Mechanical force transmission at single integrin complexes in living cells (479.1)

Abstract

Mechanical interactions between cells and the extracellular matrix (ECM) play central roles in directing cell migration, proliferation, and stem‐cell differentiation. However, fundamental aspects of how cells detect and generate mechanical forces at the cell‐ECM interface remain poorly understood. Here we describe the use of molecular tension sensors to visualize the forces experienced by single cellular adhesion molecules with nanometer, piconewton, and second resolutions. The molecular tension sensors consist of a Förster resonant energy transfer (FRET) donor and acceptor pair separated by a protein domain that acts as an extensible spring. Sensor molecules are immobilized to an avidin‐coated glass coverslip at one end and present an integrin‐binding site at the other. Cellular integrins transmit force to the FRET pairs, resulting in decreased FRET with increasing load. We find that human foreskin fibroblasts (HFFs) adhere to sensor‐functionalized surfaces and develop focal adhesions as evidenced by paxillin localization and actin stress fiber formation. We observe a bimodal distribution of FRET efficiency values for sensor molecules beneath HFFs, with one peak corresponding to zero load and the other indicating a distribution of forces between 1 and 4 pN. The relatively narrow range of forces that we observe suggests that mechanical tension at individual adhesion complexes is subject to active feedback and control. Ongoing work makes use of molecular‐scale force measurements to elucidate the mechanically activated signaling events that underlie cell migration and adhesion.