Comparative analysis of promoter methylation and gene expression endpoints between tumorous and non-tumorous tissues from HCV-positive patients with hepatocellular carcinoma

Abstract

Transcriptional silencing of tumor suppressor genes and other cancer-related genes induced by promoter CpG island hypermethylation is an important epigenetic mechanism of hepatocarcinogenesis. Previous studies have established methylation profiles of hepatocellular carcinomas (HCCs) and demonstrated that methylation of several candidate genes in resected tissues may be associated with time to recurrence. The goals of our study were to test whether specific promoter methylation and mRNA levels of candidate genes, as well as global changes in DNA methylation, can be linked with time to recurrence and clinicopathological variables in a homogenous study group of HCC patients. Forty-three tumorous and 45 non-tumorous liver tissue samples from the surgical margin were obtained from HCV-positive, HBV-negative HCC patients who underwent tumor resection surgery and who were monitored for tumor recurrence thereafter (median follow-up time: 16 months (range, 0 – 79 months)). Methylation-specific PCR was used to assess the promoter methylation status of P16(INK4a), SOCS-1, RASSF1A, APC, GSTP1, RIZ1, and MGMT genes, while the level of LINE-1 methylation was used as marker of global DNA methylation levels. Methylation frequencies in P16(INK4a), RASSF1A, APC, GSTP1, and RIZ1 genes were significantly greater in tumorous versus non-tumorous tissues. Methylation of RIZ1 in non-tumorous tissues was significantly associated with time to recurrence. Additionally, genomic DNA was significantly more hypomethylated in tumorous tissues, and this change was associated with shorter recurrence, but not with clinicopathological features. In conclusion, this study supports the role of aberrant methylation in the pathobiology of HCV-positive HCCs. The finding that RIZ1 methylation and increased levels of LINE-1 hypomethylation in non-tumorous tissues are associated with time to recurrence underscores the importance of assessing the epigenetic state of the liver remnant.

Are there opportunities for chemotherapy in the treatment of hepatocellular cancer?

“…In a series from Taiwan, hypermethylation was found in 39% HCC and there appeared to be a relationship between hypermethylation and aflatoxin B 1 DNA adducts [65]. However, other studies, including those from Japan, have found relatively low levels of MGMT hypermethylation in comparison to other target genes [66,67].…”

Association of hypomethylation of LINE-1 repetitive element in blood leukocyte DNA with an increased risk of hepatocellular carcinoma

“…Global DNA hypomethylation seems to occur in early neoplasia and has been regarded as an important component of cancer development (Das and Singal, 2004;Zhu et al, 2011). Compared with normal tissue counterparts, lower global DNA methylation was observed in tumor tissues in a broad panel of cancers including HCC (Das and Singal, 2004;Formeister et al, 2010). Animal studies have shown that experimentallyinduced hypomethylation can lead to cancer development at multiple sites (Wilson et al, 1984;Thomas and Williams, 1992;Gaudet et al, 2003), indicating the causal role of global DNA hypomethylation in cancer development.…”

Hepatitis viruses exploitation of host DNA methyltransferases functions

“…HCV core genotype 1 has shown several oncogenic properties, such as the activation of STAT3 and its downstream molecules, c-myc and cyclin D [73], the suppression of the c-fos promoter [74] and the activation of the AMPK/ERK cascade, inducing cell cycle progression [75]. Besides these classical mechanisms, a link between HCV infection and the aberrant methylation levels of some HCC-related genes, namely p16/INK4A, SOCS1, RASSF1A, APC, GSTP1 and RIZ1, was already demonstrated [56,76]. Two in vitro studies reported hypermethylated levels of E-cadherin promoter in hepatocytes expressing the HCV core protein genotype 1b [18,77].…”