Omi/HtrA2 catalytic cleavage of inhibitor of apoptosis (IAP) irreversibly inactivates IAPs and facilitates caspase activity in apoptosis.
Omi/HtrA2 is a mitochondrial serine protease that is released into the cytosol during apoptosis to antagonize inhibitors of apoptosis (IAPs) and contribute to caspase-independent cell death. Here, we demonstrate that Omi/HtrA2 directly cleaves various IAPs in vitro, and the cleavage efficiency is determined by its IAP-binding motif, AVPS. Cleavage of IAPs such as c-IAP1 substantially reduces its ability to inhibit and ubiquitylate caspases. In contrast to the stoichiometric anti-IAP activity by Smac/DIABLO, Omi/HtrA2 cleavage of c-IAP1 is catalytic and irreversible, thereby more efficiently inactivating IAPs and promoting caspase activity. Elimination of endogenous Omi by RNA interference abolishes c-IAP1 cleavage and desensitizes cells to apoptosis induced by TRAIL. In addition, overexpression of cleavage-site mutant c-IAP1 makes cells more resistant to TRAIL-induced caspase activation. This IAP cleavage by Omi is independent of caspase. Taken together, these results indicate that unlike Smac/DIABLO, Omi/HtrA2's catalytic cleavage of IAPs is a key mechanism for it to irreversibly inactivate IAPs and promote apoptosis.
Yang
Qi-Heng
QH
Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
Church-Hajduk
Robin
R
Ren
Jinyu
J
Newton
Michelle L
ML
Du
Chunying
C
D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D002384:Catalysis; D004789:Enzyme Activation / Q000502:physiology; D006367:HeLa Cells; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008025:Ligases / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000378:metabolism; D009154:Mutation; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C412403:DIABLO protein, human; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008562:Membrane Glycoproteins; D024101:Mitochondrial Proteins; D011506:Proteins; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D025801:Ubiquitin; C494833:BIRC2 protein, human; D044767:Ubiquitin-Protein Ligases; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; D020169:Caspases; D008025:Ligases