title: Mitotic bypass via an occult cell cycle phase following DNA topoisomerase II inhibition in p53 functional human tumor cells.
abstract: Cells cycle checkpoints guard against the inapproriate commitment to critical cell events such as mitosis. The bisdioxxopiperazzine ICRF-193, a catalytic inhibitor of DNA topoisomerase II causes a reversible stalling of the exit of cells from G(2) at the decatenation checkpoint (DC) and can generate tetraploidy via the compromising of chromosome segregation and mitotic failure. We have addressed an alternative origin-endocycle entry-for the tetraploidisation step in ICRF-193 exposed cells. Here we show that DC-proficient p53-functional tumor cells can undergo a transition to tetraploidy and subbsequent aneuploidy via an initial bypass of mitosis and the mitotic spindle checkpoint. DC-deficient SV4-tranformed cells move exclusively through mitosis to tetraploidy. In p53-functional tumor cells, escape through mitosis is enhanced by dominant negative p53 co-expression. The mitotic bypass transition phase (termed G(2)(endo)) disconnects cyclin B1 degradation from nuclear envelope breakdown and allows cells to evade the action of Taxol. G(2)(endo) constitutes a novel and alternative cell cycle phase-lasting some 8 h-with distinct molecular motifs at its boundaries for G(2) exit and subsequent entry into a delayed G(1) tetraploid state. The result challenge the paradigm that checkpoint breaching leads directly to abnormal ploidy states via mitosis alone. We further propose that the induction of bypass could: facilitate the covert development of tetraploidy in p53 functional cancers, lead to a misinterpretation of phase allocation during cell cycle arrest and contribbute to tumor cell drug resistance.
authors.affiliation: Department of Pathology, University of Wales College of Medicine, Heath Park, Cardiff, UK. smithpj2@cf.ac.uk
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Smith
authors.forename: Nuria
authors.initials: N
authors.lastname: Marquez
authors.forename: Marie
authors.initials: M
authors.lastname: Wiltshire
authors.forename: Sally
authors.initials: S
authors.lastname: Chappell
authors.forename: Kerenza
authors.initials: K
authors.lastname: Njoh
authors.forename: Lee
authors.initials: L
authors.lastname: Campbell
authors.forename: Imtiaz A
authors.initials: IA
authors.lastname: Khan
authors.forename: Oscar
authors.initials: O
authors.lastname: Silvestre
authors.forename: Rachel J
authors.initials: RJ
authors.lastname: Errington
mesh_terms: D002453:Cell Cycle / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D043171:Chromosomal Instability / Q000187:drug effects; D019926:Cyclin B / Q000235:genetics / Q000378:metabolism; D056744:Cyclin B1; D003593:Cytoplasm / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D054659:Diketopiperazines; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D008938:Mitosis / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D010879:Piperazines / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
chemical_list: C534699:CCNB1 protein, human; D019926:Cyclin B; D056744:Cyclin B1; D054659:Diketopiperazines; D010879:Piperazines; D059005:Topoisomerase II Inhibitors; D016159:Tumor Suppressor Protein p53; D049452:Green Fluorescent Proteins; C070899:4,4'-(1,2-dimethyl-1,2-ethanediyl)bis-2,6-piperazinedione; D004250:DNA Topoisomerases, Type II