Integrins—A Versatile and Old Family of Cell Adhesion Molecules

Abstract

In multicellular organisms, cell-cell contacts within a tissue as well as contacts between cells and the extracellular matrix, which scaffolds the tissue, are indispensably required for the physiological function of the tissue and its development. These cell-cell and cell-matrix interactions are mediated by cell surface proteins, termed cell adhesion molecules (CAMs). Different groups of CAMs have been discovered,¹ among which are integrins,^2–4 immunoglobulin-cell adhesion molecules (IgCAMs),⁵ cadherins,^6–8 selectins,^9,10 CD44-related molecules¹¹ and transmembrane proteoglycans.¹² The most numerous and most versatile group of CAMs are integrins. The name “integrin” was first coined by Tamkun et al,¹³ who described an integral transmembrane protein linking the extracellular matrix with the intracellular cytoskeleton. Soon it became clear that integrins not only serve this architectural function as anchoring molecules, but also play a role as receptors for extracellular matrix proteins, which transduce signals from the environment into the cell and trigger various cellular behaviors, such as cell spreading, migration and anchorage-dependent growth.⁴ In the opposite way, called inside-out signaling, the cell is also able to regulate the binding affinity of the integrin for its extracellular ligand. By binding and dragging the bound ligand along the cell surface, integrins enable the cell to change its environment.¹⁴