Journal of Biological Chemistry
Volume 288, Issue 17, 26 April 2013, Pages 12014-12021
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Cell Biology
Identification of a Novel Anti-apoptotic E3 Ubiquitin Ligase That Ubiquitinates Antagonists of Inhibitor of Apoptosis Proteins SMAC, HtrA2, and ARTS*

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Identification of new anti-apoptotic genes is important for understanding the molecular mechanisms underlying apoptosis and tumorigenesis. The present study identified a novel anti-apoptotic gene named AREL1, which encodes a HECT (homologous to E6-AP carboxyl terminus) family E3 ubiquitin ligase. AREL1 interacted with and ubiquitinated IAP antagonists such as SMAC, HtrA2, and ARTS. However, AREL1 was cytosolic and did not localize to nuclei or mitochondria. The interactions between AREL1 and the IAP antagonists were specific for apoptosis-stimulated cells, in which the IAP antagonists were released into the cytosol from mitochondria. Furthermore, the ubiquitination and degradation of SMAC, HtrA2, and ARTS were significantly enhanced in AREL1-expressing cells following apoptotic stimulation, indicating that AREL1 binds to and ubiquitinates cytosolic but not mitochondria-associated forms of IAP antagonists. Furthermore, the anti-apoptotic role of AREL1-mediated degradation of SMAC, HtrA2, and ARTS was shown by simultaneous knockdown of three IAP antagonists, which caused the inhibition of caspase-3 cleavage, XIAP degradation, and induction of apoptosis. Therefore, the present study suggests that AREL1-mediated ubiquitination and degradation of cytosolic forms of three IAP antagonists plays an important role in the regulation of apoptosis.

Apoptosis
Caspase
Cell Signaling
E3 Ubiquitin Ligase
Xiap
AREL1
IAP Antagonists

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*

This work was supported by grants from the 21C Frontier Functional Human Genome Project, the Research Program for Regulation of Aging and Cancer, and the Basic Research Promotion Fund (KRF-2008-359-C00030, NRF-2009-353-C00070, and 2012R1A1A3002027) from the Korean Research Foundation, which was funded by the Korean Ministry of Education, Science, and Technology.

1

Both authors contributed equally to this work.