Several studies have shown that allergenic house dust mite proteases can induce proinflammatory cytokine release from respiratory epithelium. Here we investigated the signal transduction pathway by which the cysteine protease allergen Der p 1 regulates the production of IL-8 in the A549 human airways epithelial cells.

Purified natural Der p 1 was used to activate A549 cells. IL-8 mRNA expression and cytokine release were evaluated by RT-PCR and ELISA, respectively. Immunoblotting and electrophoretic mobility shift assays were performed to study downstream signaling.

Der p 1 induced IL-8 protein production, IL-8 mRNA expression, and strong ERK1/2 activation, but only a slight transient activation of JNK and p38. Der p 1 mediated a time-dependent increase in DNA binding activity of AP-1 and only a transient activation of NF-kappaB. Inhibition of Der p 1-induced ERK1/2 activation by the highly specific MEK inhibitor U0126 blocked IL-8 mRNA expression and largely attenuated IL-8 production. This was correlated with abrogation of AP-1 DNA binding activity. The Der p 1-induced IL-8 production through PAR-2 activation was not evidenced as no calcium mobilization and similar IL-8 expression level were observed when PAR-2-transfected or control HeLa cells were treated with Der p 1. In contrast, PAR-2 agonist peptide and trypsin induced prominent calcium response and IL-8 release only in PAR-2-transfected HeLa cells.

Der p 1 induced IL-8 expression in airway epithelial cells by activating ERK-1/2 pathway and enhancing transcriptional function of AP-1.