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Matrix adhesions provide critical signals for cell growth or differentiation. Adhesion formation depends upon a number of steps that follow integrin binding to matrix ligands. In an early step, integrins form clusters that support actin polymerization by an unknown mechanism. This raises the question of how actin polymerization occurs at the integrin clusters. We report here that a major formin in mouse fibroblasts, FHOD1 is recruited to integrin clusters, resulting in actin assembly. Using cell-spreading assays on lipid bilayer, solid substrates and high-resolution force sensing pillar arrays, we find that knockdown of FHOD1 impairs spreading, coordinated application of adhesive force and adhesion maturation. Finally we show that targeting of FHOD1 to the integrin sites depends on the direct interaction with Src family kinases, and is upstream of the activation by Rho Kinase. Thus our findings provide novel insights into the mechanisms of cell migration with implications for development and disease.

Reorganization of membrane components plays an important role in signal transduction. Patterned hybrid live cell-supported membrane junctions provide spatial controls over the lateral transport of signaling molecules inside the cell. Here, we introduce a new technique which allows us to mechanically manipulate the membrane curvatures at hybrid membrane junctions. We demonstrate that large scale of protein patterns in the T cell immunological synapse can be altered merely by imposing a defined membrane curvature from supporting substrates. Our observation suggests that mechanical perturbations of membrane junctions via geometrical modulations result in decreasing actin velocity as well as remodeling actin retrograde flow. We also explore the effects of membrane diffusion barriers on cytoskeletal regulations and receptor transport processes. Flow-based particle tracking algorithms reveal that actin centripetal retrograde flow directs the inward transport of T cell receptor (TCR) clusters. We find that slower actin flow over confined TCR clusters whereas it stays the same level elsewhere. Actin flow regains its velocity after passing through confined TCR clusters. We demonstrate that the dissipated coupling of TCR clusters and actin network can feedback into a frictional coupling model.