Abstract
Osteopontin (OPN) is a phosphorylated glycoprotein with a molecular weight of 60kDa secreted by activated macrophages and lymphocytes. It consists of a cell adhesive sequence, arginine-glycine-aspartic acid (RGD), at the center of its structure and a specific sequence, argnine-serine (RS), which can be cleaved with thrombin at several amino acids toward amino-terminal from the RGD sequence. OPN is a multifunctional glycoprotein, with roles in not only cell adhesion but also cell migration, cancer metastasis, angiogenesis, inhibition of inducible nitric oxide synthase, resistance to infection and suppression of antibody production from B-cells. These functions are regulated by posttranslational modification, including thrombin cleavage, glycosylation and phosphorylation. It has been shown that OPN plays an important role in granuloma formation, mycobacterium infection and cancer metastasis by several studies using the OPN knockout mouse. We have shown that OPN is involved in the pathogenesis of pulmonary fibrosis, pulmonary involvement in sarcoidosis and cancer angiogenesis. Much attention has recently been paid to the role of OPN in the pathogenesis of pulmonary diseases.
