The proteasome is required for rapid initiation of death receptor-induced apoptosis.
Due to their tremendous apoptosis-inducing potential, proteasomal inhibitors (PIs) have recently entered clinical trials. Here we show, however, that various PIs rescued proliferating tumor cells from death receptor-induced apoptosis. This protection correlated with the stabilization of X-linked IAP (XIAP) and c-FLIP and the inhibition of caspase activation. Together with the observation that PIs could not protect cells expressing XIAP or c-FLIP short interfering RNAs (siRNAs) from death receptor-induced apoptosis, our results demonstrate that PIs mediate their protective effect via the stabilization of these antiapoptotic proteins. Furthermore, we show that once these proteins were eliminated, either by long-term treatment with death receptor ligands or by siRNA-mediated suppression, active caspases accumulated to an even larger extent in the presence of PIs. Together, our data support a biphasic role for the proteasome in apoptosis, as they show that its constitutive activity is crucial for the rapid initiation of the death program by eliminating antiapoptotic proteins, whereas at later stages, the proteasome acts in an antiapoptotic manner due to the proteolysis of caspases. Thus, for a successful PI-based tumor therapy, it is crucial to carefully evaluate basal proteasomal activity and the status of antiapoptotic proteins, as their PI-mediated prolonged stability might even cause adverse effects, leading to the survival of a tumor.
Sohn
Dennis
D
Institute of Molecular Medicine, University of Düsseldorf, Building 23.12, Universitätsstrasse 1, D-40225 Düsseldorf, Germany.
Totzke
Gudrun
G
Essmann
Frank
F
Schulze-Osthoff
Klaus
K
Levkau
Bodo
B
Jänicke
Reiner U
RU
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins / Q000187:drug effects / Q000378:metabolism; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000187:drug effects / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D018124:Receptors, Tumor Necrosis Factor / Q000187:drug effects / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins / Q000187:drug effects / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000378:metabolism / Q000494:pharmacology; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D019014:fas Receptor / Q000187:drug effects / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D053418:Death Domain Receptor Signaling Adaptor Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D007976:Leupeptins; D008562:Membrane Glycoproteins; D061988:Proteasome Inhibitors; D034741:RNA, Small Interfering; D018124:Receptors, Tumor Necrosis Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D047988:Tumor Necrosis Factor Receptor-Associated Peptides and Proteins; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; D019014:fas Receptor; D020169:Caspases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde