| Summary: | 博士 === 國立臺灣大學 === 毒理學研究所 === 87 === ABSTRACT
B-Lapachone (B-Lap) has been found to inhibit DNA topoisomerases (Topo) by a mechanism distinct from that of other commonly known Topo inhibitors. In the present study, we demonstrated a pronounced elevation of H2O2 and O2- in human leukemia HL-60 cells treated with b-Lap. Treatment with other Topo poisons, such as camptothecin (CPT), VP-16, and GL331, did not have the same effect. On the other hand, antioxidant vitamin C (Vit. C) treatment effectively antagonized b-Lap-induced apoptosis. This suggested that a reactive oxygen species (ROS)-related pathway was involved in b-Lap-induced apoptosis program. We also found that c-Jun NH2-terminal kinase (JNK), but not p38-mitogen-activated protein kinase (MAPK) or extracellular signal-regulated kinase 1/2 (ERK1/2) was persistently activated in apoptosis induced by b-Lap. Overexpression of a dominant-negative mutant MAPK kinase kinase 1 (MEKK1-DN) or treatment with JNK-specific antisense oligonucleotide or Vit. C all prevented b-Lap-induced JNK activation and the subsequent apoptosis. Only the expression of MEKK1-DN, but not Vit. C treatment, blocked the JNK activity induced by CPT, VP-16 or GL331. These results confirm again that ROS acts as a mediator for JNK activation during b-Lap-induced apoptosis. Furthermore, we found that b-Lap can stimulate CPP32/Yama activity, which was, however, markedly inhibited by the MEKK1-DN expression or Vit. C treatment. Again, CPT-induced CPP32/Yama activation can be abolished by MEKK1-DN but not by Vit. C treatment. Taken together, these results indicate that b-Lap, but not other Topo inhibitors, triggers apoptosis signaling, i.e., JNK and subsequent CPP32/Yama activation are mediated by the generation of ROS.
|
|---|
