Oncogenic signaling alters cell shape and mechanics to facilitate cell division under confinement

Abstract

When cells enter mitosis, they become spherical and mechanically stiffen. We used MCF10A cell lines as a model system in which to investigate the effect of induced oncogene expression on mitotic entry. We find that activation of oncogenic Ras V12 , for as little as five hours, changes the way cells divide. Ras V12 -dependent activation of the MEK-ERK signalling cascade alters acto-myosin contractility to enhance mitotic rounding. Ras V12 also affects cell mechanics, so that Ras V12 expressing cells are softer in interphase but stiffen more upon entry into mitosis. As a consequence, Ras V12 expression augments the ability of cells to round up and divide faithfully when confined underneath a stiff hydrogel. Conversely, inhibition of the Ras-ERK pathway reduces mitotic rounding under confinement, resulting in chromosome segregation defects. These data suggest a novel mechanism by which oncogenic Ras-ERK signalling can aid division in stiff environments like those found in tumours.

EMT-induced cell mechanical changes enhance mitotic rounding strength

“…In particular, we observed a softer, less contractile cortex in post-EMT interphase cells and a more contractile, stiffer cortex phenotype in post-EMT mitotic cells in comparison to the respective pre-EMT phenotype. Our observation that post-EMT interphase cells have a softer actin cytoskeleton is in agreement with a study by Osborne et al that reported softening of adherent cells upon EMT 43 and with reports that metastatic cancer cells are on average softer than healthy and non-metastatic cells 20,[44][45][46] . Here, we show for the first time opposite changes in cell cortex mechanics in interphase and mitotic cells upon EMT (Figure 2e-g).…”

“…Thus, it has been hypothesized that the actin cortex of cancer cells exhibits oncogenic adaptations that allow for ongoing mitotic rounding and division inside tumors 19 . In fact, it was shown that the human oncogene Ect2 contributes to mitotic rounding through RhoA activation 7,10 and that Ras overexpression promotes mitotic rounding 20 . Epithelial-mesenchymal transition (EMT) is a cellular transformation in which epithelial cells loose epithelial polarity and intercellular adhesiveness gaining migratory potential [21][22][23] .…”

Mechanoaccumulation of non-muscle myosin IIB during mitosis requires its translocation activity

“…The polyacrylamide gel used for cell compression was prepared as described in Matthews et al and Le Berre et al with modifications (Le Berre et al, 2014;Matthews et al, 2020). Briefly, 18 mm glass coverslips (Sangon, F518211) were treated with 10 l Binding-silane (Sangon, C500226) for 10 minutes and then were rinsed with 100% ethanol and air-dried.…”

“…These cellular forces together lead to mitotic cell rounding that provides an ideal cell geometry to undergo mitosis and cytokinesis (Lancaster et al, 2013). Establishing and maintaining cell surface tension to sustain a minimum cell height for a functional cell geometry during mitosis is particularly important when cells are dividing in a physically confined tissue environment (Cattin et al, 2015;Matthews et al, 2020). Within a tissue environment, cells constantly experience mechanical stresses such as compressive stress from surrounding cells and the extracellular matrix.…”

“…This is particularly significant in an overgrowth tumor environment where the excessive cell proliferation, cell infiltration and matrix deposition results in an accumulation of solid stress or compressive stress inside the tumors (Nia et al, 2016;Nia et al, 2020). Cells that are not able to withstand the compressive stress during mitosis have defects in their mitotic spindle stability and form multipolar spindles that lead to chromosome mis-segregation and aneuploidy (Lancaster et al, 2013;Matthews et al, 2020). Thus, the ability to generate and sustain cell surface tension in mitotic cells in a crowded environment is important in maintaining their genome integrity (Cadart et al, 2014;Taubenberger et al, 2020).…”