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p21(WAF1/CIP1) inhibits initiator caspase cleavage by TRAIL death receptor DR4
1Laboratory of Molecular Oncology and Cell Cycle Regulation, Departments of Medicine, Genetics, Cancer Center, Howard Hughes Medical Institute, Institute for Human Gene Therapy, 437 CRB, 415 Curie Boulevard, Philadelphia, Pennsylvania 19104, USA.
Abstract:
Death receptors of the Tumor Necrosis Factor (TNF) family form membrane-bound self-activating signaling complexes that initiate apoptosis through cleavage of proximal caspases including CASP8 and 10. Here we show that overexpression of the cytoplasmic domain (CD) of the DR4 TRAIL receptor (TNFRSF10A, TRAIL R1) in human breast, lung, and colon cancer cell lines, using an adenovirus vector (Ad-DR4-CD), leads to p53-independent apoptotic cell death involving cleavage of CASP8 and 10 proximally and CASP3, 6, and 7 distally. DR4-CD overexpression also leads to cleavage of poly(ADP-ribose) polymerase (PARP) and the DNA fragmentation factor (DFF45; ICAD). Importantly, normal lung fibroblasts are resistant to DR4-CD overexpression and show no evidence of PARP-, CASP8- or CASP3-cleavage despite similar levels of adenovirus-delivered DR4-CD protein as the cancer cells. These results suggest that DR4 may signal death through known caspases and that further studies are required to evaluate Ad-DR4-CD as a novel anti-cancer agent. Finally, we show that overexpression of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) (CDKN1A), or its N-terminal 91 amino acids containing cell cycle-inhibitory activity, inhibits DR4-CD-dependent proximal caspase cleavage. The blockage of initiator caspase activation provides a novel insight into how p21 may suppress apoptosis and enhance cell survival.
Insights
Overexpressing the DR4 TRAIL receptor cytoplasmic domain induces cancer cell death independently of p53. Normal cells resist this effect, suggesting Ad-DR4-CD as a potential anti-cancer therapy.
Area of Science:
- Molecular Biology
- Cell Biology
- Cancer Research
Background:
- Death receptors initiate apoptosis via caspase activation.
- The DR4 TRAIL receptor plays a role in programmed cell death.
Purpose of the Study:
- To investigate the apoptotic effects of overexpressing the DR4 cytoplasmic domain (DR4-CD).
- To evaluate the potential of Ad-DR4-CD as an anti-cancer agent.
- To explore the role of p21 in DR4-CD-mediated apoptosis.
Main Methods:
- Adenovirus-mediated overexpression of DR4-CD in human cancer cell lines and normal fibroblasts.
- Analysis of caspase cleavage (CASP8, 10, 3, 6, 7), PARP cleavage, and DNA fragmentation.
- Assessment of p53-independent apoptosis.
- Investigating the effect of p21 overexpression on DR4-CD signaling.
Main Results:
- DR4-CD overexpression induced p53-independent apoptosis in cancer cells, involving caspase and PARP cleavage.
- Normal fibroblasts were resistant to DR4-CD-induced apoptosis.
- Overexpression of p21 inhibited DR4-CD-dependent proximal caspase cleavage.
Conclusions:
- DR4-CD signaling activates known caspase pathways leading to apoptosis.
- Normal cells exhibit resistance to DR4-CD, indicating therapeutic potential.
- p21 suppresses apoptosis by inhibiting initiator caspase activation, offering insights into cell survival mechanisms.