Dose Dependence of Hypermethylation of Gene Promoters in Blood Leukocytes in Humans Occupationally Exposed to External γ-Radiation

Abstract—A study of promoter hypermethylation of cell cycle (RASSF1A, p16/INK4A, p14/ARF, p53, АТМ), xenobiotic detoxification (GSTP1), antioxidant defense (SOD3), and estrogen receptor (ESR1) genes in blood leukocytes of 88 nuclear industry workers from the Mayak facility (53–86 years old at sampling) exposed to prolonged external γ-radiation was carried out. Accumulated doses to red bone marrow (RBM) ranged from 0.2 to 2.95 Gy. The time between the end of work with radiation and blood sampling was on average 15.95 ± 1.22 years. Fifty unirradiated residents of Ozyorsk matched by age to the exposed group were enrolled as a control group. Promoter hypermethylation was analyzed using methylation-sensitive polymerase chain reaction (PCR) assay. The trend towards dependence of promoter hypermethylation of p14/ARF and RASSFA genes on age rather than radiation exposure (logistic regression: p = 0.072) confirms previous results. The frequency of individuals with promoter methylation of at least one of the following six genes: p16/INK4A, GSTP1, р53, АТМ,SOD3,ESR1, in irradiated group was significantly higher than in the control group (62.5 versus 34%, respectively, p = 0.001, OR = 3.24, 95% CI 1.56–6.69). A significantly elevated frequency of individuals with hypermethylated СpG islands in GSTP1 and SOD3 promoters was revealed among exposed subjects compared to the control group (p = 0.014 and p = 0.021, respectively). A statistically significant association between the cumulative dose and the number of methylated promoters was revealed (r = 0.304, р = 3.2 × 10^–4). Therefore, the dose-dependent hypermethylation of CpG islands in gene promoters that is revealed in blood leukocytes long term after external exposure to γ-radiation was found.