DNA double-strand breaks trigger apoptosis in p53-deficient fibroblasts.
DNA double-strand breaks (DSBs) are induced by ionizing radiation (IR) and various radiomimetic agents directly, or indirectly as a consequence of DNA repair, recombination and replication of damaged DNA. They are ultimately involved in the generation of chromosomal aberrations and were reported to cause genomic instability, gene amplification and reproductive cell death. To address the question of whether DSBs act as a trigger of apoptosis, we induced DSBs by means of restriction enzyme electroporation and compared the effect with IR in mouse fibroblasts that differ in p53 status [wild-type (+/+) versus p53-deficient (-/-) cells]. We show that (i) electroporation of PVU:II is highly efficient in the induction of DSBs, (ii) electroporation of PVU:II increases the rate of apoptosis, but not of necrosis in p53-/- cells, (iii) treatment with gamma-rays induces both apoptosis and necrosis in p53-/- cells, (iv) the frequency of DSBs correlates with the yield of apoptosis and (v) both PVU:II and gamma-ray treatment reduce the level of anti-apoptotic Bcl-2 protein in p53-/- cells whereas the level of Bax remains unaltered. Cells expressing wild-type p53 were more resistant than p53-deficient cells as to the induction of apoptosis and did not show Bcl-2 decline upon treatment with PVU:II and gamma-rays. The data provide evidence that blunt-ended DSBs induced by restriction enzyme PVU:II act as a highly efficient trigger of apoptosis, but not of necrosis. This process is related to Bcl-2 decline and does not require p53.
Lips
J
J
Division of Applied Toxicology, Institute of Toxicology, University of Mainz, Obere Zahlbacher Str. 67, D-55131 Mainz, Germany.
Kaina
B
B
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D020552:Comet Assay; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004260:DNA Repair; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D018274:Electroporation; D005347:Fibroblasts / Q000378:metabolism*; D005720:Gamma Rays; D016158:Genes, p53 / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D009336:Necrosis; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011839:Radiation, Ionizing; D011995:Recombination, Genetic; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D051028:bcl-2-Associated X Protein
C494827:Bax protein, mouse; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D004247:DNA; C025630:CAGCTG-specific type II deoxyribonucleases; D015252:Deoxyribonucleases, Type II Site-Specific