Expression of hurpin, a serine proteinase inhibitor, in normal and pathological skin: overexpression and redistribution in psoriasis and cutaneous carcinomas.

Hurpin was identified by differential display analysis studying UV-repressible genes in the keratinocyte cell line HaCaT. We have previously reported that hurpin mRNA is overexpressed in psoriatic skin compared to non-lesional or normal skin; hurpin inhibits cathepsin L and that, after overexpression in keratinocytes, hurpin decreases UV-induced apoptosis. To further study the expression of hurpin, we have isolated monoclonal antibodies against hurpin and analyzed its expression in normal and diseased skin by immunohistochemistry (IHC). In the epidermis of normal skin, we found hurpin to be mainly expressed in the stratum basale. In contrast, we found an enhanced expression of hurpin in the stratum spinosum and stratum granulosum in the majority of diseased skin samples. Within the dermis of normal and diseased skin, hurpin was detected in sebaceous and sweat glands, hair follicles, and endothelial cells of blood vessels. Hurpin was localized in the cytoplasm in normal and diseased skin. Additionally to IHC, we analyzed hurpin expression in selected skin diseases by semiquantitative reverse-transcription polymerase chain reaction. We found overexpression of hurpin mRNA in psoriasis, squamous cell carcinoma (SCC), and actinic keratosis. In contrast, expression of hurpin in melanoma and basal cell carcinoma was comparable to that in normal skin. Overall, the strongest overexpression was observed in SCC and psoriasis. Individual differences in hurpin expression between patients were observed. The increased expression and redistribution of hurpin in diseased skin suggests its possible involvement in inflammatory processes or the regulation of endogenous or pathogen-derived proteinase activity. Additional studies will elucidate the physiological role of hurpin.

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