Type I and type II reactions in TRAIL-induced apoptosis -- results from dose-response studies.
Death receptor-induced apoptosis is paradigmatically mediated via the recruitment of FADD adapter molecule to the ligand/receptor complex and subsequent activation of caspase-8. However, several observations provided evidence that components of the mitochondrial apoptosis pathway are involved in death receptor-mediated apoptosis. In this regard, caspase-8-mediated activation of Bid induces the release of cytochrome c from the mitochondria, which, in turn, triggers the formation of the apoptosome protein complex, resulting in the activation of caspase-9. Whereas Bax or Bak were shown to be required for the proapoptotic effect of Bid, Bcl-2 was described to interfere with its action. Up to now, contradictory results regarding the role of Bcl-2 in TRAIL-induced apoptosis have been published. In order to study the influence of Bcl-2 on TRAIL-induced cell death more detailed, we utilized a tetracycline-regulated Bcl-2 expression system in Jurkat T cells. After having analysed the dose response for TRAIL-induced activation of caspase-8, -9, -3, breakdown of the mitochondrial membrane potential, and changes in the apoptotic morphology in cells expressing different Bcl-2 levels, we conclude that overexpression of Bcl-2 mediates a partial resistance towards lower doses of TRAIL that can be overcome when higher doses of TRAIL are applied. Thus, the requirement of the mitochondrial pathway for death receptor-induced apoptosis in type II cells should be reconsidered, since the protective effect of Bcl-2 is limited to lower TRAIL doses or early observation time points.
Rudner
Justine
J
Department of Radiation Oncology, University of Tuebingen, Hoppe-Seyler-Str. 3, Tuebingen D-72076, Germany.
Jendrossek
Verena
V
Lauber
Kirsten
K
Daniel
Peter T
PT
Wesselborg
Sebastian
S
Belka
Claus
C
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins; D020169:Caspases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D019169:Jurkat Cells; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; D008562:Membrane Glycoproteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D020169:Caspases