Abstract
FL5.12 pro-B lymphoma cells utilize the mitochondrial pathway to apoptosis in response to tumor necrosis factor (TNF) receptor occupation, yet high levels of the Bcl-2 family antiapoptotic protein, BCl-XL, fail to protect these cells against TNF-receptor-activated death. Bcl-XL expression delays, but does not totally block, the release of mitochondrial cytochrome c (cyt c in these cells in response to TNFα-induced apoptosis and caspase-9 is processed prior to mitochondrial cyt c release under these circumstances. Early processing of caspase-9 also occurred in Apaf-1 knockout murine fibroblasts in response to TNF-receptor occupation. A caspase-9-specific inhibitor was more effective in delaying the progression of apoptosis in the FL5.12 Bcl-XL cells than was an inhibitor specific to caspase-3. Furthermore, downregulation of caspase-9 levels by RNA interference resulted in partial protection of these cells against TNF-receptor-activated apoptosis, indicating that caspase-9 activation contributed to early amplification of the caspase cascade. Consistent with this, proteolytic processing of caspase-9 was observed prior to processing by caspase-3, suggesting that caspase-3 was not responsible for early caspase-9 activation. We show that murine caspase-9 is efficiently processed by active caspase-8 at SEPD, the motif at which caspase-9 autoprocesses following its recruitment to the apoptosome. Our results suggest that, in addition to processing procaspase-3 and the BH3 protein Bid, active caspase-8 can cleave and activate procaspase-9 in response to TNF receptor crosslinking in murine cells.
Original language | English (US) |
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Pages (from-to) | 1005-1015 |
Number of pages | 11 |
Journal | Cell Death and Differentiation |
Volume | 10 |
Issue number | 9 |
DOIs | |
State | Published - Sep 1 2003 |
Bibliographical note
Funding Information:The authors are grateful to Craig Thompson for stimulating discussions and for a critical reading of the manuscript. We also thank Manuel Melendez for excellent technical assistance. This work was supported by a grant from the Leukemia Research Fund.
Keywords
- Apoptosis
- Caspase-8
- Caspase-9
- Cytochrome c release
- Death receptors