Protease-activated receptor-2 induces proinflammatory cytokine and chemokine gene expression in canine keratinocytes

Although the molecular basis of the allergenicity remains to be fully elucidated, the ability of allergens to elicit allergic responses is at least partly attributed to their proteolytic activity. Protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor that is activated by site-specific proteolysis by serine proteases and is known to mediate inflammatory processes in various tissues. In this study, we investigated the effects of trypsin, a major serine protease, and a human PAR-2 agonist peptide (SLIGKV-NH2) on proinflammatory cytokine and chemokine gene expression in the canine keratinocyte cell line CPEK. The expression of PAR-2 mRNA and protein in CPEK cells was detected by RT-PCR and Western blotting, respectively. The localization of PAR-2 in CPEK was examined by immunofluorescence. The mRNA expression levels of proinflammatory cytokines and chemokines were quantified by real-time RT-PCR. The free intracellular Ca2+ concentration was measured using the Ca2+-sensitive fluorescent dye. CPEK cells constitutively expressed PAR-2 mRNA and protein. Stimulation of CPEK cells with trypsin induced significant upregulation of the mRNA expression levels of tumor necrosis factor alpha (TNF-α, P < 0.05), granulocyte-macrophage colony-stimulating factor (GM-CSF, P < 0.01), thymus and activation regulated chemokine (TARC/CCL17, P < 0.01), and interleukin 8 (IL-8/CXCL8, P < 0.01). Similarly, the PAR-2 agonist peptide increased the mRNA expression levels of TNF-α (P < 0.05), GM-CSF (P < 0.05), TARC/CCL17 (P < 0.05), and IL-8/CXCL8 (P < 0.05) in CPEK cells. Both trypsin and the PAR-2 agonist peptide increased the intracellular Ca2+ concentration and PAR-2 internalization. These results suggest that PAR-2 activation can augment inflammatory cytokine and chemokine expression in canine keratinocytes, and it may initiate allergic inflammation through the proteolytic activity of allergens in canine atopic dermatitis.