Fig. 3. Cell-type-specific modulation of DNA-PKcs phosphorylation at T2609 and S2056 following γ-ray irradiation by cAMP signaling. (A, B, C) PGE2 effects upon the phosphorylation of DNA-PKcs on T2609 and ATM on S1981 following γ-ray irradiation in SK-MEL-28 cells (A), HeLa cells (B), and A549 cells (C). The cells were treated with PGE2 with/without pretreatment with okadaic acid (100 nM, 30 minutes). The treated cells were exposed to γ-rays and collected after 1 hour for analysis by western blotting. The empty bars present the phosphorylation of DNA-PKcs at T2609, and the filled bars present the phosphorylation at ATM on S1981. (D) PGE2 effects upon the phosphorylation of DNA-PKcs at S2056 following exposure to γ-rays. (E) Bar graph obtained by densitometric analysis of images in (D). The cells were irradiated with γ-rays after pretreatment with PGE2, and the irradiated cells were collected for analysis by western blotting. The empty bars present SK-MEL-28 cells, the filled bars present HeLa cells, and the slant bars present A549 cells. The means ± standard error calculated from the three independent experiments were presented as columns. An asterisk (*) denotes statistically significant differences compared with the irradiated control, and double asterisk (**) denotes differences indicating statistical significance compared with the PGE2- stimulated cells (P ≤ 0.05, Mann-Whitney U test).