UV irradiation triggers ubiquitin-dependent degradation of p21(WAF1) to promote DNA repair

Cell. 2003 Sep 5;114(5):599-610. doi: 10.1016/j.cell.2003.08.001.


p53-mediated increase in cyclin-dependent kinase inhibitor p21(WAF1) protein is thought to be the major mediator of cell cycle arrest after DNA damage. Previously p21 protein levels have been reported to increase or to decrease after UV irradiation. We show that p21 protein is degraded after irradiation of a variety of cell types with low but not high doses of UV. Cell cycle arrest occurs despite p21 degradation via Tyr(15) inhibitory phosphorylation of cdk2 and differs from the classical p21-dependent checkpoint elicited by ionizing radiation. In contrast to the basal turnover of p21, degradation of p21 switches to ubiquitin/Skp2-dependent proteasome pathway following UV irradiation. ATR activation after UV irradiation is essential for signaling p21 degradation. Finally, UV-induced p21 degradation is essential for optimal DNA repair. These results provide novel insight into regulation of p21 protein and its role in the cellular response to DNA damage.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Animals
  • Caffeine / pharmacology
  • Cell Cycle
  • Cell Cycle Proteins / metabolism
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / metabolism*
  • Cycloheximide / pharmacology
  • DNA Damage*
  • DNA Repair*
  • Detergents / pharmacology
  • Dose-Response Relationship, Drug
  • HeLa Cells
  • Humans
  • Mice
  • Microscopy, Fluorescence
  • Models, Biological
  • Octoxynol / pharmacology
  • Phosphorylation
  • Precipitin Tests
  • Protein Synthesis Inhibitors / pharmacology
  • S-Phase Kinase-Associated Proteins
  • Signal Transduction
  • Temperature
  • Time Factors
  • Transfection
  • Tyrosine / metabolism
  • Ubiquitin / metabolism*
  • Ultraviolet Rays*


  • CDKN1A protein, human
  • Cdkn1a protein, mouse
  • Cell Cycle Proteins
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Detergents
  • Protein Synthesis Inhibitors
  • S-Phase Kinase-Associated Proteins
  • Ubiquitin
  • Caffeine
  • Tyrosine
  • Octoxynol
  • Cycloheximide