Asnacios, A. | bioRxiv Science

bioRxiv2020

Intracellular stiffening competes with cortical softening in glioblastoma cells

Cancer cell softening increases with the progression of the disease, suggesting that mechanical phenotyping could be used as a diagnostic or prognostic method. Here we investigate the cell mechanics of gliomas, brain tumors that originate from glial cells or glial progenitors. We use two microrheology techniques, a single cell parallel plates rheometer to probe whole cell mechanics and optical-tweezers to probe intracellular rheology. We show that cell mechanics discriminates human glioma cells of different grades. When probed globally, grade IV glioblastoma cells are softer than grade III astrocytoma cells, while they are surprisingly stiffer at the intracellular level. We explain this difference between global and local intracellular behaviours by changes in the composition and spatial organization of the cytoskeleton and by changes in nuclear mechanics. Our study highlights the need to combine rheology techniques for potential diagnostic or prognostic methods based on cancer cell mechanophenotyping.

biophysics↗

bioRxiv2019

Vinculin targeting by Shigella IpaA promotes stable cell adhesion independent of mechanotransduction

The Shigella effector IpaA co-opts the focal adhesion protein vinculin to promote bacterial invasion. Here, we show that IpaA triggers an unreported mode of vinculin activation through the cooperative binding of its three vinculin-binding sites (VBSs) leading to vinculin oligomerization via its D1 and D2 head subdomains and highly stable adhesions resisting actin relaxing drugs. Using cross-linking mass spectrometry, we found that while IpaA VBSs1-2 bound to D1, IpaA VBS3 interacted with D2, a subdomain masked to other known VBSs. Structural modeling indicated that as opposed to canonical activation linked to interaction with D1, these combined VBSs interactions triggered major allosteric changes leading to D1D2 oligomerization. A cysteine-clamp preventing these changes and D1D2 oligomerization impaired growth of vinculin microclusters and cell adhesion. We propose that D1D2-mediated vinculin oligomerization occurs during the maturation of adhesion structures to enable the scaffolding of high-order vinculin complexes, and is triggered by Shigella IpaA to promote bacterial invasion in the absence of mechanotransduction. SummaryThe Shigella IpaA effector binds to cryptic vinculin sites leading to oligomerization via its head domain. This vinculin oligomerization mode appears required for the maturation and strengthening of cell adhesion but is co-opted by invasive bacteria independent of actomyosin contractility.

microbiology↗