Role of transcription factor NF-kappaB in asbestos-induced TNFalpha response from macrophages

Asbestos exposure in humans is associated with inflammatory, fibrotic, and malignant diseases in the lung. Increasing evidence supports the hypothesis that the production of proinflammatory cytokines such as tumor necrosis factor-alpha (TNFalpha) is an important mediator of the pathologic responses of asbestosis. In this study, we examine the role of nuclear transcription factor-kappaB (NF-kappaB) and free oxygen radicals in asbestos-induced TNFalpha gene and protein expression in lung macrophages. Exposure of the cells to crocidolite asbestos caused a parallel increase in TNFalpha production and NF-kappaB activation, as analyzed by enzyme-linked immunosorbent assay and electrophoretic mobility shift assay. Inhibition of NF-kappaB by SN50, an inhibitor of NF-kappaB nuclear translocation, or by sequence-specific oligonucleotides directed against the NF-kappaB binding site of TNFalpha promoter attenuated the asbestos effect on TNFalpha production. Gene transfection assays using an expression plasmid containing a luciferase reporter gene and a TNFalpha-derived NF-kappaB gene promoter further indicated the dependence of NF-kappaB activation on asbestos-induced gene expression. The effects of asbestos on NF-kappaB and TNFalpha activation were inhibited by oxygen radical scavengers and were enhanced by antioxidant enzyme inhibitors. These results indicate that asbestos-induced TNFalpha gene expression is mediated through a process that involves NF-kappaB activation and free radical reactions.