title: Induction of mitochondrial manganese superoxide dismutase confers resistance to apoptosis in acute myeloblastic leukaemia cells exposed to etoposide.
abstract: We investigated the possible roles of mitochondrial manganese superoxide dismutase (MnSOD) and bcl-2 in etoposide-induced cell death in acute myeloblastic leukaemia (AML) using two subclones of the OCI/AML-2 cell line, the etoposide-sensitive (ES) and the etoposide-resistant (ER), as models. Cell death after 24 h exposure to 10 micromol/l etoposide was about 60% and 70% in the ES subclone and about 20% and 25% in the ER subclone, when analysed by trypan blue and annexin V respectively. Cytochrome c efflux from mitochondria to cytosol was observed after 4 h of exposure in both subclones, whereas the activation of caspase-3 was not detectable until after 12 h of exposure in the ES subclone and 24 h of exposure in the ER subclone, using Western blotting. The decrease in mitochondrial membrane potential, when analysed by the JC-1 probe fluorocytometrically, also appeared to take place later in the ER than in the ES subclone. Both subclones showed evident basal expression of MnSOD and bcl-2 by Western blotting. Etoposide caused a potent induction of MnSOD, more than 400% at 12 h, in the ER but not in the ES subclone. No significant change in bcl-2 expression could be observed in either of the subclones during exposure to etoposide when analysed by Western blotting or flow cytometry. In conclusion, we suggest that MnSOD might have a special role in the protection of AML cells against etoposide-induced cell death. Although unable to influence the cytochrome c efflux to cytosol, MnSOD might prevent the disruption of mitochondrial membrane potential, which evidently leads to cell death by releasing various activators of apoptosis.
authors.affiliation: Department of Clinical Chemistry, University of Oulu, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Mäntymaa
authors.forename: T
authors.initials: T
authors.lastname: Siitonen
authors.forename: T
authors.initials: T
authors.lastname: Guttorm
authors.forename: M
authors.initials: M
authors.lastname: Säily
authors.forename: V
authors.initials: V
authors.lastname: Kinnula
authors.forename: E R
authors.initials: ER
authors.lastname: Savolainen
authors.forename: P
authors.initials: P
authors.lastname: Koistinen
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000627:therapeutic use*; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004790:Enzyme Induction / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000627:therapeutic use; D005047:Etoposide / Q000627:therapeutic use*; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy / Q000201:enzymology* / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D013482:Superoxide Dismutase / Q000096:biosynthesis* / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D005047:Etoposide; D013482:Superoxide Dismutase; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases