Molecular cloning, tissue-specific expression, and cellular localization of human prostasin mRNA

Exosome-Mediated Activation of the Prostasin-Matriptase Serine Protease Cascade in B Lymphoma Cells

Prostasin and matriptase are extracellular membrane serine proteases with opposing effects in solid epithelial tumors. Matriptase is an oncoprotein that promotes tumor initiation and progression, and prostasin is a tumor suppressor that reduces tumor invasion and metastasis. Previous studies have shown that a subgroup of Burkitt lymphoma have high levels of ectopic matriptase expression but no prostasin. Reducing the matriptase level via small interfering RNAs in B lymphoma cells impeded tumor xenograft growth in mice. Here, we report a novel approach to matriptase regulation in B cancer cells by prostasin via exosomes to initiate a prostasin-matriptase protease activation cascade. The activation and shedding of matriptase were monitored by measuring its quantity and trypsin-like serine protease activity in conditioned media. Sustained activation of the protease cascade in the cells was achieved by the stable expression of prostasin. The B cancer cells with prostasin expression presented phenotypes consistent with its tumor suppressor role, such as reduced growth and increased apoptosis. Prostasin exosomes could be developed as an agent to initiate the prostasin-matriptase cascade for treating B lymphoma with further studies in animal models.

Prostasin regulates PD-L1 expression in human lung cancer cells

The serine protease prostasin is a negative regulator of lipopolysaccharide-induced inflammation and has a role in the regulation of cellular immunity. Prostasin expression in cancer cells inhibits migration and metastasis, and reduces epithelial–mesenchymal transition. Programmed death-ligand 1 (PD-L1) is a negative regulator of the immune response and its expression in cancer cells interferes with immune surveillance. The aim of the present study was to investigate if prostasin regulates PD-L1 expression. We established sublines overexpressing various forms of prostasin as well as a subline deficient for the prostasin gene from the Calu-3 human lung cancer cells. We report here that PD-L1 expression induced by interferon-γ (IFNγ) is further enhanced in cells overexpressing the wildtype membrane-anchored prostasin. The PD-L1 protein was localized on the cell surface and released into the culture medium in extracellular vesicles (EVs) with the protease-active prostasin. The epidermal growth factor-epidermal growth factor receptor (EGF-EGFR), protein kinase C (PKC), and mitogen-activated protein kinase (MAPK) participated in the prostasin-mediated up-regulation of PD-L1 expression. A Gene Set Enrichment Analysis (GSEA) of patient lung tumors in The Cancer Genome Atlas (TCGA) database revealed that prostasin and PD-L1 regulate common signaling pathways during tumorigenesis and tumor progression.

Zymogen-locked mutant prostasin (Prss8) leads to incomplete proteolytic activation of the epithelial sodium channel (ENaC) and severely compromises triamterene tolerance in mice

AIM

The serine protease prostasin (Prss8) is expressed in the distal tubule and stimulates proteolytic activation of the epithelial sodium channel (ENaC) in co-expression experiments in vitro. The aim of this study was to explore the role of prostasin in proteolytic ENaC activation in the kidney in vivo.

METHODS

We used genetically modified knockin mice carrying a Prss8 mutation abolishing proteolytic activity (Prss8-S238A) or a mutation leading to a zymogen-locked state (Prss8-R44Q). Mice were challenged with low sodium diet and diuretics. Regulation of ENaC activity by Prss8-S238A and Prss8-R44Q was studied in vitro using the Xenopus laevis oocyte expression system.

RESULTS

Co-expression of murine ENaC with Prss8-wt or Prss8-S238A in oocytes caused maximal proteolytic ENaC activation, whereas ENaC was activated only partially in oocytes co-expressing Prss8-R44Q. This was paralleled by a reduced proteolytic activity at the cell surface of Prss8-R44Q expressing oocytes. Sodium conservation under low sodium diet was preserved in Prss8-S238A and Prss8-R44Q mice but with higher plasma aldosterone concentrations in Prss8-R44Q mice. Treatment with the ENaC inhibitor triamterene over four days was tolerated in Prss8-wt and Prss8-S238A mice, whereas Prss8-R44Q mice developed salt wasting and severe weight loss associated with hyperkalemia and acidosis consistent with impaired ENaC function and renal failure.

CONCLUSION

Unlike proteolytically inactive Prss8-S238A, zymogen-locked Prss8-R44Q produces incomplete proteolytic ENaC activation in vitro and causes a severe renal phenotype in mice treated with the ENaC inhibitor triamterene. This indicates that Prss8 plays a role in proteolytic ENaC activation and renal function independent of its proteolytic activity.

Proteinase-Mediated Macrophage Signaling in Psoriatic Arthritis

Objective

Multiple proteinases are present in the synovial fluid (SF) of an arthritic joint. We aimed to identify inflammatory cell populations present in psoriatic arthritis (PsA) SF compared to osteoarthritis (OA) and rheumatoid arthritis (RA), identify their proteinase-activated receptor 2 (PAR2) signaling function and characterize potentially active SF serine proteinases that may be PAR2 activators.

Methods

Flow cytometry was used to characterize SF cells from PsA, RA, OA patients; PsA SF cells were further characterized by single cell 3’-RNA-sequencing. Active serine proteinases were identified through cleavage of fluorogenic trypsin- and chymotrypsin-like substrates, activity-based probe analysis and proteomics. Fluo-4 AM was used to monitor intracellular calcium cell signaling. Cytokine expression was evaluated using a multiplex Luminex panel.

Results

PsA SF cells were dominated by monocytes/macrophages, which consisted of three populations representing classical, non-classical and intermediate cells. The classical monocytes/macrophages were reduced in PsA compared to OA/RA, whilst the intermediate population was increased. PAR2 was elevated in OA vs. PsA/RA SF monocytes/macrophages, particularly in the intermediate population. PAR2 expression and signaling in primary PsA monocytes/macrophages significantly impacted the production of monocyte chemoattractant protein-1 (MCP-1). Trypsin-like serine proteinase activity was elevated in PsA and RA SF compared to OA, while chymotrypsin-like activity was elevated in RA compared to PsA. Tryptase-6 was identified as an active serine proteinase in SF that could trigger calcium signaling partially via PAR2.

Conclusion

PAR2 and its activating proteinases, including tryptase-6, can be important mediators of inflammation in PsA. Components within this proteinase-receptor axis may represent novel therapeutic targets.

The cell-surface anchored serine protease TMPRSS13 promotes breast cancer progression and resistance to chemotherapy

Breast cancer progression is accompanied by increased expression of extracellular and cell-surface proteases capable of degrading the extracellular matrix as well as cleaving and activating downstream targets. The type II transmembrane serine proteases (TTSPs) are a family of cell-surface proteases that play critical roles in numerous types of cancers. Therefore, the aim of this study was to identify novel and uncharacterized TTSPs with differential expression in breast cancer and to determine their potential roles in progression. Systematic in silico data analysis followed by immunohistochemical validation identified increased expression of the TTSP family member, TMPRSS13 (transmembrane protease, serine 13), in invasive ductal carcinoma patient tissue samples compared to normal breast tissue. To test whether loss of TMPRSS13 impacts tumor progression, TMPRSS13 was genetically ablated in the oncogene-induced transgenic MMTV-PymT tumor model. TMPRSS13 deficiency resulted in a significant decrease in overall tumor burden and growth rate, as well as a delayed formation of detectable mammary tumors, thus suggesting a causal relationship between TMPRSS13 expression and the progression of breast cancer. Complementary studies using human breast cancer cell culture models revealed that siRNA-mediated silencing of TMPRSS13 expression decreases proliferation, induces apoptosis, and attenuates invasion. Importantly, targeting TMPRSS13 expression renders aggressive triple-negative breast cancer cell lines highly responsive to chemotherapy. At the molecular level, knockdown of TMPRSS13 in breast cancer cells led to increased protein levels of the tumor-suppressive protease prostasin. TMPRSS13/prostasin co-immunoprecipitation and prostasin zymogen activation experiments identified prostasin as a potential novel target for TMPRSS13. Regulation of prostasin levels may be a mechanism that contributes to the pro-oncogenic properties of TMPRSS13 in breast cancer. TMPRSS13 represents a novel candidate for targeted therapy in combination with standard of care chemotherapy agents in patients with hormone receptor-negative breast cancer or in patients with tumors refractory to endocrine therapy.

Protease propeptide structures, mechanisms of activation, and functions

Proteases are a diverse group of hydrolytic enzymes, ranging from single-domain catalytic molecules to sophisticated multi-functional macromolecules. Human proteases are divided into five mechanistic classes: aspartate, cysteine, metallo, serine and threonine proteases, based on the catalytic mechanism of hydrolysis. As a protective mechanism against uncontrolled proteolysis, proteases are often produced and secreted as inactive precursors, called zymogens, containing inhibitory N-terminal propeptides. Protease propeptide structures vary considerably in length, ranging from dipeptides and propeptides of about 10 amino acids to complex multifunctional prodomains with hundreds of residues. Interestingly, sequence analysis of the different protease domains has demonstrated that propeptide sequences present higher heterogeneity compared with their catalytic domains. Therefore, we suggest that protease inhibition targeting propeptides might be more specific and have less off-target effects than classical inhibitors. The roles of propeptides, besides keeping protease latency, include correct folding of proteases, compartmentalization, liganding, and functional modulation. Changes in the propeptide sequence, thus, have a tremendous impact on the cognate enzymes. Small modifications of the propeptide sequences modulate the activity of the enzymes, which may be useful as a therapeutic strategy. This review provides an overview of known human proteases, with a focus on the role of their propeptides. We review propeptide functions, activation mechanisms, and possible therapeutic applications.

The proteome of frozen-thawed pig spermatozoa is dependent on the ejaculate fraction source

The preservation of sperm functional parameters and fertility post-cryopreservation largely varies in the porcine, a species with a fractionated ejaculate. Although intrinsic individual differences have primarily been linked to this variation, differences in protein abundance among frozen-thawed (FT)-spermatozoa are far more relevant. This study, performed in two experiments, looked for proteomic quantitative differences between FT-sperm samples differing in post-thaw viability, motility, apoptosis, membrane lipid peroxidation and nuclear DNA fragmentation. The spermatozoa were either derived from the sperm-rich ejaculate fraction (SRF) or the entire ejaculate (Experiment 1) or from the first 10 mL of the SRF, the remaining SRF and the post-SRF (Experiment 2). Quantitative sperm proteomic differences were analysed using a LC-ESI-MS/MS-based SWATH approach. In Experiment 1, FT-spermatozoa from the SRF showed better preservation parameters than those from the entire ejaculate, with 26 Sus scrofa proteins with functional sperm relevance showing relative quantitative differences (FC ≥ 1.5) between sperm sources. In Experiment 2, FT-spermatozoa from the first 10 mL of the SRF and the remaining SRF were qualitatively better than those from the post-SRF, and 187 proteins showed relative quantitative differences among the three ejaculate sources. The results indicate that quantitative proteome differences are linked to sperm cryosurvival.

The catalytic, stem, and transmembrane portions of matriptase-2 are required for suppressing the expression of the iron-regulatory hormone hepcidin

Matriptase-2 (MT2) is a type-II transmembrane, trypsin-like serine protease that is predominantly expressed in the liver. It is a key suppressor for the expression of hepatic hepcidin, an iron-regulatory hormone that is induced via the bone morphogenetic protein signaling pathway. A current model predicts that MT2 suppresses hepcidin expression by cleaving multiple components of the induction pathway. MT2 is synthesized as a zymogen that undergoes autocleavage for activation and shedding. However, the biologically active form of MT2 and, importantly, the contributions of different MT2 domains to its function are largely unknown. Here we examined the activities of truncated MT2 that were generated by site-directed mutagenesis or Gibson assembly master mix, and found that the stem region of MT2 determines the specificity and efficacy for substrate cleavage. The transmembrane domain allowed MT2 activation after reaching the plasma membrane, and the cytoplasmic domain facilitated these processes. Further in vivo rescue studies indicated that the entire extracellular and transmembrane domains of MT2 are required to correct the low-hemoglobin, low-serum iron, and high-hepcidin status in MT2 ^-/- mice. Unlike in cell lines, no autocleavage of MT2 was detected in vivo in the liver, implying that MT2 may also function independently of its proteolytic activity. In conjunction with our previous studies implicating the cytoplasmic domain as an intracellular iron sensor, these observations reveal the importance of each MT2 domain for MT2-mediated substrate cleavage and for its biological function.

The Role of Hepsin in Endometrial Carcinoma

PURPOSE

Endometrial carcinoma is the sixth most common cancer in women worldwide and the most common invasive cancer of the female genital tract in developed countries. It is hoped that through a better understanding of the alterations implicated in endometrial cancer pathogenesis and prognosis, a more complete profile of risk factors and targeted therapy can be developed. Hepsin is a member of the type II transmembrane serine protease family. The importance of hepsin in prostate cancer has been demonstrated by several studies. However, the role of hepsin in endometrial carcinoma is yet to be identified. This study aimed to evaluate the immunohistochemical expression of hepsin in endometrial carcinoma, trying to explore its diagnostic and prognostic value.

MATERIALS AND METHODS

This retrospective study was conducted on 27 endometrial carcinoma and 18 endometrial hyperplasia cases. Immunohistochemical expression of hepsin was evaluated in tissue specimens and results were correlated with the available clinicopathlogic parameters.

RESULTS

Positive hepsin expression was seen in all (100%) carcinoma and 17/18 (94.44%) endometrial hyperplasia cases. The H-score of hepsin expression in endometrial carcinoma was significantly higher than that of hyperplasia cases (P=0.012). A significant negative association was found between hepsin expression in endometrial carcinoma cases regarding the grade and the size of tumors (P=0.018 and 0.008, respectively) as well as myometrial invasion (P=0.027).

CONCLUSIONS

Hepsin could play an important role in the pathogenesis and the early carcinogenesis of endometrial carcinoma and could serve as a prognostic biomarker in this tumor.

Tissue distribution and subcellular localizations determine in vivo functional relationship among prostasin, matriptase, HAI-1, and HAI-2 in human skin

The membrane-bound serine proteases prostasin and matriptase and the Kunitz-type protease inhibitors HAI-1 and HAI-2 are all expressed in human skin and may form a tightly regulated proteolysis network, contributing to skin pathophysiology. Evidence from other systems, however, suggests that the relationship between matriptase and prostasin and between the proteases and the inhibitors can be context-dependent. In this study the in vivo zymogen activation and protease inhibition status of matriptase and prostasin were investigated in the human skin. Immunohistochemistry detected high levels of activated prostasin in the granular layer, but only low levels of activated matriptase restricted to the basal layer. Immunoblot analysis of foreskin lysates confirmed this in vivo zymogen activation status and further revealed that HAI-1 but not HAI-2 is the prominent inhibitor for prostasin and matriptase in skin. The zymogen activation status and location of the proteases does not support a close functional relation between matriptase and prostasin in the human skin. The limited role for HAI-2 in the inhibition of matriptase and prostasin is the result of its primarily intracellular localization in basal and spinous layer keratinocytes, which probably prevents the Kunitz inhibitor from interacting with active prostasin or matriptase. In contrast, the cell surface expression of HAI-1 in all viable epidermal layers renders it an effective regulator for matriptase and prostasin. Collectively, our study suggests the importance of tissue distribution and subcellular localization in the functional relationship between proteases and protease inhibitors.

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.

Selective Inhibition of Prostasin in Human Enterocytes by the Integral Membrane Kunitz-Type Serine Protease Inhibitor HAI-2

Mutations of hepatocyte growth factor activator inhibitor (HAI)-2 in humans cause sodium loss in the gastrointestinal (GI) tract in patients with syndromic congenital sodium diarrhea (SCSD). Aberrant regulation of HAI-2 target protease(s) was proposed as the cause of the disease. Here functional linkage of HAI-2 with two membrane-associated serine proteases, matriptase and prostasin was analyzed in Caco-2 cells and the human GI tract. Immunodepletion-immunoblot analysis showed that significant proportion of HAI-2 is in complex with activated prostasin but not matriptase. Unexpectedly, prostasin is expressed predominantly in activated forms and was also detected in complex with HAI-1, a Kunitz inhibitor highly related to HAI-2. Immunohistochemistry showed a similar tissue distribution of prostasin and HAI-2 immunoreactivity with the most intense labeling near the brush borders of villus epithelial cells. In contrast, matriptase was detected primarily at the lateral plasma membrane, where HAI-1 was also detected. The tissue distribution profiles of immunoreactivity against these proteins, when paired with the species detected suggests that prostasin is under tight control by both HAI-1 and HAI-2 and matriptase by HAI-1 in human enterocytes. Furthermore, HAI-1 is a general inhibitor of prostasin in a variety of epithelial cells. In contrast, HAI-2 was not found to be a significant inhibitor for prostasin in mammary epithelial cells or keratinocytes. The high levels of constitutive prostasin zymogen activation and the selective prostasin inhibition by HAI-2 in enterocytes suggest that dysregulated prostasin proteolysis may be particularly important in the GI tract when HAI-2 function is lost and/or dysregulated.

Natural Endogenous Human Matriptase and Prostasin Undergo Zymogen Activation via Independent Mechanisms in an Uncoupled Manner

The membrane-associated serine proteases matriptase and prostasin are believed to function in close partnership. Their zymogen activation has been reported to be tightly coupled, either as a matriptase-initiated proteolytic cascade or through a mutually dependent mechanism involving the formation of a reciprocal zymogen activation complex. Here we show that this putative relationship may not apply in the context of human matriptase and prostasin. First, the tightly coupled proteolytic cascade between matriptase and prostasin might not occur when modest matriptase activation is induced by sphingosine 1-phospahte in human mammary epithelial cells. Second, prostasin is not required and/or involved in matriptase autoactivation because matriptase can undergo zymogen activation in cells that do not endogenously express prostasin. Third, matriptase is not required for and/or involved in prostasin activation, since activated prostasin can be detected in cells expressing no endogenous matriptase. Finally, matriptase and prostasin both undergo zymogen activation through an apparently un-coupled mechanism in cells endogenously expressing both proteases, such as in Caco-2 cells. In these human enterocytes, matriptase is detected primarily in the zymogen form and prostasin predominantly as the activated form, either in complexes with protease inhibitors or as the free active form. The negligible levels of prostasin zymogen with high levels of matriptase zymogen suggests that the reciprocal zymogen activation complex is likely not the mechanism for matriptase zymogen activation. Furthermore, high level prostasin activation still occurs in Caco-2 variants with reduced or absent matriptase expression, indicating that matriptase is not required and/or involved in prostasin zymogen activation. Collectively, these data suggest that any functional relationship between natural endogenous human matriptase and prostasin does not occur at the level of zymogen activation.

Sodium channel Nax is a regulator in epithelial sodium homeostasis

The mechanisms by which the epidermis responds to disturbances in barrier function and restores homeostasis are unknown. With a perturbation of the epidermal barrier, water is lost, resulting in an increase in extracellular sodium concentration. We demonstrate that the sodium channel Nax functions as a sodium sensor. With increased extracellular sodium, Nax up-regulates prostasin, which results in activation of the sodium channel ENaC, resulting in increased sodium flux and increased downstream mRNA synthesis of inflammatory mediators. Nax is present in multiple epithelial tissues, and up-regulation of its downstream genes is found in hypertrophic scars. In animal models, blocking Nax expression results in improvement in scarring and atopic dermatitis-like symptoms, both of which are pathological conditions characterized by perturbations in barrier function. These findings support an important role for Nax in maintaining epithelial homeostasis.

Dietary salt regulates uroguanylin expression and signaling activity in the kidney, but not in the intestine

The peptide uroguanylin (Ugn) is expressed at significant levels only in intestine and kidney, and is stored in both tissues primarily (perhaps exclusively) as intact prouroguanylin (proUgn). Intravascular infusion of either Ugn or proUgn evokes well-characterized natriuretic responses in rodents. Furthermore, Ugn knockout mice display hypertension and salt handling deficits, indicating that the Na(+) excretory mechanisms triggered when the peptides are infused into anesthetized animals are likely to operate under normal physiological conditions, and contribute to electrolyte homeostasis in conscious animals. Here, we provide strong corroborative evidence for this hypothesis, by demonstrating that UU gnV (the rate of urinary Ugn excretion) approximately doubled in conscious, unrestrained rats consuming a high-salt diet, and decreased by ~15% after salt restriction. These changes in UU gnV were not associated with altered plasma proUgn levels (shown here to be an accurate index of intestinal proUgn secretion). Furthermore, enteric Ugn mRNA levels were unaffected by salt intake, whereas renal Ugn mRNA levels increased sharply during periods of increased dietary salt consumption. Together, these data suggest that diet-evoked Ugn signals originate within the kidney, rather than the intestine, thus strengthening a growing body of evidence against a widely cited hypothesis that Ugn serves as the mediator of an entero-renal natriuretic signaling axis, while underscoring a likely intrarenal natriuretic role for the peptide. The data further suggest that intrarenal Ugn signaling is preferentially engaged when salt intake is elevated, and plays only a minor role when salt intake is restricted.

Distinct Developmental Functions of Prostasin (CAP1/PRSS8) Zymogen and Activated Prostasin

The membrane-anchored serine prostasin (CAP1/PRSS8) is essential for barrier acquisition of the interfollicular epidermis and for normal hair follicle development. Consequently, prostasin null mice die shortly after birth. Prostasin is found in two forms in the epidermis: a one-chain zymogen and a two-chain proteolytically active form, generated by matriptase-dependent activation site cleavage. Here we used gene editing to generate mice expressing only activation site cleavage-resistant (zymogen-locked) endogenous prostasin. Interestingly, these mutant mice displayed normal interfollicular epidermal development and postnatal survival, but had defects in whisker and pelage hair formation. These findings identify two distinct in vivo functions of epidermal prostasin: a function in the interfollicular epidermis, not requiring activation site cleavage, that can be mediated by the zymogen-locked version of prostasin and a proteolysis-dependent function of activated prostasin in hair follicles, dependent on zymogen conversion by matriptase.

Ibuprofen regulates the expression and function of membrane-associated serine proteases prostasin and matriptase

BACKGROUND

The glycosylphosphatidylinositol-anchored extracellular membrane serine protease prostasin is expressed in normal bladder urothelial cells. Bladder inflammation reduces prostasin expression and a loss of prostasin expression is associated with epithelial-mesenchymal transition (EMT) in human bladder transitional cell carcinomas. Non-steroidal anti-inflammatory drugs (NSAIDs) decrease the incidence of various cancers including bladder cancer, but the molecular mechanisms underlying the anticancer effect of NSAIDs are not fully understood.

METHODS

The normal human bladder urothelial cell line UROtsa, the normal human trophoblast cell line B6Tert-1, human bladder transitional cell carcinoma cell lines UM-UC-5 and UM-UC-9, and the human breast cancer cell line JIMT-1 were used for the study. Expression changes of the serine proteases prostasin and matriptase, and cyclooxygenases (COX-1 and COX-2) in these cells following ibuprofen treatments were analyzed by means of reverse-transcription/quantitative polymerase chain reaction (RT-qPCR) and immunoblotting. The functional role of the ibuprofen-regulated prostasin in epithelial tight junction formation and maintenance was assessed by measuring the transepithelial electrical resistance (TEER) and epithelial permeability in the B6Tert-1 cells. Prostasin's effects on tight junctions were also evaluated in B6Tert-1 cells over-expressing a recombinant human prostasin, silenced for prostasin expression, or treated with a functionally-blocking prostasin antibody. Matriptase zymogen activation was examined in cells over-expressing prostasin.

RESULTS

Ibuprofen increased prostasin expression in the UROtsa and the B6Tert-1 cells. Cyclooxygenase-2 (COX-2) expression was up-regulated at both the mRNA and the protein levels in the UROtsa cells by ibuprofen in a dose-dependent manner, but was not a requisite for up-regulating prostasin expression. The ibuprofen-induced prostasin contributed to the formation and maintenance of the epithelial tight junctions in the B6Tert-1 cells. The matriptase zymogen was down-regulated in the UROtsa cells by ibuprofen possibly as a result of the increased prostasin expression because over-expressing prostasin leads to matriptase activation and zymogen down-regulation in the UROtsa, JIMT-1, and B6Tert-1 cells. The expression of prostasin and matriptase was differentially regulated by ibuprofen in the bladder cancer cells.

CONCLUSIONS

Ibuprofen has been suggested for use in treating bladder cancer. Our results bring the epithelial extracellular membrane serine proteases prostasin and matriptase into the potential molecular mechanisms of the anticancer effect of NSAIDs.

Increased expression of prostasin contributes to early-onset severe preeclampsia through inhibiting trophoblast invasion

OBJECTIVE

To investigate the potential role of prostasin, as an invasion suppressor, in the process of trophoblast invasion in preeclampsia.

STUDY DESIGN

This case-control study included 19 early-onset severe preeclampsia (⩽ 34 weeks), 20 late-onset severe preeclampsia (>34 weeks) and 20 normal term pregnant women. Immunohistochemistry was conducted to identify the cellular localization of prostasin, as well as the matrix metalloproteinase 2 (MMP2) and MMP9 in the placenta tissues. Enzyme-linked immunosorbent assay was performed to analyze the expression of these three proteins in placental homogenates. The effect of prostasin on the invasive and migratory ability of trophoblast cells was detected by transwell assays. We also examined the regulation of the prostasin antibody in the MMP2 and MMP9 secretion by HTR-8/SVneo cells via blocking the prostasin activity.

RESULT

This study demonstrated that the prostasin, MMP2 and MMP9 were all expressed in the placental syncytiotrophoblasts. Increased expression of prostasin was detected in cases with early-onset severe preeclampsia compared with the late-onset and control groups (P < 0.05), whereas the expression patterns of MMP2 and MMP9 in placental homogenates were opposite to that of prostasin (P < 0.05). Recombinant prostasin inhibited the invasion and migration of trophoblast cells, whereas prostasin antibody enhanced the MMP2 and MMP9 secretion in a dose- and time-dependent manner.

CONCLUSION

These findings suggest that prostasin may suppress the invasion process in preeclampsia by attenuating MMP2 and MMP9 secretion.

The CAP1/Prss8 catalytic triad is not involved in PAR2 activation and protease nexin-1 (PN-1) inhibition

Serine proteases, serine protease inhibitors, and protease-activated receptors (PARs) are responsible for several human skin disorders characterized by impaired epidermal permeability barrier function, desquamation, and inflammation. In this study, we addressed the consequences of a catalytically dead serine protease on epidermal homeostasis, the activation of PAR2 and the inhibition by the serine protease inhibitor nexin-1. The catalytically inactive serine protease CAP1/Prss8, when ectopically expressed in the mouse, retained the ability to induce skin disorders as well as its catalytically active counterpart (75%, n=81). Moreover, this phenotype was completely normalized in a PAR2-null background, indicating that the effects mediated by the catalytically inactive CAP1/Prss8 depend on PAR2 (95%, n=131). Finally, nexin-1 displayed analogous inhibitory capacity on both wild-type and inactive mutant CAP1/Prss8 in vitro and in vivo (64% n=151 vs. 89% n=109, respectively), indicating that the catalytic site of CAP1/Prss8 is dispensable for nexin-1 inhibition. Our results demonstrate a novel inhibitory interaction between CAP1/Prss8 and nexin-1, opening the search for specific CAP1/Prss8 antagonists that are independent of its catalytic activity.

The protease inhibitor HAI-2, but not HAI-1, regulates matriptase activation and shedding through prostasin

The membrane-anchored serine proteases, matriptase and prostasin, and the membrane-anchored serine protease inhibitors, hepatocyte growth factor activator inhibitor (HAI)-1 and HAI-2, are critical effectors of epithelial development and postnatal epithelial homeostasis. Matriptase and prostasin form a reciprocal zymogen activation complex that results in the formation of active matriptase and prostasin that are targets for inhibition by HAI-1 and HAI-2. Conflicting data, however, have accumulated as to the existence of auxiliary functions for both HAI-1 and HAI-2 in regulating the intracellular trafficking and activation of matriptase. In this study, we, therefore, used genetically engineered mice to determine the effect of ablation of endogenous HAI-1 and endogenous HAI-2 on endogenous matriptase expression, subcellular localization, and activation in polarized intestinal epithelial cells. Whereas ablation of HAI-1 did not affect matriptase in epithelial cells of the small or large intestine, ablation of HAI-2 resulted in the loss of matriptase from both tissues. Gene silencing studies in intestinal Caco-2 cell monolayers revealed that this loss of cell-associated matriptase was mechanistically linked to accelerated activation and shedding of the protease caused by loss of prostasin regulation by HAI-2. Taken together, these data indicate that HAI-1 regulates the activity of activated matriptase, whereas HAI-2 has an essential role in regulating prostasin-dependent matriptase zymogen activation.

Prostasin may contribute to chemoresistance, repress cancer cells in ovarian cancer, and is involved in the signaling pathways of CASP/PAK2-p34/actin

Ovarian cancer is the deadliest of gynecologic cancers, largely due to the development of drug resistance in chemotherapy. Prostasin may have an essential role in the oncogenesis. In this study, we show that prostasin is decreased in an ovarian cancer drug-resistant cell line and in ovarian cancer patients with high levels of excision repair cross-complementing 1, a marker for chemoresistance. Our cell cultural model investigation demonstrates prostasin has important roles in the development of drug resistance and cancer cell survival. Forced overexpression of prostasin in ovarian cancer cells greatly induces cell death (resulting in 99% cell death in a drug-resistant cell line and 100% cell death in other tested cell lines). In addition, the surviving cells grow at a much lower rate compared with non-overexpressed cells. In vivo studies indicate that forced overexpression of prostasin in drug-resistant cells greatly inhibits the growth of tumors and may partially reverse drug resistance. Our investigation of the molecular mechanisms suggests that prostasin may repress cancer cells and/or contribute to chemoresistance by modulating the CASP/P21-activated protein kinase (PAK2)-p34 pathway, and thereafter PAK2-p34/JNK/c-jun and PAK2-p34/mlck/actin signaling pathways. Thus, we introduce prostain as a potential target for treating/repressing some ovarian tumors and have begun to identify their relevant molecular targets in specific signaling pathways.

Prostasin: An Epithelial Sodium Channel Regulator

Prostasin is a glycophosphatidylinositol-anchored protein which is found in prostate gland, kidney, bronchi, colon, liver, lung, pancreas, and salivary glands. It is a serine protease with trypsin-like substrate specificity which was first purified from seminal fluid in 1994. In the last decade, its diverse roles in various biological and physiological processes have been elucidated. Many studies done to date suggest that prostasin is one of several membrane peptidases regulating epithelial sodium channels in mammals. A comprehensive literature search was conducted from the websites of Pubmed Central, the US National Library of Medicine's digital archive of life sciences literature and the National Library of Medicine. The data was also assessed from journals and books that published relevant articles in this field. Understanding the mechanism by which prostasin and its inhibitors regulate sodium channels has provided a new insight into the treatment of hypertension and some other diseases like cystic fibrosis. Prostasin plays an important role in epidermal growth factor receptor (EGFR) signal modulation. Extracellular proteases have been implicated in tumor metastasis and local tissue invasion because of their ability to degrade extracellular matrices.

A matriptase-prostasin reciprocal zymogen activation complex with unique features: prostasin as a non-enzymatic co-factor for matriptase activation

Matriptase and prostasin are part of a cell surface proteolytic pathway critical for epithelial development and homeostasis. Here we have used a reconstituted cell-based system and transgenic mice to investigate the mechanistic interrelationship between the two proteases. We show that matriptase and prostasin form a reciprocal zymogen activation complex with unique features. Prostasin serves as a critical co-factor for matriptase activation. Unexpectedly, however, prostasin-induced matriptase activation requires neither prostasin zymogen conversion nor prostasin catalytic activity. Prostasin zymogen conversion to active prostasin is dependent on matriptase but does not require matriptase zymogen conversion. Consistent with these findings, wild type prostasin, activation cleavage site-mutated prostasin, and catalytically inactive prostasin all were biologically active in vivo when overexpressed in the epidermis of transgenic mice, giving rise to a severe skin phenotype. Our finding of non-enzymatic stimulation of matriptase activation by prostasin and activation of prostasin by the matriptase zymogen provides a tentative mechanistic explanation for several hitherto unaccounted for genetic and biochemical observations regarding these two membrane-anchored serine proteases and their downstream targets.

Prostasin is required for matriptase activation in intestinal epithelial cells to regulate closure of the paracellular pathway

The type II transmembrane serine protease matriptase is a key regulator of epithelial barriers in skin and intestine. In skin, matriptase acts upstream of the glycosylphosphatidylinositol-anchored serine protease, prostasin, to activate the prostasin zymogen and initiate a proteolytic cascade that is required for stratum corneum barrier functionality. Here, we have investigated the relationship between prostasin and matriptase in intestinal epithelial barrier function. We find that similar to skin, matriptase and prostasin are components of a common intestinal epithelial barrier-forming pathway. Depletion of prostasin by siRNA silencing in Caco-2 intestinal epithelium inhibits barrier development similar to loss of matriptase, and the addition of recombinant prostasin to the basal side of polarized Caco-2 epithelium stimulates barrier forming changes similar to the addition of recombinant matriptase. However, in contrast to the proteolytic cascade in skin, prostasin functions upstream of matriptase to activate the endogenous matriptase zymogen. Prostasin is unable to proteolytically activate the matriptase zymogen directly but induces matriptase activation indirectly. Prostasin requires expression of endogenous matriptase to stimulate barrier formation since matriptase depletion by siRNA silencing abrogates prostasin barrier-forming activity. Active recombinant matriptase, however, does not require the expression of endogenous prostasin for barrier-forming activity. Together, these data show that matriptase and not prostasin is the primary effector protease of tight junction assembly in simple columnar epithelia and further highlight a spatial and tissue-specific aspect of cell surface proteolytic cascades.

The channel-activating protease CAP1/Prss8 is required for placental labyrinth maturation

The serine protease CAP1/Prss8 is crucial for skin barrier function, lung alveolar fluid clearance and has been unveiled as diagnostic marker for specific cancer types. Here, we show that a constitutive knockout of CAP1/Prss8 leads to embryonic lethality. These embryos presented no specific defects, but it is during this period, and in particular at E13.5, that wildtype placentas show an increased expression of CAP1/Prss8, thus suggesting a placental defect in the knockout situation. The placentas of knockout embryos exhibited significantly reduced vascular development and incomplete cellular maturation. In contrary, epiblast-specific deletion of CAP1/Prss8 allowed development until birth. These CAP1/Prss8-deficient newborns presented abnormal epidermis, and died soon after birth due to impaired skin function. We thus conclude that a late placental insufficiency might be the primary cause of embryonic lethality in CAP1/Prss8 knockouts. This study highlights a novel and crucial role for CAP1/Prss8 in placental development and function.

The Phosphorylated Sodium Chloride Cotransporter in Urinary Exosomes Is Superior to Prostasin as a Marker for Aldosteronism

Urinary exosomes are vesicles derived from renal tubular epithelial cells. Exosomes often contain several disease-associated proteins and are thus useful targets for identifying biomarkers of disease. Here, we hypothesized that the phosphorylated (active) form of the sodium chloride cotransporter (pNCC) or prostasin could serve as biomarkers for aldosteronism. We tested this in 2 animal models of aldosteronism (aldosterone infusion or low-sodium diet) and in patients with primary aldosteronism. Urinary exosomes were isolated from 24-hour urine or spot urine using ultracentrifugation. In rats, a normal or a high dose of aldosterone for 2, 3, or 8 days increased pNCC 3-fold in urinary exosomes ( P <0.05 for all). A low-sodium diet also increased pNCC in urinary exosomes approximately 1.5-fold after 4 and after 8 days of treatment. The effects of these maneuvers on prostasin in urinary exosomes were less clear, showing a significant 1.5-fold increase only after 2 and 3 days of high-aldosterone infusion. In urinary exosomes of patients with primary aldosteronism, pNCC was 2.6-fold higher ( P <0.05) while prostasin was 1.5-fold higher ( P =0.07) than in patients with essential hypertension. Urinary exosomal pNCC and, to a lesser extent, prostasin are promising markers for aldosteronism in experimental animals and patients. These markers may be used to assess the biological activity of aldosterone and, potentially, as clinical biomarkers for primary aldosteronism.

Activity and inhibition of prostasin and matriptase on apical and basolateral surfaces of human airway epithelial cells

Prostasin is a membrane-anchored protease expressed in airway epithelium, where it stimulates salt and water uptake by cleaving the epithelial Na(+) channel (ENaC). Prostasin is activated by another transmembrane tryptic protease, matriptase. Because ENaC-mediated dehydration contributes to cystic fibrosis (CF), prostasin and matriptase are potential therapeutic targets, but their catalytic competence on airway epithelial surfaces has been unclear. Seeking tools for exploring sites and modulation of activity, we used recombinant prostasin and matriptase to identify substrate t-butyloxycarbonyl-l-Gln-Ala-Arg-4-nitroanilide (QAR-4NA), which allowed direct assay of proteases in living cells. Comparisons of bronchial epithelial cells (CFBE41o-) with and without functioning cystic fibrosis transmembrane conductance regulator (CFTR) revealed similar levels of apical and basolateral aprotinin-inhibitable activity. Although recombinant matriptase was more active than prostasin in hydrolyzing QAR-4NA, cell surface activity resisted matriptase-selective inhibition, suggesting that prostasin dominates. Surface biotinylation revealed similar expression of matriptase and prostasin in epithelial cells expressing wild-type vs. ΔF508-mutated CFTR. However, the ratio of mature to inactive proprostasin suggested surface enrichment of active enzyme. Although small amounts of matriptase and prostasin were shed spontaneously, prostasin anchored to the cell surface by glycosylphosphatidylinositol was the major contributor to observed QAR-4NA-hydrolyzing activity. For example, the apical surface of wild-type CFBE41o- epithelial cells express 22% of total, extractable, aprotinin-inhibitable, QAR-4NA-hydrolyzing activity and 16% of prostasin immunoreactivity. In conclusion, prostasin is present, mature and active on the apical surface of wild-type and CF bronchial epithelial cells, where it can be targeted for inhibition via the airway lumen.

Proteolytic activation of the epithelial sodium channel and therapeutic application of a serine protease inhibitor for the treatment of salt-sensitive hypertension

Proteases are involved in numerous essential biological processes including blood clotting, controlled cell death, and tissue differentiation. Prostasin, a glycosylphosphatidylinositol-anchored serine protease, has been identified as a potential regulator of the epithelial sodium channel (ENaC) function in the kidney, lung, and airways. ENaC is composed of three homologous subunits α, β, and, γ. The dual cleavage of α subunit by furin and γ subunit by prostasin and furin releases inhibitory segments from ENaC, leading to the channel activation. Protease nexin-1, an endogenous prostasin inhibitor, inhibits ENaC activity through the suppression of prostasin activity, strongly suggesting the possibility that a coordinated regulation of serine proteases and serine protease inhibitors plays a key role in the sodium handling in the kidney. Camostat mesilate (CM), a synthetic serine protease inhibitor, reduced prostasin activity and subsequently decreased ENaC current. Oral administration of CM to Dahl salt-sensitive rats resulted in a significant decrease in blood pressure with an elevation of the urinary sodium/potassium ratio. These findings suggest that synthetic serine protease inhibitors such as CM might represent a new class of antihypertensive drugs in patients with salt-sensitive hypertension.

Transport via the transcytotic pathway makes prostasin available as a substrate for matriptase

The matriptase-prostasin proteolytic cascade is essential for epidermal tight junction formation and terminal epidermal differentiation. This proteolytic pathway may also be operative in a variety of other epithelia, as both matriptase and prostasin are involved in tight junction formation in epithelial monolayers. However, in polarized epithelial cells matriptase is mainly located on the basolateral plasma membrane whereas prostasin is mainly located on the apical plasma membrane. To determine how matriptase and prostasin interact, we mapped the subcellular itinerary of matriptase and prostasin in polarized colonic epithelial cells. We show that zymogen matriptase is activated on the basolateral plasma membrane where it is able to cleave relevant substrates. After activation, matriptase forms a complex with the cognate matriptase inhibitor, hepatocyte growth factor activator inhibitor (HAI)-1 and is efficiently endocytosed. The majority of prostasin is located on the apical plasma membrane albeit a minor fraction of prostasin is present on the basolateral plasma membrane. Basolateral prostasin is endocytosed and transcytosed to the apical plasma membrane where a long retention time causes an accumulation of prostasin. Furthermore, we show that prostasin on the basolateral membrane is activated before it is transcytosed. This study shows that matriptase and prostasin co-localize for a brief period of time at the basolateral plasma membrane after which prostasin is transported to the apical membrane as an active protease. This study suggests a possible explanation for how matriptase or other basolateral serine proteases activate prostasin on its way to its apical destination.

Regulation of renal sodium handling through the interaction between serine proteases and serine protease inhibitors

Sodium balance, extracellular fluid volume, and ultimately blood pressure are maintained by precise regulation of the activity of epithelial sodium channels (ENaC). Multiple mechanisms such as hormones, intracellular factors, and other regulatory factors contribute to regulation of ENaC activity. Prostasin, a glycosylphosphatidylinositol-anchored serine protease, has been identified as an activator of ENaC that increases its open probability. Furin cleaves αENaC at two sites and γENaC at one site at the Golgi. Prostasin cleaves γENaC at one site that is distinct from the furin site at the plasma membrane. Dual cleavage of α- and γ-subunit releases inhibitory segments from ENaC, leading to channel activation. Protease nexin-1 (PN-1), an endogenous prostasin inhibitor, inhibits ENaC activity through suppression of prostasin activity. Aldosterone and transforming growth factor-β1 reciprocally regulate expression of prostasin, PN-1, and ENaC in renal epithelial cell, resulting in sodium retention or natriuresis, respectively. These findings strongly suggest the possibility that coordinated regulation of serine protease, serpin, and ENaC expression plays a key role in sodium handling in the kidney.

Interleukin-6 stimulates epithelial sodium channels in mouse cortical collecting duct cells

The aim of this study is to elucidate the effects of interleukin-6 (IL-6) on the expression and activity of the epithelial sodium channel (ENaC), which is one of the key mechanisms underlying tubular sodium reabsorption. M-1 cortical collecting duct cells were treated with IL-6 (100 ng/ml) for 12 h. Real-time polymerase chain reaction and immunoblotting were employed to examine the mRNA and protein abundance. Transepithelial voltage (V(te)) and resistance (R(te)) were measured with an ohm/voltmeter (EVOM, WPI). The equivalent current was calculated as the ratio of V(te) to R(te.) Treatment with IL-6 (n = 5) increased the mRNA abundance of alpha-ENaC by 11 +/- 7% (P = not significant), beta-ENaC by 78 +/- 14% (P = 0.01), gamma-ENaC by 185 +/- 38% (P = 0.02), and prostasin by 29 +/- 5% (P = 0.01), all normalized by beta-actin. Treatment with IL-6 increased the protein expression of alpha-ENaC by 19 +/- 3% (P = 0.001), beta-ENaC by 89 +/- 21% (P = 0.01), gamma-ENaC by 36 +/- 12% (P = 0.02), and prostasin by 33 +/- 6% (P = 0.02). The amiloride-sensitive sodium current increased by 37 +/- 5%, from 6.0 +/- 0.4 to 8.2 +/- 0.3 muA/cm(2) (P < 0.01), in the cells treated with IL-6 compared with controls (P = 0.01). Aprotinin (28 microg/ml), a prostasin inhibitor, reduced the amiloride-sensitive sodium current by 61 +/- 5%, from 6.1 +/- 0.3 to 3.7 +/- 0.2 muA/cm(2) (P = 0.01). The magnitude of the IL-6-induced amiloride-sensitive sodium current in the presence of aprotinin dropped by 57 +/- 2%, from 8.6 +/- 0.2 to 4.9 +/- 0.2 muA/cm(2) (P < 0.01). This study has identified a novel function of IL-6, namely, IL-6 may activate ENaC. Therefore, renal inflammation mediated by IL-6 likely contributes to impaired pressure natriuresis.

Regulation of adrenal aldosterone production by serine protease prostasin

A serine protease prostasin has been demonstrated to have a pivotal role in the activation of the epithelial sodium channel. Systemic administration of adenovirus carrying human prostasin gene in rats resulted in an increase in plasma prostasin and aldosterone levels. However, the mechanism by which the elevation of prostasin levels in the systemic circulation stimulated the plasma aldosterone levels remains unknown. Therefore, we examined if prostasin increases the aldosterone synthesis in a human adrenocortical cell line (H295R cells). Luciferase assay using CYP11B2 promoter revealed that prostasin significantly increased the transcriptional activity of CYP11B2. Prostasin significantly increased both CYP11B2 mRNA expression and aldosterone production in a dose-dependent manner. Surprisingly, treatment with camostat mesilate, a potent prostasin inhibitor, had no effect on the aldosterone synthesis by prostasin and also a protease-dead mutant of prostasin significantly stimulated the aldosterone production. A T-type/L-type calcium channel blocker and a protein kinase C (PKC) inhibitor significantly reduced the aldosterone synthesis by prostasin. Our findings suggest a stimulatory effect of prostasin on the aldosterone synthesis by adrenal gland through the nonproteolytic action and indicate a new role of prostasin in the systemic circulation.

Regulation of sodium transport by ENaC in the kidney

PURPOSE OF REVIEW

The amiloride-sensitive epithelial sodium channel (ENaC) plays a major role in the regulation of sodium transport in the collecting duct and hence sodium balance. This review describes recent findings in the regulation of ENaC function by serine proteases in particular and other regulatory aspects.

RECENT FINDINGS

Regulation of ENaC occurs at many levels (biophysical, transcriptional, post-translational modifications, assembly, membrane insertion, retrieval, recycling, degradation, etc.). Recent studies have recognized and delineated proteolytic cleavage, particularly of the alpha and gamma subunits, as major mechanisms of activation. Release of peptide fragments from these two subunits appears to be an important aspect of activation. These proteolytic mechanisms of ENaC activation have also been demonstrated in vivo and strongly suggested in clinical circumstances, particularly the nephrotic syndrome. In the nephrotic syndrome, filtered plasminogen may be cleaved by tubular urokinase to yield plasmin which can activate ENaC. In addition to these mechanisms, regulation by ubiquitination and deubiquitination represents a pivotal process. Several important deubiquitinating enzymes have been identified as important in ENaC retention in, or recycling to, the apical membrane. New aspects of the genomic control of ENaC transcription have also been found including histone methylation.

SUMMARY

The mechanisms of regulation of ENaC are increasingly understood to be a complex interplay of many different levels and systems. Proteolytic cleavage of alpha and gamma subunits plays a major role in ENaC activation. This may be particularly clinically relevant in nephrotic syndrome in which plasmin may activate ENaC activity.

Prostasin inhibits cell invasion in human choriocarcinomal JEG-3 cells

Controlled invasion of the uterine wall by the trophoblast cells is pivotal for the successful pregnancy, and various kinds of protease are involved in this process. Serine protease prostasin has been shown to participate in the proteolytic activation of epithelial sodium channel as well as cleavage of epidermal growth factor receptor extracellular domain in human epithelial cells. Its physiological significance in human placentation has been suggested but not validated. In the present study, we found that prostasin was expressed at a relatively high level in human placenta trophoblasts in early pregnant weeks. In the in vitro cultured human choriocarcinomal JEG-3 cells, treatment with functional antibody against prostasin led to promotion in cell invasion capability, as well as increase in the production of MMP-2, MMP-26, TIMP-1, and TIMP-4. Our data indicated that this serine protease may function as an invasion suppressor in human trophoblast, participating in the invasion-restrictive regulation of trophoblasts to avoid their over-penetration into the uterine wall.

Activation of the epithelial sodium channel (ENaC) by serine proteases

The study of human monogenic diseases [pseudohypoaldosteronism type 1 (PHA-1) and Liddle's syndrome] as well as mouse models mimicking the salt-losing syndrome (PHA-1) or salt-sensitive hypertension (Liddle's syndrome) have established the epithelial sodium channel ENaC as a limiting factor in vivo in the control of ionic composition of the extracellular fluid, regulation of blood volume and blood pressure, lung alveolar clearance, and airway mucociliary clearance. In this review, we discuss more specifically the activation of ENaC by serine proteases. Recent in vitro and in vivo experiments indicate that membrane-bound serine proteases are of critical importance in the activation of ENaC in different organs, such as the kidney, the lung, or the cochlea. Progress in understanding the basic mechanism of proteolytic activation of ENaC is accelerating, but uncertainty about the most fundamental aspects persists, leaving numerous still-unanswered questions.

Expression of prostasin and its inhibitors during colorectal cancer carcinogenesis

Background

Clinical trials where cancer patients were treated with protease inhibitors have suggested that the serine protease, prostasin, may act as a tumour suppressor. Prostasin is proteolytically activated by the serine protease, matriptase, which has a very high oncogenic potential. Prostasin is inhibited by protease nexin-1 (PN-1) and the two isoforms encoded by the mRNA splice variants of hepatocyte growth factor activator inhibitor-1 (HAI-1), HAI-1A, and HAI-1B.

Methods

Using quantitative RT-PCR, we have determined the mRNA levels for prostasin and PN-1 in colorectal cancer tissue (n = 116), severe dysplasia (n = 13), mild/moderate dysplasia (n = 93), and in normal tissue from the same individuals. In addition, corresponding tissues were examined from healthy volunteers (n = 23). A part of the cohort was further analysed for the mRNA levels of the two variants of HAI-1, here denoted HAI-1A and HAI-1B. mRNA levels were normalised to β-actin. Immunohistochemical analysis of prostasin and HAI-1 was performed on normal and cancer tissue.

Results

The mRNA level of prostasin was slightly but significantly decreased in both mild/moderate dysplasia (p < 0.001) and severe dysplasia (p < 0.01) and in carcinomas (p < 0.05) compared to normal tissue from the same individual. The mRNA level of PN-1 was more that two-fold elevated in colorectal cancer tissue as compared to healthy individuals (p < 0.001) and elevated in both mild/moderate dysplasia (p < 0.01), severe dysplasia (p < 0.05) and in colorectal cancer tissue (p < 0.001) as compared to normal tissue from the same individual. The mRNA levels of HAI-1A and HAI-1B mRNAs showed the same patterns of expression. Immunohistochemistry showed that prostasin is located mainly on the apical plasma membrane in normal colorectal tissue. A large variation was found in the degree of polarization of prostasin in colorectal cancer tissue.

Conclusion

These results show that the mRNA level of PN-1 is significantly elevated in colorectal cancer tissue. Future studies are required to clarify whether down-regulation of prostasin activity via up regulation of PN-1 is causing the malignant progression or if it is a consequence of it.

Urinary prostasin: a possible biomarker for renal pressure natriuresis in black adolescents

Prostasin is a membrane-bound/secretive serine protease interacting with aldosterone and the epithelial sodium channel in the kidney. We and others have previously proposed the concept of stress-induced pressure natriuresis (SIPN) where increased urinary sodium excretion (UNaV) is coupled with elevated blood pressure (BP) in response to behavioral stress in normotensive adolescents. This study thus aimed to test the relationship between prostasin and pressure natriuresis using the SIPN model. A cohort of 102 normotensive black adolescents (mean age: 17.0 +/- 1.2 y; 56% females) were placed on a controlled sodium (4000 +/- 200 mg/d) and potassium (2600 +/- 200 mg/d) diet for three days before testing. The SIPN protocol consisted of a 1-h baseline period, a 1-h stress period (competitive video game), and a 1-h recovery period. During the stress period, BP elevation was coupled with an increase in UNaV. Urinary prostasin concentration had more than a 2-fold reduction from baseline (38.4 +/- 32.7 ng/mL) to stress (17.2 +/- 16.0 ng/mL), and further declined during recovery (12.1 +/- 16.2 ng/mL) (p < 0.001). Urinary prostasin was inversely correlated with UNaV during stress (r = -0.43, p = 0.0001), even after being normalized by urinary creatinine. Our data suggest that urinary prostasin could be a novel biomarker and/or mechanism for renal pressure natriuresis in normotensive black adolescents.

T-SP1: a novel serine protease-like protein predominantly expressed in testis

Here, we describe a novel member in the group of membrane-anchored chymotrypsin (S1)-like serine proteases, namely testis serine protease 1 (T-SP1), as it is principally expressed in testis tissue. The human T-SP1 gene encompasses 28.7 kb on the short arm of chromosome 8 and consists of seven exons. Rapid amplification of cDNA ends (RACE) experiments revealed that due to alternative splicing three different variants (T-SP1/1, -2, -3) are detectable in testis tissue displaying pronounced heterogeneity at their 3'-end. T-SP1/1 consists of an 18 amino acid signal peptide and of a 49 amino acid propeptide. The following domain with the catalytic triad of His(108), Asp(156), and Ser(250) shares sequence identities of 42% and 40% with the blood coagulation factor XI and plasma kallikrein, respectively. Only T-SP1/1 contains a hydrophobic part at the C-terminus, which provides the basis for cell membrane anchoring. Using a newly generated polyclonal anti-T-SP1 antibody, expression of the T-SP1 protein was found in the Leydig and Sertoli cells of the testis and in the epithelial cells of the ductuli efferentes. Notably, T-SP1 protein was also detectable in prostate cancer and in some ovarian cancer tissues, indicating tumor-related synthesis of T-SP1 beyond testis tissue.

Camostat mesilate inhibits prostasin activity and reduces blood pressure and renal injury in salt-sensitive hypertension

Prostasin, a glycosylphosphatidylinositol-anchored serine protease, regulates epithelial sodium channel (ENaC) activity. Sodium reabsorption through ENaC in distal nephron segments is a rate-limiting step in transepithelial sodium transport. Recently, proteolytic cleavage of ENaC subunits by prostasin has been shown to activate ENaC. Therefore, we hypothesized that serine protease inhibitors could inhibit ENaC activity in the kidney, leading to a decrease in blood pressure. We investigated the effects of camostat mesilate, a synthetic serine protease inhibitor, and FOY-251, an active metabolite of camostat mesilate, on sodium transport in the mouse cortical collecting duct cell line (M-1 cells) and on blood pressure in Dahl salt-sensitive rats. Treatment with camostat mesilate or FOY-251 decreased equivalent current (Ieq) in M-1 cells in a dose-dependent manner and inhibited the protease activity of prostasin in vitro. Silencing of the prostasin gene also reduced equivalent current in M-1 cells. The expression level of prostasin protein was not changed by application of camostat mesilate or FOY-251 to M-1 cells. Oral administration of camostat mesilate to Dahl salt-sensitive rats fed a high-salt diet resulted in a significant decrease in blood pressure with elevation of the urinary Na/K ratio, decrease in serum creatinine, reduction in urinary protein excretion, and improvement of renal injury markers such as collagen 1, collagen 3, transforming growth factor-beta1, and nephrin. These findings suggest that camostat mesilate can decrease ENaC activity in M-1 cells probably through the inhibition of prostasin activity, and that camostat mesilate can have beneficial effects on both hypertension and kidney injury in Dahl salt-sensitive rats. Camostat mesilate might represent a new class of antihypertensive drugs with renoprotective effects in patients with salt-sensitive hypertension.

Prostasin, a potential tumor marker in ovarian cancer--a pilot study

INTRODUCTION

Ovarian cancer is generally diagnosed at advanced stages of the disease; therefore, poor prognoses are typical. The development of tumor markers is thus of utmost importance. Prostasin is a protease that in normal tissues is highly expressed only in the prostate gland and seminal fluid. A previous study showed that prostasin is highly overexpressed in ovarian cancer cell lines. This study sought to evaluate the expression of prostasin in ovarian cancer.

METHODS

Fresh tumor samples of ovarian epithelial cancer (n: 12) were analyzed for expression of prostasin mRNA (messenger ribonucleic acid) by conventional and real time quantitative PCR (polymerase chain reaction). As a standard control, a normal prostate sample was analyzed.

RESULTS

Using conventional PCR, prostasin was detected in all but one sample. Using quantitative PCR, prostasin was over-expressed in all but one of the samples as compared to the control (prostate).

CONCLUSIONS

These findings indicate that prostasin is overexpressed in many epithelial ovarian cancers. Further studies of prostasin as a potential biomarker for this disease are warranted.

Structure of human prostasin, a target for the regulation of hypertension

Prostasin (also called channel activating protease-1 (CAP1)) is an extracellular serine protease implicated in the modulation of fluid and electrolyte regulation via proteolysis of the epithelial sodium channel. Several disease states, particularly hypertension, can be affected by modulation of epithelial sodium channel activity. Thus, understanding the biochemical function of prostasin and developing specific agents to inhibit its activity could have a significant impact on a widespread disease. We report the expression of the prostasin proenzyme in Escherichia coli as insoluble inclusion bodies, refolding and activating via proteolytic removal of the N-terminal propeptide. The refolded and activated enzyme was shown to be pure and monomeric, with kinetic characteristics very similar to prostasin expressed from eukaryotic systems. Active prostasin was crystallized, and the structure was determined to 1.45 A resolution. These apoprotein crystals were soaked with nafamostat, allowing the structure of the inhibited acyl-enzyme intermediate structure to be determined to 2.0 A resolution. Comparison of the inhibited and apoprotein forms of prostasin suggest a mechanism of regulation through stabilization of a loop which interferes with substrate recognition.

Ichthyosis, follicular atrophoderma, and hypotrichosis caused by mutations in ST14 is associated with impaired profilaggrin processing

Congenital ichthyosis encompasses a heterogeneous group of disorders of cornification. Isolated forms and syndromic ichthyosis can be differentiated. We have analyzed two consanguineous families from the United Arab Emirates and Turkey with an autosomal recessive syndrome of diffuse congenital ichthyosis, patchy follicular atrophoderma, generalized and diffuse nonscarring hypotrichosis, marked hypohidrosis, and woolly hair (OMIM 602400). By genome-wide analysis, we found a homozygous interval on chromosome 11q24-q25 and obtained a LOD score of 4.0 at D11S910. We identified a homozygous splice-site mutation in the Arab patients and a frame-shift deletion in the Turkish patient in the gene suppression of tumorigenicity-14 (ST14). The product of ST14, matriptase, is a type II transmembrane serine protease synthesized in most human epithelia. Two missense mutations in ST14 were recently described in patients with a phenotype of ichthyosis and hypotrichosis, indicating diverse activities of matriptase in the epidermis and hair follicles. Here we have further demonstrated the loss of matriptase in differentiated patient keratinocytes, reduced proteolytic activation of prostasin, and disturbed processing of profilaggrin. As filaggrin monomers play a pivotal role in epidermal barrier formation, these findings reveal the link between congenital disorders of keratinization and filaggrin processing in the human skin.

Prostasin: a possible candidate gene for human hypertension

BACKGROUND

Prostasin, a serine protease, is suggested to be a novel mechanism regulating the epithelial sodium channel (ENaC) expressed in the distal nephron. This study aimed to evaluate whether the human prostasin gene is a novel candidate gene underlying blood pressure (BP) elevation.

METHODS

In a sample of healthy African-American (AA) and European-American (EA) twin subjects aged 17.6 +/- 3.3 years (n = 920, 45% AAs), race-specific tagging single-nucleotide polymorphisms (tSNPs) were identified to tag all the available SNPs +/- 2 kb up- and downstream of the prostasin gene from HapMap at r2 of 0.8-1.0. Selection yielded four tSNPs in AAs and one in EAs, with one tSNP (rs12597511: C to T) present in both AAs and EAs.

RESULTS

For rs12597511, CT and TT genotypes exhibited higher systolic BP (SBP) than CC genotype (115.9 +/- 1.1 mm Hg vs. 113.7 +/- 0.6 mm Hg, P = 0.025 (AAs); and 110.7 +/- 0.5 mm Hg vs. 109.6 +/- 0.6 mm Hg, P = 0.115 (EAs)). CT and TT genotypes compared with CC genotype showed a significant increase in diastolic BP (DBP) in both racial groups (62.5 +/- 0.7 mm Hg vs. 60.4 +/- 0.4 mm Hg, P = 0.003 (AAs); and 58.2 +/- 0.3 mm Hg vs. 56.7 +/- 0.4 mm Hg, P = 0.007 (EAs)). Furthermore, there was an increase in radial pulse wave velocity (PWV) in subjects with CT and TT genotype as compared with those with CC genotype (6.5 +/- 0.1 vs. 6.1 +/- 0.1 m/s, P < 0.0001) (EAs); and 6.7 +/- 0.1 vs. 6.6 +/- 0.1 m/s, P = 0.354 (AAs)). Analyses combining AAs and EAs consistently demonstrated a statistical significance of rs12597511 on all the phenotypes including SBP/DBP and PWV.

CONCLUSION

Genetic variation of the prostasin gene may be implicated in the development of hypertension in youths..

The epidermal growth factor receptor (EGFR) is proteolytically modified by the Matriptase-Prostasin serine protease cascade in cultured epithelial cells

Prostasin is expressed at the apical surface of normal epithelial cells and suppresses in vitro invasion of cancer cells. Prostasin re-expression in the PC-3 prostate carcinoma cells down-regulated the epidermal growth factor receptor (EGFR) protein expression and EGF-induced phosphorylation of the extracellular signal-regulated kinases (Erk1/2). We report here that prostasin and its activating enzyme matriptase are capable of inducing proteolytic cleavages in the EGFR extracellular domain (ECD) when co-expressed in the FT-293 cells, generating two amino-terminally truncated fragments EGFR135 and EGFR110, at 135 and 110 kDa. Prostasin's role in EGFR cleavage is dependent on the serine active-site but not the GPI-anchor. The modifications of EGFR were confirmed to be on the primary structure by deglycosylation. EGFR135 and EGFR110 are not responsive to EGF stimulation, indicating loss of the ligand-binding domains. EGFR110 is constitutively phosphorylated and in its presence Erk1/2 phosphorylation is increased in the absence of EGF. The protease-induced EGFR cleavages are not dependent on EGFR phosphorylation. The EGFR ECD proteolytic modification by matriptase-prostasin is also observed in the BEAS-2B normal lung epithelial cells, the BPH-1 benign prostate hyperplasia and the MDA-MB-231 breast cancer cell lines; and represents a novel mechanism for epithelial cells to modulate EGF-EGFR signaling.

Co-localization of the channel activating protease prostasin/(CAP1/PRSS8) with its candidate activator, matriptase

Prostasin (CAP1/PRSS8) is a glycosylphosphatidylinositol-anchored membrane serine protease believed to be critical for the regulation of epithelial sodium channel (ENaC) activity. Prostasin is synthesized as an inactive zymogen that requires a site-specific endoproteolytic cleavage to be converted to an active protease. We have recently reported that the tumor-associated type II transmembrane serine protease, matriptase is necessary and sufficient for prostasin activation in the epidermis. In this study, the interrelationship between the two membrane serine proteases was investigated further by using enzymatic gene trapping combined with immunohistochemistry to delineate the spatial expression of matriptase and prostasin in mouse tissues. We utilized a knock-in mouse with a promoterless beta-galactosidase marker gene inserted into the matriptase locus, as a unique tool for precise assessment of endogenous matriptase expression. The spatial expression of matriptase and prostasin in mouse tissues was delineated by combining in situ beta-galactosidase matriptase staining with immunohistochemical detection of prostasin. We report that prostasin displays a near-ubiquitous co-localization with its candidate activator matriptase in a variety of normal epithelial tissues. These include simple, stratified, and pseudo-stratified epithelium of the integumentary system, digestive tract, respiratory tract, and urogenital tract. However, matriptase and prostasin expression segregates during epithelial multi-stage carcinogenesis to eventually become localized in separate compartments of the tumor. These data suggest that a matriptase-prostasin zymogen activation cascade may be functionally operative in multiple epithelial tissues, but matriptase promotes epithelial carcinogenesis independent of prostasin.

Alveolar epithelial transport in the adult lung

The alveolar surface comprises >99% of the internal surface area of the lungs. At birth, the fetal lung rapidly converts from a state of net fluid secretion, which is necessary for normal fetal lung development, to a state in which there is a minimal amount of alveolar liquid. The alveolar surface epithelium facing the air compartment is composed of TI and TII cells. The morphometric characteristics of both cell types are fairly constant over a range of mammalian species varying in body weight by a factor of approximately 50,000. From the conservation of size and shape across species, one may infer that both TI and TII cells also have important conserved functions. The regulation of alveolar ion and liquid transport has been extensively investigated using a variety of experimental models, including whole animal, isolated lung, isolated cell, and cultured cell model systems, each with their inherent strengths and weaknesses. The results obtained with different model systems and a variety of different species point to both interesting parallels and some surprising differences. Sometimes it has been difficult to reconcile results obtained with different model systems. In this section, the primary focus will be on aspects of alveolar ion and liquid transport under normal physiologic conditions, emphasizing newer data and describing evolving paradigms of lung ion and fluid transport. We will highlight some of the unanswered questions, outline the similarities and differences in results obtained with different model systems, and describe some of the complex and interweaving regulatory networks.

Regulation of the epithelial Na+ channel by peptidases

Recent investigations point to an important role for peptidases in regulating transcellular ion transport by the epithelial Na(+) channel, ENaC. Several peptidases, including furins and proteasomal hydrolases, modulate ENaC maturation and disposal. More idiosyncratically, apical Na(+) transport by ENaC in polarized epithelia of kidney, airway, and gut is stimulated constitutively by one or more trypsin-family serine peptidases, as revealed by inhibition of amiloride-sensitive Na(+) transport by broad-spectrum antipeptidases, including aprotinin and bikunin/SPINT2. In vitro, the transporting activity of aprotinin-suppressed ENaC can be restored by exposure to trypsin. The prototypical channel-activating peptidase (CAP) is a type 1 membrane-anchored tryptic peptidase first identified in Xenopus kidney cells. Frog CAP1 strongly upregulates Na(+) transport when coexpressed with ENaC in oocytes. The amphibian enzyme's apparent mammalian orthologue is prostasin, otherwise known as CAP1, which is coexpressed with ENaC in a variety of epithelia. In airway cells, prostasin is the major basal regulator of ENaC activity, as suggested by inhibition and knockdown experiments. Other candidate regulators of mature ENaC include CAP2/TMPRSS4 and CAP3/matriptase (also known as membrane-type serine protease 1/ST14). Mammalian CAPs are potential targets for treatment of ENaC-mediated Na(+) hyperabsorption by the airway in cystic fibrosis (CF) and by the kidney in hypertension. CAPs can be important for mammalian development, as indicated by embryonic lethality in mice with null mutations of CAP1/prostasin. Mice with selectively knocked out expression of CAP1/prostasin in the epidermis and mice with globally knocked out expression of CAP3/matriptase exhibit phenotypically similar defects in skin barrier function and neonatal death from dehydration. In rats, transgenic overexpression of human prostasin disturbs salt balance and causes hypertension. Thus, several converging lines of evidence indicate that ENaC function is regulated by peptidases, and that such regulation is critical for embryonic development and adult function of organs such as skin, kidney, and lung.

Evidence for a matriptase-prostasin proteolytic cascade regulating terminal epidermal differentiation

Recent gene ablation studies in mice have shown that matriptase, a type II transmembrane serine protease, and prostasin, a glycosylphosphatidylinositol-anchored membrane serine protease, are both required for processing of the epidermis-specific polyprotein, profilaggrin, stratum corneum formation, and acquisition of epidermal barrier function. Here we present evidence that matriptase acts upstream of prostasin in a zymogen activation cascade that regulates terminal epidermal differentiation and is required for prostasin zymogen activation. Enzymatic gene trapping of matriptase combined with prostasin immunohistochemistry revealed that matriptase was co-localized with prostasin in transitional layer cells of the epidermis and that the developmental onset of expression of the two membrane proteases was coordinated and correlated with acquisition of epidermal barrier function. Purified soluble matriptase efficiently converted soluble prostasin zymogen to an active two-chain form that formed SDS-stable complexes with the serpin protease nexin-1. Whereas two forms of prostasin with molecular weights corresponding to the prostasin zymogen and active prostasin were present in wild type epidermis, prostasin was exclusively found in the zymogen form in matriptase-deficient epidermis. These data suggest that matriptase, an autoactivating protease, acts upstream from prostasin to initiate a zymogen cascade that is essential for epidermal differentiation.