Regulation of no synthesis induced by inflammatory mediators in RAW264.7 cells: Collagen prevents inhibitory by osteopontin

Osteopontin has been shown to inhibit the induction of inducible nitric oxi de synthase (iNOS, or NOS2) by lipopolysaccharide and interferon-gamma in t he RAW264.7 mouse monocyte/macrophage line and in primary mouse proximal tu bule epithelial cells. However, the RAW264.7 cells become refractory to the action of OPN after several subcultures or under dilute culture conditions , possibly because of changes in the composition of the extraacellular matr ix. We make this suggestion because if the cells are plated on a collagen t ype I or collagen type IV substrate the inhibitory action of OPN is complet ely suppressed; this is not the case on substrates consisting of laminin, f ibronectin, poly-D-lysine, or poly-(2-hydroxyethylmethylacrylate). These ob servations imply that macrophages are sensitive to regulation by OPN only i n certain physiological contexts. Both hyaluronate, which binds CD44, and r at IgCs are also able to inhibit the induction of NO synthesis by the infla mmatory mediators. The similar actions of HA and OPN are consistent with th e possibility that CD44 may be a receptor for OPN. (C) 2000 Academic Press.