Heterogeneous suppression of experimentally induced colon cancer metastasis in rat liver lobes by inhibition of extracellular cathepsin B

Functional characterization of endo-lysosomal compartments by correlative live-cell and volume electron microscopy

Fluorescent biosensors are valuable tools to monitor protein activities and the functional state of organelles in live cells. However, the information provided by fluorescent microscopy (FM) is mostly limited in resolution and lacks ultrastructural context information. Protein activities are confined to organelle zones with a distinct membrane morphology, which can only be seen by electron microscopy (EM). EM, however, intrinsically lacks information on protein activities. The lack of methods to integrate these two imaging modalities has hampered understanding the functional organization of cellular organelles. Here we introduce "functional correlative microscopy" (functional CLEM) to directly infer functional information from live cells to EM with nanometer resolution. We label and visualize live cells with fluorescent biosensors after which they are processed for EM and imaged using a volume electron microscopy technique. Within a single dataset we correlate hundreds of fluorescent spots enabling quantitative analysis of the functional-ultrastructural data. We employ our method to monitor essential functional parameters of late endo-lysosomal compartments, i.e., pH, calcium, enzyme activities and cholesterol content. Our data reveal a steep functional difference in enzyme activity between late endosomes and lysosomes and unexpectedly high calcium levels in late endosomes. The presented CLEM workflow is compatible with a large repertoire of probes and paves the way for large scale functional studies of all types of cellular structures.

Lamp1 mediates lipid transport, but is dispensable for autophagy in Drosophila

The endolysosomal system not only is an integral part of the cellular catabolic machinery that processes and recycles nutrients for synthesis of biomaterials, but also acts as signaling hub to sense and coordinate the energy state of cells with growth and differentiation. Lysosomal dysfunction adversely influences vesicular transport-dependent macromolecular degradation and thus causes serious problems for human health. In mammalian cells, loss of the lysosome associated membrane proteins LAMP1 and LAMP2 strongly affects autophagy and cholesterol trafficking. Here we show that the previously uncharacterized Drosophila Lamp1 is a bona fide ortholog of vertebrate LAMP1 and LAMP2. Surprisingly and in contrast to lamp1 lamp2 double-mutant mice, Drosophila Lamp1 is not required for viability or autophagy, suggesting that fly and vertebrate LAMP proteins acquired distinct functions, or that autophagy defects in lamp1 lamp2 mutants may have indirect causes. However, Lamp1 deficiency results in an increase in the number of acidic organelles in flies. Furthermore, we find that Lamp1 mutant larvae have defects in lipid metabolism as they show elevated levels of sterols and diacylglycerols (DAGs). Because DAGs are the main lipid species used for transport through the hemolymph (blood) in insects, our results indicate broader functions of Lamp1 in lipid transport. Our findings make Drosophila an ideal model to study the role of LAMP proteins in lipid assimilation without the confounding effects of their storage and without interfering with autophagic processes.Abbreviations: aa: amino acid; AL: autolysosome; AP: autophagosome; APGL: autophagolysosome; AV: autophagic vacuole (i.e. AP and APGL/AL); AVi: early/initial autophagic vacuoles; AVd: late/degradative autophagic vacuoles; Atg: autophagy-related; CMA: chaperone-mediated autophagy; Cnx99A: Calnexin 99A; DAG: diacylglycerol; eMI: endosomal microautophagy; ESCRT: endosomal sorting complexes required for transport; FB: fat body; HDL: high-density lipoprotein; Hrs: Hepatocyte growth factor regulated tyrosine kinase substrate; LAMP: lysosomal associated membrane protein; LD: lipid droplet; LDL: low-density lipoprotein; Lpp: lipophorin; LTP: Lipid transfer particle; LTR: LysoTracker Red; MA: macroautophagy; MCC: Manders colocalization coefficient; MEF: mouse embryonic fibroblast MTORC: mechanistic target of rapamycin kinase complex; PV: parasitophorous vacuole; SNARE: soluble N-ethylmaleimide sensitive factor attachment protein receptor; Snap: Synaptosomal-associated protein; st: starved; TAG: triacylglycerol; TEM: transmission electron microscopy; TFEB/Mitf: transcription factor EB; TM: transmembrane domain; tub: tubulin; UTR: untranslated region.

Cathepsin B is a potential therapeutic target for coronavirus disease 2019 patients with lung adenocarcinoma

Coronavirus disease 2019 (COVID-19) was declared a serious global public health emergency. Hospitalization and mortality rates of lung cancer patients diagnosed with COVID-19 are higher than those of patients presenting with other cancers. However, the reasons for the outcomes being disproportionately severe in lung adenocarcinoma (LUAD) patients with COVID-19 remain elusive. The present study aimed to identify the possible causes for disproportionately severe COVID-19 outcomes in LUAD patients and determine a therapeutic target for COVID-19 patients with LUAD. We used publicly available data from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases and various bioinformatics tools to identify and analyze the genes implicated in SARS-CoV-2 infection in LUAD patients. Upregulation of the SARS-CoV-2 infection-related molecules dipeptidyl peptidase 4, basigin, cathepsin B (CTSB), methylenetetrahydrofolate dehydrogenase, and peptidylprolyl isomerase B rather than angiotensin-converting enzyme 2 may explain the relatively high susceptibility of LUAD patients to SARS-CoV-2 infection. CTSB was highly expressed in the LUAD tissues after SARS-CoV-2 infection, and its expression was positively correlated with immune cell infiltration and proinflammatory cytokine expression. These findings suggest that CTSB plays a vital role in the hyperinflammatory response in COVID-19 patients with LUAD and is a promising target for the development of a novel drug therapy for COVID-19 patients.

Reduction of proteinuria through podocyte alkalinization

Podocytes are highly differentiated cells and critical elements for the filtration barrier of the kidney. Loss of their foot process (FP) architecture (FP effacement) results in urinary protein loss. Here we show a novel role for the neutral amino acid glutamine in structural and functional regulation of the kidney filtration barrier. Metabolic flux analysis of cultured podocytes using genetic, toxic, and immunologic injury models identified increased glutamine utilization pathways. We show that glutamine uptake is increased in diseased podocytes to couple nutrient support to increased demand during the disease state of FP effacement. This feature can be utilized to transport increased amounts of glutamine into damaged podocytes. The availability of glutamine determines the regulation of podocyte intracellular pH (pHi). Podocyte alkalinization reduces cytosolic cathepsin L protease activity and protects the podocyte cytoskeleton. Podocyte glutamine supplementation reduces proteinuria in LPS-treated mice, whereas acidification increases glomerular injury. In summary, our data provide a metabolic opportunity to combat urinary protein loss through modulation of podocyte amino acid utilization and pHi.

V-ATPase inhibition by archazolid leads to lysosomal dysfunction resulting in impaired cathepsin B activation in vivo

The myxobacterial agent archazolid inhibits the vacuolar proton pump V-ATPase. V-ATPases are ubiquitously expressed ATP-dependent proton pumps, which are known to regulate the pH in endomembrane systems and thus play a crucial role in endo- and exocytotic processes of the cell. As cancer cells depend on a highly active secretion of proteolytic proteins in order to invade tissue and form metastases, inhibition of V-ATPase is proposed to affect the secretion profile of cancer cells and thus potentially abrogate their metastatic properties. Archazolid is a novel V-ATPase inhibitor. Here, we show that the secretion pattern of archazolid treated cancer cells includes various prometastatic lysosomal proteins like cathepsin A, B, C, D and Z. In particular, archazolid induced the secretion of the proforms of cathepsin B and D. Archazolid treatment abrogates the cathepsin B maturation process leading to reduced intracellular mature cathepsin B protein abundance and finally decreased cathepsin B activity, by inhibiting mannose-6-phoshate receptor-dependent trafficking. Importantly, in vivo reduced cathepsin B protein as well as a decreased proteolytic cathepsin B activity was detected in tumor tissue of archazolid-treated mice. Our results show that inhibition of V-ATPase by archazolid reduces the activity of prometastatic proteases like cathepsin B in vitro and in vivo.

Acid ceramidase-mediated production of sphingosine 1-phosphate promotes prostate cancer invasion through upregulation of cathepsin B

Invasiveness is one of the key features of aggressive prostate cancer; however, our understanding of the precise mechanisms effecting invasion remains limited. The ceramide hydrolyzing enzyme acid ceramidase (AC), overexpressed in most prostate tumors, causes an aggressive and invasive phenotype through downstream effectors that have not yet been well characterized. Here, we demonstrate that AC, through generation of sphingosine-1-phosphate (S1P), promotes Ets1 nuclear expression and binding to the promoter region of matrix-degrading protease cathepsin B. Through confocal microscopy and flow cytometry, we found that AC overexpression promotes pericellular localization of cathepsin B and its translocation to the outer leaflet of the cell membrane. AC overexpressing cells have an increased abundance of cathepsin B-enriched invasive structures and enhanced ability to invade through a collagen matrix, but not in the presence of an inhibitor of cathepsin B. In human prostate tissues, AC and cathepsin B overexpression were strongly associated and may relate to poor outcome. These results demonstrate a novel pathway by which AC, through S1P, promotes an invasive phenotype in prostate cancer by causing overexpression and secretion of cathepsin B through activation and nuclear expression of Ets1. As prostate cancer prognosis is dramatically worse when invasion has occurred, this study provides critical insight into the progression toward lethal prostate cancer.

Analyzing lysosomes in live cells

Lysosomes are an important cellular organelle that receive and degrade macromolecules from the secretory, endocytic, autophagic, and phagocytic membrane-trafficking pathways. Defects in lysosome function lead to the development of disease with often-severe consequences to the individual. Since the discovery of lysosomes by Christian de Duve over 50 years ago, research into endocytic and lysosomal biology has allowed for the development of tools to understand further the role of lysosomes in cells. There are now several fluorescent probes that can be used to visualize and assess membrane traffic to the lysosome as well as probes to assess the activity of lysosomal hydrolases in live cells. This chapter describes the current methods used to measure lysosome function in live cells.

Activatable Optical Probes for the Detection of Enzymes

The early detection of many human diseases is crucial if they are to be treated successfully. Therefore, the development of imaging techniques that can facilitate early detection of disease is of high importance. Changes in the levels of enzyme expression are known to occur in many diseases, making their accurate detection at low concentrations an area of considerable active research. Activatable fluorescent probes show immense promise in this area. If properly designed they should exhibit no signal until they interact with their target enzyme, reducing the level of background fluorescence and potentially endowing them with greater sensitivity. The mechanisms of fluorescence changes in activatable probes vary. This review aims to survey the field of activatable probes, focusing on their mechanisms of action as well as illustrating some of the in vitro and in vivo settings in which they have been employed.

Imaging enzymes at work: metabolic mapping by enzyme histochemistry

For the understanding of functions of proteins in biological and pathological processes, reporter molecules such as fluorescent proteins have become indispensable tools for visualizing the location of these proteins in intact animals, tissues, and cells. For enzymes, imaging their activity also provides information on their function or functions, which does not necessarily correlate with their location. Metabolic mapping enables imaging of activity of enzymes. The enzyme under study forms a reaction product that is fluorescent or colored by conversion of either a fluorogenic or chromogenic substrate or a fluorescent substrate with different spectral characteristics. Most chromogenic staining methods were developed in the latter half of the twentieth century but still find new applications in modern cell biology and pathology. Fluorescence methods have rapidly evolved during the last decade. This review critically evaluates the methods that are available at present for metabolic mapping in living animals, unfixed cryostat sections of tissues, and living cells, and refers to protocols of the methods of choice.

Cathepsin L, target in cancer treatment?

Cathepsin L, a cysteine protease, is considered to be a potential therapeutic target in cancer treatment. Proteases are involved in the development and progression of cancer. Inhibition of activity of specific proteases may slow down cancer progression. In this review, we evaluate recent studies on the inhibition of cathepsin L in cancer. The effects of cathepsin L inhibition as a monotherapy on apoptosis and angiogenesis in cancer are ambiguous. Cathepsin L inhibition seems to reduce invasion and metastasis, but there is concern that selective cathepsin L inhibition induces compensatory activity by other cathepsins. The combination of cathepsin L inhibition with conventional chemotherapy seems to be more promising and has yielded more consistent results. Future research should be focused on the mechanisms and effects of this combination therapy.

Cathepsin B release from rodent intestine mucosa due to mechanical injury results in extracellular matrix damage in early post-traumatic phases

An in vivo model was used to investigate the role of cathepsins in mouse intestine after mechanical manipulation. Inspection of different intestine segments by immunofluorescence microscopy provided evidence for a local release of cathepsin B from cells of individual gut sections shortly after traumatic injury. Densitometry of immunoblots ruled out alterations in cathepsin B expression levels. Because similar results were obtained with both mouse and rat intestine trauma models, we were interested in identifying potential targets of released cathepsin B in early post-traumatic phases. Immunoblotting revealed initial declines followed by an increase in protein levels of claudin-1 and E-cadherin, indicating that tight junctions and cell-cell adhesions were only transiently compromised by surgical trauma. Apical aminopeptidase N and dipeptidyl peptidase IV were only slightly affected, whereas basolateral low-density lipoprotein receptors were strongly up-regulated in response to trauma. As potential targets of cathepsin B released from injured cells, we identified collagen IV and laminin of the basement membrane that was damaged during initial post-traumatic stages. Because increased collagen IV expression was observed in the intestine of cathepsin B-deficient animals, we propose a direct role of cathepsin B in that it contributes to acute post-traumatic extracellular matrix damage and may thereby facilitate onset of post-operative ileus.

The cathepsin family and their role in colorectal cancer. Pathol Res Pract. 2008;204:491-500. [PMID: 18573619 DOI: 10.1016/j.prp.2008.04.010]

Cathepsins are a class of globular proteases, initially described as intracellular peptide hydrolases, although several cathepsins also have extracellular functions. Cathepsins B, C, F, H, L, K, O, S, V, W, and X are cysteine proteases of the papain family, and represent the largest and best-known class of the cathepsins. Cathepsin G is a serine carboxypeptidases, and cathepsins D and E are aspartic proteases. Cathepsins are synthesized as inactive proenzymes and processed to become mature and active enzymes. Endogenous protein inhibitors, such as cystatins and some serpins, inhibit active enzymes. As primarily lysosomal proteases, cathepsins play important roles in proteolysis during physiological processes, as well as in several diseases. On the basis of their ability to degrade extracellular matrix proteins, cathepsins have been implicated to play a role in invasion and metastasis of colorectal cancer. In the present review, the role of cathepsins in the disease process of colorectal cancers and the correlation of cathepsin expression and activity with clinicopathological features is discussed. Furthermore, we give an overview of the recent developments of cathepsins in animal models and in in vitro experiments of colorectal disease, and provide information on inhibitors of cathepsins as possible therapeutics.

Is there a genetic signature for liver metastasis in colorectal cancer?

Even though liver metastasis accounts for the vast majority of cancer deaths in patients with colorectal cancer (CRC), fundamental questions about the molecular and cellular mechanisms of liver metastasis still remain unanswered. Determination of gene expression profiles by microarray technology has improved our knowledge of CRC molecular pathways. However, defined gene signatures are highly variable among studies. Expression profiles and molecular markers have been specifically linked to liver metastases mechanistic paths in CRC. However, to date, none of the identified signatures or molecular markers has been successfully validated as a diagnostic or prognostic tool applicable to routine clinical practice. To obtain a genetic signature for liver metastasis in CRC, measures to improve reproducibility, to increase consistency, and to validate results need to be implemented. Alternatives to expression profiling with microarray technology are continuing to be used. In the recent past, many genes codifying for proteins that are directly or indirectly involved in adhesion, invasion, angiogenesis, survival and cell growth have been linked to mechanisms of liver metastases in CRC.

Cysteine cathepsin proteases as pharmacological targets in cancer

Proteolytic activity is required for several key pro-tumorigenic processes: angiogenesis, invasion and metastasis. Consequently, increases in protease expression and activity are frequently reported in human cancers, and correlate with malignant progression and poor patient prognosis. Cysteine cathepsin proteases have recently emerged as an important class of proteolytic enzymes in cancer development, and cysteine cathepsin inhibitors have been proposed as anticancer agents. In this review, we highlight recent studies that now allow us to evaluate critically whether cysteine cathepsin inhibition represents a viable therapeutic strategy for the treatment of cancer.

Immunonanoparticles − an effective tool to impair harmful proteolysis in invasive breast tumor cells

Breast cancer cells exhibit excessive proteolysis, which is responsible for extensive extracellular matrix degradation, invasion and metastasis. Besides other proteases, lysosomal cysteine protease cathepsin B has been implicated in these processes and the impairment of its intracellular activity was suggested to reduce harmful proteolysis and hence diminish progression of breast tumors. Here, we present an effective system composed of poly(D,L-lactide-coglycolide) nanoparticles, a specific anti-cytokeratin monoclonal IgG and cystatin, a potent protease inhibitor, that can neutralize the excessive intracellular proteolytic activity as well as invasive potential of breast tumor cells. The delivery system distinguishes between breast and other cells due to the monoclonal antibody specifically recognizing cytokeratines on the membrane of breast tumor cells. Bound nanoparticles are rapidly internalized by means of endocytosis releasing the inhibitor cargo within the lysosomes. This enables intracellular cathepsin B proteolytic activity to be inhibited, reducing the invasive and metastatic potential of tumor cells without affecting proteolytic functions in normal cells and processes. This approach may be applied for treatment of breast and other tumors in which intracellular proteolytic activity is a part of the process of malignant progression.

Cysteine cathepsins: regulators of antitumour immune response

Cysteine cathepsins are lysosomal cysteine proteases that are involved in a number of important biological processes, including intracellular protein turnover, propeptide and hormone processing, apoptosis, bone remodelling and reproduction. In cancer, the cathepsins have been linked to extracellular matrix remodelling and to the promotion of tumour cell motility, invasion, angiogenesis and metastasis, resulting in poor outcome of cancer patients; however, cysteine cathepsins are also involved at different levels of the innate and adaptive immune responses. Their best known role in this aspect is their contribution to major histocompatibility complex class II antigen presentation, the processing of progranzymes into proteolytically active forms, cytotoxic lymphocyte self-protection, cytokine and growth factor degradation and, finally, the induction of cytokine expression and modulation of integrin function. This review is focused on the role of cysteine cathepsins in the antitumour immune response and the evaluation of their pro- and anticancer behaviours during the regulation of these processes.

Improved Acylation Method Enables Efficient Delivery of Functional Palmitoylated Cystatin into Epithelial Cells

The effective delivery of therapeutic proteins to the site of action is of great importance in achieving an effective therapy. Due to hydrophilicity, proteins are generally poorly transported across biological membranes. Chemical acylation represents one of the basic methods for improving their membrane permeability. A novel method for acylation is presented, based on the formation of palmitoylchloride dispersion in aqueous acetonitrile solution, using chicken cystatin as a model protein. We examined the effects of palmitoylchloride/cystatin molar ratio, reaction pH and introduction of successive palmitoylation cycles on the protein modification degree. The reaction products were analysed by capillary electrophoresis and SDS-PAGE, and the in vitro inhibitory activity was determined by N-benzoyl-D,L-arginine-beta-naphthylamide assay. Using cell culture-based assays, we examined the transport properties of unmodified and palmitoylated cystatin, its efficiency to inhibit intracellular enzymes, and its cytotoxicity. We demonstrated that palmitoylated cystatin rapidly internalized into the cell and caused a complete loss of cathepsin B activity. In contrast, the unmodified control cystatin was unable to inhibit the intracellular enzymes. These results strongly suggest protein palmitoylation to be a very effective strategy for improving cell internalization.

Lysosomal destabilization contributes to apoptosis of germinal center B-lymphocytes

During germinal center (GC) reactions, B-lymphocytes with high-affinity B-cell receptors are selected. Regulation of apoptosis is a key process in selecting such wanted B-cells and in eliminating B-cells with unwanted specificities. In this paper, we show that apoptosis in human GC B-cells involves lysosomal destabilization, which is strictly controlled by caspase-8 activity, but not by caspase-9 activity. Ligation of CD40 provides resistance to lysosomal destabilization. Experimental lysosomal rupture by the lysosomotropic drug O-methyl-l-serine dodecylamide hydrochloride (MSDH) induces apoptosis in GC B-cells, including phosphatidyl serine exposure, mitochondrial inactivation, and DNA fragmentation. These apoptotic features occur in the absence of caspase-3 activity. Follicular dendritic cells (FDCs) protect binding B-lymphocytes from lysosomal destabilization, in both the absence and the presence of MSDH. Our study demonstrates that lysosomal leakage induces apoptosis of GC B-cells in a caspase-3-independent manner and that high-affinity binding to FDCsprevents lysosomal leakage and apoptosis in GC B-cells.

Antiprotease therapy in cancer: hot or not?

The activity of a set of peptidases (proteases) involved in cancer progression is collectively known as the cancer 'degradome'. Invasion and metastasis were initially considered as late events in cancer development and the processes in which proteases were involved. However, recent studies indicate that invasion and metastasis are not late events, but can occur during early stages as well. Moreover, other processes occurring in various stages of cancer progression are also protease-dependent, such as (upregulation of) cell proliferation, (downregulation of) apoptosis, involvement of white blood cells, angiogenesis and induction of multi-drug resistance. Proteolytic activity in tumours is regulated in a complex manner, as both genetically unstable cancer cells and stable stromal cells, such as fibroblasts, endothelial cells and inflammatory cells, are involved. In vitro studies and studies using animal models have clearly shown protease dependency of many processes in carcinogenesis. However, clinical trials using protease inhibitors have thus far been unsuccessful except for a few applications of matrix metalloprotease (MMP) inhibitors when used in combination with cytostatic anticancer agents and/or in the early stages of cancer. Antithrombotics, such as low-molecular-weight heparin and warfarin, were also successful in clinical trials, probably by interfering with proteases of the coagulation cascade. The two-way association between cancer and thrombosis has long been recognised in the clinic. The poor outcome of other clinical trials of protease inhibitors is probably due to the late stages of cancer of the patient populations included, and the limited understanding of the complex regulation and effects of the activity of the various proteases in tumours depending on, among others, tumour type and stage, interactions between the cancer cells, other cells and the extracellular matrix in tumours. Therefore, a better fundamental understanding of the proteolytic complexity in tumours is essential before clinical trials can be rationally designed. At present, antithrombotics, the urokinase-type plasminogen activator system, the membrane-bound membrane-type 1-MMP, cathepsin L and the proteasome seem the most promising candidates as targets for anticancer strategies in early stages of cancer in combination with cytotoxic drugs. Moreover, metronomic therapy is an attractive approach using low doses of inhibitors for prolonged periods of time without interruption to specifically target endothelial cells that are involved in angiogenesis.

Intracellular proteolytic activity of cathepsin B is associated with capillary-like tube formation by endothelial cells in vitro

The lysosomal cysteine protease cathepsin B is implicated in degradation of extracellular matrix (ECM), a crucial step in a variety of physiological and pathological processes, including tumor dissemination and angiogenesis. In this study, we analyzed the contribution of extracellular and intracellular cathepsin B activity on the formation of capillary-like tubular structures by human umbilical vein endothelial cells (HUVECs) grown on Matrigel matrix, using general and specific cysteine protease inhibitors. We demonstrated, by confocal assay using quenched fluorescent protein substrate DQ-collagen IV, that endothelial cells degrade ECM both intracellularly and pericellularly. Intracellular cathepsin B activity detected by degradation of Z-Arg-Arg cresyl violet substrate was co-localized with the products of DQ-collagen IV degradation in the perinuclear region and in the capillary-like tubular structures. Treatment of cells with membrane-permeable CA-074 Me effectively abolished intracellular cathepsin B activity, and resulted in reduced tube length (32.3+/-9.4% at 10 microM), total tubule area (49.6+/-12.4% at 10 microM), and the number of branch points of tubules (47.5+/-7.7% at 10 microM) in a dose-dependent manner. In contrast, CA-074 (0.1-10 microM), a membrane-impermeable cathepsin B specific inhibitor, general cysteine protease inhibitors chicken cystatin (5 microM) and E-64 (10 microM), and the metalloprotease inhibitor Minocycline (10 microM) showed no significant inhibitory effect in our angiogenesis model. These results show that, besides multiple regulatory molecules, intracellular cathepsin B also contributes to the neovascularization process and should be considered as a potential therapeutic target.

Cathepsin B mediates TRAIL-induced apoptosis in oral cancer cells

PURPOSE

The death ligand TRAIL (tumor necrosis factor-related apoptosis inducing ligand) triggers apoptosis in a variety of cancer cells, which implies the potential for therapeutic applications. The purpose of this study was to investigate the role of the lysosomal protease cathepsin B (CB) in mediating TRAIL-induced cell death in oral squamous cell carcinoma (OSCC) cells.

METHODS

OSCC cell lines from primary tumor and lymph node metastasis were examined for expression of apoptosis markers by Western blots, enzyme activity assays, nuclear fragmentation assays, and FACS analysis. Gene-specific ribozymes or chemical inhibitors were used to inhibit CB or caspases in target cells.

RESULTS

TRAIL-induced activation of caspase-3, cleavage of Bid and poly-ADP-ribose polymerase, release of cytochrome c, and DNA fragmentation were blocked either by a pan-caspase inhibitor (zVAD-fmk) or a CB inhibitor (CA074Me), consistent with the involvement of TRAIL as well as CB in cell death. The primary tumor cells were more susceptible to apoptosis than their corresponding lymph node metastatic cells. Stable transfection of a ribozyme which inhibited CB expression also decreased the apoptotic process.

CONCLUSIONS

We conclude that TRAIL-induced apoptotic cell death in OSCC cells is mediated through CB or through caspase activation. Our data point to a new tumor-suppressive role for CB in OSCC which is opposed to the invasion- and metastasis-promoting functions of lysosomal proteases.

Extracellular matrix degrading enzymes at the prostasome surface

Prostasomes, prostatic secretory vesicles found in human ejaculates, were analyzed to verify the existence at their surfaces of enzymes involved in the degradation of the extracellular matrix. Findings were compared with those of prostasomes isolated from two human adenocarcinoma cell lines that reflect clinical features and molecular pathways of androgen-insensitive and hormone-responsive prostate cancer. Our aim was to determine whether neoplastic transformation is accompanied by changes of glycosidase and protease activities. Our results show that decreases of dipeptidyl peptidase IV and increases of urokinase plasminogen activator and cathepsin B are consistent with the clinical features of the cell lines, whereas increases of glycosidase activities seem to be of scarce biological significance.

Late stage inhibition of hematogenous melanoma metastasis by cystatin C over-expression

Background

Tumor metastasis is a frequent cause of treatment failure for cancer patients. A key feature of metastatic cancer cells is their invasive ability. Cysteine proteases contribute to invasive properties of many cancer cell types. To analyze the contribution of cysteine proteases to metastasis we have over-expressed in B16 melanoma cells the natural cysteine protease inhibitor, cystatin C. We measured in vitro invasion of cystatin over-expression clones with Boyden chamber type assays. Tail-vein injections of cells were used to compare lung tumor colonization. Subcutaneous tumor growth and tumor cell metastasis from primary tumors were also analyzed. Apoptosis of tumor cells was measured in lung tissues following melanoma cell injection.

Results

Results show the in vitro invasion of cystatin C over-expressing cells was dramatically inhibited. Lung tumor colonization was also reduced. Increased tumor cell apoptosis was found to be an important factor and may be related to the reduced tumor burden noted in this system of melanoma metastasis.

Conclusion

Cysteine proteases therefore, may be a target for future anti-metastatic therapies.

Poly(lactide-co-glycolide) nanoparticles as a carrier system for delivering cysteine protease inhibitor cystatin into tumor cells

Cystatins are able to inhibit the tumor-associated activity of intracellular cysteine proteases cathepsins B and L and have been suggested as potential anticancer drugs. We have incorporated chicken cystatin, a model protein inhibitor of cysteine proteases, in poly(lactide-co-glycolide) (PLGA) nanoparticles (NPs) to improve its bioavailability and delivery into tumor cells. Cystatin-loaded NPs, 300-350 nm in diameter, were prepared by the double emulsion solvent diffusion method using low energy emulsification to preserve the biological activity of the protein. PLGA NPs and cystatin-loaded PLGA NPs at concentrations higher than 80 microg/ml were cytotoxic towards MCF-10A neoT cells, but not free cystatin at concentrations up to 5 microM. To visualize the uptake of cystatin into living MCF-10A neoT cells, NPs loaded with Alexa Fluor 488-labeled cystatin were added to the culture medium. They rapidly internalized into the cells, whereas the uptake of free-labeled cystatin was very slow. Cystatin, released from the NPs, effectively inhibited cathepsin B activity, as detected by degradation of specific Z-Arg-Arg cresyl violet substrate. In contrast, the same amount of free cystatin showed no inhibition of intracellular cathepsin B. Our results show that PLGA NPs are a useful carrier system for rapid delivery of protein inhibitors into tumor cells, enabling effective inhibition of intracellular proteolysis. The approach can be applied to other protein drugs active against intracellular targets.

The metastatic potential of human pancreatic cell lines in the liver of nude mice correlates well with cathepsin B activity

BACKGROUND

Cathepsin B, a lysosomal cysteine protease, has a major role in the mechanisms of tumor metastasis. The aim of the present work was to examine the correlation between cathepsin B activity and the metastatic potential of human pancreatic cancer.

METHODS

The primary cell line COLO 357 and the derivative tumor cell lines FG, L3.1, L3.2, L3.3, L3.4, and L3.5, which are characterized by progressively increasing metastatic potential, were injected intrasplenically in the athymic mice. Cathepsin B activity, metastasis, and ultrastructural characteristics were assessed.

RESULTS

An increased number of liver tumor nodules was observed with each subsequent intrasplenic inoculation (p = 0.001), associated with lymph node, splenic, and pancreatic involvement. Cathepsin B activity progressively increased (p = 0.001) and was strongly positively correlated with the metastatic potential. However, no correlation was found between the metastatic potential and ultrastructural characteristics.

CONCLUSIONS

These findings further support the central role of cathepsin B in metastasis in a combined in vitro/in vivo model.

Metabolic mapping of proteinase activity with emphasis on in situ zymography of gelatinases: review and protocols

Proteases are essential for protein catabolism, regulation of a wide range of biological processes, and in the pathogenesis of many diseases. Several techniques are available to localize activity of proteases in tissue sections or cell preparations. For localization of the activity of matrix metalloproteinases, in situ zymography was introduced some decades ago. The procedure is based on zymography using SDS polyacrylamide gels containing gelatin, casein, or fibrin as substrate. For in situ zymography, either a photographic emulsion containing gelatin or a fluorescence-labeled proteinaceous macromolecular substrate is brought into contact with a tissue section or cell preparation. After incubation, enzymatic activity is revealed as white spots in a dark background or as black spots in a fluorescent background. However, this approach does not allow precise localization of proteinase activity because of limited sensitivity. A major improvement in sensitivity was achieved with the introduction of dye-quenched (DQ-)gelatin, which is gelatin that is heavily labeled with FITC molecules so that its fluorescence is quenched. After cleavage of DQ-gelatin by gelatinolytic activity, fluorescent peptides are produced that are visible against a weakly fluorescent background. The incubation with DQ-gelatin can be combined with simultaneous immunohistochemical detection of a protein on the same section. To draw valid conclusions from the findings with in situ zymography, specific inhibitors need to be used and the technique has to be combined with immunohistochemistry and zymography. In that case, in situ zymography provides data that extend our understanding of the role of specific proteinases in various physiological and pathological conditions.

Adenovirus-Mediated Expression of Antisense Urokinase Plasminogen Activator Receptor and Antisense Cathepsin B Inhibits Tumor Growth, Invasion, and Angiogenesis in Gliomas

We have shown previously that urokinase plasminogen activator receptor (uPAR) and cathepsin B are overexpressed during glioma progression, particularly at the leading edge of the tumor. In the present study, we simultaneously down-regulated uPAR and cathepsin B in SNB19 glioma cell monolayer or SNB19 spheroids using an adenoviral vector carrying antisense uPAR and antisense cathepsin B and a combination of these genes as determined by Western blot analysis. The Ad-uPAR-Cath B-infected cells revealed a marked reduction in tumor growth and invasiveness as compared with the parental and vector controls. In vitro and in vivo angiogenic assays demonstrated inhibition of capillary-like structure formation and microvessel formation after Ad-uPAR-Cath B infection of SNB19 cells when compared with Ad-cytomegalovirus (CMV)-infected or mock-infected controls. Furthermore, using a near infrared fluorescence probe, in vivo imaging for cathepsin B indicated low/undetectable levels of fluorescence after injection of the Ad-uPAR-Cath B construct into pre-established s.c. tumors as compared with Ad-CMV-treated and untreated tumors. The effect with bicistronic construct (Ad-uPAR-Cath B) was much higher than with single (Ad-uPAR/Ad-Cath B) constructs. These results indicate that the down-regulation of cathepsin B and uPAR plays a significant role in inhibiting tumor growth, invasion, and angiogenesis. Hence, the targeting of these two proteases may be a potential therapy for brain tumors and other cancers.

Podocyte migration during nephrotic syndrome requires a coordinated interplay between cathepsin L and alpha3 integrin

Podocyte foot process effacement and disruption of the slit diaphragm are typically associated with glomerular proteinuria and can be induced in rats by the injection of puromycin aminonucleoside. Here, we show that the induction of puromycin aminonucleoside nephrosis involves podocyte migration conducted by a coordinated interplay between the cysteine protease cathepsin L and alpha(3) integrin. Puromycin aminonucleoside treatment up-regulates cathepsin L expression in podocytes in vivo as well as expression and enzymatic activity of cathepsin L in podocytes in vitro. Isolated podocytes from mice lacking cathepsin L are protected from cell puromycin aminonucleoside-induced cell detachment. The functional significance of cathepsin L expression was underscored by the observation that puromycin aminonucleoside-induced cell migration was slowed down in cathepsin L-deficient podocytes and by the preservation of cell-cell contacts and expression of vital slit diaphragm protein CD2AP. Cathepsin L expression and activity were induced in podocytes lacking alpha(3) integrin. Similarly, acute functional inhibition of alpha(3) integrin in wild type podocytes with a blocking antibody increased the expression of cathepsin L activity. Down-regulation of alpha(3) integrin protected against puromycin aminonucleoside-induced podocyte detachment. In summary, these data establish that podocyte foot process effacement is a migratory event involving a novel interplay between cathepsin L and alpha(3) integrin.

Cysteine proteases as disease markers

This review comprises issues concerning cysteine cathepsins (CCs): human peptidases belonging to papain family (C1) of clan CA of cysteine proteases: cathepsins B, L, H, S, K, F, V, X, W, O and C. The involvement of these enzymes in physiological and pathological processes is described, especially with respect to their application as diagnostic and prognostic markers. They participate in precursor protein activation (including proenzymes and prohormones), MHC-II-mediated antigen presentation, bone remodeling, keratinocytes differentiation, hair follicle cycle, reproduction and apoptosis. Cysteine cathepsins upregulation has been demonstrated in many human tumors, including breast, lung, brain, gastrointestinal, head and neck cancer, and melanoma. Besides cancer diseases, they have been implied to participate in inflammatory diseases, such as inflammatory myopathies, rheumatoid arthritis, and periodontitis. Also, certain hereditary disorders are connected with mutations in CCs genes, what is observed in pycnodysostosis resulted from catK gene mutation and Papillon-Lefevre and Haim-Munk syndrome caused by catC gene defect. The potential application of cysteine cathepsins in diagnosis and/or prognosis is discussed in cancer diseases (breast, lung, head and neck, ovarian, gastrointestinal cancers, melanoma), as well as other disorders (periodontitis, rheumatoid arthritis, osteoarthritis).

Structural examination of tryptase- and chymase-positive mast cells in livers, containing metastases from gastrointestinal cancers

Human mast cells are categorized into mast cells positive only for tryptase (MC(T)) and mast cells positive for both tryptase and chymase (MC(TC)). The structural appearance of tryptase-, and chymase-positive mast cells in metastatic liver disease and the variations in MC(T) and MC(TC) numbers in accordance with the origin of the primary tumors have been described in the present study. Liver mast cells are analyzed immunocytochemically using tryptase and chymase and by quantitative morphometry in 30 patients with colorectal (n = 15), gastric (n = 8), and pancreatic (n = 7) cancers and in 5 control livers. The numbers of MC(T) and MC(TC) are increased in the extratumoral liver tissue (mainly portal tracts) as compared to controls. The numbers of MC(T) and MC(TC) in and around metastases with moderate or high grade of differentiation are statistically significantly higher, as compared to those with low grades of differentiation. The numbers of MC(TC) are greater than that of MC(T) in the extratumoral liver tissue and in metastases themselves. Ultrastructurally, mast cells immunostained with tryptase and chymase have three types of granules: electron dense granules with darkly precipitated reaction product, electron lucent granules without reaction product and electron lucent granules with sparse reaction product (altered granules). Both types of mast cells have small and large in size granules, resembling the MC(TC) phenotype described earlier. Tryptase-positive mast cells have granules with discrete scrolls and particulate and beaded pattern. Chymase-positive mast cells have granules with finely granular or particulate material. Substance P (SP)- and vasointestinal polypeptide (VIP)-positive mast cells are not observed in livers with metastases. The present study suggests that liver mast cells are mainly from the MC(TC) type, and are accumulated in peritumoral and metastatic areas. They may play a role in the formation of tumor stroma, or in tumor immunology in liver metastases from various primary gastrointestinal cancers.

Functional Imaging of Proteolysis: Stromal and Inflammatory Cells Increase Tumor Proteolysis

The underlying basement membrane is degraded during progression of breast and colon carcinoma. Thus, we imaged degradation of a quenched fluorescent derivative of basement membrane type IV collagen (DQ-collagen IV) by living human breast and colon tumor spheroids. Proteolysis of DQ-collagen IV by HCT 116 and HKh-2 human colon tumor spheroids was both intracellular and pericellular. In contrast, proteolysis of DQ-collagen IV by BT20 human breast tumor spheroids was pericellular. As stromal elements can contribute to proteolytic activities associated with tumors, we also examined degradation of DQ-collagen IV by human monocytes/macrophages and colon and breast fibroblasts. Fibroblasts themselves exhibited a modest amount of pericellular degradation. Degradation was increased 4–17-fold in cocultures of fibroblasts and tumor cells as compared to either cell type alone. Inhibitors of matrix metalloproteinases, plasmin, and the cysteine protease, cathepsin B, all reduced degradation in the cocultures. Monocytes did not degrade DQ-collagen IV; however, macrophages degraded DQ-collagen IV intracellularly. In coculture of tumor cells, fibroblasts, and macrophages, degradation of DQ-collagen IV was further increased. Imaging of living tumor and stromal cells has, thus, allowed us to establish that tumor proteolysis occurs pericellularly and intracellularly and that tumor, stromal, and inflammatory cells all contribute to degradative processes.

Proteinases and their inhibitors in the immune system

The most important roles of proteinases in the immune system are found in apoptosis and major histocompatibility complex (MHC) class II-mediated antigen presentation. A variety of cysteine proteinases, serine proteinases, and aspartic proteinases as well as their inhibitors are involved in the regulation of apoptosis in neutrophils, monocytes, and dendritic cells, in selection of specific B and T lymphocytes, and in killing of target cells by cytotoxic T cells and natural killer cells. In antigen presentation, endocytosed antigens are digested into antigenic peptides by both aspartic and cysteine proteinases. In parallel, MHC class II molecules are processed by aspartic and cysteine proteinases to degrade the invariant chain that occupies the peptide-binding site. Proteinase activity in these processes is highly regulated, particularly by posttranslational activation and the balance between active proteinases and specific endogenous inhibitors such as cystatins, thyropins, and serpins. This article discusses the regulation of proteolytic processes in apoptosis and antigen presentation in immune cells and the consequences of therapeutic interference in the balance of proteinases and their inhibitors.

In situ localization of gelatinolytic activity in the extracellular matrix of metastases of colon cancer in rat liver using quenched fluorogenic DQ-gelatin

Matrix metalloproteinases (MMPs) such as gelatinases are believed to play an important role in invasion and metastasis of cancer. In this study we investigated the possible role of MMP-2 and MMP-9 in an experimental model of colon cancer metastasis in rat liver. We demonstrated with gelatin zymography that the tumors contained MMP-2 and MMP-9, but only MMP-2 was present in the active form. Immunolocalization of MMP-2 showed that the protein was localized at basement membranes of colon cancer cells and in intratumor stroma, associated with extracellular matrix (ECM) components. However, zymography and immunohistochemistry (IHC) do not provide information on the localization of MMP activity. Therefore, we developed an in situ zymography technique using the quenched fluorogenic substrate DQ-gelatin in unfixed cryostat sections. The application of DQ-gelatin in combination with a gelled medium allows precise localization of gelatinolytic activity. Fluorescence due to gelatinolytic activity was found in the ECM of tumors and was localized similarly to both MMP-2 protein and collagen type IV, its natural substrate. The localization of MMP-2 activity and collagen type IV at similar sites suggests a role of MMP-2 in remodeling of ECM of stroma in colon cancer metastases in rat liver.

Expression of cell adhesion molecules, their ligands and tumour necrosis factor alpha in the liver of patients with metastatic gastrointestinal carcinomas

The expression of the following cell adhesion molecules, their beta1 and beta2 integrin ligands and the cytokine tumour necrosis factor-alpha (TNF-alpha) was investigated by light and electron microscope immunohistochemistry in the liver tissue in 20 patients with colorectal and gastric cancer also presenting with liver metastases: intercellular adhesion molecule-1 (ICAM-1), vascular endothelial adhesion molecule-1 (VCAM-1), E-selectin, leucocyte function-associated antigen-1 (LFA-1), macrophage antigen-1 (Mac-1), and very late antigen-4 (VLA-4). We have found a parallel enhancement of the adhesion molecules and of TNF-alpha in liver sinusoids surrounding metastases. The expression of ICAM-1 was enhanced on sinusoidal cells in all zones of the acinus. VCAM-1 immune reactivity was diffuse but less intensive in the lobule. E-selectin expression was observed in sinusoidal cells attached to metastases. In tumour metastases the expression of ICAM-1, VCAM-1, and E-selectin was visible on the tumour vascular endothelium. Tumour infiltrating host cells sowing positive immunoreactivity for ICAM-1, VCAM-1, LFA-1, Mac-1, and VLA-4 were located mainly at the boundary between liver parenchyma and the metastasis. At the ultrastructural level, ICAM-1-positive immune deposits were observed on the cellular membrane and in some transport vesicles of gastric metastatic cells. Further, the expression of all adhesion molecules was confirmed to sinusoidal endothelial cells and tumour vessels. It is concluded that the enhanced expression of adhesion molecules in liver sinusoids could be a marker for the assessment of the ability of sinusoidal endothelial cells to control the recruitment of leukocytes and monocytes to the metastatic site. They could also direct the adhesion of new circulating tumour cells to sinusoidal endothelium.

Enzyme cytochemical techniques for metabolic mapping in living cells, with special reference to proteolysis

Specific enzymes play key roles in many pathophysiological processes and therefore are targets for therapeutic strategies. The activity of most enzymes is largely determined by many factors at the post-translational level. Therefore, it is essential to study the activity of target enzymes in living cells and tissues in a quantitative manner in relation to pathophysiological processes to understand its relevance and the potential impact of its targeting by drugs. Proteases, in particular, are crucial in every aspect of life and death of an organism and are therefore important targets. Enzyme activity in living cells can be studied with various tools. These can be endogenous fluorescent metabolites or synthetic chromogenic or fluorogenic substrates. The use of endogenous metabolites is rather limited and nonspecific because they are involved in many biological processes, but novel chromogenic and fluorogenic substrates have been developed to monitor activity of enzymes, and particularly proteases, in living cells and tissues. This review discusses these substrates and the methods in which they are applied, as well as their advantages and disadvantages for metabolic mapping in living cells.

Promotion of colon cancer metastases in rat liver by fish oil diet is not due to reduced stroma formation

Recently, it was demonstrated that dietary omega-3 polyunsaturated fatty acids (PUFAs) induce 10-fold more metastases in number and 1000-fold in volume in an animal model of colon cancer metastasis in rat liver. It was observed that tumors of rats on a fish oil diet lacked peritumoral stroma unlike tumors in livers of rats on a low fat diet or a diet containing omega-6 PUFAs. In the present study, only one-third of the tumors in livers of rats on omega-3 PUFA diet contained peritumoral stroma, whereas peritumoral stroma was present in 87% of the tumors in livers of rats on low fat diet. To explain these findings, we tested the hypothesis that fish oil exerts a direct inhibiting effect on the formation of extracellular matrix in tumor stroma as a consequence of blocking transformation of fat storing cells into myofibroblasts. It was found with immunohistochemical analysis of desmin as marker for fat storing cells and alpha-smooth muscle actin as marker for myofibroblasts that numbers of myofibroblasts were higher in tumors containing intratumoral stroma only than in tumors containing both peritumoral and intratumoral stroma. As most of the tumors in fish oil-treated rats contained intratumoral stroma only, this suggests that transformation of fat storing cells into myofibroblasts was highest in tumor stroma of fish oil-treated rats. Therefore, it is unlikely that the lack of stroma around tumors in fish oil-treated rats is due to inhibition of transformation of fat storing cells into myofibroblasts, but lack of peritumoral stroma is rather a consequence of rapid development of tumors in livers of fish oil-treated rats.

The history of Z-VAD-FMK, a tool for understanding the significance of caspase inhibition

Dr. Robert Smith is one of the pioneers in histochemistry. One of his most important achievements is the recognition of proteolysis as a major physiological and pathophysiological process. As a consequence, he developed selective fluorogenic and chromogenic substrates and specific inhibitors of proteases that allow the (histochemical) analysis of protease activity. One of the latest successes is the design of Z-VAD-fluoromethylketone (FMK), the specific caspase inhibitor, that is a key compound for studies on apoptosis. Its development was originally meant for therapeutic use but unforeseen cytotoxicity of a metabolic derivative of the FMK compound disabled its potential as a drug. However, as a tool for fundamental research it is a great success. The history of Z-VAD-FMK is an example of the creative brain and the tireless perseverance of Robert Smith for which histochemistry and cytochemistry owes him so much. This history of Z-VAD-FMK is a well-deserved tribute at the occasion of his 70th birthday.

Down-regulation of cathepsin B expression impairs the invasive and tumorigenic potential of human glioblastoma cells

Increases in abundance of cathepsin B transcript and protein correlate with increases in tumor grade and alterations in subcellular localization and activity of cathepsin B. The enzyme is able to degrade the components of the extracellular matrix (ECM) and activate other proteases capable of degrading ECM. To investigate the role played by this protease in the invasion of brain tumor cells, we transfected SNB19 human glioblastoma cells with a plasmid containing cathepsin B cDNA in antisense orientation. Control cells were transfected with vector alone. Clones expressing antisense cathepsin B cDNA exhibited significant reductions in cathepsin B mRNA, enzyme activity and protein compared to controls. Matrigel Invasion assay showed that the antisense-transfected cells had a markedly diminished invasiveness compared with controls. When tumor spheroids containing antisense transfected SNB19 cells expressing reduced cathepsin B were co-cultured with fetal rat brain aggregates, invasion of fetal rat brain aggregates was significantly reduced. Green Fluorescent Protein (GFP) expressing parental cells and antisense transfectants were generated for detection in mouse brain tissue without any post-chemical treatment. Intracerebral injection of SNB19 stable antisense transfectants resulted in reduced tumor formation in nude mice. These results strongly support a role for cathepsin B in the invasiveness of human glioblastoma cells and suggest cathepsin B antisense may prove useful in cancer therapy.

In vivo molecular target assessment of matrix metalloproteinase inhibition

A number of different matrix metalloproteinase (MMP) inhibitors have been developed as cytostatic and anti-angiogenic agents and are currently in clinical testing. One major hurdle in assessing the efficacy of such drugs has been the inability to sense or image anti-proteinase activity directly and non-invasively in vivo. We show here that novel, biocompatible near-infrared fluorogenic MMP substrates can be used as activatable reporter probes to sense MMP activity in intact tumors in nude mice. Moreover, we show for the first time that the effect of MMP inhibition can be directly imaged using this approach within hours after initiation of treatment using the potent MMP inhibitor, prinomastat (AG3340). The developed probes, together with novel near-infrared fluorescence imaging technology will enable the detailed analysis of a number of proteinases critical for advancing the therapeutic use of clinical proteinase inhibitors.

Tenascin immunoreactivity in the large bowel and the liver in patients with colorectal cancer

The expression of tenascin in colorectal tumours and liver was investigated in 30 patients with colorectal adenocarcinomas. Tissue samples were immersion-fixed in 4% paraformaldehyde solution. Free-floating cryostat sections were incubated with monoclonal antibody against tenascin, and examined by light and electron microscopy. Tenascin immunostaining was positive in sub-basement membrane zones and in newly-formed connective tissue of the primary tumour and perisinusoidally in the liver. The immunoreactivity in the sub-basement membrane zones of tumour glands in well- and moderately-differentiated tumours was more intensely expressed compared to that in poorly-differentiated tumours (p = 0.007 and p = 0.001 respectively, chi2-test). Perisinusoidal tenascin deposition was more often detected in the liver of patients with well-differentiated tumours (p = 0.006, chi2-test). The presence of metastases was accompanied by low tenascin deposition (p < 0.005, Fisher's exact test). Ultrastructurally tenascin deposits were observed around single tumour cells and glands in the primary tumours, and close to hepatic stellate cells in the liver. Finally, the role of tenascin deposition in the stimulation of tumour cell proliferation and mobility is discussed.

Endotoxin-induced mortality in bile duct-ligated rats after administration of reconstituted high-density lipoprotein

Cholestatic patients have substantial morbidity because of increased susceptibility to endotoxin (lipopolysaccharide [LPS]). Although reconstituted high-density lipoprotein (rHDL) can bind and neutralize LPS, cholestasis is associated with a near complete absence of HDL. Effects of rHDL infusion on the outcome of LPS-induced inflammatory responses in cholestatic rats were determined. Bile duct-ligated (BDL) and sham rats were treated with rHDL or saline and challenged with LPS. Distribution of cholesterol over the lipoprotein subclasses changed by ligation: levels in low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) were increased 2-fold and 5-fold, respectively, and were decreased in HDL 2-fold. rHDL treatment did not affect cholesterol distribution. LPS was mainly found in the HDL fraction, and ligation affected only levels of HDL-bound LPS (50% decrease; P<.05). Although rHDL infusion effectively normalized the lipoprotein-bound LPS distribution, it resulted in increased sensitivity (mortality: 88% in the ligation + rHDL group versus 44% in the ligation + saline group, 25% in the sham + saline group, and 0% in the sham + rHDL group, P <.05). In accordance with these results, plasma tumor necrosis factor (TNF) was significantly highest in the BDL + rHDL group at several hours after LPS challenge as well as the accumulation of LPS in the liver (P<.05). rHDL infusion leads to increased LPS-induced mortality in cholestatic rats. These results sharply contrast with the protective effects of rHDL suppletion in experimental endotoxemia in animals and human volunteers without biliary obstruction and suggest that there may be danger in administration of rHDL to cholestatic patients.

Imaging proteolysis by living human breast cancer cells

Malignant progression is accompanied by degradation of extracellular matrix proteins. Here we describe a novel confocal assay in which we can observe proteolysis by living human breast cancer cells (BT20 and BT549) through the use of quenched-fluorescent protein substrates. Degradation thus was imaged, by confocal optical sectioning, as an accumulation of fluorescent products. With the BT20 cells, fluorescence was localized to pericellular focal areas that coincide with pits in the underlying matrix. In contrast, fluorescence was localized to intracellular vesicles in the BT549 cells, vesicles that also label for lysosomal markers. Neither intracellular nor pericellular fluorescence was observed in the BT549 cells in the presence of cytochalasin B, suggesting that degradation occurred intracellularly and was dependent on endocytic uptake of substrate. In the presence of a cathepsin B-selective cysteine protease inhibitor, intracellular fluorescence was decreased approximately 90% and pericellular fluorescence decreased 67% to 96%, depending on the protein substrate. Matrix metallo protease inhibitors reduced pericellular fluorescence approximately 50%, i.e., comparably to a serine and a broad spectrum cysteine protease inhibitor. Our results suggest that: 1) a proteolytic cascade participates in pericellular digestion of matrix proteins by living human breast cancer cells, and 2) the cysteine protease cathepsin B participates in both pericellular and intracellular digestion of matrix proteins by living human breast cancer cells.

Comparative localization of cathepsin B protein and activity in colorectal cancer

Cathepsin B is a lysosomal cysteine proteinase that may participate in cancer progression. We compared localization of its protein and activity during progression of human colorectal cancer. In adenomas and carcinomas, protein expression and, particularly, activity were elevated compared with those in normal colorectal mucosa. In normal mucosa, cathepsin B protein expression was moderate in stroma and variable in epithelium, whereas activity was mainly present in distinct areas of stroma directly underneath the surface of the colon and in epithelium at the surface of the colon. Stroma in adenomas and carcinomas contained moderate to high protein levels but little activity except for areas of angiogenesis, inflammation, and necrosis, in which activity was high. In adenomas and the majority of well-differentiated carcinomas and moderately differentiated carcinomas, cathepsin B protein and activity were found in granular form in the epithelium, close to the basement membrane. Protein and activity levels were low and diffusely distributed in cancer cells in the remainder of the well-differentiated and moderately differentiated carcinomas and in all poorly differentiated carcinomas. Invasive fronts in most cancers contained moderate protein levels but high activity. We conclude that (a) activity localization is essential to understand the role of cathepsin B in cancer progression, and (b) cathepsin B activity in human colon is associated with invasion of cancer cells, endothelial cells, and inflammatory cells, and in cell death, both apoptotic and necrotic.

Direct comparison of the sensitivity of enzyme histochemical and immunohistochemical methods: cathepsin B expression in human colorectal mucosa

Immunohistochemical localization of the proteinase cathepsin B has been compared directly with localization of cathepsin B activity with a catalytic (enzyme) histochemical method. The 2 approaches demonstrate principally different aspects of an enzyme. The immunohistochemical method localizes the enzyme protein whether it is active or not whereas the catalytic method visualizes the functionally active enzyme only. Sensitivity of both approaches to localize low amounts of enzyme protein or activity has never been compared. In the present study, we show that cathepsin B protein has a wider distribution pattern than cathepsin B activity in human colorectal mucosa, which means that inactive cathepsin B protein is present. With respect to sensitivity of the methods, it is shown that cathepsin B protein could only be demonstrated properly when strong signal amplification was applied by using Nanogold with silver enhancement, whereas activity could be demonstrated with a simple and direct fluorogenic histochemical assay. It is concluded that catalytic histochemical methods are relatively simple methods for the localization of activity of enzymes in tissues and cells and that their sensitivity is high in comparison with immunohistochemical methods.

Signal amplification in immunohistochemistry at the light microscopic level using biotinylated tyramide and nanogold-silver staining

Signal amplification techniques greatly enhance the sensitivity of immunohistochemical (IHC) and in situ hybridization (ISH) methods. In particular, catalyzed signal amplification (CSA) using labeled tyramide or Nanogold-silver staining is an important signal amplification tool. We have applied a combination of both techniques, as has been introduced for ISH, for a further increase in sensitivity of an IHC method to detect cathepsin B. This lysosomal proteinase can also be expressed extracellularly, particularly in relation to cancer metastasis. Higher sensitivity of the IHC method was needed because existing methods failed to demonstrate cathepsin B protein where cathepsin B activity was found with a fluorescence enzyme histochemical method. Combined CSA and Nanogold-silver staining provided the sensitivity that was required. Moreover, this signal amplification method enabled the use of a 10-fold lower concentration of primary antibody (1 microg/ml). Nonspecific background staining was low provided that endogenous biotin, avidin, and peroxidase were completely blocked. The method was reproducible when all steps, and particularly the silver enhancement step, were rigidly controlled. The method resulted in localization patterns of cathepsin B protein that were in agreement with those of cathepsin B activity in serial sections of rat liver containing colon cancer metastases. We concluded that combined application of CSA and Nanogold-silver staining provides high sensitivity for immunohistochemical methods and that activity localization by an enzyme histochemical method is a very attractive alternative to IHC localization of an enzyme because it is at least as sensitive, it is rapid and simple, and it provides direct information on the function of an enzyme.

Fluorescent microplate assay for cancer cell-associated cathepsin B

Cathepsin B and in particular cell-surface and secreted cathepsin B has been implicated in the invasive and metastatic phenotype of numerous types of cancer. We describe here a method to easily survey cancer cell lines for cathepsin B activity using the highly selective substrate Z-Arg-Arg-AMC. Intact human U87 glioma cells hydrolyze Z-Arg-Arg-AMC with a Km of 460 microM at pH 7.0 and 37 degrees C. This is nearly the same as the Km of 430 microM obtained with purified cathepsin B assayed under the same conditions. The pericellular (i.e. both cell-surface and released) cathepsin B activity was inhibited by the cysteine protease inhibitors E-64, leupeptin, Mu-Np2-HphVS-2Np, Mu-Leu-HpHVSPh and the cathepsin B selective inhibitor Mu-Tyr(3,5 I2)-HphVSPh with IC50 values similar to those observed for the inhibition of purified human liver cathepsin B. Other human cancer cell lines with measurable pericellular cathepsin B activity included HT-1080 fibrosarcoma, MiaPaCa pancreatic, PC-3 prostate and HCT-116 colon. Cathepsin B activity correlated with protein levels of cathepsin B as determined by immunoblot analysis. Pericellular cathepsin B activity was also detected in the rat cell lines MatLyLu prostate and Mat B III adenocarcinoma and in the murine lines B16a melanoma and Lewis lung carcinoma. The ability to determine pericellular cathepsin B activity will be useful in selecting appropriate cell lines for use in vivo when analyzing the effects of inhibiting cathepsin B activity on tumor growth and metastasis.

Ito cell morphology, alpha-smooth muscle actin and collagen type IV expression in the liver of patients with gastric and colorectal tumors

The alteration in sinusoidal collagen type IV occurrence, and myofibroblastic (alpha-SMA-positive) Ito cellular transformation are described in the liver of patients with malignant gastric and colorectal tumors, using electron microscopy as well as light microscopical and ultrastructural immunohistochemistry. The ultrastructural finding revealed transformation of Ito cells mostly into transitional cells in highly differentiated primary tumors and into transitional and myofibroblast-like cells with expressed changes in the other sinusoidal cells in poorly differentiated tumors. Ito cell numbers increased significantly in the livers of cancer patients. A highly significant statistical association was obtained between Ito cell numbers on the one hand and collagen type IV and alpha-SMA immunoreactivity on the other hand in the pericentral zone of the liver lobule. Ultrastructural immunohistochemistry showed increased collagen IV immune deposits in the space of Disse, assembled for the most part around and inside transitional cells. Alpha-SMA immunoreactivity was detected in activated Ito cells diffuse in the lobule, with stronger expression in the intermediate and pericentral zones. It is suggested that stimuli which can influence Ito cell transformation are produced by tumor cells from the primary tumor (TGF-beta1, TNF-alpha, PDGF-beta etc.) and from the metastasizing gastric or colorectal tumor cells--matrix metalloproteinase-2 (MMP-2). It is suggested that sinusoidal extracellular matrix deterioration creates a barrier for cancer invasion on the one hand, or possibly facilitates metastasizing by ensurance of matrix for adhesion on the other hand.

Unraveling the role of proteases in cancer

Investigators have been studying the expression and activity of proteases in the final steps of tumor progression, invasion and metastasis, for the past 30 years. Recent studies, however, indicate that proteases are involved earlier in progression, e.g., in tumor growth both at the primary and metastatic sites. Extracellular proteases may co-operatively influence matrix degradation and tumor cell invasion through proteolytic cascades, with individual proteases having distinct roles in tumor growth, invasion, migration and angiogenesis. In this review, we use cathepsin B as an example to examine the involvement of proteases in tumor progression and metastasis. We discuss the effect of interactions among tumor cells, stromal cells, and the extracellular matrix on the regulation of protease expression. Further elucidation of the role of proteases in cancer will allow us to design more effective inhibitors and novel protease-based drugs for clinical use.