Measuring cell adhesion forces during the cell cycle by force spectroscopy

Force spectroscopy has been used to measure the adhesion of Saos-2 cells to a glass surface at different phases of the cell cycle. The cells were synchronized in three phases of the cell cycle: G(1), S, and G(2)M. Cells in these phases were compared with unsynchronized and native mitotic cells. Individual cells were attached to an atomic force microscope cantilever, brought into brief contact with the glass surface, and then pulled off again. The force-distance curves obtained allowed the work and maximum force of detachment as well as the number, amplitude, and position of discrete unbinding steps to be determined. A statistical analysis of the data showed that the number of binding proteins or protein complexes present at the cell surface and their binding properties remain similar throughout the cell cycle. This, despite the huge changes in cell morphology and adhesion that occur as the cells enter mitosis. These changes are rather associated with the changes in cytoskeletal organization, which can be quantified by force spectroscopy as changes in cell stiffness.