In the extracellular matrix, fibronectin provides essential connections to cells through interaction with integrins and other receptors that regulate cell adhesion, migration, and differentiation. Fibronectin is secreted as a large dimeric glycoprotein with subunits that range in size from 230 kDa to 270 kDa. Fibronectin is composed of three different types of modules termed type I, II, and III repeats, as well as two fibrin binding and two heparin binding domains, a collagen interaction region and cell attachment domain. The diverse set of binding domains provides fibronectin with the ability to interact simultaneously with other fibronectin molecules, other ECM components (e.g., collagens and proteoglycans), cell surface receptors, and extracellular enzymes. Plasma fibronectin (soluble dimeric form) is secreted by hepatocytes, while cellular fibronectin (dimeric or cross-linked multimeric forms), made by fibroblasts, epithelial and other cell types, is deposited as fibrils in the extracellular matrix. Fibronectin fibrilogenesis has important functions during tissue development, and during pathological progression of tissues and wound healing.
