EMT‐Induced Cell‐Mechanical Changes Enhance Mitotic Rounding Strength

Abstract

To undergo mitosis successfully, most animal cells need to acquire a round shape to provide space for the mitotic spindle. This mitotic rounding relies on mechanical deformation of surrounding tissue and is driven by forces emanating from actomyosin contractility. Cancer cells are able to maintain successful mitosis in mechanically challenging environments such as the increasingly crowded environment of a growing tumor, thus, suggesting an enhanced ability of mitotic rounding in cancer. Here, it is shown that the epithelial-mesenchymal transition (EMT), a hallmark of cancer progression and metastasis, gives rise to cell-mechanical changes in breast epithelial cells. These changes are opposite in interphase and mitosis and correspond to an enhanced mitotic rounding strength. Furthermore, it is shown that cell-mechanical changes correlate with a strong EMT-induced change in the activity of Rho GTPases RhoA and Rac1. Accordingly, it is found that Rac1 inhibition rescues the EMT-induced cortex-mechanical phenotype. The findings hint at a new role of EMT in successful mitotic rounding and division in mechanically confined environments such as a growing tumor.

EMT changes actin cortex rheology in a cell-cycle dependent manner

“…In conclusion, we observe here a trend of decreasing interphase cortical moduli and increasing mitotic cortical moduli in conjunction with increasing malignant potential. Similar trends for interphase cell mechanics in dependence of malignancy were reported previously [10,[14][15][16][17][18][19][20]. Furthermore, stiffening of mitotic cells upon cancerous transformation and EMT has been shown in [10,30].…”

“…Similar trends for interphase cell mechanics in dependence of malignancy were reported previously [10,[14][15][16][17][18][19][20]. Furthermore, stiffening of mitotic cells upon cancerous transformation and EMT has been shown in [10,30]. EMT is known to be a hallmark of cancer progression and malignancy [6,31].…”

“…EMT is commonly linked to early steps in metastasis promoting cell migration and cancer cell invasiveness [6][7][8][9]. Furthermore, EMT was shown to give rise to major changes in the molecular regulation of the actin cortex; the cytoskeletal regulator proteins RhoA and Rac1 undergo characteristic activity changes upon EMT indicating EMT-induced changes in the polymerisation process and the structure of the actin cytoskeleton [10][11][12][13]. While mechanical changes of cancer cells have been documented in many studies [10,[14][15][16][17][18][19][20], a detailed study of EMTinduced rheological changes of the actin cortex is still lacking.…”

Binding Dynamics of α-Actinin-4 in Dependence of Actin Cortex Tension

“…We previously showed that large cell surface tension in mitosis drives cells into droplet shapes with constant mean curvature in mechanical confinement. Using the previously developed analysis scheme for such droplet-shaped cells, we could determine cortical tension of measured cells from the corresponding AFM readout and cellular imaging 11,12,17,18 . We first investigated a HeLa cell line with GFP-labeled α-actinin-4 (Actn4-EGFP).…”

“…To increase fluorescence intensity, the aperture of the pinhole was set to 3 Airy units corresponding to an optical section thickness of 6 µm. Stationary state AFM forces were used to calculate cortical tension as described previously 12,17 . Briefly, as part of this analysis, cell height and cross-sectional area of the cell in the equatorial plane were used to estimate cell volume and other geometrical parameters (contact area, mean curvature) as described in 12 .…”