Nbs1 promotes ATM dependent phosphorylation events including those required for G1/S arrest

Oncogene. 2002 Jun 20;21(27):4191-9. doi: 10.1038/sj.onc.1205596.


Cell lines from Nijmegen Breakage Syndrome (NBS) and ataxia telangiectasia (A-T) patients show defective S phase checkpoint arrest. In contrast, only A-T but not NBS cells are significantly defective in radiation-induced G1/S arrest. Phosphorylation of some ATM substrates has been shown to occur in NBS cells. It has, therefore, been concluded that Nbs1 checkpoint function is S phase specific. Here, we have compared NBS with A-T cell lines (AT-5762ins137) that express a low level of normal ATM protein to evaluate the impact of residual Nbs1 function in NBS cells. The radiation-induced cell cycle response of these NBS and 'leaky' A-T cells is almost identical; normal G2/M arrest after 2 Gy, intermediate G1/S arrest depending on the dose and an A-T-like S phase checkpoint defect. Thus, the checkpoint assays differ in their sensitivity to low ATM activity. Radiation-induced phosphorylation of the ATM-dependent substrates Chk2, RPAp34 and p53-Ser15 are similarly impaired in AT-5762ins137 and NBS cells in a dose dependent manner. In contrast, NBS cells show normal ability to activate ATM kinase following irradiation in vitro and in vivo. We propose that Nbs1 facilitates ATM-dependent phosphorylation of multiple downstream substrates, including those required for G1/S arrest.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Ataxia Telangiectasia / genetics*
  • Ataxia Telangiectasia Mutated Proteins
  • Cell Cycle Proteins / metabolism*
  • Cells, Cultured / metabolism
  • Cells, Cultured / radiation effects
  • Checkpoint Kinase 2
  • Chromosome Breakage / genetics*
  • DNA-Binding Proteins
  • Dose-Response Relationship, Radiation
  • G1 Phase / physiology*
  • G1 Phase / radiation effects
  • Genes, cdc*
  • Histones / metabolism
  • Humans
  • Immunologic Deficiency Syndromes / genetics*
  • Neoplastic Syndromes, Hereditary / genetics*
  • Nuclear Proteins / metabolism*
  • Phosphorylation
  • Protein Kinases / metabolism
  • Protein Processing, Post-Translational*
  • Protein-Serine-Threonine Kinases / metabolism*
  • Radiation Tolerance / genetics
  • S Phase / physiology*
  • Syndrome
  • Tumor Suppressor Protein p53 / metabolism
  • Tumor Suppressor Proteins


  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • Histones
  • NBN protein, human
  • Nuclear Proteins
  • Tumor Suppressor Protein p53
  • Tumor Suppressor Proteins
  • Protein Kinases
  • Checkpoint Kinase 2
  • ATM protein, human
  • Ataxia Telangiectasia Mutated Proteins
  • CHEK2 protein, human
  • Protein-Serine-Threonine Kinases