Inhibition of ubiquitin-mediated degradation of MOAP-1 by apoptotic stimuli promotes Bax function in mitochondria

doi:10.1073/pnas.0700007104

Inhibition of ubiquitin-mediated degradation of MOAP-1 by apoptotic stimuli promotes Bax function in mitochondria

Institute of Molecular and Cell Biology, 61 Biopolis Drive (Proteos), Singapore 138673

Edited by Xiaodong Wang, University of Texas Southwestern Medical Center, Dallas, TX, and approved May 2, 2007 (received for review January 2, 2007)

Abstract

The multidomain proapoptotic protein Bax of the Bcl-2 family is a central regulator for controlling the release of apoptogenic factors from mitochondria. Recent evidence suggests that the Bax-associating protein MOAP-1 may act as an effector for promoting Bax function in mitochondria. Here, we report that MOAP-1 protein is rapidly up-regulated by multiple apoptotic stimuli in mammalian cells. MOAP-1 is a short-lived protein (t _1/2 ≈ 25 min) that is constitutively degraded by the ubiquitin-proteasome system. Induction of MOAP-1 by apoptotic stimuli ensues through inhibition of its polyubiquitination process. Elevation of MOAP-1 levels sensitizes cells to apoptotic stimuli and promotes recombinant Bax-mediated cytochrome c release from isolated mitochondria. Mitochondria depleted of short-lived proteins by cycloheximide (CHX) become resistant to Bax-mediated cytochrome c release. Remarkably, incubation of these mitochondria with in vitro-translated MOAP-1 effectively restores the cytochrome c releasing effect of recombinant Bax. We propose that apoptotic stimuli can facilitate the proapoptotic function of Bax in mitochondria through stabilization of MOAP-1.

Footnotes

*To whom correspondence should be addressed. E-mail: mcbyuck{at}imcb.a-star.edu.sg
Author contributions: N.Y.F., S.K.S., and V.C.Y. designed research; N.Y.F. and S.K.S. performed research; N.Y.F., S.K.S., and V.C.Y. analyzed data; and N.Y.F. and V.C.Y. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0700007104/DC1.
Abbreviations:

Cyto c,

cytochrome c;

ETOP,

etoposide;

CHX,

cycloheximide;

IB,

immunoblotting;

IP,

immunoprecipitation;

MOAP-1,

modulator of apoptosis;

THA,

thapsigargin;

TRAIL,

tumor necrosis factor-related apoptosis-inducing ligand;

UPS,

the ubiquitin/proteasome system;

Ub,

ubiquitin.
Freely available online through the PNAS open access option.