Mutation in the glucose-6-phosphate dehydrogenase gene leads to inactivation of Ku DNA end binding during oxidative stress.
Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the oxidative pentose phosphate cycle, regulates the NADPH/NADP(+) ratio in eukaryotic cells. G6PD deficiency is one of the most common mutations in humans and is known to cause health problems for hundreds of millions worldwide. Although it is known that decreased G6PD functionality can result in increased susceptibility to oxidative stress, the molecular targets of this stress are not known. Using a Chinese hamster ovary G6PD-null mutant, we previously demonstrated that exposure to a thiol-specific oxidant, hydroxyethyldisulfide, caused enhanced radiation sensitivity and an inability to repair DNA double strand breaks. We now demonstrate a molecular mechanism for these observations: the direct inhibition of DNA end binding activity of the Ku heterodimer, a DNA repair protein, by oxidation of its cysteine residues. Inhibition of Ku DNA end binding was found to be reversible by treatment of the nuclear extract with dithiothreitol, suggesting that the homeostatic regulation of reduced cysteine residues in Ku is a critical function of G6PD and the oxidative pentose cycle. In summary, we have discovered a new layer of DNA damage repair, that of the functional maintenance of repair proteins themselves. In view of the rapidly escalating number of roles ascribed to Ku, these results may have widespread ramifications.
Ayene
Iraimoudi S
IS
Department of Radiation Oncology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA. ayenei@mail.med.upenn.edu
Stamato
Thomas D
TD
Mauldin
Stanley K
SK
Biaglow
John E
JE
Tuttle
Steven W
SW
Jenkins
Susan F
SF
Koch
Cameron J
CJ
D000818:Animals; D034961:Antigens, Nuclear; D015153:Blotting, Western; D016466:CHO Cells; D002467:Cell Nucleus / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D003545:Cysteine / Q000737:chemistry; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D004265:DNA Helicases; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004220:Disulfides / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D000431:Ethanol / Q000031:analogs & derivatives* / Q000494:pharmacology; D005954:Glucosephosphate Dehydrogenase / Q000235:genetics*; D000072200:Ku Autoantigen; D008956:Models, Chemical; D009154:Mutation; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism*; D018384:Oxidative Stress; D011485:Protein Binding; D019163:Reducing Agents / Q000494:pharmacology; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013997:Time Factors; D014162:Transfection
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D004220:Disulfides; D009687:Nuclear Proteins; D019163:Reducing Agents; D013438:Sulfhydryl Compounds; D009243:NAD; D000431:Ethanol; C031319:2-hydroxyethyl disulfide; D009249:NADP; D004247:DNA; D005954:Glucosephosphate Dehydrogenase; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D003545:Cysteine; D004229:Dithiothreitol