High levels of chromosome aberrations correlate with impaired in vitro radiation-induced apoptosis and DNA repair in human B-chronic lymphocytic leukaemia cells.
OBJECTIVE
To investigate the relationship between the susceptibility of B-chronic lymphoid leukaemia (B-CLL) cells to DNA damage-induced apoptosis, the kinetics of DNA strand-break rejoining, and chromosome damage after exposure to ionizing irradiation.


METHODS
Lymphocytes from B-CLL patients were gamma-irradiated in vitro with 0.2-5 Gy and stimulated by Staphylococcus aureus cowan I (SAC I) for estimation of chromosomal damage. Induction of apoptosis after irradiation was studied in 50 patients by two methods: morphological characterization of apoptotic cells after fluorescent staining (Hoechst), and specific quantification of mono- and oligonucleosomes in cytoplasmic cell fractions (ELISA assay). Morphological chromosome damage was scored in the first cell generation after irradiation (13 patients). In parallel, the kinetics of DNA single-strand break rejoining were investigated by the alkaline comet assay (12 patients).


RESULTS
Ionizing irradiation did not induce apoptosis in lymphocytes from a subset of B-CLL patients. The results suggest that B-CLL cells resistant to radiation-induced apoptosis could repair DNA strand-breaks more rapidly and showed a higher level of chromosome aberrations than radiation-sensitive B-CLL cells.


CONCLUSIONS
Each of three biological effects observed (apoptosis, kinetics of DNA single-strand-break repair, chromosomal damage) might be explained by different modifications occurring in irradiated B-CLL cells. Their convergence strongly suggests that resistance to apoptotic death initiation by DNA damage may be impeded by a rapid engaging of the DNA repair mechanisms. The higher level of chromosome aberrations observed in these cells suggests that the type of DNA repair system involved may generate inaccurate repair.
Laboratoire de Radiobiologie et Oncologie, CEA, DSV/DRR, 92265 Fontenay aux Roses, France.
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Blaise
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Alapetite
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Masdehors
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Merle-Beral
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Roulin
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Delic
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Sabatier
D017209:Apoptosis; D001402:B-Lymphocytes / Q000528:radiation effects; D002869:Chromosome Aberrations; D020552:Comet Assay; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007945:Leukemia, Lymphoid / Q000378:metabolism* / Q000532:radiotherapy*; D011839:Radiation, Ionizing; D013997:Time Factors
D004247:DNA