Evidence that cell shedding from plantar stratum corneum in vitro involves endogenous proteolysis of the desmosomal protein desmoglein I

Moisturizing at a molecular level - The basis of Corneocare

BACKGROUND

This review covers the last 20 years of research we and our collaborators have conducted on ethnic differences in facial skin moisturization placed in historical context with previous research.

METHODS

We have focussed particularly on the biochemical and cellular gradients of the stratum corneum (SC) with the aim of discovering new skin moisturization and SC maturation mechanisms, identifying new technologies and/or providing conceptual innovations for ingredients that will improve our understanding and treatment of dry skin. Specifically, we discuss gradients for corneodesmosomes and proteases, corneocyte phenotype-inducing enzymes, filaggrin and natural moisturizing factor (NMF), and barrier lipids. These gradients are interdependent and influence greatly corneocyte maturation.

RESULTS

The interrelationship between corneodesmolysis and the covalent attachment of ω-hydroxy ceramides and ω-hydroxy fatty acids to the corneocyte protein envelope forming the corneocyte lipid envelope is especially relevant in our new understanding of mechanisms leading to dry skin. This process is initiated by a linoleoyl-ω-acyl ceramide transforming enzyme cascade including 12R lipoxygenase (12R-LOX), epidermal lipoxygenase-3 (eLOX3), epoxide hydrolase 3 (EPHX3), short-chain dehydrogenase/reductase family 9C member 7 (SDR9C7), ceramidase and transglutaminase 1.

CONCLUSION

Our research has opened the opportunity of using novel treatment systems for dry skin based on lipids, humectants, niacinamide and inhibitors of the plasminogen system. It is clear that skin moisturization is a more complex mechanism than simple skin hydration.

Selective Substrates and Inhibitors for Kallikrein-Related Peptidase 7 (KLK7) Shed Light on KLK Proteolytic Activity in the Stratum Corneum

Proteases have pivotal roles in the skin's outermost layer, the epidermis. In the stratum corneum, serine proteases from the kallikrein-related peptidase (KLK) family have been implicated in several key homeostatic processes, including desquamation. However, the precise contribution of specific KLKs to each process remains unclear. To address this, we used a chemical biology approach and designed selective substrates and inhibitors for KLK7, the most abundant KLK protease in the stratum corneum. The resulting KLK7 inhibitor is the most potent inhibitor of this protease reported to date (K_i = 140 pM), and displays at least 1,000-fold selectivity over several proteases that are related by function (KLK5 and KLK14) or specificity (chymotrypsin). We then used substrates and inhibitors for KLK5, KLK7, and KLK14 to explore the activity of each protease in the stratum corneum using casein zymography and an ex vivo desquamation assay. These experiments provide the most detailed assessment of each KLK's contribution to corneocyte shedding in the plantar stratum corneum, revealing that inhibition of KLK7 alone is sufficient to block shedding, whereas KLK5 is also a major contributor. Collectively, these findings unveil chemical tools for studying KLK activity and demonstrate their potential for characterizing KLK biological functions in epidermal homeostasis.

Retention of corneodesmosomes and increased expression of protease inhibitors in dandruff

BACKGROUND

Dandruff is a common, relapsing and uncomfortable scalp condition affecting a large proportion of the global population. The appearance of flakes on the scalp and in the hair line, and associated itch are thought to be consequences of a damaged skin barrier, altered corneocyte cohesion and abnormal desquamation in dandruff. The balance between skin proteases and protease inhibitors is essential for driving the key events, including corneodesmosome degradation, in the desquamation process and to maintain stratum corneum (SC) barrier integrity.

OBJECTIVES

To investigate the distribution of corneodesmosomes, the key component of the SC cohesivity and barrier function, and the protease inhibitors lympho-epithelial Kazal-type-related inhibitor (LEKTI-1) and squamous cell carcinoma antigen (SCCA1) in the scalp of dandruff-affected participants.

METHODS

The methods utilized were immunohistochemistry, scanning immunoelectron microscopy, phase-contrast microscopy, Western blotting and serine protease activity assay on tape-stripped SC or scalp skin biopsies.

RESULTS

In SC samples from healthy subjects, corneodesmosomes were peripherally located in the corneocytes. In samples of dandruff lesions, corneodesmosomes were located both peripherally and on the entire surface area of the corneocytes. LEKTI-1 and SCCA1 protein levels and parakeratosis were found to be highly elevated in the lesional samples.

CONCLUSIONS

The persistence of nonperipheral corneodesmosomes is a characteristic feature of the perturbed desquamation seen in dandruff. The increased expression levels of LEKTI-1 and SCCA1 are consistent with the view that the dandruff condition is characterized by an imbalance in protease-protease inhibitor interaction in the SC.

Cleavage of transmembrane junction proteins and their role in regulating epithelial homeostasis

Epithelial tissues form a selective barrier that separates the external environment from the internal tissue milieu. Single epithelial cells are densely packed and associate via distinct intercellular junctions. Intercellular junction proteins not only control barrier properties of the epithelium but also play an important role in regulating epithelial homeostasis that encompasses cell proliferation, migration, differentiation and regulated shedding. Recent studies have revealed that several proteases target epithelial junction proteins during physiological maturation as well as in pathologic states such as inflammation and cancer. This review discusses mechanisms and biological consequences of transmembrane junction protein cleavage. The influence of junction protein cleavage products on pathogenesis of inflammation and cancer is discussed.

Cellular changes that accompany shedding of human corneocytes

Corneocyte desquamation has been ascribed to either: 1) proteolytic degradation of corneodesmosomes (CD); 2) disorganization of extracellular lamellar bilayers; and/or 3) ‘swell-shrinkage-slough’ (SSS) from hydration/dehydration. To address the cellular basis for normal exfoliation, we compared changes in lamellar bilayer architecture and CD structure in DSquame® strips from the 1st vs. 5th stripping (‘outer’ vs. ‘mid’-stratum corneum [SC], respectively) from 9 normal adult forearms. Strippings were either processed for standard EM or for ruthenium (Ru-V)- or osmium-tetroxide (Os-V) vapor fixation, followed by immediate epoxy embedment, an artifact-free protocol that to our knowledge is previously unreported. CDs are largely intact in the mid-SC, but replaced by electron-dense (hydrophilic) clefts (lacunae) that expand laterally, splitting lamellar arrays in the outer SC. Some undegraded DSG1/DSC1 redistribute uniformly into corneocyte envelopes (CEs) in the outer SC (shown by proteomics, Z-stack confocal imaging and immunoEM). CEs then thicken, likely facilitating exfoliation by increasing corneocyte rigidity. In vapor-fixed images, hydration only altered the volume of the extracellular compartment, expanding lacunae further separating membrane arrays. During dehydration, air replaced water, maintaining the expanded extracellular compartment. Hydration also provoked degradation of membranes by activating contiguous acidic ceramidase activity. Together, these studies identify several parallel mechanisms that orchestrate exfoliation from the surface of normal human skin.

Stratum corneum dysfunction in dandruff

Synopsis

Dandruff is characterized by a flaky, pruritic scalp and affects up to half the world’s population post-puberty. The aetiology of dandruff is multifactorial, influenced by Malassezia, sebum production and individual susceptibility. The commensal yeast Malassezia is a strong contributory factor to dandruff formation, but the presence of Malassezia on healthy scalps indicates that Malassezia alone is not a sufficient cause. A healthy stratum corneum (SC) forms a protective barrier to prevent water loss and maintain hydration of the scalp. It also protects against external insults such as microorganisms, including Malassezia, and toxic materials. Severe or chronic barrier damage can impair proper hydration, leading to atypical epidermal proliferation, keratinocyte differentiation and SC maturation, which may underlie some dandruff symptoms. The depleted and disorganized structural lipids of the dandruff SC are consistent with the weakened barrier indicated by elevated transepidermal water loss. Further evidence of a weakened barrier in dandruff includes subclinical inflammation and higher susceptibility to topical irritants. We are proposing that disruption of the SC of the scalp may facilitate dandruff generation, in part by affecting susceptibility to metabolites from Malassezia. Treatment of dandruff with cosmetic products to directly improve SC integrity while providing effective antifungal activity may thus be beneficial.

Résumé

Les pellicules se caractérisent par un cuir chevelu prurigineux, squameux, et affectent jusqu’à la moitié de la population post-pubertaire du monde. L’étiologie des pellicules est multifactorielle, influencée par Malassezia, par la production de sébum, et par la susceptibilité individuelle. La levure commensale Malassezia est un facteur fortement contributif à la formation de pellicules, mais la présence de Malassezia aussi sur les cuirs chevelus sains indique que Malassezia seule n’est pas une cause suffisante. Un stratum corneum (SC) sain forme une barrière protectrice pour empêcher la perte d’eau et maintenir l’hydratation du cuir chevelu. Il protège également contre les agressions externes tels les micro-organismes, y compris Malassezia, ou des substances toxiques. Des dommages aigus ou chroniques au niveau de la barrière peuvent nuire à une bonne hydratation, conduisant à des effets atypiques de la prolifération épidermique, de la différenciation des kératinocytes, et de la maturation du SC, ce qui peut expliquer une partie des symptômes des pellicules. L’appauvrissement et la désorganisation des lipides structurels d’un stratum corneum sujet aux pellicules sont compatibles avec la notion d’une barrière affaiblie telle qu’indiquée par une perte d’eau transépidermique élevée. Une preuve supplémentaire d’une barrière affaiblie dans les cas des pellicules est fournie par un niveau d’inflammation infraclinique et une plus grande susceptibilité aux irritants topiques. Nous proposons que la perturbation du SC du cuir chevelu facilite la production de pellicules, en partie en augmentant la sensibilité aux métabolites de Malassezia. Le traitement des pellicules avec des produits cosmétiques pour améliorer directement l’intégrité du SC, tout en offrant une activité antifongique efficace peut donc être bénéfique.

Desmoglein as a target in skin disease and beyond

Much of the original research on desmosomes and their biochemical components was through analysis of skin and mucous membranes. The identification of desmogleins 1 and 3, desmosomal adhesion glycoproteins, as targets in pemphigus, a fatal autoimmune blistering disease of the skin and mucous membranes, provided the first link between desmosomes, desmogleins, and human diseases. The clinical and histological similarities of staphylococcal scalded skin syndrome or bullous impetigo and pemphigus foliaceus led us to identify desmoglein 1 as the proteolytic target of staphylococcal exfoliative toxins. Genetic analysis of striate palmoplantar keratoderma and hypotrichosis identified their responsible genes as desmogleins 1 and 4, respectively. More recently, these fundamental findings in cutaneous biology were extended beyond the skin. Desmoglein 2, which is expressed earliest among the four isoforms of desmoglein in development and found in all desmosome-bearing epithelial cells, was found to be mutated in arrythmogenic right ventricular cardiomyopathy and has also been identified as a receptor for a subset of adenoviruses that cause respiratory and urinary tract infections. The story of desmoglein research illuminates how dermatological research, originally focused on one skin disease, pemphigus, has contributed to understanding the biology and pathophysiology of many seemingly unrelated tissues and diseases.

Kallikrein-5 promotes cleavage of desmoglein-1 and loss of cell-cell cohesion in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) ranks among the top 8 causes of cancer death worldwide, with only a 60% 5-year survival rate, highlighting the need for discovery of novel biomarkers and therapeutic targets. We have previously reported that expression of a panel of serine proteinase kallikreins (KLK 5, 7, 8, and 10) is correlated with formation of more aggressive OSCC tumors in a murine orthotopic OSCC model and is elevated in human OSCC. Current studies focus on understanding the potential role of KLK5 in OSCC progression. In initial studies, KLK levels in malignant OSCC cells (SCC25) were compared with cells from normal oral mucosa (OKF/6) and pre-malignant oral keratinocytes (pp126) using qPCR. A marked elevation of all KLKs was observed in aggressive SCC25 cells relative to OKF/6 cells. In normal skin, KLKs are involved in desquamation during epidermal differentiation via proteolytic cleavage of the desmosomal cadherin component desmoglein 1 (Dsg1). As loss of cell-cell cohesion is prevalent in tumor metastasis, Dsg1 integrity was evaluated. Results show that SCC25 cells exhibit cleavage of Dsg1, which is blocked by proteinase inhibitor treatment as well as by siRNA silencing of KLK5 expression. Furthermore, cell-cell aggregation assays demonstrate that silencing of KLK5 enforces cell-cell adhesion; conversely, overexpression of KLK5 in normal oral mucosal cells (OKF/6) enhances cell dispersal. These data suggest that KLK5 may promote metastatic dissemination of OSCC by promoting loss of junctional integrity through cleavage of desmoglein 1.

New non-invasive method for evaluation of the stratum corneum structure in diseases with abnormal keratinization by immunofluorescence microscopy of desmoglein 1 distribution in tape-stripped samples

The corneodesmosomes in the stratum corneum are critical for the maintenance of stratum corneum integrity. To evaluate the normal and diseased keratinization states in the epidermis, we studied the distribution of desmoglein 1 (DSG1), a major component of corneodesmosomes, in samples of the stratum corneum obtained by tape stripping, a non-invasive method. Samples were collected from lesional skin of four patients with psoriasis and three with lichen planus, and from non-lesional skin of three volunteers. Upper stratum corneum cells were obtained by tape stripping and skin biopsies were obtained from adjacent sites. Tape-stripped samples were examined by immunofluorescence microscopy using anti-DSG1 monoclonal antibody, in combination with histopathology of skin biopsies. In normal human stratum corneum, which shows basket-woven orthokeratosis, DSG1-containing fluorescent dots were distributed on the lateral cell-cell contact areas of plasma membrane, but not on the dorsal/ventral plasma membrane, and formed a well-ordered hexagonal network structure. In psoriatic stratum corneum, fluorescent dots were distributed throughout the cell membrane at ventral aspects of corneocytes as well as at the lateral cell-cell contacts. In lichen planus, fluorescent dots were distributed homogeneously and/or heterogeneously on the ventral surface in some cells. Adjacent cells lacked DSG1 at the lateral cell-cell contacts, but were instead separated by distinctive black-gap lines. These results suggest that the intercellular adhesion by DSG1 may depend on the lateral plasma membrane in normal human stratum corneum, on the dorsal/ventral plasma membrane in lichen planus, and on both lateral and dorsal/ventral plasma membranes in psoriatic stratum corneum. Tape stripping and DSG1 immunofluorescence visualizes adhesion features of corneocytes and has considerable potential for evaluation of abnormal keratinization and the process of healing in response to treatment.

Analysis of human kallikrein 7 expression as a potential biomarker in cervical neoplasia

Overexpression of kallikrein 7, a proteolytic enzyme important for epithelial cell shedding, may be causally involved in carcinogenesis, particularly in tumor metastasis and invasion. In this study, we have evaluated hK7 (human kallikrein 7) protein levels by immunohistochemistry in 367 cervical histological samples including 35 cases of cervicitis, 31 low-grade cervical intraepithelial neoplasia, 51 high-grade cervical intraepithelial neoplasia (H-SIL), 197 squamous cervical carcinomas (SCC) and 53 cervical adenocarcinomas. We have observed that hK7 staining increased with the severity of cervical disease. Intense hK7 staining was found in 15.2% of cervicitis samples, in contrast to 55% of H-SIL and 68% of SCC. Moreover, 92.5% of adenocarcinomas also exhibited intense hK7 staining. Differences in the expression of hK7 could potentially be used as a biomarker for the characterization of different stages of cervical disease.

The biology of cystatin M/E and its cognate target proteases

Cystatin M/E is a member of a superfamily of evolutionarily-related cysteine protease inhibitors that provide regulatory and protective functions against uncontrolled proteolysis by cysteine proteases. Although most cystatins are ubiquitously expressed, high levels of cystatin M/E expression are mainly restricted to the epithelia of the skin (epidermis, hair follicles, sebaceous glands, and sweat glands) and to a few extracutaneous tissues. The identification of its physiological targets and the localization of these proteases in skin have suggested a regulatory role for cystatin M/E in epidermal differentiation. In vitro biochemical approaches as well as the use of in vivo mouse models have revealed that cystatin M/E is a key molecule in a biochemical pathway that controls skin barrier formation by the regulation of both crosslinking and desquamation of the stratum corneum. Cystatin M/E directly controls the activity of cathepsin V, cathepsin L, and legumain, thereby regulating the processing of transglutaminases. Misregulation of this pathway by unrestrained protease activity, as seen in cystatin M/E-deficient mice, leads to abnormal stratum corneum and hair follicle formation, as well as to severe disturbance of skin barrier function. Here, we review the current knowledge on cystatin M/E in skin barrier formation and its potential role as a tumor suppressor gene.

Abundant expression of Kallikrein 1 gene in human keratinocytes was mediated by GATA3

Among Tissue kallikrein genes (KLKs), KLK1 is abundantly expressed in human skin. Although its putative promoter is known to have various cis-elements, they have not been functionally tested. In the present study, the regulation mechanism of KLK1 promoter supporting such abundant expression was examined. Luciferase assay targeting the KLK1 promoter (nucleotide -1153/+40 from the major transcriptional start site) was performed on NHEK human keratinocyte. -954/-855, -428/-236, and -100/+40 had the induction activity. The motif search program failed to find unique binding motifs in -428/-236, whereas both -954/-855 and -100/+40 had a unique GATAs binding motif. Electrophoretic mobility shift assay (EMSA) and DNA footprinting confirmed the binding of NHEK nuclear protein to these motifs that were supershifted by anti-GATA3 antibody. Among GATA isoforms, GATA3 alone could be amplified in RNA obtained from NHEK. Moreover, introduction of GATA3 into fibroblastic NIH3T3 cells enhanced the activity of KLK1 promoter containing -954/+40, while that of GATA3 dominant negative mutant to NHEK cells impaired the same promoter's activity. Thus, GATA3 was found to bind the site located at -954/-855 and to be a key regulator of abundant KLK1 expression in human keratinocyte.

A Fluorescence Lifetime-Based Assay for Protease Inhibitor Profiling on Human Kallikrein 7

Fluorescence lifetime is an intrinsic parameter describing the fluorescence process. Changes in the fluorophore's physicochemical environment can lead to changes in the fluorescence lifetime. When used as the readout in biological assays, it is thought to deliver superior results to conventional optical readouts. Hence it has the potential to replace readout technologies currently established in drug discovery such as absorption, luminescence or fluorescence intensity. Here we report the development of an activity assay for human kallikrein 7, a serine protease involved in skin diseases. As a probe, we have selected a blue-fluorescent acridone dye, featuring a remarkably long lifetime that can be quenched by either of the 2 natural amino acids, tyrosine and tryptophan. Incorporating this probe and 1 of the quenching amino acids on either side of the scissile bond of the substrate peptide enables us to monitor the enzymatic activity by quantifying the increase in the fluorescence lifetime signal. A systematic investigation of substrate structures has led to a homogenous, microplate-based, compound profiling assay that yields inhibitory constants down into the single-digit nanomolar range. This type of assay has now been added to our standard portfolio of screening techniques, and is routinely used for compound profiling. ( Journal of Biomolecular Screening 2009:1-9)

Kallikrein 7 enhances pancreatic cancer cell invasion by shedding E-cadherin

BACKGROUND

Pancreatic cancer (PaC) is characterized by local invasion and early metastasis. Serine proteases have been associated with invasion and metastasis of many cancers due to their ability to degrade extracellular matrix (ECM) proteins and to activate other proteases; thus, the serine proteases expressed in PaC were investigated.

METHODS

An expression profile of serine proteases was generated from both normal and malignant pancreatic tissues using a polymerase chain reaction (PCR)-based screen and differential expression of kallikrein 7 was examined by reverse-transcriptase PCR (RT-PCR) and immunohistochemical analyses. The ability of human kallikrein 7 (hK7) to cleave the epithelial cell adhesion molecule E-cadherin was tested in vitro using both recombinant E-cadherin and BxPC-3 cells and the effects of hK7 proteolytic activity on pancreatic cell invasion and aggregation were examined.

RESULTS

Expression profiling revealed that kallikrein 7 (KLK7) was overexpressed in pancreatic adenocarcinomas and its differential expression was confirmed by RT-PCR analysis. hK7 was observed in neoplastic cells of all tumors examined with moderate-to-intense staining in 70% of tumors examined (16/23). In contrast, only 15% of nonmalignant tissue specimens (2/13) displayed moderate hK7 staining, whereas the remaining specimens yielded weak, if any, immunoreactivity. Using in vitro assays, hK7 was shown to cleave E-cadherin and the soluble E-cadherin fragment produced significantly enhanced Panc-1 cell invasion through ECM proteins with a corresponding reduction in Panc-1 cell aggregation.

CONCLUSIONS

These results suggest that aberrant expression of KLK7 plays an important role in PaC and provides novel insight into the effects of elevated hK7 proteinase activity in this, and perhaps other, adenocarcinomas.

A potential role for multiple tissue kallikrein serine proteases in epidermal desquamation

Desquamation of the stratum corneum is a serine protease-dependent process. Two members of the human tissue kallikrein (KLK) family of (chymo)tryptic-like serine proteases, KLK5 and KLK7, are implicated in desquamation by digestion of (corneo)desmosomes and inhibition by desquamation-related serine protease inhibitors (SPIs). However, the epidermal localization and specificity of additional KLKs also supports a role for these enzymes in desquamation. This study aims to delineate the probable contribution of KLK1, KLK5, KLK6, KLK13, and KLK14 to desquamation by examining their interactions, in vitro, with: 1) colocalized SPI, lympho-epithelial Kazal-type-related inhibitor (LEKTI, four recombinant fragments containing inhibitory domains 1-6 (rLEKTI(1-6)), domains 6-8 and partial domain 9 (rLEKTI(6-9')), domains 9-12 (rLEKTI(9-12)), and domains 12-15 (rLEKTI(12-15)), secretory leukocyte protease inhibitor, and elafin and 2) their ability to digest the (corneo)desmosomal cadherin, desmoglein 1. KLK1 was not inhibited by any SPI tested. KLK5, KLK6, KLK13, and KLK14 were potently inhibited by rLEKTI(1-6), rLEKTI(6-9'), and rLEKTI(9-12) with Ki values in the range of 2.3-28.4 nm, 6.1-221 nm, and 2.7-416 nm for each respective fragment. Only KLK5 was inhibited by rLEKTI(12-15) (Ki = 21.8 nm). No KLK was inhibited by secretory leukocyte protease inhibitor or elafin. Apart from KLK13, all KLKs digested the ectodomain of desmoglein 1 within cadherin repeats, Ca2+ binding sites, or in the juxtamembrane region. Our study indicates that multiple KLKs may participate in desquamation through cleavage of desmoglein 1 and regulation by LEKTI. These findings may have clinical implications for the treatment of skin disorders in which KLK activity is elevated.

Influence of calcium on the proteolytic degradation of the calmodulin-like skin protein (calmodulin-like protein 5) in psoriatic epidermis

The calmodulin-like skin protein (CLSP) or so-called calmodulin-like protein 5, a recently discovered skin-specific calcium-binding protein, is closely related to keratinocyte differentiation. The 16-kDa protein is proteolytically degraded in the upper layers of the stratum corneum (SC) of healthy skin. With the use of specific new monoclonal antibodies to CLSP, we were able to demonstrate that the abnormal elevated levels of CLSP, characteristic of psoriatic epidermis, were probably not due to an overexpression of the protein, but most likely the result of its non-degradation. Further in vitro experiments using recombinant CLSP and in situ data clearly showed that calcium protected and chelator accelerated CLSP degradation. These data indicate that CLSP degradation in the SC of psoriatic skin might be hindered by the abnormally elevated calcium concentration. No degradation of CLSP in psoriatic epidermis keeping its ability to bind protein as transglutaminase 3 may have a physiological role in skin diseases such as psoriasis.

Colocalization of cystatin M/E and cathepsin V in lamellar granules and corneodesmosomes suggests a functional role in epidermal differentiation

Cystatin M/E is a cysteine protease inhibitor with two distinct binding sites for papain-like cysteine proteases (family C1) and the asparaginyl endopeptidase (AEP) legumain of family C13. We have previously demonstrated that deficiency of cystatin M/E in mice causes ichthyosiform skin changes and barrier disruption, which could be caused by unrestrained AEP activity. Recently, we provided biochemical evidence that human cathepsin V (CTSV) and cathepsin L (CTSL) are additional biological targets for human cystatin M/E. To address the possible role of these three proteases and their inhibitor in epidermal differentiation, we investigated the localization of these proteins in normal human skin. Whereas CTSL and AEP were broadly expressed in epithelial cells of the skin, we found a specific colocalization of cystatin M/E and CTSV in the stratum granulosum and in the root sheets of the hair follicle, using immunofluorescence microscopy. Immunoelectron microscopy revealed that cystatin M/E and CTSV are separately transported within the lamellar granules. Cystatin M/E was also found in the extracellular space in the stratum corneum associated with corneodesmosomes, where it was closely associated with CTSV. Based on the striking stratum-specific colocalization of cystatin M/E and CTSV, we propose that these molecules could have an important role in epidermal differentiation and desquamation.

Oligonucleotide microarray analysis of ameloblastoma compared with dentigerous cyst

BACKGROUND

Ameloblastoma is a benign, but locally invasive tumor known for its high rate of recurrence. However, few comprehensive genetic studies have been conducted about its tumorigenesis. Our aim was to identify possible genes involved in the development and progression of ameloblastoma, using microarray analysis with dentigerous cyst as a control.

METHODS

Total RNA was extracted from two fresh dentigerous cysts and ameloblastoma specimens. Following microarray analysis, semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry were performed on selected genes.

RESULTS

Seventy-three genes were overexpressed and 49 were underexpressed. These genes were divided into categories according to function. The microarray results for 13 selected genes were verified with semiquantitative RT-PCR.

CONCLUSIONS

We identified important genes related to the development and progression of ameloblastoma through a large-scale gene expression analysis. This study will stimulate further investigations on genes significant for early diagnosis and prognosis of ameloblastoma.

Effects of glycolic acid on desquamation-regulating proteinases in human stratum corneum

In order to investigate the mechanism of glycolic acid (GA) function in human stratum corneum, we monitored changes in cathepsin D-like (CD) and chymotrypsin-like (SCCE) proteinases for 3 weeks following topical GA application (50% w/v, pH 0.9) for 30 min to human skin. In the early phase, weakened stratum corneum cohesion in the lower layers was observed on day 2 and the amount of active CD in the upper layer of the stratum corneum was significantly decreased from 30 min until day 2, whereas that in the lower layer remained normal. In contrast, the amount of active SCCE showed no change during the experimental period. The surface pH of the stratum corneum drastically decreased to pH 2 at 30 min and slightly recovered to around pH 3 until 1 day after treatment. From 9 to 19 days, a decrease in corneocyte cell area and a remarkable long-term increase in the amount of active CD in the upper layer were observed. In an in vitro study, the activities of desquamation-regulating proteinases were shown to have remarkably increased at around pH 3, due to activation of CD at its optimal pH. These results suggest that GA functions via at least two different mechanisms, acute activation of CD in the lower layer by acidification around pH 3, along with inactivation of CD in the upper layer, and long-term enhancement of de novo CD production in the few weeks following GA treatment.

Epidermal desquamation

Epidermal desquamation, a continuous but insensible bodily activity, is largely ignored unless the rate or amount of scale production becomes abnormal. It is the last topic to be considered in any serious discussion of epidermal growth and differentiation, but is becoming an increasingly fertile ground for investigation. This review summarizes: (a) methods for measuring desquamation; (b) variables that affect normal desquamation; (c) mechanisms of desquamation; (d) the role of desquamation in nutritional homeostasis; and (e) the role of desquamation as a first line of defense. Consideration is given to whether desquamation might be harnessed to eliminate or remediate toxins that have accumulated in the body.

Cathepsin D, but not cathepsin E, degrades desmosomes during epidermal desquamation

BACKGROUND

We previously reported that an ambient aspartic proteinase is crucial to desquamation of the stratum corneum at pH 5. Identification of this aspartic proteinase by using enzyme inhibitors suggested it to be cathepsin D, although we could not exclude cathepsin E.

OBJECTIVES

To determine the identity of this aspartic proteinase and its distribution within the stratum corneum.

METHODS

We measured enzyme activities of cathepsin D and cathepsin E in the salt and detergent extracts from callus stratum corneum, using a fluorogenic peptide as a substrate and comparing the effect of addition of Ascaris pepsin inhibitor (specific for cathepsin E) with that of pepstatin A (which inhibits both cathepsin D and cathepsin E). Both enzymes were then extracted and purified from plantar stratum corneum samples and identified by Western blotting. Immunofluorescence microscopy was used to investigate the localization of proteinases within human plantar stratum corneum sample sections.

RESULTS

We found that 20% of total aspartic proteinase activity could be attributed to cathepsin E, the remainder to cathepsin D. Two subunits of cathepsin D were identified, a mature active form at 33 kDa and an intermediate active form at 48 kDa; cathepsin E was also identified at 48 kDa, although in a stained band 10-fold weaker in the immunoblot. Immunofluorescence microscopy showed the antibody to cathepsin D to be localized in the lipid envelopes of the stratum corneum, whereas that to cathepsin E stained the tissue diffusely. The labelling for cathepsin D was similar to that observed for desmosomes, and immunoelectron microscopy confirmed that cathepsin D was present on desmosomes. On the other hand, cathepsin E occurred intracellularly within the squames.

CONCLUSIONS

We conclude that cathepsin D, and not cathepsin E, causes desquamation by degrading desmosomes.

The stratum corneum barrier: the final frontier

The stratum corneum (SC) is the differentiated end product of the mammalian epidermis. It is vital to constancy of the milieu interieur (the environment within) because it prevents water loss and the penetration by potentially toxic xenobiotics, damaging radiation, and pathogenic microbes. The intercorneocyte space contains complex nonpolar lipids that constitute the water barrier. The formation of the SC in the process of keratinization is complex providing multiple opportunities for disorders to arise. The final act of keratinization is desquamation and for this to occur the controlled release of single corneocytes is required in which proteases play an important role. Tests and techniques are described that measure the structure and function of the SC.

Degradation of corneodesmosome proteins by two serine proteases of the kallikrein family, SCTE/KLK5/hK5 and SCCE/KLK7/hK7

Corneodesmosin (CDSN), desmoglein 1 (DSG1), and desmocollin 1 (DSC1) are adhesive proteins of the extracellular part of the corneodesmosomes, the junctional structures that mediate corneocyte cohesion. The degradation of these proteins at the epidermis surface is necessary for desquamation. Two serine proteases of the kallikrein family synthesized as inactive precursors have been implicated in this process: the stratum corneum chymotryptic enzyme (SCCE/KLK7/hK7) and the stratum corneum tryptic enzyme (SCTE/KLK5/hK5). Here, we analyzed the capacity of these enzymes to cleave DSG1, DSC1, and epidermal or recombinant forms of CDSN, at an acidic pH close to that of the stratum corneum. SCCE directly cleaved CDSN and DSC1 but was unable to degrade DSG1. But incubation with SCTE induced degradation of the three corneodesmosomal components. Using the recombinant form of CDSN, either with its N-glycan chain or enzymatically deglycosylated, we also demonstrated that oligosaccharide residues do not protect CDSN against proteolysis by SCCE. Moreover, our results suggest that SCTE is able to activate the proform of SCCE. These results strongly suggest that the two kalikreins are involved in desquamation. A model is proposed for desquamation that could be regulated by a precisely controlled protease-protease inhibitor balance.

Human Tissue Kallikreins: Physiologic Roles and Applications in Cancer

Tissue kallikreins are members of the S1 family (clan SA) of trypsin-like serine proteases and are present in at least six mammalian orders. In humans, tissue kallikreins (hK) are encoded by 15 structurally similar, steroid hormone–regulated genes (KLK) that colocalize to chromosome 19q13.4, representing the largest cluster of contiguous protease genes in the entire genome. hKs are widely expressed in diverse tissues and implicated in a range of normal physiologic functions from the regulation of blood pressure and electrolyte balance to tissue remodeling, prohormone processing, neural plasticity, and skin desquamation. Several lines of evidence suggest that hKs may be involved in cascade reactions and that cross-talk may exist with proteases of other catalytic classes. The proteolytic activity of hKs is regulated in several ways including zymogen activation, endogenous inhibitors, such as serpins, and via internal (auto)cleavage leading to inactivation. Dysregulated hK expression is associated with multiple diseases, primarily cancer. As a consequence, many kallikreins, in addition to hK3/PSA, have been identified as promising diagnostic and/or prognostic biomarkers for several cancer types, including ovarian, breast, and prostate. Recent data also suggest that hKs may be causally involved in carcinogenesis, particularly in tumor metastasis and invasion, and, thus, may represent attractive drug targets to consider for therapeutic intervention.

The stratum corneum: structure and function in health and disease

Our understanding of the formation, structure, composition, and maturation of the stratum corneum (SC) has progressed enormously over the past 30 years. Today, there is a growing realization that this structure, while faithfully providing a truly magnificent barrier to water loss, is a unique, intricate biosensor that responds to environmental challenges and surface trauma by initiating a series of biologic processes which rapidly seek to repair the damage and restore barrier homeostasis. The detailed ultrastructural, biochemical, and molecular dissection of the classic "bricks and mortar" model of the SC has provided insights into the basis of dry, scaly skin disorders that range from the cosmetic problems of winter xerosis to severe conditions such as psoriasis. With this knowledge comes the promise of increasingly functional topical therapies.

Expression and localization of tissue kallikrein mRNAs in human epidermis and appendages

Tissue kallikreins are a group of serine proteases that are found in many organs and biologic fluids. Tissue kallikrein genes (KLKs) are found on chromosome 19q13.3-4 as a gene cluster encoding 15 different serine proteases. In skin, two tissue kallikrein proteins, hK5 and hK7, are expressed in the stratum corneum and are known to be involved in desquamation of corneocytes. The possible involvement of other kallikrein proteins has not been clarified, however, nor has the significance of each member in the serine protease activity of skin been delineated. In the study described here, we examined expression and localization of KLK mRNA in normal human skin by means of RT-PCR and in situ hybridization. Quantitative RT-PCR analysis showed abundant expression of KLK1 and KLK11 mRNA, moderate expression of KLK4, KLK5, KLK6, KLK7, and KLK13 mRNA, and low expression of KLK8 mRNA in normal human skin. For KLK4, KLK8, and KLK13 mRNA, splice variants were identified to be their major mRNA species. Two variants for KLK13 mRNA were novel. The amount of the serine protease inhibitor Kazal-type 5 (SPINK5) mRNA was comparable to KLK1 and KLK11 mRNA. In situ hybridization revealed intense expression of all KLK mRNA studied except KLK12 mRNA in the stratum granulosum of normal epidermis, where SPINK5 mRNA coexisted. Excluding KLK13 mRNA, they are also expressed in hair sheath, eccrine sweat glands, and sebaceous glands. Coexpression of various KLK and SPINK5 mRNA suggests that their proteins are the candidates to balance and maintain serine protease activities in both the skin and appendages.

Gelatinase expression at positive patch test reactions

Matrix metalloproteases (MMPs) are proteolytic enzymes involved in tissue remodelling and extracellular matrix (ECM) turnover. They are secreted in a latent form and activated at the cellular surface by a membrane type-1 MMP (MT1-MMP) and a tissue inhibitor of MMP-2 (TIMP-2) that is also responsible for striking a balance between the proteolytic enzymes and TIMP-2. In allergic contact dermatitis (ACD) patients, MMP-2 and MMP-9, two members of the MMPs family, were increased during the challenge phase, in involved but not uninvolved skin. In contrast, TIMP-2 was more evident in uninvolved than involved skin, while no differences were observed with regard to MT1-MMP staining. Comparing the serum of ACD patients with that of healthy subjects, these differences were not observed. These data suggest that MMP-2 and MMP-9 could play a role in the mechanisms inducing alterations of the epidermal architecture, and in the pathogenesis of the lesions.

The spectrum of pathogenic mutations in SPINK5 in 19 families with Netherton syndrome: implications for mutation detection and first case of prenatal diagnosis

The Comèl-Netherton syndrome is an autosomal recessive multisystemic disorder characterized by localized or generalized congenital ichthyosis, hair shaft abnormalities, immune deficiency, and markedly elevated IgE levels. Life-threatening complications during infancy include temperature and electrolyte imbalance, recurrent infections, and failure to thrive. To study the clinical presentations of the Comèl-Netherton syndrome and its molecular cause, we ascertained 19 unrelated families of various ethnic backgrounds. Results of initial linkage studies mapped the Comèl-Netherton syndrome in 12 multiplex families to a 12 cM interval on 5q32, thus confirming genetic homogeneity of Comèl-Netherton syndrome across families of different origins. The Comèl-Netherton syndrome region harbors the SPINK5 gene, which encodes a multidomain serine protease inhibitor (LEKTI) predominantly expressed in epithelial and lymphoid tissues. Recently, recessive mutations in SPINK5 were identified in several Comèl-Netherton syndrome patients from consanguineous families. We used heteroduplex analysis followed by direct DNA sequencing to screen all 33 exons and flanking intronic sequences of SPINK5 in the affected individuals of our cohort. Mutation analysis revealed 17 distinct mutations, 15 of which were novel, segregating in 14 Comèl-Netherton syndrome families. The nucleotide changes included four non-sense mutations, eight small deletions or insertions leading to frameshift, and five splice site defects, all of which are expected to result in premature terminated or altered translation of SPINK5. Almost half of the mutations clustered between exons 2 and 8, including two recurrent mutations. Genotype-phenotype correlations suggested that homozygous nucleotide changes resulting in early truncation of LEKT1 are associated with a severe phenotype. For the first time, we used molecular data to perform prenatal testing, thus demonstrating the feasibility of molecular diagnosis in the Comèl-Netherton syndrome.

Cadherin function: breaking the barrier

Three desmoglein isoforms collaborate with desmocollins to build the adhesive core of desmosomes. A recent study has shown that altering the ratio of desmoglein isoforms influences epidermal barrier function, suggesting distinct roles for these cadherins that extend beyond adhesion.

Refined characterization of corneodesmosin proteolysis during terminal differentiation of human epidermis and its relationship to desquamation

Corneodesmosin is a putative adhesion glycoprotein located in the extracellular part of the desmosomes in the upper layers of the epidermis. Synthesized by granular keratinocytes as a 52-56-kDa protein, corneodesmosin is progressively proteolysed during corneocyte maturation. This processing is a prerequisite for desquamation. Two glycine- and serine-rich domains of the protein might take on the conformation of adhesive secondary structures similar to glycine loops. Corneodesmosin proteolysis was further characterized. Deglycosylation experiments and reactivity with lectins demonstrated that the corneodesmosin carbohydrate moiety does not prevent the proteolysis. Immunoblotting, immunohistochemistry, and immunoelectron microscopy experiments using affinity-purified anti-peptide antibodies raised to four of the five structural domains of corneodesmosin and a monoclonal antibody against its fifth central domain showed that the first step in corneodesmosin processing is the cleavage of its extremities and probably occurs before its incorporation into desmosomes. Then the glycine loop-related domains are cleaved, first the N-terminal and then part of the C-terminal domain. At the epidermis surface, the multistep proteolytic cleavage leaves intact only the central domain, which was detected on exfoliated corneocytes and probably lacks adhesive properties. Importantly, corneodesmosin was demonstrated to be a preferred substrate of two serine proteases involved in desquamation, the stratum corneum tryptic and chymotryptic enzymes.

Cystatin M/E Expression is Restricted to Differentiated Epidermal Keratinocytes and Sweat Glands: a New Skin-Specific Proteinase Inhibitor that is a Target for Cross-Linking by Transglutaminase

Using serial analysis of gene expression on cultured human keratinocytes we found high expression levels of genes putatively involved in host protection and defense, such as proteinase inhibitors and antimicrobial proteins. One of these expressed genes was the recently discovered cysteine proteinase inhibitor cystatin M/E that has not been characterized so far at the protein level with respect to tissue distribution and additional biologic properties. Here we report that cystatin M/E has a tissue-specific expression pattern in which high expression levels are restricted to the stratum granulosum of normal human skin, the stratum granulosum/spinosum of psoriatic skin, and the secretory coils of eccrine sweat glands. Low expression levels were found in the nasal cavity. The presence of cystatin M/E in skin and the lack of expression in a variety of other tissues was verified both at the protein level by immunohistochemistry or western blotting, and at the mRNA level by reverse transcriptase polymerase chain reaction or northern blotting. Using biotinylated hexapeptide probes we found that cystatin M/E is an efficient substrate for tissue type transglutaminase and for transglutaminases extracted from stratum corneum, and that it acts as an acyl acceptor but not as an acyl donor. Western blot analysis showed that recombinant cystatin M/E could be cross-linked to a variety of proteins extracted from stratum corneum. In vitro, we found that cystatin M/E expression in cultured keratinocytes is upregulated at the mRNA and protein level, upon induction of differentiation. We demonstrate that cystatin M/E, which has a putative signal peptide, is indeed a secreted protein and is found in vitro in culture supernatant and in vivo in human sweat by enzyme-linked immunosorbent assay or western blotting. Cystatin M/E showed moderate inhibition of cathepsin B but was not active against cathepsin C. We speculate that cystatin M/E is unlikely to be a physiologically relevant inhibitor of intracellular lysosomal cysteine proteinases but rather functions as an inhibitor of self and nonself cysteine proteinases that remain to be identified.

Persistence of both peripheral and non-peripheral corneodesmosomes in the upper stratum corneum of winter xerosis skin versus only peripheral in normal skin

To understand the biochemical abnormalities that underlie the reduced desquamation observed in dry skin, we analyzed corneodesmosome degradation in normal and winter xerosis skin. Western blotting of total proteins from corneocytes obtained by varnish-strippings from the legs of 56 volunteers with normal (26) or xerotic (30) skin was performed using antibodies specific for (corneo)desmosome proteins. In the whole population, the amounts of desmoglein 1 and plakoglobin were found to be correlated, but were not related to the amounts of corneodesmosin. This suggests simultaneous proteolysis for the former proteins differing from that of corneodesmosin. Neither entire desmoplakins nor any proteolysis-derived fragments were detected. The amounts of corneodesmosin, desmoglein 1, and plakoglobin detected were found to be significantly higher in xerotic compared with normal skin extracts. Conventional and freeze-fracture electron microscopy showed the absence of nonperipheral corneodesmosomes in the upper stratum corneum of normal skin but the presence of a significant number of these structures in the same layer of winter xerosis skin. These results provide a more precise description of the proteolysis of corneodesmosome components in the upper cornified layer of the epidermis. They support previous studies demonstrating the importance of corneodesmosome degradation in desquamation and reveal that the nonperipheral corneodesmosomes, which are totally degraded during maturation of the stratum corneum in normal skin, persist in winter xerosis, probably leading to abnormal desquamation.

S gene (Corneodesmosin) diversity and its relationship to psoriasis; high content of cSNP in the HLA-linked S gene

Psoriasis is a heterogeneous disease in which several reports suggest the presence of a susceptibility gene in or in the proximity of the human leukocyte antigen complex in chromosome 6p. There is an association between HLA-Cw6 and young onset of the disease. The S gene (corneodesmosin), located 160 kb telomeric of HLA-C, is a strong candidate for psoriasis due to its reportedly exclusive expression in differentiating keratinocytes. We have studied this gene in a large Swedish psoriasis population and we report a strikingly high degree of polymorphism in the coding parts of the gene, 1 every 100 base pairs. We used a stratified approach to compare the polymorphic variants in patients and controls. A single nucleotide polymorphism in the coding region leading to an amino acid exchange (Ser-->Phe) that differed significantly between patients and controls was identified (position 619). Owing to a high allele frequency in a larger control group, however, and an insignificant influence of the variant on the age at onset distribution curve based on a large psoriasis population, we could not confirm that this coding single nucleotide polymorphism was involved in disease etiology. We also examined the single nucleotide polymorphism in position 1243, recently proposed to have an influence on the pathogenesis of the disease. This polymorphism showed less association to the disease as compared with the single nucleotide polymorphism at positions 619 and 722. Such a high degree of variation present also in an HLA gene which is not involved in immune response indicates the difficulty involved in assessing the role of a specific allele in the pathogenesis of a complex disease in this region. A strong association effect due to linkage disequilibrium in an extended region in the HLA complex is also a complicating factor.

Stratum corneum tryptic enzyme in normal epidermis: a missing link in the desquamation process?

Stratum corneum chymotryptic enzyme may be important in desquamation. It has also been suggested that other proteases, especially stratum corneum tryptic enzyme, may be involved. Stratum corneum tryptic enzyme has been purified and its cDNA has been cloned. Results from expression analyses indicate that stratum corneum tryptic enzyme is as skin specific as stratum corneum chymotryptic enzyme. In this work we have produced and characterized antibodies specific for stratum corneum tryptic enzyme. We have also by means of biochemical, immunochemical, and immunohistochemical methods performed studies on stratum corneum tryptic enzyme in normal human epidermis. Antibodies against bacterial recombinant stratum corneum tryptic enzyme were produced and purified by affinity chromatography. Two types of antibodies were obtained: one reacting only with pro-stratum corneum tryptic enzyme and one specific for the catalytically active part of stratum corneum tryptic enzyme. Immunohistochemistry with the antibodies reacting with pro-stratum corneum tryptic enzyme showed a staining pattern similar to stratum corneum chymotryptic enzyme-specific antibodies, i.e., the expression was confined to cornifying epithelia with a need of desquamation-like processes. Extracts of tape strips with superficial human stratum corneum were found to contain precursors as well as active forms of stratum corneum tryptic enzyme and stratum corneum chymotryptic enzyme. The enzymes had maximal activity at pH 8, but both had considerable activity also at pH 5.5. The results were compatible for a role of stratum corneum tryptic enzyme in desquamation. Stratum corneum tryptic enzyme may act in concert with stratum corneum chymotryptic enzyme and/or function as a stratum corneum chymotryptic enzyme-activating enzyme. The presence in normal superficial stratum corneum of precursors as well as of active forms of stratum corneum chymotryptic enzyme and stratum corneum tryptic enzyme, and the activity of both enzymes over a broad range of pH-values, suggest some possible ways by which the desquamation may be regulated.

Purification, molecular cloning, and expression of a human stratum corneum trypsin-like serine protease with possible function in desquamation

A new human 33-kDa serine protease was purified from human epidermis, and its cDNA was cloned from a keratinocyte library, from mRNA from a human keratinocyte line (HaCat) and from mRNA from human skin. Polyclonal antibodies specific for the new protein detected three groups of proteins in partially purified extracts of cornified eptihelium of human plantar skin. The three components are proposed to correspond to proenzyme, active enzyme, and proteolytically modified active enzyme. After N-deglycosylation, there was a decrease in apparent molecular mass of all detected components. Expression of the cloned cDNA in a eukaryotic virus-derived system yielded a recombinant protein that could be converted to an active protease by treatment with trypsin. Polymerase chain reaction analyses of cDNA from a number of human tissues showed high expression of the new enzyme in the skin and low expression in brain, placenta, and kidney. Homology searches yielded the highest score for porcine enamel matrix protease (55% amino acid sequence homology). High scores were also obtained for human and mouse neuropsin and for human stratum corneum chymotryptic enzyme. The function of this new protease, tentatively named stratum corneum tryptic enzyme, may be related to stratum corneum turnover and desquamation in the epidermis.

Role of endogenous cathepsin D-like and chymotrypsin-like proteolysis in human epidermal desquamation

Even though the skin surface is acidic (about pH 5), most in vitro studies on desquamation have been performed at alkaline pH. We demonstrate that the standard in vitro model system, which achieves squame shedding upon incubation of plantar stratum corneum for 1 day in an alkaline buffer that must include a chelating agent, can be extended to a more realistic model in which the incubation is for 4 days, at varying pHs from 5 to 8, without exogenous chelators. Desmoglein I from stratum corneum was degraded by the squames shed at pH 5 as well as at pH 8. Squame shedding was inhibited to varying extents by the addition of proteinase inhibitors, whose specificity suggested that the crucial enzymatic activity at pH 8 was a chymotrypsin-like serine proteinase, while a similar activity at pH 5 was accompanied by an aspartic proteinase activity of comparable strength. Four degradation peaks were observed when the insulin B chain was reacted with shed squames at pH 5. Two of these peptides were suppressed by the addition of phenylmethylsulphonyl fluoride, the other two by pepstatin A; chymostatin inhibited all four, but E-64 and leupeptin showed no effect. The implied specificity was confirmed by reacting the insulin (without squames) with the standard enzymes human liver cathepsin D and pancreatic chymotrypsin, reproducing the expected degradation products. These results suggest that epidermal desquamation at acidic pH requires two proteolytic activities, one of which is an analogue of chymotrypsin and the other of cathepsin D. Endogenous proteinases corresponding to these activities have been previously identified, namely the stratum corneum chymotryptic enzyme and the mature active form of cathepsin D.

Molecular cloning and tissue expression of the murine analog to human stratum corneum chymotryptic enzyme

Human stratum corneum chymotryptic enzyme (SCCE) may play a central part in epidermal homeostasis. Its proposed function is to catalyze the degradation of intercellular structures, including desmosomes, in the stratum corneum as part of the desquamation process. In order to facilitate physiologic and pathophysiologic studies on SCCE we have looked for the corresponding murine enzyme. A cDNA obtained by reverse transcription-polymerase chain reaction with total RNA prepared from mouse tails as starting material was cloned, and the expression of the corresponding mRNA studied. The murine cDNA showed 77% homology to human SCCE cDNA. It had an open-reading frame encoding a protein comprising 249 amino acids with 82% amino acid sequence homology to human SCCE including the conserved sequences of the catalytic traid of mammalian serine proteases. The murine protein was deduced to have a 21 amino acid signal peptide and a four amino acid propeptide ending with a tryptic cleavage site, followed by a sequence motif identical to the N-terminal amino acid sequence of native active human SCCE. As in human SCCE the P2 position of the propeptide was occupied by an acidic amino acid residue, and the position corresponding to the suggested bottom of the primary substrate specificity pouch occupied by an asparagine residue. Analyses of mouse tissues by reverse transcriptase-polymerase chain reaction showed high expression in the skin, low expression in lung, kidney, brain, heart, and spleen, and no expression in liver or skeletal muscle. In situ hybridization of mouse skin showed expression in high suprabasal keratinocytes and in the luminal parts of hair follicles. Our results strongly suggest that we have cloned the murine analog of human SCCE cDNA.

Dry condition affects desquamation of stratum corneum in vivo

We examined whether a dry condition actually induces scaly skin in vivo. Hairless mice were kept in a high humidity condition or a low humidity condition and skin changes were examined. Scales appeared on the backs of mice kept for 3 days under the dry condition. The weight of stratum corneum (SC) was increased at this point, and these alterations were not accompanied with hyperproliferation of the nucleated cell layer of the epidermis. A decrease of desmosomal degradation was observed, though, desquamation-related enzyme activity was not altered. The regulation mechanism of desquamation is not yet clear, however, in vitro experiments suggest that the water content in SC is an important factor. The water content of SC was decreased in the dry condition. These results indicate that a dry environment perturbs desmosome degradation in intact SC by decreasing the water content of SC, and the consequent impairment of desquamation in normal skin in vivo may lead to the induction of a scaly skin surface.

The expression of stratum corneum chymotryptic enzyme in human anagen hair follicles: further evidence for its involvement in desquamation-like processes

At sites with a continuous formation of cornified epithelia, there is need for continuous cell shedding in order to maintain normal anatomy. Stratum corneum chymotryptic enzyme (SCCE) has been suggested to mediate this process by degrading intercellular cohesive structures in interfollicular epidermis. In the hair follicle, there are several different kinds of cornification processes. With the exception of the formation of the hair shaft, these processes lead to a continuous formation of structures that have to be shed continuously in order to avoid distorting the anatomy of the follicle. In this work, we have investigated the possible involvement of SCCE in the turnover of cornified cells in anagen hair follicles. Using immunohistochemistry, we demonstrated the expression of SCCE in all parts of the follicle where cells are keratinized and eventually shed, i.e. in the uppermost follicle (distal to the opening of the sebaceous duct), in the sebaceous duct and in all parts of the inner root sheath (IRS). SCCE expression was also seen in those cells of the outer root sheath that are believed to move along with the IRS from the bulb and eventually become keratinized and sloughed in the part of the follicle situated between the terminal edge of the IRS and the opening of the sebaceous duct. We could not detect any SCCE in cells forming the hair shaft. Thus, there was a strong correlation between SCCE expression and the continuous formation and shedding of cornified epithelia in anagen hair follicles. This correlation was stronger for SCCE than for a number of common markers of terminal differentiation in keratinocytes. Our results give further support to a part for SCCE in desquamation-like processes. Whether SCCE is involved in diseases affecting hair growth remains to be elucidated.

Expression cloning of human corneodesmosin proves its identity with the product of the S gene and allows improved characterization of its processing during keratinocyte differentiation

In human epidermis and other cornified squamous epithelia, corneodesmosin is located in the desmosomes of the upper living layers, and in related structures of the cornified layers, the corneodesmosomes. During maturation of the cornified layers, the protein undergoes a series of cleavages, thought to be a prerequisite of desquamation. Partial amino acid sequencing of corneodesmosin fragments suggested that it is related to the product of the S gene, previously identified in the human major histocompatibility complex. We report the expression cloning of corneodesmosin cDNA from a human epidermis library screened with monoclonal antibodies. Sequencing demonstrated that corneodesmosin is really the product of the S gene. However, analysis of 20 alleles of the gene revealed that its product is 27 amino acids longer than initially reported. Two additional polymorphic sites were described, and the position of the unique intron was ascertained. Corneodesmosin cDNA expression in COS-7 cells led to secretion of the protein. Precise epitope mapping allowed further characterization of the molecular forms of corneodesmosin present in the most superficial cornified layers, where fragments corresponding to the central region of the protein were detected. This indicated a cleavage of the N- and C-terminal domains of corneodesmosin before desquamation. These serine- and glycine-rich domains are proposed to mediate an adhesive function.

Cholesterol sulfate inhibits proteases that are involved in desquamation of stratum corneum

We previously reported that desmosomes play a key role in the adhesion of corneocytes, and their digestion by two types of serine proteases leads to desquamation. Patients with recessive X-linked ichthyosis show hyperkeratosis attributable to desmosomes, associated with an increased content of cholesterol sulfate (CS) and an increased thickness of stratum corneum. In this study, therefore, we examined the possibility that CS provokes the abnormal desquamation, acting as a protease inhibitor. Scaling was induced on mice after topical application of chymostatin and leupeptin. Visible scale was also observed on mice after topical application of CS. We found that the stratum corneum thickness of CS-treated mice was increased in comparison with that of vehicle-treated mice. The thickness of the epidermis and the labeling index with proliferating cell nuclear antigen from CS-treated mice was almost the same as that from vehicle-treated mice. Moreover, in the stratum corneum of CS-treated mice, the content of desmosomes was higher than that in vehicle-treated mice. CS also inhibited the protease-induced cell dissociation of human stratum corneum sheets. In vitro, CS competitively inhibited both types of serine protease: the Ki for trypsin was 5.5 x 10(-6) M and that for chymotrypsin was 2.1 x 10(-6) M. These results indicate that CS retards desquamation by acting as a protease inhibitor. Thus, accumulation of stratum corneum in recessive X-linked ichthyosis may be a result of the inhibition by excessive CS of proteases involved in the dissolution of desmosomes, required for desquamation of the stratum corneum.

Characterization and purification of human corneodesmosin, an epidermal basic glycoprotein associated with corneocyte-specific modified desmosomes

Using monoclonal antibodies, we identified a new protein in mammalian epidermis, which we called corneodesmosin. It is located in the extracellular part of the modified desmosomes in the cornified layer of the tissue, and its proteolysis (from 52-56 to 33 kDa) is thought to be a major prerequisite of desquamation. We have now further characterized human corneodesmosin. Proteolysis of purified cornified cell envelopes produced immunoreactive fragments, confirming the covalent linkage of the protein to these structures. Sequential extraction of epidermal proteins indicated that the 52-56-kDa precursor form of the protein exists in two distinct pools, one extracted with a nondenaturing hypotonic buffer, and the other with urea. Two-dimensional gel analysis and reactivity with phosphoserine-specific antibodies showed that it is a basic phosphoprotein. Deglycosylation experiments, reactivity with lectins, and chromatography on concanavalin A-Sepharose indicated that corneodesmosin is N-glycosylated. Partial sequences, 10 and 15 amino acids long, of the purified 52-56-kDa corneodesmosin showed identity with sequences predicted from a previously cloned gene, proved to be expressed in the epidermis and designated S. This indicates that corneodesmosin is probably encoded by the S gene, the function of which was unknown until now. A model of corneodesmosin maturation during cornification is proposed.

Biologically active, alternatively processed interleukin-1 beta in psoriatic scales

The aims of the present work were to elucidate the biochemical properties of interleukin-1 beta (IL-1 beta) in psoriatic scales to get information on the processing of epidermal IL-1 beta in psoriasis, and to elucidate whether the IL-1 beta in psoriatic scales possesses biological activity. By means of ion exchange chromatography, IL-1 beta in extracts of psoriatic scales was purified to a stage where it could be analyzed with electrophoretic methods and immunoblotting. Compared to mature recombinant human IL-1 beta (Ala 117 IL-1 beta), IL-1 beta in psoriatic scales had a slightly higher apparent molecular mass and a more acidic isoelectric point, as revealed by two-dimensional electrophoresis under denaturing conditions. Isoelectric focusing under non-denaturing conditions of IL-1 beta partially purified from psoriatic scales, or from non-inflamed plantar stratum corneum (Nylander Lundqvist, E., Bäck, O. and Egelrud, T., J. Immunol. 1996. 157: 1699), and of mature IL-1 beta, followed by immunoblotting with IL-1 beta-specific antibodies, showed that psoriatic scales contained two components with IL-1 beta-like immunoreactivity which were isoelectric at pH 6.1 and 6.3, respectively. These components could also be detected in extracts of plantar stratum corneum, which also contained small amounts of an IL-1 beta-like component isoelectric at pH 6.9. Mature IL-1 beta was isoelectric at pH 6.9. No IL-1 beta-like biological activity could be detected in crude extracts of psoriatic scales. These extracts also contained high amounts of IL-1 receptor antagonist. Partially purified preparations of IL-1 beta from psoriatic scales, in which an apparently total separation of IL-1 beta and IL-1 receptor antagonist had been achieved, could induce expression of E-selectin in human umbilical vein endothelial cells. This activity was inhibited by antibodies specific for IL-1 beta, but not by antibodies specific for IL-1 alpha. It is concluded that psoriatic scales contain biologically active IL-1 beta, which has been processed by a mechanism which may be similar to that present in non-inflamed plantar stratum corneum, and which does not involve IL-1 beta converting enzyme.