Osteopontin (OPN) is a multifunctional protein. It is released by macrophages, T cells and epithelial cells. It has 261 amino acid residues with a molecular mass of 29,283 Da. Osteopontin is also called as uropontin. Osteopontin from bovine milk is highly glycosylated and phosphorylated. SPP1 gene (secreted phosphoprotein 1) codes for osteopontin. This gene is located on human chromosome 4 and cow chromosome 6. It has seven exons and six introns.
Osteopontin stimulates cell mediated responses, chemotaxis of inflammatory cells and anti-inflammatory responses. It binds to av-containing integrins and stimulate cell adhesion and migration. Osteopontin promotes Th1 type immunity.
A secreted, highly acidic, calcium binding, phosphorylated glycoprotein that is chemotactic for macrophages, smooth muscle cells, endothelial cells, and glial cells. In activated macrophages, OPN inhibits nitric oxide production and cytotoxicity. Human, mouse, rat, pig, and bovine OPN share 40% amino acid sequence identity.