Osteopontin: a protein with diverse functions

Abstract

In this review most of the various known, suspected, or postulated functions of osteopontin, a secreted highly acidic phosphoprotein, are discussed in terms of what we currently know about the protein. These include 1 ) binding of OPN both to cells via a GRGDS cell adhesion sequence that recognizes the α v β 3 integrin and to extracellular matrix components via poorly characterized motifs, 2 ) regulation of the formation and remodeling of mineralized tissue, 3 ) recruiting and stimulating macrophages and lymphocytes as part of a nonspecific response to microbial infections, 4 ) multiple interactions with Ca 2+ that likely influence OPN protein conformation and may be important in Ca 2+ ‐mediated or Ca 2+ ‐dependent processes, 5 ) inhibiting the growth of calcium oxalate crystals by disruption of the growing crystal lattice, 6 ) effects on gene expression, Ca 2+ regulation, and nitric oxide production, and 7 ) involvement in cell migration. OPN production is frequently augmented when cell signaling pathways are activated by any of a variety of stimuli, for example in cancer cells.— Denhardt, D. T., Guo, X. Osteopontin: a protein with diverse functions. FASEB J. 7: 1475‐1482; 1993.