Nature Genetics
25, 115 - 119 (2000)
doi:10.1038/75508
ATM-dependent phosphorylation of nibrin in response to radiation exposureMagtouf Gatei1, David Young1, Karen M. Cerosaletti2, Ami Desai-Mehta2, Kevin Spring1, Sergei Kozlov1, Martin F. Lavin1, 3, Richard A. Gatti4, Patrick Concannon2
& KumKum Khanna1, 31
The Queensland Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane, Queensland, Australia. 2
Molecular Genetics Programme, Virginia Mason Research Centre, and Department of Immunology, University of Washington School of Medicine, Seattle, Washington, USA. 3
Joint Oncology Programme, The Department of Pathology and The Department of Surgery, University of Queensland, Brisbane, Queensland, Australia. 4
Department of Pathology, UCLA School of Medicine, Los Angeles, California, USA.
Correspondence should be addressed to KumKum Khanna kumkumK@qimr.edu.auMutations in the gene ATM are responsible for the genetic disorder ataxia-telangiectasia (A-T), which is characterized by cerebellar dysfunction, radiosensitivity, chromosomal instability and cancer predisposition. Both the A-T phenotype and the similarity of the ATM protein to other DNA-damage sensors suggests a role for ATM in biochemical pathways involved in the recognition, signalling and repair of DNA double-strand breaks (DSBs). There are strong parallels between the pattern of radiosensitivity, chromosomal instability and cancer predisposition in A-T patients and that in patients with Nijmegen breakage syndrome (NBS). The protein defective in NBS, nibrin (encoded by NBS1), forms a complex with MRE11 and RAD50 (refs 1,2). This complex localizes to DSBs within 30 minutes after cellular exposure to ionizing radiation (IR) and is observed in brightly staining nuclear foci after a longer period of time3. The overlap between clinical and cellular phenotypes in A-T and NBS suggests that ATM and nibrin may function in the same biochemical pathway. Here we demonstrate that nibrin is phosphorylated within one hour of treatment of cells with IR. This response is abrogated in A-T cells that either do not express ATM protein or express near full-length mutant protein. We also show that ATM physically interacts with and phosphorylates nibrin on serine 343 both in vivo and in vitro. Phosphorylation of this site appears to be functionally important because mutated nibrin (S343A) does not completely complement radiosensitivity in NBS cells. ATM phosphorylation of nibrin does not affect nibrin-MRE11-RAD50 association as revealed by radiation-induced foci formation. Our data provide a biochemical explanation for the similarity in phenotype between A-T and NBS.
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