Identification of a New Biological Function for the Integrin αvβ3: Initiation of Fibronectin Matrix Assembly

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Abstract
Fibronectin matrix assembly is a complex cellular process initiated by specific fibronectin-binding cell surface receptors. Although the integrin α5β1 has been implicated in the assembly of fibronectin matrices, fibroblastic cells derived from α5 integrin null mutant embryos assemble a fibronectin matrix. Thus, alternative receptors must support this process. Al though the platelet integrin αIIbβ3 supports fibronectin matrix assembly, its expression is restricted to platelets. We report that αvβ3 integrin, a fibronectin receptor expressed on many cell types provides an alternative pathway for the assembly of soluble fibronectin into the extracellular matrix. This process occurs independent of α5β1, is also modulated by activation, and the resulting matrix is biochemically indistinguishable from that assembled under the control of α5β1. Matrix assembly requires binding to the RGD site in the 10th type III repeat of fibronectin, as well as the participation of the amino-terminal matrix assembly domain. The participation of two distinct integrins in fibronectin matrix assembly suggests a model for the involvement of integrins in a dual system of extracellular matrix assembly and recognition controlled by intracellular activation of extracellular receptors.