Journal
ONCOGENE
Volume 26, Issue 48, Pages 6954-6958Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/sj.onc.1210516
Keywords
p21; Rb; p27; damage response
Funding
- NCI NIH HHS [R01 CA62099, R01 CA95727] Funding Source: Medline
- NIA NIH HHS [R01 AG17921] Funding Source: Medline
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Damage-induced G1 checkpoint in mammalian cells involves upregulation of p53, which activates transcription of p21(Waf1) (CDKN1A). Inhibition of cyclin-dependent kinase (CDK)2 and CDK4/6 by p21 leads to dephosphorylation and activation of Rb. We now show that ectopic p21. expression in human HT1080 fibrosarcoma cells causes not only dephosphorylation but also depletion of Rb; this effect was p53-independent and susceptible to a proteasome inhibitor. CDK inhibitor p27 (CDKN1B) also caused Rb dephosphorylation and depletion, but another CDK inhibitor p16 (CDKN2A) induced only dephosphorylation but not depletion of Rb. Rb depletion was observed in both HT1080 and HCT116 colon carcinoma cells, where p21. was induced by DNA-damaging agents. Rb depletion after DNA damage did not occur in the absence of p21, and it was reduced when p21 induction was inhibited by p21-targeting short hairpin RNA or by a transdominant inhibitor of p53. These results indicate that p2l both activates Rb through dephosphorylation and inactivates it through degradation, suggesting negative feedback regulation of damage-induced cell-cycle checkpoint arrest.
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