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Omi/HtrA2 catalytic cleavage of inhibitor of apoptosis (IAP) irreversibly inactivates IAPs and facilitates caspase activity in apoptosis

Genes & Dev., 15 June 2003
Vol. 17, Issue 12, p. 1487-1496
DOI: 10.1101/gad.1097903

Omi/HtrA2 catalytic cleavage of inhibitor of apoptosis (IAP) irreversibly inactivates IAPs and facilitates caspase activity in apoptosis

  1. Qi-Heng Yang1,
  2. Robin Church-Hajduk2,
  3. Jinyu Ren1,
  4. Michelle L. Newton1, and
  5. Chunying Du1,3
  1. 1Stowers Institute for Medical Research, Kansas City, Missouri 64110, USA
  2. 2Department of Anesthesiology, St. Luke's Hospital/UMKC, Kansas City, Missouri 64111, USA


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.

  • Apoptosis
  • mitochondria
  • Omi/HtrA2
  • Smac
  • IAPs
  • caspases


  • Corresponding author.

  • 3 E-MAIL cdu{at}; FAX (816) 926-2055.

  • Article and publication are at

    • Accepted April 29, 2003.
    • Received March 27, 2003.


Q.-H. Yang, R. Church-Hajduk, J. Ren, M. L. Newton, and C. Du, Omi/HtrA2 catalytic cleavage of inhibitor of apoptosis (IAP) irreversibly inactivates IAPs and facilitates caspase activity in apoptosis. Genes & Dev. 17, 1487-1496 (2003).

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