Osteopontin is induced by nitric oxide in RAW 264.7 cells

Nitric oxide (NO) produced by macrophages is thought to contribute to vario us pathological conditions. Osteopontin (OPN) is a phosphorylated glycoprot ein produced principally by macrophages, OPN inhibits inducible nitric oxid e synthase (iNOS), which generates large amounts of NO production. However, the relationship between NO and endogenous OPN in activated macrophages ha s not yet been elucidated. We therefore examined expression of endogenous i NOS and OPN in a murine macrophage cell line, RAW 264.7 cells, by treating the cells with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma), T reatment of cells with LPS and IFN-gamma resulted in an increase of iNOS mR NA to maximum at 12 h after stimulation. In contrast, OPN mRNA was induced more slowly than iNOS mRNA, Induction of both iNOS and OPN mRNA in RAW 264. 7 cells was markedly suppressed by addition of the specific iNOS inhibitor S-2-aminoethyl isothiourea dihydrobromide, The NOS inhibitor NG-methyl-L-ar ginine also suppressed induction of OPN mRNA but hardly affected iNOS mRNA expression. The NO-releasing agent spermine-NONOate but not peroxynitrite e nhanced induction of OPN mRNA, These results suggest that NO directly up-re gulates the endogenous OPN in macrophages stimulated with LPS and IFN-gamma , This up-regulation of endogenous OPN may represent a negative feedback sy stem acting to reduce iNOS expression.