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| 4: Cancer Res. 2003 Apr 1;63(7):1483-9. |
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- Bax plays a pivotal role in thapsigargin -induced
apoptosis of human colon cancer HCT116 cells by controlling Smac/Diablo and
Omi/HtrA2 release from mitochondria.
Yamaguchi H, Bhalla K, Wang HG.
Department of Interdisciplinary Oncology, University of South Florida College
of Medicine, Tampa, Florida 33612, USA.
Bax is a crucial mediator of the mitochondrial pathway for apoptosis, and loss
of this proapoptotic Bcl-2 family protein contributes to drug resistance in
human cancers. We report here that the endoplasmic reticulum Ca(2+)-ATPase
inhibitor thapsigargin (THG) induces apoptosis of human colon cancer HCT116
cells through a Bax-dependent signaling pathway controlling the cytosolic
release of mitochondrial apoptogenic molecules. Treating HCT116 cells with THG
results in caspase-8 activation; Bid cleavage; Bax conformational change and
mitochondrial translocation; the release of cytochrome c, Smac/Diablo, and
Omi/HtrA2 into the cytosol; caspase-3 activation; and apoptosis. In contrast,
knockout of Bax completely abrogates the full processing/activation of
caspase-3 but has no effect on the processing of caspase-8 and the initial
cleavage of caspase-3 to p24 fragment after THG treatment. The
caspase-8-specific inhibitor z-IETD-fmk, as well as pan-caspase inhibitor z-VAD-fmk,
but not the calpain inhibitor E-64d, prevents Bid cleavage, Bax conformational
change, and subsequent caspase-3 processing and apoptosis. Caspase-8
processing is dependent on de novo protein synthesis; DR5 expression is
strongly up-regulated by THG treatment. Moreover, the absence of Bax blocks
THG-induced Omi and Smac release from mitochondria, and expression of
cytosolic Omi (GFP-IETD-Omi) or Smac (GFP-IETD-Smac) restores the sensitivity
of Bax-knockout HCT116 cells to apoptosis in response to THG treatment. Taken
together, our results indicate that Bax-dependent Smac and Omi release plays
an essential role in caspase-3 activation and apoptosis induced by THG in
human colon cancer HCT116 cells.
PMID: 12670894 [PubMed - indexed for MEDLINE]
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