title: Reactive oxygen species activate a Ca2+-dependent cell death pathway in the unicellular organism Trypanosoma brucei brucei.
abstract: Here we examine a cell death process induced by reactive oxygen species (ROS) in the haemoflagellate Trypanosoma brucei brucei. Ca2+ distribution in cellular compartments was measured with stable transformants expressing aequorin targeted to the cytosol, nucleus or mitochondrion. Within 1.5 h of ROS production, mitochondrial Ca2+ transport was impaired and the Ca2+ barrier between the nuclear envelope and cytosol was disrupted. Consequently the mitochondrion did not accumulate Ca2+ efficiently in response to an extracellular stimulus, and excess Ca2+ accumulated in the nucleus. The terminal transferase deoxytidyl uridine end labelling assay revealed that, 5 h after treatment with ROS, extensive fragmentation of nuclear DNA occurred in over 90% of the cells. Permeability changes in the plasma membrane did not occur until an additional 2 h had elapsed. The intracellular Ca2+ buffer, EGTA acetoxymethyl ester, prevented DNA fragmentation and prolonged the onset of changes in cell permeability. Despite some similarities to apoptosis, nuclease activation was not a consequence of caspase 3, caspase 1, calpain, serine protease, cysteine protease or proteasome activity. Moreover, trypanosomes expressing mouse Bcl-2 were not protected from ROS even though protection from mitochondrial dysfunction and ROS have been reported for mammalian cells. Overall, these results demonstrate that Ca2+ pathways can induce pathology in trypanosomes, although the specific proteins involved might be distinct from those in metazoans.
authors.affiliation: Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275, USA.
authors.forename: E L
authors.initials: EL
authors.lastname: Ridgley
authors.forename: Z H
authors.initials: ZH
authors.lastname: Xiong
authors.forename: L
authors.initials: L
authors.lastname: Ruben
mesh_terms: D000331:Aequorin; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D000001:Calcimycin / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002465:Cell Movement / Q000187:drug effects; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D053938:DNA Fragmentation / Q000187:drug effects; D004533:Egtazic Acid / Q000494:pharmacology; D019254:Genes, bcl-2 / Q000235:genetics / Q000502:physiology; D006706:Homeostasis / Q000187:drug effects; D008555:Melitten / Q000494:pharmacology; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D019820:Xanthine / Q000494:pharmacology; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D011480:Protease Inhibitors; D017382:Reactive Oxygen Species; D019820:Xanthine; D008555:Melitten; D000001:Calcimycin; D000331:Aequorin; D004533:Egtazic Acid; C033170:4-bromo-A-23187; D014969:Xanthine Oxidase; D012697:Serine Endopeptidases; D003546:Cysteine Endopeptidases; D002118:Calcium