Fig. 4. Mediation of cell-type-specific effects of cAMP by PKA on the phosphorylation of DNA-PKcs at T2609. (A, B, C) Effects of PGE2, H-89 and 6-Phe-cAMP on T2609 phosphorylation resulting from exposure to γ-rays in SK-MEL-28 cells (A), HeLa cells (B), and A549 cells (C). (D) Confocal images of DNA-ligase IV recruited to DSBs following γ-ray irradiation in SK-MEL-28 cells, HeLa cells and A549 cells. (E, F, G) Effects of PGE2 and H-89 on DNA-ligase IV foci per cell, obtained from the images in D of SK-MEL-28 cells (E), HeLa cells (F) and A549 cells (G). The cells were incubated with PGE2 after pretreatment with 20 μM H-89 for 30 minutes or were treated with 50 μM 6-Phe-cAMP for 30 minutes. Next, the cells were exposed to γ-rays, and collected after 1 hour for analysis by western blotting or confocal microscopy. Green color represents XRCC4 and DNA-Ligase IV, and blue color represents DAPI stained nucleus (100-fold amplification). 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 a double asterisk (**) denotes statistically significant differences compared with the PGE2- stimulated cells (P ≤ 0.05, Mann-Whitney U test).