Display of Cell Surface Sites for Fibronectin Assembly Is Modulated by Cell Adherence to 1F3 and C-Terminal Modules of Fibronectin

Background Fibronectin-null cells assemble soluble fibronectin shortly after adherence to a substrate coated with intact fibronectin but not when adherent to the cell-binding domain of fibronectin (modules 7 F3- 10 F3). Interactions of adherent cells with regions of adsorbed fibronectin other than modules 7 F3- 10 F3, therefore, are required for early display of the cell surface sites that initiate and direct fibronectin assembly. Methodology/Principal Findings To identify these regions, coatings of proteolytically derived or recombinant pieces of fibronectin containing modules in addition to 7 F3- 10 F3 were tested for effects on fibronectin assembly by adherent fibronectin-null fibroblasts. Pieces as large as one comprising modules 2 F3- 14 F3, which include the heparin-binding and cell adhesion domains, were not effective in supporting fibronectin assembly. Addition of module 1 F3 or the C-terminal modules to modules 2 F3- 14 F3 resulted in some activity, and addition of both 1 F3 and the C-terminal modules resulted in a construct, 1 F3-C, that best mimicked the activity of a coating of intact fibronectin. Constructs 1 F3-C V0, 1 F3-C V64, and 1 F3-C Δ(V 15 F3 10 F1) were all able to support fibronectin assembly, suggesting that 1 F3 through 11 F1 and/or 12 F1 were important for activity. Coatings in which the active parts of 1 F3-C were present in different proteins were much less active than intact 1 F3-C. Conclusions These results suggest that 1 F3 acts together with C-terminal modules to induce display of fibronectin assembly sites on adherent cells.