Cleavage of CDK inhibitor p21(Cip1/Waf1) by caspases is an early event during DNA damage-induced apoptosis.
Activation of the p53-mediated DNA damage response induces either G1 cell cycle arrest or apoptosis. The G1 cell cycle arrest is in part caused by the p53-dependent transcriptional activation of the CDK inhibitor, p21(Cip1/Waf1). We report here that human p21 protein is rapidly induced but selectively cleaved during the apoptotic response to gamma-irradiation. Such an event occurred early, well before the morphological appearance of apoptosis. Ectopical expression of p53 in tumor cells alone could induce p21 expression, followed by p21 cleavage and apoptosis. The cleavage of p21 could be reproduced in extracts prepared from irradiated cells or by recombinant caspase-3, suggesting that a caspase-like activity is responsible for this cleavage. p21 binds independently to both CDK2 and proliferation cell nuclear antigen (PCNA). Our studies indicated that p21 cleavage by the caspase-like activity specifically abolished its interaction with PCNA, suggesting that p21 cleavage may interfere with normal PCNA-dependent repair. Our data suggest that p21 may serve as a critical checkpoint regulator for both cell cycle arrest and apoptosis during the p53-mediated DNA damage response. Manipulation of the checkpoint regulators involved in cell cycle arrest and apoptosis may thus provide a novel strategy to cancer therapy.
Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
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Gervais
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Seth
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Zhang
D017209:Apoptosis / Q000528:radiation effects; D042846:CDC2-CDC28 Kinases; D053148:Caspase 3; D020169:Caspases; D019925:Cyclin A / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004249:DNA Damage; D006801:Humans; D008970:Molecular Weight; D010446:Peptide Fragments / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
C493956:CDKN1A protein, human; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D010446:Peptide Fragments; D018809:Proliferating Cell Nuclear Antigen; D016159:Tumor Suppressor Protein p53; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases