Key Concepts of Section 20.5

• Many cells have integrin-containing clusters of proteins (e.g., focal adhesions, 3-D adhesions, podosomes) that physically and functionally connect cells to the ECM and facilitate inside-out and outside-in signaling.

• Via interaction with integrins, the three-dimensional structure of the ECM surrounding a cell can profoundly influence the behavior of the cell.

• Integrins exist in at least two conformations (bent/inactive, straight/active) that differ in their affinity for ligands and in their interactions with cytosolic adapter proteins (see Figure 20-38); switching between these two conformations allows regulation of integrin activity, which is important for control of cell adhesion and movements.

• Dystroglycan, an adhesion receptor, forms a large complex with dystrophin, other adapter proteins, and signaling molecules (see Figure 20-39). This complex links the actin cytoskeleton to the surrounding ECM, providing mechanical stability to muscle. Mutations in various components of this complex cause different types of muscular dystrophy.

• Neural cell-adhesion molecules, which belong to the immunoglobulin (Ig) family of CAMs, mediate Ca²⁺-independent cell-cell adhesion in neural and other tissues.

• The combinatorial and sequential interaction of several types of CAMs (e.g., selectins, integrins, and ICAMs) is critical for the specific adhesion of different types of leukocytes to endothelial cells in response to local signals induced by infection or inflammation (see Figure 20-40).