title: Claspin is phosphorylated in the Chk1-binding domain by a kinase distinct from Chk1.
abstract: Chk1 protein kinase plays a critical role in checkpoints that restrict progression through the cell cycle if DNA replication has not been completed or DNA damage has been sustained. ATR-dependent activation of Chk1 is mediated by Claspin. Phosphorylation of Claspin at two sites (Thr916 and Ser945 in humans) in response to DNA replication arrest or DNA damage recruits Chk1 to Claspin. Chk1 is subsequently phosphorylated by ATR and fully activated to control cell cycle progression. We show that ablation of Chk1 by siRNA in human cells or its genetic deletion in chicken DT40 cells does not prevent phosphorylation of Claspin at Thr916 (Ser911 in chicken). Chk1, however, does play other roles, possibly indirect, in the phosphorylation of Claspin and its induction. These results demonstrate that phosphorylation of Claspin within the Chk1-binding domain is catalysed by an ATR-dependent kinase distinct from Chk1.
authors.affiliation: Biomedical Research Centre, Level 5, College of Medicine Dentistry and Nursing, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland, UK.
authors.forename: Lara N
authors.initials: LN
authors.lastname: Bennett
authors.forename: Conor
authors.initials: C
authors.lastname: Larkin
authors.forename: David A
authors.initials: DA
authors.lastname: Gillespie
authors.forename: Paul R
authors.initials: PR
authors.lastname: Clarke
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D064007:Ataxia Telangiectasia Mutated Proteins; D002384:Catalysis; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D002645:Chickens / Q000235:genetics / Q000378:metabolism; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000494:pharmacology; D013912:Threonine / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C488158:CLSPN protein, human; D018797:Cell Cycle Proteins; D034741:RNA, Small Interfering; D013912:Threonine; D004247:DNA; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases