Elevated tolerance to aneuploidy in cancer cells: estimating the fitness effects of chromosome number alterations by in silico modelling of somatic genome evolution

PLoS One. 2013 Jul 24;8(7):e70445. doi: 10.1371/journal.pone.0070445. Print 2013.

Abstract

An unbalanced chromosome number (aneuploidy) is present in most malignant tumours and has been attributed to mitotic mis-segregation of chromosomes. However, recent studies have shown a relatively high rate of chromosomal mis-segregation also in non-neoplastic human cells, while the frequency of aneuploid cells remains low throughout life in most normal tissues. This implies that newly formed aneuploid cells are subject to negative selection in healthy tissues and that attenuation of this selection could contribute to aneuploidy in cancer. To test this, we modelled cellular growth as discrete time branching processes, during which chromosome gains and losses were generated and their host cells subjected to selection pressures of various magnitudes. We then assessed experimentally the frequency of chromosomal mis-segregation as well as the prevalence of aneuploid cells in human non-neoplastic cells and in cancer cells. Integrating these data into our models allowed estimation of the fitness reduction resulting from a single chromosome copy number change to an average of ≈30% in normal cells. In comparison, cancer cells showed an average fitness reduction of only 6% (p = 0.0008), indicative of aneuploidy tolerance. Simulations based on the combined presence of chromosomal mis-segregation and aneuploidy tolerance reproduced distributions of chromosome aberrations in >400 cancer cases with higher fidelity than models based on chromosomal mis-segregation alone. Reverse engineering of aneuploid cancer cell development in silico predicted that aneuploidy intolerance is a stronger limiting factor for clonal expansion of aneuploid cells than chromosomal mis-segregation rate. In conclusion, our findings indicate that not only an elevated chromosomal mis-segregation rate, but also a generalised tolerance to novel chromosomal imbalances contribute to the genomic landscape of human tumours.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aneuploidy*
  • Cells, Cultured
  • Child
  • Child, Preschool
  • Chromosome Aberrations
  • Chromosome Segregation / genetics
  • Clonal Evolution / genetics
  • Clonal Evolution / physiology
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / metabolism*
  • Fibroblasts / metabolism
  • Humans
  • In Situ Hybridization, Fluorescence
  • Infant
  • Karyotype
  • Male

Grants and funding

Funding: Swedish Childhood Cancer Foundation, Swedish Cancer Society, Swedish Research Council, Gunnar Nilsson Cancer Foundation, and the BioCare Strategic Research Programme. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.