Tissue factor pathway inhibitor-2 as a frequently silenced tumor suppressor gene in hepatocellular carcinoma

Defining the molecular signature of chemotherapy-mediated lung tumor phenotype modulation and increased susceptibility to T-cell killing

Chemotherapy with platinum doublets, including cisplatin plus vinorelbine, is standard of care for non-small-cell lung cancer. Sublethal exposure to certain chemotherapeutic agents has been demonstrated to alter the phenotype or biology of human tumor cells, rendering them more susceptible to cytotoxic T lymphocyte (CTL)-mediated lysis. The effects of cisplatin/vinorelbine on tumor sensitivity to T-cell cytotoxicity and its molecular mechanisms, however, have not been fully elucidated. We examined the effect of this chemotherapy on growth, cell-surface phenotype, and CTL-mediated lysis of five distinct human lung carcinoma cell lines in vitro and examined the molecular mechanisms associated with enhanced CTL sensitivity. These studies demonstrate that sublethal exposure of human lung tumor cells to the platinum doublet modulates tumor cell phenotype and increases sensitivity to major histocompatibility complex-restricted perforin/granzyme-mediated CTL killing. These studies also demonstrate that exposure to chemotherapy markedly decreased the protein secretion ratio of transforming growth factor-β/interleukin (IL)-8. We examined the gene expression profile of two lung tumor cell lines to identify a shared gene signature in response to sublethal cisplatin/vinorelbine and found coordinate expression of only 16 transcripts, including those for cytokine/chemokine expression and apoptosis such as tumor necrosis factor-α, IL8, CXCL5, and B cell lymphoma-2-like genes (BCL-2). Overall, these results suggest that sublethal exposure to cisplatin/vinorelbine increases sensitivity to perforin/granzyme-mediated CTL killing by modulation of (a) tumor phenotype, (b) cytokine/chemokine milieu, and (c) the proapoptotic/antiapoptotic gene ratio. The data presented here propose a complex mechanism that is distinct from and complementary to that of immunogenic cell death. This molecular signature may be useful in predicting responses to immunotherapy as well as provide the rationale for the potential clinical benefit of the combined use of vaccine with cisplatin/vinorelbine regimens.

Reduced expression of tissue factor pathway inhibitor-2 contributes to apoptosis and angiogenesis in cervical cancer

Background

Tissue factor pathway inhibitor-2 (TFPI-2) is an extracellular matrix associated broad-spectrum Kunitz-type serine proteinase inhibitor. Recently, down regulation of TFPI-2 was suggested to be involved in tumor invasion and metastasis in some cancers.

Methods

This study involved 12 normal cervical squamous epithelia, 48 cervical intraepithelial neoplasia (CIN), and 68 cervical cancer. The expression of TFPI-2, Ki-67 and vascular endothelial growth factor (VEGF) were investigated by immunohistochemistry staining. The apoptolic index(AI) was determined with an in situ end-labeling assay(TUNEL). And the marker of CD34 staining was used as an indicator of microvessel density (MVD).

Results

TFPI-2 expression has a decreasing trend with the progression of cervical cancer and was significantly correlated with FIGO stage, lymph node metastasis and HPV infection. In addition, there were significant positive correlations between the grading of TFPI-2 expression and AI(P = 0.004). In contrast, the expression of TFPI-2 and VEGF or MVD was negatively correlated (both p < 0.001). However, we did not establish any significant correlation between Ki-67 and TFPI-2 expression in cervical cancer.

Conclusions

The results suggested that the expression of TFPI-2 had a decreasing trend with tumor progression of cervical cancer. There was a close association between the expression of TFPI-2 and tumor cell apoptosis and angiogenesis in patients with cervical cancer. TFPI-2 may play an inhibitive role during the development of cervical cancer.

Glucagon counteracts interleukin-6-dependent gene expression by redundant action of Epac and PKA

Inflammation is the biological response to injurious stimuli. In the initial phase of the inflammatory process, interleukin-6 (IL-6) is the main inducer of acute phase protein expression in the liver. A prolonged acute phase response is characterised by a disturbed glucose homeostasis and elevated levels of IL-6, insulin, and counterregulatory hormones such as glucagon. Several studies deal with the impact of IL-6 on glucagon-dependent gene expression. In contrast, only very little is known about the influence of G-protein-coupled receptors on IL-6 signalling. Therefore, the aim of this study is to elucidate the regulation of IL-6-induced gene expression by glucagon. We could reveal a novel mechanism of negative regulation of IL-6-induced MAP kinase activation by glucagon in primary murine hepatocytes. IL-6-dependent induction of the ERK-dependent target geneTfpi2, coding for a Kunitz-type serine protease inhibitor, was strongly down-regulated by glucagon treatment. Studying the underlying mechanism revealed a redundant action of the signalling molecules exchange protein activated by cyclic AMP (Epac) and protein kinase A. The metabolic hormone glucagon interferes in IL-6-induced gene expression. This observation is indicative for a regulatory role of G-protein-coupled receptors in the IL-6-dependent inflammatory response.

TFPI-2 methylation predicts poor prognosis in non-small cell lung cancer

BACKGROUND

Methylation of human tissue factor pathway inhibitor-2 (TFPI-2) gene has been detected in several types of cancer, including non-small cell lung cancer (NSCLC). However, an association between the methylation status of TFPI-2 gene and prognosis has not yet been investigated.

METHODS

Methylation of TFPI-2 gene was examined in a consecutive series of 133 non-metastatic NSCLC patients using methylation-specific PCR (MSP). Univariate and multivariate analyses were conducted to investigate the association between clinical variables and overall survival time.

RESULTS

Methylation of TFPI-2 gene was detected in 36 of 133 patients (27.1%). Of these 36 patients, seventeen individuals (47.2%) carried stage III tumors. The 5-year disease free survival rate among patients carrying methylated TFPI-2 tumors was significantly lower as compared to those with unmethylated TFPI-2 tumors (35.5% versus 6.1%, P<0.0001). Moreover, methylation of TFPI-2 gene was found to be an independent prognostic factor for poor overall survival based on multivariate analysis models (P=0.013), as was age >62 years old (P<0.0001) and TNM stage of disease (P<0.0001).

CONCLUSIONS

The results of the present study suggest that methylation of TFPI-2 gene is an independent factor for an unfavorable prognosis in patients with NSCLC.

Tissue factor pathway inhibitor-2 inhibits the growth and invasion of hepatocellular carcinoma cells and is inactivated in human hepatocellular carcinoma

Human tissue factor pathway inhibitor-2 (TFPI-2) is an extracellular matrix-associated Kunitz-type serine proteinase inhibitor that inhibits the plasmin- and trypsin-mediated activation of matrix metalloproteinases and inhibits tumor progression, invasion and metastasis. Previous studies have shown that TFPI-2 is downregulated in the progression of various tumors. The purpose of this study was to investigate the expression and function of TFPI-2 in hepatocellular carcinoma (HCC). In situ hybridization was used to detect human TFPI-2 mRNA and immunohistochemistry was performed to examine the role of TFPI-2 expression in hepatocarcinoma tissues. Cell proliferation was assessed using MTT assay. In situ hybridization and immunohistochemical analyses revealed that the expression of TFPI-2 in hepatocarcinoma tissues was markedly lower than that in tumor-adjacent normal hepatic tissues. Restored expression of TFPI-2 in HepG(2) cells inhibits cell proliferation and invasion. Taken together, the results suggest that TFPI-2 has a tumor-suppression action and its inactivation may contribute to HCC.

Detection of methylated tissue factor pathway inhibitor 2 and human long DNA in fecal samples of patients with colorectal cancer in China

BACKGROUND

To investigate the feasibility of detecting methylated tissue factor pathway inhibitor (TFPI2) and quantifying human long DNA with fluorescent quantitative Alu PCR in fecal DNA as a non-invasive screening tool for colorectal cancer (CRC).

MATERIALS AND METHODS

Methylation-specific PCR (MSP) was performed to analyze TFPI2 gene promoter methylation status in a blinded fashion in stool samples taken from 30 endoscopically diagnosed healthy controls, 20 patients with adenomas, and 60 patients with colorectal cancer. Real-time Alu PCR was used to quantify human long DNA.

RESULTS

The specificity of fecal TFPI2 MSP assay and long DNA assay was 100% and 83.3%, respectively. The sensitivity of fecal TFPI2 MSP assay and long DNA assay was 68.3% and 53.3%, respectively. The sensitivity of fecal DNA assay (either marker being positive) was 86.7%, which was high for CRC.

CONCLUSIONS

Our results have demonstrated the feasibility of using TFPI2 methylation and quantify human long DNA with fluorescent quantitative Alu PCR in fecal samples as a new noninvasive test for CRC.

Transcriptional repressive H3K9 and H3K27 methylations contribute to DNMT1-mediated DNA methylation recovery

DNA methylation and histone modifications are two major epigenetic events regulating gene expression and chromatin structure, and their alterations are linked to human carcinogenesis. DNA methylation plays an important role in tumor suppressor gene inactivation, and can be revised by DNA methylation inhibitors. The reversible nature of DNA methylation forms the basis of epigenetic cancer therapy. However, it has been reported that DNA re-methylation and gene re-silencing could occur after removal of demethylation treatment and this may significantly hamper the therapeutic value of DNA methylation inhibitors. In this study we have provided detailed evidence demonstrating that mammalian cells possess a bona fide DNA methylation recovery system. We have also shown that DNA methylation recovery was mediated by the major human DNA methyltransferase, DNMT1. In addition, we found that H3K9-tri-methylation and H3K27-tri-methylation were closely associated with this DNA methylation recovery. These persistent transcriptional repressive histone modifications may have a crucial role in regulating DNMT1-mediated DNA methylation recovery. Our findings may have important implications towards a better understanding of epigenetic regulation and future development of epigenetic therapeutic intervention.

TFPI-2 is a putative tumor suppressor gene frequently inactivated by promoter hypermethylation in nasopharyngeal carcinoma

Background

Epigenetic silencing of tumor suppressor genes play important roles in NPC tumorgenesis. Tissue factor pathway inhibitor-2 (TFPI-2), is a protease inhibitor. Recently, TFPI-2 was suggested to be a tumor suppressor gene involved in tumorigenesis and metastasis in some cancers. In this study, we investigated whether TFPI-2 was inactivated epigenetically in nasopharyngeal carcinoma (NPC).

Methods

Transcriptional expression levels of TFPI-2 was evaluated by RT-PCR. Methylation status were investigated by methylation specific PCR and bisulfate genomic sequencing. The role of TFPI-2 as a tumor suppressor gene in NPC was addressed by re-introducing TFPI-2 expression into the NPC cell line CNE2.

Results

TFPI-2 mRNA transcription was inactivated in NPC cell lines. TFPI-2 was aberrantly methylated in 66.7% (4/6) NPC cell lines and 88.6% (62/70) of NPC primary tumors, but not in normal nasopharyngeal epithelia. TFPI-2 expression could be restored in NPC cells after demethylation treatment. Ectopic expression of TFPI-2 in NPC cells induced apoptosis and inhibited cell proliferation, colony formation and cell migration.

Conclusions

Epigenetic inactivation of TFPI-2 by promoter hypermethylation is a frequent and tumor specific event in NPC. TFPI-2 might be considering as a putative tumor suppressor gene in NPC.

Epigenetic mechanisms involved in the pathogenesis of hepatobiliary malignancies

Primary tumors of the liver and biliary tree are increasing in frequency and portend a miserable prognosis. Epigenetic regulation of gene expression has emerged as a fundamental aspect of cancer development and progression. The molecular mechanisms of carcinogenesis in hepatocellular carcinoma and cholangiocarcinoma involve a complex interplay of both genetic and epigenetic factors. Recent studies investigating the possible epigenetic mechanisms induced in the disease have shed new light on the molecular underpinnings of hepatobiliary cancers. In addition, epigenetic modifications of DNA in cancer and precancerous lesions offer hope and the promise of novel biomarkers for early cancer detection, prediction, prognosis and response to treatment. Furthermore, the reversal of epigenetic changes represents a potential target for novel therapeutic strategies and medication design.

Tissue factor pathway inhibitor 2 (TFPI2) is frequently silenced by aberrant promoter hypermethylation in gastric cancer

Aberrant methylation of promoter CpG islands is associated with transcriptional inactivation of tumor-suppressor genes in cancer. TFPI2, a Kunitz-type serine proteinase inhibitor, has been identified as a putative tumor-suppressor gene from genome-wide screening for aberrant methylation, using a microarray combined with the methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-aza-dCyd) in various types of tumors. We assessed the methylation status of TFPI2 and investigated its expression pattern in human primary gastric cancer (GC) tissues and in GC cell lines. Hypermethylation of the promoter CpG island, which was observed in more or less all of GC cell lines, was prevalent in a high proportion of primary GC tissues (15/18, or 83%), compared with noncancerous (4/18, or 22%) or normal (0/3, or 0%) stomach tissues, and expression of TFPI2 mRNA was reduced in 7 of the 17 primary GC tissues (41%). Moreover, immunohistochemical analyses showed decreased levels of TFPI-2 protein, compared with adjacent noncancerous tissues in 8 of the 20 primary GC tissues examined (40%). TFPI2 mRNA expression was restored in gene-silenced GC cells after treatment with 5-aza-dCyd. Aberrant methylation of TFPI2 promoter CpG island occurred not only in GC cells but also in primary GC tissues at a high frequency, suggesting that epigenetic silencing of TFPI2 may contribute to gastric carcinogenesis.

Molecular targets for liver cancer therapy: From screening of target genes to clinical trials

Cancer arises from the accumulation of genetic alterations, and the inactivation of oncogenes, or recovery of suppressor genes, are promising strategies for cancer treatment. Genome-based drug research starts with identification of target genes and is accomplished by exploitation of target-based drugs such as monoclonal antibodies, small molecules and antisense drugs. Recently, clinical trials for treatment of advanced hepatocellular carcinoma (HCC) have been performed, and the effectiveness of sorafenib, an oral multikinase inhibitor of the vascular endothelial growth factor receptor and Ras kinase, has been demonstrated. In addition to known target genes, microarray technology has enabled us to constitute novel therapeutic targets, and many researchers have applied this technology in studies of HCC and have identified candidate target genes, validated to affect cell growth. In addition, promoter arrays for whole-genome epigenetic aberration analysis, ChIP-chip analysis using tiling arrays, and high-throughput sequencing systems have been applied to drug discovery. To elucidate the status of therapeutic target genes in vivo, development of diagnostic markers for stratification of patients is a pressing need. Here, we review recent advances in microarray technology for liver cancer, discuss the innovations and approaches to therapeutic target discovery, and present data regarding the outcome of gene target therapy using monoclonal antibodies and molecular diagnostic markers in our laboratory.

Genetic and epigenetic silencing of SCARA5 may contribute to human hepatocellular carcinoma by activating FAK signaling

The epigenetic silencing of tumor suppressor genes is a crucial event during carcinogenesis and metastasis. Here, in a human genome-wide survey, we identified scavenger receptor class A, member 5 (SCARA5) as a candidate tumor suppressor gene located on chromosome 8p. We found that SCARA5 expression was frequently downregulated as a result of promoter hypermethylation and allelic imbalance and was associated with vascular invasion in human hepatocellular carcinoma (HCC). Furthermore, SCARA5 knockdown via RNAi markedly enhanced HCC cell growth in vitro, colony formation in soft agar, and invasiveness, tumorigenicity, and lung metastasis in vivo. By contrast, SCARA5 overexpression suppressed these malignant behaviors. Interestingly, SCARA5 was found to physically associate with focal adhesion kinase (FAK) and inhibit the tyrosine phosphorylation cascade of the FAK-Src-Cas signaling pathway. Conversely, silencing SCARA5 stimulated the signaling pathway via increased phosphorylation of certain tyrosine residues of FAK, Src, and p130Cas; it was also associated with activation of MMP9, a tumor metastasis-associated enzyme. Taken together, these data suggest that the plasma membrane protein SCARA5 can contribute to HCC tumorigenesis and metastasis via activation of the FAK signaling pathway.

Genetic and epigenetic marker-based DNA test of stool is a promising approach for colorectal cancer screening

Colorectal cancer (CRC) is one of the most common malignancies and leading cause of cancer-related deaths in the world.1 However, it may be treated effectively by surgical removal of the cancerous tissue if detected at early stages. Conventional tools for screening CRC are either invasive or inaccurate. Therefore, there is an urgent need to develop a reliable screening tools for CRC to significantly reduce its morbidity. In this regard, a novel DNA markers-based detection in stool is emerging as a promising approach.

Methylation of TFPI2 in stool DNA: a potential novel biomarker for the detection of colorectal cancer

We have used a gene expression array-based strategy to identify the methylation of tissue factor pathway inhibitor 2 (TFPI2), a potential tumor suppressor gene, as a frequent event in human colorectal cancers (CRC). TFPI2 belongs to the recently described group of embryonic cell Polycomb group (PcG)-marked genes that may be predisposed to aberrant DNA methylation in early stages of colorectal carcinogenesis. Aberrant methylation of TFPI2 was detected in almost all CRC adenomas (97%, n = 56) and stages I to IV CRCs (99%, n = 115). We further explored the potential of TFPI2 as a biomarker for the early detection of CRC using stool DNA-based assays in patients with nonmetastatic CRC and average-risk noncancer controls who were candidates for screening. TFPI2 methylation was detected in stool DNA from stage I to III CRC patients with a sensitivity of 76% to 89% and a specificity of 79% to 93%. Detection of TFPI2 methylation in stool DNA may act as a useful adjunct to the noninvasive strategies for screening of CRCs in the future.

HAI-2 is epigenetically downregulated in human hepatocellular carcinoma, and its Kunitz domain type 1 is critical for anti-invasive functions

Pharmacological demethylation-based gene expression profile analysis is a useful tool to identify epigenetically silenced tumour suppressor genes. HGF activator inhibitor 2 (HAI-2), a serine protease inhibitor, has been identified as one of the candidate tumour suppressor genes in human hepatocellular carcinoma (HCC) with this technique. In this study, we aimed to characterise the epigenetic status and tumour suppressive function of HAI-2 in HCC. We validated that HAI-2 expression was either absent or low in most of the HCC cell lines tested, and 5-Aza-2'-deoxycytidine treatment significantly restored its expression in 9 (75%) of these 12 cell lines. HAI-2 was found to be frequently underexpressed in human HCCs (p < 0.001). With bisulphite DNA sequencing and methylation-specific PCR, we found that the promoter of the HAI-2 gene was frequently hypermethylated in both HCC cell lines and human HCCs. Ectopic expression of HAI-2 significantly inhibited cell migration and invasiveness of HCC cells in vitro and suppressed tumourigenicity in vivo. In addition, we also provided the first evidence that HAI-2 mediated its tumour suppressor function via the Kunitz domain 1 (KD-1), as KD-1 but not KD-2 inactivating mutant abolished its anti-tumour invasiveness in vitro. Our findings suggest that HAI-2 is a candidate tumour suppressor gene that is frequently hypermethylated and underexpressed in human HCCs, and the KD-1 domain of HAI-2 is the key region responsible for its anti-invasive function.

Current progress in epigenetic research for hepatocarcinomagenesis

Hepatocellular carcinoma is the main type of primary liver cancer, and also one of the most malignant tumors. At present, the pathogenesis mechanisms of liver cancer are not entirely clear. It has been shown that inactivation of tumor suppressor genes and activation of oncogenes play a significant role in carcinogenesis, caused by the genetic and epigenetic aberrance. In the past, people generally thought that genetic mutation is a key event of tumor pathogenesis, and somatic mutation of tumor suppressor genes is in particular closely associated with oncogenesis. With deeper understanding of tumors in recent years, increasing evidence has shown that epigenetic silencing of those genes, as a result of aberrant hypermethylation of CpG islands in promoters and histone modification, is essential to carcinogenesis and metastasis. The term epigenetics refers to heritable changes in gene expression caused by regulation mechanisms, other than changes in the underlying DNA sequence. Specific epigenetic processes include DNA methylation, genome imprinting, chromotin remodeling, histone modification and microRNA regulations. This paper reviews recent epigenetics research progress in the hepatocellular carcinoma study, and tries to depict the relationships between hepatocellular carcinomagenesis and DNA methylation as well as microRNA regulation.

Methylation of Tip30 promoter is associated with poor prognosis in human hepatocellular carcinoma

PURPOSE

To investigate Tip30 promoter methylation status in human hepatocellular carcinoma (HCC) and the correlation with clinicopathologic features and prognosis.

EXPERIMENTAL DESIGN

The methylation status of CpG islands in Tip30 promoter was examined in 15 HCC cell lines as well as 59 paired HCC and adjacent nontumor tissues. The associations between Tip30 methylation status and the survival of patients were analyzed.

RESULTS

Tip30 promoter was hypermethylated in 6 of 10 HCC cell lines with reduced Tip30 mRNA. DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine, greatly enhanced TIP30 expression and sensitized HCC cells to cytotoxic drug-induced cell death. The promoter region of Tip30 was identified and the main promoter activity was located in the -135 to -45 region sited within a CpG island. The minimal promoter element contained four Sp1 binding sites, which were hypermethylated in HCC cell-derived promoters. Moreover, analyses of Tip30 promoter methylation status in 59 paired HCC tissues showed that 47% of the cases were hypermethylated. Recurrence rate (95% versus 67%; P = 0.011) and mortality (82% versus 53%; P = 0.033) were significantly higher in patients with methylated Tip30. Disease-free survival was significantly higher in patients with unmethylated Tip30 (33.3% versus 4.5%; P = 0.036).

CONCLUSIONS

Our results show that epigenetic silencing of Tip30 gene expression by CpG island DNA hypermethylation is associated with poor prognosis in patients with HCC.

Tissue factor pathway inhibitor-2 gene methylation is associated with low expression in carotid atherosclerotic plaques

BACKGROUND

The tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine-protease inhibitor which is expressed in atherosclerotic plaques. Epigenetic regulation of the TFPI-2 gene, through methylation of CpG islands, has been advocated in cancer. We hypothesized that TFPI-2 gene methylation could regulate TFPI-2 expression in atherosclerosis.

METHODS

We used Methylation Specific PCR (MSP) and pyrosequencing in order to identify 18 CpG of the TFPI-2 promoter, in 59 carotid atherosclerotic plaques and 26 control mammary arteries.

RESULTS

MSP showed methylation of the TFPI-2 gene (MSP+) in 16 plaques (27%), while no methylation (MSP-) was found in control arteries. Pyrosequencing confirmed that MSP+ plaques presented higher methylation levels than MSP- ones and arteries (p=0.03 and 0.01). Moreover, the TFPI-2 mRNA levels were lower in methylated plaques than in unmethylated ones and than in arteries (p=0.04 and <0.0001). The methylated plaques contained less lipids and macrophage infiltration than unmethylated ones. Their TFPI-2 immunoreactivity was mainly detected in the macrophages located in the media on the adventitial side, rather than in the lipid-rich core.

CONCLUSION

Methylation of the TFPI-2 gene takes place in atherosclerotic plaques and is associated with decreased TFPI-2 expression. The place of this process in atherosclerosis progression remains to be investigated.

High-dimensional biology to comprehend hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and is the third leading cause of death from cancer. The diverse etiology, high morbidity/mortality, lack of diagnostic markers for early diagnosis and the highly variable clinical course of HCC have hindered advances in diagnosis and treatment. Microsatellite instability, chromosomal aberrations, mutations in key cell cycle genes and epigenetic changes have been reported in HCC. Availability of modern technologies advance 'high-dimensional biology' (HDB), a term that refers to the simultaneous study of the genetic variants (genome), transcription (mRNA; transcriptome), peptides and proteins (proteomics), and metabolites (metabolomics) for the intermediate products of metabolism of an organ, tissue or organism. The growing interest in omics-based research has enabled the simultaneous examination of thousands of genes, transcripts and proteins of interest, with high-throughput techniques and advanced analytical tools for data analysis. The use of each approach towards functional omics has lead to the classification of HCC into molecular subgroups. Here we review the use of HDB as a tool for the identification of markers for screening, diagnosis, molecular classification and the discovery of new therapeutic drug targets of HCC. With the extensive use of HDB, it may be possible in the near future, to have custom-made therapeutic regimens for HCC based on the molecular subtype, ultimately leading to an improved survival of HCC patients.

DNA methylation in hepatocellular carcinoma

As for many other tumors, development of hepatocellular carcinoma (HCC) must be understood as a multistep process with accumulation of genetic and epigenetic alterations in regulatory genes, leading to activation of oncogenes and inactivation or loss of tumor suppressor genes (TSG). In the last decades, in addition to genetic alterations, epigenetic inactivation of (tumor suppressor) genes by promoter hypermethylation has been recognized as an important and alternative mechanism in tumorigenesis. In HCC, aberrant methylation of promoter sequences occurs not only in advanced tumors, it has been also observed in premalignant conditions just as chronic viral hepatitis B or C and cirrhotic liver. This review discusses the epigenetic alterations in hepatocellular carcinoma focusing DNA methylation.

Molecular pathogenesis of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer and the third leading cause of cancer death worldwide. Hepatocarcinogenesis is a multistep process evolving from normal through chronic hepatitis/cirrhosis and dysplastic nodules to HCC. With advances in molecular methods, there is a growing understanding of the molecular mechanisms in hepatocarcinogenesis. Hepatocarcinogenesis is strongly linked to increases in allelic losses, chromosomal changes, gene mutations, epigenetic alterations and alterations in molecular cellular pathways. Some of these alterations are accompanied by a stepwise increase in the different pathological disease stages in hepatocarcinogenesis. Overall, a detailed understanding of the underlying molecular mechanisms involved in the progression of HCC is of fundamental importance to the development of effective prevention and treatment regimes for HCC.