Reactive Oxygen Species Induce Epigenetic Instability through the Formation of 8-Hydroxydeoxyguanosine in Human Hepatocarcinogenesis

Abstract

Chronic hepatitis C (CHC) triggers oxidative stress and contributes to the emergence of hepatocellular carcinoma (HCC). We previously reported that tumor suppressor gene (TSG) methylation is a critical factor during the early stages of hepatocarcinogenesis. In this study, we clarify the association between oxidative stress and epigenetic alterations during hepatocarcinogenesis. We examined DNA oxidation and methylation profiles in 128 liver biopsy samples from CHC patients. The DNA oxidation and methylated TSG numbers were quantified using immunohistochemical analysis of 8-hydroxydeoxyguanosine (8-OHdG) and quantitative PCR for 11 TSGs, respectively. The quantitative chromatin immunoprecipitation-PCR (ChIP-qPCR) assay in HepG2 and fetal liver Hc cells treated with H₂O₂ was used to quantify trimethyl-H3K4, acetylated-H4K16 (an active chromatin marker), trimethyl-H3K27 (a repressive chromatin marker) and 8-OHdG. We analyzed 30 promoters of 25 different TSGs by qPCR. The high levels of 8-OHdG was the only variable that was significantly associated with the increased number of methylated TSGs in CHC (p < 0.0001). The ChIP-qPCR revealed that after H₂O₂ treatment of the cell lines, the 8-OHdG-bound promoters showed a modification from an active chromatin (trimethyl-H3K4 and acetylated-H4K16 dominant) to a repressive chromatin (trimethyl-H3K27 dominant) status. We conclude that oxidative stress alters the chromatin status, which leads to abnormal methylation of TSGs, and contributes to hepatocarcinogenesis in CHC patients.

Genetic basis of hepatitis virus-associated hepatocellular carcinoma: linkage between infection, inflammation, and tumorigenesis

“…Inhibition of natural killer cells or administration of a neutralizing IFN-c antibody inhibits methylation changes, suggesting that natural killer cell function is a key player in inducing aberrant DNA methylation in human hepatocytes after initial HBV and HCV infection [144]. ROS induced by chronic HCV infection could alter histone modification to the repressive form at CpG island-containing tumor suppressor gene promoters, leading to tumor suppressor gene inactivation [145]. These findings suggest that chronic inflammation associated with hepatitis virus infection might cause epigenetic alterations through the immune response as well as through the induction of oxidative stress.…”

Low-Dose Gamma Irradiation Enhances Superoxide Anion Production by Nonirradiated Cells Through TGF-β1-Dependent Bystander Signaling

“…Gene promoters with 8-OHdG adduct formation have been reported to change the chromatin status from active chromatin with trimethyl-H3K4 and acetylated-H4K16 to a repressive form expressing trimethyl-H3K27 (115). The change in chromatin status was associated with gene methylation.…”

Comparison of blueberry ( Vaccinium spp. ) and vitamin C via antioxidative and epigenetic effects in human

“…3,25 For example, the generation of ROS and 8-OHdG could play a critical role in the abnormal methylation of tumor suppressor genes in the liver of chronic hepatitis C. Nishida et al 3 demonstrated that the 8-OHdG levels were associated with increased numbers of methylated tumor suppressors, and that tumor suppressor genes carrying higher levels of 8-OHdG facilitated the modification of the active chromatin to a repressive form after stimulation by ROS. In addition, the methylation of a tumor suppressor gene, e.g., runt-related transcription factor 3, was significantly increased in bladder cancer cells exposed to H2O2.…”

“…2 Growing evidence supports a role for reactive oxygen species (ROS) in epigenetic processes through the generation of oxidative stress. 3 On the other hand, epigenetic processes are also influenced by a variety of dietary antioxidants. For example, maternal dietary antioxidant supplementation mitigated DNA methylation changes in the irradiated offspring.…”