Defect in the induction of nitric oxide synthase by lipopolysaccharide (LPS) in an LPS-resistant mutant of a murine macrophage-like cell line, J774.1

Abstract

Nitric oxide (.NO)-generating activity was examined in a lipopolysaccharide (LPS)-resistant mutant of a murine macrophage-like cell line, J774.1, treated with LPS or LPS and interferon-gamma (IFN-gamma). This mutant, an LPS1916 cell line, showed no NO2- accumulation in the culture medium, and no expression of NOS activity in the cell extract, .NO synthase (NOS(II)) protein or NOS(II) mRNA on treatment with up to 10(4) ng/ml LPS, although the parental cell line, JA-4, showed significant .NO production. The addition of 10 U/ml IFN-gamma, together with more than 1 ng/ml LPS to JA-4 cells, increased .NO production remarkably, while IFN-gamma did not reverse the defect of .NO production in LPS1916 cells when they were treated with less than 10 ng/ml LPS; however, it induced .NO production by the mutant cells with more than 100 ng/ml LPS. Analysis of NOS activity, NOS(II) protein and NOS(II) mRNA revealed that LPS1916 cells are not devoid of the NOS(II) gene, but are rather defective in transcription of the gene in response to LPS, and this defect is partly reversed by IFN-gamma with higher LPS doses at more than 100 ng/ml. In addition, the delay of NOS(II) mRNA induction in LPS1916 cells, compared to that in JA-4 cells, treated with LPS+IFN-gamma seems to suggest some additional inducer(s) of NOS(II) transcription, followed by LPS signaling.