Cells in tissues are mechanically coupled both to the ECM and neighboring cells, but the coordination and interdependency of forces sustained at cell-ECM and cell-cell adhesions are unknown. In this paper, we demonstrate that the endogenous force sustained at the cell-cell contact between a pair of epithelial cells is approximately 100 nN, directed perpendicular to the cell-cell interface and concentrated at the contact edges. This force is stably maintained over time despite significant fluctuations in cell-cell contact length and cell morphology. A direct relationship between the total cellular traction force on the ECM and the endogenous cell-cell force exists, indicating that the cell-cell tension is a constant fraction of the cell-ECM traction. Thus, modulation of ECM properties that impact cell-ECM traction alters cell-cell tension. Finally, we show in a minimal model of a tissue that all cells experience similar forces from the surrounding microenvironment, despite differences in the extent of cell-ECM and cell-cell adhesion. This interdependence of cell-cell and cell-ECM forces has significant implications for the maintenance of the mechanical integrity of tissues, mechanotransduction, and tumor mechanobiology.

During normal development and in disease, cohesive tissues undergo rearrangements that require integration of signals from cell adhesions to neighboring cells and to the extracellular matrix (ECM). How a range of cell behaviors is coordinated by these different adhesion complexes is unknown. To analyze epithelial cell motile behavior in response to combinations of cell-ECM and cell-cell adhesion cues, we took a reductionist approach at the single-cell scale by using unique, functionalized micropatterned surfaces comprising alternating stripes of ECM (collagenIV) and adjustable amounts of E-cadherin-Fc (EcadFc). On these surfaces, individual cells spatially segregated integrin-and cadherin-based complexes between collagenIV and EcadFc surfaces, respectively. Cell migration required collagenIV and did not occur on surfaces functionalized with only EcadFc. However, E-cadherin adhesion dampened lamellipodia activity on both collagenIV and EcadFc surfaces and biased the direction of cell migration without affecting the migration rate, all in an EcadFc concentration-dependent manner. Traction force microscopy showed that spatial confinement of integrin-based adhesions to collagenIV stripes induced anisotropic cell traction on collagenIV and migration directional bias. Selective depletion of different pools of αE-catenin, an E-cadherin and actin binding protein, identified a membrane-associated pool required for E-cadherin-mediated adhesion and down-regulation of lamellipodia activity and a cytosolic pool that down-regulated the migration rate in an E-cadherin adhesion-independent manner. These results demonstrate that there is crosstalk between E-cadherin-and integrin-based adhesion complexes and that E-cadherin regulates lamellipodia activity and cell migration directionality, but not cell migration rate.D uring development, cohesive tissues exhibit extensive rearrangements that range from en masse migration, such as in wound healing (1), to complex local cell rearrangements, such as cell intercalation (2). In extreme cases in development (3) and in diseases such as metastatic cancers (4), tissue cohesion is lost and single-cell migration enabled, which results in cells populating distant sites. These morphogenetic processes reveal the importance of a fine coregulation, or crosstalk, between tissue cohesion (cadherin-based cell-cell adhesion) and cell migration [integrinbased extracellular matrix (ECM) adhesion] in the maintenance of tissue integrity and function.Interest in the crosstalk between cell-cell adhesion and cell migration dates back to the pioneering studies of Abercrombie and Heaysman in the 1950s (5, 6) and even earlier (7). Abercrombie coined the term "contact inhibition" to describe how cell-cell interactions between fibroblasts initially inhibited and then redirected their migration. Whether cell-cell contact inhibition of cell migration results from cell-cell contact-dependent spatial redistribution or down-regulation of the cell migration machinery, or both remains unknown.A major component of inte...

The mechanism that drives the segregation of cells into tissuespecific subpopulations during development is largely attributed to differences in intercellular adhesion. This process requires the cadherin family of calcium-dependent glycoproteins. A widely held view is that protein-level discrimination between different cadherins on cell surfaces drives this sorting process. Despite this postulated molecular selectivity, adhesion selectivity has not been quantitatively verified at the protein level. In this work, molecular force measurements and bead aggregation assays tested whether differences in cadherin bond strengths could account for cell sorting in vivo and in vitro. Studies were conducted with chicken N-cadherin, canine E-cadherin, and Xenopus C-cadherin. Both qualitative bead aggregation and quantitative force measurements show that the cadherins cross-react. Furthermore, heterophilic adhesion is not substantially weaker than homophilic adhesion, and the measured differences in adhesion do not correlate with cell sorting behavior. These results suggest that the basis for cell segregation during morphogenesis does not map exclusively to protein-level differences in cadherin adhesion.cell adhesion ͉ force probe ͉ selectivity ͉ surface forces apparatus B oth the formation of distinct tissues during morphogenesis and the maintenance of adult tissue structure are regulated by adhesive contacts between cells. One family of adhesion proteins, cadherins, is critical to several processes associated with the formation and maintenance of tissues. The genetic regulation of the spatiotemporal expression patterns of cadherins in vivo is believed to play a central role in embryogenesis, cell differentiation, and the maintenance of the multicellular structure of an organism (1-5). One prevalent hypothesis is that differences in adhesion between cells direct cell segregation during morphogenesis, analogous to liquid-liquid phase separation (6). A fundamental unresolved question is whether this sorting out is encoded by protein-specific or cell-specific differences in adhesion. A common hypothesis is that preferential binding between identical cadherins (homophilic) relative to heterophilic binding between dissimilar cadherins induces the cell segregation.Both the adhesive and the selectivity functions of classic cadherins map to the extracellular (EC) region (7), which comprises five tandemly arranged EC domains, EC1-5, numbered from the outermost domain (Fig. 1) (8). Classical cadherins also contain a transmembrane segment and a cytoplasmic domain. Cadherins form multiple bonds that require different EC domains (9-12). A common feature of the classical cadherins is that the N-terminal domains bind by inserting the tryptophan 2 (W2) residue from one protein into a hydrophobic pocket on an opposed N-terminal domain (13-16). However, given the weak adhesion between the outer domains (11, 12), it is questionable whether the tryptophan binding accounts for both cadherin selectivity and robust adhesion.The most extensively ci...

This work describes quantitative force and bead aggregation measurements of the adhesion and binding mechanisms of canine E-cadherin mutants W2A, D134A, D103A, D216A, D325A, and D436A. The W2A mutation affects the formation of the N-terminal strand dimer, and the remaining mutations target calcium binding sites at the interdomain junctions. Surface force measurements show that the full ectodomain of canine E-cadherin forms two bound states that span two intermembrane gap distances. The outer bond coincides with adhesion between the N-terminal extracellular domains (EC1) and the inner bond corresponds to adhesion via extracellular domain 3 (EC3). The W2A, D103A, D134A, and D216A mutations all eliminated adhesion between the N-terminal domains, and they attenuated or nearly eliminated the inner bond. The W2A mutant, which does not destabilize the protein structure, attenuates binding via EC3, which is separated from the mutation by several hundred amino acids. This long-range effect suggests that the presence or absence of tryptophan-2 docking allosterically alters the adhesive function of distal sites on the protein. This finding appears to reconcile the multidomain binding mechanism with mutagenesis studies, which suggested that W2 is the sole binding interface. The effects of the calcium site mutations indicate that structural perturbations cooperatively impact large regions of the protein structure. However, the influence of the calcium sites on cadherin structure and function depends on their location in the protein.

Abstract/Summary Adhesions are a central mechanism by which cells mechanically interact with the surrounding extracellular matrix (ECM) and neighboring cells. In both cell-ECM and cell-cell adhesions, forces generated within the actin cytoskeleton are transmitted to the surrounding environment and are essential for numerous morphogenic processes. Despite differences in many molecular components that regulate cell-cell and cell-ECM adhesions, the roles of F-actin dynamics and mechanical forces in adhesion regulation are surprisingly similar. Moreover, force transmission at adhesions occurs concomitantly with dynamic F-actin; proteins comprising the adhesion of F-actin to the plasma membrane must accommodate this movement while still facilitating force transmission. Thus, despite different molecular architectures, integrin and cadherin-mediated adhesions operate with common biophysical characteristics to transmit and respond to mechanical forces in a multicellular tissue.