Membrane invagination and vesicle formation are key steps in endocytosis and cellular trafficking. Here, we show that endocytic coat proteins with prion-like domains (PLDs) form hemispherical puncta in the budding yeast, Saccharomyces cerevisiae. These puncta have the hallmarks of biomolecular condensates and organize proteins at the membrane for actin-dependent endocytosis. They also enable membrane remodeling to drive actin-independent endocytosis. The puncta, which we refer to as endocytic condensates, form and dissolve reversibly in response to changes in temperature and solution conditions. We find that endocytic condensates are organized around dynamic protein–protein interaction networks, which involve interactions among PLDs with high glutamine contents. The endocytic coat protein Sla1 is at the hub of the protein–protein interaction network. Using active rheology, we inferred the material properties of endocytic condensates. These experiments show that endocytic condensates are akin to viscoelastic materials. We use these characterizations to estimate the interfacial tension between endocytic condensates and their surroundings. We then adapt the physics of contact mechanics, specifically modifications of Hertz theory, to develop a quantitative framework for describing how interfacial tensions among condensates, the membrane, and the cytosol can deform the plasma membrane to enable actin-independent endocytosis.

Cancer invasion through dense extracellular matrices (ECMs) is mediated by matrix metalloproteinases (MMPs) which degrade the ECM thereby creating paths for migration. However, how this degradation influences the phenotype of cancer cells is not fully clear. Here we address this question by probing the function of MMPs in regulating biophysical properties of cancer cells relevant to invasion. We show that MMP catalytic activity regulates cell spreading, motility, contractility and cortical stiffness by stabilizing integrins at the membrane and activating focal adhesion kinase. Interestingly, cell rounding and cell softening on stiff gels induced by MMP inhibition is attenuated on MMP pre-conditioned surfaces. Together, our results suggest that MMP catalytic activity regulates invasiveness of cancer cells by modulating integrins.

The progressive death of retinal ganglion cells and resulting visual deficits are hallmarks of glaucoma, but the underlying mechanisms remain unclear. In many neurodegenerative diseases, cell death induced by primary insult is followed by a wave of secondary loss. Gap junctions (GJs), intercellular channels composed of subunit connexins, can play a major role in secondary cell death by forming conduits through which toxic molecules from dying cells pass to and injure coupled neighbors. Here we have shown that pharmacological blockade of GJs or genetic ablation of connexin 36 (Cx36) subunits, which are highly expressed by retinal neurons, markedly reduced loss of neurons and optic nerve axons in a mouse model of glaucoma. Further, functional parameters that are negatively affected in glaucoma, including the electroretinogram, visual evoked potential, visual spatial acuity, and contrast sensitivity, were maintained at control levels when Cx36 was ablated. Neuronal GJs may thus represent potential therapeutic targets to prevent the progressive neurodegeneration and visual impairment associated with glaucoma.

Epithelial to mesenchymal transition (EMT), the process during which epithelial cells lose adhesions with neighbouring cells and get converted to migratory and invasive cells, is closely tied to cancer progression. Cancer progression is also marked by increased deposition and cross linking of fibrillar extracellular matrix (ECM) proteins including collagen and fibronectin, which lead to increase in ECM density and increased cell-matrix adhesions. Thus, an imbalance between cell-matrix and cell-cell adhesions underlies cancer progression. Though several experimental studies have shown a crosstalk between cell-cell and cell-matrix adhesions, the extent to which changes in ECM density can trigger EMT via formation of cell-matrix adhesions and disassembly of cell-cell adhesions remains incompletely understood. In this paper, we have developed a computational framework for studying modulation of cell-cell adhesion by ECM density, integrating findings from multiple studies that connect ECM-mediated adhesion signaling and growth factor signaling with cell-cell adhesion. Here, we have specifically tracked changes in the levels of the E-cadherin-β catenin (Eβ) complex in response to alterations in ECM density. Our results illustrate a tug-of-war between ECM density and E-cadherin in determining Eβ levels both for a single cell as well as for a cell population, with increase in ligand density weakening cell-cell adhesions and increase in E-cadherin levels counterbalancing the effect of ECM density. Consistent with model predictions, lower levels of membrane to cytoplasmic ratios of E-cadherin were observed in MCF-7 human breast cancer cells plated on substrates with increasing collagen density. By performing simulations for a heterogeneous population consisting of both normal and EMT cells, we demonstrate that ligand density and the fraction of EMT cells collectively determine the scattering potential of a cell population. Taken together, our findings are in support of a model where increase in cell-matrix adhesions negatively regulates cell-cell adhesions thereby contributing to EMT and enhanced cellular invasion.

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