Radon-induced demethylation of Cdk2 CpG island in the rat lung

Radon exposure has been linked to lung carcinogenesis in both human and animal studies. The identification of sequential changes in DNA methylation during tumour progression and the elucidation of their interplay with genetic changes will broaden our molecular understanding of this disease. Rats were exposed to 120 or 400 working level months (WLM) of radon, lung pathological changes were examined by haematoxylin and eosin staining, lung single cell suspension cell cycles were detected by flow cytometry, lung cell cycle regulated gene (Cdkn2a, P53, Cdk4/2, Mdm4/2 and Rb1 genes) expression was quantified by real-time PCR and methylation of CpG islands in the promoters of cell cycle-regulated genes were detected by bisulfite sequencing PCR. The alveolar walls of rat lungs after exposured to radon exhibited papillae and the lung bronchial epithelial cells stained positively for proliferating cell nuclear antigen. The bronchial epithelial cells displayed some hyperplasia after challenged by 400 WLM of radon. Moreover, G1 arrest decreased; Rb1, Mdm2/4, and Cdk2/4 expression decreased and Cdk2 was demethylated at the second and sixth CpG loci from base pairs 3092704 to 3092953 of chromosome 7. Cdk2 demethylation may be applicable as a biomarker of early lung damage that was induced by radon and other environmental carcinogens.