title: Thymoquinone induces apoptosis through activation of caspase-8 and mitochondrial events in p53-null myeloblastic leukemia HL-60 cells.
abstract: Thymoquinone (TQ), the major biologically active component isolated from a traditional medicinal herb, Nigella sativa Linn, is a potential chemopreventive and chemotherapeutic compound. Despite the promising antineoplastic activities of TQ, the molecular mechanism of its pharmacologic effects is poorly understood. Here, we report that TQ exhibits antiproliferative effect, induces apoptosis, disrupts mitochondrial membrane potential and triggers the activation of caspases 8, 9 and 3 in myeloblastic leukemia HL-60 cells. The apoptosis induced by TQ was inhibited by a general caspase inhibitor, z-VAD-FMK; a caspase-3-specific inhibitor, z-DEVD-FMK; as well as a caspase-8-specific inhibitor, z-IETD-FMK. Moreover, the caspase-8 inhibitor blocked the TQ-induced activation of caspase-3, PARP cleavage and the release of cytochrome c from mitochondria into the cytoplasm. In addition, TQ treatment of HL-60 cells caused a marked increase in Bax/Bcl2 ratios due to upregulation of Bax and downregulation of Bcl2 proteins. These results indicate that TQ-induced apoptosis is associated with the activation of caspases 8, 9 and 3, with caspase-8 acting as an upstream activator. Activated caspase-8 initiates the release of cytochrome c during TQ-induced apoptosis. Overall, these results offer a potential mechanism for TQ-induced apoptosis in p53-null HL-60 cancer cells.
authors.affiliation: Department of Radiology, Ohio State University, Columbus, OH 43210, USA. wani.2@osu.edu
authors.forename: Mohamed A
authors.initials: MA
authors.lastname: El-Mahdy
authors.forename: Qianzheng
authors.initials: Q
authors.lastname: Zhu
authors.forename: Qi-En
authors.initials: QE
authors.lastname: Wang
authors.forename: Gulzar
authors.initials: G
authors.lastname: Wani
authors.forename: Altaf A
authors.initials: AA
authors.lastname: Wani
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D016227:Benzoquinones / Q000494:pharmacology*; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018922:HL-60 Cells; D006801:Humans; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency*
chemical_list: D016227:Benzoquinones; D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D016159:Tumor Suppressor Protein p53; C505530:CASP8 protein, human; D053181:Caspase 8; D020169:Caspases; C003466:thymoquinone