Receptor Family

Integrins: Adhesion receptors with signaling capabilities Integrins are cell surface molecules that are composed of two subunits. In human there are multiple chains (1-9, and B, D, E, G, H, L, M, V, and X) and eight chains (1-8). Each combination shows unique ligand specificity and signalling properties. The main role of integrins is to bridge ligands of the extracellular matrix (ECM) with the cytoskeleton. Most integrins recognize several ECM proteins, and individual matrix proteins can bind to several integrins. By recognizing cognate ECM, the integrins provide the context within which cells respond to extracellular signals. Clustering of integrins leads to cytoskeletal remodeling The extracellular region of integrin -chains typically contains seven homologous repeats where that of -chains contains a unique sequence with several cysteine-rich domains. The intracellular domain of integrins is short and shows no apparent enzymatic activity. However, a plethora of downstream molecules, including kinases, can transduce signals initiated by ligand-binding, which induces integrin molecules to cluster. Receptor clustering serves to expand the region of adhesion and at the same time influences intracellular processes such as migration, differentiation, and proliferation. Survival of a cell is dependent upon the surrounding ECM, and cell death upon detachment from specific ECMs is termed anoikis, a mechanism that delimits the spreading of cells out of their tissue boundary. Thus, cells that detach from their original location or penetrate to adjacent tissues are deterred by their contact with nonsupportive ECM. Malignant cells, in many cases, lose their integrin specificity and thus are capable of metastasizing and spreading uncontrollably. Proteins similar to mammalian integrins are present on the protozoan cell surface. Although they enable some parasitic protozoans to adhere to the epithelia of their mammalian hosts, they do not facilitate homologous aggregation of protozoans. The role of integrins as self-adhering molecules could have evolved during the emergence of metazoans. Integrins are present in C. elegans, D. melanogaster, and most likely, D. discoideum.
no tree for this subfamily