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

Matriptase-dependent epidermal pre-neoplasm in zebrafish embryos caused by a combination of hypotonic stress and epithelial polarity defects

Aberrantly up-regulated activity of the type II transmembrane protease Matriptase-1 has been associated with the development and progression of a range of epithelial-derived carcinomas, and a variety of signaling pathways can mediate Matriptase-dependent tumorigenic events. During mammalian carcinogenesis, gain of Matriptase activity often results from imbalanced ratios between Matriptase and its cognate transmembrane inhibitor Hai1. Similarly, in zebrafish, unrestrained Matriptase activity due to loss of hai1a results in epidermal pre-neoplasms already during embryogenesis. Here, based on our former findings of a similar tumor-suppressive role for the Na+/K+-pump beta subunit ATP1b1a, we identify epithelial polarity defects and systemic hypotonic stress as another mode of aberrant Matriptase activation in the embryonic zebrafish epidermis in vivo. In this case, however, a different oncogenic pathway is activated which contains PI3K, AKT and NFkB, rather than EGFR and PLD (as in hai1a mutants). Strikingly, epidermal pre-neoplasm is only induced when epithelial polarity defects in keratinocytes (leading to disturbed Matriptase subcellular localization) occur in combination with systemic hypotonic stress (leading to increased proteolytic activity of Matriptase). A similar combinatorial effect of hypotonicity and loss of epithelial polarity was also obtained for the activity levels of Matriptase-1 in human MCF-10A epithelial breast cells. Together, this is in line with the multi-factor concept of carcinogenesis, with the notion that such factors can even branch off from one and the same initiator (here ATP1a1b) and can converge again at the level of one and the same mediator (here Matriptase). In sum, our data point to tonicity and epithelial cell polarity as evolutionarily conserved regulators of Matriptase activity that upon de-regulation can constitute an alternative mode of Matriptase-dependent carcinogenesis in vivo.

Type II Transmembrane Serine Proteases as Modulators in Adipose Tissue Phenotype and Function

Adipose tissue is a crucial organ in energy metabolism and thermoregulation. Adipose tissue phenotype is controlled by various signaling mechanisms under pathophysiological conditions. Type II transmembrane serine proteases (TTSPs) are a group of trypsin-like enzymes anchoring on the cell surface. These proteases act in diverse tissues to regulate physiological processes, such as food digestion, salt-water balance, iron metabolism, epithelial integrity, and auditory nerve development. More recently, several members of the TTSP family, namely, hepsin, matriptase-2, and corin, have been shown to play a role in regulating lipid metabolism, adipose tissue phenotype, and thermogenesis, via direct growth factor activation or indirect hormonal mechanisms. In mice, hepsin deficiency increases adipose browning and protects from high-fat diet-induced hyperglycemia, hyperlipidemia, and obesity. Similarly, matriptase-2 deficiency increases fat lipolysis and reduces obesity and hepatic steatosis in high-fat diet-fed mice. In contrast, corin deficiency increases white adipose weights and cell sizes, suppresses adipocyte browning and thermogenic responses, and causes cold intolerance in mice. These findings highlight an important role of TTSPs in modifying cellular phenotype and function in adipose tissue. In this review, we provide a brief description about TTSPs and discuss recent findings regarding the role of hepsin, matriptase-2, and corin in regulating adipose tissue phenotype, energy metabolism, and thermogenic responses.

Intersection of Coagulation and Fibrinolysis by the Glycosylphosphatidylinositol (GPI)-Anchored Serine Protease Testisin

Hemostasis is a delicate balance between coagulation and fibrinolysis that regulates the formation and removal of fibrin, respectively. Positive and negative feedback loops and crosstalk between coagulation and fibrinolytic serine proteases maintain the hemostatic balance to prevent both excessive bleeding and thrombosis. Here, we identify a novel role for the glycosylphosphatidylinositol (GPI)-anchored serine protease testisin in the regulation of pericellular hemostasis. Using in vitro cell-based fibrin generation assays, we found that the expression of catalytically active testisin on the cell surface accelerates thrombin-dependent fibrin polymerization, and intriguingly, that it subsequently promotes accelerated fibrinolysis. We find that the testisin-dependent fibrin formation is inhibited by rivaroxaban, a specific inhibitor of the central prothrombin-activating serine protease factor Xa (FXa), demonstrating that cell-surface testisin acts upstream of factor X (FX) to promote fibrin formation at the cell surface. Unexpectedly, testisin was also found to accelerate fibrinolysis by stimulating the plasmin-dependent degradation of fibrin and enhancing plasmin-dependent cell invasion through polymerized fibrin. Testisin was not a direct activator of plasminogen, but it is able to induce zymogen cleavage and the activation of pro-urokinase plasminogen activator (pro-uPA), which converts plasminogen to plasmin. These data identify a new proteolytic component that can regulate pericellular hemostatic cascades at the cell surface, which has implications for angiogenesis, cancer biology, and male fertility.

Biochemical and molecular characterization of novel keratinolytic protease from Bacillus licheniformis (KRLr1)

The keratin-degrading bacterium Bacillus licheniformis secretes a keratinase with potential industrial interest. Here, the Keratinase gene was intracellularly expressed in Escherichia coli BL21(DE3) using pET-21b (+) vector. Phylogenetic tree analysis showed that KRLr1 is closely related to Bacillus licheniformis keratinase that belongs to the serine peptidase/subtilisin-like S8 family. Recombinant keratinase appeared on the SDS-PAGE gel with a band of about 38 kDa and was confirmed by western blotting. Expressed KRLr1 was purified by Ni-NTA affinity chromatography with a yield of 85.96% and then refolded. It was found that this enzyme has optimum activity at pH 6 and 37°C. PMSF inhibited the KRLr1 activity and Ca²⁺ and Mg²⁺ increased the KRLr1 activity. Using keratin 1% as the substrate, the thermodynamic values were determined as K_m 14.54 mM, k_cat 912.7 × 10^-3 (S^-1), and k_cat/K_m 62.77 (M^-1 S^-1). Feather digestion by recombinant enzyme using HPLC method, showed that the amino acids cysteine, phenylalanine, tyrosine and lysine had the highest amount compared to other amino acids obtained from digestion. Molecular dynamics (MD) simulation of HADDOCK docking results exhibited that KRLr1 enzyme was able to interact strongly with chicken feather keratine 4 (FK4) compared to chicken feather keratine 12 (FK12). These properties make keratinase KRLr1 a potential candidate for various biotechnological applications.

TMPRSS13 zymogen activation, surface localization, and shedding is regulated by proteolytic cleavage within the non-catalytic stem region

TMPRSS13 is a member of the type II transmembrane serine protease (TTSP) family. Here we characterize a novel post-translational mechanism important for TMPRSS13 function: proteolytic cleavage within the extracellular TMPRSS13 stem region located between the transmembrane domain and the first site of N-linked glycosylation at asparagine (N)-250 in the scavenger receptor cysteine rich (SRCR) domain. Importantly, the catalytic competence of TMPRSS13 is essential for stem region cleavage, suggesting an autonomous mechanism of action. Site-directed mutagenesis of the 10 basic amino acids (four arginine and six lysine residues) in this region abrogated zymogen activation and catalytic activity of TMPRSS13, as well as phosphorylation, cell surface expression, and shedding. Mutation analysis of individual arginine residues identified R223, a residue located between the low-density lipoprotein receptor class A domain and the SRCR domain, as important for stem region cleavage. Mutation of R223 causes a reduction in the aforementioned functional processing steps of TMPRSS13. These data provide further insight into the roles of different post-translational modifications as regulators of the function and localization of TMPRSS13. Additionally, the data suggest the presence of complex interconnected regulatory mechanisms that may serve to ensure the proper levels of cell-surface and pericellular TMPRSS13-mediated proteolysis under homeostatic conditions.

Evaluating the role of trypsin in silk degumming: An in silico approach

The trypsin being universal enzyme forming family of proteases catalyzes the hydrolysis of proteins into amino acids and regenerates the serine hydroxyl an active site. The trypsin enzyme from D. saccharalis, uses sericin as its preferred substrate. Presence of catalytic triad (serine, aspartic acid and histidine) at the substrate binding site of this enzyme is very important for the catalytic activity. In the current study, the interacting mechanism between the substrate sericin protein and enzyme trypsin protein were explored by integrating various computational approaches including physico-chemical properties, biophysical properties, dynamics, gene ontology, molecular docking, protein - protein interactions, binding free energy calculation and structural motifs were studied. The evolutionary study performed by MEGA X showed that trypsin protein sequence (ALE15212.1) is closely related to cocoonase protein sequence (ADG26770.1) from Antheraea pernyi. 3-D models of trypsin and sericin proteins were predicted using I-TASSER and further validated by PROCHECK, and ProSAweb softwares. The predicted trypsin structure model was assigned E.C. no. 3.4.21.4 which refers hydrolytic mechanism. Gene Ontology predicted by QuickGO showed that trypsin has serine hydrolase activity (GO: 00017171), and part of proteolysis (GO: 0006508) as well as protein metabolic process (GO:0019538) actvity. Molecular docking studies between trypsin and sericin proteins were conducted by the HADDOCK 2.4 having best docked protein complex with Z-score - 1.9. 2D and 3D protein-protein interaction was performed with LIGPLOT⁺ and HAWKDOCK, PDBsum, respectively. The amino acid residues interacting across proteins interface are sericin_chain A representing "Ser133, Tyr214, Thr188, Thr243, Ser225, Ser151, Ser156, His294, Arg293, Gly296″ and trypsin_chain B "Lys120, Tyr246, Asn119, Glu239, Ser62, Tyr194, Ile197, Ser171, Tyr169, Gly170″. Based on our results trypsin shows similarity with cocoonase and presumably trypsin can be used as an alternative source in cocoon degumming.

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.

Selective targeting of metastatic ovarian cancer using an engineered anthrax prodrug activated by membrane-anchored serine proteases

Treatments for advanced and recurrent ovarian cancer remain a challenge due to a lack of potent, selective, and effective therapeutics. Here, we developed the basis for a transformative anticancer strategy based on anthrax toxin that has been engineered to be selectively activated by the catalytic power of zymogen-activating proteases on the surface of malignant tumor cells to induce cell death. Exposure to the engineered toxin is cytotoxic to ovarian tumor cell lines and ovarian tumor spheroids derived from patient ascites. Preclinical studies demonstrate that toxin treatment induces tumor regression in several in vivo ovarian cancer models, including patient-derived xenografts, without adverse side effects, supportive of progression toward clinical evaluation. These data lay the groundwork for developing therapeutics for treating women with late-stage and recurrent ovarian cancers, utilizing a mechanism distinct from current anticancer therapies.

Enoxaparin augments alpha-1-antitrypsin inhibition of TMPRSS2, a promising drug combination against COVID-19

The cell surface serine protease Transmembrane Protease 2 (TMPRSS2) is required to cleave the spike protein of SARS-CoV-2 for viral entry into cells. We determined whether negatively-charged heparin enhanced TMPRSS2 inhibition by alpha-1-antitrypsin (AAT). TMPRSS2 activity was determined in HEK293T cells overexpressing TMPRSS2. We quantified infection of primary human airway epithelial cells (hAEc) with human coronavirus 229E (HCoV-229E) by immunostaining for the nucleocapsid protein and by the plaque assay. Detailed molecular modeling was undertaken with the heparin-TMPRSS2-AAT ternary complex. Enoxaparin enhanced AAT inhibition of both TMPRSS2 activity and infection of hAEc with HCoV-229E. Underlying these findings, detailed molecular modeling revealed that: (i) the reactive center loop of AAT adopts an inhibitory-competent conformation compared with the crystal structure of TMPRSS2 bound to an exogenous (nafamostat) or endogenous (HAI-2) TMPRSS2 inhibitor and (ii) negatively-charged heparin bridges adjacent electropositive patches at the TMPRSS2-AAT interface, neutralizing otherwise repulsive forces. In conclusion, enoxaparin enhances AAT inhibition of both TMPRSS2 and coronavirus infection. Such host-directed therapy is less likely to be affected by SARS-CoV-2 mutations. Furthermore, given the known anti-inflammatory activities of both AAT and heparin, this form of treatment may target both the virus and the excessive inflammatory consequences of severe COVID-19.

Insufficiency of hepatocyte growth factor activator inhibitor-1 confers lymphatic invasion of tongue carcinoma cells

Hepatocyte growth factor (HGF) activator inhibitor type‐1 (HAI‐1), encoded by the SPINT1 gene, is a transmembrane protease inhibitor that regulates membrane‐anchored serine proteases, particularly matriptase. Here, we explored the role of HAI‐1 in tongue squamous cell carcinoma (TSCC) cells. An immunohistochemical study of HAI‐1 in surgically resected TSCC revealed the cell surface immunoreactivity of HAI‐1 in the main portion of the tumor. The immunoreactivity decreased in the infiltrative front, and this decrease correlated with enhanced lymphatic invasion as judged by podoplanin immunostaining. In vitro homozygous deletion of SPINT1 (HAI‐1KO) in TSCC cell lines (HSC3 and SAS) suppressed the cell growth rate but significantly enhanced invasion in vitro. The loss of HAI‐1 resulted in enhanced pericellular activities of proteases, such as matriptase and urokinase‐type plasminogen activator, which induced activation of HGF/MET signaling in the co‐culture with pro‐HGF‐expressing fibroblasts and plasminogen‐dependent plasmin generation, respectively. The enhanced plasminogen‐dependent plasmin generation was abrogated partly by matriptase silencing. Culture supernatants of HAI‐1KO cells had enhanced potency for converting the proform of vascular endothelial growth factor‐C (VEGF‐C), a lymphangiogenesis factor, into the mature form in a plasminogen‐dependent manner. Furthermore, HGF significantly stimulated VEGF‐C expression in TSCC cells. Orthotopic xenotransplantation into nude mouse tongue revealed enhanced lymphatic invasion of HAI‐1KO TSCC cells compared to control cells. Our results suggest that HAI‐1 insufficiency leads to dysregulated pericellular protease activity, which eventually orchestrates robust activation of protease‐dependent growth factors, such as HGF and VEGF‐C, in a tumor microenvironment to contribute to TSCC progression.

Evolutionary history of type II transmembrane serine proteases involved in viral priming

Type II transmembrane serine proteases (TTSPs) are a family of trypsin-like membrane-anchored serine proteases that play key roles in the regulation of some crucial processes in physiological conditions, including cardiac function, digestion, cellular iron homeostasis, epidermal differentiation, and immune responses. However, some of them, in particular TTSPs expressed in the human airways, were identified as host factors that promote the proteolytic activation and spread of respiratory viruses such as influenza virus, human metapneumovirus, and coronaviruses, including SARS-CoV-2. Given their involvement in viral priming, we hypothesized that members of the TTSP family may represent targets of positive selection, possibly as the result of virus-driven pressure. Thus, we investigated the evolutionary history of sixteen TTSP genes in mammals. Evolutionary analyses indicate that most of the TTSP genes that have a verified role in viral proteolytic activation present signals of pervasive positive selection, suggesting that viral infections represent a selective pressure driving the evolution of these proteases. We also evaluated genetic diversity in human populations and we identified targets of balancing selection in TMPRSS2 and TMPRSS4. This scenario may be the result of an ancestral and still ongoing host–pathogen arms race. Overall, our results provide evolutionary information about candidate functional sites and polymorphic positions in TTSP genes.

TMPRSS4 promotes cancer stem-like properties in prostate cancer cells through upregulation of SOX2 by SLUG and TWIST1

Background

Transmembrane serine protease 4 (TMPRSS4) is a cell surface–anchored serine protease. Elevated expression of TMPRSS4 correlates with poor prognosis in colorectal cancer, gastric cancer, prostate cancer, non–small cell lung cancer, and other cancers. Previously, we demonstrated that TMPRSS4 promotes invasion and proliferation of prostate cancer cells. Here, we investigated whether TMPRSS4 confers cancer stem–like properties to prostate cancer cells and characterized the underlying mechanisms.

Methods

Acquisition of cancer stem–like properties by TMPRSS4 was examined by monitoring anchorage-independent growth, tumorsphere formation, aldehyde dehydrogenase (ALDH) activation, and resistance to anoikis and drugs in vitro and in an early metastasis model in vivo. The underlying molecular mechanisms were evaluated, focusing on stemness-related factors regulated by epithelial–mesenchymal transition (EMT)-inducing transcription factors. Clinical expression and significance of TMPRSS4 and stemness-associated factors were explored by analyzing datasets from The Cancer Genome Atlas (TCGA).

Results

TMPRSS4 promoted anchorage-independent growth, ALDH activation, tumorsphere formation, and therapeutic resistance of prostate cancer cells. In addition, TMPRSS4 promoted resistance to anoikis, thereby increasing survival of circulating tumor cells and promoting early metastasis. These features were accompanied by upregulation of stemness-related factors such as SOX2, BMI1, and CD133. SLUG and TWIST1, master EMT-inducing transcription factors, made essential contributions to TMPRSS4-mediated cancer stem cell (CSC) features through upregulation of SOX2. SLUG stabilized SOX2 via preventing proteasomal degradation through its interaction with SOX2, while TWIST1 upregulated transcription of SOX2 by interacting with the proximal E-box element in the SOX2 promoter. Clinical data showed that TMPRSS4 expression correlated with the levels of SOX2, PROM1, SNAI2, and TWIST1. Expression of SOX2 was positively correlated with that of TWIST1, but not with other EMT-inducing transcription factors, in various cancer cell lines.

Conclusions

Together, these findings suggest that TMPRSS4 promotes CSC features in prostate cancer through upregulation of the SLUG- and TWIST1-induced stem cell factor SOX2 beyond EMT. Thus, TMPRSS4/SLUG–TWIST1/SOX2 axis may represent a novel mechanism involved in the control of tumor progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-02147-7.

Hepsin regulates TGFβ signaling via fibronectin proteolysis

Transforming growth factor‐beta (TGFβ) is a multifunctional cytokine with a well‐established role in mammary gland development and both oncogenic and tumor‐suppressive functions. The extracellular matrix (ECM) indirectly regulates TGFβ activity by acting as a storage compartment of latent‐TGFβ, but how TGFβ is released from the ECM via proteolytic mechanisms remains largely unknown. In this study, we demonstrate that hepsin, a type II transmembrane protease overexpressed in 70% of breast tumors, promotes canonical TGFβ signaling through the release of latent‐TGFβ from the ECM storage compartment. Mammary glands in hepsin CRISPR knockout mice showed reduced TGFβ signaling and increased epithelial branching, accompanied by increased levels of fibronectin and latent‐TGFβ1, while overexpression of hepsin in mammary tumors increased TGFβ signaling. Cell‐free and cell‐based experiments showed that hepsin is capable of direct proteolytic cleavage of fibronectin but not latent‐TGFβ and, importantly, that the ability of hepsin to activate TGFβ signaling is dependent on fibronectin. Altogether, this study demonstrates a role for hepsin as a regulator of the TGFβ pathway in the mammary gland via a novel mechanism involving proteolytic downmodulation of fibronectin.

Posttranslational modifications of serine protease TMPRSS13 regulate zymogen activation, proteolytic activity, and cell surface localization

TMPRSS13, a member of the type II transmembrane serine protease (TTSP) family, harbors four N-linked glycosylation sites in its extracellular domain. Two of the glycosylated residues are located in the scavenger receptor cysteine-rich (SRCR) protein domain, while the remaining two sites are in the catalytic serine protease (SP) domain. In this study, we examined the role of N-linked glycosylation in the proteolytic activity, autoactivation, and cellular localization of TMPRSS13. Individual and combinatory site-directed mutagenesis of the glycosylated asparagine residues indicated that glycosylation of the SP domain is critical for TMPRSS13 autoactivation and catalytic activity toward one of its protein substrates, the prostasin zymogen. Additionally, SP domain glycosylation-deficient TMPRSS13 displayed impaired trafficking of TMPRSS13 to the cell surface, which correlated with increased retention in the endoplasmic reticulum. Importantly, we showed that N-linked glycosylation was a critical determinant for subsequent phosphorylation of endogenous TMPRSS13. Taken together, we conclude that glycosylation plays an important role in regulating TMPRSS13 activation and activity, phosphorylation, and cell surface localization.

Host Serine Proteases: A Potential Targeted Therapy for COVID-19 and Influenza

The ongoing pandemic illustrates limited therapeutic options for controlling SARS-CoV-2 infections, calling a need for additional therapeutic targets. The viral spike S glycoprotein binds to the human receptor angiotensin-converting enzyme 2 (ACE2) and then is activated by the host proteases. Based on the accessibility of the cellular proteases needed for SARS-S activation, SARS-CoV-2 entrance and activation can be mediated by endosomal (such as cathepsin L) and non-endosomal pathways. Evidence indicates that in the non-endosomal pathway, the viral S protein is cleaved by the furin enzyme in infected host cells. To help the virus enter efficiently, the S protein is further activated by the serine protease 2 (TMPRSS2), provided that the S has been cleaved by furin previously. In this review, important roles for host proteases within host cells will be outlined in SARS-CoV-2 infection and antiviral therapeutic strategies will be highlighted. Although there are at least five highly effective vaccines at this time, the appearance of the new viral mutations demands the development of therapeutic agents. Targeted inhibition of host proteases can be used as a therapeutic approach for viral infection.

Recent advances in rotavirus reverse genetics and its utilization in basic research and vaccine development

Rotaviruses are segmented double-stranded RNA viruses with a high frequency of gene reassortment, and they are a leading cause of global diarrheal deaths in children less than 5 years old. Two-thirds of rotavirus-associated deaths occur in low-income countries. Currently, the available vaccines in developing countries have lower efficacy in children than those in developed countries. Due to added safety concerns and the high cost of current vaccines, there is a need to develop cost-effective next-generation vaccines with improved safety and efficacy. The reverse genetics system (RGS) is a powerful tool for investigating viral protein functions and developing novel vaccines. Recently, an entirely plasmid-based RGS has been developed for several rotaviruses, and this technological advancement has significantly facilitated novel rotavirus research. Here, we review the recently developed RGS platform and discuss its application in studying infection biology, gene reassortment, and development of vaccines against rotavirus disease.

Crystal structure of inhibitor-bound human MSPL that can activate high pathogenic avian influenza

The structure of extracellular domain of MSPL and inhibitor complex helps to understand the TTSP functions, including TMPRSS2, and provides the insights of the infection of influenza and SARS-CoV.

Infection of certain influenza viruses is triggered when its HA is cleaved by host cell proteases such as proprotein convertases and type II transmembrane serine proteases (TTSP). HA with a monobasic motif is cleaved by trypsin-like proteases, including TMPRSS2 and HAT, whereas the multibasic motif found in high pathogenicity avian influenza HA is cleaved by furin, PC5/6, or MSPL. MSPL belongs to the TMPRSS family and preferentially cleaves [R/K]-K-K-R↓ sequences. Here, we solved the crystal structure of the extracellular region of human MSPL in complex with an irreversible substrate-analog inhibitor. The structure revealed three domains clustered around the C-terminal α-helix of the SPD. The inhibitor structure and its putative model show that the P1-Arg inserts into the S1 pocket, whereas the P2-Lys and P4-Arg interacts with the Asp/Glu-rich 99-loop that is unique to MSPL. Based on the structure of MSPL, we also constructed a homology model of TMPRSS2, which is essential for the activation of the SARS-CoV-2 spike protein and infection. The model may provide the structural insight for the drug development for COVID-19.

Unravelling high-affinity binding compounds towards transmembrane protease serine 2 enzyme in treating SARS-CoV-2 infection using molecular modelling and docking studies

The coronavirus disease-19 (COVID-19) outbreak that is caused by a highly contagious severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has become a zoonotic pandemic, with approximately 24.5 million positive cases and 8.3 lakhs deaths globally. The lack of effective drugs or vaccine provoked the research for drug candidates that can disrupt the spread and progression of the virus. The identification of drug molecules through experimental studies is time-consuming and expensive, so there is a need for developing alternative strategies like in silico approaches which can yield better outcomes in less time. Herein, we selected transmembrane protease serine 2 (TMPRSS2) enzyme, a potential pharmacological target against SARS-CoV-2, involved in the spread and pathogenesis of the virus. Since 3D structure is not available for this protein, the present study aims at homology modelling and validation of TMPRSS2 using Swiss-model server. Validation of the modelled TMPRSS2 using various online tools confirmed model accuracy, topology and stereochemical plausibility. The catalytic triad consisting of Serine-441, Histidine-296 and Aspartic acid-345 was identified as active binding site of TMPRSS2 using existing ligands. Molecular docking studies of various drugs and phytochemicals against the modelled TMPRSS2 were performed using camostat as a standard drug. The results revealed eight potential drug candidates, namely nafamostat, meloxicam, ganodermanontriol, columbin, myricetin, proanthocyanidin A2, jatrorrhizine and baicalein, which were further studied for ADME/T properties. In conclusion, the study unravelled eight high affinity binding compounds, which may serve as potent antagonists against TMPRSS2 to impact COVID-19 drug therapy.

Spontaneous binding of potential COVID-19 drugs (Camostat and Nafamostat) to human serine protease TMPRSS2

Effective treatment or vaccine is not yet available for combating SARS coronavirus 2 (SARS-CoV-2) that caused the COVID-19 pandemic. Recent studies showed that two drugs, Camostat and Nafamostat, might be repurposed to treat COVID-19 by inhibiting human TMPRSS2 required for proteolytic activation of viral spike (S) glycoprotein. However, their molecular mechanisms of pharmacological action remain unclear. Here, we perform molecular dynamics simulations to investigate their native binding sites on TMPRSS2. We revealed that both drugs could spontaneously and stably bind to the TMPRSS2 catalytic center, and thereby inhibit its proteolytic processing of the S protein. Also, we found that Nafamostat is more specific than Camostat for binding to the catalytic center, consistent with reported observation that Nafamostat blocks the SARS-CoV-2 infection at a lower concentration. Thus, this study provides mechanistic insights into the Camostat and Nafamostat inhibition of the SARS-CoV-2 infection, and offers useful information for COVID-19 drug development.

CNS implications of COVID-19: a comprehensive review

COVID-19 was first reported in December 2019 in the Wuhan city of China, and since then it has spread worldwide taking a heavy toll on human life and economy. COVID-19 infection is commonly associated with symptoms like coughing, fever, and shortness of breath, besides, the reports of muscle pain, anosmia, hyposmia, and loss of taste are becoming evident. Recent reports suggest the pathogenic invasion of the SARS-CoV-2 into the CNS, that could thereby result in devastating long term complications, primarily because some of these complications may go unnoticed for a long time. Evidence suggest that the virus could enter the CNS through angiotensin-converting enzyme-2 (ACE-2) receptor, neuronal transport, haematogenous route, and nasal route via olfactory bulb, cribriform plate, and propagates through trans-synaptic signalling, and shows retrograde movement into the CNS along nerve fiber. COVID-19 induces CNS inflammation and neurological degenerative damage through a diverse mechanism which includes ACE-2 receptor damage, cytokine-associated injury or cytokine storm syndrome, secondary hypoxia, demyelination, blood-brain barrier disruption, neurodegeneration, and neuroinflammation. Viral invasion into the CNS has been reported to show association with complications like Parkinsonism, Alzheimer's disorder, meningitis, encephalopathy, anosmia, hyposmia, anxiety, depression, psychiatric symptoms, seizures, stroke, etc. This review provides a detailed discussion of the CNS pathogenesis of COVID-19. Authors conclude that the COVID-19 cannot just be considered as a disorder of the pulmonary or peripheral system, rather it has a significant CNS involvement. Therefore, CNS aspects of the COVID-19 should be monitored very closely to prevent long term CNS complications, even after the patient has recovered from COVID-19.

Inhibitors of type II transmembrane serine proteases in the treatment of diseases of the respiratory tract - A review of patent literature

INTRODUCTION

Type II transmembrane serine proteases (TTSPs) of the human respiratory tract generate high interest owing to their ability, among other roles, to cleave surface proteins of respiratory viruses. This step is critical in the viral invasion of coronaviruses, including SARS-CoV-2 responsible for COVID-19, but also influenza viruses and reoviruses. Accordingly, these cell surface enzymes constitute appealing therapeutic targets to develop host-based therapeutics against respiratory viral diseases. Additionally, their deregulated levels or activity has been described in non-viral diseases such as fibrosis, cancer, and osteoarthritis, making them potential targets in these indications.

AREAS COVERED

Areas covered: This review includes WIPO-listed patents reporting small molecules and peptide-based inhibitors of type II transmembrane serine proteases of the respiratory tract.

EXPERT OPINION

Expert opinion: Several TTSPs of the respiratory tract represent attractive pharmacological targets in the treatment of respiratory infectious diseases (notably COVID-19 and influenza), but also against idiopathic pulmonary fibrosis and lung cancer. The current emphasis is primarily on TMPRSS2, matriptase, and hepsin, yet other TTSPs await validation. Compounds listed herein are predominantly peptidomimetic inhibitors, some with covalent reversible mechanisms of action and high potencies. Their selectivity profile, however, are often only partially characterized. Preclinical data are promising and warrant further advancement in the above diseases.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

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

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

Perimitochondrial Enzymatic Self-Assembly for Selective Targeting the Mitochondria of Cancer Cells

Emerging evidence indicates that mitochondria contribute to drug resistance in cancer, but how to selectively target the mitochondria of cancer cells remains less explored. Here, we show perimitochondrial enzymatic self-assembly for selectively targeting the mitochondria of liver cancer cells. Nanoparticles of a peptide-lipid conjugate, being a substrate of enterokinase (ENTK), encapsulate chloramphenicol (CLRP), a clinically used antibiotic that is deactivated by glucuronidases in cytosol but not in mitochondria. Perimitochondrial ENTK cleaves the Flag-tag on the conjugate to deliver CLRP selectively into the mitochondria of cancer cells, thus inhibiting the mitochondrial protein synthesis, inducing the release of cytochrome c into the cytosol and resulting in cancer cell death. This strategy selectively targets liver cancer cells over normal liver cells. Moreover, blocking the mitochondrial protein synthesis sensitizes the cancer cells, relying on glycolysis and/or OXPHOS, to cisplatin. This work illustrates a facile approach, selectively targeting mitochondria of cancer cells and repurposing clinically approved ribosome inhibitors, to interrupt the metabolism of cancer cells for cancer treatment.

LncRNA TRPC7-AS1 regulates nucleus pulposus cellular senescence and ECM synthesis via competing with HPN for miR-4769-5p binding

Intervertebral disc (IVD) degeneration (IDD) is identified as an abnormal, cell-mediated, age-dependent and genetics-dependent molecular degeneration process in which NPCs (nucleus pulposus cells) senesce and the balance of ECM (extracellular matrix) synthesis and catabolism is disrupted. Increasing evidence reveals that IDD can be modulated by genetic factors, including non-coding RNAs. In the present study, we downloaded non-coding RNA profiling (GSE56081 and GSE63492) and performed GO annotation and enrichment analysis and association analyses on differentially-expressed genes. LncRNA TRPC7-AS1, miR-4769-5p, and Hepsin (HPN) may form a lncRNA-miRNA-mRNA network that can regulate NPC proliferation, senescence and ECM in IDD. LncRNA TRPC7-AS1 directly targets miR-4769-5p while miR-4769-5p directly targets HPN 3'UTR. miR-4769-5p overexpression inhibited HPN expression, suppressed NPC senescence, promoted NPC viability, and promoted ECM synthesis. The effect of TRPC7-AS1 silence on NPCs was similar as miR-4769-5p overexpression while the effect of HPN overexpression was opposite to miR-4769-5p overexpression. miR-4769-5p suppression or HPN overexpression could significantly attenuate the effect of TRPC7-AS1 silence. LncRNA TRPC7-AS1 relieves miR-4769-5p-induced inhibition on HPN via acting as a ceRNA, thus regulating NPC viability, senescence, and ECM synthesis. In summary, we regard lncRNA-miRNA-mRNA modulation as a new potent target for IDD treatment.

TMPRSS2 and TMPRSS4 promote SARS-CoV-2 infection of human small intestinal enterocytes

Gastrointestinal symptoms and fecal shedding of SARS-CoV-2 RNA are frequently observed in COVID-19 patients. However, it is unclear whether SARS-CoV-2 replicates in the human intestine and contributes to possible fecal-oral transmission. Here, we report productive infection of SARS-CoV-2 in ACE2⁺ mature enterocytes in human small intestinal enteroids. Expression of two mucosa-specific serine proteases, TMPRSS2 and TMPRSS4, facilitated SARS-CoV-2 spike fusogenic activity and promoted virus entry into host cells. We also demonstrate that viruses released into the intestinal lumen were inactivated by simulated human colonic fluid, and infectious virus was not recovered from the stool specimens of COVID-19 patients. Our results highlight the intestine as a potential site of SARS-CoV-2 replication, which may contribute to local and systemic illness and overall disease progression.

TMPRSS2 and TMPRSS4 promote SARS-CoV-2 infection of human small intestinal enterocytes

Gastrointestinal symptoms and fecal shedding of SARS-CoV-2 RNA are frequently observed in COVID-19 patients. However, it is unclear whether SARS-CoV-2 replicates in the human intestine and contributes to possible fecal-oral transmission. Here, we report productive infection of SARS-CoV-2 in ACE2+ mature enterocytes in human small intestinal enteroids. Expression of two mucosa-specific serine proteases, TMPRSS2 and TMPRSS4, facilitated SARS-CoV-2 spike fusogenic activity and promoted virus entry into host cells. We also demonstrate that viruses released into the intestinal lumen were inactivated by simulated human colonic fluid, and infectious virus was not recovered from the stool specimens of COVID-19 patients. Our results highlight the intestine as a potential site of SARS-CoV-2 replication, which may contribute to local and systemic illness and overall disease progression.

An investigation of the relationship between TMPRSS6 gene expression, genetic variants and clinical findings in breast cancer

Breast cancer is one of the most common types of cancer among women worldwide. The TMPRSS6 (Transmembrane Serine Protease 6) gene encodes matriptase-2, which plays an important role in iron hemostasis as the hepcidin regulator and may play a role in breast cancer susceptibility. In this study, we examined the expression levels of the TMPRSS6 gene in healthy tissues and tumor tissues of breast cancer patients; and the relationship between these levels and pathological findings. The relationship between TMPRSS6 polymorphisms (rs733655, rs5756506, rs2413450, rs855791, rs2235324, rs4820268) and patients' hematological parameters. The gene expression study encompassed 47 breast cancer patients and the gene polymorphism study consisted of 181 breast cancer patients and 100 healthy controls. Gene expression analysis was performed by qRT-PCR. The genotyping of TMPRSS6 polymorphisms was performed by RT-PCR. TMPRSS6 gene expression levels in tumor tissues were found to be 1.88 times higher than the expression levels in the control tissues. We examined the relationship between TMPRSS6 gene expression levels and pathological data, statistically significant relationship was found between patient's estrogen receptor (ER) and HER2 findings and TMPRSS6 gene expression (respectively p = 0.02, p = 0.002). When the relationship between TMPRSS6 gene polymorphisms related genotypes distributions and hematological findings was investigated, a significant relationship was identified between mean corpuscular hemoglobin concentration (MCHC) parameter and the polymorphism of only the rs733655. According to our findings, the increase in TMPRSS6 gene expression in cancerous tissues shows that matriptase-2 may be effective in the cancer process. Thus TMPRSS6 gene polymorphisms may affect the disease process by affecting the blood parameters of patients.

Glycan-Dependent and -Independent Dual Recognition between DC-SIGN and Type II Serine Protease MSPL/TMPRSS13 in Colorectal Cancer Cells

A class of glycoproteins such as carcinoembryonic antigen (CEA)/CEA-related cell adhesion molecule 1(CEACAM1), CD26 (DPPIV), and mac-2 binding protein (Mac-2BP) harbor tumor-associated glycans in colorectal cancer. In this study, we identified type II transmembrane mosaic serine protease large-form (MSPL) and its splice variant transmembrane protease serine 13 (TMPRSS13) as ligands of Dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) on the colorectal cancer cells. DC-SIGN is a C-type lectin expressed on dendritic cells, serves as a pattern recognition receptor for numerous pathogens such as human immunodeficiency virus (HIV) and M. tuberculosis. DC-SIGN recognizes these glycoproteins in a Ca2+ dependent manner. Meanwhile, we found that MSPL proteolytically cleaves DC-SIGN in addition to the above glycan-mediated recognition. DC-SIGN was degraded more efficiently by MSPL when treated with ethylenediaminetetraacetic acid (EDTA), suggesting that glycan-dependent interaction of the two molecules partially blocked DC-SIGN degradation. Our findings uncovered a dual recognition system between DC-SIGN and MSPL/TMPRSS13, providing new insight into the mechanism underlying colorectal tumor microenvironment.

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.

Specifically targeting cancer proliferation and metastasis processes: the development of matriptase inhibitors

Matriptase is a type II transmembrane serine protease, which has been suggested to play critical roles in numerous pathways of biological developments. Matriptase is the activator of several oncogenic proteins, including urokinase-type plasminogen activator (uPA), hepatocyte growth factor (HGF) and protease-activated receptor 2 (PAR-2). The activations of these matriptase substrates subsequently lead to the generation of plasmin, matrix metalloproteases (MMPs), and the triggers for many other signaling pathways related to cancer proliferation and metastasis. Accordingly, matriptase is considered an emerging target for the treatments of cancer. Thus far, inhibitors of matriptase have been developed as potential anti-cancer agents, which include small-molecule inhibitors, peptide-based inhibitors, and monoclonal antibodies. This review covers established literature to summarize the chemical and biochemical aspects, especially the inhibitory mechanisms and structure-activity relationships (SARs) of matriptase inhibitors with the goal of proposing the strategies for their future developments in anti-cancer therapy.

Iterative, multiplexed CRISPR-mediated gene editing for functional analysis of complex protease gene clusters

Elucidation of gene function by reverse genetics in animal models frequently is complicated by the functional redundancy of homologous genes. This obstacle often is compounded by the tight clustering of homologous genes, which precludes the generation of multigene-deficient animals through standard interbreeding of single-deficient animals. Here, we describe an iterative, multiplexed CRISPR-based approach for simultaneous gene editing in the complex seven-member human airway trypsin-like protease/differentially expressed in a squamous cell carcinoma (HAT/DESC) cluster of membrane-anchored serine proteases. Through four cycles of targeting, we generated a library of 18 unique congenic mouse strains lacking combinations of HAT/DESC proteases, including a mouse strain deficient in all seven proteases. Using this library, we demonstrate that HAT/DESC proteases are dispensable for term development, postnatal health, and fertility and that the recently described function of the HAT-like 4 protease in epidermal barrier formation is unique among all HAT/DESC proteases. The study demonstrates the potential of iterative, multiplexed CRISPR-mediated gene editing for functional analysis of multigene clusters, and it provides a large array of new congenic mouse strains for the study of HAT/DESC proteases in physiological and in pathophysiological processes.

A2A Receptor Homodimer-Disrupting Sequence Efficiently Delivered by a Protease-Resistant, Cyclic CPP Vector

G-protein-coupled receptors associate into dimers/oligomers whose function is not well understood. One approach to investigate this issue is to challenge oligomerization by peptides replicating transmembrane domains and to study their effect on receptor functionality. The disruptor peptides are typically delivered by means of cell-penetrating vectors such as the human immunodeficiency virus (HIV) transcription trans-activation protein Tat. In this paper we report a cyclic, Tat-like peptide that significantly improves its linear analogue in targeting interreceptor sequences in the transmembrane space. The same cyclic Tat-like vector fused to a transmembrane region not involved in receptor oligomerization was totally ineffective. Besides higher efficacy, the cyclic version has enhanced proteolytic stability, as shown by trypsin digestion experiments.

Promoter Hypomethylation Is Responsible for Upregulated Expression of HAI-1 in Hepatocellular Carcinoma

An upregulated expression of hepatocyte growth factor activator inhibitor type 1 (HAI-1) in hepatocellular carcinomas (HCC) associates with poor prognosis, but the underlying mechanism for expression regulation has not been elucidated. HAI-1 was expressed in HCC cell line Hep3B cells at a high level but absent or has a low level in other HCC cell lines HepG2 and SMMC7721 and immortal normal liver cell line L02 at transcriptional and translational levels, respectively. A dual-luciferase reporter assay showed that transcriptional activity of HAI-1 in the promoter region (-452 bp to -280 bp from the mRNA start site) was strongly enhanced in Hep3B and SMMC7721. Bisulfite genomic sequencing results of the HAI-1 promoter region showed an inverse correlation between levels of promoter methylation and expression in HCC cells. The expression level of HAI-1 in SMMC7721, HepG2, and L02 cells was elevated after 5-Aza-2′-deoxycytidine treatment. Hypomethylation of the HAI-1 promoter region contributed to the elevated HAI-1 expression in HCC tissues. In addition, the hypomethylation of the HAI-1 promoter region correlated with poor differentiation status of HCC tissues. Our findings indicate that promoter hypomethylation is an important mechanism for aberrant HAI-1 expression regulation in HCC.

Excess hepsin proteolytic activity limits oncogenic signaling and induces ER stress and autophagy in prostate cancer cells

The serine protease hepsin is frequently overexpressed in human prostate cancer (PCa) and is associated with matrix degradation and PCa progression in mice. Curiously, low expression of hepsin is associated with poor survival in different cancer types, and transgenic overexpression of hepsin leads to loss of viability in various cancer cell lines. Here, by comparing isogenic transfectants of the PCa cell line PC-3 providing inducible overexpression of wild-type hepsin (HPN) vs. the protease-deficient mutant HPN^S353A, we were able to attribute hepsin-mediated tumor-adverse effects to its excess proteolytic activity. A stem-like expression signature of surface markers and adhesion molecules, Notch intracellular domain release, and increased pericellular protease activity were associated with low expression levels of wild-type hepsin, but were partially lost in response to overexpression. Instead, overexpression of wild-type hepsin, but not of HPN^S353A, induced relocalization of the protein to the cytoplasm, and increased autophagic flux in vitro as well as LC3B punctae frequency in tumor xenografts. Confocal microscopy revealed colocalization of wild-type hepsin with both LC3B punctae as well as with the autophagy cargo receptor p62/SQSTM1. Overexpression of wild type, but not protease-deficient hepsin induced expression and nuclear presence of CHOP, indicating activation of the unfolded protein response and ER-associated protein degradation (ERAD). Whereas inhibitors of ER stress and secretory protein trafficking slightly increased viability, combined inhibition of the ubiquitin-proteasome degradation pathway (by bortezomib) with either ER stress (by salubrinal) or autophagy (by bafilomycin A1) revealed a significant decrease of viability during overexpression of wild-type hepsin in PC-3 cells. Our results demonstrate that a precise control of Hepsin proteolytic activity is critical for PCa cell fate and suggest, that the interference with ERAD could be a promising therapeutic option, leading to induction of proteotoxicity in hepsin-overexpressing tumors.

Anti-cancer activity of the novel 2-hydroxydiarylamide derivatives IMD-0354 and KRT1853 through suppression of cancer cell invasion, proliferation, and survival mediated by TMPRSS4

Elevated expression of transmembrane serine protease 4 (TMPRSS4) correlates with poor prognosis in non-small cell lung cancer, gastric cancer, colorectal cancer, prostate cancer, and other cancer patients. Previously, we demonstrated that TMPRSS4 mediates tumor cell invasion, migration, proliferation, and metastasis. In addition, we reported novel 2-hydroxydiarylamide derivatives, IMD-0354 and KRT1853, as TMPRSS4 serine protease inhibitors. Here, we further evaluated the effects of the representative derivatives on TMPRSS4-mediated cellular function and signaling. IMD-0354 and KRT1853 inhibited cancer cell invasion, migration, and proliferation in TMPRSS4-expressing prostate, colon, and lung cancer cells. Both compounds suppressed TMPRSS4-mediated induction of Sp1/3, AP-1, and NF-κB transcription factors. Furthermore, TMPRSS4 promoted cancer cell survival and drug resistance, and both compounds enhanced anoikis sensitivity as well as reduced bcl-2 and survivin levels. Importantly, KRT1853 efficiently reduced tumor growth in prostate and colon cancer xenograft models. These results strongly recommend KRT1853 for further development as a novel anti-cancer agent.

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.

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.

Knockdown of TMPRSS3 inhibits gastric cancer cell proliferation, invasion and EMT via regulation of the ERK1/2 and PI3K/Akt pathways

The transmembrane protease, serine 3 (TMPRSS3), a member of the type II transmembrane serine protease family, plays an important role in mediating tissue development, homeostasis and various biological processes. Recently, TMPRSS3 has been reported to be involved in cancer progression. However, the role of TMPRSS3 in gastric cancer (GC) remains largely unknown. In this study, we found that TMPRSS3 was highly expressed in GC tissues and cell lines. Knockdown of TMPRSS3 inhibited GC cell proliferation, invasion and epithelial-mesenchymal transition (EMT) in vitro as well as suppressed GC cell growth and dissemination in vivo. These inhibitory effects were mediated by regulation of the ERK1/2 signaling pathway. Moreover, TMPRSS3-mediated ERK1/2 activation was dependent on the PI3K/Akt pathway. In conclusion, TMPRSS3 contributed to GC progression via activation of the PI3K/Akt/ERK signaling pathway and might act as a therapeutic target for GC treatment.

The epithelial sodium channel (ENaC) as a therapeutic target for cystic fibrosis lung disease

INTRODUCTION

Cystic fibrosis is an autosomal recessive disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that codes for the CFTR anion channel. In the absence of functional CFTR, the epithelial Na⁺ channel is also dysregulated. Airway surface liquid (ASL) hydration is maintained by a balance between epithelial sodium channel (ENaC)-led Na⁺ absorption and CFTR-dependent anion secretion. This finely tuned homeostatic mechanism is required to maintain sufficient airway hydration to permit the efficient mucus clearance necessary for a sterile lung environment. In CF airways, the lack of CFTR and increased ENaC activity lead to ASL/mucus dehydration that causes mucus obstruction, neutrophilic infiltration, and chronic bacterial infection. Rehydration of ASL/mucus in CF airways can be achieved by inhibiting Na⁺ absorption with pharmacological inhibitors of ENaC. Areas covered: In this review, we discuss ENaC structure and function and its role in CF lung disease and focus on ENaC inhibition as a potential therapeutic target to rehydrate CF mucus. We also discuss the failure of the first generation of pharmacological inhibitors of ENaC and recent alternate strategies to attenuate ENaC activity in the CF lung. Expert opinion: ENaC is an attractive therapeutic target to rehydrate CF ASL that may serve as a monotherapy or function in parallel with other treatments. Given the increased number of strategies being employed to inhibit ENaC, this is an exciting and optimistic time to be in this field.

Irreversible modifications of receptor tyrosine kinases

Each group of the 56 receptor tyrosine kinases (RTK) binds with one or more soluble growth factors and coordinates a vast array of cellular functions. These outcomes are tightly regulated by inducible post-translational events, such as tyrosine phosphorylation, ubiquitination, ectodomain shedding, and regulated intramembrane proteolysis. Because of the delicate balance required for appropriate RTK function, cells may become pathogenic upon dysregulation of RTKs themselves or their post-translational covalent modifications. For example, reduced ectodomain shedding and decreased ubiquitination of the cytoplasmic region, both of which enhance growth factor signals, characterize malignant cells. Whereas receptor phosphorylation and ubiquitination are reversible, proteolytic cleavage events are irreversible, and either modification might alter the subcellular localization of RTKs. Herein, we focus on ectodomain shedding by metalloproteinases (including ADAM family proteases), cleavage within the membrane or cytoplasmic regions of RTKs (by gamma-secretases and caspases, respectively), and complete receptor proteolysis in lysosomes and proteasomes. Roles of irreversible modifications in RTK signaling, pathogenesis, and pharmacology are highlighted.

The Role of Hepsin in Endometrial Carcinoma

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

The impaired proteases and anti-proteases balance in Idiopathic Pulmonary Fibrosis

Idiopathic Pulmonary Fibrosis (IPF) is a devastating chronic, progressive and irreversible disease that remains refractory to current therapies. Matrix metalloproteinases (MMPs) and their inhibitors, tissue inhibitors of MMPs (TIMPs), have been implicated in the development of pulmonary fibrosis since decades. Coagulation signalling deregulation, which influences several key inflammatory and fibro-proliferative responses, is also essential in IPF pathogenesis, and a growing body of evidence indicates that Protease-Activated Receptors (PARs) inhibition in IPF may be promising for future evaluation. Therefore, proteases and anti-proteases aroused great biomedical interest over the past years, owing to the identification of their potential roles in lung fibrosis. During these last decades, numerous other proteases and anti-proteases have been studied in lung fibrosis, such as matriptase, Human airway trypsin-like protease (HAT), Hepatocyte growth factor activator (HGFA)/HGFA activator inhibitor (HAI) system, Plasminogen activator inhibitor (PAI)-1, Protease nexine (PN)-1, cathepsins, calpains, and cystatin C. Herein, we provide a general overview of the proteases and anti-proteases unbalance during lung fibrogenesis and explore potential therapeutics for IPF.

TMPRSS4 induces invasion and proliferation of prostate cancer cells through induction of Slug and cyclin D1

TMPRSS4 is a novel type II transmembrane serine protease found at the cell surface that is highly expressed in pancreatic, colon, and other cancer tissues. Previously, we demonstrated that TMPRSS4 mediates tumor cell invasion, migration, and metastasis. We also found that TMPRSS4 activates the transcription factor activating protein-1 (AP-1) to induce cancer cell invasion. Here, we explored TMPRSS4-mediated cellular functions and the underlying mechanisms. TMPRSS4 induced Slug, an epithelial-mesenchymal transition (EMT)-inducing transcription factor, and cyclin D1 through activation of AP-1, composed of c-Jun and activating transcription factor (ATF)-2, which resulted in enhanced invasion and proliferation of PC3 prostate cancer cells. In PC3 cells, not only c-Jun but also Slug was required for TMPRSS4-mediated proliferation and invasion. Interestingly, Slug induced phosphorylation of c-Jun and ATF-2 to activate AP-1 through upregulation of Axl, establishing a positive feedback loop between Slug and AP-1, and thus induced cyclin D1, leading to enhanced proliferation. Using data from The Cancer Genome Atlas, we found that Slug expression positively correlated with that of c-Jun and cyclin D1 in human prostate cancers. Expression of Slug was positively correlated with that of cyclin D1 in various cancer cell lines, whereas expression of other EMT-inducing transcription factors was not. This study demonstrates that TMPRSS4 modulates both invasion and proliferation via Slug and cyclin D1, which is a previously unrecognized pathway that may regulate metastasis and cancer progression.

Priming Time: How Cellular Proteases Arm Coronavirus Spike Proteins

Coronaviruses are enveloped RNA viruses that infect mammals and birds. Infection of humans with globally circulating human coronaviruses is associated with the common cold. In contrast, transmission of animal coronaviruses to humans can result in severe disease: The severe acute respiratory syndrome (SARS) and the Middle East respiratory syndrome (MERS) are responsible for hundreds of deaths in Asia and the Middle East, respectively, and are both caused by members of the genus Betacoronavirus, SARS-CoV, and MERS-CoV that were zoonotically transmitted from an animal host to humans. At present, neither vaccines nor specific treatment is available to combat coronavirus infection in humans, and novel antiviral strategies are urgently sought. The viral spike protein (S) mediates the first essential step in coronavirus infection, viral entry into target cells. For this, the S protein critically depends on priming by host cell proteases, and the responsible enzymes are potential targets for antiviral intervention. Recent studies revealed that the endosomal cysteine protease cathepsin L and the serine proteases furin and TMPRSS2 prime the S proteins of SARS-CoV and MERS-CoV and provided evidence that successive S protein cleavage at two sites is required for S protein priming. Moreover, mechanisms that control protease choice were unraveled, and insights were obtained into which enzyme promotes viral spread in the host. Here, we will provide basic information on S protein function and proteolytic priming, and we will then discuss recent progress in our understanding of the priming of the S proteins of SARS-CoV and MERS-CoV.

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

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

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.