title: Chk1 regulates the S phase checkpoint by coupling the physiological turnover and ionizing radiation-induced accelerated proteolysis of Cdc25A.
abstract: 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.
authors.affiliation: Danish Cancer Society, Institute of Cancer Biology, Strandboulevarden 49, DK-2100 Copenhagen Ø, Denmark.
authors.forename: Claus Storgaard
authors.initials: CS
authors.lastname: Sørensen
authors.forename: Randi G
authors.initials: RG
authors.lastname: Syljuåsen
authors.forename: Jacob
authors.initials: J
authors.lastname: Falck
authors.forename: Tine
authors.initials: T
authors.lastname: Schroeder
authors.forename: Lars
authors.initials: L
authors.lastname: Rönnstrand
authors.forename: Kum Kum
authors.initials: KK
authors.lastname: Khanna
authors.forename: Bin-Bing
authors.initials: BB
authors.lastname: Zhou
authors.forename: Jiri
authors.initials: J
authors.lastname: Bartek
authors.forename: Jiri
authors.initials: J
authors.lastname: Lukas
mesh_terms: 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
chemical_list: 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