to investigate the influence of HBX on the expression of total miRNAs in liver in relation to HCC. Comparative analysis of the data from human normal liver cells (L02) and human HCC cells (HepG2), with or without HBX, identified 19 differentially expressed miRNAs, including 5 with known association to HBX. Target gene prediction for the aberrantly expressed miRNAs identified a total of 304 potential target genes, involved in sundry pathways. Finally, pathway analysis of the HBXinduced miRNAs pathway showed that 5 of the total miRNAs formed an internetwork, suggesting that HBX might exert its pathological effects on hepatic cells through functional synergy with miRNAs that regulated common pathways in liver cells. Therefore, this work provides new insights into the mechanisms of HCC as well as potential diagnostic markers or therapeutic targets for use in clinical management of HCC.

The bovine herpesvirus-1 major tegument protein, VP8, interacts with host HSP60 concomitant with deregulation of mitochondrial function

The U_L47 gene product, VP8, is a major tegument protein of BoHV-1. While VP8 is not essential for virus replication in cell culture, a U_L47-deleted virus exhibits a smaller tegument structure and is avirulent in cattle. To obtain pure VP8 protein for structural analysis, we expressed a N-terminally truncated version of VP8 in Eschericia coli. However, the recombinant VP8 was consistently co-purified with a tightly associated bacterial protein; this protein was identified by mass spectrometry as GroEL, which has considerable homology with mammalian heat shock protein-60 (HSP60), thus suggesting a new role for VP8 in virus-host interaction. A physical interaction of HSP60 and VP8 in both VP8-transfected and BoHV-1-infected cells was demonstrated by immunoprecipitation. Analysis of different truncated VP8 constructs revealed that amino acids 259-482 and 632-741 are involved in binding to HSP60. Full-length VP8 and VP8 219-741 (containing both interacting domains, 259-482 and 632-741) co-localized with HSP60 and mitochondria. VP8 was localized in the mitochondria from 2 to 14 h post infection in BoHV-1-infected cells. The mitochondrial membrane potential was reduced in both VP8-transfected and BoHV-1-infected cells and was further diminished by overexpression of HSP60 in the presence of VP8. In addition, VP8 expression decreased the ATP concentration during transfection, as well as BoHV-1 infection. Thus, VP8 may play a role in the deregulation of mitochondrial function through interaction with HSP60. This is consistent with the fact that BoHV-1 infection is known to promote mitochondrial dysfunction.

Characterization of HBV integration patterns and timing in liver cancer and HBV-infected livers

Integration of Hepatitis B virus (HBV) into the human genome can cause genetic instability, leading to selective advantages for HBV-induced liver cancer. Despite the large number of studies for HBV integration into liver cancer, little is known about the mechanism of initial HBV integration events owing to the limitations of materials and detection methods. We conducted an HBV sequence capture, followed by ultra-deep sequencing, to screen for HBV integrations in 111 liver samples from human-hepatocyte chimeric mice with HBV infection and human clinical samples containing 42 paired samples from non-tumorous and tumorous liver tissues. The HBV infection model using chimeric mice verified the efficiency of our HBV-capture analysis and demonstrated that HBV integration could occur 23 to 49 days after HBV infection via microhomology-mediated end joining and predominantly in mitochondrial DNA. Overall HBV integration sites in clinical samples were significantly enriched in regions annotated as exhibiting open chromatin, a high level of gene expression, and early replication timing in liver cells. These data indicate that HBV integration in liver tissue was biased according to chromatin accessibility, with additional selection pressures in the gene promoters of tumor samples. Moreover, an integrative analysis using paired non-tumorous and tumorous samples and HBV-related transcriptional change revealed the involvement of TERT and MLL4 in clonal selection. We also found frequent and non-tumorous liver-specific HBV integrations in FN1 and HBV-FN1 fusion transcript. Extensive survey of HBV integrations facilitates and improves the understanding of the timing and biology of HBV integration during infection and HBV-related hepatocarcinogenesis.

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.

Mitochondrial Proteins Coded by Human Tumor Viruses

Viruses must exploit the cellular biosynthetic machinery and evade cellular defense systems to complete their life cycles. Due to their crucial roles in cellular bioenergetics, apoptosis, innate immunity and redox balance, mitochondria are important functional targets of many viruses, including tumor viruses. The present review describes the interactions between mitochondria and proteins coded by the human tumor viruses human T-cell leukemia virus type 1, Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus, human hepatitis viruses B and C, and human papillomavirus, and highlights how these interactions contribute to viral replication, persistence and transformation.

A comparative study of hepatitis B virus X protein mutants K130M, V131I and KV130/131MI to investigate their roles in fibrosis, cirrhosis and hepatocellular carcinoma

Hepatitis B virus (HBV) genomic mutations A1762T, G1764A and AG1762/1764TA cause production of HBV X protein (HBx) mutants, namely K130M, V131I and KV130/131MI. These mutations are important biomarkers for the development of cirrhosis and hepatocellular carcinoma (HCC) in chronic HBV patients. This study comparatively analyses the impact of intracellular expression of HBx mutants on HCC cell line Huh7. It was found that expression of KV130/131MI induced: cell proliferation, altered expression of cell cycle regulatory genes in favour of cell proliferation, intracellular reactive oxygen species (ROS) production and mitochondrial depolarization. KV130/131MI may be directly involved in host cell proliferation and hepatocarcinogenesis via altering expression of cell cycle regulatory genes. KV130/131MI may also play pivotal roles in fibrosis and cirrhosis via inducing ROS production and mitochondrial depolarization. Furthermore, these might be the possible reasons for higher occurrence of AG1762/1764TA as compared to A1762T and G1764A in cirrhosis and HCC patients.

Functional interaction of endoplasmic reticulum stress and hepatitis B virus in the pathogenesis of liver diseases

Hepatitis B virus (HBV) is a non-cytopathic virus that causes acute and chronic inflammatory liver diseases, often leading to the pathogenesis of hepatocellular carcinoma (HCC). Although many studies for the roles of HBV on pathogenesis of the liver diseases, such as non-alcoholic fatty liver disease (NAFLD), hepatic inflammation, cirrhosis, and HCC, have been reported, the mechanisms are not fully understood. Endoplasmic reticulum (ER) and mitochondria have the protective mechanisms to restore their damaged function by intrinsic or extrinsic stresses, but their chronic dysfunctions are associated with the pathogenesis of the various diseases. Furthermore, HBV can affect intra- or extracellular homeostasis through induction of ER and mitochondrial dysfunctions, leading to liver injury. Therefore, the mechanism by which HBV induces ER or mitochondrial stresses may be a therapeutic target for treatment of liver diseases.

Postoperative aspartate aminotransferase to lymphocyte ratio index change is an independent predictor of survival in patients with small hepatocellular carcinoma

Elevated preoperative aspartate aminotransferase (AST) to lymphocyte ratio index (ALRI) is reported to be a prognostic factor for patients with hepatocellular carcinoma (HCC) after treatment. However, [DELTA] ALRI which represents the change from postoperative ALRI to preoperative ALRI change has received little attention. The present study was designed to evaluate the prognostic value of [DELTA] ALRI in small HCC patients after liver resection.A retrospective cohort study was performed to analyze 241 patients with small HCC who underwent liver resection. Patients were divided into Group A ([DELTA] ALRI < 0, n = 142) and group B ([DELTA] ALRI ≥ 0, n = 99) according to postoperative ALRI change. Clinical data, overall survival (OS), and recurrence-free survival (RFS) were compared between the 2 groups, and a multivariate analysis was used to identify prognostic factors.The 1, 3, and 5-year OS rates were 96.5%, 84.9%, and 70.8%, respectively, for group A, and 94.9%, 75.8%, and 59.7%, respectively for group B (P = .014). The corresponding 1, 3, and 5-year RFS rates were 78.2%, 54.6%, and 52.3%, respectively, for group A, and 62.6%, 40.1%, 24.5%, respectively, for group B (P < .001). The results of univariate and multivariate analysis indicated that [DELTA] ALRI was an independent prognostic factor for both RFS (P < .001, hazard ratio [HR] 2.192, 95% confidence interval 1.527-3.147) and OS (P < .001, HR 2.381, 95% confidence interval 1.503-3.771).A positive [DELTA] ALRI after liver resection predicts decreased OS and RFS in patients with small HCC.

X protein variants of the autochthonous Latin American hepatitis B virus F genotype promotes human hepatocyte death by the induction of apoptosis and autophagy

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The impact of BCP mutations on HBV-X biologic activity was analyzed.

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Genotype F wild type and mutant HBV-X induce apoptosis of human hepatocytes.

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HBV-X variants modulate the expression of Bcl-2 family proteins.

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Subgenotypes F1b and F4 HBV-X and variants induce autophagy of human hepatocytes.

The hepatitis B virus X protein (HBV-X) is a multifunctional regulatory protein associated with the pathogenesis of liver disease in chronic HBV infection. Basal core promoter mutations (BCP), associated with the clinical course of chronic HBV infection, affect HBV-X at 130–131 positions. The role of these mutations on HBV-X biological activity remains largely unknown. The aim of this study was to analyze the impact of the presence of different amino acids at 130–131 positions of HBV-X on the biological activity of the protein. Transient expression of wild type and mutant F1b and F4 HBV-X increased cell mortality by the induction of apoptosis in human hepatoma cells. The wild type and mutant HBV-X differentially modulate the expression of pro-apoptotic (Bax) and anti-apoptotic (Bcl-2 and Bcl-X) regulatory proteins of the Bcl-2 family. Furthermore, the expression of HBV-X variants of both subgenotypes induced autophagy of human tumoral hepatocytes. In conclusion, HBV-X variants of the Latin American HBV F genotype promotes human hepatocytes death by the induction of apoptosis and autophagy. The results of this work describe some of the molecular mechanisms by which HBV-X variants contribute to the pathogenesis of liver diseases in the infected liver and help to the biological characterization of genotype F, responsible of the majority of HBV infections in Argentina.

Voltage-Dependent Anion Channel 1 Interacts with Ribonucleoprotein Complexes To Enhance Infectious Bursal Disease Virus Polymerase Activity

Infectious bursal disease virus (IBDV) is a double-stranded RNA (dsRNA) virus. Segment A contains two overlapping open reading frames (ORFs), which encode viral proteins VP2, VP3, VP4, and VP5. Segment B contains one ORF and encodes the viral RNA-dependent RNA polymerase, VP1. IBDV ribonucleoprotein complexes are composed of VP1, VP3, and dsRNA and play a critical role in mediating viral replication and transcription during the virus life cycle. In the present study, we identified a cellular factor, VDAC1, which was upregulated during IBDV infection and found to mediate IBDV polymerase activity. VDAC1 senses IBDV infection by interacting with viral proteins VP1 and VP3. This association is caused by RNA bridging, and all three proteins colocalize in the cytoplasm. Furthermore, small interfering RNA (siRNA)-mediated downregulation of VDAC1 resulted in a reduction in viral polymerase activity and a subsequent decrease in viral yield. Moreover, overexpression of VDAC1 enhanced IBDV polymerase activity. We also found that the viral protein VP3 can replace segment A to execute polymerase activity. A previous study showed that mutations in the C terminus of VP3 directly influence the formation of VP1-VP3 complexes. Our immunoprecipitation experiments demonstrated that protein-protein interactions between VDAC1 and VP3 and between VDAC1 and VP1 play a role in stabilizing the interaction between VP3 and VP1, further promoting IBDV polymerase activity.IMPORTANCE The cellular factor VDAC1 controls the entry and exit of mitochondrial metabolites and plays a pivotal role during intrinsic apoptosis by mediating the release of many apoptogenic molecules. Here we identify a novel role of VDAC1, showing that VDAC1 interacts with IBDV ribonucleoproteins (RNPs) and facilitates IBDV replication by enhancing IBDV polymerase activity through its ability to stabilize interactions in RNP complexes. To our knowledge, this is the first report that VDAC1 is specifically involved in regulating IBDV RNA polymerase activity, providing novel insight into virus-host interactions.

Hepatitis B virus X protein activates E3 ubiquitin ligase Siah-1 to control virus propagation via a negative feedback loop

The seven in absentia homologue 1 (Siah-1) protein is an E3 ubiquitin ligase that induces ubiquitin-dependent proteasomal degradation of HBx, the principal regulatory protein of hepatitis B virus (HBV); however, its role in HBV propagation remains unknown. Here, we found that HBx upregulates Siah-1 levels in HepG2 but not in Hep3B cells, in which p53 is absent. For this effect, HBx sequentially activated ataxia telangiectasia mutated kinase and checkpoint kinase 2 via phosphorylation at the Ser-1981 and Thr-68 residues, respectively, which led to the activation of p53 via phosphorylation at the Ser-15 and Ser-20 residues. As a result, HBx was heavily ubiquitinated by Siah-1 and degraded by the ubiquitin-proteasome system in HepG2 cells, whereas this effect was marginal or undetectable in Hep3B cells. Knock-down of p53 in HepG2 cells downregulated Siah-1 levels and subsequently upregulated HBx levels, whereas ectopic p53 expression in Hep3B cells upregulated Siah-1 levels and subsequently downregulated HBx levels. In addition, Siah-1 knock-down impaired the ubiquitination and proteasomal degradation of HBx in HepG2 cells, whereas ectopic Siah-1 expression induced ubiquitin-dependent proteasomal degradation of HBx in Hep3B cells. The effects of HBx on p53 and Siah-1 were exactly reproduced in a 1.2-mer HBV replicon system, mimicking the natural course of HBV infection. In particular, Siah-1 knock-down upregulated the levels of HBx derived from the HBV replicon, resulting in an increase in HBV production. In conclusion, HBx modulates its own protein level via a negative feedback loop involving p53 and Siah-1 to control HBV propagation.

Protein kinase CK2 regulates redox homeostasis through NF-κB and Bcl-xL in cardiomyoblasts

Oxygen consumption is particularly elevated in cardiac cells as they are equipped with a large number of mitochondria and high levels of respiratory chain components. Consequently, production of reactive oxygen species (ROS) is tightly controlled as an imbalance in redox reactions can lead to irreversible cellular damage. siRNA-mediated down-regulation of protein kinase CK2 has been implicated in the accumulation of ROS in cells. The present study was undertaken in order to investigate the role of CK2 in redox homeostasis in cardiomyoblasts. We found that inhibition or silencing of CK2 causes elevated levels of ROS, notably superoxide radical, and this is accompanied by suppression of NF-κB transcriptional activity and mitochondrial dysfunction. We show that CK2 regulates the expression of manganese superoxide dismutase, the enzyme catalyzing the dismutation of superoxide, in cancer cells but not in cardiomyoblasts. Furthermore, we report evidence that impaired expression of CK2 results in destabilization of the Bcl-2 mammalian homolog Bcl-xL, which is known to stabilize the mitochondrial membrane potential, through a mechanism involving disruption of the chaperone function of heat shock protein 90. Analysis of differential mRNA expression related to oxidative stress revealed that CK2 silencing caused a statistically significant deregulation of four genes associated with the oxidative damage, i.e., Fmo2, Ptgs1, Dhcr24, and Ptgs2. Overall, the results reported here are consistent with the notion that CK2 plays a role in conferring protection against oxidative stress by positively regulating pro-survival signaling molecules and the protein folding machinery in cardiomyoblasts.

Hepatitis B virus X protein sensitizes HL-7702 cells to oxidative stress-induced apoptosis through modulation of the mitochondrial permeability transition pore

Chronic hepatitis B virus (HBV) infection is a leading cause of liver cirrhosis and cancer. Among the pathogenic factors of HBV, HBV X protein (HBx) is attracting increased attention. Although it is documented that HBx is a multifunctional regulator that modulates cell inflammation and apoptosis, the exact mechanism remains controversial. In the present study, we explored the effect of HBx on oxidative stress-induced apoptosis in normal liver cell line, HL-7702. Our results showed that the existence of HBx affected mitochondrial biogenesis by modulating the opening of the mitochondrial permeability transition pore (MPTP). Notably, this phenomenon was associated with a pronounced translocation of Bax from the cytosol to the mitochondria during the period of exposure to oxidative stress with a release of cytochrome c and activation of cleaved caspase-3 and PARP. Moreover, MPTP blockage with cyclosporin A prevented the translocation of Bax, and inhibited oxidative stress-induced apoptotic killing in the HBx-expressing HL-7702 cells. Our findings suggest that HBx exhibits pro-apoptotic effects upon normal liver cells following exposure to oxidative stress by modulating the MPTP gateway.

USP16 Downregulation by Carboxyl-terminal Truncated HBx Promotes the Growth of Hepatocellular Carcinoma Cells

Hepatitis B virus (HBV) infection is a major factor that contributes to the development of hepatocellular carcinoma (HCC). HBV X protein (HBx) has been shown to accelerate HCC progression by promoting tumour growth and metastasis. In the clinic, carboxyl-terminal truncated HBx (Ct-HBx) proteins are frequently present in HCC tumour tissues, but not in non-tumorous tissues. In this study, we analysed deubiquitinase expression profiles in cells with or without ectopic expression of the Ct-HBx proteins and observed that the expression of ubiquitin specific peptidase 16 (USP16) was substantially inhibited by Ct-HBx proteins. Liver tumour cells with forced down-regulation of USP16 exhibited increased capabilities for colony formation and tumour growth in vivo. In addition, USP16 inhibition promoted stem-like properties in tumour cells, as evidenced by their spheroid formation and chemo-responsiveness. Furthermore, ectopic expression of USP16 in tumour cells significantly abrogated the tumour promoting activities of the Ct-HBx proteins (HBxΔ35), leading to decreased tumour cell viability and tumour growth. In human HCCs, USP16 was frequently downregulated, and the decreased expression of USP16 was correlated with high tumour stages and poor differentiation status. Taken together, our study suggests that USP16 downregulation is a critical event in Ct-HBx-mediated promotion of HCC tumorigenicity and malignancy.

Covariation Analysis of Serumal and Urinary Metabolites Suggests Aberrant Glycine and Fatty Acid Metabolism in Chronic Hepatitis B

BACKGROUND

Chronic hepatitis b (CHB) is one of the most serious viral diseases threatening human health by putting patients at lifelong risk of cirrhosis and hepatocellular carcinoma (HCC). Although some proofs of altered metabolites in CHB were accumulated, its metabolic mechanism remains poorly understood. Analyzing covariations between metabolites may provide new hints toward underlying metabolic pathogenesis in CHB patients.

METHODS

The present study collected paired urine and serum samples from the same subjects including 145 CHB and 23 healthy controls. A large-scale analysis of metabolites' covariation within and across biofluids was systematically done to explore the underlying biological evidences for reprogrammed metabolism in CHB. Randomization and relative ranking difference were introduced to reduce bias caused by different sample size. More importantly, functional indication was interpreted by mapping differentially changed covariations to known metabolic pathways.

RESULTS

Our results suggested reprogrammed pathways related to glycine metabolism, fatty acids metabolism and TCA cycle in CHB patients. With further improvement, the covariation analysis combined with network association study would pave new alternative way to interpret functional clues in clinical multi-omics data.

Metformin induces apoptosis via a mitochondria-mediated pathway in human breast cancer cells in vitro

Breast cancer is the most commonly occurring cancer and second leading cause of mortality in women. Metformin is a widely prescribed anti-hyperglycemic drug, which is emerging as a potential cancer preventative and treatment agent. However, the mechanisms underlying the suppressive effects of metformin on cancer cell growth and the induction of cancer cell apoptosis are not fully elucidated. The present study aimed to identify the pathways regulated by metformin in two breast cancer cell lines, MDA-MB-231 and MDA-MB-435. Cells were treated with various concentrations of metformin and then evaluated with respect to viability, proliferation, adenosine triphosphate (ATP) and reactive oxygen species (ROS) levels, mitochondrial membrane potential (∆ψm), and the expression of anti- and pro-apoptotic proteins. Metformin caused apoptosis in a concentration- and time-dependent manner, and decreased cell viability and ATP production. Furthermore, metformin induced the generation of ROS and decreased the ∆ψm. Moreover, metformin downregulated the expression of the anti-apoptotic proteins B-cell lymphoma 2 (BCL-2) and myeloid cell leukemia-1, and upregulated the expression of the pro-apoptotic BCL-2-associated X protein in MDA-MB-231 cells. These results demonstrate that the apoptotic and cytotoxic effects of metformin on breast cancer cells are mediated by the intrinsic mitochondria-mediated apoptosis pathway.

Hepatitis B Virus X and Regulation of Viral Gene Expression

The efficient replication of hepatitis B virus (HBV) requires the HBV regulatory hepatitis B virus X (HBx) protein. The exact contributions of HBx are not fully understood, in part because of the limitations of the assays used for its study. When HBV replication is driven from a plasmid DNA, the contribution of HBx is modest. However, there is an absolute requirement for HBx in assays that recapitulate the infectious virus life cycle. There is much evidence that HBx can contribute directly to HBV replication by acting on viral promoters embedded within protein coding sequences. In addition, HBx may also contribute indirectly by modulating cellular pathways to benefit virus replication. Understanding the mechanism(s) of HBx action during virus replication may provide insight into novel ways to disrupt chronic HBV replication.

The enhanced expression of death receptor 5 (DR5) mediated by HBV X protein through NF-kappaB pathway is associated with cell apoptosis induced by (TNF-α related apoptosis inducing ligand) TRAIL in hepatoma cells

Background

HBV X protein (HBX) is associated with cell apoptosis mediated by TNF-α related apoptosis inducing ligand (TRAIL), while the role of HBX on the expressions of TRAIL receptors death receptor 4 (DR4) and DR5 are unclear. In this study, we detected the cell apoptosis induced by TRAIL as well as gene and protein expressions of DR4 and DR5 in Huh-7 cells steadily transfected with HBX (Huh-7-HBX cells). In addition, we investigated the activation of different pathways associated with the expressions of TRAIL receptors in Huh-7-HBX cells.

Methods

The apoptosis of Huh-7-HBX cells induced by TRAIL was evaluated by flow cytometry analysis. The levels of DR4 and DR5 expression in cells were determined by real-time PCR and western blotting analysis. The activities of JNK pathway and NF-kappaB (NF-κB) pathway were demonstrated by western blotting assay.

Results

Compared to control cells, the percentage of cell apoptosis was increased in Huh-7-HBX cells. The increased expressions of DR4 and DR5 on gene and protein levels were observed in Huh-7-HBX cells. Further researches suggested that activation of JNK pathway was increased but not involved in the expression of TRAIL receptors in HBX positive cells. The activation of NF-κB pathway increased and was responsible for DR5 expression and cell apoptosis in HBX positive cells.

Conclusions

These results demonstrate that increased apoptosis induced by TRAIL is associated with increased expression of DR5 that mediated by HBX through NF-κB pathway. This finding provides a critical insight into the mechanism of hepatocyte apoptosis mediated by HBX in HBV infection.

Immune-mediated Liver Injury in Hepatitis B Virus Infection

Hepatitis B virus (HBV) is responsible for approximately 350 million chronic infections worldwide and is a leading cause of broad-spectrum liver diseases such as hepatitis, cirrhosis and liver cancer. Although it has been well established that adaptive immunity plays a critical role in viral clearance, the pathogenetic mechanisms that cause liver damage during acute and chronic HBV infection remain largely known. This review describes our current knowledge of the immune-mediated pathogenesis of HBV infection and the role of immune cells in the liver injury during hepatitis B.

Tissue distribution of olive flounder VDAC2 and its expression in fish cell lines

Voltage-dependent anion channel (VDAC) is located in the mitochondrial outer membrane, which plays a crucial role in regulating cell life and death. In this study, the tissue distribution of olive flounder Paralichthys olivaceus VDAC2 (PoVDAC2) was detected by quantitative real-time PCR and Western blot analysis. The qRT-PCR results showed that the expression level of PoVDAC2 was abundant in heart, muscle and gill tissues. Western blot analysis revealed a protein of 32 kDa detected in all six tissues. Furthermore, a recombinant eukaryotic expression plasmid pEGFP-N3-PoVDAC2 was successfully constructed and transiently expressed the fusion protein in fish cell lines. Subcellular localization indicated that PoVDAC2-GFP was distributed in a punctate mitochondria-like pattern throughout the cytoplasm in flounder embryonic cells (FEC). The distribution of native VDAC2 in untransfected fish cells was also investigated by immunofluorescence microscopy. The punctate VDAC2 fluorescence signals of both FEC and EPC cells were identically observed in the cytoplasm but not in the nucleus. These results laid a foundation for investigating the functional relevance of VDAC response to pathogens in flounder.

HBx co-localizes with COXIII in HL-7702 cells to upregulate mitochondrial function and ROS generation

Hepatocellular carcinoma (HCC) is one of the most common malignant diseases, and HBx leads to the development of HBV-associated HCC. Mitochondria are key organelles that regulate apoptosis, cellular energetics and signal transduction pathways, and are the source of HBx-induced reactive oxygen species (ROS). Recent findings have shown that HBx interacts with the inner mitochondrial membrane protein, COXIII, via the yeast two-hybrid system, mating experiment and coimmunoprecipitation. The aim of the present study was to examine the co-localizaiton of HBx and COXIII in HL-7702 cells and to investigate ensuing alterations of mitochondrial function. An HL-7702 cell line stably expressing the HBx gene by lentivirus vectors was constructed. Confocal microscopy was utilized to assess the interaction between HBx protein and COXIII. Expression of COXIII, activities of cytochrome c oxidase (COX) and the mitochondrial membrane potential, which were functionally relevant to the HBx protein-COXIII interaction, were investigated in cell cultures. Moreover, the intracellular ROS levels were detected by flow cytometry. The results demonstrated that HBx co-localized with the inner mitochondrial protein, COXIII, in HL-7702 cells, causing the upregulation of COXIII protein expression as well as COX activity. However, HBx did not alter the mitochondrial membrane potential and mitochondria exhibited only slight swelling in HL-7702-HBx cells. Moreover, HBx elevated the generation of mitochondrial ROS in HL-7702-HBx cells. The main finding of the present study was that the co-localization of HBx and COXIII leads to upregulation of the mitochondrial function and ROS generation, which are associated with the oncogenesis of HBV-associated HCC.

C-terminal-truncated hepatitis B virus X protein enhances the development of diethylnitrosamine-induced hepatocellular carcinogenesis

Hepatitis B virus X protein (HBx) is involved in the development of hepatocellular carcinoma (HCC). The HBx sequence is a preferential site of integration into the human genome, leading to the formation of C-terminal-truncated HBx proteins (Ct-HBx). We previously reported that Ct-HBx proteins were able to potentiate cell transformation in vitro. Our present goal was to compare the ability of Ct-HBx and full-length HBx (FL-HBx) proteins to develop or enhance HCC in transgenic mice. In the absence of treatment, neither Ct-HBx- nor FL-HBx-transgenic mice developed HCC. In young mice treated with diethylnitrosamine (DEN) at 8 months of age, a significantly higher incidence and number of liver lesions were observed in Ct-HBx mice than in FL-HBx and control mice. The earlier development of tumours in Ct-HBx-transgenic mice was associated with increased liver inflammation. At 10 months, macroscopic and microscopic analyses showed that, statistically, FL-HBx mice developed more liver lesions with a larger surface area than control mice. Furthermore, during DEN-induced initiation of HCC, Ct-HBx- and FL-HBx-transgenic mice showed higher expression of IL-6, TNF-α and IL-1β transcripts, activation of STAT3, ERK and JNK proteins and an increase in cell apoptosis. In conclusion, in DEN-treated transgenic mice, the expression of Ct-HBx protein causes a more rapid onset of HCC than does FL-HBx protein. HBV genome integration leading to the expression of a truncated form of HBx protein may therefore facilitate HCC development in chronically infected patients.

Accurately mapping the location of the binding site for the interaction between hepatitis B virus X protein and cytochrome c oxidase III

The hepatitis B virus (HBV) X protein (HBx) plays an important pathogenetic role in hepatocarcinoma tumorigenesis. As HBx does not have the ability to bind to double-stranded DNA (dsDNA), protein-protein interaction is crucial for HBx functions. In a previous study, we screened a novel HBx-interacting protein, the cytochrome c oxidase subunit III (COXIII). In the present study, we aimed to accurately map the location of the binding site for the interaction of HBx with COXIII. Two fragments of HBx mutants (X1 aa1-72 and X2 aa1-117) were amplified by polymerase chain reaction (PCR) and separately inserted into the pAS2-1 plasmid. PCR and gene sequencing confirmed the correct insertion of the mutant fragments in the plasmid. The tanscription of the mutant fragments in yeast cells was demonstrated by RT-PCR and western blot analysis confirmed that they were accurately translated into fusion proteins. Hybridization on solid medium and the detection of β-galactosidase (β-gal) activity indicated that the binding site for the interaction between HBx and COXIII was located between aa72 and aa117. Specific interactions between the HBxX2 protein and COXIII were verified by co-immunoprecipitation. To the best of our knowledge, this is the first study showing to demonstrate that aa72-117 in HBx is the key region for binding with COXIII.