title: Ionizing radiation induces mitochondrial reactive oxygen species production accompanied by upregulation of mitochondrial electron transport chain function and mitochondrial content under control of the cell cycle checkpoint.
abstract: Whereas ionizing radiation (Ir) instantaneously causes the formation of water radiolysis products that contain some reactive oxygen species (ROS), ROS are also suggested to be released from biological sources in irradiated cells. It is now becoming clear that these ROS generated secondarily after Ir have a variety of biological roles. Although mitochondria are assumed to be responsible for this Ir-induced ROS production, it remains to be elucidated how Ir triggers it. Therefore, we conducted this study to decipher the mechanism of Ir-induced mitochondrial ROS production. In human lung carcinoma A549 cells, Ir (10 Gy of X-rays) induced a time-dependent increase in the mitochondrial ROS level. Ir also increased mitochondrial membrane potential, mitochondrial respiration, and mitochondrial ATP production, suggesting upregulation of the mitochondrial electron transport chain (ETC) function after Ir. Although we found that Ir slightly enhanced mitochondrial ETC complex II activity, the complex II inhibitor 3-nitropropionic acid failed to reduce Ir-induced mitochondrial ROS production. Meanwhile, we observed that the mitochondrial mass and mitochondrial DNA level were upregulated after Ir, indicating that Ir increased the mitochondrial content of the cell. Because irradiated cells are known to undergo cell cycle arrest under control of the checkpoint mechanisms, we examined the relationships between cell cycle and mitochondrial content and cellular oxidative stress level. We found that the cells in the G2/M phase had a higher mitochondrial content and cellular oxidative stress level than cells in the G1 or S phase, regardless of whether the cells were irradiated. We also found that Ir-induced accumulation of the cells in the G2/M phase led to an increase in cells with a high mitochondrial content and cellular oxidative stress level. This suggested that Ir upregulated mitochondrial ETC function and mitochondrial content, resulting in mitochondrial ROS production, and that Ir-induced G2/M arrest contributed to the increase in the mitochondrial ROS level by accumulating cells in the G2/M phase.
authors.affiliation: Laboratory of Radiation Biology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Yamamori
authors.forename: Hironobu
authors.initials: H
authors.lastname: Yasui
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamazumi
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Wada
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Nakamura
authors.forename: Hideo
authors.initials: H
authors.lastname: Nakamura
authors.forename: Osamu
authors.initials: O
authors.lastname: Inanami
mesh_terms: D000255:Adenosine Triphosphate / Q000819:agonists / Q000096:biosynthesis; D017209:Apoptosis; D045744:Cell Line, Tumor; D004272:DNA, Mitochondrial / Q000819:agonists / Q000187:drug effects / Q000528:radiation effects; D004579:Electron Transport; D059565:G2 Phase Cell Cycle Checkpoints; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000528:radiation effects*; D008928:Mitochondria / Q000187:drug effects / Q000528:radiation effects*; D009574:Nitro Compounds / Q000494:pharmacology; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation; D018384:Oxidative Stress / Q000187:drug effects / Q000528:radiation effects; D011422:Propionates / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000819:agonists* / Q000528:radiation effects; D013997:Time Factors; D015854:Up-Regulation
chemical_list: D004272:DNA, Mitochondrial; D009574:Nitro Compounds; D011422:Propionates; D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate; C015392:3-nitropropionic acid