Identification and discrimination of extracellularly active cathepsins B and L in high-invasive melanoma cells

Cathepsin B Regulates Mice Granulosa Cells' Apoptosis and Proliferation In Vitro

Cathepsin B (CTSB), a lysosomal cysteine protease’s high expression and activity, has been reported to cause poor-quality embryos in porcine and bovine. Nevertheless, CTSB functions in mice granulosa cells remain to explore. To discuss the CTSB functional role in follicular dynamics, we studied apoptosis, proliferation, cell cycle progression, and related signaling pathways in primary mouse granulosa cells transfected with small interference RNA specific to CTSB (siCTSB) for 48 h. Further, mRNA and protein expression of cell proliferation regulators (Myc and cyclin D2), apoptosis regulators (caspase 3, caspase 8, TNF-α, and Bcl2), steroidogenesis-related genes (FSHR and CYP11A1), and autophagy markers (LC3-I and ATG5) were investigated. In addition, the effect of CTSB on steroidogenesis and autophagy was also examined. Flow cytometry analysis assay displayed that silencing of CTSB decreased the early and total apoptosis rate by downregulating TNF-α, caspase 8, and caspase 3, and upregulating Bcl2. By regulating Myc and cyclin D2 expression and activating the p-Akt and p-ERK pathways, CTSB knockdown increased GC proliferation and number. A significant decline in estradiol and progesterone concentrations was observed parallel to a significant decrease in autophagy-related markers LC3-I and ATG5 compared to the control group. Herein, we demonstrated that CTSB serves as a proapoptotic agent and plays a critical role in folliculogenesis in female mice by mediating apoptosis, autophagy, proliferation, and steroidogenesis. Hence, CTSB could be a potential prognostic agent for female infertility.

Role of lysosomes in physiological activities, diseases, and therapy

Long known as digestive organelles, lysosomes have now emerged as multifaceted centers responsible for degradation, nutrient sensing, and immunity. Growing evidence also implicates role of lysosome-related mechanisms in pathologic process. In this review, we discuss physiological function of lysosomes and, more importantly, how the homeostasis of lysosomes is disrupted in several diseases, including atherosclerosis, neurodegenerative diseases, autoimmune disorders, pancreatitis, lysosomal storage disorders, and malignant tumors. In atherosclerosis and Gaucher disease, dysfunction of lysosomes changes cytokine secretion from macrophages, partially through inflammasome activation. In neurodegenerative diseases, defect autophagy facilitates accumulation of toxic protein and dysfunctional organelles leading to neuron death. Lysosomal dysfunction has been demonstrated in pathology of pancreatitis. Abnormal autophagy activation or inhibition has been revealed in autoimmune disorders. In tumor microenvironment, malignant phenotypes, including tumorigenesis, growth regulation, invasion, drug resistance, and radiotherapy resistance, of tumor cells and behaviors of tumor-associated macrophages, fibroblasts, dendritic cells, and T cells are also mediated by lysosomes. Based on these findings, a series of therapeutic methods targeting lysosomal proteins and processes have been developed from bench to bedside. In a word, present researches corroborate lysosomes to be pivotal organelles for understanding pathology of atherosclerosis, neurodegenerative diseases, autoimmune disorders, pancreatitis, and lysosomal storage disorders, and malignant tumors and developing novel therapeutic strategies.

Cysteine Cathepsins: Potential Applications in Diagnostics and Therapy of Malignant Tumors

Cysteine cathepsins are proteolytic enzymes involved in protein degradation in lysosomes and endosomes. Cysteine cathepsins have been also found in the tumor microenvironment during carcinogenesis, where they are implicated in proliferation, invasion and metastasis of tumor cells through the degradation of extracellular matrix, suppression of cell-cell interactions, and promotion of angiogenesis. In this regard, cathepsins can have a diagnostic value and represent promising targets for antitumor drugs aimed at inhibition of these proteases. Moreover, cysteine cathepsins can be used as activators of novel targeted therapeutic agents. This review summarizes recent discovered roles of cysteine cathepsins in carcinogenesis and discusses new trends in cancer therapy and diagnostics using cysteine cathepsins as markers, targets, or activators.

Antitumor effect of chiral organotelluranes elicited in a murine melanoma model

Protease roles in cancer progression have been demonstrated and their inhibitors display antitumor effects. Cathepsins are lysosomal cysteine proteases that have increased expression in tumor cells, and tellurium compounds were described as potent cysteine protease inhibitors and also assayed in several animal models. In this work, the two enantiomeric forms of 1-[Butyl(dichloro)-λ⁴-tellanyl]-2-[1S-methoxyethyl]benzene (organotelluranes RF-13R and RF-13S) were evaluated as inhibitors of cathepsins B and L, showing significant enantiodiscrimination. We observed their cytotoxic effects on a murine melanoma model, effectively inhibiting tumor progression in vivo. The enantiomers were able to inhibit melanoma cell viability, migration and invasion in vitro. Besides, RF-13S and RF-13R were able to inhibit endothelial cell angiogenesis using a tube formation assay in vitro, in a stereodependent manner. These organotelluranes affected cell morphology, showing disassembling of the actin cytoskeleton. These results suggest organotelluranes as potential antitumor agents, acting directly on tumor cell proliferation, migration and invasion, and on endothelial cells, disrupting angiogenesis, showing low toxicity and high efficiency. Taken together our results suggest that this class of compounds should be further studied to reveal their potential as antitumoral agents.

Direct detection of cysteine peptidases for MALDI-TOF MS analysis using fluorogenic substrates

A method is described for the direct detection of unstable cysteine peptidase activity in polyacrylamide gels after native electrophoresis using new selective fluorogenic peptide substrates, pyroglutamyl-phenylalanyl-alanyl-4-amino-7-methylcoumaride (Glp-Phe-Ala-AMC) and pyroglutamyl-phenylalanyl-alanyl-4-amino-7-trifluoromethyl-coumaride (Glp-Phe-Ala-AFC). The detection limit of the model enzyme papain was 17 pmol (0.29 μg) for Glp-Phe-Ala-AMC and 43 pmol (0.74 μg) for Glp-Phe-Ala-AFC, with increased sensitivity and selectivity compared to the traditional method of protein determination with Coomassie G-250 staining or detection of activity using chromogenic substrates. Using this method, we easily identified the target digestive peptidases of Tenebrio molitor larvae by matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis. The method offers simplicity, high sensitivity, and selectivity compared to traditional methods for improved identification of unstable cysteine peptidases in multi-component biological samples.

Heat-shock-induced cathepsin B activity during IVF and culture compromises the developmental competence of bovine embryos

Heat stress can cause significant reproductive dysfunction in mammals and previous studies report that expression and activity of cathepsin B (CTSB), a lysosomal cysteine protease, is negatively correlated with the developmental competence of bovine oocytes and embryos. However, the relationship between heat shock (HS) and CTSB remains largely unknown. Here, we investigated the effects of HS during IVF and early embryonic stages of IVC on CTSB activity and developmental competence in bovine embryos. HS (40 °C for 6 h during IVF and 20 h during IVC) caused a significant increase in CTSB activity irrespective of the developmental stage or duration of HS. The developmental rate to the blastocyst stage was also significantly decreased by HS. Additionally, HS during IVC significantly increased the number of apoptotic cells in blastocysts. Notably, these HS-induced changes in blastocyst development and quality were significantly improved by inhibition of CTSB activity, indicating a key role for CTSB. These results showed that CTSB activity plays an essential role in HS-induced dysfunction in bovine embryo development, and that inhibition of this activity could enhance the developmental competence of heat-shocked embryos.

Inhibition of cathepsin B activity reduces apoptosis by preventing cytochrome c release from mitochondria in porcine parthenotes

Cathepsin B, a lysosomal cysteine protease of the papain family, has recently been implicated in the quality and developmental competence of bovine preimplantation embryos. In this study, to determine whether inhibition of cathepsin B activity can improve porcine oocyte maturation and early embryo developmental competence, we supplemented in vitro maturation or embryo culture media with E-64, a cathepsin B inhibitor. Cathepsin B activity was high in poor quality germinal vesicle stage oocytes, but no differences in mRNA expression or protein localization were observed between good and poor quality oocytes, which were categorized based on morphology. Following treatment with 1 μM E-64, cathepsin B activity sharply decreased in 4-cell and blastocyst stage embryos. E-64 had no effect on cell number but significantly (P < 0.05) increased blastocyst formation and decreased the number of apoptotic cells in blastocysts. It also significantly (P < 0.05) enhanced mitochondrial membrane potential in blastocysts, reducing the release of cytochrome c and resulting in decreased expression of Caspase-3 and Caspase-9. In conclusion, inhibition of cathepsin B activity in porcine parthenotes using 1 μM E-64 resulted in attenuation of apoptosis via a reduction in the release of cytochrome c from mitochondria.

Inhibition of cathepsin B activity by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is the most potent toxic isomer in the dioxin-like family. Due to its resistance to metabolic degradation, this ubiquitous environmental pollutant readily accumulates in multiple organs. Cathepsin B is a lysosomal cysteine protease playing an essential role in the intracellular protein turnover. Alterations in its expression, activity, and localization may facilitate the development of many pathologies, including cancer. TCDD, due to its extremely lipophilic nature, may diffuse through biological membranes and affect lysosomal enzymes, including cathepsins. Therefore, in this study we performed two enzymatic assays, spectrofluorimetry and gelatin zymography, in order to evaluate the effect of TCDD on purified bovine cathepsin B. We showed that the dioxin decreases the enzyme's activity in a dose-dependent manner. The reversibility of TCDD-induced inhibition of the protease was also examined, suggesting that TCDD does not bind covalently to the enzyme's active site, acting rather as a reversible inhibitor.

Mechanism of Trypanosoma brucei gambiense resistance to human serum

The African parasite Trypanosoma brucei gambiense accounts for 97% of human sleeping sickness cases. T. b. gambiense resists the specific human innate immunity acting against several other tsetse-fly-transmitted trypanosome species such as T. b. brucei, the causative agent of nagana disease in cattle. Human immunity to some African trypanosomes is due to two serum complexes designated trypanolytic factors (TLF-1 and -2), which both contain haptoglobin-related protein (HPR) and apolipoprotein LI (APOL1). Whereas HPR association with haemoglobin (Hb) allows TLF-1 binding and uptake via the trypanosome receptor TbHpHbR (ref. 5), TLF-2 enters trypanosomes independently of TbHpHbR (refs 4, 5). APOL1 kills trypanosomes after insertion into endosomal/lysosomal membranes. Here we report that T. b. gambiense resists TLFs via a hydrophobic β-sheet of the T. b. gambiense-specific glycoprotein (TgsGP), which prevents APOL1 toxicity and induces stiffening of membranes upon interaction with lipids. Two additional features contribute to resistance to TLFs: reduction of sensitivity to APOL1 requiring cysteine protease activity, and TbHpHbR inactivation due to a L210S substitution. According to such a multifactorial defence mechanism, transgenic expression of T. b. brucei TbHpHbR in T. b. gambiense did not cause parasite lysis in normal human serum. However, these transgenic parasites were killed in hypohaptoglobinaemic serum, after high TLF-1 uptake in the absence of haptoglobin (Hp) that competes for Hb and receptor binding. TbHpHbR inactivation preventing high APOL1 loading in hypohaptoglobinaemic serum may have evolved because of the overlapping endemic area of T. b. gambiense infection and malaria, the main cause of haemolysis-induced hypohaptoglobinaemia in western and central Africa.

Oxygen-glucose deprivation (OGD) and interleukin-1 (IL-1) differentially modulate cathepsin B/L mediated generation of neuroprotective perlecan LG3 by neurons

Brain extracellular matrix (ECM) is highly degraded after cerebral ischemia. The perlecan c-terminal fragment LG3 is generated at increased levels by proteolytic processing as long as 3 days after ischemia. It has previously been shown that oxygen-glucose deprivation (OGD), reperfusion and interleukin-1 α (IL-1α) stimulate brain cells to yield increased levels of LG3. This LG3, in turn, is neuroprotective against OGD, and may therefore represent one of the brain's defenses against ischemic injury. Here, we investigate whether, in neurons, this increased LG3 is the result of increased perlecan generation and cellular release, increased protease release (to generate LG3 from previous extracellularly deposited perlecan) or both. We found that pre-synthesized perlecan may be exocytosed by neurons during OGD and de novo synthesis of perlecan is increased during reperfusion, even 24 h after OGD. Furthermore, while cathepsin L activity was seen to be marginally important to generate LG3 during normoxic conditions, cathepsin B activity was found to be important to generate increased levels of LG3 following OGD and reperfusion. On the other hand, IL-1α treatment raised levels of cathepsin L in neuronal media, and both cathepsin L and cathepsin B were demonstrated to be important for increasing LG3 levels after IL-1α treatment.

Secretome signature of invasive glioblastoma multiforme

The incurability of malignant glioblastomas is mainly attributed to their highly invasive nature coupled with resistance to chemo- and radiation therapy. Because invasiveness is partially dictated by the proteins these tumors secrete we used SILAC to characterize the secretomes of four glioblastoma cell lines (LN18, T98, U118 and U87). Although U87 and U118 cells both secreted high levels of well-known invasion promoting proteins, a Matrigel invasion assay showed U87 cells to be eight times more invasive than U118 cells, suggesting that additional proteins secreted by U87 cells may contribute to the highly invasive phenotype. Indeed, we identified a number of proteins highly or exclusively expressed by U87 cells as compared to the less invasive cell lines. The most striking of these include ADAM9, ADAM10, cathepsin B, cathepsin L1, osteopontin, neuropilin-1, semaphorin-7A, suprabasin, and chitinase-3-like protein 1. U87 cells also expressed significantly low levels of some cell adhesion proteins such as periostin and EMILIN-1. Correlation of secretome profiles with relative levels of invasiveness using Pavlidis template matching further indicated potential roles for these proteins in U87 glioblastoma invasion. Antibody inhibition of CH3L1 reduced U87 cell invasiveness by 30%.

Cathepsin B inhibition interferes with metastatic potential of human melanoma: an in vitro and in vivo study

BACKGROUND

Cathepsins represent a group of proteases involved in determining the metastatic potential of cancer cells. Among these are cysteinyl- (e.g. cathepsin B and cathepsin L) and aspartyl-proteases (e.g. cathepsin D), normally present inside the lysosomes as inactive proenzymes. Once released in the extracellular space, cathepsins contribute to metastatic potential by facilitating cell migration and invasiveness.

RESULTS

In the present work we first evaluated, by in vitro procedures, the role of cathepsins B, L and D, in the remodeling, spreading and invasiveness of eight different cell lines: four primary and four metastatic melanoma cell lines. Among these, we considered two cell lines derived from a primary cutaneous melanoma and from a supraclavicular lymph node metastasis of the same patient. To this purpose, the effects of specific chemical inhibitors of these proteases, i.e. CA-074 and CA-074Me for cathepsin B, Cathepsin inhibitor II for cathepsin L, and Pepstatin A for cathepsin D, were evaluated. In addition, we also analyzed the effects of the biological inhibitors of these cathepsins, i.e. specific antibodies, on cell invasiveness. We found that i) cathepsin B, but not cathepsins L and D, was highly expressed at the surface of metastatic but not of primary melanoma cell lines and that ii) CA-074, or specific antibodies to cathepsin B, hindered metastatic cell spreading and dissemination, whereas neither chemical nor biological inhibitors of cathepsins D and L had significant effects. Accordingly, in vivo studies, i.e. in murine xenografts, demonstrated that CA-074 significantly reduced human melanoma growth and the number of artificial lung metastases.

CONCLUSIONS

These results suggest a reappraisal of the use of cathepsin B inhibitors (either chemical or biological) as innovative strategy in the management of metastatic melanoma disease.

Detection of femtomole quantities of mature cathepsin K with zymography

Cathepsin K, the most potent mammalian collagenase, has been implicated in osteoporosis, cancer metastasis, atherosclerosis, and arthritis. Although procathepsin K is stable and readily detected, the active mature cathepsin K eludes detection by in vitro methods due to its shorter half-life and inactivation at neutral pH. We describe, for the first time, reliable detection, visualization, and quantification of mature cathepsin K to femtomole resolution using gelatin zymography. The specificity of the method was validated with cathepsin K knockdown using small interfering RNA (siRNA) transfection of human monocyte-derived macrophages, and enzymatic activity confirmed with benzyloxycarbonyl-glycine-proline-arginine-7-amino-4-methylcoumarin (Z-GPR-AMC) substrate hydrolysis was fit to a computational model of enzyme kinetics. Furthermore, cathepsin K zymography was used to show that murine osteoclasts secrete more cathepsin K than is stored intracellularly, and this was opposite to the behavior of the macrophages from which they were differentiated. In summary, this inexpensive, species-independent, antibody-free protocol describes a sensitive method with broad potential to elucidate previously undetectable cathepsin K activity.

Cystatin E/M suppresses legumain activity and invasion of human melanoma

Background

High activity of cysteine proteases such as legumain and the cathepsins have been shown to facilitate growth and invasion of a variety of tumor types. In breast cancer, several recent studies have indicated that loss of the cysteine protease inhibitor cystatin E/M leads to increased growth and metastasis. Although cystatin E/M is normally expressed in the skin, its role in cysteine protease regulation and progression of malignant melanoma has not been studied.

Methods

A panel of various non-melanoma and melanoma cell lines was used. Cystatin E/M and C were analyzed in cell media by immunoblotting and ELISA. Legumain, cathepsin B and L were analyzed in cell lysates by immunoblotting and their enzymatic activities were analyzed by peptide substrates. Two melanoma cell lines lacking detectable secretion of cystatin E/M were transfected with a cystatin E/M expression plasmid (pCST6), and migration and invasiveness were studied by a Matrigel invasion assay.

Results

Cystatin E/M was undetectable in media from all established melanoma cell lines examined, whereas strong immunobands were detected in two of five primary melanoma lines and in two of six lines derived from patients with metastatic disease. Among the four melanoma lines secreting cystatin E/M, the glycosylated form (17 kD) was predominant compared to the non-glycosylated form (14 kD). Legumain, cathepsin B and L were expressed and active in most of the cell lines, although at low levels in the melanomas expressing cystatin E/M. In the melanoma lines where cystatin E/M was secreted, cystatin C was generally absent or expressed at a very low level. When melanoma cells lacking secretion of cystatin E/M were transfected with pCST6, their intracellular legumain activity was significantly inhibited. In contrast, cathepsin B activity was not affected. Furthermore, invasion was suppressed in cystatin E/M over-expressing melanoma cell lines as measured by the transwell Matrigel assay.

Conclusions

These results suggest that the level of cystatin E/M regulates legumain activity and hence the invasive potential of human melanoma cells.

The functional expression and characterisation of a cysteine peptidase from the invasive stage of the neuropathogenic schistosome Trichobilharzia regenti

A transcriptional product of a gene encoding cathepsin B-like peptidase in the bird schistosome Trichobilharzia regenti was identified and cloned. The enzyme was named TrCB2 due to its 77% sequence similarity to cathepsin B2 from the important human parasite Schistosoma mansoni. The zymogen was expressed in the methylotropic yeast Pichia pastoris; procathepsin B2 underwent self-processing in yeast media. The peptidolytic activity of the recombinant enzyme was characterised using synthetic fluorogenic peptide substrates at optimal pH 6.0. Functional studies using different specific inhibitors proved the typical cathepsin B-like nature of the enzyme. The S(2) subsite specificity profile of recombinant TrCB2 was obtained. Using monospecific antibodies against the recombinant enzyme, the presence of cathepsin B2 was confirmed in extracts from cercariae (infective stage) and schistosomula (early post-cercarial stage) of T. regenti on Western blots. Also, cross-reactivity was observed between T. regenti and S. mansoni cathepsins B2 in extracts of cercariae, schistosomula or adults. In T. regenti, the antisera localised the enzyme to post-acetabular penetration glands of cercariae implying an important role in the penetration of host skin. The ability of recombinant TrCB2 to degrade skin, serum and nervous tissue proteins was evident. Elastinolytic activity suggests that the enzyme might functionally substitute the histolytic role of the serine class elastase known from S. mansoni and Schistosoma haematobium but not found in Schistosoma japonicum or in bird schistosomes.

Cathepsins and osteosarcoma: Expression analysis identifies cathepsin K as an indicator of metastasis

Osteosarcoma is the most frequent malignant bone tumor with a poor survival rate for patients with metastasis. Previous studies have shown that beside other proteases, distinct sets of cathepsins are involved in the process of metastasis of different tumors. In this study we investigated the expression of cathepsin proteases in human osteosarcoma metastasis. First, the mRNA expression of 14 human cathepsins was studied in SAOS-2 osteosarcoma cells and the highly metastatic LM5 and LM7 sublines by reverse transcriptase (RT)-polymerase chain reaction (PCR). The expression of cathepsin D, K, and L mRNA was found upregulated and that of cathepsin F, H, and V downregulated in the highly metastatic LM5 and LM7 cells. A subgroup of the cathepsin proteases was further studied at the protein level by Western blot analysis of cell extracts. The expression of cathepsin B and H was decreased and that of cathepsin D, K, and L was increased in the highly metastatic cell lines as compared to the SAOS-2 cell line. Diagnostic relevance of cathepsin K expression in osteosarcoma was revealed upon correlation of survival and metastasis with immunohistochemical cathepsin K staining of biopsies collected from 92 patients prior to chemotherapy. Patients with metastatic high-grade osteosarcoma and low cathepsin K expression at diagnosis had a better prognosis than those with high expression. Thus, it appears that cathepsin K expression is of predictive prognostic value for patients with high-grade tumors and metastasis at diagnosis.

A heparin binding motif on the pro-domain of human procathepsin L mediates zymogen destabilization and activation

The molecular mechanism by which heparin modulates the processing of procathepsin L in the extracellular environment is proposed. We show that heparin reduces the stability of the pro form of cathepsin L at pH 5 by binding to a putative heparin binding motif (BBXB) in the pro-domain. Mutations to this motif on procathepsin L reduce heparin binding affinity and heparin-induced destabilization; in contrast, heparin only slightly destabilizes the mature cathepsin L domain. Gel analysis further shows that heparin makes procathepsin L a much better substrate for cathepsin L. Thus, heparin enhances the rate of zymogen activation by destabilization upon binding to the BBXB motif. Determining the mechanism by which procathepsin L is activated in the extracellular matrix is important to the understanding of the role that cathepsin L plays in tumour invasion.

Identification of differentially expressed genes of the Pacific oyster Crassostrea gigas exposed to prolonged thermal stress

Groups of oysters (Crassostrea gigas) were exposed to 25 degrees C for 24 days (controls to 13 degrees C) to explore the biochemical and molecular pathways affected by prolonged thermal stress. This temperature is 4 degrees C above the summer seawater temperature encountered in western Brittany, France where the animals were collected. Suppression subtractive hybridization was used to identify specific up- and downregulated genes in gill and mantle tissues after 7-10 and 24 days of exposure. The resulting libraries contain 858 different sequences that potentially represent highly expressed genes in thermally stressed oysters. Expression of 17 genes identified in these libraries was studied using real-time PCR in gills and mantle at different time points over the course of the thermal stress. Differential gene expression levels were much higher in gills than in the mantle, showing that gills are more sensitive to thermal stress. Expression of most transcripts (mainly heat shock proteins and genes involved in cellular homeostasis) showed a high and rapid increase at 3-7 days of exposure, followed by a decrease at 14 days, and a second, less-pronounced increase at 17-24 days. A slow-down in protein synthesis occurred after 24 days of thermal stress.

Dual contrasting roles of cysteine cathepsins in cancer progression: apoptosis versus tumour invasion

Cysteine cathepsins have been known for a long time to play an important role in cancer progression and metastasis. Several studies have proposed the concept of anti-cathepsin therapy in cancer treatment. On the other hand, cysteine cathepsins have been recently found to play a role in tumour cell death through mediation of apoptosis. The purpose of this mini-review is therefore to provide an insight into the mechanisms by which cysteine cathepsins modulate apoptosis and/or participate in tumour invasion, and to evaluate the impact of these enzymes on both tumour progression and development of potential strategies for cancer treatment.

Melanoma invasion - current knowledge and future directions

The acquisition of invasive behaviour is the key transition in the progression of benign melanocyte hyperplasia to life threatening melanoma. Understanding this transition and the mechanisms of invasion are the key to understanding why malignant melanoma is such a devastating disease and will aid treatment strategies. Underlying the invasive behaviour is increased cell motility caused by changes in cytoskeletal organization and altered contacts with the extra-cellular matrix (ECM). In addition, changes in the interactions of melanoma cells with keratinocytes and fibroblasts enable them to survive and proliferate outside their normal epidermal location. Proteomic and genomic initiatives are greatly increasing our knowledge of which gene products are deregulated in invasive and metastatic melanoma; however, the next challenge is to understand how these genes promote the invasion of melanoma cells. In recent years new models have been developed that more closely recapitulate the conditions of melanoma invasion in vivo. It is hoped that these models will give us a better understanding of how the genes implicated in melanoma progression affect the motility of melanoma cells and their interactions with the ECM, stromal cells and blood vessels. This review will summarise our current understanding of melanoma invasion and focus on the new model systems that can be used to study melanoma.

Characterization of thimet oligopeptidase and neurolysin activities in B16F10-Nex2 tumor cells and their involvement in angiogenesis and tumor growth

Background

Angiogenesis is a fundamental process that allows tumor growth by providing nutrients and oxygen to the tumor cells. Beyond the oxygen diffusion limit from a capillary blood vessel, tumor cells become apoptotic. Angiogenesis results from a balance of pro- and anti-angiogenic stimuli. Endogenous inhibitors regulate enzyme activities that promote angiogenesis. Tumor cells may express pro-angiogenic factors and hydrolytic enzymes but also kinin-degrading oligopeptidases which have been investigated.

Results

Angiogenesis induced by B16F10-Nex2 melanoma cells was studied in a co-culture with HUVEC on Matrigel. A stimulating effect on angiogenesis was observed in the presence of B16F10-Nex2 lysate and plasma membrane. In contrast, the B16F10-Nex2 culture supernatant inhibited angiogenesis in a dose-dependent manner. This effect was abolished by the endo-oligopeptidase inhibitor, JA-2. Thimet oligopeptidase (TOP) and neurolysin activities were then investigated in B16F10-Nex2 melanoma cells aiming at gene sequencing, enzyme distribution and activity, influence on tumor development, substrate specificity, hydrolytic products and susceptibility to inhibitors. Fluorescence resonance energy transfer (FRET) peptides as well as neurotensin and bradykinin were used as substrates. The hydrolytic activities in B16F10-Nex2 culture supernatant were totally inhibited by o-phenanthrolin, JA-2 and partially by Pro-Ile. Leupeptin, PMSF, E-64, Z-Pro-Prolinal and captopril failed to inhibit these hydrolytic activities. Genes encoding M3A enzymes in melanoma cells were cloned and sequenced being highly similar to mouse genes. A decreased proliferation of B16F10-Nex2 cells was observed in vitro with specific inhibitors of these oligopeptidases. Active rTOP but not the inactive protein inhibited melanoma cell development in vivo increasing significantly the survival of mice challenged with the tumor cells. On Matrigel, rTOP inhibited the bradykinin – induced angiogenesis. A possible regulation of the homologous tumor enzyme in the perivascular microenvironment is suggested based on the observed rTOP inhibition by an S-nitrosothiol NO donor.

Conclusion

Data show that melanoma cells secrete endo-oligopeptidases which have an important role in tumor proliferation in vitro and in vivo. rTOP inhibited growth of subcutaneously injected B16F10-Nex2 cells in mice. TOP from tumor cells and bradykinin in endothelial cells are two antagonist factors that may control angiogenesis essential for melanoma growth. A regulatory role of NO or S-nitrosothiols is suggested.

Cloning, expression, and characterization of an alternatively spliced variant of human heparanase

Heparanase is an endoglycosidase that cleaves heparan sulfate in the extracellular matrix (ECM) and hence participates in ECM degradation and remodeling. Heparanase is involved in fundamental biological processes such as cancer metastasis, angiogenesis, and inflammation. Alternative splicing in the coding region of human heparanase was not reported. Here, we report the cloning of a splice variant of human heparanase that lacks exon 5 and is missing 174 bp compared to the wild-type cDNA. Splice 5 is expressed as a 55 kDa protein compared to the 65 and 50 kDa latent and active wild-type enzyme. Splice 5 was not detected in the incubation medium of tumor cells as opposed to the wild-type latent heparanase. Splice 5 escaped proteolytic cleavage, was devoid of HS degradation activity and exhibited diffused rather than granular cellular localization.