The ATM-Chk2-Cdc25A checkpoint pathway guards against radioresistant DNA synthesis.
When exposed to ionizing radiation (IR), eukaryotic cells activate checkpoint pathways to delay the progression of the cell cycle. Defects in the IR-induced S-phase checkpoint cause 'radioresistant DNA synthesis', a phenomenon that has been identified in cancer-prone patients suffering from ataxia-telangiectasia, a disease caused by mutations in the ATM gene. The Cdc25A phosphatase activates the cyclin-dependent kinase 2 (Cdk2) needed for DNA synthesis, but becomes degraded in response to DNA damage or stalled replication. Here we report a functional link between ATM, the checkpoint signalling kinase Chk2/Cds1 (Chk2) and Cdc25A, and implicate this mechanism in controlling the S-phase checkpoint. We show that IR-induced destruction of Cdc25A requires both ATM and the Chk2-mediated phosphorylation of Cdc25A on serine 123. An IR-induced loss of Cdc25A protein prevents dephosphorylation of Cdk2 and leads to a transient blockade of DNA replication. We also show that tumour-associated Chk2 alleles cannot bind or phosphorylate Cdc25A, and that cells expressing these Chk2 alleles, elevated Cdc25A or a Cdk2 mutant unable to undergo inhibitory phosphorylation (Cdk2AF) fail to inhibit DNA synthesis when irradiated. These results support Chk2 as a candidate tumour suppressor, and identify the ATM-Chk2-Cdc25A-Cdk2 pathway as a genomic integrity checkpoint that prevents radioresistant DNA synthesis.
Falck
J
J
Institute of Cancer Bioloyg, Danish Cancer Society, Copenhagen, Denmark.
Mailand
N
N
Syljuåsen
R G
RG
Bartek
J
J
Lukas
J
J
D000483:Alleles; D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000235:genetics* / Q000528:radiation effects; D018797:Cell Cycle Proteins; D002460:Cell Line; D064447:Checkpoint Kinase 2; D004261:DNA Replication / Q000528:radiation effects*; D004268:DNA-Binding Proteins; D006801:Humans; D051379:Mice; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011836:Radiation Tolerance; D011839:Radiation, Ionizing; D016196:S Phase / Q000528:radiation effects; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D025521:Tumor Suppressor Proteins; D020687:cdc25 Phosphatases / Q000502:physiology* / Q000528:radiation effects
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D025521:Tumor Suppressor Proteins; D012694:Serine; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; C578634:CHEK2 protein, human; C578633:Chek2 protein, mouse; D017346:Protein Serine-Threonine Kinases; C517004:CDC25A protein, human; C517005:Cdc25a protein, mouse; D020687:cdc25 Phosphatases