INHIBITION OF INDUCIBLE NITRIC-OXIDE SYNTHASE GENE-EXPRESSION BY GLUCOCORTICOID-INDUCED PROTEIN(S) IN LIPOPOLYSACCHARIDE-STIMULATED J774 CELLS

Glucocorticoids inhibit inducible-type NO synthase activity in a Varie ty of cell types. We report here that proteins recovered from the medi um of dexamethasone-treated J774 macrophages (1, 10, 100 mu g/ml) inhi bited lipopolysaccharide-stimulated nitrite generation by 10.0 +/- 3.0 %, 32.3 +/- 5.3% and 55.0 +/- 6.0%, respectively, and inducible NO syn thase mRNA expression in these cells. Immunoblotting analysis of crude and partially purified glucocorticoid-induced proteins with an anti-l ipocortin-1 polyclonal antiserum revealed the presence of lipocortin-1 -like immunoreactive species with a molecular mass of 35-37 kDa. Furth ermore, inhibition of lipopolysaccharide-induced nitrite production by glucocorticoid-induced proteins in J774 cells was reversed by additio n of anti-lipocortin-1 neutralizing polyclonal antibody (1:60 dilution ; 4 h before lipopolysaccharide). Comparison of glucocorticoid-induced proteins inhibition of both nitrite production and inducible NO synth ase mRNA expression suggests that these effects result mainly from inh ibition of lipopolysaccharide-mediated inducible NO synthase gene expr ession. These results indicate that negative regulation of inducible N O synthase by glucocorticoids is, at least in part, mediated by glucoc orticoid-induced proteins that involve also members of the lipocortin- like superfamily. (C) 1997 Elsevier Science B.V.