title: Apaf-1 and caspase-9 deficiency prevents apoptosis in a Bax-controlled pathway and promotes clonogenic survival during paclitaxel treatment.
abstract: Taxane derivatives such as paclitaxel elicit their antitumor effects at least in part by induction of apoptosis, but the underlying mechanisms are incompletely understood. Here, we used different cellular models with deficiencies in key regulators of apoptosis to elucidate the mechanism of paclitaxel-induced cell death. Apoptosis by paclitaxel was reported to depend on the activation of the initiator caspase-10; however, we clearly demonstrate that paclitaxel kills murine embryonic fibroblasts (MEFs) devoid of caspase-10 as well as human tumor cell lines deficient in caspase-10, caspase-8, or Fas-associating protein with death domain. In contrast, the lack of Apaf-1 or caspase-9, key regulators of the mitochondrial pathway, not only entirely protected against paclitaxel-induced apoptosis but could even confer clonogenic survival, depending on the cell type and drug concentration. Thus, paclitaxel triggers apoptosis not through caspase-10, but via caspase-9 activation at the apoptosome. This conclusion is supported by the fact that Bcl-2-overexpressing cells and Bax/Bak doubly-deficient MEFs were entirely resistant to paclitaxel-induced apoptosis. Interestingly, also the single knockout of Bim or Bax, but not that of Bak or Bid, conferred partial resistance, suggesting a particular role of these mediators in the cell-death pathway activated by paclitaxel.
authors.affiliation: Institute of Molecular Medicine, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors.forename: Katja
authors.initials: K
authors.lastname: Janssen
authors.forename: Stephan
authors.initials: S
authors.lastname: Pohlmann
authors.forename: Reiner U
authors.initials: RU
authors.lastname: Jänicke
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulze-Osthoff
authors.forename: Ute
authors.initials: U
authors.lastname: Fischer
mesh_terms: D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics*; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000502:physiology; D053477:Apoptotic Protease-Activating Factor 1 / Q000235:genetics*; D000072224:Bcl-2-Like Protein 11; D053455:Caspase 10 / Q000235:genetics / Q000502:physiology; D053453:Caspase 9 / Q000235:genetics*; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D002999:Clone Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D019169:Jurkat Cells; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D017239:Paclitaxel / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D051028:bcl-2-Associated X Protein / Q000502:physiology*
chemical_list: D000972:Antineoplastic Agents, Phytogenic; C506593:Apaf1 protein, mouse; D051017:Apoptosis Regulatory Proteins; D053477:Apoptotic Protease-Activating Factor 1; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D008565:Membrane Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D051028:bcl-2-Associated X Protein; D053455:Caspase 10; D053453:Caspase 9; D017239:Paclitaxel