Hepatitis C virus nonstructural protein NS4B transforms NIH3T3 cells in cooperation with the Ha-ras oncogene

Genomics of Viral Hepatitis-Associated Liver Tumors

Virus-related liver carcinogenesis is one of the main contributors of cancer-related death worldwide mainly due to the impact of chronic hepatitis B and C infections. Three mechanisms have been proposed to explain the oncogenic properties of hepatitis B virus (HBV) infection: induction of chronic inflammation and cirrhosis, expression of HBV oncogenic proteins, and insertional mutagenesis into the genome of infected hepatocytes. Hepatitis B insertional mutagenesis modifies the function of cancer driver genes and could promote chromosomal instability. In contrast, hepatitis C virus promotes hepatocellular carcinoma (HCC) occurrence mainly through cirrhosis development whereas the direct oncogenic role of the virus in human remains debated. Finally, adeno associated virus type 2 (AAV2), a defective DNA virus, has been associated with occurrence of HCC harboring insertional mutagenesis of the virus. Since these tumors developed in a non-cirrhotic context and in the absence of a known etiological factor, AAV2 appears to be the direct cause of tumor development in these patients via a mechanism of insertional mutagenesis altering similar oncogenes and tumor suppressor genes targeted by HBV. A better understanding of virus-related oncogenesis will be helpful to develop new preventive strategies and therapies directed against specific alterations observed in virus-related HCC.

Genetic variant of RXR involved in the vitamin D metabolic pathway was linked to HCV infection outcomes among a high-risk Chinese population

Genetic variation of related genes in Vitamin D (VD) metabolic pathway played an important role in antiviral immune response and chronic hepatitis C virus (HCV) infection. Retinoid X receptor (RXR) is one of the key genes in the metabolism pathway of VD. This study aims to investigate the effect of single nucleotide polymorphisms (SNPs) in RXR on the outcomes of HCV infection. Three SNPs (RXRɑ-rs4842194, rs1045570 and RXRβ-rs2076310) were genotyped using Sequenom MassARRAY platform in 515 spontaneous clearance subjects, 830 persistent infection subjects, and 1062 uninfected subjects. Multivariate stepwise regression analyss was used to identify the prediction factors for HCV infection outcomes. The USCS Brower and RNAfold web serves were performed to further explore the potential biological functions of positive SNPs. The results of logistic regression analysis after adjusting for age, gender and types of high-risk population showed that subjects with RXRβ rs2076310-T (recessive model: adjusted OR = 1.598, 95%CI = 1.126-2.267, P = 0.009; additive model: adjusted OR = 1.196, 95%CI = 1.011-1.416, P = 0.037) had a significantly increased possibility of HCV infection chronicity. Rs2076310, age, types of high-risk population and aspartate aminotransferase were independent predictors of chronic HCV infection (P < 0.05). And the area under the receiver operating characteristic curve of combined effects of these factors was 0.679. Bioinformatics analysis indicated that rs2076310 could affect the gene expression level by affecting the transcriptional regulatory activity of the corresponding gene region. These findings indicated that genetic variation of RXRβ was associated with the risk of HCV infection chronicity among a high-risk Chinese population.

The bZIP Proteins of Oncogenic Viruses

Basic leucine zipper (bZIP) transcription factors (TFs) govern diverse cellular processes and cell fate decisions. The hallmark of the leucine zipper domain is the heptad repeat, with leucine residues at every seventh position in the domain. These leucine residues enable homo- and heterodimerization between ZIP domain α-helices, generating coiled-coil structures that stabilize interactions between adjacent DNA-binding domains and target DNA substrates. Several cancer-causing viruses encode viral bZIP TFs, including human T-cell leukemia virus (HTLV), hepatitis C virus (HCV) and the herpesviruses Marek’s disease virus (MDV), Epstein–Barr virus (EBV) and Kaposi’s sarcoma-associated herpesvirus (KSHV). Here, we provide a comprehensive review of these viral bZIP TFs and their impact on viral replication, host cell responses and cell fate.

Marmoset Viral Hepatic Inflammation Induced by Hepatitis C Virus Core Protein via IL-32

Common marmosets infected with GB virus-B (GBV-B) chimeras containing hepatitis C virus (HCV) core and envelope proteins (CE1E2p7) developed more severe hepatitis than those infected with HCV envelope proteins (E1E2p7), suggesting that HCV core protein might be involved in the pathogenesis of viral hepatitis. The potential role of HCV core in hepatic inflammation was investigated. Six individual cDNA libraries of liver tissues from HCV CE1E2p7 or E1E2p7 chimera-infected marmosets (three animals per group) were constructed and sequenced. By differential expression gene analysis, 30 of 632 mRNA transcripts were correlated with the immune system process, which might be associated with hepatitis. A protein–protein interaction network was constituted by STRING database based on these 30 differentially expressed genes (DEGs), showing that IL-32 might play a central regulatory role in HCV core-related hepatitis. To investigate the effect of HCV core protein on IL-32 production, HCV core expressing and mock constructs were transfected into Huh7 cells. IL-32 mRNA and secretion protein were detected at significantly higher levels in cells expressing HCV core protein than in those without HCV core expression (P < 0.01 and P < 0.001, respectively). By KEGG enrichment analysis and using the specific signaling pathway inhibitor LY294002 for inhibition of PI3K, IL-32 expression was significantly reduced (P < 0.001). In conclusion, HCV core protein induces an increase of IL-32 expression via the PI3K pathway in hepatic cells, which played a major role in development of HCV-related severe hepatitis.

An insight into the molecular characteristics of hepatitis C virus for clinicians

Hepatitis C virus (HCV) consists of envelope proteins, core proteins, and genome RNA. The structural genes and non-structural genes in the open reading frame of its genome encode functional proteins essential to viral life cycles, ranging from virus attachment to progeny virus secretion. After infection, the host cells suffer damage from virus-induced oxidative stress, steatosis, and activation of proto-oncogenes. Every process during the viral life cycle can be considered as targets for direct acting antivirals. However, protective immunity cannot be easily acquired for the volatility in HCV antigenic epitopes. Understanding its molecular characteristics, especially pathogenesis and targets the drugs act on, not only helps professionals to make optimal therapeutic decisions, but also helps clinicians who do not specialize in infectious diseases/hepatology to provide better management for patients. This review serves to provide an insight for clinicians and this might provide a possible solution for any possible collision.

Systems Biology Reveals NS4B-Cyclophilin A Interaction: A New Target to Inhibit YFV Replication

Yellow fever virus (YFV) replication is highly dependent on host cell factors. YFV NS4B is reported to be involved in viral replication and immune evasion. Here interactions between NS4B and human proteins were determined using a GST pull-down assay and analyzed using 1-DE and LC-MS/MS. We present a total of 207 proteins confirmed using Scaffold 3 Software. Cyclophilin A (CypA), a protein that has been shown to be necessary for the positive regulation of flavivirus replication, was identified as a possible NS4B partner. 59 proteins were found to be significantly increased when compared with a negative control, and CypA exhibited the greatest difference, with a 22-fold change. Fisher's exact test was significant for 58 proteins, and the p value of CypA was the most significant (0.000000019). The Ingenuity Systems software identified 16 pathways, and this analysis indicated sirolimus, an mTOR pathway inhibitor, as a potential inhibitor of CypA. Immunofluorescence and viral plaque assays showed a significant reduction in YFV replication using sirolimus and cyclosporine A (CsA) as inhibitors. Furthermore, YFV replication was strongly inhibited in cells treated with both inhibitors using reporter BHK-21-rep-YFV17D-LucNeoIres cells. Taken together, these data suggest that CypA-NS4B interaction regulates YFV replication. Finally, we present the first evidence that YFV inhibition may depend on NS4B-CypA interaction.

HCV core protein promotes hepatocyte proliferation and chemoresistance by inhibiting NR4A1

This study investigated the effect of HCV core protein on the proliferation of hepatocytes and hepatocellular carcinoma cells (HCC), the influence of HCV core protein on HCC apoptosis induced by the chemotherapeutic agent cisplatin, and the mechanism through which HCV core protein acts as a potential oncoprotein in HCV-related HCC by measuring the levels of NR4A1 and Runt-related transcription factor 3 (RUNX3), which are associated with tumor suppression and chemotherapy resistance. In the present study, PcDNA3.1-core and RUNX3 siRNA were transfected into LO2 and HepG2 cells using Lipofectamine 2000. LO2-core, HepG2-core, LO2-RUNX3 (low) and control cells were treated with different concentrations of cisplatin for 72 h, and cell proliferation and apoptosis were assayed using the CellTiter 96(®)Aqueous Non-Radioactive Cell Proliferation Assay Kit. Western blot and real time PCR analyses were used to detect NR4A1, RUNX3, smad7, Cyclin D1 and BAX. Confocal microscopy was used to determine the levels of NR4A1 in HepG2 and HepG2-core cells. The growth rate of HepG2-core cells was considerably greater than that of HepG2 cells. HCV core protein increased the expression of cyclin D1 and decreased the expressions of NR4A1 and RUNX3. In LO2 - RUNX3 (low), the rate of cell proliferation and the level of cisplatin resistance were the same as in the LO2 -core. These results suggest that HCV core protein decreases the sensitivity of hepatocytes to cisplatin by inhibiting the expression of NR4A1 and promoting the expression of smad7, which negatively regulates the TGF-β pathway. This effect results in down regulation of RUNX3, a target of the TGF-β pathway. Taken together, these findings indicate that in hepatocytes, HCV core protein increases drug resistance and inhibits cell apoptosis by inhibiting the expressions of NR4A1 and RUNX3.

Gene therapies for hepatitis C virus

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis and infects approximately three to four million people per year, about 170 million infected people in total, making it one of the major global health problems. In a minority of cases HCV is cleared spontaneously, but in most of the infected individuals infection progresses to a chronic state associated with high risk to develop liver cirrhosis, hepatocellular cancer, or liver failure. The treatment of HCV infection has evolved over the years. Interferon (IFN)-α in combination with ribavirin has been used for decades as standard therapy. More recently, a new standard-of-care treatment has been approved based on a triple combination with either HCV protease inhibitor telaprevir or boceprevir. In addition, various options for all-oral, IFN-free regimens are currently being evaluated. Despite substantial improvement of sustained virological response rates, some intrinsic limitations of these new direct-acting antivirals, including serious side effects, the risk of resistance development and high cost, urge the development of alternative or additional therapeutic strategies. Gene therapy represents a feasible alternative treatment. Small RNA technology, including RNA interference (RNAi) techniques and antisense approaches, is one of the potentially promising ways to investigate viral and host cell factors that are involved in HCV infection and replication. With this, newly developed gene therapy regimens will be provided to treat HCV. In this chapter, a comprehensive overview guides you through the current developments and applications of RNAi and microRNA-based gene therapy strategies in HCV treatment.

Mitochondrial iron accumulation exacerbates hepatic toxicity caused by hepatitis C virus core protein

Patients with long-lasting hepatitis C virus (HCV) infection are at major risk of hepatocellular carcinoma (HCC). Iron accumulation in the livers of these patients is thought to exacerbate conditions of oxidative stress. Transgenic mice that express the HCV core protein develop HCC after the steatosis stage and produce an excess of hepatic reactive oxygen species (ROS). The overproduction of ROS in the liver is the net result of HCV core protein-induced dysfunction of the mitochondrial respiratory chain. This study examined the impact of ferric nitrilacetic acid (Fe-NTA)-mediated iron overload on mitochondrial damage and ROS production in HCV core protein-expressing HepG2 (human HCC) cells (Hep39b cells). A decrease in mitochondrial membrane potential and ROS production were observed following Fe-NTA treatment. After continuous exposure to Fe-NTA for six days, cell toxicity was observed in Hep39b cells, but not in mock (vector-transfected) HepG2 cells. Moreover, mitochondrial iron ((59)Fe) uptake was increased in the livers of HCV core protein-expressing transgenic mice. This increase in mitochondrial iron uptake was inhibited by Ru360, a mitochondrial Ca(2+) uniporter inhibitor. Furthermore, the Fe-NTA-induced augmentation of mitochondrial dysfunction, ROS production, and cell toxicity were also inhibited by Ru360 in Hep39b cells. Taken together, these results indicate that Ca(2+) uniporter-mediated mitochondrial accumulation of iron exacerbates hepatocyte toxicity caused by the HCV core protein.

Oxidative stress and hepatic Nox proteins in chronic hepatitis C and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common liver cancer and a leading cause of cancer-related mortality in the world. Hepatitis C virus (HCV) is a major etiologic agent of HCC. A majority of HCV infections lead to chronic infection that can progress to cirrhosis and, eventually, HCC and liver failure. A common pathogenic feature present in HCV infection, and other conditions leading to HCC, is oxidative stress. HCV directly increases superoxide and H2O2 formation in hepatocytes by elevating Nox protein expression and sensitizing mitochondria to reactive oxygen species generation while decreasing glutathione. Nitric oxide synthesis and hepatic iron are also elevated. Furthermore, activation of phagocytic NADPH oxidase (Nox) 2 of host immune cells is likely to exacerbate oxidative stress in HCV-infected patients. Key mechanisms of HCC include genome instability, epigenetic regulation, inflammation with chronic tissue injury and sustained cell proliferation, and modulation of cell growth and death. Oxidative stress, or Nox proteins, plays various roles in these mechanisms. Nox proteins also function in hepatic fibrosis, which commonly precedes HCC, and Nox4 elevation by HCV is mediated by transforming growth factor β. This review summarizes mechanisms of oncogenesis by HCV, highlighting the roles of oxidative stress and hepatic Nox enzymes in HCC.

Interaction networks of hepatitis C virus NS4B: implications for antiviral therapy

Hepatitis C virus (HCV) is an important human pathogen infecting more than 170 million people worldwide with approximately three million new cases each year. HCV depends heavily on interactions between viral proteins and host factors for its survival and propagation. Among HCV viral proteins, the HCV non-structural protein 4B (NS4B) has been shown to mediate virus-host interactions that are essential for HCV replication and pathogenesis and emerged as the target for anti-HCV therapy. Here, we reviewed recent knowledge about the NS4B interaction networks with host factors and its possible regulatory mechanisms, which will both advance our understanding of the role of NS4B in HCV life cycle and illuminate potential viral and host therapeutic targets.

Persistent expression of hepatitis C virus non-structural proteins leads to increased autophagy and mitochondrial injury in human hepatoma cells

HCV infection is a major cause of chronic liver disease and liver cancer in the United States. To address the pathogenesis caused by HCV infection, recent studies have focused on the direct cytopathic effects of individual HCV proteins, with the objective of identifying their specific roles in the overall pathogenesis. However, this approach precludes examination of the possible interactions between different HCV proteins and organelles. To obtain a better understanding of the various cytopathic effects of and cellular responses to HCV proteins, we used human hepatoma cells constitutively replicating HCV RNA encoding either the full-length polyprotein or the non-structural proteins, or cells constitutively expressing the structural protein core, to model the state of persistent HCV infection and examined the combination of various HCV proteins in cellular pathogenesis. Increased reactive oxygen species (ROS) generation in the mitochondria, mitochondrial injury and degeneration, and increased lipid accumulation were common among all HCV protein-expressing cells regardless of whether they expressed the structural or non-structural proteins. Expression of the non-structural proteins also led to increased oxidative stress in the cytosol, membrane blebbing in the endoplasmic reticulum, and accumulation of autophagocytic vacuoles. Alterations of cellular redox state, on the other hand, significantly changed the level of autophagy, suggesting a direct link between oxidative stress and HCV-mediated activation of autophagy. With the wide-spread cytopathic effects, cells with the full-length HCV polyprotein showed a modest antioxidant response and exhibited a significant increase in population doubling time and a concomitant decrease in cyclin D1. In contrast, cells expressing the non-structural proteins were able to launch a vigorous antioxidant response with up-regulation of antioxidant enzymes. The population doubling time and cyclin D1 level were also comparable to that of control cells. Finally, the cytopathic effects of core protein appeared to focus on the mitochondria without remarkable disturbances in the cytosol.

Hepatitis B and C virus hepatocarcinogenesis: lessons learned and future challenges

Worldwide, hepatocellular carcinoma (HCC) is one of the most common cancers. It is thought that 80% of hepatocellular carcinomas are linked to chronic infections with the hepatitis B (HBV) or hepatitis C (HCV) viruses. Chronic HBV and HCV infections can alter hepatocyte physiology in similar ways and may utilize similar mechanisms to influence the development of HCC. There has been significant progress towards understanding the molecular biology of HBV and HCV and identifying the cellular signal transduction pathways that are altered by HBV and HCV infections. Although the precise molecular mechanisms that link HBV and HCV infections to the development of HCC are not entirely understood, there is considerable evidence that both inflammatory responses to infections with these viruses, and associated destruction and regeneration of hepatocytes, as well as activities of HBV- or HCV-encoded proteins, contribute to hepatocyte transformation. In this review, we summarize progress in defining mechanisms that may link HBV and HCV infections to the development of HCC, discuss the challenges of directly defining the processes that underlie HBV- and HCV-associated HCC, and describe areas that remain to be explored.

Hepatitis C virus NS3 protein can activate the Notch-signaling pathway through binding to a transcription factor, SRCAP

Persistent infections of hepatitis C virus (HCV) are known to be a major risk factor for causing hepatocellular carcinomas. Nonstructural protein 3 (NS3) of HCV has serine protease and RNA helicase domains, and is essential for the viral replication. Further, NS3 is also considered to be involved in the development of HCV-induced hepatocellular carcinomas. In this report, we focus on the function of NS3 protein, and propose a novel possible molecular mechanism which is thought to be related to the tumorigenesis caused by the persistent infection of HCV. We identified SRCAP (Snf2-related CBP activator protein) as a NS3 binding protein using yeast two-hybrid screening, and a co-immunoprecipitation assay demonstrated that NS3 can bind to SRCAP in mammalian cells. The results of a reporter gene assay using Hes-1 promoter which is known to be a target gene activated by Notch, indicate that NS3 and SRCAP cooperatively activate the Hes-1 promoter in Hep3B cells. In addition, we show in this report that also p400, which is known as a protein closely resembling SRCAP, would be targeted by NS3. NS3 exhibited binding activity also to the 1449–1808 region of p400 by a co-immunoprecipitation assay, and further the activation of the Notch-mediated transcription of Hes-1 promoter by NS3 decreased significantly by the combined silencing of SRCAP and p400 mRNA using short hairpin RNA. These results suggest that the HCV NS3 protein is involved in the activation of the Notch-signaling pathway through the targeting to both SRCAP and p400.

Epidemiology and management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a major world health problem because of the high incidence and case fatality rate. In most patients, the diagnosis of HCC is made at an advanced stage, which limits the application of curative treatments. Most HCCs develop in patients with underlying chronic liver disease. Chronic viral hepatitis B and C are the major causes of liver cirrhosis and HCC. Recent improvements in treatment of viral hepatitis and in methods for surveillance and therapy for HCC have contributed to better survival of patients with HCC. This article reviews the epidemiology, cause, prevention, clinical manifestations, surveillance, diagnosis, and treatment approach for HCC.

New opportunities in anti-hepatitis C virus drug discovery: targeting NS4B

Current therapy for chronic hepatitis C virus (HCV) infection constitutes a combination of pegylated interferon alfa-2a or alpha-2b and ribavirin. Although successful for many patient populations, this regimen has numerous limitations, including non-response, relapse, poor tolerability and long duration of treatment. To address these shortcomings, new small molecule agents are advancing in clinical development. Most of the current clinical candidates act by directly inhibiting key enzymes in the viral life-cycle: the NS5B polymerase, or the NS3/4A protease. Less well-studied, the non-structural 4B (NS4B) protein has recently emerged as an alternative target for Direct-acting Antiviral Agents (DAAs). NS4B is a 27-kDa membrane protein that is primarily involved in the formation of membrane vesicles--also named membranous web--used as scaffold for the assembly of the HCV replication complex. In addition, NS4B contains NTPase and RNA binding activities, as well as anti-apoptotic properties. This review summarizes the current understanding of the structure and functions of NS4B, an essential component of the replication machinery of HCV. In this literature and patent review, we report the recent developments in anti-NS4B drug discovery. These advances open the possibility for future combination therapies with other DAAs.

[Epidemiology, natural history and pathogenesis of hepatocellular carcinoma]

Hepatocellular carcinoma (HCC) is the main type of primary liver cancers and the third most common cause of cancer mortality worldwide. In France, rising number between 5000 and 6000 cases are diagnosed each year. The major risk factor for hepatocellular carcinoma is chronic hepatitis: viral hepatitis B, viral hepatitis C, consumption of alcohol, hemochromatosis. Hepatocellular carcinoma is closely associated to liver cirrhosis, which is a true precancerous state. Because hepatocarcinogenesis is a long and heterogeneous process, there is still much to understand. Many genetic and epigenetic alterations are described leading to changes in cellular signalling cascades involved in regulation of growth, differentiation, apoptosis, motility. Hepatitis viruses play a direct oncogenic role through the interaction between viral and cellular proteins, which control cell homeostasis, or by the integration of hepatitis B virus genome into the host genome. Furthermore, hepatitis viruses play an indirect oncogenic role by causing chronic inflammation and hepatocyte regeneration related to viral hepatopathy. In expectation of a better understanding of hepatocarcinogenesis and new treatments, prevention from risk factors and ultrasonographic screening of patients with cirrhosis should increase prognosis.

Oncogenic potential of hepatitis C virus proteins

Chronic hepatitis C virus (HCV) infection is a major risk factor for liver disease progression, and may lead to cirrhosis and hepatocellular carcinoma (HCC). The HCV genome contains a single-stranded positive sense RNA with a cytoplasmic lifecycle. HCV proteins interact with many host-cell factors and are involved in a wide range of activities, including cell cycle regulation, transcriptional regulation, cell proliferation, apoptosis, lipid metabolism, and cell growth promotion. Increasing experimental evidences suggest that HCV contributes to HCC by modulating pathways that may promote malignant transformation of hepatocytes. At least four of the 10 HCV gene products, namely core, NS3, NS5A and NS5B play roles in several potentially oncogenic pathways. Induction of both endoplasmic reticulum (ER) stress and oxidative stress by HCV proteins may also contribute to hepatocyte growth promotion. The current review identifies important functions of the viral proteins connecting HCV infections and potential for development of HCC. However, most of the putative transforming potentials of the HCV proteins have been defined in artificial cellular systems, and need to be established relevant to infection and disease models. The new insight into the mechanisms for HCV mediated disease progression may offer novel therapeutic targets for one of the most devastating human malignancies in the world today.

Hepatocellular carcinoma in patients with chronic hepatitis C virus infection without cirrhosis

AIM: To investigate and characterise patients with chronic hepatitis C virus (HCV) infection presenting with hepatocellular carcinoma (HCC) in the absence of cirrhosis.

METHODS: Patients with chronic hepatitis C infection without cirrhosis presenting with HCC over a 2-year period were identified. The clinical case notes, blood test results and histological specimens were reviewed to identify whether additional risk factors for the development of HCC were present.

RESULTS: Six patients (five male, one female) with chronic hepatitis C infection without cirrhosis presented to a single centre with HCC over a 2-year period. Five patients were treated by surgical resection and one patient underwent liver transplantation. Evaluation of generous histological specimens confirmed the presence of HCC and the absence of cirrhosis in all cases. The degree of fibrosis of the background liver was staged as mild (n = 1), moderate (n = 4) or bridging fibrosis (n = 1). Review of the clinical case notes revealed that all cases had an additional risk factor for the development of HCC (four had evidence of past hepatitis B virus infection; two had a history of excessive alcohol consumption; a further patient had prolonged exposure to immune suppression).

CONCLUSION: HCC does occur in patients with non-cirrhotic HCV infection who have other risk factors for hepatocarcinogenesis.

Hepatocellular carcinoma in non-cirrhotic liver: a reappraisal

Although not frequently, hepatocellular carcinoma (HCC) can ensue in a non-cirrhotic liver. As compared to cirrhotic HCC, this kind of tumour has some peculiarities, such as: (a) a lower male preponderance and a bimodal age distribution; (b) a lower prevalence of the three main risk factors (hepatitis B and C virus infections and alcohol abuse), with an increased prevalence of other etiologic factors, such as exposure to genotoxic substances and sex hormones, inherited diseases, genetic mutations; (c) a more advanced tumour stage at the time of diagnosis, as it is usually detected due to the occurrence of cancer-related symptoms, outside any scheduled surveillance program; (d) a much higher amenability to hepatic resection, due to the low risk of liver failure even after extended parenchymal mutilation; (e) overall and disease-free survivals after resection of non-advanced tumours (meeting the Milano criteria) comparable to that obtained with liver transplantation in cirrhotic patients carrying an early tumour; (f) overall survival strictly dependent on tumour burden (and its recurrence) and barely influenced by liver function.

Recent insights on risk factors of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a disease prevalent in many populations worldwide. It initiates many economic and health problems in management modalities and leads to increasing mortality rates. Worldwide, trials have attempted to discover specific early markers for detection and prediction of the disease, hoping to set a more precise strategy for liver cancer prevention. Unfortunately, many economic, cultural and disciplinary levels contribute to confounding preventive strategies. Many risk factors contribute to predisposition to HCC, which can present individually or simultaneously. Previous articles discussed many risk factors for hepatocellular carcinogenesis; however, most of them didn't consider collectively the most recent data relating to causes. In this article, the pathogenesis and risk factors of HCC are discussed. Most of the intermediary steps of HCC involve molecular and transcriptional events leading to hepatocyte malignant transformation. These steps are mainly triggered by hepatitis B, C or transfusion-transmitted virus, either alone, or with other factors. Diabetes seems to be a major contributing risk factor. Schistosomiasis, a blood infestation, mostly affects Nile basin inhabitants leading to bladder, renal and hepatic cancers. Alcoholism, food and water pollutants and some drugs can also lead to HCC. Additionally, some hereditary diseases, as hemochromatosis, α-1-antitrypsin deficiency and tyrosinaemia are known to lead to the development of HCC, if not well managed.

Hepatitis C virus-induced hepatocarcinogenesis

Although there is strong evidence that hepatitis C virus (HCV) is one of the leading causes of hepatocellular carcinoma (HCC), there is still much to understand regarding the mechanism of HCV-induced transformation. While liver fibrosis resulting from long-lasting chronic inflammation and liver regeneration resulting from immune-mediated cell death are likely factors that contribute to the development of HCC, the direct role of HCV proteins remains to be determined. In vitro studies have shown that HCV expression may interfere with cellular functions that are important for cell differentiation and cell growth. However, most studies were performed in artificial models which can only give clues for potential mechanisms that need to be confirmed in more relevant models. Furthermore, the difficulty to identify HCV proteins and infected liver cells in patients, contributes to the complexity of our current understanding. For these reasons, there is currently very little experimental evidence for a direct oncogenic role of HCV. Further studies are warranted to clarify these issues.

Cancer and viral infections in immunocompromised individuals

Over the last 30 years, the increasing use of organ and stem cell transplantation and the AIDS epidemic have led to the realization that some, but not all, human cancers occur more frequently in immunosuppressed individuals. With the notable exception of non-melanoma skin cancer (NMSC), most tumors that show strongly increased incidence rates in both transplant recipients and AIDS patients have been found to have a viral etiology. Among these are Kaposi sarcoma, diffuse large cell B-cell lymphoma, cervical cancer, liver cancer, Merkel cell carcinoma and a subset of Hodgkin's disease. A viral etiology for NMSC, i.e., beta- and gamma-subtypes of human papillomavirus, has been suggested and investigated for many years, but remains controversial. In addition, the moderately increased incidence rates of several other cancers in immunosuppressed individuals (e.g., Vajdic and van Leeuwen, Int J Cancer, in press) could indicate that additional infectious causes for at least some human cancers remain to be discovered. The controversy surrounding the role of cutaneous papillomavirus subtypes in the pathogenesis of NMSC illustrates the difficulties encountered when weighing the epidemiological and molecular biology evidence arguing for an involvement of highly prevalent viruses in certain types of cancer.

Hepatitis C virus NS4B induces unfolded protein response and endoplasmic reticulum overload response-dependent NF-kappaB activation

Hepatitis C virus nonstructural protein 4B (NS4B) is an endoplasmic reticulum (ER) membrane associated protein and a potent causative factor of ER stress. Here we reported that unfolded protein response (UPR) can be activated by HCV NS4B through inducing both XBP1 mRNA splicing and ATF6 cleavage in human hepatic cells. Flow cytometric analysis revealed that HCV NS4B stimulates the production of reactive oxygen species (ROS) by perturbing intracellular Ca(2+) homeostasis. Luciferase assay showed that HCV NS4B also activates the multifunctional transcription factor, NF-kappaB, in a dose-dependent manner through Ca(2+) signaling and ROS. Further immunoblot analysis showed that HCV NS4B promotes NF-kappaB translocation into the nucleus via protein-tyrosine kinase (PTK) mediated phosphorylation and subsequent degradation of IkappaBalpha. These studies provide an important insight into the implication of NS4B in HCV life cycle and HCV-associated liver disease by affecting host intracellular signal transduction pathways.

Mutations in the hepatitis C virus core gene are associated with advanced liver disease and hepatocellular carcinoma

PURPOSE

Hepatitis C virus (HCV) infection can promote the development of hepatocellular carcinoma (HCC). Published data implicate the HCV core gene in oncogenesis. We tested the hypothesis that core gene sequences from HCC patients differ from those of patients without cirrhosis/HCC.

EXPERIMENTAL DESIGN

Full-length HCV sequences from HCC patients and controls were obtained from the investigators and GenBank and compared with each other. A logistic regression model was developed to predict the HCC risk of individual point mutations and other sequence features. Mutations in partial sequences (bases 36-288) from HCC patients and controls were also analyzed. The first base of the AUG start codon was designated position 1.

RESULTS

A logistic regression model developed through analysis of full-length core gene sequences identified seven polymorphisms significantly associated with increased HCC risk (36G/C, 209A, 271U/C, 309A/C, 435A/C, 481A, and 546A/C) and an interaction term (for 209A-271U/C) that had an odds ratio <1.0. Three of these polymorphisms could be analyzed in the partial sequences. Two of them, 36G/C and 209A, were again associated with increased HCC risk, but 271U/C was not. The odds ratio of 209A-271U/C was not significant.

CONCLUSIONS

HCV core genes from patients with and without HCC differ at several positions. Of interest, 209A has been associated with IFN resistance and HCC in previous studies. Our findings suggest that HCV core gene sequence data might provide useful information about HCC risk. Prospective investigation is needed to establish the temporal relationship between appearance of the viral mutations and development of HCC.

Hepatitis C virus nonstructural 4B protein modulates sterol regulatory element-binding protein signaling via the AKT pathway

Hepatitis C virus (HCV) infection is often associated with hepatic steatosis and yet the molecular mechanisms of HCV-associated steatosis are poorly understood. Because sterol regulatory element-binding proteins (SREBPs) are the major transcriptional factors in lipogenic gene expression including fatty acid synthase (FAS), we examined the effects of HCV nonstructural proteins on the signaling pathways of SREBP. In this study, we demonstrated that HCV nonstructural 4B (NS4B) protein increased the transcriptional activities of SREBPs. We also showed that HCV NS4B enhanced the protein expression levels of SREBPs and FAS. This was further confirmed in the context of viral RNA replication and HCV infection. The up-regulation of both SREBP and FAS by NS4B protein required phosphatidylinositol 3-kinase activity. We also demonstrated that NS4B protein induced a lipid accumulation in hepatoma cells. In addition, NS4B protein synergistically elevated the transcriptional activity of HCV core-mediated SREBP-1. These results strongly suggest that NS4B may play an important role in HCV-associated liver pathogenesis by modulating the SREBP signaling pathway.

The nucleotide binding motif of hepatitis C virus NS4B can mediate cellular transformation and tumor formation without Ha-ras co-transfection

Hepatitis C virus (HCV) is an important cause of chronic liver disease and is complicated by hepatocellular carcinoma (HCC). Mechanisms whereby the virus promotes cellular transformation are poorly understood. We hypothesized that the guanosine triphosphatase activity encoded in the HCV NS4B protein's nucleotide binding motif (NBM) might play a role in the transformation process. Here we report that NS4B can transform NIH-3T3 cells, leading to tumor formation in vivo. This transformation was independent of co-transfection with activated Ha-ras. Detailed analyses of NS4B mutants revealed that this transforming activity could be progressively inhibited and completely abrogated by increasing genetic impairment of the NS4B nucleotide binding motif.

CONCLUSION

NS4B has in vitro and in vivo tumorigenic potential, and the NS4B transforming activity is indeed mediated by its NBM. Moreover, our results suggest that pharmacological inhibition of the latter might inhibit not only HCV replication but also the associated HCC.

Molecular virology of the hepatitis C virus: implication for novel therapies

With the advent of second-generation agents that for the first time specifically target individual HCV proteins, HCV-specific therapy has arrived. The study of HCV molecular virology has helped make this possible and is helping us to identify additional new antiviral targets that will be targeted by third-generation drugs. Key to these efforts is the development of high-efficiency HCV replicons. The future effective pharmacologic control of HCV will likely consist of a cocktail of simultaneously administered virus-specific agents with independent targets. This should minimize the emergence of resistance against any single agent. The way we treat HCV should change dramatically over the next few years.

Correlation of amino acid variations within nonstructural 4B protein with initial viral kinetics during interferon-alpha-based therapy in HCV-1b-infected patients

Chronic hepatitis C is a major cause of liver cirrhosis leading to chronic liver failure and hepatocellular carcinoma. Different hepatitis C virus (HCV) proteins have been associated with resistance to interferon-alpha-based therapy. However, the exact mechanisms of virus-mediated interferon resistance are not completely understood. The importance of amino acid (aa) variations within the HCV nonstructural (NS)4B protein for replication efficiency and viral decline during the therapy is unknown. We investigated pretreatment sera from 42 patients with known outcome to interferon-based therapy. The complete NS4B gene was amplified and sequenced. Mutational analyses of predicted conformational, functional, structural and phylogenetic properties of the deduced aa sequences were performed. The complete NS4B protein was highly conserved with a median frequency of 0.015 +/- 0.009 aa exchanges (median +/- SD, 4.00 +/- 2.31). Especially within the predicted transmembranous domains of the NS4B protein, the mean number of aa variations was low (median frequency, 0.013 +/- 0.013). Neither the number of aa variations nor specific aa exchanges were correlated with HCV RNA serum concentration at baseline. A rapid initial HCV RNA decline of >/=1.5 log(10) IU/mL at week 2 of interferon-based therapy was associated with a higher frequency of nonconservative aa exchanges within the complete NS4B protein in comparison with patients with a nonrapid HCV RNA decline (median frequency, 0.011 +/- 0.005 vs 0.004 +/- 0.003, P = 0.006). Overall, the aa sequence of the NS4B protein was highly conserved, indicating an important role for replication in vivo. Amino acid variations with relevant changes of physicochemical properties may influence replication efficiency, associated with a rapid early virological response.

Subversion of innate host antiviral strategies by the hepatitis C virus

Since its discovery in 1989, Hepatitis C Virus (HCV) has been recognized as a major cause of chronic hepatitis, end-stage cirrhosis and hepatocellular carcinoma affecting world wide more than 210 million people. The fact that 80% of newly infected patients fail to control infection, the slow development of overt disease and immune-response as well as the unsatisfying results of current IFN/ribavirin combination therapy suggests that the hepatitis C virus developed powerful strategies to evade and to antagonize the immune response of the host and to resist the antiviral actions of interferons. During the last 10 years several viral strategies have been uncovered for control and evasion from cellular antiviral host response initiated by the pathogen-associated molecular pattern recognizing receptors RIG1 and TLR3 and mediated by the release of type I interferon and subsequent induction of interferon stimulated genes. This review highlights recent results providing an idea of how the hepatitis C virus interferes with the different steps of initial antiviral host-response and establishes persistent infection.

[Pathogenesis of the hepatocellular carcinoma associated with hepatitis C virus]

Hepatitis C virus (HCV) is known as one of major causative agents of hepatocellular carcinoma (HCC) in the world. The pathogenesis of HCC associated with HCV, however, has not been fully elucidated yet, although the chronic inflammation induced by HCV infection is considered to contribute greatly to the HCC development. Some HCV gene products have been shown to possess transformation activities in cultured cells. Several oncogenic signal pathways in the cells were modulated by the exogenous expression of the HCV proteins. A few lines of the transgenic mice producing the core protein among those products was also reported to develop liver steatosis and HCC without apparent inflammation after rearing for a relatively long period. So, the functions of the core on the modulation of cellular events have been extensively examined and characterized. Here, I would summarize the progress of the research for the pathogenesis of HCC associated with HCV.

Viral hepatitis and liver cancer: the case of hepatitis C

Chronic infection with the hepatitis C virus (HCV) is a major risk factor for the development of hepatocellular carcinoma (HCC) worldwide. The pathogenesis of HCC in HCV infection has extensively been analysed. Hepatitis C virus-induced chronic inflammation and the effects of cytokines in the development of fibrosis and liver cell proliferation are considered as one of the major pathogenic mechanisms. Increasing experimental evidence suggests that HCV contributes to HCC by directly modulating pathways that promote the malignant transformation of hepatocytes. Hepatitis C virus is an RNA virus that does not integrate into the host genome but HCV proteins interact with many host-cell factors well beyond their roles in the viral life cycle and are involved in a wide range of activities, including cell signaling, transcription, cell proliferation, apoptosis, membrane rearrangements, vesicular trafficking and translational regulation. At least four of the HCV gene products, namely HCV core, NS3, NS4B and NS5A, have been shown to exhibit transformation potential in tissue culture and several potentially oncogenic pathways have been shown to be altered by the expression of HCV proteins. Both HCV core and NS5A induce the accumulation of wild-type beta-catenin and the Wnt-beta-catenin pathway emerges as a common target for HCV (and HBV) in human HCCs, also independently from axin/beta-catenin gene mutations. Induction of both endoplasmic reticulum stress and oxidative stress by HCV proteins might also contribute to HCV transformation. Most of the putative transforming functions of the HCV proteins have been defined in artificial cellular systems, which may not be applicable to HCV infection in vivo, and still need to be established in relevant infection and disease models.

E2 of hepatitis C virus inhibits apoptosis

Hepatitis C virus (HCV) is the major causative agent of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma, and can be involved in very long chronic infections up to 30 years or more. Therefore, it has been speculated that HCV possesses mechanisms capable of modulating host defense systems such as innate and adaptive immunity. To investigate this virus-host interaction, we generated HCV replicons containing various HCV structural proteins and then analyzed the sensitivity of replicon-containing cells to the apoptosis-inducing agent, TRAIL. TRAIL-induced apoptosis was monitored by cleavage of procaspase-3 and procaspase-9 as well as that of their substrate poly(ADP-ribose) polymerase. TRAIL-induced apoptosis was inhibited in cells expressing HCV E2. Moreover, expression of HCV E2 enhanced the colony forming efficiency of replicon-containing cells by 25-fold. Blockage of apoptosis by E2 seems to be related to inhibition of TRAIL-induced cytochrome c release from the mitochondria. Based on these results, we propose that E2 augments persistent HCV infection by blocking host-induced apoptosis of infected cells.

Interactions between virus proteins and host cell membranes during the viral life cycle

The structure and function of cells are critically dependent on membranes, which not only separate the interior of the cell from its environment but also define the internal compartments. It is therefore not surprising that the major steps of the life cycle of viruses of animals and plants also depend on cellular membranes. Indeed, interactions of viral proteins with host cell membranes are important for viruses to enter into host cells, replicate their genome, and produce progeny particles. To replicate its genome, a virus first needs to cross the plasma membrane. Some viruses can also modify intracellular membranes of host cells to create a compartment in which genome replication will take place. Finally, some viruses acquire an envelope, which is derived either from the plasma membrane or an internal membrane of the host cell. This paper reviews recent findings on the interactions of viral proteins with host cell membranes during the viral life cycle.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Genetic similarity of hepatitis C virus and fibrosis progression in chronic and recurrent infection after liver transplantation

The effect of hepatitis C virus (HCV) genetic heterogeneity on clinical features of post-transplantation hepatitis C is controversial. Different regions of the HCV genome have been associated with apoptosis, fibrosis, and other pathways leading to liver damage in chronic HCV infection. Besides, differences in immunodominant regions, such as NS3, may influence HCV-specific immune responses and disease outcome. In the liver transplant setting, a recent study has reported a positive association between HCV-1b Core region genetic relatedness 5-year post-transplantation and histological severity of recurrent hepatitis C. We have compared nucleotide sequences of HCV Core, NS3 and NS5b regions in HCV-1b-infected patients 3 years post-transplantation (n = 22). A cohort of nontransplanted patients (n = 22) was used as control of natural chronic HCV-1b infection. Histological evaluation was used to define the rate of fibrosis progression. Molecular variance analysis did not show significant differences in HCV sequences between transplanted and nontransplanted patients, or between those with fast or slow fibrosis progression. The same results were obtained when analysing phylogenetic trees for Core, NS3 and NS5b regions. A more appropriate clustering method (using minimum spanning networks) revealed a significant positive relationship between HCV genetic similarity in Core (r = 0.550, P < 0.01) and NS5b regions (r = 0.847, P < 0.01) and the yearly rate of fibrosis progression in nontransplanted patients which, in contrast, was not observed in transplanted patients. Our results indicate that some strains of HCV-1b might be more pathogenic in the natural course of chronic infection by this virus subtype. In the liver transplant setting, when the immune response is severely compromised, other mechanisms are probably more important in determining hepatitis C progression.

Subcellular localization and membrane topology of the Dengue virus type 2 Non-structural protein 4B

Dengue virus (DV) is a member of the family Flaviviridae. These positive strand RNA viruses encode a polyprotein that is processed in case of DV into 10 proteins. Although for most of these proteins distinct functions have been defined, this is less clear for the highly hydrophobic non-structural protein (NS) 4B. Despite its possible role as an antagonist of the interferon-induced antiviral response, this protein may play an additional more direct role for viral replication. In this study we determined the subcellular localization, membrane association, and membrane topology of DV NS4B. We found that NS4B resides primarily in cytoplasmic foci originating from the endoplasmic reticulum. NS4B colocalizes with NS3 and double-stranded RNA, an intermediate of viral replication, arguing that NS4B is part of the membrane-bound viral replication complex. Biochemical analysis revealed that NS4B is an integral membrane protein, and that its preceding 2K signal sequence is not required for this integration. We identified three membrane-spanning segments in the COOH-terminal part of NS4B that are sufficient to target a cytosolic marker protein to intracellular membranes. Furthermore, we established a membrane topology model of NS4B in which the NH2-terminal part of the protein is localized in the endoplasmic reticulum lumen, whereas the COOH-terminal part is composed of three trans-membrane domains with the COOH-terminal tail localized in the cytoplasm. This topology model provides a good starting point for a detailed investigation of the function of NS4B in the DV life cycle.

Molecular virology of the hepatitis C virus: implication for novel therapies

The study of hepatitis C virus (HCV) molecular virology is helping to shape the future of our anti-HCV strategies by identifying new antiviral targets. With the advent of agents that specifically target individual HCV proteins, HCV-specific therapy has arrived. Key to these efforts is the development of high-efficiency HCV replicons. The future effective pharmacologic control of HCV will likely consist of a cocktail of simultaneously administered virus-specific agents with independent targets. This should minimize the emergence of resistance against any single agent. The way we treat HCV should change dramatically over the next few years.

Gene expression profiles of HeLa Cells impacted by hepatitis C virus non-structural protein NS4B

By a cDNA array representing 2308 signal transduction-related genes, we studied the expression profiles of HeLa cells stably transfected by Hepatitis C virus nonstructural protein 4B (HCV-NS4B). The alterations of the expression of four genes were confirmed by real-time quantitative RTPCR; and the aldo-keto reductase family 1, member C1 (AKR1C1) enzyme activity was detected in HCV-NS4B transiently transfected HeLa cells and Huh-7, a human hepatoma cell line. Of the 2,308 genes we examined, 34 were up-regulated and 56 were down-regulated. These 90 genes involved oncogenes, tumor suppressors, cell receptors, complements, adhesions, transcription and translation, cytoskeleton and cellular stress. The expression profiling suggested that multiple regulatory pathways were affected by HCV-NS4B directly or indirectly. And since these genes are related to carcinogenesis, host defense system and cell homeostatic mechanism, we can conclude that HCV-NS4B could play some important roles in the pathogenesis mechanism of HCV.

Relation between hepatocyte G1 arrest, impaired hepatic regeneration, and fibrosis in chronic hepatitis C virus infection

BACKGROUNDS & AIMS

An increased risk of hepatitis C virus (HCV)-related cirrhosis is associated with hepatic steatosis, older age, and high alcohol consumption, which could be explained by synergistic effects on cell proliferation. We aimed to investigate hepatocyte cell cycle state and phase distribution in chronic HCV infection.

METHODS

Liver biopsy specimens diagnostic for chronic HCV (70), liver regeneration following transplant-related ischemic-reperfusion injury (15), and "normal" liver adjacent to colorectal cancer metastasis (10) were studied. Immunohistochemistry was used to detect cell cycle phase markers cyclin D1 (maximal in G 1 ), cyclin A (S), cyclin B1 (cytoplasmic during G 2 ) and phosphorylated histone 3 protein (mitosis), mini-chromosome maintenance protein 2 (Mcm-2; present throughout the cell cycle), and cyclin-dependent kinase inhibitor p21, which inhibits G 1 /S progression.

RESULTS

Hepatocyte Mcm-2 expression was elevated in chronic HCV and liver regeneration (13% vs 26.4%) but negligible in "normal" liver. In proportion to Mcm-2, there was no difference in cyclin D1 between chronic HCV infection and liver regeneration (51.6% of Mcm-2-positive hepatocytes vs 52.6%). In contrast, there was a striking reduction in cyclin A (3% vs 16.3%), cyclin B1 (.4% vs 2.3%), and phosphorylated histone 3 protein (0% vs 3.8%) in chronic HCV infection compared with liver regeneration. In chronic HCV infection, Mcm-2 and p21 expression were associated with fibrosis stage and positive serum HCV RNA.

CONCLUSIONS

The data are consistent with hepatocyte G 1 arrest in chronic HCV infection. This could impair hepatocellular function and limit hepatic regeneration.

An N-terminal amphipathic helix in hepatitis C virus (HCV) NS4B mediates membrane association, correct localization of replication complex proteins, and HCV RNA replication

Like other positive-strand RNA viruses, hepatitis C virus (HCV) is believed to replicate its RNA in association with host cell cytoplasmic membranes. Because of its association with such membranes, NS4B, one of the virus's nonstructural proteins, may play an important role in this process, although the mechanistic details are not well understood. We identified a putative N-terminal amphipathic helix (AH) in NS4B that mediates membrane association. Introduction of site-directed mutations designed to disrupt the hydrophobic face of the AH abolishes the AH's ability to mediate membrane association. An AH in NS4B is conserved across HCV isolates. Completely disrupting the amphipathic nature of NS4B's N-terminal helix abolished HCV RNA replication, whereas partial disruption resulted in an intermediate level of replication. Finally, immunofluorescence studies revealed that HCV replication complex components were mislocalized in the AH-disrupted mutant. These results identify a key membrane-targeting domain which can form the basis for developing novel antiviral strategies.

Pathogenesis of hepatitis C-associated hepatocellular carcinoma

Epidemiologic, clinical, and virologic data have shown a close association between chronic infection with hepatitis C virus (HCV) and the development of hepatocellular carcinoma (HCC). In many countries of the developed world, HCV infection accounts for more than half of the cases of HCC. HCC usually arises after 2-4 decades of infection, typically in the context of an underlying cirrhosis. Treatment of hepatitis C with interferon-alfa can lead to sustained clearance of HCV, and small prospective studies as well as larger retrospective analyses suggest that interferon therapy leads to a decrease in the incidence of HCC. Without a reliable tissue culture system or a small animal model of HCV infection, analysis of the mechanisms by which HCV leads to cancer has been difficult. Nevertheless, both in vitro expression systems and in vivo transgenic mice studies suggest that HCV has an inherent carcinogenic potential. Understanding the pathogenesis of HCV-associated HCC is important in developing effective means of prevention and treatment of this highly malignant form of cancer.

Screening of genes differentially expressed in HepG2 cells transfected with non-structural protein 4B ofhepatitis C virus

AIM: To screen genes differently expressed in human hepatoblastoma cell line HepG2 transfected with non-structural protein 4B (NS4B) of hepatitis C virus (HCV) , and to further elucidate the molecular biological mechanism of NS4B in chronic hepatitis C and carcinogenesis, and progression of hepatoma.

METHODS: Sequence-specific primers of HCV NS4B were designed and synthesized. The plasmid pBRTM3011, in which the full length of HCV-H cDNA genome was contained, was treated as the template to amplify the NS4B-coded DNA fragment with polymerase chain reaction (PCR) technique. The expressive vector of pcDNA3.1(-)-NS4B was constructed by routine molecular biological methods. The technology of cDNA microarray was adopted to detect the mRNA extracted from the HepG2 cells transfected with pcDNA3.1(-)-NS4B and pcDNA3.1(-) using lipofectamine, respectively. The expression of NS4B protein in the transfected vector was confirmed by Western blot with single chain variable region antibody.

RESULTS: The expressive vector was constructed and confirmed after restriction enzyme digestion and DNA sequencing analysis. The expression of NS4B protein in the transfected vector was confirmed by Western blot with single chain variable region antibody. High quality mRNA and cDNA were prepared. Among 1 152 genes of the DNA microarray, we found 56 genes were differently expressed in HepG2 cells transfected with NS4B, in which 22 genes were significantly up-regulated and 34 were significantly down-regulated.

CONCLUSION: Differently expressed genes are successfully screened in HepG2 cells transfected with NS4B by cDNA microarray, which may help to further elucidate the molecular mechanism of NS4B in HCV infection and development of hepatocellular carcinoma.

Activation of RNA polymerase I transcription by hepatitis C virus core protein

The hepatitis C virus (HCV) core protein has been implicated in the transregulation of various RNA polymerase (Pol) II dependent genes as well as in the control of cellular growth and proliferation. In this study, we show that the core protein, whether individually expressed or produced as part of the HCV viral polyprotein, is the only viral product that has the potential to activate RNA Pol I transcription. Deletion analysis demonstrated that the fragment containing the N-terminal 1-156 residues, but not the 1-122 residues, of HCV core protein confers the same level of transactivation activity as the full-length protein. Moreover, the integrity of the Ser(116) and Arg(117) residues of HCV core protein was found to be critical for its transregulatory functions. We used DNA affinity chromatography to analyze the human ribosomal RNA promoter associated transcription machinery, and the results indicated that recruitment of the upstream binding factor and RNA Pol I to the ribosomal RNA promoter is enhanced in the presence of HCV core protein. Additionally, the HCV core protein mediated activation of ribosomal RNA transcription is accompanied by the hyperphosphorylation of upstream binding factor on serine residues, but not on threonine residues. Moreover, HCV core protein is present within the RNA Pol I multiprotein complex, indicating its direct involvement in facilitating the formation of a functional transcription complex. Protein-protein interaction studies further indicated that HCV core protein can associate with the selectivity factor (SL1) via direct contact with a specific component, TATA-binding protein (TBP). Additionally, the HCV core protein in cooperation with TBP is able to activate RNA Pol II and Pol III mediated transcription, in addition to RNA Pol I transcription. Thus, the results of this study suggest that HCV has evolved a mechanism to deregulate all three nuclear transcription systems, partly through targeting of the common transcription factor, TBP. Notably, the ability of the HCV core protein to upregulate RNA Pol I and Pol III transcription supports its active role in promoting cell growth, proliferation, and the progression of liver carcinogenesis during HCV infection.

Steatosis and intrahepatic lymphocyte recruitment in hepatitis C virus transgenic mice

To assess the effects of constitutive hepatitis C virus (HCV) gene expression on liver, transgenic mice carrying the entire HCV open reading frame inserted in the alpha1 antitrypsin (A1AT) gene were generated. Expression of A1AT/HCV mRNA was found to be mainly limited to perivascular areas of the liver as indicated by in situ hybridization analysis. HCV core protein was detected in Western blots of liver extracts, whereas the expression of E2, NS3 and NS5 proteins was revealed by immunostaining of liver samples using HCV-specific antisera. Histological analysis of HCV transgenic mice showed that these animals develop extensive steatosis, but very little necrosis of liver tissue. Moreover, a consistent T cell infiltrate and a slight hepatocyte proliferation were observed. Phenotypic analysis of cells infiltrating the liver indicated that recruitment and/or expansion of residing CD8(+), NK, NKT and gammadelta T cells occurred in transgenic animals. Among these cells, a large fraction of CD8(+) T lymphocytes released mainly IL-10 and, to a lesser extent, IFN-gamma upon mitogenic stimulation in vitro. Furthermore, both intrahepatic lymphocytes and splenocytes did not produce cytokines in response to HCV antigens. Thus, these data indicate that constitutive expression of HCV proteins may be responsible for intrahepatic lymphocyte recruitment in absence of viral antigen recognition. This response is likely to be driven by virus-induced cellular factors and may play a significant role in the immunopathology of chronic HCV infection and liver disease.

Pathophysiology of hepatitis C virus infection and related liver disease

Hepatitis C virus (HCV) infects over 170 million people worldwide. Chronic infection occurs in 50-80% of cases and eventually leads to cirrhosis and hepatocellular carcinoma. The HCV lifecycle is only partly understood owing to the lack of a productive cell culture system. Several molecules have been implicated in the receptor complex at the surface of target cells, but the mode of HCV entry remains unknown. Persistent infection appears to be due to weak CD4+and CD8+ T-cell responses during acute infection, which fail to control viral replication. When chronic infection is established, HCV does not appear to be cytopathic. Liver lesions appear to result from locally driven immune responses, which are mainly non-specific. Local inflammation triggers fibrogenesis, in which hepatic stellate cells play a major role. Cirrhosis is facilitated by external factors, such as chronic alcohol consumption and viral co-infections. Patients with cirrhosis are at high risk of developing hepatocellular carcinoma. The role of HCV proteins in hepatocarcinogenesis is unknown. Further progress in our understanding of HCV infection and pathogenesis awaits the advent of new model systems and technologies.