title: Programmed cell death in Blastocystis hominis occurs independently of caspase and mitochondrial pathways.
abstract: We demonstrated previously that a cytotoxic monoclonal antibody (MAb) 1D5 elicits a programmed cell death (PCD) response in Blastocystis hominis and showed that caspase-3-like protease influences but is not essential for PCD in MAb 1D5-treated B. hominis. We also showed that mitochondrial dysregulation played a role in cell death. In the current study, we further analyzed the signaling pathways involved in PCD mediated by MAb 1D5. B. hominis cells were treated with MAb 1D5 or control MAb 5, either with or without pretreatment with a pan-caspase inhibitor, zVAD.fmk, and/or a mitochondrial transition pore blocker, cyclosporine A (CA). Flow cytometric examination of cell size, mitochondrial membrane potential (delta psi(m)), caspase activation and in situ DNA fragmentation showed that zVAD.fmk and CA, used independently or in combination, failed to inhibit MAb 1D5-mediated PCD. Interestingly, cell exposure to either inhibitor resulted in partial inhibition of DNA fragmentation while combined exposure of cells to inhibitors abolished DNA fragmentation completely. This study sheds new light on the conserved nature of PCD pathways in parasitic protozoa and is also the first report describing caspase- and mitochondria-independent cell death pathways in a protozoan parasite.
authors.affiliation: Laboratory of Molecular and Cellular Parasitology, Department of Microbiology, Faculty of Medicine, National University of Singapore, 5 Science Drive 2, Singapore 117597, Singapore.
authors.forename: A M A
authors.initials: AM
authors.lastname: Nasirudeen
authors.forename: Kevin S W
authors.initials: KS
authors.lastname: Tan
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal; D017209:Apoptosis / Q000276:immunology / Q000502:physiology*; D016845:Blastocystis hominis / Q000166:cytology / Q000502:physiology*; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology*; D016572:Cyclosporine / Q000494:pharmacology; D053938:DNA Fragmentation / Q000187:drug effects; D004789:Enzyme Activation; D005434:Flow Cytometry; D020287:In Situ Nick-End Labeling; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000911:Antibodies, Monoclonal; D061945:Caspase Inhibitors; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D016572:Cyclosporine; D020169:Caspases