Hepatitis B Virus Pre-S Gene Deletions and Pre-S Deleted Proteins: Clinical and Molecular Implications in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent and fatal human cancers worldwide and its development and prognosis are intimately associated with chronic infection with hepatitis B virus (HBV). The identification of genetic mutations and molecular mechanisms that mediate HBV-induced tumorigenesis therefore holds promise for the development of potential biomarkers and targets for HCC prevention and therapy. The presence of HBV pre-S gene deletions in the blood and the expression of pre-S deleted proteins in the liver tissues of patients with chronic hepatitis B and HBV-related HCC have emerged as valuable biomarkers for higher incidence rates of HCC development and a higher risk of HCC recurrence after curative surgical resection, respectively. Moreover, pre-S deleted proteins are regarded as important oncoproteins that activate multiple signaling pathways to induce DNA damage and promote growth and proliferation in hepatocytes, leading to HCC development. The signaling molecules dysregulated by pre-S deleted proteins have also been validated as potential targets for the prevention of HCC development. In this review, we summarize the clinical and molecular implications of HBV pre-S gene deletions and pre-S deleted proteins in HCC development and recurrence and highlight their potential applications in HCC prevention and therapy.     

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.     

Molecular mechanism of hepatitis B virus X protein function in hepatocarcinogenesis

Many factors are considered to contribute to hepatitis B virus(HBV)-associated hepatocellular carcinoma(HCC),including products of HBV,HBV integration and mutation,and host susceptibility. HBV X protein(HBx) can interfere with several signaling pathways associated with cell proliferation and invasion,and HBx C-terminal truncation has been suggested to impact the development of HCC. This review focuses on the pathological functions of HBx in HBV-induced hepatocarcinogenesis. As a transactivator,HBx can affect regulatory non-coding RNAs(nc RNAs),including micro RNAs and long nc RNAs. HBx is also involved in epigenetic modification and DNA repair. HBx interacts with various signal-transduction pathways,such as the p53,Wnt,and nuclear factor-κB pathways. We conclude that HBx hastens the development of hepatoma.     

广西肝癌中HBV感染与N_ras基因突变的研究

AIM To observe the roles of N-ras gene mutation and hepatitis B virus (HBV) infection in the carcinogenesis of hepatocellular carcinoma (HCC) in Guangxi, China.METHODS The polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and immunohistochemistry were used to detect N-ras gene mutation and HBV infection in 29 cases of HCC.RESULTS The aberration rates at codon 2-37 of N-ras were 79.31% in HCCs and 80.77% in adjacent non-tumorous liver tissues. More than 2 point mutations of N-ras gene were observed in 22 (75.86%) cases. HBsAg and HBxAg positive rates were 86.2% and 79.3%. There was a parallel tendency between HBV marker detections and the mutation rate of N-ras gene.CONCLUSION HBV infection and N-ras gene mutation may be involved in the carcinogenesis and development of HCC in Guangxi. Since the aflatoxin B1 contamination is one of risk factors for HCC in this area, it may contribute to the mutation of N-ras gene in carcinogenesis of HCC.INTRODUCTIONHepatocellular carcinoma (HCC) is one of common malignant tumors in People′s Republic of China. Guangxi is a high incidence area of HCC. Many factors are involved in hepatocarcinogenesis. Many studies revealed that hepatitis B virus (HBV) infection might be a risk factor for hepatocellular carcinogenesis. One theory for hepatocarcinogenesis is that the oncogene(s) may be transactivated by hepatitis B x antigen (HBxAg)[1]. It is found recently that activation of N-ras gene may be the molecular basis for the carcinogenesis and development of HCC[2,3]. There have been reports about overexpression of N-ras oncogene in human HCC[4], but a few dealt with the roles of N-ras gene mutation and HBV infection, and their relationship with HCC. We analyzed the N-ras gene mutation and HBV infection in HCC by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and immunohistochemistry in 29 cases of human HCC.     

An update on the molecular genetics of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is associated with multiple risk factors and is believed to arise from preneoplastic lesions, usually in the background of cirrhosis. Extensive studies on HCC and its precursors have demonstrated complex and heterogeneous genetic or chromosomal abnormalities along the way from preneoplastic lesions to HCCs. These genetic abnormalities include loss of heterozygosity, microsatellite instability, gene alterations, and aberrant global gene expression profiles. Although some genetic alterations involving the p53 family, Rb family, and Wnt pathways are particularly important in the development of HCCs, the molecular pathogenesis of HCC differs with etiology in some extent. Recent studies using DNA microarray technique have identified some unique gene expression profiles in hepatitis B virus (HBV)- and hepatitis C virus (HCV)-associated HCCs. Gene expression profiling also allows people to distinguish HCCs from normal tissue or preneoplastic lesions and to evaluate metastatic or recurrent potentials. These unique genes or gene products associated with malignant transformation and recurrent or metastatic potentials may serve as molecular markers for early diagnosis, prediction of prognosis, and responsiveness to therapy. To date, information that has accumulated for the past several decades is still incomplete, and we still are faced with a great challenge in deciphering the molecular mechanisms of HCCs.     

Frequent amplification of c-myc in ground squirrel liver tumors associated with past or ongoing infection with a hepadnavirus.

Persistent infection with hepatitis B virus (HBV) is a major cause of hepatocellular carcinoma (HCC) in humans. HCC has also been observed in animals chronically infected with two other hepadnaviruses: ground squirrel hepatitis virus (GSHV) and woodchuck hepatitis virus (WHV). A distinctive feature of WHV is the early onset of woodchuck tumors, which may be correlated with a direct role of the virus as an insertional mutagen of myc genes: c-myc, N-myc, and predominantly the woodchuck N-myc2 retroposon. In the present study, we searched for integrated GSHV DNA and genetic alterations of myc genes in ground squirrel HCCs. Viral integration into host DNA was detected in only 3/14 squirrel tumors and did not result in insertional activation of myc genes, despite the presence of a squirrel locus homologous to the woodchuck N-myc2 gene. This suggests that GSHV may differ from WHV in its reduced ability to induce mutagenic integration events. However, the high frequency of c-myc amplification (6/14) observed in ground squirrel HCCs indicates that myc genes might be preferential effectors in the tumorigenic processes associated with rodent hepadnaviruses, a feature not reported so far in HBV-induced carcinogenesis. Together with previous observations, our results suggest that hepadnaviruses, despite close genetic and biological properties, may use different pathways in the genesis of liver cancer.     

N-ras gene mutation and hepatitis B virus infection in hepatocellular carcinomas in Guangxi,China

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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.     

The tree shrews: useful animal models for the viral hepatitis and hepatocellular carcinoma

Hepatitis B virus (HBV)-induced hepatitis and hepatocellular carcinoma (HCC) are major diseases worldwide. HBV infection and chemical carcinogens such as aflatoxin B1 are known to be two key factors in the development of HCC. Animal models for hepatitis and HCC are very useful in the in vivo studies of mechanism involved in the development and prevention of these diseases and the pre-clinical research of drugs for the treatment of these diseases. Now, several animals, such as woodchucks, ground squirrels, chimpanzees, ducks and tree shrews, have been used to establish hepatitis and HCC models. HCC occurs in some woodchucks and ground squirrels that are infected with their own hepatitis viruses and exposed to carcinogens. Chimpanzees and ducks can be infected with human and duck hepatitis B viruses, respectively, but HCC is rarely observed in these animals. The tree shrews are non-rodent, small animals and close to primates in evolution. This review focuses on the establishment of human HBV-induced hepatitis and human HBV-associated HCC in tree shrews and their applications in the study of HCC development.     

Molecular targets for prevention of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors in some areas of the world with an extremely poor prognosis. The major etiologic risk factors for HCC development include toxins (alcohol, aflatoxin B1), androgens and estrogens, hepatitis B virus (HBV) and hepatitis C virus (HCV) infection as well as various inherited metabolic disorders, such as alpha-1-antitrypsin deficiency and hemochromatosis. The molecular pathogenesis of HCC development is very complex and involves alterations in the structure or expression of several tumor suppressor genes, oncogenes and, possibly, mechanisms leading to a genetic instability due to mismatch repair deficiency or chromosomal instability and aneuploidy due to defective chromosomal segregation. Central to the molecular pathogenesis of HCCs are mutations of various genes and a genetic instability which in most cases result from chronic liver disease and the associated enhanced liver cell regeneration and mitotic activity. The prognosis of HCC patients is generally very poor. Most studies report a five year survival rate of less than 5% in symptomatic HCC patients. Furthermore, these tumors have been shown to be quite resistant to radio- or chemotherapy. Investigations of the natural history and clinical course of HCCs revealed long-term survival of patients only with small asymptomatic HCCs that could be treated surgically or by non-surgical interventions. Apart from exploring and refining new HCC treatment strategies, the implementation of existing and the development of novel measures to prevent HCC development are most important. Primary HCC prevention includes among others universal hepatitis B vaccination, antiviral therapy of patients with chronic hepatitis B or C, reduction of food contamination with aflatoxins, elimination of excessive alcohol etc. Also for some genetic diseases there is the potential for HCC prevention by identifying affected family members at risk, such as patients with precirrhotic hemochromatosis. Reduction of iron overload by phlebotomy has been shown to eliminate the progression hemochromatosis to liver cirrhosis and HCC. Preventive measures, therefore, should have a major impact on the incidence of HCCs in patients with acquired and inherited liver diseases. Further, the prevention of a local recurrence or the development of new HCC lesions in patients after successful surgical or non-surgical HCC treatment (secondary prevention) is of paramount importance and is expected to significantly improve disease-free and overall patient survival. Based on rapid scientific advances, molecular diagnosis, gene therapy and molecular prevention are becoming increasingly part of our patient management and will eventually complement and in part replace existing diagnostic, therapeutic and preventive strategies. Overall, this should result in a reduction of the incidence of HCCs, one of the most devastating malignancies worldwide.     

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.     

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...     

Prevention of hepatocellular carcinoma in patients with chronic hepatitis B

Patients with chronic hepatitis B are at significant risk for hepatocellular carcinoma(HCC). Globally,over half a million people each year are diagnosed with HCC,with marked geographical variations. Despite overwhelming evidence for a causal role of hepatitis B virus(HBV) infection in the development of HCC and a well-established relationship between high baseline hepatitis B viral load and cumulative risk of HCC,the molecular basis for this association has not been fully elucidated. In addition,a beneficial role for antiviral therapy in preventing the development of HCC has been difficult to establish. This review examines the biological and molecular mechanisms of HBV-related hepatocarcinogenesis,recent results on the effect of modern nucleos(t)ides on the rate of HCC development in high risk HBV cohorts and the potential mechanisms by which long-term antiviral therapy with potent inhibitors of HBV replication might reduce the risk of HCC in patients with chronic hepatitis B. Although evidence from randomized controlled trials shows the favourable effects of antiviral agentsin achieving profound and durable suppression of HBV DNA levels while improving liver function and histology,robust evidence of other long-term clinical outcomes,such as prevention of HCC,are limited.     

Approaches for Detection of Hepatitis B Virus Pre-S Gene Deletions and Pre-S Deleted Proteins and Their Application in Prediction of Higher Risk of Hepatocellular Carcinoma Development and Recurrence

Hepatocellular carcinoma (HCC) is among the most common and lethal human cancers worldwide and is closely associated with chronic hepatitis B virus (HBV) infection. Pre-S deleted proteins are naturally occurring mutant forms of HBV large surface proteins that are expressed by HBV surface genes harboring deletion mutations over the pre-S gene segments. It has been well demonstrated that HBV pre-S deleted proteins function as important oncoproteins, which promote malignant phenotypes of hepatocytes through the activation of multiple oncogenic signaling pathways and result in HCC formation. The oncogenic signaling pathways activated by pre-S deleted proteins have been verified as potential therapeutic targets for the prevention of HCC development. Moreover, the presence of pre-S gene deletions and the expression of pre-S deleted proteins in the blood and liver tissues of HBV-infected patients have been evaluated as valuable biomarkers for predicting a higher risk of HCC development and recurrence after curative surgical resection. Therefore, the precise detection of pre-S gene deletions and pre-S deleted proteins holds great promise as regards identifying the patients at higher risk of HCC development and recurrence, thus aiding in more timely and better treatments to improve their survival. This review summarizes the major approaches used for the detection of pre-S gene deletions and pre-S deleted proteins, including the approaches based on Sanger DNA sequencing, pre-S gene chips, next-generation sequencing and immunohistochemistry staining, and it highlights their important applications in the prediction of higher risks of HCC development and recurrence.     

Pathways and gene expression profiles in hepatocellular carcinoma

Hepatocarcinogenesis is a process attributed to progressive genomic changes which alter the hepatocellular phenotype producing cellular intermediates evolving into clearly neoplastic cells (hepatocellular carcinoma, HCC). During the preneoplastic phase, the liver is often the site of chronic hepatitis and/or cirrhosis, and this process leads to the production of monoclonal populations of aberrant and dysplastic hepatocytes that develop genetic and chromosomal alterations. At the moment three main molecular pathways of liver carcinogenesis have been described and several attempts of genetic classification of HCC have been proposed. The definition of genomic and molecular changes which occur during the development of HCC should improve the classification and prognostis of liver tumors. The development of sorafenib and other new targeted developing therapies were rendered possible by the discovery and understanding of the molecular and genetic pathogenesis of hepatocellular carcinoma. Besides viruses, such as Hepatitis B virus (HBV) and Hepatitis C virus (HCV), may contribute to cancer development by several ways; however, additional factors, such as host immunity and chronic inflammation and host cellular mutations also play a role in the transformation process. The understanding of these pathways will in the future enable the clinician to focus the treatment patients with HCC and customize single or combination therapy.     

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.     

Molecular Therapies in Hepatocellular Carcinoma: What Can We Target?

Numerous signaling pathways, such as Ras/Raf/MAPK, have been implicated in hepatic carcinogenesis. There are at least 35 combination therapy studies for advanced stage hepatocellular carcinoma (HCC) ongoing, and numerous reagents are being tested targeting novel signaling cascades. The management of HCC has changed substantially in recent times, and the successful development of sorafenib has prompted further expansion on molecular targeted therapies to potentially inhibit different pathways in hepatocarcinogenesis.     

Does antiviral therapy for hepatitis B and C prevent hepatocellular carcinoma?

Approximately 75% to 80% of hepatocellular carcinomas (HCC) worldwide are attributed to chronic hepatitis B virus (HBV) and chronic hepatitis C virus (HCV) infection. Thus, effective prevention of HBV and HCV infection and progression from acute HBV and HCV infection to chronic hepatitis, cirrhosis and HCC might prevent as many as 450,000 deaths from HCC each year. The most effective approach to preventing HCC is to prevent HBV and HCV infection through vaccination. Indeed HBV vaccine is the first vaccine demonstrated to prevent cancers. However, a vaccine for HCV is not available and for persons who are chronically infected with HBV or HCV, antiviral therapy is the only option for preventing HCC. Direct evidence supporting a benefit of antiviral therapy on the prevention of HCC has been shown in a few randomized controlled trials. There is abundant evidence that antiviral therapy, in patients with long-term virological response, can improve liver histology, providing indirect support that antiviral therapy may prevent HCC by slowing progression of liver disease and possibly even reversing liver damage. Nevertheless, the risk of HCC remains in patients with chronic HBV or chronic HCV infection if treatment is initiated after cirrhosis is established. These data indicate that treatment might be of greater benefit if instituted earlier in the course of chronic hepatitis B or C. Safer, more effective, and more affordable antiviral therapies are needed for both hepatitis B and hepatitis C so more patients can benefit from treatment and more HCCs can be prevented.