ATM phosphorylates p95/nbs1 in an S-phase checkpoint pathway.
The rare diseases ataxia-telangiectasia (AT), caused by mutations in the ATM gene, and Nijmegen breakage syndrome (NBS), with mutations in the p95/nbs1 gene, share a variety of phenotypic abnormalities such as chromosomal instability, radiation sensitivity and defects in cell-cycle checkpoints in response to ionizing radiation. The ATM gene encodes a protein kinase that is activated by ionizing radiation or radiomimetic drugs, whereas p95/nbs1 is part of a protein complex that is involved in responses to DNA double-strand breaks. Here, because of the similarities between AT and NBS, we evaluated the functional interactions between ATM and p95/nbs1. Activation of the ATM kinase by ionizing radiation and induction of ATM-dependent responses in NBS cells indicated that p95/nbs1 may not be required for signalling to ATM after ionizing radiation. However, p95/nbs1 was phosphorylated on serine 343 in an ATM-dependent manner in vitro and in vivo after ionizing radiation. A p95/nbs1 construct mutated at the ATM phosphorylation site abrogated an S-phase checkpoint induced by ionizing radiation in normal cells and failed to compensate for this functional deficiency in NBS cells. These observations link ATM and p95/nbs1 in a common signalling pathway and provide an explanation for phenotypic similarities in these two diseases.
Lim
D S
DS
Department of Hematology-Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Kim
S T
ST
Xu
B
B
Maser
R S
RS
Lin
J
J
Petrini
J H
JH
Kastan
M B
MB
D001260:Ataxia Telangiectasia; D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004247:DNA / Q000096:biosynthesis / Q000528:radiation effects; D004268:DNA-Binding Proteins; D004789:Enzyme Activation / Q000528:radiation effects; D006801:Humans; D016296:Mutagenesis; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins
D064007:Ataxia Telangiectasia Mutated Proteins; D018797:Cell Cycle Proteins; D004247:DNA; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011993:Recombinant Fusion Proteins; D012694:Serine; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; C112156:NBN protein, human; C576324:ATM protein, human