ECM dimensionality tunes actin tension to modulate the endoplasmic reticulum and spheroid phenotype

Abstract

Primary tissue organoids and cell spheroids recapitulate tissue physiology with remarkable fidelity. We investigated how engagement with a three dimensional laminin-rich extracellular matrix supports the polarized, stress resilient spheroid phenotype of mammary epithelial cells. Cells within a three dimensional laminin-rich extracellular matrix decreased and redistributed the actin crosslinker filamin to reduce their cortical actin tension. Cells with low actin tension had increased plasma membrane protrusions that promoted negative plasma membrane curvature and fostered protein associations with the plasma membrane, consistent with efficient protein secretion. By contrast, cells engaging a laminin-rich extracellular matrix in two dimensions had high filamin-dependent cortical actin tension, exhibited compromised endoplasmic reticulum function including increased expression of PKR-like Endoplasmic Reticulum Kinase signaling effectors, and had compromised protein secretion. Cells with low filamin-mediated cortical actin tension and reduced endoplasmic reticulum stress response signaling secreted, and assembled, a polarized endogenous basement membrane and survived better, and their spheroids were more resistant to exogenous stress. The findings implicate filamin-dependent cortical actin tension in endoplasmic reticulum function and highlight a role for mechanics in organoid homeostasis.

Data driven and biophysical insights into the regulation of trafficking vesicles by extracellular matrix stiffness

“…Recent evidence indicates that tension experienced by membranes also modulates the recruitment dynamics of curvature-inducing proteins with upregulation in binding to membranes at low tension ( Kai et al., 2021 ; Mercier et al., 2020 ; Tsujita et al., 2021 ). This tension-dependent recruitment of curvature-inducing proteins combined with our model’s prediction of curvature generation by recruited proteins being sensitive to cortical tension suggests an interesting mechanosensitive regulatory axis that could be exploited to alter/hijack intracellular trafficking mechanisms by cancer cells to gain fitness advantage.…”