Mitochondrial Complex II Dysfunction Can Contribute Significantly to Genomic Instability after Exposure to Ionizing Radiation

Dayal, D., Martin, S. M., Owens, K. M., Aykin-Burns, N., Zhu, Y., Boominathan, A., Pain, D., Limoli, C. L., Goswami, P. C., Domann, F. E. and Spitz, D. R. Mitochondrial Complex 11 Dysfunction Can Contribute Significantly to Genomic Instability after Exposure to Ionizing Radiation. Radiat. Res. 172, 737745(2009). Ionizing radiation induces chronic metabolic oxidative stress and a mutator phenotype in hamster fibroblasts that is mediated by H2O2, but the intracellular source of H2O2 is not well defined. To determine the role of mitochondria in the radiation-induced mutator phenotype, end points of mitochondrial function were determined in unstable (CS-9 and LS-12) and stable (114) hamster fibroblast cell lines derived from GM10115 cells exposed to 10 Gy X rays. Cell lines isolated after irradiation demonstrated a 20-40% loss of mitochondrial membrane potential and an increase in mitochondrial content compared to the parental cell line GM10115. Surprisingly, no differences were observed in steady-state levels of ATP (P > 0.05). Unstable clones demonstrated increased oxygen consumption (two- to threefold; CS-9) and/or increased mitochondrial electron transport chain (ETC) complex H activity (twofold; LS-12). Using Western blot analysis and Blue Native gel electrophoresis, a significant increase in complex 11 subunit B protein levels was observed in LS-12 cells. Furthermore, immunoprecipitation assays revealed evidence of abnormal complex 11 assembly in LS-12 cells. Treatment of LS-12 cells with an inhibitor of ETC complex 11 (thenoyltrifluoroacetone) resulted in significant decreases in the steady-state levels of H2O2 and a 50% reduction in mutation frequency as well as a 16% reduction in CAD gene amplification frequency. These data show that radiation-induced genomic instability was accompanied by evidence of mitochondrial dysfunction leading to increased steady-state levels of H2O2 that contributed to increased mutation frequency and gene amplification. These results support the hypothesis that mitochondrial dysfunction originating from complex It can contribute to radiation-induced genomic instability by increasing steady-state levels of reactive oxygen species. (C) 2009 by Radiation Research Society