Activation of c-myc by woodchuck hepatitis virus insertion in hepatocellular carcinoma

Carcinogenic mechanisms of virus-associated lymphoma

The development of lymphoma is a complex multistep process that integrates numerous experimental findings and clinical data that have not yet yielded a definitive explanation. Studies of oncogenic viruses can help to deepen insight into the pathogenesis of lymphoma, and identifying associations between lymphoma and viruses that are established and unidentified should lead to cellular and pharmacologically targeted antiviral strategies for treating malignant lymphoma. This review focuses on the pathogenesis of lymphomas associated with hepatitis B and C, Epstein-Barr, and human immunodeficiency viruses as well as Kaposi sarcoma-associated herpesvirus to clarify the current status of basic information and recent advances in the development of virus-associated lymphomas.

Hematological and neurological expressed 1 (HN1) activates c-Myc signaling by inhibiting ubiquitin-mediated proteasomal degradation of c-Myc in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a poor prognosis due to the usually advanced stage at diagnosis. Sustained activation of the MYC oncogene is implicated in the development of HCC; however, the molecular mechanisms of MYC deregulation in HCC are poorly understood. Here, real-time PCR and western blotting were used to measure the expression of hematological and neurological expressed 1 (HN1) in HCC cells. Expression of HN1 and MYC in clinical specimens was analyzed using immunohistochemistry. The role of HN1 in HCC proliferation, migration, and invasion was explored in vitro and in vivo. MYC expression was measured using real-time PCR and western blotting. MYC transcriptional activity was assessed using a luciferase reporter system. Expression of MYC target genes was quantified using real-time PCR. Protein interaction between MYC and HN1 was assessed using co-immunoprecipitation and western blotting. We identified HN1 as a novel regulatory factor of the glycogen synthase kinase (GSK) 3β-MYC axis. HN1 expression is elevated in liver tumor tissues and cells, and significantly correlates with poor survival in HCC patients. Upregulation of HN1 promotes, and silencing of HN1 represses, the proliferation and metastasis of liver cancer cells in vitro and in vivo. Moreover, our results demonstrate that HN1 sustains stabilization and persistent activity of MYC via interaction with GSK3β in HCC. Importantly, the tumor-promoting effects of HN1 on HCC cells were attenuated by suppressing MYC. In conclusion, constitutive activation of MYC by HN1 promotes the progression of HCC; therefore, HN1 might be a novel therapeutic target for HCC.

Interleukin 24 promotes cell death in renal epithelial cells and is associated with acute renal injury

Ischemia-reperfusion injury is a major cause of acute kidney injury. Many cytokines are involved in the pathogenesis of renal ischemia-reperfusion injury. IL24 is a member of the IL10 family and has gained importance because of its apoptosis-inducing effects in tumor disease besides its immunoregulative function. Littles is known about the role of IL24 in kidney disease. Using a mouse model, we found that IL24 is upregulated in the kidney after renal ischemia-reperfusion injury and that tubular epithelial cells and infiltrating inflammatory cells are the source of IL24. Mice lacking IL24 are protected from renal injury and inflammation. Cell culture studies showed that IL24 induces apoptosis in renal tubular epithelial cells, which is accompanied by an increased endoplasmatic reticulum stress response. Moreover, IL24 induces robust expression of endogenous IL24 in tubular cells, fostering ER-stress and apoptosis. In kidney transplant recipients with delayed graft function and patients at high risk to develop acute kidney injury after cardiac surgery IL24 is upregulated in the kidney and serum. Taken together, IL24 can serve as a biomarker, plays an important mechanistic role involving both extracellular and intracellular targets, and is a promising therapeutic target in patients at risk of or with ischemia-induced acute kidney injury.

Molecular Mechanisms and Animal Models of HBV-Related Hepatocellular Carcinoma: With Emphasis on Metastatic Tumor Antigen 1

Hepatocellular carcinoma (HCC) is an important cause of cancer death worldwide, and hepatitis B virus (HBV) infection is a major etiology, particularly in the Asia-Pacific region. Lack of sensitive biomarkers for early diagnosis of HCC and lack of effective therapeutics for patients with advanced HCC are the main reasons for high HCC mortality; these clinical needs are linked to the molecular heterogeneity of hepatocarcinogenesis. Animal models are the basis of preclinical and translational research in HBV-related HCC (HBV-HCC). Recent advances in methodology have allowed the development of several animal models to address various aspects of chronic liver disease, including HCC, which HBV causes in humans. Currently, multiple HBV-HCC animal models, including conventional, hydrodynamics-transfection-based, viral vector-mediated transgenic, and xenograft mice models, as well as the hepadnavirus-infected tree shrew and woodchuck models, are available. This review provides an overview of molecular mechanisms and animal models of HBV-HCC. Additionally, the metastatic tumor antigen 1 (MTA1), a cancer-promoting molecule, was introduced as an example to address the importance of a suitable animal model for studying HBV-related hepatocarcinogenesis.

The Role of Viruses in Carcinogenesis and Molecular Targeting: From Infection to Being a Component of the Tumor Microenvironment

About a tenth of all cancers are caused by viruses or associated with viral infection. Recent global events including the coronavirus disease-2019 (COVID-19) pandemic means that human encounter with viruses is increased. Cancer development in individuals with viral infection can take many years after infection, demonstrating that the involvement of viruses in cancer development is a long and complex process. This complexity emanates from individual genetic heterogeneity and the many steps involved in cancer development owing to viruses. The process of tumorigenesis is driven by the complex interaction between several viral factors and host factors leading to the creation of a tumor microenvironment (TME) that is ideal and promotes tumor formation. Viruses associated with human cancers ensure their survival and proliferation through activation of several cellular processes including inflammation, migration, and invasion, resistance to apoptosis and growth suppressors. In addition, most human oncoviruses evade immune detection and can activate signaling cascades including the PI3K-Akt-mTOR, Notch and Wnt pathways associated with enhanced proliferation and angiogenesis. This expert review examines and synthesizes the multiple biological factors related to oncoviruses, and the signaling cascades activated by these viruses contributing to viral oncogenesis. In particular, I examine and review the Epstein-Barr virus, human papillomaviruses, and Kaposi's sarcoma herpes virus in a context of cancer pathogenesis. I conclude with a future outlook on therapeutic targeting of the viruses and their associated oncogenic pathways within the TME. These anticancer strategies can be in the form of, but not limited to, antibodies and inhibitors.

Characterization of hepatitis B virus infection and viral DNA integration in non-Hodgkin lymphoma

Hepatitis B virus (HBV) infection has been reported to be associated with non-Hodgkin lymphoma (NHL). However, the evidence is limited to the seroepidemiological study. There is a lack of evidence showing the HBV infection and integration in NHL cells. Here, we reported that in the Shanghai area, the positive rates of serum HBsAg (OR: 3.11; 95% CI: 2.20-4.41) and HBeAg (OR: 3.99; 95% CI: 1.73-9.91) were significantly higher in patients with NHL. HBsAg, HBcAg and HBV DNA were detected in 34.4%, 45.2% and 47.0% of the NHL tissues, respectively. Furthermore, by using a high-throughput viral integration detection approach (HIVID), integrated HBV DNA was identified from 50% (6/12) HBV-related NHL tissues. There were a total of 313 HBV integration sites isolated from the NHL tissues, among which four protein-coding genes (FAT2, SETX, ITGA10 and CD63) were interrupted by HBV DNA in their exons. Seven HBV preferential target genes (ANKS1B, HDAC4, EGFLAM, MAN1C1, XKR6, ZBTB38 and CCDC91) showed significantly altered expression levels in NHL, suggesting a potential role of these genes in NHL development. Taken together, HBV integration is a common phenomenon in NHL. This finding opens up a new direction of research into the mechanistic link between HBV infection and NHL.

HIV-HBV and HIV-HCV Coinfection and Liver Cancer Development

Liver diseases that are caused by the hepatitis B virus (HBV) and hepatitis C virus (HCV), including cirrhosis and hepatocellular carcinoma (HCC), have become increasingly important in patients infected with the human immunodeficiency virus (HIV) as their life expectancy is getting longer with successful anti-HIV therapy. Due to their shared transmission routes, dual infection by HIV and HBV or HIV and HCV, and triple infection by all three viruses are fairly common and affect millions of people worldwide. Whereas the immunodeficiency caused by HIV enhances the likelihood of HBV and HCV persistence, hepatotoxicity associated with anti-HIV therapy can worsen the liver diseases associated with HBV or HCV persistence. Evidence suggests HIV infection increases the risk of HBV- or HCV-associated HCC risk although the precise mechanisms of enhanced hepatocarcinogenesis remain to be fully elucidated. Recent success in curing HCV infection, and the availability of therapeutic options effective in long-term suppression of both HIV and HBV replication, bring hope, fortunately, to those who are coinfected but also highlight the need for judicious selection of antiviral therapies.

MicroRNA-1294 inhibited oral squamous cell carcinoma growth by targeting c-Myc

Oral squamous cell carcinoma (OSCC) is the predominant histological type of oral cancer. The 5-year survival rate of OSCC is only ~50%. c-Myc is a known oncogene and target gene in various cancer types, including OSCC. The presnet study revealed that c-Myc is one of the target genes of miR-1294. Results indicated lower levels of miR-1294 in OSCC tissues samples collected from 24 patients with OSCC. Notably, overexpression of miR-1294 inhibited proliferation and migration in OSCC cell lines and inhibition of miR-1294 promoted cell growth and migration in OSCC cell lines. Moreover, miR-1294 can target the 3′UTR of c-Myc, as we identified a negative correlation between c-Myc mRNA expression and miR-1294 expression in 24 OSCC tissues. In conclusion, the data demonstrate the tumor suppressive role of miR-1294 in OSCC.

Expression of hepatitis B virus surface antigens induces defective gonad phenotypes in Caenorhabditis elegans

AIM

To test whether a simple animal, Caenorhabditis elegans (C. elegans), can be used as an alternative model to study the interaction between hepatitis B virus antigens (HBsAg) and host factors.

METHODS

Three plasmids that were able to express the large, middle and small forms of HBsAgs (LHBsAg, MHBsAg, and SHBsAg, respectively) driven by a ubiquitous promoter (fib-1) and three that were able to express SHBsAg driven by different tissue-specific promoters were constructed and microinjected into worms. The brood size, egg-laying rate, and gonad development of transgenic worms were analyzed using microscopy. Levels of mRNA related to endoplasmic reticulum stress, enpl-1, hsp-4, pdi-3 and xbp-1, were determined using reverse transcription polymerase reaction (RT-PCRs) in three lines of transgenic worms and dithiothreitol (DTT)-treated wild-type worms.

RESULTS

Severe defects in egg-laying, decreases in brood size, and gonad retardation were observed in transgenic worms expressing SHBsAg whereas moderate defects were observed in transgenic worms expressing LHBsAg and MHBsAg. RT-PCR analysis revealed that enpl-1, hsp-4 and pdi-3 transcripts were significantly elevated in worms expressing LHBsAg and MHBsAg and in wild-type worms pretreated with DTT. By contrast, only pdi-3 was increased in worms expressing SHBsAg. To further determine which tissue expressing SHBsAg could induce gonad retardation, we substituted the fib-1 promoter with three tissue-specific promoters (myo-2 for the pharynx, est-1 for the intestines and mec-7 for the neurons) and generated corresponding transgenic animals. Moderate defective phenotypes were observed in worms expressing SHBsAg in the pharynx and intestines but not in worms expressing SHBsAg in the neurons, suggesting that the secreted SHBsAg may trigger a cross-talk signal between the digestive track and the gonad resulting in defective phenotypes.

CONCLUSION

Ectopic expression of three forms of HBsAg that causes recognizable phenotypes in transgenic worms suggests that C. elegans can be used as an alternative model for studying virus-host interactions because the resulting phenotype is easily detected through microscopy.

Advances and Challenges in Studying Hepatitis B Virus In Vitro

Hepatitis B virus (HBV) is a small DNA virus that infects the liver. Current anti-HBV drugs efficiently suppress viral replication but do not eradicate the virus due to the persistence of its episomal DNA. Efforts to develop reliable in vitro systems to model HBV infection, an imperative tool for studying HBV biology and its interactions with the host, have been hampered by major limitations at the level of the virus, the host and infection readouts. This review summarizes major milestones in the development of in vitro systems to study HBV. Recent advances in our understanding of HBV biology, such as the discovery of the bile-acid pump sodium-taurocholate cotransporting polypeptide (NTCP) as a receptor for HBV, enabled the establishment of NTCP expressing hepatoma cell lines permissive for HBV infection. Furthermore, advanced tissue engineering techniques facilitate now the establishment of HBV infection systems based on primary human hepatocytes that maintain their phenotype and permissiveness for infection over time. The ability to differentiate inducible pluripotent stem cells into hepatocyte-like cells opens the door for studying HBV in a more isogenic background, as well. Thus, the recent advances in in vitro models for HBV infection holds promise for a better understanding of virus-host interactions and for future development of more definitive anti-viral drugs.

Interactions between Myc and Mediators of Inflammation in Chronic Liver Diseases

Most chronic liver diseases (CLDs) are characterized by inflammatory processes with aberrant expressions of various pro- and anti-inflammatory mediators in the liver. These mediators are the driving force of many inflammatory liver disorders, which often result in fibrosis, cirrhosis, and liver tumorigenesis. c-Myc is involved in many cellular events such as cell growth, proliferation, and differentiation. c-Myc upregulates IL-8, IL-10, TNF-α, and TGF-β, while IL-1, IL-2, IL-4, TNF-α, and TGF-β promote c-Myc expression. Their interactions play a central role in fibrosis, cirrhosis, and liver cancer. Molecular interference of their interactions offers possible therapeutic potential for CLDs. In this review, current knowledge of the molecular interactions between c-Myc and various well known inflammatory mediators is discussed.

Molecular biology of hepatitis B virus infection

Human hepatitis B virus (HBV) is the prototype of a family of small DNA viruses that productively infect hepatocytes, the major cell of the liver, and replicate by reverse transcription of a terminally redundant viral RNA, the pregenome. Upon infection, the circular, partially double-stranded virion DNA is converted in the nucleus to a covalently closed circular DNA (cccDNA) that assembles into a minichromosome, the template for viral mRNA synthesis. Infection of hepatocytes is non-cytopathic. Infection of the liver may be either transient (<6 months) or chronic and lifelong, depending on the ability of the host immune response to clear the infection. Chronic infections can cause immune-mediated liver damage progressing to cirrhosis and hepatocellular carcinoma (HCC). The mechanisms of carcinogenesis are unclear. Antiviral therapies with nucleoside analog inhibitors of viral DNA synthesis delay sequelae, but cannot cure HBV infections due to the persistence of cccDNA in hepatocytes.

SCP1 regulates c-Myc stability and functions through dephosphorylating c-Myc Ser62

Serine 62 (Ser62) phosphorylation affects the c-Myc protein stability in cancer cells. However, the mechanism for dephosphorylating c-Myc is not well understood. In this study, we identified carboxyl-terminal domain RNA polymerase II polypeptide A small phosphatase 1 (SCP1) as a novel phosphatase specifically dephosphorylating c-Myc Ser62. Ectopically expressed SCP1 strongly dephosphorylated c-Myc Ser62, destabilized c-Myc protein and suppressed c-Myc transcriptional activity. Knockdown of SCP1 increased the c-Myc protein levels in liver cancer cells. SCP1 interacted with c-Myc both in vivo and in vitro. In addition, Ser245 at the C-terminus of SCP1 was essential for its phosphatase activity towards c-Myc. Functionally, SCP1 negatively regulated the cancer cell proliferation. Collectively, our findings indicate that SCP1 is a potential tumor suppressor for liver cancers through dephosphorylating c-Myc Ser62.

Hepatocellular carcinoma

The hepatitis B virus (HBV) is a widespread human pathogen that causes liver inflammation, cirrhosis, and hepatocellular carcinoma (HCC). Recent sequencing technologies have refined our knowledge of the genomic landscape and pathogenesis of HCC, but the mechanisms by which HBV exerts its oncogenic role remain controversial. In a prevailing view, inflammation, liver damage, and regeneration may foster the accumulation of genetic and epigenetic defects leading to cancer onset. However, a more direct and specific contribution of the virus is supported by clinical and biological observations. Among genetically heterogeneous HCCs, HBV-related tumors display high genomic instability, which may be attributed to the ability of HBV to integrate its DNA into the host cell genome, provoking chromosomal alterations and insertional mutagenesis of cancer genes. The viral transactivator HBx may also participate in transformation by deregulating diverse cellular machineries. A better understanding of the complex mechanisms linking HBV to HCC will improve prevention and treatment strategies.

Primary seronegative but molecularly evident hepadnaviral infection engages liver and induces hepatocarcinoma in the woodchuck model of hepatitis B

Hepadnavirus at very low doses establishes in woodchucks asymptomatic, serologically undetectable but molecularly evident persistent infection. This primary occult infection (POI) preferentially engages the immune system and initiates virus-specific T cell response in the absence of antiviral antibody induction. The current study aimed to determine whether POI with time may culminate in serologically identifiable infection and hepatitis, and what are, if any, its pathological consequences. Juvenile woodchucks were intravenously injected with inocula containing 10 or 100 virions of woodchuck hepatitis virus (WHV) to induce POI and followed for life or up to 5.5 years thereafter. All 10 animals established molecularly detectable infection with virus DNA in serum (<100–200 copies/mL) and in circulating lymphoid cells, but serum WHV surface antigen and antibodies to WHV core antigen remained undetectable for life. By approximately 2.5–3.5 years post-infection, circulating virus transiently increased to 10³ copies/mL and virus replication became detectable in the livers, but serological markers of infection and biochemical or histological evidence of hepatitis remained undetectable. Nonetheless, typical hepatocellular carcinoma (HCC) developed in 2/10 animals. WHV DNA integration into hepatic and lymphatic system genomes was identified in 9/10 animals. Virus recovered from the liver virus-negative or virus-positive phases of POI displayed the wild-type sequence and transmitted infection to healthy woodchucks causing hepatitis and HCC. In summary, for the first time, our data demonstrate that an asymptomatic hepadnaviral persistence initiated by very small amounts of otherwise pathogenic virus, advancing in the absence of traditional serological markers of infection and hepatitis, coincides with virus DNA integration into the host's hepatic and immune system genomes, retains liver pro-oncogenic potency and is capable of transmitting liver pathogenic infection. This emphasizes the role for primary occult hepatitis B virus infection in the development of seemingly cyptogenic HCC in seronegative but virus DNA reactive patients.

Introduction of highly sensitive molecular assays for detection of hepatitis B virus (HBV) identified the existence of persistent occult HBV infection years after recovery from an episode of hepatitis B and in individuals exposed to HBV but without symptoms and classical markers of infection. Because HBV integrates into human DNA and is a potent human carcinogen, it is postulated that occult HBV infection can be a cause of hepatic cancer in many individuals in which the tumor origin remains currently unknown. A causative relation between occult HBV infection and hepatocarcinoma is highly challenging to investigate in humans since occult HBV persistence is rarely diagnosed with current clinical assays and cancer development takes 15–30 years. However, we have established excellent models of occult HBV infection in the eastern North American woodchucks which are naturally susceptible to a virus closely related to HBV and in which chronic infection advances to liver cancer. In the current study, exploring experimental primary occult infection in woodchucks, we proved that the silently progressing infection, which is not detectable by serological markers, can culminate in hepatocellular carcinoma and that the persisting virus remains infectious, and causes hepatitis and liver cancer when transmitted to virus-naïve hosts.

Tackling hepatitis B virus-associated hepatocellular carcinoma--the future is now

Hepatocellular carcinoma (HCC) is one of the most lethal and prevalent cancers in many developing countries including India. Among the various etiological factors being implicated in the cause of HCC, the most important cause, however, is hepatitis B virus (HBV) infection. Among all HBV genes, HBx is the most critical carcinogenic component, the molecular mechanisms of which have not been completely elucidated. Despite its clinical significance, there exists a very elemental understanding of the molecular, cellular, and environmental mechanisms that drive disease pathogenesis in HCC infected with HBV. Furthermore, there are only limited therapeutic options, the clinical benefits of which are insignificant. Therefore, the quest for novel and effective therapeutic regimen against HBV-related HCC is of paramount importance. This review attempts to epitomize the current state of knowledge of this most common and dreaded liver neoplasm, highlighting the putative treatment avenues and therapeutic research strategies that need to be implemented with immediate effect for tackling HBV-related HCC that has plagued the medical and scientific fraternity for decades. Additionally, this review proposes a novel "five-point" management algorithm for HBV-related HCC apart from portraying the unmet needs, principal challenges, and scientific perspectives that are relevant to controlling this accelerating global health crisis.

The expression and effects the CABYR-c transcript of CABYR gene in hepatocellular carcinoma

BACKGROUND AND AIM

CABYR, a calcium-binding tyrosine phosphorylation regulated fibrous sheath protein, was initially reported to be testis-specific and subsequently shown to be present in brain tumors, pancreas cancer and lung cancer. This study aimed to investigate the expression and effects of the CABYR-c transcript of CABYR gene in hepatocellular carcinoma.

METHODS

mRNA and protein expression of CABYR-c was examined in 20 paired hepatocellular carcinoma tissues and adjacent non-cancerous tissues by real-time quantitative RT-polymerase chain reaction (PCR) and western blot analysis respectively. HepG2 cells were treated with the antisense oligodeoxynucleotides targeting CABYR-c mRNA (CABYR-c antisense oligonucleotides [AS ODNs]) for indicated times, the AS ODNs inhibition effect was evaluated by measuring the CABYR-c mRNA expression level of HepG2 cells after treatment using real-time quantitative RT-PCR, then cell proliferation was studied using MTT assay, and cell cycle distribution and apoptosis were detected by flow cytometry as well.

RESULTS

CABYR-c mRNA levels in hepatocellular carcinoma tissues were significantly higher than that in the paired adjacent non-cancerous tissues (27.5 ± 1.2 versus 2.5 ± 0. 9, P < 0.01). CABYR-c protein expression level in hepatocellular carcinoma tissues was also significantly higher than that in adjacent non-cancerous tissues. CABYR-c mRNA expression in HepG2 cells was most effective down-regulated after treatment of 600 nM CABYR-c AS ODNs for 48 h, which was selected for subsequent experiments. Incubation with 600 nM CABYR-c AS ODNs inhibited the cell growth of HepG2 cells in a dose- and time-dependent manner. The maximum inhibitory effect achieved at 600 nM after 72 h treatment (30.92 ± 3.25%, P < 0.01). HepG2 cells treated 600 nM CABYR-c AS ODNs for 48 h exhibited an increasing proportion of cells in G0/G1 phase (P < 0.05) and a decreasing proportion of cells in S phase (P < 0.05), compared with untreated controls. No obvious differences were observed in G2/M phase. The fraction of apoptotic HepG2 cells in CABYR-c AS ODNs treated group was less than that of untreated control group (P < 0.05).

CONCLUSION

CABYR-c is highly expressed in hepatocellular carcinoma tissues and may play an oncogenic role in heptocarcinogenesis as well as its progression.

Hepatitis B virus X protein impedes the DNA repair via its association with transcription factor, TFIIH

Background

Hepatitis B virus (HBV) infections play an important role in the development of hepatocellular carcinoma (HCC). HBV X protein (HBx) is a multifunctional protein that can modulate various cellular processes and plays a crucial role in the pathogenesis of HCC. HBx is known to interact with DNA helicase components of TFIIH, a basal transcriptional factor and an integral component of DNA excision repair.

Results

In this study, the functional relevance of this association was further investigated in the context to DNA repair. By site-directed mutagenesis HBx's critical residues for interaction with TFIIH were identified. Similarly, TFIIH mutants lacking ATPase domain and the conserved carboxyl-terminal domain failed to interact with HBx. Yeast and mammalian cells expressing HBx^wt conferred hypersensitivity to UV irradiation, which is interpreted as a basic deficiency in nucleotide excision repair. HBx^mut120 (Glu to Val) was defective in binding to TFIIH and failed to respond to UV.

Conclusions

We conclude that HBx may act as the promoting factor by inhibiting DNA repair causing DNA damage and accumulation of errors, thereby contributing to HCC development.

Establishing a new animal model for hepadnaviral infection: susceptibility of Chinese Marmota-species to woodchuck hepatitis virus infection

Hepatitis B virus infection (HBV) is a major medical problem in China. The lack of a suitable infection model in China is recognized as an obstacle for research on HBV in China. Chinese Marmota-species is phylogenetically closely related to Marmota monax, thus, it might be suitable to serve as an animal model for HBV infection. Therefore, we attempted to prove the claim about the existence of woodchuck hepatitis virus (WHV)-like viruses in Chinese Marmota-species and to determine the susceptibility of these species to experimental WHV infection. In the present study, 653 sera from three Chinese Marmota-species, Marmota himalayana, Marmota baibacina and Marmota bobak, were screened for WHV-like viruses by serological and molecular assays. The susceptibility to WHV of three species was investigated by experimental infection and monitored by testing of anti-WHc and WHsAg by ELISA, detection of WHV DNA by PCR, and detection of WHV replication intermediates and antigens in liver samples. No evidence for the existence of a genetically closely related virus to WHV in three Chinese Marmota-species was found by serological assays and PCR. M. himalayana was susceptible to WHV infection as inoculated animals became positive for anti-WHc, WHsAg and WHV DNA. Further, WHV replication intermediates and proteins were detected in liver samples. In contrast, M. baibacina remained negative for tested virological parameters. M. bobak species showed a limited susceptibility to WHV. Our data do not support early reports about WHV-like viruses in China. M. himalayana is suitable for the establishment of a model for hepadnaviral infection.

Nucleotide changes related to hepatocellular carcinoma in the enhancer 1/x-promoter of hepatitis B virus subgenotype C2 in cirrhotic patients

Hepatocellular carcinoma (HCC) is widely known to develop more frequently in cirrhotic patients with a high expression of Hepatitis B virus X protein (HBx), which is controlled by the enhancer 1 (Enh1)/X-promoter. To examine the effect of the mutations in the Enh1/X-promoter region in hepatitis B virus (HBV) genomes on the development of HCC, we investigated the differences in HBV isolated from cirrhotic patients with or without HCC along with the promoter activities of certain specific mutations within the Enh1/X-promoter. We examined 160 hepatitis B surface antigen (HBsAg)-positive cirrhotic patients (80 HCC patients, 80 non-HCC patients) by evaluating the biochemical, virological, and molecular characteristics. We evaluated the functional differences in certain specific mutations within the Enh1/X-promoter. The isolated sequences included all of the subgenotypes C2. The sites that showed higher mutation rates in the HCC group were G1053A and G1229A, which were found to be independent risk factors through multiple logistic analysis (P < 0.05). Their promoter activities were elevated 2.38- and 4.68-fold, respectively, over that of the wild type in the HepG2 cells. Similarly, both the mRNA and protein levels of HBx in these two mutants were much higher than that in wild type-transfected HepG2 cells. Mutated nucleotides of the Enh1/X-promoter, especially G1053A and G1229A mutations in the HBV subgenotype C2 of patients with cirrhosis, can be risk factors for hepatocarcinogenesis, and this might be due to an increase in the HBx levels through the transactivation of the Enh1/X-promoter.

Molecular mechanisms underlying hepatocellular carcinoma

Hepatocarcinogenesis is a complex process that remains still partly understood. That might be explained by the multiplicity of etiologic factors, the genetic/epigenetic heterogeneity of tumors bulks and the ignorance of the liver cell types that give rise to tumorigenic cells that have stem cell-like properties. The DNA stress induced by hepatocyte turnover, inflammation and maybe early oncogenic pathway activation and sometimes viral factors, leads to DNA damage response which activates the key tumor suppressive checkpoints p53/p21^Cip1 and p16^INK4a/pRb responsible of cell cycle arrest and cellular senescence as reflected by the cirrhosis stage. Still obscure mechanisms, but maybe involving the Wnt signaling and Twist proteins, would allow pre-senescent hepatocytes to bypass senescence, acquire immortality by telomerase reactivation and get the last genetic/epigenetic hits necessary for cancerous transformation. Among some of the oncogenic pathways that might play key driving roles in hepatocarcinogenesis, c-myc and the Wnt/β-catenin signaling seem of particular interest. Finally, antiproliferative and apoptosis deficiencies involving TGF-β, Akt/PTEN, IGF2 pathways for instance are prerequisite for cancerous transformation. Of evidence, not only the transformed liver cell per se but the facilitating microenvironment is of fundamental importance for tumor bulk growth and metastasis.

Liver cell transformation in chronic HBV infection

Epidemiological studies have provided overwhelming evidence for a causal role of chronic HBV infection in the development of hepatocellular carcinoma (HCC), but the molecular mechanisms underlying virally-induced tumorigenesis remain largely debated. In the absence of a dominant oncogene encoded by the HBV genome, indirect roles have been proposed, including insertional activation of cellular oncogenes by HBV DNA integration, induction of genetic instability by viral integration or by the regulatory protein HBx, and long term effects of viral proteins in enhancing immune-mediated liver disease. In this chapter, we discuss different models of HBV-mediated liver cell transformation based on animal systems of hepadnavirus infection as well as functional studies in hepatocyte and hepatoma cell lines. These studies might help identifying the cellular effectors connecting HBV infection and liver cell transformation.

A pre-S gene chip to detect pre-S deletions in hepatitis B virus large surface antigen as a predictive marker for hepatoma risk in chronic hepatitis B virus carriers

BACKGROUND

Chronic hepatitis B virus (HBV) infection is an important cause of hepatocellular carcinoma (HCC) worldwide. The pre-S1 and -S2 mutant large HBV surface antigen (LHBS), in which the pre-S1 and -S2 regions of the LHBS gene are partially deleted, are highly associated with HBV-related HCC.

METHODS

The pre-S region of the LHBS gene in two hundred and one HBV-positive serum samples was PCR-amplified and sequenced. A pre-S oligonucleotide gene chip was developed to efficiently detect pre-S deletions in chronic HBV carriers. Twenty serum samples from chronic HBV carriers were analyzed using the chip.

RESULTS

The pre-S deletion rates were relatively low (7%) in the sera of patients with acute HBV infection. They gradually increased in periods of persistent HBV infection: pre-S mutation rates were 37% in chronic HBV carriers, and as high as 60% in HCC patients. The Pre-S Gene Chip offers a highly sensitive and specific method for pre-S deletion detection and is less expensive and more efficient (turnaround time 3 days) than DNA sequencing analysis.

CONCLUSION

The pre-S1/2 mutants may emerge during the long-term persistence of the HBV genome in carriers and facilitate HCC development. Combined detection of pre-S mutations, other markers of HBV replication, and viral titers, offers a reliable predictive method for HCC risks in chronic HBV carriers.

Detection of clonally expanded hepatocytes in chimpanzees with chronic hepatitis B virus infection

During a hepadnavirus infection, viral DNA integrates at a low rate into random sites in the host DNA, producing unique virus-cell junctions detectable by inverse nested PCR (invPCR). These junctions serve as genetic markers of individual hepatocytes, providing a means to detect their subsequent proliferation into clones of two or more hepatocytes. A previous study suggested that the livers of 2.4-year-old woodchucks (Marmota monax) chronically infected with woodchuck hepatitis virus contained at least 100,000 clones of >1,000 hepatocytes (W. S. Mason, A. R. Jilbert, and J. Summers, Proc. Natl. Acad. Sci. USA 102:1139-1144, 2005). However, possible correlations between sites of viral-DNA integration and clonal expansion could not be explored because the woodchuck genome has not yet been sequenced. In order to further investigate this issue, we looked for similar clonal expansion of hepatocytes in the livers of chimpanzees chronically infected with hepatitis B virus (HBV). Liver samples for invPCR were collected from eight chimpanzees chronically infected with HBV for at least 20 years. Fifty clones ranging in size from approximately 35 to 10,000 hepatocytes were detected using invPCR in 32 liver biopsy fragments (approximately 1 mg) containing, in total, approximately 3 x 10(7) liver cells. Based on searching the analogous human genome, integration sites were found on all chromosomes except Y, approximately 30% in known or predicted genes. However, no obvious association between the extent of clonal expansion and the integration site was apparent. This suggests that the integration site per se is not responsible for the outgrowth of large clones of hepatocytes.

[Molecular mechanisms of hepatitis B virus-associated hepatocellular carcinoma]

Hepatocellular carcinoma (HCC) is one of the most common malignant diseases in the world. The hepatitis B virus (HBV) replicates non-cytopathically in hepatocytes, and most of the liver injury associated with this infection reflects the immune response. Epidemiological studies have clearly demonstrated that a chronic HBV infection is a major etiological factor in the development of HCC. The pathogenesis of HBV-associated HCC has been studied extensively, and the molecular changes during the malignant transformation have been identified. The main carcinogenic mechanism of HBV-associated HCC is related to the long term-inflammatory changes caused by a chronic hepatitis B infection, which might involve the integration of the HBV. Integration of the HBV DNA into the host genome occurs at the early steps of clonal tumorous expansion. The hepatitis B x protein (HBx) is a multifunctional regulatory protein that communicates directly or indirectly with a variety of host targets, and mediates many opposing cellular functions, including its function in cell cycle regulation, transcriptional regulation, signaling, encoding of the cytoskeleton and cell adhesion molecules, as well as oncogenes and tumor suppressor genes. Continued study of the mechanisms of hepatocarcinogenesis will refine our current understanding of the molecular and cellular basis for neoplastic transformations in the liver. This review summarizes the current knowledge of the mechanisms involved in HBV-associated hepatocarcinogenesis.

HIV-HBV and HIV-HCV coinfection and liver cancer development

Liver diseases caused by chronic HBV or HCV infection, including cirrhosis and HCC, are emerging as an increasingly important problem faced by millions of HIV-infected patients who are coinfected with HBV or HCV. On one hand, HIV-induced immune suppression enhances the risk of chronic viral hepatitis, increases HBV or HCV load, and may hasten the progression to cirrhosis and liver cancer. On the other hand, significant hepatotoxicity is associated with a number of antiretroviral drugs, further exacerbating liver damage associated with chronic viral hepatitis. The exact risk of HCC in HIV and HBV or HCV coinfected patients remains to be fully assessed. The elucidation of the multiple virus-virus and virus-host interactions that underlie viral hepatocarcinogenesis and potential HIV enhancement awaits the establishment of appropriate in vitro and in vivo model systems. As millions of HIV-infected patients in the developing countries are gaining access to HAART therapy for their HIV infections, endemic HBV and HCV infections and their associated liver diseases will only become more problematic on a global level. To ameliorate the suffering from HBV- and HCV-induced liver cancer in HIV patients, more effective treatment for chronic HBV and HCV infections are needed. The long time frame of viral hepatocarcinogenesis may afford a window of opportunity to develop and improve such treatment.

Hepatitis B virus-induced oncogenesis

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world with an annual incidence of more than 500 000 in the year 2000. Its incidence is rising in many countries. Recently, it has been estimated that about 53% of HCC cases in the world are related to hepatitis B virus (HBV). The epidemiological association of HBV with HCC is well established. In recent studies, it was revealed that HBsAg carriers have a 25-37 times increased risk of developing HCC as compared to non-infected people. At present, HBV-associated carcinogenesis can be seen as a multi-factorial process that includes both direct and indirect mechanisms that might act synergistically. The integration of HBV DNA into the host genome occurs at early steps of clonal tumor expansion. The integration has been shown in a number of cases to affect a variety of cancer-related genes and to exert insertional mutagenesis. The permanent liver inflammation, induced by the immune response, resulting in a degeneration and regeneration process confers to the accumulation of critical mutations in the host genome. In addition to this, the regulatory proteins HBx and the PreS2 activators that can be encoded by the integrate exert a tumor promoter-like function resulting in positive selection of cells producing a functional regulatory protein. Gene expression profiling and proteomic techniques may help to characterize the molecular mechanisms driving HBV-associated carcinogenesis, and thus potentially identify new strategies in diagnosis and therapy.

Hepatitis B virus pre-S mutants, endoplasmic reticulum stress and hepatocarcinogenesis

Although hepatitis B virus (HBV) has been documented to cause hepatocellular carcinoma (HCC), the exact role of HBV in the development of HCC remains enigmatic. Several hypotheses have been proposed to explain the potential mechanism, including insertional mutagenesis of HBV genomes and transcriptional activators of HBV gene products such as hepatitis B x protein (HBx) and truncated middle S mutants. In the past few years, we have identified two types of large HBV surface antigens (LHBs) with deletions at the pre-S1 (DeltaS1-LHBs) and pre-S2 (DeltaS2-LHBs) regions in ground glass hepatocytes. The pre-S mutant LHBs are retained in the endoplasmic reticulum (ER) and escape from immune attack. The pre-S mutants, particularly DeltaS2-LHBs, are increasingly prevalent in patients with hepatitis B e antigen (HBeAg)-positive chronic HBV infection, ranging from 6% before the 3rd decade to 35% in the 6th decade. In HCC patients, the two pre-S mutants were detected in 60% of HCC patients, in the serum and in HCC tissues. Pre-S mutant LHBs can initiate ER stress to induce oxidative DNA damage and genomic instability. Furthermore, pre-S mutant LHBs can upregulate cyclooxygenase-2 and cyclin A to induce cell cycle progression and proliferation of hepatocytes. In transgenic mice, the pre-S mutants can induce dysplasia of hepatocytes and development of HCC. In a nested control study, the presence of pre-S mutants carried a high risk of developing HCC in HBV carriers. In summary, the findings we describe in this review suggest a potential role for HBV pre-S mutants in HBV-related hepatocarcinogenesis, providing a model of viral carcinogenesis associated with ER stress.

c-Myc, genome instability, and tumorigenesis: the devil is in the details

The c-myc oncogene acts as a pluripotent modulator of transcription during normal cell growth and proliferation. Deregulated c-myc activity in cancer can lead to excessive activation of its downstream pathways, and may also stimulate changes in gene expression and cellular signaling that are not observed under non-pathological conditions. Under certain conditions, aberrant c-myc activity is associated with the appearance of DNA damage-associated markers and karyotypic abnormalities. In this chapter, we discuss mechanisms by which c-myc may be directly or indirectly associated with the induction of genomic instability. The degree to which c-myc-induced genomic instability influences the initiation or progression of cancer is likely to depend on other factors, which are discussed herein.

Hepatitis B virus-related insertional mutagenesis in chronic hepatitis B patients as an early drastic genetic change leading to hepatocarcinogenesis

Growing evidence demonstrates that hepatitis B virus (HBV) integration and resulting insertional mutagenesis play an important role in cell growth or maintenance in hepatocellular carcinomas (HCCs). To determine if HBV integration occurs and affects cellular genes at such a stage of infection, we analysed viral-host junctions in chronic hepatitis tissues without HCC using PCR amplification with primers specific to human Alu-repeat and HBV. We obtained 42 independent viral-host junctions from six patients examined and identified chromosomal locations for 20 of the 42 junctions. In six clones, each integration apparently affected a single gene. These six candidate genes included one known tumor suppressor gene, three human homologs of drosophila genes that are critical for organ development, one putative oncogene and one recently found chemokine. Our data, together with previously reported HBV integrants in HCCs, suggested preferential HBV integration into chromosome 3 (P = 0.022). Our virus-tagging approach provided (a) firm evidence of HBV integration in hepatocytes at an early stage of chronic infection and (b) revealed cellular genes possibly affected by HBV integration and potentially involved in early steps of the process leading to carcinogenesis.

Pathogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common malignant tumours worldwide. The major aetiologies and risk factors for the development of HCC are well defined and some of the multiple steps involved in hepatocarcinogenesis have been elucidated in recent years. However, no clear picture of how and in what sequence these factors interact at the molecular level has emerged yet. Malignant transformation of hepatocytes may occur as a consequence of various aetiologies, such as chronic viral hepatitis, alcohol, and metabolic disorders, in the context of increased cellular turnover induced by chronic liver injury, regeneration and cirrhosis. Activation of cellular oncogenes, inactivation of tumour suppressor genes, genomic instability, including DNA mismatch repair defects and impaired chromosomal segregation, overexpression of growth and angiogenic factors, and telomerase activation may contribute to the development of HCC. Overall, HCCs are genetically very heterogeneous tumours. New technologies, including gene expression profiling and proteomic analyses, should allow us to further elucidate the molecular events underlying HCC development and identify novel diagnostic markers as well as therapeutic targets.

Molecular mechanisms in hepatocellular carcinoma development

Hepatocellular carcinoma (HCC) is one of the most common cancers in the world. It usually develops in patients with chronic viral hepatitis, aflatoxin exposure, or excessive alcohol use. Most patients with HCC present with advanced disease and have a poor prognosis. The implementation of antiviral drugs and the availability of a vaccine for hepatitis B should help reduce the incidence of HCC. Considerable effort has now focused on unraveling the molecular pathogenesis of HCC in order to design better treatments, or to prevent the disease altogether. However, so far, the pathogenesis of HCC appears to be quite heterogeneous among patients. In particular, several mechanisms of tumorigenesis seem to be involved, including loss of tumor suppressor gene function, oncogene activation, direct viral effects, DNA methylation, and angiogenesis. It is not clear which events are critical in tumor initiation versus tumor progression. RNA expression arrays and proteomics hold promise to provide further clues about this common and complex cancer.

c-Fos is a mediator of the c-myc-induced apoptotic signaling in serum-deprived hepatoma cells via the p38 mitogen-activated protein kinase pathway

The proto-oncogene c-myc encodes a transcription factor that plays a pivotal role in cell proliferation, differentiation, and apoptosis. The signaling mechanism of c-Myc-induced apoptosis was investigated on the human hepatoma Huh7 cells under growth factor-deprived conditions. The apoptotic process did not involve p53. Rather it was dependent on the expression of c-Fos. Activation of caspases 3 and 9 and down-regulation of Bcl2 were observed in the apoptotic process, indicating it to be a mitochondria-dependent event. An increase in the p38 mitogen-activated protein kinase that was mediated by a Rac1-dependent and cdc42-independent pathway eventually leading to up-regulation of c-Fos activity was also observed. Deletion analysis of the promoter region of the c-fos gene indicated that the ATF2-responsive element conferred the Myc-induced expression of c-Fos. Co-expression of the dominant-negative mutants of c-Fos, p38, and Rac1 blocked the Myc-mediated apoptosis. SB20358, a chemical inhibitor of p38 pathway, also specifically blocked the apoptotic signaling by c-Myc. Furthermore, co-expression of the hepatitis B virus X protein (HBx) along with Myc abrogated the apoptotic signals. The HBx expression was associated with an increase in the levels of phosphorylated AKT and down-regulation of c-Fos by Myc. Thus, c-Fos seems be a new mediator of c-Myc-induced apoptosis.

Integration of woodchuck hepatitis and N-myc rearrangement determine size and histologic grade of hepatic tumors

Integrations of woodchuck hepatitis virus (WHV) DNA and rearrangements of the N-myc 2 gene have been detected frequently in hepatocellular carcinoma (HCC) of Eastern woodchucks (Marmota monax) chronically infected with WHV. Fifty-five hepatocellular neoplasms and matched nontumor hepatic tissue specimens obtained postmortem from 13 chronic WHV carriers were analyzed and the frequency of WHV DNA integrations and of N-myc rearrangements compared in tumors of different size and histologic grade. Four small tumor nodules were classified histologically as adenomas and integrated sequences of WHV DNA were detected in two of the four tumor nodules. In one of the two nodules, there was evidence of N-myc rearrangement. Fifty-one neoplasms were classified as HCC. Seven were grade 1 HCCs. WHV DNA integrations were demonstrated in 43% but none had N-myc rearrangements. Twenty grade 2 HCCs had WHV DNA integrations in 80% and in 38% N-myc rearrangements were present. Twenty-four grade 3 HCCs had integrations of WHV DNA in 79% and N-myc rearrangements in 74%. In two other grade 3 HCCs, rearrangements of N-myc were detected in the absence of WHV DNA integrations. The 12 largest tumors in the series all were grade 2 or 3 HCCs, and in 83%, both WHV DNA integrations and N-myc rearrangements were demonstrated. In conclusion, molecular changes observed in this study suggest a progression of genetic alterations providing either a significant proliferative stimulation and/or a growth advantage in hepatocarcinogenesis of woodchucks with chronic WHV infection.

Scaffold attachment region located in a locus targeted by hepadnavirus integration in hepatocellular carcinomas

The role of viral integration in HBV induced hepatocellular carcinoma (HCC) is still controversial. In the WHV/woodchuck animal model, WHV integration was found to activate the N-myc2 oncogene either by enhancer insertion in proximity of the gene, or by integration in a distantly located uncoding locus, win. In addition, we have reported that N-myc2 activation also results from WHV integration in the b3n locus, located several kilobases downstream of N-myc2. In this work we report the search for function(s) of the b3n locus that might be possibly affected by WHV integration and indirectly activate N-myc2. A 0.5 kb region of the sequence of this locus exhibited unusual features, typical of scaffold/matrix attachment regions (S/MAR). Standard in vitro binding assays are commonly used to assess if a DNA fragment is a S/MAR. DNA fragments cloned from the b3n locus were tested for in vitro binding affinity for both heterologous and autologous nuclear scaffold preparations. Only the fragment spanning the region rich of S/MAR motifs was found to bind specifically nuclear scaffolds, thus demonstrating that a S/MAR element is present in the b3n locus. Based on these findings, we speculate that WHV integration might deregulate the S/MAR element and indirectly affect the expression of the N-myc2 gene located upstream of the S/MAR. Our findings also suggest that the role of HBV integration should be reconsidered, because a similar mechanism has not been investigated to date in human HCC.

Integrations of the hepatitis B virus (HBV) and human papillomavirus (HPV) into the human telomerase reverse transcriptase (hTERT) gene in liver and cervical cancers

Chronic infections with the hepatitis B virus (HBV) and high-risk human papillomaviruses (HPVs) are important risk factors for hepatocellular carcinoma (HCC) and cervical cancer (CC), respectively. HBV and HPV are DNA viruses that almost invariably integrate into the host genome in invasive tumors. The viral integration sites occur throughout the genome, leading to the presumption that there are no preferred sites of integration. A number of viral integrations have been shown to occur within the vicinity of important cancer-related genes. In studies of HBV-induced HCC and HPV-induced CC, we have identified two HBV and three HPV integrations into the human telomerase reverse transcriptase (hTERT) gene. Detailed characterization of the integrations revealed that four integrations occurred within the hTERT promoter and upstream region and the fifth integration occurred in intron 3 of the hTERT gene. None of the integrations altered the hTERT coding sequence and all resulted in juxtaposition of viral enhancers near hTERT, with potential activation of hTERT expression. Our work supports the hypothesis that the sites of oncogenic viral integration are nonrandom and that genes at the sites of viral integration may play important roles in carcinogenesis.

Long-term high-dose interferon-alpha therapy delays Hepadnavirus-related hepatocarcinogenesis in X/myc transgenic mice

The role of interferon-alpha (IFN-alpha) remains unclear in prevention of virus-induced hepatocellular carcinoma in humans. We have investigated it herewith in the X/myc transgenic mouse model of Hepadnavirus-related hepatocarcinogenesis because of upregulation of c-myc oncogene in the liver. We have demonstrated that IFN-alpha can downregulate dose-dependently hepatocyte proliferation and c-myc overexpression at early premalignant stages, while it does not affect either hepatocyte apoptosis or telomerase activity at these steps. However, continuous and long-term administration of IFN-alpha dose-dependently delays tumor onset in dysplastic livers and increases overall survival of animals, more efficiently whether started before the onset of dysplasia. The present study therefore highlights that early preventive administration of IFN-alpha can slow down evolution towards hepatocellular carcinoma via repression of c-myc and hepatocyte proliferation at premalignant steps in experimental c-myc-induced hepatocarcinogenesis. However, the transient effect observed in this study emphasizes a need to clarify the possible mechanisms of acquired resistance and subsequent therapeutic escape. Our experimental model may be a pertinent tool to explore antioncogenic properties of IFN-alpha in human cirrhotic livers showing c-myc upregulation.

Characterization of integration patterns and flanking cellular sequences of hepatitis B virus in childhood hepatocellular carcinomas

Hepatitis B virus (HBV) DNA integration into host chromosomes is detected in more than 80% of HBV-related hepatocellular carcinomas (HCC), yet its significance in tumor development remains obscure. In this study, we re-examined the integration pattern of HBV in childhood HCC tissues, which has less environmental confounding factors than adult HCC. The HBV junctions and flanking cellular sequences were amplified from five childhood HCC patients by the inverse polymerase chain reaction (IPCR) method using primers located near HBV direct repeats (DR) 1 and 2. The viral junctions in nine of the ten obtained IPCR clones were demonstrated to be located near HBV DR1, and their patterns were classified to type I integrants. Southern blot analyses demonstrate that the cellular junctions derived from two of the five HCC tissues were male specific and contained sequences homologous to human long interspersed DNA elements (LINE-1). HBV integrant of one HCC tissue (1217T) was integrated into a RNA binding motif Y chromosome (RBMY) gene. The expression of RBMY, which is normally found only in male germ cells, was detected in HCC tissue 1217T by RT-PCR but not in the corresponding non-tumor liver tissue. The prevalence of RBMY expression in liver tissues from the tumor and non-tumor parts of ten other HCC children and seven biliary atresia (BA) children was studied by RT-PCR. No RBMY transcripts were detected in the non-tumor parts of HCC patients or the cirrhotic livers of BA children, whereas 30% (three of ten) of HCC tissues specifically expressed RBMY. The results indicate that HBV integration and activation of RBMY gene expression in liver cells may be associated with the development of childhood HCC.

A mouse model of hepatocellular carcinoma: ectopic expression of fibroblast growth factor 19 in skeletal muscle of transgenic mice

Most mouse models of hepatocellular carcinoma have expressed growth factors and oncogenes under the control of a liver-specific promoter. In contrast, we describe here the formation of liver tumors in transgenic mice overexpressing human fibroblast growth factor 19 (FGF19) in skeletal muscle. FGF19 transgenic mice had elevated hepatic alpha-fetoprotein mRNA as early as 2 months of age, and hepatocellular carcinomas were evident by 10 months of age. Increased proliferation of pericentral hepatocytes was demonstrated by 5-bromo-2'-deoxyuridine incorporation in the FGF19 transgenic mice before tumor formation and in nontransgenic mice injected with recombinant FGF19 protein. Areas of small cell dysplasia were initially evident pericentrally, and dysplastic/neoplastic foci throughout the hepatic lobule were glutamine synthetase-positive, suggestive of a pericentral origin. Consistent with chronic activation of the Wingless/Wnt pathway, 44% of the hepatocellular tumors from FGF19 transgenic mice had nuclear staining for beta-catenin. Sequencing of the tumor DNA encoding beta-catenin revealed point mutations that resulted in amino acid substitutions. These findings suggest a previously unknown role for FGF19 in hepatocellular carcinomas.

Hepatitis B virus and hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major global cause of hepatocellular carcinoma (HCC). Individuals who are chronic carriers have a greater than 100-fold increased relative risk of developing the tumour. Several mechanisms of HBV-induced HCC have been proposed. Integration of HBV DNA into the genome of hepatocytes occurs commonly, although integration at cellular sites that are important for regulation of hepatocyte proliferation appears to be a rare event. Functions of the HBx protein are also potentially oncogenic. These include transcriptional activation of cellular growth regulatory genes, modulation of apoptosis and inhibition of nucleotide excision repair of damaged cellular DNA. The effects of HBx are mediated by interaction with cellular proteins and activation of cell signalling pathways. Variations in HBV genome sequences may be important in hepatocarcinogenesis, although their significance has not yet been completely elucidated. Necroinflammatory hepatic disease, which often accompanies chronic HBV infection, may contribute indirectly to hepatocyte transformation in a number of ways, including by facilitating HBV DNA integration, predisposing to the acquisition of cellular mutations and generating mutagenic oxygen reactive species. Although HCC is a malignancy with a poor prognosis, the availability of an effective vaccine against HBV infection, and its inclusion in the Expanded Programme of Immunization of many countries, augurs well for the eventual elimination of HBV-associated HCC.

The woodchuck model of hepatitis B virus infection

The woodchuck hepatitis virus (WHV) was the first of the mammalian and avian hepadnaviruses described after discovery of the virus of hepatitis B (HBV). Woodchucks chronically infected with WHV develop progressively severe hepatitis and hepatocellular carcinoma, which present as lesions that are remarkably similar to those associated with HBV infection in humans. The initial virological studies and studies of pathogenesis utilized woodchucks that had been trapped in the wild and had acquired WHV infection naturally. Research with wild woodchucks was complicated by lack of knowledge of their backgrounds (e.g., dietary history, exposure to parasites or environmental toxins, and source and duration of WHV infection). Breeding colonies of woodchucks have been established and maintained in laboratory animal facilities, and laboratory-reared woodchucks are superior for experimental studies of pathogenesis or hepatocarcinogenesis. It is possible to infect neonatal woodchucks born in the laboratory with standardized inocula and produce a high rate of chronic WHV carriers that are useful for controlled investigations. WHV has been shown experimentally to cause hepatocellular carcinoma, supporting conclusions based on epidemiological and molecular virological studies that HBV is an important etiological factor in human hepatocarcinogenesis. Chronic WHV carrier woodchucks have become a valuable animal model for the preclinical evaluation of antiviral therapy for HBV infection, providing useful pharmacokinetic and pharmacodynamic results in a relevant animal disease model. It also has been shown that the pattern of toxicity and hepatic injury observed in woodchucks treated with certain fluorinated pyrimidines is remarkably similar to that observed in humans that were treated with the same drugs, suggesting the woodchuck has significant potential for the preclincial assessment of antiviral drug toxicity.

New animal models of hepatitis B and C

The narrow host range of infection and lack of suitable tissue culture systems for the propagation of hepatitis B and C viruses are limitations that have prevented a more thorough understanding of persistent infection and the pathogenesis of chronic liver disease. With hepatitis B virus (HBV), this lack of knowledge has been partially overcome by the discovery and characterization of HBV-like viruses in wild animals. With hepatitis C virus (HCV), related flaviviruses have been used as surrogate systems for such studies. Other laboratories have developed transgenic mice that express virus gene products and/or support virus replication. Some HBV transgenic mouse models develop fulminant hepatitis, acute hepatitis, or chronic liver disease after adoptive transfer, and others spontaneously develop hepatocellular carcinoma (HCC), as in human infections. Among HCV transgenic mice, most develop no disease, but acute hepatitis has been observed in one model, and HCC in another. Although mice are not susceptible to HBV and HCV, their ability to replicate these viruses and to develop liver diseases characteristic of human infections provides new opportunities to study pathogenesis and develop novel therapeutics.

X protein of hepatitis B virus modulates cytokine and growth factor related signal transduction pathways during the course of viral infections and hepatocarcinogenesis

Hepatitis B virus produces chronic infections of the liver leading to cirrhosis and hepatocellular carcinoma. The X protein of hepatitis B virus (HBx) is a multifunctional protein that can interact with p53 but can also influence a variety of signal transduction pathways within the cell. In most instances this small viral protein favors cell survival and probably initiates hepatocarcinogenesis. HBx upregulates the activity of a number of transcription factors including NF-kappa B, AP-1, CREB, and TBP. However, the majority of HBx is localized to the cytoplasm where it interacts with and stimulates protein kinases such as protein kinase C, Janus kinase/STAT, IKK, PI-3-K, stress-activated protein kinase/Jun N-terminal kinase, and protein kinase B/Akt. This small viral protein can localize to the mitochondrion. HBx may act as an adaptor or kinase activator to influence signal transduction pathways. This review will attempt to analyze the involvement of HBx in signal transduction pathways during hepatitis B viral infections and hepatocellular carcinoma development.

Liver cancer

The prognosis of patients with HCC remains dismal. Even in the subgroups of patients who have the most favorable characteristics and are eligible for surgical resection, the 5-year survival rate is less than 25%. For patients with more advanced disease, the median survival time is less than 1 year. The good news in HCC research is that the disease can be prevented. In Taiwan, the rate of HCC in children aged 6 to 9 years decreased from 5.2 per million population before the neonatal vaccination program began in 1984 to 1.3 per million population in the first vaccinated cohort. Treatment of viral hepatitis with IFN may decrease the rates of long-term development of HCC. Other agents that may prevent second primary tumors following resection of HCC, such as polyprenoic acid and acylic retinoid, are also being investigated.

Preliminary results of interferon-alpha therapy on woodchuck hepatitis virus-induced hepatocarcinogenesis: possible benefit in female transgenic mice

BACKGROUND

C-myc activation is a potent oncogenic event in hepatocarcinogenesis. The aim of this study was to test the preventive effect of interferon-alpha (IFN-alpha) on the development of dysplasia and subsequent hepatocellular carcinoma (HCC) in transgenic (Tg) mice overexpressing c-myc in the liver.

METHODS

The WHV/c-myc Tg mice recapitulating woodchuck hepatitis virus-induced hepatocarcinogenesis were treated with IFN-alpha, starting early in life until sacrifice at pre-neoplastic or neoplastic stages. Transgene expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR), hepatocyte proliferation was assessed by bromodeoxyuridine incorporation and RT-PCR for proliferating cell nuclear antigen, and apoptosis was assessed by in situ nick-end-labeling of DNA.

RESULTS

C-myc expression and hepatocyte proliferation were significantly reduced in treated female mice, without modification of apoptosis, correlating with a lower severity of dysplasia in 9/12 treated animals at pre-neoplastic stages. At the neoplastic stage, 2/3 treated females neither exhibited carcinoma nor dysplasia, while all 6/6 untreated mice and 3/3 treated males developed carcinomas.

CONCLUSIONS

Inhibition of c-myc and hepatocyte proliferation by long-term administration of IFN-alpha was associated with a decrease, or a delay, of oncogenesis in the mouse Tg HCC model. Whether c-myc and hepatocyte proliferation down-regulation could be relevant parameters of IFN-alpha efficiency for hepatocarcinogenesis prevention in cirrhotic patients should be established.

Hepatitis B virus and hepatocellular carcinoma

Chronic hepatitis B virus (HBV) infection is a major global cause of hepatocellular carcinoma (HCC). Individuals who are chronic carriers have a greater than 100-fold increased relative risk of developing the tumour. Several mechanisms of HBV-induced HCC have been proposed. Integration of HBV DNA into the genome of hepatocytes occurs commonly, although integration at cellular sites that are important for regulation of hepatocyte proliferation appears to be a rare event. Functions of the HBx protein are also potentially oncogenic. These include transcriptional activation of cellular growth regulatory genes, modulation of apoptosis and inhibition of nucleotide excision repair of damaged cellular DNA. The effects of HBx are mediated by interaction with cellular proteins and activation of cell signalling pathways. Variations in HBV genome sequences may be important in hepatocarcinogenesis, although their significance has not yet been completely elucidated. Necroinflammatory hepatic disease, which often accompanies chronic HBV infection, may contribute indirectly to hepatocyte transformation in a number of ways, including by facilitating HBV DNA integration, predisposing to the acquisition of cellular mutations and generating mutagenic oxygen reactive species. Although HCC is a malignancy with a poor prognosis, the availability of an effective vaccine against HBV infection, and its inclusion in the Expanded Programme of Immunization of many countries, augurs well for the eventual elimination of HBV-associated HCC.

Analysis of integrated hepatitis B virus DNA and flanking cellular sequence by inverse polymerase chain reaction

Although hepatitis B virus (HBV) DNA has been detected in the human hepatoma cell line, HAGS 2.1, viral and cellular junction sequences have not been investigated fully. To facilitate the analysis of HBV DNA integration sites in HAGS 2.1 cells, a combination of conventional polymerase chain reaction (PCR) and inverse PCR (IPCR) was carried out to identify the junction between the viral and the cellular gene. The HBV integrant and its cellular counterpart sequence were cloned and analyzed. The sequencing data indicated that the breakpoints on the HBV integrant are at nucleotide 2111 of the C gene and nucleotide 1558 of the X gene. The length of the integrated HBV DNA in HAGS 2.1 was approximately 2.6 kb, which includes partial C, P, and X genes and an intact S gene. The cellular sequence flanking the integrated HBV gene was very similar to a human satellite III repetitive sequence with 43 and 56 of GGAAT repeats on the left- and right-hand side, respectively. Although the findings on the viral-cellular junction in HAGS 2.1 cells cannot explain the liver tumorigenesis, the current study shows that by choosing the nearest restriction site, which can be determined by conventional PCR rather than using a unique site within the integrated viral sequence to do IPCR, gives a higher successful rate for cloning and the subsequent analysis of the viral-cellular junctions.