Presentation DNA Methylation Alterations in Human Lymphocyte Induced by Gamma Radiation in Vitro

Younghyun, Lee  ,  Okayasu, Ryuichi

It is well-known that epigenetic changes, such as DNA methylation, microRNA expression and histone modification play an important role in the process of carcinogenesis. This study was performed to evaluate DNA methylation changes in normal human blood lymphocytes induced by gamma rays in vitro. Human blood lymphocytes were exposed to various doses of g-rays and cultured in RPMI 1640 medium for 72hr. Global DNA methylation levels were evaluated using colorimetric DNA methylation quantification kits, and the methylation levels of specific locus and repeat elements such as long interspersed element-1 (LINE-1) and Satellite 2 (Sat2) were examined using fluorescence-based real-time PCR. The expression of DNA methyltransferases (DNMTs) was observed using quantitative real-time PCR to investigate the mechanisms involved in radiation-induced DNA methylation alterations. Gamma-irradiation decreased global DNA methylation level in a dose dependent manner (control: 100%, 0.5 Gy: 95.97%, 1Gy: 82.91%, 2Gy: 74.21%). The decreased expression of DNMTs was observed in 2Gy irradiated lymphocyte (DNMT1: 21 ± 18 %, DNMT3a: 41 ± 27 %, DNMT3b: 50 ± 13 % of control value). The levels of Sat2 and LINE-1 methylation were increased slightly in gamma irradiated cells. The methylation level in Mut L homologue-1 (MLH1) promoter region was increased in 2Gy irradiated cells (control: 0.062 ± 0.02 %, 2Gy: 0.16 ± 0.03 % of fully methylated DNA), whereas the MLH1 mRNA expression was decreased (2Gy: 80 ± 5 % of control value). These results suggest that exposure to ionizing radiation can induce DNA methylation changes such as hypomethylation of global DNA, hypermethylation of repeat elements and MLH1, and these alterations may lead to genomic instability and carcinogenesis.
ICRR2015 (15th International Congress of Radiation Research)

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