Oxidative stress alters global histone modification and DNA methylation

The JmjC-domain-containing histone demethylases (JHDMs) can remove histone lysine-methylation and thereby regulate gene expression. The JmjC-domain uses iron Fe (II) and α-ketoglutarate (αKG) as cofactors in an oxidative demethylation reaction via hydroxymethyl-lysine. We hypothesize that reactive oxygen species will oxidize Fe (II) to Fe (III), thereby attenuating the activity of JmjC-domain-containing histone demethylases. To minimize secondary responses from cells, extremely short periods of oxidative stress (3 hours) were used to investigate this question. Cells that were exposed to hydrogen peroxide (H(2)O(2)) for 3 hours, exhibited increases in several histone methylation marks including H3K4me3 and decreases of histone acetylation marks including H3K9ac and H4K8ac; pre-incubation with ascorbate attenuated these changes. The oxidative stress level was measured by generation of 2′, 7′-dichlorofluorescein (DCF), GSH/GSSG ratio and protein carbonyl content. A cell free system indicated H(2)O(2) inhibited histone demethylase activity where increased Fe (II) rescued this inhibition. TET protein also showed a decreased activity under oxidative stress. Cells exposed to a low dose and long term (3 weeks) oxidative stress also showed increased global levels of H3K4me3 and H3K27me3. However, these global methylation changes did not persist after washout. The cells exposed to short term oxidative stress also appeared to have higher activity of class I/II histone deacetylase (HDAC) but not class III HDAC. In conclusion, we have found that oxidative stress transiently alters epigenetic program process through modulating the activity of enzymes responsible for demethylation and deacetylation of histones.