title: The cell-cycle checkpoint kinase Chk1 is required for mammalian homologous recombination repair.
abstract: The essential checkpoint kinase Chk1 is required for cell-cycle delays after DNA damage or blocked DNA replication. However, it is unclear whether Chk1 is involved in the repair of damaged DNA. Here we establish that Chk1 is a key regulator of genome maintenance by the homologous recombination repair (HRR) system. Abrogation of Chk1 function with small interfering RNA or chemical antagonists inhibits HRR, leading to persistent unrepaired DNA double-strand breaks (DSBs) and cell death after replication inhibition with hydroxyurea or DNA-damage caused by camptothecin. After hydroxyurea treatment, the essential recombination repair protein RAD51 is recruited to DNA repair foci performing a vital role in correct HRR. We demonstrate that Chk1 interacts with RAD51, and that RAD51 is phosphorylated on Thr 309 in a Chk1-dependent manner. Consistent with a functional interplay between Chk1 and RAD51, Chk1-depleted cells failed to form RAD51 nuclear foci after exposure to hydroxyurea, and cells expressing a phosphorylation-deficient mutant RAD51(T309A) were hypersensitive to hydroxyurea. These results highlight a crucial role for the Chk1 signalling pathway in protecting cells against lethal DNA lesions through regulation of HRR.
authors.affiliation: Danish Cancer Society, Institute of Cancer Biology, DK-2100 Copenhagen, Denmark.
authors.forename: Claus Storgaard
authors.initials: CS
authors.lastname: Sørensen
authors.forename: Lasse Tengbjerg
authors.initials: LT
authors.lastname: Hansen
authors.forename: Jaroslaw
authors.initials: J
authors.lastname: Dziegielewski
authors.forename: Randi G
authors.initials: RG
authors.lastname: Syljuåsen
authors.forename: Cecilia
authors.initials: C
authors.lastname: Lundin
authors.forename: Jiri
authors.initials: J
authors.lastname: Bartek
authors.forename: Thomas
authors.initials: T
authors.lastname: Helleday
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology; D000071877:Checkpoint Kinase 1; D006224:Cricetinae; D004247:DNA; D004249:DNA Damage; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D011494:Protein Kinases / Q000502:physiology*; D051135:Rad51 Recombinase; D011995:Recombination, Genetic; D015398:Signal Transduction
chemical_list: D004268:DNA-Binding Proteins; D004247:DNA; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C495153:RAD51 protein, human; D051135:Rad51 Recombinase; D006918:Hydroxyurea; D002166:Camptothecin