Hepatitis B virus infection and the risk of hepatocellular carcinoma

Epidemiological studies have provided overwhelming evidence for a causal role of chronic hepatitis B virus(HBV) infection in the development of hepatocellular carcinoma(HCC).However,the pathogenesis of HBV infection and carcinogenesis of HBV-associated HCC are still elusive.This review will summarize the current knowledge on the mechanisms involved in HBV-related liver carcinogenesis.The role of HBV in tumor formation appears to be complex,and may involve both direct and indirect mechanisms.Integration of H...     

Hepatocellular carcinoma: The virus or the liver?

Hepatocellular carcinoma (HCC) represents a major public health problem being one of the most common causes of cancer-related deaths worldwide. Hepatitis B (HBV) and C viruses have been classified as oncoviruses and are responsible for the majority of HCC cases, while the role of hepatitis D virus (HDV) in liver carcinogenesis has not been elucidated. HDV/HBV coinfection is related to more severe liver damage than HBV mono-infection and recent studies suggest that HDV/HBV patients are at increased risk of developing HCC compared to HBV mono-infected patients. HBV is known to promote hepatocarcinogenesis via DNA integration into host DNA, disruption of molecular pathways by regulatory HBV x (HBx) protein and excessive oxidative stress. Recently, several molecular mechanisms have been proposed to clarify the pathogenesis of HDV-related HCC including activation of signalling pathways by specific HDV antigens, epigenetic dysregulation and altered gene expression. Alongside, ongoing chronic inflammation and impaired immune responses have also been suggested to facilitate carcinogenesis. Finally, cellular senescence seems to play an important role in chronic viral infection and inflammation leading to hepatocarcinogenesis. In this review, we summarize the current literature on the impact of HDV in HCC development and discuss the potential interplay between HBV, HDV and neighbouring liver tissue in liver carcinogenesis.     

Hepatocellular carcinoma and hepatitis B virus

Chronic hepatitis B is the most common cause of hepatocellular carcinoma (HCC) in Asia. Integration of hepatitis B virus (HBV) genome is likely an early event of carcinogenesis. The integrated HBV genome may activate neighboring cellular genes directly to offer a selective growth advantage to the liver cells. Production of hepatitis B X protein can act as a transactivator on various cellular genes for tumor development. Hepatic inflammation and cirrhosis also favors the process of carcinogenesis. Various viral factors associated with hepatocellular carcinoma development include HBV genotype, basal core promoter mutations, and high viral load. Polymorphisms at the androgen receptor-regulating genes and cytokine genes are possible host factors associated with HCC. This review article summarizes the pathogenesis of HBV-related carcinogenesis and the viral and host factors that may increase the risk of HCC development.     

Role of hepatitis B virus DNA integration in human hepatocarcinogenesis

Liver cancer ranks sixth in cancer incidence, and is the third leading cause of cancer-related deaths worldwide. Hepatocellular carcinoma (HCC) is the most common type of liver cancer, which arises from hepatocytes and accounts for approximately 70%-85% of cases. Hepatitis B virus (HBV) frequently causes liver inflammation, hepatic damage and subsequent cirrhosis. Integrated viral DNA is found in 85%-90% of HBV-related HCCs. Its presence in tumors from non-cirrhotic livers of children or young adults further supports the role of viral DNA integration in hepatocarcinogenesis. Integration of subgenomic HBV DNA fragments into different locations within the host DNA is a significant feature of chronic HBV infection. Integration has two potential consequences: (1) the host genome becomes altered (“cis” effect); and (2) the HBV genome becomes altered (“trans” effect). The cis effect includes insertional mutagenesis, which can potentially disrupt host gene function or alter host gene regulation. Tumor progression is frequently associated with rearrangement and partial gain or loss of both viral and host sequences. However, the role of integrated HBV DNA in hepatocarcinogenesis remains controversial. Modern technology has provided a new paradigm to further our understanding of disease mechanisms. This review summarizes the role of HBV DNA integration in human carcinogenesis.     

Hepatocellular carcinoma in patients with chronic hepatitis C virus infection in the Asia–Pacific region

Hepatocellular carcinoma (HCC) is the third-leading cause of cancer-related mortality worldwide. Although hepatitis B still remains the most common risk factor worldwide, chronic hepatitis C virus (HCV) infection is the driving force for the increased incidence of HCC especially in Western countries and Japan. In hepatitis B virus (HBV)-endemic areas, after successful vaccination programs against HBV, chronic HCV infection is now emerging as an important cause of chronic liver diseases. Unlike patients with chronic hepatitis B, those with chronic hepatitis C (CHC) develop HCC in the presence of established cirrhosis in most cases. However, a significant minority of CHC develops HCC in the absence of cirrhosis. Although HCV is a RNA virus with little potential for integrating its genetic material into host genome, various HCV proteins, including core, envelope, and nonstructural proteins, have oncogenic properties by inducing oxidative stress, disturbing cellular regulatory pathways associated with proliferation and apoptosis, and suppressing host immune responses. Overall, a combination of virus-specific, host genetic, environmental, and immune-related factors are likely to determine progression to HCC. Strategies aimed at eliminating the virus may provide opportunities for effective prevention of the development of HCC. Pegylated interferon plus ribavirin therapy appears to be effective at reducing the risk of HCC in patients who achieve sustained virologic responses. In summary, with the emerging importance of CHC, mechanisms of HCV-associated hepatocellular carcinogenesis should be clarified to provide insight into advanced therapeutic and preventive approaches, which eventually decrease the incidence and mortality of HCC.     

Autophagy related protein 9A increase in hepatitis B virus-associated hepatocellular carcinoma and the role in apoptosis

The majority of hepatocellular carcinoma (HCC) cases are associated with the hepatitis B virus (HBV) infection. Autophagy related protein 9A (ATG9A) is a transmembrane protein required for autophagosome formation. In order to investigate the role of ATG9A in HBV-associated HCC, ATG9A protein expression was determined in tumor liver tissues and compared with adjacent nontumor tissues from HCC patients with or without HBV infection. In HBV-associated HCC tissues, ATG9A protein level was increased in tumor liver tissues, but not in cases of non-HBV HCC. Our findings suggested that ATG9A might be involved in HBV and cancer cell survival. Therefore, we aimed to analyze the function of ATG9A in HBV replication using RNA interference to evaluate the HBV DNA level using real-time PCR. In the present study, there were no significant differences between shATG9A-transfected HepG2.2.15 cells and the mock control. However, we found that silencing ATG9A affected apoptosis in HepG2.2.15 and HepG2 cell lines. Our results indicated that ATG9A might be partly involved in the survival of HCC. Thus, the inhibition of ATG9A together with other targets might be a potential drug target for HCC treatment.     

How did hepatitis B virus effect the host genome in the last decade?

The principal reason of chronic liver disease, cirrhosis and hepatocellular carcinoma is chronic viral hepatitis all over the world. Hepatitis B virus (HBV) has some mutagenic effects on the host genome. HBV may be exhibiting these mutagenic effects through integrating into the host genome, through its viral proteins or through some epigenetic mechanisms related with HBV proteins. This review aims to summarize the molecular mechanisms used by HBV for effecting host genome determined in the last decade. The focus will be on the effects of integration, HBV proteins, especially HBV X protein and epigenetic mechanisms on the host genome. These interactions between HBV and the host genome also forms the underlying mechanisms of the evolution of hepatocellular carcinoma.     

Hepatocellular carcinoma: role of hepatitis B and hepatitis C viruses proteins in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the most important primary hepatic cancer, being a common cancer type worldwide. Many aetiological factors have been related with HCC development, such as cirrhosis, hepatitis viruses and alcohol. Chronic infection with hepatitis B (HBV) and C viruses (HCV) often results in cirrhosis and enhances the probability of developing HCC. The underlying mechanisms that lead to malignant transformation of infected cells, however, remain unclear. HBV is a DNA virus that integrates into the host genome, and this integration is believed, in part, to be carcinogenic. Besides, the virus encodes a 17 kDa protein, HBx, which is known to be a causative agent in the formation of HCC. On the contrary, HCV is a RNA virus that does not integrate into the host genome but likely induces HCC through host protein interactions or via the inflammatory response to the virus. Products encoded in the HCV genome interfere with and disturb intracellular signal transduction. Some HCV proteins, such as the core protein, NS3 and NS5A, have seen to have a regulatory effect on cellular promoters, to interact with a number of cellular proteins, and to be involved in programmed-cell death modulation under certain conditions. The identification of these proteins functions in HCC development and the subsequent development of strategies to inhibit protein-protein interactions may be the first step towards reducing the chronicity and/or of the carcinogenicity of these two viruses.     

Differential integration rates of hepatitis B virus DNA in the liver of children with chronic hepatitis B virus infection and hepatocellular carcinoma

BACKGROUND AND AIM: Integration of hepatitis B virus-DNA (HBV-DNA) into the host genome, a phenomenon found frequently in hepatocellular carcinomas (HCC) and causally linked to oncogenesis, has not been well characterized in children. The aim of the present study was to determine the prevalence of HBV integration more accurately and to decide whether the integration rate varies at different stages of chronic HBV infection in children. METHODS: Of 13 children with chronic hepatitis, 14 liver biopsy tissues were analyzed. One liver tissue with pure liver cirrhosis, nine non-tumor, and nine tumor liver tissues from children with HCC were analyzed by a very sensitive method, inverse polymerase chain reaction (IPCR). RESULTS: Thirteen genuine viral-host junctional sequences from 23 patients were successfully isolated and proved that IPCR is a useful method in this context. The results also indicated that the detection rate of HBV-DNA integration increased in parallel with the progress of liver histology towards the neoplastic transformation, with 0% in the liver of chronic hepatitis, 22.2% in non-tumor livers of HCC patients, and 66.7% in tumor liver tissues of HCC patients. CONCLUSION: The present results indicate that integration of HBV-DNA into the host genome was rarely confirmed at the early stage of chronic hepatitis in children until the stage of HCC formation.     

Characteristic clinical features of hepatocellular carcinoma associated with Budd-Chiari syndrome: evidence of different carcinogenic process from hepatitis B virus-associated hepatocellular carcinoma

OBJECTIVE: Budd-Chiari syndrome (BCS) is a known risk factor for hepatocellular carcinoma (HCC). Considering the pathophysiological mechanism of BCS, BCS-associated HCC may have a different carcinogenic process to hepatitis B virus (HBV)-associated HCC, resulting in different characteristic clinical features. METHODS: The clinical, radiological and histopathological characteristics of 15 HCCs associated with BCS were analysed and compared with 211 HBV-associated HCCs. RESULTS: HCC associated with BCS showed a female predominance in contrast to a male predominance in HCC associated with HBV infection. Child classes of BCS-associated HCC patients were not different from the classes of HBV-associated HCC. BCS tended to be associated with the single nodular type of HCC. Only one BCS-associated HCC patient had portal vein invasion at the time of diagnosis, compared with 96 patients with HBV-associated HCC. No HCC patients with BCS showed biliary invasion, compared with 47 HBV-associated HCC patients. The median survival period of HCC patients associated with BCS was 58 months, which was much longer than the median survival period of 10 months in HBV-associated HCC. All of the three BCS-associated HCCs available for histological examination were well differentiated. CONCLUSIONS: Patients with HCC associated with BCS seemed to survive for much longer periods than those with HBV due to the low invasiveness of the tumour. Such unique clinical features may be evidence of different carcinogenic processes in BCS-associated and HBV-associated HCC.     

Molecular mechanisms of gender disparity in hepatitis B virus-associated hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is one of the most common causes of hepatocellular carcinoma (HCC), a malignant tumor with high mortality worldwide. One remarkable clinical feature of HBV-related HCC is that its incidence is higher in males and postmenopausal females compared to other females. Increasing evidence indicates that HBV-associated HCC may involve gender disparity and that it may be a type of hormone-responsive malignant tumor. Sex hormones, such as androgen and estrogen, have been shown to play very different roles in the progression of an HBV infection and in the development of HBV-related HCC. Through binding to their specific cellular receptors and affecting the corresponding signaling pathways, sex hormones can regulate the transactivation of HBx, cause the chronic release of inflammatory cytokines in the hepatocellular microenvironment, and participate in epigenetic and genetic alternations in hepatocytes. All of these functions may be related to the initiation and progression of HBV-associated HCC. A thorough investigation of the molecular mechanisms underlying the gender-related disparity in HBV-related HCC should provide a new perspective for better understanding its pathogenesis and exploring more effective methods for the prevention and treatment of this disease.     

Do hepatitis B virus and hepatitis C virus co‐infections increase hepatocellular carcinoma occurrence through synergistically modulating lipogenic gene expression?

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infections cause a wide range of liver diseases including hepatocellular carcinoma (HCC). Because of the similar modes of transmission, HBV HCV co-infections are found in approximately 7-20 million people globally. Compared with HBV or HCV mono-infections, co-infections are associated with more severe liver diseases and higher risk of HCC. Abnormal lipid biosynthesis and metabolism has been increasingly recognized as a cause for cancer. While HBV infection does not seem to significantly increase the risk of developing hepatic steatosis, steatosis is a prominent feature of chronic hepatitis C (CHC). In addition, steatosis in HBV or HCV mono-infections is a significant and independent risk factor for HCC. However, whether and how HBV HCV co-infections synergistically increase the risk of HCC development through modulating lipid metabolism is not well understood. Possible mechanisms by which steatosis causes HCC include: activation of sterol regulatory element-binding protein-mediated lipogenesis through the PI3K-Akt pathway, abnormal activation of peroxisome proliferator-activated receptors and endoplasmic reticulum stress. Here, we review the potential mechanisms by which HBV HCV co-infections may increase HCC risk through modulation of lipogenic gene expression. We begin with reviewing the impact of HBV and HCV on host lipogenic gene expression and carcinogenesis. We then discuss the potential mechanisms by which HBV and HCV can increase carcinogenesis through synergistically activating lipid biosynthesis and metabolism. We end by sharing our thoughts on future research directions in this emerging paradigm with an ultimate goal of developing effective therapeutics.     

Interaction between the Hepatitis B Virus and Cellular FLIP Variants in Viral Replication and the Innate Immune System

During viral evolution and adaptation, many viruses have utilized host cellular factors and machinery as their partners. HBx, as a multifunctional viral protein encoded by the hepatitis B virus (HBV), promotes HBV replication and greatly contributes to the development of HBV-associated hepatocellular carcinoma (HCC). HBx interacts with several host factors in order to regulate HBV replication and evolve carcinogenesis. The cellular FADD-like IL-1β-converting enzyme (FLICE)-like inhibitory protein (c-FLIP) is a major factor that functions in a variety of cellular pathways and specifically in apoptosis. It has been shown that the interaction between HBx and c-FLIP determines HBV fate. In this review, we provide a comprehensive and detailed overview of the interplay between c-FLIP and HBV in various environmental circumstances. We describe strategies adapted by HBV to establish its chronic infection. We also summarize the conventional roles of c-FLIP and highlight the functional outcome of the interaction between c-FLIP and HBV or other viruses in viral replication and the innate immune system.     

Hepatitis B-associated vasculitis in Alaska Natives: viral genotype, clinical and serologic outcome.

BACKGROUND: The highest incidence of hepatitis B virus (HBV)-associated vasculitis in the world has been reported in Alaska Natives. We examined the incidence of HBV-associated vasculitis before and after mass HBV vaccine immunization and the association between HBV genotype and vasculitis in a population-based cohort study in Alaska natives chronically infected with HBV. METHODS: Genotyping was performed in vasculitis cases and 644 hepatitis B-positive controls without vasculitis using polymerase chain reaction and sequencing of the S gene. Occurrence of HBV vasculitis from 1974 to 2004 was calculated. HBV vasculitis patients and controls were also tested for basal core promoter and precore mutations. RESULTS: Fifteen cases of HBV-associated vasculitis were identified: 13 (86%) had genotype D and one each genotype A and F. Genotype D was more commonly found in patients with vasculitis than controls [odd ratio (OR)=5.9, confidence interval (95% CI) 1.2, 21.8; P<0.015). CONCLUSIONS: HBV-associated vasculitis was associated with genotype D.     

COOH-terminal deletion of HBx gene is a frequent event in HBV-associated hepatocellular carcinoma

AIM：To investigate the hepatitis B virus （HBV） x gene （HBx） state in the tissues of HBV-related hepatocellular carcinoma （HCC） in Chinese patients and whether there were particular HBx mutations. METHODS： HBx gene was amplified and direct sequencing was used in genomic DNA samples from 20 HCC and corresponding non-cancerous liver tissues from HBsAg-positive patients. HBV DNA integration and HBx deleted mutation were validated in 45 HCC patients at different stages by Southern blot analysis and polymerase chain reaction methods.
RESULTS： The frequencies of HBx point mutations were significantly lower in HCC than their corresponding non- cancerous liver tissues （11/19 vs 18/19, P = 0.019）. In contrast, deletions in HBx gene were significantly higher in HCC than their non-cancerous liver tissues （16/19 vs 4/19, P 〈 0.001）. The deletion of HBx COOH-terminal was detected in 14 HCC tissues. A specific integration of HBx at 17p13 locus was also found in 8 of 16 HCC, and all of them also exhibited full-length HBx deletions. Integrated or integrated coexistence with replicated pattern was obtained in 45.5% （20/45） - 56.8% （25/45） tumors and 40.9% （18/45） - 52.3% （23/45） non-tumor tissues.
CONCLUSION： HBx deletion, especially the COOH- terminal deletion of HBx is a frequent event in HBV-associated HCC tissues in China. HBV integration had also taken place in partial HCC tissues. This supporting the hypothesis that deletion and probably integrated forms of the HBx gene may be implicated in liver carcinogenesis.     

Viral hepatitis B and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer in the world, some 630,000 new cases being diagnosed each year. 82% of cases are related to viral hepatitis, 55% to hepatitis B virus (HBV), 89% of those in regions where HBV is endemic. There is a striking parallel between the geographical distribution of the rates of chronic HBV infection and that of HCC. In the majority of HCC cases (70-90%) there is underlying liver cirrhosis. However, because HBV is an oncogenic virus, it can cause HCC in the absence of cirrhosis. The annual risk of HBV-induced HCC varies according to the presence or absence of concomitant cirrhosis. In HBV carriers without cirrhosis, the risk is 0.02-03% in Caucasians and 0.4-0.6% per year in Asians. In those with cirrhosis, the risk is 2.2% and 3.7% respectively in Caucasians and Asians. HBV likely causes HCC via both indirect (necro-inflammation and regeneration injury) and direct (by integration of its DNA in the host genome) pathways. During recent years it has become evident that HBV viral load >2000 IU/mL is associated with a high risk of malignant transformation. The most effective measure of prevention of HBV-related HCC is prevention of HBV infection by vaccination. A universal vaccination program in Taiwan was shown to be effective in reducing the rate of childhood and early adulthood HCC. In patients already infected with HBV, antiviral therapy remains the best strategy. Interferon-alfa therapy appears to be effective in preventing HCC in cirrhosis in Asia but not in Europe. Medium-term nucleos/tide-analogue therapy significantly reduces but does not eliminate the risk of HCC, especially in patients with pre-existing cirrhosis. Maintenance of virological remission is important for the reduction of HCC risk. With more potent antiviral drugs currently available (entecavir, tenofovir), long-term HBV DNA suppression is now possible with very low risk of drug resistance.     

Occult hepatitis B virus and hepatocellular carcinoma

Occult hepatitis B virus (HBV) infection (OBI) is a challenging pathobiological and clinical issue that has been widely debated for several decades. By definition, OBI is characterized by the persistence of HBV DNA in the liver tissue (and in some cases also in the serum) in the absence of circulating HBV surface antigen (HBsAg). Many epidemiological and molecular studies have indicated that OBI is an important risk factor for hepatocellular carcinoma (HCC) development. OBI may exert direct pro-oncogenic effects through the activation of the same oncogenic mechanisms that are activated in the course of an HBsAg-positive infection. Indeed, in OBI as in HBV-positive infection, HBV DNA can persist in the hepatocytes both integrated into the host genome as well as free episome, and may maintain the capacity to produce proteins-mainly X protein and truncated preS-S protein - provided with potential transforming properties. Furthermore, OBI may indirectly favor HCC development. It has been shown that the persistence of very low viral replicative activity during OBI may induce mild liver necro-inflammation continuing for life, and substantial clinical evidence indicates that OBI can accelerate the progression of liver disease towards cirrhosis that is considered the most important risk factor for HCC development.     

Hepatitis B virus DNA integration in hepatocellular carcinoma after interferon-induced disappearance of hepatitis C virus

OBJECTIVES: Hepatocellular carcinoma (HCC) has been reported in patients in whom hepatitis C virus (HCV) was eliminated by interferon (IFN) therapy. We examined the pathogenesis of HCC in patients with sustained viral response. METHODS: Operable HCC developed in 7 of 342 patients cured of HCV infection by IFN monotherapy. No patient abused alcohol or had diabetes mellitus or obesity. Resected specimens of HCC were histologically evaluated. DNA extracted from HCC was examined by polymerase chain reaction (PCR) to locate hepatitis B virus (HBV) DNA. HBV integration sites in human genome were identified by cassette-ligation-mediated PCR. RESULTS: HBV DNA was not amplified in serum samples from any of the seven patients with HCC and was found in liver in four patients. In the latter four patients, HBV DNA was integrated into the human genome of HCC. In two of these patients, covalently closed circular HBV (cccHBV) was also detected. The patients with HBV DNA integration were free of HCV for more than 3 yr. In two of the three patients without HBV DNA integration, the surrounding liver showed cirrhosis. The liver of HCC with HBV DNA integration had not progressed to cirrhosis. Three of the four tumors with HBV integration had one integration site each, located at chromosomes 11q12, 11q22-23, and 22q11, respectively. The other tumor had two integration sites, situated at chromosomes 11q13 and 14q32. At chromosome 11q12, HBV DNA was integrated into protein-coding genome, the function of which remains unclear. CONCLUSION: Integrated HBV DNA may play a role in hepatocarcinogenesis after the clearance of HCV by IFN treatment.