Intracellular signaling by cathepsin X: Molecular mechanisms and diagnostic and therapeutic opportunities in cancer

Multifunctional roles of γ-enolase in the central nervous system: more than a neuronal marker

Enolase, a multifunctional protein with diverse isoforms, has generally been recognized for its primary roles in glycolysis and gluconeogenesis. The shift in isoform expression from α-enolase to neuron-specific γ-enolase extends beyond its enzymatic role. Enolase is essential for neuronal survival, differentiation, and the maturation of neurons and glial cells in the central nervous system. Neuron-specific γ-enolase is a critical biomarker for neurodegenerative pathologies and neurological conditions, not only indicating disease but also participating in nerve cell formation and neuroprotection and exhibiting neurotrophic-like properties. These properties are precisely regulated by cysteine peptidase cathepsin X and scaffold protein γ1-syntrophin. Our findings suggest that γ-enolase, specifically its C-terminal part, may offer neuroprotective benefits against neurotoxicity seen in Alzheimer's and Parkinson's disease. Furthermore, although the therapeutic potential of γ-enolase seems promising, the effectiveness of enolase inhibitors is under debate. This paper reviews the research on the roles of γ-enolase in the central nervous system, especially in pathophysiological events and the regulation of neurodegenerative diseases.

Single cell RNA-sequencing reveals the cellular senescence of placental mesenchymal stem/stromal cell in preeclampsia

INTRODUCTION

Preeclampsia (PE) is a severe obstetric complication closely associated with placental dysfunction. Placental mesenchymal stem/stromal cells (PMSCs) modulate placental development while PE PMSCs are excessively senescent to disturb placental function. Nevertheless, the senescence mechanism of PE PMSCs remains unclear.

METHODS

PE-related single-cell RNA sequencing datasets (GSE173193), data of chip detection (GSE99007) and bulk transcriptome RNA sequencing datasets (GSE75010) were extracted from the GEO database. Firstly, the functional enrichment analyses of the differentially expressed genes (DEGs) in PMSCs were conducted. Then, the clusters of PE PMSCs were distinguished according to the expressions of senescence-related genes (SRGs) by consensus clustering analysis. Cell cycle analysis, senescence β-galactosidase, Transwell, and tube formation were conducted. Next, the expressions of the senescence-associated secretory phenotype (SASPs) were displayed. The characteristic genes of PE were screened by the least absolute shrinkage and selection operator analysis. CTSZ was suppressed in PMSCs and the cellular senescence levels were evaluated.

RESULTS

In this study, The DEGs in PMSCs were closely associated with cellular senescence. The score of SRGs was significantly higher and most of the SASPs were abnormally expressed in the senescent group. Seven characteristic genes of PE were identified, thereinto, CTSZ reduction may accelerate the senescence in PMSCs in vitro.

DISCUSSION

Combined with bioinformatic analysis and lab experiments, our study emphatically revealed the abnormal cellular senescence in PE PMSCs, in which CTSZ, one of the PE characteristic genes, regulated the cellular senescence levels in PMSCs. These findings might help to deepen the understanding of the senescence mechanism of PMSCs in PE.

Compensational role between cathepsins

Cathepsins, a family of lysosomal peptidases, play a crucial role in maintaining cellular homeostasis by regulating protein turnover and degradation as well as many specific regulatory actions that are important for proper cell function and human health. Alterations in the activity and expression of cathepsins have been observed in many diseases such as cancer, inflammation, neurodegenerative disorders, bone remodelling-related conditions and others. These changes are not exclusively harmful, but rather appear to be a compensatory response on the lack of one cathepsin in order to maintain tissue integrity. The upregulation of specific cathepsins in response to the inhibition or dysfunction of other cathepsins suggests a fine-tuned system of proteolytic balance and understanding the compensatory role of cathepsins may improve therapeutic potential of cathepsin's inhibitors. Selectively targeting one cathepsin or modulating their activity could offer new treatment strategies for a number of diseases. This review emphasises the need for comprehensive research into cathepsin biology in the context of disease. The identification of the specific cathepsins involved in compensatory responses, the elucidation of the underlying molecular mechanisms and the development of targeted interventions could lead to innovative therapeutic approaches.

The many roles of cathepsins in restenosis

Drug-eluting stents (DES) and dual antiplatelet regimens have significantly improved the clinical management of ischemic heart disease; however, the drugs loaded with DES in clinical practice are mostly paclitaxel or rapamycin derivatives, which target symptoms of post implantation proliferation and inflammation, leading to delayed re-endothelialization and neo-atherosclerosis. Along with the treatments already in place, there is a need for novel strategies to lessen the negative clinical outcomes of DES delays as well as a need for greater understanding of their pathobiological mechanisms. This review concentrates on the function of cathepsins (Cats) in the inflammatory response and granulation tissue formation that follow Cat-induced damage to the vasculature scaffold, as well as the functions of Cats in intimal hyperplasia, which is characterized by the migration and proliferation of smooth muscle cells, and endothelial denudation, re-endothelialization, and/or neo-endothelialization. Additionally, Cats can alter essential neointima formation and immune response inside scaffolds, and if Cats are properly controlled in vivo, they may improve scaffold biocompatibility. This unique profile of functions could lead to an original concept for a cathepsin-based coronary intervention treatment as an adjunct to stent placement.

The role of lysosomal peptidases in glioma immune escape: underlying mechanisms and therapeutic strategies

Glioblastoma is the most common primary malignant tumor of the central nervous system, which has the characteristics of strong invasion, frequent recurrence, and rapid progression. These characteristics are inseparable from the evasion of glioma cells from immune killing, which makes immune escape a great obstacle to the treatment of glioma, and studies have confirmed that glioma patients with immune escape tend to have poor prognosis. The lysosomal peptidase lysosome family plays an important role in the immune escape process of glioma, which mainly includes aspartic acid cathepsin, serine cathepsin, asparagine endopeptidases, and cysteine cathepsins. Among them, the cysteine cathepsin family plays a prominent role in the immune escape of glioma. Numerous studies have confirmed that glioma immune escape mediated by lysosomal peptidases has something to do with autophagy, cell signaling pathways, immune cells, cytokines, and other mechanisms, especially lysosome organization. The relationship between protease and autophagy is more complicated, and the current research is neither complete nor in-depth. Therefore, this article reviews how lysosomal peptidases mediate the immune escape of glioma through the above mechanisms and explores the possibility of lysosomal peptidases as a target of glioma immunotherapy.

A multifunctional nanoplatform delivering carbon monoxide and a cysteine protease inhibitor to mitochondria under NIR light shows enhanced synergistic anticancer efficacy

Photoactivated chemotherapy has attracted widespread attention due to its ability to circumvent the shortcomings of hypoxia in tumor tissues compared with traditional photodynamic therapy. In this work, novel multifunctional nanoplatform (1), Ru-inhibitor@TPPMnCO@N-GQDs, was designed and prepared, which was capable of mitochondria-targeted co-delivery of the cysteine protease inhibitor and carbon monoxide (CO) stimulated with an 808 nm near infrared (NIR) laser. Nanoplatform (1) was prepared by covalent attachment of a mitochondria-targeted CO donor (TPPMnCO) and a Ru(II)-caged cysteine protease inhibitor (Ru-inhibitor) on the surface of fluorescent N-doped graphene quantum dots (N-GQDs). Nanoplatform (1) preferentially accumulated in the mitochondria of cancer cells and instantly delivered CO and the cysteine protease inhibitor upon 808 nm NIR light irradiation, thus damaging mitochondria and leading to significant in vitro and in vivo anticancer efficacy. In addition, nanoplatform (1) has good biocompatibility and did not exert any toxic side effects on mice during the period of treatment. The targeted subcellular mitochondrial co-delivery of CO and the cysteine protease inhibitor may provide new insights into CO and enzyme inhibitor combined therapies for cancer treatment.

Upregulation of Cathepsin X in Glioblastoma: Interplay with γ-Enolase and the Effects of Selective Cathepsin X Inhibitors

Glioblastoma (GBM) is the most common and deadly primary brain tumor in adults. Understanding GBM pathobiology and discovering novel therapeutic targets are critical to finding efficient treatments. Upregulation of the lysosomal cysteine carboxypeptidase cathepsin X has been linked to immune dysfunction and neurodegenerative diseases, but its role in cancer and particularly in GBM progression in patients is unknown. In this study, cathepsin X expression and activity were found to be upregulated in human GBM tissues compared to low-grade gliomas and nontumor brain tissues. Cathepsin X was localized in GBM cells as well as in tumor-associated macrophages and microglia. Subsequently, potent irreversible (AMS36) and reversible (Z7) selective cathepsin X inhibitors were tested in vitro. Selective cathepsin X inhibitors decreased the viability of patient-derived GBM cells as well as macrophages and microglia that were cultured in conditioned media of GBM cells. We next examined the expression pattern of neuron-specific enzyme γ-enolase, which is the target of cathepsin X. We found that there was a correlation between high proteolytic activity of cathepsin X and C-terminal cleavage of γ-enolase and that cathepsin X and γ-enolase were colocalized in GBM tissues, preferentially in GBM-associated macrophages and microglia. Taken together, our results on patient-derived material suggest that cathepsin X is involved in GBM progression and is a potential target for therapeutic approaches against GBM.

Lysosomal peptidases – Intriguing roles in cancer progression and neurodegeneration

Lysosomal peptidases are hydrolytic enzymes capable of digesting waste proteins that are targeted to lysosomes via endocytosis and autophagy. Besides intracellular protein catabolism, they play more specific roles in several other cellular processes and pathologies, either within lysosomes, upon secretion into the cell cytoplasm or extracellular space, or bound to the plasma membrane. In cancer, lysosomal peptidases are generally associated with disease progression, as they participate in crucial processes leading to changes in cell morphology, signaling, migration, and invasion, and finally metastasis. However, they can also enhance the mechanisms resulting in cancer regression, such as apoptosis of tumor cells or antitumor immune responses. Lysosomal peptidases have also been identified as hallmarks of aging and neurodegeneration, playing roles in oxidative stress, mitochondrial dysfunction, abnormal intercellular communication, dysregulated trafficking, and the deposition of protein aggregates in neuronal cells. Furthermore, deficiencies in lysosomal peptidases may result in other pathological states, such as lysosomal storage disease. The aim of this review was to highlight the role of lysosomal peptidases in particular pathological processes of cancer and neurodegeneration and to address the potential of lysosomal peptidases in diagnosing and treating patients.

Evaluation of novel cathepsin-X inhibitors in vitro and in vivo and their ability to improve cathepsin-B-directed antitumor therapy

New therapeutic targets that could improve current antitumor therapy and overcome cancer resistance are urgently needed. Promising candidates are lysosomal cysteine cathepsins, proteolytical enzymes involved in various critical steps during cancer progression. Among them, cathepsin X, which acts solely as a carboxypeptidase, has received much attention. Our results indicate that the triazole-based selective reversible inhibitor of cathepsin X named Z9 (1-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-2-((4-isopropyl-4H-1,2,4-triazol-3-yl)thio)ethan-1-one) significantly reduces tumor progression, both in vitro in cell-based functional assays and in vivo in two independent tumor mouse models: the FVB/PyMT transgenic and MMTV-PyMT orthotopic breast cancer mouse models. One of the mechanisms by which cathepsin X contributes to cancer progression is the compensation of cathepsin-B activity loss. Our results confirm that cathepsin-B inhibition is compensated by an increase in cathepsin X activity and protein levels. Furthermore, the simultaneous inhibition of both cathepsins B and X with potent, selective, reversible inhibitors exerted a synergistic effect in impairing processes of tumor progression in in vitro cell-based assays of tumor cell migration and spheroid growth. Taken together, our data demonstrate that Z9 impairs tumor progression both in vitro and in vivo and can be used in combination with other peptidase inhibitors as an innovative approach to overcome resistance to antipeptidase therapy.

Characterization of a Trichinella spiralis cathepsin X and its promotion for the larval invasion of mouse intestinal epithelial cells

The aim of this study was to ascertain the characteristics of a Trichinella spiralis cathepsin X (TsCX) and its role on larval invasion of intestinal epithelial cells (IECs). The full-length of TsCX cDNA sequence was cloned and expressed in Escherichia coli BL21. The results of RT-PCR, IFA and Western blot revealed that TsCX was expressed at T. spiralis muscle larvae (ML), intestinal infective larvae, adult worm and newborn larvae, and it was located in whole worm section. The results of Far western and confocal microscopy demonstrated that there was a specific binding of rTsCX and IEC, and the binding site was located within the IEC cytoplasm. rTsCX promoted T. spiralis larval invasion of mouse IECs while anti-rTsCX antibody inhibited larval invasion into the IECs. Silencing TsCX by specific siRNA reduced the TsCX expression and larval invasive capacity. These results indicated that TsCX specifically binds to IECs and promotes larval invasion of intestinal epithelia, and it might be a potential target of vaccines against enteral stages of T. spiralis.

Proteases Regulate Cancer Stem Cell Properties and Remodel Their Microenvironment

Proteolytic activity is perturbed in tumors and their microenvironment, and proteases also affect cancer stem cells (CSCs). CSCs are the therapy-resistant subpopulation of cancer cells with tumor-initiating capacity that reside in specialized tumor microenvironment niches. In this review, we briefly summarize the significance of proteases in regulating CSC activities with a focus on brain tumor glioblastoma. A plethora of proteases and their inhibitors participate in CSC invasiveness and affect intercellular interactions, enhancing CSC immune, irradiation, and chemotherapy resilience. Apart from their role in degrading the extracellular matrix enabling CSC migration in and out of their niches, we review the ability of proteases to modulate CSC properties, which prevents their elimination. When designing protease-oriented therapies, the multifaceted roles of proteases should be thoroughly investigated.

The Role of Cysteine Peptidases in Hematopoietic Stem Cell Differentiation and Modulation of Immune System Function

Cysteine cathepsins are primarily involved in the degradation and recycling of proteins in endo-lysosomal compartments but are also gaining recognition as pivotal proteolytic contributors to various immune functions. Through their extracellular proteolytic activities within the hematopoietic stem cell niche, they are involved in progenitor cell mobilization and differentiation. Cysteine cathepsins, such as cathepsins L and S contribute to antigen-induced adaptive immunity through major histocompatibility complex class II antigen presentation whereas cathepsin X regulates T-cell migration. By regulating toll-like receptor signaling and cytokine secretion cysteine cathepsins activate innate immune cells and affect their functional differentiation. Cathepsins C and H are expressed in cytotoxic T lymphocytes and natural killer cells and are involved in processing of pro-granzymes into proteolytically active forms. Cytoplasmic activities of cathepsins B and L contribute to the maintenance of homeostasis of the adaptive immune response by regulating cell death of T and B lymphocytes. The expression pattern, localization, and activity of cysteine cathepsins is tightly connected to their function in immune cells. Furthermore, cysteine cathepsins together with their endogenous inhibitors, serve as mediators in the interplay between cancer and immune cells that results in immune cell anergy. The aim of the present article is to review the mechanisms of dysregulation of cysteine cathepsins and their inhibitors in relation to immune dysfunction to address new possibilities for regulation of their function.

Control of mitosis, inflammation, and cell motility by limited leakage of lysosomes

Lysosomal membrane permeabilization and subsequent leakage of lysosomal hydrolases into the cytosol are considered as the major hallmarks of evolutionarily conserved lysosome-dependent cell death. Contradicting this postulate, new sensitive methods that can detect a minimal lysosomal membrane damage have demonstrated that lysosomal leakage does not necessarily equal cell death. Notably, cells are not only able to survive minor lysosomal membrane permeabilization, but some of their normal functions actually depend on leaked lysosomal hydrolases. Here we discuss emerging data suggesting that spatially and temporally controlled lysosomal leakage delivers lysosomal hydrolases to specific subcellular sites of action and controls at least three essential cellular processes, namely mitotic chromosome segregation, inflammatory signaling, and cellular motility.

Expression of CARD8 in human atherosclerosis and its regulation of inflammatory proteins in human endothelial cells

The Caspase activation and recruitment domain 8 (CARD8) protein is a component of innate immunity and overexpression of CARD8 mRNA was previously identified in atherosclerosis. However, very little is known about the regulation of CARD8 in endothelial cells and atherosclerosis. The aim of this study was to investigate CARD8 in the regulation of cytokine and chemokine expression in endothelial cells. Sections of human atherosclerotic lesions and non-atherosclerotic arteries were immunostained for CARD8 protein. Expression of CARD8 was correlated to mediators of inflammation in atherosclerotic lesions using Biobank of Karolinska Endarterectomies microarray data. The CARD8 mRNA was knocked-down in human umbilical vein endothelial cells (HUVECs) in vitro, followed by quantitative RT-PCR analysis and OLINK Proteomics. Endothelial and smooth muscle cells in arterial tissue expressed CARD8 and CARD8 correlated with vWF, CD163 and the expression of inflammatory genes, such as CXCL1, CXCL6 and PDGF-A in plaque. Knock-down of CARD8 in HUVECs significantly altered proteins involved in inflammatory response, such as CXCL1, CXCL6, PDGF-A, MCP-1 and IL-6. The present study suggest that CARD8 regulate the expression of cytokines and chemokines in endothelial cells and atherosclerotic lesions, suggesting that CARD8 plays a significant role in endothelial activation.

Novel Opportunities for Cathepsin S Inhibitors in Cancer Immunotherapy by Nanocarrier-Mediated Delivery

Cathepsin S (CatS) is a secreted cysteine protease that cleaves certain extracellular matrix proteins, regulates antigen presentation in antigen-presenting cells (APC), and promotes M2-type macrophage and dendritic cell polarization. CatS is overexpressed in many solid cancers, and overall, it appears to promote an immune-suppressive and tumor-promoting microenvironment. While most data suggest that CatS inhibition or knockdown promotes anti-cancer immunity, cell-specific inhibition, especially in myeloid cells, appears to be important for therapeutic efficacy. This makes the design of CatS selective inhibitors and their targeting to tumor-associated M2-type macrophages (TAM) and DC an attractive therapeutic strategy compared to the use of non-selective immunosuppressive compounds or untargeted approaches. The selective inhibition of CatS can be achieved through optimized small molecule inhibitors that show good pharmacokinetic profiles and are orally bioavailable. The targeting of these inhibitors to TAM is now more feasible using nanocarriers that are functionalized for a directed delivery. This review discusses the role of CatS in the immunological tumor microenvironment and upcoming possibilities for a nanocarrier-mediated delivery of potent and selective CatS inhibitors to TAM and related APC to promote anti-tumor immunity.

Targeting Cancer Lysosomes with Good Old Cationic Amphiphilic Drugs

Being originally discovered as cellular recycling bins, lysosomes are today recognized as versatile signaling organelles that control a wide range of cellular functions that are essential not only for the well-being of normal cells but also for malignant transformation and cancer progression. In addition to their core functions in waste disposal and recycling of macromolecules and energy, lysosomes serve as an indispensable support system for malignant phenotype by promoting cell growth, cytoprotective autophagy, drug resistance, pH homeostasis, invasion, metastasis, and genomic integrity. On the other hand, malignant transformation reduces the stability of lysosomal membranes rendering cancer cells sensitive to lysosome-dependent cell death. Notably, many clinically approved cationic amphiphilic drugs widely used for the treatment of other diseases accumulate in lysosomes, interfere with their cancer-promoting and cancer-supporting functions and destabilize their membranes thereby opening intriguing possibilities for cancer therapy. Here, we review the emerging evidence that supports the supplementation of current cancer therapies with lysosome-targeting cationic amphiphilic drugs.

Overexpression of carboxypeptidase X M14 family member 2 predicts an unfavorable prognosis and promotes proliferation and migration of osteosarcoma

Background

Carboxypeptidase X, M14 family member 2 (CPXM2), has been associated with several human developmental disorders. However, whether CPXM2 is involved in oncogenesis or tumor progression remains unclear. Currently, the clinical relevance and function of CPXM2 in human osteosarcoma were investigated.

Materials and methods

The expression of CPXM2 in osteosarcoma cell lines and tissues were explored by immunohistochemistry and western blotting assays. A eukaryotic expression plasmid was transfected into fetal osteoblast cells to overexpress CPXM2 and the endogenous CPXM2 in osteosarcoma cells was silenced through an RNA interference (RNAi) method transfection. These transfections were validated via western blotting, and the expression levels of several key molecules involved in the epithelial mesenchymal transition was also determined via western blotting. The expression levels of CPXM2 in a fetal osteoblast cell line with CPXM2 overexpressing and an osteosarcoma CPXM2-knockout cell line was confirmed via reverse transcription-quantitative polymerase chain reaction (RT-qPCR), western blotting and immunofluorescence. The malignant phenotype of osteosarcoma cells was indicated by the cholecystokinin octapeptide, colony formation assay, scratch wound healing assay, and Transwell® migration assay.

Results

We found that CPXM2 was overexpressed in osteosarcoma and that the overexpression was associated with an unfavorable prognosis and tumor node metastasis staging. The knockdown of CPXM2 in cultured osteosarcoma cells significantly impeded cell proliferation and migration. In addition, the upregulation of CPXM2 in fetal osteoblast cells significantly promoted cell proliferation and migration. Besides, western blotting results revealed that several key molecules involved in the epithelial mesenchymal transition (EMT) were regulated by CPXM2.

Conclusion

Taken together, these results imply an active role for CPXM2 in promoting tumor aggressiveness via epithelial to mesenchymal transition (EMT) modulation in osteosarcoma.

pH- and enzyme-triggered drug release as an important process in the design of anti-tumor drug delivery systems

It is necessary to design a reasonable drug delivery system(DDS) for targeted release to overcome the potential toxicity and poor selectivity of anti-tumor drug. How a drug is released from a DDS is a critical issue that determines whether the DDS is designed successfully. We all know that the microenvironment of tumors is quite different from normal tissues, such as its acidic environment, different expression levels of some enzymes, etc. These features are widely used in the design of DDSs and play an important role in the drug release process in vivo. Numerous DDSs have been designed and synthesized. This article attention to how drugs are released from DDSs. We summarizes and classify the characteristic enzymes and chemical bonds used in the drug release process by browsing a large number of papers, and describes how they are applied in DDSs with specific examples. By understanding these acid-sensitive chemical bonds and over-expressed enzymes in tumors, different DDSs can be designed for different drug structures to solve specific problems of anti-tumor drugs.

Overexpression of CPXM2 predicts an unfavorable prognosis and promotes the proliferation and migration of gastric cancer

Carboxypeptidase X, M14 family member 2 (CPXM2), has been associated with several human disorders such as developmental diseases. However, whether CPXM2 is involved in oncogenesis or tumor progression remains unclear. In the present study, we used clinical samples from gastric cancer (GC) patients to investigate potential roles of CPXM2 in GC. We also analyzed datasets from the Oncomine database, The Cancer Genome Atlas (TCGA), and the Kaplan‑Meier Plotter to validate these results. We found that CPXM2 was overexpressed in GC and that the overexpression was associated with an unfavorable prognosis, regardless of the Lauren classification and tumor node metastasis staging. In addition, knockdown of CPXM2 in cultured GC cells significantly impeded cell proliferation and migration, as indicated by the cholecystokinin octapeptide, colony formation assay, scratch wound healing assay, and Transwell® migration assay. Furthermore, gene set enrichment analysis using RNA‑seq data from TCGA indicated that high CPXM2 expression in GC patients was positively correlated with the HALLMARK_APICAL_JUNCTION and HALLMARK_EPITHELIAL_MESENCHYMAL_TRANSITION gene sets. Finally, western blotting results revealed that several key molecules involved in the epithelial mesenchymal transition were regulated by CPXM2. Taken together, these results imply an active role for CPXM2 in promoting tumor aggressiveness via epithelial to mesenchymal transition (EMT) modulation in GCs.

Cystatins in cancer progression: More than just cathepsin inhibitors

Cystatins are endogenous and reversible inhibitors of cysteine peptidases that are important players in cancer progression. Besides their primary role as regulators of cysteine peptidase activity, cystatins are involved in cancer development and progression through proteolysis-independent mechanisms. Mechanistic studies of cystatin function revealed that they affect all stages of cancer progression including tumor growth, apoptosis, invasion, metastasis and angiogenesis. Recently, the involvement of cystatins in the antitumor immune responses was reported. In this review, we discuss molecular mechanisms and clinical aspects of cystatins in cancer. Altered expression of cystatins in cancer resulting in harmful excessive cysteine peptidase activity has been a subject of several studies in order to find correlations with clinical outcome and therapy response. However, involvement in anti-tumor immune response and signaling cascades leading to cancer progression designates cystatins as possible targets for development of new anti-tumor drugs.

Cathepsins: Potent regulators in carcinogenesis

Cathepsins (CTS) are mainly lysosomal acid hydrolases extensively involved in the prognosis of different diseases, and having a distinct role in tumor progression by regulating cell proliferation, autophagy, angiogenesis, invasion, and metastasis. As all these processes conjunctively lead to cancer progression, their site-specific regulation might be beneficial for cancer treatment. CTS regulate activation of the proteolytic cascade and protein turnover, while extracellular CTS is involved in promoting extracellular matrix degradation and angiogenesis, thereby stimulating invasion and metastasis. Despite cancer regulation, the involvement of CTS in cellular adaptation toward chemotherapy and radiotherapy augments their therapeutic potential. However, lysosomal permeabilization mediated cytosolic translocation of CTS induces programmed cell death. This complex behavior of CTS generates the need to discuss the different aspects of CTS associated with cancer regulation. In this review, we mainly focused on the significance of each cathepsin in cancer signaling and their targeting which would provide noteworthy information in the context of cancer biology and therapeutics.

Cystatin F as a regulator of immune cell cytotoxicity

Cysteine cathepsins are lysosomal peptidases involved in the regulation of innate and adaptive immune responses. Among the diverse processes, regulation of granule-dependent cytotoxicity of cytotoxic T-lymphocytes (CTLs) and natural killer (NK) cells during cancer progression has recently gained significant attention. The function of cysteine cathepsins is regulated by endogenous cysteine protease inhibitors-cystatins. Whereas other cystatins are generally cytosolic or extracellular proteins, cystatin F is present in endosomes and lysosomes and is thus able to regulate the activity of its target directly. It is delivered to endosomal/lysosomal vesicles as an inactive, disulphide-linked dimer. Proteolytic cleavage of its N-terminal part leads to the monomer, the only form that is a potent inhibitor of cathepsins C, H and L, involved in the activation of granzymes and perforin. In NK cells and CTLs the levels of active cathepsin C and of granzyme B are dependent on the concentration of monomeric, active cystatin F. In tumour microenvironment, inactive dimeric cystatin F can be secreted from tumour cells or immune cells and further taken up by the cytotoxic cells. Subsequent monomerization and inhibition of cysteine cathepsins within the endosomal/lysosomal vesicles impairs granzyme and perforin activation, and provokes cell anergy. Further, the glycosylation pattern has been shown to be important in controlling secretion of cystatin F from target cells, as well as internalization by cytotoxic cells and trafficking to endosomal/lysosomal vesicles. Cystatin F is therefore an important mediator used by bystander cells to reduce NK and T-cell cytotoxicity.

Localization patterns of cathepsins K and X and their predictive value in glioblastoma

Background

Glioblastoma is a highly aggressive central nervous system neoplasm characterized by extensive infiltration of malignant cells into brain parenchyma, thus preventing complete tumor eradication. Cysteine cathepsins B, S, L and K are involved in cancer progression and are overexpressed in glioblastoma. We report here for the first time that cathepsin X mRNA and protein are also abundantly present in malignant glioma.

Materials and methods

Gene expression of cathepsins K and X was analyzed using publically-available tran-scriptomic datasets and correlated with glioma grade and glioblastoma subtype. Kaplan-Maier survival analysis was performed to evaluate the predictive value of cathepsin K and X mRNA expression. Cathepsin protein expression was localized and semi-quantified in tumor tissues by immunohistochemistry.

Results

Highest gene expression of cathepsins K and X was found in glioblastoma, in particular in the mesenchymal subtype. Overall, high mRNA expression of cathepsin X, but not that of cathepsin K, correlated with poor patients’ survival. Cathepsin K and X proteins were abundantly and heterogeneously expressed in glioblastoma tissue. Immuno-labeling of cathepsins K and X was observed in areas of CD133-positive glioblastoma stem cells, localized around arterioles in their niches that also expressed SDF-1α and CD68. mRNA levels of both cathepsins K and X correlated with mRNA levels of markers of glioblastoma stem cells and their niches.

Conclusions

The presence of both cathepsins in glioblastoma stem cell niche regions indicates their possible role in regulation of glioblastoma stem cell homing in their niches. The clinical relevance of this data needs to be elaborated in further prospective studies.

Increased expression and altered localization of cathepsin Z are associated with progression to jaundice stage in primary biliary cholangitis

Our recent genome-wide association study found that the NELFCD/CTSZ locus was significantly associated with progression of primary biliary cholangitis (PBC) to jaundice stage in the Japanese population. In this study, we investigated the role of cathepsin Z in the etiology and pathology of PBC. Serum cathepsin Z levels were measured using enzyme-linked immunosorbent assay. The expression and localization of cathepsin Z in liver specimens were analyzed by western blotting and immunohistochemistry. In PBC patients, serum cathepsin Z levels were significantly increased with disease progression. In addition, its levels were positively correlated with alanine transaminase, aspartate transaminase and total bilirubin, and were negatively correlated with platelet count and albumin. Cathepsin Z expression was markedly increased in hepatocytes at later stages of PBC, and its localization was altered from the peri-bile canaliculus to the cytoplasm, where a fraction was no longer colocalized with endosomal/lysosomal vesicles. Similar altered expression of cathepsin Z was observed in end-stage of other cholestatic liver diseases including sepsis, obstructive jaundice, and Alagille syndrome. Our results indicate that altered expression and localization of cathepsin Z in hepatocytes are characteristic features of PBC and other cholestatic liver diseases, and are implicated in the progression of PBC.

Cysteine cathepsins B, X and K expression in peri-arteriolar glioblastoma stem cell niches

Glioblastoma (GBM) is the most lethal brain tumor also due to malignant and therapy-resistant GBM stem cells (GSCs) that are localized in protecting hypoxic GSC niches. Some members of the cysteine cathepsin family of proteases have been found to be upregulated in GBM. Cathepsin K gene expression is highly elevated in GBM tissue versus normal brain and it has been suggested to regulate GSC migration out of the niches. Here, we investigated the cellular distribution of cathepsins B, X and K in GBM tissue and whether these cathepsins are co-localized in GSC niches. Therefore, we determined expression of these cathepsins in serial paraffin sections of 14 human GBM samples and serial cryostat sections of two samples using immunohistochemistry and metabolic mapping of cathepsin activity using selective fluorogenic substrates. We detected cathepsins B, X and K in peri-arteriolar GSC niches in 9 out of 16 GBM samples, which were defined by co-expression of the GSC marker CD133, the niche marker stromal-derived factor-1α (SDF-1α) and smooth muscle actin as a marker for arterioles. The expression of cathepsin B and X was detected in stromal cells and cancer cells throughout the GBM sections, whereas cathepsin K expression was more restricted to arteriole-rich regions in the GBM sections. Metabolic mapping showed that cathepsin B, but not cathepsin K is active in GSC niches. On the basis of these findings, it is concluded that cathepsins B, X and K have distinct functions in GBM and that cathepsin K is the most likely GSC niche-related cathepsin of the three cathepsins investigated.

NELFCD and CTSZ loci are associated with jaundice-stage progression in primary biliary cholangitis in the Japanese population

Approximately 10–20% of patients with primary biliary cholangitis (PBC) progress to jaundice stage regardless of treatment with ursodeoxycholic acid and bezafibrate. In this study, we performed a GWAS and a replication study to identify genetic variants associated with jaundice-stage progression in PBC using a total of 1,375 patients (1,202 early-stage and 173 jaundice-stage) in a Japanese population. SNP rs13720, which is located in the 3′UTR of cathepsin Z (CTSZ), showed the strongest association (odds ratio [OR] = 2.15, P = 7.62 × 10⁻⁷) with progression to jaundice stage in GWAS. High-density association mapping at the CTSZ and negative elongation factor complex member C/D (NELFCD) loci, which are located within a strong linkage disequilibrium (LD) block, revealed that an intronic SNP of CTSZ, rs163800, was significantly associated with jaundice-stage progression (OR = 2.16, P = 8.57 × 10⁻⁸). In addition, eQTL analysis and in silico functional analysis indicated that genotypes of rs163800 or variants in strong LD with rs163800 influence expression levels of both NELFCD and CTSZ mRNA. The present novel findings will contribute to dissect the mechanism of PBC progression and also to facilitate the development of therapies for PBC patients who are resistant to current therapies.

Identification and characterization of the novel reversible and selective cathepsin X inhibitors

Cathepsin X is a cysteine peptidase involved in the progression of cancer and neurodegenerative diseases. Targeting this enzyme with selective inhibitors opens a new possibility for intervention in several therapeutic areas. In this study triazole-based reversible and selective inhibitors of cathepsin X have been identified. Their selectivity and binding is enhanced when the 2,3-dihydrobenzo[b][1,4]dioxine moiety is present as the R¹ substituent. Of a series of selected triazole-benzodioxine derivatives, compound 22 is the most potent inhibitor of cathepsin X carboxypeptidase activity (K_i = 2.45 ± 0.05 μM) with at least 100-fold greater selectivity in comparison to cathepsin B or other related cysteine peptidases. Compound 22 is not cytotoxic to prostate cancer cells PC-3 or pheochromocytoma PC-12 cells at concentrations up to 10 μM. It significantly inhibits the migration of tumor cells and increases the outgrowth of neurites, both processes being under the control of cathepsin X carboxypeptidase activity. Compound 22 and other characterized triazole-based inhibitors thus possess a great potential for further development resulting in several in vivo applications.

Proteases and cytokines as mediators of interactions between cancer and stromal cells in tumours

Proteolytic enzymes are highly relevant in different processes of cancer progression. Their interplay with other signalling molecules such as cytokines represents important regulation of multicellular cross-talk. In this review, we discuss protease regulation mechanisms of cytokine signalling in various types of cancer. Additionally, we highlight the reverse whereby cytokines have an impact on protease expression in an autocrine and paracrine manner, representing complex feedback mechanisms among multiple members of these two protein families. The relevance of the protease-cytokine axis is illustrated in glioblastoma, where interactions between normal mesenchymal stem cells and cancer cells play an important role in this very malignant form of brain cancer.

Gamma-enolase: a well-known tumour marker, with a less-known role in cancer

Background

Gamma-enolase, known also as neuron-specific enolase (NSE), is an enzyme of the glycolytic pathway, which is expressed predominantly in neurons and cells of the neuroendocrine system. As a tumour marker it is used in diagnosis and prognosis of cancer; however, the mechanisms enrolling it in malignant progression remain elusive. As a cytoplasmic enzyme gamma-enolase is involved in increased aerobic glycolysis, the main source of energy in cancer cells, supporting cell proliferation. However, different cellular localisation at pathophysiological conditions, proposes other cellular engagements.

Conclusions

The C-terminal part of the molecule, which is not related to glycolytic pathway, was shown to promote survival of neuronal cells by regulating neuronal growth factor receptor dependent signalling pathways, resulting also in extensive actin cytoskeleton remodelling. This additional function could be important also in cancer cells either to protect cells from stressful conditions and therapeutic agents or to promote tumour cell migration and invasion. Gamma-enolase might therefore have a multifunctional role in cancer progression: it supports increased tumour cell metabolic demands, protects tumour cells from stressful conditions and promotes their invasion and migration.

Characterization of cathepsin X in colorectal cancer development and progression

The lysosomal cysteine carboxypeptidase cathepsin X (CTSX), localized predominantly in immune cells, has been associated with the development and progression of cancer. To determine its specific role in colorectal carcinoma (CRC), we analyzed CTSX expression in non-malignant mucosa and carcinoma of 177 patients as well as in 111 adenomas and related it with clinicopathological parameters. Further, the role of CTSX in the adhesion and invasion of the colon carcinoma cell lines HT-29 and HCT116 was investigated in an in vitro culture cell system with fibroblasts and monocytes, reflecting the situation at the tumor invasion front. Epithelial CTSX expression significantly increased from normal mucosa to adenoma and carcinoma, with highest expression levels in high grade intraepithelial neoplasia and in early tumor stages. Loss of CTSX occurred with tumor progression, and correlated with advanced local invasion, lymph node and distal metastasis, lymphatic vessel and vein invasion, tumor cell budding and poorer overall survival of patients with CRC. The subcellular distribution of CTSX changed from vesicular paranuclear expression in the tumor center to submembranous expression in cells of the invasion front. Peritumoral macrophages showed highest expression of CTSX. In vitro assays identified CTSX as relevant factor for cell-cell adhesion and tumor cell anchorage to fibroblasts and basal membrane components, whereas inhibition of CTSX caused increased invasiveness of colon carcinoma cells in mono- and co-culture. In conclusion, CTSX is involved in early tumorigenesis and in the stabilization of tumor cell formation in CRC. The results suggest that loss of CTSX may be needed for tumor cell detachment, local invasion and tumor progression. In addition, CTSX in tumor-associated macrophages indicates a role for CTSX in the anti-tumor immune response.