SKALP ELAFIN IS AN INDUCIBLE PROTEINASE-INHIBITOR IN HUMAN EPIDERMAL-KERATINOCYTES/

Skin-derived antileukoproteinase (SKALP), otherwise known as elafin, i s a recently discovered epidermal proteinase inhibitor with specificit y for polymorphonuclear leukocyte (PMN)-derived elastase and proteinas e-3; in addition to the proteinase-inhibiting domain, SKALP contains s everal transglutaminase substrate motifs. SKALP is virtually absent in normal human epidermis but is found in a number of inflammatory skin diseases, including psoriasis. Here we report the induction and proces sing of SKALP in vivo and in vitro. SKALP expression in vivo could be demonstrated following injury in normal human epidermis, using histolo gy, western blotting, northern blotting and a functional assay. In vit ro, SKALP expression was studied in conventional submerged keratinocyt e culture systems and in keratinocytes cultured in an air-liquid inter face model. Induction of SKALP activity in epidermis could be measured as early as 16 hours after skin injury; immunohistological examinatio n showed that SKALP expression was confined to the outer layers of the stratum spinosum and the stratum granulosum. Northern blot analysis r evealed a 0.8 kb transcript, both in vivo (psoriatic skin, injured ski n) and in vitro (cultured keratinocytes). Western blot analysis showed that the major SKALP form in vivo was a low molecular mass fragment, containing the antiproteinase domain. In all cultures that were positi ve for SKALP, larger (8-10 kDa) forms of SKALP, containing the N-termi nal transglutaminase substrate motifs in addition to the antiproteinas e domain, were found. SKALP expression in cultured cells was found to be dependent on the system used. In a submerged culture system, SKALP could be induced by fetal calf serum. These findings demonstrate that SKALP is an inducible proteinase inhibitor and support the concept tha t SKALP acts as a regulatory molecule in cutaneous homeostasis.