POTENTIATION OF NITRIC-OXIDE SYNTHASE EXPRESSION BY SUPEROXIDE IN INTERLEUKIN 1-BETA-STIMULATED RAT MESANGIAL CELLS

Exposure of mesangial cells to superoxide, generated by the hypoxanthi ne/xanthine oxidase system or by the redox cycler 2,3-dimethoxy-1,4-na phthoquinone caused a concentration-dependent amplification of interle ukin (IL)-1 beta-stimulated nitrite production. The effect of superoxi de was accompanied by an increase in inducible nitric oxide synthase ( iNOS) protein and iNOS mRNA levels, Incubation of mesangial cells with superoxide alone did not induce iNOS expression. To elucidate whether the increase of iNOS expression is due to transcriptional upregulatio n we fused a 4.5-kb genomic iNOS fragment that contains the transcript ional start site of the rat iNOS gene to a luciferase reporter gene. I n transient transfection studies, superoxide caused a 10-fold augmenta tion of iNOS promoter activity in IL-1 beta-challenged mesangial cells . Our data identify superoxide as a co-stimulatory factor amplifying c ytokine-induced iNOS gene expression and subsequent nitric oxide (NO) synthesis. (C) 1998 Federation of European Biochemical Societies.