Chk1 regulates the S phase checkpoint by coupling the physiological turnover and ionizing radiation-induced accelerated proteolysis of Cdc25A.
Chk1 kinase coordinates cell cycle progression and preserves genome integrity. Here, we show that chemical or genetic ablation of human Chk1 triggered supraphysiological accumulation of the S phase-promoting Cdc25A phosphatase, prevented ionizing radiation (IR)-induced degradation of Cdc25A, and caused radioresistant DNA synthesis (RDS). The basal turnover of Cdc25A operating in unperturbed S phase required Chk1-dependent phosphorylation of serines 123, 178, 278, and 292. IR-induced acceleration of Cdc25A proteolysis correlated with increased phosphate incorporation into these residues generated by a combined action of Chk1 and Chk2 kinases. Finally, phosphorylation of Chk1 by ATM was required to fully accelerate the IR-induced degradation of Cdc25A. Our results provide evidence that the mammalian S phase checkpoint functions via amplification of physiologically operating, Chk1-dependent mechanisms.
Sørensen
Claus Storgaard
CS
Danish Cancer Society, Institute of Cancer Biology, Strandboulevarden 49, DK-2100 Copenhagen Ø, Denmark.
Syljuåsen
Randi G
RG
Falck
Jacob
J
Schroeder
Tine
T
Rönnstrand
Lars
L
Khanna
Kum Kum
KK
Zhou
Bin-Bing
BB
Bartek
Jiri
J
Lukas
Jiri
J
D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000502:physiology* / Q000528:radiation effects; D018797:Cell Cycle Proteins; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D004261:DNA Replication / Q000528:radiation effects; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011839:Radiation, Ionizing; D016196:S Phase / Q000528:radiation effects; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; 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; C000605867:CHEK1 protein, human; C578634:CHEK2 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D020687:cdc25 Phosphatases