The anti-apoptotic protein BCL2L1/Bcl-xL is neutralized by pro-apoptotic PMAIP1/Noxa in neuroblastoma, thereby determining bortezomib sensitivity independent of prosurvival MCL1 expression.
Neuroblastoma is the most frequent extracranial solid tumor in children. Here, we report that the proteasome inhibitor bortezomib (PS-341, Velcade) activated the pro-apoptotic BH3-only proteins PMAIP1/Noxa and BBC3/Puma and induced accumulation of anti-apoptotic MCL1 as well as repression of anti-apoptotic BCL2L1/Bcl-xL. Retroviral expression of Bcl-xL, but not of MCL1, prevented apoptosis by bortezomib. Gene knockdown of Noxa by shRNA technology significantly reduced apoptosis, whereas Puma knockdown did not affect cell death kinetics. Immunoprecipitation revealed that endogenous Noxa associated with both, Bcl-xL and MCL1, suggesting that in neuronal cells Noxa can neutralize Bcl-xL, explaining the pronounced protective effect of Bcl-xL. Tetracycline-regulated Noxa expression did not trigger cell death per se but sensitized to bortezomib treatment in a dose-dependent manner. This implies that the induction of Noxa is necessary but not sufficient for bortezomib-induced apoptosis. We conclude that MCL1 steady-state expression levels do not affect sensitivity to proteasome-inhibitor treatment in neuronal tumor cells, and that both the repression of Bcl-xL and the activation of Noxa are necessary for bortezomib-induced cell death.
Hagenbuchner
Judith
J
Department of Pediatrics IV, Biocenter, Medical University Innsbruck, Tyrolean Cancer Research Institute, 6020 Innsbruck, Austria.
Ausserlechner
Michael J
MJ
Porto
Verena
V
David
Reinhard
R
Meister
Bernhard
B
Bodner
Martin
M
Villunger
Andreas
A
Geiger
Kathrin
K
Obexer
Petra
P
D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism* / Q000627:therapeutic use; D017209:Apoptosis / Q000502:physiology; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D001897:Boronic Acids / Q000378:metabolism* / Q000627:therapeutic use; D000069286:Bortezomib; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D002648:Child; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D006801:Humans; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009447:Neuroblastoma / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D011480:Protease Inhibitors / Q000378:metabolism* / Q000627:therapeutic use; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D011719:Pyrazines / Q000378:metabolism* / Q000627:therapeutic use; D053218:Receptors, Death Domain / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D019076:Transgenes; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism*
D000970:Antineoplastic Agents; D051017:Apoptosis Regulatory Proteins; C438378:BBC3 protein, human; D001897:Boronic Acids; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C498702:PMAIP1 protein, human; D011480:Protease Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011719:Pyrazines; D053218:Receptors, Death Domain; D051020:bcl-X Protein; D000069286:Bortezomib; D020169:Caspases