Effect of collagen and cell shape on binding of fibronectin to cells

Using quantitative immunologic methods, we have examined the binding of fibronectin to cells in suspension and in monolayer culture. Much of the fibronectin which accumulates in the cell layer is produced by the cells, while the rest is derived from the serum used in the culture medium. Cells in suspension bind less exogenous fibronectin than do cells in monolayer, but in both cases binding is enhanced two- to six-fold by the addition of soluble collagen. Serum also enhanced fibronectin binding to cells through a component(s) other than fibronectin since fibronectin-free serum had a similar effect. Certain gangliosides which are known to bind to fibronectin block the binding of fibronectin to the cell surface even in the presence of soluble collagen. The data indicate that as the cells attach to the collagen substrate, additional receptors on the cell surface become available for binding fibronectin.