Cell–Matrix Adhesion

The overall architecture of a tissue is determined by adhesion mechanisms that involve not only cell-cell interactions but also cell-matrix interactions. In animals, epithelia and most organized groups of cells like muscle are surrounded or underlain by an extracellular matrix (ECM) of collagen fibers, proteoglycans, and multiadhesive matrix proteins. This layer of matrix material serves several roles. It organizes cells into tissues and coordinates their cellular functions. In addition, the matrix provides a route for cell migrations, and molecules in the matrix activate classic signal-transduction pathways that induce cell growth, proliferation, and gene expression. These many effects of the matrix involve membrane-bound CAMs that bind directly to components of the ECM and the cytoskeleton. The principal class of CAMs that mediate cell-matrix adhesion is the integrins. However, other CAMs, including selectins and syndecan proteoglycans, also bind molecules in the matrix.