C-terminal truncated hepatitis B virus X protein promotes hepatocellular carcinogenesis through induction of cancer and stem cell-like properties

Reactivation of hepatitis B virus infection – an important aspect of multifaceted problem

In this editorial we comment on the article published in the recent issue of the World Journal of Gastroenterology. We focus specifically on the problem of occult hepatitis B virus (HBV) infection, that is a result of previous hepatitis B (PHB) and a source for reactivation of HBV. The prevalence of PHB is underestimated due to the lack of population testing programs. However, this condition not only complicate anticancer treatment, but may be responsible for the development of other diseases, like cancer or autoimmune disorders. Here we unveil possible mechanisms responsible for realization of these processes and suggest practical approaches for diagnosis and treatment.

Cancer stem cells: advances in knowledge and implications for cancer therapy

Cancer stem cells (CSCs), a small subset of cells in tumors that are characterized by self-renewal and continuous proliferation, lead to tumorigenesis, metastasis, and maintain tumor heterogeneity. Cancer continues to be a significant global disease burden. In the past, surgery, radiotherapy, and chemotherapy were the main cancer treatments. The technology of cancer treatments continues to develop and advance, and the emergence of targeted therapy, and immunotherapy provides more options for patients to a certain extent. However, the limitations of efficacy and treatment resistance are still inevitable. Our review begins with a brief introduction of the historical discoveries, original hypotheses, and pathways that regulate CSCs, such as WNT/β-Catenin, hedgehog, Notch, NF-κB, JAK/STAT, TGF-β, PI3K/AKT, PPAR pathway, and their crosstalk. We focus on the role of CSCs in various therapeutic outcomes and resistance, including how the treatments affect the content of CSCs and the alteration of related molecules, CSCs-mediated therapeutic resistance, and the clinical value of targeting CSCs in patients with refractory, progressed or advanced tumors. In summary, CSCs affect therapeutic efficacy, and the treatment method of targeting CSCs is still difficult to determine. Clarifying regulatory mechanisms and targeting biomarkers of CSCs is currently the mainstream idea.

Cancer stem cell-immune cell crosstalk in the tumor microenvironment for liver cancer progression

Crosstalk between cancer cells and the immune microenvironment is determinant for liver cancer progression. A tumor subpopulation called liver cancer stem cells (CSCs) significantly accounts for the initiation, metastasis, therapeutic resistance, and recurrence of liver cancer. Emerging evidence demonstrates that the interaction between liver CSCs and immune cells plays a crucial role in shaping an immunosuppressive microenvironment and determining immunotherapy responses. This review sheds light on the bidirectional crosstalk between liver CSCs and immune cells for liver cancer progression, as well as the underlying molecular mechanisms after presenting an overview of liver CSCs characteristic and their microenvironment. Finally, we discuss the potential application of liver CSCs-targeted immunotherapy for liver cancer treatment.

Stemness markers in hepatocellular carcinoma of Eastern vs. Western population: Etiology matters?

Hepatocellular carcinoma (HCC) is one of the most common cancers with a high mortality rate. HCC development is associated with its underlying etiologies, mostly caused by infection of chronic hepatitis B virus (HBV) and hepatitis C virus (HCV), alcohol, non-alcoholic fatty liver disease, and exposure to aflatoxins. These variables, together with human genetic susceptibility, contribute to HCC molecular heterogeneity, including at the cellular level. HCC initiation, tumor recurrence, and drug resistance rates have been attributed to the presence of liver cancer stem cells (CSC). This review summarizes available data regarding whether various HCC etiologies may be associated to the appearance of CSC biomarkers. It also described the genetic variations of tumoral tissues obtained from Western and Eastern populations, in particular to the oncogenic effect of HBV in the human genome.

Overview of hepatocellular carcinoma: from molecular aspects to future therapeutic options

Hepatocellular carcinoma (HCC) is the seventh most highly prevalent malignant tumor globally and the second most common cause of mortality. HCC develops with complex pathways that occur through multistage biological processes. Non-alcoholic fatty liver disease, metabolic-associated fatty liver disease, alcoholic liver disease, autoimmune hepatitis, hepatitis B, and hepatitis C are the causative etiologies of HCC. HCC develops as a result of epigenetic changes, protein-coding gene mutations, and altered signaling pathways. Biomarkers and potential therapeutic targets for HCC open up new possibilities for treating the disease. Immune checkpoint inhibitors are included in the treatment options in combination with molecular targeted therapy.

A state-of-the-art review on the NRF2 in Hepatitis virus-associated liver cancer

According to a paper released and submitted to WHO by IARC scientists, there would be 905,700 new cases of liver cancer diagnosed globally in 2020, with 830,200 deaths expected as a direct result. Hepatitis B virus (HBV) hepatitis C virus (HCV), and hepatitis D virus (HDV) all play critical roles in the pathogenesis of hepatocellular carcinoma (HCC), despite the rising prevalence of HCC due to non-infectious causes. Liver cirrhosis and HCC are devastating consequences of HBV and HCV infections, which are widespread worldwide. Associated with a high mortality rate, these infections cause about 1.3 million deaths annually and are the primary cause of HCC globally. In addition to causing insertional mutations due to viral gene integration, epigenetic alterations and inducing chronic immunological dysfunction are all methods by which these viruses turn hepatocytes into cancerous ones. While expanding our knowledge of the illness, identifying these pathways also give possibilities for novel diagnostic and treatment methods. Nuclear factor erythroid 2-related factor 2 (NRF2) activation is gaining popularity as a treatment option for oxidative stress (OS), inflammation, and metabolic abnormalities. Numerous studies have shown that elevated Nrf2 expression is linked to HCC, providing more evidence that Nrf2 is a critical factor in HCC. This aberrant Nrf2 signaling drives cell proliferation, initiates angiogenesis and invasion, and imparts drug resistance. As a result, this master regulator may be a promising treatment target for HCC. In addition, the activation of Nrf2 is a common viral effect that contributes to the pathogenesis, development, and chronicity of virus infection. However, certain viruses suppress Nrf2 activity, which is helpful to the virus in maintaining cellular homeostasis. In this paper, we discussed the influence of Nrf2 deregulation on the viral life cycle and the pathogenesis associated with HBV and HCV. We summed up the mechanisms for the modulation of Nrf2 that are deregulated by these viruses. Moreover, we describe the molecular mechanism by which Nrf2 is modulated in liver cancer, liver cancer stem cells (LCSCs), and liver cancer caused by HBV and HCV. Video Abstract.

Hepatitis B Virus-Associated Hepatocellular Carcinoma

Hepatitis B virus (HBV) is DNA-based virus, member of the Hepadnaviridae family, which can cause liver disease and increased risk of hepatocellular carcinoma (HCC) in infected individuals, replicating within the hepatocytes and interacting with several cellular proteins. Chronic hepatitis B can progressively lead to liver cirrhosis, which is an independent risk factor for HCC. Complications as liver decompensation or HCC impact the survival of HBV patients and concurrent HDV infection worsens the disease. The available data provide evidence that HBV infection is associated with the risk of developing HCC with or without an underlying liver cirrhosis, due to various direct and indirect mechanisms promoting hepatocarcinogenesis. The molecular profile of HBV-HCC is extensively and continuously under study, and it is the result of altered molecular pathways, which modify the microenvironment and lead to DNA damage. HBV produces the protein HBx, which has a central role in the oncogenetic process. Furthermore, the molecular profile of HBV-HCC was recently discerned from that of HDV-HCC, despite the obligatory dependence of HDV on HBV. Proper management of the underlying HBV-related liver disease is fundamental, including HCC surveillance, viral suppression, and application of adequate predictive models. When HBV-HCC occurs, liver function and HCC characteristics guide the physician among treatment strategies but always considering the viral etiology in the treatment choice.

Hepatitis B virus DNA integration as a novel biomarker of hepatitis B virus-mediated pathogenetic properties and a barrier to the current strategies for hepatitis B virus cure

Chronic infection with Hepatitis B Virus (HBV) is a major cause of liver-related morbidity and mortality worldwide. HBV-DNA integration into the human genome is recognized as a frequent event occurring during the early phases of HBV infection and characterizing the entire course of HBV natural history. The development of refined molecular biology technologies sheds new light on the functional implications of HBV-DNA integration into the human genome, including its role in the progression of HBV-related pathogenesis and in triggering the establishment of pro-oncogenic mechanisms, promoting the development of hepatocellular carcinoma. The present review provides an updated and comprehensive overview of the current body of knowledge on HBV-DNA integration, focusing on the molecular mechanisms underlying HBV-DNA integration and its occurrence throughout the different phases characterizing the natural history of HBV infection. Furthermore, here we discuss the main clinical implications of HBV integration as a biomarker of HBV-related pathogenesis, particularly in reference to hepatocarcinogenesis, and how integration may act as a barrier to the achievement of HBV cure with current and novel antiviral therapies. Overall, a more refined insight into the mechanisms and functionality of HBV integration is paramount, since it can potentially inform the design of ad hoc diagnostic tools with the ability to reveal HBV integration events perturbating relevant intracellular pathways and for identifying novel therapeutic strategies targeting alterations directly related to HBV integration.

Whole exome HBV DNA integration is independent of the intrahepatic HBV reservoir in HBeAg-negative chronic hepatitis B

OBJECTIVE

The involvement of HBV DNA integration in promoting hepatocarcinogenesis and the extent to which the intrahepatic HBV reservoir modulates liver disease progression remains poorly understood. We examined the intrahepatic HBV reservoir, the occurrence of HBV DNA integration and its impact on the hepatocyte transcriptome in hepatitis B 'e' antigen (HBeAg)-negative chronic hepatitis B (CHB).

DESIGN

Liver tissue from 84 HBeAg-negative patients with CHB with low (n=12), moderate (n=25) and high (n=47) serum HBV DNA was analysed. Covalently closed circular DNA (cccDNA), pregenomic RNA (pgRNA) were evaluated by quantitative PCR, whole exome and transcriptome sequencing was performed by Illumina, and the burden of HBV DNA integrations was evaluated by digital droplet PCR.

RESULTS

Patients with low and moderate serum HBV DNA displayed comparable intrahepatic cccDNA and pgRNA, significantly lower than in patients with high HBV DNA, while hepatitis B core-related antigen correlated strongly with the intrahepatic HBV reservoir, reflecting cccDNA quantity. Whole exome integration was detected in a significant number of patients (55.6%, 14.3% and 25% in high, moderate and low viraemic patients, respectively), at a frequency ranging from 0.5 to 157 integrations/1000 hepatocytes. Hepatitis B surface antigen >5000 IU/mL predicted integration within the exome and these integrations localised in genes involved in hepatocarcinogenesis, regulation of lipid/drug metabolism and antiviral/inflammatory responses. Transcript levels of specific genes, including the proto-oncogene hRAS, were higher in patients with HBV DNA integration, supporting an underlying oncogenic risk in patients with low-level to moderate-level viraemia.

CONCLUSIONS

HBV DNA integration occurs across all HBeAg-negative patients with CHB, including those with a limited HBV reservoir; localising in genes involved in carcinogenesis and altering the hepatocyte transcriptome.

Senescence in HBV-, HCV- and NAFLD- Mediated Hepatocellular Carcinoma and Senotherapeutics: Current Evidence and Future Perspective

Cell senescence constitutes a physiological process that serves as protection from malignant transformation of cells. However, recent scientific discoveries also identify cell senescence as pivotal in hepatocellular cancer (HCC) biology. The review herein aimed to accumulate evidence on senescence as a mediator of HCC occurrence in hepatitis B (HBV), C (HCV) virus infections, and non-alcoholic fatty liver disease (NAFLD). In HBV infection, the carcinogenic HBV X protein frequently mutates during chronic infection, and subsequently exhibits different effects on senescence. In HCV infection, senescent non-functional T-cells do not effectively clear pre-malignant hepatocytes. Furthermore, the HCV Core protein inhibits the occurrence of normal stress-induced hepatocyte senescence, allowing damaged cells to maintain their proliferative potential. In NAFLD-mediated HCC, current data point towards the gut microbiome and hepatic stellate cell senescence. Additionally, senescence contributes in the development of resistance in targeted therapies, such as sorafenib. Finally, the promising role of senotherapeutics in HCC was also explored. Overall, although we may still be at a primitive stage in fully unraveling the role of senescence in cancer, it seems that understanding and harnessing senescence may have the potential to revolutionize the way we treat hepatocellular cancer.

Regulators of liver cancer stem cells

Hepatocellular carcinoma (HCC) is a leading cause of cancer deaths. It is often detected at a stage when there are few therapeutic options. Liver cancer stem cells (LCSCs) are highly tumorigenic and resistant to chemotherapy and radiation therapy. Their presence in HCC is a major reason why HCC is difficult to treat. The development of LCSCs is regulated by a variety of factors. This review summarizes recent advances on the factors that regulate the development of LCSCs. Due to the importance of LCSCs in the development of HCC, a better understanding of how LCSCs are regulated will help to improve the treatments for HCC patients.

Emerging Regulatory Mechanisms Involved in Liver Cancer Stem Cell Properties in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the predominant form of primary liver cancer and one of the leading causes of cancer-related deaths worldwide. A growing body of evidence supports the hypothesis that HCC is driven by a population of cells called liver cancer stem cells (LCSCs). LCSCs have been proposed to contribute to malignant HCC progression, including promoting tumor occurrence and growth, mediating tumor metastasis, and treatment resistance, but the regulatory mechanism of LCSCs in HCC remains unclear. Understanding the signaling pathways responsible for LCSC maintenance and survival may provide opportunities to improve patient outcomes. Here, we review the current literature about the origin of LCSCs and the niche composition, describe the current evidence of signaling pathways that mediate LCSC stemness, then highlight several mechanisms that modulate LCSC properties in HCC progression, and finally, summarize the new developments in therapeutic strategies targeting LCSCs markers and regulatory pathways.

Targeting Farnesoid X receptor (FXR) for developing novel therapeutics against cancer

Cancer is one of the lethal diseases that arise due to the molecular alterations in the cell. One of those alterations associated with cancer corresponds to differential expression of Farnesoid X receptor (FXR), a nuclear receptor regulating bile, cholesterol homeostasis, lipid, and glucose metabolism. FXR is known to regulate several diseases, including cancer and cardiovascular diseases, the two highly reported causes of mortality globally. Recent studies have shown the association of FXR overexpression with cancer development and progression in different types of cancers of breast, lung, pancreas, and oesophagus. It has also been associated with tissue-specific and cell-specific roles in various cancers. It has been shown to modulate several cell-signalling pathways such as EGFR/ERK, NF-κB, p38/MAPK, PI3K/AKT, Wnt/β-catenin, and JAK/STAT along with their targets such as caspases, MMPs, cyclins; tumour suppressor proteins like p53, C/EBPβ, and p-Rb; various cytokines; EMT markers; and many more. Therefore, FXR has high potential as novel biomarkers for the diagnosis, prognosis, and therapy of cancer. Thus, the present review focuses on the diverse role of FXR in different cancers and its agonists and antagonists.

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.

Viral Biomarkers for Hepatitis B Virus-Related Hepatocellular Carcinoma Occurrence and Recurrence

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide and the fourth leading cause of cancer-related death. The most common risk factor for developing HCC is chronic infection with hepatitis B virus (HBV). Early stages of HBV-related HCC (HBV-HCC) are generally asymptomatic. Moreover, while serum alpha-fetoprotein (AFP) and abdominal ultrasound are widely used to screen for HCC, they have poor sensitivity. Thus, HBV-HCC is frequently diagnosed at an advanced stage, in which there are limited treatment options and high mortality rates. Serum biomarkers with high sensitivity and specificity are crucial for earlier diagnosis of HCC and improving survival rates. As viral-host interactions are key determinants of pathogenesis, viral biomarkers may add greater diagnostic power for HCC than host biomarkers alone. In this review, we summarize recent research on using virus-derived biomarkers for predicting HCC occurrence and recurrence; including circulating viral DNA, RNA transcripts, and viral proteins. Combining these viral biomarkers with AFP and abdominal ultrasound could improve sensitivity and specificity of early diagnosis, increasing the survival of patients with HBV-HCC. In the future, as the mechanisms that drive HBV-HCC to become clearer, new biomarkers may be identified which can further improve early diagnosis of HBV-HCC.

Differential roles of farnesoid X receptor (FXR) in modulating apoptosis in cancer cells

Cancer is one of the leading causes of mortality in the world. The conventional treatment strategies of cancer are surgery, radiation, and chemotherapy. However, in the advanced stage of the disease chemotherapy is the prime treatment and it is effective in only less than 10% of the patients. Therefore, there is an urgent need to find out novel therapeutic targets and delineate the mechanism of action of these targets for better management of this disease. Recent studies have shown that some of the proteins have differential role in different cancers. Therefore, it is pertinent that the targeting of these proteins should be based on the type of cancer. The nuclear receptor, FXR, is one of the vital proteins that regulate cell apoptosis. Besides, it also regulates other processes such as cell proliferation, angiogenesis, invasion, and migration. Studies suggest that the low or high expression of FXR is associated with the progression of carcinogenesis depending on the cancer types. Due to the diverse expression, it functions as both tumor suppressor and promoter. Previous studies suggest the overexpression of FXR in breast, lung, esophageal, and prostate cancer, which is related to poor survival and poor prognosis in patients. Therefore, targeting FXR with agonists and antagonists play different outcome in different cancers. Hence, this review describes the role of FXR in different cancers and the role of its inhibitors and activators for the prevention and treatment of various cancers.

The Role of IGF/IGF-1R Signaling in Hepatocellular Carcinomas: Stemness-Related Properties and Drug Resistance

Insulin-like Growth Factor (IGF)/IGF-1 Receptor (IGF-1R) signaling is known to regulate stem cell pluripotency and differentiation to trigger cell proliferation, organ development, and tissue regeneration during embryonic development. Unbalanced IGF/IGF-1R signaling can promote cancer cell proliferation and activate cancer reprogramming in tumor tissues, especially in the liver. Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death, with a high incidence and mortality rate in Asia. Most patients with advanced HCC develop tyrosine kinase inhibitor (TKI)-refractoriness after receiving TKI treatment. Dysregulation of IGF/IGF-1R signaling in HCC may activate expression of cancer stemness that leads to TKI refractoriness and tumor recurrence. In this review, we summarize the evidence for dysregulated IGF/IGF-1R signaling especially in hepatitis B virus (HBV)-associated HCC. The regulation of cancer stemness expression and drug resistance will be highlighted. Current clinical treatments and potential therapies targeting IGF/IGF-1R signaling for the treatment of HCC will be discussed.

Partial abrogation of FXR-KNG1 signaling by carboxyl-terminal truncated HBx-C30 in hepatitis B virus-associated hepatocellular carcinoma

Hepatitis B virus (HBV) X protein (HBx) is a key regulator of HBV-associated hepatocarcinogenesis. C-terminal-truncated HBx is frequently detected in hepatocellular carcinoma (HCC). The role of HBx, especially C-terminal-truncated HBx, in HCC pathogenesis has been controversial. To elucidate the biological role of C-terminal-truncated HBx underlying HBV-associated hepato-oncogenesis, we constructed a vector expressing HBx-C30 (deletion of 30 aa from the C terminus of HBx) and functionally analyzed its regulation on farnesoid X receptor (FXR) signaling, which is known to inhibit hepatocarcinogenesis. In the present study, we found full-length HBx and HBx C-terminal truncation coexist in HCC, and both full length HBx and HBx-C30 can activate FXR signaling. Moreover, HBx-C30 weakly coactivates FXR-KNG1 signaling compared to full-length HBx.

Immunotherapy for targeting cancer stem cells in hepatocellular carcinoma

The rapid development and remarkable success of checkpoint inhibitors have provided significant breakthroughs in cancer treatment, including hepatocellular carcinoma (HCC). However, only 15-20% of HCC patients can benefit from checkpoint inhibitors. Cancer stem cells (CSCs) are responsible for recurrence, metastasis, and local and systemic therapy resistance in HCC. Accumulating evidence has suggested that HCC CSCs can create an immunosuppressive microenvironment through certain intrinsic and extrinsic mechanisms, resulting in immune evasion. Intrinsic evasion mechanisms mainly include activation of immune-related CSC signaling pathways, low-level expression of antigen presenting molecules, and high-level expression of immunosuppressive molecules. External evasion mechanisms are mainly related to HBV/HCV infection, alcoholic/nonalcoholic steatohepatitis, hypoxia stimulation, abnormal angiogenesis, and crosstalk between CSCs and immune cells. A better understanding of the complex mechanisms of CSCs involved in immune evasion will contribute to therapies for HCC. Here we will outline the detailed mechanisms of immune evasion for CSCs, and provide an overview of the current immunotherapies targeting CSCs in HCC.

Mechanisms of Hepatitis B Virus-Induced Hepatocarcinogenesis

Hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC). There are approximately 250 million people in the world that are chronically infected by this virus, resulting in nearly 1 million deaths every year. Many of these patients die from severe liver diseases, including HCC. HBV may induce HCC through the induction of chronic liver inflammation, which can cause oxidative stress and DNA damage. However, many studies also indicated that HBV could induce HCC via the alteration of hepatocellular physiology that may involve genetic and epigenetic changes of the host DNA, the alteration of cellular signaling pathways, and the inhibition of DNA repair mechanisms. This alteration of cellular physiology can lead to the accumulation of DNA damages and the promotion of cell cycles and predispose hepatocytes to oncogenic transformation.

Molecular mechanisms of viral hepatitis induced hepatocellular carcinoma

Chronic infection with viral hepatitis affects half a billion individuals worldwide and can lead to cirrhosis, cancer, and liver failure. Liver cancer is the third leading cause of cancer-associated mortality, of which hepatocellular carcinoma (HCC) represents 90% of all primary liver cancers. Solid tumors like HCC are complex and have heterogeneous tumor genomic profiles contributing to complexity in diagnosis and management. Chronic infection with hepatitis B virus (HBV), hepatitis delta virus (HDV), and hepatitis C virus (HCV) are the greatest etiological risk factors for HCC. Due to the significant role of chronic viral infection in HCC development, it is important to investigate direct (viral associated) and indirect (immune-associated) mechanisms involved in the pathogenesis of HCC. Common mechanisms used by HBV, HCV, and HDV that drive hepatocarcinogenesis include persistent liver inflammation with an impaired antiviral immune response, immune and viral protein-mediated oxidative stress, and deregulation of cellular signaling pathways by viral proteins. DNA integration to promote genome instability is a feature of HBV infection, and metabolic reprogramming leading to steatosis is driven by HCV infection. The current review aims to provide a brief overview of HBV, HCV and HDV molecular biology, and highlight specific viral-associated oncogenic mechanisms and common molecular pathways deregulated in HCC, and current as well as emerging treatments for HCC.

Hepatitis B virus X gene mutants emerge during antiviral therapy and increase cccDNA levels to compensate for replication suppression

BACKGROUND

Hepatitis B virus (HBV) X gene (HBx) mutants can develop during the natural course of chronic HBV infection. However, little is known about whether the emergence of HBx mutants during long-term antiviral therapy is an adaptation of HBV to antiviral stress. This study was to identify HBx mutants that emerged in patients experiencing Lamivudine resistance or suboptimal treatment.

METHODS

Forty-six Lamivudine-resistant patients and 46 patients with suboptimal treatment responses to Entecavir were enrolled in this study. HBx mutants were identified by sequence analysis and their roles in the HBV replication cycle were characterized.

RESULTS

We show that deletion/truncation/insertion mutations were only detected in the Lamivudine resistance group, while synonymous mutations were found in both groups. Follow-up analyses revealed that five patients in the Lamivudine group developed hepatocellular carcinoma, while patients in the Entecavir group did not. These mutants were characterized by a significant decrease in transactivation of the pre-S1 promoter, and varying effects on transactivation of the X promoter. Co-transfection of HBx-mutant plasmid and HBV replication-competent clone into HepG2 cells resulted in increased nuclear-to-cytoplamic HBV core antigen, HBV-DNA ratios, and nuclear covalently closed circular DNA (cccDNA). Antiviral drug sensitivity assays revealed that these mutants exhibited a compensatory effect to counteract antiviral drug suppression, resulting in elevated secretory HBV-DNA levels.

CONCLUSIONS

Our study demonstrates that HBx mutants can emerge during Lamivudine or Entecavir therapy. These mutants exhibit altered transactivation of the HBV pre-S1 and X promoters, leading to increased cccDNA levels to compensate for replication suppression.

Insights into Hepatitis B Virus DNA Integration-55 Years after Virus Discovery

Hepatitis B virus (HBV), which was discovered in 1965, is a threat to global public health. HBV infects human hepatocytes and leads to acute and chronic liver diseases, and there is no cure. In cells infected by HBV, viral DNA can be integrated into the cellular genome. HBV DNA integration is a complicated process during the HBV life cycle. Although HBV integration normally results in replication-incompetent transcripts, it can still act as a template for viral protein expression. Of note, it is a primary driver of hepatocellular carcinoma (HCC). Recently, with the development of detection methods and research models, the molecular biology and the pathogenicity of HBV DNA integration have been better revealed. Here, we review the advances in the research of HBV DNA integration, including molecular mechanisms, detection methods, research models, the effects on host and viral gene expression, the role of HBV integrations in the pathogenesis of HCC, and potential treatment strategies. Finally, we discuss possible future research prospects of HBV DNA integration.

•

HBV DNA integration is associated with hepatocarcinogenesis via multiple mechanisms

•

HBV double-stranded linear DNA (dslDNA) is the dominant substrate for integration into the host genome

•

The insertion sites of HBV DNA integration occur throughout the whole host genome using the NHEJ or MMEJ DNA repair pathway

•

HBV DNA integration should be used as a clinical indicator for disease monitoring and treatment of patients with HBV infection

Cancer stemness in hepatocellular carcinoma: mechanisms and translational potential

Cancer stemness, referring to the stem-cell-like phenotype of cancer cells, has been recognised to play important roles in different aspects of hepatocarcinogenesis. A number of well-established cell-surface markers already exist for liver cancer stem cells, with potential new markers of liver cancer stem cells being identified. Both genetic and epigenetic factors that affect various signalling pathways are known to contribute to cancer stemness. In addition, the tumour microenvironment—both physical and cellular—is known to play an important role in regulating cancer stemness, and the potential interaction between cancer stem cells and their microenvironment has provided insight into the regulation of the tumour-initiating ability as well as the cellular plasticity of liver CSCs. Potential specific therapeutic targeting of liver cancer stemness is also discussed. With increased knowledge, effective druggable targets might be identified, with the aim of improving treatment outcome by reducing chemoresistance.

The Cancer Stem Cell in Hepatocellular Carcinoma

The recognition of intra-tumoral cellular heterogeneity has given way to the concept of the cancer stem cell (CSC). According to this concept, CSCs are able to self-renew and differentiate into all of the cancer cell lineages present within the tumor, placing the CSC at the top of a hierarchical tree. The observation that these cells—in contrast to bulk tumor cells—are able to exclusively initiate new tumors, initiate metastatic spread and resist chemotherapy implies that CSCs are solely responsible for tumor recurrence and should be therapeutically targeted. Toward this end, dissecting and understanding the biology of CSCs should translate into new clinical therapeutic approaches. In this article, we review the CSC concept in cancer, with a special focus on hepatocellular carcinoma.

C-terminal truncated HBx reduces doxorubicin cytotoxicity via ABCB1 upregulation in Huh-7 hepatocellular carcinoma cells

Hepatitis B virus (HBV) encoding the HBV x protein (HBx) is a known causative agent of hepatocellular carcinoma (HCC). Its pathogenic activities in HCC include interference with several signaling pathways associated with cell proliferation and apoptosis. Mutant C-terminal-truncated HBx isoforms are frequently found in human HCC and have been shown to enhance proliferation and invasiveness leading to HCC malignancy. We investigated the molecular mechanism of the reduced doxorubicin cytotoxicity by C-terminal truncated HBx. Cells transfected with C-terminal truncated HBx exhibited reduced cytotoxicity to doxorubicin compared to those transfected with full-length HBx. The doxorubicin resistance of cells expressing C-terminal truncated HBx correlated with upregulation of the ATP binding cassette subfamily B member 1(ABCB1) transporter, resulting in the enhanced efflux of doxorubicin. Inhibiting the activity of ABCB1 and silencing ABCB1 expression by small interfering ribonucleic acid (siRNA) increased the cytotoxicity of doxorubicin. These results indicate that elevated ABCB1 expression induced by C-terminal truncation of HBx was responsible for doxorubicin resistance in HCC. Hence, co-treatment with an ABCB1 inhibitor and an anticancer agent may be effective for the treatment of patients with liver cancer containing the C-terminal truncated HBx.

APLN promotes hepatocellular carcinoma through activating PI3K/Akt pathway and is a druggable target

Background: The pathogenesis of hepatocellular carcinoma (HCC) is a multistep process contributed by the accumulation of molecular alterations. We identified Apelin (APLN) as an outlier gene up-regulated in hepatocellular carcinoma (HCC) through RNA-Seq and microarray analysis. We aimed to investigate its function, mechanism of action and clinical implication in HCC. Methods: Gene expression and clinical implication of APLN were assessed in multiple human HCC cohorts. Ectopic expression and silencing of APLN were performed to determine its function. The therapeutic potential of APLN and its downstream pathway was investigated using in vitro and in vivo models. Results: APLN overexpression was commonly observed in more than 80% of HCCs and independently predicted poorer survival of patients in three independent HCC cohorts. Apelin up-regulation was mediated by active β-catenin, which binds to the APLN promoter to induce transcription. Ectopic APLN expression in HCC cells promoted cell proliferation, accelerated G1/S progression and inhibited apoptosis, whilst APLN knockdown exerted opposite effects in vitro and inhibited HCC xenograft growth in mice. Mechanistically, APLN activated phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway via APLN receptor, leading to increased expression of phospho-glycogen synthase kinase 3β (p-GSK3β) and cyclin D1. Pharmacological targeting of APLN by ML221 was safe and effective in inhibiting APLN-PI3K/Akt cascade and HCC growth in vitro and in vivo. Conclusions: Our findings unraveled an oncogenic role of APLN in HCC, and that targeting of APLN might be a promising for HCC treatment. APLN may serve as an independent prognostic factor for HCC patients.

Hepatitis B virus X protein: The X factor in chronic hepatitis B virus disease progression

Introduction

Hepatitis B virus (HBV) is the most common aetiological factor causing hepatocellular carcinoma (HCC). HBx gene plays an enigmatic role in HBV-related HCC. In this study we have analysed amino acid substitutions in HBx from HBV-infected individuals of different clinical stages.

Materials and Methods

HBV-infected individuals (n = 93) were recruited in the study. DNA was extracted from plasma, amplified, and DNA sequencing was performed using specific primers targeting HBx gene (540 bp).

Results

Among the study participants, 57% had chronic HBV infection, 30% had chronic liver disease (CLD) and 13% had HBV related HCC. Genotypes such as D1, D2, D3, A1, C2 and B2 were identified of which genotype D2 was predominant (78%). HBxC-terminal deletion was observed in four hepatitis B e antigen (HBeAg) negative participants with CLD. The frequency of aminoacid substitution in proapoptotic domain was higher in HBeAg negative participants including I127V (34%), K130M (34%), V131I (40%). The frequency of double mutation (K130M+V131I) and triple mutation (I127V+K130M+V131I) were found to be higher (32% and 36%) in HBeAg negative participants. Also, we identified L5M substitution (4.3%) in HBeAg positive participants with advanced liver disease.

Conclusion

In HBx gene, aminoacid substitutions at positions 127, 130, 131 are associated with poor expression of HBeAg. We suggest screening for HBx aminoacid substitutions especially in patients with HBeAg negative chronic HBV infection to predict the clinical outcome and enable early treatment to prevent disease progression.

Hepatitis B virus-X protein regulates high mobility group box 1 to promote the formation of hepatocellular carcinoma

Hepatitis B virus (HBV) infection is a risk factor for hepatocellular carcinoma (HCC). HBV X protein (HBx) is an important carcinogen for HBV-induced HCC. When the HBx gene is integrated into the host cell genome, it is difficult to eradicate. The identification of an effective target to inhibit the oncogenic function of HBx is therefore critically important. The present study demonstrated that HBx, particularly truncated HBx, was expressed in several HBV-derived cell lines (e.g., Hep3B and SNU423). By analyzing data from The Cancer Genome Atlas, it was revealed that high expression of high mobility group box 1 (HMGB1) was associated with the process and prognosis of HCC. In vitro experiments confirmed that HBx could regulate the expression of HMGB1 and knockdown of HMGB1 could decrease the ability of HBx to promote cellular proliferation. HBx could also upregulate six transcription factors (GATA binding protein 3, Erb-B2 receptor tyrosine kinase 3, heat shock transcription factor 1, nuclear factor κB subunit 1, TATA-box binding protein and Kruppel-like factor 4), which could directly regulate HMGB1. By analyzing genes that are co-expressed with HMGB1, several signaling pathways associated with the development of HCC were identified. HBx and HMGB1 were revealed to be involved in these pathways, which may be the mechanism by which HBx promotes HCC by regulating HMGB1. These findings suggested that HMGB1 may be an effective target for inhibiting HBV-induced HCC.

Episomal HBV persistence within transcribed host nuclear chromatin compartments involves HBx

Background

In hepatocyte nuclei, hepatitis B virus (HBV) genomes occur episomally as covalently closed circular DNA (cccDNA). The HBV X protein (HBx) is required to initiate and maintain HBV replication. The functional nuclear localization of cccDNA and HBx remains unexplored.

Results

To identify virus–host genome interactions and the underlying nuclear landscape for the first time, we combined circular chromosome conformation capture (4C) with RNA-seq and ChIP-seq. Moreover, we studied HBx-binding to HBV episomes. In HBV-positive HepaRG hepatocytes, we observed preferential association of HBV episomes and HBx with actively transcribed nuclear domains on the host genome correlating in size with constrained topological units of chromatin. Interestingly, HBx alone occupied transcribed chromatin domains. Silencing of native HBx caused reduced episomal HBV stability.

Conclusions

As part of the HBV episome, HBx might stabilize HBV episomal nuclear localization. Our observations may contribute to the understanding of long-term episomal stability and the facilitation of viral persistence. The exact mechanism by which HBx contributes to HBV nuclear persistence warrants further investigations.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0204-2) contains supplementary material, which is available to authorized users.

Associations between serum HBX quasispecies and their integration in hepatocellular carcinoma

HBV quasispecies are closely related to the course and outcome of liver disease. However, whether the complexity and diversity of HBX quasispecies affects its integration in the liver cell and thereby enhances the resultant carcinogenesis is still not clear. 15 HCC patients were recruited; genomic DNA and HBV DNA were extracted from liver cancer tissue and serum respectively. The integrated HBX fragment in liver cancer tissue was amplified by Alu repeat sequence-polymerase chain reaction (Alu-PCR) and sequenced. The serum HBX gene was amplified by nested PCR and sequenced. Quasispecies complexity and diversity, phylogenetic characteristics, lymphocyte count and survival time between HBX-integrated and HBX-unintegrated patients were evaluated. Results showed that the integrated HBX fragment was detected in the tumor tissue of nine patients, and the integration rate was 60.00% (9/15). Compared with the HBX-unintegrated patients, the HBX-integrated patients had a higher quasispecies complexity (P=0.028 and 0.004, at the nucleotide and amino acid levels, respectively). The HBX-integrated patients had a tendency of higher quasispecies diversity, lower lymphocyte count and the survival time. A total of 12 mutation sites were revealed in the HBX-integrated fragment after alignment with the reference sequence. In these, the HBX-integrated groups had significantly higher mutation frequencies at C1497T, A1630G, G1721A, A1762T/G1764A and A1774G. This study revealed influence factors of HBX integration both in virus and the host. The increased complexity and diversity of HBX quasispecies might destroy the host immune balance, and lead to HBX integration ultimately.

How Hepatitis B virus causes cirrhosis and liver cancer

Hepatitis B virus is a major pathogen infecting the liver, causing high morbidity and mortality worldwide, particularly in developing countries. The mechanism underlying progression from infections of Hepatitis B virus to cirrhosis and liver cancer is not fully determined. Here we propose that the HBV X protein traps protons and Cl^-, and induces the expression of collagen in the liver, which forms potent hydrogen bonds with trapped protons. The presence of collagen in the liver marks the progression to fibrosis. The X protein and collagen concertedly build up HCl locally, triggering disease advances to liver cancer in some patients with liver cirrhosis. The hypothesis can be tested in Hepatitis B primate model with the administration of calcium and weak acids to ascertain physiological changes and monitor tumorigenesis rate. The experiments will pave the way for better intervention of human infections with Hepatitis B virus.

Chronic viral hepatitis and its association with liver cancer

Chronic infection with hepatitis viruses represents the major causative factor for end-stage liver diseases, including liver cirrhosis and primary liver cancer (hepatocellular carcinoma, HCC). In this review, we highlight the current understanding of the molecular mechanisms that drive the hepatocarcinogenesis associated with chronic hepatitis virus infections. While chronic inflammation (associated with a persistent, but impaired anti-viral immune response) plays a major role in HCC initiation and progression, hepatitis viruses can also directly drive liver cancer. The mechanisms by which hepatitis viruses induce HCC include: hepatitis B virus DNA integration into the host cell genome; metabolic reprogramming by virus infection; induction of the cellular stress response pathway by viral gene products; and interference with tumour suppressors. Finally, we summarise the limitations of hepatitis virus-associated HCC model systems and the development of new techniques to circumvent these shortcomings.

HBV DNA Integration: Molecular Mechanisms and Clinical Implications

Chronic infection with the Hepatitis B Virus (HBV) is a major cause of liver-related morbidity and mortality. One peculiar observation in cells infected with HBV (or with closely‑related animal hepadnaviruses) is the presence of viral DNA integration in the host cell genome, despite this form being a replicative dead-end for the virus. The frequent finding of somatic integration of viral DNA suggests an evolutionary benefit for the virus; however, the mechanism of integration, its functions, and the clinical implications remain unknown. Here we review the current body of knowledge of HBV DNA integration, with particular focus on the molecular mechanisms and its clinical implications (including the possible consequences of replication-independent antigen expression and its possible role in hepatocellular carcinoma). HBV DNA integration is likely to influence HBV replication, persistence, and pathogenesis, and so deserves greater attention in future studies.

Defining the relationship between farsenoid X receptor, hepatitis B virus X protein and hepatocellular carcinoma: It's complicated

The relationship between hepatitis B virus X protein (HBx), farsenoid X receptor (FXR) and hepatocellular carcinoma (HCC) is a complicated one in that we have a viral protein interaction that can drive tumorigenesis or inhibit HCC depending upon transactivation of full-length or truncated HBx. In the current article the authors have elegantly described a system of HBx-FXR interaction that demonstrates inhibition of HCC tumor growth via activation of full-length HBx. The paper employs both in vivo and in vitro studies including using FXR knockout mice crossed with HBx induced mice. Overall, studies on the interaction between HBx and FXR have been riddled with complication and this paper sheds important light on the relationship that may be key in developing much needed therapies for HCC.

The evolving concept of liver cancer stem cells

Liver cancer is an often fatal malignant tumor with a high recurrence rate and chemoresistance. The major malignant phenotypes of cancer, including recurrence, metastasis, and chemoresistance, are related to the presence of cancer stem cells (CSCs). In the past few decades, CSCs have been identified and characterized in many tumors including liver cancer. Accumulated evidence has revealed many aspects of the biological behavior of liver CSCs and the mechanism of their regulation. Based on these findings, a number of studies have investigated eradication of liver CSCs. This review focuses on the recent advances in our understanding of the biology of liver CSCs and the development of strategies for their treatment.

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

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

HBV is a risk factor for poor patient prognosis after curative resection of hepatocellular carcinoma: A retrospective case-control study

Controversy exists regarding pathological factors affecting the prognosis of hepatocellular carcinoma (HCC) patients with hepatitis B virus (HBV-HCC). Their postoperative clinical behaviors and the exact HBV Deoxyribonucleic Acid (DNA) thresholds that distinguish good and poor prognoses are unknown. This study aimed to compare clinicopathological, pre- and postoperative clinical factors and overall and recurrence-free survival (RFS) between HBV-HCC patients and nonhepatitis B and nonhepatitis C HCC (NBC-HCC) patients to determine the optimal prognostic HBV DNA threshold.Data from 1440 patients with HBV-HCC and NBC-HCC who underwent curative hepatectomy were retrospectively analyzed.Liver function in the HBV-HCC group was significantly worse than in the NBC-HCC group. Compared with NBC-HCC patients, HBV-HCC patients had significantly more vascular invasion and advanced HCC. The HBV-HCC patients also had significantly worse liver function and more complications. Further survival analysis showed significantly lower overall and RFS rates and a higher early recurrence rate in the HBV-HCC group. Univariate analysis indicated that HBV was a risk factor for overall and RFS. Finally, X-tile analysis revealed that the optimal HBV DNA cutoff points for predicting RFS and overall survival in HCC patients were 10,100 and 12,800 IU/mL, respectively.After hepatectomy for HCC, HBV-HCC patients had more complications and a worse prognosis than NBC-HCC patients. Antiviral therapy should be considered before hepatectomy in patients with high (more than approximately 10 IU/mL) HBV DNA levels.

The secretome of MUSE cells contains factors that may play a role in regulation of stemness, apoptosis and immunomodulation

Mesenchymal stromal cells (MSCs) are a heterogeneous population, which contain several cell phenotypes: mesenchymal stem cells, progenitor cells, fibroblasts and other type of cells. Previously, we identified unique stem cells that we named multilineage-differentiating stress enduring (Muse) cells as one to several percent of MSCs of the bone marrow, adipose tissue and dermis. Among different cell populations in MSCs, Muse cells, positive for pluripotent surface marker SSEA-3, may represent cells responsible for pluripotent-like property of MSCs, since they express pluripotency genes, able to differentiated into triploblastic cells from a single cells and are self-renewable. MSCs release biologically active factors that have profound effects on local cellular dynamics. A thorough examination of MSC secretome seems essential for understanding the physiological functions exerted by these cells in our organism and also for rational cellular therapy design. In this setting, studies on secretome of Muse cells may shed light on pathways that are associated with their specific features. Our findings evidenced that secretomes of MSCs and Muse cells contain factors that regulate extracellular matrix remodeling, ox-redox activities and immune system. Muse cells appear to secrete factors that may preserve their stem cell features, allow survival under stress conditions and may contribute to their immunomodulation capacity. In detail, the proteins belonging to protein kinase A signaling, FXR/RXR activation and LXR/RXR activation pathways may play a role in regulation of Muse stem cell features. These last 2 pathways together with proteins associated with antigen presentation pathway and coagulation system may play a role in immunomodulation.

Hepatitis B Virus X Protein and Hepatocarcinogenesis

Chronic hepatitis B virus (HBV) infection is one of the most associated factors in hepatocarcinogenesis. HBV is able to integrate into the host genome and encode the multi-functional hepatitis B virus x protein (HBx). Although the mechanism between HBx and carcinogenesis is still elusive, recent studies have shown that HBx was able to influence various signaling pathways, as well as epigenetic and genetic processes. This review will examine and summarize recent literature about HBx’s role in these various processes.