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 ⁷F3-¹⁰F3). Interactions of adherent cells with regions of adsorbed fibronectin other than modules ⁷F3-¹⁰F3, 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 ⁷F3-¹⁰F3 were tested for effects on fibronectin assembly by adherent fibronectin-null fibroblasts. Pieces as large as one comprising modules ²F3-¹⁴F3, which include the heparin-binding and cell adhesion domains, were not effective in supporting fibronectin assembly. Addition of module ¹F3 or the C-terminal modules to modules ²F3-¹⁴F3 resulted in some activity, and addition of both ¹F3 and the C-terminal modules resulted in a construct, ¹F3-C, that best mimicked the activity of a coating of intact fibronectin. Constructs ¹F3-C V0, ¹F3-C V64, and ¹F3-C Δ(V¹⁵F3¹⁰F1) were all able to support fibronectin assembly, suggesting that ¹F3 through ¹¹F1 and/or ¹²F1 were important for activity. Coatings in which the active parts of ¹F3-C were present in different proteins were much less active than intact ¹F3-C.

Conclusions

These results suggest that ¹F3 acts together with C-terminal modules to induce display of fibronectin assembly sites on adherent cells.