Multipolar mitosis and aneuploidy after chrysotile treatment: a consequence of abscission failure and cytokinesis regression

Our plain-English summary of Multipolar mitosis and aneuploidy after chrysotile treatment: a consequence of abscission failure and cytokinesis regression, by B.A. Cortez, P. Rezende-Teixeira, S. Redick, et al (Oncotarget, 2016).

The study

• Authors: B.A. Cortez, P. Rezende-Teixeira, S. Redick, S. Doxsey, G.M. Machado-Santelli
• Journal: Oncotarget
• Published: 2016;7(8):8979-92
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Chrysotile, like other types of asbestos, has been associated with mesothelioma, lung cancer and asbestosis. However, the cellular abnormalities induced by these fibers involved in cancer development have not been elucidated yet. Previous works show that chrysotile fibers induce features of cancer cells, such as aneuploidy, multinucleation and multipolar mitosis. In the present study, normal and cancer derived human cell lines were treated with chrysotile and the cellular and molecular mechanisms related to generation of aneuploid cells was elucidated. The first alteration observed was cytokinesis regression, the main cause of multinucleated cells formation and centrosome amplification. The multinucleated cells formed after cytokinesis regression were able to progress through cell cycle and generated aneuploid cells after abnormal mitosis. To understand the process of cytokinesis regression, localization of cytokinetic proteins was investigated. It was observed mislocalization of Anillin, Aurora B, Septin 9 and Alix in the intercellular bridge, and no determination of secondary constriction and abscission sites. Fiber treatment also led to overexpression of genes related to cancer, cytokinesis and cell cycle. The results show that chrysotile fibers induce cellular and molecular alterations in normal and tumor cells that have been related to cancer initiation and progression, and that tetraploidization and aneuploid cell formation are striking events after fiber internalization, which could generate a favorable context to cancer development.

In plain English

This was a laboratory study of cell cultures, not of people. The authors exposed two human cell lines to chrysotile asbestos (Chrysotile 5R, Quebec Standard) at 125 µg/ml for 24 or 48 hours. RPE-1 cells came from normal human retina epithelium, and LC-HK2 cells came from a human non-small cell lung carcinoma. In RPE-1 cells, cells with two or more nuclei were 8.2-fold more frequent than in untreated cells at 24 hours and 15-fold at 48 hours. At 48 hours, multipolar mitosis, not seen in controls, made up 17% of dividing RPE-1 cells. Time-lapse imaging showed that around 20% of dividing cells in both lines fused back into one cell with more than one nucleus at the end of division (cytokinesis regression). Several proteins needed to finish division were misplaced. Tetraploid cells (doubled chromosome number) increased in both lines. Aneuploid cells (abnormal chromosome counts) were seen in dividing cells only in the cancer line. The authors suggested that aneuploid normal cells might multiply too slowly to be detected. The authors concluded that chrysotile can induce cancer-associated characteristics in normal epithelial cells.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory (in vitro) cell-culture experiment using microscopy, time-lapse imaging, chromosome counts, flow cytometry and gene-expression measurement
• Who was studied: Two human cell lines: LC-HK2, from human non-small cell lung carcinoma, and hTERT RPE-1, derived from normal human retina epithelium. No people or animals were studied.
• Exposure: Chrysotile 5R (Quebec Standard) fibers from SAMA Mineração de Amianto Ltda (Minaçu, Brazil), added at 125 µg/ml for 24 h or 48 h. Some cultures were then given fiber-free recovery periods of 48 h, 3 or 4 days.
• Main results:
  • In RPE-1 cells, bi- and multinucleated cells combined were 8.2-fold more frequent than in control cells after 24 h of chrysotile treatment and 15-fold more frequent at 48 h.
  • In RPE-1 cells at 48 h of treatment, multipolar mitosis, which was not observed in control cells, made up 17% of mitotic cells.
  • In RPE-1 metaphase spreads, tetraploid cells were 2% in controls and rose to 10% after 48 h of chrysotile treatment. After 48 h of recovery they returned to control levels.
  • In LC-HK2 cancer cells, after 96 h of recovery the tetraploid population decreased, but the diploid population was 37%. The authors described this as a dramatic change in chromosome number.
  • Time-lapse imaging showed that around 20% of dividing RPE-1 and LC-HK2 cells regressed to form a single cell with more than one nucleus after 4 to 16 h in cytokinesis.
  • Bipolar mitotic control RPE-1 cells had 40 to 47 centromeres. Multipolar mitotic chrysotile-treated RPE-1 cells had 73 to 122 (average 96), which the authors linked to cell division failure.
  • The division protein Aurora B was properly located in about 90% of control cytokineses. After chrysotile treatment it was mislocated in 20-40% of cytokineses.
  • Secondary constriction sites (a late step of division) were present in 58% of control RPE-1 bridges and 72% of control LC-HK2 bridges. After 24 h of treatment these fell to 43% and 45%.
  • After 48 h of treatment, both cell lines showed increased expression of the AURKB and SEPT2 genes. Gene-expression differences did not exceed 2.5-fold.
  • In RPE-1 cells, the mitotic index fell from 3.2% to 1.2% after 48 h of treatment.
  • Aneuploid cells in mitosis were observed only in the cancer-derived LC-HK2 cells. In normal RPE-1 cells, aneuploid cells were not observed in metaphase spreads.
• The authors' conclusion: The authors concluded that chrysotile fibers can induce cancer-associated characteristics in normal epithelial cells and can increase these properties in cancer cells. They also concluded that the aneuploidy resulted from cytokinesis regression and tetraploidization, probably through mislocalization of Aurora B, Anillin and Septins.
• Limitations the authors state:
  • The authors noted that aneuploid RPE-1 cells might proliferate at low rates, reducing the chance of detecting them in these experiments.
  • The authors stated that the proposed cellular response delaying abscission should be further investigated.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Lung cancer.

Medical terms in this study, explained in our Lexicon: Chrysotile, Mesothelioma, Lung Cancer.

Related studies

• The fate of chrysotile-induced multipolar mitosis and aneuploid population in cultured lung cancer cells — A. Cortez Bde, G. Quassollo, et al. (2011)
• Chromosome nondisjunction during bipolar mitoses of binucleated intermediates promote aneuploidy formation along with multipolar mitoses rather than chromosome loss in micronuclei induced by asbestos — T. Zhang, L. Lv, et al. (2017)
• Chrysotile effects on human lung cell carcinoma in culture: 3-D reconstruction and DNA quantification by image analysis — B.A. Cortez, G.M. Machado-Santelli (2008)
• Induction by asbestos fibers of anaphase abnormalities: mechanism for aneuploidy induction and possibly carcinogenesis — T.W. Hesterberg, J.C. Barrett (1985)
• Intracellular protein binding to asbestos induces aneuploidy in human lung fibroblasts — R.A. MacCorkle, S.D. Slattery, et al. (2006)
• Detection of aneuploidy-inducing carcinogens in the Syrian hamster embryo (SHE) cell transformation assay — D.P. Gibson, M.J. Aardema, et al. (1995)

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