title: S phase cell-cycle arrest following DNA damage is independent of the p53/p21(WAF1) signalling pathway.
abstract: It is now likely that the cyclin-kinase inhibitor, p21(WAF1/SD11), is a key effector of p53-mediated cell-cycle arrest at the G(1)/S checkpoint following DNA damage. More recently, however, in vitro data has suggested that this pathway may also mediate the acute inhibition of DNA synthesis seen in cells already in S phase. Here we address this question in an intact cell system using normal human diploid fibroblasts in which p53 function is manipulated by expression of a dominant-negative mutant (ala(143)) introduced by a retroviral vector. Induction of DNA strand breaks in normal control fibroblasts by exposure to bleomycin led as expected to G(1)/S cell cycle arrest, induction of p2l(WAF1) and a rapid reduction in the rate of DNA synthesis in cells already in S phase. Stable expression of mutant p53 abrogated the G(1)/S (but not the G(2)/M) cell cycle checkpoint and abolished the induction of p21(WAF1), but had no significant effect on the inhibition of DNA replication in S phase nuclei. We conclude that, despite the in vitro evidence for inhibitory activity on PCNA/polymerase delta, p21(WAF1) induction does not appear to be essential for the acute inhibition of DNA synthesis in the intact cell following strand-break damage in S phase.
authors.affiliation: CRC Thyroid Tumour Biology Group, Department of Pathology, University of Wales College of Medicine, Cardiff, UK.
authors.forename: F S
authors.initials: FS
authors.lastname: Wyllie
authors.forename: M F
authors.initials: MF
authors.lastname: Haughton
authors.forename: J A
authors.initials: JA
authors.lastname: Bond
authors.forename: J M
authors.initials: JM
authors.lastname: Rowson
authors.forename: C J
authors.initials: CJ
authors.lastname: Jones
authors.forename: D
authors.initials: D
authors.lastname: Wynford-Thomas
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D001761:Bleomycin / Q000494:pharmacology; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis* / Q000187:drug effects; D004249:DNA Damage; D006801:Humans; D007399:Interphase / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D008297:Male; D009154:Mutation; D016196:S Phase / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: D000903:Antibiotics, Antineoplastic; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016159:Tumor Suppressor Protein p53; D001761:Bleomycin; D004247:DNA