Clustering of alpha(5)beta(1) integrins determines adhesion strength whereas alpha(v)beta(3) and talin enable mechanotransduction.

A key molecular link between cells and the extracellular matrix is the binding between fibronectin and integrins alpha(5)beta(1) and alpha(v)beta(3). However, the roles of these different integrins in establishing adhesion remain unclear. We tested the adhesion strength of fibronectin-integrin-cytoskeleton linkages by applying physiological nanonewton forces to fibronectin-coated magnetic beads bound to cells. We report that the clustering of fibronectin domains within 40 nm led to integrin alpha(5)beta(1) recruitment, and increased the ability to sustain force by over six-fold. This force was supported by alpha(5)beta(1) integrin clusters. Importantly, we did not detect a role of either integrin alpha(v)beta(3) or talin 1 or 2 in maintaining adhesion strength. Instead, these molecules enabled the connection to the cytoskeleton and reinforcement in response to an applied force. Thus, high matrix forces are primarily supported by clustered alpha(5)beta(1) integrins, while less stable links to alpha(v)beta(3) integrins initiate mechanotransduction, resulting in reinforcement of integrin-cytoskeleton linkages through talin-dependent bonds.