Proteomic Identification of Cysteine Cathepsin Substrates Shed from the Surface of Cancer Cells

Cysteine cathepsins: From diagnosis to targeted therapy of cancer

Cysteine cathepsins are a fascinating group of proteolytic enzymes that play diverse and crucial roles in numerous biological processes, both in health and disease. Understanding these proteases is essential for uncovering novel insights into the underlying mechanisms of a wide range of disorders, such as cancer. Cysteine cathepsins influence cancer biology by participating in processes such as extracellular matrix degradation, angiogenesis, immune evasion, and apoptosis. In this comprehensive review, we explore foundational research that illuminates the diverse and intricate roles of cysteine cathepsins as diagnostic markers and therapeutic targets for cancer. This review aims to provide valuable insights into the clinical relevance of cysteine cathepsins and explore their capacity to advance personalised and targeted medical interventions in oncology.

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

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

Neutrophil-Derived Proteases in Lung Inflammation: Old Players and New Prospects

Neutrophil-derived proteases are critical to the pathology of many inflammatory lung diseases, both chronic and acute. These abundant enzymes play roles in key neutrophil functions, such as neutrophil extracellular trap formation and reactive oxygen species release. They may also be released, inducing tissue damage and loss of tissue function. Historically, the neutrophil serine proteases (NSPs) have been the main subject of neutrophil protease research. Despite highly promising cell-based and animal model work, clinical trials involving the inhibition of NSPs have shown mixed results in lung disease patients. As such, the cutting edge of neutrophil-derived protease research has shifted to proteases that have had little-to-no research in neutrophils to date. These include the cysteine and serine cathepsins, the metzincins and the calpains, among others. This review aims to outline the previous work carried out on NSPs, including the shortcomings of some of the inhibitor-orientated clinical trials. Our growing understanding of other proteases involved in neutrophil function and neutrophilic lung inflammation will then be discussed. Additionally, the potential of targeting these more obscure neutrophil proteases will be highlighted, as they may represent new targets for inhibitor-based treatments of neutrophil-mediated lung inflammation.

Cathepsin L-mediated EGFR cleavage affects intracellular signalling pathways in cancer

Proteolytic activity in the tumour microenvironment is an important factor in cancer development since it can also affect intracellular signalling pathways via positive feedback loops that result in either increased tumour growth or resistance to anticancer mechanisms. In this study, we demonstrated extracellular cathepsin L-mediated cleavage of epidermal growth factor receptor (EGFR) and identified the cleavage site in the extracellular domain after R224. To further evaluate the relevance of this cleavage, we cloned and expressed a truncated version of EGFR, starting at G225, in HeLa cells. We confirmed the constitutive activation of the truncated protein in the absence of ligand binding and determined possible changes in intracellular signalling. Furthermore, we determined the effect of truncated EGFR protein expression on HeLa cell viability and response to the EGFR inhibitors, tyrosine kinase inhibitor (TKI) erlotinib and monoclonal antibody (mAb) cetuximab. Our data reveal the nuclear localization and phosphorylation of EGFR and signal trancducer and activator of transcription 3 (STAT3) in cells that express the truncated EGFR protein and suggest that these phenomena cause resistance to EGFR inhibitors.

An Engineered M13 Filamentous Nanoparticle as an Antigen Carrier for a Malignant Melanoma Immunotherapeutic Strategy

Bacteriophages, prokaryotic viruses, hold great potential in genetic engineering to open up new avenues for vaccine development. Our study aimed to establish engineered M13 bacteriophages expressing MAGE-A1 tumor peptides as a vaccine for melanoma treatment. Through in vivo experiments, we sought to assess their ability to induce robust immune responses. Using phage display technology, we engineered two M13 bacteriophages expressing MAGE-A1 peptides as fusion proteins with either pVIII or pIIII coat proteins. Mice were intraperitoneally vaccinated three times, two weeks apart, using two different engineered bacteriophages; control groups received a wild-type bacteriophage. Serum samples taken seven days after each vaccination were analyzed by ELISA assay, while splenocytes harvested seven days following the second boost were evaluated by ex vivo cytotoxicity assay. Fusion proteins were confirmed by Western blot and nano-LC-MS/MS. The application of bacteriophages was safe, with no adverse effects on mice. Engineered bacteriophages effectively triggered immune responses, leading to increased levels of anti-MAGE-A1 antibodies in proportion to the administered bacteriophage dosage. Anti-MAGE-A1 antibodies also exhibited a binding capability to B16F10 tumor cells in vitro, as opposed to control samples. Splenocytes demonstrated enhanced CTL cytotoxicity against B16F10 cells. We have demonstrated the immunogenic capabilities of engineered M13 bacteriophages, emphasizing their potential for melanoma immunotherapy.

Cathepsin V drives lung cancer progression by shaping the immunosuppressive environment and adhesion molecules cleavage

Cathepsin V (CTSV) is a cysteine cathepsin protease that plays a crucial role in extracellular matrix degradation. CTSV is correlated with poor prognosis in various cancers, but the underlying mechanism remains elusive. Here, we observed that CSTV is upregulated in lung cancer and is a poor prognosis factor for lung cancer. CTSV acts as a driver in the metastasis of lung cancer both in vitro and in vivo. CTSV promotes lung cancer metastasis by downregulating adhesion molecules, including fibronectin, E-cadherin, and N-cadherin. Our data revealed that CTSV functions by mediating the fragmentation of fibronectin, E-cadherin, and N-cadherin in cleavage, remodeling the extracellular matrix (ECM). The rationally designed antibody targeting CTSV blocks its cleaving ability towards fibronectin, E-cadherin, and N-cadherin, suppressing migration and invasion. Furthermore, we found that CTSV expression is negatively correlated with immune cell infiltration and immune scores and inhibits T cell activity. Targeting CTSV with specific antibodies effectively suppressed lung cancer metastasis in a mouse model. Our study demonstrates the critical role of CTSV in the immunity and metastasis of lung cancer, suggesting that the CTSV-targeting approach is a promising strategy for lung cancer.

Targeting Cathepsin L in Cancer Management: Leveraging Machine Learning, Structure-Based Virtual Screening, and Molecular Dynamics Studies

Cathepsin L (CTSL) expression is dysregulated in a variety of cancers. Extensive empirical evidence indicates their direct participation in cancer growth, angiogenic processes, metastatic dissemination, and the development of treatment resistance. Currently, no natural CTSL inhibitors are approved for clinical use. Consequently, the development of novel CTSL inhibition strategies is an urgent necessity. In this study, a combined machine learning (ML) and structure-based virtual screening strategy was employed to identify potential natural CTSL inhibitors. The random forest ML model was trained on IC50 values. The accuracy of the trained model was over 90%. Furthermore, we used this ML model to screen the Biopurify and Targetmol natural compound libraries, yielding 149 hits with prediction scores >0.6. These hits were subsequently selected for virtual screening using a structure-based approach, yielding 13 hits with higher binding affinity compared to the positive control (AZ12878478). Two of these hits, ZINC4097985 and ZINC4098355, have been shown to strongly bind CTSL proteins. In addition to drug-like properties, both compounds demonstrated high affinity, ligand efficiency, and specificity for the CTSL binding pocket. Furthermore, in molecular dynamics simulations spanning 200 ns, these compounds formed stable protein-ligand complexes. ZINC4097985 and ZINC4098355 can be considered promising candidates for CTSL inhibition after experimental validation, with the potential to provide therapeutic benefits in cancer management.

Macrophage-Derived Cathepsin S Remodels the Extracellular Matrix to Promote Liver Fibrogenesis

BACKGROUND & AIMS

Liver fibrosis is an intrinsic wound-healing response to chronic injury and the major cause of liver-related morbidity and mortality worldwide. However, no effective diagnostic or therapeutic strategies are available, owing to its poorly characterized molecular etiology. We aimed to elucidate the mechanisms underlying liver fibrogenesis.

METHODS

We performed a quantitative proteomic analysis of clinical fibrotic liver samples to identify dysregulated proteins. Further analyses were performed on the sera of 164 patients with liver fibrosis. Two fibrosis mouse models and several biochemical experiments were used to elucidate liver fibrogenesis.

RESULTS

We identified cathepsin S (CTSS) up-regulation as a central node for extracellular matrix remodeling in the human fibrotic liver by proteomic screening. Increased serum CTSS levels efficiently predicted liver fibrosis, even at an early stage. Secreted CTSS cleaved collagen 18A1 at its C-terminus, releasing endostatin peptide, which directly bound to and activated hepatic stellate cells via integrin α5β1 signaling, whereas genetic ablation of Ctss remarkably suppressed liver fibrogenesis via endostatin reduction in vivo. Further studies identified macrophages as the main source of hepatic CTSS, and splenectomy effectively attenuated macrophage infiltration and CTSS expression in the fibrotic liver. Pharmacologic inhibition of CTSS ameliorated liver fibrosis progression in the mouse models.

CONCLUSIONS

CTSS functions as a novel profibrotic factor by remodeling extracellular matrix proteins and may represent a promising target for the diagnosis and treatment of liver fibrosis.

Cleavage of Occludin by Cigarette Smoke-Elicited Cathepsin S Increases Permeability of Lung Epithelial Cells

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is an irreversible disease mainly caused by smoking. COPD is characterized by emphysema and chronic bronchitis associated with enhanced epithelial permeability.

HYPOTHESIS

Lung biopsies from smokers revealed a decreased expression level of occludin, which is a protein involved in the cohesion of epithelial tight junctions. Moreover, the occludin level correlated negatively with smoking history (pack-years), COPD grades, and cathepsin S (CatS) activity. Thus, we examined whether CatS could participate in the modulation of the integrity of human lung epithelial barriers.

METHODS AND RESULTS

Cigarette smoke extract (CSE) triggered the upregulation of CatS by THP-1 macrophages through the mTOR/TFEB signaling pathway. In a co-culture model, following the exposure of macrophages to CSE, an enhanced level of permeability of lung epithelial (16HBE and NHBE) cells towards FITC-Dextran was observed, which was associated with a decrease in occludin level. Similar results were obtained using 16HBE and NHBE cells cultured at the air-liquid interface. The treatment of THP-1 macrophages by CatS siRNAs or by a pharmacological inhibitor restored the barrier function of epithelial cells, suggesting that cigarette smoke-elicited CatS induced an alteration of epithelial integrity via the proteolytic injury of occludin.

CONCLUSIONS

Alongside its noteworthy resistance to oxidative stress induced by cigarette smoke oxidants and its deleterious elastin-degrading potency, CatS may also have a detrimental effect on the barrier function of epithelial cells through the cleavage of occludin. The obtained data emphasize the emerging role of CatS in smoking-related lung diseases and strengthen the relevance of targeting CatS in the treatment of emphysema and COPD.

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 S (CTSS) activity in health and disease - A treasure trove of untapped clinical potential

Amongst the lysosomal cysteine cathepsin family of proteases, cathepsin S (CTSS) holds particular interest due to distinctive properties including a normal restricted expression profile, inducible upregulation and activity at a broad pH range. Consequently, while CTSS is well-established as a member of the proteolytic cocktail within the lysosome, degrading unwanted and damaged proteins, it has increasingly been shown to mediate a number of distinct, more selective roles including antigen processing and antigen presentation, and cleavage of substrates both intra and extracellularly. Increasingly, aberrant CTSS expression has been demonstrated in a variety of conditions and disease states, marking it out as both a biomarker and potential therapeutic target. This review seeks to contextualise CTSS within the cysteine cathepsin family before providing an overview of the broad range of pathologies in which roles for CTSS have been identified. Additionally, current clinical progress towards specific inhibitors is detailed, updating the position of the field in exploiting this most unique of proteases.

Inhibitory prodrug mechanism for cysteine cathepsin-targeted self-controlled drug release

Tumour-associated macrophages (TAMs) support tumour development and have emerged as important regulators of therapeutic response to cytostatic agents. To target TAMs, we have developed a novel drug delivery approach which induces drug release as it inhibits cysteine cathepsin activity. This inhibitory prodrug (IPD) approach establishes a self-regulated system where drug release stops after all cysteine cathepsins are inhibited. This could improve the therapeutic window for drugs with severe side effects. We demonstrate and characterise this self-regulation concept with a fluorogenic IPD model. Next, we applied this IPD strategy to deliver cytotoxic drugs, as doxorubicin and monomethyl auristatin E, which are efficiently released and dose-dependently eliminate RAW264.7 macrophages. Lastly, by exploiting the increased cathepsin activity in TAM-like M2-polarised primary macrophages, we show that IPD-Dox selectively eliminates M2 over M1 macrophages. This demonstrates the potential of our IPD strategy for selective drug delivery and modulation of the tumour microenvironment.

Spatial localization of cathepsins: Implications in immune activation and resolution during infections

Cathepsins were first described, as endolysosomal proteolytic enzymes in reference to the organelles where they degrade the bulk of endogenous and exogenous substrates in a slightly acidic environment. These substrates include pathogens internalized via endocytosis and/or marked for destruction by autophagy. However, the role of cathepsins during infection far exceeds that of direct digestion of the pathogen. Cathepsins have been extensively investigated in the context of tumour associated immune cells and chronic inflammation. Several cathepsin-dependent immune responses develop in the endocytic pathway while others take place in the cytosol, the nucleus, or in the extracellular space. In this review we highlight the spatial localization of cathepsins and their implications in immune activation and resolution pathways during infection.

Helicobacter pylori infection induces stem cell-like properties in Correa cascade of gastric cancer

Gastric cancer (GC) is the fourth leading cause of cancer-related death. Its poor prognosis is attributed to unclear pathogenesis. Currently, the most widely accepted model for elucidating the mechanism of GC is the Correa cascade, which covers several histological lesions of the gastric mucosa. GC stem cells (CSCs) are crucial for oncogenesis in the Correa cascade and GC progression. As Helicobacter pylori (H. pylori) is the etiological factor in the Correa cascade, growing evidence suggests that enhancement of gastric stem cell-like properties and increase in CSCs correlate with H. pylori infection. In this paper, we review recent studies that present pathogenic mechanisms by which H. pylori induces gastric stem cell-like properties and CSCs, which may supplement the existing Correa model of GC. First, the dysfunction of developmental signaling pathways associated with H. pylori infection leads to the enhancement of gastric stemness. Second, H. pylori infection promotes alteration of the gastric mucosal microenvironment. In addition, epithelial-mesenchymal transition (EMT) may contribute to H. pylori-induced gastric stemness. Taken together, understanding these pathogeneses will provide potential therapeutic targets for the treatment of CSCs and malignant GC in H. pylori induced-Correa cascade of GC.

Behind every smile there's teeth: Cathepsin B's function in health and disease with a kidney view

Cathepsin B (CatB) is a very abundant lysosomal protease with endo- and carboxydipeptidase activities and even ligase features. In this review, we will provide a general characterization of CatB and describe structure, structure-derived properties and location-dependent proteolytic actions. We depict CatB action within lysosome and its important roles in lysosomal biogenesis, lysosomal homeostasis and autophagy rendering this protease a key player in orchestrating lysosomal functions. Lysosomal leakage and subsequent escape of CatB into the cytosol lead to harmful actions, e.g. the role in activating the NLPR3 inflammasome, affecting immune responses and cell death. The second focus of this review addresses CatB functions in the kidney, i.e. the glomerulus, the proximal tubule and collecting duct with strong emphasis of its role in pathology of the respective segment. Finally, observations regarding CatB functions that need to be considered in cell culture will be discussed. In conclusion, CatB a physiologically important molecule may, upon aberrant expression in different cellular context, become a harmful player effectively showing its teeth behind its smile.

A New Role of Acute Phase Proteins: Local Production Is an Ancient, General Stress-Response System of Mammalian Cells

The prevailing general view of acute-phase proteins (APPs) is that they are produced by the liver in response to the stress of the body as part of a systemic acute-phase response. We demonstrated a coordinated, local production of these proteins upon cell stress by the stressed cells. The local, stress-induced APP production has been demonstrated in different tissues (kidney, breast cancer) and with different stressors (hypoxia, fibrosis and electromagnetic heat). Thus, this local acute-phase response (APR) seems to be a universal mechanism. APP production is an ancient defense mechanism observed in nematodes and fruit flies as well. Local APP production at the tissue level is also supported by sporadic literature data for single proteins; however, the complex, coordinated, local appearance of this stress response has been first demonstrated only recently. Although a number of literature data are available for the local production of single acute-phase proteins, their interpretation as a local, coordinated stress response is new. A better understanding of the role of APPs in cellular stress response may also be of diagnostic/prognostic and therapeutic significance.

Cathepsin F and Fibulin-1 as novel diagnostic biomarkers for brain metastasis of non-small cell lung cancer

Background

The lack of non-invasive methods for detection of early micro-metastasis is a major cause of the poor prognosis of non-small cell lung cancer (NSCLC) brain metastasis (BM) patients. Herein, we aimed to identify circulating biomarkers based on proteomics for the early diagnosis and monitoring of patients with NSCLC BM.

Methods

Upregulated proteins were detected by secretory proteomics in the animal-derived high brain metastatic lung cancer cell line. A well-designed study composed of three independent cohorts was then performed to verify these blood-based protein biomarkers: the serum discovery and verification cohorts (n = 80; n = 459), and the tissue verification cohort (n = 76). Logistic regression was used to develop a diagnostic biomarker panel. Model validation cohort (n = 160) was used to verify the stability of the constructed predictive model. Changes in serum Cathepsin F (CTSF) levels of patients were tracked to monitor the treatment response. Progression-free survival (PFS) and overall survival (OS) were analysed to assess their prognostic relevance.

Results

CTSF and Fibulin-1 (FBLN1) levels were specifically upregulated in sera and tissues of patients with NSCLC BM compared with NSCLC without BM and primary brain tumour. The combined diagnostic performance of CTSF and FBLN1 was superior to their individual ones. CTSF serum changes were found to reflect the therapeutic response of patients with NSCLC BM and the trends of progression were detected earlier than the magnetic resonance imaging changes. Elevated expression of CTSF in NSCLC BM tissues was associated with poor PFS, and was found to be an independent prognostic factor.

Conclusions

We report a novel blood-based biomarker panel for early diagnosis, monitoring of therapeutic response, and prognostic evaluation of patients with NSCLC BM.

ASPER-29 suppresses the metastasis of pancreatic cancer cells by dual inhibition of cathepsin-L and cathepsin-S

Pancreatic cancer will be the second leading cause of cancer-related mortality worldwide due to its high rate of metastasis. Cathepsins (CATs) are effectors of invasive growth in various cancers. Currently, targeting CATs represents an attractive strategy for the treatment of highly metastatic cancers with high CATs activity, such as pancreatic cancer. To develop a stronger antimetastatic agent, ASPER-29, a novel inhibitor of CATs designed by using the asperphenamate derivative BBP as a lead compound, was synthesized, and its therapeutic potential in pancreatic cancer metastasis was investigated in this study. Molecular docking and enzyme inhibition assays proved that ASPER-29 can inhibit the activity of CAT-L and CAT-S by binding with these enzymes in classical action modes. Furthermore, ASPER-29 significantly inhibited the activity of CAT-L and CAT-S but had no effect on their expression in PANC-1 and BxPC-3 cells. The in vitro antimetastatic activities of ASPER-29 were examined by wound healing and Transwell chamber assays. We found that ASPER-29 inhibited the migration and invasion of PANC-1 and BxPC-3 cells in a concentration-dependent manner. Moreover, the in vivo antimetastatic effects of ASPER-29 were confirmed in a mouse xenotransplantation model. H&E staining and immunohistochemistry assays of Ki67 and CEACAM6 proved that ASPER-29 treatment significantly blocked the metastasis of pancreatic cancer cells to lung and liver tissues. Additionally, the activity of both CAT-L and CAT-S was markedly inhibited in the lung and liver tissues of ASPER-29-administered mice compared with the mice in the model group, suggesting that the metastasis-blocking effect of ASPER-29 should be mediated via inhibition of the activity of CAT-L and CAT-S in pancreatic cancer cells. Together, our results demonstrated that ASPER-29, as a novel inhibitor of CAT-L and CAT-S, possessed the evident ability to block the metastasis of pancreatic cancer cells.

Helicobacter pylori and gastric cancer: a lysosomal protease perspective

The intimate involvement of pathogens with the heightened risk for developing certain cancers is an area of research that has captured a great deal of attention over the last 10 years. One firmly established paradigm that highlights this aspect of disease progression is in the instance of Helicobacter pylori infection and the contribution it makes in elevating the risk for developing gastric cancer. Whilst the molecular mechanisms that pinpoint the contribution that this microorganism inflicts towards host cells during gastric cancer initiation have come into greater focus, another picture that has also emerged is one that implicates the host's immune system, and the chronic inflammation that can arise therefrom, as being a central contributory factor in disease progression. Consequently, when taken with the underlying role that the extracellular matrix plays in the development of most cancers, and how this dynamic can be modulated by proteases expressed from the tumor or inflammatory cells, a complex and detailed relationship shared between the individual cellular components and their surroundings is coming into focus. In this review article, we draw attention to the emerging role played by the cathepsin proteases in modulating the stage-specific progression of Helicobacter pylori-initiated gastric cancer and the underlying immune response, while highlighting the therapeutic significance of this dynamic and how it may be amenable for novel intervention strategies within a basic research or clinical setting.

Therapeutic potential of targeting cathepsin S in pulmonary fibrosis

Cathepsin S (CTSS), a lysosomal protease, belongs to a family of cysteine cathepsin proteases that promote degradation of damaged proteins in the endolysosomal pathway. Aberrant CTSS expression and regulation are associated with the pathogenesis of several diseases, including lung diseases. CTSS overexpression causes a variety of pathological processes, including pulmonary fibrosis, with increased CTSS secretion and accelerated extracellular matrix remodeling. Compared to many other cysteine cathepsin family members, CTSS has unique features that it presents limited tissue expression and retains its enzymatic activity at a neutral pH, suggesting its decisive involvement in disease microenvironments. In this review, we investigated the role of CTSS in lung disease, exploring recent studies that have indicated that CTSS mediates fibrosis in unique ways, along with its structure, substrates, and distinct regulation. We also outlined examples of CTSS inhibitors in clinical and preclinical development and proposed CTSS as a potential therapeutic target for pulmonary fibrosis.

Identification of Desmoglein-2 as a novel target of Helicobacter pylori HtrA in epithelial cells

BACKGROUND

High temperature requirement A (HtrA) is an active serine protease secreted by the group-I carcinogen Helicobacter pylori (H. pylori). The human cell adhesion protein and tumor suppressor E-cadherin (hCdh1) expressed on the surface of gastric epithelial cells was identified as the first HtrA substrate. HtrA-mediated hCdh1 cleavage and subsequent disruption of intercellular adhesions are considered as important steps in H. pylori pathogenesis. In this study, we performed a proteomic profiling of H. pylori HtrA (HpHtrA) to decipher the complex mechanism of H. pylori interference with the epithelial barrier integrity.

RESULTS

Using a proteomic approach we identified human desmoglein-2 (hDsg2), neuropilin-1, ephrin-B2, and semaphorin-4D as novel extracellular HpHtrA substrates and confirmed the well characterized target hCdh1. HpHtrA-mediated hDsg2 cleavage was further analyzed by in vitro cleavage assays using recombinant proteins. In infection experiments, we demonstrated hDsg2 shedding from H. pylori-colonized MKN28 and NCI-N87 cells independently of pathogen-induced matrix-metalloproteases or ADAM10 and ADAM17.

CONCLUSIONS

Characterizing the substrate specificity of HpHtrA revealed efficient hDsg2 cleavage underlining the importance of HpHtrA in opening intercellular junctions. Video Abstract.

Rational design of thioamide peptides as selective inhibitors of cysteine protease cathepsin L

Aberrant levels of cathepsin L (Cts L), a ubiquitously expressed endosomal cysteine protease, have been implicated in many diseases such as cancer and diabetes. Significantly, Cts L has been identified as a potential target for the treatment of COVID-19 due to its recently unveiled critical role in SARS-CoV-2 entry into the host cells. However, there are currently no clinically approved specific inhibitors of Cts L, as it is often challenging to obtain specificity against the many highly homologous cathepsin family cysteine proteases. Peptide-based agents are often promising protease inhibitors as they offer high selectivity and potency, but unfortunately are subject to degradation in vivo. Thioamide substitution, a single-atom O-to-S modification in the peptide backbone, has been shown to improve the proteolytic stability of peptides addressing this issue. Utilizing this approach, we demonstrate herein that good peptidyl substrates can be converted into sub-micromolar inhibitors of Cts L by a single thioamide substitution in the peptide backbone. We have designed and scanned several thioamide stabilized peptide scaffolds, in which one peptide, RS 1A, was stabilized against proteolysis by all five cathepsins (Cts L, Cts V, Cts K, Cts S, and Cts B) while inhibiting Cts L with >25-fold specificity against the other cathepsins. We further showed that this stabilized RS 1A peptide could inhibit Cts L in human liver carcinoma lysates (IC50 = 19 μM). Our study demonstrates that one can rationally design a stabilized, specific peptidyl protease inhibitor by strategic placement of a thioamide and reaffirms the place of this single-atom modification in the toolbox of peptide-based rational drug design.

Peptide profiling in cow urine reveals molecular signature of physiology-driven pathways and in-silico predicted bioactive properties

Peptidomics allows the identification of peptides that are derived from proteins. Urinary peptidomics has revolutionized the field of diagnostics as the samples represent complete systemic changes happening in the body. Moreover, it can be collected in a non-invasive manner. We profiled the peptides in urine collected from different physiological states (heifer, pregnancy, and lactation) of Sahiwal cows. Endogenous peptides were extracted from 30 individual cows belonging to three groups, each group comprising of ten animals (biological replicates n = 10). Nano Liquid chromatography Mass spectrometry (nLC-MS/MS) experiments revealed 5239, 4774, and 5466 peptides in the heifer, pregnant and lactating animals respectively. Urinary peptides of <10 kDa size were considered for the study. Peptides were extracted by 10 kDa MWCO filter. Sequences were identified by scanning the MS spectra ranging from 200 to 2200 m/z. The peptides exhibited diversity in sequences across different physiological states and in-silico experiments were conducted to classify the bioactive peptides into anti-microbial, anti-inflammatory, anti-hypertensive, and anti-cancerous groups. We have validated the antimicrobial effect of urinary peptides on Staphylococcus aureus and Escherichia coli under an in-vitro experimental set up. The origin of these peptides was traced back to certain proteases viz. MMPs, KLKs, CASPs, ADAMs etc. which were found responsible for the physiology-specific peptide signature of urine. Proteins involved in extracellular matrix structural constituent (GO:0005201) were found significant during pregnancy and lactation in which tissue remodeling is extensive. Collagen trimers were prominent molecules under cellular component category during lactation. Homophilic cell adhesion was found to be an important biological process involved in embryo attachment during pregnancy. The in-silico study also highlighted the enrichment of progenitor proteins on specific chromosomes and their relative expression in context to specific physiology. The urinary peptides, precursor proteins, and proteases identified in the study offers a base line information in healthy cows which can be utilized in biomarker discovery research for several pathophysiological studies.

The lnc-CTSLP8 upregulates CTSL1 as a competitive endogenous RNA and promotes ovarian cancer metastasis

Background

Ovarian cancer is highly lethal and has a poor prognosis due to metastasis. Long non-coding RNAs (lncRNAs) are key regulators of tumor development, but their role in ovarian cancer metastasis remains unclear.

Methods

The expression of lnc-CTSLP8 in ovarian cancer was analyzed in public databases (TCGA and GEO) and validated via qRT-PCR. Lnc-CTSLP8 overexpression and knockout cell lines were constructed using a lentiviral vector and the CRISP/Cas9 system. Cell proliferation, colony formation, migration, and invasion were analyzed. An ovarian orthotopic tumor mouse model was used for the in vivo study. Changes in autophagosomes, autolysosomes, and mitochondria in ovarian cancer cells were observed via transmission electron microscopy. EMT markers were detected by immunoblotting and immunofluorescence assays. RNA immunoprecipitation, RNA pull-down, and dual luciferase reporter assays were performed to confirm the interaction between lnc-CTSLP8 and miR-199a-5p.

Results

A novel pseudogene, lnc-CTSLP8, was identified in ovarian cancer, with significantly elevated expression in metastatic tumor tissues compared to primary ovarian tumors. When overexpressed, lnc-CTSLP8 promoted ovarian cancer in vitro and in vivo by acting as a sponge for miR-199a-5p. Autophagy and EMT in ovarian cancer were also enhanced by lnc-CTSLP8. Mechanistically, lnc-CTSLP8 upregulated CTSL1 as a competitive endogenous RNA and exhibited oncogenic effects. Moreover, CTSL1 inhibitor treatment and miR-199a-5p overexpression abrogated the effects of lnc-CTSLP8 overexpression.

Conclusions

lnc-CTSLP8 acts as a ceRNA in ovarian cancer and represents a potential therapeutic target for metastatic ovarian cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-021-01957-z.

Key Matrix Remodeling Enzymes: Functions and Targeting in Cancer

Tissue functionality and integrity demand continuous changes in distribution of major components in the extracellular matrices (ECMs) under normal conditions aiming tissue homeostasis. Major matrix degrading proteolytic enzymes are matrix metalloproteinases (MMPs), plasminogen activators, atypical proteases such as intracellular cathepsins and glycolytic enzymes including heparanase and hyaluronidases. Matrix proteases evoke epithelial-to-mesenchymal transition (EMT) and regulate ECM turnover under normal procedures as well as cancer cell phenotype, motility, invasion, autophagy, angiogenesis and exosome formation through vital signaling cascades. ECM remodeling is also achieved by glycolytic enzymes that are essential for cancer cell survival, proliferation and tumor progression. In this article, the types of major matrix remodeling enzymes, their effects in cancer initiation, propagation and progression as well as their pharmacological targeting and ongoing clinical trials are presented and critically discussed.

The Tumor Proteolytic Landscape: A Challenging Frontier in Cancer Diagnosis and Therapy

In recent decades, dysregulation of proteases and atypical proteolysis have become increasingly recognized as important hallmarks of cancer, driving community-wide efforts to explore the proteolytic landscape of oncologic disease. With more than 100 proteases currently associated with different aspects of cancer development and progression, there is a clear impetus to harness their potential in the context of oncology. Advances in the protease field have yielded technologies enabling sensitive protease detection in various settings, paving the way towards diagnostic profiling of disease-related protease activity patterns. Methods including activity-based probes and substrates, antibodies, and various nanosystems that generate reporter signals, i.e., for PET or MRI, after interaction with the target protease have shown potential for clinical translation. Nevertheless, these technologies are costly, not easily multiplexed, and require advanced imaging technologies. While the current clinical applications of protease-responsive technologies in oncologic settings are still limited, emerging technologies and protease sensors are poised to enable comprehensive exploration of the tumor proteolytic landscape as a diagnostic and therapeutic frontier. This review aims to give an overview of the most relevant classes of proteases as indicators for tumor diagnosis, current approaches to detect and monitor their activity in vivo, and associated therapeutic applications.

Application of a Highly Selective Cathepsin S Two-step Activity-Based Probe in Multicolor Bio-Orthogonal Correlative Light-Electron Microscopy

Cathepsin S is a lysosomal cysteine protease highly expressed in immune cells such as dendritic cells, B cells and macrophages. Its functions include extracellular matrix breakdown and cleavage of cell adhesion molecules to facilitate immune cell motility, as well as cleavage of the invariant chain during maturation of major histocompatibility complex II. The identification of these diverse specific functions has brought the challenge of delineating cathepsin S activity with great spatial precision, relative to related enzymes and substrates. Here, the development of a potent and highly selective two-step activity-based probe for cathepsin S and the application in multicolor bio-orthogonal correlative light-electron microscopy is presented. LHVS, which has been reported as a selective inhibitor of cathepsin S with nanomolar potency, formed the basis for our probe design. However, in competitive activity-based protein profiling experiments LHVS showed significant cross-reactivity toward Cat L. Introduction of an azide group in the P2 position expanded the selectivity window for cathepsin S, but rendered the probe undetectable, as demonstrated in bio-orthogonal competitive activity-based protein profiling. Incorporation of an additional azide handle for click chemistry on the solvent-exposed P1 position allowed for selective labeling of cathepsin S. This highlights the influence of click handle positioning on probe efficacy. This probe was utilized in multicolor bio-orthogonal confocal and correlative light-electron microscopy to investigate the localization of cathepsin S activity at an ultrastructural level in bone marrow-derived dendritic cells. The tools developed in this study will aid the characterization of the variety of functions of cathepsin S throughout biology.

Proteolytic Processing of CD44 and Its Implications in Cancer

CD44 is a transmembrane glycoprotein expressed in several healthy and tumor tissues. Modifications in its structure contribute differently to the activity of this molecule. One modification that has provoked interest is the consecutive cleavage of the CD44 extracellular ectodomain by enzymes that belong mainly to the family of metalloproteases. This process releases biologically active substrates, via alternative splice forms of CD44, that generate CD44v3 or v6 isoforms which participate in the transcriptional regulation of genes and proteins associated to signaling pathways involved in the development of cancer. These include the protooncogene tyrosine-protein kinase Src (c-Src)/signal transducer and activator of transcription 3 (STAT3), the epithelial growth factor receptor, the estrogen receptor, Wnt/βcatenin, or Hippo signaling pathways all of which are associated to cell proliferation, differentiation, or cancer progression. Whereas CD44 still remains as a very useful prognostic cell marker in different pathologies, the main topic is that the generation of CD44 intracellular fragments assists the regulation of transcriptional proteins involved in the cell cycle, cell metabolism, and most importantly, the regulation of some stem cell-associated markers.

Platform to Discover Protease-Activated Antibiotics and Application to Siderophore-Antibiotic Conjugates

Here we present a platform for discovery of protease-activated prodrugs and apply it to antibiotics that target Gram-negative bacteria. Because cleavable linkers for prodrugs had not been developed for bacterial proteases, we used substrate phage to discover substrates for proteases found in the bacterial periplasm. Rather than focusing on a single protease, we used a periplasmic extract of E. coli to find sequences with the greatest susceptibility to the endogenous mixture of periplasmic proteases. Using a fluorescence assay, candidate sequences were evaluated to identify substrates that release native amine-containing payloads. We next designed conjugates consisting of (1) an N-terminal siderophore to facilitate uptake, (2) a protease-cleavable linker, and (3) an amine-containing antibiotic. Using this strategy, we converted daptomycin-which by itself is active only against Gram-positive bacteria-into an antibiotic capable of targeting Gram-negative Acinetobacter species. We similarly demonstrated siderophore-facilitated delivery of oxazolidinone and macrolide antibiotics into a number of Gram-negative species. These results illustrate this platform's utility for development of protease-activated prodrugs, including Trojan horse antibiotics.

Cathepsin V suppresses GATA3 protein expression in luminal A breast cancer

Background

Lysosomal cysteine protease cathepsin V has previously been shown to exhibit elevated expression in breast cancer tissue and be associated with distant metastasis. Research has also identified that cathepsin V expression is elevated in tumour tissues from numerous other malignancies, but despite this, there has been limited examination of the function of this protease in cancer. Here we investigate the role of cathepsin V in breast cancer in order to delineate the molecular mechanisms by which this protease contributes to tumourigenesis.

Methods

Lentiviral transductions were used to generate shRNA cell line models, with cell line validation undertaken using RQ-PCR and Western blotting. Phenotypic changes of tumour cell biology were examined using clonogenic and invasion assays. The relationship between GATA3 expression and cathepsin V was primarily analysed using Western blotting. Site-directed mutagenesis was used to generate catalytic mutant and shRNA-resistant constructs to confirm the role of cathepsin V in regulating GATA3 expression.

Results

We have identified that elevated cathepsin V expression is associated with reduced survival in ER-positive breast cancers. Cathepsin V regulates the expression of GATA3 in ER-positive breast cancers, through promoting its degradation via the proteasome. We have determined that depletion of cathepsin V results in elevated pAkt-1 and reduced GSK-3β expression, which rescues GATA3 from proteasomal degradation.

Conclusions

In this study, we have identified that cysteine protease cathepsin V can suppress GATA3 expression in ER-positive breast cancers by facilitating its turnover via the proteasome. Therefore, targeting cathepsin V may represent a potential therapeutic strategy in ER-positive breast cancers, by restoring GATA3 protein expression, which is associated with a more favourable clinical outcome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-020-01376-6.

MYC as a Multifaceted Regulator of Tumor Microenvironment Leading to Metastasis

The Myc family of oncogenes is deregulated in many types of cancer, and their over-expression is often correlated with poor prognosis. The Myc family members are transcription factors that can coordinate the expression of thousands of genes. Among them, c-Myc (MYC) is the gene most strongly associated with cancer, and it is the focus of this review. It regulates the expression of genes involved in cell proliferation, growth, differentiation, self-renewal, survival, metabolism, protein synthesis, and apoptosis. More recently, novel studies have shown that MYC plays a role not only in tumor initiation and growth but also has a broader spectrum of functions in tumor progression. MYC contributes to angiogenesis, immune evasion, invasion, and migration, which all lead to distant metastasis. Moreover, MYC is able to promote tumor growth and aggressiveness by recruiting stromal and tumor-infiltrating cells. In this review, we will dissect all of these novel functions and their involvement in the crosstalk between tumor and host, which have demonstrated that MYC is undoubtedly the master regulator of the tumor microenvironment. In sum, a better understanding of MYC’s role in the tumor microenvironment and metastasis development is crucial in proposing novel and effective cancer treatment strategies.

Oxidative damage of lysosomes in regulated cell death systems: Pathophysiology and pharmacologic interventions

Lysosomes are small specialized organelles containing a variety of different hydrolase enzymes that are responsible for degradation of all macromolecules, entering the cells through the endosomal system or originated from the internal sources. This allows for transport and recycling of nutrients and internalization of surface proteins for antigen presentation as well as maintaining cellular homeostasis. Lysosomes are also important storage compartments for metal ions and nutrients. The integrity of lysosomal membrane is central to maintaining their normal function, but like other cellular membranes, lysosomal membrane is subject to damage mediated by reactive oxygen species. This results in spillage of lysosomal enzymes into the cytoplasm, leading to proteolytic damage to cellular systems and organelles. Several forms of lysosomal dependent cell death have been identified in diseases. Examination of these events are important for finding treatment strategies relevant to cancer or neurodegenerative diseases as well as autoimmune deficiencies. In this review, we have examined the current literature on involvement of lysosomes in induction of programed cell death and have provided an extensive list of therapeutic approaches that can modulate cell death. Exploitation of these mechanisms can lead to novel therapies for cancer and neurodegenerative diseases.

The Ins and Outs of Cathepsins: Physiological Function and Role in Disease Management

Cathepsins are the most abundant lysosomal proteases that are mainly found in acidic endo/lysosomal compartments where they play a vital role in intracellular protein degradation, energy metabolism, and immune responses among a host of other functions. The discovery that cathepsins are secreted and remain functionally active outside of the lysosome has caused a paradigm shift. Contemporary research has unraveled many versatile functions of cathepsins in extralysosomal locations including cytosol and extracellular space. Nevertheless, extracellular cathepsins are majorly upregulated in pathological states and are implicated in a wide range of diseases including cancer and cardiovascular diseases. Taking advantage of the differential expression of the cathepsins during pathological conditions, much research is focused on using cathepsins as diagnostic markers and therapeutic targets. A tailored therapeutic approach using selective cathepsin inhibitors is constantly emerging to be safe and efficient. Moreover, recent development of proteomic-based approaches for the identification of novel physiological substrates offers a major opportunity to understand the mechanism of cathepsin action. In this review, we summarize the available evidence regarding the role of cathepsins in health and disease, discuss their potential as biomarkers of disease progression, and shed light on the potential of extracellular cathepsin inhibitors as safe therapeutic tools.

Epithelial-to-mesenchymal transition as the driver of changing carcinoma and glioblastoma microenvironment

Epithelial-to-mesenchymal transition (EMT) is an essential molecular and cellular process that is part of normal embryogenesis and wound healing, and also has a ubiquitous role in various types of carcinoma and glioblastoma. EMT is activated and regulated by specific microenvironmental endogenous triggers and a complex network of signalling pathways. These mostly include epigenetic events that affect protein translation-controlling factors and proteases, altogether orchestrated by the switching on and off of oncogenes and tumour-suppressor genes in cancer cells. The hallmark of cancer-linked EMT is that the process is incomplete, as it is opposed by the reverse process of mesenchymal-to-epithelial transition, which results in a hybrid epithelial/mesenchymal phenotype that shows notable cell plasticity. This is a characteristic of cancer stem cells (CSCs), and it is of the utmost importance in their niche microenvironment, where it governs CSC migratory and invasive properties, thereby creating metastatic CSCs. These cells have high resistance to therapeutic treatments, in particular in glioblastoma.

Leading the invasion: The role of Cathepsin S in the tumour microenvironment

Elevated expression of the cysteine protease Cathepsin S has been correlated with a number of different cancer types in recent years. As tools have been developed to enable more accurate examination of individual cathepsin species, our knowledge and appreciation of the role that this protease plays in facilitating cancer has increased exponentially. This review focuses on our current understanding of the role of Cathepsin S within tumours and the surrounding microenvironment. While various publications have shown that Cathepsin S can be derived from tumour cells themselves, a plethora of more recent studies have identified that Cathepsin S can also be derived from other cell types within the tumour microenvironment including endothelial cells, macrophages and T cells. Furthermore, specific proteolytic substrates cleaved by Cathepsin S have also been identified which have reinforced our hypothesis that this protease facilitates key steps within tumours leading to their invasion, angiogenesis and metastasis.

Cysteine Cathepsins Inhibition Affects Their Expression and Human Renal Cancer Cell Phenotype

Renal cancer would greatly benefit from new therapeutic strategies since, in advanced stages, it is refractory to classical chemotherapeutic approaches. In this context, lysosomal protease cysteine cathepsins may represent new pharmacological targets. In renal cancer, they are characterized by a higher expression, and they were shown to play a role in its aggressiveness and spreading. Traditional studies in the field were focused on understanding the therapeutic potentialities of cysteine cathepsin inhibition, while the direct impact of such therapeutics on the expression of these enzymes was often overlooked. In this work, we engineered two fluoromethyl ketone-based peptides with inhibitory activity against cathepsins to evaluate their potential anticancer activity and impact on the lysosomal compartment in human renal cancer. Molecular modeling and biochemical assays confirmed the inhibitory properties of the peptides against cysteine cathepsin B and L. Different cell biology experiments demonstrated that the peptides could affect renal cancer cell migration and organization in colonies and spheroids, while increasing their adhesion to biological substrates. Finally, these peptide inhibitors modulated the expression of LAMP1, enhanced the expression of E-cadherin, and altered cathepsin expression. In conclusion, the inhibition of cysteine cathepsins by the peptides was beneficial in terms of cancer aggressiveness; however, they could affect the overall expression of these proteases.

Cathepsin S: investigating an old player in lung disease pathogenesis, comorbidities, and potential therapeutics

Dysregulated expression and activity of cathepsin S (CTSS), a lysosomal protease and a member of the cysteine cathepsin protease family, is linked to the pathogenesis of multiple diseases, including a number of conditions affecting the lungs. Extracellular CTSS has potent elastase activity and by processing cytokines and host defense proteins, it also plays a role in the regulation of inflammation. CTSS has also been linked to G-coupled protein receptor activation and possesses an important intracellular role in major histocompatibility complex class II antigen presentation. Modulated CTSS activity is also associated with pulmonary disease comorbidities, such as cancer, cardiovascular disease, and diabetes. CTSS is expressed in a wide variety of immune cells and is biologically active at neutral pH. Herein, we review the significance of CTSS signaling in pulmonary diseases and associated comorbidities. We also discuss CTSS as a plausible therapeutic target and describe recent and current clinical trials examining CTSS inhibition as a means for treatment.

Protease-activated prodrugs: strategies, challenges, and future directions

Proteases play critical roles in virtually all biological processes, including proliferation, cell death and survival, protein turnover, and migration. However, when dysregulated, these enzymes contribute to the progression of multiple diseases, with cancer, neurodegenerative disorders, inflammation, and blood disorders being the most prominent examples. For a long time, disease-associated proteases have been used for the activation of various prodrugs due to their well-characterized catalytic activity and ability to selectively cleave only those substrates that strictly correspond with their active site architecture. To date, versatile peptide sequences that are cleaved by proteases in a site-specific manner have been utilized as bioactive linkers for the targeted delivery of multiple types of cargo, including fluorescent dyes, photosensitizers, cytotoxic drugs, antibiotics, and pro-antibodies. This platform is highly adaptive, as multiple protease-labile conjugates have already been developed, some of which are currently in clinical use for cancer treatment. In this review, recent advancements in the development of novel protease-cleavable linkers for selective drug delivery are described. Moreover, the current limitations regarding the selectivity of linkers are discussed, and the future perspectives that rely on the application of unnatural amino acids for the development of highly selective peptide linkers are also presented.

Proteolysis of Gingival Keratinocyte Cell Surface Proteins by Gingipains Secreted From Porphyromonas gingivalis - Proteomic Insights Into Mechanisms Behind Tissue Damage in the Diseased Gingiva

Porphyromonas gingivalis, the main etiologic agent of periodontitis, secretes cysteine proteases named gingipains. HRgpA and RgpB gingipains have Arg-specificity, while Kgp gingipain is Lys-specific. Together they can cleave an array of proteins and importantly contribute to the development of periodontitis. In this study we focused on gingipain-exerted proteolysis at the cell surface of human gingival epithelial cells [telomerase immortalized gingival keratinocytes (TIGK)] in order to better understand the molecular mechanisms behind tissue destruction in periodontitis. Using mass spectrometry, we investigated the whole sheddome/degradome of TIGK cell surface proteins by P. gingivalis strains differing in gingipain expression and by purified gingipains, and performed the first global proteomic analysis of gignpain proteolysis at the membrane. Incubation of TIGK cells with P. gingivalis resulted in massive degradation of proteins already at low multiplicity of infection, whereas incubating cells with purified gingipains resulted in more discrete patterns, indicative of a combination of complete degradation and shedding of membrane proteins. Most of the identified gingipain substrates were molecules involved in adhesion, suggesting that gingipains may cause tissue damage through cleavage of cell contacts, resulting in cell detachment and rounding, and consequently leading to anoikis. However, HRgpA and RgpB gingipains differ in their mechanism of action. While RgpB rapidly degraded the proteins, HRgpA exhibited a much slower proteolysis indicative of ectodomain shedding, as demonstrated for the transferrin receptor protein 1 (TFRC). These results reveal a molecular underpinning to P. gingivalis-induced tissue destruction and enhance our knowledge of the role of P. gingivalis proteases in the pathobiology of periodontitis. Proteomics data are available via ProteomeXchange with identifier PXD015679.

Prognostic role and therapeutic susceptibility of cathepsin in various types of solid tumor and leukemia: A systematic review

Cathepsins (CTSs) are multifunctional proteins that can play prominent roles in cancer progression and metastasis. In this systematic review, we compared the prognosis of CTS subtypes overexpression in leukemia and solid tumors, and investigated the effect of different factors on CTS prognosis. We systematically searched published articles indexed in PubMed, Scopus, Cochrane library, ISI Web of Science, and EmBase databases from February 2000 until January 2020. Among the selected leukemia and solid tumors studies, overexpression of CTS subtypes in newly diagnosed and treated patients were with poor prognosis in 43 studies (79.6%) and with good prognosis in 9 studies (16.6%). However, there were 2 studies (3.8%) with either good or poor prognosis, depending on conditions and caner stage and host cell. The relation between CTS and human leukocyte antigen (HLA) in leukemia and solid tumors was mentioned in 7 studies (13%). Overexpression of CTS subtypes in all new case patients had contributed to the induction of poor prognosis. It seems that CTS subtypes, based on the type of cancer and its stage, the type of host cells, and the probable relation with HLA, breed good or poor prognosis in patients with cancer. Therefore, monitoring the overexpression of CTS subtypes and determining the effect of each of these factors on CTS prognosis could be helpful in predicting cancer prognosis both in newly diagnosed or under treatment patients. They could also be useful in finding ways for improving the efficiency of contemporary therapeutic strategies in various types of leukemia and solid tumors.

Cysteine cathepsins as therapeutic targets in inflammatory diseases

Introduction: Cysteine cathepsins are involved in the development and progression of numerous inflammation-associated diseases such as cancer, arthritis, bone and immune disorders. Consequently, there is a drive to progress research efforts focused on cathepsin use in diagnostics and as therapeutic targets in disease.Areas covered: This review discusses the potential of cysteine cathepsins as therapeutic targets in inflammation-associated diseases and recent advances in preclinical and clinical research. We describe direct targeting of cathepsins for treatment purposes and their indirect use in diagnostics.Expert opinion: The targeting of cysteine cathepsins has not translated into the clinic; this failure is attributed to off- and on-target side effects and/or the lack of companion biomarkers. This field now embraces developments in diagnostic imaging, the activation of prodrugs and antibody-drug conjugates for targeted drug delivery. The future lies in improved molecular tools and therapeutic concepts that will find a wide spectrum of uses in diagnostic and therapeutic applications.

The Acute Phase Response Is a Prominent Renal Proteome Change in Sepsis in Mice

(1) Background: Sepsis-induced acute kidney injury (AKI) is the most common form of acute kidney injury (AKI). We studied the temporal profile of the sepsis-induced renal proteome changes. (2) Methods: Male mice were injected intraperitoneally with bacterial lipopolysaccharide (LPS) or saline (control). Renal proteome was studied by LC-MS/MS (ProteomeXchange: PXD014664) at the early phase (EP, 1.5 and 6 h after 40 mg/kg LPS) and the late phase (LP, 24 and 48 h after 10 mg/kg LPS) of LPS-induced AKI. Renal mRNA expression of acute phase proteins (APP) was assessed by qPCR. (3) Results: Renal proteome change was milder in EP vs. LP. APPs dominated the proteome in LP (proteins upregulated at least 4-fold (APPs/all): EP, 1.5 h: 0/10, 6 h: 1/10; LP, 24 h: 22/47, 48 h: 17/44). Lipocalin-2, complement C3, fibrinogen, haptoglobin and hemopexin were the most upregulated APPs. Renal mRNA expression preceded the APP changes with peak effects at 24 h, and indicated renal production of the majority of APPs. (4) Conclusions: Gene expression analysis revealed local production of APPs that commenced a few hours post injection and peaked at 24 h. This is the first demonstration of a massive, complex and coordinated acute phase response of the kidney involving several proteins not identified previously.

Cathepsin E expression and activity: Role in the detection and treatment of pancreatic cancer

Cathepsin E (CTSE) is an intracellular, hydrolytic aspartic protease found to be expressed in cells of the immune and gastrointestinal systems, lymphoid tissues, erythrocytes, and cancer cells. The precise functions are not fully understood; however, various studies have investigated its numerous cell-type specific roles. CTSE expression has been shown to be a potential early biomarker for pancreatic ductal adenocarcinoma (PDAC). PDAC patients have low survival rates mostly due to the lack of early detection methods. CTSE-specific activity probes have been developed and tested to assist in tumor imaging and functional studies investigating the role of CTSE expression in PDAC tumors. Furthermore, a CTSE protease-specific, photodynamic therapy pro-drug was developed to explore its potential use to treat tumors that express CTSE. Since CTSE is expressed in pancreatic diseases that are risk factors for PDAC, such as pancreatic cysts and chronic pancreatitis, learning about its function in these disease types could assist in early PDAC detection and in understanding the biology of PDAC progression. Overall, CTSE expression and activity shows potential to detect PDAC and other pancreatic diseases. Further research is needed to fully understand its functions and potential translational applicability.

Functional analysis and gene expression profiling of extracellular cathepsin Z in red sea bream, Pagrus major

Cathepsin Z (CTSZ) is a lysosomal cysteine protease that is known to be involved in the maintenance of homeostasis and the biological mechanisms of immune cells. In this study, we have confirmed the tissue specific expression of the cathepsin Z (PmCTSZ) gene in Pagrus major, and confirmed its biological function after producing recombinant protein using Escherichia coli (E. coli). Multiple sequence alignment analysis revealed that the active site of the cysteine proteases and three N-glycosylation sites of the deduced protein sequence were highly conserved among all of the organisms. Phylogenetic analysis revealed that PmCTSZ was included in the clusters of CTSZ and the cysteine proteases of other bony fish and is most closely related to Japanese flounder CTSZ. PmCTSZ was distributed in all of the tissues from healthy red sea bream that were used in the experiment and was most abundantly found in the spleen and gill. Analysis of mRNA expression after bacterial (Edwardsiella piscicida: E. piscicida and Streptococcus iniae: S. iniae) or viral (red seabream iridovirus: RSIV) challenge showed significant gene expression regulation in immune-related tissues, but they maintained relatively normal levels of expression. We produced recombinant PmCTSZ (rPmCTSZ) using an E. coli expression system and confirmed the biological function of extracellular rPmCTSZ in vitro. We found that bacterial proliferation was significantly inhibited by rPmCTSZ, and the leukocytes of red sea bream also induced apoptosis and viability reduction.

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.

The multifaceted roles of tumor-associated proteases and harnessing their activity for prodrug activation

The role of proteases in cancer was originally thought to be limited to the breakdown of basement membranes and extracellular matrix (ECM), thereby promoting cancer cell invasion into surrounding normal tissues. It is now well understood that proteases play a much more complicated role in all stages of cancer progression and that not only tumor cells, but also stromal cells are an important source of proteases in the tumor microenvironment. Among all the proteolytic enzymes potentially associated with cancer, some proteases have taken on heightened importance due to their significant up-regulation and ability to participate at multiple stages of cancer progression and metastasis. In this review, we discuss some of the advances in understanding of the roles of several key proteases from different classes in the development and progression of cancer and the potential to leverage their upregulated activity for the development of novel targeted treatment strategies.

Degradomics in Biomarker Discovery

The upregulation of protease expression and proteolytic activity is implicated in numerous pathological conditions such as neurodegeneration, cancer, cardiovascular and autoimmune diseases, and bone degeneration. During disease progression, various proteases form characteristic patterns of cleaved proteins and peptides, which can affect disease severity and course of progression. It has been shown that qualitative and quantitative monitoring of cleaved protease substrates can provide relevant prognostic, diagnostic, and therapeutic information. As proteolytic fragments and peptides generated in the affected tissue are commonly translocated to blood, urine, and other proximal fluids, their possible application as biomarkers is the subject of ongoing research. The field of degradomics has been established to enable the global identification of proteolytic events on the organism level, utilizing proteomic approaches and sample preparation techniques that facilitate the detection of proteolytic processing of protease substrates in complex biological samples. In this review, some of the latest developments in degradomic methodologies used for the identification and validation of biologically relevant proteolytic events and their application in the search for clinically relevant biomarker candidates are presented. The current state of degradomics in clinics is discussed and the future perspectives of the field are outlined.

Host cell-surface proteins as substrates of gingipains, the main proteases of Porphyromonas gingivalis

Gingipains are extracellular cysteine proteases of the oral pathogen Porphyromonas gingivalis and are its most potent virulence factors. They can degrade a great variety of host proteins, thereby helping the bacterium to evade the host immune response, deregulate signaling pathways, trigger anoikis and, finally, cause tissue destruction. Host cell-surface proteins targeted by gingipains are the main focus of this review and span three groups of substrates: immune-regulatory proteins, signaling pathways regulators and adhesion molecules. The analysis of published data revealed that gingipains predominantly inactivate their substrates by cleaving them at one or more sites, or through complete degradation. Sometimes, gingipains were even found to initially shed their membrane substrates, but this was mostly just the first step in the degradation of cell-surface proteins.

Stefin A-functionalized liposomes as a system for cathepsins S and L-targeted drug delivery

Proteolytic activity in the tumor microenvironment is one of the key elements supporting tumor development and metastasis. One of the key families of proteases that are overexpressed in various types of cancer and implicated in different stages of tumor progression are cysteine cathepsins. Among them, cathepsins S and L can be secreted into the tumor microenvironment by tumor and/or immune cells, making them promising drug delivery targets. Here we present a new system for cathepsin S/L targeting using a liposomal drug carrier system functionalized with the endogenous cysteine cathepsin inhibitor, stefin A. The selective targeting of cathepsins by stefin A-conjugated liposomes was confirmed in vitro and in vivo, demonstrating the potential of this approach for cancer diagnosis and treatment.

Cysteine Cathepsins and their Extracellular Roles: Shaping the Microenvironment

For a long time, cysteine cathepsins were considered primarily as proteases crucial for nonspecific bulk proteolysis in the endolysosomal system. However, this view has dramatically changed, and cathepsins are now considered key players in many important physiological processes, including in diseases like cancer, rheumatoid arthritis, and various inflammatory diseases. Cathepsins are emerging as important players in the extracellular space, and the paradigm is shifting from the degrading enzymes to the enzymes that can also specifically modify extracellular proteins. In pathological conditions, the activity of cathepsins is often dysregulated, resulting in their overexpression and secretion into the extracellular space. This is typically observed in cancer and inflammation, and cathepsins are therefore considered valuable diagnostic and therapeutic targets. In particular, the investigation of limited proteolysis by cathepsins in the extracellular space is opening numerous possibilities for future break-through discoveries. In this review, we highlight the most important findings that establish cysteine cathepsins as important players in the extracellular space and discuss their roles that reach beyond processing and degradation of extracellular matrix (ECM) components. In addition, we discuss the recent developments in cathepsin research and the new possibilities that are opening in translational medicine.