Analysis of Proteins with Caseinolytic Activity in a Human Stratum Corneum Extract Revealed a Yet Unidentified Cysteine Protease and Identified the So-Called “Stratum Corneum Thiol Protease” as Cathepsin L2

Abstract

Desquamation is described as a protease-dependent phenomenon where serine proteases with a basic pH optimum play a key role. Recently proteases with an acidic pH optimum were identified in the stratumcorneum and associated with desquamation, e.g., cathepsin D and the stratum corneum thiol protease. The purpose of this study was to investigate if human stratum corneum contains proteases different from the above, exhibiting similar properties. After gel filtration, we identified four distinct proteolytic activities in a human stratum corneum extract, a cathepsin-E-like activity (80 kDa), a cathepsin-D activity (40 kDa), a yet unknown cathepsin-L-like form (28 kDa) exhibiting the highest caseinolytic activity, and a chymotrypsin-like protein (24 kDa) containing the acidic activity of the well described stratum corneum chymotryptic enzyme. We named the new 28 kDa protease stratum corneum cathepsin-L-like enzyme. Characterization of stratum corneum cathepsin-L-like enzyme provided clear evidence that this new protease, despite its membership to the cathepsin-L-like family, is distinct from cathepsin L and from the recently described stratum corneum thiol protease. Its ability to hydrolyze corneodesmosin, a marker of corneocyte cohesion, was in favor of a role of stratum corneum cathepsin-L-like enzyme in the desquamation process. A more detailed analysis did not allow us to identify stratum corneum cathepsin-L-like enzyme at the molecular level but revealed that stratum corneum thiol protease is identical with the recently described cathepsin L2 protease. Reverse transcription polymerase chain reaction studies and the use of a specific antibody revealed that, in contrast to earlier reports, expression of stratum corneum thiol protease in human epidermis is not related to keratinocyte differentiation. Our results indicate that the stratum corneum thiol protease is probably expressed as a pro-enzyme in the lower layers of the epidermis and in part activated by a yet unidentified mechanism in the upper layers during keratinocyte differentiation.

Death penalty for keratinocytes: apoptosis versus cornification

“…77 Furthermore, cathepsin L2 has been detected in stratum corneum extracts. 78 This protease seems to be activated during epidermal differentiation and secreted into the intercellular space. Schematic structure of procaspase-14 as compared to other short-prodomain caspases (human).…”

A Novel Protease Inhibitor of the α2-Macroglobulin Family Expressed in the Human Epidermis

“…Alternatively, binding to ␣2ML1 could protect KLK7 either from hydrolysis by other proteases or from inhibitors such as the serine protease inhibitor SPINK5, which plays a pivotal role in controlling KLK5-and KLK7-like activities in the upper epidermis (48,49). Beside KLK7, cathepsin L2, also called stratum corneum thiol protease and cathepsin L-like are papain-like cysteine proteases that are thought to be involved in desquamation (50). The high efficient inhibition of papain by ␣2ML1 suggests that cathepsin L2 and cathepsin L-like may also be physiological targets of ␣2ML1 in vivo.…”

Cutaneous water loss and lipids of the stratum corneum in house sparrowsPasser domesticusfrom arid and mesic environments

“…Most of these processes involve the creation of gradients of ions across the SC that influence water permeation through lipid layers. For example, changes in the pH and calcium gradient across the SC alter the permeability of the skin, and affect barrier recovery after disruption (Menon et al, 1994;Bernard et al, 2003;Fluhr et al, 2004a,b). Despite the variety of biological mechanisms known to modify the performance of the permeability barrier in the skin, no studies have attempted to separate the contribution of physical and biological factors in the formation of the epidermal water barrier.…”