Purification and cloning of hepatocyte growth factor activator inhibitor type 2, a Kunitz-type serine protease inhibitor

SPINT2 mutations in the Kunitz domain 2 found in SCSD patients inactivate HAI-2 as prostasin inhibitor via abnormal protein folding and N-glycosylation

Mutations in the Kunitz-type serine protease inhibitor HAI-2, encoded by SPINT2, are responsible for the pathogenesis of syndromic congenital sodium diarrhea (SCSD), an intractable secretory diarrhea of infancy. Some of the mutations cause defects in the functionally required Kunitz domain 1 and/or subcellular targeting signals. Almost all SCSD patients, however, harbor SPINT2 missense mutations that affect the functionally less important Kunitz domain 2. How theses single amino acid substitutions inactivate HAI-2 was, here, investigated by the doxycycline-inducible expression of three of these mutants in HAI-2-knockout Caco-2 human colorectal adenocarcinoma cells. Examining protein expressed from these HAI-2 mutants reveals that roughly 50% of the protein is synthesized as disulfide-linked oligomers that lose protease inhibitory activity due to the distortion of the Kunitz domains by disarrayed disulfide bonding. Although the remaining protein is synthesized as monomers, its glycosylation status suggests that the HAI-2 monomer remains in the immature, lightly glycosylated form, and is not converted to the heavily glycosylated mature form. Heavily glycosylated HAI-2 possesses full anti-protease activity and appropriate subcellular targeting signals, including the one embedded in the complex-type N-glycan. As predicted, these HAI-2 mutants cannot suppress the excessive prostasin proteolysis caused by HAI-2 deletion. The oligomerization and glycosylation defects have also been observed in a colorectal adenocarcinoma line that harbors one of these SPINT2 missense mutations. Our study reveals that the abnormal protein folding and N-glycosylation can cause widespread HAI-2 inactivation in SCSD patents.

Unraveling dedifferentiation and metastasis traces in pancreatic ductal adenocarcinoma ductal cells: Insights from single-cell RNA sequencing analysis of ITGB4 and C19orf33

Pancreatic Ductal Adenocarcinoma (PDAC) ranks among the most prevalent gastrointestinal malignancies, with risk factors including smoking, alcohol abuse, diabetes mellitus, obesity, age, family history, and genetic predisposition. Extensive research has focused on unraveling biomarkers and molecular intricacies associated with PDAC. Leveraging data from the Gene Expression Omnibus microarray and single-cell RNA sequencing datasets, our study identified ITGB4 and C19orf33 as potentially differentially expressed genes in PDAC samples when contrasted with non-malignant tissues. Notably, these genes exhibited a strong correlative expression pattern, primarily within ductal cells. Gene Expression Profiling Interactive Analysis corroborated our findings, further confirming the correlation between ITGB4 and C19orf33. Additionally, we conducted experiments involving two pivotal PDAC-related cell lines, MIA PaCa-2 and PANC-1, treated with oxaliplatin and 5-Fluorouracil. We also assessed the expression of these candidate genes in PDAC samples in comparison to adjacent normal tissues. Our findings revealed that C19orf33 is upregulated in PDAC samples, and treatment of PDAC cells with chemotherapeutic agents led to a correlated decrease in the expression of both ITGB4 and C19orf33. These co-expressed and correlated genes are implicated in relevant signaling pathways, suggesting shared biological activities that may contribute to the promotion of metastasis within malignant ductal cells. This study identifies ITGB4 and C19orf33 as key genes potentially shedding light on the molecular mechanisms driving tumorigenesis and metastasis in PDAC. These genes hold promise as potential diagnostic and therapeutic targets, offering valuable insights into the management of this challenging disease.

SPINT2 is involved in the proliferation, migration and phenotypic switching of aortic smooth muscle cells: Implications for the pathogenesis of thoracic aortic dissection

Thoracic aortic dissection (TAD) is a severe and extremely dangerous cardiovascular disease. Proliferation, migration and phenotypic switching of vascular smooth muscle cells (SMCs) are major pathogenetic mechanisms involved in the development of TAD. The present study was designed to investigate the expression and potential function of serine peptidase inhibitor Kunitz type 2 (SPINT2) in TAD. The gene expression profile data for ascending aorta from patients with TAD were downloaded from the GEO database with the accession number GSE52093. Bioinformatics analysis using GEO2R indicated that the differentially expressed SPINT2 was prominently decreased in TAD. The expression levels of SPINT2 mRNA and protein in aortic dissection specimens and normal aorta tissues were measured using reverse transcription-quantitative PCR and western blotting. SPINT2 expression was downregulated in clinical samples from aortic dissection specimens of patients with TAD compared with the corresponding expression noted in tissues derived from patients without TAD. In vitro, platelet-derived growth factor BB (PDGF-BB) was applied to induce the isolated primary mouse aortic SMC phenotypic modulation (a significant upregulation in the expression levels of synthetic markers), and the SMCs were infected with the adenoviral vector, Ad-SPINT2, to construct SPINT2-overexpressed cell lines. SMC viability was detected by an MTT assay and SMC proliferation was detected via the presence of Ki-67-positive cells (immunofluorescence staining). To explore the effects of SPINT2 on SMC migration, a wound healing assay was conducted. ELISA and western blotting assays were used to measure the content and expression levels of MMP-2 and MMP-9. The expression levels of vimentin, collagen I, α-SMA and SM22α were measured using western blotting. The PDGF-BB-induced proliferation and migration of SMCs were recovered by SPINT2 overexpression. The increase in the expression levels of SPINT2 reduced the expression levels of active matrix metalloproteinases (MMPs), MMP-2 and MMP-9. Overexpression of SPINT2 suppressed SMC switching from a contractile to a synthetic type, as evidenced by decreased vimentin and collagen I expression levels along with increased α-smooth muscle actin and smooth muscle protein 22-α expression levels. Furthermore, activation of ERK was inhibited in SPINT2-overexpressing SMCs. A specific ERK agonist, 12-O-tetradecanoylphorbol-13-acetate, reversed the SPINT2-mediated inhibition of SMC migration and the phenotypic switching. Collectively, the data indicated that SPINT2 was implicated in the proliferation, migration and phenotypic switching of aortic SMCs, suggesting that it may be involved in TAD progression.

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

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

N-glycosylation on Asn-57 is required for the correct HAI-2 protein folding and protease inhibitory activity

Hepatocyte growth factor activator inhibitor (HAI)-2 is an integral membrane Kunitz-type serine protease inhibitor that regulates the proteolysis of matriptase and prostasin in a cell-type selective manner. The cell-type selective nature of HAI-2 function depends largely on whether the inhibitor and potential target enzymes are targeted to locations in close proximity. The N-glycan moiety of HAI-2 can function as a subcellular targeting signal. HAI-2 is synthesized with 1 of 2 different N-glycan modifications: one of oligomannose-type, which largely remains in the endoplasmic reticulum/GA, and another of complex-type, which is targeted toward the apical surface in vesicle-like structures, and could function as an inhibitor of matriptase and prostasin. HAI-2 contains 2 putative N-glycosylation sites, Asn-57 and Asn-94, point mutations of which were generated and characterized in this study. The protein expression profile of the HAI-2 mutants indicates that Asn-57, and not Asn-94, is responsible for the N-glycosylation of both HAI-2 species, suggesting that the form with oligomannose-type N-glycan is the precursor of the form with complex-type N-glycan. Unexpectedly, the vast majority of non-glycosylated HAI-2 is synthesized into multiple disulfide-linked oligomers, which lack protease inhibitory function, likely due to distorted conformations caused by the disarrayed disulfide linkages. Although forced expression of HAI-2 in HAI-2 knockout cells artificially enhances HAI-2 oligomerization, disulfide-linked HAI-2 oligomers can also be observed in unmodified cells. These results suggest that N-glycosylation on Asn-57 is required for folding into a functional HAI-2 with full protease suppressive activity and correct subcellular targeting signal.

Possible role of combined therapy targeting MET and pro-HGF activation for renal cell carcinoma: analysis by human HGF-producing SCID mice

MET is a high-affinity receptor tyrosine kinase of HGF (hepatocyte growth factor). HGF is secreted as an inactive single-chain precursor (pro-HGF), which requires proteolytic activation for conversion to an active form. HGF activator inhibitor (HAI)-2 is a transmembrane Kunitz-type serine protease inhibitor, which inhibits all pro-HGF-activating enzymes. In RCC, increased expression of MET and decreased expression of HAI-2 were reported to be poor prognostic factors. In the current study, we tried to inhibit the growth of RCC cells by dual inhibition of both MET phosphorylation and pro-HGF-activation using MET inhibitor and HAI-2 overexpression. A transgenic mouse model which expressed human HGF (HGF mouse) was used for in vivo analysis to evaluate the HGF/MET signaling axis accurately. Initially, doxycycline-induced HAI-2 overexpression RCC cells (786-O-HAI2) were prepared. The cells were cultured with pro-HGF, and inhibitory effect of MET inhibitor (SCC244) and HAI-2 was evaluated by phosphorylation of MET and cell proliferation. Next, the cells were subcutaneously implanted to HGF mice and the growth inhibition was determined by SCC244 and HAI-2. Single use of each inhibitor showed significant inhibition in MET phosphorylation, migration and proliferation of 786-O-HAI2 cells; however, the strongest effect was observed by combined use of both inhibitors. Although in vivo analysis also showed apparent downregulation of MET phosphorylation and growth inhibition in combined treatment, statistical significance was not observed compared with single use of MET inhibitor. Combined treatment with MET-TKI and HAI-2 suggested to consider as a candidate for new strong therapy for RCC.

The serine protease matriptase inhibits migration and proliferation in multiple myeloma cells

BACKGROUND

Multiple myeloma (MM) is an incurable malignancy of plasma cells. The serine protease matriptase is frequently dysregulated in human carcinomas, which facilitates tumor progression and metastatic dissemination. The importance of matriptase in hematological malignancies is yet to be clarified. In this study, we aimed to characterize the role of matriptase in MM.

MATERIALS AND METHODS

mRNA expression of matriptase and its inhibitors hepatocyte growth factor activator inhibitor (HAI)-1 and HAI-2 was studied in primary MM cells from patient samples and human myeloma cell lines (HMCLs). We further investigated the effect of matriptase on migration and proliferation of myeloma cells in vitro. By use of the CoMMpass database, we assessed the clinical relevance of matriptase in MM patients.

RESULTS

Matriptase was expressed in 96% of patient samples and all HMCLs tested. Overexpression of matriptase in vitro reduced proliferation, and significantly decreased cytokine-induced migration. Conversely, matriptase knockdown significantly enhanced migration. Mechanistically, overexpression of matriptase inhibited activation of Src kinase.

CONCLUSIONS

Our findings may suggest a novel role of matriptase as a tumor suppressor in MM pathogenesis.

The Transmembrane Protease TMPRSS2 as a Therapeutic Target for COVID-19 Treatment

TMPRSS2 is a type II transmembrane protease with broad expression in epithelial cells of the respiratory and gastrointestinal tract, the prostate, and other organs. Although the physiological role of TMPRSS2 remains largely elusive, several endogenous substrates have been identified. TMPRSS2 serves as a major cofactor in SARS-CoV-2 entry, and primes glycoproteins of other respiratory viruses as well. Consequently, inhibiting TMPRSS2 activity is a promising strategy to block viral infection. In this review, we provide an overview of the role of TMPRSS2 in the entry processes of different respiratory viruses. We then review the different classes of TMPRSS2 inhibitors and their clinical development, with a focus on COVID-19 treatment.

The difference in the intracellular Arg/Lys-rich and EHLVY motifs contributes to distinct subcellular distribution of HAI-1 versus HAI-2

The integral membrane, Kunitz-type, serine protease inhibitors, HAI-1 and HAI-2, closely resemble one another structurally and with regard to their specificity and potency against proteases. Structural complementarity between the Kunitz domains and serine protease domains renders the membrane-associated serine proteases, matriptase and prostasin, the primary target proteases of the HAIs. The shared biochemical enzyme-inhibitor relationships are, however, at odds with their behavior at the cellular level, where HAI-1 appears to be the default inhibitor of these proteases and HAI-2 a cell-type-selective inhibitor, even though they are widely co-expressed. The limited motility of these proteins caused by their membrane anchorages may require their co-localization within a certain distance to allow the establishment of a cellular level functional relationship between the proteases and the inhibitors. The differences in their subcellular localization with HAI-1 both inside the cell and on the cell surface, compared to HAI-2 predominately in intracellular granules has, therefore, been implicated in the differential manner of their control of matriptase and prostasin proteolysis. The targeting signals present in the intracellular domains of the HAIs are systematically investigated herein. Studies involving domain swap and point mutation, in combination with immunocytochemistry and cell surface biotinylation/avidin depletion, reveal that the different subcellular localization between the HAIs can largely be attributed to differences in the intracellular Arg/Lys-rich and EHLVY motifs. These intrinsic differences in the targeting signal render the HAIs as two independent rather than redundant proteolysis regulators.

Targeted HAI-2 deletion causes excessive proteolysis with prolonged active prostasin and depletion of HAI-1 monomer in intestinal but not epidermal epithelial cells

Mutations of SPINT2, the gene encoding the integral membrane, Kunitz-type serine inhibitor HAI-2, primarily affect the intestine, while sparing many other HAI-2-expressing tissues, causing sodium loss in patients with syndromic congenital sodium diarrhea. The membrane-bound serine protease prostasin was previously identified as a HAI-2 target protease in intestinal tissues but not in the skin. In both tissues, the highly related inhibitor HAI-1 is, however, the default inhibitor for prostasin and the type 2 transmembrane serine protease matriptase. This cell-type selective functional linkage may contribute to the organ-selective damage associated with SPINT 2 mutations. To this end, the impact of HAI-2 deletion on matriptase and prostasin proteolysis was, here, compared using Caco-2 human colorectal adenocarcinoma cells and HaCaT human keratinocytes. Greatly enhanced prostasin proteolytic activity with a prolonged half-life and significant depletion of HAI-1 monomer were observed with HAI-2 loss in Caco-2 cells but not HaCaT cells. The constitutive, high level prostasin zymogen activation observed in Caco-2 cells, but not in HaCaT cells, also contributes to the excessive prostasin proteolytic activity caused by HAI-2 loss. HAI-2 deletion also caused increased matriptase zymogen activation, likely as an indirect result of increased prostasin proteolysis. This increase in activated matriptase, however, only had a negligible role in depletion of HAI-1 monomer. Our study suggests that the constitutive, high level of prostasin zymogen activation and the cell-type selective functional relationship between HAI-2 and prostasin renders Caco-2 cells more susceptible than HaCaT cells to the loss of HAI-2, causing a severe imbalance favoring prostasin proteolysis.

Elevated Circulating and Placental SPINT2 Is Associated with Placental Dysfunction

Biomarkers for placental dysfunction are currently lacking. We recently identified SPINT1 as a novel biomarker; SPINT2 is a functionally related placental protease inhibitor. This study aimed to characterise SPINT2 expression in placental insufficiency. Circulating SPINT2 was assessed in three prospective cohorts, collected at the following: (1) term delivery (n = 227), (2) 36 weeks (n = 364), and (3) 24-34 weeks' (n = 294) gestation. SPINT2 was also measured in the plasma and placentas of women with established placental disease at preterm (<34 weeks) delivery. Using first-trimester human trophoblast stem cells, SPINT2 expression was assessed in hypoxia/normoxia (1% vs. 8% O2), and following inflammatory cytokine treatment (TNFα, IL-6). Placental SPINT2 mRNA was measured in a rat model of late-gestational foetal growth restriction. At 36 weeks, circulating SPINT2 was elevated in patients who later developed preeclampsia (p = 0.028; median = 2233 pg/mL vs. controls, median = 1644 pg/mL), or delivered a small-for-gestational-age infant (p = 0.002; median = 2109 pg/mL vs. controls, median = 1614 pg/mL). SPINT2 was elevated in the placentas of patients who required delivery for preterm preeclampsia (p = 0.025). Though inflammatory cytokines had no effect, hypoxia increased SPINT2 in cytotrophoblast stem cells, and its expression was elevated in the placental labyrinth of growth-restricted rats. These findings suggest elevated SPINT2 is associated with placental insufficiency.

Integrative omics analysis reveals effective stratification and potential prognosis markers of pan-gastrointestinal cancers

Gastrointestinal (GI) tract cancers are the most common malignant cancers with high mortality rate. Pan-cancer multi-omics data fusion provides a powerful strategy to examine commonalities and differences among various cancer types and benefits for the identification of pan-cancer drug targets. Herein, we conducted an integrative omics analysis on The Cancer Genome Atlas pan-GI samples including six carcinomas and stratified into 9 clusters, i.e. 5 single-type-dominant clusters and 4 mixed clusters, the clustering reveals the molecular features of different subtypes, other than the organ and cell-of-origin classifications. Especially the mixed clusters revealed the homogeneity of pan-GI cancers. We demonstrated that the prognosis differences among pan-GI subtypes based on multi-omics integration are more significant than clustering by single-omics. The potential prognostic markers for pan-GI stratification were identified by proportional hazards model, such as PSCA (for colorectal and stomach cancer) and PPP1CB (for liver and pancreatic cancer), which have prominent prognostic power supported by high concordance index.

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Pan-cancer multi-omics strategy reveals homogeneity and heterogeneity of pan-GI cancers

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Identify 9 iclusters with significantly different survival and molecular features

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Potential prognostic markers have prominent power supported by concordance index

Novel cell types and developmental lineages revealed by single-cell RNA-seq analysis of the mouse crista ampullaris

This study provides transcriptomic characterization of the cells of the crista ampullaris, sensory structures at the base of the semicircular canals that are critical for vestibular function. We performed single-cell RNA-seq on ampullae microdissected from E16, E18, P3, and P7 mice. Cluster analysis identified the hair cells, support cells and glia of the crista as well as dark cells and other nonsensory epithelial cells of the ampulla, mesenchymal cells, vascular cells, macrophages, and melanocytes. Cluster-specific expression of genes predicted their spatially restricted domains of gene expression in the crista and ampulla. Analysis of cellular proportions across developmental time showed dynamics in cellular composition. The new cell types revealed by single-cell RNA-seq could be important for understanding crista function and the markers identified in this study will enable the examination of their dynamics during development and disease.

The Kunitz-type serine protease inhibitor Spint2 is required for cellular cohesion, coordinated cell migration and cell survival during zebrafish hatching gland development

We have previously shown that the Kunitz-type serine protease inhibitor Spint1a, also named Hai1a, is required in the zebrafish embryonic epidermis to restrict the activity of the type II transmembrane serine protease (TTSP) Matriptase1a/St14a, thereby ensuring epidermal homeostasis. A closely related Kunitz-type inhibitor is Spint2/Hai2, which in mammals plays multiple developmental roles that are either redundant or non-redundant with those of Spint1. However, the molecular bases for these non-redundancies are not fully understood. Here, we study spint2 during zebrafish development. It is co-expressed with spint1a in multiple embryonic epithelia, including the outer/peridermal layer of the epidermis. However, unlike spint1a, spint2 expression is absent from the basal epidermal layer but present in hatching gland cells. Hatching gland cells derive from the mesendodermal prechordal plate, from where they undergo a thus far undescribed transit into, and coordinated sheet migration within, the interspace between the outer and basal layer of the epidermis to reach their final destination on the yolk sac. Hatching gland cells usually survive their degranulation that drives embryo hatching but die several days later. In spint2 mutants, cohesion among hatching gland cells and their collective intra-epidermal migration are disturbed, leading to a discontinuous organization of the gland. In addition, cells undergo precocious cell death before degranulation, so that embryos fail to hatch. Chimera analyses show that Spint2 is required in hatching gland cells, but not in the overlying periderm, their potential migration and adhesion substrate. Spint2 acts independently of all tested Matriptases, Prostasins and other described Spint1 and Spint2 mediators. However, it displays a tight genetic interaction with and acts at least partly via the cell-cell adhesion protein E-cadherin, promoting both hatching gland cell cohesiveness and survival, in line with formerly reported effects of E-cadherin during morphogenesis and cell death suppression. In contrast, no such genetic interaction was observed between Spint2 and the cell-cell adhesion molecule EpCAM, which instead interacts with Spint1a. Our data shed new light onto the mechanisms of hatching gland morphogenesis and hatching gland cell survival. In addition, they reveal developmental roles of Spint2 that are strikingly different from those of Spint1, most likely due to differences in the expression patterns and relevant target proteins.

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

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

Inhibition of TMPRSS2 by HAI-2 reduces prostate cancer cell invasion and metastasis

TMPRSS2 is an important membrane-anchored serine protease involved in human prostate cancer progression and metastasis. A serine protease physiologically often comes together with a cognate inhibitor for execution of proteolytically biologic function; however, TMPRSS2's cognate inhibitor is still elusive. To identify the cognate inhibitor of TMPRSS2, in this study, we applied co-immunoprecipitation and LC/MS/MS analysis and isolated hepatocyte growth factor activator inhibitors (HAIs) to be potential inhibitor candidates for TMPRSS2. Moreover, the recombinant HAI-2 proteins exhibited a better inhibitory effect on TMPRSS2 proteolytic activity than HAI-1, and recombinant HAI-2 proteins had a high affinity to form a complex with TMPRSS2. The immunofluorescence images further showed that TMPRSS2 was co-localized to HAI-2. Both KD1 and KD2 domain of HAI-2 showed comparable inhibitory effects on TMPRSS2 proteolytic activity. In addition, HAI-2 overexpression could suppress the induction effect of TMPRSS2 on pro-HGF activation, extracellular matrix degradation and prostate cancer cell invasion. We further determined that the expression levels of TMPRSS2 were inversely correlated with HAI-2 levels during prostate cancer progression. In orthotopic xenograft animal model, TMPRSS2 overexpression promoted prostate cancer metastasis, and HAI-2 overexpression efficiently blocked TMPRSS2-induced metastasis. In summary, the results together indicate that HAI-2 can function as a cognate inhibitor for TMPRSS2 in human prostate cancer cells and may serve as a potential factor to suppress TMPRSS2-mediated malignancy.

Dysregulation of Type II Transmembrane Serine Proteases and Ligand-Dependent Activation of MET in Urological Cancers

Unlike in normal epithelium, dysregulated overactivation of various proteases have been reported in cancers. Degradation of pericancerous extracellular matrix leading to cancer cell invasion by matrix metalloproteases is well known evidence. On the other hand, several cell-surface proteases, including type II transmembrane serine proteases (TTSPs), also induce progression through activation of growth factors, protease activating receptors and other proteases. Hepatocyte growth factor (HGF) known as a multifunctional growth factor that upregulates cancer cell motility, invasiveness, proliferative, and anti-apoptotic activities through phosphorylation of MET (a specific receptor of HGF). HGF secreted as inactive zymogen (pro-HGF) from cancer associated stromal fibroblasts, and the proteolytic activation by several TTSPs including matriptase and hepsin is required. The activation is strictly regulated by HGF activator inhibitors (HAIs) in physiological condition. However, downregulation is frequently observed in cancers. Indeed, overactivation of MET by upregulation of matriptase and hepsin accompanied by the downregulation of HAIs in urological cancers (prostate cancer, renal cell carcinoma, and bladder cancer) are also reported, a phenomenon observed in cancer cells with malignant phenotype, and correlated with poor prognosis. In this review, we summarized current reports focusing on TTSPs, HAIs, and MET signaling axis in urological cancers.

Cell surface-anchored serine proteases in cancer progression and metastasis

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

Loss of SPINT2 expression frequently occurs in glioma, leading to increased growth and invasion via MMP2

PURPOSE

High-grade gliomas (HGG) remain one of the most aggressive tumors, which is primarily due to its diffuse infiltrative nature. Serine proteases and metalloproteases are known to play key roles in cellular migration and invasion mechanisms. SPINT2, also known as HAI-2, is an important serine protease inhibitor that can affect MET signaling. SPINT2 has been found to be frequently downregulated in various tumors, whereby hypermethylation of its promoter appears to serve as a common mechanism. Here, we assessed the clinical relevance of SPINT2 expression and promoter hypermethylation in pediatric and adult HGG and explored its functional role.

METHODS

A series of 371 adult and 77 pediatric primary HGG samples was assessed for SPINT2 protein expression (immunohistochemistry) and promoter methylation (methylation-specific PCR) patterns. After SPINT2 knockdown and knock-in in adult and pediatric HGG cell lines, a variety of in vitro assays was carried out to determine the role of SPINT2 in glioma cell viability and invasion, as well as their mechanistic associations with metalloprotease activities.

RESULTS

We found that SPINT2 protein expression was frequently absent in adult (85.3%) and pediatric (100%) HGG samples. The SPINT2 gene promoter was found to be hypermethylated in approximately half of both adult and pediatric gliomas. Through functional assays we revealed a suppressor activity of SPINT2 in glioma cell proliferation and viability, as well as in their migration and invasion. These functions appear to be mediated in part by MMP2 expression and activity.

CONCLUSIONS

We conclude that dysregulation of SPINT2 is a common event in both pediatric and adult HGG, in which SPINT2 may act as a tumor suppressor.

A Noncanonical Role for Plasminogen Activator Inhibitor Type 1 in Obesity-Induced Diabetes

Obesity is a major risk factor for type 2 diabetes because of chronic hepatic inflammation and resultant insulin resistance. Hepatocyte growth factor (HGF) is responsible for resetting hepatic homeostasis after injury following activation by urokinase-type plasminogen activator (u-PA; encoded by the PLAU gene). Plasminogen activator inhibitor type-1 (PAI-1; encoded by the SERPINE1 gene), a u-PA inhibitor and antifibrinolytic agent, is often elevated in obesity and is linked to cardiovascular events. We hypothesized that, in addition to its role in preventing fibrinolysis, elevated PAI-1 inhibits HGF's activation by u-PA and the resultant anti-inflammatory and hepatoprotective properties. Wild-type and PAI-1 knockout (KO) mice on a high-fat diet both became significantly heavier than lean controls; however, the obese KO mice demonstrated improved glucose metabolism compared with wild-type mice. Obese KO mice also exhibited an increase in conversion of latent single-chain HGF to active two-chain HGF, coinciding with an increase in the phosphorylation of the HGF receptor (HGFR or MET, encoded by the MET gene), as well as dampened inflammation. These results strongly suggest that, in addition to its other functions, PAI-mediated inhibition of HGF activation prohibits the resolution of inflammation in the context of obesity-induced type 2 diabetes.

SPINT2 is hypermethylated in both IDH1 mutated and wild-type glioblastomas, and exerts tumor suppression via reduction of c-Met activation

PURPOSE

Both IDH1-mutated and wild-type gliomas abundantly display aberrant CpG island hypermethylation. However, the potential role of hypermethylation in promoting gliomas, especially the most aggressive form, glioblastoma (GBM), remains poorly understood.

METHODS

We analyzed RRBS-generated methylation profiles for 11 IDH1^WT gliomas (including 7 GBMs), 24 IDH1^MUT gliomas (including 6 GBMs), and 5 normal brain samples and employed TCGA GBM methylation profiles as a validation set. Upon classification of differentially methylated CpG islands by IDH1 status, we used integrated analysis of methylation and gene expression to identify SPINT2 as a top cancer related gene. To explore functional consequences of SPINT2 methylation in GBM, we validated SPINT2 methylation status using targeted bisulfite sequencing in a large cohort of GBM samples. We assessed DNA methylation-mediated SPINT2 gene regulation using 5-aza-2'-deoxycytidine treatment, DNMT1 knockdown and luciferase reporter assays. We conducted functional analyses of SPINT2 in GBM cell lines in vitro and in vivo.

RESULTS

We identified SPINT2 as a candidate tumor-suppressor gene within a group of CpG islands (designated G_T-CMG) that are hypermethylated in both IDH1^MUT and IDH1^WT gliomas but not in normal brain. We established that SPINT2 downregulation results from promoter hypermethylation, and that restoration of SPINT2 expression reduces c-Met activation and tumorigenic properties of GBM cells.

CONCLUSIONS

We defined a previously under-recognized group of coordinately methylated CpG islands common to both IDH1^WT and IDH1^MUT gliomas (G_T-CMG). Within G_T-CMG, we identified SPINT2 as a top cancer-related candidate and demonstrated that SPINT2 suppressed GBM via down-regulation of c-Met activation.

Aberrant regulation favours matriptase proteolysis in neoplastic B-cells that co-express HAI-2

Matriptase is ectopically expressed in neoplastic B-cells, in which matriptase activity is enhanced by negligible expression of its endogenous inhibitor, hepatocyte growth factor activator inhibitor (HAI)-1. HAI-1, however, is also involved in matriptase synthesis and intracellular trafficking. The lack of HAI-1 indicates that other related inhibitor, such as HAI-2, might be expressed. Here, we show that HAI-2 is commonly co-expressed in matriptase-expressing neoplastic B-cells. The level of active matriptase shed after induction of matriptase zymogen activation in 7 different neoplastic B-cells was next determined and characterised. Our data reveal that active matriptase can only be generated and shed by those cells able to activate matriptase and in a rough correlation with the levels of matriptase protein. While HAI-2 can potently inhibit matriptase, the levels of active matriptase are not proportionally suppressed in those cells with high HAI-2. Our survey suggests that matriptase proteolysis might aberrantly remain high in neoplastic B-cells regardless of the levels of HAI-2.

Congenital sodium diarrhea and chorioretinal coloboma with optic disc coloboma in a patient with biallelic SPINT2 mutations, including p.(Tyr163Cys)

Congenital sodium diarrhea is a rare and life-threatening disorder characterized by a severe, secretory diarrhea containing high concentrations of sodium, leading to hyponatremia and metabolic acidosis. It may occur in isolation or in association with systemic features such as facial dysmorphism, choanal atresia, imperforate anus, and corneal erosions. Mutations in the serine protease inhibitor, Kunitz-Type 2 (SPINT2) gene have been associated with congenital sodium diarrhea and additional syndromic features. We present a child with congenital sodium diarrhea, cleft lip and palate, corneal erosions, optic nerve coloboma, and intermittent exotropia who was found to have biallelic mutations in SPINT2. One mutation, c.488A > G, predicting p.(Tyr163Cys), has been previously associated with a syndromic form of congenital sodium diarrhea. The other mutation, c.166_167dupTA, predicting p.(Asn57Thrfs*24) has not previously been reported and is likely a novel pathogenic variant for this disorder. We found only one other report of an optic nerve coloboma associated with SPINT2 mutations and this occurred in a patient with congenital tufting enteropathy. Our patient confirms an association of ocular coloboma with presumed loss of SPINT2 function.

Hepatocyte growth factor activator inhibitor-2 stabilizes Epcam and maintains epithelial organization in the mouse intestine

Mutations in SPINT2 encoding the epithelial serine protease inhibitor hepatocyte growth factor activator inhibitor-2 (HAI-2) are associated with congenital tufting enteropathy. However, the functions of HAI-2 in vivo are poorly understood. Here we used tamoxifen-induced Cre-LoxP recombination in mice to ablate Spint2. Mice lacking Spint2 died within 6 days after initiating tamoxifen treatment and showed severe epithelial damage in the whole intestinal tracts, and, to a lesser extent, the extrahepatic bile duct. The intestinal epithelium showed enhanced exfoliation, villous atrophy, enterocyte tufts and elongated crypts. Organoid crypt culture indicated that Spint2 ablation induced Epcam cleavage with decreased claudin-7 levels and resulted in organoid rupture. These organoid changes could be rescued by addition of serine protease inhibitors aprotinin, camostat mesilate and matriptase-selective α-ketobenzothiazole as well as by co-deletion of Prss8, encoding the serine protease prostasin. These results indicate that HAI-2 is an essential cellular inhibitor for maintaining intestinal epithelium architecture.

Hepatocyte growth factor plays a particular role in progression of overall cardiac damage in experimental pulmonary hypertension

Background: HGF/MET pathway may have a role in pulmonary hypertension (PH). However, the link between the pathway and development of target organ damage in PH remains elusive. We aimed to demonstrate the relation between plasma HGF and HGF/MET tissue expressions in affected organs during PH progression. Methods: 12 weeks old male Wistar rats were injected with monocrotaline (MCT, 60 mg/kg, s.c.) to induce PH and sacrificed after 1, 2 and 4 weeks. Controls received saline. mRNA levels of HGF regulatory complex (Hgf, Met, Hgfa, Hai-1, Hai-2) were determined in right and left ventricles (RV, LV), lungs, pulmonary artery and liver by RT-qPCR. HGF protein levels in plasma were analysed by ELISA. Results: PH development was associated with a progressive elevation of HGF plasma levels that correlated with relative RV mass. Furthermore, Hgf mRNA expressions at week 4 were upregulated solely in the cardiac ventricles while being downregulated in a. pulmonalis, lungs and liver. Met and Hai-1/Hai-2 followed a similar pattern and were upregulated in cardiac ventricles, where Hgfa remained unchanged, but downregulated in lungs. Conclusion: We suggest that cardiac overexpression of Hgf might contribute to increased plasma HGF in MCT-induced PH. HGF could be exploited as a cardiospecific biomarker and HGF/MET pathway as a target in drug discovery for PH.

Hepatocyte Growth Factor Activator: A Proteinase Linking Tissue Injury with Repair

Hepatocyte growth factor (HGF) promotes pleiotropic signaling through its specific receptor tyrosine kinase, MET. As such, it has important roles in the regeneration of injured tissues. Since HGF is produced mainly by mesenchymal cells and MET is expressed in most epithelial, endothelial and somatic stem cells, HGF functions as a typical paracrine growth factor. HGF is secreted as an inactive precursor (proHGF) and requires proteolytic activation to initiate HGF-induced MET signaling. HGF activator (HGFAC) is a serum activator of proHGF and produces robust HGF activities in injured tissues. HGFAC is a coagulation factor XII-like serine endopeptidase that circulates in the plasma as a zymogen (proHGFAC). Thrombin, kallikrein-related peptidase (KLK)-4 or KLK-5 efficiently activates proHGFAC. The activated HGFAC cleaves proHGF at Arg494-Val495, resulting in the formation of the active disulfide-linked heterodimer HGF. Macrophage stimulating protein, a ligand of RON, is also activated by HGFAC in vivo. Although HGFAC functions primarily at the site of damaged tissue, a recent report has suggested that activated HGFAC relays a signal to stem cells in non-injured tissues via proHGF activation in the stem cell niche. This review focuses on current knowledge regarding HGFAC-mediated proHGF activation and its roles in tissue regeneration and repair.

Aberrant methylation and silencing of the SPINT2 gene in high-grade gliomas

Hepatocyte growth factor activator inhibitor type 2 (HAI‐2), encoded by the SPINT2 gene, is a membrane‐anchored protein that inhibits proteases involved in the activation of hepatocyte growth factor (HGF), a ligand of MET receptor. Epigenetic silencing of the SPINT2 gene has been reported in a human glioblastoma cell line (U87) and glioblastoma‐derived cancer stem cells. However, the incidence of SPINT2 methylation in tumor tissues obtained from glioma patients is unknown. In this study, we analyzed the methylation status of the SPINT2 gene of eight human glioblastoma cell lines and surgically resected glioma tissues of different grades (II, III, and IV) by bisulfite sequence analysis and methylation‐specific PCR. Most glioblastoma lines (7/8) showed methylation of the SPINT2 gene with a significantly reduced level of SPINT2mRNA compared to cultured astrocytes and normal brain tissues. However, all glioblastoma lines expressed mRNA for HGF activator (HGFAC), a target protease of HAI‐2/SPINT2. Forced expression of SPINT2 reduced MET phosphorylation of U87 glioblastoma cells both in vitro and in intracranial xenografts in nude mice. Methylation‐specific PCR analysis of the resected glioma tissues indicated notable methylation of the SPINT2 gene in 33.3% (2/6), 71.4% (10/14), and 74.3% (26/35) of grade II, III, and IV gliomas, respectively. Analysis of RNA sequencing data in a public database indicated an increased HGFAC/SPINT2 expression ratio in high‐grade compared to low‐grade gliomas (P = .01). In summary, aberrant methylation of the SPINT2 gene is frequently observed in high‐grade gliomas and might confer MET signaling in the glioma cells.

Transcriptome profile of rat genes in bone marrow-derived macrophages at different activation statuses by RNA-sequencing

The underlying mechanisms of macrophage polarization have been detected by genome-wide transcriptome analysis in a variety of mammals. However, the transcriptome profile of rat genes in bone marrow-derived macrophages (BMM) at different activation statuses has not been reported. Therefore, we performed RNA-Sequencing to identify gene expression signatures of rat BMM polarized in vitro with different stimuli. The differentially expressed genes (DEGs) among unactivated (M0), classically activated pro-inflammatory (M1), and alternatively activated anti-inflammatory macrophages (M2) were analyzed by using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis. In this study, not only we have identified the changes of global gene expression in rat M0, M1 and M2, but we have also made clear systematically the key genes and signaling pathways in the differentiation process of M0 to M1 and M2. These will provide a foundation for future researches of macrophage polarization.

Study on the methylation status of SPINT2 gene and its expression in cervical carcinoma

BACKGROUND

Cervical cancer is one of the malignant tumors which seriously threaten the women health worldwide. SPINT2 is an endogenous inhibitor of hepatocyte growth factor activator and down regulated or even silenced in many human malignant tumors.

OBJECTIVE

This study was performed to explore the promoter methylation status of SPINT2 gene and the effect on its expression in cervical carcinoma.

METHODS

HPV-positive and -negative cervical cancer cell lines, 50 cases of cervical carcinoma tissues, and 20 cases of normal cervical tissues were used for this study. The methylation status of promoter and the first exon of SPINT2 gene were analyzed. The expression of SPINT2 was analyzed by qRT-PCR.

RESULTS

HPV E6/E7 infection affects SPINT2 methylation rate in cell lines. SPINT2 methylation rate of HT-3E6/E7 was 8.8%, while the methylation rate of SPINT2 in HT-3 was 0%. In cervical tissues, the methylation rate of SPINT2 in cervical cancers was 54%, while the methylation rate of SPINT2 in normal cervical samples was 25%. As for cervical cancers, the methylation rate of SPINT2 gene was higher in grade 3 than those of grade 2.

CONCLUSIONS

The expression of SPINT2 gene is regulated by its methylation status, and the methylation status of SPINT2 is altered by HPV infection. The aberrant methylation status of SPINT2 gene may play an important role in the development of cervical cancer.

Isolated choanal and gut atresias: pathogenetic role of serine protease inhibitor type 2 (SPINT2) gene mutations unlikely

Background

Choanal (CA) and gastrointestinal atresias (GA) are an important feature of syndromic congenital sodium diarrhea (sCSD), a disorder recently associated with mutations in the gene for serine protease inhibitor type 2 (SPINT2). It is, however, not known whether isolated non-syndromic CA and GA themselves might result from SPINT2 mutations.

Methods

We performed a prospective cohort study to investigate 19 CA and/or GA patients without diarrhea (“non-sCSD”) for potential sCSD characteristic clinical features and SPINT2 mutations.

Results

We found a heterozygous SPINT2 splice mutation (c.593-1G>A), previously demonstrated in sCSD in homozygous form, in only 1 of the 19 patients of the “non-sCSD” cohort. This patient presented with isolated anal atresia and borderline low laboratory parameters of sodium balance. In the remaining 18 non-sCSD CA/GA patients investigated, SPINT2 sequence analysis and clinical markers of sodium homeostasis were normal. None of the 188 healthy controls tested in a regional Tyrolean population harbored the c.593-1G>A mutation, which is also not listed in the ExAc and gnomAD databases.

Conclusions

The finding of only one heterozygous SPINT2 mutation in 19 patients with isolated CA/GA was not statistically significant. Therefore, SPINT2 mutations are an unlikely cause of non-sCSD atresia.

Trial registration ISRCTN73824458. Retrospectively registered 28 September 2014

Hepatocyte growth factor activator inhibitors (HAI-1 and HAI-2): Emerging key players in epithelial integrity and cancer

The growth, survival, and metabolic activities of multicellular organisms at the cellular level are regulated by intracellular signaling, systemic homeostasis and the pericellular microenvironment. Pericellular proteolysis has a crucial role in processing bioactive molecules in the microenvironment and thereby has profound effects on cellular functions. Hepatocyte growth factor activator inhibitor type 1 (HAI-1) and HAI-2 are type I transmembrane serine protease inhibitors expressed by most epithelial cells. They regulate the pericellular activities of circulating hepatocyte growth factor activator and cellular type II transmembrane serine proteases (TTSPs), proteases required for the activation of hepatocyte growth factor (HGF)/scatter factor (SF). Activated HGF/SF transduces pleiotropic signals through its receptor tyrosine kinase, MET (coded by the proto-oncogene MET), which are necessary for cellular migration, survival, growth and triggering stem cells for accelerated healing. HAI-1 and HAI-2 are also required for normal epithelial functions through regulation of TTSP-mediated activation of other proteases and protease-activated receptor 2, and also through suppressing excess degradation of epithelial junctional proteins. This review summarizes current knowledge regarding the mechanism of pericellular HGF/SF activation and highlights emerging roles of HAIs in epithelial development and integrity, as well as tumorigenesis and progression of transformed epithelial cells.

Activated HGF-c-Met Axis in Head and Neck Cancer

Head and neck squamous cell carcinoma (HNSCC) is a highly morbid disease. Recent developments including Food and Drug Administration (FDA) approved molecular targeted agent’s pembrolizumab and cetuximab show promise but did not improve the five-year survival which is currently less than 40%. The hepatocyte growth factor receptor; also known as mesenchymal–epithelial transition factor (c-Met) and its ligand hepatocyte growth factor (HGF) are overexpressed in head and neck squamous cell carcinoma (HNSCC); and regulates tumor progression and response to therapy. The c-Met pathway has been shown to regulate many cellular processes such as cell proliferation, invasion, and angiogenesis. The c-Met pathway is involved in cross-talk, activation, and perpetuation of other signaling pathways, curbing the cogency of a blockade molecule on a single pathway. The receptor and its ligand act on several downstream effectors including phospholipase C gamma (PLCγ), cellular Src kinase (c-Src), phosphotidylinsitol-3-OH kinase (PI3K) alpha serine/threonine-protein kinase (Akt), mitogen activate protein kinase (MAPK), and wingless-related integration site (Wnt) pathways. They are also known to cross-talk with other receptors; namely epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor (VEGFR) and specifically contribute to treatment resistance. Clinical trials targeting the c-Met axis in HNSCC have been undertaken because of significant preclinical work demonstrating a relationship between HGF/c-Met signaling and cancer cell survival. Here we focus on HGF/c-Met impact on cellular signaling in HNSCC to potentiate tumor growth and disrupt therapeutic efficacy. Herein we summarize the current understanding of HGF/c-Met signaling and its effects on HNSCC. The intertwining of c-Met signaling with other signaling pathways provides opportunities for more robust and specific therapies, leading to better clinical outcomes.

The Kunitz Domain I of Hepatocyte Growth Factor Activator Inhibitor-2 Inhibits Matriptase Activity and Invasive Ability of Human Prostate Cancer Cells

Dysregulation of pericellular proteolysis is often required for tumor invasion and cancer progression. It has been shown that down-regulation of hepatocyte growth factor activator inhibitor-2 (HAI-2) results in activation of matriptase (a membrane-anchored serine protease), human prostate cancer cell motility and tumor growth. In this study, we further characterized if HAI-2 was a cognate inhibitor for matriptase and identified which Kunitz domain of HAI-2 was required for inhibiting matriptase and human prostate cancer cell motility. Our results show that HAI-2 overexpression suppressed matriptase-induced prostate cancer cell motility. We demonstrate that HAI-2 interacts with matriptase on cell surface and inhibits matriptase proteolytic activity. Moreover, cellular HAI-2 harnesses its Kunitz domain 1 (KD1) to inhibit matriptase activation and prostate cancer cell motility although recombinant KD1 and KD2 of HAI-2 both show an inhibitory activity and interaction with matriptase protease domain. The results together indicate that HAI-2 is a cognate inhibitor of matriptase, and KD1 of HAI-2 plays a major role in the inhibition of cellular matritptase activation as well as human prostate cancer invasion.

KLK14 interactions with HAI-1 and HAI-2 serine protease inhibitors: A molecular dynamics and relative free-energy calculations study

Kallikrein 14 (KLK14) is a serine protease linked to several pathologies including prostate cancer and positively correlates with Gleason score. Though KLK14 functioning in cancer is poorly understood, it has been implicated in HGF/Met signaling, given that KLK14 proteolytically inhibits HGF activator-inhibitor 1 (HAI-1), which strongly inhibits pro-HGF activators, thereby contributing to tumor progression. In this work, KLK14 binding to either hepatocyte growth factor activator inhibitor type-1 (HAI-1) or type-2 (HAI-2) was essayed using homology modeling, molecular dynamic simulations and free-energy calculations through MM/PBSA and MM/GBSA. KLK14 was successfully modeled. Calculated free energies suggested higher binding affinity for the KLK14/HAI-1 interaction than for KLK14/HAI-2. This difference in binding affinity is largely explained by the higher stability of the hydrogen-bond networks in KLK14/HAI-1 along the simulation trajectory. A key arginine residue in both HAI-1 and HAI-2 is responsible for their interaction with the S1 pocket in KLK14. Additionally, MM/GBSA free-energy decomposition postulates that KLK14 Asp174 and Trp196 are hotspots for binding HAI-1 and HAI-2.

CSF-Based Analysis for Identification of Potential Serum Biomarkers of Neural Tube Defects

The protein composition of cerebrospinal fluid (CSF) in neural tube defects (NTDs) remains unknown. We investigated the protein composition of CSF from 9 infants with NTDs using isobaric tags for relative and absolute quantitation (iTRAQ). We identified 568 proteins in the CSF of infants with spina bifida, which is the most common type of NTD. Among these, 18 proteins were associated with neural tube closure in the CSF during human embryonic neurulation and 5 were involved in NTDs. Based on these results, an animal model was further utilized to investigate early serum biomarkers for NTDs. We found that the myristoylated alanine-rich C-kinase substrate, Kunitz-type protease inhibitor 2, and apolipoprotein B-100 protein levels were decreased in both embryos and the sera of pregnant Sprague-Dawley rats carrying embryos with NTDs. CSF proteins may be useful in the discovery of potential serum biomarkers for NTDs.

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

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

The crystal structure of a multidomain protease inhibitor (HAI-1) reveals the mechanism of its auto-inhibition

Hepatocyte growth factor activator inhibitor 1 (HAI-1) is a membrane-bound multidomain protein essential to the integrity of the basement membrane during placental development and is also important in maintaining postnatal homeostasis in many tissues. HAI-1 is a Kunitz-type serine protease inhibitor, and soluble fragments of HAI-1 with variable lengths have been identified in vivo The full-length extracellular portion of HAI-1 (sHAI-1) shows weaker inhibitory activity toward target proteases than the smaller fragments, suggesting auto-inhibition of HAI-1. However, this possible regulatory mechanism has not yet been evaluated. Here, we solved the crystal structure of sHAI-1 and determined the solution structure by small-angle X-ray scattering. These structural analyses revealed that, despite the presence of long linkers, sHAI-1 exists in a compact conformation in which sHAI-1 active sites in Kunitz domain 1 are sterically blocked by neighboring structural elements. We also found that in the presence of target proteases, sHAI-1 adopts an extended conformation that disables the auto-inhibition effect. Our results also reveal the roles of non-inhibitory domains of this multidomain protein and explain the low activity of the full-length protein. The structural insights gained here improve our understanding of the regulation of HAI-1 inhibitory activities and point to new approaches for better controlling these activities.

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.

Deregulated matriptase activity in oral squamous cell carcinoma promotes the infiltration of cancer-associated fibroblasts by paracrine activation of protease-activated receptor 2

Cancer-associated fibroblasts (CAFs) are known to contribute to cancer progression. We have reported that cell surface expression of hepatocyte growth factor activator inhibitor 1 (HAI-1) is decreased in invasive oral squamous cell carcinoma (OSCC) cells. This study examined if HAI-1-insufficiency contributes to CAF recruitment in OSCC. Serum-free conditioned medium (SFCM) from a human OSCC line (SAS) stimulated the migration of 3 human fibroblast cell lines, NB1RGB, MRC5 and KD. SFCM from HAI-1-knockdown SAS showed an additive effect on the migration of NB1RGB and MRC5, but not KD. SAS SFCM induced protease-activated receptor-2 (PAR-2) expression in NB1RGB and MRC5, but not in KD, and a PAR-2 antagonist blocked the stimulatory effect of HAI-1 knockdown on migration of the PAR-2 expressing cell lines. Moreover, HAI-1-deficient SFCM showed additive stimulatory effects on the migration of wild-type but not PAR-2-deficient mouse fibroblasts. Therefore, the enhanced migration induced by HAI-1-insufficiency was mediated by PAR-2 activation in fibroblasts. This activation resulted from the deregulation of the activity of matriptase, a PAR-2 agonist protease. HAI-1 may thus prevent CAF recruitment to OSCC by controlling matriptase activity. When HAI-1 expression is reduced on OSCC, matriptase may contribute to CAF accumulation by paracrine activation of fibroblast PAR-2. Immunohistochemical analysis of resected OSCC revealed increased PAR2-positive CAFs in 35% (33/95) of the cases studied. The increased PAR-2 positive CAFs tended to correlate with infiltrative histology of the invasion front and shorter disease-free survival of the patients.

Congenital Sodium Diarrhea: A Form of Intractable Diarrhea, With a Link to Inflammatory Bowel Disease

Congenital diarrheal disorders (CDDs) represent a group of challenging clinical conditions for pediatricians because of the severity of the presentation and the broad range of possible differential diagnoses. CDDs arise from alterations in the transport of nutrients and electrolytes across the intestinal mucosa, from enterocyte and enteroendocrine cell differentiation and/or polarization defects, and from the modulation of the intestinal immune response. Advances were made recently in deciphering the etiology and pathophysiology of one of these disorders, congenital sodium diarrhea (CSD). CSD refers to an intractable diarrhea of intrauterine onset with high fecal sodium loss. CSD is clinically and genetically heterogeneous. A syndromic form of CSD features choanal and intestinal atresias as well as recurrent corneal erosions. Small bowel histology frequently detects an epithelial "tufting" dysplasia. It is autosomal recessively inherited, and caused by SPINT2 mutations. The nonsyndromic form of CSD can be caused by dominant activating mutations in GUCY2C, encoding intestinal receptor guanylate cyclase C (GC-C), and by autosomal recessive SLC9A3 loss-of-function mutations. SLC9A3 encodes Na/H antiporter 3, the major intestinal brush border Na/H exchanger, and a downstream target of GC-C. A number of patients with GUCY2C and SLC9A3 mutations developed inflammatory bowel disease. Both the number of recognized CDD forms as well as the number of underlying disease genes are gradually increasing. Knowledge of these CDD genes enables noninvasive, next-generation gene panel-based testing to facilitate an early diagnosis in CDD. Primary Na/H antiporter 3 and GC-C malfunction is implicated as a predisposition for inflammatory bowel disease in subset of patients.

Plasticity of the brush border - the yin and yang of intestinal homeostasis

The brush border on the apical surface of enterocytes is a highly specialized structure well-adapted for efficient digestion and nutrient transport, whilst at the same time providing a protective barrier for the intestinal mucosa. The brush border is constituted of a densely ordered array of microvilli, protrusions of the plasma membrane, which are supported by actin-based microfilaments and interacting proteins and anchored in an apical network of actomyosin and intermediate filaments, the so-called terminal web. The highly dynamic, specialized apical domain is both an essential partner for the gut microbiota and an efficient signalling platform that enables adaptation to physiological stimuli from the external and internal milieu. Nevertheless, genetic alterations or various pathological stresses, such as infection, inflammation, and mechanical or nutritional alterations, can jeopardize this equilibrium and compromise intestinal functions. Long-time neglected, the intestinal brush-border shall be enlightening again as the central actor of the complex but essential intestinal homeostasis. Here, we review the processes and components involved in brush border organization and discuss pathological mechanisms that can induce brush border defects and their physiological consequences.

The basal chorionic trophoblast cell layer: An emerging coordinator of placenta development

During gestation, fetomaternal exchange occurs in the villous tree (labyrinth) of the placenta. Development of this structure depends on tightly coordinated cellular processes of branching morphogenesis and differentiation of specialized trophoblast cells. The basal chorionic trophoblast (BCT) cell layer that localizes next to the chorioallantoic interface is of critical importance for labyrinth morphogenesis in rodents. Gcm1-positive cell clusters within this layer initiate branching morphogenesis thereby guiding allantoic fetal blood vessels towards maternal blood sinuses. Later these cells differentiate and contribute to the syncytiotrophoblast of the fetomaternal barrier. Additional cells within the BCT layer sustain continued morphogenesis, possibly through a repopulating progenitor population. Several mouse mutants highlight the importance of a structurally intact BCT epithelium, and a growing number of studies addresses its patterning and epithelial architecture. Here, we review and discuss emerging concepts in labyrinth development focussing on the biology of the BCT cell layer.

SPINT2 Deregulation in Prostate Carcinoma

SPINT2 is a tumor suppressor gene that inhibits proteases implicated in cancer progression, like HGFA, hepsin and matriptase. Loss of SPINT2 expression in tumors has been associated with gene promoter hypermethylation; however, little is known about the mechanisms of SPINT2 deregulation in prostate cancer (PCa). We aimed to analyze SPINT2 expression levels and understand the possible regulation by SPINT2 promoter hypermethylation in PCa. In a cohort of 57 cases including non-neoplastic and PCa tissues, SPINT2 expression and promoter methylation was analyzed by immunohistochemistry and methylation-specific PCR, respectively. Methylation status of the SPINT2 promoter was also evaluated by bisulfite sequencing and 5-aza-2'-deoxycytidine treatment. Oncomine and TCGA databases were used to perform in silico PCa analysis of SPINT2 mRNA and methylation levels. A reduction in SPINT2 expression levels from non-neoplastic to PCa tissues was observed; however, none of the cases exhibited SPINT2 promoter methylation. Both bisulfite sequencing and 5-aza demonstrated that SPINT2 promoter is not methylated in PCa cells. Bioinformatics approaches did not show downregulation of SPINT2 at the mRNA level and, in corroboration with our results, SPINT2 promoter region is reported to be unmethylated. Our study suggests an involvement of SPINT2 in PCa tumorigenesis, probably in association with a post-translational regulation of SPINT2.

N-Glycan Branching Affects the Subcellular Distribution of and Inhibition of Matriptase by HAI-2/Placental Bikunin

The gene product of SPINT 2, that encodes a transmembrane, Kunitz-type serine protease inhibitor independently designated as HAI-2 or placenta bikunin (PB), is involved in regulation of sodium absorption in human gastrointestinal track. Here, we show that SPINT 2 is expressed as two species of different size (30-40- versus 25-kDa) due to different N-glycans on Asn-57. The N-glycan on 25-kDa HAI-2 appears to be of the oligomannose type and that on 30-40-kDa HAI-2 to be of complex type with extensive terminal N-acetylglucosamine branching. The two different types of N-glycan differentially mask two epitopes on HAI-2 polypeptide, recognized by two different HAI-2 mAbs. The 30-40-kDa form may be mature HAI-2, and is primarily localized in vesicles/granules. The 25-kDa form is likely immature HAI-2, that remains in the endoplasmic reticulum (ER) in the perinuclear regions of mammary epithelial cells. The two different N-glycans could, therefore, represent different maturation stages of N-glycosylation with the 25-kDa likely a precursor of the 30-40-kDa HAI-2, with the ratio of their levels roughly similar among a variety of cells. In breast cancer cells, a significant amount of the 30-40-kDa HAI-2 can translocate to and inhibit matriptase on the cell surface, followed by shedding of the matriptase-HAI-2 complex. The 25-kDa HAI-2 appears to have also exited the ER/Golgi, being localized at the cytoplasmic face of the plasma membrane of breast cancer cells. While the 25-kDa HAI-2 was also detected at the extracellular face of plasma membrane at very low levels it appears to have no role in matriptase inhibition probably due to its paucity on the cell surface. Our study reveals that N-glycan branching regulates HAI-2 through different subcellular distribution and subsequently access to different target proteases.

Epigenetic Silencing of SPINT2 Promotes Cancer Cell Motility via HGF-MET Pathway Activation in Melanoma

Aberrant HGF-MET signaling activation via interactions with surrounding stromal cells in tumor microenvironment plays significant roles in malignant tumor progression. However, extracellular proteolytic regulation of HGF activation which is influenced by the tumor microenvironment and its consequential effects on melanoma malignancy remain uncharacterized. In this study we identified SPINT2: a proteolytic inhibitor of hepatocyte growth factor activator (HGFA), which plays a significant role in the suppression of the HGF-MET pathway and malignant melanoma progression. SPINT2 expression is significantly lower in metastatic melanoma tissues compared to those in early stage primary melanomas which also corresponded with DNA methylation levels isolated from tissue samples. Treatment with the DNA hypomethylating agent decitabine in cultured melanoma cells induced transcriptional reactivation of SPINT2, suggesting that this gene is epigenetically silenced in malignant melanomas. Furthermore, we show that ectopically expressed SPINT2 in melanoma cells inhibits HGF induced MET-AKT signaling pathway and decreases malignant phenotype potential such as cell motility, and invasive growth of melanoma cells. These results suggest that SPINT2 is associated with tumor suppressive functions in melanoma by inhibiting an extracellular signal regulator of HGF which is typically activated by tumor-stromal interactions. These findings indicate that epigenetic impairment of the tightly regulated cytokine-receptor communications in tumor microenvironment may contribute to malignant tumor progression.

Differential subcellular localization renders HAI-2 a matriptase inhibitor in breast cancer cells but not in mammary epithelial cells

The type 2 transmembrane serine protease matriptase is under tight control primarily by the actions of the integral membrane Kunitz-type serine protease inhibitor HAI-1. Growing evidence indicates that HAI-2 might also be involved in matriptase inhibition in some contexts. Here we showed that matriptase inhibition by HAI-2 depends on the subcellular localizations of HAI-2, and is observed in breast cancer cells but not in mammary epithelial cells. HAI-2 is co-expressed with matriptase in 21 out of 26 human epithelial and carcinoma cells examined. HAI-2 is also a potent matriptase inhibitor in solution, but in spite of this, HAI-2 inhibition of matriptase is not observed in all contexts where HAI-2 is expressed, unlike what is seen for HAI-1. Induction of matriptase zymogen activation in mammary epithelial cells results in the formation of matriptase-HAI-1 complexes, but matriptase-HAI-2 complexes are not observed. In breast cancer cells, however, in addition to the appearance of matriptase-HAI-1 complex, three different matriptase-HAI-2 complexes, are formed following the induction of matriptase activation. Immunofluorescent staining reveals that activated matriptase is focused at the cell-cell junctions upon the induction of matriptase zymogen activation in both mammary epithelial cells and breast cancer cells. HAI-2, in contrast, remains localized in vesicle/granule-like structures during matriptase zymogen activation in human mammary epithelial cells. In breast cancer cells, however, a proportion of the HAI-2 reaches the cell surface where it can gain access to and inhibit active matriptase. Collectively, these data suggest that matriptase inhibition by HAI-2 requires the translocation of HAI-2 to the cell surface, a process which is observed in some breast cancer cells but not in mammary epithelial cells.