Cytoskeletal mechanics in confluent epithelial cells probed through integrins and E-cadherins

Mechanical forces associated with the cytoskeleton (CSK) and transmitted to adjacent cells or to the extracellular matrix (ECM) influence cellular functions. We investigated the force transfer across cell-to-ECM and cell- to-cell connections using magnetic twisting cytometry. We probed the CSK through integrins and E-cadherins in confluent epithelial cell lines (MCF7). At high applied stress (>10 dyn/cm²), stiffness (stress/strain) of the CSK coupled through integrins was greater than stiffness coupled through E- cadherins. The stiffness reduction after microfilament or microtubule disruption with cytochalasin D or colchicine was greater for integrins. At low applied stress, disruption of microfilaments had very little effect on stiffness probed through either receptor type, indicating a correspondingly small contribution of microfilaments to the CSK mechanics in these confluent cells. This differs from results in nonconfluent MCF7 cells and from predictions that are based on prestressed models in which tensile stresses presumably associated with the microfilaments are the origin of prestress and, in consequence, cell stiffness. In addition, there was substantial cell spreading on collagen I-coated dishes, in contrast to little spreading on dishes coated with E-cadherin antibody. This result, together with observations of a relatively high cell stiffness probed through integrins compared with the small stiffness probed through E-cadherins, suggests that mechanical force transmission might also be important in regulating cell spreading. We conclude that the degree of confluency may be associated with different mechanics and functions of the CSK network.