p21(WAF1/CIP1) inhibits initiator caspase cleavage by TRAIL death receptorDR4

Death receptors of the Tumor Necrosis Factor (TNF) family form membrane-bou nd self-activating signaling complexes that initiate apoptosis through clea vage of proximal caspases including GASPS and 10. Here we show that overexp ression of the cytoplasmic domain (GD) of the DR4 TRAIL receptor (TNFRSF10A , TRAIL R1) in human breast, lung, and colon cancer cell lines, using an ad enovirus vector (Ad-DR4-CD), leads to p53-independent apoptotic cell death involving cleavage of GASPS and 10 proximally and CASP3, 6, and 7 distally, DR4-CD overexpression also leads to cleavage of poly(ADP-ribose) polymeras e (PARP) and the DNA fragmentation factor (DFF45; ICAD). Importantly, norma l lung fibroblasts are resistant to DR4-CD overexpression and show no evide nce of PARP-, CASP8- or CASP3-cleavage despite similar levels of adenovirus -delivered DR4-CD protein as the cancer cells. These results suggest that D R4 may signal death through known caspases and that further studies are req uired 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-inhibitor y activity, inhibits DR4-CD-dependent proximal caspase cleavage. The blocka ge of initiator caspase activation provides a novel insight into how p21 ma y suppress apoptosis and enhance cell survival. (C) 2000 Academic Press.