Integrin dynamics and matrix assembly: Tensin-dependent translocation of alpha(5)beta(1) integrins promotes early fibronectin fibrillogenesis

Fibronectin matrix assembly is a multistep, integrin-dependent process,To i nvestigate the role of integrin dynamics in fibronectin fibrillogenesis, we developed an antibody-chasing technique for simultaneous tracking of two i ntegrin populations by different antibodies. We established that whereas th e vitronectin receptor alpha(v)beta(3) remains within focal contacts, the f ibronectin receptor alpha(5)beta(1) translocates from focal contacts into a nd along extracellular matrix (ECM) contacts. This escalator-like transloca tion occurs relative to the focal contacts at 6.5 +/- 0.7 mu m/h and is ind ependent of cell migration. It is induced by ligation of alpha(5)beta(1) in tegrins and depends on interactions with a functional actin cytoskeleton an d vitronectin receptor ligation. During cell spreading, translocation of li gand-occupied alpha(5)beta(1) integrins away from focal contacts and along bundles of actin filaments generates ECM contacts. Tensin is a primary cyto skeletal component of these ECM contacts, and a novel dominant-negative inh ibitor of tensin blocked ECM contact formation, integrin translocation, and fibronectin fibrillogenesis without affecting focal contacts. We propose t hat translocating alpha(5)beta(1) integrins induce initial fibronectin fibr illogenesis by transmitting cytoskeleton-generated tension to extracellular fibronectin molecules. Blocking this integrin translocation by a variety o f treatments prevents the formation of ECM contacts and fibronectin fibrill ogenesis. These studies identify a localized, directional, integrin translo cation mechanism for matrix assembly.