Methylation of PARP-1 promoter involved in the regulation of nano-SiO2-induced decrease of PARP-1 mRNA expression

Abstract

Nano silicon dioxide (nano-SiO2) is becoming more and more widely applied in the fields of industry. The potential toxic effects of nano-SiO2 and its hazard to human health are drawing more attention. The mRNA expression of poly(ADP-ribose) polymerases-1(PARP-1), a pivotal repair gene, has been decreased by nano-SiO2 exposure. However, the effect of epigenetic modification on nano-SiO2-induced low PARP-1 expression has not been reported. In this study, HaCaT cells with or without DNA methyltransferase 1(DNMT1) knock down were incubated with nano-SiO2 and then further treated with DNMT inhibitor, 5-aza-2-deoxycytidine (DAC), which is a kind of key epigenetic modification reagents. Real-time Q-PCR and western blotting were used to examine the mRNA and protein expression of PARP-1. For promoter methylation status of PARP-1, methylation-specific PCR (MSP) and Bisulfite sequencing assay were performed. Results showed a dramatic decrease of PARP-1 expression on mRNA and protein level and a simultaneously obvious increase in the level of PARP-1 methylation in nano-SiO2-treated cells compared to the control group. Further, the expression and promoter methylation of PARP-1 in HaCaT cells were restored following DNMT1 knock down, suggesting that the effects of PARP-1 promoter hypermethylation are mediated at least in part by DNMT1. Taken together, methylation of PARP-1 promoter might be involved in the regulation of nano-SiO2-induced decrease of PARP-1 expression.