Annals of the New York Academy of Sciences [ANN. N.Y. ACAD. SCI.], NEW YORK ACADEMY OF SCIENCES, NEW YORK, NY (USA), 1995, vol. 760, 388 pp.

Osteopontin (OPN) is produced by both matrix-producing osteoblasts, at the mineralization front, and by bone resorbing osteoclasts. In the kidney, it is found in the loop of Henle and the distal convoluted tubules and increases during nephritis. In blood vessels, it is found in arterial smooth muscle cells and its level increases in atherosclerotic plaques and during restenosis, following balloon angioplasty. It is also found in the inner ear and in the epithelial cells of the gallbladder, urinary and reproductive tracts, gastrointestinal tracts, mammary gland, bronchi, salivary glands and sweat ducts. OPN is secreted, binds calcium and was found to bind covalently to the ubiquitous extracellular protein fibronectin. OPN contains the GRGDS sequence recognized by several integrins and was shown in vitro to serve as an attachment substrate to several cell types, primarily via the alpha sub(v) beta sub(3) integrin. OPN thus seems to have evolved as a major player in the injury/repair cascade, fulfilling distinct functions at its various stages, many mediated by its receptor alpha sub(v) beta sub(3). Viewing this molecule in that context could explain its widespread localization, its diverse proposed functions and its response to cytokines and other stimuli.