The catalytic subunit of DNA-dependent protein kinase is downstream of ATM and feeds forward oxidative stress in the selenium-induced senescence response

Selenium induces a senescence response in cells through induction of ataxia-telangiectasia mutated (ATM) and reactive oxygen species (ROS). Although a role of the catalytic subunit of DNA-dependent protein kinase (DNA-PK_cs) in DNA double-strand break repair is established, it is unclear how these proteins function in response to selenium-induced oxidative stress and senescence induction. In this study, we demonstrated that pretreating normal human diploid fibroblasts with DNA-PK kinase inhibitor NU 7026 suppressed selenium-induced senescence response. Selenium treatment induced phosphorylation of DNA-PK_cs on Thr-2647 and Ser-2056, the extent of which was decreased in the presence of ATM kinase inhibitor KU 55933 or the antioxidants N-acetylcysteine or 2,2,6,6-tetramethylpiperidine-1-oxyl. In contrast, the selenium-induced phosphorylation of ATM on Ser-1981 was not affected by NU 7026. Cells deficient in DNA-PK_cs or pretreated with NU 7026 or N-acetylcysteine were defective in selenite-induced ROS formation. Taken together, these results indicate a distinct role of DNA-PK_cs, in which this kinase can respond to and feed forward selenium-induced ROS formation and is placed downstream of ATM in the resultant senescence response.