Autosomal recessive ichthyosis with hypotrichosis caused by a mutation in ST14, encoding type II transmembrane serine protease matriptase

SERPINB7 Deficiency Increases Legumain Activity and Impairs the Epidermal Barrier in Nagashima-type Palmoplantar Keratoderma

Nagashima-type palmoplantar keratoderma (NPPK) is an autosomal recessive genodermatosis caused by loss-of-function variants in SERPINB7 and is the most prevalent form of inherited palmoplantar keratodermas among Asians. However, there is currently no effective therapy for NPPK because its pathogenesis remains unclear. In this study, Serpinb7-/- mice were generated and spontaneously developed a disrupted skin barrier, which was further exacerbated by acetone-ether-water treatment. The skin of these Serpinb7-/- mice showed weakened cytoskeletal proteins. Additionally, SERPINB7 deficiency consistently led to decreased epidermal differentiation in a three-dimensional human epidermal model. We also demonstrated that SERPINB7 was an inhibitory serpin that mainly inhibited the protease legumain. SERPINB7 bound directly with legumain and inhibited legumain activity both in vitro and in vivo. Furthermore, we found that SERPINB7 inhibited legumain in a 'protease-substrate' manner and identified the cleavage sites of SERPINB7 as Asn71 and Asn343. Overall, we found that SERPINB7 showed the nature of a cysteine protease inhibitor, and identified legumain as a key target protease of SERPINB7. Loss of SERPINB7 function led to overactivation of legumain, which might disrupt cytoskeletal proteins, contributing to the impaired skin barrier in NPPK. These findings may lead to the development of therapeutic strategies for NPPK.

Proteolytic and Antiproteolytic Activity in the Skin: Gluing the Pieces Together

Epidermal differentiation is ultimately aimed at the formation of a functional barrier capable of protecting the organism from the environment while preventing loss of biologically vital elements. Epidermal differentiation entails a delicately regulated process of cell-cell junction formation and dissolution to enable upward cell migration and desquamation. Over the past two decades, the deciphering of the genetic basis of a number of inherited conditions has delineated the pivotal role played in this process by a series of proteases and protease inhibitors, including serpins, cathepsins, and cystatins, suggesting novel avenues for therapeutic intervention in both rare and common disorders of cornification.

A novel CLDN1 variant identified in a case of ILVASC with sparse curly hair

ILVASC (ichthyosis, leukocyte vacuoles, alopecia and sclerosing cholangitis) is an extremely rare autosomal recessive syndromic ichthyosis. Herein we report on a Chinese ILVASC case with a novel phenotype of curly hair caused by a previously unrecorded homozygous mutation in CLDN1.

HAI-1 is required for the novel role of FGFBP1 in maintenance of cell morphology and F-actin rearrangement in human keratinocytes

Formation and maintenance of skin barrier function require tightly controlled membrane-associated proteolysis, in which the integral membrane Kunitz-type serine protease inhibitor, HAI-1, functions as the primary inhibitor of the membrane-associated serine proteases, matriptase and prostasin. Previously, HAI-1 loss in HaCaT human keratinocytes resulted in an expected increase in prostasin proteolysis but a paradoxical decrease in matriptase proteolysis. The paradoxical decrease in shed active matriptase is further investigated in this study with an unexpected discovery of novel functions of fibroblast growth factor-binding protein 1 (FGFBP1), which acts as an extracellular ligand that can rapidly elicit F-actin rearrangement and subsequently affect the morphology of human keratinocytes. This novel growth factor-like function is in stark contrast to the canonical activity of this protein through interactions with FGFs for its pathophysiological functions. This discovery began with the observation that HAI-1 KO HaCaT cells lose the characteristic cobblestone morphology of the parental cells and exhibit aberrant F-actin formation along with altered subcellular targeting of matriptase and HAI-2. The alterations in cell morphology and F-actin status caused by targeted HAI-1 deletion can be restored by treatment with conditioned medium from parental HaCaT cells, in which FGFBP1 was identified by tandem mass spectrometry. Recombinant FGFBP1 down to 1 ng/ml was able to revert the changes caused by HAI-1 loss. Our study reveals a novel function of FGFBP1 in the maintenance of keratinocyte morphology, which depends on HAI-1.

PRSS8, encoding prostasin, is mutated in patients with autosomal recessive ichthyosis

Ichthyosis is a genetically heterogeneous genodermatosis characterized by severely rough, dry and scaly skin. We report two consanguineous families with congenital ichthyosis. Combined positional mapping and exome sequencing of the two families revealed novel homozygous likely deleterious variants in PRSS8 (encoding prostasin) within a linkage locus on chromosome 16. One variant involved a canonical splice site and was associated with reduced abundance of the normal transcript, while the other was a missense variant that altered a highly conserved residue. The phenotype of Prss8 knockout mouse bears a striking resemblance to the one we describe in human patients, including the skin histopathology. Our data suggest a novel PRSS8-related ichthyosis disorder.

Ichthyosis

The ichthyoses are a large, heterogeneous group of skin cornification disorders. They can be inherited or acquired, and result in defective keratinocyte differentiation and abnormal epidermal barrier formation. The resultant skin barrier dysfunction leads to increased transepidermal water loss and inflammation. Disordered cornification is clinically characterized by skin scaling with various degrees of thickening, desquamation (peeling) and erythema (redness). Regardless of the type of ichthyosis, many patients suffer from itching, recurrent infections, sweating impairment (hypohidrosis) with heat intolerance, and diverse ocular, hearing and nutritional complications that should be monitored periodically. The characteristic clinical features are considered to be a homeostatic attempt to repair the skin barrier, but heterogeneous clinical presentation and imperfect phenotype-genotype correlation hinder diagnosis. An accurate molecular diagnosis is, however, crucial for predicting prognosis and providing appropriate genetic counselling. Most ichthyoses severely affect patient quality of life and, in severe forms, may cause considerable disability and even death. So far, treatment provides only symptomatic relief. It is lifelong, expensive, time-consuming, and often provides disappointing results. A better understanding of the molecular mechanisms that underlie these conditions is essential for designing pathogenesis-driven and patient-tailored innovative therapeutic solutions.

ROS is a master regulator of in vitro matriptase activation

Matriptase is a type II transmembrane serine protease that is widely expressed in normal epithelial cells and epithelial cancers. Studies have shown that regulation of matriptase expression and activation becomes deranged in several cancers and is associated with poor disease-free survival. Although the central mechanism of its activation has remained unknown, our lab has previously demonstrated that inflammatory conditions such as intracellular pH decrease strongly induces matriptase activation. In this investigation, we first demonstrate clear matriptase activation following Fulvestrant (ICI) and Tykerb (Lapatinib) treatment in HER2-amplified, estrogen receptor (ER)-positive BT474, MDA-MB-361 and ZR-75-30 or single ER-positive MCF7 cells, respectively. This activation modestly involved Phosphoinositide 3-kinase (PI3K) activation and occurred as quickly as six hours post treatment. We also demonstrate that matriptase activation is not a universal hallmark of stress, with Etoposide treated cells showing a larger degree of matriptase activation than Lapatinib and ICI-treated cells. While etoposide toxicity has been shown to be mediated through reactive oxygen species (ROS) and MAPK/ERK kinase (MEK) activity, MEK activity showed no correlation with matriptase activation. Novelly, we demonstrate that endogenous and exogenous matriptase activation are ROS-mediated in vitro and inhibited by N-acetylcysteine (NAC). Lastly, we demonstrate matriptase-directed NAC treatment results in apoptosis of several breast cancer cell lines either alone or in combination with clinically used therapeutics. These data demonstrate the contribution of ROS-mediated survival, its independence of kinase-mediated survival, and the plausibility of using matriptase activation to indicate the potential success of antioxidant therapy.

Investigating the morphology and genetics of scalp and facial hair characteristics for phenotype prediction

Microscopic traits and ultrastructure of hair such as cross-sectional shape, pigmentation, curvature, and internal structure help determine the level of variations between and across human populations. Apart from cosmetics and anthropological applications, such as determining species, somatic origin (body area), and biogeographic ancestry, the evidential value of hair has increased with rapid progression in the area of forensic DNA phenotyping (FDP). Individuals differ in the features of their scalp hair (greying, shape, colour, balding, thickness, and density) and facial hair (eyebrow thickness, monobrow, and beard thickness) features. Scalp and facial hair characteristics are genetically controlled and lead to visible inter-individual variations within and among populations of various ethnic origins. Hence, these characteristics can be exploited and made more inclusive in FDP, thereby leading to more comprehensive, accurate, and robust prediction models for forensic purposes. The present article focuses on understanding the genetics of scalp and facial hair characteristics with the goal to develop a more inclusive approach to better understand hair biology by integrating hair microscopy with genetics for genotype-phenotype correlation research.

Loricrin at the Boundary between Inside and Outside

Cornification is a specialized mode of the cell-death program exclusively allowed for terrestrial amniotes. Recent investigations suggest that loricrin (LOR) is an important cornification effector. As the connotation of its name (“lorica” meaning an armor in Latin) suggests, the keratin-associated protein LOR promotes the maturation of the epidermal structure through organizing covalent cross-linkages, endowing the epidermis with the protection against oxidative injuries. By reviewing cornification mechanisms, we seek to classify ichthyosiform dermatoses based on their function, rather than clinical manifestations. We also reviewed recent mechanistic insights into the Kelch-like erythroid cell-derived protein with the cap “n” collar homology-associated protein 1/nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway in skin health and diseases, as LOR and NRF2 coordinate the epidermis-intrinsic xenobiotic metabolism. Finally, we refine the theoretical framework of cross-talking between keratinocytes and epidermal resident leukocytes, dissecting an LOR immunomodulatory function.

Reconstructing the epidermal proteolytic cascades in health and disease

The epidermis is the outer stratified epithelium of the skin, forming the physical barrier that is indispensable for homeostasis. Epidermal proteolysis, mainly but not exclusively executed by kallikrein-related peptidases (KLKs), is tightly regulated to ensure maintenance of physiological skin renewal and an intact skin barrier. Perturbation of epidermal proteolytic networks is implicated in a wide array of rare and common skin pathologies of diverse genetic backgrounds. Recent studies of monogenic human skin diseases and newly developed animal models have revealed new mechanisms of regulation of proteolytic pathways in epidermal physiology and in disease states. These new data have challenged some accepted views, for example the role of matriptase in epidermal desquamation, which turned out to be restricted to mouse skin. The significance of PAR2 signaling in skin inflammation should also be reconsidered in the face of recent findings. Cumulatively, recent studies necessitate a sophisticated redefinition of the proteolytic and signaling pathways that operate in human skin. We elaborate how epidermal proteolysis is finely regulated at multiple levels, and in a spatial manner that was not taken into consideration so far, in which specific proteases are confined to distinct epidermal sublayers. Of interest, transglutaminases have emerged as regulators of epidermal proteolysis and desquamation by spatially fixing endogenous protease inhibitors, constituting regulatory factors that were not recognized before. Furthermore, new evidence suggests a link between proteolysis and lipid metabolism. By synthesis of established notions and recent discoveries, we provide an up-to-date critical parathesis of current knowledge and the extended complexity of proteolysis regulation and signaling pathways in skin. This article is protected by copyright. All rights reserved.

Variants in the PNPLA1 Gene in Families with Autosomal Recessive Congenital Ichthyosis Reveal Clinical Significance

The term autosomal recessive congenital ichthyosis (ARCI) is the subgroup of ichthyosis, which describes a highly heterogeneous group of genetic disorders of the skin characterized by cornification and defective keratinocytes differentiation associated with mutations in at least 14 genes including PNPLA1. To study the molecular basis of the Pakistani kindreds (A and B) affected by ARCI, whole-exome sequencing (WES) in the DNA samples of affected members was performed followed by Sanger sequencing of the candidate gene to hunt down the disease-causing sequence variant/s. WES data analysis led to the identification of a novel nonsense sequence variant (c.892C>T; p.Arg298*, family A) and a recurrent missense variant (c.102C>A; p.Asp34Glu, family B) in PNPLA1 mapped to the ARCI locus in chromosome 6p21.31. Validation and cosegregation analysis of the variants in the remaining family members of the respective families were confirmed by Sanger sequencing. The current investigation expands the spectrum of PNPLA1 mutations and helps establish the proper clinico-genetic diagnosis and correct genotype-phenotype correlation.

Pili Torti: A Feature of Numerous Congenital and Acquired Conditions

Pili torti is a rare condition characterized by the presence of the hair shaft, which is flattened at irregular intervals and twisted 180° along its long axis. It is a form of hair shaft disorder with increased fragility. The condition is classified into inherited and acquired. Inherited forms may be either isolated or associated with numerous genetic diseases or syndromes (e.g., Menkes disease, Björnstad syndrome, Netherton syndrome, and Bazex-Dupré-Christol syndrome). Moreover, pili torti may be a feature of various ectodermal dysplasias (such as Rapp-Hodgkin syndrome and Ankyloblepharon-ectodermal defects-cleft lip/palate syndrome). Acquired pili torti was described in numerous forms of alopecia (e.g., lichen planopilaris, discoid lupus erythematosus, dissecting cellulitis, folliculitis decalvans, alopecia areata) as well as neoplastic and systemic diseases (such as cutaneous T-cell lymphoma, scalp metastasis of breast cancer, anorexia nervosa, malnutrition, cataracts, and chronic graft-vs.-host disease). The condition may also be induced by several drugs (epidermal growth factor receptor inhibitors, oral retinoids, sodium valproate, and carbamide perhydrate). The diagnosis of pili torti is based on trichoscopic or microscopic examination. As pili torti is a marker of numerous congenital and acquired disorders, in every case, the search for the signs of underlying conditions is recommended.

Experimental Models for the Study of Hereditary Cornification Defects

Ichthyoses comprise a broad spectrum of keratinization disorders due to hereditary defects of cornification. Until now, mutations in more than 50 genes, mostly coding for structural proteins involved in epidermal barrier formation, have been identified as causes for different types of these keratinization disorders. However, due to the high heterogeneity and difficulties in the establishment of valid experimental models, research in this field remains challenging and translation of novel findings to clinical practice is difficult. In this review, we provide an overview of existing models to study hereditary cornification defects with focus on ichthyoses and palmoplantar keratodermas.

Targeted deletion of HAI-1 increases prostasin proteolysis but decreases matriptase proteolysis in human keratinocytes

Epidermal differentiation and barrier function require well-controlled matriptase and prostasin proteolysis, in which the Kunitz-type serine protease inhibitor HAI-1 represents the primary enzymatic inhibitor for both proteases. HAI-1, however, also functions as a chaperone-like protein necessary for normal matriptase synthesis and intracellular trafficking. Furthermore, other protease inhibitors, such as antithrombin and HAI-2, can also inhibit matriptase and prostasin in solution or in keratinocytes. It remains unclear, therefore, whether aberrant increases in matriptase and prostasin enzymatic activity would be the consequence of targeted deletion of HAI-1 and so subsequently contribute to the epidermal defects observed in HAI-1 knockout mice. The impact of HAI-1 deficiency on matriptase and prostasin proteolysis was, here, investigated in HaCaT human keratinocytes. Our results show that HAI-1 deficiency causes an increase in prostasin proteolysis via increased protein expression and zymogen activation. It remains unclear, however, whether HAI-1 deficiency increases "net" prostasin enzymatic activity because all of the activated prostasin was detected in complexes with HAI-2, suggesting that prostasin enzymatic activity is still under tight control in HAI-1-deficient keratinocytes. Matriptase proteolysis is, however, unexpectedly suppressed by HAI-1 deficiency, as manifested by decreases in zymogen activation, shedding of active matriptase, and matriptase-dependent prostasin zymogen activation. This suppressed proteolysis results mainly from the reduced ability of HAI-1-deficient HaCaT cells to activate matriptase and the rapid inhibition of nascent active matriptase by HAI-2 and other yet-to-be-identified protease inhibitors. Our study provides novel insights with opposite impacts by HAI-1 deficiency on matriptase versus prostasin proteolysis in keratinocytes.

"Structural imprinting" of the cutaneous immune effector function

Keratinization provides tolerance to desiccation and mechanical durability. Loricrin, which is an epidermal thiol-rich protein, efficiently stabilizes terminally differentiated keratinocytes and maintains redox homeostasis. The discovery of the largely asymptomatic loricrin knockout (LKO) phenotype decades ago was rather unpredicted. Nevertheless, when including redox-driven, NF-E2-related factor 2-mediated backup responses, LKO mice provide opportunities for the observation of altered or "quasi-normal" homeostasis. Specifically, given that the tissue structure, as well as the local metabolism, transmits immunological signals, we sought to dissect the consequence of truncated epidermal differentiation program from immunological perspectives. Through a review of the aggregated evidence, we have attempted to generate an integrated view of the regulation of the peripheral immune system, which possibly occurs within the squamous epithelial tissue with truncated differentiation. This synthesis might not only provide insights into keratinization but also lead to the identification of factors intrinsic to the epidermis that imprint the immune effector function.

Preparing the hair follicle canal for hair shaft emergence

The emergence of hair is a defining event during mammalian skin development, but the cellular mechanisms leading to the opening of the hair follicle canal remain poorly characterized. Our previous studies have shown that early hair buds possess a central column of differentiated keratinocytes expressing Keratin 79 (K79), which marks the future hair follicle opening. Here, we report that during late embryogenesis and early postnatal development, K79+ cells at the distal tips of these columns downregulate E-cadherin, change shape, recede and undergo cell death. These changes likely occur independently of sebaceous glands and the growing hair shaft, and serve to create an orifice for hair to subsequently emerge. Defects in this process may underlie phenomena such as ingrown hair or may potentially contribute to upper hair follicle pathologies including acne, hidradenitis suppurativa and infundibular cysts.

Mild acidity likely accelerates the physiological matriptase autoactivation process: a comparative study between spontaneous and acid-induced matriptase zymogen activation

The pathophysiological functions of matriptase, a type 2 transmembrane serine protease, rely primarily on its enzymatic activity, which is under tight control through multiple mechanisms. Among those regulatory mechanisms, the control of zymogen activation is arguably the most important. Matriptase zymogen activation not only generates the mature active enzyme but also initiates suppressive mechanisms, such as rapid inhibition by HAI-1, and matriptase shedding. These tightly coupled events allow the potent matriptase tryptic activity to fulfill its biological functions at the same time as limiting undesired hazards. Matriptase is converted to the active enzyme via a process of autoactivation, in which the activational cleavage is thought to rely on the interactions of matriptase zymogen molecules and other as yet identified proteins. Matriptase autoactivation can occur spontaneously and is rapidly followed by the formation and then shedding of matriptase-HAI-1 complexes, resulting in the presence of relatively low levels of the complex on cells. Activation can also be induced by several non-protease factors, such as the exposure of cells to a mildly acidic buffer, which rapidly causes high-level matriptase zymogen activation in almost all cell lines tested. In the current study, the structural requirements for this acid-induced zymogen activation are compared with those required for spontaneous activation through a systematic analysis of the impact of 18 different mutations in various structural domains and motifs on matriptase zymogen activation. Our study reveals that both acid-induced matriptase activation and spontaneous activation depend on the maintenance of the structural integrity of the serine protease domain, non-catalytic domains, and posttranslational modifications. The common requirements of both modes of activation suggest that acid-induced matriptase activation may function as a physiological mechanism to induce pericellular proteolysis by accelerating matriptase autoactivation.

Matriptase and prostasin proteolytic activities are differentially regulated in normal and wounded skin

Orchestrated control of multiple overlapping and sequential processes is required for the maintenance of epidermal homeostasis and the response to and recovery from a variety of skin insults. Previous studies indicate that membrane-associated serine protease matriptase and prostasin play essential roles in epidermal development, differentiation, and barrier formation. The control of proteolysis is a highly regulated process, which depends not only on gene expression but also on zymogen activation and the balance between protease and protease inhibitor. Subcellular localization can affect the accessibility of protease inhibitors to proteases and, thus, also represents an integral component of the control of proteolysis. To understand how membrane-associated proteolysis is regulated in human skin, these key aspects of matriptase and prostasin were determined in normal and injured human skin by immunohistochemistry. This staining shows that matriptase is expressed predominantly in the zymogen form at the periphery of basal and spinous keratinocytes, and prostasin appears to be constitutively activated at high levels in polarized organelle-like structures of the granular keratinocytes in the adjacent quiescent skin. The membrane-associated proteolysis appears to be elevated via an increase in matriptase zymogen activation and prostasin protein expression in areas of skin recovering from epidermal insults. There was no noticeable change observed in other regulatory aspects, including the expression and tissue distribution of their cognate inhibitors HAI-1 and HAI-2. This study reveals that the membrane-associated proteolysis may be a critical epidermal mechanism involved in responding to, and recovering from, damage to human skin.

Mutations in ASPRV1 Cause Dominantly Inherited Ichthyosis

The discovery of genetic causes of inherited skin disorders has been pivotal to the understanding of epidermal differentiation, function, and renewal. Here we show via exome sequencing that mutations in ASPRV1 (aspartic peptidase retroviral-like 1) cause a dominant Mendelian disorder featuring palmoplantar keratoderma and lamellar ichthyosis, a phenotype that has otherwise been exclusively recessive. ASPRV1 encodes a mammalian-specific and stratified epithelia-specific protease important in processing of filaggrin, a critical component of the uppermost epidermal layer. Three different heterozygous ASPRV1 missense mutations in four unrelated ichthyosis kindreds segregate with disease and disrupt protein residues within close proximity to each other and autocatalytic cleavage sites. Expression of mutant ASPRV1 proteins demonstrates that all three mutations alter ASPRV1 auto-cleavage and filaggrin processing, a function vital to epidermal barrier integrity.

The role of kallikreins in inflammatory skin disorders and their potential as therapeutic targets

The skin is a vital organ of the human body, serving numerous protective and functional roles that are essential for survival. Residing in the epidermis are various epidermal proteases responsible for the establishment and regulation of barrier function. The human tissue kallikrein-related peptidase family conserves homeostasis of the skin barrier through their roles in desquamation, antimicrobial defense, innate immune response, and barrier maintenance. The activity of kallikreins is tightly regulated and dysregulation of kallikrein activity is seen to contribute to the formation of several inflammatory skin disorders. This review highlights the roles of kallikreins in skin homeostasis and pathologies. Due to their part in these skin disorders, inhibitors of the skin kallikreins have become attractive therapeutics. Over the past few years, both natural and synthetic inhibitors of several kallikreins have been identified and are undergoing further development as treatments to restore compromised barrier function. This review summarizes the kallikrein inhibitors under development for this purpose. These inhibitors remain promising therapeutics in cases of severe skin inflammation not well managed by current therapies.

The matriptase-prostasin proteolytic cascade in dermatologic diseases

The proper development and function of skin and hair are dependent on proteolytic activities. Specifically, the matriptase-prostasin cascade is a series of proteolytic reactions in the epidermis integral to normal regulation of desquamation. An increasing amount of research describing this pathway has recently become available, and the importance of this pathway is exhibited by the association of genetic defects in this pathway with human diseases of the skin and hair. Given the relevance of this pathway to dermatology, we provide a review of the current understanding of its relevance to distinct clinical entities, including ichthyosis-hypotrichosis and Netherton syndromes.

Membrane-anchored serine proteases as regulators of epithelial function

Cleavage of proteins in the extracellular milieu, including hormones, growth factors and their receptors, ion channels, and various cell adhesion and extracellular matrix molecules, plays a key role in the regulation of cell behavior. Among more than 500 proteolytic enzymes encoded by mammalian genomes, membrane-anchored serine proteases (MASPs), which are expressed on the surface of epithelial cells of all major organs, are excellently suited to mediate signal transduction across the epithelia and are increasingly being recognized as important regulators of epithelial development, function, and disease [ 1-3]. In this minireview, we summarize current knowledge of the in vivo roles of MASPs in acquisition and maintenance of some of the defining functions of epithelial tissues, such as barrier formation, ion transport, and sensory perception.

Matriptase Cleaves EpCAM and TROP2 in Keratinocytes, Destabilizing Both Proteins and Associated Claudins

The homologs EpCAM and TROP2, which both interact with claudin-1 and claudin-7, are frequently coexpressed in epithelia including skin. Intestine uniquely expresses high levels of EpCAM but not TROP2. We previously identified EpCAM as a substrate of the membrane-anchored protease matriptase and linked HAI-2, matriptase, EpCAM and claudin-7 in a pathway that is pivotal for intestinal epithelial cells (IEC) homeostasis. Herein, we reveal that TROP2 is also a matriptase substrate. Matriptase cleaved TROP2 when purified recombinant proteins were mixed in vitro. TROP2, like EpCAM, was also cleaved after co-transfection of matriptase in 293T cells. Neither EpCAM nor TROP2 cleavage was promoted by protease-disabled matriptase or matriptase that harbored the ichthyosis-associated G827R mutation. We confirmed that EpCAM and TROP2 are both expressed in skin and detected cleavage of these proteins in human keratinocytes (HaCaT cells) after the physiologic inhibition of matriptase by HAI proteins was relieved by siRNA knockdown. Knockdown of EpCAM or TROP2 individually had only small effects on claudin-1 and claudin-7 levels, whereas elimination of both markedly diminished claudin levels. HAI-1 knockdown promoted EpCAM and TROP2 cleavage accompanied by reductions in claudins, whereas HAI-2 knockdown had little impact. Double knockdown of HAI-1 and HAI-2 induced nearly complete cleavage of EpCAM and TROP2 and drastic reductions of claudins. These effects were eliminated by concurrent matriptase knockdown. Decreases in claudin levels were also diminished by the lysosomal inhibitor chloroquine and cleaved EpCAM/TROP2 fragments accumulated preferentially. We demonstrate that TROP2 and EpCAM exhibit redundancies with regard to regulation of claudin metabolism and that an HAI, matriptase, EpCAM and claudin pathway analogous to what we described in IECs exists in keratinocytes. This study may offer insights into the mechanistic basis for matriptase dysregulation-induced ichthyosis.

Cell surface-anchored serine proteases in cancer progression and metastasis

Over the last two decades, a novel subgroup of serine proteases, the cell surface-anchored serine proteases, has emerged as an important component of the human degradome, and several members have garnered significant attention for their roles in cancer progression and metastasis. A large body of literature describes that cell surface-anchored serine proteases are deregulated in cancer and that they contribute to both tumor formation and metastasis through diverse molecular mechanisms. The loss of precise regulation of cell surface-anchored serine protease expression and/or catalytic activity may be contributing to the etiology of several cancer types. There is therefore a strong impetus to understand the events that lead to deregulation at the gene and protein levels, how these precipitate in various stages of tumorigenesis, and whether targeting of selected proteases can lead to novel cancer intervention strategies. This review summarizes current knowledge about cell surface-anchored serine proteases and their role in cancer based on biochemical characterization, cell culture-based studies, expression studies, and in vivo experiments. Efforts to develop inhibitors to target cell surface-anchored serine proteases in cancer therapy will also be summarized.

Molecular Mechanism of Epidermal Barrier Dysfunction as Primary Abnormalities

Epidermal barrier integrity could be influenced by various factors involved in epidermal cell differentiation and proliferation, cell–cell adhesion, and skin lipids. Dysfunction of this barrier can cause skin disorders, including eczema. Inversely, eczema can also damage the epidermal barrier. These interactions through vicious cycles make the mechanism complicated in connection with other mechanisms, particularly immunologic responses. In this article, the molecular mechanisms concerning epidermal barrier abnormalities are reviewed in terms of the following categories: epidermal calcium gradients, filaggrin, cornified envelopes, desquamation, and skin lipids. Mechanisms linked to ichthyoses, atopic dermatitis without exacerbation or lesion, and early time of experimental irritation were included. On the other hand, the mechanism associated with epidermal barrier abnormalities resulting from preceding skin disorders was excluded. The molecular mechanism involved in epidermal barrier dysfunction has been mostly episodic. Some mechanisms have been identified in cultured cells or animal models. Nonetheless, research into the relationship between the causative molecules has been gradually increasing. Further evidence-based systematic data of target molecules and their interactions would probably be helpful for a better understanding of the molecular mechanism underlying the dysfunction of the epidermal barrier.

Genodermatoses with teeth abnormalities

Many genodermatoses exhibit abnormal teeth findings. Studies examining these entities are scarce and narrow in their scope. This paper reviews the evolution, development, and structure of the tooth and provides a summary of genodermatoses with aberrant dental findings. The latter are classified according to the abnormal dental findings: periodontal disease, anodontia/oligodontia/hypodontia, polydontia, enamel hypoplasia, natal teeth, dental pits, and others. Finally, we provide an algorithm that dermatologists and dentists can follow to better recognize genodermatoses with dental involvement.

Proteolysis and Oxidation of Therapeutic Proteins After Intradermal or Subcutaneous Administration

The intradermal (ID) and subcutaneous (SC) routes are commonly used for therapeutic proteins (TPs) and vaccines; however, the bioavailability of TPs is typically less than small molecule drugs given via the same routes. Proteolytic enzymes in the dermal, SC, and lymphatic tissues may be responsible for the loss of TPs. In addition, the TPs may be exposed to reactive oxygen species generated in the SC tissue and the lymphatic system in response to injection-related trauma and impurities within the formulation. The reactive oxygen species can oxidize TPs to alter their efficacy and immunogenicity potential. Mechanistic understandings of the dominant proteolysis and oxidative routes are useful in the drug discovery process, formulation development, and to assess the potential for immunogenicity and altered pharmacokinetics (PK). Furthermore, in vitro tools representing the ID or SC and lymphatic system can be used to evaluate the extent of proteolysis of the TPs after the injection and before systemic entry. The in vitro clearance data may be included in physiologically based pharmacokinetic models for improved PK predictions. In this review, we have summarized various physiological factors responsible for proteolysis and oxidation of TPs after ID and SC administration.

Matriptase drives early-onset intestinal failure in a mouse model of congenital tufting enteropathy

Syndromic congenital tufting enteropathy (CTE) is a life-threatening recessive human genetic disorder that is caused by mutations in SPINT2, encoding the protease inhibitor HAI-2, and is characterized by severe intestinal dysfunction. We recently reported the generation of a Spint2-deficient mouse model of CTE. Here, we show that the CTE-associated early-onset intestinal failure and lethality of Spint2-deficient mice is caused by unchecked activity of the serine protease matriptase. Macroscopic and histological defects observed in the absence of HAI-2, including villous atrophy, luminal bleeding, loss of mucin-producing goblet cells, loss of defined crypt architecture and the resulting acute inflammatory response in the large intestine, were all prevented by intestinal-specific inactivation of the St14 gene encoding matriptase. The CTE-associated loss of the cell junctional proteins EpCAM and claudin 7 was also prevented. As a result, inactivation of intestinal matriptase allowed Spint2-deficient mice to gain weight after birth and dramatically increased their lifespan. These data implicate matriptase as a causative agent in the development of CTE and may provide a new target for the treatment of CTE in individuals carrying SPINT2 mutations.This article has an associated 'The people behind the papers' interview.

Autoactivation and calpain-1-mediated shedding of hepsin in human hepatoma cells

Hepsin is a transmembrane serine protease implicated in many biological processes, including hepatocyte growth, urinary protein secretion, auditory nerve development, and cancer metastasis. Zymogen activation is critical for hepsin function. To date, how hepsin is activated and regulated in cells remains an enigma. In this study, we conducted site-directed mutagenesis, cell expression, plasma membrane protein labeling, trypsin digestion, Western blotting, and flow cytometry experiments in human hepatoma HepG2 cells, where hepsin was originally discovered, and SMMC-7721 cells. Our results show that hepsin is activated by autocatalysis on the cell surface but not intracellularly. Moreover, we show that hepsin undergoes ectodomain shedding. In the conditioned medium from HepG2 and SMMC-7721 cells, we detected a soluble fragment comprising nearly the entire extracellular region of hepsin. By testing protease inhibitors, gene knockdown, and site-directed mutagenesis, we identified calpain-1 as a primary protease that acted extracellularly to cleave Tyr52 in the juxtamembrane space of hepsin. These results provide new insights into the biochemical and cellular mechanisms that regulate hepsin expression and activity.

Cholesterol homeostasis: Links to hair follicle biology and hair disorders

Lipids and lipid metabolism are critical factors in hair follicle (HF) biology, and cholesterol has long been suspected of influencing hair growth. Altered cholesterol homeostasis is involved in the pathogenesis of primary cicatricial alopecia, mutations in a cholesterol transporter are associated with congenital hypertrichosis, and dyslipidaemia has been linked to androgenic alopecia. The underlying molecular mechanisms by which cholesterol influences pathways involved in proliferation and differentiation within HF cell populations remain largely unknown. As such, expanding our knowledge of the role for cholesterol in regulating these processes is likely to provide new leads in the development of treatments for disorders of hair growth and cycling. This review describes the current state of knowledge with respect to cholesterol homeostasis in the HF along with known and putative links to hair pathologies.

Severe Skin Permeability Barrier Dysfunction in Knockout Mice Deficient in a Fatty Acid ω-Hydroxylase Crucial to Acylceramide Production

The skin permeability barrier is indispensable for maintaining water inside the body and preventing the invasion of pathogens and allergens; abnormalities lead to skin disorders such as atopic dermatitis and ichthyosis. Acylceramide is an essential lipid for skin barrier formation, and CYP4F22 is a fatty acid ω-hydroxylase involved in its synthesis. Mutations in CYP4F22 cause autosomal recessive congenital ichthyosis, although the symptoms vary among mutation sites and types. Here, we generated knockout mice deficient in Cyp4f39, the mouse ortholog of human CYP4F22, to investigate the effects of completely abrogating the function of the fatty acid ω-hydroxylase involved in acylceramide production on skin barrier formation. Cyp4f39 knockout mice died within 8 hours of birth. Large increases in transepidermal water loss and penetration of a dye from outside the body were observed, indicating severe skin barrier dysfunction. Histologic analyses of the epidermis revealed impairment of lipid lamella formation, accumulation of corneodesmosomes in the stratum corneum, and persistence of periderm. In addition, lipid analyses by mass spectrometry showed almost complete loss of acylceramide and its precursor ω-hydroxy ceramide. In conclusion, our findings provide clues to the molecular mechanisms of skin barrier abnormalities and the pathogenesis of ichthyosis caused by Cyp4f39 and CYP4F22 by association.

[Syndromes with scales and keratosis]

Approximately 9000 different phenotypes are known in medicine. The definition phenotype includes both manifest diseases as well as features without any disease value and the pure genetic disposition to develop a disease (e.g. tumors or complex diseases); however, most phenotypes are rare monogenic hereditary diseases. Approximately 6400 of these phenotypes have so far been elucidated by molecular genetics and are caused by mutations in 4064 different genes. Of all genetic diseases, an estimated one third are associated with skin symptoms. Genodermatoses are the phenotypes predominantly related to the skin, of which approximately 600 are familiar to dermatologists. The syndromes with scaling and keratosis include cornification disorders where the symptoms are not limited to the skin. They are associated with skin symptoms such as ichthyosis, erythroderma and palmoplantar keratoderma but show additional symptoms from other organ groups. The typical combination of symptoms may be unique to a syndrome and therefore seminal for the diagnosis.

Ectopic expression of human airway trypsin-like protease 4 in acute myeloid leukemia promotes cancer cell invasion and tumor growth

Transmembrane serine proteases have been implicated in the development and progression of solid and hematological cancers. Human airway trypsin-like protease 4 (HAT-L4) is a transmembrane serine protease expressed in epithelial cells and exocrine glands. In the skin, HAT-L4 is important for normal epidermal barrier function. Here, we report an unexpected finding of ectopic HAT-L4 expression in neutrophils and monocytes from acute myeloid leukemia (AML) patients. Such expression was not detected in bone marrow cells from normal individuals or patients with chronic myeloid leukemia, acute lymphocytic leukemia and chronic lymphocytic leukemia. In AML patients who underwent chemotherapy, persistent HAT-L4 expression in bone marrow cells was associated with minimal residual disease and poor prognostic outcomes. In culture, silencing HAT-L4 expression in AML-derived THP-1 cells by short hairpin RNAs inhibited matrix metalloproteinase-2 activation and Matrigel invasion. In mouse xenograft models, inhibition of HAT-L4 expression reduced the proliferation and growth of THP-1 cell-derived tumors. Our results indicate that ectopic HAT-L4 expression is a pathological mechanism in AML and that HAT-L4 may be used as a cell surface marker for AML blast detection and targeting.

Deficiency of the human cysteine protease inhibitor cystatin M/E causes hypotrichosis and dry skin

Purpose

We aimed to assess the biological and clinical significance of the human cysteine protease inhibitor cystatin M/E, encoded by the CTS6 gene, in diseases of human hair and skin.

Methods

Exome and Sanger sequencing was performed to reveal the genetic cause in two related patients with hypotrichosis. Immunohistochemical, biophysical, and biochemical measurements were performed on patient skin and 3D-reconstructed skin from patient-derived keratinocytes.

Results

We identified a homozygous variant c.361C>T (p.Gln121*), resulting in a premature stop codon in exon 2 of CST6 associated with hypotrichosis, eczema, blepharitis, photophobia and impaired sweating. Enzyme assays using recombinant mutant cystatin M/E protein, generated by site-directed mutagenesis, revealed that this p.Gln121* variant was unable to inhibit any of its three target proteases (legumain and cathepsins L and V). Three-dimensional protein structure prediction confirmed the disturbance of the protease/inhibitor binding sites of legumain and cathepsins L and V in the p.Gln121* variant.

Conclusion

The herein characterized autosomal recessive hypotrichosis syndrome indicates an important role of human cystatin M/E in epidermal homeostasis and hair follicle morphogenesis.

Blocking the proteolytic activity of zymogen matriptase with antibody-based inhibitors

Matriptase is a member of the type-II transmembrane serine protease (TTSP) family and plays a crucial role in the development and maintenance of epithelial tissues. As all chymotrypsin-like serine proteases, matriptase is synthesized as a zymogen (proform), requiring a cleavage event for full activity. Recent studies suggest that the zymogen of matriptase possesses enough catalytic activity to not only facilitate autoactivation, but also carry out its in vivo functions, which include activating several proteolytic and signaling cascades. Inhibition of zymogen matriptase may therefore be a highly effective approach for limiting matriptase activity. To this end, here we sought to characterize the catalytic activity of human zymogen matriptase and to develop mAb inhibitors against this enzyme form. Using a mutated variant of matriptase in which the serine protease domain is locked in the zymogen conformation, we confirmed that the zymogen form of human matriptase has catalytic activity. Moreover, the crystal structure of the catalytic domain of zymogen matriptase was solved to 2.5 Å resolution to characterize specific antibody-based matriptase inhibitors and to further structure-based studies. Finally, we describe the first antibody-based competitive inhibitors that target both the zymogen and activated forms of matriptase. We propose that these antibodies provide a more efficient way to regulate matriptase activity by targeting the protease both before and after its activation and may be of value for both research and preclinical applications.

A disease-causing novel missense mutation in the ST14 gene underlies autosomal recessive ichthyosis with hypotrichosis syndrome in a consanguineous family

Autosomal recessive ichthyosis with hypotrichosis (ARIH; MIM 602400) syndrome is characterized by diffused congenital ichthyosis and generalized non-scarring hypotrichosis. The underlying genetic cause of ARIH syndrome has been associated with sequence variants of the gene ST14, encoding type II transmembrane serine protease matriptase, which maps to chromosome 11q24.3. The current report aimed to investigate the clinical features and genetic cause of ARIH syndrome in a large consanguineous family of Pakistani origin. The technique of homozygosity mapping with highly polymorphic microsatellite markers was employed to establish linkage within the family. Sanger sequencing of exons and intron-exon boundaries of ST14 was performed to identify the potential pathogenic sequence variants, followed by structural analysis of the mutated protein. Linkage was established to chromosome 11q24.3, comprising the gene ST14. Sequence analysis led to the identification of a novel homozygous missense variant (c.1315G>A, p.Gly439Ser) in the ST14 gene that co-segregated with the disease phenotype in all affected members. Homology modelling and molecular docking analysis of ST14 with wild-type TMEFF1 protein was performed which revealed that glycine at position 439 is crucial for maintaining normal structural confirmation and interaction with the EGF domain of TMEFF1 protein. Taken together, the data strongly advocate this ST14 variant as the underlying genetic cause of ARIH syndrome in this first reported affected family from Pakistan. Moreover, the present study adds to the spectrum of mutations in the ST14 gene, implicating them in the pathogenesis of ARIH syndrome.

Activated matriptase as a target to treat breast cancer with a drug conjugate

The antitumor effects of a novel antibody drug conjugate (ADC) was tested against human solid tumor cell lines and against human triple negative breast cancer (TNBC) xenografts in immunosuppressed mice. The ADC targeting activated matriptase of tumor cells was synthesized by using the potent anti-tubulin toxin, monomethyl auristatin-E linked to the activated matriptase-specific monoclonal antibody (M69) via a lysosomal protease-cleavable dipeptide linker. This ADC was found to be cytotoxic against multiple activated matriptase-positive epithelial carcinoma cell lines in vitro and markedly inhibited growth of triple negative breast cancer xenografts and a primary human TNBC (PDX) in vivo. Overexpression of activated matriptase may be a biomarker for response to this ADC. The ADC had potent anti-tumor activity, while the unconjugated M69 antibody was ineffective in a mouse model study using MDA-MB-231 xenografts in mice. Treatment of a human TNBC (MDA-MB-231) showed potent anti-tumor effects in combination with cisplatin in mice. This ADC alone or in combination with cisplatin has the potential to improve the treatment outcomes of patients with TNBC as well as other tumors overexpressing activated matriptase.

Loss of HAI-2 in mice with decreased prostasin activity leads to an early-onset intestinal failure resembling congenital tufting enteropathy

Prostasin (CAP1/PRSS8) is a glycosylphosphatidylinositol (GPI)-anchored serine protease that is essential for epithelial development and overall survival in mice. Prostasin is regulated primarily by the transmembrane serine protease inhibitor, hepatocyte growth factor activator inhibitor (HAI)-2, and loss of HAI-2 function leads to early embryonic lethality in mice due to an unregulated prostasin activity. We have recently reported that critical in vivo functions of prostasin can be performed by proteolytically-inactive or zymogen-locked variants of the protease. Here we show that the zymogen form of prostasin does not bind to HAI-2 and, as a result, loss of HAI-2 does not affect prenatal development and survival of mice expressing only zymogen-locked variant of prostasin (Prss8 R44Q). Indeed, HAI-2-deficient mice homozygous for R44Q mutation (Spint2-/-;Prss8R44Q/R44Q) are born in the expected numbers and do not exhibit any obvious developmental abnormality at birth. However, postnatal growth in these mice is severely impaired and they all die within 4 to 7 days after birth due to a critical failure in the development of small and large intestines, characterized by a widespread villous atrophy, tufted villi, near-complete loss of mucin-producing goblet cells, loss of colonic crypt structure, and bleeding into the intestinal lumen. Intestines of Spint2-/-;Prss8R44Q/R44Q mice showed altered expression of epithelial junctional proteins, including reduced levels of EpCAM, E-cadherin, occludin, claudin-1 and -7, as well as an increased level of claudin-4, indicating that the loss of HAI-2 compromises intestinal epithelial barrier function. Our data indicate that the loss of HAI-2 in Prss8R44Q/R44Q mice leads to development of progressive intestinal failure that at both histological and molecular level bears a striking resemblance to human congenital tufting enteropathy, and may provide important clues for understanding and treating this debilitating human disease.

Mutations in SDR9C7 gene encoding an enzyme for vitamin A metabolism underlie autosomal recessive congenital ichthyosis

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of hereditary skin disorder characterized by an aberrant cornification of the epidermis. ARCI is classified into a total of 11 subtypes (ARCI1-ARCI11) based on their causative genes or loci. Of these, the causative gene for only ARCI7 has not been identified, while it was previously mapped on chromosome 12p11.2-q13.1. In this study, we performed genetic analyses for three Lebanese families with ARCI, and successfully determined the linkage interval to 9.47 Mb region on chromosome 12q13.13-q14.1, which was unexpectedly outside of the ARCI7 locus. Whole-exome sequencing and the subsequent Sanger sequencing led to the identification of missense mutations in short chain dehydrogenase/reductase family 9C, member 7 (SDR9C7) gene on chromosome 12q13.3, i.e. two families shared an identical homozygous mutation c.599T > C (p.Ile200Thr) and one family had another homozygous mutation c.214C > T (p.Arg72Trp). In cultured cells, expression of both the mutant SDR9C7 proteins was markedly reduced as compared to wild-type protein, suggesting that the mutations severely affected a stability of the protein. In normal human skin, the SDR9C7 was abundantly expressed in granular and cornified layers of the epidermis. By contrast, in a patient’s skin, its expression in the cornified layer was significantly decreased. It has previously been reported that SDR9C7 is an enzyme to convert retinal into retinol. Therefore, our study not only adds a new gene responsible for ARCI, but also further suggests a potential role of vitamin A metabolism in terminal differentiation of the epidermis in humans.

A novel mutation in ST14 at a functionally significant amino acid residue expands the spectrum of ichthyosis-hypotrichosis syndrome

Background

Mutations in the ST14 gene, encoding the serine protease matriptase, have been associated with ichthyosis-hypotrichosis syndrome (IHS), a Mendelian disorder with skin and hair manifestations which include, in addition to ichthyosis and hypotrichosis, hypohidrosis and follicular atrophoderma. However, the understanding of the specific consequences of mutations in ST14 on the development of this syndrome is incomplete.

Results

Using a targeted next-generation sequencing array of 38 ichthyosis-associated genes on a large cohort of 180 ichthyosis patients from a primarily consanguineous background, a previously unreported homozygous p.Asp482Asn mutation in ST14 was identified in a patient with IHS. This mutation affects an essential site within a ligand-binding domain of matriptase. Comparison with previous reports of IHS allowed further delineation of the phenotype of IHS in correlation with mutations present in these patients. Histological and ultrastructural analysis of skin and hair identified novel features in this disorder.

Conclusions

This study correlates genotypic and phenotypic features of the rare disorder, IHS, expands the spectrum of pathology associated with the disorder, and provides clinical evidence of the importance of the Asp482 amino acid, previously shown to have an essential role in matriptase activation.

Updated strategies for the management, pathogenesis and molecular genetics of different forms of ichthyosis syndromes with prominent hair abnormalities

Syndromic ichthyosis is rare inherited disorders of cornification with varied disease complications. This disorder appears in seventeen subtypes associated with severe systematic manifestations along with medical, cosmetic and social problems. Syndromic ichthyosis with prominent hair abnormalities covers five major subtypes: Netherton syndrome, trichothiodystrophy, ichthyosis hypotrichosis syndrome, ichthyosis hypotrichosis sclerosing cholangitis and ichthyosis follicularis atrichia photophobia syndrome. These syndromes mostly prevail in high consanguinity states, with distinctive clinical features. The known pathogenic molecules involved in ichthyosis syndromes with prominent hair abnormalities include SPINK5, ERCC2, ERCC3, GTF2H5, MPLKIP, ST14, CLDN1 and MBTPS2. Despite underlying genetic origin, most of the health professionals solely rely on phenotypic expression of these disorders that leads to improper management of patients, hence making these patients living an orphanage life. After dermal features, association of other systems such as nervous system, skeletal system, hair abnormalities or liver problems may sometimes give clues for diagnosis but still leaving place for molecular screening for efficient diagnosis. In this paper, we have presented a review of ichthyosis syndrome with prominent hair abnormalities, with special emphasis on their updated genetic consequences and disease management. Additionally, we aim to update health professionals about the practice of molecular screening in ichthyosis syndromes for appropriate diagnosis and treatment.

Matriptase shedding is closely coupled with matriptase zymogen activation and requires de novo proteolytic cleavage likely involving its own activity

The type 2 transmembrane serine protease matriptase is involved in many pathophysiological processes probably via its enzymatic activity, which depends on the dynamic relationship between zymogen activation and protease inhibition. Matriptase shedding can prolong the life of enzymatically active matriptase and increase accessibility to substrates. We show here that matriptase shedding occurs via a de novo proteolytic cleavage at sites located between the SEA domain and the CUB domain. Point or combined mutations at the four positively charged amino acid residues in the region following the SEA domain allowed Arg-186 to be identified as the primary cleavage site responsible for matriptase shedding. Kinetic studies further demonstrate that matriptase shedding is temporally coupled with matriptase zymogen activation. The onset of matriptase shedding lags one minute behind matriptase zymogen activation. Studies with active site triad Ser-805 point mutated matriptase, which no longer undergoes zymogen activation or shedding, further suggests that matriptase shedding depends on matriptase zymogen activation, and that matriptase proteolytic activity may be involved in its own shedding. Our studies uncover an autonomous mechanism coupling matriptase zymogen activation, proteolytic activity, and shedding such that a proportion of newly generated active matriptase escapes HAI-1-mediated rapid inhibition by shedding into the extracellular milieu.

Type II transmembrane serine proteases as potential targets for cancer therapy

Carcinogenesis is accompanied by increased protein and activity levels of extracellular cell-surface proteases that are capable of modifying the tumor microenvironment by directly cleaving the extracellular matrix, as well as activating growth factors and proinflammatory mediators involved in proliferation and invasion of cancer cells, and recruitment of inflammatory cells. These complex processes ultimately potentiate neoplastic progression leading to local tumor cell invasion, entry into the vasculature, and metastasis to distal sites. Several members of the type II transmembrane serine protease (TTSP) family have been shown to play critical roles in cancer progression. In this review the knowledge collected over the past two decades about the molecular mechanisms underlying the pro-cancerous properties of selected TTSPs will be summarized. Furthermore, we will discuss how these insights may facilitate the translation into clinical settings in the future by specifically targeting TTSPs as part of novel cancer treatment regimens.

Matriptase zymogen supports epithelial development, homeostasis and regeneration

Background

Matriptase is a membrane serine protease essential for epithelial development, homeostasis, and regeneration, as well as a central orchestrator of pathogenic pericellular signaling in the context of inflammatory and proliferative diseases. Matriptase is an unusual protease in that its zymogen displays measurable enzymatic activity.

Results

Here, we used gain and loss of function genetics to investigate the possible biological functions of zymogen matriptase. Unexpectedly, transgenic mice mis-expressing a zymogen-locked version of matriptase in the epidermis displayed pathologies previously reported for transgenic mice mis-expressing wildtype epidermal matriptase. Equally surprising, mice engineered to express only zymogen-locked endogenous matriptase, unlike matriptase null mice, were viable, developed epithelial barrier function, and regenerated the injured epithelium. Compatible with these observations, wildtype and zymogen-locked matriptase were equipotent activators of PAR-2 inflammatory signaling.

Conclusion

The study demonstrates that the matriptase zymogen is biologically active and is capable of executing developmental and homeostatic functions of the protease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-017-0384-4) contains supplementary material, which is available to authorized users.

HAI-2 stabilizes, inhibits and regulates SEA-cleavage-dependent secretory transport of matriptase

It has recently been shown that hepatocyte growth factor activator inhibitor-2 (HAI-2) is able to suppress carcinogenesis induced by overexpression of matriptase, as well as cause regression of individual established tumors in a mouse model system. However, the role of HAI-2 is poorly understood. In this study, we describe 3 mutations in the binding loop of the HAI-2 Kunitz domain 1 (K42N, C47F and R48L) that cause a delay in the SEA domain cleavage of matriptase, leading to accumulation of non-SEA domain cleaved matriptase in the endoplasmic reticulum (ER). We suggest that, like other known SEA domains, the matriptase SEA domain auto-cleaves and reflects that correct oligomerization, maturation, and/or folding has been obtained. Our results suggest that the HAI-2 Kunitz domain 1 mutants influence the flux of matriptase to the plasma membrane by affecting the oligomerization, maturation and/or folding of matriptase, and as a result the SEA domain cleavage of matriptase. Two of the HAI-2 Kunitz domain 1 mutants investigated (C47F, R48L and C47F/R48L) also displayed a reduced ability to proteolytically silence matriptase. Hence, HAI-2 separately stabilizes matriptase, regulates the secretory transport, possibly via maturation/oligomerization and inhibits the proteolytic activity of matriptase in the ER, and possible throughout the secretory pathway.

A Nonsense Variant in the ST14 Gene in Akhal-Teke Horses with Naked Foal Syndrome

Naked foal syndrome (NFS) is a genodermatosis in the Akhal-Teke horse breed. We provide the first scientific description of this phenotype. Affected horses have almost no hair and show a mild ichthyosis. So far, all known NFS affected horses died between a few weeks and 3 yr of age. It is not clear whether a specific pathology caused the premature deaths. NFS is inherited as a monogenic autosomal recessive trait. We mapped the disease causing genetic variant to two segments on chromosomes 7 and 27 in the equine genome. Whole genome sequencing of two affected horses, two obligate carriers, and 75 control horses from other breeds revealed a single nonsynonymous genetic variant on the chromosome 7 segment that was perfectly associated with NFS. The affected horses were homozygous for ST14:c.388G>T, a nonsense variant that truncates >80% of the open reading frame of the ST14 gene (p.Glu130*). The variant leads to partial nonsense-mediated decay of the mutant transcript. Genetic variants in the ST14 gene are responsible for autosomal recessive congenital ichthyosis 11 in humans. Thus, the identified equine ST14:c.388G>T variant is an excellent candidate causative variant for NFS, and the affected horses represent a large animal model for a known human genodermatosis. Our findings will enable genetic testing to avoid the nonintentional breeding of NFS-affected foals.

The Transmembrane Serine Protease HAT-like 4 Is Important for Epidermal Barrier Function to Prevent Body Fluid Loss

Membrane-bound proteases are essential for epidermal integrity. Human airway trypsin-like protease 4 (HAT-L4) is a type II transmembrane serine protease. Currently, its biochemical property, cellular distribution and physiological function remain unknown. Here we examined HAT-L4 expression and function in vitro and in vivo. In Western analysis, HAT-L4 expressed in transfected CHO cells appeared as a 48-kDa protein. Flow cytometry confirmed HAT-L4 expression on the cell surface with the expected membrane topology. RT-PCR and immunostaining experiments indicated that HAT-L4 was expressed in epithelial cells and exocrine glands in tissues including skin, esophagus, trachea, tongue, eye, bladder, testis and uterus. In the skin, HAT-L4 expression was abundant in keratinocytes and sebaceous glands. We generated HAT-L4 knockout mice by disrupting the Tmprss11f gene encoding HAT-L4. HAT-L4 knockout mice were viable and fertile. No defects were found in HAT-L4 knockout mice in hair growth, wound healing, water repulsion and body temperature regulation. Compared with wild-type controls, HAT-L4-deficient newborn mice had greater body fluid loss and higher mortality in a trans-epidermal body fluid loss test. In metabolic studies, HAT-L4-deficient adult mice drank water more frequently than wild-type controls did. These results indicate that HAT-L4 is important in epidermal barrier function to prevent body fluid loss.