Mechanosensitivity of Cancer Cells in Contact with Soft Substrates Using AFM

Cancer cells are usually found to be softer than normal cells, but their stiffness changes when they are in contact with different environments because of mechanosensitivity. For example, they adhere to a given substrate by tuning their cytoskeleton, thus affecting their rheological properties. This mechanism could become efficient when cancer cells invade the surrounding tissues, and they have to remodel their cytoskeleton in order to achieve particular deformations. Here we use an atomic force microscope in force modulation mode to study how local rheological properties of cancer cells are affected by a change of the environment. Cancer cells were plated on functionalized polyacrylamide substrates of different stiffnesses as well as on an endothelium substrate. A new correction of the Hertz model was developed because measurements require one to account for the precise properties of the thin, layered viscoelastic substrates. The main results show the influence of local cell rheology (the nucleus, perinuclear region, and edge locations) and the role of invasiveness. A general mechanosensitive trend is found by which the cell elastic modulus and transition frequency increase with substrate elasticity, but this tendency breaks down with a real endothelium substrate. These effects are investigated further during cell transmigration, when the actin cytoskeleton undergoes a rapid reorganization process necessary to push through the endothelial gap, in agreement with the local viscoelastic changes measured by atomic force microscopy. Taken together, these results introduce a paradigm for a new—to our knowledge—possible extravasation mechanism.