Mitochondrial complex II dysfunction can contribute significantly to genomic instability after exposure to ionizing radiation.
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.
Dayal
Disha
D
Free Radical and Radiation Biology Program, Department of Radiation Oncology, Holden Comprehensive Cancer Center, The University of Iowa, Iowa City, Iowa 52242, USA.
Martin
Sean M
SM
Owens
Kjerstin M
KM
Aykin-Burns
Nukhet
N
Zhu
Yueming
Y
Boominathan
Amutha
A
Pain
Debkumar
D
Limoli
Charles L
CL
Goswami
Prabhat C
PC
Domann
Frederick E
FE
Spitz
Douglas R
DR
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
D042963:Electron Transport Complex II