Prostaglandins prevent inducible nitric oxide synthase protein expression by inhibiting nuclear factor‐κB activation in J774 macrophages

Abstract

We investigated the effect of PGE₂ and iloprost (a prostacyclin analogue) on inducible nitric oxide synthase (iNOS) protein expression and nuclear factor‐κB (NF‐κB) activation in lipopolysaccharide (LPS)‐stimulated J774 macrophages. Incubation of J774 cells with LPS (10 μg/ml) caused an increase of iNOS protein expression which was prevented in a concentration‐dependent fashion by PGE₂ (0.1, 1, 10 μM) and iloprost (0.01, 0.1, 1 μM). Electrophoretic mobility shift assay indicated that both prostanoids blocked the activation of NF‐κB, a transcription factor necessary for NO synthase induction. PGE₂ and iloprost also blocked disappearance of IκB‐α from cytosolic fraction and nuclear translocation of NF‐κB subunits p50 and p65. These results show for the first time that PGE₂ and iloprost down‐regulate iNOS protein expression by inhibiting NF‐κB activation and suggest a negative feed‐back mechanism that may be important for limiting excessive or prolonged NO production in pathological events.