bcl-2 protein inhibits etoposide-induced apoptosis through its effects on events subsequent to topoisomerase II-induced DNA strand breaks and their repair.
Previous studies have shown that bcl-2 overexpression can inhibit apoptosis induced by DNA-damaging agents widely used in cancer chemotherapy, including X-irradiation, alkylating agents (hydroperoxycyclophosphamide, etc.), and topoisomerase II inhibitors (etoposide, etc.). However, little is known about the mechanism by which bcl-2 overexpression inhibits apoptosis triggered by these agents. In this study, we examined whether bcl-2 overexpression could have effects on etoposide-induced DNA damage and its repair. For these experiments, we developed CH31 clones (mouse B-cells) stably transfected with human bcl-2 sense plasmids and compared these clones with a parental CH31 clone or CH31 clones with antisense plasmids. Overexpression of bcl-2 protein inhibited etoposide-induced apoptosis and cytotoxicity. However, there was no or little difference in the production and repair of DNA-protein cross-links, DNA single-strand breaks, and double-strand beaks among a parental CH31 clone and CH31 clones with human bcl-2 sense or antisense plasmids. These findings indicate that (a) apoptosis or cytotoxicity induced by etoposide can be separated into early events (formation of double-strand breaks, DNA single-strand breaks, and double-strand breaks) and later events (secondary DNA fragmentation or cell death) and (b) bcl-2 inhibits apoptosis and cytotoxicity induced by etoposide at some steps between these events.
Department of Pathology, Georgetown University School of Medicine, Washington, D.C. 20007.
S
S
Kamesaki
H
H
Kamesaki
T J
TJ
Jorgensen
A
A
Tanizawa
Y
Y
Pommier
J
J
Cossman
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D004249:DNA Damage; D004260:DNA Repair; D005047:Etoposide / Q000494:pharmacology*; D051379:Mice; D009243:NAD / Q000032:analysis; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2; D059005:Topoisomerase II Inhibitors; D014407:Tumor Cells, Cultured
D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D059005:Topoisomerase II Inhibitors; D009243:NAD; D005047:Etoposide