Proteinase-activated receptor-2 in human skin: tissue distribution and activation of keratinocytes by mast cell tryptase

Proteinase-activated receptor-2 (PAR-2) is a G-protein coupled receptor. Tr yptic proteases cleave PAR-2 exposing a tethered ligand (SLIGKV), which bin ds and activates the receptor. Although PAR-2 is highly expressed by cultur ed keratinocytes and is an inflammatory mediator, its precise localization in the normal and inflamed human skin is unknown, and the proteases that ac tivate PAR-2 in the skin have not been identified. We localized PAR-2. in h uman skin by immunohistochemistry, examined PAR-2 expression by RT-PCR and RNA blotting, and investigated PAR-2 activation by mast cell tryptase. PAR- 2 was localized to keratinocytes, especially in the granular layer, to endo thelial cells, hair follicles, myoepithelial cells of sweat glands, and der mal dendritic-like cells. PAR-2 was also highly expressed in keratinocytes and endothelial cells of inflamed skin. PAR-2 mRNA was detected in normal h uman skin by RT-PCR, and in cultured human keratinocytes and dermal microva scular endothelial cells by Northern hybridization. Trypsin, tryptase and a peptide corresponding to the tethered ligand (SLIGKVNH(2)) increased [Ca2](i) in keratinocytes, measured using Fura-2/AM. Although tryptase-containi ng mast cells were sparsely scattered in the normal dermis, they were numer ous in the dermis in atopic dermatitis, and in the dermis, dermal-epidermal border, and occasionally within the lower epidermis in psoriasis. Tryptase may activate PAR-2 on keratinocytes and endothelial cells during inflammat ion.