DNA damage triggers a prolonged p53-dependent G1 arrest and long-term induction of Cip1 in normal human fibroblasts

Genes Dev. 1994 Nov 1;8(21):2540-51. doi: 10.1101/gad.8.21.2540.


The tumor suppressor p53 is a cell cycle checkpoint protein that contributes to the preservation of genetic stability by mediating either a G1 arrest or apoptosis in response to DNA damage. Recent reports suggest that p53 causes growth arrest through transcriptional activation of the cyclin-dependent kinase (Cdk)-inhibitor Cip1. Here, we characterize the p53-dependent G1 arrest in several normal human diploid fibroblast (NDF) strains and p53-deficient cell lines treated with 0.1-6 Gy gamma radiation. DNA damage and cell cycle progression analyses showed that NDF entered a prolonged arrest state resembling senescence, even at low doses of radiation. This contrasts with the view that p53 ensures genetic stability by inducing a transient arrest to enable repair of DNA damage, as reported for some myeloid leukemia lines. Gamma radiation administered in early to mid-, but not late, G1 induced the arrest, suggesting that the p53 checkpoint is only active in G1 until cells commit to enter S phase at the G1 restriction point. A log-linear plot of the fraction of irradiated G0 cells able to enter S phase as a function of dose is consistent with single-hit kinetics. Cytogenetic analyses combined with radiation dosage data indicate that only one or a small number of unrepaired DNA breaks may be sufficient to cause arrest. The arrest also correlated with long-term elevations of p53 protein, Cip1 mRNA, and Cip1 protein. We propose that p53 helps maintain genetic stability in NDF by mediating a permanent cell cycle arrest through long-term induction of Cip1 when low amounts of unrepaired DNA damage are present in G1 before the restriction point.

Publication types

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

MeSH terms

  • Blotting, Northern
  • Blotting, Western
  • Cell Cycle / physiology*
  • Cell Cycle / radiation effects
  • Cell Line
  • Chromosome Aberrations
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / biosynthesis*
  • DNA Damage*
  • Dose-Response Relationship, Radiation
  • Fibroblasts / cytology
  • Fibroblasts / metabolism
  • Fibroblasts / radiation effects
  • Flow Cytometry
  • G1 Phase / physiology
  • G1 Phase / radiation effects
  • Gamma Rays
  • Humans
  • Kinetics
  • Leukemia, Myeloid
  • Metaphase
  • Protein Kinase Inhibitors
  • RNA, Messenger / analysis
  • RNA, Messenger / biosynthesis
  • Skin
  • Time Factors
  • Tumor Suppressor Protein p53 / metabolism*


  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • Protein Kinase Inhibitors
  • RNA, Messenger
  • Tumor Suppressor Protein p53