Structure and activity of human pancreasin, a novel tryptic serine peptidase expressed primarily by the pancreas

Serine Protease 27, a Prognostic Biomarker in Pan-cancer and Associated with the Aggressive Progression of Breast Cancer

BACKGROUND

To create effective medicines, researchers must first identify the common or unique genes that drive oncogenic processes in human cancers. Serine protease 27 (PRSS27) has been recently defined as a possible driver gene in esophageal squamous cell carcinoma. However, no thorough pan-cancer study has been performed to date, including breast cancer.

METHODS

Using the TCGA (The Cancer Genome Atlas), the GEO (Gene Expression Omnibus) dataset, and multiple bioinformatic tools, we investigated the function of PRSS27 in 33 tumor types. In addition, prognosis analysis of PRSS27 in breast cancer was carried out, as well as in vitro experiments to verify its role as an oncogene. We first explored the expression of PRSS27 in over 10 tumors and then we looked into PRSS27 genomic mutations.

RESULTS

We discovered that PRSS27 has prognostic significance in breast cancer and other cancers' survival, and we developed a breast cancer prognostic prediction model by combining a defined set of clinical factors. Besides, we confirmed PRSS27 as an oncogene in breast cancer using some primary in vitro experiments.

CONCLUSION

Our pan-cancer survey has comprehensively reviewed the oncogenic function of PRSS27 in various human malignancies, suggesting that it may be a promising prognostic biomarker and tumor therapeutic target in breast cancer.

Development of a biomarker signature using grating-coupled fluorescence plasmonic microarray for diagnosis of MIS-C

Multisystem inflammatory syndrome in children (MIS-C) is a rare but serious condition that can develop 4–6 weeks after a school age child becomes infected by SARS-CoV-2. To date, in the United States more than 8,862 cases of MIS-C have been identified and 72 deaths have occurred. This syndrome typically affects children between the ages of 5–13; 57% are Hispanic/Latino/Black/non-Hispanic, 61% of patients are males and 100% have either tested positive for SARS-CoV-2 or had direct contact with someone with COVID-19. Unfortunately, diagnosis of MIS-C is difficult, and delayed diagnosis can lead to cardiogenic shock, intensive care admission, and prolonged hospitalization. There is no validated biomarker for the rapid diagnosis of MIS-C. In this study, we used Grating-coupled Fluorescence Plasmonic (GCFP) microarray technology to develop biomarker signatures in pediatric salvia and serum samples from patients with MIS-C in the United States and Colombia. GCFP measures antibody-antigen interactions at individual regions of interest (ROIs) on a gold-coated diffraction grating sensor chip in a sandwich immunoassay to generate a fluorescent signal based on analyte presence within a sample. Using a microarray printer, we designed a first-generation biosensor chip with the capability of capturing 33 different analytes from 80 μL of sample (saliva or serum). Here, we show potential biomarker signatures in both saliva and serum samples in six patient cohorts. In saliva samples, we noted occasional analyte outliers on the chip within individual samples and were able to compare those samples to 16S RNA microbiome data. These comparisons indicate differences in relative abundance of oral pathogens within those patients. Microsphere Immunoassay (MIA) of immunoglobulin isotypes was also performed on serum samples and revealed MIS-C patients had several COVID antigen-specific immunoglobulins that were significantly higher than other cohorts, thus identifying potential new targets for the second-generation biosensor chip. MIA also identified additional biomarkers for our second-generation chip, verified biomarker signatures generated on the first-generation chip, and aided in second-generation chip optimization. Interestingly, MIS-C samples from the United States had a more diverse and robust signature than the Colombian samples, which was also illustrated in the MIA cytokine data. These observations identify new MIS-C biomarkers and biomarker signatures for each of the cohorts. Ultimately, these tools may represent a potential diagnostic tool for use in the rapid identification of MIS-C.

Activation by cleavage of the epithelial Na+ channel α and γ subunits independently coevolved with the vertebrate terrestrial migration

Vertebrates evolved mechanisms for sodium conservation and gas exchange in conjunction with migration from aquatic to terrestrial habitats. Epithelial Na⁺ channel (ENaC) function is critical to systems responsible for extracellular fluid homeostasis and gas exchange. ENaC is activated by cleavage at multiple specific extracellular polybasic sites, releasing inhibitory tracts from the channel’s α and γ subunits. We found that proximal and distal polybasic tracts in ENaC subunits coevolved, consistent with the dual cleavage requirement for activation observed in mammals. Polybasic tract pairs evolved with the terrestrial migration and the appearance of lungs, coincident with the ENaC activator aldosterone, and appeared independently in the α and γ subunits. In summary, sites within ENaC for protease activation developed in vertebrates when renal Na⁺ conservation and alveolar gas exchange were required for terrestrial survival.

Mutational tail loss is an evolutionary mechanism for liberating marapsins and other type I serine proteases from transmembrane anchors

Human and mouse marapsins (Prss27) are serine proteases preferentially expressed by stratified squamous epithelia. However, mouse marapsin contains a transmembrane anchor absent from the human enzyme. To gain insights into physical forms, activities, inhibition, and roles in epithelial differentiation, we traced tail loss in human marapsin to a nonsense mutation in an ancestral ape, compared substrate preferences of mouse and human marapsins with those of the epithelial peptidase prostasin, designed a selective substrate and inhibitor, and generated Prss27-null mice. Phylogenetic analysis predicts that most marapsins are transmembrane proteins. However, nonsense mutations caused membrane anchor loss in three clades: human/bonobo/chimpanzee, guinea pig/degu/tuco-tuco/mole rat, and cattle/yak. Most marapsin-related proteases, including prostasins, are type I transmembrane proteins, but the closest relatives (prosemins) are not. Soluble mouse and human marapsins are tryptic with subsite preferences distinct from those of prostasin, lack general proteinase activity, and unlike prostasins resist antiproteases, including leupeptin, aprotinin, serpins, and α2-macroglobulin, suggesting the presence of non-canonical active sites. Prss27-null mice develop normally in barrier conditions and are fertile without overt epithelial defects, indicating that marapsin does not play critical, non-redundant roles in development, reproduction, or epithelial differentiation. In conclusion, marapsins are conserved, inhibitor-resistant, tryptic peptidases. Although marapsins are type I transmembrane proteins in their typical form, they mutated independently into anchorless forms in several mammalian clades, including one involving humans. Similar pathways appear to have been traversed by prosemins and tryptases, suggesting that mutational tail loss is an important means of evolving new functions of tryptic serine proteases from transmembrane ancestors.

Membrane-anchored serine proteases in health and disease

Serine proteases of the trypsin-like family have long been recognized to be critical effectors of biological processes as diverse as digestion, blood coagulation, fibrinolysis, and immunity. In recent years, a subgroup of these enzymes has been identified that are anchored directly to plasma membranes, either by a carboxy-terminal transmembrane domain (Type I), an amino-terminal transmembrane domain with a cytoplasmic extension (Type II or TTSP), or through a glycosylphosphatidylinositol (GPI) linkage. Recent biochemical, cellular, and in vivo analyses have now established that membrane-anchored serine proteases are key pericellular contributors to processes vital for development and the maintenance of homeostasis. This chapter reviews our current knowledge of the biological and physiological functions of these proteases, their molecular substrates, and their contributions to disease.

The cutting edge: membrane-anchored serine protease activities in the pericellular microenvironment

The serine proteases of the trypsin-like (S1) family play critical roles in many key biological processes including digestion, blood coagulation, and immunity. Members of this family contain N- or C-terminal domains that serve to tether the serine protease catalytic domain directly to the plasma membrane. These membrane-anchored serine proteases are proving to be key components of the cell machinery for activation of precursor molecules in the pericellular microenvironment, playing vital functions in the maintenance of homoeostasis. Substrates activated by membrane-anchored serine proteases include peptide hormones, growth and differentiation factors, receptors, enzymes, adhesion molecules and viral coat proteins. In addition, new insights into our understanding of the physiological functions of these proteases and their involvement in human pathology have come from animal models and patient studies. The present review discusses emerging evidence for the diversity of this fascinating group of membrane serine proteases as potent modifiers of the pericellular microenvironment through proteolytic processing of diverse substrates. We also discuss the functional consequences of the activities of these proteases on mammalian physiology and disease.

High degree of conservation of the multigene tryptase locus over the past 150-200 million years of mammalian evolution

Activated mast cells release a number of potent inflammatory mediators including histamine, proteoglycans, cytokines, and serine proteases. The proteases constitute the majority of the mast cell granule proteins, and they belong to either the chymase or the tryptase family. In mammals, these enzymes are encoded by two different loci, the mast cell chymase and the multigene tryptase loci. In mice and humans, a relatively large number of tryptic enzymes are encoded from the latter locus. These enzymes can be grouped into two subfamilies, the group 1 tryptases, with primarily membrane-anchored enzymes, and the group 2 tryptases, consisting of the soluble mast cell tryptases. In order to study the appearance of these enzymes during vertebrate evolution, we have analyzed the dog, cattle, opossum, and platypus genomes and sought orthologues in the genomes of several bird, frog, and fish species as well. Our results show that the overall structure and the number of genes within this locus have been well conserved from marsupial to placental mammals. In addition, two relatively distantly related group 2 tryptase genes and several direct homologues of some of the group 1 genes are present in the genome of the platypus, a monotreme. However, no direct homologues of the individual genes of either group 1 or 2 enzymes were identified in bird, amphibian, or fish genomes. Our results indicate that the individual genes within the multigene tryptase locus, in their present form, are essentially mammal-specific.

Mast cell peptidases: chameleons of innate immunity and host defense

Mast cells make and secrete an abundance of peptidases, which are stored in such large amounts in granules that they comprise a high fraction of all cellular protein. Perhaps no other immune cell is so generously endowed with peptidases. For many years after the main peptidases were first described, they were best known as markers of degranulation, for they are released locally in response to mast cell stimulation and can be distributed systemically and detected in blood. The principal peptidases are tryptases, chymases, carboxypeptidase A3, and dipeptidylpeptidase I (cathepsin C). Numerous studies suggest that these enzymes are important and even critical for host defense and homeostasis. Endogenous and allergen or pathogen-associated targets have been identified. Belying the narrow notion of peptidases as proinflammatory, several of the peptidases limit inflammation and toxicity of endogenous peptides and venoms. The peptidases are interdependent, so that absence or inactivity of one enzyme can alter levels and activity of others. Mammalian mast cell peptidases--chymases and tryptases especially--vary remarkably in number, expression, biophysical properties, and specificity, perhaps because they hyper-evolved under pressure from the very pathogens they help to repel. Tryptase and chymase involvement in some pathologies stimulated development of therapeutic inhibitors for use in asthma, lung fibrosis, pulmonary hypertension, ulcerative colitis, and cardiovascular diseases. While animal studies support the potential for mast cell peptidase inhibitors to mitigate certain diseases, other studies, as in mice lacking selected peptidases, predict roles in defense against bacteria and parasites and that systemic inactivation may impair host defense.

The serine protease marapsin is expressed in stratified squamous epithelia and is up-regulated in the hyperproliferative epidermis of psoriasis and regenerating wounds

The trypsin-like serine protease marapsin is a member of the large protease gene cluster at human chromosome 16p13.3, which also contains the structurally related proteases testisin, tryptase epsilon, tryptase gamma, and EOS. To gain insight into the biological functions of marapsin, we undertook a detailed gene expression analysis. It showed that marapsin expression was restricted to tissues containing stratified squamous epithelia and was absent or only weakly expressed in all other tissues, including the pancreas. Marapsin was constitutively expressed in nonkeratinizing stratified squamous epithelia of human esophagus, tonsil, cervix, larynx, and cornea. In the keratinizing stratified squamous epidermis of skin, however, its expression was induced only during epidermal hyperproliferation, such as in psoriasis and in murine wound healing. In fact, marapsin was the second most strongly up-regulated protease in psoriatic lesions, where expression was localized to the upper region of the hyperplastic epidermis. Similarly, in the hyperproliferative epithelium of regenerating murine skin wounds, marapsin localized to the suprabasal layers, where keratinocytes undergo squamous differentiation. The transient up-regulation of marapsin, which closely correlated with re-epithelialization, was virtually absent in a genetic mouse model of delayed wound closure. These results suggested a function during the process of re-epithelialization. Furthermore, in reconstituted human epidermis, a model system of epidermal differentiation, members of the IL-20 subfamily of cytokines, such as IL-22, induced marapsin expression. Consistent with a physiologic role in marapsin regulation, IL-22 was also strongly expressed in re-epithelializing skin wounds. Marapsin's restricted expression, localization, and cytokine-inducible expression suggest a role in the terminal differentiation of keratinocytes in hyperproliferating squamous epithelia.

Mast cell alpha and beta tryptases changed rapidly during primate speciation and evolved from gamma-like transmembrane peptidases in ancestral vertebrates

Human mast cell tryptases vary strikingly in secretion, catalytic competence, and inheritance. To explore the basis of variation, we compared genes from a range of primates, including humans, great apes (chimpanzee, gorilla, orangutan), Old- and New-World monkeys (macaque and marmoset), and a prosimian (galago), tracking key changes. Our analysis reveals that extant soluble tryptase-like proteins, including alpha- and beta-like tryptases, mastins, and implantation serine proteases, likely evolved from membrane-anchored ancestors because their more deeply rooted relatives (gamma tryptases, pancreasins, prostasins) are type I transmembrane peptidases. Function-altering mutations appeared at widely separated times during primate speciation, with tryptases evolving by duplication, gene conversion, and point mutation. The alpha-tryptase Gly(216)Asp catalytic domain mutation, which diminishes activity, is present in macaque tryptases, and thus arose before great apes and Old World monkeys shared an ancestor, and before the alphabeta split. However, the Arg(-3)Gln processing mutation appeared recently, affecting only human alpha. By comparison, the transmembrane gamma-tryptase gene, which anchors the telomeric end of the multigene tryptase locus, changed little during primate evolution. Related transmembrane peptidase genes were found in reptiles, amphibians, and fish. We identified soluble tryptase-like genes in the full spectrum of mammals, including marsupial (opossum) and monotreme (platypus), but not in nonmammalian vertebrates. Overall, our analysis suggests that soluble tryptases evolved rapidly from membrane-anchored, two-chain peptidases in ancestral vertebrates into soluble, single-chain, self-compartmentalizing, inhibitor-resistant oligomers expressed primarily by mast cells, and that much of present numerical, behavioral, and genetic diversity of alpha- and beta-like tryptases was acquired during primate evolution.

Expression of Prostasin Serine Protease and Protease Nexin-1 (PN-1) in Rhesus Monkey Ovary During Menstrual Cycle and Early Pregnancy

Serine proteases and their cognate serpin-class inhibitors are involved in the controlled proteolytic events during follicular development, ovulation, formation, and maintenance of the corpus luteum (CL). In this study, we investigated the expression patterns of prostasin serine protease and protease nexin-1 (PN-1), a serine protease inhibitor also called serpin-E2, in rhesus monkey ovaries during the menstrual cycle and early pregnancy, by using in situ hybridization and immunohistochemistry. Expression of prostasin was localized in oocyte, granulosa cells, and/or theca cells of early antral follicles and antral follicles, with high levels observed in preovulatory follicles. Prostasin was also localized at high levels of abundance in the CL during the menstrual cycle and early pregnancy. During the menstrual cycle, PN-1 was coordinately localized with prostasin in oocytes, granulosa cells, and theca cells of antral follicles and preovulatory follicles and in the CL. In addition, the PN-1 expression level in macaque CL during early pregnancy increased as pregnancy proceeded. We propose that prostasin may be involved in follicular development, ovulation, and CL formation, whereas PN-1 may be present to regulate the proteolysis in these processes.

Protease-proteoglycan complexes of mouse and human mast cells and importance of their beta-tryptase-heparin complexes in inflammation and innate immunity

Approximately 50% of the weight of a mature mast cell (MC) consists of varied neutral proteases stored in the cell's secretory granules ionically bound to serglycin proteoglycans that contain heparin and/or chondroitin sulfate E/diB chains. Mouse MCs express the exopeptidase carboxypeptidase A3 and at least 15 serine proteases [designated as mouse MC protease (mMCP) 1-11, transmembrane tryptase/tryptase gamma/protease serine member S (Prss) 31, cathepsin G, granzyme B, and neuropsin/Prss19]. mMCP-6, mMCP-7, mMCP-11/Prss34, and Prss31 are the four members of the chromosome 17A3.3 family of tryptases that are preferentially expressed in MCs. One of the challenges ahead is to understand why MCs express so many different protease-proteoglycan macromolecular complexes. MC-like cells that contain tryptase-heparin complexes in their secretory granules have been identified in the Ciona intestinalis and Styela plicata urochordates that appeared approximately 500 million years ago. Because sea squirts lack B cells and T cells, it is likely that MCs and their tryptase-proteoglycan granule mediators initially appeared in lower organisms as part of their innate immune system. The conservation of MCs throughout evolution suggests that some of these protease-proteoglycan complexes are essential to our survival. In support of this conclusion, no human has been identified that lacks MCs. Moreover, transgenic mice lacking the beta-tryptase mMCP-6 are unable to combat a Klebsiella pneumoniae infection effectively. Here we summarize the nature and function of some of the tryptase-serglycin proteoglycan complexes found in mouse and human MCs.

Mast cell tryptases and chymases in inflammation and host defense

Tryptases and chymases are the major proteins stored and secreted by mast cells. The types, amounts, and properties of these serine peptidases vary by mast cell subtype, tissue, and mammal of origin. Membrane-anchored gamma-tryptases are tryptic, prostasin-like, type I peptidases that remain membrane attached on release and act locally. Soluble tryptases, including their close relatives, mastins, form inhibitor-resistant oligomers that act more remotely. Befitting their greater destructive potential, chymases are quickly inhibited after release, although some gain protection by associating with proteoglycans. Most chymase-like enzymes, including mast cell cathepsin G, hydrolyze chymotryptic substrates, an uncommon capability in the proteome. Some rodent chymases, however, have mutations resulting in elastolytic activity. Secreted tryptases and chymases promote inflammation, matrix destruction, and tissue remodeling by several mechanisms, including destroying procoagulant, matrix, growth, and differentiation factors and activating proteinase-activated receptors, urokinase, metalloproteinases, and angiotensin. They also modulate immune responses by hydrolyzing chemokines and cytokines. At least one chymase protects mice from intestinal worms. Tryptases and chymases can also oppose inflammation by inactivating allergens and neuropeptides causing inflammation and bronchoconstriction. Thus, like mast cells themselves, mast cell serine peptidases play multiple roles in host defense, and any accounting of benefit versus harm is necessarily context specific.

Human pancreatic digestive enzymes

A primary function of the pancreas is to produce digestive enzymes that are delivered to the small intestine for the hydrolysis of complex nutrients. Much of our understanding of digestive enzymes comes from studies in animals. New technologies and the availability of the sequence of the human genome allow for a critical review of older reports and assumptions based on animal studies. This report updates our understanding of human pancreatic digestive enzymes with a focus on new insights into the biology of human proteases, lipases and amylases.

Prostasin regulates epithelial monolayer function: cell-specific Gpld1-mediated secretion and functional role for GPI anchor

Prostasin, a trypsinlike serine peptidase, is highly expressed in prostate, kidney, and lung epithelia, where it is bound to the cell surface, secreted, or both. Prostasin activates the epithelial sodium channel (ENaC) and suppresses invasion of prostate and breast cancer cells. The studies reported here establish mechanisms of membrane anchoring and secretion in kidney and lung epithelial cells and demonstrate a critical role for prostasin in regulating epithelial monolayer function. We report that endogenous mouse prostasin is glycosylphosphatidylinositol (GPI) anchored to the cell surface and is constitutively secreted from the apical surface of kidney cortical collecting duct cells. Using site-directed mutagenesis, detergent phase separation, and RNA interference approaches, we show that prostasin secretion depends on GPI anchor cleavage by endogenous GPI-specific phospholipase D1 (Gpld1). Secretion of prostasin by kidney and lung epithelial cells, in contrast to prostate epithelium, does not depend on COOH-terminal processing at conserved Arg(322). Using stably transfected M-1 cells expressing wild-type, catalytically inactive, or chimeric transmembrane (not GPI)-anchored prostasins we establish that prostasin regulates transepithelial resistance, current, and paracellular permeability by GPI anchor- and protease activity-dependent mechanisms. These studies demonstrate a novel role for prostasin in regulating epithelial monolayer resistance and permeability in kidney epithelial cells and, furthermore, show specifically that prostasin is a critical regulator of transepithelial ion transport in M-1 cells. These functions depend on the GPI anchor as well as the peptidase activity of prostasin. These studies suggest that cell-specific Gpld1- or peptidase-dependent pathways for prostasin secretion may control prostasin functions in a tissue-specific manner.

Expression of prostasin and protease nexin-1 in rhesus monkey (Macaca mulatta) endometrium and placenta during early pregnancy

Serine proteases have been documented to play key roles in uterine matrix turnover and trophoblastic invasion during implantation. Roles of prostasin serine protease in these processes, however, are currently unclear. The present study was first conducted to investigate the colocalization of prostasin and its cognate serpin, protease nexin-1 (PN-1), in rhesus monkey endometrium and placenta on days 12, 18, and 26 of pregnancy by using in situ hybridization (ISH) and immunohistochemistry. With ISH, expression of prostasin mRNA was intensely localized in the glandular epithelium on days 12 and 18 and in the placental villi, trophoblastic column, trophoblastic shell, and fetal-maternal border on days 18 and 26. With the progress of pregnancy, expression level in the glandular epithelium was significantly decreased, and the accumulation in the placental compartments was further increased. In addition, the stroma and arterioles exhibited modest levels of prostasin signals. However, expression level of PN-1 in these compartments on adjacent sections in the three stages of early pregnancy was weak or below the level of detection. Prostasin protein expression in the endometrium was found to be consistent with the distribution patterns revealed in the ISH experiments. It may be suggested from these results that prostasin is involved in endometrial epithelial morphology establishment, tissue remodeling, and trophoblastic invasion during early pregnancy. The cognate serpin PN-1 was not coordinately expressed along with prostasin, creating a tissue environment favorable for proteolytic activities of prostasin during early pregnancy events.

Identification of a subgroup of glycosylphosphatidylinositol-anchored tryptases

The tryptase locus on mouse chromosome 17A3.3 contains 13 genes that encode enzymatically active serine proteases with different tissue expression profiles and substrate specificities. Mouse mast cell protease (mMCP) 6, mMCP-7, mMCP-11/protease serine member S (Prss) 34, tryptase 6/Prss33, tryptase epsilon/Prss22, implantation serine protease (Isp) 1/Prss28, and Isp-2 are constitutively exocytosed enzymes. We now demonstrate that tryptase 5/Prss32, pancreasin/Prss27, and testis serine protease-1 are inserted into plasma membranes via glycosylphosphatidylinositol (GPI) anchors analogous to Prss21, and that these serine proteases can be released from the cell's surface by a phosphatidylinositol-specific phospholipase C. These data suggest that the C-terminal residues play key roles in determining where tryptases compartmentalize in cells. GPI-anchored proteins are targeted to lipid rafts. Thus, our identification of a number of GPI-anchored tryptases whose genes reside at mouse chromosome 17A3.3 also implicates important biological functions for this new family of serine proteases on the surfaces of cells.

Hypermethylation of the 5' CpG island of the gene encoding the serine protease Testisin promotes its loss in testicular tumorigenesis

The Testisin gene (PRSS21) encodes a glycosylphosphatidylinositol (GPI)-linked serine protease that exhibits testis tissue-specific expression. Loss of Testisin has been implicated in testicular tumorigenesis, but its role in testis biology and tumorigenesis is not known. Here we have investigated the role of CpG methylation in Testisin gene inactivation and tested the hypothesis that Testisin may act as a tumour suppressor for testicular tumorigenesis. Using sequence analysis of bisulphite-treated genomic DNA, we find a strong relationship between hypermethylation of a 385 bp 5′ CpG rich island of the Testisin gene, and silencing of the Testisin gene in a range of human tumour cell lines and in 100% (eight/eight) of testicular germ cell tumours. We show that treatment of Testisin-negative cell lines with demethylating agents and/or a histone deacetylase inhibitor results in reactivation of Testisin gene expression, implicating hypermethylation in Testisin gene silencing. Stable expression of Testisin in the Testisin-negative Tera-2 testicular cancer line suppressed tumorigenicity as revealed by inhibition of both anchorage-dependent cell growth and tumour formation in an SCID mouse model of testicular tumorigenesis. Together, these data show that loss of Testisin is caused, at least in part, by DNA hypermethylation and histone deacetylation, and suggest a tumour suppressor role for Testisin in testicular tumorigenesis.

Urokinase-type plasminogen activator is a preferred substrate of the human epithelium serine protease tryptase epsilon/PRSS22

Tryptase epsilon is a member of the chromosome 16p13.3 family of human serine proteases that is preferentially expressed by epithelial cells. Recombinant pro-tryptase epsilon was generated to understand how the exocytosed zymogen might be activated outside of the epithelial cell, as well as to address its possible role in normal and diseased states. Using expression/site-directed mutagenesis approaches, we now show that Lys20, Cys90, and Asp92 in the protease's substrate-binding cleft regulate its enzymatic activity. We also show that Arg(-1) in the propeptide domain controls its ability to autoactivate. In vitro studies revealed that recombinant tryptase epsilon possesses a restricted substrate specificity. Once activated, tryptase epsilon cannot be inhibited effectively by the diverse array of protease inhibitors present in normal human plasma. Moreover, this epithelium protease is not highly susceptible to alpha1-antitrypsin or secretory leukocyte protease inhibitor, which are present in the lung. Recombinant tryptase epsilon could not cleave fibronectin, vitronectin, laminin, single-chain tissue-type plasminogen activator, plasminogen, or any prominent serum protein. Nevertheless, tryptase epsilon readily converted single-chain pro-urokinase-type plasminogen activator (pro-uPA/scuPA) into its mature, enzymatically active protease. Tryptase epsilon also was able to induce pro-uPA-expressing smooth muscle cells to increase their migration through a basement membrane-like extracellular matrix. The ability to activate uPA in the presence of varied protease inhibitors suggests that tryptase epsilon plays a prominent role in fibrinolysis and other uPA-dependent reactions in the lung.

Human polyserase-2, a novel enzyme with three tandem serine protease domains in a single polypeptide chain

We have cloned a human cDNA encoding a new serine protease that has been called polyserase-2 (polyserine protease-2) because it is the second identified human enzyme with several tandem serine protease domains in its amino acid sequence. The first serine protease domain contains all characteristic features of these enzymes, whereas the second and third domains lack one residue of the catalytic triad of serine proteases and are predicted to be catalytically inactive. This complex domain organization is also present in the sequences of mouse and rat polyserase-2 and resembles that of polyserase-1, which also contains three serine protease domains in its amino acid sequence. However, polyserase-2 lacks additional domains present in polyserase-1, including a type II transmembrane motif and a low-density lipoprotein receptor A module. Enzymatic analysis demonstrated that both full-length polyserase-2 and its first serine protease domain hydrolyzed synthetic peptides used for assaying serine proteases. Nevertheless, the activity of the isolated domain was greater than that of the entire protein, suggesting that the two catalytically inactive serine protease domains of polyserase-2 may modulate the activity of the first domain. Northern blot analysis showed that polyserase-2 is expressed in fetal kidney; adult skeletal muscle, liver, placenta, prostate, and heart; and tumor cell lines derived from lung and colon adenocarcinomas. Finally, analysis of post-translational processing mechanisms of polyserase-2 revealed that, contrary to those affecting to the membrane-bound polyserase-1, this novel polyprotein is a secreted enzyme whose three protease domains remain as an integral part of a single polypeptide chain.

Prostasin, a membrane-anchored serine peptidase, regulates sodium currents in JME/CF15 cells, a cystic fibrosis airway epithelial cell line

Prostasin is a tryptic peptidase expressed in prostate, kidney, lung, and airway. Mammalian prostasins are related to Xenopus channel-activating protease, which stimulates epithelial Na+channel (ENaC) activity in frogs. In human epithelia, prostasin is one of several membrane peptidases proposed to regulate ENaC. This study tests the hypothesis that prostasin can regulate ENaC in cystic fibrosis epithelia in which excessive Na+uptake contributes to salt and water imbalance. We show that prostasin mRNA and protein are strongly expressed by human airway epithelial cell lines, including immortalized JME/CF15 nasal epithelial cells homozygous for the ΔF508 cystic fibrosis mutation. Epithelial cells transfected with vectors encoding recombinant soluble prostasin secrete active, tryptic peptidase that is highly sensitive to inactivation by aprotinin. When studied as monolayers in Ussing chambers, JME/CF15 cells exhibit amiloride-sensitive, transepithelial Na+currents that are markedly diminished by aprotinin, suggesting regulation by serine-class peptidases. Overproduction of membrane-anchored prostasin in transfected JME/CF15 cells does not augment Na+currents, and trypsin-induced increases are small, suggesting that baseline serine peptidase-dependent ENaC activation is maximal in these cells. To probe prostasin’s involvement in basal ENaC activity, we silenced expression of prostasin using short interfering RNA targeting of prostasin mRNA’s 3′-untranslated region. This drops ENaC currents to 26 ± 9% of baseline. These data predict that prostasin is a major regulator of ENaC-mediated Na+current in ΔF508 cystic fibrosis epithelia and suggest that airway prostasin is a target for therapeutic inhibition to normalize ion current in cystic fibrosis airway.

Mouse prostasin gene structure, promoter analysis, and restricted expression in lung and kidney

Human prostasin is a membrane-anchored serine peptidase hypothesized to regulate lung epithelial sodium transport. It belongs to a unique family of genes on chromosome 16p11.2/13.3. Here we describe genomic cloning, promoter analysis, and expression of prostasin's mouse ortholog. The 4.3-kb mouse prostasin gene (prss8) has a six-exon organization identical to human prostasin. Prss8 spans two signal tagged-sites localized to chromosome 7. Multiple mRNA transcripts arise from two consensus initiator elements of a TATA-less promoter and an alternatively spliced, 5' untranslated region intron. Reporter assay establishes that the initiator elements and a GC-rich domain comprise the core promoter and identifies 5' flanking regions with strong enhancer and repressor activity. The 3' untranslated region overlaps the 3' untranslated region of the Myst1 gene oriented tail-to-tail at this locus. Prss8 is highly transcribed in pancreas, kidney, submaxillary gland, lung, thyroid, prostate, and epididymis, and is developmentally regulated. Using selective riboprobes and antibodies to mouse prostasin, we localized its expression to lung airway epithelial and alveolar type II cells and kidney cortical tubule epithelium. Mouse prostasin highly resembles its human ortholog in gene organization and tissue specificity, including strong expression in pulmonary epithelium, suggesting that mice will be useful for probing prostasin's functions in vivo.

Mouse chromosome 17A3.3 contains 13 genes that encode functional tryptic-like serine proteases with distinct tissue and cell expression patterns

Probing of the mouse EST data base at GenBank trade mark with known tryptase cDNAs resulted in the identification of undiscovered serine protease transcripts whose genes reside at a 1.5-Mb complex on mouse chromosome 17A3.3. Mouse tryptase-5 (mT5), tryptase-6 (mT6), and mast cell protease-11 (mMCP-11) are new members of this serine protease superfamily whose amino acid sequences are 36-54% identical to each other and to their other 10 family members. The 13 functional mouse proteases can be subdivided into two subgroups based on conserved features in their propeptides. Of the three new serine proteases, mT6 is most widely expressed in tissues. mT5 is preferentially expressed in smooth muscle, whereas mMCP-11 is preferentially expressed in the spleen and bone marrow. In contrast to mT5 and mT6, mMCP-11 is also expressed in mast cells. Although mT6 and mMCP-11 are constitutively secreted when expressed in mammalian and insect cells, mT5 remains membrane-associated. The fact that recombinant mT5, mT6, and mMCP-11 possess non-identical expression patterns and substrate specificities suggests that each protease has a unique function in vivo. Of the 13 functional mouse tryptase genes identified at the complex, 12 have orthologs that reside in the syntenic region of human chromosome 16p13.3. The establishment of these ortholog pairs helps clarify the evolutionary relationship of the serine protease locus in the two species. This information provides a useful framework for the functional analysis of each protease using gene targeting and other molecular approaches.