The extracellular matrix or ECM holds cells together to form a tissue and allows the cells within the tissue to communicate. ECM comprises proteins such as fibronectin, collagen, laminin, etc. The most abundant protein in this space is collagen. Collagen fibers are interwoven with carbohydrate-containing protein molecules called proteoglycans. ECM allows cell migration and provides a structural scaffold at cell adhesion that anchors the cell when the extracellular matrix proteins interact with transmembrane protein receptors.

An ECM ligand binds to the receptor and changes its conformation. The receptor, in turn, changes the conformation of the microfilaments positioned just under the plasma membrane. These conformational changes induce chemical signals within the cell that reach the nucleus and turn “on” or “off” the transcription of specific DNA sections, affecting the production of associated proteins, thus changing cellular activities.

Integrins are the most prominent transmembrane receptors that mediate cell-matrix junctions like focal adhesions and hemidesmosomes. On the cytosolic side, integrins bind to actin and intermediate filaments while they bind to fibronectin and collagen in the ECM face.

Adapted from section 5.1 Components and structure, 4.2 Epithelial tissue, and 3.4 Unique characteristics of eukaryotic cells, Openstax biology 2e