title: Abrogation of the S phase DNA damage checkpoint results in S phase progression or premature mitosis depending on the concentration of 7-hydroxystaurosporine and the kinetics of Cdc25C activation.
abstract: DNA damage causes cell cycle arrest in G(1), S, or G(2) to prevent replication on damaged DNA or to prevent aberrant mitosis. The G(1) arrest requires the p53 tumor suppressor, yet the topoisomerase I inhibitor SN38 induces p53 after the G(1) checkpoint such that the cells only arrest in S or G(2). Hence, SN38 facilitates comparison of p53 wild-type and mutant cells with regard to the efficacy of drugs such as 7-hydroxystaurosporine (UCN-01) that abrogate S and G(2) arrest. UCN-01 abrogated S and G(2) arrest in the p53 mutant breast tumor cell line MDA-MB-231 but not in the p53 wild-type breast line, MCF10a. This resistance to UCN-01 in the p53 wild-type cells correlated with suppression of cyclins A and B. In the p53 mutant cells, low concentrations of UCN-01 caused S phase cells to progress to G(2) before undergoing mitosis and death, whereas high concentrations caused rapid premature mitosis and death of S phase cells. UCN-01 inhibits Chk1/2, which should activate the mitosis-inducing phosphatase Cdc25C, yet this phosphatase remained inactive during S phase progression induced by low concentrations of UCN-01, probably because Cdc25C is also inhibited by the constitutive kinase, C-TAK1. High concentrations of UCN-01 caused rapid activation of Cdc25C, which is attributed to inhibition of C-TAK1, as well as Chk1/2. Hence, UCN-01 has multiple effects depending on concentration and cell phenotype that must be considered when investigating mechanisms of checkpoint regulation.
authors.affiliation: Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
authors.forename: Ethan A
authors.initials: EA
authors.lastname: Kohn
authors.forename: Nicola D
authors.initials: ND
authors.lastname: Ruth
authors.forename: Mary Kay
authors.initials: MK
authors.lastname: Brown
authors.forename: Mark
authors.initials: M
authors.lastname: Livingstone
authors.forename: Alan
authors.initials: A
authors.lastname: Eastman
mesh_terms: D000470:Alkaloids / Q000378:metabolism*; D001940:Breast / Q000166:cytology; D002166:Camptothecin / Q000031:analogs & derivatives / Q000494:pharmacology; D018797:Cell Cycle Proteins / Q000378:metabolism*; D016923:Cell Death; D002478:Cells, Cultured; D019925:Cyclin A / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D004249:DNA Damage; D004791:Enzyme Inhibitors / Q000378:metabolism*; D005260:Female; D016193:G1 Phase; D018816:Genes, cdc / Q000502:physiology*; D006801:Humans; D000077146:Irinotecan; D007700:Kinetics; D008938:Mitosis; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D016196:S Phase; D019311:Staurosporine / Q000031:analogs & derivatives; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D020687:cdc25 Phosphatases / Q000378:metabolism*
chemical_list: D000470:Alkaloids; D018797:Cell Cycle Proteins; D019925:Cyclin A; D019926:Cyclin B; D004791:Enzyme Inhibitors; D059004:Topoisomerase I Inhibitors; D016159:Tumor Suppressor Protein p53; D000077146:Irinotecan; C054852:7-hydroxystaurosporine; C111833:MARK3 protein, human; D017346:Protein Serine-Threonine Kinases; C517009:CDC25C protein, human; D020687:cdc25 Phosphatases; D019311:Staurosporine; D002166:Camptothecin