Adhesion formation and transformation at the cell-matrix interface

Abstract

Matrix-activated integrins form different cell-matrix adhesion structures. Extracellular microenvironment and traction forces play an important role in adhesion assembly, including focal adhesion, podosome, and cancer invadopodia. We have explored the role of force in podosome development using matrix ligands bound to fluid supported membranes that do not support traction forces. With fluid RGD-membranes, fibroblasts that normally do not form podosomes on rigid matrices will form podosomes within 45 minutes. Podosomes are defined by doughnut-shaped RGD rings and characteristic core components, including F-actin, cortactin, and Arp2/3. Here, we employ RGD-membranes with nano-partitions and demonstrate that dense partitions (lines spaced by 1μm) in RGD-membranes suppress podosome formation. Dense nano-partitioned RGD-membranes locally facilitate contractile traction force development, and cells can pull integrin clusters to the lines and generate force on them. On the other hand, when cells are unable to generate forces on clusters (e.g. with wider separations of partitions (4μm) or myosin inhibition), cells can assemble podosomes. In addition, within a single cell, clusters over continuous RGD-membranes will form podosomes whereas cluster pulled to barriers will not. Inhibition of formin or actomyosin activity does not suppress podosome formation on RGD-membrane. However, inhibition of PI3K activity or activation of RhoA-mediated cellular contractility block podosomes. The local increase of phosphatidylinositol (3,4,5)-trisphosphate level and sequential recruitment of PI3K and PTEN are associated with podosome formation process. Thus, we suggest that force on integrin clusters will stimulate regular adhesion formation, whereas PI3K activation at an integrin cluster in the absence of force will stimulate podosome formation.