Activation of Transcription Factors by Diesel Exhaust Particles in Human Bronchial Epithelial Cells in Vitro

Abstract

Diesel exhaust particles (DEP) are suspected to be involved in the aggravation of inflammatory respiratory diseases. We have shown previously, in human bronchial epithelial cell line 16HBE 14_o-, that DEP induced the release of the proinflammatory cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-8 (IL-8) after 24 h of exposure. Gene expression of these cytokines is regulated by transcription factors including NF-κB and AP-1, which are known to be sensitive to oxidative stress. Their activation by DEP was investigated in comparison with a pure oxidant, H₂O₂ A 4-h exposure to DEP (10 μg/cm²) or to H₂O₂ (100 µM) increased NF-κB DNA binding in 16HBE cells as assessed by electrophoretic mobility shift assay. AP-1 was only activated by H₂0₂ in the same conditions. Organic extracts of DEP increased NF-κB DNA binding as did native DEP, suggesting the role of the polycyclic aromatic hydrocarbons (PAH) in this NF-κB increased DNA binding. Dimethylthiourea (DMTU), an antioxidant, inhibited the NF-κB DNA binding induced by DEP, suggesting an involvement of reactive oxygen species (ROS) in the transduction pathways leading to NF-κB activation. Moreover, the MEK pathway inhibitor PD98059 inhibited DEP-induced NF-κB DNA binding. The role of Erk 1/2 was likely implicated, since DEP induced an increase of Erk phosphorylation.