title: Nickel-induced histone hypoacetylation: the role of reactive oxygen species.
abstract: The carcinogenicity of specific insoluble nickel compounds is mainly due to their intracellular generation of Ni2+ ion and its suppression on gene transcription, while the inhibition of Ni2+ on histone acetylation plays an important role in the suppression or silencing of genes. Recent studies on Ni2+ and histone H4 acetylation suggest that Ni2+ inhibits the acetylation of histone H4 through binding with its N-terminal histidine-18. It is well known that bound Ni2+ readily produces reactive oxygen species (ROS) in vivo, a critical factor inversely related with the occurrence of resistance of mammalian cells to Ni2+. Thus, we tried to find the possible role of ROS in the induction of Ni2+ on histone acetylation in the present study. We found that a high concentration of Ni2+ (no less than 600 microM) caused a significant decrease of histone acetylation in human hepatoma cells. This inhibition was shown to result mainly from the influence of Ni2+ on the overall histone acetyltransferase (HAT) activity indicated by the histone acetylation assay with the presence of a specific histone deacetylase (HDAC) inhibitor, trichostatin A (TSA). The in vitro HAT and HDAC assays further confirmed this result. At the same time, we found that the exposure of hepatoma cells to Ni2+ generated ROS. Coadministration of hydrogen peroxide with Ni2+ generated more ROS and more histone acetylation inhibition. Addition of the antioxidants 2-mercaptoethanol (2-ME) at 2 mM or N-acetyl-cysteine (NAC) at 1 mM, with Ni2+ together, completely suppressed ROS generation and significantly diminished the induced histone hypoacetylation. The data presented here prove that the ROS generation plays a role in the inhibition of histone acetylation, and, hence, the gene suppression and carcinogenesis caused by Ni2+ exposure, providing a new door for us to continuously understand the mechanism of ROS in the carcinogenicity of Ni2+ and the resistance of mammalian cells to Ni2+.
authors.affiliation: School of Life Sciences, Lanzhou University, Lanzhou, Gansu 730000, China. kangjiuhong@lzu.edu.cn
authors.forename: Jiuhong
authors.initials: J
authors.lastname: Kang
authors.forename: Yuntao
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
authors.forename: Haifeng
authors.initials: H
authors.lastname: Chen
authors.forename: Changjun
authors.initials: C
authors.lastname: Lin
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
authors.forename: Yingxian
authors.initials: Y
authors.lastname: Ou
mesh_terms: D000107:Acetylation; D000123:Acetyltransferases / Q000037:antagonists & inhibitors*; D000975:Antioxidants / Q000494:pharmacology; D002273:Carcinogens / Q000633:toxicity*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004791:Enzyme Inhibitors / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology; D051548:Histone Acetyltransferases; D056572:Histone Deacetylase Inhibitors; D006657:Histones / Q000378:metabolism*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006877:Hydroxamic Acids / Q000494:pharmacology; D009532:Nickel / Q000633:toxicity*; D017382:Reactive Oxygen Species / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D002273:Carcinogens; D004338:Drug Combinations; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D017382:Reactive Oxygen Species; C012589:trichostatin A; D009532:Nickel; D006861:Hydrogen Peroxide; D000123:Acetyltransferases; D051548:Histone Acetyltransferases