Cells with H3K79 hypomethylation show higher sensitivity to γ-irradiation. (A) Hypomethylated T-REx-293 cells show higher irradiation sensitivity. T-REx-293 cells expressing CALM-AF10 or hDOT1L knockdown siRNA were treated with different doses of γ-irradiation. After 7 days, the percentage of surviving cells was determined. The original T-REx-293 cell line stably transfected with empty vector was included for comparison. The H3K79 hypomethylation in T-REx-293 cells expressing the CALM-AF10 fusion protein or hDOT1L knockdown siRNA was confirmed by Western analysis (right panel). (B) Hypomethylated U937T cells show higher irradiation sensitivity. U937T cells expressing stably transfected AF10 or its deletion mutant were treated with different doses of γ-irradiation, and the number of surviving cells was determined by colony formation assay. (C) Irradiation survival test of MEF cells deficient in H3K79 methylation. Wild-type (WT) and Dot1L knockout (Dot1L KO) MEF cells were treated with different doses of γ-irradiation. The cell survival experiments were carried out 3 times in duplicate, and the percentage of cells not treated was set to 100%. The P values of survival percentage of normal methylation versus survival percentage of hypomethylation were lower than .01 at the radiation doses from 0.5 Gy to 3 Gy.