Diminished Capacity for p53 in Mediating a Radiation-Induced G1 Arrest in Established Human Tumor Cell Lines

Oncogene. 1995 Nov 2;11(9):1885-92.


It has been reported that the p53 gene mediates an ionizing radiation-induced G1 arrest in mammalian cells. To further characterize this important phenomenon, a panel of seven human diploid fibroblast cell strains and 14 human tumor cell lines from a variety of sources with both wild-type and mutant p53 status were assayed for their susceptibility to G1 arrest after gamma-ray irradiation by a continuous labeling [3H]thymidine incorporation technique. An irreversible G1-block involving 20-70% of the cell population was observed in diploid fibroblasts irradiated with 4 Gy. The block was abolished by transfection with the Human Papilloma Virus E6 gene and in an ataxia telangiectasia (AT) cell line, indicating a role for the AT and p53 genes respectively in this process. In contrast to wild-type normal fibroblast cell strains, the G1-block in all tumor cell lines was significantly reduced, irrespective of their p53 status. None of the nine human tumor cell lines with mutant p53 genes showed a significant G1-block following irradiation with 4 Gy. Among the five tumor cell lines expressing wild-type p53, two showed no apparent G1-block. The remaining three showed a G1-block involving only 8-15% of the cell population, a block much smaller in magnitude than that seen in diploid fibroblasts. Finally, a diploid fibroblast cell strain and a tumor cell line, both showing a normal p53 and p21/WAF1 expression pattern, were examined for pRb phosphorylation before and after irradiation. The diploid fibroblast cell strain showed a significant G1-arrest and a clear inhibition of pRb phosphorylation by irradiation whereas the tumor cells showed no G1-arrest and no inhibition of pRb phosphorylation. These results suggest that (1) multiple genetic factors may modulate the occurrence and magnitude of the G1-arrest induced by exposure to ionizing radiation, (2) the capacity for p53 to mediate a radiation-induced G1 arrest is significantly reduced in tumor cells, (3) the disruption of G1-block modulating factor(s) other than p53 may be an important step in carcinogenesis.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Ataxia Telangiectasia
  • Base Sequence
  • Blotting, Western
  • Cell Cycle / genetics*
  • Cell Line
  • Cell Survival / drug effects
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins / biosynthesis
  • DNA Primers
  • DNA Replication / radiation effects
  • Enzyme Inhibitors / metabolism
  • Fibroblasts
  • G1 Phase
  • Gamma Rays
  • Gene Expression / radiation effects*
  • Genes, p53*
  • Humans
  • Molecular Sequence Data
  • Mutation*
  • Phosphorylation
  • Polymerase Chain Reaction
  • Reference Values
  • Retinoblastoma Protein / metabolism
  • Thymidine / metabolism
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / biosynthesis


  • CDKN1A protein, human
  • Cyclin-Dependent Kinase Inhibitor p21
  • Cyclins
  • DNA Primers
  • Enzyme Inhibitors
  • Retinoblastoma Protein
  • Tumor Suppressor Protein p53
  • Thymidine