Nbs1 promotes ATM dependent phosphorylation events including those required for G1/S arrest.
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.
Girard
Pierre-Marie
PM
MRC Cell Mutation Unit, University of Sussex, Brighton, East Sussex, BN1 9RR, UK.
Riballo
Enriqueta
E
Begg
Adrian C
AC
Waugh
Alastair
A
Jeggo
Penny A
PA
D001260:Ataxia Telangiectasia / Q000235:genetics*; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002478:Cells, Cultured / Q000378:metabolism / Q000528:radiation effects; D064447:Checkpoint Kinase 2; D019457:Chromosome Breakage / Q000235:genetics*; D004268:DNA-Binding Proteins; D004307:Dose-Response Relationship, Radiation; D016193:G1 Phase / Q000502:physiology* / Q000528:radiation effects; D018816:Genes, cdc; D006657:Histones / Q000378:metabolism; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000235:genetics*; D009386:Neoplastic Syndromes, Hereditary / Q000235:genetics*; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011836:Radiation Tolerance / Q000235:genetics; D016196:S Phase / Q000502:physiology*; D013577:Syndrome; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D006657:Histones; C112156:NBN protein, human; D009687:Nuclear Proteins; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases