Arsenite-induced histone H3 modification and its effects on EGR1 and FOS expression in HeLa cells.

It is evident that trivalent arsenicals do not have mutagenicity, but they are human carcinogens. Recently, epigenetic modification has been considered as one of the important causes of arsenical carcinogenicity. Here we examined global histone H3 modification by trivalent inorganic arsenite (iAs(III)) and its contribution to gene expression in HeLa cells. iAs(III) induced histone H3K9 dimethylation (H3K9me2) and trimethylation (H3K9me3), histone H3S10 phosphorylation (H3S10p), histone H3T11 phosphorylation (H3T11p) and histone H3K9S10 trimethyl-phosphorylation (H3K9me3S10p). Among these modifications, H3S10p, H3T11p and H3K9me3S10p were observed as a punctate signal in interphase cells, which seems to associate with remodeling of the chromatin structure at the specific locus. A chromatin immunoprecipitation assay was performed to examine histone H3 modifications around the FOS, EGR1 and IL8 promoters, as previous studies revealed some relation between histone H3 modification and induction of these genes. iAs(III) increased H3S10p and H3K9me3S10p in the FOS promoter around the SRE/ELK1 binding site (-400 to -200) and CRE-binding site (-50). In contrast, histone H3 around the EGR1 promoter of SRE/CRE-binding site (-200 to -50) was modified to H3S10p and H3K9me3S10p by iAs(III). Reporter gene assays with deletion mutants of the FOS and EGR1 promoters revealed that the around SRE/ELK1 site is important for iAs(III)-mediated FOS induction, and SRE/CRE site for EGR1 induction. Collectively, these results demonstrate that iAs(III) induces histone H3 modifications around the transcription factor binding sites of the FOS and EGR1 promoter, and these modifications seem to be important in transcriptional activation of these genes. Trivalent inorganic arsenite induced modification of three adjacent amino acids, Lys9, Ser10 and Thr11 of histone H3. Among these modifications, histone H3S10 phosphorylation and histone H3K9S10 trimethyl-phosphorylation were observed as a punctate signal in interphase cells, and these modifications were increased around the transcription factor binding sites of the FOS and EGR1 promoter. Histone H3 modifications seem to induce chromatin relaxation and then activate the transcription of FOS and EGR1 by trivalent inorganic arsenite.