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Epigenetic Repogramming by an Environmental Carcinogen Through Chromatin Domain Disruption [RNA-Seq]

ABSTRACT: Alterations in chromatin modifications, including DNA methylation and histone modification patterns, have been characterized under exposure of several environmental pollutants, including nickel. As with other carcinogenic metals, the mutagenic potential of nickel compounds is low and is not well correlated with its carcinogenic effects. Nickel exposure, however, is associated with alterations in chromatin modifications and related transcriptional programs, suggesting an alternative pathway whereby nickel exposure can lead to disease. To investigate the extent to which nickel exposure disrupts chromatin patterns, we profiled several histone modifications, including H3K4me3, H3K9ac, H3K27me3 and H3K9me2 as well as the insulator binding protein CTCF and the transcriptomes of control BEAS-2B cells and cells treated with nickel for 72 hours. Our results show significant alterations of the repressive histone modification H3K9me2 in nickel-exposed cells with spreading of H3K9me2 into new domains associated with gene silencing. We furthermore show that local regions of active chromatin can protect genes from nickel-induced H3K9me2 spreading. Interestingly, we show that nickel exposure selectively disrupts weaker CTCF sites, leading to spreading of H3K9me2 at these regions. These results have major implications in the understanding of how environmental carcinogens can affect chromatin dynamics and the consequences of chromatin domain disruption in disease progression.

ORGANISM(S): Homo sapiens

PROVIDER: GSE56052 | GEO | 2014/09/26

SECONDARY ACCESSION(S): PRJNA242307

REPOSITORIES: GEO

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Project description:Histone modifications associated with gene silencing typically mark large contiguous regions of the genome forming repressive chromatin domain structures. Since the repressive domains exist in close proximity to active regions, maintenance of domain structure is critically important. This study shows that nickel, a nonmutagenic carcinogen, can disrupt histone H3 lysine 9 dimethylation (H3K9me2) domain structures genome-wide, resulting in spreading of H3K9me2 marks into the active regions, which is associated with gene silencing. Our results suggest inhibition of DNA binding of the insulator protein CCCTC-binding factor (CTCF) at the H3K9me2 domain boundaries as a potential reason for H3K9me2 domain disruption. These findings have major implications in understanding chromatin dynamics and the consequences of chromatin domain disruption during pathogenesis. Investigations into the genomic landscape of histone modifications in heterochromatic regions have revealed histone H3 lysine 9 dimethylation (H3K9me2) to be important for differentiation and maintaining cell identity. H3K9me2 is associated with gene silencing and is organized into large repressive domains that exist in close proximity to active genes, indicating the importance of maintenance of proper domain structure. Here we show that nickel, a nonmutagenic environmental carcinogen, disrupted H3K9me2 domains, resulting in the spreading of H3K9me2 into active regions, which was associated with gene silencing. We found weak CCCTC-binding factor (CTCF)-binding sites and reduced CTCF binding at the Ni-disrupted H3K9me2 domain boundaries, suggesting a loss of CTCF-mediated insulation function as a potential reason for domain disruption and spreading. We furthermore show that euchromatin islands, local regions of active chromatin within large H3K9me2 domains, can protect genes from H3K9me2-spreadingM-bM-^@M-^Sassociated gene silencing. These results have major implications in understanding H3K9me2 dynamics and the consequences of chromatin domain disruption during pathogenesis.

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Epigenetic Repogramming by an Environmental Carcinogen Through Chromatin Domain Disruption [RNA-Seq]

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