Molecular mechanisms of iNOS induction by IL-1b and IFN-g in rat aortic smooth muscle cells

Teng, Xingwu, Hanfang Zhang, Connie Snead, and John D. Catravas. Molecular mechanisms of iNOS induction by IL-1b and IFN-g in rat aortic smooth muscle cells. Am J Physiol Cell Physiol 282: C144–C152, 2002;—In rat aortic smooth muscle cells (RASMC), interferon (IFN)-g enhanced nitrite accumulation and type II nitric oxide synthase (iNOS) protein expression induced by interleukin (IL)-1b. IFN-g alone had no effect on nitrite accumulation or iNOS protein. IL-1b, but not IFN-g, induced nuclear factor (NF)-kB and CCAAT box/enhancer binding protein (C/EBP) nuclear binding. Conversely, IFN-g, but not IL-1b, induced signal transducer and activator of transcription (STAT) 1 and interferon regulatory factor (IRF)-1 binding. In a 21.4-kb rat iNOS promoter segment, deletion of an IFN-g-activated site (GAS) increased IL-1b-induced activity but inhibited IFN-g-enhanced activity, suggesting a two-way effect of the GAS site on iNOS induction: enhancing induction through STAT1 activation and inhibiting induction through a non-IFN-g-mediated mechanism. Deletion of both an IRF and a C/EBP site reduced the IL-1b-induced and the IFN-g-enhanced activities. However, IRF site mutations decreased the IFN-g-enhanced activity without affecting the IL-1b-induced activity. Insertion of two IRF sites increased the IFN-g-enhanced, but not the IL-1b-induced, activity. Mutations of a reverse NF-kB site did not significantly change IFN-g-enhanced activity. We conclude that in RASMC, NF-kB and C/EBP mediate the IL-1b-induced iNOS expression, whereas IRF-1 and STAT1 mediate the IFN-g-enhanced iNOS induction.