Mechanisms of GM-CSF increase by diesel exhaust particles in human airway epithelial cells

Mechanisms of GM-CSF increase by diesel exhaust particles in human airway e pithelial cells. Am. J. Physiol. Lung Cell. Mel. Physiol. 278: L25-L32, 200 0.-We have previously shown that exposure to diesel exhaust particles (DEPs ) stimulates human airway epithelial cells to secrete the inflammatory cyto kines interleukin-8, interleukin-1 beta, and granulocyte-macrophage colony- stimulating factor (GM-CSF) involved in allergic diseases. In the present p aper, we studied the mechanisms underlying the increase in GM-CSF release e licited by DEPs using the human bronchial epithelial cell line 16HBE14o-. R T-PCR analysis has shown an increase in GM-CSF mRNA levels after DEP treatm ents. Comparison of the effects of DEPs, extracted DEPs, or extracts of DEP s has shown that the increase in GM-CSF release is mainly due to the adsorb ed organic compounds and not to the metals present on the DEP surface becau se the metal chelator desferrioxamine had no inhibitory effect. Furthermore , radical scavengers inhibited the DEP-induced GM-CSF release, showing invo lvement of reactive oxygen species in this response. Moreover genistein, a tyrosine kinase inhibitor, abrogated the effects of DEPs on GM-CSF release, whereas protein kinase (PK) C, PKA, cyclooxygenase, or lipoxygenase inhibi tors had no effect. PD-98059, an inhibitor of mitogen-activated protein kin ase, diminished the effects of DEPs, whereas SB-203580, an inhibitor of p38 mitogen-activated protein kinase, had a lower effect, and DEPs did actuall y increase the active, phosphorylated form of the extracellular signal-regu lated kinase as shown by Western blotting. In addition, cytochalasin D, whi ch inhibits the phagocytosis of DEPs, reduced the increase in GM-CSF releas e after DEP treatment. Together, these data suggest that the increase in GM -CSF release is mainly due to the adsorbed organic compounds and that the e ffect of native DEPs requires endocytosis of the particles. Reactive oxygen species and tyrosine kinase(s) may be involved in the DEP-triggered signal ing of the GM-CSF response.