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Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c

Published on: June 29, 2011

Regulation of apoptosis by XIAP ubiquitin-ligase activity

Andrew J Schile1, María García-Fernández, Hermann Steller

  • 1Howard Hughes Medical Institute, The Rockefeller University, New York, NY 10065, USA.

Genes & Development
|August 19, 2008
PubMed

Insights

Inhibitor of Apoptosis Proteins (IAPs) like XIAP normally suppress caspases. Inactivating XIAP’s E3 ubiquitin-ligase activity paradoxically increased, rather than decreased, caspase activity and promoted tumor suppression.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Cancer Research

Background:

  • Inhibitor of Apoptosis Proteins (IAPs) are frequently overexpressed in human tumors.
  • IAPs target caspases, key regulators of apoptosis, making them significant pharmacological targets.
  • The precise in vivo function of individual mammalian IAPs as E3 ubiquitin-ligases is not well understood.

Purpose of the Study:

  • To investigate the physiological function of XIAP (X-linked inhibitor of apoptosis protein) ubiquitin-ligase activity.
  • To determine the role of XIAP's RING motif in protein stability and caspase regulation in vivo.

Main Methods:

  • Gene targeting in mice to inactivate the XIAP RING motif (XIAP DeltaRING).
  • Analysis of XIAP protein stability in apoptotic thymocytes.
  • Measurement of caspase-3 enzyme activity in embryonic stem cells and fibroblasts.
  • Assessment of apoptosis sensitivity in XIAP DeltaRING embryonic fibroblasts treated with TNF-alpha.
  • Evaluation of XIAP's role in tumor suppression using the Emu-Myc lymphoma model.

Main Results:

  • Inactivation of the XIAP RING motif stabilized XIAP protein, indicating ubiquitin-ligase activity is crucial for its degradation.
  • XIAP DeltaRING cells exhibited increased caspase activity and apoptosis.
  • XIAP DeltaRING embryonic fibroblasts showed heightened sensitivity to TNF-alpha-induced apoptosis.
  • Deletion of the XIAP RING motif improved survival in a mouse lymphoma model.

Conclusions:

  • XIAP's E3 ubiquitin-ligase activity is essential for inhibiting caspases and maintaining protein stability.
  • XIAP ubiquitin-ligase activity plays a critical role in tumor suppression in vivo.
  • Targeting XIAP's E3 ubiquitin-ligase function represents a potential therapeutic strategy for cancer.

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