Alterations of histone modifications by cobalt compounds

Area of Science:

• Epigenetics
• Molecular Biology
• Toxicology

Background:

• Histone modifications play a crucial role in regulating gene expression and maintaining epigenetic homeostasis.
• Cobalt compounds are known carcinogens, but their precise molecular mechanisms, particularly concerning epigenetic alterations, remain incompletely understood.

Purpose of the Study:

• To investigate the effects of cobalt chloride (CoCl2) on global histone modifications in human lung carcinoma (A549) and bronchial epithelial (Beas-2B) cells.
• To elucidate the underlying molecular mechanisms responsible for cobalt-induced changes in histone modifications.
• To explore the potential link between cobalt-induced epigenetic alterations and gene expression changes relevant to tumorigenesis.

Main Methods:

• Exposure of A549 and Beas-2B cells to varying concentrations of CoCl2.
• Global analysis of histone modifications including methylation (H3K4me3, H3K9me2, H3K9me3, H3K27me3, H3K36me3) and acetylation (AcH4), as well as histone ubiquitination (uH2A, uH2B).
• In vitro assays to assess the impact of cobalt ions on histone methyltransferase and demethylase (JMJD2A) activity.
• In vitro ubiquitination and deubiquitination assays.
• Gene expression profiling using microarray analysis.

Main Results:

• CoCl2 exposure significantly increased global levels of H3K4me3, H3K9me2, H3K9me3, H3K27me3, H3K36me3, uH2A, and uH2B, while decreasing AcH4 in both cell lines.
• Cobalt-induced increases in H3K4me3 and H3K27me3 were dependent on histone methylation processes, as indicated by the blocking effect of methionine-deficient medium.
• Cobalt ions enhanced H3K9me3 and H3K36me3 by inhibiting JMJD2A demethylase activity in vitro, likely through competition with iron for the enzyme's active site.
• Cobalt-induced histone H2A and H2B ubiquitination resulted from the inhibition of deubiquitinating enzyme activity.
• Microarray analysis revealed that CoCl2 exposure altered the expression of hundreds of genes involved in various cellular functions, including tumorigenesis.

Conclusions:

• This study provides the first evidence that cobalt ions disrupt cellular epigenetic homeostasis.
• Cobalt-induced alterations in histone modifications occur through multiple mechanisms, including modulation of methylation/demethylation and ubiquitination/deubiquitination pathways.
• The observed epigenetic changes and subsequent alterations in gene expression patterns may contribute to cobalt's role in carcinogenesis.