title: Chk1-dependent slowing of S-phase progression protects DT40 B-lymphoma cells against killing by the nucleoside analogue 5-fluorouracil.
abstract: Chk1 plays a crucial role in the DNA damage and replication checkpoints in vertebrates and may therefore be an important determinant of tumour cell responses to genotoxic anticancer drugs. To evaluate this concept we compared the effects of the nucleoside analogue 5-fluorouracil (5FU) on cell cycle progression and clonogenic survival in DT40 B-lymphoma cells with an isogenic mutant derivative in which Chk1 function was ablated by gene targeting. We show that 5FU activates Chk1 in wild-type DT40 cells and that 5FU-treated cells accumulate in the S phase of the cell cycle due to slowing of the overall rate of DNA replication. In marked contrast, Chk1-deficient DT40 cells fail to slow DNA replication upon initial exposure to 5FU, despite equivalent inhibition of the target enzyme thymidylate synthase, and instead accumulate progressively in the G1 phase of the following cell cycle. This G1 accumulation cannot be reversed rapidly by exogenous thymidine or removal of 5FU, and is associated with increased incorporation of 5FU into genomic DNA and severely diminished clonogenic survival. Taken together, these results demonstrate that a Chk1-dependent replication checkpoint which slows S phase progression can protect tumour cells against the cytotoxic effects of 5FU.
authors.affiliation: Beatson Institute for Cancer Research, Glasgow, UK.
authors.forename: H M R
authors.initials: HM
authors.lastname: Robinson
authors.forename: R
authors.initials: R
authors.lastname: Jones
authors.forename: M
authors.initials: M
authors.lastname: Walker
authors.forename: G
authors.initials: G
authors.lastname: Zachos
authors.forename: R
authors.initials: R
authors.lastname: Brown
authors.forename: J
authors.initials: J
authors.lastname: Cassidy
authors.forename: D A F
authors.initials: DA
authors.lastname: Gillespie
mesh_terms: D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D004261:DNA Replication; D004789:Enzyme Activation; D005472:Fluorouracil / Q000633:toxicity*; D006801:Humans; D016393:Lymphoma, B-Cell; D011494:Protein Kinases / Q000378:metabolism*; D016196:S Phase / Q000187:drug effects / Q000502:physiology*
chemical_list: D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D005472:Fluorouracil