title: Triptolide induces Bcl-2 cleavage and mitochondria dependent apoptosis in p53-deficient HL-60 cells.
abstract: Triptolide, a bioactive component of the Chinese medicinal herb Tripterygium wilfordii Hook F., induces p53-mediated apoptosis in cancer cells. This study demonstrated that triptolide activated an alternative p53-independent apoptotic pathway in HL-60 cells. In the absence of an intact p53 and without changing Bax level, at nM range triptolide induced apoptosis with concomitant DNA fragmentation, S phase cell cycle arrest, mitochondrial cytochrome c release and the activation of caspases. Besides, both caspases 8 and 9 were activated and the simultaneous inhibition of both was required to completely block triptolide's apoptotic effect. Importantly, triptolide induced the appearance of a truncated 23kD Bcl-2 which was inhibited by the general caspase inhibitor Z-VAD-FMK. In the MCF-7 cells that possessed the wild type p53 but lacked caspases 3, triptolide induced cell death with an increase in p53 but Bcl-2 remained unaltered. On the other hand, transfected cells overexpressing the 28kD Bcl-2 became more resistant to triptolide and upon triptolide treatment accumulated in the G(1) instead of S phase. After 36h treatment, triptolide activated JNK pathways, at the same time inactivated the ERK and p38 pathways. However, SP600125, a specific JNK inhibitor, could not inhibit the triptolide-mediated cleavage of caspase 3, indicated that activation of JNK might not be related to the apoptotic effects of triptolide. Our data suggest that in the absence of an intact p53 and without altering Bax level triptolide induces apoptosis activates a positive amplification loop involving caspase-mediated Bcl-2 cleavage/activation, mitochondrial cytochrome c release and further activation of caspases.
authors.affiliation: Department of Biology and Chemistry, Bioactive Products Research Group, City University of Hong Kong, Kowloon, Hong Kong SAR., China.
authors.forename: Chi-Keung
authors.initials: CK
authors.lastname: Wan
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.forename: Hon-Yeung
authors.initials: HY
authors.lastname: Cheung
authors.forename: Mengsu
authors.initials: M
authors.lastname: Yang
authors.forename: Wang-Fun
authors.initials: WF
authors.lastname: Fong
mesh_terms: D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle; D045304:Cytochromes c / Q000378:metabolism; D004224:Diterpenes / Q000494:pharmacology*; D004789:Enzyme Activation; D004852:Epoxy Compounds; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018922:HL-60 Cells; D006801:Humans; D006868:Hydrolysis; D008928:Mitochondria / Q000201:enzymology; D010616:Phenanthrenes / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D004224:Diterpenes; D004852:Epoxy Compounds; D010616:Phenanthrenes; D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53; C001899:triptolide; D045304:Cytochromes c; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases