Abstract
Prolylcarboxypeptidase (PRCP) is s serine protease that recently emerged as a regulator of the central melanocortin system, i. e. control of food intake and energy metabolism, by degrading α-MSH (1-13) into biologically inactive α-MSH (1-12). Therefore, we wondered if PRCP may also play a role in regulation of the peripheral melanocortin system. As a first step towards answering this question we examined the expression of PRCP in various cutaneous cell types at RNA and protein level in vitro. PRCP transcripts were detected in normal human melanocytes, normal human keratinocytes and human dermal fibroblasts (HDFs) from different donors as shown by endpoint reverse transcriptase- polymerase chain reaction (RT-PCR). However, Western immunoblotting revealed expression of PRCP protein only in HDFs but not in the other cell types. Here, PRCP could be visualized as a granular cytoplasmic staining as shown by immunofluorescence analysis. As detected by liquid chromatography coupled with mass spectrometry, HDFs treated with alpha-MSH formed alpha-MSH (1-12) in conditioned media suggesting expression and secretion of functionally active PRCP. Interestingly, quantitative real-time RT-PCR analysis further revealed a time-dependent upregulatory effect of both tumor necrosis factor and ultraviolet A irradiation but not interleukin-1beta on PRCP mRNA in HDFs. However, Western immunoblotting of total cell lysates and detection of PRCP in cell culture supernatants employing ELISA did not reveal upregulation of this enzyme in HDFs exposed to these stressors. Immunohistochemical studies of normal and diseased human skin further revealed that PRCP is mainly expressed in neutrophilic granulocytes, endothelial cells and activated dermal fibroblasts, i. e. during wound healing and in hypertrophic scars but not within the epidermis. Further studies are underway to further define the biological role of PRCP in such conditions.
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