Introduction: Endothelial protein C receptor (EPCR) is a specific receptor for the natural anticoagulant activated protein C (APC). We have demonstrated that EPCR is strongly expressed by the basal layer of keratinocytes in skin epidermis as well as in cultured keratinocytes. In these cells, EPCR mediates the wound healing phenotype of APC. The aim of this study was to investigate whether EPCR itself is required for normal epidermal keratinocyte growth.

Methods: Human keratinocytes were isolated from neonatal foreskin, cultured in serum free medium and transfected with EPCR siRNA or plasmid. The growth of cells was measured by MTT assay. The expression and co-localisation of EPCR to stem cell markers p63, integrin beta1 were detected by flow cytometry and immunofluorescent staining respectively. Activation of MAP kinase was evaluated by western blot.

Results: EPCR was highly expressed in foreskin epidermis, mainly on basal keratinocytes, and co-localised with integrin beta1. In culture under basal conditions, there was variation in the level of EPCR expression by keratinocytes with the higher EPCR-expressing cells also exhibiting higher levels of p63 and integrin beta1. Collagen-enriched keratinocytes expressed more EPCR than non-enriched cells. In culture, keratinocyte growth was significantly decreased by approximately 20% in response to EPCR siRNA or EPCR blocking antibody treatment for 72 hours. In contrast, overexpression of EPCR for 72 hours significantly stimulated cell growth.

Conclusion: Keratinocytes coordinately express EPCR and stem cell markers. Transfection and blocking studies indicate that EPCR is required for the normal growth of these cells. These data suggest that EPCR directly contributes to re-epithelialisation during wound healing.