We’ve previously reported that carcinogenic nickel compounds decreased global histone H4 acetylation and silenced the transgene in G12 Chinese hamster cells. and directly decreased the activity of a Fe(II)-2-oxoglutarate-dependent histone H3K9 demethylase in nuclear extract in vitro. These results are the first to show a histone H3K9 demethylase activity dependent on both iron and 2-oxoglutarate. Exposure to nickel ions also increased H3K9 dimethylation at the locus in G12 cells and repressed the expression of the transgene. An extended nickel ion exposure led to increased frequency of the transgene silencing which was readily reversed by treatment with DNA-demethylating agent 5-aza-2′-deoxycytidine. Collectively our data strongly indicate that nickel ions induce transgene silencing by increasing histone H3K9 dimethylation and this effect is usually mediated by the inhibition of H3K9 demethylation. Posttranslational modifications of histone N-terminal tails are important in chromatin business gene transcription and DNA replication and repair (19). To date a diverse array of histone modifications has been identified including acetylation methylation phosphorylation and ubiquitination (28). Among them methylation of histone H3 lysine 9 (H3K9) is INO-1001 one of the best-studied modifications. H3K9 may be mono- di- or trimethylated without changing the positive charge of the lysine residue. Trimethylated H3K9 is typically connected with constitutive heterochromatin while mono- and dimethylated H3K9 are mainly located in euchromatin and generally linked to repressed promoter regions (29). Suv39h family enzymes are responsible for trimethylation of H3K9 in vivo (27 29 while G9a and GLP/EuHMTase 1 are two major histone methyltransferases responsible for H3K9 dimethylation in vivo (35 36 Genetic ablation of either G9a or GLP/EuHMTase 1 dramatically diminished global H3K9 dimethylation in mouse embryonic stem cells (35 36 Methylation of histone lysines had long been thought of as a “permanent” modification since there was no known enzyme to demethylate. However this dogma was challenged by the recent discoveries of histone H3 lysine 4 (H3K4) demethylase LSD1 and H3 lysine 36 (H3K36) demethylase JHDM1 (JmjC domain-containing histone demethylase 1) (32 39 Although both LSD1 and JHDM1 can remove the methyl group from lysine residues on histone H3 they utilize different systems to demethylate. LSD1 is certainly a flavin-dependent amine oxidase and gets rid of the methyl group from mono- or dimethyl H3K4 by catalyzing the oxidation of amine for an imine intermediate (32). The imine intermediate is certainly then hydrolyzed to create an unpredictable carbinolamine which produces one Xdh formaldehyde molecule and therefore completes removing one methyl group (32). In different ways from LSD1 JHDM1 belongs for an iron- and 2-oxoglutarate-dependent dioxygenase family members and its own JmjC domain is crucial for the binding of both Fe(II) and 2-oxoglutarate (39). Like the removal of methylation from 1-methyladenine and 3-methylcytosine catalyzed by DNA fix enzyme AlkB (13 37 JHDM1 demethylates H3K36 by catalyzing the era of extremely reactive oxygen types to strike the methyl group in substrates (39). The oxidized item is certainly unpredictable and spontaneously produces one formaldehyde molecule which leads to removing one methyl group from H3K36 (39). To time more than 100 JmjC domain-containing proteins have been identified (1 7 Although LSD1 INO-1001 has been reported to demethylate H3K9 dimethylation when associated with the androgen receptor (24) it is still likely that one of these JmjC domain-containing proteins is responsible for the oxidative demethylation on H3K9 as proposed by Trewick et al. (38). Nickel compounds are highly carcinogenic but exhibit insignificant mutagenic activity (21). By using Chinese hamster V79-derived cell clones that possess a single copy of the (bacterial xanthine INO-1001 guanine phosphoribosyltransferase) transgene inserted either near the INO-1001 telomere of chromosome 1 (G12 cells) or into euchromatin on chromosome 6 (G10 cells) we were able to demonstrate that water-insoluble nickel compounds (NiS and Ni3S2) silenced the transgene via epigenetic mechanisms in G12 cells but not in G10 cells (21). It is helpful to know that the loss of endogenous (hypoxanthine guanine phosphoribosyltransferase) function in G12.