Stimulation of integrin-mediated cell contractility by fibronectin polymerization

Ligation of integrins with extracellular matrix molecules induces the clust ering of actin and actin-binding proteins to focal adhesions, which serves to mechanically couple the matrix with the cytoskeleton, During wound heali ng and development, matrix deposition and remodeling may impart additional tensile forces that modulate integrin-mediated cell functions, including ce ll migration and proliferation. We have utilized the ability of cells to co ntract floating collagen gels to determine the effect of fibronectin polyme rization on mechanical tension generation by cells. Our data indicate that fibronectin polymerization promotes cell spreading in collagen gels and sti mulates cell contractility by a Rho-dependent mechanism, Fibronectin-stimul ated contractility was dependent on integrin ligation; however, integrin li gation by fibronectin fragments was not sufficient to induce either tension generation or cell spreading. Furthermore, treatment of cells with polyval ent RGD peptides or pre-polymerized fibronectin did not stimulate cell cont ractility. Fibronectin-induced contractility was blocked by agents that inh ibit fibronectin polymerization, suggesting that the process of fibronectin polymerization is critical in triggering cytoskeletal tension generation. These data indicate that Rho-mediated cell contractility is regulated by th e process of fibronectin polymerization and suggest a novel mechanism by wh ich extracellular matrix fibronectin regulates cytoskeletal organization an d cell function.