The amino-terminal matrix assembly domain of fibronectin stabilizes cell shape and prevents cell cycle progression

Adhesion to the extracellular matrix modulates the cellular response to gro wth factors and is critical for cell cycle progression, The present study w as designed to address the relationship between fibronectin matrix assembly and cell shape or shape dependent cellular processes, The binding of fibro nectin's amino-terminal matrix assembly domain to adherent cells represents the initial step in the assembly of exogenous fibronectin into the extrace llular matrix, When added to monolayers of pulmonary artery endothelial cel ls, the 70 kDa fragment of fibronectin (which contains the matrix assembly domain) stabilized both the extracellular fibronectin matrix as well as the actin cytoskeleton against cytochalasin D-mediated structural reorganizati on. This activity appeared to require specific fibronectin sequences as fib ronectin fragments containing the cell adhesion domain as well as purified vitronectin were ineffective inhibitors of cytochalasin D-induced cytoarchi tectural restructuring. Such pronounced morphologic consequences associated with exposure to the 70 kDa fragment suggested that this region of the fib ronectin molecule may affect specific growth traits known to be influenced by cell shape. To assess this possibility, the 70 kDa fragment was added to scrape-wounded monolayers of bovine microvessel endothelium and the effect s on two shape-dependent processes (i,e, migration and proliferation) were measured as a function of time after injury and location from the wound. Th e addition of amino-terminal fragments of fibronectin to the monolayer sign ificantly inhibited (by >50%) wound closure, Staining of wounded monolayers with BrdU, moreover, indicated that either the 70 kDa or 25 kDa amino-term inal fragments of fibronectin, but not the 40 kDa collagen binding fragment , also inhibited cell cycle progression, These results suggest that the bin ding of fibronectin's aminoterminal region to endothelial cell layers inhib its cell cycle progression by stabilizing cell shape.