title: Role for casein kinase 1 in the phosphorylation of Claspin on critical residues necessary for the activation of Chk1.
abstract: The mediator protein Claspin is critical for the activation of the checkpoint kinase Chk1 during checkpoint responses to stalled replication forks. This function involves the Chk1-activating domain (CKAD) of Claspin, which undergoes phosphorylation on multiple conserved sites. These phosphorylations promote binding of Chk1 to Claspin and ensuing activation of Chk1 by ATR. However, despite the importance of this regulatory process, the kinase responsible for these phosphorylations has remained unknown. By using a multifaceted approach, we have found that casein kinase 1 gamma 1 (CK1γ1) carries out this function. CK1γ1 phosphorylates the CKAD of Claspin efficiently in vitro, and depletion of CK1γ1 from human cells by small interfering RNA (siRNA) results in dramatically diminished phosphorylation of Claspin. Consequently, the siRNA-treated cells display impaired activation of Chk1 and resultant checkpoint defects. These results indicate that CK1γ1 is a novel component of checkpoint responses that controls the interaction of a key checkpoint effector kinase with its cognate mediator protein.
authors.affiliation: Division of Biology 147-75, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Zheng
authors.initials: Z
authors.lastname: Meng
authors.forename: Luisa
authors.initials: L
authors.lastname: Capalbo
authors.forename: David M
authors.initials: DM
authors.lastname: Glover
authors.forename: William G
authors.initials: WG
authors.lastname: Dunphy
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D047389:Casein Kinase I / Q000235:genetics / Q000378:metabolism*; D059447:Cell Cycle Checkpoints; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000201:enzymology*; D004789:Enzyme Activation; D018816:Genes, cdc; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C488158:CLSPN protein, human; D029721:Drosophila Proteins; D007527:Isoenzymes; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D047389:Casein Kinase I; D000071877:Checkpoint Kinase 1; C479663:gish protein, Drosophila