title: p21CDKN1A allows the repair of replication-mediated DNA double-strand breaks induced by topoisomerase I and is inactivated by the checkpoint kinase inhibitor 7-hydroxystaurosporine.
abstract: This study provides evidence for the importance of p21(CDKN1A) for the repair of replication-mediated DNA double-strand breaks (DSBs) induced by topoisomerase I. We report that defects of p21(CDKN1A) and p53 enhance camptothecin-induced histone H2AX phosphorylation (gammaH2AX), a marker for DNA DSBs. In human colon carcinoma HCT116 cells with wild-type (wt) p53, gammaH2AX reverses after camptothecin removal. By contrast, gammaH2AX increases after camptothecin removal in HCT116 cells deficient for p53 (p53-/-) or p21(CDKN1A) (p21-/-) as the cells reach the late-S and G2 phases. Since p21-/- cells exhibit similar S-phase arrest as wt cells in response to camptothecin and aphidicolin does not abrogate the enhanced gammaH2AX formation in p21-/- cells, we conclude that enhanced gammaH2AX formation in p21-/- cells is not due to re-replication. The cell cycle checkpoint abrogator and Chk1/Chk2 inhibitor 7-hydroxystaurosporine (UCN-01) also increases camptothecin-induced gammaH2AX formation and inhibits camptothecin-induced p21(CDKN1A) upregulation in HCT116 wt cells. TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling) assays demonstrate that gammaH2AX formation in late S and G2 cells following CPT treatment corresponds to DNA breaks. However, these breaks are not related to apoptotic DNA fragmentation. We propose that p21(CDKN1A) prevents the collapse of replication forks damaged by stabilized topoisomerase I cleavage complexes.
authors.affiliation: Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: T
authors.initials: T
authors.lastname: Furuta
authors.forename: R L
authors.initials: RL
authors.lastname: Hayward
authors.forename: L-H
authors.initials: LH
authors.lastname: Meng
authors.forename: H
authors.initials: H
authors.lastname: Takemura
authors.forename: G J
authors.initials: GJ
authors.lastname: Aune
authors.forename: W M
authors.initials: WM
authors.lastname: Bonner
authors.forename: M I
authors.initials: MI
authors.lastname: Aladjem
authors.forename: K W
authors.initials: KW
authors.lastname: Kohn
authors.forename: Y
authors.initials: Y
authors.lastname: Pommier
mesh_terms: D016590:Aphidicolin / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D019457:Chromosome Breakage; D003110:Colonic Neoplasms / Q000188:drug therapy / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000037:antagonists & inhibitors / Q000502:physiology*; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000502:physiology*; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000494:pharmacology*; D045325:HCT116 Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D016196:S Phase / Q000187:drug effects; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology
chemical_list: D050759:Cyclin-Dependent Kinase Inhibitor p21; C468783:H2AX protein, human; D006657:Histones; D047428:Protein Kinase Inhibitors; D016159:Tumor Suppressor Protein p53; D016590:Aphidicolin; C054852:7-hydroxystaurosporine; D004247:DNA; D011493:Protein Kinase C; D004264:DNA Topoisomerases, Type I; D019311:Staurosporine