Differential roles for NF-κB in endotoxin and oxygen induction of interleukin-8 in the macrophage

Abstract

The alveolar macrophage is an important source of interleukin (IL)-8 during pulmonary injury. The IL-8 gene promoter sequence contains nuclear factor (NF)-κB, NF-IL6, and activator protein (AP)-1 binding sequences. These sites may have differing regulatory roles in hyperoxia-exposed macrophages than in those stimulated by bacterial lipopolysaccharide (LPS). U-937 and THP-1 macrophage-like cells were exposed to air-5% CO2or 95% O2-5% CO2, with or without 1.0 μg/ml of LPS, and transfected with an IL-8 promoter-reporter containing NF-κB, NF-IL6, or AP-1 mutations. Hyperoxia and LPS caused additive increases in IL-8 production by U-937 cells, whereas THP-1 cells responded only to LPS. An NF-κB mutation ablated baseline and O2- and LPS-stimulated reporter activity in both cell lines, whereas NF-IL6 mutations had little effect. An AP-1 mutation had an intermediate effect. LPS, but not hyperoxia, stimulated nuclear translocation of NF-κB in both cell lines. Pharmacological blockade of NF-κB nuclear translocation ablated LPS-, but not hyperoxia-, stimulated IL-8 production. Although an intact promoter NF-κB site is crucial to macrophage IL-8 production, only LPS-stimulated production appears to require additional nuclear translocation of NF-κB.