Figure 2. Pharmacologic inhibition of ATM rescues oxidative stress-induced senescence by suppressing ATM- and NEMO-mediated NF-κB activation. (A) Representative images of primary WT and Ercc1-/- MEFs were induced to undergo senescence by serial passaging at 20% oxygen. At passage 5, MEFs were grown in the presence or absence of KU-55933 (10 μM) for 72 hrs. Senescence was determined by SA-βgal staining. Images were obtained at the magnification of 10x. (B) Quantitation of the percent SA-βgal positive cells. Graph represents the mean +/- s.e.m. of three independent experiments. Student’s t-test, ***p <0.001, ****p <0.0001. (C) Passage 5 Ercc1-/- MEFs treated with vehicle or KU-55933 (10 μM) for 72 hours were collected and levels of p21 and p16INK4a were determined by western blotting. (D) Passage 5 Ercc1-/- MEFs were treated with KU-55933 (10 μM) for 72 hours and whole cell lysate (CL) and nuclear extracts (NE) were analyzed by immunoblotting for expression of proteins involved in the DNA damage response. (E) Whole cell lysate (CL) and nuclear extract (NE) were extracted from Ercc1-/- MEFs treated with 10 μM of KU-55933 for analysis of nuclear NEMO and p65. GAPDH was used as a loading control of total proteins and LaminA/C as a loading control of nuclear protein. (F) Passage 5 WT and Ercc1-/- MEFs transfected with a NF-κB-luciferase reporter construct were cultured in the presence or absence of KU-55933 (10 μM) and were collected for luciferase assays after 72 hours. (G) qRT-PCR analysis of mRNA expression in passage 5 WT and Ercc1-/- MEFs treated with or without of KU-55933 (10 μM) for 72 hrs. P values were determined using a Student’s t-test. *p<0.05, **p<0.01, ***p <0.001.