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XIAP regulates DNA damage-induced apoptosis downstream of caspase-9 cleavage
1Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA. Rakesh_Datta@dfci.harvard.edu
Abstract:
The IAP (inhibitor of apoptosis) family of anti-apoptotic proteins regulates programmed cell death. Of the six known human IAP-related proteins, XIAP is the most potent inhibitor. To study the mechanistic effects of XIAP on DNA damage-induced apoptosis, we prepared U-937 cells that stably overexpress XIAP. The results demonstrate that XIAP inhibits apoptosis induced by 1-[beta-d-arabinofuranosyl]cytosine (ara-C) and other genotoxic agents. XIAP had no detectable effect on ara-C-induced release of mitochondrial cytochrome c and attenuated cleavage of procaspase-9. In addition, we show that ara-C induces the association of XIAP with the cleaved fragments of caspase-9 and thereby inhibition of caspase-9 activity. The results also demonstrate that ara-C induces cleavage of procaspase-3 by a caspase-8-dependent mechanism and that XIAP inhibits caspase-3 activity. These results demonstrate that XIAP functions downstream of procaspase-9 cleavage as an inhibitor of both proteolytically processed caspase-9 and -3 in the cellular response to genotoxic stress.
Insights
The inhibitor of apoptosis protein XIAP blocks programmed cell death by inhibiting caspase-9 and caspase-3 activity following DNA damage. This finding reveals XIAP
Area of Science:
- Cellular biology
- Molecular biology
- Biochemistry
Background:
- The inhibitor of apoptosis (IAP) protein family regulates programmed cell death.
- X-linked inhibitor of apoptosis protein (XIAP) is the most potent IAP family member.
- Understanding XIAP's role in DNA damage-induced apoptosis is crucial.
Purpose of the Study:
- To investigate the mechanistic effects of XIAP on DNA damage-induced apoptosis.
- To elucidate how XIAP influences caspase activation pathways.
Main Methods:
- Overexpression of XIAP in U-937 cells.
- Treatment with genotoxic agents, including 1-[beta-d-arabinofuranosyl]cytosine (ara-C).
- Analysis of apoptosis markers, cytochrome c release, and caspase cleavage/activity.
Main Results:
- XIAP inhibited ara-C and other genotoxic agent-induced apoptosis.
- XIAP did not affect mitochondrial cytochrome c release but attenuated procaspase-9 cleavage.
- XIAP associated with cleaved caspase-9, inhibiting its activity, and also inhibited caspase-3 activity.
Conclusions:
- XIAP functions downstream of procaspase-9 cleavage.
- XIAP acts as a potent inhibitor of both caspase-9 and caspase-3.
- XIAP plays a significant role in suppressing apoptosis under genotoxic stress.