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Department of Physiology, The University of Tennessee Health Science Center, Memphis, Tennessee 38163
C1297, 2002; 10.1152/ajpcell.00351.2001.We
have shown previously that depletion of polyamines delays
apoptosis induced by camptothecin in rat intestinal epithelial
cells (IEC-6). Mitochondria play an important role in the regulation of
apoptosis in mammalian cells because apoptotic signals
induce mitochondria to release cytochrome c. The latter
interacts with Apaf-1 to activate caspase-9, which in turn activates
downstream caspase-3. Bcl-2 family proteins are involved in the
regulation of cytochrome c release from mitochondria. In
this study, we examined the effects of polyamine depletion on the
activation of the caspase cascade, release of cytochrome c
from mitochondria, and expression and translocation of Bcl-2 family
proteins. We inhibited ornithine decarboxylase, the first rate-limiting
enzyme in polyamine synthesis, with
-difluoromethylornithine (DFMO)
to deplete cells of polyamines. Depletion of polyamines prevented
camptothecin-induced release of cytochrome c from
mitochondria and decreased the activity of caspase-9 and caspase-3. The
mitochondrial membrane potential was not disrupted when cytochrome
c was released. Depletion of polyamines decreased
translocation of Bax to mitochondria during apoptosis. The
expression of antiapoptotic proteins Bcl-xL and Bcl-2
was increased in DFMO-treated cells. Caspase-8 activity and cleavage of
Bid were decreased in cells depleted of polyamines. These results
suggest that polyamine depletion prevents IEC-6 cells from
apoptosis by preventing the translocation of Bax to mitochondria, thus preventing the release of cytochrome c.
polyamines;
-difluoromethylornithine; mitochondria; Bcl-2
protein; caspase-9
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