Requirements for alpha 5 beta 1 integrin-mediated retraction of fibronectin-fibrin matrices

Retraction of the blood clot by nucleated cells contributes both to hemosta sis and to tissue remodeling. Although plasma fibronectin (FN) is a key com ponent of the clot, its role in clot retraction is unclear. In this report, we demonstrate that the incorporation of FN into fibrin matrices significa ntly improves clot retraction by nucleated cells expressing the integrin al pha(5)beta(1). Further, we show that FN-fibrin clots support increased cell spreading when compared with fibrin matrices. To determine the structural requirements for FN in this process, recombinant FN monomers deficient in l igand binding or fibrin cross-linking were incorporated into fibrin clots. We show that recombinant FN monomers support clot retraction by Chinese ham ster ovary cells expressing the integrin alpha(5)beta(1). This process depe nds on both the Arg-Gly-Asp (RGD) and the synergy cell-binding sites and on covalent FN-fibrin binding, demonstrating that cross-linking within the cl ot is important for cell-FN interactions. These data show that alpha(5)beta (1) can bind to FN within a clot to promote clot retraction and support cel l shape change. This provides strong evidence that alpha(5)beta(1)-FN inter actions may contribute to the cellular events required for wound contractio n.