Biphasic reduction of histone H3 phosphorylation in response to N-nitroso compounds induced DNA damage.

BACKGROUND

N-nitroso compounds (NOC) can cause cancers in a wide variety of animal species, and many of them are also potential human carcinogens. However, their underlying genotoxic mechanisms occurred within the context of chromatin, such as aberrant histone modifications, remained elusive.

METHODS

We investigated the dynamic landscapes of histone modifications after N-nitroso compound N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitroso-urea (MNU) exposure. Among the altered histone modifications, we also investigated the control mechanisms of histone H3 phosphorylation changes and its possible implications on transcriptional repression.

RESULTS

Significantly, we find a specific biphasic reduction of histone H3 phosphorylation at serine 10 (H3S10ph) and serine 28 (H3S28ph), and a rapid decrease of histone H4 acetylation upon MNNG and MNU exposure. Further investigations reveal that the first hypophosphorylation of H3 occurs in a poly(ADP-ribosyl)ation enzyme PARP-1 (Poly(ADP-Ribose) Polymerase 1) dependent manner, whereas the second decline of H3 phosphorylation is at least partially under the control of histone kinase VRK1 (vaccinia-related kinase 1) and dependent on the tumor suppressor protein p53. In addition, DNA damage induced down-regulation of H3S10/S28 phosphorylation also functions in transcriptional repression of genes, such as cell-cycle regulators.

CONCLUSIONS

Alkylating damage induced by NOC elicits a biphasic reduction of histone H3 phosphorylation with distinct control mechanisms, which is contributing to DNA damage responses such as the repair-facilitated transcriptional repression.

GENERAL SIGNIFICANCE

Identification of the dynamic changes and underlying mechanisms of histone modifications upon NOC exposure would be of great help in understanding the epigenetic regulations of NOC induced DNA damage responses.