Phorbol ester activation of a proteolytic cascade capable of activating latent transforming growth factor-betaL a process initiated by the exocytosis of cathepsin B

Human cystatin C in fibrotic diseases

Human cystatin C (hCC), which has a pervasive distribution within body fluids and is ubiquitously expressed by numerous cells and tissues, is a highly potent extracellular inhibitor of cysteine proteases. Besides measurement of serum creatinine, which is the most widely used technique for appraising glomerular filtration rate (GFR), hCC has emerged as a relevant GFR biomarker, because its quantification in serum is less sensitive to interferences with factors such as age, muscle mass or diet. Moreover, there are growing body of evidence that hCC overexpression and/or oversecretion, which is primarily driven by TGF-β1, occur during fibrogenesis (cardiac, liver, oral, and lung fibrosis). Even though molecular mechanisms and signaling pathways governing the regulation of hCC remain to be deciphered more acutely, current data sustain that hCC expression relates to myofibrogenesis and that hCC could be a specific and valuable biomarker of fibrotic disease.

Lysosomes in Cancer-At the Crossroad of Good and Evil

Although it has been known for decades that lysosomes are central for degradation and recycling in the cell, their pivotal role as nutrient sensing signaling hubs has recently become of central interest. Since lysosomes are highly dynamic and in constant change regarding content and intracellular position, fusion/fission events allow communication between organelles in the cell, as well as cell-to-cell communication via exocytosis of lysosomal content and release of extracellular vesicles. Lysosomes also mediate different forms of regulated cell death by permeabilization of the lysosomal membrane and release of their content to the cytosol. In cancer cells, lysosomal biogenesis and autophagy are increased to support the increased metabolism and allow growth even under nutrient- and oxygen-poor conditions. Tumor cells also induce exocytosis of lysosomal content to the extracellular space to promote invasion and metastasis. However, due to the enhanced lysosomal function, cancer cells are often more susceptible to lysosomal membrane permeabilization, providing an alternative strategy to induce cell death. This review summarizes the current knowledge of cancer-associated alterations in lysosomal structure and function and illustrates how lysosomal exocytosis and release of extracellular vesicles affect disease progression. We focus on functional differences depending on lysosomal localization and the regulation of intracellular transport, and lastly provide insight how new therapeutic strategies can exploit the power of the lysosome and improve cancer treatment.

TGF-β as a therapeutic target in the infarcted and failing heart: cellular mechanisms, challenges, and opportunities

INTRODUCTION

Myocardial fibrosis accompanies most cardiac conditions and can be reparative or maladaptive. Transforming Growth Factor (TGF)-β is a potent fibrogenic mediator, involved in repair, remodeling, and fibrosis of the injured heart.

AREAS COVERED

This review manuscript discusses the role of TGF-β in heart failure focusing on cellular mechanisms and therapeutic implications. TGF-β is activated in infarcted, remodeling and failing hearts. In addition to its fibrogenic actions, TGF-β has a broad range of effects on cardiomyocytes, immune, and vascular cells that may have both protective and detrimental consequences. TGF-β-mediated effects on macrophages promote anti-inflammatory transition, whereas actions on fibroblasts mediate reparative scar formation and effects on pericytes are involved in maturation of infarct neovessels. On the other hand, TGF-β actions on cardiomyocytes promote adverse remodeling, and prolonged activation of TGF-β signaling in fibroblasts stimulates progression of fibrosis and heart failure.

EXPERT OPINION

Understanding of the cell-specific actions of TGF-β is necessary to design therapeutic strategies in patients with myocardial disease. Moreover, to implement therapeutic interventions in the heterogeneous population of heart failure patients, mechanism-driven classification of both HFrEF and HFpEF patients is needed. Heart failure patients with prolonged or overactive fibrogenic TGF-β responses may benefit from cautious TGF-β inhibition.

B cell peripheral tolerance is promoted by cathepsin B protease

B cells that bind soluble autoantigens receive chronic signaling via the B cell receptor (signal-1) in the absence of strong costimulatory signals (signal-2), and this leads to their elimination in peripheral tissues. The factors determining the extent of soluble autoantigen-binding B cell elimination are not fully understood. Here we demonstrate that the elimination of B cells chronically exposed to signal-1 is promoted by cathepsin B (Ctsb). Using hen egg lysozyme-specific (HEL-specific) immunoglobulin transgenic (MD4) B cells and mice harboring circulating HEL, we found improved survival and increased proliferation of HEL-binding B cells in Ctsb-deficient mice. Bone marrow chimera experiments established that both hematopoietic and nonhematopoietic sources of Ctsb were sufficient to promote peripheral B cell deletion. The depletion of CD4+ T cells overcame the survival and growth advantage provided by Ctsb deficiency, as did blocking CD40L or removing CD40 from the chronically antigen-engaged B cells. Thus, we suggest that Ctsb acts extracellularly to reduce soluble autoantigen-binding B cell survival and that its actions restrain CD40L-dependent pro-survival effects. These findings identify a role for cell-extrinsic protease activity in establishing a peripheral self-tolerance checkpoint.

Cysteine cathepsins: A long and winding road towards clinics

Biomedical research often focuses on properties that differentiate between diseased and healthy tissue; one of the current focuses is elevated expression and altered localisation of proteases. Among these proteases, dysregulation of cysteine cathepsins can frequently be observed in inflammation-associated diseases, which tips the functional balance from normal physiological to pathological manifestations. Their overexpression and secretion regularly exhibit a strong correlation with the development and progression of such diseases, making them attractive pharmacological targets. But beyond their mostly detrimental role in inflammation-associated diseases, cysteine cathepsins are physiologically highly important enzymes involved in various biological processes crucial for maintaining homeostasis and responding to different stimuli. Consequently, several challenges have emerged during the efforts made to translate basic research data into clinical applications. In this review, we present both physiological and pathological roles of cysteine cathepsins and discuss the clinical potential of cysteine cathepsin-targeting strategies for disease management and diagnosis.

Cathepsin B and Plasma Kallikrein Are Reliable Biomarkers to Discriminate Clinically Significant Hepatic Fibrosis in Patients with Chronic Hepatitis-C Infection

We aimed to determine the biomarker performance of the proteolytic enzymes cathepsin B (Cat B) and plasma kallikrein (PKa) and transforming growth factor (TGF)-β to detect hepatic fibrosis (HF) in chronic hepatitis C (CHC) patients. We studied 53 CHC patients and 71 healthy controls (HCs). Hepatic-disease stage was determined by liver biopsies, aminotransferase:platelet ratio index (APRI) and Fibrosis (FIB)4. Hepatic inflammation and HF in CHC patients were stratified using the METAVIR scoring system. Cat-B and PKa activities were monitored fluorometrically. Serum levels of TGF-β (total and its active form) were determined using ELISA-like fluorometric methods. Increased serum levels of Cat B and PKa were found (p < 0.0001) in CHC patients with clinically significant HF and hepatic inflammation compared with HCs. Levels of total TGF-β (p < 0.0001) and active TGF-β (p < 0.001) were increased in CHC patients compared with HCs. Cat-B levels correlated strongly with PKa levels (r = 0.903, p < 0.0001) in CHC patients but did not correlate in HCs. Levels of Cat B, PKa and active TGF-β increased with the METAVIR stage of HF. Based on analyses of receiver operating characteristic (ROC) curves, Cat B and PKa showed high diagnostic accuracy (area under ROC = 0.99 ± 0.02 and 0.991 ± 0.007, respectively) for distinguishing HF in CHC patients from HCs. Taken together, Cat B and PKa could be used as circulating biomarkers to detect HF in HCV-infected patients.

Bibliometric Analysis of Cathepsin B Research From 2011 to 2021

Cathepsin B (CTSB) is a lysosomal protease implicated in the progression of various diseases. A large number of CTSB-related studies have been conducted to date. However, there is no comprehensive bibliometric analysis on this subject. In our study, we performed quantitative analysis of CTSB-related publications retrieved from the Science Citation Index Expanded (SCIE) of the Web of Science Core Collection (reference period: 2011–2021). A total of 3,062 original articles and reviews were retrieved. The largest number of publications were from USA (n = 847, 27.66%). The research output of each country showed positive correlation with gross domestic product (GDP) (r = 0.9745, P < 0.0001). Active collaborations between countries/regions were also observed. Reinheckel T and Sloane BF were perhaps the most impactful researchers in the research landscape of CTSB. Plos ONE was the most prevalent (119/3,062, 3.89%) and cited journal (3,021 citations). Comprehensive analysis of the top citations, co-citations, and keywords was performed to acquire the theoretical basis and hotspots of CTSB-related research. The main topics included CTSB-related cancers and inflammatory diseases, CTSB-associated cell death pattern, and the applications of CTSB. These results provide comprehensive insights into the current status of global CTSB-related research especially in pancreas, which is worthy of continued follow-up by practitioners and clinicians in this field.

Potential drug discovery for COVID-19 treatment targeting Cathepsin L using a deep learning-based strategy

Cathepsin L (CTSL), a cysteine protease that can cleave and activate the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein, could be a promising therapeutic target for coronavirus disease 2019 (COVID-19). However, there is still no clinically available CTSL inhibitor that can be used. Here, we applied Chemprop, a newly trained directed-message passing deep neural network approach, to identify small molecules and FDA-approved drugs that can block CTSL activity to expand the discovery of CTSL inhibitors for drug development and repurposing for COVID-19. We found 5 molecules (Mg-132, Z-FA-FMK, leupeptin hemisulfate, Mg-101 and calpeptin) that were able to significantly inhibit the activity of CTSL in the nanomolar range and inhibit the infection of both pseudotype and live SARS-CoV-2. Notably, we discovered that daptomycin, an FDA-approved antibiotic, has a prominent CTSL inhibitory effect and can inhibit SARS-CoV-2 pseudovirus infection. Further, molecular docking calculation showed stable and robust binding of these compounds with CTSL. In conclusion, this study suggested for the first time that Chemprop is ideally suited to predict additional inhibitors of enzymes and revealed the noteworthy strategy for screening novel molecules and drugs for the treatment of COVID-19 and other diseases with unmet needs.

Transforming growth factor-β in myocardial disease

Transforming growth factor-β (TGFβ) isoforms are upregulated and activated in myocardial diseases and have an important role in cardiac repair and remodelling, regulating the phenotype and function of cardiomyocytes, fibroblasts, immune cells and vascular cells. Cardiac injury triggers the generation of bioactive TGFβ from latent stores, through mechanisms involving proteases, integrins and specialized extracellular matrix (ECM) proteins. Activated TGFβ signals through the SMAD intracellular effectors or through non-SMAD cascades. In the infarcted heart, the anti-inflammatory and fibroblast-activating actions of TGFβ have an important role in repair; however, excessive or prolonged TGFβ signalling accentuates adverse remodelling, contributing to cardiac dysfunction. Cardiac pressure overload also activates TGFβ cascades, which initially can have a protective role, promoting an ECM-preserving phenotype in fibroblasts and preventing the generation of injurious, pro-inflammatory ECM fragments. However, prolonged and overactive TGFβ signalling in pressure-overloaded cardiomyocytes and fibroblasts can promote cardiac fibrosis and dysfunction. In the atria, TGFβ-mediated fibrosis can contribute to the pathogenic substrate for atrial fibrillation. Overactive or dysregulated TGFβ responses have also been implicated in cardiac ageing and in the pathogenesis of diabetic, genetic and inflammatory cardiomyopathies. This Review summarizes the current evidence on the role of TGFβ signalling in myocardial diseases, focusing on cellular targets and molecular mechanisms, and discussing challenges and opportunities for therapeutic translation.

Cathepsin B is highly expressed in pancreatic cancer stem-like cells and is associated with patients' surgical outcomes

Cancer stem-like cells (CSLCs) in solid tumors are resistant to conventional chemotherapy and molecularly targeted therapy, which is thought to contribute to cancer recurrence and metastasis. The present study aimed to identify biomarkers for pancreatic CSLCs (P-CSLCs). Using our previously reported methods, P-CSLC-enriched populations were generated from pancreatic cancer cell lines. The protein expression profiles of these populations were compared with those of parental cells using two-dimensional electrophoresis, tandem mass spectrometry, flow cytometry and immunohistochemistry. Protein expression in surgical specimens was also evaluated for relationships with clinical outcomes. A lysosomal cysteine protease, cathepsin B (CTSB), was significantly upregulated in P-CSLCs compared with that in the parental cells, as shown using western blotting. Flow cytometry analysis also confirmed that CTSB was more highly expressed on the surface of P-CSLCs compared with that on parental cells. Moreover, PCLCs had elevated cellular secretions of CTSB compared with the parental cells. Finally, CTSB expression was evaluated in 69 resected tumor specimens, and high expression was associated with the patients' clinicopathological features and surgical outcomes. The present results suggested that CTSB is a biomarker for poor survival in patients with pancreatic cancer, which is possibly associated with P-CSLCs. This novel biomarker may also have potential as a therapeutic target.

Acidosis and proteolysis in the tumor microenvironment

The glycolytic phenotype of the Warburg effect is associated with acidification of the tumor microenvironment. In this review, we describe how acidification of the tumor microenvironment may increase the invasive and degradative phenotype of cancer cells. As a template of an extracellular acidic microenvironment that is linked to proteolysis, we use the resorptive pit formed between osteoclasts and bone. We describe similar changes that have been observed in cancer cells in response to an acidic microenvironment and that are associated with proteolysis and invasive and metastatic phenotypes. This includes consideration of changes observed in the intracellular trafficking of vesicles, i.e., lysosomes and exosomes, and in specialized regions of the membrane, i.e., invadopodia and caveolae. Cancer-associated cells are known to affect what is generally referred to as tumor proteolysis but little direct evidence for this being regulated by acidosis; we describe potential links that should be verified.

Cysteine Cathepsins in Tumor-Associated Immune Cells

Cysteine cathepsins are key regulators of the innate and adaptive arms of the immune system. Their expression, activity, and subcellular localization are associated with the distinct development and differentiation stages of immune cells. They promote the activation of innate myeloid immune cells since they contribute to toll-like receptor signaling and to cytokine secretion. Furthermore, they control lysosomal biogenesis and autophagic flux, thus affecting innate immune cell survival and polarization. They also regulate bidirectional communication between the cell exterior and the cytoskeleton, thus influencing cell interactions, morphology, and motility. Importantly, cysteine cathepsins contribute to the priming of adaptive immune cells by controlling antigen presentation and are involved in cytotoxic granule mediated killing in cytotoxic T lymphocytes and natural killer cells. Cathepins'aberrant activity can be prevented by their endogenous inhibitors, cystatins. However, dysregulated proteolysis contributes significantly to tumor progression also by modulation of the antitumor immune response. Especially tumor-associated myeloid cells, such as tumor-associated macrophages and myeloid-derived suppressor cells, which are known for their tumor promoting and immunosuppressive functions, constitute the major source of excessive cysteine cathepsin activity in cancer. Since they are enriched in the tumor microenvironment, cysteine cathepsins represent exciting targets for development of new diagnostic and therapeutic moieties.

Fordin: A novel type I ribosome inactivating protein from Vernicia fordii modulates multiple signaling cascades leading to anti-invasive and pro-apoptotic effects in cancer cells in vitro

Fordin, which is derived from Vernicia fordii, is a novel type I ribosome inactivating protein (RIP) with RNA N-glycosidase activity. In the present study, fordin was expressed by Escherichia coli and purified using nickel affinity chromatography. Previous studies have demonstrated RIP toxicity in a variety of cancer cell lines. To understand the therapeutic potential of fordin on tumors, the present study investigated the effects of fordin on the viability of several tumor and normal cell lines. The results demonstrated that fordin induced significant cytotoxicity in four cancer cell lines, compared with the normal cell line. Specifically, profound apoptosis and inhibition of cell invasion were observed following fordin exposure in U-2 OS and HepG2 cells; however, the molecular mechanism underlying the action of RIP remains to be fully elucidated. In the present study, it was found that the anticancer effects of fordin were associated with suppression of the nuclear factor (NF)-κB signaling pathway. In U-2 OS and HepG2 cells, fordin inhibited the expression of inhibitor of NF-κB (IκB) kinase, leading to downregulation of the phosphorylation level of IκB, which quelled the nuclear translocation of NF-κB. Fordin also reduced the mRNA and protein levels of NF-κB downstream targets associated with cell apoptosis and metastasis, particularly B-cell lymphoma-2-related protein A1 (Blf-1) and matrix metalloproteinase (MMP)-9. The inactivation of NF-κB and the reduction in the expression levels of Blf-1 and MMP-9 mediated by fordin were also confirmed by co-treatment with lipopolysaccharide or p65 small interfering RNA. These findings suggested a possible mechanism for the fordin-induced effect on tumor cell death and metastasis. The results of the present study demonstrated the multiple anticancer effects of fordin in U-2 OS and HepG2 cells, in part by inhibiting activation of the NF-κB signaling pathway.

Cathepsin K associates with lymph node metastasis and poor prognosis in oral squamous cell carcinoma

Background

Lymph node metastasis (LNM) is a major determinant of prognosis and treatment planning of oral squamous cell carcinoma (OSCC). Cysteine cathepsins constitute a family of proteolytic enzymes with known role in the degradation of the extracellular matrix. Involvement in pathological processes, such as inflammation and cancer progression, has been proved. The aim of the study was to discover the clinicopathological and prognostic implications of cathepsin K (CTSK) expression in oral squamous cell carcinoma.

Methods

Eighty-three patients with primary OSCC, treated surgically between 1996 and 2000, were included. Gene expression data were acquired from a previously reported study. Human papilloma virus (HPV) status was previously determined by an algorithm for HPV-16. CTSK Protein expression was semi-quantitatively determined by immunohistochemistry in tumor and stromal cells. Expression data were correlated with various clinicopathological variables.

Results

Elevated gene and protein expression of CTSK were strongly associated to LNM and perineural invasion (p < 0.01). Logistic regression analysis highlighted increased CTSK protein expression in tumor cells as the most significant independent factor of lymphatic metastasis (OR = 7.65, CI:2.31–23.31, p = 0.001). Survival analysis demonstrated CTSK protein expression in both stromal and tumor cells as significant indicators of poor 5-year disease specific survival (HR = 2.40, CI:1.05–5.50, p = 0.038 for stromal cells; HR = 2.79, CI:1.02–7.64, p = 0.045 for tumor cells).

Conclusion

Upregulation of CTSK seems to be associated with high incidence of lymphatic spread and poor survival in OSCC. CTSK could therefore serve as a predictive biomarker for OSCC.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4315-8) contains supplementary material, which is available to authorized users.

Cruzipain Activates Latent TGF-β from Host Cells during T. cruzi Invasion

Several studies indicate that the activity of cruzipain, the main lysosomal cysteine peptidase of Trypanosoma cruzi, contributes to parasite infectivity. In addition, the parasitic invasion process of mammalian host cells is described to be dependent on the activation of the host TGF-β signaling pathway by T. cruzi. Here, we tested the hypothesis that cruzipain could be an important activator of latent TGF-β and thereby trigger TGF-β-mediated events crucial for the development of Chagas disease. We found that live epimastigotes of T. cruzi, parasite lysates and purified cruzipain were able to activate latent TGF-β in vitro. This activation could be inhibited by the cysteine peptidase inhibitor Z-Phe-Ala-FMK. Moreover, transfected parasites overexpressing chagasin, a potent endogenous cruzipain inhibitor, prevented latent TGF-β activation. We also observed that T. cruzi invasion, as well as parasite intracellular growth, were inhibited by the administration of Z-Phe-Ala-FMK or anti-TGF-β neutralizing antibody to Vero cell cultures. We further demonstrated that addition of purified cruzipain enhanced the invasive activity of trypomastigotes and that this effect could be completely inhibited by addition of a neutralizing anti-TGF-β antibody. Taken together, these results demonstrate that the activities of cruzipain and TGF-β in the process of cell invasion are functionally linked. Our data suggest that cruzipain inhibition is an interesting chemotherapeutic approach for Chagas disease not only because of its trypanocidal activity, but also due to the inhibitory effect on TGF-β activation.

uPA/PAI system, cathepsin B and hepatocellular carcinoma

Urokinase-type plasminogen activator and plasminogen activator inhibitor (uPA/PAI) are a pair of proteolytic enzyme activator/activator inhibitor. Cathepsin B is a lysosomal cysteine protease. It has been proved that cathepsin B can activate uPA. uPA/PAI and cathepsin B are closely related to the invasion, migration and tumor angiogenesis of malignant neoplasms. The uPA/PAI system and cathepsin B play an important role in the occurrence and development of liver cancer.

Transforming growth factor β--at the centre of systemic sclerosis

Transforming growth factor β (TGF-β) has long been implicated in fibrotic diseases, including the multisystem fibrotic disease systemic sclerosis (SSc). Expression of TGF-β-regulated genes in fibrotic skin and lungs of patients with SSc correlates with disease activity, which points to this cytokine as the central mediator of pathogenesis. Patients with SSc often develop pulmonary arterial hypertension (PAH), a particularly lethal complication caused by vascular dysfunction. Several genetic diseases with vascular features related to SSc, such as familial PAH and hereditary haemorrhagic telangiectasia, are caused by mutations in the TGF-β-sensing ALK-1 signalling pathway. These observations suggest that increased TGF-β signalling causes both vascular and fibrotic features of SSc. The question of how latent TGF-β becomes activated in local SSc tissues is, therefore, central to the understanding of SSc. Both TGF-β1 and TGF-β3 can be activated by integrins αvβ6 and αvβ8, whose upregulation in bronchial epithelial cells can activate TGF-β in SSc lungs. Other αv integrins, thrombospondin-1 or altered TGF-β sequestration by matrix proteins might be important in other target tissues. How the immune system triggers this process remains unclear, although links between inflammation and TGF-β activation are emerging. Together, these observations provide an increasingly secure framework for understanding TGF-β in SSc pathogenesis.

Cathepsin B: multiple roles in cancer

Proteases, including intracellular proteases, play roles at many different stages of malignant progression. Our focus here is cathepsin B, a lysosomal cysteine cathepsin. High levels of cathepsin B are found in a wide variety of human cancers, levels that often induce secretion and association of cathepsin B with the tumor cell membrane. In experimental models, such as transgenic models of murine pancreatic and mammary carcinomas, causal roles for cathepsin B have been demonstrated in initiation, growth/tumor cell proliferation, angiogenesis, invasion, and metastasis. Tumor growth in transgenic models is promoted by cathepsin B in tumor-associated cells, for example, tumor-associated macrophages, as well as in tumor cells. In transgenic models, the absence of cathepsin B has been associated with enhanced apoptosis, yet cathepsin B also has been shown to contribute to apoptosis. Cathepsin B is part of a proteolytic pathway identified in xenograft models of human glioma; targeting only cathepsin B in these tumors is less effective than targeting cathepsin B in combination with other proteases or protease receptors. Understanding the mechanisms responsible for increased expression of cathepsin B in tumors and association of cathepsin B with tumor cell membranes is needed to determine whether targeting cathepsin B could be of therapeutic benefit.

Regulation of TGF-β1-driven differentiation of human lung fibroblasts: emerging roles of cathepsin B and cystatin C

Lung matrix homeostasis partly depends on the fine regulation of proteolytic activities. We examined the expression of human cysteine cathepsins (Cats) and their relative contribution to TGF-β1-induced fibroblast differentiation into myofibroblasts. Assays were conducted using both primary fibroblasts obtained from patients with idiopathic pulmonary fibrosis and human lung CCD-19Lu fibroblasts. Pharmacological inhibition and genetic silencing of Cat B diminished α-smooth muscle actin expression, delayed fibroblast differentiation, and led to an accumulation of intracellular 50-kDa TGF-β1. Moreover, the addition of Cat B generated a 25-kDa mature form of TGF-β1 in Cat B siRNA-pretreated lysates. Inhibition of Cat B decreased Smad 2/3 phosphorylation but had no effect on p38 MAPK and JNK phosphorylation, indicating that Cat B mostly disturbs TGF-β1-driven canonical Smad signaling pathway. Although mRNA expression of cystatin C was stable, its secretion, which was inhibited by brefeldin A, increased during TGF-β1-induced differentiation of idiopathic pulmonary fibrosis and CCD-19Lu fibroblasts. In addition, cystatin C participated in the control of extracellular Cats, because its gene silencing restored their proteolytic activities. These data support the notion that Cat B participates in lung myofibrogenesis as suggested for stellate cells during liver fibrosis. Moreover, we propose that TGF-β1 promotes fibrosis by driving the effective cystatin C-dependent inhibition of extracellular matrix-degrading Cats.

The effect of catalase on migration and invasion of lung cancer cells by regulating the activities of cathepsin S, L, and K

Abundant clinical evidences indicate that up-regulation of several cathepsins in many human cancers is correlated with malignant progression and poor patient prognosis. In addition, a decrease in catalase activity or accumulation of hydrogen peroxide correlates with cancer metastasis. Recent studies indicate that cathepsin activation and expression can be modulated via H2O2 treatment. However, the actual relationship between catalase and cathepsins is not yet fully understood. In the present study, we found that catalase expression (or activity) was higher, while intracellular and extracellular Cat S, Cat L, and Cat K activities were lower in the non-invasive CL1-0 cells compared to the highly invasive CL1-5 cells. After CL1-0 cells were transfected with catalase-shRNA, the corresponding ROS (H2O2) level and Cat S, Cat L, or Cat K expression (or activity) was up-regulated, accompanied by an increase in cell migration and invasion. On the other hand, ROS (H2O2) level, cathepsin S, L, and K activities, cell migration and invasion were decreased in catalase-overexpressed CL1-5 cells. It is suggested that catalase may regulate cathepsin activity by controlling the production of ROS (H2O2), leading to variation in migration and invasion ability of lung cancer cells.

TGF-β signaling, activated stromal fibroblasts, and cysteine cathepsins B and L drive the invasive growth of human melanoma cells

Accumulating evidence indicates that interactions between cancer cells and stromal cells are important for the development/progression of many cancers. Herein, we found that the invasive growth of melanoma cells in three-dimensional-Matrigel/collagen-I matrices is dramatically increased on their co-culture with embryonic or adult skin fibroblasts. Studies with fluorescent-labeled cells revealed that the melanoma cells first activate the fibroblasts, which then take the lead in invasion. To identify the physiologically relevant invasion-related proteases involved, we performed genome-wide microarray analyses of invasive human melanomas and benign nevi; we found up-regulation of cysteine cathepsins B and L, matrix metalloproteinase (MMP)-1 and -9, and urokinase- and tissue-type plasminogen activators. The mRNA levels of cathepsins B/L and plasminogen activators, but not MMPs, correlated with metastasis. The invasiveness/growth of the melanoma cells with fibroblasts was inhibited by cell membrane-permeable inhibitors of cathepsins B/L, but not by wide-spectrum inhibitors of MMPs. The IHC analysis of primary melanomas and benign nevi revealed cathepsin B to be predominantly expressed by melanoma cells and cathepsin L to be predominantly expressed by the tumor-associated fibroblasts surrounding the invading melanoma cells. Finally, cathepsin B regulated TGF-β production/signaling, which was required for the activation of fibroblasts and their promotion of the invasive growth of melanoma cells. These data provide a basis for testing inhibitors of TGF-β signaling and cathepsins B/L in the therapy of invasive/metastatic melanomas.

pH regulators in invadosomal functioning: proton delivery for matrix tasting

Invadosomes are actin-rich finger-like cellular structures sensing and interacting with the surrounding extracellular matrix (ECM) and involved in its proteolytic remodeling. Invadosomes are structures distinct from other adhesion complexes, and have been identified in normal cells that have to cross tissue barriers to fulfill their function such as leukocytes, osteoclasts and endothelial cells. They also represent features of highly aggressive cancer cells, allowing them to escape from the primary tumor, to invade surrounding tissues and to reach systemic circulation. They are localized to the ventral membrane of cells grown under 2-dimensional conditions and are supposed to be present all around cells grown in 3-dimensional matrices. Indeed invadosomes are key structures in physiological processes such as inflammation and the immune response, bone remodeling, tissue repair, but also in pathological conditions such as osteopetrosis and the development of metastases. Invadosomes are subdivided into podosomes, found in normal cells, and into invadopodia specific for cancer cells. While these two structures exhibit differences in organization, size, number and half-life, they share similarities in molecular composition, participation in cell-matrix adhesion and promoting matrix degradation. A key determinant in invadosomal function is the recruitment and release of proteases, such as matrix metalloproteinases (MMPs), serine proteases and cysteine cathepsins, together with their activation in a tightly controlled and highly acidic microenvironment. Therefore numerous pH regulators such as V-ATPases and Na(+)/H(+) exchangers, are found in invadosomes and are directly involved in their constitution as well as their functioning. This review focuses on the participation of pH regulators in invadosome function in physiological and pathological conditions, with a particular emphasis on ECM remodeling by osteoclasts during bone resorption and by cancer cells.

Live-cell imaging of tumor proteolysis: impact of cellular and non-cellular microenvironment

Our laboratory has had a longstanding interest in how the interactions between tumors and their microenvironment affect malignant progression. Recently, we have focused on defining the proteolytic pathways that function in the transition of breast cancer from the pre-invasive lesions of ductal carcinoma in situ (DCIS) to invasive ductal carcinomas (IDCs). We use live-cell imaging to visualize, localize and quantify proteolysis as it occurs in real-time and thereby have established roles for lysosomal cysteine proteases both pericellularly and intracellularly in tumor proteolysis. To facilitate these studies, we have developed and optimized 3D organotypic co-culture models that recapitulate the in vivo interactions of mammary epithelial cells or tumor cells with stromal and inflammatory cells. Here we will discuss the background that led to our present studies as well as the techniques and models that we employ. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Inhibition of cathepsin B activity attenuates extracellular matrix degradation and inflammatory breast cancer invasion

Introduction

Inflammatory breast cancer (IBC) is an aggressive, metastatic and highly angiogenic form of locally advanced breast cancer with a relatively poor three-year survival rate. Breast cancer invasion has been linked to proteolytic activity at the tumor cell surface. Here we explored a role for active cathepsin B on the cell surface in the invasiveness of IBC.

Methods

We examined expression of the cysteine protease cathepsin B and the serine protease urokinase plasminogen activator (uPA), its receptor uPAR and caveolin-1 in two IBC cell lines: SUM149 and SUM190. We utilized a live cell proteolysis assay to localize in real time the degradation of type IV collagen by IBC cells. IBC patient biopsies were examined for expression of cathepsin B and caveolin-1.

Results

Both cell lines expressed comparable levels of cathepsin B and uPA. In contrast, levels of caveolin-1 and uPAR were greater in SUM149 cells. We observed that uPA, uPAR and enzymatically active cathepsin B were colocalized in caveolae fractions isolated from SUM149 cells. Using a live-cell proteolysis assay, we demonstrated that both IBC cell lines degrade type IV collagen. The SUM149 cells exhibit predominantly pericellular proteolysis, consistent with localization of proteolytic pathway constitutents to caveolar membrane microdomains. A functional role for cathepsin B was confirmed by the ability of CA074, a cell impermeable and highly selective cathepsin B inhibitor, to significantly reduce pericellular proteolysis and invasion by SUM149 cells. A statistically significant co-expression of cathepsin B and caveolin-1 was found in IBC patient biopsies, thus validating our in vitro data.

Conclusion

Our study is the first to show that the proteolytic activity of cathepsin B and its co-expression with caveolin-1 contributes to the aggressiveness of IBC.

Cysteine cathepsins: from structure, function and regulation to new frontiers

It is more than 50 years since the lysosome was discovered. Since then its hydrolytic machinery, including proteases and other hydrolases, has been fairly well identified and characterized. Among these are the cysteine cathepsins, members of the family of papain-like cysteine proteases. They have unique reactive-site properties and an uneven tissue-specific expression pattern. In living organisms their activity is a delicate balance of expression, targeting, zymogen activation, inhibition by protein inhibitors and degradation. The specificity of their substrate binding sites, small-molecule inhibitor repertoire and crystal structures are providing new tools for research and development. Their unique reactive-site properties have made it possible to confine the targets simply by the use of appropriate reactive groups. The epoxysuccinyls still dominate the field, but now nitriles seem to be the most appropriate “warhead”. The view of cysteine cathepsins as lysosomal proteases is changing as there is now clear evidence of their localization in other cellular compartments. Besides being involved in protein turnover, they build an important part of the endosomal antigen presentation. Together with the growing number of non-endosomal roles of cysteine cathepsins is growing also the knowledge of their involvement in diseases such as cancer and rheumatoid arthritis, among others. Finally, cysteine cathepsins are important regulators and signaling molecules of an unimaginable number of biological processes. The current challenge is to identify their endogenous substrates, in order to gain an insight into the mechanisms of substrate degradation and processing. In this review, some of the remarkable advances that have taken place in the past decade are presented. This article is part of a Special Issue entitled: Proteolysis 50 years after the discovery of lysosome.

Cathepsin B and cystatin C play an inflammatory role in gouty arthritis of the knee

BACKGROUND

To relate the expression of the matrix degrading proteinase cathepsin B and its endogenous inhibitor cystatin C in the synovial fluid (SF) to the clinical and laboratory variables of joint inflammation in gouty arthritis of the knee.

METHODS

Thirty-nine SF samples were obtained from inflamed knees of patients with acute gout. The levels of cathepsin B, cystatin C, urokinase-type plasminogen activator (uPA), soluble uPA receptor (suPAR) and PA inhibitor type-1 (PAI-1), activities of matrix metalloproteinase-2 (MMP-2) and MMP-9, and cell counts as well as local arthritis activity scores (LAS) were examined.

RESULTS

The increases of cathepsin B levels correlated with increased leukocyte and neutrophil counts, latent MMP-9 (pro-MMP-9) activities, uPA, suPAR and PAI-1 levels, and uPA/PAI-1 ratios. Increased cystatin C levels corresponded closely with increased LAS, leukocyte and neutrophil counts, pro-MMP-9 activities, uPA, suPAR and PAI-1 levels, and uPA/PAI-1 ratios. Moreover, there was a correlation between cathepsin B and cystatin C levels.

CONCLUSIONS

These results show a high correlation between the cathepsin B/cystatin C system and markers of joint inflammation in acute gout of the knee, demonstrating the pathologic role of cathepsin B and cystatin C in inflammation.

Cathepsin B is the driving force of esophageal cell invasion in a fibroblast-dependent manner

Esophageal cancer, which frequently exhibits coordinated loss of E-cadherin (Ecad) and transforming growth factor beta (TGFbeta) receptor II (TbetaRII), has a high mortality rate. In a three-dimensional organotypic culture model system, esophageal keratinocytes expressing dominant-negative mutant versions of both Ecad and TbetaRII (ECdnT) invade into the underlying matrix embedded with fibroblasts. We also find that cathepsin B induction is necessary for fibroblast-mediated invasion. Furthermore, the ECdnT cells in this physiological context activate fibroblasts through the secretion of TGFbeta1, which, in turn, is activated by cathepsin B. These results suggest that the interplay between the epithelial compartment and the surrounding microenvironment is crucial to invasion into the extracellular matrix.

A dyad of lymphoblastic lysosomal cysteine proteases degrades the antileukemic drug L-asparaginase

l-Asparaginase is a key therapeutic agent for treatment of childhood acute lymphoblastic leukemia (ALL). There is wide individual variation in pharmacokinetics, and little is known about its metabolism. The mechanisms of therapeutic failure with l-asparaginase remain speculative. Here, we now report that 2 lysosomal cysteine proteases present in lymphoblasts are able to degrade l-asparaginase. Cathepsin B (CTSB), which is produced constitutively by normal and leukemic cells, degraded asparaginase produced by Escherichia coli (ASNase) and Erwinia chrysanthemi. Asparaginyl endopeptidase (AEP), which is overexpressed predominantly in high-risk subsets of ALL, specifically degraded ASNase. AEP thereby destroys ASNase activity and may also potentiate antigen processing, leading to allergic reactions. Using AEP-mediated cleavage sequences, we modeled the effects of the protease on ASNase and created a number of recombinant ASNase products. The N24 residue on the flexible active loop was identified as the primary AEP cleavage site. Sole modification at this site rendered ASNase resistant to AEP cleavage and suggested a key role for the flexible active loop in determining ASNase activity. We therefore propose what we believe to be a novel mechanism of drug resistance to ASNase. Our results may help to identify alternative therapeutic strategies with the potential of further improving outcome in childhood ALL.

The chemotherapeutic agents XK469 (2-{4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy}propionic acid) and SH80 (2-{4-[(7-bromo-2-quinolinyl)oxy]phenoxy}propionic acid) inhibit cytokinesis and promote polyploidy and induce senescence

The therapeutic usefulness of the quinoxaline derivatives XK469 (2-{4-[(7-chloro-2-quinoxalinyl)oxy]phenoxy}propionic acid) and SH80 (2-{4-[(7-bromo-2-quinolinyl)oxy]phenoxy}propionic acid) has been attributed to their abilities to induce G(2)/M arrest and apoptotic or autophagic cell death. Concentrations of XK469 or SH80 > or = 5 microM were cytostatic to cultures of the normal murine melanocyte cell line Melan-a. Higher concentrations caused dose-dependent cytotoxicity. Concentrations > or =10 microM provoked dramatic morphological changes typified by marked increases in cell size and granularity. XK469/SH80-treated cultures accumulated tetraploid (4N) DNA-containing cells within 24 h of treatment, an 8N population within 3 days, and a 16N population within 5 days. Increases in ploidy correlated with the appearance of multinucleated cells. Under no circumstances did cells exhibit evidence of furrow formation. Both drugs suppressed cytokinesis in additional mammalian cell lines. Cytotoxic concentrations of XK469 elevated DEVDase activities (a measure of procaspase-3/7 activation) and enhanced cellular staining by a fluorescent analog of the pan caspase inhibitor valine-alanine-aspartic acid-fluoromethyl ketone within 48 to 96 h of treatment. Within 48 h of treatment, cytostatic and cytotoxic concentrations of XK469 elevated p21 contents, reduced Bcl-2 and Bcl-XL contents, and induced autophagy, as monitored by the accumulation of phosphatidylethanolamine-modified cleavage product of microtubule-associated protein light chain 3 (LC3-II). Cultures treated with > or =10 microM XK469 or SH80 for 5 days could not be induced to divide upon removal of drugs. Such cultures maintained high LC3-II contents, exhibited reduced cyclin E and D1 contents, and extensively expressed senescence-associated beta-galactosidase within 14 to 17 days of cessation of drug treatment. Hence, XK469 and SH80 inhibit cytokinesis, promote polyploidy, and induce senescence in Melan-a cells.

Lysosomal cathepsin B participates in the podosome-mediated extracellular matrix degradation and invasion via secreted lysosomes in v-Src fibroblasts

Podosomes mediate cell migration and invasion by coordinating the reorganization of actin cytoskeleton and focal matrix degradation. MMP and serine proteases have been found to function at podosomes. The lysosomal cysteine cathepsins, a third major class of matrix-degrading enzymes involved in tumor invasion and tissue remodeling, have yet to be linked to podosomes with the exception of cathepsin K in osteoclasts. Using inhibitors and shRNA-mediated depletion, we show that cathepsin B participates in podosomes-mediated focal matrix degradation and invasion in v-Src-transformed fibroblasts. We observed that lysosomal marker LAMP-1 localized at the center of podosome rosettes protruding into extracellular matrix using confocal microscopy. Time-lapse live-cell imaging revealed that lysosomal vesicles moved to and fused with podosomes. Disruption of lysosomal pH gradient with Bafilomycin A1, chloroquine, or ammonium chloride greatly enhanced the formation of podosomes and increased the matrix degradation. Live-cell imaging showed that actin structures, induced shortly after Bafilomycin A1 treatment, were closely associated with lysosomes. Overall, our results suggest that cathepsin B, delivered by lysosomal vesicles, is involved in the matrix degradtion of podosomes.

Targeting of extracellular proteases required for the progression of pancreatic cancer

BACKGROUND

Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related death in the United States. Its lethality is due, in large part, to its resistance to traditional chemotherapeutics. As a result, there is an enormous effort being put into basic research to identify proteins that are required for PDA progression so that they may be specifically targeted for therapy.

OBJECTIVE

To compile and analyze the evidence that suggests that extracellular proteases are significant contributors to PDA progression.

METHODS

We focus on three different extracellular protease subclasses expressed in PDA: metalloproteases, serine proteases and cathepsins. Based on data from PDA and other cancers, we suggest their probable roles in PDA.

RESULTS/CONCLUSIONS

Of the proteases expressed in PDA, many appear to have overlapping functions, based on the substrates they process, making therapeutics complicated. Two protease families most likely to have unique, critical functions during tumor progression, and therefore strong potential as therapeutic targets, are the a disintegrin and metalloproteases (ADAMs) and the cathepsins.

Leukocyte cell surface proteinases: regulation of expression, functions, and mechanisms of surface localization

A number of proteinases are expressed on the surface of leukocytes including members of the serine, metallo-, and cysteine proteinase superfamilies. Some proteinases are anchored to the plasma membrane of leukocytes by a transmembrane domain or a glycosyl phosphatidyl inositol (GPI) anchor. Other proteinases bind with high affinity to classical receptors, or with lower affinity to integrins, proteoglycans, or other leukocyte surface molecules. Leukocyte surface levels of proteinases are regulated by: (1) cytokines, chemokines, bacterial products, and growth factors which stimulate synthesis and/or release of proteinases by cells; (2) the availability of surface binding sites for proteinases; and/or (3) internalization or shedding of surface-bound proteinases. The binding of proteinases to leukocyte surfaces serves many functions including: (1) concentrating the activity of proteinases to the immediate pericellular environment; (2) facilitating pro-enzyme activation; (3) increasing proteinase stability and retention in the extracellular space; (4) regulating leukocyte function by proteinases signaling through cell surface binding sites or other surface proteins; and (5) protecting proteinases from inhibition by extracellular proteinase inhibitors. There is strong evidence that membrane-associated proteinases on leukocytes play critical roles in wound healing, inflammation, extracellular matrix remodeling, fibrinolysis, and coagulation. This review will outline the biology of membrane-associated proteinases expressed by leukocytes and their roles in physiologic and pathologic processes.

Cathepsin B is essential for regeneration of scratch-wounded normal human epidermal keratinocytes

Migration, proliferation and differentiation of keratinocytes are important processes during tissue regeneration and wound healing of the skin. Here, we focussed on proteases that contribute to extracellular matrix (ECM) remodeling as a prerequisite of keratinocyte migration. In particular, we assessed the significance of the mammalian cysteine peptidase cathepsin B for human keratinocytes during regeneration from scratch wounding. We describe the construction of a scratch apparatus that allows applying scratches of defined length, width and depth to cultured cells in a reproducible fashion. The rationale for our approach derived from our previous work where we have shown that HaCaT keratinocytes secrete cathepsin B into the extracellular space during spontaneous and induced migration. Here, we observed rapid removal of type IV collagen from underneath lamellipodial extensions of keratinocytes at the advancing fronts of regenerating monolayers, indicating that proteolytic ECM remodeling starts upon initiation of keratinocyte migration. Furthermore, we verified our previous results with HaCaT cells by using normal human epidermal keratinocytes (NHEK) and show that non-cell-permeant cathepsin B-specific inhibitors delayed full regeneration of the monolayers from scratch wounding in both cell systems, HaCaT and NHEK. Application of a single dose of cathepsin B inhibitor directly after scratch wounding of keratinocytes demonstrated that cathepsin B is essential during initial stages of wound healing, while its contribution to the subsequent processes of proliferation and differentiation of keratinocytes was of less significance. This notion was supported by our observation that the cathepsin B inhibitors used in this study did not affect proliferation rates of keratinocytes of regenerating cultures. Thus, we conclude that cathepsin B is indeed involved in ECM remodeling after its secretion from migrating keratinocytes. Cathepsin B might directly cleave ECM constituents or it may initiate proteolytic cascades that involve other proteases with the ability to degrade ECM components. Because cathepsin B is important for enabling migration of both, HaCaT cells and NHEK, our results support the notion that HaCaT keratinocytes represent an excellent cell culture model for analysis of human epidermal skin keratinocyte migration.

Endocytosis provides a major alternative pathway for lysosomal biogenesis in kidney proximal tubular cells

Recruitment of acid hydrolases to lysosomes generally occurs by intracellular sorting based on recognition of a common mannose 6-phosphate signal in the transGolgi network and selective transport to late endosomes/lysosomes. Here we provide evidence for an alternative, efficient secretion-recapture pathway mediated by megalin and exemplified by cathepsin B in kidney proximal convoluted tubules (PCT). We found that in mouse kidneys with defective megalin expression [megalin knockout (KO)] or apical PCT trafficking (ClC-5 KO), the (pro)cathepsin B mRNA level was essentially preserved, but the protein content was greatly decreased and the enzyme was excreted in the urine as mannose 6-phosphate-devoid species. In polarized PCT-derived cells, purified cathepsin B was avidly and selectively taken up at the apical membrane, and uptake was abolished by the megalin competitor, receptor-associated protein. Direct interaction of cathepsin B with megalin was demonstrated by surface plasmon resonance. Procathepsin B was detected in normal mouse serum. Purified cathepsin B injected into mice was efficiently taken up by kidneys (approximately 10% of injection) and targeted to lysosomes where it remained active, as shown by autoradiography and subcellular fractionation. A single cathepsin B injection into cathepsin B KO mice could reconstitute full lysosomal enzyme activity in the kidneys. These findings demonstrate a pathway whereby circulating lysosomal enzymes are continuously filtered in glomeruli, reabsorbed by megalin-mediated endocytosis, and transferred into lysosomes to exert their function, providing a major source of enzymes to PCT. These results also extend the significance of megalin in PCT and have several physiopathological and clinical implications.

Sphingosine kinase-1 is cleaved by cathepsin B in vitro: identification of the initial cleavage sites for the protease

Previous work has identified sphingosine kinase-1 (SK1) as a substrate for the cysteine protease cathepsin B in vitro. In this study, the mechanism of SK1 cleavage by cathepsin B was investigated. We identified two initial cleavage sites for the protease, the first at histidine 122 and the second at arginine 199. Mutation analysis showed that replacement of histidine 122 with a tyrosine maintained the activity of SK1 while significantly reducing cleavage by cathepsin B at the initial cleavage site. The efficacy of cleavage of SK1 at arginine 199, however, was not affected. These studies demonstrate that SK1 is cleaved by cathepsin B in a sequential manner after basic amino acids, and that the initial cleavages at the two identified sites occur independently of each other.

Cysteine cathepsins: multifunctional enzymes in cancer

Cysteine cathepsins are highly upregulated in a wide variety of cancers by mechanisms ranging from gene amplification to post-transcriptional modification. Their localization within intracellular lysosomes often changes during neoplastic progression, resulting in secretion of both inactive and active forms and association with binding partners on the tumour cell surface. Secreted, cell-surface and intracellular cysteine cathepsins function in proteolytic pathways that increase neoplastic progression. Direct proof for causal roles in tumour growth, migration, invasion, angiogenesis and metastasis has been shown by downregulating or ablating the expression of individual cysteine cathepsins in tumour cells and in transgenic mouse models of human cancer.

Function of Liver Activation-Regulated Chemokine/CC Chemokine Ligand 20 Is Differently Affected by Cathepsin B and Cathepsin D Processing

Chemokine processing by proteases is emerging as an important regulatory mechanism of leukocyte functions and possibly also of cancer progression. We screened a large panel of chemokines for degradation by cathepsins B and D, two proteases involved in tumor progression. Among the few substrates processed by both proteases, we focused on CCL20, the unique chemokine ligand of CCR6 that is expressed on immature dendritic cells and subtypes of memory lymphocytes. Analysis of the cleavage sites demonstrate that cathepsin B specifically cleaves off four C-terminally located amino acids and generates a CCL20(1-66) isoform with full functional activity. By contrast, cathepsin D totally inactivates the chemotactic potency of CCL20 by generating CCL20(1-55), CCL20(1-52), and a 12-aa C-terminal peptide CCL20(59-70). Proteolytic cleavage of CCL20 occurs also with chemokine bound to glycosaminoglycans. In addition, we characterized human melanoma cells as a novel CCL20 source and as cathepsin producers. CCL20 production was up-regulated by IL-1alpha and TNF-alpha in all cell lines tested, and in human metastatic melanoma cells. Whereas cathepsin D is secreted in the extracellular milieu, cathepsin B activity is confined to cytosol and cellular membranes. Our studies suggest that CCL20 processing in the extracellular environment of melanoma cells is exclusively mediated by cathepsin D. Thus, we propose a model where cathepsin D inactivates CCL20 and possibly prevents the establishment of an effective antitumoral immune response in melanomas.

Mechanisms of angiogenesis in gliomas

Gliomas are the most frequent primary tumors of the central nervous system in adults. Glioblastoma multiforme, the most aggressive form of astrocytic tumors, displays a rapid progression that is accompanied by particular poor prognosis of patients. Intense angiogenesis is a distinguishing pathologic characteristic of these tumors and in fact, glioblastomas are of the most highly vascularized malignant tumors. For this reason, research and therapy strategies have focused on understanding the mechanisms leading to the origin of tumor angiogenic blood vessels in order to develop new approaches that effectively block angiogenesis and cause tumor regression. We discuss here some important features of glioma angiogenesis and we present molecules and factors and their possible functions and interactions that play a role in neovascularization. In spite of the great progress that molecular biology has achieved on investigating tumor angiogenesis, many aspects remain obscure and the complexity of the angiogenic process stands for an obstacle in identifying the exact and complete molecular pathways orchestrating new blood vessels formation, which are necessary for the survival and expansion of these tumors.

Cathepsin S controls angiogenesis and tumor growth via matrix-derived angiogenic factors

The cysteine protease cathepsin S is highly expressed in malignant tissues. By using a mouse model of multistage murine pancreatic islet cell carcinogenesis in which cysteine cathepsin activity has been functionally implicated, we demonstrated that selective cathepsin S deficiency impaired angiogenesis and tumor cell proliferation, thereby impairing angiogenic islet formation and the growth of solid tumors, whereas the absence of its endogenous inhibitor cystatin C resulted in opposite phenotypes. Although mitogenic vascular endothelial growth factor, transforming growth factor-beta1, and the anti-angiogenic endostatin levels in either serum or carcinoma tissue extracts did not change in cathepsin S- or cystatin C-null mice, tumor tissue basic fibroblast growth factor and serum type 1 insulin growth factor levels were higher in cystatin C-null mice, and serum type 1 insulin growth factor levels were also increased in cathepsin S-null mice. Furthermore, cathepsin S affected the production of type IV collagen-derived anti-angiogenic peptides and the generation of bioactive pro-angiogenic gamma2 fragments from laminin-5, revealing a functional role for cathepsin S in angiogenesis and neoplastic progression.

An enzyme-linked immunosorbent assay for human cathepsin X, a potential new inflammatory marker

The human lysosomal cysteine-type carboxypeptidase cathepsin X is mainly present in monocytes and macrophages and may be released into the circulation due to constitutive and/or regulated secretion by (activated) immune cells. To define its potential diagnostic value as an inflammatory marker, we have developed a highly sensitive and specific sandwich-type immunoassay (ELISA) for cathepsin X permitting both intra- and extracellular detection and quantification. The dynamic range of the cathepsin X ELISA was determined to be 100 (detection limit) to 8000 pg/ml. Reproducibility of both within and between runs yielded coefficients of variation (CVs) of 2.7-3.5% and 6.3-7.3%, respectively. Cross-reactivity with other members (cathepsin B, L) of the thiol-dependent cathepsin family was not observed. The ELISA was used to quantify cathepsin X in leukocytes as well as in plasma of healthy volunteers and patients with multiple trauma. During the first 72 h after trauma, plasma levels of cathepsin X increased significantly, particularly in patients who died during the posttraumatic period. In comparison to the well-known inflammation marker neutrophil elastase, cathepsin X levels predicted survival with a higher significance in the later posttraumatic phase. In conclusion, this report provides the first evidence of cathepsin X immunoreactivity not only in cell lysates but also in plasma samples. We suggest that the newly developed highly reproducible ELISA will be of great value for further evaluation of this protease as a diagnostic and/or prognostic marker in inflammatory diseases.

Overexpression of stefin A in human esophageal squamous cell carcinoma cells inhibits tumor cell growth, angiogenesis, invasion, and metastasis

PURPOSE

Evidence is accumulating that an inverse correlation exists between stefin A level and malignant progression. The aim of this study is to investigate the role of stefin A in human esophageal squamous cell carcinoma cells and to evaluate the possibility of stefin A for cancer therapy.

EXPERIMENTAL DESIGN

We stably transfected stefin A cDNA into human EC9706 or KYSE150 esophageal squamous cell carcinoma cells. Subsequently, we evaluated the effect of stefin A overexpression on cell growth, cathepsin B activity, cell motility and invasion, tumor growth, and metastasis. Immunoanalysis was done to assess the expression of factor VIII and to support the localization of stefin A and cathepsin B. We also evaluated the effect of CA074Me, a selective membrane-permeant cathepsin B inhibitor.

RESULTS

Both transfection of stefin A and treatment with 10 micromol/L CA074Me significantly reduced cathepsin B activity and inhibited the Matrigel invasion. Combination of both further reduced cathepsin B activity and inhibited the Matrigel invasion. Overexpression of stefin A delayed the in vitro and in vivo growth of cells and significantly inhibited lung metastasis compared with 50% of lung metastasis in xenograft mice from EC9706 or empty vector cells. Transfection with stefin A showed a dramatic reduction of factor VIII staining in the tumors of xenograft mice.

CONCLUSIONS

Our data strongly indicate that stefin A plays an important role in the growth, angiogenesis, invasion, and metastasis of human esophageal squamous cell carcinoma cells and suggest that stefin A may be useful in cancer therapy.

Apoptosis of human endothelial cells is accompanied by proteolytic processing of latent TGF-beta binding proteins and activation of TGF-beta

Transforming growth factors beta (TGF-betas) are multifunctional cytokines that modulate cell growth, differentiation and apoptosis. Numerous effects initiated by TGF-betas in vitro have been described, but the role of TGF-beta targeting and activation under physiological conditions has gained very little attention and understanding. We report here that apoptosis of human umbilical vein endothelial cells (HUVECs) is accompanied by release of truncated large latent TGF-beta complexes from the pericellular matrix followed by activation of TGF-beta. The activation of TGF-beta during apoptosis was accompanied by enhanced secretion of beta1-LAP protein, and apoptotic HUVECs acquired the capacity to induce the release of latent TGF-beta-binding proteins (LTBPs) from extracellular matrices. Activated TGF-beta, in turn, attenuated apoptotic death of HUVECs. Current results indicate that the activation of TGF-beta accompanies the apoptosis of HUVECs, and may play a protective feedback role against apoptotic cell death. The results suggest a role for TGF-beta as a putative extracellular modulator of apoptosis.

The use of cystatin C to inhibit epithelial-mesenchymal transition and morphological transformation stimulated by transforming growth factor-beta

Introduction

Transforming growth factor-β (TGF-β) is a potent suppressor of mammary epithelial cell (MEC) proliferation and is thus an inhibitor of mammary tumor formation. Malignant MECs typically evolve resistance to TGF-β-mediated growth arrest, enhancing their proliferation, invasion, and metastasis when stimulated by TGF-β. Recent findings suggest that therapeutics designed to antagonize TGF-β signaling may alleviate breast cancer progression, thereby improving the prognosis and treatment of breast cancer patients. We identified the cysteine protease inhibitor cystatin C (CystC) as a novel TGF-β type II receptor antagonist that inhibits TGF-β binding and signaling in normal and cancer cells. We hypothesized that the oncogenic activities of TGF-β, particularly its stimulation of mammary epithelial–mesenchymal transition (EMT), can be prevented by CystC.

Method

Retroviral infection was used to constitutively express CystC or a CystC mutant impaired in its ability to inhibit cathepsin protease activity (namely Δ14CystC) in murine NMuMG MECs and in normal rat kidney (NRK) fibroblasts. The effect of recombinant CystC administration or CystC expression on TGF-β stimulation of NMuMG cell EMT in vitro was determined with immunofluorescence to monitor rearrangements of actin cytoskeletal architecture and E-cadherin expression. Soft-agar growth assays were performed to determine the effectiveness of CystC in preventing TGF-β stimulation of morphological transformation and anchorage-independent growth in NRK fibroblasts. Matrigel invasion assays were performed to determine the ability of CystC to inhibit NMuMG and NRK motility stimulated by TGF-β.

Results

CystC and Δ14CystC both inhibited NMuMG cell EMT and invasion stimulated by TGF-β by preventing actin cytoskeletal rearrangements and E-cadherin downregulation. Moreover, both CystC molecules completely antagonized TGF-β-mediated morphological transformation and anchorage-independent growth of NRK cells, and inhibited their invasion through synthetic basement membranes. Both CystC and Δ14CystC also inhibited TGF-β signaling in two tumorigenic human breast cancer cell lines.

Conclusion

Our findings show that TGF-β stimulation of initiating metastatic events, including decreased cell polarization, reduced cell–cell contact, and elevated cell invasion and migration, are prevented by CystC treatment. Our findings also suggest that the future development of CystC or its peptide mimetics hold the potential to improve the therapeutic response of human breast cancers regulated by TGF-β.

Bone microenvironment modulates expression and activity of cathepsin B in prostate cancer

Prostate cancers metastasize to bone leading to osteolysis. Here we assessed proteolysis of DQ-collagen I (a bone matrix protein) and, for comparison, DQ-collagen IV, by living human prostate carcinoma cells in vitro. Both collagens were degraded, and this degradation was reduced by inhibitors of matrix metallo, serine, and cysteine proteases. Because secretion of the cysteine protease cathepsin B is increased in human breast fibroblasts grown on collagen I gels, we analyzed cathepsin B levels and secretion in prostate cells grown on collagen I gels. Levels and secretion were increased only in DU145 cells--cells that expressed the highest baseline levels of cathepsin B. Secretion of cathepsin B was also elevated in DU145 cells grown in vitro on human bone fragments. We further investigated the effect of the bone microenvironment on cathepsin B expression and activity in vivo in a SCID-human model of prostate bone metastasis. High levels of cathepsin B protein and activity were found in DU145, PC3, and LNCaP bone tumors, although the PC3 and LNCaP cells had exhibited low cathepsin B expression in vitro. Our results suggest that tumor-stromal interactions in the context of the bone microenvironment can modulate the expression of the cysteine protease cathepsin B.

HaCaT keratinocytes secrete lysosomal cysteine proteinases during migration

Cathepsin B, a lysosomal cysteine proteinase, was detected within vesicles of cellular protrusions forming cell-cell contact sites between keratinocytes of the stratum spinosum of human skin. This observation suggested the possibility that secretion of the protease into the pericellular spaces could be involved in the dissociation of cell-cell contacts to enable intraepidermal keratinocyte migration. To determine whether cathepsin B is indeed secreted from migrating keratinocytes, we first used subconfluent HaCaT cells as a culture model to study spontaneous keratinocyte migration. A cathepsin B-specific fluorescent affinity label proved the association of mature cathepsin B with the surfaces of HaCaT cells at the leading edges of growing cells. Second, we used scratch-wounds of confluent HaCaT monolayers as a model of induced keratinocyte migration. Cathepsin B was detected within lysosomes, i.e. vesicles within the perinuclear region of non-wounded cells. Expression of cathepsin B was up-regulated and cathepsin B-positive vesicles showed a redistribution from perinuclear to peripheral regions of keratinocytes at the wound margins within 4 h after wounding. Enzyme cytochemistry further showed that cell surface-associated cathepsin B was proteolytically active at the leading fronts of migrating keratinocytes. In addition, increased amounts of mature forms of cathepsin B were detected within the conditioned media of HaCaT cells during the first 4 h after scratch-wounding. In contrast, and as a control, the activity of the cytosolic enzyme lactate dehydrogenase was not significantly higher in media of wounded cells as compared with non-wounded controls, arguing for a specific induction of cathepsin B secretion upon wounding and migration of the cells. This was further substantiated by applying various cathepsin B-specific inhibitors after wounding. These experiments showed that the migration ability of keratinocytes was reduced due to the blockage of functional cathepsin B. Thus, our results strongly suggest that cell surface-associated cathepsin B is a protease that contributes to the remodelling of the extracellular matrix and thereby promotes keratinocyte migration during wound healing.

Cysteine cathepsins in human cancer

Proteases play causal roles in the malignant progression of human tumors. This review centers on the roles in this process of cysteine cathepsins, i.e., peptidases belonging to the papain family (C1) of the CA clan of cysteine proteases. Cysteine cathepsins, most likely along with matrix metalloproteases (MMPs) and serine proteases, degrade the extracellular matrix, thereby facilitating growth and invasion into surrounding tissue and vasculature. Studies on tumor tissues and cell lines have shown changes in expression, activity and distribution of cysteine cathepsins in numerous human cancers. Molecular, immunologic and pharmacological strategies to modulate expression and activity of cysteine cathepsins have provided evidence for a causal role for these enzymes in tumor progression and invasion. Clinically, the levels, activities and localization of cysteine cathepsins and their endogenous inhibitors have been shown to be of diagnostic and prognostic value. Understanding the roles that cysteine proteases play in cancer could lead to the development of more efficacious therapies.