Structure and functions of syndecans in vertebrates

Syndecans constitute a family of transmembrane proteoglycans that perform multiple functions during development, damage repair, tumor growth, angiogenesis, and neurogenesis. Through mediating binding of a great number of extracellular ligands to their receptors, these proteoglycans trigger a cascade of reactions regulating, thereby, various processes in a cell: cytoskeleton formation, proliferation, differentiation, adhesion, and migration. In fibroblasts, syndecans are responsible for cell adhesion by modulating functions of integrins through interaction with fibronectin at the external side of a cell and with cytoskeleton and signaling molecules inside the cell. The extracellular domain of syndecans is subjected to periodic shedding from the cell membrane. This process may be stimulated in response to inflammation, tissue damage, and other pathological manifestations. Cleaved domain may act as either competitive inhibitor or activator of signaling cascades. This review summarizes and analyzes the available data regarding structure, main biochemical properties, and functions of syndecans in vertebrates.