LINE‐1 hypomethylation induced by reactive oxygen species is mediated via depletion of S‐adenosylmethionine

Abstract

Whether long interspersed nuclear element-1 (LINE-1) hypomethylation induced by reactive oxygen species (ROS) was mediated through the depletion of S-adenosylmethionine (SAM) was investigated. Bladder cancer (UM-UC-3 and TCCSUP) and human kidney (HK-2) cell lines were exposed to 20 μM H2O2 for 72 h to induce oxidative stress. Level of LINE-1 methylation, SAM and homocysteine (Hcy) was measured in the H2O2 -exposed cells. Effects of α-tocopheryl acetate (TA), N-acetylcysteine (NAC), methionine, SAM and folic acid on oxidative stress and LINE-1 methylation in the H2O2 -treated cells were explored. Viabilities of cells treated with H2O2 were not significantly changed. Intracellular ROS production and protein carbonyl content were significantly increased, but LINE-1 methylation was significantly decreased in the H2O2 -treated cells. LINE-1 methylation was restored by TA, NAC, methionine, SAM and folic acid. SAM level in H2O2 -treated cells was significantly decreased, while total glutathione was significantly increased. SAM level in H2O2 -treated cells was restored by NAC, methionine, SAM and folic acid; while, total glutathione level was normalized by TA and NAC. Hcy was significantly decreased in the H2O2 -treated cells and subsequently restored by NAC. In conclusion, in bladder cancer and normal kidney cells exposed to H2O2 , SAM and Hcy were decreased, but total glutathione was increased. Treatments with antioxidants (TA and NAC) and one-carbon metabolites (SAM, methionine and folic acid) restored these changes. This pioneer finding suggests that exposure of cells to ROS activates glutathione synthesis via the transsulfuration pathway leading to deficiency of Hcy, which consequently causes SAM depletion and eventual hypomethylation of LINE-1.

Low-Dose Ionizing Radiation Exposure, Oxidative Stress and Epigenetic Programing of Health and Disease

“…SAM is utilized by DNMTs and histone methyltransferases and therefore, oxidative stress-mediated inhibition of SAM results in genomic hypomethylation (111). Similarly, LINE-1 methylation was shown to significantly decreased in H 2 O 2 treated HK-2 kidney cells (112). This study demonstrated that exposure of cells to ROS leads to homocysteine deficiency, which consequently causes SAM depletion and eventual hypomethylation of LINE-1 (112).…”

Oxidative DNA damage induces hypomethylation in a compromised base excision repair colorectal tumourigenesis

“…Recently, Kloypan et al (2015) demonstrated that in colorectal cancer LINE-1 hypomethylation is associated with the oxidative stress-mediated activation of the ten-eleven translocation hydroxylase enzymes that cooperate with BER in controlling the formation and replacement of 5-hydroxymethylcytosine (5 hmC). Finally, ROS are considered to be responsible for aberrant DNA methylation in different cancer models (Campos et al , 2007; Lim et al , 2008; Quan et al , 2011; Ziech et al , 2011; Kloypan et al , 2015) and during chronic inflammation and inflammation-associated carcinogenesis, such as ulcerative colitis and Crohn's disease (Iborra et al , 2011; Hartnett and Egan, 2012). All these data suggest that increased oxidative DNA damage and/or lack of DNA repair are strongly correlated not only with genetic but also with aberrant DNA methylation in cancer.…”

The epigenetic landscape related to reactive oxygen species formation in the cardiovascular system

“…In addition, in conditions of oxidative stress, methionine is required for the synthesis of cysteine to produce the antioxidant glutathione and is thus depleted for SAM synthesis (Cyr and Domann, ). In support, long‐term exposure to H 2 O 2 decreased SAM levels but increased glutathione levels, leading to hypomethylation of the long interspersed nuclear element‐1 (LINE‐1) (Kloypan et al , ). LINE‐1 hypomethylation as an indicator of global methylation status was found in blood from patients with ischaemic heart disease and stroke and has been related to higher risk for these diseases (Baccarelli et al , ).…”