The role of adsorbed proteins in animal cell adhesion

Abstract

Animal cell adhesion to extracellular matrices is a fundamental aspect of their behavior that derives from the organization of cells into large ensembles in the formation of specialized tissues and organs. Most cells in animals are adherent throughout their lives, e.g. fibroblasts and myoblasts. Even those that are not normally adherent such as the platelets and white cells in blood must undergo an adhesion step to perform their ultimate biological function. Thus, platelets adhere to matrices and each other when activated in order to stem blood flow, and neutrophils and monocytes must adhere to endothelial cells prior to their passage out of the blood to sites of inflammation and infection. Adhesion of animal cells to extracellular matrices is mediated by membrane bound receptor proteins, the integrins, that bind specifically to specialized adhesion proteins such as fibronectin, vitronectin, and fibrinogen. This paper briefly reviews the integrin receptor-extracellular adhesion protein system as well as the three known cell-cell adhesion receptor systems. Examples illustrating how the roles of the integrins and the adhesion proteins in cell attachment have been denned are presented. The adsorption behavior of the adhesion proteins fibrinogen, fibronectin, and vitronectin onto synthetic substrates, and changes in their biologic activity induced by adsorption on different surfaces, are reviewed. The concept of “substrate activation” of the adhesion proteins is also described. Some of the technological innovations based on studies of cell adhesion are presented. Finally, how the properties of the adsorbing surface might be varied in order to modulate the influence of the adsorbed proteins in cell adhesion is discussed.