Exogenous hepatitis B virus envelope proteins induce endoplasmic reticulum stress: involvement of cannabinoid axis in liver cancer cells

Hepatitis B Surface Antigen Isoforms: Their Clinical Implications, Utilisation in Diagnosis, Prevention and New Antiviral Strategies

The hepatitis B surface antigen (HBsAg) is a multifunctional glycoprotein composed of large (LHB), middle (MHB), and small (SHB) subunits. HBsAg isoforms have numerous biological functions during HBV infection-from initial and specific viral attachment to the hepatocytes to initiating chronic infection with their immunomodulatory properties. The genetic variability of HBsAg isoforms may play a role in several HBV-related liver phases and clinical manifestations, from occult hepatitis and viral reactivation upon immunosuppression to fulminant hepatitis and hepatocellular carcinoma (HCC). Their immunogenic properties make them a major target for developing HBV vaccines, and in recent years they have been recognised as valuable targets for new therapeutic approaches. Initial research has already shown promising results in utilising HBsAg isoforms instead of quantitative HBsAg for correctly evaluating chronic infection phases and predicting functional cures. The ratio between surface components was shown to indicate specific outcomes of HBV and HDV infections. Thus, besides traditional HBsAg detection and quantitation, HBsAg isoform quantitation can become a useful non-invasive biomarker for assessing chronically infected patients. This review summarises the current knowledge of HBsAg isoforms, their potential usefulness and aspects deserving further research.

Pangenomic antiviral effect of REP 2139 in CRISPR/Cas9 engineered cell lines expressing hepatitis B virus surface antigen

Chronic hepatitis B remains a global health problem with 296 million people living with chronic HBV infection and being at risk of developing cirrhosis and hepatocellular carcinoma. Non-infectious subviral particles (SVP) are produced in large excess over infectious Dane particles in patients and are the major source of Hepatitis B surface antigen (HBsAg). They are thought to exhaust the immune system, and it is generally considered that functional cure requires the clearance of HBsAg from blood of patient. Nucleic acid polymers (NAPs) antiviral activity lead to the inhibition of HBsAg release, resulting in rapid clearance of HBsAg from circulation in vivo. However, their efficacy has only been demonstrated in limited genotypes in small scale clinical trials. HBV exists as nine main genotypes (A to I). In this study, the HBsAg ORFs from the most prevalent genotypes (A, B, C, D, E, G), which account for over 96% of human cases, were inserted into the AAVS1 safe-harbor of HepG2 cells using CRISPR/Cas9 knock-in. A cell line producing the D144A vaccine escape mutant was also engineered. The secretion of HBsAg was confirmed into these new genotype cell lines (GCLs) and the antiviral activity of the NAP REP 2139 was then assessed. The results demonstrate that REP 2139 exerts an antiviral effect in all genotypes and serotypes tested in this study, including the vaccine escape mutant, suggesting a pangenomic effect of the NAPs.

Quantitative analysis of acetylation in peste des petits ruminants virus-infected Vero cells

BACKGROUND

Peste des petits ruminants virus (PPRV) is a highly contagious pathogen that strongly influences the productivity of small ruminants worldwide. Acetylation is an important post-translational modification involved in regulation of multiple biological functions. However, the extent and function of acetylation in host cells during PPRV infection remains unknown.

METHODS

Dimethylation-labeling-based quantitative proteomic analysis of the acetylome of PPRV-infected Vero cells was performed.

RESULTS

In total, 1068 proteins with 2641 modification sites were detected in response to PPRV infection, of which 304 differentially acetylated proteins (DAcPs) with 410 acetylated sites were identified (fold change < 0.83 or > 1.2 and P < 0.05), including 109 up-regulated and 195 down-regulated proteins. Gene Ontology (GO) classification indicated that DAcPs were mostly located in the cytoplasm (43%) and participated in cellular and metabolic processes related to binding and catalytic activity. Functional enrichment indicated that the DAcPs were involved in the minichromosome maintenance complex, unfolded protein binding, helicase activity. Only protein processing in endoplasmic reticulum pathway was enriched. A protein-protein interaction (PPI) network of the identified proteins further indicated that a various chaperone and ribosome processes were modulated by acetylation.

CONCLUSIONS

To the best of our knowledge, this is the first study on acetylome in PPRV-infected host cell. Our findings establish an important baseline for future study on the roles of acetylation in the host response to PPRV replication and provide novel insights for understanding the molecular pathological mechanism of PPRV infection.

The endocannabinoid system, a new gatekeeper in the pharmacology of human hepatocellular carcinoma

Despite numerous prevention methodologies and treatment options, hepatocellular carcinoma (HCC) still remains as the third leading life-threatening cancer. It is thus pertinent to develop new treatment modality to fight this devastating carcinoma. Ample recent studies have shown the anti-inflammatory and antitumor roles of the endocannabinoid system in various forms of cancers. Preclinical studies have also confirmed that cannabinoid therapy can be an optimal regimen for cancer treatments. The endocannabinoid system is involved in many cancer-related processes, including induction of endoplasmic reticulum (ER) stress-dependent apoptosis, autophagy, PITRK and ERK signaling pathways, cell invasion, epithelial-mesenchymal transition (EMT), and cancer stem cell (CSC) phenotypes. Moreover, changes in signaling transduction of the endocannabinoid system can be a potential diagnostic and prognostic biomarker for HCC. Due to its pivotal role in lipid metabolism, the endocannabinoid system affects metabolic reprogramming as well as lipid content of exosomes. In addition, due to the importance of non-coding RNAs (ncRNAs), several studies have examined the relationship between microRNAs and the endocannabinoid system in HCC. However, HCC is a pathological condition with high heterogeneity, and therefore using the endocannabinoid system for treatment has faced many controversies. While some studies favored a role of the endocannabinoid system in carcinogenesis and tumor induction, others exhibited the anticancer potential of endocannabinoids in HCC. In this review, specific studies delineating the relationship between endocannabinoids and HCC are examined. Based on collected findings, detailed studies of the molecular mechanism of endocannabinoids as well as preclinical studies for investigating therapeutic or carcinogenic impacts in HCC cancer are strongly suggested.

Immunohistochemical expression of CB1 receptors in the liver of patients with HBV related-HCC

BACKGROUND AND AIMS

The most common cause of hepatocellular carcinoma (HCC), which has a high death rate, is hepatitis B virus (HBV) infection. This study aimed to examine immunoexpression of CB1 receptors in the livers of patients with HBV-related HCC in comparison with HCC and chronic HBV as well as healthy people. Patients and methods Participants in this case-controlled study were patients with only HBV (HBV; 40), only HCC (HCC; 41), and HBV-related HCC (HBV + HCC; 40) and a healthy control group (C; 30). Tissue expression of CB1 at the protein level was studied using immunohistochemical methods.

RESULTS

All groups were significantly different in terms of expression of CB1 protein (P < 0.001). The expression levels of CB1 in the liver tissue of the HBV and C groups were not significantly different (P = 0.072). The expression levels of CB1 in the liver tissue of the HBV-related HCC and HCC groups had a statistically significant increase compared to the C and HBV groups (P < 0.001). Also, the CB1 expression levels in the liver tissues of HBV-related HCC and HCC groups were significantly different (P = 0.008). The sensitivity and specificity of immunohistochemistry tests in the diagnosis of HCC using CB1 were 63.4 and 91.2, respectively. Positive and negative predictive values were 90.0 % and 65.1 %, respectively. There was no relationship between the expression of CB1and other clinicopathological variables (P < 0.05).

CONCLUSION

The present findings revealed a tumor promoting function of the CB1 receptor in HCC. CB1 is also a pathological valuable factor for identifying the pathway of inflammation during infection.

Endoplasmic Reticulum Stress in Hepatitis B Virus and Hepatitis C Virus Infection

Endoplasmic reticulum (ER) stress, a type of cellular stress, always occurs when unfolded or misfolded proteins accumulating in the ER exceed the protein folding capacity. Because of the demand for rapid viral protein synthesis after viral infection, viral infections become a risk factor for ER stress. The hepatocyte is a cell with large and well-developed ER, and hepatitis virus infection is widespread in the population, indicating the interaction between hepatitis viruses and ER stress may have significance for managing liver diseases. In this paper, we review the process that is initiated by the hepatocyte through ER stress against HBV and HCV infection and explain how this information can be helpful in the treatment of HBV/HCV-related diseases.

Critical Updates on Chronic Hepatitis B Virus Infection in 2021

Chronic hepatitis B virus (HBV) infection is a global healthcare burden in the form of chronic liver disease, cirrhosis, liver failure and liver cancer. There is no definite cure for the virus and even though extensive vaccination programs have reduced the burden of liver disease in the future population, treatment options to eradicate the virus from the host are still lacking. In this review, we discuss in detail current updates on the structure and applied biology of the virus in the host, examine updates to current treatment and explore novel and state-of-the-art therapeutics in the pipeline for management of chronic HBV. Furthermore, we also specifically review clinical updates on HBV-related acute on chronic liver failure (ACLF). Current treatments for chronic HBV infection have seen important updates in the form of considerations for treating patients in the immune tolerant phase and some clarity on end points for treatment and decisions on finite therapy with nucleos(t)ide inhibitors. Ongoing cutting-edge research on HBV biology has helped us identify novel target areas in the life cycle of the virus for application of new therapeutics. Due to improvements in the area of genomics, the hope for therapeutic vaccines, vector-based treatments and focused management aimed at targeting host integration of the virus and thereby a total cure could become a reality in the near future. Newer clinical prognostic tools have improved our understanding of timing of specific treatment options for the catastrophic syndrome of ACLF secondary to reactivation of HBV. In this review, we discuss in detail pertinent updates regarding virus biology and novel therapeutic targets with special focus on the appraisal of prognostic scores and treatment options in HBV-related ACLF.

Endoplasmic reticulum stress: Multiple regulatory roles in hepatocellular carcinoma

BACKGROUND

Endoplasmic reticulum (ER) stress is a basic cellular stress response that maintains cellular protein homeostasis under endogenous or exogenous stimuli, which depends on the stimulus, its intensity, and action time. The ER produces a corresponding cascade reaction for crosstalk of adaptive and/or pro-death regulation with other organelles. Hepatocellular carcinoma(HCC) is one of the most common malignant solid tumors with an extremely poor prognosis. Viral hepatitis infection, cirrhosis, and steatohepatitis are closely related to the occurrence and development of HCC, and ER stress has gradually been shown to be a major mechanism. Moreover, an increasing need for protein and lipid products and relative deficiencies of oxygen and nutrients for rapid proliferation and endoplasmic reticulum stress are undoubtedly involved. Therefore, to fully and comprehensively understand the regulatory role of endoplasmic reticulum stress in the occurrence and progression of HCC is of vital importance to explore its pathogenesis and develop novel anti-cancer strategies.

METHODOLOGY

We searched for relevant publications in the PubMed databases using the keywords "Endoplasmic reticulum stress", "hepatocellular carcinoma" in last five years,and present an overview of the current knowledge that links ER stress and HCC, which includes carcinogenesis, progression, and anti-cancer strategies, and propose directions of future research.

RESULT

ER stress were confirmed to be multiple regulators or effectors of cancer, which also be confirmed to drive tumorigenesis and progression of HCC. Targeting ER stress signaling pathway and related molecules could play a critical role for anti-HCC and has become a research hotspot for anti-cancer in recent years.

CONCLUSION

ER stress are critical for the processes of the tumorigenesis and progression of tumors. For HCC, ER stress was associated with tumorigenesis, development, metastasis, angiogenesis and drug resistance, targeting ER stress has emerged as a potential anti-tumor strategy.

Lost Small Envelope Protein Expression from Naturally Occurring PreS1 Deletion Mutants of Hepatitis B Virus Is Often Accompanied by Increased HBx and Core Protein Expression as Well as Genome Replication

Hepatitis B virus (HBV) transcribes coterminal mRNAs of 0.7 to 3.5 kb from the 3.2-kb covalently closed circular DNA, with the 2.1-kb RNA being most abundant. The 0.7-kb RNA produces HBx protein, a transcriptional transactivator, while the 3.5-kb pregenomic RNA (pgRNA) drives core and P protein translation as well as genome replication. The large (L) and small (S) envelope proteins are translated from the 2.4-kb and 2.1-kb RNAs, respectively, with the majority of the S protein being secreted as noninfectious subviral particles and detected as hepatitis B surface antigen (HBsAg). pgRNA transcription could inhibit transcription of subgenomic RNAs. The present study characterized naturally occurring in-frame deletions in the 3' preS1 region, which not only codes for L protein but also serves as the promoter for 2.1-kb RNA. The human hepatoma cell line Huh7 was transiently transfected with subgenomic expression constructs for envelope (and HBx) proteins, dimeric constructs, or constructs mimicking covalently closed circular DNA. The results confirmed lost 2.1-kb RNA transcription and HBsAg production from many deletion mutants, accompanied by increases in other (especially 2.4-kb) RNAs, intracellular HBx and core proteins, and replicative DNA but impaired virion and L protein secretion. The highest intracellular L protein levels were achieved by mutants that had residual S protein expression or retained the matrix domain in L protein. Site-directed mutagenesis of a high replicating deletion mutant suggested that increased HBx protein expression and blocked virion secretion both contributed to the high replication phenotype. Our findings could help explain why such deletions are selected at a late stage of chronic HBV infection and how they contribute to viral pathogenesis. IMPORTANCE Expression of hepatitis B e antigen (HBeAg) and overproduction of HBsAg by wild-type HBV are implicated in the induction of immune tolerance to achieve chronic infection. How HBV survives the subsequent immune clearance phase remains incompletely understood. Our previous characterization of core promoter mutations to reduce HBeAg production revealed the ability of the 3.5-kb pgRNA to diminish transcription of coterminal RNAs of 2.4 kb, 2.1 kb, and 0.7 kb. The later stage of chronic HBV infection often selects for in-frame deletions in the preS region. Here, we found that many 3' preS1 deletions prevented transcription of the 2.1-kb RNA for HBsAg production, which was often accompanied by increases in intracellular 3.5-, 0.7-, and especially 2.4-kb RNAs, HBx and core proteins, and replicative DNA but lost virion secretion. These findings established the biological consequences of preS1 deletions, thus shedding light on why they are selected and how they contribute to hepatocarcinogenesis.

ITRAQ-based quantitative proteomics reveals the proteome profiles of MDBK cells infected with bovine viral diarrhea virus

Background

Bovine viral diarrhea (BVD) which is caused by Bovine viral diarrhea virus (BVDV), is an acute, contagious disease. In spite of the use of vaccines and elimination projects, BVDV still causes severe economic losses to the cattle industry for the past few years. The current study presents a preliminary analysis of the pathogenic mechanisms from the perspective of protein expression levels in infected host cells at different points in time to elucidate the infection process associated with BVDV.

Methods

We used the isobaric tags for relative and absolute quantitation (iTRAQ) technology coupled with liquid chromatography-tandem mass spectrometric (LC–MS/MS) approach for a quantitative proteomics comparison of BVDV NADL-infected MDBK cells and non-infected cells. The functions of the proteins were deduced by functional annotation and their involvement in metabolic processes explored by KEGG pathway analysis to identify their interactions.

Results

There were 357 (47.6% downregulated, 52.4% upregulated infected vs. control), 101 (52.5% downregulated, 47.5% upregulated infected vs. control), and 66 (21.2% downregulated, 78.8% upregulated infected vs. control) proteins were differentially expressed (fold change > 1.5 or < 0.67) in the BVDV NADL-infected MDBK cells at 12, 24, and 48 h after infection. GO analysis showed that the differentially expressed proteins (DEPs) are mainly involved in metabolic processes, biological regulation and localization. KEGG enrichment analysis showed that some signaling pathways that involved in the regulation of BVDV NADL-infection and host resistance are significantly (P < 0.05) enriched at different stages of the BVDV NADL-infection, such as Endocytosis signaling pathway, FoxO signaling pathway, Homologous recombination signaling pathway and Lysosome pathway.

Conclusions

These results revealed that the DEPs in BVDV NADL-infected MDBK cells have a wide range of regulatory effects; in addition, they provide a lot of resources for the study of host cell proteomics after BVDV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01592-2.

The Mechanisms of HBV-Induced Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a common malignancy, and the hepatitis B virus (HBV) is its major pathogenic factor. Over the past decades, it has been confirmed that HBV infection could promote disease progression through a variety of mechanisms, ultimately leading to the malignant transformation of liver cells. Many factors have been identified in the pathogenesis of HBV-associated HCC (HBV-HCC), including HBV gene integration, genomic instability caused by mutation, and activation of cancer-promoting signaling pathways. As research in the progression of HBV-HCC progresses, the role of many new mechanisms, such as epigenetics, exosomes, autophagy, metabolic regulation, and immune suppression, is also being continuously explored. The occurrence of HBV-HCC is a complex process caused by interactions across multiple genes and multiple steps, where the synergistic effects of various cancer-promoting mechanisms accelerate the process of disease evolution from inflammation to tumorigenesis. In this review, we aim to provide a brief overview of the mechanisms involved in the occurrence and development of HBV-HCC, which may contribute to a better understanding of the role of HBV in the occurrence and development of HCC.

Increased BST-2 expression by HBV infection promotes HBV-associated HCC tumorigenesis

Background

The majority of hepatocellular carcinoma (HCC) is closely associated with hepatitis B virus (HBV) infection, while the mechanism of HCC induced by HBV is debatable. Bone marrow stromal cell antigen 2 (BST-2), an N-glycoprotein, has been characterized as an oncogenic factor in several types of cancer. However, whether BST-2 plays an important role in HCC tumorigenesis remains unknown.

Methods

A total of 182 HCC tumorous and adjacent nontumor liver tissues were collected. HepG2, Huh7, L02, HepAD38, and HEK293T cell lines were adopted in this study. Tumor proliferation was detected by CCK8, transwell, wound healing, colony formation assays in vitro, and in vivo tumorigenesis was measured by mouse xenografts. NF-κB activation was determined by luciferase assay and Western blot. Protein expression was detected by Western blot, ELISA, or qPCR. Immunoprecipitation was used to confirm the interaction between BST-2 and Syk.

Results

Here, we observed the higher BST-2 expression in HBV-infected HCC than their paired adjacent tissues and HBV-uninfected HCC tissues, particularly more aberrant non-N-glycosylated BST-2 in HBV-infected HCC tumors. We also observed the increased ER degradation-enhancing α-mannosidase-like protein 3 (EDEM3), which is trimming of N-linked glycans by sequential removal of mannose residues, might result in more non-N-glycosylated form of BST-2. Moreover, we demonstrated that BST-2 and non-N-glycosylated BST-2 N65/92A mutant, not only enhanced the tumor characteristics of hepatoma cell lines in vitro, but also enhanced the growth of mouse xenografts in vivo. Mechanically, N65/92A mutant has stronger ability to promote HCC than BST-2 via NF-κB/ERK1/2 but not NF-κB/anti-apoptotic factors pathway. NF-κB inhibitor attenuated BST-2-mediated tumorigenesis of HCC.

Conclusions

Our findings illuminate the novel function of BST-2 as an oncogene of HBV-associated HCC, and highlight the novel relationship of N-glycosylation of BST-2 in regulating HCC tumorigenesis in vitro.

Hepatocyte Endoplasmic Reticulum Stress Inhibits Hepatitis B Virus Secretion and Delays Intracellular Hepatitis B Virus Clearance After Entecavir Treatment

Background: The aim of this study was to explore the effects of endoplasmic reticulum (ER) stress on hepatitis B virus (HBV) replication and the antiviral effect of entecavir (ETV).

Methods: Thapsigargin (TG) and stearic acid (SA) were used to induce ER stress in HepG2.2.15 cells and HepAD38 cells that contained an integrated HBV genome, while ETV was used to inhibit HBV replication. The expression levels of glucose-regulated protein 78 (GRP78) and phosphorylated eukaryotic translation initiation factor 2 subunit alpha (p-eIF2α) were measured by western blotting. Intracellular HBV DNA was determined by qPCR; HBsAg by western blotting; HBV RNA by real-time RT-qPCR; HBsAg and HBeAg in supernatants by enzyme-linked immunosorbent assay (ELISA); and HBV DNA in supernatants by qPCR.

Results: TG and SA induced ER stress in HepG2.2.15 cells and HepAD38 cells from 12 to 48 h post treatment. However, 4-phenylbutyric acid (PBA) partly alleviated the TG-induced ER stress. Moreover, TG inhibited HBsAg, HBeAg, and HBV DNA secretion from 12 to 48 h, while different concentrations of SA inhibited HBsAg and HBV DNA secretion at 48 h. TG promoted intracellular HBV DNA and HBsAg accumulation and the transcription of the HBV 3.5-kb mRNA and S mRNA. PBA treatment restored the secretion of HBsAg and HBV DNA. Finally, ER stress accelerated extracellular HBV DNA clearance but delayed intracellular HBV DNA clearance after ETV treatment.

Conclusions: Hepatocyte ER stress promoted intracellular HBV DNA and HBsAg accumulation by inhibiting their secretion. Our study also suggested that hepatocyte ER stress delayed intracellular HBV DNA clearance after ETV treatment.

Quantitative analysis of the splice variants expressed by the major hepatitis B virus genotypes

Hepatitis B virus (HBV) is a major human pathogen that causes liver diseases. The main HBV RNAs are unspliced transcripts that encode the key viral proteins. Recent studies have shown that some of the HBV spliced transcript isoforms are predictive of liver cancer, yet the roles of these spliced transcripts remain elusive. Furthermore, there are nine major HBV genotypes common in different regions of the world, these genotypes may express different spliced transcript isoforms. To systematically study the HBV splice variants, we transfected human hepatoma cells, Huh7, with four HBV genotypes (A2, B2, C2 and D3), followed by deep RNA-sequencing. We found that 13-28 % of HBV RNAs were splice variants, which were reproducibly detected across independent biological replicates. These comprised 6 novel and 10 previously identified splice variants. In particular, a novel, singly spliced transcript was detected in genotypes A2 and D3 at high levels. The biological relevance of these splice variants was supported by their identification in HBV-positive liver biopsy and serum samples, and in HBV-infected primary human hepatocytes. Interestingly the levels of HBV splice variants varied across the genotypes, but the spliced pregenomic RNA SP1 and SP9 were the two most abundant splice variants. Counterintuitively, these singly spliced SP1 and SP9 variants had a suboptimal 5' splice site, supporting the idea that splicing of HBV RNAs is tightly controlled by the viral post-transcriptional regulatory RNA element.

HBV evolution and genetic variability: Impact on prevention, treatment and development of antivirals

Hepatitis B virus (HBV) poses a major global health burden with 260 million people being chronically infected and 890,000 dying annually from complications in the course of the infection. HBV is a small enveloped virus with a reverse-transcribed DNA genome that infects hepatocytes and can cause acute and chronic infections of the liver. HBV is endemic in humans and apes representing the prototype member of the viral family Hepadnaviridae and can be divided into 10 genotypes. Hepadnaviruses have been found in all vertebrate classes and constitute an ancient viral family that descended from non-enveloped progenitors more than 360 million years ago. The de novo emergence of the envelope protein gene was accompanied with the liver-tropism and resulted in a tight virus-host association. The oldest HBV genomes so far have been isolated from human remains of the Bronze Age and the Neolithic (~7000 years before present). Despite the remarkable stability of the hepadnaviral genome over geological eras, HBV is able to rapidly evolve within an infected individual under pressure of the immune response or during antiviral treatment. Treatment with currently available antivirals blocking intracellular replication of HBV allows controlling of high viremia and improving liver health during long-term therapy of patients with chronic hepatitis B (CHB), but they are not sufficient to cure the disease. New therapy options that cover all HBV genotypes and emerging viral variants will have to be developed soon. In addition to the antiviral treatment of chronically infected patients, continued efforts to expand the global coverage of the currently available HBV vaccine will be one of the key factors for controlling the rising global spread of HBV. Certain improvements of the vaccine (e.g. inclusion of PreS domains) could counteract known problems such as low or no responsiveness of certain risk groups and waning anti-HBs titers leading to occult infections, especially with HBV genotypes E or F. But even with an optimal vaccine and a cure for hepatitis B, global eradication of HBV would be difficult to achieve because of an existing viral reservoir in primates and bats carrying closely related hepadnaviruses with zoonotic potential.

Cholestasis impairs hepatic lipid storage via AMPK and CREB signaling in hepatitis B virus surface protein transgenic mice

Clinical studies demonstrated that nonalcoholic steatohepatitis is associated with liver-related outcomes in chronic hepatitis B. Furthermore, primary biliary fibrosis and biliary atresia occurred in patients with HBV infection. Interestingly, hepatitis B virus surface protein (HBs) transgenic mice spontaneously develop hepatic steatosis. Our aim is to investigate the effect of Abcb4 knockout-induced cholestasis on liver steatosis in HBs transgenic mice. Hybrids of HBs transgenic and Abcb4-/- mice were bred on the BALB/c genetic background. Lipid synthesis, storage, and catabolism as well as proteins and genes that control lipid metabolism were analyzed using HPTLC, qPCR, western blot, electrophoretic mobility shift assay (EMSA), lipid staining, and immunohistochemistry. Hepatic neutral lipid depots were increased in HBs transgenic mice and remarkably reduced in Abcb4-/- and HBs/Abcb4-/- mice. Similarly, HPTLC-based quantification analyses of total hepatic lipid extracts revealed a significant reduction in the amount of triacylglycerols (TAG), while the amount of free fatty acids (FFA) was increased in Abcb4-/- and HBs/Abcb4-/- in comparison to wild-type and HBs mice. PLIN2, a lipid droplet-associated protein, was less expressed in Abcb4-/- and HBs/Abcb4-/-. The expression of genes-encoding proteins involved in TAG synthesis and de novo lipogenesis (Agpat1, Gpat1, Mgat1, Dgat1, Dgat2, Fasn, Hmgcs1, Acc1, Srebp1-c, and Pparγ) was suppressed, and AMPK and CREB were activated in Abcb4-/- and HBs/Abcb4-/- compared to wild-type and HBs mice. Simulating cholestatic conditions in cell culture resulted in AMPK and CREB activation while FASN and PLIN2 were reduced. A concurrent inhibition of AMPK signaling revealed normal expression level of FASN and PLIN2, suggesting that activation of AMPK-CREB signaling regulates hepatic lipid metabolism, i.e. synthesis and storage, under cholestatic condition. In conclusions, in vivo and mechanistic in vitro data suggest that cholestasis reduces hepatic lipid storage via AMPK and CREB signaling. The results of the current study could be the basis for novel therapeutic strategies as NASH is a crucial factor that can aggravate chronic liver diseases.

The potential role of HLA-G in the pathogenesis of HBV infection: Immunosuppressive or immunoprotective?

The non-classical human leukocyte antigens (HLA)-G could be generally considered as a potent tolerogenic molecule, which modulates immune responses. HLA-G due to the immunosuppressive properties may play an important role in the pathogenesis of infections related to the liver. HLA-G may display two distinct activities in the pathological conditions so that it could be protective in the autoimmune and inflammatory diseases or could be suppressive of the immune system in the infections or cancers. HLA-G might be used as a novel therapeutic target for liver diseases in the future. Indeed, new therapeutic agents targeting HLA-G expression or antibodies which block HLA-G activity are being developed and tested. However, further consideration of the HLA-G function in liver disease is required. This review aims to summarize the role of HLA-G in the liver of patients with HBV infection.

Diagnostic and Prognostic Values of MANF Expression in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors, and its prognosis is still poor. Mesencephalic astrocyte-derived neurotrophic factor (MANF) plays a key role in endoplasmic reticulum stress. ER stress plays a key role in HCC carcinogenesis. To confirm the clinical and prognostic value of MANF in HCC, we investigated the expression level of MANF in HCC as recorded in databases, and the results were verified by experiment. Survival analysis was probed by the Kaplan–Meier method. Cox regression models were used to ascertain the prognostic value of MANF in HCC tissue microarray. The diagnostic value of MANF in HCC was evaluated by receiver operating characteristic curve analysis. Potential correlation between MANF and selected genes was also analyzed. Results showed that MANF was overexpressed in HCC. Patients with high MANF expression levels had a worse prognosis and higher risk of tumor recurrence. Furthermore, the expression level of MANF had good diagnostic power. Correlation analysis revealed potential regulatory networks of MANF in HCC, laying a foundation for further study of the role of MANF in tumorigenesis. In conclusion, MANF was overexpressed in HCC and related to the occurrence and development of HCC. It is a potential diagnostic and prognostic indicator of HCC.

Role of alcohol in pathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) and alcohol abuse often contribute to the development of end-stage liver disease. Alcohol abuse not only causes rapid progression of liver disease in HBV infected patients but also allows HBV to persist chronically. Importantly, the mechanism by which alcohol promotes the progression of HBV-associated liver disease are not completely understood. Potential mechanisms include a suppressed immune response, oxidative stress, endoplasmic reticulum and Golgi apparatus stresses, and increased HBV replication. Certainly, more research is necessary to gain a better understanding of these mechanisms such that treatment(s) to prevent rapid liver disease progression in alcohol-abusing HBV patients could be developed. In this review, we discuss the aforementioned factors for the higher risk of liver diseases in alcohol-induced HBV pathogenies and suggest the areas for future studies in this field.

Cannabinoid receptor 1 knockout alleviates hepatic steatosis by downregulating perilipin 2

The endocannabinoid (EC) system has been implicated in the pathogenesis of several metabolic diseases, including nonalcoholic fatty liver disease (NAFLD). With the current study we aimed to verify the modulatory effect of endocannabinoid receptor 1 (CB1)-signaling on perilipin 2 (PLIN2)-mediated lipophagy. Here, we demonstrate that a global knockout of the cannabinoid receptor 1 gene (CB1^-/-) reduced the expression of the lipid droplet binding protein PLIN2 in the livers of CB1^-/- and hepatitis B surface protein (HBs)-transgenic mice, which spontaneously develop hepatic steatosis. In addition, the pharmacologic activation and antagonization of CB1 in cell culture also caused an induction or reduction of PLIN2, respectively. The decreased PLIN2 expression was associated with suppressed lipogenesis and triglyceride (TG) synthesis and enhanced autophagy as shown by increased colocalization of LC3B with lysosomal-associated membrane protein 1 (LAMP1) in HBs/CB1^-/- mice. The induction of autophagy was further supported by the increased expression of LAMP1 in CB1^-/- and HBs/CB1^-/- mice. LAMP1 and PLIN2 were co-localized in HBs/CB1^-/- indicating autophagy of cytoplasmic lipid droplets (LDs) i.e., lipophagy. Lipolysis of lipid droplets was additionally indicated by elevated expression of lysosomal acid lipase. In conclusion, these results suggest that loss of CB1 signaling leads to reduced PLIN2 abundance, which triggers lipophagy. Our new findings about the association between CB1 signaling and PLIN2 may stimulate translational studies analyzing new diagnostic and therapeutic options for NAFLD.

iTRAQ-based high-throughput proteomics analysis reveals alterations of plasma proteins in patients infected with human bocavirus

Human bocavirus (HBoV) is a member of the genus Bocavirus, family Parvoviridae, and subfamily Parvovirus and was first identified in nasopharyngeal aspirates of Swedish children with acute respiratory tract infection (ARTI) in 2005. It is the causative agent of nasopharyngeal aspirate disease and death in children. The HboV genomic structure is a linear single-stranded DNA (ssDNA). Its clinical pathogenic characteristics have been extensively studied, however, at present the molecular mechanism underlying the pathogenesis of HBoV infection is not completely clear. In this study, a total of 293 differentially expressed proteins (DEPs) between ARTI cases and healthy plasma samples were characterized using isobaric tags for relative and absolute quantitation (iTRAQ)-coupled bioinformatics analysis, among which 148 were up-regulated and 135 were down-regulated. Gene Ontology (GO) and Cluster of Orthologous Groups of proteins (COG) annotated an enrichment of DEPs in complement activation and biological processes like immunity, inflammation, signal transduction, substance synthesis, and metabolism. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis enriched DEPs mainly in the Wnt signaling pathway (ko04310), PPAR signaling pathway (ko03320), intestinal immune network for IgA production (ko04672), complement and coagulation cascades (ko04610), Toll-like receptor signaling pathway (ko04620) and B cell receptor signaling pathway (ko04662). Further, expression levels of three candidate proteins (upregulated PPP2R1A and CUL1, and downregulated CETP) were validated using western blotting. Our investigation is the first analysis of the proteomic profile of HBoV-infected ARTI cases using the iTRAQ approach, providing a foundation for a better molecular understanding of the pathogenesis of ARTI in children.

Hepatocellular carcinoma: Therapeutic advances in signaling, epigenetic and immune targets

Hepatocellular carcinoma (HCC) remains a global medical burden with rising incidence due to chronic viral hepatitis and non-alcoholic fatty liver diseases. Treatment of advanced disease stages is still unsatisfying. Besides first and second generation tyrosine kinase inhibitors, immune checkpoint inhibitors have become central for the treatment of HCC. New modalities like epigenetic therapy using histone deacetylase inhibitors (HDACi) and cell therapy approaches with chimeric antigen receptor T cells (CAR-T cells) are currently under investigation in clinical trials. Development of such novel drugs is closely linked to the availability and improvement of novel preclinical and animal models and the identification of predictive biomarkers. The current status of treatment options for advanced HCC, emerging novel therapeutic approaches and different preclinical models for HCC drug discovery and development are reviewed here.

Naturally Occurring Hepatitis B Virus Mutations Leading to Endoplasmic Reticulum Stress and Their Contribution to the Progression of Hepatocellular Carcinoma

Hepatitis B virus (HBV) infection is a global health problem that causes a wide range of pathological outcomes, including cirrhosis and hepatocellular carcinoma (HCC). Endoplasmic reticulum (ER) stress induction by HBV infection has been implicated in liver carcinogenesis and disease progression with chronic inflammation via enhanced inflammation, oxidative stress-mediated DNA damage, and hepatocyte proliferation. In the natural course of HBV infection, the accumulation of naturally occurring mutations in the HBV genome can generate several mutant types of HBV-encoded proteins, including three different proteins in the S ORF (SHBs, MHBs, and LHBs) and HBcAg in the C ORF, which could contribute to enhanced ER stress in infected hepatocytes mainly via increased ER accumulation of mutant proteins. However, it seems that there may be distinct capacity and pathway in ER stress-induction and distinct resulting clinical outcomes between HBV variants. In addition, the role of HBxAg mutations in ER stress remains unknown. However, it has been reported that HBxAg itself could exert ER stress in infected cells, resulting in HCC generation in chronic HBV patients. To date, review papers regarding ER stress-mediated HBV mutation have been limited into a specific mutation type: preS2 deletion. So, in this review, we will discuss details about various mutation types in all four regions of the HBV genome (preS1, preS2, S, and C) related to ER stress and their distinct ER stress mechanisms and clinical outcomes in terms of mutation types.

XBP1 activation enhances MANF expression via binding to endoplasmic reticulum stress response elements within MANF promoter region in hepatitis B

As an endoplasmic reticulum (ER) stress-related protein, mesencephalic astrocyte-derived neurotrophic factor (MANF) is involved in inflammatory diseases, such as rheumatoid arthritis. However, the mechanisms of the transcriptional regulation of MANF is still undefined. Here, we showed that MANF expression was upregulated in hepatitis B tissues and hepatoma cells, and positively correlated with the spliced X-box binding protein-1 (XBP1s). Both overexpression of XBP1s and tunicamycin treatment were able to enhance MANF transcription. On the contrary, inhibition of XBP1 splicing by IRE1α endonuclease inhibitor or knockdown of XBP1s with siRNA attenuated MANF expression. Two ER stress-responsive elements (ERSE) were found in the promoter region of MANF (ERSE I and ERSE II). The chromatin immunoprecipitation and reporter gene assay showed that XBP1s mainly binds to ERSE I to promote MANF transcription. Moreover, MANF was found to interact with XBP1s to enhance its own expression. Our findings uncover a new mechanism of ERSE-dependent transcriptional regulation of MANF, as well as a key role of XBP1s in promoting the MANF expression.

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

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

Targeting autophagy in liver cancer

Autophagy is a catabolic cellular process conserved in animals. It is characterized by the main role of recycling all the non-functional products of the cells. Once, autophagy players detect non-functioning sub-cellular organelles and proteins, they start the so-called nucleation process. The organelles will be surrounded by a double membrane vesicle mainly constituted by endoplasmic reticulum (ER) membrane and autophagy proteins, e.g., MAP1LC3B, Beclin-1, VPS34, Unc-51 like autophagy activating kinase (ULK1) and ubiquitination-related proteins. Then the autophagic membrane will go through an elongation phase involving additional autophagy players. Once the autophagic vesicle is complete, the sub-cellular organelles will be isolated from the rest of the cytosol and driven to the final fusion with lysosomes. Here, the digestion process will end. Alteration and or impairment of autophagy have been shown to be correlated with development of diseases affecting the central nervous system, e.g., Alzheimer and other neurodegenerative diseases. Nonetheless, autophagy defect is responsible for tumorigenesis in blood and solid malignancies, in particular liver cancer. Malignancies of the liver are determined by several genetics and epigenetics mechanisms triggering the up-regulation of survival mechanisms and resistance to cell death. Furthermore, liver cancer could result from pathologic conditions like cirrhosis and fibrosis related to virus infection, aflatoxin, alcohol consumption and high fat diet together with insulin resistance. The role exerted by autophagy in the pathogenesis of the liver and tumor development has been evidenced in recent years. The alteration of autophagy assumes a fundamental role for liver tumorigenesis determining an accumulation of non-functional proteins and organelles that trigger oxidative stress leading to genotoxic stress and gene alterations. Furthermore, the absence of this degradation mechanism could prompt the cells to alter their metabolic status and turn into malignant cells. Interestingly, the heterozygous loss of function of Beclin-1 is able to trigger liver tumorigenesis or even the simple accumulation of proteins caused by the block of the final autolysosome fusion and degradation process is responsible for liver cancer development. This review highlights the importance of targeting the autophagy process in liver cancer in order to restore its function and to promote autophagy-mediated cell demise.

Recent advances in exosome-based nanovehicles as RNA interference therapeutic carriers

RNA interference (RNAi) therapeutics (siRNA, miRNA, etc.) represent an emerging medicinal remedy for a variety of ailments. However, their low serum stability and low cellular uptake significantly restrict their clinical applications. Exosomes are biologically derived nanodimensional vesicle ranging from a few nanometers to a hundred. In the last few years, several reports have been published demonstrating the emerging applications of these exogenous membrane vesicles, particularly in carrying different RNAi therapeutics to adjacent or distant targeted cells. In this report, we explored the numerous aspects of exosomes from structure to clinical implications with special emphasis on their application in delivering RNAi-based therapeutics. siRNA and miRNA have attracted great interest in recent years due to their specific application in treating many complex diseases including cancer. We highlight strategies to obviate the challenges of their low bioavailability for gene therapy.

iTRAQ-based Proteomic Analysis of Porcine Kidney Epithelial PK15 cells Infected with Pseudorabies virus

Pseudorabies virus (PRV) is one of the most important pathogens of swine, resulting in severe economic losses to the pig industry. To improve our understanding of the host responses to PRV infection, we applied isobaric tags for relative and absolute quantification (iTRAQ) labeling coupled with liquid chromatography-tandem mass spectrometry to quantitatively identify the differentially expressed cellular proteins in PRV-infected PK15 cells. In total, relative quantitative data were identified for 4333 proteins in PRV and mock- infected PK15 cells, among which 466 cellular proteins were differentially expressed, including 234 upregulated proteins and 232 downregulated proteins. Bioinformatics analysis disclosed that most of these differentially expressed proteins were involved in metabolic processes, cellular growth and proliferation, endoplasmic reticulum (ER) stress response, cell adhesion and cytoskeleton. Moreover, expression levels of four representative proteins, beta-catenin, STAT1, GRB2 and PCNA, were further confirmed by western blot analysis. This is the first attempt to analyze the protein profile of PRV-infected PK15 cells using iTRAQ technology, and our findings may provide valuable information to help understand the host response to PRV infection.

Hepatitis B virus surface proteins accelerate cholestatic injury and tumor progression in Abcb4-knockout mice

Understanding of the pathophysiology of cholestasis associated carcinogenesis could challenge the development of new personalized therapeutic approaches and thus improve prognosis. Simultaneous damage might aggravate hepatic injury, induce chronic liver disease and even promote carcinogenesis. We aimed to study the effect of Hepatitis B virus surface protein (HBsAg) on cholestatic liver disease and associated carcinogenesis in a mouse model combining both impairments. Hybrids of Abcb4^−/− and HBsAg transgenic mice were bred on fibrosis susceptible background BALB/c. Liver injury, serum bile acid concentration, hepatic fibrosis, and carcinogenesis were enhanced by the combination of simultaneous damage in line with activation of c-Jun N-terminal kinase (JNK), proto-oncogene c-Jun, and Signal transducer and activator of transcription 3 (STAT3). Activation of Protein Kinase RNA-like Endoplasmic Reticulum Kinase (PERK) and Eukaryotic translation initiation factor 2A (eIF2α) indicated unfolded protein response (UPR) in HBsAg-expressing mice and even in Abcb4^−/− without HBsAg-expression. CONCLUSION: Cholestasis-induced STAT3- and JNK-pathways may predispose HBsAg-associated tumorigenesis. Since STAT3- and JNK-activation are well characterized critical regulators for tumor promotion, the potentiation of their activation in hybrids suggests an additive mechanism enhancing tumor incidence.