The effect of acute dichlorodiphenyltrichloroethane exposure on hypermethylation status and down-regulation of p53 and p16INK4a genes in rat liver.
Environ Toxicol. 2016 May ;31(5):584-92. Epub 2014 Nov 20. PMID: 25410620
The aim of the study was to investigate the early effect of acute dichlorodiphenyltrichloroethane (DDT) exposure on the methylation status of the promoter region of two tumor suppressor genes: p53 and p16(INK4a) (p16) in rat liver. We analyzed their transcript and protein expression profiles concurrently with the examination of transcriptional and protein expression levels of DNA (cytosine-5)-methyltransferase 1 (Dnmt1). Male Wistar rats were treated with a single dose of DDT (57 mg kg(-1) of body weight) and the methylation status of p53 and p16 genes was examined after 24 h using methylation-sensitive restriction analysis-MSRA. The obtained results indicate that DDT induced alternations in methylation of the promoter region in both p53 and p16 genes. In all the tested samples, the promoter CpG islands of p53 (-261, -179, and -450) were methylated within 100% as compared to control samples (0%). The methylation status of the p16 promoter (-11 and +77) was also altered due to exposure to DDT. Methylated cytosines were detectable in 75% of the tested DNA samples. The Real-time PCR and western blot analyses showed a decrease in mRNA and protein levels of p53, respectively, which was related to the increase in DNA synthesis. These relationships were also observed for mRNA and protein expressions of p16, although to a slighter extent. We also showed that hypermethylation in the promoter region of both tumor suppressor genes was consistent with an increased Dnmt1 mRNA level, and this relationship was further confirmed at the protein level of DNMT1. Concluding, our data suggests that epigenetically mediated changes in gene expression may play an important role in the mechanism of DDT toxicity, including carcinogenic action.