Identification of Lympho-Epithelial Kazal-Type Inhibitor 2 in Human Skin as a Kallikrein-Related Peptidase 5-Specific Protease Inhibitor

Ulf Meyer-Hoffert,Jens-Michael Schröder,Zhihong Wu,Ludovic Tailleux

doi:10.1371/journal.pone.0004372

Ulf Meyer-Hoffert, Jens-Michael Schröder + Show 2 more

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https://doi.org/10.1371/journal.pone.0004372

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Abstract

Kallikreins-related peptidases (KLKs) are serine proteases and have been implicated in the desquamation process of the skin. Their activity is tightly controlled by epidermal protease inhibitors like the lympho-epithelial Kazal-type inhibitor (LEKTI). Defects of the LEKTI-encoding gene serine protease inhibitor Kazal type (Spink)5 lead to the absence of LEKTI and result in the genodermatose Netherton syndrome, which mimics the common skin disease atopic dermatitis. Since many KLKs are expressed in human skin with KLK5 being considered as one of the most important KLKs in skin desquamation, we proposed that more inhibitors are present in human skin. Herein, we purified from human stratum corneum by HPLC techniques a new KLK5-inhibiting peptide encoded by a member of the Spink family, designated as Spink9 located on chromosome 5p33.1. This peptide is highly homologous to LEKTI and was termed LEKTI-2. Recombinant LEKTI-2 inhibited KLK5 but not KLK7, 14 or other serine proteases tested including trypsin, plasmin and thrombin. Spink9 mRNA expression was detected in human skin samples and in cultured keratinocytes. LEKTI-2 immune-expression was focally localized at the stratum granulosum and stratum corneum at palmar and plantar sites in close localization to KLK5. At sites of plantar hyperkeratosis, LEKTI-2 expression was increased. We suggest that LEKTI-2 contributes to the regulation of the desquamation process in human skin by specifically inhibiting KLK5.

Highlights

The skin protects us from water loss and mechanical damage
In this study we aimed to identify major substances that might contribute to the epithelial barrier shield by inhibiting the epidermal serine protease KLK5
We identified a new peptide termed Lymphoepithelial Kazal-type-related inhibitor (LEKTI)-2 as a specific inhibitor for KLK5, which is encoded by Spink9, a novel member of the serine protease inhibitor Kazal type (Spink) gene family

Summary

Introduction

The skin protects us from water loss and mechanical damage. The surface-exposed epidermis, a self-renewing stratified squamous epithelium composed of several layers of keratinocytes, is most important for the barrier defense against these challenges. Keratinocytes in the outmost stratum corneum (SC) of the epidermis are shed off and replaced by newly differentiated cells originating from epidermal stem cells located in the basal layer. They undergo a specific differentiation process and form the cornified envelope, which is a rigid and insoluble protein and lipid structure with essential properties of the barrier function [1,2]. The activity of the KLKs is regulated by the pH and specific protease inhibitors in human skin. Lymphoepithelial Kazal-type-related inhibitor (LEKTI) [14], the product of Spink, includes in its primary structure 15 different serine protease inhibitory domains [14]. Though LEKTI is absent, NS patients can still develop hyperkeratosis – a clinical sign of inhibited desquamation

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