Hepatitis B virus X protein-elevated MSL2 modulates hepatitis B virus covalently closed circular DNA by inducing degradation of APOBEC3B to enhance hepatocarcinogenesis

Ubiquitin: A double-edged sword in hepatitis B virus-induced hepatocellular carcinoma

Hepatitis B virus is one of the leading causes behind the neoplastic transformation of liver tissue and associated mortality. Despite the availability of many therapies and vaccines, the pathogenic landscape of the virus remains elusive; urging the development of novel strategies based on the fundamental infectious and transformative modalities of the virus-host interactome. Ubiquitination is a widely observed post-translational modification of several proteins, which either regulates the proteins' turnover or impacts their functionalities. In recent years, ample amount of literature has accumulated regarding the ubiquitination dynamics of the HBV proteins as well as the host proteins during HBV infection and carcinogenesis; with direct and detailed characterization of the involvement of HBV in these processes. Interestingly, while many of these ubiquitination events restrict HBV life cycle and carcinogenesis, several others promote the emergence of hepatocarcinoma by putting the virus in an advantageous position. This review sums up the snowballing literature on ubiquitination-mediated regulation of the host-HBV crosstalk, with special emphasis on its influence on the establishment and progression of hepatocellular carcinoma on a molecular level. With the advent of cutting-edge ubiquitination-targeted therapeutic approaches, the findings emanating from this review may potentiate the identification of novel anti-HBV targets for the formulation of novel anticancer strategies to control the HBV-induced hepato-carcinogenic process on a global scale.

Hepatitis B: Model Systems and Therapeutic Approaches

Hepatitis B virus (HBV) infection is a major global health issue and ranks among the top causes of liver cirrhosis and hepatocellular carcinoma. Although current antiviral medications, including nucleot(s)ide analogs and interferons, could inhibit the replication of HBV and alleviate the disease, HBV cannot be fully eradicated. The development of cellular and animal models for HBV infection plays an important role in exploring effective anti-HBV medicine. During the past decades, advancements in several cell culture systems, such as HepG2.2.15, HepAD38, HepaRG, hepatocyte-like cells, and primary human hepatocytes, have propelled the research in inhibiting HBV replication and expression and thus enriched our comprehension of the viral life cycle and enhancing antiviral drug evaluation efficacy. Mouse models, in particular, have emerged as the most extensively studied HBV animal models. Additionally, the present landscape of HBV therapeutics research now encompasses a comprehensive assessment of the virus's life cycle, targeting numerous facets and employing a variety of immunomodulatory approaches, including entry inhibitors, strategies aimed at cccDNA, RNA interference technologies, toll-like receptor agonists, and, notably, traditional Chinese medicine (TCM). This review describes the attributes and limitations of existing HBV model systems and surveys novel advancements in HBV treatment modalities, which will offer deeper insights toward discovering potentially efficacious pharmaceutical interventions.

Novel Approaches to Inhibition of HBsAg Expression from cccDNA and Chromosomal Integrants: A Review

Hepatitis B virus (HBV) is a widely prevalent liver infection that can cause acute or chronic hepatitis. Although current treatment modalities are highly effective in the suppression of viral levels, they cannot eliminate the virus or achieve definitive cure. This is a consequence of the complex nature of HBV-host interactions. Major challenges to achieving sustained viral suppression include the presence of a high viral burden from the HBV DNA and hepatitis B surface antigen (HBsAg), the presence of reservoirs for HBV replication and antigen production, and the HBV-impaired innate and adaptive immune response of the host. Those therapeutic methods include cell entry inhibitors, HBsAg inhibitors, gene editing approaches, immune-targeting therapies and direct inhibitors of covalently closed circular DNA (cccDNA). Novel approaches that target these key mechanisms are now being studied in preclinical and clinical phases. In this review article, we provide a comprehensive review on mechanisms by which HBV escapes elimination from current treatments, and highlight new agents to achieve a definitive HBV cure.

Role of hepatitis B virus non-structural protein HBx on HBV replication, interferon signaling, and hepatocarcinogenesis

Hepatitis B, a global health concern caused by the hepatitis B virus (HBV), infects nearly 2 billion individuals worldwide, as reported by the World Health Organization (WHO). HBV, a hepatotropic DNA virus, predominantly targets and replicates within hepatocytes. Those carrying the virus are at increased risk of liver cirrhosis and hepatocellular carcinoma, resulting in nearly 900,000 fatalities annually. The HBV X protein (HBx), encoded by the virus's open reading frame x, plays a key role in its virulence. This protein is integral to viral replication, immune modulation, and liver cancer progression. Despite its significance, the precise molecular mechanisms underlying HBx remain elusive. This review investigates the HBx protein's roles in HBV replication, interferon signaling regulation, and hepatocellular carcinoma progression. By understanding the complex interactions between the virus and its host mediated by HBx, we aim to establish a solid foundation for future research and the development of HBx-targeted therapeutics.

Cabozantinib inhibits HBV-RNA transcription by decreasing STAT3 binding to the enhancer region of cccDNA

BACKGROUND

Precision medicine and customized therapeutics based on the features of each patient are important for maximizing therapeutic effects. Because most cases of HCC occur in the damaged liver through various etiologies, such as hepatitis virus infection, steatohepatitis, and autoimmune hepatitis, there should be a rationale for the choice of therapeutic options based on these etiologies. Although cabozantinib, an oral multikinase inhibitor, has demonstrated clinical effectiveness in advanced HCC, subgroup analyses showed a lower HR for death in HBV-related HCC. This study aimed to determine the therapeutic effects of cabozantinib in HBV-related HCC.

METHODS

Using HBV infection models and gene knockout cells, we determined the crucial signaling axis responsible for the effects of cabozantinib on HBV. A chromatin immunoprecipitation assay was performed to determine the interaction between the signaling molecules and HBV DNA. Agonists and inhibitors were used for confirmation.

RESULTS

Cabozantinib inhibited HBV replication through the HGF-mesenchymal-epithelial transition factor-signal transducer and activator of transcription 3 (MET-STAT3) signaling axis. The importance of STAT3 in viral replication has been confirmed using gene-edited STAT3 knockout cells. The chromatin immunoprecipitation assay revealed that the binding levels of phosphorylated STAT3 to enhancer region 1 of HBV covalently closed circular DNA were significantly increased by HGF stimulation.

CONCLUSIONS

Cabozantinib has favorable therapeutic effects on HBV-related HCC because it inhibits HCC not only directly but also indirectly by means of inhibitory effects on HBV.

HBx-Induced HSPA8 Stimulates HBV Replication and Suppresses Ferroptosis to Support Liver Cancer Progression

Hepatitis B virus (HBV) infection is a major driver of hepatocarcinogenesis. Ferroptosis is a type of iron-mediated cell death that can suppress liver transformation. Previous studies have linked HBV to ferroptosis in liver fibrosis and acute liver failure. However, whether ferroptosis is involved in HBV-mediated liver cancer is poorly understood. Here, we identified heat shock protein family A member 8 (HSPA8) as a crucial host factor that modulates HBV replication and ferroptosis in liver cancer. Hepatitis B X protein (HBx) upregulated HSPA8 by coactivating the transcription factor heat shock factor 1 (HSF1) in cells. HSPA8 enhanced HBV replication by recruiting hepatitis B core protein (HBc) to the HBV covalently closed circular DNA (cccDNA) minichromosome, forming a positive feedback loop. Moreover, HSPA8 suppressed ferroptosis in liver cancer cells by upregulating the expression of SLC7A11/GPX4 and decreasing erastin-mediated reactive oxygen species and Fe2+ accumulation in cells in vitro and in vivo. Inhibition of HSPA8 reduced the growth of HBV-positive liver tumors and increased sensitivity to erastin. In conclusion, HBx-elevated HSPA8 regulates both HBV replication and ferroptosis in liver cancer. Targeting HSPA8 could be a promising strategy for controlling HBV and hepatocarcinogenesis.

SIGNIFICANCE

HBV-induced upregulation of HSPA8 promotes hepatocarcinogenesis by suppressing ferroptosis and stimulating HBV replication, identifying HSPA8 as a potential therapeutic target in liver cancer.

Phosphorylation of UHRF2 affects malignant phenotypes of HCC and HBV replication by blocking DHX9 ubiquitylation

Hepatitis B virus (HBV) infection is one of main contributors to poor prognosis and rapid progression of hepatocellular cancer (HCC). We previously identified the important role of the phosphorylation of ubiquitin-like with PHD and ring finger domains (UHRF2) in HBV-associated HCC. In this study we identify upregulated UHRF2 protein levels in HBV-associated HCC cells and tissues. UHRF2 overexpression promotes the viability, proliferation, migration and invasiveness of HBV-positive HCC cell lines, and enhances HBV DNA replication. To obtain a comprehensive understanding of the interaction networks of UHRF2 and their underlying mechanism, this study suggests that UHRF2 facilitates the ubiquitin-proteasome-mediated proteolysis of DExD/H (Asp-Glu-Ala-His) -box helicase enzyme 9 (DHX9). However, phosphorylation of UHRF2 by HBx at S643 inhibits E3 ubiquitin ligase activity of UHRF2 and improves DHX9 protein stability. Furthermore, results suggest that HBx promotes phosphorylation of UHRF2 by the ETS1-CDK2 axis through the downregulation of miR-222-3p in HBV-associated HCC specimens and cells. Our findings suggest that HBx-induced phosphorylation of UHRF2 S643 acts as a "switch" in HBV-associated HCC oncogenesis, activating the positive feedback between phosphorylated UHRF2 and HBV, provide evidence that UHRF2 is a new regulator and a potential prognostic indicator of poor prognosis for HBV-associated HCC.

The pathogenesis of liver cancer and the therapeutic potential of bioactive substances

Liver cancer is the third most common cause of cancer-related deaths in the world and has become an urgent problem for global public health. Bioactive substances are widely used for the treatment of liver cancer due to their widespread availability and reduced side effects. This review summarizes the main pathogenic factors involved in the development of liver cancer, including metabolic fatty liver disease, viral infection, and alcoholic cirrhosis, and focuses on the mechanism of action of bioactive components such as polysaccharides, alkaloids, phenols, peptides, and active bacteria/fungi. In addition, we also summarize transformation methods, combined therapy and modification of bioactive substances to improve the treatment efficiency against liver cancer, highlighting new ideas in this field.

HBx Mediated Increase of DDX17 Contributes to HBV-Related Hepatocellular Carcinoma Tumorigenesis

HBV is strongly associated with HCC development and DEAD-box RNA helicase 17 (DDX17) is a very important member of the DEAD box family that plays key roles in HCC development by promoting cancer metastasis. However, the important role of DDX17 in the pathogenesis of HBV-related HCC remains unclear. In this study, we investigated the role of DDX17 in the replication of HBV and the development of HBV-associated HCC. Based on data from the GEO database and HBV-infected cells, we found that DDX17 was upregulated by the HBV viral protein X (HBx). Mechanistically, increased DDX17 expression promoted HBV replication and transcription by upregulating ZWINT. Further study showed that DDX17 could promote HBx-mediated HCC metastasis. Finally, the promotive effect of DDX17 on HBV and HBV-related HCC was confirmed in vivo. In summary, the results revealed the novel role of DDX17 in the replication of HBV and the metastasis of HBV-associated HCC.

LncRNAs driving feedback loops to boost drug resistance: sinuous pathways in cancer

Feedback loops mediate signaling pathways to maintain cellular homeostasis. There are two types, positive and negative feedback loops. Both are subject to alterations, and consequently can become pathogenic in the development of diseases such as cancer. Long noncoding RNAs (lncRNAs) are regulators of signaling pathways through feedback loops hidden as the dark regulatory elements yet to be described with great impact on cancer tumorigenesis, development, and drug resistance. Several feedback loops have been studied in cancer, however, how they are regulated by lncRNAs is hardly evident, setting a trending topic in oncological research. In this review, we recapitulate and discuss the feedback loops that are regulated by lncRNAs to promote drug resistance. Furthermore, we propose additional strategies that allow us to identify, analyze and comprehend feedback loops regulated by lncRNAs to induce drug resistance or even to gain insight into novel feedback loops that are stimulated under the pressure of treatment and consequently increase its efficacy. This knowledge will be useful to optimize the therapeutic use of oncological drugs.

IFN-α inhibits HBV transcription and replication by promoting HDAC3-mediated de-2-hydroxyisobutyrylation of histone H4K8 on HBV cccDNA minichromosome in liver

The epigenetic modification of hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) plays a crucial role in cccDNA transcription and viral persistence. Interferon-α (IFN-α) is a pivotal agent against HBV cccDNA. However, the mechanism by which IFN-α modulates the epigenetic regulation of cccDNA remains poorly understood. In this study, we report that IFN-α2b enhances the histone deacetylase 3 (HDAC3)-mediated de-2-hydroxyisobutyrylation of histone H4 lysine 8 (H4K8) on HBV cccDNA minichromosome to restrict the cccDNA transcription in liver. By screening acetyltransferases and deacetylases, we identified that HDAC3 was an effective restrictor of HBV transcription and replication. Moreover, we found that HDAC3 was able to mediate the de-2-hydroxyisobutyrylation of H4K8 in HBV-expressing hepatoma cells. Then, the 2-hydroxyisobutyrylation of histone H4K8 (H4K8hib) was identified on the HBV cccDNA minichromosome, promoting the HBV transcription and replication. The H4K8hib was regulated by HDAC3 depending on its deacetylase domain in the system. The low level of HDAC3 and high level of H4K8hib were observed in the liver tissues from HBV-infected human liver-chimeric mice. The levels of H4K8hib on HBV cccDNA minichromosome were significantly elevated in the liver biopsy specimens from clinical hepatitis B patients, which was consistent with the high transcriptional activity of cccDNA. Strikingly, IFN-α2b effectively facilitated the histone H4K8 de-2-hydroxyisobutyrylation mediated by HDAC3 on the HBV cccDNA minichromosome in primary human hepatocytes and hepatoma cells, leading to the inhibition of HBV transcription and replication. Our finding provides new insights into the mechanism by which IFN-α modulates the epigenetic regulation of HBV cccDNA minichromosome.

Role of hepatitis B virus in development of hepatocellular carcinoma: Focus on covalently closed circular DNA

Chronic infection with hepatitis B virus (HBV) remains a major global health problem, especially in developing countries. It may lead to prolonged liver damage, fibrosis, cirrhosis, and hepatocellular carcinoma. Persistent chronic HBV infection is related to host immune response and the stability of the covalently closed circular DNA (cccDNA) in human hepatocytes. In addition to being essential for viral transcription and replication, cccDNA is also suspected to play a role in persistent HBV infections or hepatitis relapses since cccDNA is very stable in non-dividing human hepatocytes. Understanding the pathogenicity and oncogenicity of HBV components would be essential in the development of new diagnostic tools and treatment strategies. This review summarizes the role and molecular mechanisms of HBV cccDNA in hepatocyte transformation and hepatocarcinogenesis and current efforts to its detection and targeting.

LINC01431 Promotes Histone H4R3 Methylation to Impede HBV Covalently Closed Circular DNA Transcription by Stabilizing PRMT1

Covalently closed circular DNA (cccDNA) is the transcriptional template of hepatitis B virus (HBV), which interacts with both host and viral proteins to form minichromosome in the nucleus and is resistant to antiviral agents. Identification of host factors involved in cccDNA transcriptional regulation is expected to prove a new venue for HBV therapy. Recent evidence suggests the involvement of long noncoding RNAs (lncRNAs) in mediating the interaction of host factors with various viruses, however, lncRNAs that HBV targets and represses cccDNA transcription have not been fully elucidated. Here, the authors identified LINC01431 as a novel host restriction factor for HBV transcription. Mechanically, LINC01431 competitively bound with type I protein arginine methyltransferase (PRMT1) to block the HBx-mediated PRMT1 ubiquitination and degradation. Consequently, LINC01431 increased the occupancy of PRMT1 on cccDNA, leading to enhanced H4R3me2a modification and reduced acetylation of cccDNA-bound histones, thereby repressing cccDNA transcription. In turn, to facilitate viral replication, HBV transcriptionally repressed LINC01431 expression by HBx-mediated repression of transcription factor Zinc fingers and homeoboxes 2 (ZHX2). Collectively, the study demonstrates LINC01431 as a novel epigenetic regulator of cccDNA minichromosome and highlights a feedback loop of HBx-LINC01431-PRMT1 in HBV replication, which provides potential therapeutic targets for HBV treatment.

In Hepatocellular Carcinoma, miRNA-296-3p Targets MSL2 and Suppresses Cell Proliferation and Invasion

Hepatocellular carcinoma (HCC) is the third-highest cause of cancer-related death in the world. miRNAs have a role in cell division, differentiation, and death biological processes. They are typically dysregulated in cancers, affecting tumor progression. miRNA-296-3p appears to play a crucial role in cancer control, according to new research. However, its expression and roles in HCC are unknown. This study used qRT-PCR and western blotting to detect the miRNA-296-3p and male-specific lethal 2 (MSL2) expression. In addition, cell proliferation, migration, invasion, and apoptosis were studied using CCK-8, flow cytometric analysis, colony formation assay, wound healing test, and transwell assays. The results show that miRNA-296-3p is underexpressed in HCC cell lines, particularly in Huh-7 and HepG2 cells. miRNA-296-3p overexpression lowers the ability of HCC cells to proliferate, migrate, and invade while increasing cell death. Luciferase reporter experiments revealed that the MSL2 is a direct target of miRNA-296-3p. Furthermore, overexpression of miRNA-296-3p reduced MSL2 mRNA and protein levels considerably, according to our findings. Furthermore, the rescue experiments showed that the MSL2 overexpression partially blocked the inhibition effects of miRNA-296-3p mimic on the proliferation and migration of HCC cells. The above results show that miRNA-296-3p may have a repressive effect in HCC by targeting MSL2 and could be used as a therapeutic target for HCC treatment.

The Functions of Hepatitis B Virus Encoding Proteins: Viral Persistence and Liver Pathogenesis

About 250 million people worldwide are chronically infected with Hepatitis B virus (HBV), contributing to a large burden on public health. Despite the existence of vaccines and antiviral drugs to prevent infection and suppress viral replication respectively, chronic hepatitis B (CHB) cure remains a remote treatment goal. The viral persistence caused by HBV is account for the chronic infection which increases the risk for developing liver cirrhosis and hepatocellular carcinoma (HCC). HBV virion utilizes various strategies to escape surveillance of host immune system therefore enhancing its replication, while the precise mechanisms involved remain elusive. Accumulating evidence suggests that the proteins encoded by HBV (hepatitis B surface antigen, hepatitis B core antigen, hepatitis B envelope antigen, HBx and polymerase) play an important role in viral persistence and liver pathogenesis. This review summarizes the major findings in functions of HBV encoding proteins, illustrating how these proteins affect hepatocytes and the immune system, which may open new venues for CHB therapies.

HBx-upregulated MAFG-AS1 promotes cell proliferation and migration of hepatoma cells by enhancing MAFG expression and stabilizing nonmuscle myosin IIA

To identify hepatitis B virus (HBV)-related lncRNA(s), we previously examined the transcription profiles of the HBV-transgenic cell line HepG2-4D14 and parental HepG2 cells by RNA deep sequencing and identified 38 upregulated long noncoding RNAs (lncRNAs). In the present study, the lncRNA MAFG-AS1 is investigated in detail because its gene is located adjacent to the MAFG gene, which is an important transcription factor involved in cell proliferation. The level of MAFG-AS1 is significantly higher in HCC tissue than in nontumor tissues. TCGA data show that the expression level of MAFG-AS1 is negatively correlated with survival of HCC patients. GEO cohort data show that compared with healthy tissues, the expression level of MAFG-AS1 is significantly higher in HBV-infected liver tissues. Real-time PCR and luciferase reporter assay data show that HBx can enhance the transcription of MAFG-AS1. Gain-of-function and loss-of-function experiments indicate that MAFG-AS1 promotes proliferation, migration, and invasion of HCC cells. Tumor formation assay results demonstrate that knockdown of MAFG-AS1 significantly inhibits cell proliferation in nude mice. Furthermore, MAFG-AS1 enhances the transcription of adjacent MAFG via E2F1. Additionally, MAFG-AS1 interacts with three subunits (MYH9, MYL12B, and MYL6) of nonmuscle myosin IIA (NM IIA). Knockdown of MAFG-AS1 inhibits ATPase activity of MYH9, interaction of NM IIA subunits, and cell cycle progression. Thus, the lncRNA MAFG-AS1 is upregulated by HBV and promotes proliferation and migration of HCC cells. Our findings suggest that MAFG-AS1 is a potential oncogene that may contribute to HBV-related HCC development.

Molecular pathways in viral hepatitis-associated liver carcinogenesis: An update

Hepatocellular carcinoma (HCC) is the most common type of cancer among primary malignant tumors of the liver and is a consequential cause of cancer-related deaths worldwide. In recent years, uncovering the molecular mechanisms involved in the development and behavior of this tumor has led to the identification of multiple potential treatment targets. Despite the vast amount of data on this topic, HCC remains a challenging tumor to treat due to its aggressive behavior and complex molecular profile. Therefore, the number of studies aiming to elucidate the mechanisms involved in both carcinogenesis and tumor progression in HCC continues to increase. In this context, the close association of HCC with viral hepatitis has led to numerous studies focusing on the direct or indirect involvement of viruses in the mechanisms contributing to tumor development and behavior. In line with these efforts, this review was undertaken to highlight the current understanding of the molecular mechanisms by which hepatitis B virus (HBV) and hepatitis C virus (HCV) participate in oncogenesis and tumor progression in HCC and summarize new findings. Cumulative evidence indicates that HBV DNA integration promotes genomic instability, resulting in the overexpression of genes related to cancer development, metastasis, and angiogenesis or inactivation of tumor suppressor genes. In addition, genetic variations in HBV itself, especially preS2 deletions, may play a role in malignant transformation. Epigenetic dysregulation caused by both viruses might also contribute to tumor formation and metastasis by modifying the methylation of DNA and histones or altering the expression of microRNAs. Similarly, viral proteins of both HBV and HCV can affect pathways that are important anticancer targets. The effects of these two viruses on the Hippo-Yap-Taz pathway in HCC development and behavior need to be investigated. Additional, comprehensive studies are also needed to determine these viruses' interaction with integrins, farnesoid X, and the apelin system in malignant transformation and tumor progression. Although the relationship of persistent inflammation caused by HBV and HCV hepatitis with carcinogenesis is well defined, further studies are warranted to decipher the relationship among inflammasomes and viruses in carcinogenesis and elucidate the role of virus-microbiota interactions in HCC development and progression.

Aspirin modulates 2-hydroxyisobutyrylation of ENO1K281 to attenuate the glycolysis and proliferation of hepatoma cells

Aspirin can efficiently inhibit the glycolysis and proliferation of cancer cells, however, the underlying mechanism is poorly understood. Here, we report that aspirin attenuates the glycolysis and proliferation of hepatoma cells through modulating the levels of lysine 2-hydroxyisobutyrylation (Khib) of enolase 1 (ENO1). We found that aspirin decreased the levels of glucose consumption and lactate production in hepatoma cells. Moreover, 4 mM aspirin reduced the activities of ENO1, a key enzyme of glycolysis, and decreased the levels of ENO1 Khib in the cells. Interestingly, we identified that 4 mM aspirin could decrease the levels of Khib on many proteins by using pan Khib antibody in the cells. Interestingly, the activities of ENO1 could be rescued by the transient overexpression of ENO1, but not by ENO1 mutant (K281R). Moreover, we identified that the C646, an inhibitor of p300 which is a writer of Khib, could reduce the levels of ENO1 Khib, resulting in the decrease of ENO1 activities. The treatment with PDTC, an inhibitor of NF-κB which is a target of aspirin, could work well as C646 in the cells. Both of aspirin and C646 (or PDTC) displayed a stronger effect than the single treatment in the system. Functionally, ENO1, but not ENO1 mutant (K281R), could rescue the aspirin-induced inhibition of proliferation of liver cancer cells in vitro, suggesting that ENO1K281 is involved in the aspirin-mediated inhibition of liver cancer. Our finding provides new insights into the mechanism by which aspirin attenuates the glycolysis and proliferation of hepatoma cells.

Histone acetyltransferase 1 is a succinyltransferase for histones and non-histones and promotes tumorigenesis

Lysine succinylation (Ksucc) is an evolutionarily conserved and widespread post-translational modification. Histone acetyltransferase 1 (HAT1) is a type B histone acetyltransferase, regulating the acetylation of both histone and non-histone proteins. However, the role of HAT1 in succinylation modulation remains unclear. Here, we employ a quantitative proteomics approach to study succinylation in HepG2 cancer cells and find that HAT1 modulates lysine succinylation on various proteins including histones and non-histones. HAT1 succinylates histone H3 on K122, contributing to epigenetic regulation and gene expression in cancer cells. Moreover, HAT1 catalyzes the succinylation of PGAM1 on K99, resulting in its increased enzymatic activity and the stimulation of glycolytic flux in cancer cells. Clinically, HAT1 is significantly elevated in liver cancer, pancreatic cancer, and cholangiocarcinoma tissues. Functionally, HAT1 succinyltransferase activity and the succinylation of PGAM1 by HAT1 play critical roles in promoting tumor progression in vitro and in vivo. Thus, we conclude that HAT1 is a succinyltransferase for histones and non-histones in tumorigenesis.

Anti-oncogene PTPN13 inactivation by hepatitis B virus X protein counteracts IGF2BP1 to promote hepatocellular carcinoma progression

Hepatitis B x protein (HBx) affects cellular protein expression and participates in the tumorigenesis and progression of hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). Metabolic reprogramming contributed to the HCC development, but its role in HBV-related HCC remains largely unclear. Tyrosine-protein phosphatase nonreceptor type 13 (PTPN13) is a significant regulator in tumor development, however, its specific role in hepatocarcinogenesis remains to be explored. Here, we found that decreased PTPN13 expression was associated with HBV/HBx. Patients with low PTPN13 expression showed a poor prognosis. Functional assays revealed that PTPN13 inhibited proliferation and tumorigenesis in vitro and in vivo. Further mechanistic studies indicated that HBx inhibited PTPN13 expression by upregulating the expression of DNMT3A and interacting with DNMT3A. Furthermore, we found that DNMT3A bound to the PTPN13 promoter (-343 to -313 bp) in an epigenetically controlled manner associated with elevated DNA methylation and then inhibited PTPN13 transcription. In addition, we identified IGF2BP1 as a novel PTPN13-interacting gene and demonstrated that PTPN13 influences c-Myc expression by directly and competitively binding to IGF2BP1 to decrease the intracellular concentration of functional IGF2BP1. Overexpressing PTPN13 promoted c-Myc mRNA degradation independent of the protein tyrosine phosphatase (PTP) activity of PTPN13. Importantly, we discovered that the PTPN13-IGF2BP1-c-Myc axis was important for cancer cell growth through promoting metabolic reprogramming. We verified the significant negative correlations between PTPN13 expression and c-Myc, PSPH, and SLC7A1 expression in clinical HCC tissue samples. In summary, our findings demonstrate that PTPN13 is a novel regulator of HBV-related hepatocarcinogenesis and may play an important role in HCC. PTPN13 may serve as a prognostic marker and therapeutic target in HBV-related HCC patients.

Long noncoding RNA RP11-757G1.5 sponges miR-139-5p and upregulates YAP1 thereby promoting the proliferation and liver, spleen metastasis of colorectal cancer

BACKGROUND

Accumulating evidence indicates that long non-coding RNAs (lncRNAs) acting as crucial regulators in tumorigenesis. However, its biological functions of lncRNAs in colorectal cancer (CRC) have not been systematically clarified.

METHODS

An unbiased screening was performed to identify disregulated lncRNAs revealed to be implicated in CRC carcinogenesis according to an online-available data dataset. In situ hybridization (ISH), RT-qPCR and RNA fluorescence in situ hybridization (RNA-FISH) were applied to detect RP11-757G1.5 expression in CRC tissues and cell lines. The associations of RP11-757G1.5 with clinicopathological characteristics were analyzed. Their effects on prognosis were analyzed by the Kaplan-Meier analysis, Log-rank test, Univariate and Multivariate Cox regression analysis. The potential biological function of RP11-757G1.5 in CRC was investigated by Colony formation, Edu cell proliferation, Flow cytometry, Wound healing and Transwell assays. Bioinformatics binding site analysis, Luciferase reporter assay, Ago2 immunoprecipitation assays, RNA pull-down assay, RT-qPCR and Western blotting were utilized to demonstrate the mechanism of RP11-757G1.5 acts as a molecular sponge of miR-139-5p to regulate the expression of YAP1. Finally, we further explore the potential role of RP11-757G1.5 in CRC orthotopic xenografts in vivo.

RESULTS

We discovered a novel oncogenic lncRNA RP11-757G1.5, that was overexpressed in CRC tissues, especially in aggressive cases. Moreover, up-regulation of RP11-757G1.5 strongly correlated with poor clinical outcomes of patients with CRC. Functional analyses revealed that RP11-757G1.5 promoted cell proliferation in vitro and in vivo. Furthermore, RP11-757G1.5 stimulated cell migration and invasion in vitro and in vivo. Mechanistic studies illustrated that RP11-757G1.5 regulated the expression of YAP1 through sponging miR-139-5p and inhibiting its activity thereby promoting CRC progression and development.

CONCLUSIONS

Altogether, these results reveal a novel RP11-757G1.5/miR-139-5p/YAP1 regulatory axis that participates in CRC carcinogenesis and progression.

IFN-α confers epigenetic regulation of HBV cccDNA minichromosome by modulating GCN5-mediated succinylation of histone H3K79 to clear HBV cccDNA

Background

Hepatitis B virus covalently closed circular DNA (HBV cccDNA) is assembled by histones and non-histones into a chromatin-like cccDNA minichromosome in the nucleus. The cellular histone acetyltransferase GCN5, displaying succinyltransferase activity, is recruited onto cccDNA to modulate HBV transcription in cells. Clinically, IFN-α is able to repress cccDNA. However, the underlying mechanism of IFN-α in the depression of cccDNA mediated by GCN5 is poorly understood. Here, we explored the effect of IFN-α on GCN5-mediated succinylation in the epigenetic regulation of HBV cccDNA minichromosome.

Results

Succinylation modification of the cccDNA minichromosome has been observed in HBV-infected human liver-chimeric mice and HBV-expressing cell lines. Moreover, histone H3K79 succinylation by GCN5 was identified in the system. Interestingly, the mutant of histone H3K79 efficiently blocked the replication of HBV, and interference with GCN5 resulted in decreased levels of HBV DNA, HBsAg, and HBeAg in the supernatant from de novo HBV-infected HepaRG cells. Consistently, the levels of histone H3K79 succinylation were significantly elevated in the livers of HBV-infected human liver-chimeric mice. The knockdown or overexpression of GCN5 or the mutant of GCN5 could affect the binding of GCN5 to cccDNA or H3K79 succinylation, leading to a change in cccDNA transcription activity. In addition, Southern blot analysis validated that siGCN5 decreased the levels of cccDNA in the cells, suggesting that GCN5-mediated succinylation of histone H3K79 contributes to the epigenetic regulation of cccDNA minichromosome. Strikingly, IFN-α effectively depressed histone H3K79 succinylation in HBV cccDNA minichromosome in de novo HepG2-NTCP and HBV-infected HepaRG cells.

Conclusions

IFN-α epigenetically regulates the HBV cccDNA minichromosome by modulating GCN5-mediated succinylation of histone H3K79 to clear HBV cccDNA. Our findings provide new insights into the mechanism by which IFN-α modulate the epigenetic regulation of HBV cccDNA minichromosome.

Hepatitis B virus biology and life cycle

Hepatitis B virus (HBV) specifically infects hepatocytes and causes severe liver diseases. The HBV life cycle is unique in that the genomic DNA (relaxed-circular partially double-stranded DNA: rcDNA) is converted to a molecular template DNA (covalently closed circular DNA: cccDNA) to amplify a viral RNA intermediate, which is then reverse-transcribed back to viral DNA. The highly stable characteristics of cccDNA result in chronic infection and a poor rate of cure. This complex life cycle of HBV offers a variety of targets to develop antiviral agents. We provide here an update on the current knowledge of HBV biology and its life cycle, which may help to identify new antiviral targets.

Specificity in Ubiquitination Triggered by Virus Infection

Ubiquitination is a prominent posttranslational modification, in which the ubiquitin moiety is covalently attached to a target protein to influence protein stability, interaction partner and biological function. All seven lysine residues of ubiquitin, along with the N-terminal methionine, can each serve as a substrate for further ubiquitination, which effectuates a diverse combination of mono- or poly-ubiquitinated proteins with linear or branched ubiquitin chains. The intricately composed ubiquitin codes are then recognized by a large variety of ubiquitin binding domain (UBD)-containing proteins to participate in the regulation of various pathways to modulate the cell behavior. Viruses, as obligate parasites, involve many aspects of the cell pathways to overcome host defenses and subjugate cellular machineries. In the virus-host interactions, both the virus and the host tap into the rich source of versatile ubiquitination code in order to compete, combat, and co-evolve. Here, we review the recent literature to discuss the role of ubiquitin system as the infection progresses in virus life cycle and the importance of ubiquitin specificity in the regulation of virus-host relation.

Hepatitis B Virus-X Downregulates Expression of Selenium Binding Protein 1

Selenium binding protein 1 (SELENBP1) has been known to be reduced in various types cancer, and epigenetic change is shown to be likely to account for the reduction of SELNEBP1 expression. With cDNA microarray comparative analysis, we found that SELENBP1 is markedly decreased in hepatitis B virus-X (HBx)-expressing cells. To clarify the effect of HBx on SELENBP1 expression, we compared the expression levels of SELENBP1 mRNA and protein by semi-quantitative RT-PCR, Northern blot, and Western blot. As expected, SELENBP1 expression was shown to be reduced in cells expressing HBx, and reporter gene analysis showed that the SELENBP1 promoter is repressed by HBx. In addition, the stepwise deletion of 5′ flanking promoter sequences resulted in a gradual decrease in basal promoter activity and inhibition of SELENBP1 expression by HBx. Moreover, immunohistochemistry on tissue microarrays containing 60 pairs of human liver tissue showed decreased intensity of SELENBP1 in tumor tissues as compared with their matched non-tumor liver tissues. Taken together, our findings suggest that inhibition of SELENBP1 expression by HBx might act as one of the causes in the development of hepatocellular carcinoma caused by HBV infection.

IFN-α2b inhibits the ethanol enriched-HBV cccDNA through blocking a positive feedback loop of HBx/MSL2/cccDNA/HBV/HBx in liver

Hepatitis B virus (HBV) is a major risk factor for liver diseases, in which HBV covalently closed circular DNA (cccDNA), as the genomic form that templates viral transcription, plays crucial roles in sustaining viral persistence. Clinically, the excessive ethanol intake accelerates the progression of liver diseases with HBV infection. Here, we supposed that ethanol might trigger HBV cccDNA in the liver. Interestingly, we observed that the ethanol remarkably elevated the levels of HBeAg, HBsAg, HBV DNA and cccDNA in HBV-expressing hepatoma cells. Mechanically, the ethanol increased the levels of HBx and MSL2 in vivo and in HBV-expressing HepG2 cells, but not in HBV-free HepG2 cells. Moreover, the down-regulation of MSL2 by small interference RNA could block the ethanol-promoted HBV cccDNA in HepG2.2.15 cells. As a commonly administered treatment for HBV, the effect of IFNα on ethanol-triggered HBV cccDNA remains poorly understood. Strikingly, we showed that the treatment with IFN-α2b inhibited the ethanol-promoted cccDNA through depressing MSL2 in the cells. Thus, we conclude that IFN-α2b inhibits the ethanol-enriched HBV cccDNA through blocking a positive feedback loop of HBx/MSL2/cccDNA/HBV/HBx. Our finding provides new insights into the mechanism by which IFN-α2b inhibits ethanol-enhanced HBV cccDNA. Therapeutically, IFNα may contribute to the cccDNA induced by ethanol in liver.

The Prognostic Significance of APOBEC3B and PD-L1/PD-1 in Nasopharyngeal Carcinoma

PURPOSE

Apolipoprotein B mRNA editing enzyme catalytic polypeptide-like 3B (APOBEC3B) is a recently discovered protein that is considered important in causing mutations in tumor cell genome bases. Whether APOBEC3B is expressed in nasopharyngeal carcinoma (NPC) still remains unknown. Studies have shown that programmed-cell-death receptor-1 ligand (PD-L1) is highly expressed in NPC, but its clinical significance has not been fully elucidated. We aimed to evaluate APOBEC3B and PD-L1 protein expression in NPC and also investigate their prognostic significance.

MATERIALS AND METHODS

One hundred and three patients with NPC were retrospectively collected in this study, and were followed-up for 5 years. The expression of APOBEC3B and PD-L1/PD-1 in NPC was detected by immunohistochemical staining.

RESULTS

High expression of APOBEC3B was observed in 42.7% of NPC patients. The high expression rate of APOBEC3B was 31.5% in patients without recurrence or metastasis within 5 years, and 55.1% in those patients with recurrence or metastasis, and the difference was statistically significant (P=0.016). There was no significant difference in APOBEC3B expression among patients with different sex, age group, and clinical stage (P>0.05). The positive expression rate of PD-L1 was 55.3% in all patients with NPC. There was no significant difference in PD-L1 expression among patients with different sex, age group, clinical stage, and tumor recurrence or metastasis condition (P> 0.05). There was no significant correlation between the expression of APOBEC3B and PD-L1 in NPC patients. The positive expression rate of PD-1 was 1.9% (2/103) in patients with NPC.

CONCLUSIONS

APOBEC3B showed association with aggressive behavior and poor outcome in NPC, and is also considered as a potential marker for predicting NPC recurrence or metastasis. PD-L1 is not associated with the aggressive behavior and poor outcome in NPC.

Silencing MYH9 blocks HBx-induced GSK3β ubiquitination and degradation to inhibit tumor stemness in hepatocellular carcinoma

MYH9 has dual functions in tumors. However, its role in inducing tumor stemness in hepatocellular carcinoma (HCC) is not yet determined. Here, we found that MYH9 is an effective promoter of tumor stemness that facilitates hepatocellular carcinoma pathogenesis. Importantly, targeting MYH9 remarkably improved the survival of hepatocellular carcinoma-bearing mice and promoted sorafenib sensitivity of hepatocellular carcinoma cells in vivo. Mechanistic analysis suggested that MYH9 interacted with GSK3β and reduced its protein expression by ubiquitin-mediated degradation, which therefore dysregulated the β-catenin destruction complex and induced the downstream tumor stemness phenotype, epithelial-mesenchymal transition, and c-Jun signaling in HCC. C-Jun transcriptionally stimulated MYH9 expression and formed an MYH9/GSK3β/β-catenin/c-Jun feedback loop. X protein is a hepatitis B virus (HBV)-encoded key oncogenic protein that promotes HCC pathogenesis. Interestingly, we observed that HBV X protein (HBX) interacted with MYH9 and induced its expression by modulating GSK3β/β-catenin/c-Jun signaling. Targeting MYH9 blocked HBX-induced GSK3β ubiquitination to activate the β-catenin destruction complex and suppressed cancer stemness and EMT. Based on TCGA database analysis, MYH9 was found to be elevated and conferred poor prognosis for hepatocellular carcinoma patients. In clinical samples, high MYH9 expression levels predicted poor prognosis of hepatocellular carcinoma patients. These findings identify the suppression of MYH9 as an alternative approach for the effective eradication of CSC properties to inhibit cancer migration, invasion, growth, and sorafenib resistance in HCC patients. Our study demonstrated that MYH9 is a crucial therapeutic target in HCC.

Targeting Hepatitis B Virus Covalently Closed Circular DNA and Hepatitis B Virus X Protein: Recent Advances and New Approaches

Chronic Hepatitis B virus (HBV) infection remains a worldwide concern and public health problem. Two key aspects of the HBV life cycle are essential for viral replication and thus the development of chronic infections: the establishment of the viral minichromosome, covalently closed circular (ccc) DNA, within the nucleus of infected hepatocytes and the expression of the regulatory Hepatitis B virus X protein (HBx). Interestingly, nuclear HBx redirects host epigenetic machinery to activate cccDNA transcription. In this Perspective, we provide an overview of recent advances in understanding the regulation of cccDNA and the mechanistic and functional roles of HBx. We also describe the progress toward targeting both cccDNA and HBx for therapeutic purposes. Finally, we outline standing questions in the field and propose complementary chemical biology approaches to address them.

HAT1 signaling confers to assembly and epigenetic regulation of HBV cccDNA minichromosome

Rationale: Hepatitis B virus (HBV) is a leading cause of liver diseases. HBV covalently closed circular DNA (cccDNA) is a critical obstacle of complete elimination by anti-HBV therapy. HBV cccDNA accumulates in nucleus as a chromatin-like cccDNA minichromosome assembled by histones and non-histones. However, the underlying mechanism of modulation of cccDNA minichromosome in hepatocytes is poorly understood.

Methods: A human liver-chimeric mouse model was established. The cccDNA-ChIP, Southern blot analysis, confocal assays, RIP assays and RNA pull-down assays, et al. were performed to assess the mechanism of assembly and epigenetic regulation of cccDNA minichromosome in human liver-chimeric mouse model, human primary hepatocytes (PHH), dHepaRG, HepG2-NTCP cell lines and clinical liver tissues.

Results: Importantly, the expression levels of HAT1, CAF-1 and lncRNA HULC were significantly elevated in the liver from HBV-infected human liver-chimeric mice. Strikingly, the depletion of HAT1 reduced HBV replication and cccDNA accumulation, and impaired the assembly of histone H3/H4 and the deposition of HBx and p300 onto cccDNA to form cccDNA minichromosome in the cells. Mechanically, chromatin assembly factor-1 (CAF-1) was involved in the events. Interestingly, HAT1 modified the acetylation of histone H3K27/H4K5/H4K12 on cccDNA minichromosome. Moreover, lncRNA HULC-scaffold HAT1/HULC/HBc complex was responsible for the modification on cccDNA minichromosome. Additionally, HBV activated HAT1 through HBx-co-activated transcriptional factor Sp1 in a positive feedback manner.

Conclusion: HAT1 signaling contributes to assembly and epigenetic regulation of HBV cccDNA minichromosome.

Antiviral therapy may decrease HBx, affecting cccDNA and MSL2 in hepatocarcinogenesis

Chronic hepatitis B virus (HBV) is the leading cause of hepatocellular carcinoma (HCC). Covalently closed circular DNA (cccDNA) is an intermediate in the life cycle of HBV. HBV-encoded X protein (HBx), a key viral oncoprotein, can be specifically ubiquitylated by male specific lethal 2 (MSL2), which causes upregulation of HBx activity and promotes transcription, cell proliferation and tumor growth. The present study compared the levels of cccDNA, MSL2 mRNA and HBx mRNA in tumor and peri-tumor tissues, and clarified the effect of antiviral therapy on these indicators. Levels of intrahepatic cccDNA, MSL2 mRNA and HBx mRNA were determined using quantitative PCR in patients with HBV-associated HCC who had undergone liver surgery. A total of 50 patients were included in the present study. Prior to surgery, 31 patients had undergone antiviral treatment. Intrahepatic cccDNA levels were significantly higher in the tumor tissues compared with the peri-tumor tissues (P=0.001), particularly in the hepatitis B e antigen-positive (P=0.008), tumor recurrence (P=0.002) and <3 cm tumor size (P=0.003) groups. Furthermore, in patients with preoperative cirrhosis, levels of cccDNA and MSL2 mRNA were significantly higher in tumor tissues compared with that in peri-tumor tissues (P<0.001 and P=0.023, respectively). The expression levels of HBx mRNA in antiviral-treated tumors and peri-tumor tissues were significantly lower compared with those in untreated tissues (P=0.026 and P=0.035). The levels of cccDNA and MSL2 mRNA in the HBx-positive group were significantly higher in tumor tissues compared with those in peri-tumor tissues (P=0.026 and P=0.013). In conclusion, cccDNA participated in the tumorigenesis of HBV-associated HCC, and antiviral therapy was found to modulate hepatocarcinogenesis by decreasing the levels of HBx to inhibit the tumorigenic effect of MSL2 and cccDNA.

Mapping the Interactions of HBV cccDNA with Host Factors

Hepatitis B virus (HBV) infection is a major health problem affecting about 300 million people globally. Although successful administration of a prophylactic vaccine has reduced new infections, a cure for chronic hepatitis B (CHB) is still unavailable. Current anti-HBV therapies slow down disease progression but are not curative as they cannot eliminate or permanently silence HBV covalently closed circular DNA (cccDNA). The cccDNA minichromosome persists in the nuclei of infected hepatocytes where it forms the template for all viral transcription. Interactions between host factors and cccDNA are crucial for its formation, stability, and transcriptional activity. Here, we summarize the reported interactions between HBV cccDNA and various host factors and their implications on HBV replication. While the virus hijacks certain cellular processes to complete its life cycle, there are also host factors that restrict HBV infection. Therefore, we review both positive and negative regulation of HBV cccDNA by host factors and the use of small molecule drugs or sequence-specific nucleases to target these interactions or cccDNA directly. We also discuss several reporter-based surrogate systems that mimic cccDNA biology which can be used for drug library screening of cccDNA-targeting compounds as well as identification of cccDNA-related targets.

HBx regulates transcription factor PAX8 stabilization to promote the progression of hepatocellular carcinoma

Transcription factor PAX8 expression is upregulated in several types of cancers. However, little is known about the function of PAX8 in the progression of hepatoma and its regulatory mechanisms. Here, we show that PAX8 silencing inhibits the proliferation and clonogenicity of hepatoma cells and its growth in vivo. The HBV X protein (HBx) does not directly interacts, but stabilizes PAX8 by inhibiting proteasome-dependent ubiquitination and degradation. Furthermore, the E3 ubiquitin ligase complex component Skp2 through its LRR domain directly interacts with the Prd domain of PAX8 and targets PAX8 by recognizing its lysine 275 for ubiquitination and degradation in hepatoma cells. In addition, HBx directly interacts and is colocalized with Skp2 to inhibit its recognition and subsequent ubiquitination and degradation of PAX8 in hepatoma cells. Moreover, HBx upregulates the expression and phosphorylation of Aurora A, a serine-threonine kinase, which interacts with and phosphorylates PAX8 at S209 and T277, compromising the Skp2-recognized PAX8 ubiquitination and destabilization. Thus, HBx stabilizes PAX8 protein by inhibiting the Skp2 targeted PAX8 ubiquitination and enhancing the Aurora A-mediated its phosphorylation, contributing to the progression of hepatoma. Our findings suggest that PAX8 may a new target for design of therapies and uncover new insights into the pathogenesis of hepatoma.

LncRNA PCNAP1 modulates hepatitis B virus replication and enhances tumor growth of liver cancer

Rationale: Hepatitis B virus (HBV) is a major risk factor for liver cancer, in which HBV covalently closed circular DNA (cccDNA) plays crucial roles. However, the effect of pseudogene-derived long noncoding RNAs (lncRNAs) acting as functional regulators of their ancestral gene expression on HBV replication and hepatocellular carcinoma (HCC) remains unclear. In this study, we speculated that the pseudogene-derived lncRNA PCNAP1 and its ancestor PCNA might modulate HBV replication and promote hepatocarcinogenesis.

Methods: We investigated the roles of lncRNA PCNAP1 in contribution of HBV replication through modulating miR-154/PCNA/HBV cccDNA signaling in hepatocarcinogenesis by using CRISPR/Cas9, Southern blot analysis, confocal assays, et al. in primary human hepatocytes (PHH), HepaRG cells, HepG2-NTCP cells, hepatoma carcinoma cells, human liver-chimeric mice model, transgenetic mice model, in vitro tumorigenicity and clinical patients.

Results: Interestingly, the expression levels of PCNAP1 and PCNA were significantly elevated in the liver of HBV-infectious human liver-chimeric mice. Clinically, the mRNA levels of PCNAP1 and PCNA were increased in the liver of HBV-positive/HBV cccDNA-positive HCC patients. Mechanistically, PCNA interacted with HBV cccDNA in a HBc-dependent manner. PCNAP1 enhanced PCNA through sponging miR-154 targeting PCNA mRNA 3′UTR. Functionally, PCNAP1 or PCNA remarkably enhanced HBV replication and accelerated the growth of HCC in vitro and in vivo.

Conclusion: We conclude that lncRNA PCNAP1 enhances the HBV replication through modulating miR-154/PCNA/HBV cccDNA signaling and the PCNAP1/PCNA signaling drives the hepatocarcinogenesis. Our finding provides new insights into the mechanism by which lncRNA PCNAP1 enhances HBV replication and hepatocarcinogenesis.

The interaction of hepatitis B virus with the ubiquitin proteasome system in viral replication and associated pathogenesis

Background

The ubiquitin proteasome system (UPS) regulates the expression levels of cellular proteins by ubiquitination of protein substrates followed by their degradation via the proteasome. As a highly conserved cellular degradation mechanism, the UPS affects a variety of biological processes and participates in viral propagation.

Main body

During hepatitis B virus (HBV) infection, the UPS is shown to act as a double-edged sword in viral pathogenesis. On the one hand, the UPS acts as a host defense mechanism to selectively recognize HBV proteins as well as special cellular proteins that favor the viral life cycle and induces their ubiquitin-dependent proteasomal degradation to limit HBV infection. On the other hand, the HBV has evolved to subvert the UPS function for its own advantage. Moreover, in the infected hepatocytes, certain cellular proteins that are dependent on the UPS are involved in abnormal biological processes which are mediated by HBV.

Conclusion

The molecular interaction of HBV with the UPS to modulate viral propagation and pathogenesis is summarized in the review. Considering the important role of the UPS in HBV infection, a better understanding of the HBV-UPS interaction could provide novel insight into the mechanisms that are involved in viral replication and pathogenesis and help to develop potential treatment strategies targeting the UPS.

Pevonedistat, a Neuronal Precursor Cell-Expressed Developmentally Down-Regulated Protein 8-Activating Enzyme Inhibitor, Is a Potent Inhibitor of Hepatitis B Virus

Hepatitis B virus (HBV) infection is a major health concern worldwide. To prevent HBV-related mortality, elimination of viral proteins is considered the ultimate goal of HBV treatment; however, currently available nucleos(t)ide analogs rarely achieve this goal, as viral transcription from episomal viral covalently closed circular DNA (cccDNA) is not prevented. HBV regulatory protein X was recently found to target the protein structural maintenance of chromosomes 5/6 (Smc5/6) for ubiquitination and degradation by DDB1-CUL4-ROC1 E3 ligase, resulting in enhanced viral transcription from cccDNA. This ubiquitin-dependent proteasomal pathway requires an additional ubiquitin-like protein for activation, neuronal precursor cell-expressed developmentally down-regulated protein 8 (NEDD8). Here, we show that pevonedistat, a NEDD8-activating enzyme inhibitor, works efficiently as an antiviral agent. Pevonedistat significantly restored Smc5/6 protein levels and suppressed viral transcription and protein production in the HBV minicircle system in in vitro HBV replication models and in human primary hepatocytes infected naturally with HBV. Conclusion: These results indicate that pevonedistat is a promising compound to treat chronic HBV infection.

Type III interferon-induced CBFβ inhibits HBV replication by hijacking HBx

Hepatitis B virus (HBV) and its associated chronic infection remain serious health threats worldwide. However, there is still no impactful approach for clinical treatment of hepatitis B patients. Therefore, developing a better understanding of the interactions between HBV and its host is particularly important. HBV infection has been reported to induce type-III but not type-I or type-II interferon (IFN). In this study, we identified CBFβ, an HIV enhancer, as an HBV restriction factor that is specifically induced by type-III IFN in the early stages of HBV infection. Type-III IFN-induced IL-10 played an important role in the production of CBFβ. Interestingly, the interaction between CBFβ- and HBV-encoded regulatory protein X (HBx) enhanced the stability of CBFβ, but notably blocked HBx-mediated promotion of HBV replication. CBFβ expression was lower in HBV patients than in healthy persons, and the addition of serum from HBV patients inhibited CBFβ expression in HepG2 cells. On the contrary, HBV via HBsAg inhibited type-III IFN-induced CBFβ expression and decreased the anti-HBV activity of type-III IFN, suggesting that HBV inhibits antiviral interferon-stimulated gene (ISG) expression and induces IFN resistance. Collectively, our results demonstrate that type-III IFN-triggered and IL-10-induced CBFβ are crucial factors for inhibiting HBV replication, and the HBx-CBFβ-HBsAg axis reveals a new molecular mechanism of interaction between HBV and its hosts.

HoxA10 Facilitates SHP-1-Catalyzed Dephosphorylation of p38 MAPK/STAT3 To Repress Hepatitis B Virus Replication by a Feedback Regulatory Mechanism

Hepatitis B virus (HBV) infection is the leading cause of chronic hepatitis B (CHB), liver cirrhosis (LC), and hepatocellular carcinoma (HCC). This study reveals a distinct mechanism underlying the regulation of HBV replication. HBV activates homeobox A10 (HoxA10) in human hepatocytes, leukocytes, peripheral blood mononuclear cells (PBMCs), HepG2-NTCP cells, leukocytes isolated from CHB patients, and HBV-associated HCC tissues. HoxA10 in turn represses HBV replication in human hepatocytes, HepG2-NTCP cells, and BALB/c mice. Interestingly, we show that during early HBV infection, p38 mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription 3 (STAT3) were activated to facilitate HBV replication; however, during late HBV infection, HoxA10 was induced to attenuate HBV replication. Detailed studies reveal that HoxA10 binds to p38 MAPK, recruits SH2-containing protein tyrosine phosphatase 1 (SHP-1) to facilitate SHP-1 in catalyzing dephosphorylation of p38 MAPK/STAT3, and thereby attenuates p38 MAPK/STAT3 activation and HBV replication. Furthermore, HoxA10 binds to the HBV enhancer element I (EnhI)/X promoter, competes with STAT3 for binding of the promoter, and thereby represses HBV transcription. Taken together, these results show that HoxA10 attenuates HBV replication through repressing the p38 MAPK/STAT3 pathway by two approaches: HoxA10 interacts with p38 MAPK and recruits SHP-1 to repress HBV replication, and HoxA10 binds to the EnhI/X promoter and competes with STAT3 to attenuate HBV transcription. Thus, the function of HoxA10 is similar to the action of interferon (IFN) in terms of inhibition of HBV infection; however, the mechanism of HoxA10-mediated repression of HBV replication is different from the mechanism underlying IFN-induced inhibition of HBV infection.IMPORTANCE Two billion people have been infected with HBV worldwide; about 240 million infected patients developed chronic hepatitis B (CHB), and 650,000 die each year from liver cirrhosis (LC) or hepatocellular carcinoma (HCC). This work elucidates a mechanism underlying the control of HBV replication. HBV infection activates HoxA10, a regulator of cell differentiation and cancer progression, in human cells and patients with CHB and HCC. HoxA10 subsequently inhibits HBV replication in human tissue culture cells and mice. Additionally, HoxA10 interacts with p38 MAPK to repress the activation of p38 MAPK and STAT3 and recruits and facilitates SHP-1 to catalyze the dephosphorylation of p38 MAPK and STAT3. Moreover, HoxA10 competes with STAT3 for binding of the HBV X promoter to repress HBV transcription. Thus, this work reveals a negative regulatory mechanism underlying the control of HBV replication and provides new insights into the development of potential agents to control HBV infection.

A novel lncRNA MCM3AP-AS1 promotes the growth of hepatocellular carcinoma by targeting miR-194-5p/FOXA1 axis

Background

Hepatocellular carcinoma (HCC) is the most common malignant liver tumor with poor clinical outcomes. Increasing amount of long non-coding RNAs (lncRNAs) have been revealed to be implicated in the carcinogenesis and progression of HCC. However, the expressions, clinical significances, and roles of most lncRNAs in HCC are still unknown.

Methods

The expression of lncRNA MCM3AP antisense RNA 1 (MCM3AP-AS1) in HCC tissues and cell lines was detected by qRT-PCR and fluorescence in situ hybridization. Immunoblotting, CCK-8, EdU, colony formation and flow cytometry were performed to investigate the role of MCM3AP-AS1 in HCC cell proliferation, cell cycle and apoptosis in vitro. A subcutaneous tumor mouse model was constructed to analyze in vivo growth of HCC cells after MCM3AP-AS1 knockdown. The interactions among MCM3AP-AS1, miR-194-5p and FOXA1 were measured by RNA pull-down, RNA immunoprecipitation and luciferase reporter assay.

Results

We revealed a novel oncogenic lncRNA MCM3AP-AS1, which is overexpressed in HCC and positively correlated with large tumor size, high tumor grade, advanced tumor stage and poor prognosis of HCC patients. MCM3AP-AS1 knockdown suppressed HCC cell proliferation, colony formation and cell cycle progression, and induced apoptosis in vitro, and depletion of MCM3AP-AS1 inhibited tumor growth of HCC in vivo. Mechanistically, MCM3AP-AS1 directly bound to miR-194-5p and acted as competing endogenous RNA (ceRNA), and subsequently facilitated miR-194-5p’s target gene forkhead box A1 (FOXA1) expression in HCC cells. Interestingly, FOXA1 restoration rescued MCM3AP-AS1 knockdown induced proliferation inhibition, G1 arrest and apoptosis of HCC cells.

Conclusions

Our results recognized MCM3AP-AS1 as a novel oncogenic lncRNA, which indicated poor clinical outcomes in patients with HCC. MCM3AP-AS1 exerted an oncogenic role in HCC via targeting miR-194-5p and subsequently promoted FOXA1 expression. Our findings suggested that MCM3AP-AS1 could be a potential prognostic biomarker and therapeutic target for HCC.

Electronic supplementary material

The online version of this article (10.1186/s12943-019-0957-7) contains supplementary material, which is available to authorized users.

Retracted Article: MicroRNA-1271 modulates hepatitis B virus replication, cell proliferation and apoptosis in hepatitis B virus-related hepatocellular carcinoma by targeting SIRT1

Chronic hepatitis B virus (HBV) infection is a leading cause of hepatocellular carcinoma (HCC). Certain studies have revealed that microRNAs play crucial roles in HBV-related HCC. The aim of this study was to investigate the effects of microRNA-1271 (miR-1271) on HBV replication, cell proliferation and apoptosis in HBV-related HCC. The expression of HBV DNA and miR-1271 was detected by quantitative real time-polymerase chain reaction (qRT-PCR). The mRNA and protein levels of SIRT1 were detected by qRT-PCR and western blot analysis, respectively. HBV replication was assessed by the expression of HBV DNA and the levels of HBsAg and HBeAg. Cell proliferation was assessed by cell counting kit-8 (CCK-8) and 5-bromo-2-deoxyuidine (BrdU) assay, and apoptosis was evaluated by flow cytometry assay, enzyme-linked immunosorbent assay (ELISA) and the activity of caspase-3. The relationship between miR-1271 and SIRT1 was predicated by online software and confirmed by dual-luciferase reporter assay, RNA immunoprecipitation (RIP) and pull-down assay. We first found that the expression of miR-1271 was downregulated and SIRT1 was upregulated in both HBV-related HCC tissues and cells. Overexpression of miR-1271 inhibited HBV replication and cell proliferation whilst promoting apoptosis in HBV-related HCC cells. Subsequently, SIRT1 was identified as a target of miR-1271. Moreover, overexpression of SIRT1 reversed the effects of miR-1271 overexpression on HBV replication, cell proliferation and apoptosis in HBV-related HCC cells. In conclusion, our study demonstrated that miR-1271 inhibited HBV replication and proliferation and promoted apoptosis of HBV-related HCC cells via targeting SIRT1, which might contribute to the diagnosis and therapy of HBV-related HCC.

MiR-1271 suppressed HBV-related HCC cells development by downregulating SIRT1.

Hepatitis B virus X protein enhances hepatocarcinogenesis by depressing the targeting of NUSAP1 mRNA by miR-18b

Objective

The aim of this study was to investigate the underlying mechanism whereby HBx modulates the targeting of NUSAP1 by miR-18b to enhance hepatocarcinogenesis.

Methods

We employed an integrated approach of bioinformatics analysis and molecular experiments in hepatoma cells, HBV transgenic mice, and clinical liver cancer tissues to investigate the role of HBx-regulated miR-18b in the development of liver cancer.

Results

In this study, we report that the HBx-mediated tumor suppressor miR-18b modulates hepatocarcinogenesis during the host-HBV interaction. The expression levels of miR-18b were lower in clinical HBV-positive liver cancer tissues and liver tissues of HBV-transgenic mice. Interestingly, HBx inhibited miR-18b expression by inducing the methylation of CpG islands in its promoter. Accordingly, we tested the hypothesis that HBx enhanced hepatocarcinogenesis by increasing the expression of target genes of miR-18b. Moreover, we identified nucleolar spindle-associated protein 1 (NUSAP1) as one of the target genes of miR-18b. NUSAP1 was expressed at high levels in liver cancer tissues. Interestingly, HBx up-regulated NUSAP1 by suppressing miR-18b. Functionally, miR-18b significantly inhibited the proliferation of hepatoma cells by depressing NUSAP1 levels in vivo and in vitro.

Conclusions

Thus, we conclude that the targeting of NUSAP1 mRNA by the tumor suppressor miR-18b is controlled by HBx-modulated promoter methylation during the host-virus interaction, leading to hepatocarcinogenesis. Our findings provide new insights into the mechanism by which HBx-mediated miRNAs modulate hepatocarcinogenesis.

Aspirin inhibits the proliferation of hepatoma cells through controlling GLUT1-mediated glucose metabolism

Aspirin can efficiently inhibit liver cancer growth, but the mechanism is poorly understood. In this study, we report that aspirin modulates glucose uptake through downregulating glucose transporter 1 (GLUT1), leading to the inhibition of hepatoma cell proliferation. Our data showed that aspirin significantly decreased the levels of reactive oxygen species (ROS) and glucose consumption in hepatoma cells. Interestingly, we identified that GLUT1 and HIF1α could be decreased by aspirin. Mechanically, we demonstrated that the -1008/-780 region was the regulatory element of transcriptional factor NF-κB in GLUT1 promoter by luciferase report gene assays. PDTC, an inhibitor of NF-κB, could suppress the expression of GLUT1 in HepG2 and H7402 cells, followed by affecting the levels of ROS and glucose consumption. CoCl₂-activated HIF1α expression could slightly rescue the GLUT1 expression inhibited by aspirin or PDTC, suggesting that aspirin depressed GLUT1 through targeting NF-κB or NF-κB/HIF1α signaling. Moreover, we found that GLUT1 was highly expressed in clinical HCC tissues relating to their paired adjacent normal tissues. Importantly, we observed that high level of GLUT1 was significantly correlated with the poor relapse-free survival of HCC patients by analysis of public data. Functionally, overexpression of GLUT1 blocked the PDTC-induced or aspirin-induced inhibition of glucose metabolism in HepG2 cells. Conversely, aspirin failed to work when GLUT1 was stably knocked down in the cells. Administration of aspirin could depress the growth of hepatoma cells through controlling GLUT1 in vitro and in vivo. Thus, our finding provides new insights into the mechanism by which aspirin depresses liver cancer.

Post-translational Modification Control of HBV Biological Processes

Hepatitis B virus infection remains a global healthy issue that needs to be urgently solved. Novel strategies for anti-viral therapy are based on exploring the effective diagnostic markers and therapeutic targets of diseases caused by hepatitis B virus (HBV) infection. It is well-established that not only viral proteins themselves but also key factors from the host control the biological processes associated with HBV, including replication, transcription, packaging, and secretion. Protein post-translational modifications (PTMs), such as phosphorylation, acetylation, methylation, and ubiquitination, have been shown to control protein activity, regulate protein stability, promote protein interactions and alter protein subcellular localization, leading to the modulation of crucial signaling pathways and affected cellular processes. This review focuses on the functions and effects of diverse PTMs in regulating important processes in the HBV life cycle. The potential roles of PTMs in the pathogenesis of HBV-associated liver diseases are also discussed.

The long noncoding RNA MALAT-1 functions as a competing endogenous RNA to regulate MSL2 expression by sponging miR-338-3p in myasthenia gravis

Myasthenia gravis (MG) is a cell-dependent autoimmune disease commonly associated with thymic pathology. Metastasis-associated lung adenocarcinoma transcript 1 (MALAT-1) has been associated with gene regulation and alternative splicing. It has shown relationship with proliferation, apoptosis, migration, and invasion. In this study, we found that MALAT-1 expression was downregulated in MG. The level of the miR-338-3p was increased in peripheral blood mononuclear cells from MG patients compared with those from control subjects. MALAT-1 competed for binding to miR-338-3p with male-specific lethal 2 (MSL2) in luciferase reporter assays. We confirmed the MALAT-1-miR-338-3p-MSL2 interaction network in MG in vitro. Thus, MALAT-1 directly induced MSL2 expression in MG by acting as a competing endogenous RNA for miR-338-3p, suggesting that it may serve as a therapeutic target for MG treatment.

HBV suppresses ZHX2 expression to promote proliferation of HCC through miR-155 activation

Initiation of hepatocellular carcinoma (HCC) by chronic hepatitis B virus (HBV) infection is a complex process that includes both oncogene activation and tumor suppressor inhibition. The HBV X (HBx) protein has an important and complex role in processes leading to HCC. We previously identified the mammalian Zinc fingers and homeoboxes 2 (ZHX2) gene as an HCC-associated tumor suppressor gene. In the present study, we investigated whether the oncogenic properties of HBV and, more specifically, HBx, involved ZHX2 silencing. Our data indicates that ZHX2 expression is significantly decreased in tumor tissues from HBV-positive HCC patients and livers from HBV transgenic mice. In vitro and in vivo studies confirmed that HBV-encoded proteins, particularly HBx, inhibits both the expression and tumor suppression properties of ZHX2. Further analyses identified miR-155, a well-known oncomiR in various cancers, as an important link between HBx and ZHX2 inhibition. Increased miR-155 levels were found in HBV-positive tumors, livers of HBV transgenic mice and HBx-overexpressing hepatoma cell lines. MiR-155 overexpression reduced ZHX2 levels via miR-155 seed sites in the ZHX2 3'UTR, whereas blocking miR-155 levels led to increased ZHX2 levels. Taken together, our data indicate that HCC-promoting properties of HBV may include ZHX2 silencing via a miR-155 dependent pathway and suggests a novel therapy for HBV-related HCC.

When Hepatitis B Virus Meets Interferons

Chronic hepatitis B virus (HBV) infection imposes a severe burden on global public health. Currently, there are no curative therapies for millions of chronic HBV-infected patients (Lok et al., 2017). Interferon (IFN; including pegylated IFN) is an approved anti-HBV drug that not only exerts direct antiviral activity, but also augments immunity against HBV infection. Through a systematic review of the literature, here we summarize and present recent progress in research regarding the interactions between IFN and HBV as well as dissect the antiviral mechanisms of IFN. We focus on inhibition of HBV replication by IFN-stimulated genes (ISGs) as well as inhibition of IFN signaling by HBV and viral proteins. Finally, we briefly discuss current IFN-based HBV treatment strategies. This review may help to better understand the mechanisms involved in the therapeutic action of IFN as well as the crosstalk between IFN and HBV, and facilitate the development of both direct-acting and immunology-based new HBV drugs.

Hepatitis B virus pathogenesis: Fresh insights into hepatitis B virus RNA

Hepatitis B virus (HBV) is still a worldwide health concern. While divergent factors are involved in its pathogenesis, it is now clear that HBV RNAs, principally templates for viral proteins and viral DNAs, have diverse biological functions involved in HBV pathogenesis. These functions include viral replication, hepatic fibrosis and hepatocarcinogenesis. Depending on the sequence similarities, HBV RNAs may act as sponges for host miRNAs and may deregulate miRNA functions, possibly leading to pathological consequences. Some parts of the HBV RNA molecule may function as viral-derived miRNA, which regulates viral replication. HBV DNA can integrate into the host genomic DNA and produce novel viral-host fusion RNA, which may have pathological functions. To date, elimination of HBV-derived covalently closed circular DNA has not been achieved. However, RNA transcription silencing may be an alternative practical approach to treat HBV-induced pathogenesis. A full understanding of HBV RNA transcription and the biological functions of HBV RNA may open a new avenue for the development of novel HBV therapeutics.

A Highly Sensitive and Robust Method for Hepatitis B Virus Covalently Closed Circular DNA Detection in Single Cells and Serum

Despite implications of persistence of hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) in the development of hepatocellular carcinoma (HCC), little is known about serum cccDNA in HBV-infected diseases. We developed a cccDNA-selective droplet digital PCR (ddPCR) to assess cccDNA content and dynamics across different stages of HCC development. One hundred forty-seven serum samples and 35 formalin-fixed, paraffin-embedded tumor tissues were derived from patients with HCC or HBV hepatitis/cirrhosis. After specific amplification and selective digestion, probe-based ddPCR was used to quantify cccDNA copy numbers in single cells and clinical samples. The cccDNA in single HepG2.2.15 cells ranged from 0 to 10.8 copies/cell. Compared with non-HCC patients, HCC patients showed a higher cccDNA-positive rate (89.9% versus 53.2%; P = 4.22 × 10^-6) and increased serum cccDNA contents (P = 0.002 and P = 0.041 for hepatitis and cirrhosis patients, respectively). Serum cccDNA ranged from 84 to 1.07 × 10⁵ copies/mL. Quantification of serum cccDNA and HBV-DNA was an effective way to discriminate HCC patients from non-HCC patients, with areas under the curve of receiver operating characteristic of 0.847 (95% CI, 0.759-0.935; sensitivity, 74.5%; specificity, 93.7%). cccDNA-selective ddPCR is sensitive to detect cccDNA in single cells and different clinical samples. Combined analysis of serum cccDNA and HBV-DNA may be a promising strategy for HBV-induced HCC surveillance and antiviral therapy evaluation.