NS3 protein of Hepatitis C virus associates with the tumour suppressor p53 and inhibits its function in an NS3 sequence-dependent manner

From viruses to cancer: exploring the role of the hepatitis C virus NS3 protein in carcinogenesis

Hepatitis C virus (HCV) chronically infects approximately 170 million people worldwide and is a known etiological agent of hepatocellular carcinoma (HCC). The molecular mechanisms of HCV-mediated carcinogenesis are not fully understood. This review article focuses on the oncogenic potential of NS3, a viral protein with transformative effects on cells, although the precise mechanisms remain elusive. Unlike the more extensively studied Core and NS5A proteins, NS3's roles in cancer development are less defined but critical. Research indicates that NS3 is implicated in several carcinogenic processes such as proliferative signaling, cell death resistance, genomic instability and mutations, invasion and metastasis, tumor-related inflammation, immune evasion, and replicative immortality. Understanding the direct impact of viral proteins such as NS3 on cellular transformation is crucial for elucidating HCV's role in HCC development. Overall, this review sheds light on the molecular mechanisms used by NS3 to contribute to hepatocarcinogenesis, and highlights its significance in the context of HCV-associated HCC, underscoring the need for further investigation into its specific molecular and cellular actions.

p53 and RNA viruses: The tug of war

Host factors play essential roles in viral infection, and their interactions with viral proteins are necessary for establishing effective pathogenesis. p53 is a host factor that maintains genomic integrity by controlling cell-cycle progression and cell survival. It is a well-known tumor suppressor protein that gets activated by various stress signals, thereby regulating cellular pathways. The cellular outcomes from different stresses are tightly related to p53 dynamics, including its alterations at gene, mRNA, or protein levels. p53 also contributes to immune responses leading to the abolition of viral pathogens. In turn, the viruses have evolved strategies to subvert p53-mediated host responses to improve their life cycle and pathogenesis. Some viruses attenuate wild-type p53 (WT-p53) function for successful pathogenesis, including degradation and sequestration of p53. In contrast, some others exploit the WT-p53 function through regulation at the transcriptional/translational level to spread infection. One area in which the importance of such host factors is increasingly emerging is the positive-strand RNA viruses that cause fatal viral infections. In this review, we provide insight into all the possible mechanisms of p53 modulation exploited by the positive-strand RNA viruses to establish infection. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Translation > Regulation RNA in Disease and Development > RNA in Disease.

HCV and HCC Tango-Deciphering the Intricate Dance of Disease: A Review Article

Hepatitis C virus (HCV) is a major cause of hepatocellular carcinoma (HCC) accounting for around one-third of all HCC cases. Prolonged inflammation in chronic hepatitis C (CHC), maintained through a variety of pro- and anti-inflammatory mediators, is one of the aspects of carcinogenesis, followed by mitochondrial dysfunction and oxidative stress. Immune response dysfunction including the innate and adaptive immunity also plays a role in the development, as well as in the recurrence of HCC after treatment. Some of the tumor suppressor genes inhibited by the HCV proteins are p53, p73, and retinoblastoma 1. Mutations in the telomerase reverse transcriptase promoter and the oncogene catenin beta 1 are two more important carcinogenic signaling pathways in HCC associated with HCV. Furthermore, in HCV-related HCC, numerous tumor suppressor and seven oncogenic genes are dysregulated by epigenetic changes. Epigenetic regulation of gene expression is considered as a lasting "epigenetic memory", suggesting that HCV-induced changes persist and are associated with liver carcinogenesis even after cure. Epigenetic changes and immune response dysfunction are recognized targets for potential therapy of HCC.

The molecular mechanisms of virus-induced human cancers

Cancer is a serious public health problem globally. Many human cancers are induced by viruses. Understanding of the mechanisms by which oncogenic (tumorigenic) viruses induce cancer is essential in the prevention and control of cancer. This review covers comprehensive characteristics and molecular mechanisms of the main virus-attributed cancers caused by human papillomavirus, hepatitis B virus, hepatitis C virus, Epstein-Barr virus, human herpesvirus type 8, human T-cell lymphotropic virus, human polyomaviruses, Merkel cell polyomavirus, and HIV. Oncogenic viruses employ biological processes to replicate and avoid detection by host cell immune systems. Tumorigenic infectious agents activate oncogenes in a variety of ways, allowing the pathogen to block host tumour suppressor proteins, inhibit apoptosis, enhance cell proliferation, and promote invasion of host cells. Furthermore, this review assesses many pathways of viruses linked to cancer, including host cellular communication perturbation, DNA damage mechanisms, immunity, and microRNA targets that promote the beginning and progression of cancer. The current cancer prevention is primarily focused on non-communicable diseases, but infection-attributable cancer also needs attention to significantly reduce the rising cancer burden and related deaths.

Transcriptional Analysis of TP53 Gene in Chronic Hepatitis C Patients Treated with Sofosbuvir, Daclatasvir, Pegylated Interferon, and Ribavirin

Hepatitis C virus (HCV) is a major public health problem that affects more than 170 million people globally. HCV is a principal cause of hepatocellular carcinoma (HCC) around the globe due to the high frequency of hepatitis C infection, and the high rate of HCC is seen in patients with HCV cirrhosis. TP53 is considered as a frequently altered gene in all cancer types, and it carries an interferon response element in its promoter region. In addition to that, the TP53 gene also interacts with different HCV proteins. HCV proteins especially NS3 protein and core protein induce the mutations in the TP53 gene that lower the expression of this gene in HCV patients and leads to HCC development. In this study, we examined the transcriptional analysis of the TP53 gene in HCV-infected patients administered with different combinations of antiviral therapies including sofosbuvir + daclatasvir, sofosbuvir + ribavirin, and pegylated interferon + ribavirin. This study included 107 subjects; 15 treated with sofosbuvir + daclatasvir, 58 treated with sofosbuvir + ribavirin, 11 treated with interferon + ribavirin, 8 untreated, 10 HCC patients, and 5 were healthy controls. Total RNA was extracted from the PMBCs of HCV infected patients and reverse transcribed into cDNA using a gene specific reverse primer. The expression level of TP53 mRNA was analyzed using quantitative PCR. The expression of TP53 mRNA was notably upregulated in rapid virological response (RVR), early virological response (EVR), and sustained virological response (SVR) groups as compared to non-responders and naïve groups. The expression of TP53 mRNA was seen high in HCC as compared to control groups. Additionally, it has been demonstrated that sofosbuvir + daclatasvir treatment stimulates significant elevation in TP53 gene expression as compared to (sofosbuvir + ribavirin) and (IFN + ribavirin) treatment. This study indicates that the TP53 gene expression is highly upregulated in RVR, EVR, and SVR groups as compared to control groups. Moreover, sofosbuvir + daclatasvir therapy induces significant rise in TP53 mRNA expression levels as compared to (sofosbuvir + ribavirin) and (IFN + ribavirin) treatment. According to these results, it can be concluded that sofosbuvir + daclatasvir plays a significant role in preventing HCV patients from developing severe liver complications as compared to other administered therapies. This study is novel as no such type of study has been conducted previously on the expression of TP53 in local HCV-infected population treated with different combinations of therapies. This study is helpful for the development of new therapeutic strategies and for improving existing therapies.

Hepatocellular carcinoma and hepatitis C virus treatments: The bold and the beautiful

The occurrence of hepatocellular carcinoma (HCC) is one of the most serious complications of hepatitis C virus (HCV) infection. Recently, effective antiviral medications have made sustained viral response (SVR) or cure a realistic therapeutic goal for most chronic HCV patients. Given HCV's tumorigenic propensity, it is not surprising that achieving SVR is helpful in preventing HCC. This review briefly summarizes and discusses the existing evidence on the relationship between hepatic carcinogenesis and viral eradication by antivirals, which is mainly divided into interferon-based and direct-acting antivirals (DAAs) based therapy. DAAs have changed the treatment landscape of chronic HCV, reaching high rates of SVR even in patients with advanced cirrhosis, with few contraindications and little side effects. Although some early reports suggested that DAA treatment increased the chance of HCC occurrence, more subsequent observational studies have refuted this theory. The probability of HCC recurrence after HCV eradication appears to be decreasing over time following SVR. Despite virological suppression/cure, individuals with liver cirrhosis are still at risk of HCC and should be monitored. There is a considerable need for markers/scores to predict the long-term risk of HCC in patients with HCV-related liver disease who attain SVR with direct-acting antivirals.

A single mutation in the E2 glycoprotein of hepatitis C virus broadens the claudin specificity for its infection

Entry of the hepatitis C virus (HCV) into host cells is a multistep process mediated by several host factors, including a tight junction protein claudin-1 (CLDN1). We repeatedly passaged HCV-JFH1-tau, an HCV substrain with higher infectivity, on Huh7.5.1-8 cells. A multi-passaged HCV-JFH1-tau lot was infectious to CLDN1-defective S7-A cells, non-permissive to original HCV-JFH1-tau infection. We identified a single mutation, M706L, in the E2 glycoprotein of the HCV-JFH1-tau lot as an essential mutation for infectivity to S7-A cells. The pseudovirus JFH1/M706L mutant could not infect human embryonic kidney 293 T (HEK293T) cells lacking CLDN family but infected HEK293T cells expressing CLDN1, CLDN6, or CLDN9. Thus, this mutant virus could utilize CLDN1, and other CLDN6 and CLDN9, making HCV possible to infect cells other than hepatocytes. iPS cells, one of the stem cells, do not express CLDN1 but express CLDN6 and other host factors required for HCV infection. We confirmed that the HCV-JFH1-tau-derived mutant with an M706L mutation infected iPS cells in a CLDN6-dependent manner. These results demonstrated that a missense mutation in E2 could broaden the CLDN member specificity for HCV infection. HCV may change its receptor requirement through a single amino acid mutation and infect non-hepatic cells.

HCV and tumor-initiating stem-like cells

Neoplasms contain tumor-initiating stem-like cells (TICs) that are characterized by increased drug resistance. The incidence of many cancer types have trended downward except for few cancer types, including hepatocellular carcinoma (HCC). Therefore mechanism of HCC development and therapy resistance needs to be understood. These multiple hits by hepatitis C virus (HCV) eventually promotes transformation and TIC genesis, leading to HCC development. This review article describes links between HCV-associated HCC and TICs. This review discusses 1) how HCV promotes genesis of TICs and HCC development; 2) how this process avails itself as a novel therapeutic target for HCC treatment; and 3) ten hall marks of TIC oncogenesis and HCC development as targets for novel therapeutic modalities.

Viral hepatitis and hepatocellular carcinoma: From molecular pathways to the role of clinical surveillance and antiviral treatment

Hepatocellular carcinoma (HCC) is a global health challenge. Due to the high prevalence in low-income countries, hepatitis B virus (HBV) and hepatitis C virus infections remain the main risk factors for HCC occurrence, despite the increasing frequencies of non-viral etiologies. In addition, hepatitis D virus coinfection increases the oncogenic risk in patients with HBV infection. The molecular processes underlying HCC development are complex and various, either independent from liver disease etiology or etiology-related. The reciprocal interlinkage among non-viral and viral risk factors, the damaged cellular microenvironment, the dysregulation of the immune system and the alteration of gut-liver-axis are known to participate in liver cancer induction and progression. Oncogenic mechanisms and pathways change throughout the natural history of viral hepatitis with the worsening of liver fibrosis. The high risk of cancer incidence in chronic viral hepatitis infected patients compared to other liver disease etiologies makes it necessary to implement a proper surveillance, both through clinical-biochemical scores and periodic ultrasound assessment. This review aims to outline viral and microenvironmental factors contributing to HCC occurrence in patients with chronic viral hepatitis and to point out the importance of surveillance programs recommended by international guidelines to promote early diagnosis of HCC.

Hepatitis C Virus NS3/4A Inhibition and Host Immunomodulation by Tannins from Terminalia chebula: A Structural Perspective

Terminalia chebula Retz. forms a key component of traditional folk medicine and is also reported to possess antihepatitis C virus (HCV) and immunomodulatory activities. However, information on the intermolecular interactions of phytochemicals from this plant with HCV and human proteins are yet to be established. Thus, by this current study, we investigated the HCV NS3/4A inhibitory and host immune-modulatory activity of phytocompounds from T. chebula through in silico strategies involving network pharmacology and structural bioinformatics techniques. To start with, the phytochemical dataset of T. chebula was curated from biological databases and the published literature. Further, the target ability of the phytocompounds was predicted using BindingDB for both HCV NS3/4A and other probable host targets involved in the immune system. Further, the identified targets were docked to the phytochemical dataset using AutoDock Vina executed through the POAP pipeline. The resultant docked complexes with significant binding energy were subjected to 50 ns molecular dynamics (MD) simulation in order to infer the stability of complex formation. During network pharmacology analysis, the gene set pathway enrichment of host targets was performed using the STRING and Reactome pathway databases. Further, the biological network among compounds, proteins, and pathways was constructed using Cytoscape 3.6.1. Furthermore, the druglikeness, side effects, and toxicity of the phytocompounds were also predicted using the MolSoft, ADVERpred, and PreADMET methods, respectively. Out of 41 selected compounds, 10 were predicted to target HCV NS3/4A and also to possess druglike and nontoxic properties. Among these 10 molecules, Chebulagic acid and 1,2,3,4,6-Pentagalloyl glucose exhibited potent HCV NS3/4A inhibitory activity, as these scored a lowest binding energy (BE) of −8.6 kcal/mol and −7.7 kcal/mol with 11 and 20 intermolecular interactions with active site residues, respectively. These findings are highly comparable with Asunaprevir (known inhibitor of HCV NS3/4A), which scored a BE of −7.4 kcal/mol with 20 key intermolecular interactions. MD studies also strongly suggest that chebulagic acid and 1,2,3,4,6-Pentagalloyl glucose as promising leads, as these molecules showed stable binding during 50 ns of production run. Further, the gene set enrichment and network analysis of 18 protein targets prioritized 10 compounds and were predicted to potentially modulate the host immune system, hemostasis, cytokine levels, interleukins signaling pathways, and platelet aggregation. On overall analysis, this present study predicts that tannins from T. chebula have a potential HCV NS3/4A inhibitory and host immune-modulatory activity. However, further experimental studies are required to confirm the efficacies.

Adaptive homeostasis and the p53 isoform network

All living organisms have developed processes to sense and address environmental changes to maintain a stable internal state (homeostasis). When activated, the p53 tumour suppressor maintains cell and organ integrity and functions in response to homeostasis disruptors (stresses) such as infection, metabolic alterations and cellular damage. Thus, p53 plays a fundamental physiological role in maintaining organismal homeostasis. The TP53 gene encodes a network of proteins (p53 isoforms) with similar and distinct biochemical functions. The p53 network carries out multiple biological activities enabling cooperation between individual cells required for long‐term survival of multicellular organisms (animals) in response to an ever‐changing environment caused by mutation, infection, metabolic alteration or damage. In this review, we suggest that the p53 network has evolved as an adaptive response to pathogen infections and other environmental selection pressures.

p53 and rb promoter methylation in hepatitis C virus-related chronic hepatitis and hepatocellular carcinoma

Aim: To identify methylation in p53 and rb during hepatitis C virus (HCV) infection in individuals in Pakistan. Materials & methods: Methylation-specific PCR was used on liver biopsies from hepatocellular carcinoma and chronic hepatitis C patients and on blood samples from healthy individuals. Real-time PCR was used to assess changes in the expression of p53 and rb in Huh-7 cells transfected with HCV-3a. Results: The p53 and rb promoters were methylated in hepatocellular carcinoma patients. The presence of HCV-3a- Core (p = 0.03), HCV-3a- NS-3 (p = 0.01) and HCV-3a- NS-5a (p = 0.02) downregulated p53 expression. Exposure to HCV-3a- Core (p = 0.04) downregulated rb expression. Conclusion: It can be hypothesized that HCV-induced epigenetic modifications may lead to the development of hepatic cancer that in turn inactivates p53 and rb.

Molecular mechanisms of viral hepatitis induced hepatocellular carcinoma

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

HCV infection and the risk of head and neck cancer: A meta-analysis

Recent evidence has consistently suggested a role for HCV in the etiology of head and neck squamous cell carcinoma (HNSCC), but the conclusions of these studies have often been limited by small sample size. Therefore, a meta-analysis was performed to summarize present evidence on the association between HCV infection and HNSCC. After screening citations from literature search, eight observational studies investigating the association between HCV and cancer(s) of either oral cavity, oropharynx, hypopharynx or larynx were included. For each cancer site, risk ratios from individual studies were displayed in forest plots; pooled risk ratios (RR) and corresponding confidence intervals (CI) were calculated. A significant association was found between HCV infection and cancers of the oral cavity (RR = 2.13; 95%: 1.61-2.83), oropharynx (RR = 1.81; 95% CI: 1.21-2.72), and larynx (RR = 2.57; 95% CI: 1.11-5.94). A similar picture emerged for hypopharyngeal cancer, though this result did not fully reach statistical significance because of the small number of available studies (RR = 2.15; 95% CI: 0.73-6.31). These findings remained similar after exclusion of patients with HIV co-infection. Our results highlighted the importance of surveillance of the upper aerodigestive tract in patients with known chronic HCV infections in order to enable HNSCC early diagnosis. In addition, they could be a reminder of the possibility of undiagnosed HCV infection to the clinicians treating HNSCC.

Hepatitis C Virus NS3 Protein Plays a Dual Role in WRN-Mediated Repair of Nonhomologous End Joining

Hepatitis C virus (HCV) NS3 protein possesses protease and helicase activities and is considered an oncoprotein in virus-derived hepatocellular carcinoma. The NS3-associated oncogenesis has been studied but not fully understood. In this study, we have identified novel interactions of the NS3 protein with DNA repair factors, Werner syndrome protein (WRN) and Ku70, in both an HCV subgenomic replicon system and Huh7 cells expressing NS3. HCV NS3 protein inhibits WRN-mediated DNA repair and reduces the repair efficiency of nonhomologous end joining. It interferes with Ku70 recruitment to the double-strand break sites and alters the nuclear distribution of WRN-Ku repair complex. In addition, WRN is a substrate of the NS3/4A protease; the level of WRN protein is regulated by both the proteasome degradation pathway and HCV NS3/4A protease activity. The dual role of HCV NS3 and NS3/4A proteins in regulating the function and expression level of the WRN protein intensifies the effect of impairment on DNA repair. This may lead to an accumulation of DNA mutations and genome instability and, eventually, tumor development.IMPORTANCE HCV infection is a worldwide problem of public health and a major contributor to hepatocellular carcinoma. The single-stranded RNA virus with RNA-dependent RNA polymerase experiences a high error rate and develops strategies to escape the immune system and hepatocarcinogenesis. Studies have revealed the involvement of HCV proteins in the impairment of DNA repair. The present study aimed to further elucidate mechanisms by which the viral NS3 protein impairs the repair of DNA damage. Our results clearly indicate that HCV NS3/4A protease targets WRN for degradation, and, at the same time, diminishes the repair efficiency of nonhomologous end joining by interfering with the recruitment of Ku protein to the DNA double-strand break sites. The study describes a novel mechanism by which the NS3 protein influences DNA repair and provides new insight into the molecular mechanism of HCV pathogenesis.

Peroxiredoxin 1, a Novel HBx-Interacting Protein, Interacts with Exosome Component 5 and Negatively Regulates Hepatitis B Virus (HBV) Propagation through Degradation of HBV RNA

Hepatitis B virus (HBV) infection is a major risk factor for the development of chronic liver diseases, including cirrhosis and hepatocellular carcinoma (HCC). A growing body of evidence suggests that HBV X protein (HBx) plays a crucial role in viral replication and HCC development. Here, we identified peroxiredoxin 1 (Prdx1), a cellular hydrogen peroxide scavenger, as a novel HBx-interacting protein. Coimmunoprecipitation analysis coupled with site-directed mutagenesis revealed that the region from amino acids 17 to 20 of the HBx, particularly HBx Cys¹⁷, is responsible for the interaction with Prdx1. Knockdown of Prdx1 by siRNA significantly increased the levels of intracellular HBV RNA, HBV antigens, and extracellular HBV DNA, whereas knockdown of Prdx1 did not increase the activities of HBV core, enhancer I (Enh1)/X, preS1, and preS2/S promoters. Kinetic analysis of HBV RNA showed that knockdown of Prdx1 inhibited HBV RNA decay, suggesting that Prdx1 reduces HBV RNA levels posttranscriptionally. The RNA coimmunoprecipitation assay revealed that Prdx1 interacted with HBV RNA. The exosome component 5 (Exosc5), a member of the RNA exosome complexes, was coimmunoprecipitated with Prdx1, suggesting its role in regulation of HBV RNA stability. Taken together, these results suggest that Prdx1 and Exosc5 play crucial roles in host defense mechanisms against HBV infection.IMPORTANCE Hepatitis B virus (HBV) infection is a major global health problem. HBx plays important roles in HBV replication and viral carcinogenesis through its interaction with host factors. In this study, we identified Prdx1 as a novel HBx-binding protein. We provide evidence suggesting that Prdx1 promotes HBV RNA decay through interaction with HBV RNA and Exosc5, leading to downregulation of HBV RNA. These results suggest that Prdx1 negatively regulates HBV propagation. Our findings may shed new light on the roles of Prdx1 and Exosc5 in host defense mechanisms in HBV infection.

Clinicopathological features of HCV-positive splenic diffuse large B cell lymphoma

The hepatitis C virus (HCV) is a single-stranded RNA virus which is thought to be involved in the onset of B cell lymphoma. HCV-positive diffuse large B cell lymphoma (DLBCL) has been reported to clinically manifest in extranodal lesions (e.g., in the liver, spleen, and stomach). Here, we investigated HCV-positive and -negative primary splenic DLBCL (p-spDLBCL) and non-primary splenic DLBCL (ordinary DLBCL). Furthermore, to examine HCV lymphomagenesis, RNA in situ hybridization (ISH), RT-PCR (reverse-transcription polymerase chain reaction), and NS3 immunostaining of HCV viral nonstructural proteins were performed. HCV-positive p-spDLBCL patients presented fewer B symptoms (asymptomatic) and better performance status, with elevated presence of splenic macronodular lesions and more germinal center B cell (GCB) sub-group cases than HCV-negative p-spDLBCL patients. However, HCV-positive ordinary DLBCL patients were found to have more non-GCB sub-group cases than HCV-negative ordinary DLBCL patients. HCV-positive DLBCL patients showed 20.6% (7/34) NS3 positivity, 16.7% (1/6) HCV-RNA in situ positivity, and 22.2% (2/9) detection of HCV-RNA in tumor tissue by RT-PCR. Splenic samples were found to have a higher frequency of HCV detection than lymph node samples, thus suggesting that HCV may be closely related to lymphomagenesis, especially in splenic lymphoma.

Molecular Mechanisms Involved in HCC Recurrence after Direct-Acting Antiviral Therapy

Chronic hepatitis C is associated with a high risk of developing hepatocellular carcinoma (HCC) because of a direct effect of the Hepatitis C Virus (HCV) proteins and an indirect oncogenic effect of chronic inflammation and impaired immune response. The treatment of chronic hepatitis C markedly reduces all-cause mortality; in fact, interferon-based treatment has shown a reduction of HCC incidence of more than 70%. The recent introduction of the highly effective direct-acting antivirals (DAAs) has completely changed the scenario of chronic hepatitis C (CHC) with rates of HCV cure over 90%. However, an unexpectedly high incidence of HCC recurrence was observed in patients after DAA treatment (27% versus 0.4–2% in patients who received interferon treatment). The mechanism that underlies the high rate of tumor relapse is currently unknown and is one of the main issues in hepatology. We reviewed the possible mechanisms involved in HCC recurrence after DAA treatment.

Breaking Bad: How Viruses Subvert the Cell Cycle

Interactions between the host and viruses during the course of their co-evolution have not only shaped cellular function and the immune system, but also the counter measures employed by viruses. Relatively small genomes and high replication rates allow viruses to accumulate mutations and continuously present the host with new challenges. It is therefore, no surprise that they either escape detection or modulate host physiology, often by redirecting normal cellular pathways to their own advantage. Viruses utilize a diverse array of strategies and molecular targets to subvert host cellular processes, while evading detection. These include cell-cycle regulation, major histocompatibility complex-restricted antigen presentation, intracellular protein transport, apoptosis, cytokine-mediated signaling, and humoral immune responses. Moreover, viruses routinely manipulate the host cell cycle to create a favorable environment for replication, largely by deregulating cell cycle checkpoints. This review focuses on our current understanding of the molecular aspects of cell cycle regulation that are often targeted by viruses. Further study of their interactions should provide fundamental insights into cell cycle regulation and improve our ability to exploit these viruses.

Oncogenic Signaling Induced by HCV Infection

The liver is frequently exposed to toxins, metabolites, and oxidative stress, which can challenge organ function and genomic stability. Liver regeneration is therefore a highly regulated process involving several sequential signaling events. It is thus not surprising that individual oncogenic mutations in hepatocytes do not necessarily lead to cancer and that the genetic profiles of hepatocellular carcinomas (HCCs) are highly heterogeneous. Long-term infection with hepatitis C virus (HCV) creates an oncogenic environment by a combination of viral protein expression, persistent liver inflammation, oxidative stress, and chronically deregulated signaling events that cumulate as a tipping point for genetic stability. Although novel direct-acting antivirals (DAA)-based treatments efficiently eradicate HCV, the associated HCC risk cannot be fully eliminated by viral cure in patients with advanced liver disease. This suggests that HCV may persistently deregulate signaling pathways beyond viral cure and thereby continue to perturb cancer-relevant gene function. In this review, we summarize the current knowledge about oncogenic signaling pathways derailed by chronic HCV infection. This will not only help to understand the mechanisms of hepatocarcinogenesis but will also highlight potential chemopreventive strategies to help patients with a high-risk profile of developing HCC.

Molecular Mechanisms of Hepatocarcinogenesis Following Sustained Virological Response in Patients with Chronic Hepatitis C Virus Infection

Despite the success of direct-acting antiviral (DAA) agents in treating chronic hepatitis C virus (HCV) infection, the number of cases of HCV-related hepatocellular carcinoma (HCC) is expected to increase over the next five years. HCC develops over the span of decades and is closely associated with fibrosis stage. HCV both directly and indirectly establishes a pro-inflammatory environment favorable for viral replication. Repeated cycles of cell death and regeneration lead to genomic instability and loss of cell cycle control. DAA therapy offers >90% sustained virological response (SVR) rates with fewer side effects and restrictions than interferon. While elimination of HCV helps to restore liver function and reverse mild fibrosis, post-SVR patients remain at elevated risk of HCC. A series of studies reporting higher than expected rates of HCC development among DAA-treated patients ignited debate over whether use of DAAs elevates HCC risk compared to interferon. However, recent prospective and retrospective studies based on larger patient cohorts have found no significant difference in risk between DAA and interferon therapy once other factors are taken into account. Although many mechanisms and pathways involved in hepatocarcinogenesis have been elucidated, our understanding of drivers specific to post-SVR hepatocarcinogenesis is still limited, and lack of suitable in vivo and in vitro experimental systems has hampered efforts to examine etiology-specific mechanisms that might serve to answer this question more thoroughly. Further research is needed to identify risk factors and biomarkers for post-SVR HCC and to develop targeted therapies based on more complete understanding of the molecules and pathways implicated in hepatocarcinogenesis.

The implication of CRISPR/Cas9 genome editing technology in combating human oncoviruses

It is evidenced that 20% of all tumors in humans are caused by oncoviruses, including human papilloma viruses, Epstein-Barr virus, Kaposi sarcoma virus, human polyomaviruses, human T-lymphotrophic virus-1, and hepatitis B and C viruses. Human immunodeficiency virus is also involved in carcinogenesis, although not directly, but by facilitating the infection of many oncoviruses through compromising the immune system. Being intracellular parasites with the property of establishing latency and integrating into the host genome, these viruses are a therapeutic challenge for biomedical researchers. Therefore, strategies able to target nucleotide sequences within episomal or integrated viral genomes are of prime importance in antiviral or anticancerous armamentarium. Recently, clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) has emerged as a powerful genome editing tool. Standing out as a precise and efficient oncoviruses method, it has been extensively applied in recent experimental ventures in the field of molecular medicine, particularly in combating infections including tumor inducing viruses. This review is aimed at collating the experimental and clinical advances in CRISPR/Cas9 technology in terms of its applications against oncoviruses. Primarily, it will focus on the application of CRISPR/Cas9 in combating tumor viruses, types of mechanisms targeted, and the significant outcomes till date. The technical pitfalls of the CRISPR/Cas9 and the comparative approaches in evaluating this technique with respect to other available alternatives are also described briefly. Furthermore, the review also discussed the clinical aspects and the ethical, legal, and social issues associated with the use of CRISPR/Cas9.

Relationship between epithelial-to-mesenchymal transition and the inflammatory microenvironment of hepatocellular carcinoma

Epithelial-to-mesenchymal transition (EMT) is a complex process involving multiple genes, steps and stages. It refers to the disruption of tight intercellular junctions among epithelial cells under specific conditions, resulting in loss of the original polarity, order and consistency of the cells. Following EMT, the cells show interstitial cell characteristics with the capacity for adhesion and migration, while apoptosis is inhibited. This process is critically involved in embryogenesis, wound-healing, tumor invasion and metastasis. The tumor microenvironment is composed of infiltrating inflammatory cells, stromal cells and the active medium secreted by interstitial cells. Most patients with hepatocellular carcinoma (HCC) have a history of hepatitis virus infection. In such cases, major components of the tumor microenvironment include inflammatory cells, inflammatory factors and virus-encoded protein are major components. Here, we review the relationship between EMT and the inflammatory tumor microenvironment in the context of HCC. We also further elaborate the significant influence of infiltrating inflammatory cells and inflammatory mediators as well as the products expressed by the infecting virus in the tumor microenvironment on the EMT process.

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.

Roles of p53 in extrinsic factor-induced liver carcinogenesis

Liver cancer remains one of the most common human cancers with a high mortality rate. Therapies for hepatocellular carcinoma (HCC) remain ineffective, due to the heterogeneity of HCC with regard to both the etiology and mutation spectrum, as well as its chemotherapy resistant nature; thus surgical resection and liver transplantation remain the gold standard of patient care. The most common etiologies of HCC are extrinsic factors. Humans have multiple defense mechanisms against extrinsic factor-induced carcinogenesis, of which tumor suppressors play crucial roles in preventing normal cells from becoming cancerous. The tumor suppressor p53 is one of the most frequently mutated genes in liver cancer. p53 regulates expression of genes involved in cell cycle progression, cell death, and cellular metabolism to avert tumor development due to carcinogens. This review article mainly summarizes extrinsic factors that induce liver cancer and potentially have etiological association with p53, including aflatoxin B1, vinyl chloride, non-alcoholic fatty liver disease, iron overload, and infection of hepatitis viruses.

Hepatitis C Virus Indirectly Disrupts DNA Damage-Induced p53 Responses by Activating Protein Kinase R

Many DNA tumor viruses promote cellular transformation by inactivating the critically important tumor suppressor protein p53. In contrast, it is not known whether p53 function is disrupted by hepatitis C virus (HCV), a unique, oncogenic RNA virus that is the leading infectious cause of liver cancer in many regions of the world. Here we show that HCV-permissive, liver-derived HepG2 cells engineered to constitutively express microRNA-122 (HepG2/miR-122 cells) have normal p53-mediated responses to DNA damage and that HCV replication in these cells potently suppresses p53 responses to etoposide, an inducer of DNA damage, or nutlin-3, an inhibitor of p53 degradation pathways. Upregulation of p53-dependent targets is consequently repressed within HCV-infected cells, with potential consequences for cell survival. Despite this, p53 function is not disrupted by overexpression of the complete HCV polyprotein, suggesting that altered p53 function may result from the host response to viral RNA replication intermediates. Clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9-mediated ablation of double-stranded RNA (dsRNA)-activated protein kinase R (PKR) restored p53 responses while boosting HCV replication, showing that p53 inhibition results directly from viral activation of PKR. The hepatocellular abundance of phosphorylated PKR is elevated in HCV-infected chimpanzees, suggesting that PKR activation and consequent p53 inhibition accompany HCV infection in vivo. These findings reveal a feature of the host response to HCV infection that may contribute to hepatocellular carcinogenesis.

Chronic infection with hepatitis C virus (HCV) is the leading cause of liver cancer in most developed nations. However, the mechanisms whereby HCV infection promotes carcinogenesis remain unclear. Here, we demonstrate that HCV infection inhibits the activation of p53 following DNA damage. Contrary to previous reports, HCV protein expression is insufficient to inhibit p53. Rather, p53 inhibition is mediated by cellular protein kinase R (PKR), which is activated by HCV RNA replication and subsequently suppresses global protein synthesis. These results redefine our understanding of how HCV infection influences p53 function. We speculate that persistent disruption of p53-mediated DNA damage responses may contribute to hepatocellular carcinogenesis in chronically infected individuals.

Hepatitis C virus NS3 protein enhances hepatocellular carcinoma cell invasion by promoting PPM1A ubiquitination and degradation

Background

Growing evidence suggests that hepatitis C virus (HCV) contributes to hepatocellular carcinoma (HCC) by directly modulating oncogenic signaling pathways. Protein phosphatase magnesium-dependent 1A (PPM1A) has recently emerged as an important tumor suppressor as it can block a range of tumor-centric signaling pathways through protein dephosphorylation. However, the role and regulatory mechanisms of PPM1A in HCV-infected cells have not been reported.

Methods

Total, cytoplasmic, and nuclear PPM1A protein after HCV infection or overexpression of HCV nonstructural protein 3 (NS3) were detected by western blotting. The expression of PPM1A in normal liver and HCV-related HCC tissues was quantified by immunohistochemistry. The effects of HCV infection and NS3 expression on the PPM1A protein level were systematically analyzed, and the ubiquitination level of PPM1A was determined by precipitation with anti-PPM1A and immunoblotting with either anti-ubiquitin or anti-PPM1A antibody. Finally, the roles of NS3 and PPM1A in hepatoma cell migration and invasion were assessed by wound healing and transwell assays, respectively.

Results

HCV infection and replication decreased PPM1A abundance, mediated by NS3, in hepatoma cells. Compared to normal liver tissues, the expression of PPM1A was significantly decreased in the HCC tumor tissues and adjacent non-tumor tissues. NS3 directly interacted with PPM1A to promote PPM1A ubiquitination and degradation, which was dependent on its protease domain. Blockade of PPM1A through small interfering RNA significantly promoted HCC cell migration, invasion, and epithelial mesenchymal transition (EMT), which were further intensified by TGF-β1 stimulation, in vitro. Furthermore, restoration of PPM1A abrogated the NS3-mediated promotion of HCC migration and invasion to a great extent, which was dependent on its protein phosphatase function.

Conclusions

Our findings demonstrate that the HCV protein NS3 can downregulate PPM1A by promoting its ubiquitination and proteasomal degradation, which might contribute to the migration and invasion of hepatoma cells and may represent a new strategy of HCV in carcinogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0510-8) contains supplementary material, which is available to authorized users.

Oral Combination Vaccine, Comprising Bifidobacterium Displaying Hepatitis C Virus Nonstructural Protein 3 and Interferon-α, Induces Strong Cellular Immunity Specific to Nonstructural Protein 3 in Mice

We previously generated an oral hepatitis C virus (HCV) vaccine using Bifidobacterium displaying the HCV nonstructural protein 3 (NS3) polypeptide. NS3-specific cellular immunity is important for viral clearance and recovery from HCV infection. In this study, we enhanced the cellular immune responses induced by our oral HCV vaccine, Bifidobacterium longum 2165 (B. longum 2165), by combining interferon-α (IFN-α) as an adjuvant with the vaccine in a mouse experimental model. IFN-α is a widely used cytokine meeting the standard of care (SOC) for HCV infection and plays various immunoregulatory roles. We treated C57BL/6N mice with B. longum 2165 every other day and/or IFN-α twice a week for a month and then analyzed the immune responses using spleen cells. We determined the induction of NS3-specific cellular immunity by cytokine quantification, intracellular cytokine staining, and a cytotoxic T lymphocyte (CTL) assay targeting EL4 tumor cells expressing NS3/4A protein (EL4-NS3/4A). We also treated mice bearing EL4-NS3/4A tumor with the combination therapy in vivo. The results confirmed that the combination therapy of B. longum 2165 and IFN-α induced significantly higher IFN-γ secretion, higher population of CD4⁺T and CD8⁺T cells secreting IFN-γ, and higher CTL activity against EL4-NS3/4A cells compared with the control groups of phosphate-buffered saline, B. longum 2165 alone, and IFN-α alone (p < 0.05). We also confirmed that the combination therapy strongly enhanced tumor growth inhibitory effects in vivo with no serious adverse effects (p < 0.05). These results suggest that the combination of B. longum 2165 and IFN-α could induce a strong cellular immunity specific to NS3 protein as a combination therapy augmenting the current SOC immunotherapy against chronic HCV infection.

Insights for hepatitis C virus related hepatocellular carcinoma genetic biomarkers: Early diagnosis and therapeutic intervention

The current review explores the role of emerging molecular contributing factors in liver carcinogenesis on top of hepatitis C virus (HCV). Here we will try to discuss the role genetic and epigenetic factors in pathogenesis of hepatocellular carcinoma. Understanding the role of these factors will help in discovering the mystery of liver carcinogenesis on top of chronic HCV infection. Moreover, use of the studied molecular factors will provide the hepatologists with tailored diagnostic promising biomarkers and flatten the way for establishment of emerging molecular treatment based on exploring the molecular subscription of this aggressive liver cancer.

Molecular mechanisms of hepatitis C virus-induced hepatocellular carcinoma

Hepatitis C virus (HCV) is a major leading cause of hepatocellular carcinoma (HCC). HCV-induced hepatocarcinogenesis is a multistep process resulting from a combination of pathway alterations that are either caused directly by viral factors or immune mediated as a consequence of a chronic state of inflammation. Host genetic variation is now emerging as an additional element that contribute to increase the risk of developing HCC. The advent of direct-acting antiviral agents foresees a rapid decline of HCC rate in HCV patients. However, a full understanding of the HCV-mediated tumourigenic process is required to elucidate if pro-oncogenic signatures may persist after virus clearance, and to identify novel tools for HCC prevention and therapy. In this review, we summarize the current knowledge of the molecular mechanisms responsible for HCV-induced hepatocarcinogenesis.

Nonstructural 3 Protein of Hepatitis C Virus Modulates the Tribbles Homolog 3/Akt Signaling Pathway for Persistent Viral Infection

Hepatitis C virus (HCV) infection often causes chronic hepatitis, liver cirrhosis, and ultimately hepatocellular carcinoma. However, the mechanisms underlying HCV-induced liver pathogenesis are still not fully understood. By transcriptome sequencing (RNA-Seq) analysis, we recently identified host genes that were significantly differentially expressed in cell culture-grown HCV (HCVcc)-infected cells. Of these, tribbles homolog 3 (TRIB3) was selected for further characterization. TRIB3 was initially identified as a binding partner of protein kinase B (also known as Akt). TRIB3 blocks the phosphorylation of Akt and induces apoptosis under endoplasmic reticulum (ER) stress conditions. HCV has been shown to enhance Akt phosphorylation for its own propagation. In the present study, we demonstrated that both mRNA and protein levels of TRIB3 were increased in the context of HCV replication. We further showed that promoter activity of TRIB3 was increased by HCV-induced ER stress. Silencing of TRIB3 resulted in increased RNA and protein levels of HCV, whereas overexpression of TRIB3 decreased HCV replication. By employing an HCV pseudoparticle entry assay, we further showed that TRIB3 was a negative host factor involved in HCV entry. Both in vitro binding and immunoprecipitation assays demonstrated that HCV NS3 specifically interacted with TRIB3. Consequently, the association of TRIB3 and Akt was disrupted by HCV NS3, and thus, TRIB3-Akt signaling was impaired in HCV-infected cells. Moreover, HCV modulated TRIB3 to promote extracellular signal-regulated kinase (ERK) phosphorylation, activator protein 1 (AP-1) activity, and cell migration. Collectively, these data indicate that HCV exploits the TRIB3-Akt signaling pathway to promote persistent viral infection and may contribute to HCV-mediated pathogenesis.

IMPORTANCE

TRIB3 is a pseudokinase protein that acts as an adaptor in signaling pathways for important cellular processes. So far, the functional involvement of TRIB3 in virus-infected cells has not yet been demonstrated. We showed that both mRNA and protein expression levels of TRIB3 were increased in the context of HCV RNA replication. Gene silencing of TRIB3 increased HCV RNA and protein levels, and thus, overexpression of TRIB3 decreased HCV replication. TRIB3 is known to promote apoptosis by negatively regulating the Akt signaling pathway under ER stress conditions. Most importantly, we demonstrated that the TRIB3-Akt signaling pathway was disrupted by NS3 in HCV-infected cells. These data provide evidence that HCV modulates the TRIB3-Akt signaling pathway to establish persistent viral infection.

Hepatitis C Virus Infection Induces Autophagy as a Prosurvival Mechanism to Alleviate Hepatic ER-Stress Response

Hepatitis C virus (HCV) infection frequently leads to chronic liver disease, liver cirrhosis and hepatocellular carcinoma (HCC). The molecular mechanisms by which HCV infection leads to chronic liver disease and HCC are not well understood. The infection cycle of HCV is initiated by the attachment and entry of virus particles into a hepatocyte. Replication of the HCV genome inside hepatocytes leads to accumulation of large amounts of viral proteins and RNA replication intermediates in the endoplasmic reticulum (ER), resulting in production of thousands of new virus particles. HCV-infected hepatocytes mount a substantial stress response. How the infected hepatocyte integrates the viral-induced stress response with chronic infection is unknown. The unfolded protein response (UPR), an ER-associated cellular transcriptional response, is activated in HCV infected hepatocytes. Over the past several years, research performed by a number of laboratories, including ours, has shown that HCV induced UPR robustly activates autophagy to sustain viral replication in the infected hepatocyte. Induction of the cellular autophagy response is required to improve survival of infected cells by inhibition of cellular apoptosis. The autophagy response also inhibits the cellular innate antiviral program that usually inhibits HCV replication. In this review, we discuss the physiological implications of the HCV-induced chronic ER-stress response in the liver disease progression.

HCV Infection and Interferon-Based Treatment Induce p53 Gene Transcription in Chronic Hepatitis C Patients

It is suggested that the tumor suppressor p53 gene, classified as an interferon-stimulated gene, is implicated in the interferon (IFN)-mediated innate immunity against viruses. This study aimed to examine the transcriptional response of the p53 gene to hepatitis C virus (HCV) infection and IFN-based therapy in chronic hepatitis C (CHC) patients. The study included 65 CHC patients (HCV genotype 1), treated with pegylated IFN-α and ribavirin, and 51 healthy individuals. p53 gene expression was quantified by real-time polymerase chain reaction in peripheral blood mononuclear cells (PBMCs). Analyses were performed before and at weeks 4 and 12 of treatment. p53 gene expression was significantly upregulated in CHC patients compared with healthy controls and at week 4 of therapy. No significant differences in p53 mRNA expression between rapid virologic responders, complete early virologic responders, and nonresponders were observed. No significant correlation was found between p53 gene expression and viral load. The results obtained indicate that HCV infection and IFN-based treatment induces p53 gene transcription in PBMCs. The p53 gene may therefore play a role in HCV infection but is not directly involved in treatment-induced HCV elimination. Moreover, variations in p53 gene expression do not determine on-treatment response in patients with chronic HCV genotype 1 infection.

HCV infection-associated hepatocellular carcinoma in humanized mice

BACKGROUND AND AIMS

Hepatitis C virus (HCV) infection is a major risk factor for chronic hepatitis, cirrhosis and hepatocellular carcinoma (HCC). Our aim is to explore molecular changes that underlie HCV infection-associated HCC in a humanized mouse model, in order to identify markers of HCC progression.

METHODS

Liver proteins from human hepatocyte-engrafted and HCV-infected MUP-uPA/SCID/Bg mice were compared with either uninfected controls or HCV-infected but HCC-negative mice by Western blotting. MicroRNA markers of HCC positive or uninfected mouse liver were analyzed by RT-PCR.

RESULTS

We describe the depletion of tumor suppressor proteins and induction of oncoproteins and oncogenic microRNAs (oncomiRs) in HCV-infection associated HCC. Similar depletion of PTEN protein in both HCC-positive and HCV-infected but HCC-negative liver suggests that PTEN depletion is an early, precancerous marker of HCC. By contrast, induction of oncoprotein cMyc, oncomiRs (miR21, miR221 and miR141) and inflammatory response proteins correspond to HCC progression.

CONCLUSIONS

While the loss of PTEN is important for the initiation of HCV infection-associated HCC, PTEN depletion by itself is insufficient for tumor progression. Liver tumor progression requires induction of oncoproteins and oncomiRs. Overall, human hepatocyte-engrafted (MUP-uPA/SCID/Bg) mice provide a suitable small animal model for studying the effects of oncogenic changes that promote HCV infection associated HCC.

HCV upregulates Bim through the ROS/JNK signalling pathway, leading to Bax-mediated apoptosis

We previously reported that hepatitis C virus (HCV) infection induces Bax-triggered, mitochondrion-mediated apoptosis by using the HCV J6/JFH1 strain and Huh-7.5 cells. However, it was still unclear how HCV-induced Bax activation. In this study, we showed that the HCV-induced activation and mitochondrial accumulation of Bax were significantly attenuated by treatment with a general antioxidant, N-acetyl cysteine (NAC), or a specific c-Jun N-terminal kinase (JNK) inhibitor, SP600125, with the result suggesting that the reactive oxygen species (ROS)/JNK signalling pathway is upstream of Bax activation in HCV-induced apoptosis. We also demonstrated that HCV infection transcriptionally activated the gene for the pro-apoptotic protein Bim and the protein expression of three major splice variants of Bim (BimEL, BimL and BimS). The HCV-induced increase in the Bim mRNA and protein levels was significantly counteracted by treatment with NAC or SP600125, suggesting that the ROS/JNK signalling pathway is involved in Bim upregulation. Moreover, HCV infection led to a marked accumulation of Bim on the mitochondria to facilitate its interaction with Bax. On the other hand, downregulation of Bim by siRNA (small interfering RNA) significantly prevented HCV-mediated activation of Bax and caspase 3. Taken together, these observations suggest that HCV-induced ROS/JNK signalling transcriptionally activates Bim expression, which leads to Bax activation and apoptosis induction.

Hepatitis C virus-induced hepatocellular carcinoma

Hepatitis C virus (HCV) is a leading etiology of hepatocellular carcinoma (HCC). The interaction of HCV with its human host is complex and multilayered; stemming in part from the fact that HCV is a RNA virus with no ability to integrate in the host's genome. Direct and indirect mechanisms of HCV-induced HCC include activation of multiple host pathways such as liver fibrogenic pathways, cellular and survival pathways, interaction with the immune and metabolic systems. Host factors also play a major role in HCV-induced HCC as evidenced by genomic studies identifying polymorphisms in immune, metabolic, and growth signaling systems associated with increased risk of HCC. Despite highly effective direct-acting antiviral agents, the morbidity and incidence of liver-related complications of HCV, including HCC, is likely to persist in the near future. Clinical markers to selectively identify HCV subjects at higher risk of developing HCC have been reported however they require further validation, especially in subjects who have experienced sustained virological response. Molecular biomarkers allowing further refinement of HCC risk are starting to be implemented in clinical platforms, allowing objective stratification of risk and leading to individualized therapy and surveillance for HCV individuals. Another role for molecular biomarker-based stratification could be enrichment of HCC chemoprevention clinical trials leading to smaller sample size, shorter trial duration, and reduced costs.

Hepatitis C virus-associated cancer

Hepatitis C virus (HCV) is one of the major etiologic agents of liver cancer. HCV is an RNA virus that, unlike hepatitis B virus, is unable to integrate into the host genome. Through complex interactions between viral and host proteins that induce host responses and promote inflammation, fibrosis, and ultimately cirrhosis, HCV infection can result in the development of hepatocellular carcinoma (HCC). The HCV oncogenic process involves genetic and epigenetic alterations and oncogenic effects mediated by viral proteins in the activation of cellular oncogenes, inactivation of tumor-suppressor genes, and dysregulation of multiple signal-transduction pathways. Advances in genetics and gene expression profiling have enhanced our current understanding of the pathways involved in HCV-associated liver cancer development. In this review, we summarize the current understanding of mechanisms of hepatocarcinogenesis induced by HCV infection.

Pathogenesis and prevention of hepatitis C virus-induced hepatocellular carcinoma

Hepatitis C virus (HCV) is one of the major aetiologic agents that causes hepatocellular carcinoma (HCC) by generating an inflammatory, fibrogenic, and carcinogenic tissue microenvironment in the liver. HCV-induced HCC is a rational target for cancer preventive intervention because of the clear-cut high-risk condition, cirrhosis, associated with high cancer incidence (1% to 7% per year). Studies have elucidated direct and indirect carcinogenic effects of HCV, which have in turn led to the identification of candidate HCC chemoprevention targets. Selective molecular targeted agents may enable personalized strategies for HCC chemoprevention. In addition, multiple experimental and epidemiological studies suggest the potential value of generic drugs or dietary supplements targeting inflammation, oxidant stress, or metabolic derangements as possible HCC chemopreventive agents. While the successful use of highly effective direct-acting antiviral agents will make important inroads into reducing long-term HCC risk, there will remain an important role for HCC chemoprevention even after viral cure, given the persistence of HCC risk in persons with advanced HCV fibrosis, as shown in recent studies. The successful development of cancer preventive therapies will be more challenging compared to cancer therapeutics because of the requirement for larger and longer clinical trials and the need for a safer toxicity profile given its use as a preventive agent. Molecular biomarkers to selectively identify high-risk population could help mitigate these challenges. Genome-wide, unbiased molecular characterization, high-throughput drug/gene screening, experimental model-based functional analysis, and systems-level in silico modelling are expected to complement each other to facilitate discovery of new HCC chemoprevention targets and therapies.

The role of cirrhosis in the etiology of hepatocellular carcinoma

Abundant evidence supports the belief of a causal relationship between cirrhosis and hepatocellular carcinoma, but one that differs between high- and low-incidence regions of the tumor. In high-incidence regions, the cirrhosis is of the macronodular variety, is typically asymptomatic, and is caused predominantly by chronic hepatitis B virus infection, whereas in low-incidence regions, the cirrhosis, although usually macronodular, may be micronodular, is commonly symptomatic and of long-standing, and is caused by chronic hepatitis C virus infection, alcohol abuse over many years, the metabolic syndrome, or hereditary hemochromatosis. In a minority of patients, hepatocellular carcinoma develops in the absence of cirrhosis, supporting a direct hepatocarcinogenic effect of some of the causal agents. Cirrhosis is the major risk factor for tumor formation in patients with chronic hepatitis C virus infection. This virus does not integrate into cellular DNA, and malignant transformation results from increased liver cell turnover induced by recurring injury and regeneration of cells in the context of persisting inflammation, oxidative DNA damage, fibrosis, cirrhosis, and changes induced by the virus at a DNA level that have yet to be fully defined. Hepatitis B virus causes malignant transformation by both direct and indirect routes. The direct route results, in part, from integration of the viral DNA into host cellular DNA; transcriptional activation of host growth regulatory genes by hepatitis B virus-encoded proteins; and effects on apoptosis, cell signaling, and DNA repair. The direct route may share some similarities with that of hepatitis C virus infection. The metabolic syndrome may cause malignant transformation by production of oxidative stress and the induction of a variety of mutations, including some in the p53 gene.

Hepatitis C virus NS3 protein enhances cancer cell invasion by activating matrix metalloproteinase-9 and cyclooxygenase-2 through ERK/p38/NF-κB signal cascade

Hepatitis C virus (HCV) infection causes acute and chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma (HCC). However, the mechanisms by which HCV causes the diseases are largely unknown. Here, we elucidated the effects of HCV on the invasion and migration of hepatoma cells, with the aim to reveal the mechanism by which HCV infection induces HCC. We initially showed that matrix metalloproteinase-9 (MMP-9) was elevated in the sera of HCV-infected patients, and demonstrated that HCV nonstructural protein 3 (NS3) activated MMP-9 transcription through nuclear factor-κB (NF-κB) by stimulating translocation of NF-κB from cytosol to the nucleus to enhance its binding to MMP-9 promoter. In addition, cyclooxygenase-2 (COX-2) and extracellular signal-regulated kinase (ERK1/2)/mitogen-activated protein kinase (p38) pathway were involved in HCV-activated MMP-9 expression. Moreover, NS3 enhanced hepatoma cell invasion and migration through MMP-9 and COX-2. Thus, this study provides new insights into the roles of HCV NS3, MMP-9 and COX-2 in regulating cancer cell invasion.

Induction of cell-mediated immune responses in mice by DNA vaccines that express hepatitis C virus NS3 mutants lacking serine protease and NTPase/RNA helicase activities

Effective therapeutic vaccines against virus infection must induce sufficient levels of cell-mediated immune responses against the target viral epitopes and also must avoid concomitant risk factors, such as potential carcinogenic properties. The nonstructural protein 3 (NS3) of hepatitis C virus (HCV) carries a variety of CD4(+) and CD8(+) T cell epitopes, and induces strong HCV-specific T cell responses, which are correlated with viral clearance and resolution of acute HCV infection. On the other hand, NS3 possesses serine protease and nucleoside triphosphatase (NTPase)/RNA helicase activities, which not only play important roles in viral life cycle but also concomitantly interfere with host defense mechanisms by deregulating normal cellular functions. In this study, we constructed a series of DNA vaccines that express NS3 of HCV. To avoid the potential harm of NS3, we introduced mutations to the catalytic triad of the serine protease (H57A, D81A and S139A) and the NTPase/RNA helicase domain (K210N, F444A, R461Q and W501A) to eliminate the enzymatic activities. Immunization of BALB/c mice with each of the DNA vaccine candidates (pNS3[S139A/K210N], pNS3[S139A/F444A], pNS3[S139A/R461Q] and pNS3[S139A/W501A]) that expresses an NS3 mutant lacking both serine protease and NTPase/helicase activities induced T cell immune responses to the degree comparable to that induced by the wild type NS3 and the NS3/4A complex, as demonstrated by interferon-γ production and cytotoxic T lymphocytes activities against NS3. The present study has demonstrated that plasmids expressing NS3 mutants, NS3(S139A/K210N), NS3(S139A/F444A), NS3(S139A/R461Q) and NS3(S139A/W501A), which lack both serine protease and NTPase/RNA helicase activities, would be good candidates for safe and efficient therapeutic DNA vaccines against HCV infection.

Studies on the role of NS3 and NS5A non-structural genes of hepatitis C virus genotype 3a local isolates in apoptosis

BACKGROUND

Hepatitis C virus (HCV) is the causative agent of chronic liver diseases, which usually lead to liver fibrosis, liver cirrhosis, and hepatocellular carcinoma (HCC). Among the non-structural genes of HCV, NS3 and NS5A play important roles in apoptosis. The NS3 and NS5A genes of HCV interact with the p53 tumor suppressor gene differentially. The objective of this study was to analyze the interaction of NS3 and NS5A genes of HCV genotype 3a with the p53 gene, subgenomic HCV replicons harboring NS3 and NS5A genes.

METHODS

Huh-7 cell lines stably expressing NS3 and NS5A genes were generated. The stable cell lines were confirmed by Western blot, reverse transcriptase PCR, and immunofluorescence assay. HCV NS3- and NS5A-expressing cell lines were transfected with p53-expressing clone.

RESULTS

NS3 and NS5A both interact with p53 by down-regulating the expression of the p53 gene. In HCV subgenomic harboring cells, the interaction of NS3 and NS5A with p53 was observed consistently. The suppression of p53 gene expression by NS3 and NS5A was observed significantly as compared with NS3- and NS5A-negative control Huh-7 cells.

CONCLUSION

It is concluded that both of the non-structural genes, NS3 and NS5A, of HCV play important roles in the hepatocarcinogenesis of HCV by interacting directly or indirectly in different manners with the p53 gene.

Interaction of Hepatitis C Viral Proteins with Cellular Oncoproteins in the Induction of Liver Cancer

Hepatitis C virus infection is a major health problem all over the world. A large proportion of patients infected by HCV develop liver cirrhosis or cancer. However, the mechanism(s) remain to be elucidated. Since HCV does not carry any known oncogene, it is thought that interaction between virally encoded proteins and host proteins is responsible for carcinogenesis. Many crucial interactions between HCV-encoded proteins and host proteins have been reported. In this review we focus on the interaction of viral proteins with important regulators of cell cycle—oncoproteins YB-1, p53, and cyclin D1—which play a major role in cell proliferation, apoptosis, DNA repair, and genomic stability. Genetic variants of HCV accumulate in patients and alter these interactions of host cell proteins. It is a battle between the virus and host and the final outcome depends on the winner; if the host succeeds in clearing the virus the patient may not develop serious liver diseases. On the other hand, if the virus dominates by evolving quasispecies which code for altered proteins that interact differently with host proteins, or induce mutations in host protooncogenes, then the patient may develop liver cirrhosis and/or liver cancer.

'Liver let die': oxidative DNA damage and hepatotropic viruses

Chronic infections by the hepatotropic viruses hepatitis B virus (HBV) and hepatitis C virus (HCV) are major risk factors for the development of hepatocellular carcinoma (HCC). It is estimated that more than 700,000 individuals per year die from HCC, and around 80 % of HCC is attributable to HBV or HCV infection. Despite the clear clinical importance of virus-associated HCC, the underlying molecular mechanisms remain largely elusive. Oxidative stress, in particular DNA lesions associated with oxidative damage, play a major contributory role in carcinogenesis, and are strongly linked to the development of many cancers, including HCC. A large body of evidence demonstrates that both HBV and HCV induce hepatic oxidative stress, with increased oxidative DNA damage being observed both in infected individuals and in murine models of infection. Here, we review the impact of HBV and HCV on the incidence and repair of oxidative DNA damage. We begin by giving a brief overview of oxidative stress and the repair of DNA lesions induced by oxidative stress. We then review in detail the evidence surrounding the mechanisms by which both viruses stimulate oxidative stress, before focusing on how the viral proteins themselves may perturb the cellular response to oxidative DNA damage, impacting upon genome stability and thus hepatocarcinogenesis.

Virus associated malignancies: the role of viral hepatitis in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the third leading fatal cancer worldwide and its incidence continues to increase. Chronic viral hepatitis involving either hepatitis B virus (HBV) or hepatitis C virus (HCV) infection is the leading etiology for HCC, making HCC prevention a major goal of antiviral therapy. While recent clinical observations and translational research have enhanced our understanding of the molecular mechanisms driving the initiation and progression of HCC, much remains unknown. Current data indicates that HCC tumors are highly complex and heterogeneous resulting from the aberrant function of multiple molecular pathways. This complex biology is responsible, at least in part, for the absence of highly efficient target-directed therapies for this deadly cancer. Additionally, the direct or indirect effect of HBV and HCV infection on the development of HCC is still a contentious issue. Thus, the question remains whether viral hepatitis-associated HCC stems from virus-specific factors, and/or from a general mechanism involving inflammation and tissue regeneration. In this review we summarize general mechanisms implicated in HCC, emphasizing data generated by new technologies available today. We also highlight specific pathways by which HBV and HCV could be involved in HCC pathogenesis. However, improvements to current in vitro and in vivo systems for both viruses will be needed to rigorously define the temporal sequence and specific pathway dysregulations that drive the strong clinical link between chronic hepatitis virus infection and HCC.

Hepatitis C virus NS2 protein inhibits DNA damage pathway by sequestering p53 to the cytoplasm

Chronic hepatitis C virus (HCV) infection is an important cause of morbidity and mortality globally, and often leads to end-stage liver disease. The DNA damage checkpoint pathway induces cell cycle arrest for repairing DNA in response to DNA damage. HCV infection has been involved in this pathway. In this study, we assess the effects of HCV NS2 on DNA damage checkpoint pathway. We have observed that HCV NS2 induces ataxia-telangiectasia mutated checkpoint pathway by inducing Chk2, however, fails to activate the subsequent downstream pathway. Further study suggested that p53 is retained in the cytoplasm of HCV NS2 expressing cells, and p21 expression is not enhanced. We further observed that HCV NS2 expressing cells induce cyclin E expression and promote cell growth. Together these results suggested that HCV NS2 inhibits DNA damage response by altering the localization of p53, and may play a role in the pathogenesis of HCV infection.

Hepatitis C virus and hepatocarcinogenesis

Hepatitis C virus (HCV) is an RNA virus that is unable to integrate into the host genome. However, its proteins interact with various host proteins and induce host responses. The oncogenic process of HCV infection is slow and insidious and probably requires multiple steps of genetic and epigenetic alterations, the activation of cellular oncogenes, the inactivation of tumor suppressor genes, and dysregulation of multiple signal transduction pathways. Stellate cells may transdifferentiate into progenitor cells and possibly be linked to the development of hepatocellular carcinoma (HCC). Viral proteins also have been implicated in several cellular signal transduction pathways that affect cell survival, proliferation, migration and transformation. Current advances in gene expression profile and selective messenger RNA analysis have improved approach to the pathogenesis of HCC. The heterogeneity of genetic events observed in HCV-related HCCs has suggested that complex mechanisms underlie malignant transformation induced by HCV infection. Considering the complexity and heterogeneity of HCCs of both etiological and genetic aspects, further molecular classification is required and an understanding of these molecular complexities may provide the opportunity for effective chemoprevention and personalized therapy for HCV-related HCC patients in the future. In this review, we summarize the current knowledge of the mechanisms of hepatocarcinogenesis induced by HCV infection.