HAI-2 suppresses the invasive growth and metastasis of prostate cancer through regulation of matriptase

Extracellular proteolysis in cancer: Proteases, substrates, and mechanisms in tumor progression and metastasis

A vast ensemble of extracellular proteins influences the development and progression of cancer, shaped and reshaped by a complex network of extracellular proteases. These proteases, belonging to the distinct classes of metalloproteases, serine proteases, cysteine proteases, and aspartic proteases, play a critical role in cancer. They often become dysregulated in cancer, with increases in pathological protease activity frequently driven by the loss of normal latency controls, diminished regulation by endogenous protease inhibitors, and changes in localization. Dysregulated proteases accelerate tumor progression and metastasis by degrading protein barriers within the extracellular matrix (ECM), stimulating tumor growth, reactivating dormant tumor cells, facilitating tumor cell escape from immune surveillance, and shifting stromal cells toward cancer-promoting behaviors through the precise proteolysis of specific substrates to alter their functions. These crucial substrates include ECM proteins and proteoglycans, soluble proteins secreted by tumor and stromal cells, and extracellular domains of cell surface proteins, including membrane receptors and adhesion proteins. The complexity of the extracellular protease web presents a significant challenge to untangle. Nevertheless, technological strides in proteomics, chemical biology, and the development of new probes and reagents are enabling progress and advancing our understanding of the pivotal importance of extracellular proteolysis in cancer.

ST14 interacts with TMEFF1 and is a predictor of poor prognosis in ovarian cancer

TMEFF1 is a new protein involved in the physiological functions of the central nervous system, and we previously reported TMEFF1 can promote ovarian cancer. ST14 was determined to be involved in the processes of epidermal differentiation, epithelial cell integrity, and vascular endothelial cell migration, etc. The relationship between ST14 and TMEFF1 in the ovary remains unknown. In this study, we detected the expression of ST14 and TMEFF1 in 130 different ovarian cancer tissues through immunohistochemistry. We determined ST14 and TMEFF1 were highly expressed in ovarian cancer, indicating a higher degree of tumor malignancy and a worse prognosis. Tissues significantly expressing ST14 also highly expressed TMEFF1, and the expression of the two proteins was positively correlated. Consistently, immunofluorescence double staining demonstrated the co-localization of ST14 and TMEFF1 in the same region, and immunoprecipitation confirmed the interaction between ST14 and TMEFF1. TMEFF1 expression was also reduced after knocking down ST14 through Western blot. MTT, wound healing and Transwell assays results determined that knockdown of ST14 inhibited proliferation, migration and invasion of ovarian cancer cells in vitro, but the inhibitory effect was restored after adding TMEFF1 exogenous protein. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways analysis showed that ST14 and its related genes were enriched in the processes of epithelial formation, intercellular adhesion, protein localization, and mitosis regulation. We also clarified the kinase, microRNA, and transcription factor target networks and the impact of genetic mutations on prognosis. Overall, high expression of ST14 and TMEFF1 in ovarian cancer predicts higher tumor malignancy and a worse prognosis. ST14 and TMEFF1 co-localize and interact with each other in ovarian cancer. ST14 can regulate TMEFF1 expression to promote proliferation, migration and invasion of ovarian cancer cells. We speculate that the relationship between ST14 and TMEFF1 in ovarian cancer could become a potential target for anti-cancer therapy.

A dual role for ERK-1/2 in the regulation of plasmin activity and cell migration in metastatic NSCLC-H1299 cells

Occupational and environmental exposure of various toxins or cigarette smoke causes non-small cell lung carcinoma (NSCLC); a devastating disease with a very low survival rate after metastasis. Increased activity of plasmin is a hallmark in NSCLC metastasis. It is accepted that metastatic cells exhibit higher plasmin activity than cells from primary tumors. Mechanisms behind this elevation, however, are barely understood. We compared plasmin activity and cell migration of A549 cells derived from a primary lung tumor with metastatic H1299 lung cells isolated from lymph nodes. Surprisingly, we found higher plasmin activity and migration for A549 cells. mRNA levels of the plasminogen activator inhibitor-1 (PAI-1) were higher in H1299 cells and activity of extracellular-regulated kinases-1/2 (ERK-1/2) was increased. An inhibitor of ERK-1/2 decreased PAI-1 mRNA levels and increased plasmin activity or cell migration in H1299 cells. Transforming growth factor-β (TGF-β) decreased plasmin activity and migration in A549 cells but enhanced both in H1299 cells. The cytokine massively increased PAI-1 and decreased urokinase plasminogen activator (uPA) levels in A549 cells but strongly induced uPA and only weakly PAI- 1 expression in H1299 cells. Consequently, TGF-β enhanced plasmin activity and cell migration in H1299. Additionally, TGF-β activated ERK-1/2 stronger in H1299 than in A549 cells. Accordingly, an ERK-1/2 inhibitor completely reversed the effects of TGF-β on uPA expression, plasmin activity and migration in H1299 cells. Hence, we provide first data indicating TGF-β-promoted increased plasmin activity and suggest that blocking TGF-β-promoted ERK-1/2 activity might be a straightforward approach to inhibit NSCLC metastasis.

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.

Identification of blood protein biomarkers associated with prostate cancer risk using genetic prediction models: analysis of over 140,000 subjects

Prostate cancer (PCa) brings huge public health burden in men. A growing number of conventional observational studies report associations of multiple circulating proteins with PCa risk. However, the existing findings may be subject to incoherent biases of conventional epidemiologic studies. To better characterize their associations, herein, we evaluated associations of genetically predicted concentrations of plasma proteins with PCa risk. We developed comprehensive genetic prediction models for protein levels in plasma. After testing 1308 proteins in 79 194 cases and 61 112 controls of European ancestry included in the consortia of BPC3, CAPS, CRUK, PEGASUS, and PRACTICAL, 24 proteins showed significant associations with PCa risk, including 16 previously reported proteins and eight novel proteins. Of them, 14 proteins showed negative associations and 10 showed positive associations with PCa risk. For 18 of the identified proteins, potential functional somatic changes of encoding genes were detected in PCa patients in The Cancer Genome Atlas (TCGA). Genes encoding these proteins were significantly involved in cancer-related pathways. We further identified drugs targeting the identified proteins, which may serve as candidates for drug repurposing for treating PCa. In conclusion, this study identifies novel protein biomarker candidates for PCa risk, which may provide new perspectives on the etiology of PCa and improve its therapeutic strategies.

Genome-wide association studies in the Japanese population identified genetic loci and target gene associated with epidermal turnover

The epidermis is an essential organ for life by retaining water and as a protective barrier. The epidermis is maintained through metabolism, in which basal cells produced from epidermal stem cells differentiate into spinous cells, granular cells and corneocytes, and are finally shed from the epidermal surface. This is epidermal turnover, and with aging, there is a decline in epidermis function. Other factors that may affect epidermal turnover include ultraviolet damage and genetic factors. These genetic factors are of particular interest as little is known. Although recent skin-focused genome-wide association studies (GWAS) have been conducted, the genetic regions associated with epidermal turnover are almost uninvestigated. Therefore, we conducted a GWAS on epidermal turnover in the Japanese population, using the corneocyte area, which correlates to the rate of epidermal turnover, as an indicator. As a result, rs2278431 (p = 1.29 × 10-7 ) in 19q13.2 was associated with corneocyte size. Furthermore, eQTL analysis suggested that rs2278431 was related to the SPINT2 gene. In addition, SPINT2 knockdown studies using epidermal keratinocytes revealed that SPINT2 is involved in keratinocyte proliferation and in corneocyte size regulation in reconstructed epidermis. These results suggest that rs2278431 is involved in the expression of SPINT2 and affects epidermal turnover.

Matriptase-2 regulates iron homeostasis primarily by setting the basal levels of hepatic hepcidin expression through a nonproteolytic mechanism

Matriptase-2 (MT2), encoded by TMPRSS6, is a membrane-anchored serine protease. It plays a key role in iron homeostasis by suppressing the iron-regulatory hormone, hepcidin. Lack of functional MT2 results in an inappropriately high hepcidin and iron-refractory iron-deficiency anemia. Mt2 cleaves multiple components of the hepcidin-induction pathway in vitro. It is inhibited by the membrane-anchored serine protease inhibitor, Hai-2. Earlier in vivo studies show that Mt2 can suppress hepcidin expression independently of its proteolytic activity. In this study, our data indicate that hepatic Mt2 was a limiting factor in suppressing hepcidin. Studies in Tmprss6-/- mice revealed that increases in dietary iron to ∼0.5% were sufficient to overcome the high hepcidin barrier and to correct iron-deficiency anemia. Interestingly, the increased iron in Tmprss6-/- mice was able to further upregulate hepcidin expression to a similar magnitude as in wild-type mice. These results suggest that a lack of Mt2 does not impact the iron induction of hepcidin. Additional studies of wild-type Mt2 and the proteolytic-dead form, fMt2S762A, indicated that the function of Mt2 is to lower the basal levels of hepcidin expression in a manner that primarily relies on its nonproteolytic role. This idea is supported by the studies in mice with the hepatocyte-specific ablation of Hai-2, which showed a marginal impact on iron homeostasis and no significant effects on iron regulation of hepcidin. Together, these observations suggest that the function of Mt2 is to set the basal levels of hepcidin expression and that this process is primarily accomplished through a nonproteolytic mechanism.

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.

Structure and activity of human TMPRSS2 protease implicated in SARS-CoV-2 activation

Transmembrane protease, serine 2 (TMPRSS2) has been identified as key host cell factor for viral entry and pathogenesis of SARS-CoV-2. Specifically, TMPRSS2 proteolytically processes the SARS-CoV-2 Spike (S) protein, enabling virus-host membrane fusion and infection of the airways. We present here a recombinant production strategy for enzymatically active TMPRSS2 and characterization of its matured proteolytic activity, as well as its 1.95 Å X-ray cocrystal structure with the synthetic protease inhibitor nafamostat. Our study provides a structural basis for the potent but nonspecific inhibition by nafamostat and identifies distinguishing features of the TMPRSS2 substrate binding pocket that explain specificity. TMPRSS2 cleaved SARS-CoV-2 S protein at multiple sites, including the canonical S1/S2 cleavage site. We ranked the potency of clinical protease inhibitors with half-maximal inhibitory concentrations ranging from 1.4 nM to 120 µM and determined inhibitor mechanisms of action, providing the groundwork for drug development efforts to selectively inhibit TMPRSS2.

Environment-Sensitive Ectodomain Shedding of Epithin/PRSS14 Increases Metastatic Potential of Breast Cancer Cells by Producing CCL2

Epithin/PRSS14 is a membrane serine protease that plays a key role in tumor progression. The protease exists on the cell surface until its ectodomain shedding, which releases most of the extracellular domain. Previously, we showed that the remaining portion on the membrane undergoes intramembrane proteolysis, which results in the liberation of the intracellular domain and the intracellular domainmediated gene expression. In this study, we investigated how the intramembrane proteolysis for the nuclear function is initiated. We observed that ectodomain shedding of epithin/PRSS14 in mouse breast cancer 4T1 cells increased depending on environmental conditions and was positively correlated with invasiveness of the cells and their proinvasive cytokine production. We identified selenite as an environmental factor that can induce ectodomain shedding of the protease and increase C-C motif chemokine ligand 2 (CCL2) secretion in an epithin/PRSS14-dependent manner. Additionally, by demonstrating that the expression of the intracellular domain of epithin/PRSS14 is sufficient to induce CCL2 secretion, we established that epithin/PRSS14- dependent shedding and its subsequent intramembrane proteolysis are responsible for the metastatic conversion of 4T1 cells under these conditions. Consequently, we propose that epithin/PRSS14 can act as an environment-sensing receptor that promotes cancer metastasis by liberating the intracellular domain bearing transcriptional activity under conditions promoting ectodomain shedding.

Gene-associated methylation status of ST14 as a predictor of survival and hormone receptor positivity in breast Cancer

Background

Genomic profiles of specific gene sets have been established to guide personalized treatment and prognosis for patients with breast cancer (BC). However, epigenomic information has not yet been applied in a clinical setting. ST14 encodes matriptase, a proteinase that is widely expressed in BC with reported prognostic value.

Methods

In this present study, we evaluated the effect of ST14 DNA methylation (DNAm) on overall survival (OS) of patients with BC as a representative example to promote the use of the epigenome in clinical decisions. We analyzed publicly available genomic and epigenomic data from 1361 BC patients. Methylation was characterized by the β-value from CpG probes based on sequencing with the Illumina Human 450 K platform.

Results

A high mean DNAm (β > 0.6779) across 34 CpG probes for ST14, as the gene-associated methylation (GAM) pattern, was associated with a longer OS after adjusting age, stage, histology and molecular features in Cox model (p value < 0.001). A high GAM status was also associated with a higher XBP1 expression level and higher proportion of hormone-positive BC (p value < 0.001). Pathway analysis revealed that altered GAM was related to matrisome-associated pathway.

Conclusions

Here we show the potential role of ST14 DNAm in BC prognosis and warrant further study.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08645-3.

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.

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.

A JUN N-terminal kinase inhibitor induces ectodomain shedding of the cancer-associated membrane protease Prss14/epithin via protein kinase CβII

Serine protease 14 (Prss14)/epithin is a transmembrane serine protease that plays essential roles in tumor progression and metastasis and therefore is a promising target for managing cancer. Prss14/epithin shedding may underlie its activity in cancer and worsen outcomes; accordingly, a detailed understanding of the molecular mechanisms in Prss14/epithin shedding may inform the design of future cancer therapies. On the basis of our previous observation that an activator of PKC, phorbol 12-myristate 13-acetate (PMA), induces Prss14/epithin shedding, here we further investigated the intracellular signaling pathway involved in this process. While using mitogen-activated protein kinase inhibitors to investigate possible effectors of downstream PKC signaling, we unexpectedly found that an inhibitor of c-Jun N-terminal kinase (JNK), SP600125, induces Prss14/epithin shedding even in the absence of PMA. SP600125-induced shedding, like that stimulated by PMA, was mediated by tumor necrosis factor-α–converting enzyme. In contrast, a JNK activator, anisomycin, partially abolished the effects of SP600125 on Prss14/epithin shedding. Moreover, the results from loss-of-function experiments with specific inhibitors, short hairpin RNA–mediated knockdown, and overexpression of dominant-negative PKCβII variants indicated that PKCβII is a major player in JNK inhibition– and PMA-mediated Prss14/epithin shedding. SP600125 increased phosphorylation of PKCβII and tumor necrosis factor-α–converting enzyme and induced their translocation into the plasma membrane. Finally, in vitro cell invasion experiments and bioinformatics analysis of data in The Cancer Genome Atlas breast cancer database revealed that JNK and PKCβII are important for Prss14/epithin-mediated cancer progression. These results provide important information regarding strategies against tumor metastasis.

Comprehensive review of targeted therapy for colorectal cancer

Colorectal cancer (CRC) is among the most lethal and prevalent malignancies in the world and was responsible for nearly 881,000 cancer-related deaths in 2018. Surgery and chemotherapy have long been the first choices for cancer patients. However, the prognosis of CRC has never been satisfying, especially for patients with metastatic lesions. Targeted therapy is a new optional approach that has successfully prolonged overall survival for CRC patients. Following successes with the anti-EGFR (epidermal growth factor receptor) agent cetuximab and the anti-angiogenesis agent bevacizumab, new agents blocking different critical pathways as well as immune checkpoints are emerging at an unprecedented rate. Guidelines worldwide are currently updating the recommended targeted drugs on the basis of the increasing number of high-quality clinical trials. This review provides an overview of existing CRC-targeted agents and their underlying mechanisms, as well as a discussion of their limitations and future trends.

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.

SPINT2 inhibits proteases involved in activation of both influenza viruses and metapneumoviruses

Viruses possessing class I fusion proteins require proteolytic activation by host cell proteases to mediate fusion with the host cell membrane. The mammalian SPINT2 gene encodes a protease inhibitor that targets trypsin-like serine proteases. Here we show the protease inhibitor, SPINT2, restricts cleavage-activation efficiently for a range of influenza viruses and for human metapneumovirus (HMPV). SPINT2 treatment resulted in the cleavage and fusion inhibition of full-length influenza A/CA/04/09 (H1N1) HA, A/Aichi/68 (H3N2) HA, A/Shanghai/2/2013 (H7N9) HA and HMPV F when activated by trypsin, recombinant matriptase or KLK5. We also demonstrate that SPINT2 was able to reduce viral growth of influenza A/CA/04/09 H1N1 and A/X31 H3N2 in cell culture by inhibiting matriptase or TMPRSS2. Moreover, inhibition efficacy did not differ whether SPINT2 was added at the time of infection or 24 h post-infection. Our data suggest that the SPINT2 inhibitor has a strong potential to serve as a novel broad-spectrum antiviral.

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.

STYK1 promotes tumor growth and metastasis by reducing SPINT2/HAI-2 expression in non-small cell lung cancer

Non-small cell lung cancer (NSCLC) is the leading cause of cancer deaths worldwide. However, the molecular mechanisms underlying NSCLC progression remains not fully understood. In this study, 347 patients with complete clinicopathologic characteristics who underwent NSCLC surgery were recruited for the investigation. We verified that elevated serine threonine tyrosine kinase 1 (STYK1) or decreased serine peptidase inhibitor Kunitz type 2 (SPINT2/HAI-2) expression significantly correlated with poor prognosis, tumor invasion, and metastasis of NSCLC patients. STYK1 overexpression promoted NSCLC cells proliferation, migration, and invasion. STYK1 also induced epithelial–mesenchymal transition by E-cadherin downregulation and Snail upregulation. Moreover, RNA-seq, quantitative polymerase chain reaction (qRT-PCR), and western blot analyses confirmed that STYK1 overexpression significantly decreased the SPINT2 level in NSCLC cells, and SPINT2 overexpression obviously reversed STYK1-mediated NSCLC progression both in vitro and in vivo. Further survival analyses showed that NSCLC patients with high STYK1 level and low SPINT2 level had the worst prognosis and survival. These results indicated that STYK1 facilitated NSCLC progression via reducing SPINT2 expression. Therefore, targeting STYK1 and SPINT2 may be a novel therapeutic strategy for NSCLC.

A Novel Antibody-Toxin Conjugate to Treat Mantle Cell Lymphoma

Matriptase is a transmembrane serine protease, synthesized as an inactive single-chain zymogen on the endoplasmic reticulum and transported to the plasma membrane. Matriptase is activated in different epithelial and some B-cell malignancies and changes its conformation and activity is inhibited mainly by its endogenous inhibitor HAI-1. Activated matriptase plays a key role in tumor initiation as well as tumor progression, including invasiveness, and metastasis. To target the anti-mitotic toxin (monomethyl auristatin-E) to activated matriptase, a novel antibody to activated matriptase was conjugated with this toxin via a valine-citrulline-PABA linker. In a previous study, this antibody-toxin conjugate was found to be effective against triple negative breast cancer cell lines and xenografts, alone, or in combination with cisplatin (1). In this study, we examined the anti-tumor effect of the antibody toxin conjugate (ADC) against activated matriptase positive mantle cell lymphoma cell lines (JeKo-1, Maver, Mino, and Z138). This ADC was cytotoxic to these cell lines with IC₅₀s between 5 and 14 μg/mL. The ADC also showed a dose dependent anti-tumor effect on the JeKo-1 xenograft in mice without toxicity.

HAI-2 as a novel inhibitor of plasmin represses lung cancer cell invasion and metastasis

Background

Dysregulation of pericellular proteolysis usually accounts for cancer cell invasion and metastasis. Isolation of a cell-surface protease system for lung cancer metastasis is an important issue for mechanistic studies and therapeutic target identification.

Methods

Immunohistochemistry of a tissue array (n = 64) and TCGA database (n = 255) were employed to assess the correlation between serine protease inhibitors (SPIs) and lung adenocarcinoma progression. The role of SPI in cell motility was examined using transwell assays. Pulldown and LC/MS/MS were performed to identify the SPI-modulated novel protease(s). A xenografted mouse model was harnessed to demonstrate the role of the SPI in lung cancer metastasis.

Results

Hepatocyte growth factor activator inhibitor-2 (HAI-2) was identified to be downregulated following lung cancer progression, which was related to poor survival and tumour invasion. We further isolated a serum-derived serine protease, plasmin, to be a novel target of HAI-2. Downregulation of HAI-2 promotes cell surface plasmin activity, EMT, and cell motility. HAI-2 can suppress plasmin-mediated activations of HGF and TGF-β1, EMT and cell invasion. In addition, downregulated HAI-2 increased metastasis of lung adenocarcinoma via upregulating plasmin activity.

Conclusion

HAI-2 functions as a novel inhibitor of plasmin to suppress lung cancer cell motility, EMT and metastasis.

Membrane-Anchored Serine Proteases and Protease-Activated Receptor-2-Mediated Signaling: Co-Conspirators in Cancer Progression

Pericellular proteolysis provides a significant advantage to developing tumors through the ability to remodel the extracellular matrix, promote cell invasion and migration, and facilitate angiogenesis. Recent advances demonstrate that pericellular proteases can also communicate directly to cells by activation of a unique group of transmembrane G-protein-coupled receptors (GPCR) known as protease-activated receptors (PAR). In this review, we discuss the specific roles of one of four mammalian PARs, namely PAR-2, which is overexpressed in advanced stage tumors and is activated by trypsin-like serine proteases that are highly expressed or otherwise dysregulated in many cancers. We highlight recent insights into the ability of different protease agonists to bias PAR-2 signaling and the newly emerging evidence for an interplay between PAR-2 and membrane-anchored serine proteases, which may co-conspire to promote tumor progression and metastasis. Interfering with these pathways might provide unique opportunities for the development of new mechanism-based strategies for the treatment of advanced and metastatic cancers.

Ceramide Metabolism Balance, a Multifaceted Factor in Critical Steps of Breast Cancer Development

Ceramides are key lipids in energetic-metabolic pathways and signaling cascades, modulating critical physiological functions in cells. While synthesis of ceramides is performed in endoplasmic reticulum (ER), which is altered under overnutrition conditions, proteins associated with ceramide metabolism are located on membrane arrangement of mitochondria and ER (MAMs). However, ceramide accumulation in meta-inflammation, condition that associates obesity with a chronic low-grade inflammatory state, favors the deregulation of pathways such as insulin signaling, and induces structural rearrangements on mitochondrial membrane, modifying its permeability and altering the flux of ions and other molecules. Considering the wide biological processes in which sphingolipids are implicated, they have been associated with diseases that present abnormalities in their energetic metabolism, such as breast cancer. In this sense, sphingolipids could modulate various cell features, such as growth, proliferation, survival, senescence, and apoptosis in cancer progression; moreover, ceramide metabolism is associated to chemotherapy resistance, and regulation of metastasis. Cell–cell communication mediated by exosomes and lipoproteins has become relevant in the transport of several sphingolipids. Therefore, in this work we performed a comprehensive analysis of the state of the art about the multifaceted roles of ceramides, specifically the deregulation of ceramide metabolism pathways, being a key factor that could modulate neoplastic processes development. Under specific conditions, sphingolipids perform important functions in several cellular processes, and depending on the preponderant species and cellular and/or tissue status can inhibit or promote the development of metabolic and potentially breast cancer disease.

Mutant cytoskeletal and ECM peptides sensitive to the ST14 protease are associated with a worse outcome for glioblastoma multiforme

We previously identified a set of the most frequently mutated cytoskeleton- and extracellular matrix-related proteins (CECMPs) in numerous cancer datasets. In this report, we used a bioinformatics approach to assess the impact of amino acid (AA) substitutions on the sensitivity of CECMPs to the ST14 protease (matriptase I), a transmembrane serine protease previously implicated in cancer development. Results indicated that AA substitutions in glioblastoma multiforme (GBM) CECMPs are skewed toward increased resistance to the ST14 protease, in comparison to the wild-type peptide sequence. Furthermore, the protease resistant AA substitutions represent relatively high binding affinities to HLA class I proteins, when assessing the binding specificities using HLA class I alleles matched to the source of the mutant AA. Moreover, samples representing AA substitutions that increased protease sensitivity also represented reduced overall and disease-free survival periods for patients with glioblastoma. To assess tumor specimen immunogenicity, we identified T-cell receptor (TCR) V(D)J recombinations in GBM exome files. The overlap between ST14 protease sensitive mutant barcodes and the TCR V(D)J recombination read positive barcodes represented significantly reduced survival.

Dysregulated HAI-2 Plays an Important Role in Renal Cell Carcinoma Bone Metastasis through Ligand-Dependent MET Phosphorylation

MET, a c-met proto-oncogene product and hepatocyte growth factor (HGF) receptor, is known to play an important role in cancer progression, including bone metastasis. In a previous study, we reported increased expression of MET and matriptase, a novel activator of HGF, in bone metastasis. In this study, we employed a mouse model of renal cell carcinoma (RCC) bone metastasis to clarify the significance of the HGF/MET signaling axis and the regulator of HGF activator inhibitor type-2 (HAI-2). Luciferase-transfected 786-O cells were injected into the left cardiac ventricle of mice to prepare the mouse model of bone metastasis. The formation of bone metastasis was confirmed by whole-body bioluminescent imaging, and specimens were extracted. Expression of HGF/MET-related molecules was analyzed. Based on the results, we produced HAI-2 stable knockdown 786-O cells, and analyzed invasiveness and motility. Expression of HGF and matriptase was increased in bone metastasis compared with the control, while that of HAI-2 was decreased. Furthermore, we confirmed increased phosphorylation of MET in bone metastasis. The expression of matriptase was upregulated, and both invasiveness and motility were increased significantly by knockdown of HAI-2. The significance of ligand-dependent MET activation in RCC bone metastasis is considered, and HAI-2 may be an important regulator in this system.

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

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

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.

Hepatocyte growth factor activator inhibitor type-2 (HAI-2)/SPINT2 contributes to invasive growth of oral squamous cell carcinoma cells

Hepatocyte growth factor activator inhibitor (HAI)-1/SPINT1 and HAI-2/SPINT2 are membrane-anchored protease inhibitors having homologous Kunitz-type inhibitor domains. They regulate membrane-anchored serine proteases, such as matriptase and prostasin. Whereas HAI-1 suppresses the neoplastic progression of keratinocytes to invasive squamous cell carcinoma (SCC) through matriptase inhibition, the role of HAI-2 in keratinocytes is poorly understood. In vitro homozygous knockout of the SPINT2 gene suppressed the proliferation of two oral SCC (OSCC) lines (SAS and HSC3) but not the growth of a non-tumorigenic keratinocyte line (HaCaT). Reversion of HAI-2 abrogated the growth suppression. Matrigel invasion of both OSCC lines was also suppressed by the loss of HAI-2. The levels of prostasin protein were markedly increased in HAI-2-deficient cells, and knockdown of prostasin alleviated the HAI-2 loss-induced suppression of OSCC cell invasion. Therefore, HAI-2 has a pro-invasive role in OSCC cells through suppression of prostasin. In surgically resected OSCC tissues, HAI-2 immunoreactivity increased along with neoplastic progression, showing intense immunoreactivities in invasive OSCC cells. In summary, HAI-2 is required for invasive growth of OSCC cells and may contribute to OSCC progression.

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.

Type II transmembrane serine proteases as potential targets for cancer therapy

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

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.

Inhibition of cyclooxygenase-2-mediated matriptase activation contributes to the suppression of prostate cancer cell motility and metastasis

Chronic inflammation plays an important role in cancer development and progression. Cyclooxygenases-2 (COX-2) is a key enzyme in generating prostaglandins causing inflammation, is often found to be overexpressed in prostate cancer (PCa) and is correlated with PCa cell invasion and metastasis. We aim to investigate the molecular mechanism of how COX-2 promotes PCa cell invasion and metastasis and to evaluate the effect of COX-2 inhibitors in a selected model of PCa progression. Our results showed that the expression of COX-2 and Interleukin 1β (IL-1β) was upregulated in highly invasive PCa cells and was correlated with the activated levels of membrane-anchored serine protease matriptase. The expression levels of COX-2 were increased and were correlated with matriptase levels in PCa specimens. Moreover, results showed that COX-2 overexpression or a COX-2 product Prostaglandin E₂ (PGE₂) caused an increase in matriptase activation and PCa cell invasion, whereas COX-2 silencing antagonized matriptase activation and cell invasion. In addition, the inhibition of COX-2-mediated matriptase activation by Celebrex and sulindac sulfide suppressed the androgen-independent and COX2-overexpressing PCa PC-3 cell invasion, tumor growth and lung metastasis in an orthotopic xenograft model. Our results indicate that COX-2/matriptase signaling contributes to the invasion, tumor growth and metastasis of COX-2-overexpressing and androgen-independent PCa cells.

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.

Selective depletion of tumour suppressors Deleted in Colorectal Cancer (DCC) and neogenin by environmental and endogenous serine proteases: linking diet and cancer

BACKGROUND

The related tumour suppressor proteins Deleted in Colorectal Cancer (DCC) and neogenin are absent or weakly expressed in many cancers, whereas their insertion into cells suppresses oncogenic behaviour. Serine proteases influence the initiation and progression of cancers although the mechanisms are unknown.

METHODS

The effects of environmental (bacterial subtilisin) and endogenous mammalian (chymotrypsin) serine proteases were examined on protein expression in fresh, normal tissue and human neuroblastoma and mammary adenocarcinoma lines. Cell proliferation and migration assays (chemoattraction and wound closure) were used to examine cell function. Cells lacking DCC were transfected with an ectopic dcc plasmid.

RESULTS

Subtilisin and chymotrypsin selectively depleted DCC and neogenin from cells at nanomolar concentrations without affecting related proteins. Cells showed reduced adherence and increased migration, but after washing they re-attached within 24 h, with recovery of protein expression. These effects are induced by chymotryptic activity as they are prevented by chymostatin and the soybean Bowman-Birk inhibitor typical of many plant protease inhibitors.

CONCLUSIONS

Bacillus subtilis, which secretes subtilisin is widely present in soil, the environment and the intestinal contents, while subtilisin itself is used in meat processing, animal feed probiotics and many household cleaning agents. With chymotrypsin present in chyme, blood and tissues, these proteases may contribute to cancer development by depleting DCC and neogenin. Blocking their activity by Bowman-Birk inhibitors may explain the protective effects of a plant diet. Our findings identify a potential non-genetic contribution to cancer cell behaviour which may explain both the association of processed meats and other factors with cancer incidence and the protection afforded by plant-rich diets, with significant implications for cancer prevention.

Targeting the membrane-anchored serine protease testisin with a novel engineered anthrax toxin prodrug to kill tumor cells and reduce tumor burden

The membrane-anchored serine proteases are a unique group of trypsin-like serine proteases that are tethered to the cell surface via transmembrane domains or glycosyl-phosphatidylinositol-anchors. Overexpressed in tumors, with pro-tumorigenic properties, they are attractive targets for protease-activated prodrug-like anti-tumor therapies. Here, we sought to engineer anthrax toxin protective antigen (PrAg), which is proteolytically activated on the cell surface by the proprotein convertase furin to instead be activated by tumor cell-expressed membrane-anchored serine proteases to function as a tumoricidal agent. PrAg's native activation sequence was mutated to a sequence derived from protein C inhibitor (PCI) that can be cleaved by membrane-anchored serine proteases, to generate the mutant protein PrAg-PCIS. PrAg-PCIS was resistant to furin cleavage in vitro, yet cytotoxic to multiple human tumor cell lines when combined with FP59, a chimeric anthrax toxin lethal factor-Pseudomonas exotoxin fusion protein. Molecular analyses showed that PrAg-PCIS can be cleaved in vitro by several serine proteases including the membrane-anchored serine protease testisin, and mediates increased killing of testisin-expressing tumor cells. Treatment with PrAg-PCIS also potently attenuated the growth of testisin-expressing xenograft tumors in mice. The data indicates PrAg can be engineered to target tumor cell-expressed membrane-anchored serine proteases to function as a potent tumoricidal agent.

Metastatic Progression of Prostate Cancer Is Mediated by Autonomous Binding of Galectin-4-O-Glycan to Cancer Cells

Metastatic prostate cancer continues to pose a difficult therapeutic challenge. Prostate cancer progression is associated with aberrant O-glycosylation of cancer cell surface receptors, but the functional impact of such events is uncertain. Here we report spontaneous metastasis of human prostate cancer xenografts that express high levels of galectin-4 along with genetic signatures of EGFR-HER2 signaling and O-glycosylation. Galectin-4 expression in clinical specimens of prostate cancer correlated with poor patient survival. Galectin-4 binding to multiple receptor tyrosine kinases stimulated their autophosphorylation, activated expression of pERK, pAkt, fibronectin, and Twist1, and lowered expression of E-cadherin, thereby facilitating epithelial-mesenchymal transition, invasion, and metastasis. In vivo investigations established that galectin-4 expression enabled prostate cancer cells to repopulate tumors in orthotopic and heterotopic tissues. Notably, these effects of galectin-4 relied upon O-glycosylation mediated by C1GALT1, a galactosyltransferase implicated in other cancers. Parallel changes in galectin-4 and O-glycosylation triggered aberrant receptor signaling and more aggressive invasive character in prostate cancer cells, which through better survival in the circulation also contributed to the bulk cell progeny of distal tumors. Our findings establish galectin-4 and C1GALT1-mediated glycosylation in a signaling axis that is activated during prostate cancer progression, with implications for therapeutic targeting of advanced metastatic disease. Cancer Res; 76(19); 5756-67. ©2016 AACR.

c-Met as a Target for Personalized Therapy

MET and its ligand HGF are involved in many biological processes, both physiological and pathological, making this signaling pathway an attractive therapeutic target in oncology. Downstream signaling effects are transmitted via mitogen-activated protein kinase (MAPK), PI3K (phosphoinositide 3-kinase protein kinase B)/AKT, signal transducer and activator of transcription proteins (STAT), and nuclear factor-κB. The final output of the terminal effector components of these pathways is activation of cytoplasmic and nuclear processes leading to increases in cell proliferation, survival, mobilization and invasive capacity. In addition to its role as an oncogenic driver, increasing evidence implicates MET as a common mechanism of resistance to targeted therapies including EGFR and VEGFR inhibitors. In the present review, we summarize the current knowledge on the role of the HGF-MET signaling pathway in cancer and its therapeutic targeting (HGF activation inhibitors, HGF inhibitors, MET antagonists and selective/nonselective MET kinase inhibitors). Recent advances in understanding the role of this pathway in the resistance to current anticancer strategies used in lung, kidney and pancreatic cancer are discussed.

c-Met as a Target for Personalized Therapy

MET and its ligand HGF are involved in many biological processes, both physiological and pathological, making this signaling pathway an attractive therapeutic target in oncology. Downstream signaling effects are transmitted via mitogen-activated protein kinase (MAPK), PI3K (phosphoinositide 3-kinase protein kinase B)/AKT, signal transducer and activator of transcription proteins (STAT), and nuclear factor-κB. The final output of the terminal effector components of these pathways is activation of cytoplasmic and nuclear processes leading to increases in cell proliferation, survival, mobilization and invasive capacity. In addition to its role as an oncogenic driver, increasing evidence implicates MET as a common mechanism of resistance to targeted therapies including EGFR and VEGFR inhibitors. In the present review, we summarize the current knowledge on the role of the HGF-MET signaling pathway in cancer and its therapeutic targeting (HGF activation inhibitors, HGF inhibitors, MET antagonists and selective/nonselective MET kinase inhibitors). Recent advances in understanding the role of this pathway in the resistance to current anticancer strategies used in lung, kidney and pancreatic cancer are discussed.

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.

Androgen-Induced TMPRSS2 Activates Matriptase and Promotes Extracellular Matrix Degradation, Prostate Cancer Cell Invasion, Tumor Growth, and Metastasis

Dysregulation of androgen signaling and pericellular proteolysis is necessary for prostate cancer progression, but the links between them are still obscure. In this study, we show how the membrane-anchored serine protease TMPRSS2 stimulates a proteolytic cascade that mediates androgen-induced prostate cancer cell invasion, tumor growth, and metastasis. We found that matriptase serves as a substrate for TMPRSS2 in mediating this proinvasive action of androgens in prostate cancer. Further, we determined that higher levels of TMPRSS2 expression correlate with higher levels of matriptase activation in prostate cancer tissues. Lastly, we found that the ability of TMPRSS2 to promote prostate cancer tumor growth and metastasis was associated with increased matriptase activation and enhanced degradation of extracellular matrix nidogen-1 and laminin β1 in tumor xenografts. In summary, our results establish that TMPRSS2 promotes the growth, invasion, and metastasis of prostate cancer cells via matriptase activation and extracellular matrix disruption, with implications to target these two proteases as a strategy to treat prostate cancer.

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.

Matriptase promotes inflammatory cell accumulation and progression of established epidermal tumors

Deregulation of matriptase is a consistent feature of human epithelial cancers and correlates with poor disease outcome. We have previously shown that matriptase promotes multi-stage squamous cell carcinogenesis in transgenic mice through dual activation of pro-hepatocyte growth factor-cMet-Akt-mTor proliferation/survival signaling and PAR-2-Gαi-NFκB inflammatory signaling. Matriptase was congenitally and constitutively deregulated in our prior studies, and therefore it was unclear if aberrant matriptase signaling supports only initiation of tumor formation or if it is also critical for the progression of established tumors. To determine this, we here have generated triple-transgenic mice with constitutive deregulation of matriptase and simultaneous inducible expression of the cognate matriptase inhibitor, hepatocyte growth factor inhibitor (HAI)-2. As expected, constitutive expression of HAI-2 suppressed the formation of matriptase-dependent tumors in 7,12-Dimethylbenz(a)anthracene-treated mouse skin. Interestingly, however, the induction of HAI-2 expression in already established tumors markedly impaired malignant progression and caused regression of individual tumors. Tumor regression correlated with reduced accumulation of tumor-associated inflammatory cells, likely caused by diminished expression of pro-tumorigenic inflammatory cytokines. The data suggest that matriptase-dependent signaling may be a therapeutic target for both squamous cell carcinoma chemoprevention and for the treatment of established tumors.

Sequence and conformational specificity in substrate recognition: several human Kunitz protease inhibitor domains are specific substrates of mesotrypsin

Mesotrypsin is an isoform of trypsin that is uniquely resistant to polypeptide trypsin inhibitors and can cleave some inhibitors rapidly. Previous studies have shown that the amyloid precursor protein Kunitz protease inhibitor domain (APPI) is a specific substrate of mesotrypsin and that stabilization of the APPI cleavage site in a canonical conformation contributes to recognition by mesotrypsin. We hypothesized that other proteins possessing potential cleavage sites stabilized in a similar conformation might also be mesotrypsin substrates. Here we evaluated a series of candidate substrates, including human Kunitz protease inhibitor domains from amyloid precursor-like protein 2 (APLP2), bikunin, hepatocyte growth factor activator inhibitor type 2 (HAI2), tissue factor pathway inhibitor-1 (TFPI1), and tissue factor pathway inhibitor-2 (TFPI2), as well as E-selectin, an unrelated protein possessing a potential cleavage site displaying canonical conformation. We find that Kunitz domains within APLP2, bikunin, and HAI2 are cleaved by mesotrypsin with kinetic profiles of specific substrates. TFPI1 and TFPI2 Kunitz domains are cleaved less efficiently by mesotrypsin, and E-selectin is not cleaved at the anticipated site. Cocrystal structures of mesotrypsin with HAI2 and bikunin Kunitz domains reveal the mode of mesotrypsin interaction with its canonical substrates. Our data suggest that major determinants of mesotrypsin substrate specificity include sequence preferences at the P1 and P'2 positions along with conformational stabilization of the cleavage site in the canonical conformation. Mesotrypsin up-regulation has been implicated previously in cancer progression, and proteolytic clearance of Kunitz protease inhibitors offers potential mechanisms by which mesotrypsin may mediate pathological effects in cancer.

HATL5: a cell surface serine protease differentially expressed in epithelial cancers

Over the last two decades, cell surface proteases belonging to the type II transmembrane serine protease (TTSP) family have emerged as important enzymes in the mammalian degradome, playing critical roles in epithelial biology, regulation of metabolic homeostasis, and cancer. Human airway trypsin-like protease 5 (HATL5) is one of the few family members that remains uncharacterized. Here we demonstrate that HATL5 is a catalytically active serine protease that is inhibited by the two Kunitz type serine protease inhibitors, hepatocyte growth factor activator inhibitor (HAI)-1 and 2, as well as by serpinA1. Full-length HATL5 is localized on the cell surface of cultured mammalian cells as demonstrated by confocal microscopy. HATL5 displays a relatively restricted tissue expression profile, with both transcript and protein present in the cervix, esophagus, and oral cavity. Immunohistochemical analysis revealed an expression pattern where HATL5 is localized on the cell surface of differentiated epithelial cells in the stratified squamous epithelia of all three of these tissues. Interestingly, HATL5 is significantly decreased in cervical, esophageal, and head and neck carcinomas as compared to normal tissue. Analysis of cervical and esophageal cancer tissue arrays demonstrated that the squamous epithelial cells lose their expression of HATL5 protein upon malignant transformation.