title: LINE-1 gene hypomethylation and p16 gene hypermethylation in HepG2 cells induced by low-dose and long-term triclosan exposure: The role of hydroxyl group.
abstract: Triclosan (TCS), a frequently used antimicrobial agent in pharmaceuticals and personal care products, exerts liver tumor promoter activities in mice. Previous work showed high-dose TCS (1.25-10μM) induced global DNA hypomethylation in HepG2 cells. However, whether or how tumor suppressor gene methylation changed in HepG2 cells after low-dose and long-term TCS exposure is still unknown. We investigate here the effects and mechanisms of DNA methylation of global DNA(GDM), repetitive genes, and liver tumor suppressor gene (p16) after exposing HepG2 cells to low-dose TCS (0.625-5nM)for two weeks using HPLC-MS/MS, Methylight, Q-MSP, Pyrosequencing, and Massarray methods. We found that low-dose TCS exposure decreased repetitive elements LINE-1 methylation levels, but not global DNA methylation, through down-regulating DNMT1 (DNA methyltransferase 1) and MeCP2 (methylated DNA binding domain) expression, and up-regulating 8-hydroxy-2-deoxyguanosine (8-OHdG) levels. Interestingly, low-dose TCS elevated p16 gene methylation and inhibited p16 expression, which were not observed in high-dose (10μM) group. Meanwhile, methyl-triclosan could not induce these two types of DNA methylation changes, suggesting the involvement of hydroxyl in TCS-mediated DNA methylation changes. Collectively, our results suggested low concentrations of TCS adversely affected HepG2 cells through DNA methylation dysregulation, and hydroxyl group in TCS played an important role in the effects. This study provided a better understanding on hepatotoxicity of TCS at environmentally relevant concentrations through epigenetic pathway.
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Liudan
authors.initials: L
authors.lastname: Zeng
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China. Electronic address: mahuimin@gig.ac.cn.
authors.forename: Huimin
authors.initials: H
authors.lastname: Ma
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Graduate School of the Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Shangxia
authors.initials: S
authors.lastname: Pan
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Jing
authors.initials: J
authors.lastname: You
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Gan
authors.initials: G
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Zhiqing
authors.initials: Z
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Guoying
authors.initials: G
authors.lastname: Sheng
authors.affiliation: State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China.
authors.forename: Jiamo
authors.initials: J
authors.lastname: Fu
mesh_terms: D000891:Anti-Infective Agents, Local / Q000494:pharmacology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D047628:Estrogen Receptor alpha / Q000235:genetics; D019942:Genes, p16; D056945:Hep G2 Cells; D006801:Humans; D006900:Hydroxylation; D020084:Long Interspersed Nucleotide Elements / Q000235:genetics*; D051783:Methyl-CpG-Binding Protein 2 / Q000235:genetics; D014260:Triclosan / Q000494:pharmacology*
chemical_list: D000891:Anti-Infective Agents, Local; D019941:Cyclin-Dependent Kinase Inhibitor p16; C506487:ESR1 protein, human; D047628:Estrogen Receptor alpha; C497392:MECP2 protein, human; D051783:Methyl-CpG-Binding Protein 2; D014260:Triclosan; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human; C000619381:Dnmt1 protein, mouse
keywords: DNA methylation; Hydroxyl group; LINE-1; Low-dose; Triclosan; p16