Endogenous Force Transmission Between Epithelial Cells and a Role for α-Catenin

In epithelial tissues, epithelial cells adhere to each other as well as to the underlying extra-cellular matrix (ECM). E-cadherin-based intercellular junctions play an important role in tissue integrity. These junctions experience cell-generated mechanical forces via apparent adaptor proteins such as beta (β) catenin, alpha (α) catenin and vinculin. Abnormalities in these junctions may result in skin related diseases and cancers. Here, I devised methods to determine the endogenous intercellular force within cell pairs as well as in large epithelial islands. I further ascertained the factors that affect the level of inter-cellular tension. Experiments with pairs of epithelial cells exogenously expressing either of two altered E-cadherin constructs on top of endogenous E-cadherin showed that the inter-cellular tension for these cases was similar to wild type cells. This implied that the endogenous E-cadherin was dominant in setting the level of cell-cell contact tension. To analyze intercellular force transmission within large islands, I extended the traction force imbalance method to large micro-patterned islands. It was shown that colony level intercellular forces exerted at the midline by one half of the colony on the other were tensile in nature and showed significant anisotropy with respect to the midline orientation. Finally, to determine what molecular factors set the level of tension transmitted through single cell-cell contacts, I determined the inter-cellular tension in pairs of cells with perturbed α-catenin. I found that α-catenin knockout not only decreased inter-cellular tension but also the traction forces exerted at the cell-ECM interface. This may be due to roles outside of cell-cell junctions for α-catenin. However, α-catenin mutants with altered binding to vinculin binding did not show significant differences in inter-cellular tension compared to wild type cells. Thus, α-catenin is essential for normal levels of intercellular tension, but the forces transmitted at cell-cell contacts are not very sensitive to the level of vinculin at the cell-cell contact in cell pairs. This may be because vinculin can also be recruited to cell-cell contacts by molecules other than α-catenin, such as β-catenin. These results highlight some essential and non-essential molecular factors regulating cell-cell junctional tension level