Immunolocalization of protease‐activated receptor‐2 in skin: receptor activation stimulates interleukin‐8 secretion by keratinocytes in vitro

The protease‐activated receptor‐2 (PAR‐2) is a seven transmembrane domain receptor related to the thrombin receptor, which is activated in vitro by cleavage by trypsin. Affinity‐purified rabbit IgG raised against a peptide corresponding to the trypsin cleavage site of PAR‐2 was used for an immunohistochemical study of skin. The expression of PAR‐2 in epidermis was striking, with keratinocytes showing abundant intercellular and cytoplasmic staining. Basal cells showed the strongest staining intensity and the stratum corneum was negative. Staining with control IgG used at the same concentration was consistently negative. The functional expression of PAR‐2 by the simian virus transformed human skin keratinocyte cell line SVK14 was demonstrated by Northern blot analysis, flow cytometric analysis and the measurement of intracellular calcium. Treatment of SVK14 with trypsin or a receptor agonist peptide (SLIGKV‐NH2) caused a dose‐dependent increase in the secretion of the chemokine interleukin‐8 (IL‐8) in vitro. The effect of the peptide was specific, since control acetylated peptide was without activity. We conclude that PAR‐2 is highly expressed by epidermal keratinocytes and receptor activation in vitro leads to increased IL‐8 secretion by keratinocytes. These data raise the possibility that PAR‐2 may play a role in epidermal homeostasis and inflammatory conditions.