Determining how variations in cell and nuclear size contribute to mitosis and tumorigenicity in cancer cells that undergo whole genome doubling

Abstract

Whole genome doubling (WGD) is a frequent event in human tumors associated with metastasis and poor prognosis. The genetic redundancy afforded by WGD is thought to attenuate the deleterious effects of gene mutations and chromosome missegregation, thereby enabling the propagation of genomic and functional diversity that promote cancer evolution. This is supported by several lines of evidence showing that WGD leads to the accumulation of aneuploidy in human cells and is sufficient to induce tumorigenesis in mice. While the genomic effects of WGD are well established, the morphological alterations that accompany WGD, such as changes to cell and nuclear size, and their functional consequences are less clear. Cell and nuclear size abnormalities are associated with cancer progression and can affect cell physiology by altering gene expression, metabolism, cytoskeletal structure, and proliferation. Prior work in non-transformed and cancer cell lines showed that tetraploid (4N) cells experience a two-fold increase in cell and nuclear size, consistent with the change in DNA content, compared to the diploid (2N) cells from which they are derived. In cancer cells, however, cell and nuclear size do not always correlate with DNA content. This suggests that we do not understand how cell and nuclear size scale in response to changes in ploidy and if this relationship contributes to tetraploid cell physiology and cancer development. Therefore, this work examines the effects of WGD on cell and nuclear size in near-2N non-transformed and cancer cell lines, and how changes in cell and nuclear size after WGD affect mitotic fidelity and tumorigenic potential. I show that cell and nuclear size do not always scale with DNA content in cancer cells that undergo WGD, resulting in 4N cancer cells that vary in size. With this experimental system, I demonstrate that the small and large 4N cells have distinct mitotic spindle geometries, which influence mitotic progression and spindle assembly checkpoint silencing. Finally, I find that cell and nuclear size after WGD are associated with cell fitness, chromosomal instability, and tumorigenicity in cancer cell lines and clinical outcome in human tumors.