Force-dependent integrin-cytoskeleton linkage formation requires downregulation of focal complex dynamics by Shp2

As cells encounter new regions of the substrate, they develop bonds with new matrix molecules for migration, matrix remodeling and force generation. How cells orchestrate the assembly of adhesion sites is only partially understood. Here we show that fibroblasts deficient in the SH2 domain containing protein tyrosine phosphatase 2 (Shp2) have an increased number of immature focal complexes deficient in α-actinin. Inhibition of FAK restored α-actinin to focal complexes, whereas inhibition of RhoA did not. In correlation, adhesion site dynamics, measured by fluorescence recovery after photobleaching (FRAP) of GFP-paxillin and GFP-vinculin were dramatically increased in Shp2^-/- cells and restored to normal by FAK inhibition. Shp2^-/- cells failed to strengthen initial integrin-cytoskeleton linkages, as measured by optical tweezers and large bead assays, and were rescued by inhibition of FAK. In contrast, affinity modulation of adhesion receptors was unaffected. In addition, reinforcement correlated with α-actinin assembly through decreased dynamics. This shows for the first time that adhesion site dynamics are regulated during adhesion formation and that force-dependent strengthening of integrin-cytoskeleton linkages is correlated with α-actinin assembly and decreased adhesion site dynamics.