ASBESTOS INDUCTION OF NUCLEAR TRANSCRIPTION FACTORS AND INTERLEUKIN-8GENE-REGULATION

Proinflammatory cytokines and chemotactic peptides are strongly implic ated as mediators of the pathophysiologic responses of asbestosis and other chronic inflammatory lung diseases. Recent studies in our labora tory have demonstrated that asbestos fibers stimulate lung epithelial cells to produce interleukin-8 (IL-8), the major neutrophil chemoattra ctant in the lung. The mechanisms by which asbestos regulates IL-8 exp ression were studied using the pulmonary type II-like epithelial cell line A549. Membrane permeable hydroxyl scavengers inhibited asbestos i nduced IL-8 expression. Using A549 cells transfected with the -546 IL- 8 construct linked to a chloramphenicol acetyl transferase reporter ge ne, we have shown that these antioxidants directly inhibited asbestos- stimulated IL-8 promoter-dependent transcription. Asbestos fibers as w ell as reactive oxygen species generating systems hypoxanthine-xanthin e oxidase and hydrogen peroxide stimulated DNA binding activity to the regulatory elements in the IL-8 promoter, binding sites of nuclear fa ctor (NF)-kappa B- and NF-IL-6-like transcription factors. Asbestos-in ducible DNA binding activity was partially inhibited by tetramethylthi ourea, a hydroxyl radical scavenger. IL-8 secretion was also suppresse d by staurosporine, an inhibitor of protein kinase C, and by inhibitor s of tyrosine kinase such as herbimycin A and genistein. The suppressi on paralleled the effect of these inhibitors on asbestos-induced DNA b inding to the NF-kappa B- and NF-IL-6-like binding sites of the IL-8 p romoter. Taken together, the results suggest that asbestos-induced red ox changes and phosphorylation events, mediated by staurosporine-sensi tive and tyrosine kinase(s), activate nuclear proteins which recognize the NF-kappa B/NF-IL-6 binding sites of the IL-8 promoter and contrib ute to the regulation of IL-8 gene expression.