Integrin adhesion receptors extracellular matrix

Figure. 4. Principle of the cell adhesion to artificial materials. In cell culture media or body fluids, the material is spontaneously adsorbed with cell adhesion-mediating extracellular matrix proteins (e g., vitronectin, fibronectin). The cells then adhere to specific amino acid sequences of these proteins by their adhesion receptors of integrin or non-integrin type [38-41].

Integrins, selectins, cadherins, claudins and other cell adhesion molecules are involved in the interaction of cells with other cells or with extracellular matrix components. Some of them also serve as receptors by inducing outside-in or additional inside-out signaling. 

Adhesion molecules such as LI, neural cell adhesion molecule (N-CAM) and N-cadherin promote axonal regeneration by homophilic interactions between axons and Schwann cell surfaces (see Ch. 7). The expression of p75 (low affinity NGF receptor, Ch. 27) is also increased at the Schwann cell surface after injury. Extracellular matrix molecules, such as tenascin and proteoglycans, increase the regenerative potential of damaged peripheral nerves by binding to integrins on the axonal surface. 

Receptors (adhesion receptors) that interact with macromolecular components of the extracellular matrix (such as collagen) and convey to the cytoskeletal system instructions on cell migration or adherence to the matrix. Integrins (discussed in Chapter 10) illustrate this general type of transduction mechanism. 

Integrins are widely expressed cell surface receptors involved in cell-cell adhesion and interactions of cells with the extracellular matrix. Integrins enable the cellular uptake of structures as large as bacteria and as small as viruses. Thus, they constitute good targets for developing selective gene delivery systems. 

Integrins are a family of transmembrane heterodimeric glycoproteins that are receptors for specific epitopes of extracellular matrix proteins and for other cell-surface molecules (Kramer et al, 1993). Integrins exist as a dimer complex composed of an a-subunit (120-180 kD) noncovalently associated with a /1-subunit (90-110 kD) (Hynes, 1992). At least 8 /1-subunits and 14 -units have been identified and are concentrated at loci, called focal adhesion sites, of close proximity between cells and extracellular matrices on substrates (Hynes, 1992). Focal adhesion sites are points of aggregation of, and are physically associated with, intracellular cytoskeletal molecules that control, direct, and modulate cell function in response to extracellular signals (Schwartz, 1992). 

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