Fibronectin.

The current knowledge of the structure, expression and functions and fibronectin is reviewed. Fibronectin is a high molecular glycoprotein present in the blood, connective tissue and at cell surface. It is synthesized by many types of differentiated cells and is believed to be involved in the attachment of cells to the surrounding extracellular matrix. Fibronectin has affinity to the other main components of extracellular matrix, collagen and glycosaminoglycans. It also interacts with cell surfaces as shown by the fact that fibronectin-collagen complexes, or fibronectin alone when insolubilized on a surface such as plastic, enhances the attachment of various types of cells to such surfaces. It seems that fibronectin, through its binding to collagen and to the cell surface, forms a bridge between the cell and its surrounding matrix. Circulating fibronectin may participate in the formation of extracellular matrix in tissues. It may also function as a nonspecific opsonin design to facilitate the uptake of tissue debris by phagocytic cells. Studies aimed at elucidating the significance of fibronectin in physiological phenomena and in disease have only just begun. The abundance of fibronectin in basement membrane structures and the development changes observed in its expression lead one to believe that the attachment (or lack of it) of cells to fibronectin plays a significant role in morphogenetic events or in normal development. Malignantly transformed cells tend to lack cell-associated fibronectin. The significance of the lack of surface fibronectin in transformed cells is a matter of some controversy, but it fibronectin is indeed the main mechanism that anchors cells to the extracellular matrix, disturbances of this mechanism could play an important role in malignancy and many other diseases.