title: Bcl-2 inhibitors sensitize tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by uncoupling of mitochondrial respiration in human leukemic CEM cells.
abstract: Previous studies have shown that the lymphoblastic leukemia CEM cell line is resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis because of a low expression of caspase-8. Bcl-2 inhibitors, BH3I-2' and HA14-1, are small cell-permeable nonpeptide compounds, are able to induce apoptosis by mediating cytochrome c release, and also lead to dissipation of the mitochondrial membrane potential (DeltaPsim). This study aimed to use the Bcl-2 inhibitors to sensitize CEM cells to TRAIL-induced apoptosis by switching on the mitochondrial apoptotic pathway. We found that a low dose of BH3I-2' or HA14-1, which did not induce cytochrome c release, greatly sensitized CEM cells to TRAIL-induced apoptosis. In a similar manner to the classical uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), both BH3I-2' and HA14-1 induced a reduction in DeltaPsim, a generation of reactive oxygen species (ROS), an increased mitochondrial respiration, and a decreased ATP synthesis. This uncoupling function of the Bcl-2 inhibitors was responsible for the synergy with TRAIL-induced apoptosis. CCCP per se did not induce apoptosis but again sensitized CEM cells to TRAIL-induced apoptosis by uncoupling mitochondrial respiration. The uncoupling effect facilitated TRAIL-induced Bax conformational change and cytochrome c release from mitochondria. Inhibition of caspases failed to block TRAIL-mediated cell death when mitochondrial respiration was uncoupled. We observed that BH3I-2', HA14-1, or CCCP can overcome resistance to TRAIL-induced apoptosis in TRAIL-resistant cell lines, such as CEM, HL-60, and U937. Our results suggest that the uncoupling of mitochondrial respiration can sensitize leukemic cells to TRAIL-induced apoptosis. However, caspase activation per se does not represent an irreversible point of commitment to TRAIL-induced cell death when mitochondrial respiration is uncoupled.
authors.affiliation: Department of Haematology, Barts and The London Queen Mary's School of Medicine and Dentistry, London, United Kingdom.
authors.forename: Ji-Hui
authors.initials: JH
authors.lastname: Hao
authors.forename: Ming
authors.initials: M
authors.lastname: Yu
authors.forename: Feng-Ting
authors.initials: FT
authors.lastname: Liu
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Newland
authors.forename: Li
authors.initials: L
authors.lastname: Jia
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D001549:Benzamides / Q000494:pharmacology*; D001578:Benzopyrans / Q000494:pharmacology*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D004357:Drug Synergism; D018922:HL-60 Cells; D006801:Humans; D020014:K562 Cells; D015458:Leukemia, T-Cell / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects* / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology*; D010085:Oxidative Phosphorylation / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors*; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D014475:Uncoupling Agents / Q000494:pharmacology*; D051028:bcl-2-Associated X Protein
chemical_list: C474172:3-iodo-5-chloro-N-(2-chloro-5-((4-chlorophenyl)sulphonyl)phenyl)-2-hydroxybenzamide; D051017:Apoptosis Regulatory Proteins; C494826:BAX protein, human; D001549:Benzamides; D001578:Benzopyrans; D008562:Membrane Glycoproteins; D009570:Nitriles; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D014475:Uncoupling Agents; D051028:bcl-2-Associated X Protein; C456800:ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D045304:Cytochromes c