Proteasome inhibition can induce an autophagy-dependent apical activation of caspase-8

• Published in: Cell death and differentiation Vol. 18; no. 10; pp. 1584 - 1597
• Main Authors: Laussmann, M A, Passante, E, Düssmann, H, Rauen, J A, Würstle, M L, Delgado, M E, Devocelle, M, Prehn, J H M, Rehm, M
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 01.10.2011
• Subjects: Animals; Apoptosis; Apoptosis - genetics; Apoptosis - physiology; Autophagy; Autophagy - genetics; Autophagy - physiology; Autophagy-Related Protein 5; Boronic Acids - pharmacology; Bortezomib; Caspase 3 - metabolism; Caspase 7 - metabolism; Caspase 8 - genetics; Caspase 8 - metabolism; Cell cycle; Cell death; Fas-Associated Death Domain Protein - metabolism; Flow Cytometry; Fluorescence Resonance Energy Transfer; Health physics; HeLa Cells; Humans; Immunoblotting; Ligands; Mice; Mice, Mutant Strains; Microscopy, Fluorescence; Microtubule-Associated Proteins; Original Paper; Peptide Hydrolases - metabolism; Physiology; Proteasome Endopeptidase Complex - drug effects; Proteasome Endopeptidase Complex - metabolism; Proteins; Proto-Oncogene Proteins c-bcl-2 - genetics; Proto-Oncogene Proteins c-bcl-2 - metabolism; Pyrazines - pharmacology; Tumor necrosis factor-TNF; X-Linked Inhibitor of Apoptosis Protein - antagonists & inhibitors; X-Linked Inhibitor of Apoptosis Protein - genetics; X-Linked Inhibitor of Apoptosis Protein - metabolism; Ireland; Bcl-2; proteasome; apoptosis; caspase-8; Bortezomib
• ISSN: 1350-9047; 1476-5403
• DOI: 10.1038/cdd.2011.27

Antiapoptotic Bcl-2 family proteins are often highly expressed in chemotherapy-resistant cancers and impair mitochondrial outer membrane permeabilisation (MOMP), an important requirement for caspase activation via the intrinsic apoptosis pathway. Interestingly, although Bcl-2 overexpression in HeLa cervical cancer cells abrogated caspase processing in response to intrinsic apoptosis induction by staurosporine, tunicamycin or etoposide, residual caspase processing was observed following proteasome inhibition by bortezomib ([(1R)-3-methyl-1-({(2S)-3-phenyl-2-[(pyrazin-2-ylcarbonyl)amino]propanoyl}amino)butyl]boronic acid), epoxomicin (N-acetyl-N-methyl-lisoleucyl-L-isoleucyl-N-[(1S)-3-methyl-1-[[(2R)-2-methyloxiranyl]carbonyl]butyl]-L-threoninamide) or MG-132 (N-(benzyloxycarbonyl)leucinylleucinylleucinal). Similar responses were found in Bcl-2-overexpressing H460 NSCLC cells and Bax/Bak-deficient mouse embyronic fibroblasts. Mild caspase processing resulted in low DEVDase activities, which were MOMP independent and persisted for long periods without evoking immediate cell death. Surprisingly, depletion of caspase-3 and experiments in caspase-7-depleted MCF-7-Bcl-2 cells indicated that the DEVDase activity did not originate from effector caspases. Instead, Fas-associated death domain (FADD)-dependent caspase-8 activation was the major contributor to the slow, incomplete substrate cleavage. Caspase-8 activation was independent of death ligands, but required the induction of autophagy and the presence of Atg5. Depletion of XIAP or addition of XIAP-antagonising peptides resulted in a switch towards efficient apoptosis execution, suggesting that the requirement for MOMP was bypassed by activating the caspase-8/caspase-3 axis. Combination treatments of proteasome inhibitors and XIAP antagonists therefore represent a promising strategy to eliminate highly resistant cancer cells, which overexpress antiapoptotic Bcl-2 family members.