title: Early G2/M checkpoint failure as a molecular mechanism underlying etoposide-induced chromosomal aberrations.
abstract: Topoisomerase II (Topo II) inhibitors are cell cycle-specific DNA-damaging agents and often correlate with secondary leukemia with chromosomal translocations involving the mixed-lineage leukemia/myeloid lymphoid leukemia (MLL) gene on chromosome 11 band q23 (11q23). In spite of the clinical importance, the molecular mechanism for this chromosomal translocation has yet to be elucidated. In this study, we employed 2-color FISH and detected intracellular chromosomal translocations induced by etoposide treatment. Cells such as ataxia-telangiectasia mutated-deficient fibroblasts and U2OS cells, in which the early G2/M checkpoint after treatment with low concentrations of etoposide has been lost, executed mitosis with etoposide-induced DNA double-strand breaks, and 2-color FISH signals located on either side of the MLL gene were segregated in the postmitotic G1 phase. Long-term culture of cells that had executed mitosis under etoposide treatment showed frequent structural abnormalities of chromosome 11. These findings provide convincing evidence for Topo II inhibitor-induced 11q23 translocation. Our study also suggests an important role of the early G2/M checkpoint in preventing fixation of chromosomal abnormalities and reveals environmental and genetic risk factors for the development of chromosome 11 translocations, namely, low concentrations of Topo II inhibitors and dysfunctional early G2/M checkpoint control.
authors.affiliation: Department of Pediatrics and Developmental Biology, Graduate Medical School, and Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Nakada
authors.forename: Yoko
authors.initials: Y
authors.lastname: Katsuki
authors.forename: Issei
authors.initials: I
authors.lastname: Imoto
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nagasawa
authors.forename: Johji
authors.initials: J
authors.lastname: Inazawa
authors.forename: Shuki
authors.initials: S
authors.lastname: Mizutani
mesh_terms: D001859:Bone Neoplasms; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division; D002460:Cell Line; D045744:Cell Line, Tumor; D002869:Chromosome Aberrations / Q000139:chemically induced*; D002871:Chromosome Banding; D002880:Chromosomes, Human, Pair 11; D003001:Cloning, Molecular; D005047:Etoposide / Q000494:pharmacology*; D016195:G2 Phase; D005786:Gene Expression Regulation; D015972:Gene Expression Regulation, Neoplastic; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D051788:Myeloid-Lymphoid Leukemia Protein / Q000187:drug effects / Q000235:genetics*; D012516:Osteosarcoma; D014178:Translocation, Genetic
chemical_list: C497422:KMT2A protein, human; D051788:Myeloid-Lymphoid Leukemia Protein; D005047:Etoposide; D011495:Histone-Lysine N-Methyltransferase