Mouse but not human embryonic stem cells are deficient in rejoining of ionizing radiation-induced DNA double-strand breaks.
Mouse embryonic stem (mES) cells will give rise to all of the cells of the adult mouse, but they failed to rejoin half of the DNA double-strand breaks (dsb) produced by high doses of ionizing radiation. A deficiency in DNA-PK(cs) appears to be responsible since mES cells expressed <10% of the level of mouse embryo fibroblasts (MEFs) although Ku70/80 protein levels were higher than MEFs. However, the low level of DNA-PK(cs) found in wild-type cells appeared sufficient to allow rejoining of dsb after doses <20Gy even in G1 phase cells. Inhibition of DNA-PK(cs) with wortmannin and NU7026 still sensitized mES cells to radiation confirming the importance of the residual DNA-PK(cs) at low doses. In contrast to wild-type cells, mES cells lacking H2AX, a histone protein involved in the DNA damage response, were radiosensitive but they rejoined double-strand breaks more rapidly. Consistent with more rapid dsb rejoining, H2AX(-/-) mES cells also expressed 6 times more DNA-PK(cs) than wild-type mES cells. Similar results were obtained for ATM(-/-) mES cells. Differentiation of mES cells led to an increase in DNA-PK(cs), an increase in dsb rejoining rate, and a decrease in Ku70/80. Unlike mouse ES, human ES cells were proficient in rejoining of dsb and expressed high levels of DNA-PK(cs). These results confirm the importance of homologous recombination in the accurate repair of double-strand breaks in mES cells, they help explain the chromosome abnormalities associated with deficiencies in H2AX and ATM, and they add to the growing list of differences in the way rodent and human cells deal with DNA damage.
Bañuelos
C A
CA
Medical Biophysics Department, British Columbia Cancer Research Centre, 675 W. 10th Avenue, Vancouver, BC, Canada.
Banáth
J P
JP
MacPhail
S H
SH
Zhao
J
J
Eaves
C A
CA
O'Connor
M D
MD
Lansdorp
P M
PM
Olive
P L
PL
D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism; D064007:Ataxia Telangiectasia Mutated Proteins; D002135:Calcium-Binding Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004260:DNA Repair; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000528:radiation effects*; D016193:G1 Phase; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011839:Radiation, Ionizing; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D034961:Antigens, Nuclear; D064007:Ataxia Telangiectasia Mutated Proteins; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D006657:Histones; D000072200:Ku Autoantigen; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins; C109198:CIB1 protein, human; C468783:H2AX protein, human; C576324:ATM protein, human; C576325:Atm protein, mouse; C497264:Prkdc protein, mouse; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; C475961:gamma-H2AX protein, mouse