Regulation of interleukin-8 (IL-8) gene expresssion in THP-1 cells by organic dust

Concentrated animal feeding operation (CAFO) has become a common practice in animal production industry due to its efficiency and cost-effectiveness. Workers in CAFOs are exposed to high levels of air-borne dust containing microbial pathogens and organic and inorganic substances and are at a greater risk of developing acute respiratory symptoms and chronic lung diseases. Interleukin-8 (IL-8), a C-X-C chemokine, functions as chemotactic factor for neutrophils and T-cells and plays pivotal roles in innate immunity and inflammation. The aim of this study was to elucidate molecular mechanisms of IL-8 gene regulation by poultry dust in THP-1 monocytic cells. Results of Northern blotting and enzyme linked immunosorbent assays showed that dust extract induced IL-8 mRNA and protein levels in a time- and concentration dependent manner. Nuclear run-on assays and promoter assay by transient transfection indicated that dust extract enhanced IL-8 gene transcription to increase IL-8 mRNA levels. DNA binding and mutational studies revealed that dust extract increased AP-1 and NF-κB binding to IL-8 promoter and both AP-1 and NF-κB are necessary for the induction of promoter activity. Dust induction of IL-8 expression was associated with the activations of protein kinase C (PKC) and mitogen activated protein kinases (MAPKs) and sensitive to pharmacological inhibitors indicating the importance of PKC and MAPK signal transduction pathways in the induction. Dust treatment increased reactive oxygen species (ROS) levels in THP-1 cells as revealed by dihydroethidium (DHE) labeling. IL-8 mRNA and protein induction was suppressed by the hydroxyl radical scavenger dimethylthiourea indicating the importance of intracellular ROS for the induction. IL-8 induction was not suppressed by polymyxin B indicating that lipopolysaccharide in dust may not contribute to the induction. Dust extract displayed elastase- and trypsin-like activities and protease inhibitors reduced the IL-8 mRNA and protein levels indicating that proteases might play a role in the induction. In summary these studies have shown a. Poultry dust extract enhances AP-1 and NF-κB binding to the promoter to increase IL-8 gene transcription leading to increased IL-8 mRNA and protein levels. b. Increased levels of reactive oxygen species and activation of PKC and MAPK signaling pathways mediate dust extract induction of IL-8 expression. c. Lipopolysaccharide in dust extract is not important for IL-8 induction, but protease activity might be important.