• genomics;
  • HBV;
  • HCC;
  • HCV;
  • target therapy


  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References

Hepatocellular carcinoma (HCC) is a worldwide health issue that has started receiving attention but is still poorly understood. However, the hepatitis B virus (HBV) and the hepatitis C virus (HCV) are known to be two major causative agents of HCC. They differ in their modes of infection, their treatment options, their genomes and their carcinogenic abilities. However, both share a link with HCC through alterations of the host genome. In order to continue in our search for the mechanisms behind viral hepatocarcinogenesis, the individual entities (HBV, HCV, HCC and host), their natural history, treatment options and genomic properties must be further understood. Additionally, an understanding of the genomics, the link between the entities, is crucial for the success of the ongoing search for therapeutic options for HCC. Similar to most types of cancer, hepatocarcinogenesis is a multistep process involving different genetic alterations that ultimately lead to malignant transformation of the hepatocyte. As technology advances and research continues, the genetic changes and influences among these entities will prove essential to improved diagnostic and therapeutic options. It remains a challenge to provide a clear picture of the connection between virus and cancer. We review (i) the epidemiological link between HBV/HCV infection to HCC; (ii) prevention and control of chronic hepatitis B or C in reducing HCC risk; and (iii) genetic characters of viruses and hosts and the mechanisms associated with HCC susceptibilities, with the intention of providing a direction for future research and treatment.

At present, hepatocellular carcinoma (HCC) is still a worldwide health issue for which the medical oncology community is largely unprepared. Each year, 550 000 new patients are diagnosed with HCC worldwide (1, 2). Primary liver cancer remains the fifth most frequent neoplasm and, because of its poor prognosis, the third leading cause of cancer deaths (3). Despite major efforts to improve the diagnosis and treatment of HCC, therapeutic options remain inadequate. Curative treatment options are still limited to surgical resection of the tumour or liver transplantation. The studying and development of effective systemic therapies for HCC pose a problem owing to the heterogeneity of the underlying aetiologies, the aggressive nature of the disease and the lack of general consensus regarding treatment. The only unanimous agreement is that the need for effective novel therapeutic agents and strategies is obvious.

Despite this dramatic situation, at least the causative agents of HCC are better established. Epidemiological studies clearly indicate that HCC is strongly associated with chronic hepatitis B and C, being implicated in 80% of HCC cases worldwide, with the other 20% attributed to risk factors including alcohol abuse, fatty liver disease, haemochromatosis and other metabolic disorders (4). Hepatitis B virus (HBV) and hepatitis C virus (HCV) act as major causative agents of chronic hepatitis and HCC (5). However, the underlying mechanisms that lead to malignant transformation of infected cells remain unclear.

Similar to most types of cancer, hepatocarcinogenesis is a multistep process involving different genetic alterations that ultimately lead to malignant transformation of the hepatocyte. Lately, owing to the efforts of the Human Genome Project, genomic targets and networks have increasingly been elucidated. This vast amount of newly available genomic data provides a rich source to identify novel genomic targets for therapeutic intervention. From this perspective, the study of viral carcinogenesis of HCC can also be focused upon. It remains a challenge to provide a clear and consistent picture of the connection between virus and cancer. In the present article, we review the varied aspects of this connection with an emphasis on genomics, with the intention of providing a direction that future research and treatment can take.

A brief review of host genomics of hepatocarcinogenesis

  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References

The completely assembled human genome has made it possible for modern medicine to advance in genetic information and high-throughput genomic analysis. These novel and available genetic resources and analytical tools may be the key to unravel the genetic basis of HCC. One such example is chromosomal or genomic aberrations, which have been reported frequently in HCC. Moinzadeh and colleagues have recently performed a meta-analysis of available data on chromosomal aberrations and genomic hybridization analyses, and they found amplifications of the chromosomes 1q, 8q, 6p and 17q to be the most prominent ones. Among the chromosomes most frequently lost in HCC were 8p, 16q, 4q, 17p and 13q. Furthermore, in poorly differentiated HCCs, 13q and 4q were significantly underrepresented (6). These chromosomal regions contain key players in hepatocarcinogenesis such as p53 (chromosome 17p) or Rb (chromosome 13q). However, data on correlation of these chromosomal aberrations with the clinical course of the disease are not yet available.

Another example is the epigenetic changes, namely altered DNA methylation in HCC, which, in contrast to somatic mutations, is capable of regulating gene expression without changes in DNA sequence, especially in promoter regions of individual genes. Methylation of promoters may interfere with the binding of transcription factors and other regulatory mechanisms and result in decreased expression of the corresponding gene. In HCC, a ‘methylation imbalance’ was observed, where a genome-wide hypomethylation is accompanied by localized hypermethylation of CpG at the promoters of specific genes, especially for the tumour suppressor genes. It was noted that the methylation patterns were correlated with the clinical outcome of HCC patients (7). It was also reported that HCCs can be subgrouped based on their DNA methylation levels. The HCCs with a higher methylation level were associated with the occurrence of β-catenin mutations, pointing out its involvement in a distinct carcinogenic pathway showing less chromosomal instability (CIN) type of genomic abnormality (8). By including the genomic aberrations of loss of heterozygosity, gene mutations and promoter methylation, the classification of HCC was revised by a recent comprehensive and integrative transcriptome analysis into six robust subgroups associated with distinct clinical and genetic characteristics (9).

For promoters of individual genes, p16INK4a, SOCS-1, APC, GSTP1, SFRP1, RUNX3, RASSF1, p73, IGFBP3, E-Cad, etc. were reported to be hypermethylated in a significant proportion of HCCs (10, 11). Intriguingly, the methylation pattern of some genes seems to be associated with the virus infection. For example, the methylation of p16INK4A, SOCS-1, E-cad and APC was identified mainly in the virus-related rather than the virus-negative tumours (12–14). Moreover, E-cad and GSTP1 were preferentially methylated in HBV-related HCC compared with HCV-related HCC (14), suggesting the involvement of viral factors in the methylation process. Such a virus-specific epigenetic modulation mechanism has been illustrated recently in HBV. The HBx viral protein, by regulating the promoter activity of DNA methyltransferase genes (DNMTs), can promote the hypermethylation of promoters of specific genes (15). Aided by novel approaches for globally analysing the DNA methylation levels, the effect of HBx on DNMTs was further identified to induce a global hypomethylation of the host genome (15). It thus provides a mechanism for epigenetic tumorigenesis during HBV-related hepatocarcinogenesis (15).

Major molecular pathways involved in HCC and their differential regulation in HCC are another known genetic influence on hepatocellular carcinogenesis. p53 is particularly important; from the multiple and highly coordinated functions by which p53, once activated in response to cellular stress or DNA damage, tries to prevent further cellular damage (by either inducing cell-cycle arrest or permitting DNA repair or apoptosis), it can be realized why p53 is the most frequently mutated gene in human carcinogenesis. A number of studies in recent years have provided evidence that the p53 tumour suppressor gene plays a major role in hepatocarcinogenesis irrespective of the aetiology (16). However, the frequency of p53 mutations and its mutation spectrum with 75% missense mutations are exceptionally diverse in their position and nature, affecting over 200 codons scattered mainly throughout the central portion of the gene (17). In areas such as sub-Saharan Africa and China, aflatoxin B1 (AFB1) exposure is responsible for a very high incidence of HCC, and in these areas, there is a high proportion of a p53 point mutation at the third position of codon 249, resulting in a G:C to T:A transversion (18). A number of studies clearly support the findings of a positive correlation between the 249ser p53 gene mutation and the AFB1 exposure (19). Explanations include the fact that the third base at the codon 249 has an unusually high mutation rate in the presence of AFB1 (20), or that there might be a growth and/or a survival advantage of liver cells with the 249ser mutant p53 (21). Finally, to further focus on the role of p53 in HCC, a number of p53 mutant and p53 wild-type HCC cases were analysed by micro-arrays identifying 83 p53-related genes in p53 mutant HCCs when compared with wild-type p53 HCCs (22). Among these genes, an overexpression was described for cell-cycle-related genes (CCNG2, BZAP45) and cell proliferation-related genes (SSR1, ANXA2, S100A10 and PTMA). Based on their results, the authors assume that mutant p53 tumours have higher malignant potentials than those with wild-type p53. This concept is supported by previous reports demonstrating that p53 mutations constitute an unfavourable prognostic factor related to recurrence in HCC (23).

The Wnt/β-catenin pathway has also been demonstrated to function as a key regulator in tumour development and differentiation. Several lines of evidence support an essential role of this pathway in HCC, including an increased expression and nuclear accumulation of β-catenin as a feature of an activated Wnt signalling pathway (24, 25). Up to 62% of all HCC were shown to display such a deregulation of β-catenin, and a multivariate analysis has demonstrated a poorer prognosis and a higher rate of tumour recurrence in patients with nuclear accumulation of β-catenin (26). Oncogenic β-catenin mutations have also been demonstrated to promote the development of HCC; these mutations prevent β-catenin from being phosphorylated and thus prevent degradation, resulting in the activation of Wnt-/β-catenin signalling. Reports estimate the prevalence of mutations to be within 26 and 41%, and some reports describe a high association of the mutations with high exposure to AFB1 and HCV infection (27–29). First attempts to target Wnt signalling showed promising results as in vitro RNA interference against β-catenin inhibited the proliferation of paediatric hepatic tumour cells, suggesting β-catenin to be a possible target of further in vivo studies (30). Other important signalling pathways include the TGFβ, Ras signalling and Rb pathways.

Recently, multiple data sets of micro-array data from HCC genome-wide expression analysis have been published. Most of these have reported novel involvements of individual genes in HCC differentiation or development. These experiments have revealed several gene clusters and multiple genes performing essential roles in HCC differentiation. However, comparison among these different micro-array experiments remains difficult, for these experiments all defined diverse clusters of genes essential to tumour development, metastasis or tumour recurrence (31). Thus, the challenge remains to identify a small subset of key regulatory genes, which may subsequently be chosen for evaluation as novel regulatory targets interfering with tumour development.

Hepatitis viruses and hepatocarcinogenesis

  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References

Hepatocellular carcinoma is unique in that it largely occurs within an established background of chronic liver disease and cirrhosis, whose cause is mostly attributed to HBV and HCV, the main causal agents of chronic hepatitis. Viral hepatitis has emerged as a major public health problem throughout the world, causing an inflammation of the liver that affects several hundreds of millions of people. The epidemiological association of chronic HBV or HCV infection with HCC has been well established (5). Among the hepatitis viruses, HBV, HCV and hepatitis D viruses are able to persist in the host and cause chronic hepatitis. Inflammation forms the pathogenetic basis of chronic hepatitis that can lead to nodular fibrosis, which can progress to cirrhosis and, eventually, HCC.

Hepatocarcinogenesis is a multistep process, and it has been proposed that hepatitis viruses can cause HCC by a combination of two mechanisms: first by cell lysis and stimulation of mitosis, leading to an accumulation of events necessary for transformation, and second by an increase in CIN mediated by induced recombinogeneic protein(s) during chronic hepatitis (32). HCC is a consequence of accumulative somatic mutations in the genome of virus-infected liver cells. From this perspective, these cancer-related mutations can be viewed as a focus for potential targets to be researched.

MicroRNAs (miRNAs) have recently been reported to be one kind of host genetic factors associated with the carcinogenic process of liver cancers. By analysing the miRNA expression profiles of paired HCC and adjacent non-tumorous tissues, several miRNAs showed abnormal expression patterns (33, 34). The functional role of some miRNAs targeting specific oncogenes or tumour suppressor genes have been identified, such as let-7 family miRNAs targeting the Ras oncogene (35), microRNA 21 (miR-21) targeting the PTEN tumour suppressor gene (35) and miR-122 targeting the cyclin G1 cell-cycle regulator (34).

In addition to being involved in hepatocarcinogenesis, miRNAs have also been found to play a critical role in regulating the HCV replication. miR-122, which is specifically expressed and highly abundant in the human liver, was shown to possess the ability to facilitate the replication of viral RNA through targeting the 5′ non-coding region of the viral genome (36). Specific down-regulation of miR-122 by antagomir showed an effective suppression of HCV replication, further pointing out this miRNA as a possible target for antiviral therapy (37). A recent report found that HCV replication was inhibited by knocking down the Dicer expression in hepatocytes, further suggesting the requirement for functional RNAi for HCV replication (38). Notably, regulation of miRNA was found to be one mechanism for the interferon (IFN) system to combat viral infections. In the list of IFN-β-regulated miRNAs, eight miRNAs have sequence-predicted targets within the HCV genomic RNA, including miR-122 (down-regulated). The critical involvement of these miRNAs in defending the HCV replication has been well demonstrated in the HCV replicon Huh-7 cells (39). Although the involvement of miRNAs in the regulation of HBV replication has not yet been reported, this possibility still remains to be addressed. Therefore, the involvement of cellular miRNAs in virus-related hepatocarcinogenesis is highly implicated, either affecting the virus replication or the host carcinogenic process.

Influence of hepatitis B virus infection

  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References


Hepatitis B virus infection remains a global public health problem, despite the availability of a vaccine. It is estimated that there are >300 million HBV carriers in the world, of whom 1 million die annually from HBV-related liver disease (40).

Globally, HBV is the most frequent underlying cause of HCC. The annual incidence of HCC in hepatitis B carriers has been shown to be 0.5% on average, increasing with age so that at age 70 the incidence becomes 1%, reaching 2.5% in patients with known cirrhosis. Case–control studies have shown that chronic HBV carriers have a five- to 15-fold increased risk of HCC compared with the general population (41, 42). The great majority, between 70 and 90%, of HBV-related HCCs develop in patients with cirrhosis. However, HBV is also a cause for HCC in the absence of cirrhosis. Elderly patients with chronic liver disease have a higher chance to develop HCC; some large prospective studies from Asia and western Europe have reported a mean age of presentation between 50 and 60 years (43, 44).

The increased HCC risk associated with HBV infection particularly applies to areas where HBV is endemic. In these areas, it is usually transmitted from the mother to the newborn (vertical transmission) and up to 90% of infected persons follow a chronic course. This pattern is different in areas with low HCC incidence rates where HBV is acquired in adulthood through sexual and parenteral routes (horizontal transmission), with >90% of acute infections resolving spontaneously. HBV accounts for the majority of HCC in China and Africa (45, 46).

Genomics of hepatitis B virus and possible role in hepatocarcinogenesis

The HBV viral loads in adult patients are known to be important determinants for HCC risk. In addition, HBV genetic features (such as genotypes or natural genetic variants) appear to exert an additional effect on carcinogenesis.

Hepatitis B virus is classified into eight genotypes (A–H) based on an intergroup divergence of 8% or more in the complete nucleotide sequence (47). In the past few years, there has been growing evidence suggesting that HBV genotypes influence clinical outcomes, HBeAg seroconversion rates, mutational patterns in the precore and core promoter regions and response to antiviral therapy. Studies on the relationship between HBV genotypes and HCC have yielded interesting results. Most studies in east and south-east Asia showed that patients infected with HBV genotype C were more likely to develop HCC (48, 49). Longitudinal follow-up studies confirmed that HBV genotype C and high serum HBV DNA were independent predictors of HCC (50).

Studies have suggested that precore and core promoter variants were associated with more severe liver disease and HCC (51, 52). Recently, considerable data have become available supporting an association between core promoter variants and more severe liver disease. Studies have found that patients with a core promoter mutation are more likely to have a higher hepatic necro-inflammation score (53). The prevalence of core promoter mutations was higher among chronic hepatitis B patients who developed complications of cirrhosis and HCC (54). Another study that investigated chronic hepatitis B-infected patients also found that the prevalence of core promoter variants increased from 3% in inactive carriers to 64% among HCC patients (55). When controlling for other potential confounders such as gender, age, genotype and presence of cirrhosis, the core promoter variants (A1762T, G1764A) were still significantly associated with the development of HCC.

Hepatitis B virus and HCV infection represent the two foremost risk factors for developing HCC; as such, they represent major genetic influences on the host genome. HBV shares a replication strategy that includes the reverse transcription of an RNA intermediate. In a patient with chronic hepatitis, HBV DNA sequences have been shown to integrate into cellular DNA in HCC tissue and in non-tumorous tissue (56). In some cases, the HBV DNA can also be integrated during the early stages of infection (57, 58). When HBV integrations occur, they produce a wide range of genetic changes within the host genome, including deletions, translocations, the production of fusion transcripts and generalized genomic instability. Studies have shown that the integration of viral DNA is associated with deletions in portions of the host's chromosomes. Many of these chromosomal segments contain known tumour suppressor genes such as p53, Rb, cyclin D1 and p16 (59). Research over the past decade has shown that among the different HBV genes, the HBx gene seems to play a more causal role in HBV-related HCC because it is the most commonly integrated viral gene (60). Among the pathobiological effects of HBx are transcriptional coactivation of cellular and viral genes (by transcriptional alteration through modulation of RNA polymerases II and III); action as a cotranscription factor for the major histocompatibility complex, epidermal growth factor receptor and oncogenes like the c-myc, c-jun/fos or Ras-signalling pathway; decrease of nucleotide excision repair and interaction with the cellular DNA repair system; and deregulation of cell-cycle checkpoint controls.

These HBx-related effects provide many different ways as to how HBV contributes to HCC development (61–63). There are also several more direct interactions between HBx and p53 functions. HBx binds to p53 and suppresses a number of p53-dependent functions: p53 sequence-specific DNA-binding activity in vitro, p53-mediated transcriptional activation in vivo and p53 transcription (64, 65). HBx is capable of blocking p53-mediated apoptosis. Additionally, by decreasing p53's binding to XBP, HBx indirectly reduces nucleotide excision repair and XBP functions as a basic transcription factor (66). Indeed, HBx has been shown to promote liver tumour formation in some transgenic mice (67). In addition, it was also found that >95% of patients with HBV-associated cirrhosis and dysplasia were positive for HBx, and 70% of the patients with HBV-associated HCC produce the HBx protein (30, 68). Therefore, it seems likely that the HBx gene plays a role in the initiation of liver tumour formation.

The truncated form of the pre-S2/S gene is another HBV gene product that has been found to have transactivational properties. Truncated pre-S2/S sequences are often found in HBV DNA integration sites in HCC (69). Specific activation of mitogen-activated protein kinases' signalling by the truncated pre-S2/S protein has been shown to result in an activation of transcription factors such as AP-1 and nuclear factor-κB. Furthermore, by activation of this signalling cascade, the pre-S2/S activators cause an increase in the proliferation rate of hepatocytes. Cytologically, overproduction of HBV envelope proteins (pre-S2/S), particularly L and possibly M, results in their intracellular accumulation and may predispose the cell to stress, which in turn may lead to the development of HCC (70). HBV envelope protein (pre-S2/S) mutants that overaccumulate envelope polypeptides within the cell have also been found to be associated with advancing liver disease and may in part be responsible for ground glass hepatocytes and perhaps even HCC lesions (71). In addition, mutations of the core promoter region of the virus have also been described in integrated HBV sequences (72).

One additional interesting difference between HBV vs. HCV-related HCC has been the prominent male dominance in HBV-related HCC. This male preference has been noted to relate to testosterone and androgen receptor activities. Our recent studies also suggest a possible positive interaction between the HBV X protein and the androgen signalling pathway, which may provide an explanation for this phenomenon (73). All the proposed mechanisms are summarized in Fig. 1 and Table 1.


Figure 1.  Hepatitis B viral proteins involved in hepatocarcinogenesis through interaction with specific cellular proteins.

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Table 1.   Hepatitis viral factors involved in hepatocarcinogenesis through interaction with specific cellular proteins
 Associated proteinsFunctional effectReferences
 HBxp53Inactivate p53 function(74–76)
 Decrease PTEN expression 
 Inhibit apoptosis 
DDB1Stimulate HBV replication; Induce apoptosis(60, 77)
Hepatitis B X-interacting protein (HBXIP)Suppress caspase activation and apoptosis(78, 79)
Hepatitis B virus X-associated protein (HBXAP)Activation of NF-κB(80)
FLICE inhibitory protein (c-FLIP),Enhance TNF-α-induced apoptosis(81)
14-3-3Enhance SAPK/JNK activity; protection from Fas-mediated apoptosis(82)
Peroxisome proliferator-activated receptor γ (PPAR-γ)Increase proliferation and reduce apoptosis(83)
RNA polymerase II subunit 5 (RPB5)/transcription factor IIB (TFIIB)Facilitates transcriptional initiation step(84, 85)
TATA-binding protein (TBP)Modulate basal transcriptional activity(86)
TFIIHStimulates the DNA helicase activity of TFIIH(87)
CREBEnhance CREB-dependent transcription(88)
CREB-binding protein (CBP)/p300Increase CREB-mediated transcription(89)
Androgen receptor (AR)Increase AR transactivity(73)
Retinoid X receptor (RXR)Enhance RXR-mediated transcription(90)
Activating signal cointegrator 2 (ASC-2)Enhance ASC-2-dependent transcription(91)
Jun activation domain-binding protein 1 (Jab1),Enhances AP-1 activation(92)
HVDAC3Alteration of mitochondrial transmembrane potential(93)
Proteasome subunits, PSMA7/PSMC1Inhibit proteasome activity(94, 95)
Skp2Inhibit c-Myc degradation(96)
Serine/threonine protein phosphatase PP2C-αElevation of IL-6(97)
 Pre-S mutantsJun activation domain-binding protein 1 (JAB1)p27(Kip1) degradation(98)
 Core proteinLymphotoxin-β receptor (LT-βR)Modulate LT-βR signalling pathway(99)
Sp110b, a repressor for retinoic acid receptor α (RAR-α)Activate RAR-α-mediated transcription(100)
Heterogeneous nuclear ribonucleoprotein K (hnRNP K)Suppress hnRNP K activity(101)
CAP-Rf, a putative RNA helicaseEnhance CAP-Rf helicase and transactivation activity(102)
14-3-3epsilon proteinActivate the mitochondrial apoptotic pathway(103)
PKR, RNA-activated protein kinaseActivate PKR(104)
B23/YY1/P300 complexRegulate gene expression(105)
p21Waf1/Cip1/Sdi1 (p21)Unidentified(106)
Intermediate microfilament cytokeratin proteinsUnidentified(107)

Effect of treatment on hepatitis B virus carcinogenesis

In the natural history of chronic HBV infection, spontaneous or treatment-induced development of antibodies against hepatitis B surface antigen and hepatitis B envelope antigen leads to improved clinical outcomes (108). The risk of HCC is also substantially lower in persons who are completely or partially immune to HBV. There is some evidence that current treatments of chronic hepatitis B reduce the incidence of HCC. Studies in Europe suggested that IFN therapy for chronic hepatitis B improved survival and reduced the incidence of HCC, and studies from Taiwan also indicated that successful IFN therapy, the development of anti-HBe, was associated with a reduced incidence of HCC (109, 110). A single randomized-controlled trial suggests that lamivudine treatment of chronic hepatitis B carriers with cirrhosis does reduce the incidence of HCC (111). Several promising new anti-HBV agents, including entecavir and the pegylated IFNα-2a, possess potent antiviral effects with less toxicity than standard agents and minimal or no risk of inducing drug resistance (112, 113).

Hepatitis B vaccination is widely recognized as the most effective measure to prevent HBV infection. Furthermore, a recent study from Taiwan confirmed the efficacy of HBV vaccination in preventing childhood HCC (114). If this can hold true in adults, mathematical modelling estimates that routine infant hepatitis B vaccination, with 90% coverage and the first dose administered at birth, can prevent 84% of global HBV-related deaths (115).

Influence of hepatitis C virus infection

  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References


Hepatitis C virus infection, formerly known as non-A, non-B hepatitis, was first identified in 1988 (116). HCV infection is the second leading cause of chronic hepatitis, liver cirrhosis and HCC worldwide. Chronic HCV infection affects >170 million individuals worldwide, of whom an estimated 20% have or will develop cirrhosis. The annual risk of progression towards HCC is 1–4% among patients with cirrhosis, although rates of up to 7% have been reported in Japan (117, 118). In contrast to HBV infection, studies show that HCC in patients with hepatitis C occurs almost exclusively in those with cirrhosis, suggesting that cirrhosis is the major risk factor (119, 120). The onset of cirrhosis usually precedes the multistage process of tumour development, in which common themes of viral carcinogenesis can be identified. However, while chronic inflammation and cirrhosis are thought to play an important role in tumour initiation, the underlying mechanisms are incompletely understood.

Genomics of hepatitis C virus and possible role in hepatocarcinogenesis

The HCV genome is a positive-sense RNA molecule of approximately 9500 nucleotides. There are highly conserved 5′ and 3′ untranslated regions flanking an approximately 9000 nucleotide single open reading frame that encodes a large polyprotein of about 3000 amino acids (121). This protein undergoes post-translational processing by host and viral enzymes to form the structural and non-structural proteins and enzymes of the virus. The polymerase enzyme of RNA viruses such as HCV lacks proofreading ability and this feature accounts for the characteristically tremendous viral diversity of HCV. This heterogeneity is extremely important in the diagnosis of infection, pathogenesis of disease and response to treatment. In addition to viral and environmental behavioural factors, host genetic diversity is believed to contribute to the spectrum of clinical outcomes of patients chronically infected with HCV.

Over centuries, the degree of HCV diversity has evolved into several distinct genotypes of the virus. The sequence homology between genotypes is <80%. Six major genotypes of HCV have been defined, from genotype 1 to genotype 6 (122).

The development of a subgenomic HCV RNA replicon capable of replication in the human hepatoma cell line Huh7 has been a significant advance (123). Recently, complete replication of HCV in cell culture has been achieved (124). The HCV RNA genome serves as a template for replication of the virus and as viral messenger RNA for production of the virus. After cell entry, HCV polyprotein is expressed and processed by cellular and viral proteases. There is suggestive experimental evidence that HCV infection itself can promote the development of HCC. The proteins and RNA of HCV interact with many host-cell factors besides their roles in the viral life cycle. Different HCV proteins, especially core, NS3 and NS5A, have been reported to be involved in the process of hepatocarcinogenesis.

Hepatitis C virus core protein is a structural viral protein that has been shown to induce HCC in transgenic mice and has been suggested to play a central role in the development of HCC in chronic hepatitis C (125). It remains unclear how the core protein operates specifically in the development of HCC. Modulation of certain cellular gene products such as helicase lymphotoxin B receptor or dead box protein as shown in cell culture systems or induction of oxidative stress as shown in transgenic mice may contribute to hepatocarcinogenesis (126, 127). Both in vitro and in vivo studies have shown that HCV core protein expression either in cell culture or in transgenic mice led to the development of hepatic steatosis, another risk factor that contributed to carcinogenesis (128).

Hepatitis C virus core protein also modulates a number of cellular regulatory functions; it has been found to modulate the expression of the cyclin-dependent inhibitor p21WAF1 and to promote both apoptosis and cell proliferation through its physical interaction with p53 (129). The p21WAF1 gene is a major target of p53, and the p21WAF1 protein regulates the activities of cyclin/cyclin-dependent kinase complexes involved in cell-cycle control and tumour formation. The core protein in the cytoplasm can increase the amount of p21WAF1 by activating p53, and the core protein in the nucleus decreases the amount of p21WAF1 by a p53-independent pathway. The regulation of p21WAF1 expression by the core protein via subcellular localization might decide the fate of infected cells of either proliferation or apoptosis (130). In addition, HCV core protein has also been seen to regulate p73, a member of the family of p53. p73 is involved in neurogenesis and natural immune response and appears to be strongly involved in malignancy acquisition and maintenance processes (131). p73/core interaction results in the nuclear translocation of HCV core protein in the presence of p73α or p73β tumour suppressor proteins. HCV core protein may directly influence the various p73 functions, thus playing a role in HCV pathogenesis (132). These pathways are depicted in Fig. 2 and Table 1.


Figure 2.  Hepatitis C virus core protein involved in hepatocarcinogenesis through interaction with specific cellular proteins.

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Hepatitis C virus NS3 protein may exert its hepatocarcinogenic effect in the early stage on host cells by an endogenous pathway that may bring about transformation of hepatocytes. It has been reported that wild-type p53 forms a complex with NS3 protein (133). NS3 protein can also specifically repress the promoter activity of p21WAF1 in a dose-dependent manner. The effect is not cell type-specific and is synergistic when combined with HCV core protein. It has also been reported that NS3 represses the transcription of p21WAF1 by modulating the activity of p53 (134).

Hepatitis C virus NS5A protein does not yet have a defined role. Truncated versions of NS5A can act as transcriptional activators, while other recently characterized interactions of NS5A with cellular proteins indicate its pleiotropic role in HCV–host interactions. Abundant interactions with members of the cellular signalling apparatus, transcription activation machinery and cell-cycle-regulatory kinases have been described (135). Many of these interactions block the apoptotic cellular response to persistent HCV infection, which suggests a potential function of NS5A in inducing chronic liver diseases and HCC associated with HCV infection. NS5A forms a heteromeric complex with TATA box binding protein (TBP) and tumour-suppressor protein p53 (136). NS5A inhibits the binding of both p53 and TBP to their DNA consensus binding sequences in vitro. In addition, NS5A protein interacts with and partially sequestrates hTAF(II)32 and hTAF(II)28 (components of TFIID and essential coactivators of p53) in the cytoplasm and suppresses p53-mediated transcriptional trans-activation and apoptosis during HCV infection, which may contribute to the hepatocarcinogenesis of HCV infection (137).

Thus, the products encoded by the HCV genome interfere with and disturb intracellular signal transduction. The identification of the interactions between host proteins such as p53 and HCV proteins and their effects on cell-cycle control should be of great importance, mainly to develop strategies to inhibit protein–protein interactions, reducing the carcinogenicity of the virus.

In contrast to HBV-related hepatocarcinogenesis, little is known about the pathophysiology leading to HCV-related cirrhosis (70% in HCV vs. 50% in HBV) and HCC (75% in HCV vs. 29% in HBV) (138). None of the different parts of the HCV genome is integrated into the host genome. To gain a better insight into HCV-related hepatocarcinogenesis, the microarray technology has been used in several studies. Some studies have analysed HCV-related cirrhosis and showed an up-regulation of pro-inflammatory, pro-apoptotic and proproliferative genes, which might reflect groups of genes being involved in HCV-related cirrhosis during progression to HCC (139, 140). One study analysed gene expression profiles of the HCV genotypes 1b, 2a and 4d core proteins in HepG2 and Huh-7 cells and identified that each core protein has its own expression profile and that each of them seems to be implicated in HCV replication and oncogenesis (141). In another study based on the transient expression of the HCV core protein transfected into Huh-7 cells, most transcriptionally changed genes were involved in cell growth or oncogenic signalling (142). Of particular interest were growth-related genes like the Wnt-1 pathway. In primary human hepatocytes the HCV core gene was induced after senescence, immortalization and anchor-independent growth passages of the cells. Reflecting the HCV core gene introduction into these three distinct HCV-related hepatocytic stages, the following cellular pathways have been identified: cell growth regulation, immune regulation, oxidative stress and apoptosis.

Effect of treatment on hepatitis C virus carcinogenesis

The combination of pegylated IFNα and ribavirin is the current standard treatment for chronic HCV infection, yielding a sustained virological response (SVR) (143). Studies show that a SVR is generally associated with clinical and histological improvement and eradication of HCV infection in the large majority of patients (144). There are a number of studies evaluating the effect of treatment of chronic hepatitis C on the incidence of HCC. The results of these studies concluded that the benefit is mainly seen in those who were successfully treated (had SVR) (108). It remains uncertain whether IFN treatment can reduce the risk of developing HCC among patients who do not have a sustained response following treatment. However, no data have demonstrated that treating or eradicating hepatitis C completely eliminates the risk for HCC. Thus, it seems that patients with hepatitis C and cirrhosis who have achieved viral clearance on therapy should, at least for now, continue to undergo surveillance. Additionally, recent studies have concluded that SVR patients with chronic hepatitis C who are elderly, male or have an advanced histological stage are at a high risk for the development of HCC after combination therapy, and should be observed carefully for >10 years after the completion of IFN therapy (145).


  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References

We have come a long way in understanding the process behind hepatocarcinogenesis in the last decade, and yet HCC remains just as deadly. The biological heterogeneity and multiple aetiologies of HCC result in an incomplete understanding of the key molecular changes that lead to HCC development. The completely assembled human genome has made it possible for modern medicine to advance. HCCs induced by chronic HBV or chronic HCV infection have been demonstrated to display clearly distinct expression profiles, and thus, hepatocarcinogenesis caused by HBV or HCV is driven at least partially by different pathophysiological mechanisms. Developing a clearer picture of the most prominent and relevant molecular abnormalities is fundamental to developing effective therapeutic options, and should be a priority for those involved in basic and translational research. From this perspective, the study of viral carcinogenesis of HCC can be focused upon. Research should continue in the search for the genes, protein markers and other predictive biomarkers that are deregulated in HCC. As similar research is yielding results regarding various other malignant diseases, it is hoped that identifying the aberrant genes and the resultant proteins could lead to the identification of other novel pharmacological interventions for HCC.


  1. Top of page
  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References

The researches were supported by the grants from National Science Council, Department of Health, Taiwan; National Health Research Institute; and National Taiwan University. We thank Dr Wen-Hung Huang for critically reading our manuscript.


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  2. Abstract
  3. A brief review of host genomics of hepatocarcinogenesis
  4. Hepatitis viruses and hepatocarcinogenesis
  5. Influence of hepatitis B virus infection
  6. Influence of hepatitis C virus infection
  7. Conclusion
  8. Acknowledgements
  9. References
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