Lipopolysaccharide modifies amiloride-sensitive Na+ transport processes across human airway cells: role of mitogen-activated protein kinases ERK 1/2 and 5

Bacterial lipopolysaccharides (LPS) are potent inducers of proinflammatory signaling pathways via the activation of nuclear factor-kappa B (NF-kappa B) and mitogen-activated protein kinase (MAPK), causing changes in the processes that control lung fluid homeostasis and contributing to the pathogenesis of lung disease. In human H441 airway epithelial cells, incubation of cells with 15 mu g ml(-1) LPS caused a significant reduction in amiloride-sensitive I-sc from 15 +/- 2 to 8 +/- 2 mu A cm(-2) (p=0.01, n=13) and a shift in IC50 amiloride of currents from 6.8x10(-7) to 6.4x10(-6) M. This effect was associated with a decrease in the activity of 5 pS, highly Na+ selective, amiloride-sensitive < 1 mu M channels (HSC) and an increase in the activity of similar to 18 pS, nonselective, amiloride-sensitive > 10 mu M cation channels (NSC) in the apical membrane. LPS decreased alpha ENaC mRNA and protein abundance, inferring that LPS inhibited alpha ENaC gene expression. This correlated with the decrease in HSC activity, indicating that these channels, but not NSCs, were comprised of at least alpha ENaC protein. LPS increased NF-kappa B DNA binding activity and phosphorylation of extracellular signal-related kinase (ERK)1/2, but decreased phosphorylation of ERK5 in H441 cells. Pretreatment of monolayers with PD98059 (20 mu M) inhibited ERK1/2 phosphorylation, promoted phosphorylation of ERK5, increased alpha ENaC protein abundance, and reversed the effect of LPS on I-sc and the shift in amiloride sensitivity. Inhibitors of NF-kappa B activation were without effect. Taken together, our data indicate that LPS acts via ERK signaling pathways to decrease alpha ENaC transcription, reducing HSC/ENaC channel abundance, activity, and transepithelial Na+ transport in H441 airway epithelial cells.