title: Hypoxia-induced cell death in human malignant glioma cells: energy deprivation promotes decoupling of mitochondrial cytochrome c release from caspase processing and necrotic cell death.
abstract: Hypoxia induces apoptosis in primary and transformed cells and in various tumor cell lines in vitro. In contrast, there is little apoptosis and predominant necrosis despite extensive hypoxia in human glioblastomas in vivo. We here characterize ultrastructural and biochemical features of cell death in LN-229, LN-18 and U87MG malignant glioma cells in a paradigm of hypoxia with partial glucose deprivation in vitro. Electron microscopic analysis of hypoxia-challenged glioma cells demonstrated early stages of apoptosis but predominant necrosis. ATP levels declined during hypoxia, but recovered with re-exposure to normoxic conditions unless hypoxia exceeded 8 h. Longer hypoxic exposure resulted in irreversible ATP depletion and delayed cell death. Hypoxia induced mitochondrial release of cytochrome c, but there was no cleavage of caspases 3, 7, 8 or 9, and no DNA fragmentation. Ectopic expression of BCL-XL conferred protection from hypoxia-induced cell death, whereas the overexpression of the antiapoptotic proteins X-linked-inhibitor-of-apoptosis-protein and cytokine response modifier-A had no effect. These findings suggest that glioma cells resist adverse effects of hypoxia until energy stores are depleted and then undergo necrosis rather than apoptosis because of energy deprivation.
authors.affiliation: Laboratory of Molecular Neuro-Oncology, Department of Neurology, University of Tübingen, School of Medicine, Tübingen, Germany. joachim.steinbach@uni-tuebingen.de
authors.forename: J P
authors.initials: JP
authors.lastname: Steinbach
authors.forename: H
authors.initials: H
authors.lastname: Wolburg
authors.forename: A
authors.initials: A
authors.lastname: Klumpp
authors.forename: H
authors.initials: H
authors.lastname: Probst
authors.forename: M
authors.initials: M
authors.lastname: Weller
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D020169:Caspases / Q000378:metabolism*; D016923:Cell Death; D015687:Cell Hypoxia / Q000187:drug effects / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D045304:Cytochromes c / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology*; D005910:Glioma / Q000378:metabolism* / Q000473:pathology / Q000648:ultrastructure; D005947:Glucose / Q000172:deficiency; D006801:Humans; D007155:Immunologic Factors / Q000378:metabolism; D008854:Microscopy, Electron; D008928:Mitochondria / Q000378:metabolism*; D009336:Necrosis; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D013217:Starvation / Q000378:metabolism; D014407:Tumor Cells, Cultured; D051636:X-Linked Inhibitor of Apoptosis Protein; D051020:bcl-X Protein
chemical_list: C494811:BCL2L1 protein, human; D007155:Immunologic Factors; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D051020:bcl-X Protein; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D020169:Caspases; D005947:Glucose