Epigenetic factors in cancer risk: effect of chemical carcinogens on global DNA methylation pattern in human TK6 cells

Abstract

In the current study, we assessed the global DNA methylation changes in human lymphoblastoid (TK6) cells in vitro in response to 5 direct and 10 indirect-acting genotoxic agents. TK6 cells were exposed to the selected agents for 24 h in the presence and/or absence of S9 metabolic mix. Liquid chromatography-mass spectrometry was used for quantitative profiling of 5-methyl-2'-deoxycytidine. The effect of exposure on 5-methyl-2'-deoxycytidine between control and exposed cultures was assessed by applying the marginal model with correlated residuals on % global DNA methylation data. We reported the induction of global DNA hypomethylation in TK6 cells in response to S9 metabolic mix, under the current experimental settings. Benzene, hydroquinone, styrene, carbon tetrachloride and trichloroethylene induced global DNA hypomethylation in TK6 cells. Furthermore, we showed that dose did not have an effect on global DNA methylation in TK6 cells. In conclusion we report changes in global DNA methylation as an early event in response to agents traditionally considered as genotoxic.

Figure 1. Global DNA methylation in TK6 cells cultured without S9 (control S9−) and with S9 (control S9+) is shown in the box plot.

Global DNA methylation is expressed as a percentage of 5-methylcytosine versus the total number of cytosines present in the genome. The box plot describes the median (line across the box), inter-quartile range and maximum and minimum values (whiskers). Outliers are shown as open circles outside the ends of whiskers.

Figure 2. Box plot representation of global DNA methylation in control TK6 cells and TK6 cells exposed with benzene, hydroquinone, styrene, carbon tetrachloride and trichloroethylene without S9 metabolic mix.

Global DNA methylation is expressed as percentage of 5-methylcytosine versus the total number of cytosines present in the genome. The box plot describes the median (line across the box), inter-quartile range and maximum and minimum values (whiskers). Outliers are shown as open circles outside the ends of whiskers.

Figure 3. Box plot representation of global DNA methylation in control TK6 cells and TK6 cells exposed with benzene, hydroquinone, styrene, carbon tetrachloride and trichloroethylene with S9 metabolic mix.

Global DNA methylation is expressed as percentage of 5-methylcytosine versus the total number of cytosines present in the genome. The box plot describes the median (line across the box), inter-quartile range and maximum and minimum values (whiskers). Outliers are shown as open circles outside the ends of whiskers.