Osteopontin (OPN) (also known as BSP-1, ETA-1, SPP-1 or Ric) encoded by the SPP1 gene is expressed mainly in bone. Regulation of the OPN gene is incompletely understood. Different cell types may differ in their regulatory mechanisms of the OPN gene. OPN has biological function in biomineralization, bone remodeling, immune functions, chemotaxis, cell activation and apoptosis, OPN also is associated with increased myocyte apoptosis and myocardial dysfunction. OPN is associated with many physiological and pathological processes including wound healing, bone turnover, tumorigenesis, inflammation, ischemia, and immune responses. Manipulation of plasma (or local) OPN levels may be useful in the treatment of autoimmune diseases, cancer metastasis, bone (and tooth) mineralization diseases, osteoporosis, and some forms of stress.