title: Chk1 phosphorylation at Ser286 and Ser301 occurs with both stalled DNA replication and damage checkpoint stimulation.
abstract: We previously reported Chk1 to be phosphorylated at Ser286 and Ser301 by cyclin-dependent kinase (Cdk) 1 during mitosis [T. Shiromizu et al., Genes Cells 11 (2006) 477-485]. Here, we demonstrated that Chk1-Ser286 and -Ser301 phosphorylation also occurs in hydroxyurea (HU)-treated or ultraviolet (UV)-irradiated cells. Unlike the mitosis case, however, Chk1 was phosphorylated not only at Ser286 and Ser301 but also at Ser317 and Ser345 in the checkpoint response. Treatment with Cdk inhibitors diminished Chk1 phosphorylation at Ser286 and Ser301 but not at Ser317 and Ser345 with the latter. In vitro analyses revealed Ser286 and Ser301 on Chk1 to serve as two major phosphorylation sites for Cdk2. Immunoprecipitation analyses further demonstrated that Ser286/Ser301 and Ser317/Ser345 phosphorylation occur in the same Chk1 molecule during the checkpoint response. In addition, Ser286/Ser301 phosphorylation by Cdk2 was observed in Chk1 mutated to Ala at Ser317 and Ser345 (S317A/S345A), as well as Ser317/Ser345 phosphorylation by ATR was in S286A/S301A. Therefore, Chk1 phosphorylation in the checkpoint response is regulated not only by ATR but also by Cdk2.
authors.affiliation: Division of Biochemistry, Aichi Cancer Center Research Institute, Nagoya, Aichi 464-8681, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Ikegami
authors.forename: Hidemasa
authors.initials: H
authors.lastname: Goto
authors.forename: Tohru
authors.initials: T
authors.lastname: Kiyono
authors.forename: Masato
authors.initials: M
authors.lastname: Enomoto
authors.forename: Kousuke
authors.initials: K
authors.lastname: Kasahara
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Tomono
authors.forename: Keiichi
authors.initials: K
authors.lastname: Tozawa
authors.forename: Akimichi
authors.initials: A
authors.lastname: Morita
authors.forename: Kenjiro
authors.initials: K
authors.lastname: Kohri
authors.forename: Masaki
authors.initials: M
authors.lastname: Inagaki
mesh_terms: D000071877:Checkpoint Kinase 1; D004247:DNA / Q000187:drug effects / Q000528:radiation effects; D004249:DNA Damage; D004261:DNA Replication / Q000187:drug effects / Q000528:radiation effects; D006367:HeLa Cells; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D047468:Immunoprecipitation; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D012694:Serine; D004247:DNA; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D006918:Hydroxyurea