Hyperploidy induced by drugs that inhibit formation of microtubule promotes chromosome instability

Division of Neurosurgery, Yamaguchi University, Yamaguti, Yamaguchi, Japan
Genes to Cells (Impact Factor: 2.81). 03/2002; 7(2):151-62. DOI: 10.1046/j.1356-9597.2001.00509.x
Source: PubMed


Antimicrotubule drugs (AMDs), such as taxol and vincristine, are the most important addition to the chemotherapeutic armamentarium against human cancers. It has been shown that prolonged AMD treatment induces hyperploidy in G1-checkpoint-defective cancer cells and that these hyperploid cells subsequently undergo apoptosis. However, a fraction of these hyperploid cells are able to survive the prolonged mitotic stress and resume cell-cycle progression.
We established hyperploid clones that escaped from cell death after AMD treatment from two glioma cell lines, U251MG and U87MG. Subtractive comparative genomic hybridization (CGH) analysis revealed that clones derived from U87MG mainly had chromosome number changes, but that those from U251MG showed both numerical and structural chromosomal changes. Furthermore, numerous aberrations identified in U251MG clones were remarkably chromosome-specific, which may have been due to clonal selection for cells that have an advantage in growth and/or survival. All clones derived from both cell lines had abnormalities in chromosome segregation, and karyotypes of clones were more heterogeneous than those of parental cells, suggesting that cells having a higher chromosome number are subject to asymmetric chromosome segregation, resulting in a heterogeneous karyotype. All clones derived from U87MG and U251MG increased both centric and acentromeric micronuclei, suggesting the presence of chromosome structural abnormality.
AMD treatment induces hyperploid formation and chromosome instability in checkpoint-deficient cancer cells.

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Available from: Masayuki Nitta, Oct 09, 2014
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    • "A number of studies have demonstrated that the suppression of survivin results in cells with multipolar mitotic spindles that are either multinucleated or aneuploid (Li et al, 1999; Beltrami et al, 2004; Kappler et al, 2004). Some studies have also indicated that aneuploidy promotes chromosome instability (CIN) in glioma and cervical carcinoma cells (Nitta et al, 2002; Olaharski et al, 2006). Chromosome instability generally results from mitotic defects, and it promotes tumour progression. "
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    ABSTRACT: Glioblastoma is characterised by invasive growth and a high degree of radioresistance. Survivin, a regulator of chromosome segregation, is highly expressed and known to induce radioresistance in human gliomas. In this study, we examined the effect of survivin suppression on radiosensitivity in malignant glioma cells, while focusing on centrosome aberration and chromosome instability (CIN). We suppressed survivin by small interfering RNA transfection, and examined the radiosensitivity using a clonogenic assay and a trypan blue exclusion assay in U251MG (p53 mutant) and D54MG (p53 wild type) cells. To assess the CIN status, we determined the number of centrosomes using an immunofluorescence analysis, and the centromeric copy number by fluorescence in situ hybridisation. As a result, the radiosensitisation differed regarding the p53 status as U251MG cells quickly developed extreme centrosome amplification (=CIN) and enhanced the radiosensitivity, while centrosome amplification and radiosensitivity increased more gradually in D54MG cells. TUNEL assay showed that survivin inhibition did not lead to apoptosis after irradiation. This cell death was accompanied by an increased degree of aneuploidy, suggesting mitotic cell death. Therefore, survivin inhibition may be an attractive therapeutic target to overcome the radioresistance while, in addition, proper attention to CIN (centrosome number) is considered important for improving radiosensitivity in human glioma.
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    • "SIRT2 prevents microtubule poison-induced hyperploid cell formation via a block of entry to chromosome condensation After the prolonged exposure to nocodazole, U251MG cells, which carry a p53 mutation (Alonso et al., 2003), undergo a transient arrest at mitosis and subsequently escape from mitotic arrest and then undergo DNA replication , but they do not complete chromosome segregation and cell division. This phenomenon is termed 'mitotic slippage' and represents a failure to maintain a mitotic arrested state (Di Leonardo et al., 1997; Nitta et al., 2002). As a result of mitotic slippage, U251MG cells undergo DNA re-replication and form hyperploid cells, which are considered to be a frequent precursor of aneuploidy during tumorigenesis (Shackney et al., 1989). "
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    ABSTRACT: We previously identified SIRT2, an nicotinamide adenine dinucleotide (NAD)-dependent tubulin deacetylase, as a protein downregulated in gliomas and glioma cell lines, which are characterized by aneuploidy. Other studies reported SIRT2 to be involved in mitotic progression in the normal cell cycle. We herein investigated whether SIRT2 functions in the mitotic checkpoint in response to mitotic stress caused by microtubule poisons. By monitoring chromosome condensation, the exogenously expressed SIRT2 was found to block the entry to chromosome condensation and subsequent hyperploid cell formation in glioma cell lines with a persistence of the cyclin B/cdc2 activity in response to mitotic stress. SIRT2 is thus a novel mitotic checkpoint protein that functions in the early metaphase to prevent chromosomal instability (CIN), characteristics previously reported for the CHFR protein. We further found that histone deacetylation, but not the aberrant DNA methylation of SIRT2 5'untranslated region is involved in the downregulation of SIRT2. Although SIRT2 is normally exclusively located in the cytoplasm, the rapid accumulation of SIRT2 in the nucleus was observed after treatment with a nuclear export inhibitor, leptomycin B and ionizing radiation in normal human fibroblasts, suggesting that nucleo-cytoplasmic shuttling regulates the SIRT2 function. Collectively, our results suggest that the further study of SIRT2 may thus provide new insights into the relationships among CIN, epigenetic regulation and tumorigenesis.
    Preview · Article · Mar 2007 · Oncogene
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    • "This conclusion is compatible with analyses of human chromosomes in aneuploid cancer cells and cell lines, which show that the frequencies of both structural [19] [29] [43] [44] and numerical [47] [48] [49] [50] chromosome alterations are relatively low in near-diploid, but are high in near-triploid cells. Indeed, Masuda and Takahashi [29] have already suspected " some overlap in their underlying mechanisms, " because " both [chromosome] alterations occur in the same cells " ; however, the rates of spontaneous structural alterations of chromosomes of aneuploid human cells, except those that contain the highly aneuploidogenic viral T-antigen [12] [13], appear to be lower than those of aneuploid CH cells (R. Li and P. Duesberg, unpublished observations). "
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    ABSTRACT: Structurally altered or marker chromosomes are the cytogenetic hallmarks of cancer cells, but their origins are still debated. Here we propose that aneuploidy, which is ubiquitous in cancer and inevitably unbalances thousands of synergistic genes, destabilizes the structure of chromosomes by catalyzing DNA breaks. Aneuploidy catalyzes such breaks by unbalancing teams of enzymes, which synthesize and maintain DNA and nucleotide pools, and even unbalancing histones via the corresponding genes. DNA breaks then initiate deletions, amplifications, and intra- and interchromosomal rearrangements. Our hypothesis predicts that the rate at which chromosomes are altered is proportional to the degree of aneuploidy: the more abnormal the number and balance of chromosomes, the higher the rate of structural alterations. To test this prediction, we have determined the rates at which clonal cultures of diploid and aneuploid Chinese hamster cells generate new, and thus nonclonal, structurally altered chromosomes per mitosis. Based on about 20 metaphases, the number of new, structurally altered chromosomes was 0 per diploid, 0-0.23 per near-diploid, 0.2-1.4 per hypotriploid, 3.25-4.8 per hypertriploid, and 0.4 per near-tetraploid cell. Thus, instability of chromosome structure increases exponentially with the deviation of ploidy from the normal diploid and tetraploid balances. The particular chromosomes engaged in aneuploidy also affected the rates of chromosome alteration, particularly at low aneuploidy indices. We conclude that aneuploidy is sufficient to cause structural instability of chromosomes. Further, we suggest that certain structurally altered chromosomes encode cancer-specific phenotypes that cannot be generated by unbalancing intact chromosomes. We also extend the evidence for aneuploidy causing numerical instability of chromosomes autocatalytically, and adduce evidence that aneuploidy can cause the many gene mutations of cancer cells that have been attributed to various mutator genes.
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