title: Mitochondrial complex II dysfunction can contribute significantly to genomic instability after exposure to ionizing radiation.
abstract: Ionizing radiation induces chronic metabolic oxidative stress and a mutator phenotype in hamster fibroblasts that is mediated by H(2)O(2), but the intracellular source of H(2)O(2) 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 II activity (twofold; LS-12). Using Western blot analysis and Blue Native gel electrophoresis, a significant increase in complex II subunit B protein levels was observed in LS-12 cells. Furthermore, immunoprecipitation assays revealed evidence of abnormal complex II assembly in LS-12 cells. Treatment of LS-12 cells with an inhibitor of ETC complex II (thenoyltrifluoroacetone) resulted in significant decreases in the steady-state levels of H(2)O(2) 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 H(2)O(2) that contributed to increased mutation frequency and gene amplification. These results support the hypothesis that mitochondrial dysfunction originating from complex II can contribute to radiation-induced genomic instability by increasing steady-state levels of reactive oxygen species.
authors.affiliation: Free Radical and Radiation Biology Program, Department of Radiation Oncology, Holden Comprehensive Cancer Center, The University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: Disha
authors.initials: D
authors.lastname: Dayal
authors.forename: Sean M
authors.initials: SM
authors.lastname: Martin
authors.forename: Kjerstin M
authors.initials: KM
authors.lastname: Owens
authors.forename: Nukhet
authors.initials: N
authors.lastname: Aykin-Burns
authors.forename: Yueming
authors.initials: Y
authors.lastname: Zhu
authors.forename: Amutha
authors.initials: A
authors.lastname: Boominathan
authors.forename: Debkumar
authors.initials: D
authors.lastname: Pain
authors.forename: Charles L
authors.initials: CL
authors.lastname: Limoli
authors.forename: Prabhat C
authors.initials: PC
authors.lastname: Goswami
authors.forename: Frederick E
authors.initials: FE
authors.lastname: Domann
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Spitz
mesh_terms: D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D042963:Electron Transport Complex II / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D042822:Genomic Instability; D008928:Mitochondria / Q000201:enzymology*; D011839:Radiation, Ionizing
chemical_list: D042963:Electron Transport Complex II