Hepatocyte growth factor is a preferred in vitro substrate for human hepsin, a membrane-anchored serine protease implicated in prostate and ovarian cancers

Recent progress on inhibitors of the type II transmembrane serine proteases, hepsin, matriptase and matriptase-2

Members of the type II transmembrane serine proteases (TTSP) family play a vital role in cell growth and development but many are also implicated in disease. Two of the well-studied TTSPs, matriptase and hepsin proteolytically process multiple protein substrates such as the inactive single-chain zymogens pro-HGF and pro-macrophage stimulating protein into the active heterodimeric forms, HGF and macrophage stimulating protein. These two proteases also have many other substrates which are associated with cancer and tumor progression. Another related TTSP, matriptase-2 is expressed in the liver and functions by regulating iron homoeostasis through the cleavage of hemojuvelin and thus is implicated in iron overload diseases. In the present review, we will discuss inhibitor design strategy and Structure activity relationships of TTSP inhibitors, which have been reported in the literature.

Grhl2 regulation of SPINT1 expression controls salivary gland development

Development of the salivary gland is characterized by extensive branching morphogenesis and lumen formation, the latter of which is closely associated with differentiation into acinar and ductal cells. Although various molecules, including signaling and cell adhesion molecules, have been implicated in salivary gland development, transcription factors (TFs) regulating the expression of those molecules and morphological development of the gland are largely unknown. Here we show that knockdown of the epithelial TF, Grainyhead-like 2 (Grhl2), with siRNA in developing mouse submandibular salivary gland (SMG) cultured ex vivo resulted in retardation of epithelial development. This retardation was concomitant with suppression of gene expression for the cell adhesion molecules, such as E-cadherin and the extracellular protease inhibitor SPINT1, and with the disorganized deposition of the basal lamina protein laminin. ChIP-PCR demonstrated the binding of Grhl2 protein to the Spint1 gene in the SMG. Notably, addition of recombinant SPINT1 protein in cultured SMG overcame the suppressive effects of Grhl2 siRNA on epithelial development and laminin deposition. These findings show that Grhl2 regulation of SPINT1 expression controls salivary gland development.

Serine peptidase inhibitor Kunitz type 2 (SPINT2) in cancer development and progression

Understanding the molecular basis and mechanisms involved in neoplastic transformation and progression is important for the development of novel selective target therapeutic strategies. Hepatocyte growth factor (HGF)/c-MET signaling plays an important role in cell proliferation, survival, migration and motility of cancer cells. Serine peptidase inhibitor Kunitz type 2 (SPINT2) binds to and inactivates the HGF activator (HGFA), behaving as an HGFA inhibitor (HAI) and impairing the conversion of pro-HGF into bioactive HGF. The scope of the present review is to recapitulate and review the evidence of SPINT2 participation in cancer development and progression, exploring the clinical, biological and functional descriptions of the involvement of this protein in diverse neoplasias. Most studies are in agreement as to the belief that, in a large range of human cancers, the SPINT2 gene promoter is frequently methylated, resulting in the epigenetic silence of this gene. Functional assays indicate that SPINT2 reactivation ameliorates the malignant phenotype, specifically reducing cell viability, migration and invasion in diverse cancer cell lines. In sum, the SPINT2 gene is epigenetically silenced or downregulated in human cancers, altering the balance of HGF activation/inhibition ratio, which contributes to cancer development and progression.

The role of hepatocyte growth factor in corneal wound healing

Hepatocyte growth factor (HGF) is a glycoprotein produced by mesenchymal cells and operates as a key molecule for tissue generation and renewal. During corneal injury, HGF is primarily secreted by stromal fibroblasts and promotes epithelial wound healing in a paracrine manner. While this mesenchymal-epithelial interaction is well characterized in various organs and the cornea, the role of HGF in corneal stromal and endothelial wound healing is understudied. In addition, HGF has been shown to play an anti-fibrotic role by inhibiting myofibroblast generation and subsequent production of a disorganized extracellular matrix and tissue fibrosis. Therefore, HGF represents a potential therapeutic tool in numerous organs in which myofibroblasts are responsible for tissue scarring. Corneal fibrosis can be a devastating sequela of injury and can result in corneal opacification and retrocorneal membrane formation leading to severe vision loss. In this article, we concisely review the available literature regarding the role of HGF in corneal wound healing. We highlight the influence of HGF on cellular behaviors in each corneal layer. Additionally, we suggest the possibility that HGF may represent a therapeutic tool for interrupting dysregulated corneal repair processes to improve patient outcomes.

Inhibition of pro-HGF activation by SRI31215, a novel approach to block oncogenic HGF/MET signaling

The binding of hepatocyte growth factor (HGF) to its receptor MET activates a signaling cascade that promotes cell survival, proliferation, cell scattering, migration and invasion of malignant cells. HGF is secreted by cancer cells or by tumor-associated fibroblasts as pro-HGF, an inactive precursor. A key step in the regulation of HGF/MET signaling is proteolytic processing of pro-HGF to its active form by one of the three serine proteases, matriptase, hepsin or HGF activator (HGFA).We developed SRI 31215, a small molecule that acts as a triplex inhibitor of matriptase, hepsin and HGFA and mimics the activity of HAI-1/2, endogenous inhibitors of HGF activation. We demonstrated that SRI 31215 inhibits fibroblast-induced MET activation, epithelial-mesenchymal transition and migration of cancer cells. SRI 31215 overcomes primary resistance to cetuximab and gefitinib in HGF-producing colon cancer cells and prevents fibroblast-mediated resistance to EGFR inhibitors. Thus, SRI 31215 blocks signaling between cancer cells and fibroblasts and inhibits the tumor-promoting activity of cancer-associated fibroblasts.Aberrant HGF/MET signaling supports cell survival, proliferation, angiogenesis, invasion and metastatic spread of cancer cells, establishing HGF and MET as valid therapeutic targets. Our data demonstrate that inhibitors of HGF activation, such as SRI 31215, merit investigation as potential therapeutics in tumors that are addicted to HGF/MET signaling. The findings reported here also indicate that inhibitors of HGF activation overcome primary and acquired resistance to anti-EGFR therapy, providing a rationale for concurrent inhibition of EGFR and HGF to prevent therapeutic resistance and to improve the outcome of cancer patients.

The serine proteinase hepsin is an activator of pro-matrix metalloproteinases: molecular mechanisms and implications for extracellular matrix turnover

Increasing evidence implicates serine proteinases in the proteolytic cascades leading to the pathological destruction of extracellular matrices such as cartilage in osteoarthritis (OA). We have previously demonstrated that the type II transmembrane serine proteinase (TTSP) matriptase acts as a novel initiator of cartilage destruction via the induction and activation of matrix metalloproteinases (MMPs). Hepsin is another TTSP expressed in OA cartilage such that we hypothesized this proteinase may also contribute to matrix turnover. Herein, we demonstrate that addition of hepsin to OA cartilage in explant culture induced significant collagen and aggrecan release and activated proMMP-1 and proMMP-3. Furthermore, hepsin directly cleaved the aggrecan core protein at a novel cleavage site within the interglobular domain. Hepsin expression correlated with synovitis as well as tumour necrosis factor α expression, and was induced in cartilage by a pro-inflammatory stimulus. However, a major difference compared to matriptase was that hepsin demonstrated markedly reduced capacity to activate proteinase-activated receptor-2. Overall, our data suggest that hepsin, like matriptase, induces potent destruction of the extracellular matrix whilst displaying distinct efficiencies for the cleavage of specific substrates.

Hepatocyte Growth Factor, a Key Tumor-Promoting Factor in the Tumor Microenvironment

The tumor microenvironment plays a key role in tumor development and progression. Stromal cells secrete growth factors, cytokines and extracellular matrix proteins which promote growth, survival and metastatic spread of cancer cells. Fibroblasts are the predominant constituent of the tumor stroma and Hepatocyte Growth Factor (HGF), the specific ligand for the tyrosine kinase receptor c-MET, is a major component of their secretome. Indeed, cancer-associated fibroblasts have been shown to promote growth, survival and migration of cancer cells in an HGF-dependent manner. Fibroblasts also confer resistance to anti-cancer therapy through HGF-induced epithelial mesenchymal transition (EMT) and activation of pro-survival signaling pathways such as ERK and AKT in tumor cells. Constitutive HGF/MET signaling in cancer cells is associated with increased tumor aggressiveness and predicts poor outcome in cancer patients. Due to its role in tumor progression and therapeutic resistance, both HGF and MET have emerged as valid therapeutic targets. Several inhibitors of MET and HGF are currently being tested in clinical trials. Preclinical data provide a strong indication that inhibitors of HGF/MET signaling overcome both primary and acquired resistance to EGFR, HER2, and BRAF targeting agents. These findings support the notion that co-targeting of cancer cells and stromal cells is required to prevent therapeutic resistance and to increase the overall survival rate of cancer patients. HGF dependence has emerged as a hallmark of therapeutic resistance, suggesting that inhibitors of biological activity of HGF should be included into therapeutic regimens of cancer patients.

Hepatocyte growth factor in physiology and infectious diseases

Hepatocyte growth factor (HGF) is a pleiotropic cytokine composed of an α-chain and a β-chain, and these chains contain four kringle domains and a serine protease-like structure, respectively. The receptor for HGF was identified as the c-met proto-oncogene product of transmembrane receptor tyrosine kinase. HGF-induced signaling through the receptor Met provokes dynamic biological responses that support morphogenesis, regeneration, and the survival of various cells and tissues, which includes hepatocytes, renal tubular cells, and neurons. Characterization of tissue-specific Met knockout mice has further indicated that the HGF-Met system modulates immune cell functions and also plays an inhibitory role in the progression of chronic inflammation and fibrosis. However, the biological actions that are driven by the HGF-Met pathway all play a role in the acquisition of the malignant characteristics in tumor cells, such as invasion, metastasis, and drug resistance in the tumor microenvironment. Even though oncogenic Met signaling remains the major research focus, the HGF-Met axis has also been implicated in infectious diseases. Many pathogens try to utilize host HGF-Met system to establish comfortable environment for infection. Their strategies are not only simply change the expression level of HGF or Met, but also actively hijack HGF-Met system and deregulating Met signaling using their pathogenic factors. Consequently, the monitoring of HGF and Met expression, along with real-time detection of Met activation, can be a beneficial biomarker of these infectious diseases. Preclinical studies designed to address the therapeutic significance of HGF have been performed on injury/disease models, including acute tissue injury, chronic fibrosis, and cardiovascular and neurodegenerative diseases. Likewise, manipulating the HGF-Met system with complete control will lead to a tailor made treatment for those infectious diseases.

The role of type II transmembrane serine protease-mediated signaling in cancer

Pericellular proteases have long been implicated in carcinogenesis. Previous research focused on these proteins, primarily as extracellular matrix (ECM) protein-degrading enzymes which allowed cancer cells to breach the basement membrane and invade surrounding tissue. However, recently, there has been a shift in the view of cell surface proteases, including serine proteases, as proteolytic modifiers of particular targets, including growth factors and protease-activated receptors, which are critical for the activation of oncogenic signaling pathways. Of the 176 human serine proteases currently identified, a subset of 17, known as type II transmembrane serine proteases (TTSPs). Many have been shown to be relevant to cancer progression since they were first identified as a family around the turn of the century. To this end, altered expression of TTSPs appeared as a trademark of several tumor types. However, the substrates and underlying signaling pathways remained unclear. Localization of these proteins to the cell surface places them in the unique position to mediate signal transduction between the cell and its surrounding environment. Many of the TTSPs have already been shown to play key roles in processes such as postnatal development, tissue homeostasis, and tumor progression, which share overlapping molecular mechanisms. In this review, we summarize the current knowledge regarding the role of the TTSP family in pro-oncogenic signaling.

Hepatitis B virus X protein binding to hepsin promotes C3 production by inducing IL-6 secretion from hepatocytes

Hepatitis B virus (HBV) X protein (HBx) is an important effector for HBV-associated pathogenesis. In this study, we identified hepsin as an HBx-interacting protein and investigated the effects of hepsin on HBx-mediated complement component 3 (C3) secretion in hepatocytes. In vivo and in vitro binding between HBx and hepsin was confirmed by co-immunoprecipitation and Glutathione S-transferase pull-down assays. HBx synergized with hepsin to promote C3 production by potentiating interleukin-6 (IL-6) secretion. Knockdown of endogenous hepsin attenuated C3 and IL-6 secretion induced by HBx in hepatic cells. In addition, levels of hepsin protein correlated positively with C3 expression in human non-tumor liver tissues. Further exploration revealed that HBx and hepsin increased C3 promoter activity by up-regulating the expression and phosphorylation of the transcription factor CAAT/enhancer binding protein beta (C/EBP-β), which binds to the IL-6/IL-1 response element in the C3 promoter. HBx and hepsin synergistically enhanced IL-6 mRNA levels and promoter activity by increasing the nuclear translocation of nuclear factor kappaB (NF-κB). Our findings show for the first time that binding between HBx and hepsin promotes C3 production by inducing IL-6 secretion in hepatocytes.

In vitro evidence that KLK14 regulates the components of the HGF/Met axis, pro-HGF and HGF-activator inhibitor 1A and 1B

Kallikrein-related peptidase (KLK) 14 is a serine protease linked to several pathologies including prostate cancer. We show that KLK14 has biphasic effects in vitro on activating and inhibiting components of the prostate cancer associated hepatocyte growth factor (HGF)/Met system. At 5–10 nm, KLK14 converts pro-HGF to the two-chain heterodimer required for Met activation, while higher concentrations degrade the HGF α-chain. HGF activator-inhibitor (HAI)-1A and HAI-1B, which inhibit pro-HGF activators, are degraded by KLK14 when protease:inhibitor stoichiometry is 1:1 or the protease is in excess. When inhibitors are in excess, KLK14 generates HAI-1A and HAI-1B fragments known to inhibit pro-HGF activating serine proteases. These in vitro data suggest that increased KLK14 activity could contribute at multiple levels to HGF/Met-mediated processes in prostate and other cancers.

High Hepsin expression predicts poor prognosis in Gastric Cancer

Hepsin, a membrane-associated serine protease, is frequently upregulated in epithelial cancers and involved in cancer progression. Our study aims to describe the expression pattern and evaluate the clinical implication of hepsin in gastric cancer patients. The mRNA expression of hepsin was analyzed in 50 gastric cancer and matched non-tumor tissues, which was downregulated in 78% (39/50) of gastric cancer. By searching and analyzing four independent datasets from Oncomine, we obtained the similar results. Furthermore, we evaluated the hepsin expression by IHC in tissue microarray (TMA) containing 220 Gastric Cancer specimens. More importantly, Kaplan-Meier survival and Cox regression analyses were taken to access the prognosis of gastric cancer and predicted that hepsin protein expression was one of the significant and independent prognostic factors for overall survival of Gastric Cancer.

In search of a function of Manduca sexta hemolymph protease-1 in the innate immune system

Extracellular serine protease cascades mediate immune signaling and responses in insects. In the tobacco hornworm Manduca sexta, nearly 30 serine proteases (SPs) and their homologs (SPHs) are cloned from hemocytes and fat body. Some of them participate in prophenoloxidase (proPO) activation and proSpätzle processing. Here we report the cDNA cloning of hemolymph protease-1b (HP1b), which is 90% identical and 95% similar to HP1a (formerly HP1). The HP1a and HP1b mRNA levels in hemocytes was down- and up-regulated after an immune challenge, respectively. Quantitative real-time polymerase chain reactions revealed their tissue-specific and development-dependent expression, mostly in hemocytes of the feeding larvae. We isolated HP1 precursor (proHP1) from larval hemolymph and observed micro-heterogeneity caused by N-linked glycosylation. Supplementation of the purified proHP1 to plasma samples from naïve larvae or induced ones injected with bacteria caused a small PO activity increase, much lower than those elicited by recombinant proHP1a/b, but no proteolytic cleavage was detected in the zymogens. Incubation of proHP1a/b or their catalytic domains with a cationic detergent, cetylpyridinium chloride, induced an amidase activity that hydrolyzed LDLH-p-nitroanilide. Since LDLH corresponds to the P4-P1 region before the proteolytic activation site of proHP6, we propose that the active but uncleaved proHP1 may cut proHP6 to generate HP6 that in turn activates proPAP1 and proHP8. The catalytic domain of HP1a/b, which by itself does not activate purified proHP6 or hydrolyze LDLH-p-nitroanilide, somehow generated active HP6, HP8, PAP1 and PO in plasma. Together, these results indicate that proHP1 participates in the proPO activation system, although detailed mechanism needs further exploration.

Urokinase-controlled tumor penetrating peptide

Tumor penetrating peptides contain a cryptic (R/K)XX(R/K) CendR element that must be C-terminally exposed to trigger neuropilin-1 (NRP-1) binding, cellular internalization and malignant tissue penetration. The specific proteases that are involved in processing of tumor penetrating peptides identified using phage display are not known. Here we design de novo a tumor-penetrating peptide based on consensus cleavage motif of urokinase-type plasminogen activator (uPA). We expressed the peptide, uCendR (RPARSGR↓SAGGSVA, ↓ shows cleavage site), on phage or coated it onto silver nanoparticles and showed that it is cleaved by uPA, and that the cleavage triggers binding to recombinant NRP-1 and to NPR-1-expressing cells. Upon systemic administration to mice bearing uPA-overexpressing breast tumors, FAM-labeled uCendR peptide and uCendR-coated nanoparticles preferentially accumulated in tumor tissue. We also show that uCendR phage internalization into cultured cancer cells and its penetration in explants of murine tumors and clinical tumor explants can be potentiated by combining the uCendR peptide with tumor-homing module, CRGDC. Our work demonstrates the feasibility of designing tumor-penetrating peptides that are activated by a specific tumor protease. As upregulation of protease expression is one of the hallmarks of cancer, and numerous tumor proteases have substrate specificities compatible with proteolytic unmasking of cryptic CendR motifs, the strategy described here may provide a generic approach for designing proteolytically-actuated peptides for tumor-penetrative payload delivery.

Crystal Structure of a Two-domain Fragment of Hepatocyte Growth Factor Activator Inhibitor-1: FUNCTIONAL INTERACTIONS BETWEEN THE KUNITZ-TYPE INHIBITOR DOMAIN-1 AND THE NEIGHBORING POLYCYSTIC KIDNEY DISEASE-LIKE DOMAIN

Hepatocyte growth factor activator inhibitor-1 (HAI-1) is a type I transmembrane protein and inhibitor of several serine proteases, including hepatocyte growth factor activator and matriptase. The protein is essential for development as knock-out mice die in utero due to placental defects caused by misregulated extracellular proteolysis. HAI-1 contains two Kunitz-type inhibitor domains (Kunitz), which are generally thought of as a functionally self-contained protease inhibitor unit. This is not the case for HAI-1, where our results reveal how interdomain interactions have evolved to stimulate the inhibitory activity of an integrated Kunitz. Here we present an x-ray crystal structure of an HAI-1 fragment covering the internal domain and Kunitz-1. The structure reveals not only that the previously uncharacterized internal domain is a member of the polycystic kidney disease domain family but also how the two domains engage in interdomain interactions. Supported by solution small angle x-ray scattering and a combination of site-directed mutagenesis and functional assays, we show that interdomain interactions not only stabilize the fold of the internal domain but also stimulate the inhibitory activity of Kunitz-1. By completing our structural characterization of the previously unknown N-terminal region of HAI-1, we provide new insight into the interplay between tertiary structure and the inhibitory activity of a multidomain protease inhibitor. We propose a previously unseen mechanism by which the association of an auxiliary domain stimulates the inhibitory activity of a Kunitz-type inhibitor (i.e. the first structure of an intramolecular interaction between a Kunitz and another domain).

α-Ketobenzothiazole Serine Protease Inhibitors of Aberrant HGF/c-MET and MSP/RON Kinase Pathway Signaling in Cancer

Upregulation of the HGF and MSP growth-factor processing serine endopeptidases HGFA, matriptase and hepsin is correlated with increased metastasis in multiple tumor types driven by c-MET or RON kinase signaling. We rationally designed P1' α-ketobenzothiazole mechanism-based inhibitors of these proteases. Structure-activity studies are presented, which resulted in the identification of potent inhibitors with differential selectivity. The tetrapeptide inhibitors span the P1-P1' substrate cleavage site via a P1' amide linker off the benzothiazole, occupying the S3' pocket. Optimized inhibitors display sub-nanomolar enzyme inhibition against one, two, or all three of HGFA, matriptase, and hepsin. Several compounds also have good selectivity against the related trypsin-like proteases, thrombin and Factor Xa. Finally, we show that inhibitors block the fibroblast (HGF)-mediated migration of invasive DU145 prostate cancer cells. In addition to prostate cancer, breast, colon, lung, pancreas, gliomas, and multiple myeloma tumors all depend on HGF and MSP for tumor survival and progression. Therefore, these unique inhibitors have potential as new therapeutics for a diverse set of tumor types.

Design and Synthesis of Nonpeptide Inhibitors of Hepatocyte Growth Factor Activation

In this letter we report first nonpeptide inhibitors of hepatocyte growth factor (HGF) activation. These compounds inhibit the three proteases (matriptase, hepsin, and HGF activator) required for HGF maturation. We show that 6, 8a, 8b, and 8d block activation of fibroblast-derived pro-HGF, thus preventing fibroblast-induced scattering of DU145 prostate cancer cells. Compound 6 (SRI 31215) is very soluble (91 μM) and has excellent microsome stability (human t 1/2 = 162 min; mouse t 1/2 = 296 min). In mouse 6 has an in vivo t 1/2 = 5.8 h following IV administration. The high solubility of 6 and IV t 1/2 make this compound a suitable prototype "triplex inhibitor" for the study of the inhibition of HGF activation in vivo.

The serine protease hepsin mediates urinary secretion and polymerisation of Zona Pellucida domain protein uromodulin

Uromodulin is the most abundant protein in the urine. It is exclusively produced by renal epithelial cells and it plays key roles in kidney function and disease. Uromodulin mainly exerts its function as an extracellular matrix whose assembly depends on a conserved, specific proteolytic cleavage leading to conformational activation of a Zona Pellucida (ZP) polymerisation domain. Through a comprehensive approach, including extensive characterisation of uromodulin processing in cellular models and in specific knock-out mice, we demonstrate that the membrane-bound serine protease hepsin is the enzyme responsible for the physiological cleavage of uromodulin. Our findings define a key aspect of uromodulin biology and identify the first in vivo substrate of hepsin. The identification of hepsin as the first protease involved in the release of a ZP domain protein is likely relevant for other members of this protein family, including several extracellular proteins, as egg coat proteins and inner ear tectorins.

DOI:http://dx.doi.org/10.7554/eLife.08887.001

Several proteins in humans and other animals contain a region called a 'zona pellucida domain'. This domain enables these proteins to associate with each other and form long filaments. Uromodulin is one such protein that was first identified more than fifty years ago. This protein is known to play a role in human diseases such as hypertension and kidney failure, but uromodulin’s biological purpose still remains elusive.

Uromodulin is only made in the kidney and it is the most abundant protein in the urine of healthy individuals. Uromodulin also contains a so-called 'external hydrophobic patch' that must be removed before the zona pellucida domain can start to form filaments. This hydrophobic patch is removed when uromodulin is cut by an unknown enzyme; this cutting releases the rest of the uromodulin protein from the surface of the cells that line the kidney into the urine.

Brunati et al. have now tested a panel of candidate enzymes and identified that one called hepsin is able to cut uromodulin. Hepsin is embedded in the cell membrane of the cells that line the kidney. When the level of hepsin was artificially reduced in cells grown in the laboratory, uromodulin remained anchored to the cell surface, its processing was altered and it did not form filaments.

Brunati et al. next analysed mice in which the gene encoding hepsin had been deleted. While these animals did not have any major defects in their internal organs, they had much lower levels of uromodulin in their urine. Furthermore, this residual urinary protein was not cut properly and it did not assemble into filaments. Thus, these findings reveal that hepsin is the enzyme that is responsible for releasing uromodulin in the urine. This discovery could be exploited to alter the levels of uromodulin release, and further studies using mice lacking hepsin may also help to understand uromodulin’s biological role. Finally, it will be important to understand if hepsin, or a similar enzyme, is also responsible for the release of other proteins containing the zona pellucida domain.

DOI:http://dx.doi.org/10.7554/eLife.08887.002

SERPINB12 Is a Slow-Binding Inhibitor of Granzyme A and Hepsin

The clade B/intracellular serpins protect cells from peptidase-mediated injury by forming covalent complexes with their targets. SERPINB12 is expressed in most tissues, especially at cellular interfaces with the external environment. This wide tissue distribution pattern is similar to that of granzyme A (GZMA). Because SERPINB12 inhibits trypsin-like serine peptidases, we determined whether it might also neutralize GZMA. SERPINB12 formed a covalent complex with GZMA and inhibited the enzyme with typical serpin slow-binding kinetics. SERPINB12 also inhibited Hepsin. SERPINB12 may function as an endogenous inhibitor of these peptidases.

Low expression levels of hepsin and TMPRSS3 are associated with poor breast cancer survival

BACKGROUND

Hepsin, (also called TMPRSS1) and TMPRSS3 are type II transmembrane serine proteases (TTSPs) that are involved in cancer progression. TTSPs can remodel extracellular matrix (ECM) and, when dysregulated, promote tumor progression and metastasis by inducing defects in basement membrane and ECM molecules. This study investigated whether the gene and protein expression levels of these TTSPs were associated with breast cancer characteristics or survival.

METHODS

Immunohistochemical staining was used to evaluate hepsin levels in 372 breast cancer samples and TMPRSS3 levels in 373 samples. TMPRSS1 mRNA expression was determined in 125 invasive and 16 benign breast tumor samples, and TMPRSS3 mRNA expression was determined in 167 invasive and 23 benign breast tumor samples. The gene and protein expression levels were analyzed for associations with breast cancer-specific survival and clinicopathological parameters.

RESULTS

Low TMPRSS1 and TMPRSS3 mRNA expression levels were independent prognostic factors for poor breast cancer survival during the 20-year follow-up (TMPRSS1, P = 0.023; HR, 2.065; 95 % CI, 1.106-3.856; TMPRSS3, P = 0.013; HR, 2.106; 95 % CI, 1.167-3.800). Low expression of the two genes at the mRNA and protein levels associated with poorer survival compared to high levels (log rank P-values 0.015-0.042). Low TMPRSS1 mRNA expression was also an independent marker of poor breast cancer prognosis in patients treated with radiotherapy (P = 0.034; HR, 2.344; 95 % CI, 1.065-5.160). Grade III tumors, large tumor size, and metastasis were associated with low mRNA and protein expression levels.

CONCLUSIONS

The results suggest that the TTSPs hepsin and TMPRSS3 may have similar biological functions in the molecular pathology of breast cancer. Low mRNA and protein expression levels of the studied TTSPs were prognostic markers of poor survival in breast cancer.

Targeted inhibition of cell-surface serine protease Hepsin blocks prostate cancer bone metastasis

The development of effective therapies inhibiting prostate cancer progression and metastasis may substantially impact prostate cancer mortality and potentially reduce the rates of invasive treatments by enhancing the safety of active surveillance strategies. Hepsin (HPN) is a cell surface serine protease amplified in a subset of human sarcomas (7.2%), as well as in ovarian (10%), lung adeno (5.4%), lung squamous cell (4.5%), adenoid cystic (5%), breast (2.6%), uterine (1.7%) and colon (1.4%) carcinomas. While HPN is not amplified in prostate cancer, it is one of the most prominently overexpressed genes in the majority of human prostate tumors and genetic experiments in mice indicate that Hepsin promotes prostate cancer metastasis, particularly metastasis to the bone marrow. We report here the development, analysis and animal trial of the small-molecule Hepsin inhibitor HepIn-13. Long-term exposure to HepIn-13 inhibited bone, liver and lung metastasis in a murine model of metastatic prostate cancer. These findings indicate that inhibition of Hepsin with small-molecule compounds could provide an effective tool for attenuation of prostate cancer progression and metastasis.

Hepsin inhibits CDK11p58 IRES activity by suppressing unr expression and eIF-2α phosphorylation in prostate cancer

Hepsin is a type II transmembrane serine protease frequently overexpressed in prostate cancer (PCa). However, the role of hepsin in PCa remains unclear. In this study, we found that hepsin inhibited the internal ribosome entry site (IRES) activity and expression of CDK11p58, which is associated with cell cycle progression and pro-apoptotic signaling in PCa. Hepsin suppressed CDK11p58 IRES activity in PCa by modulating unr expression and eIF-2α phosphorylation. Further studies revealed that hepsin inhibited the expression of unr by directly binding to unr IRES element and suppressing its activity, and also repressed eIF-2α phosphorylation through down-regulating the expression and phosphorylation of general control non-derepressible-2 (GCN2). Taken together, our data suggest a novel role of hepsin in regulating CDK11p58 IRES activity, and imply that hepsin may act on the machinery of translation to modulate cell cycle progression and survival in PCa cells.

Transcriptome profile analysis reveals specific signatures of pollutants in Atlantic eels

Identifying specific effects of contaminants in a multi-stress field context remain a challenge in ecotoxicology. In this context, "omics" technologies, by allowing the simultaneous measurement of numerous biological endpoints, could help unravel the in situ toxicity of contaminants. In this study, wild Atlantic eels were sampled in 8 sites presenting a broad contamination gradient in France and Canada. The global hepatic transcriptome of animals was determined by RNA-Seq. In parallel, the contamination level of fish to 8 metals and 25 organic pollutants was determined. Factor analysis for multiple testing was used to identify genes that are most likely to be related to a single factor. Among the variables analyzed, arsenic (As), cadmium (Cd), lindane (γ-HCH) and the hepato-somatic index (HSI) were found to be the main factors affecting eel's transcriptome. Genes associated with As exposure were involved in the mechanisms that have been described during As vasculotoxicity in mammals. Genes correlated with Cd were involved in cell cycle and energy metabolism. For γ-HCH, genes were involved in lipolysis and cell growth. Genes associated with HSI were involved in protein, lipid and iron metabolisms. Our study proposes specific gene signatures of pollutants and their impacts in fish exposed to multi-stress conditions.

Hepatocyte growth factor: A regulator of inflammation and autoimmunity

Hepatocyte growth factor (HGF) is a pleiotropic cytokine that has been extensively studied over several decades, but was only recently recognized as a key player in mediating protection of many types of inflammatory and autoimmune diseases. HGF was reported to prevent and attenuate disease progression by influencing multiple pathophysiological processes involved in inflammatory and immune response, including cell migration, maturation, cytokine production, antigen presentation, and T cell effector function. In this review, we discuss the actions and mechanisms of HGF in inflammation and immunity and the therapeutic potential of this factor for the treatment of inflammatory and autoimmune diseases.

Inhibitors of HGFA, Matriptase, and Hepsin Serine Proteases: A Nonkinase Strategy to Block Cell Signaling in Cancer

Hepatocyte growth factor activators (HGFA), matriptase, and hepsin are S1 family trypsin-like serine proteases. These proteases proteolytically cleave the single-chain zymogen precursors, pro-HGF (hepatocyte growth factor), and pro-MSP (macrophage stimulating protein) into active heterodimeric forms. HGF and MSP are activating ligands for the oncogenic receptor tyrosine kinases (RTKs), c-MET and RON, respectively. We have discovered the first substrate-based ketothiazole inhibitors of HGFA, matriptase and hepsin. The compounds were synthesized using a combination of solution and solid-phase peptide synthesis (SPPS). Compounds were tested for protease inhibition using a kinetic enzyme assay employing fluorogenic peptide substrates. Highlighted HGFA inhibitors are Ac-KRLR-kt (5g), Ac-SKFR-kt (6c), and Ac-SWLR-kt (6g) with K is = 12, 57, and 63 nM, respectively. We demonstrated that inhibitors block the conversion of native pro-HGF and pro-MSP by HGFA with equivalent potency. Finally, we show that inhibition causes a dose-dependent decrease of c-MET signaling in MDA-MB-231 breast cancer cells. This preliminary investigation provides evidence that HGFA is a promising therapeutic target in breast cancer and other tumor types driven by c-MET and RON.

Hepatocyte growth factor activator inhibitor type‑1 in cancer: advances and perspectives (Review)

Cancer is one of the most common diseases, with high morbidity and mortality rates. Large‑scale efforts have been made to understand the pathogenesis of the disease, particularly in the advanced stages, in order to develop effective therapeutic approaches. Hepatocyte growth factor activator inhibitor type-1 (HAI-1), also known as serine protease inhibitor Kunitz type 1, inhibits the activity of several trypsin-like serine proteases. In particular, HAI-1 suppresses hepatocyte growth factor (HGF) activator and matriptase, resulting in subsequent inhibition of HGF/scatter factor and macrophage‑stimulating protein (MSP). HGF and MSP are involved in cancer development and progression, via the receptors Met receptor tyrosine kinase (RTK) and Ron RTK, respectively. Therefore, HAI-1-mediated downregulation of HGF and MSP signaling may suppress tumorigenesis and progression in certain types of cancers. Abnormal HAI-1 expression levels have been observed in various types of human cancer. The exact function of HAI-1 in cancer pathogenesis, however, has not been fully elucidated. In this review, the focus is on the potential impact of aberrant HAI-1 expression levels on tumorigenesis and progression, the underlying mechanisms, and areas that require further investigation to clarify the precise role of HAI-1 in cancer.

Cleavage specificity analysis of six type II transmembrane serine proteases (TTSPs) using PICS with proteome-derived peptide libraries

Background

Type II transmembrane serine proteases (TTSPs) are a family of cell membrane tethered serine proteases with unclear roles as their cleavage site specificities and substrate degradomes have not been fully elucidated. Indeed just 52 cleavage sites are annotated in MEROPS, the database of proteases, their substrates and inhibitors.

Methodology/Principal Finding

To profile the active site specificities of the TTSPs, we applied Proteomic Identification of protease Cleavage Sites (PICS). Human proteome-derived database searchable peptide libraries were assayed with six human TTSPs (matriptase, matriptase-2, matriptase-3, HAT, DESC and hepsin) to simultaneously determine sequence preferences on the N-terminal non-prime (P) and C-terminal prime (P’) sides of the scissile bond. Prime-side cleavage products were isolated following biotinylation and identified by tandem mass spectrometry. The corresponding non-prime side sequences were derived from human proteome databases using bioinformatics. Sequencing of 2,405 individual cleaved peptides allowed for the development of the family consensus protease cleavage site specificity revealing a strong specificity for arginine in the P1 position and surprisingly a lysine in P1′ position. TTSP cleavage between R↓K was confirmed using synthetic peptides. By parsing through known substrates and known structures of TTSP catalytic domains, and by modeling the remainder, structural explanations for this strong specificity were derived.

Conclusions

Degradomics analysis of 2,405 cleavage sites revealed a similar and characteristic TTSP family specificity at the P1 and P1′ positions for arginine and lysine in unfolded peptides. The prime side is important for cleavage specificity, thus making these proteases unusual within the tryptic-enzyme class that generally has overriding non-prime side specificity.

The androgen-regulated protease TMPRSS2 activates a proteolytic cascade involving components of the tumor microenvironment and promotes prostate cancer metastasis

TMPRSS2 is an androgen-regulated cell-surface serine protease expressed predominantly in prostate epithelium. TMPRSS2 is expressed highly in localized high-grade prostate cancers and in the majority of human prostate cancer metastases. Through the generation of mouse models with a targeted deletion of Tmprss2, we demonstrate that the activity of this protease regulates cancer cell invasion and metastasis to distant organs. By screening combinatorial peptide libraries, we identified a spectrum of TMPRSS2 substrates that include pro-hepatocyte growth factor (HGF). HGF activated by TMPRSS2 promoted c-MET receptor tyrosine kinase signaling, and initiated a proinvasive epithelial-to-mesenchymal transition phenotype. Chemical library screens identified a potent bioavailable TMPRSS2 inhibitor that suppressed prostate cancer metastasis in vivo. Together, these findings provide a mechanistic link between androgen-regulated signaling programs and prostate cancer metastasis that operate via context-dependent interactions with extracellular constituents of the tumor microenvironment.

SIGNIFICANCE

The vast majority of prostate cancer deaths are due to metastasis. Loss of TMPRSS2 activity dramatically attenuated the metastatic phenotype through mechanisms involving the HGF-c-MET axis. Therapeutic approaches directed toward inhibiting TMPRSS2 may reduce the incidence or progression of metastasis in patients with prostate cancer.

Prostate cancer progression and metastasis: potential regulatory pathways for therapeutic targeting

Skeletal metastasis in advanced prostate cancer (PCa) patients remains a significant cause of morbidity and mortality. Research utilizing animal models during the past decade has reached a consensus that PCa progression and distant metastasis can be tackled at the molecular level. Although there are a good number of models that have shown to facilitate the study of PCa initiation and progression at the primary site, models that mimic the distant dissemination of cancer cells, particularly bone metastasis, are scarce. Despite this limitation, the field has gleaned valuable knowledge on the underlying molecular mechanisms and pathways of PCa progression, including local invasion and distant metastasis, and has moved forward in developing the concepts of current therapeutic modalities. The purpose of this review is to put together recent work on pathways that are currently being targeted for therapy, as well as other prospective novel therapeutic targets to be developed in the future against metastatic and potentially lethal PCa in patients.

Functional analysis of a missense mutation in the serine protease inhibitor SPINT2 associated with congenital sodium diarrhea

Membrane-bound serine proteases play important roles in different biological processes. Their regulation by endogenous inhibitors is poorly understood. A Y163C mutation in the SPINT2 gene encoding the serine protease inhibitor Hepatocyte Growth Factor Inhibitor HAI-2 is associated with a congenital sodium diarrhea. The functional consequences of this mutation on HAI-2 activity and its physiological targets are unknown. We established a cellular assay in Xenopus laevis oocytes to study functional interactions between HAI-2 and candidate membrane-bound serine proteases expressed in the gastro-intestinal tract. We found that the wild-type form of HAI-2 is a potent inhibitor of nine gastro-intestinal serine proteases. The Y163C mutation in the second Kunitz domain of HAI-2 resulted in a complete loss of inhibitory activity on two intestinal proteases, prostasin and tmprss13. The effect of the mutation of the homologous Y68C in the first Kunitz domain of HAI-2 is consistent with a differential contribution of the two Kunitz domains of HAI-2 in the inhibition of serine proteases. By contrast to the Tyr to Cys, the Tyr to Ser substitution did not change the inhibitory potency of HAI-2, indicating that the thiol-group of the cysteine rather than the Tyr deletion is responsible for the HAI-2 loss of function. Our functional assay allowed us to identify membrane-bound serine proteases as cellular target for inhibition by HAI-2 wild type and mutants, and to better define the role of the Tyr in the second Kunitz domain in the inhibitory activity of HAI-2.

Function and clinical relevance of kallikrein-related peptidases and other serine proteases in gynecological cancers

Gynecological cancers, including malignant tumors of the ovaries, the endometrium and the cervix, account for approximately 10% of tumor-associated deaths in women of the Western world. For screening, diagnosis, prognosis, and therapy response prediction, the group of enzymes known as serine (Ser-)proteases show great promise as biomarkers. In the present review, following a summary of the clinical facts regarding malignant tumors of the ovaries, the endometrium and the cervix, and characterization of the most important Ser-proteases, we thoroughly review the current state of knowledge relating to the use of proteases as biomarkers of the most frequent gynecological cancers. Within the Ser-protease group, the kallikrein-related peptidase (KLK) family, which encompasses a subgroup of 15 members, holds particular promise, with some acting via a tumor-promoting mechanism and others behaving as protective factors. Further, the urokinase-type plasminogen activator (uPA) and its inhibitor PAI-1 (plasminogen activator inhibitor-1) seem to play an unfavorable role in gynecological tumors, while down-regulation of high-temperature requirement proteins A 1, 2 and 3 (HtrA1,2,3) is associated with malignant disease and cancer progression. Expression/activity levels of other Ser-proteases, including the type II transmembrane Ser-proteases (TTSPs) matriptase, hepsin (TMPRSS1), and the hepsin-related protease (TMPRSS3), as well as the glycosyl-phosphatidylinositol (GPI)-anchored Ser-proteases prostasin and testisin, may be of clinical relevance in gynecological cancers. In conclusion, proteases are a rich source of biomarkers of gynecological cancer, though the enzymes' exact roles and functions merit further investigation.

Non-syndromic hearing impairment in India: high allelic heterogeneity among mutations in TMPRSS3, TMC1, USHIC, CDH23 and TMIE

Mutations in the autosomal genes TMPRSS3, TMC1, USHIC, CDH23 and TMIE are known to cause hereditary hearing loss. To study the contribution of these genes to autosomal recessive, non-syndromic hearing loss (ARNSHL) in India, we examined 374 families with the disorder to identify potential mutations. We found four mutations in TMPRSS3, eight in TMC1, ten in USHIC, eight in CDH23 and three in TMIE. Of the 33 potentially pathogenic variants identified in these genes, 23 were new and the remaining have been previously reported. Collectively, mutations in these five genes contribute to about one-tenth of ARNSHL among the families examined. New mutations detected in this study extend the allelic heterogeneity of the genes and provide several additional variants for structure-function correlation studies. These findings have implications for early DNA-based detection of deafness and genetic counseling of affected families in the Indian subcontinent.

Serine protease hepsin regulates hepatocyte size and hemodynamic retention of tumor cells by hepatocyte growth factor signaling in mice

The liver architecture plays an important role in maintaining hemodynamic balance, but the mechanisms that underlie this role are not fully understood. Hepsin, a type II transmembrane serine protease, is predominantly expressed in the liver, but has no known physiological functions. Here, we report that hemodynamic balance in the liver is regulated through hepsin. Deletion of hepsin (hepsin(-/-) ) in mice resulted in enlarged hepatocytes and narrowed liver sinusoids. Using fluorescent microbeads and antihepsin treatment, we demonstrated that metastatic cancer cells preferentially colonized the hepsin(-/-) mouse liver as a result of the retention of tumor cells because of narrower sinusoids. The enlarged hepatocytes expressed increased levels of connexin, which resulted from defective prohepatocyte growth factor (pro-HGF) processing and decreased c-Met phosphorylation in the livers of hepsin(-/-) mice. Treatment of hepsin(-/-) mice with recombinant HGF rescued these phenotypes, and treatment of wild-type mice with an HGF antagonist recapitulated the phenotypes observed in hepsin(-/-) mice.

CONCLUSION

Our findings show that the maintenance of hepatic structural homeostasis occurs through HGF/c-Met/connexin signaling by hepsin, and hepsin-mediated changes in liver architecture significantly enhance tumor metastasis to the liver.

Reduced prostasin (CAP1/PRSS8) activity eliminates HAI-1 and HAI-2 deficiency-associated developmental defects by preventing matriptase activation

Loss of either hepatocyte growth factor activator inhibitor (HAI)-1 or -2 is associated with embryonic lethality in mice, which can be rescued by the simultaneous inactivation of the membrane-anchored serine protease, matriptase, thereby demonstrating that a matriptase-dependent proteolytic pathway is a critical developmental target for both protease inhibitors. Here, we performed a genetic epistasis analysis to identify additional components of this pathway by generating mice with combined deficiency in either HAI-1 or HAI-2, along with genes encoding developmentally co-expressed candidate matriptase targets, and screening for the rescue of embryonic development. Hypomorphic mutations in Prss8, encoding the GPI-anchored serine protease, prostasin (CAP1, PRSS8), restored placentation and normal development of HAI-1–deficient embryos and prevented early embryonic lethality, mid-gestation lethality due to placental labyrinth failure, and neural tube defects in HAI-2–deficient embryos. Inactivation of genes encoding c-Met, protease-activated receptor-2 (PAR-2), or the epithelial sodium channel (ENaC) alpha subunit all failed to rescue embryonic lethality, suggesting that deregulated matriptase-prostasin activity causes developmental failure independent of aberrant c-Met and PAR-2 signaling or impaired epithelial sodium transport. Furthermore, phenotypic analysis of PAR-1 and matriptase double-deficient embryos suggests that the protease may not be critical for focal proteolytic activation of PAR-2 during neural tube closure. Paradoxically, although matriptase auto-activates and is a well-established upstream epidermal activator of prostasin, biochemical analysis of matriptase- and prostasin-deficient placental tissues revealed a requirement of prostasin for conversion of the matriptase zymogen to active matriptase, whereas prostasin zymogen activation was matriptase-independent.

Vertebrate embryogenesis is dependent upon a series of precisely coordinated cell proliferation, migration, and differentiation events. Recently, the execution of these events was shown to be guided in part by extracellular cues provided by focal pericellular proteolysis by a newly identified family of membrane-anchored serine proteases. We now show that two of these membrane-anchored serine proteases, prostasin and matriptase, constitute a single proteolytic signaling cascade that is active at multiple stages of development. Furthermore, we show that failure to precisely regulate the enzymatic activity of both prostasin and matriptase by two developmentally co-expressed transmembrane serine protease inhibitors, hepatocyte growth factor activator inhibitor-1 and -2, causes an array of developmental defects, including clefting of the embryonic ectoderm, lack of placental labyrinth formation, and inability to close the neural tube. Our study also provides evidence that the failure to regulate the prostasin–matriptase cascade may derail morphogenesis independent of the activation of known protease-regulated developmental signaling pathways. Because hepatocyte growth factor activator inhibitor–deficiency in humans is known to cause an assortment of common and rare developmental abnormalities, the aberrant activity of the prostasin–matriptase cascade identified in our study may contribute importantly to genetic as well as sporadic birth defects in humans.

Allosteric antibody inhibition of human hepsin protease

Hepsin is a type II transmembrane serine protease that is expressed in several human tissues. Overexpression of hepsin has been found to correlate with tumour progression and metastasis, which is so far best studied for prostate cancer, where more than 90% of such tumours show this characteristic. To enable improved future patient treatment, we have developed a monoclonal humanized antibody that selectively inhibits human hepsin and does not inhibit other related proteases. We found that our antibody, hH35, potently inhibits hepsin enzymatic activity at nanomolar concentrations. Kinetic characterization revealed non-linear, slow, tight-binding inhibition. This correlates with the crystal structure we obtained for the human hepsin-hH35 antibody Fab fragment complex, which showed that the antibody binds hepsin around α3-helix, located far from the active centre. The unique allosteric mode of inhibition of hH35 is distinct from the recently described HGFA (hepatocyte growth factor activator) allosteric antibody inhibition. We further explain how a small change in the antibody design induces dramatic structural rearrangements in the hepsin antigen upon binding, leading to complete enzyme inactivation.

An allosteric anti-hepsin antibody derived from a constrained phage display library

The serine protease hepsin is highly upregulated in prostate cancer and is implicated in tumor progression. Therefore, specific inhibition of hepsin enzymatic activity by an antibody constitutes an attractive therapeutic approach. Here, we report the identification of the anti-hepsin antibody Fab25 by screening of a Fab phage display library with a restricted chemical diversity at the complementary determining regions. Hepsin with its S1 pocket occupied by 3,4-dichloro-isocoumarin was used as the 'bait' for library screening. Fab25 was highly specific and it potently inhibited hepsin activity toward a panel of synthetic and macromolecular substrates. Biochemical and enzymatic studies with synthetic substrates of variable length suggested that Fab25 acts as an allosteric inhibitor based on non-competitive inhibition kinetics. Isothermal titration calorimetric experiments showed that the high-affinity (K(D) 6.1 nM) binding of Fab25 with hepsin is enthalpically driven. Despite an unusually long CDR-H3 loop with several potential hepsin cleavage sites (Lys, Arg residues), Fab25 was not processed by hepsin. Antibody-25 should be valuable for investigating hepsin's role in cancer progression and for potential therapeutic applications. Furthermore, the herein presented phage display strategy using an active site-modified protease should be widely applicable for identifying potential allosteric anti-protease antibodies.

Hepatocyte growth factor activator inhibitor type 1 inhibits protease activity and proteolytic activation of human airway trypsin-like protease

Hepatocyte growth factor activator inhibitor type 1 (HAI-1) is a Kunitz-type transmembrane serine protease inhibitor initially identified as a potent inhibitor of hepatocyte growth factor activator (HGFA), a serine protease that converts pro-HGF to the active form. HAI-1 also has inhibitory activity against serine proteases such as matriptase, hepsin and prostasin. In this study, we examined effects of HAI-1 on the protease activity and proteolytic activation of human airway trypsin-like protease (HAT), a transmembrane serine protease that is expressed mainly in bronchial epithelial cells. A soluble form of HAI-1 inhibited the protease activity of HAT in vitro. HAT was proteolytically activated in cultured mammalian cells transfected with its expression vector, and a soluble form of active HAT was released into the conditioned medium. The proteolytic activation of HAT required its own serine protease activity. Co-expression of the transmembrane full-length HAI-1 inhibited the proteolytic activation of HAT. In addition, full-length HAI-1 associated with the transmembrane full-length HAT in co-expressing cells. Like other target proteases of HAI-1, HAT converted pro-HGF to the active form in vitro. These results suggest that HAI-1 functions as a physiological regulator of HAT by inhibiting its protease activity and proteolytic activation in airway epithelium.

Proteolytic activation of pro-macrophage-stimulating protein by hepsin

Macrophage-stimulating protein (MSP) is a plasminogen-related growth factor and ligand for the receptor tyrosine kinase RON. The MSP/RON system promotes wound healing and invasive tumor growth and suppresses proinflammatory immune response. MSP binding to RON requires proteolytic conversion of the inactive single-chain form (pro-MSP) into the disulfide-linked α/β heterodimer. The pro-MSP cleavage sequence (Ser-Lys-Leu-Arg(483)↓Val(484)) closely matches the substrate recognition sequences of hepsin, a type II transmembrane serine protease, that is overexpressed in several cancers. Here, we show that recombinant hepsin cleaves pro-MSP at the consensus site Arg(483)-Val(484) with superior efficiency compared with the known activators MT-SP1 and hepatocyte growth factor activator (HGFA). At least 50% of pro-MSP was processed within 1 hour at a hepsin concentration of 2.4 nmol/L and at a molar enzyme to substrate ratio of 1:500. An uncleavable single-chain variant of MSP weakly bound to a RON-Fc fusion protein, whereas hepsin-cleaved MSP bound with a K(D) of 10.3 nmol/L, suggesting that the high-affinity binding site in MSP β-chain was properly formed. LNCaP prostate cancer cells overexpressing hepsin on the cell surface efficiently activated pro-MSP, which was blocked by a specific anti-hepsin antibody. Incubation of pro-MSP with hepsin led to robust RON-mediated phosphorylation of mitogen-activated protein kinase, ribosomal S6 protein, and Akt in human A2780 ovarian carcinoma cells stably expressing RON protein. In macrophages, pro-MSP with hepsin induced chemotaxis and attenuated lipopolysaccharide-dependent production of nitric oxide. These findings suggest that the MSP/RON signaling pathway may be regulated by hepsin in tissue homeostasis and in disease pathologies, such as in cancer and immune disorders.

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.

Genotype-phenotype correlation in DFNB8/10 families with TMPRSS3 mutations

In the present study, genotype–phenotype correlations in eight Dutch DFNB8/10 families with compound heterozygous mutations in TMPRSS3 were addressed. We compared the phenotypes of the families by focusing on the mutation data. The compound heterozygous variants in the TMPRSS3 gene in the present families included one novel variant, p.Val199Met, and four previously described pathogenic variants, p.Ala306Thr, p.Thr70fs, p.Ala138Glu, and p.Cys107Xfs. In addition, the p.Ala426Thr variant, which had previously been reported as a possible polymorphism, was found in one family. All affected family members reported progressive bilateral hearing impairment, with variable onset ages and progression rates. In general, the hearing impairment affected the high frequencies first, and sooner or later, depending on the mutation, the low frequencies started to deteriorate, which eventually resulted in a flat audiogram configuration. The ski-slope audiogram configuration is suggestive for the involvement of TMPRSS3. Our data suggest that not only the protein truncating mutation p.T70fs has a severe effect but also the amino acid substitutions p.Ala306Thr and p.Val199Met. A combination of two of these three mutations causes prelingual profound hearing impairment. However, in combination with the p.Ala426Thr or p.Ala138Glu mutations, a milder phenotype with postlingual onset of the hearing impairment is seen. Therefore, the latter mutations are likely to be less detrimental for protein function. Further studies are needed to distinguish possible phenotypic differences between different TMPRSS3 mutations. Evaluation of performance of patients with a cochlear implant indicated that this is a good treatment option for patients with TMPRSS3 mutations as satisfactory speech reception was reached after implantation.

Identification of hepsin and protein disulfide isomerase A3 as targets of gelatinolytic action in rat ovarian granulosa cells during the periovulatory period

The matrix metalloproteinase (MMP) family is believed to play a role in the ovulatory process because MMP inhibitors block oocyte release. However, little is known about the mechanisms by which the MMPs affect ovulation. The present study investigated the degradomic actions of the gelatinases, MMP2 and MMP9, by identifying gelatinolytic targets in periovulatory granulosa cells. Granulosa cells were collected from immature rats 48 h after equine chorionic gonadotropin treatment and were cultured with human chorionic gonadotropin (hCG) in the absence or presence of a specific MMP2/9 inhibitor ((2R)-2-[(4-biphenylylsulfonyl)amino]-3-phenylpropionic acid) for an additional 24 h. The conditioned media was analyzed for gelatinolytic activity, progesterone, and peptide profiles. Gelatinolytic activity and progesterone were induced in response to hCG; however, there was no difference in progesterone between cells treated with or without the inhibitor. Peptide fragments of proteins altered in the presence of the gelatinase inhibitor were identified by two-dimensional gel electrophoresis and mass spectrometry. Protein disulfide isomerase A3 (PDIA3), which plays a role in protein folding, was identified as a peptide that decreased in the presence of inhibitor while the serine protease hepsin, was found to increase with inhibitor treatment. Subsequent experiments established that PDIA3 and hepsin were targets of MMP2/9 action by cleavage with MMP2 and Western blot analysis, respectively. Additionally, hepsin was identified as a gelatinolytic target in ovarian cancer cells. In the present study, proteomics has identified proteins that may be involved in novel ways in the complex cascades that are mediated by gelatinolytic MMPs during the periovulatory period.

Novel TMPRSS3 variants in Pakistani families with autosomal recessive non-syndromic hearing impairment

Mutations in the TMPRSS3 gene are known to cause autosomal recessive non-syndromic hearing impairment (ARNSHI). After undergoing a genome scan, 10 consanguineous Pakistani families with ARNSHI were found to have significant or suggestive evidence of linkage to the TMPRSS3 region. In order to elucidate if the TMPRSS3 gene is responsible for ARNSHI in these families, the gene was sequenced using DNA samples from these families. Six TMPRSS3 variants were found to cosegregate in 10 families. None of these variants were detected in 500 control chromosomes. Four novel variants, three of which are missense [c.310G>A (p.Glu104Lys), c.767C>T (p.Ala256Val) and c.1273T>C (p.Cys425Arg)] and one nonsense [c.310G>T (p.Glu104Stop)], were identified. The pathogenicity of novel missense variants was investigated through bioinformatics analyses. Additionally, the previously reported deletion c.208delC (p.His70ThrfsX19) was identified in one family and the known mutation c.1219T>C (p.Cys407Arg) was found in five families, which makes c.1219T>C (p.Cys407Arg) as the most common TMPRSS3 mutation within the Pakistani population. Identification of these novel variants lends support to the importance of elements within the low-density lipoprotein receptor A (LDLRA) and serine protease domains in structural stability, ligand binding and proteolytic activity for proper TMPRSS3 function within the inner ear.

c-Met-induced epithelial carcinogenesis is initiated by the serine protease matriptase

The progression and negative outcome of a variety of human carcinomas are intimately associated with aberrant activity of the c-Met oncogene. The underlying cause of this dysregulation, however, remains a subject of discussion, as the majority of cancer patients do not present with activating mutations in c-Met receptor itself. In this study, we show that the oncogenic protease matriptase is ubiquitously co-expressed with the c-Met in human squamous cell carcinomas and amplifies migratory and proliferative responses of primary epithelial cells to the cognate ligand for c-Met, pro-hepatocyte growth factor/scatter factor (proHGF/SF), through c-Met and Gab1 signaling. Furthermore, the selective genetic ablation of c-Met from matriptase-expressing keratinocytes completely negates the oncogenic potential of matriptase. In addition, matriptase-dependent carcinoma formation could be blocked by the pharmacological inhibition of the Akt-mammalian target of Rapamycin (mTor) pathway. Our data identify matriptase as an initiator of c-Met-Akt-mTor-dependent signaling axis in tumors and reveal mTor activation as an essential component of matriptase/c-Met-induced carcinogenesis. The study provides a specific example of how epithelial transformation can be promoted by epigenetic acquisition of the capacity to convert a widely available paracrine growth factor precursor to its signaling competent state.

Plexin-B1 silencing inhibits ovarian cancer cell migration and invasion

BACKGROUND

Elevated Plexin-B1 expression has been found in diverse human cancers and in non-neoplastic tissues, and it mediates diverse biological and pathological activities. However, whether or not Plexin-B1 expression is involved in human ovarian tumors remains unclear. In the present study, Plexin-B1 expression was explored in benign and malignant human ovarian tumor tissues. In addition, the impact of Plexin-B1 expression on ovarian cancer cell proliferation, migration and invasion were investigated in vitro.

METHODS

Plexin-B1 expression was analyzed in normal and benign ovarian tissues and serous ovarian tumors (both borderline and malignant) by immunohistochemical staining, as well as in four human ovarian cancer cell lines (A2780, C13*, SKOV3, and OV2008) by RT-PCR and western blot analyses. Furthermore, endogenous Plexin-B1 expression was suppressed by Plexin-B1 siRNA in SKOV3 cells, which overexpress Plexin-B1. Protein levels of Plexin-B1, AKT and AKTSer473 were examined by western blot analysis. Cell proliferation, migration and invasion were measured with MTT, wound healing and boyden chamber assays, respectively, and the cytoskeleton was monitored via F-actin staining.

RESULTS

Expression levels of Plexin-B1 protein were significantly higher in serous ovarian carcinomas than in normal ovaries or benign ovarian neoplasms, and in the former, Plexin-B1 expression was positively correlated with lymphatic metastasis, and the membrane and cytoplasm of cancer cells stained positively. SKOV3 cells displayed the highest Plexin-B1 expression at both the mRNA and protein levels among the four tested human ovarian cancer cell lines and was selected as a cell model for further in vitro experiments. Plexin-B1 siRNA significantly suppressed phosphorylation of AKT at Ser473 in SKOV3 cells, but it did not alter total AKT expression. In addition, silencing of Plexin-B1 in SKOV3 cells inhibited cell migration and invasion and reorganized the cytoskeleton, whereas cell proliferation was not affected.

CONCLUSION

Plexin-B1 expression correlates with malignant phenotypes of serous ovarian tumors, probably via phosphorylation of AKT at Ser473, suggesting that Plexin-B1 might be a useful biomarker and/or a novel therapeutic target.