title: MnSOD protects colorectal cancer cells from TRAIL-induced apoptosis by inhibition of Smac/DIABLO release.
abstract: The mitochondrial enzyme manganese superoxide dismutase (MnSOD) has been shown to have two faces with regard to its role in tumor development. On the one side, it is well documented that overexpression of MnSOD slows down cancer cell growth, whereas on the other side MnSOD also has a metastasis-promoting activity. We set out to examine the role of MnSOD in tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, thought to be a first-line tumor surveillance mechanism and failure to undergo apoptosis might contribute to metastasis formation. We show that overexpression of MnSOD at moderate levels is able to protect cells from TRAIL-induced apoptosis. While caspase-8 activation and Bid cleavage were not affected by MnSOD, we detected a marked decrease in caspase-3 activation pointing to a mitochondrial resistance mechanism. Indeed, we found that MnSOD-overexpressing cells showed reduced cytochrome c and no Smac/DIABLO release into the cytosol. The resulting lack of X-linked inhibitor of apoptosis (XIAP) inhibition by cytosolic Smac/DIABLO most likely caused the TRAIL resistance as RNAi against XIAP-rescued caspase-3 activity and TRAIL sensitivity. Our results show that reactive oxygen species are involved in TRAIL-induced Smac/DIABLO release and in TRAIL-triggered apoptosis. Hence, high levels of MnSOD, which decompose and neutralize these reactive oxygen species, might contribute to metastasis formation by allowing disseminated tumor cells to escape from TRAIL-mediated tumor surveillance. As part of TRAIL regimens, adjuvant treatment with XIAP inhibitors in the form of Smac/DIABLO mimetics or MnSOD inhibitors might be able to break TRAIL resistance of malignant tumor cells.
authors.affiliation: National Centre for Biomedical Engineering Science, Molecular Therapeutics Group, National University of Ireland Galway, Galway, Ireland.
authors.forename: A
authors.initials: A
authors.lastname: Mohr
authors.forename: C
authors.initials: C
authors.lastname: Büneker
authors.forename: R P
authors.initials: RP
authors.lastname: Gough
authors.forename: R M
authors.initials: RM
authors.lastname: Zwacka
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D017209:Apoptosis / Q000235:genetics*; D051017:Apoptosis Regulatory Proteins; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000201:enzymology*; D045304:Cytochromes c / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010641:Phenotype; D034622:RNA Interference; D017382:Reactive Oxygen Species / Q000378:metabolism; D013482:Superoxide Dismutase / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D014410:Tumor Stem Cell Assay; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D017382:Reactive Oxygen Species; D053221:TNF-Related Apoptosis-Inducing Ligand; D051636:X-Linked Inhibitor of Apoptosis Protein; D045304:Cytochromes c; D013482:Superoxide Dismutase; D053148:Caspase 3