Modulation of invasive properties of murine squamous carcinoma cells by heterologous expression of cathepsin B and cystatin C

Synthetic Approaches of Epoxysuccinate Chemical Probes

Synthetic chemical probes are powerful tools for investigating biological processes. They are particularly useful for proteomic studies such as activity-based protein profiling (ABPP). These chemical methods initially used mimics of natural substrates. As the techniques gained prominence, more and more elaborate chemical probes with increased specificity towards given enzyme/protein families and amenability to various reaction conditions were used. Among the chemical probes, peptidyl-epoxysuccinates represent one of the first types of compounds used to investigate the activity of the cysteine protease papain-like family of enzymes. Structurally derived from the natural substrate, a wide body of inhibitors and activity- or affinity-based probes bearing the electrophilic oxirane unit for covalent labeling of active enzymes now exists. Herein, we review the literature regarding the synthetic approaches to epoxysuccinate-based chemical probes together with their reported applications, from biological chemistry and inhibition studies to supramolecular chemistry and the formation of protein arrays.

Externally added cystatin C reduces growth of A375 melanoma cells by increasing cell cycle time

Some secreted cysteine protease inhibitors of the cystatin family appear to affect intracellular proteolysis and growth of human cells, as a result of internalization. Here, we studied the effects of external addition of the most abundant human cystatin, cystatin C, on viability and proliferation of cancer cells in culture. A dose‐dependent decrease in viable cells was seen for A375 melanoma, MCF‐7 breast cancer, and PC‐3 prostate cancer cells cultured in 1–5 µm cystatin C after 24 h. Real‐time assessment of growth rates in A375 cell cultures for 48 h by digital holographic microscopy showed an increased doubling time for cells cultured in the presence of 5 µm cystatin C (20.1 h) compared with control cells (14.7 h). A prolonged doubling time was already observed during the first 12 h, indicating a rapid general decrease in cell proliferation at the population level. Tracking of individual cells in phase holographic images showed that dividing cells incubated with 5 µm cystatin C underwent fewer mitoses during 48 h than control cells. In addition, the time between cell divisions was longer, especially for the first cell cycle. Incubation with the variant W106F‐cystatin C (with high cellular uptake rate) resulted in a lower number of viable cells and a prolonged doubling time than when cells were incubated with wild‐type cystatin C, but no effect was observed for (R24A,R25A)‐cystatin C (low cellular uptake). Thus, cystatin C causes prolonged cell division leading to decreased proliferation of melanoma cells, and internalization seems to be a prerequisite for this effect.

Investigation of the clinical significance and prospective molecular mechanisms of cystatin genes in patients with hepatitis B virus‑related hepatocellular carcinoma

The present study aimed to investigate the clinical significance and prospective molecular mechanism of cystatin (CST) genes in patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). The role of CST genes in the molecular mechanism of HCC was revealed through bioinformatics analysis. The clinical significance of CST genes was investigated using GSE14520-derived data from patients with HBV-related HCC. Gene set enrichment analysis (GSEA) was used to identify pathways in which the CST genes were enriched, as well as the association between these pathways and HCC. The expression levels of CST1, CST2, CST5, CSTA and CSTB genes were higher in HCC tissue compared with in normal tissue; conversely, CST3 and CST7 were reduced in HCC tissue. Subsequent receiver operating characteristic analysis of the CST genes demonstrated that CST7 and CSTB genes may function as potential diagnostic markers for HCC. Furthermore, the expression levels of CST6 and CST7 were strongly associated with recurrence-free survival and overall survival of patients with HBV-related HCC. GSEA of the CST genes revealed that CST7 was significantly enriched in tumor evasion and tolerogenicity, cancer progenitors, liver cancer late recurrence, liver cancer progression and several liver cancer subclasses. In addition, CST genes demonstrated homology in terms of protein structure and were revealed to be strongly co-expressed. The present findings suggested that CST7 and CSTB genes may serve as potential prognostic and diagnostic biomarkers for HCC.

Cystatins in cancer progression: More than just cathepsin inhibitors

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

Cysteine cathepsins as a prospective target for anticancer therapies-current progress and prospects

Cysteine cathepsins (CTS), being involved in both physiological and pathological processes, play an important role in the human body. During the last 30 years, it has been shown that CTS are highly upregulated in a wide variety of cancer types although they have received a little attention as a potential therapeutic target as compared to serine or metalloproteinases. Studies on the increasing problem of neoplastic progression have revealed that secretion of cell-surface- and intracellular cysteine proteases is aberrant in tumor cells and has an impact on their growth, invasion, and metastasis by taking part in tumor angiogenesis, in apoptosis, and in events of inflammatory and immune responses. Considering the role of CTS in carcinogenesis, inhibition of these enzymes becomes an attractive strategy for cancer therapy. The downregulation of natural CTS inhibitors (CTSsis), such as cystatins, observed in various types of cancer, supports this claim. The intention of this review is to highlight the relationship of CTS with cancer and to present illustrations that explain how some of their inhibitors affect processes related to neoplastic progression.

Low-level internalization of cystatin E/M affects legumain activity and migration of melanoma cells

The ratio between proteases and their inhibitors is unbalanced in cancer. The cysteine protease inhibitor cystatin C is internalized by some cancer cells, which affects cellular properties. Here we aimed to investigate if uptake of cystatin C and the related inhibitor cystatin E/M occur in melanoma cell lines and to evaluate to what extent the uptake affects the legumain activity that is typically increased in melanoma. First we studied the basic expression, secretion, and intracellular content of all type 2 cystatins as well as expression and activity of their possible target enzymes legumain and cathepsin B in MDA-MB-435S, A375, and C8161 melanoma cells. Legumain activity was measureable in all cell lines, and of the potential legumain inhibitors, cystatin C, E/M, and F, cystatin C was the one mainly produced. All cells internalized cystatin C added to culture media, leading to increased intracellular cystatin C levels by 120-200%. Cystatin E/M was internalized as well but at a modest rate. The effects on intracellular legumain activity were nevertheless pronounced, probably because the cells lacked this inhibitor, and its affinity for legumain is 100-fold higher than that of cystatin C. Likewise, the low-degree uptake resulted in reduced migration and invasion of A375 cells in Matrigel to an extent comparable with the W106F variant of cystatin C with optimal uptake properties and resulting in much higher intracellular levels. Thus, cystatin E/M appears to be a good candidate to efficiently down-regulate the increased legumain activity, possibly important for the malignant phenotype of melanoma cells.

Cationic liposome-mediated delivery of reovirus enhances the tumor cell-killing efficiencies of reovirus in reovirus-resistant tumor cells

Reovirus induces tumor cell death efficiently and specifically, and thus is currently undergoing clinical testing as an anticancer agent. In the intracellular trafficking of reovirus, proteolytic disassembly of reovirus capsid-proteins and subsequent penetration of viral particles into the cytosol are crucial steps. Cathepsins B and L are largely responsible for the proteolytic disassembly of reovirus. Reovirus efficiently lyses tumor cells exhibiting relatively high activities of cathepsins B and L, while tumor cells with low activities of cathepsins B and L are often refractory to reovirus, probably due to inefficient endo/lysosomal escape. In this study, in order to enhance the tumor cell-killing efficiencies of reovirus by promoting endo/lysosomal escape, especially in reovirus-resistant tumor cells, reovirus was complexed with a cationic liposome transfection reagent. Reovirus alone and reovirus-cationic liposome complex (reoplex) exhibited similar levels of tumor cell-killing efficiencies in reovirus-susceptible tumor cells, while reoplex mediated more than 30% higher levels of tumor cell-killing activities in reovirus-resistant tumor cells than reovirus alone. Reoplex-mediated tumor cell death was efficiently induced in the tumor cells pretreated with cathepsin inhibitors. The mRNA levels of interferon (IFN)-β and apoptotic genes were significantly elevated following reoplex treatment. These results suggest that cationic liposomes efficiently promoted delivery of reovirus to the cytosol, leading to induction of apoptosis.

Cysteine cathepsins and cystatins: from ancillary tasks to prominent status in lung diseases

Human cysteine cathepsins (family C1, clan CA) have long been regarded as ubiquitous household enzymes, primarily involved in the recycling and degradation of proteins in lysosomes. This opinion has changed considerably during recent decades, however, with the demonstration of their involvement in various physiological processes. A growing body of evidence supports the theory that cathepsins play specific functions in lung homeostasis and pathophysiological events such as asthma, lung fibrosis (including idiopathic pulmonary fibrosis), chronic obstructive pulmonary disease (embracing emphysema and chronic bronchitis), silicosis, bronchopulmonary dysplasia or tumor invasion. The objective of this review is to provide an update on the current knowledge of the role of these enzymes in the lung. Particular attention has been paid to the understanding of the role of these proteases and their natural inhibitors, cystatins (family I25, clan IH), in TGF-β1-driven fibrotic processes with an emphasis on lung fibrosis.

Expression of Cystatin SN significantly correlates with recurrence, metastasis, and survival duration in surgically resected non-small cell lung cancer patients

Cystatin SN has been considered to be involved in human cancer, but its clinical significance in non-small cell lung cancer (NSCLC) has not been elucidated. The aim of this study was to evaluate the clinical value of Cystatin SN expression in patients with surgically resected NSCLCs. A retrospective analysis of 174 patients with surgically resected NSCLCs from April 2002 to March 2005 was performed with immunohistochemistry and fluorescence in situ hybridization to analyze the protein expression and amplification of Cystatin SN. The associations between Cystatin SN expression and recurrence, metastasis, and survival were investigated. In recurrence and metastasis analysis, compared with low-Cystatin SN expression NSCLCs, high expression tumors were more likely to recur and metastasize (P < 0.001). Disease-free survival (DFS) and overall survival (OS) were significantly prolonged in the low-Cystatin SN expression subgroup compared with the high-Cystatin SN expression subgroup (DFS, P < 0.001; OS, P = 0.001). A multivariate analysis confirmed that high expression of Cystatin SN was associated with poor survival (DFS, P = 0.001; OS, P = 0.006) and was an independent prognostic indicator. The present study indicates that high expression of Cystatin SN is a significant prognostic indicator of a higher rate of recurrence, metastatic risk, and poor survival in patients with surgically resected NSCLCs.

Cystatin SN neutralizes the inhibitory effect of cystatin C on cathepsin B activity

Cystatin SN (CST1) is one of the several salivary cystatins that form tight equimolar complexes with cysteine proteases, such as the cathepsins. High expression of CST1 is correlated with advanced pTNM stage in gastric cancer. However, the functional role of CST1 in tumorigenesis has not been elucidated. In this study, we showed that CST1 was highly expressed in colon tumor tissues, compared with nontumor regions. Increased cell proliferation and invasiveness were observed in HCT116 cell lines stably transfected with CST1 cDNA (HCT116-CST1) but not in CST3-transfected cells. We also demonstrated that CST1-overexpressing cell lines exhibited increased tumor growth as well as metastasis in a xenograft nude mouse model. Interestingly, CST1 interacted with cystatin C (CST3), a potent cathepsin B (CTSB) inhibitor, with a higher affinity than the interaction between CST3 and CTSB in the extracellular space of HCT116 cells. CTSB-mediated cellular invasiveness and proteolytic activities were strongly inhibited by CST3, but in the presence of CST1 CTSB activities recovered significantly. Furthermore, domain mapping of CST1 showed that the disulfide-bonded conformation, or conserved folding, of CST1 is important for its secretion and for the neutralization of CST3 activity. These results suggest that CST1 upregulation might be involved in colorectal tumorigenesis and acts by neutralizing the inhibition of CTSB proteolytic activity by CST3.

Non-invasive optical imaging of cathepsin B with activatable fluorogenic nanoprobes in various metastatic models

An increasing number of treatments of metastases rely on diagnostics and imaging these days. The facts that the activity of cathepsin B (CB) is markedly linked to the metastatic process and that CB is found highly expressed in the pericellular regions in this process make CB an attractive target for diagnosing metastases. We have developed a CB-sensitive nanoprobe (CB-CNP) consisting of self-quenched CB-sensitive fluorogenic peptide probes conjugated onto the surface of tumor-targeting glycol chitosan nanoparticles (CNPs). The freshly prepared CB-CNP formed a spherical nanoparticle structure (280 nm in diameter) and the fluorescence intensity of CB-CNP was strongly quenched in physiological condition. However, self-quenched CB-CNP boosted strong fluorescence signals in the presence of CB, not of cathepsin l or cathepsin d, due to the CB-specific cleavage of self-quenched peptide probes. Importantly, the intravenously injected CB-CNP demonstrated the potential to discriminate metastases in vivo in three metastatic mouse models, including 4T1-luc2 liver metastases, RFP-B16F10 lung metastases and HT1080 peritoneal metastases. Indeed, Western blot analysis confirmed that the CB expression of metastases had increased compared to normal organ in these metastatic mouse models. CB-CNPs may be useful for depicting metastases through non-invasive CB molecular imaging.

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.

Overexpression of cystatin SN positively affects survival of patients with surgically resected esophageal squamous cell carcinoma

Background

Cystatin SN is a secreted protein and a cysteine proteinase inhibitor. It has been considered to be a tumor marker for gastrointestinal tract cancer in several functional researches. However, the clinicopathological and prognostic significance of Cystatin SN expression in esophageal squamous cell carcinoma (ESCC) has not been elucidated.

Methods

In our study, the expression of Cystatin SN was detected in 209 surgically resected ESCC tissues and 170 peritumoral normal esophageal mucosae by immunohistochemistry. The prognostic significance of Cystatin SN expression was analysed with Kaplan-Meier plots and the Cox proportional hazards regression models.

Results

The results showed that the immunostaining of Cystatin SN in ESCC tissues was less intense than that in the normal control tissue (P < 0.001). Compared with patients with low tumoral Cystatin SN expression, ESCC patients with tumors high-expression Cystatin SN exhibited increased disease-free survival (DFS) and overall survival (OS) (P < 0.001 and P < 0.001, respectively). Furthermore, the expression level of Cystatin SN could further stratify the ESCC patients by survival (DFS and OS) in the stage II subgroup (P < 0.001 and P < 0.001, respectively). Multivariate analyses showed that Cystatin SN expression, N status and differentiation were independent and significant predictors of survival.

Conclusions

We concluded that ESCC patients whose tumors express high levels of Cystatin SN have favourable survival compared with those patients with low Cystatin SN expression. Tumoral Cystatin SN expression may be an independent predictor of survival for patients with resectable ESCCs.

The mannose 6-phosphate-binding sites of M6P/IGF2R determine its capacity to suppress matrix invasion by squamous cell carcinoma cells

The M6P (mannose 6-phosphate)/IGF2R (insulin-like growth factor II receptor) interacts with a variety of factors that impinge on tumour invasion and metastasis. It has been shown that expression of wild-type M6P/IGF2R reduces the tumorigenic and invasive properties of receptor-deficient SCC-VII squamous cell carcinoma cells. We have now used mutant forms of M6P/IGF2R to assess the relevance of the different ligand-binding sites of the receptor for its biological activities in this cellular system. The results of the present study demonstrate that M6P/IGF2R does not require a functional binding site for insulin-like growth factor II for inhibition of anchorage-independent growth and matrix invasion by SCC-VII cells. In contrast, the simultaneous mutation of both M6P-binding sites is sufficient to impair all cellular functions of the receptor tested. These findings highlight that the interaction between M6P/IGF2R and M6P-modified ligands is not only important for intracellular accumulation of lysosomal enzymes and formation of dense lysosomes, but is also crucial for the ability of the receptor to suppress SCC-VII growth and invasion. The present study also shows that some of the biological activities of M6P/IGF2R in SCC-VII cells strongly depend on a functional M6P-binding site within domain 3, thus providing further evidence for the non-redundant cellular functions of the individual carbohydrate-binding domains of the receptor.

Cystatin C properties crucial for uptake and inhibition of intracellular target enzymes

To elucidate the molecular requirements for cancer cell internalization of the extracellular cysteine protease inhibitor cystatin C, 12 variants of the protein were produced and used for uptake experiments in MCF-7 cells. Variants with alterations in the cysteine cathepsin binding region ((Δ1-10)-, K5A-, R8G-, (R8G,L9G,V10G)-, (R8G,L9G,V10G,W106G)-, and W106G-cystatin C) were internalized to a very low extent compared with the wild-type inhibitor. Substitutions of N39 in the legumain binding region (N39K- and N39A-cystatin C) decreased the internalization and (R24A,R25A)-cystatin C, with substitutions of charged residues not involved in enzyme inhibition, was not taken up at all. Two variants, W106F- and K75A-cystatin C, showed that the internalization can be positively affected by engineering of the cystatin molecule. Microscopy revealed vesicular co-localization of internalized cystatin C with the lysosomal marker proteins cathepsin D and legumain. Activities of both cysteine cathepsins and legumain, possible target enzymes associated with cancer cell invasion and metastasis, were down-regulated in cell homogenates following cystatin C uptake. A positive effect on regulation of intracellular enzyme activity by a cystatin variant selected from uptake properties was illustrated by incubating cells with W106F-cystatin C. This resulted in more efficient down-regulation of intracellular legumain activity than when cells were incubated with wild-type cystatin C. Uptake experiments in prostate cancer cells corroborated that the cystatin C internalization is generally relevant and confirmed an increased uptake of W106F-cystatin C, in PC3 cells. Thus, intracellular cysteine proteases involved in cancer-promoting processes might be controled by cystatin uptake.

M6P/IGF2R modulates the invasiveness of liver cells via its capacity to bind mannose 6-phosphate residues

BACKGROUND & AIMS

The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R), a multifunctional protein, plays a central role in intracellular targeting of lysosomal enzymes and control of insulin-like growth factor II (IGF-II) bioactivity. Importantly, the gene encoding this receptor is frequently inactivated in a wide range of malignant tumors including hepatocellular carcinomas. Thus, M6P/IGF2R is considered a putative liver tumor suppressor. The aim of this study was to establish the impact of the receptor on the invasive properties of liver cells.

METHODS

Reconstitution experiments were performed by expression of wild type and mutant M6P/IGF2R in receptor-deficient FRL14 fetal rat liver cells. RNA interference was used to induce M6P/IGF2R downregulation in receptor-positive MIM-1-4 mouse hepatocytes.

RESULTS

We show that the M6P/IGF2R status exerts a strong impact on the invasiveness of tumorigenic rodent liver cells. M6P/IGF2R-deficient fetal rat liver cells hypersecrete lysosomal cathepsins and penetrate extracellular matrix barriers in a cathepsin-dependent manner. Forced expression of M6P/IGF2R restores intracellular transport of cathepsins to lysosomes and concomitantly reduces the tumorigenicity and invasive potential of these cells. Conversely, M6P/IGF2R knock-down in receptor-positive mouse hepatocytes causes increased cathepsin secretion as well as enhanced cell motility and invasiveness. We also demonstrate that functional M6P-binding sites are important for the anti-invasive properties of M6P/IGF2R, whereas the capacity to bind IGF-II is dispensable for the anti-invasive activity of the receptor in liver cells.

CONCLUSIONS

M6P/IGF2R restricts liver cell invasion by preventing the pericellular action of M6P-modified proteins.

Cerebrospinal fluid cathepsin B and S

Cathepsins are increased in the brain of elderly animals. We investigate the presence of cathepsin B and S in human cerebrospinal fluid (CSF) plasma and the associations with cystatin C, age and sex. We measured cathepsin B and S concentrations in CSFs from 118 persons, undergoing elective surgical procedures, with ELISA. Both cathepsin B and cathepsin S were positively correlated with age. No correlation was observed between cathepsin B or S and length, height or body mass index. Both cathepsin B and S were positively correlated to the cystatin C concentration in CSF. Calculated reference intervals were 4,893-17,636 pg/mL for cathepsin B and 2,681-11,459 pg/mL for cathepsin S. Elderly individuals had significantly higher levels of both cathepsin B (r s = 0.38, p = 0.00002) and cathepsin S (r s = 0.35, p = 0.0001) in CSF.

Transgenic expression of human cathepsin B promotes progression and metastasis of polyoma-middle-T-induced breast cancer in mice

Elevated expression of the cysteine protease cathepsin B (CTSB) has been correlated with a poor prognosis for cancer patients. In order to model high CTSB expression in mammary cancer, transgenic mice expressing human CTSB were crossed with transgenic polyoma virus middle T oncogene breast cancer mice (mouse mammary tumor virus-PymT), resulting in a 20-fold increase in cathepsin B activity in the tumors of double-transgenic animals. CTSB expression did not affect tumor onset, but CTSB transgenic mice showed accelerated tumor growth with significant increase in weight for end-stage tumors, as well as an overall worsening in their histopathological grades. Notably, the lung metastases in the CTSB transgenic animals were found to be both significantly larger and to occur at a significantly higher frequency. Ex vivo analysis of primary PymT tumor cells revealed no significant effects from elevated CTSB levels on tumor cell characteristics, that is, the formation of tumor cell colonies and the sprouting of invasive strands from PymT cell spheroids. However, tumors from CTSB-overexpressing mice showed increased numbers of tumor-associated B cells and mast cells. In addition, more CD31+ endothelial cells were detected in these tumors, correlating with higher levels of vascular endothelial growth factor (VEGF) being present in the tumor and serum. We conclude that elevated proteolytic CTSB activity facilitates progression and metastasis of PymT-induced mammary carcinomas, and is associated with increased immune cell infiltration, enhanced VEGF levels and the promotion of tumor angiogenesis.

Synergistic antitumor effects of combined cathepsin B and cathepsin Z deficiencies on breast cancer progression and metastasis in mice

The lysosomal cysteine proteases cathepsin B (Ctsb) and cathepsin Z (Ctsz, also called cathepsin X/P) have been implicated in cancer pathogenesis. Compensation of Ctsb by Ctsz in Ctsb (-/-) mice has been suggested. To further define the functional interplay of these proteases in the context of cancer, we generated Ctsz null mice, crossed them with Ctsb-deficient mice harboring a transgene for the mammary duct-specific expression of polyoma middle T oncogene (PymT), and analyzed the effects of single and combined Ctsb and Ctsz deficiencies on breast cancer progression. Single Ctsb deficiency resulted in delayed detection of first tumors and reduced tumor burden, whereas Ctsz-deficient mice had only a prolonged tumor-free period. However, only a trend toward reduced metastatic burden without statistical significance was detected in both single mutants. Strikingly, combined loss of Ctsb and Ctsz led to additive effects, resulting in significant and prominent delay of early and advanced tumor development, improved histopathologic tumor grading, as well as a 70% reduction in the number of lung metastases and an 80% reduction in the size of these metastases. We conclude that the double deficiency of Ctsb and Ctsz exerts significant synergistic anticancer effects, whereas the single deficiencies demonstrate at least partial reciprocal compensation.

Proteinases and their inhibitors in liver cancer

Proteinases are known to be involved in many cancer-related processes, particularly in the breakdown of extracellular matrix barriers in the course of tumor invasion and metastasis. In this review we summarize the current knowledge about the role of the most important matrix-degrading proteinases (cathepsins, matrix metalloproteinases, plasmin/plasminogen activators) and their respective inhibitors in liver cancer progression and metastasis.

Upregulation of the cysteine protease inhibitor, cystatin SN, contributes to cell proliferation and cathepsin inhibition in gastric cancer

BACKGROUND

Cysteine proteases like cathepsins are widely distributed proteolytic enzymes and form tight equimolar complexes with cystatins at their active sites. Among cystatins, CST1, encoding cystatin SN, is a member of the type 2 salivary cystatin family found in a variety of fluids and secretions, including plasma, tears, and saliva. CST1 was identified as an upregulated gene in gastric cancer tissues compared to noncancerous regions using our Affymetrix GeneChip microarray.

METHODS

The upregulation of CST1 in gastric cancer was analyzed using RT-PCR (n=15), immnohistochemistry, and clinicopathological (n=77) analysis. CST1-siRNA was used for the suppression of CST1 gene expression and cathepsin proteolytic activity was assayed.

RESULTS

CST1 was upregulated in cancerous lesions of gastric cancer tissues compared to noncancerous regions and clinicopathological analysis showed a significant correlation between high expression of CST1 and pTNM stage (p=0.044). In CST1-siRNA transfected cells, cell proliferation was reduced and the proteolytic activity of cathepsins was increased.

CONCLUSIONS

CST1 might be highly involved in gastric tumorigenesis and regulate the proteolytic activity of cysteine proteases.

Macrophage responses to interferon-gamma are dependent on cystatin C levels

The aim of the present investigation was to elucidate possible effects of cystatin C on inflammatory responses mediated by macrophages. Previously it has been shown that in vitro treatment of murine peritoneal macrophages with interferon-gamma (IFN-gamma) causes a down-regulation of cystatin C secretion. To investigate whether such changes in cystatin C expression in turn can affect inflammatory responses mediated by macrophages, we have compared effects of IFN-gamma on macrophages isolated from wild-type (cysC(+/+)) and cystatin C knockout (cysC(-/-)) mice. It was shown that IFN-gamma-primed cysC(-/-) macrophages exhibit significantly higher interleukin-10 (IL-10) but lower tumor necrosis factor-alpha (TNF-alpha) expression, and reduced nuclear factor (NF)-kappaB p65 activation, compared to similarly primed cysC(+/+) cells. Exogenously added cystatin C enhanced IFN-gamma-induced activation of NF-kappaB p65 and increased mRNA levels for inducible NO synthase (iNOS) in cysC(-/-) macrophages as well as levels of nitric oxide and TNF-alpha in the cell culture medium, in agreement with an enhanced pro-inflammatory response. Accordingly, IFN-gamma-induced IL-10 mRNA expression in cysC(-/-) macrophages was down-regulated by exogenously added cystatin C. Taken together, our data provide evidence that changes in cystatin C levels alter macrophage responses to IFN-gamma. The latter down-regulates the production of cystatin C, which leads to a suppressed inflammatory condition with enhanced IL-10 levels and down-regulated TNF-alpha and NF-kappaB. It is concluded that cystatin C through this effect can act as an immunomodulatory molecule.

The mannose 6-phosphate/insulin-like growth factor II receptor restricts the tumourigenicity and invasiveness of squamous cell carcinoma cells

The mannose 6-phosphate/insulin-like growth factor II receptor (M6P/IGF2R) mediates biosynthetic sorting and endocytosis of various factors that impinge on the proliferation, migration and invasiveness of tumour cells. The gene encoding M6P/IGF2R is frequently lost or mutated in a wide range of malignant tumours including squamous cell carcinomas. We have previously shown that M6P/IGF2R-deficient SCC-VII murine squamous cell carcinoma cells secrete large amounts of pro-invasive lysosomal proteinases. Furthermore, the formation of mature lysosomes is impaired in SCC-VII cells. To assess the link between M6P/IGF2R status and tumour invasion, we have now generated SCC-VII lines stably transfected with human M6P/IGF2R cDNA. Reconstitution of functional M6P/IGF2R expression in SCC-VII cells strongly improves the intracellular retention of lysosomal proteinases and restores the formation of mature lysosomes. In addition, the presence of heterologous M6P/IGF2R compromises the growth of SCC-VII cells both in vitro and in vivo. Remarkably, M6P/IGF2R expression also reduces the invasive capacity of SCC-VII cells in response to various chemoattractants. These results indicate that the M6P/IGF2R status influences the metastatic propensity of squamous cell carcinomas.

Enzymes/transporters

Tracers that specifically target tumours are highly warranted for diagnosis and to monitor cancer chemotherapy response. However, as cancer cells arise from normal cells they do not substantially differ from the normal cells and therefore tumour specific targets are rare. Fortunately, the process of malignant transformation is associated with the up- or down-regulation of enzymes and transporters that play a crucial role in tumour growth. Consequently diagnostic imaging procedures have attained their major success with tracers that target enzymes and transporters that are over-expressed in tumours. The glucose transporters, the multi drug resistance transporters (MDRPs), several kinases and the family of cathepsins are prominent examples for enzymes and receptors that can be targeted for molecular imaging.

Internalization of cystatin C in human cell lines

Altered protease activity is considered important for tumour invasion and metastasis, processes in which the cysteine proteases cathepsin B and L are involved. Their natural inhibitor cystatin C is a secreted protein, suggesting that it functions to control extracellular protease activity. Because cystatins added to cell cultures can inhibit polio, herpes simplex and coronavirus replication, which are intracellular processes, the internalization and intracellular regulation of cysteine proteases by cystatin C should be considered. The extension, mechanism and biological importance of this hypothetical process are unknown. We investigated whether internalization of cystatin C occurs in a set of human cell lines. Demonstrated by flow cytometry and confocal microscopy, A‐431, MCF‐7, MDA‐MB‐453, MDA‐MB‐468 and Capan‐1 cells internalized fluorophore‐conjugated cystatin C when exposed to physiological concentrations (1 μm). During cystatin C incubation, intracellular cystatin C increased after 5 min and accumulated for at least 6 h, reaching four to six times the baseline level. Western blotting showed that the internalized inhibitor was not degraded. It was functionally intact and extracts of cells exposed to cystatin C showed a higher capacity to inhibit papain and cathepsin B than control cells (decrease in enzyme activity of 34% and 37%, respectively). The uptake of labelled cystatin C was inhibited by unlabelled inhibitor, suggesting a specific pathway for the internalization. We conclude that the cysteine protease inhibitor cystatin C is internalized in significant quantities in various cancer cell lines. This is a potentially important physiological phenomenon not previously described for this group of inhibitors.

Cellular repressor of E1A-stimulated genes is a bona fide lysosomal protein which undergoes proteolytic maturation during its biosynthesis

Cellular repressor of E1A-stimulated genes (CREG) has been reported to be a secretory glycoprotein implicated in cellular growth and differentiation. We now show that CREG is predominantly localized within intracellular compartments. Intracellular CREG was found to lack an N-terminal peptide present in the secreted form of the protein. In contrast to normal cells, CREG is largely secreted by fibroblasts missing both mannose 6-phosphate receptors. This is not observed in cells lacking only one of them. Mass spectrometric analysis of recombinant CREG revealed that the protein contains phosphorylated oligosaccharides at either of its two N-glycosylation sites. Cellular CREG was found to cosediment with lysosomal markers upon subcellular fractionation by density-gradient centrifugation. In fibroblasts expressing a CREG-GFP fusion construct, the heterologous protein was detected in compartments containing lysosomal proteins. Immunolocalization of endogenous CREG confirmed that intracellular CREG is localized in lysosomes. Proteolytic processing of intracellular CREG involves the action of lysosomal cysteine proteinases. These results establish that CREG is a lysosomal protein that undergoes proteolytic maturation in the course of its biosynthesis, carries the mannose 6-phosphate recognition marker and depends on the interaction with mannose 6-phosphate receptors for efficient delivery to lysosomes.

Differences in the expression of cathepsin B in B16 melanoma metastatic variants depend on transcription factor Sp1

Cathepsin B contributes to the invasiveness of B16 melanoma cells in mice, with the highly metastatic B16a melanoma producing six- to eightfold more cathepsin B mRNA and protein than the less metastatic B16F1 variant. The proximal promoter region of the cathepsin B (Ctsb) gene (-149 to +94) was previously found to be capable of reproducing this pattern of differential gene activation in B16 melanoma variants. The binding of B16 melanoma nuclear proteins to this promoter region has now been mapped to three GC-boxes (Sp1 transcription factor binding sites) and a potential X-box [tax response element (TRE)/c-AMP responsive element (CRE) site]. Mutation of the GC-boxes at -55 and -37 independently decreased the expression of a luciferase reporter gene in B16a cells to the level observed in B16F1 cells. Promoter activity was also attenuated by mutations within the GC-rich segment between +6 and +16, but not by mutation of the putative X-box. Both Sp1 and Sp3 bound the GC-boxes in the Ctsb promoter, and western blotting showed the level of Sp1 to be greater in B16a compared to B16F1 cells. B16F1 cells that were made to express Sp1 at levels observed in B16a cells produced corresponding increased amounts of endogenous cathepsin B mRNA and enzyme activity. Thus, the difference in cathepsin B expression between high and low metastatic B16 melanoma variants is largely due to different levels of Sp1.

Stefin A and Stefin B: Markers for Prognosis in Operable Squamous Cell Carcinoma of the Head and Neck

PURPOSE

The aim of this study was to test the hypothesis about the protective role of high stefin A and stefin B concentrations in operable carcinoma of the head and neck.

METHODS AND MATERIALS

Stefins A and B concentrations were measured in tissue cytosols of nontumorous mucosa and primary tumors from 92 patients. For quantitative analysis of stefins in tumor cytosols, commercially available enzyme-linked immunosorbent assays were used.

RESULTS

Stefin A was upregulated in 53 patients (higher concentrations were measured in tumor samples than in nontumorous mucosa) and was downregulated in 39 patients. The corresponding numbers for stefin B were 49 and 43, respectively. A significantly higher proportion of downregulated cases were found among patients with disease re-appearance. In the Cox model, high stefin A concentrations appeared as independent predictors for favorable disease-free survival. Assuming a "broken stick" model, a significant increase in the recurrence rate after the threshold of 1063 ng/mgp (the 64th percentile in the group) was found, the hazard ratio reaching 3% of the reference value with doubling of the level of stefin A. These results were reconfirmed after pooling the data with two historical data sets into a uniform series involving 182 patients.

CONCLUSIONS

A group of patients at high risk for disease progression was identified, characterized by the downregulated stefin A protein in the tumor compared with the nontumorous mucosa. Stefin A was recognized as a promising candidate marker for prognosis in patients with operable carcinoma of the head and neck.

New assay using fluorogenic substrates and immunofluorescence staining to measure cysteine cathepsin activity in live cell subpopulations

BACKGROUND

Cathepsins are endosomal/lysosomal proteases that play important roles in regulating cell physiological processes in cardiovascular, neurological, musculoskeletal, and immunological systems. Pathophysiological processes are often associated with a change in cathepsin expression and activity, leading to the possibility of using cathepsins as disease markers for diagnosis and prognosis.

METHODS

We describe a new assay utilizing an argon laser flow cytometer to measure activities of cysteine cathepsins B, L, and S in live cells using cell permeable fluorogenic cresyl violet-conjugated peptides as selective substrates. Substrate concentration dependency and time kinetics studies were performed. The activity assay was combined with immunofluorescence staining to detect cell lineage-specific molecules and assess cathepsin activities in a heterogeneous cell population.

RESULTS

Substrate concentrations utilized were not limiting, because MFI significantly increased in a macrophage cell line stimulated with bacterial lipopolysaccharide. Selective cathepsin inhibitors demonstrated the selectivity of substrate cleavage. Cells fixed and stored before analysis had no loss of fluorescence product. Activities of cathepsins B, L and S in splenic B cells, T cells and macrophages identified by immunofluorescence staining were analyzed.

CONCLUSION

This novel technique determines cathepsin activities on a per cell basis without requiring purification of different cell types from a heterogeneous cell population.

Heterogeneous Metastasis Efficiency of Isogenic Orthotopic Colon Cancer Xenografts Reveals Distinctive Gene Expression Profiles

Hepatic and lung metastases are the leading causes of mortality and major indicators of aggressiveness in colorectal cancer. The underlying molecular mechanisms contributing to the development of metastasis are still unclear. Here, we designed a novel approach to explore gene expression profiles associated with metastasis in human colorectal cancer (hCRC). A series of ten isogenic tumors from three different hCRC models were orthotopically implanted into nude mice. In these series, we analyzed the contribution of dynamic heterogeneity, independently of any intrinsic gene expression program predictive of metastasis. When screened for the presence of disseminated tumor cells in the lung and liver, as the most common host tissues for hCRC metastases, both high- and low-metastatic efficient tumors were found among these isogenic orthotopic series. The metastasis-specific cDNA macroarray analysis of 96 genes, in both tumor populations for each of the three hCRC models, characterized a common differential gene expression within a small group of genes. Our results suggest that, independently of a gene expression profile predictive of metastasis, the progressive acquisition of additional alterations occurs during hCRC tumorigenesis. This dynamic process might determine tumor progression, namely the metastasis dissemination.

The 46-kDa mannose 6-phosphate receptor does not depend on endosomal acidification for delivery of hydrolases to lysosomes

In mammalian cells, the mannose 6-phosphate receptor pathway accounts for the transport of most soluble acid hydrolases to lysosomes. It is believed that dissociation of mannose 6-phosphate receptors and their ligands is entirely driven by the acidic environment in endosomal compartments. Indeed, pH-perturbing substances such as ammonium chloride and monensin have been shown to inhibit lysosomal enzyme targeting in cells that express both known mannose 6-phosphate receptors. We now demonstrate that ammonium chloride and monensin exert modest effects on the intracellular retention of lysosomal hydrolases in murine cells that synthesize only the 46-kDa mannose 6-phosphate receptor. Neither ammonium chloride nor monensin induces changes to the subcellular localization of lysosomal hydrolases and the 46-kDa mannose 6-phosphate receptor in these cells. This suggests that endosomal dissociation of the receptor and its ligands still occurs in the presence of these agents. We conclude that the murine 46-kDa mannose 6-phosphate receptor has the capacity to deliver its cargo proteins to lysosomes even in the absence of endosomal acidification.

The Caenorhabditis elegans CPI-2a cystatin-like inhibitor has an essential regulatory role during oogenesis and fertilization

In the present study, we characterized a sterile cpi-2a(ok1256) deletion mutant in Caenorhabditis elegans and showed that CPI-2a has an essential regulatory role during oogenesis and fertilization. We have also shown that the CPI2a inhibitor and both Ce-CPL-1 and Ce-CPZ-1 enzymes are present in the myoepithelial sheath surrounding germ cells, oocytes, and embryos as well as in the yolk granules within normal oocytes. Staining of mutant worms with anti-yolk protein antibodies has indicted that the proteins are not present in the mature oocytes. Moreover, green fluorescent protein expression was absence or reduced in cpi-2a/yp170:gfp mutant oocytes, although it was expressed in one of the successfully developed embryos. Based on these results, we hypothesize that the sterility in cpi-2a(ok1256) mutant worms is potentially caused by two possible mechanisms: 1) defects in the uptake and/or processing of yolk proteins by the growing oocytes and 2) indirect induction of defects in cell-cell signaling that is critical for promoting germ line development, oocyte maturation, ovulation, and fertilization. A defect in any of these processes would have detrimental effects on the development of normal embryos and consequently normal production of progenies as we observed in cpi-2a mutant worms. This is the first study that demonstrates the expression of cysteine proteases and their endogenous inhibitor in the gonadal sheath cells surrounding germ cells and oocytes, which indirectly have established their potential involvement in proteolytic processing of molecules within the gonadal sheath cells, such as components of the extracellular matrix or the cytoskeletal proteins, which are essential for proper cell-cell signaling activities of the gonadal sheath cells during normal maturation and ovulation processes.

Tumor cell-derived and macrophage-derived cathepsin B promotes progression and lung metastasis of mammary cancer

Proteolysis in close vicinity of tumor cells is a hallmark of cancer invasion and metastasis. We show here that mouse mammary tumor virus-polyoma middle T antigen (PyMT) transgenic mice deficient for the cysteine protease cathepsin B (CTSB) exhibited a significantly delayed onset and reduced growth rate of mammary cancers compared with wild-type PyMT mice. Lung metastasis volumes were significantly reduced in PyMT;ctsb(+/-), an effect that was not further enhanced in PyMT;ctsb(-/-) mice. Furthermore, lung colonization studies of PyMT cells with different CTSB genotypes injected into congenic wild-type mice and in vitro Matrigel invasion assays confirmed a specific role for tumor-derived CTSB in invasion and metastasis. Interestingly, cell surface labeling of cysteine cathepsins by the active site probe DCG-04 detected up-regulation of cathepsin X on PyMT;ctsb(-/-) cells. Treatment of cells with a neutralizing anti-cathepsin X antibody significantly reduced Matrigel invasion of PyMT;ctsb(-/-) cells but did not affect invasion of PyMT;ctsb(+/+) or PyMT;ctsb(+/-) cells, indicating a compensatory function of cathepsin X in CTSB-deficient tumor cells. Finally, an adoptive transfer model, in which ctsb(+/+), ctsb(+/-), and ctsb(-/-) recipient mice were challenged with PyMT;ctsb(+/+) cells, was used to address the role of stroma-derived CTSB in lung metastasis formation. Notably, ctsb(-/-) mice showed reduced number and volume of lung colonies, and infiltrating macrophages showed a strongly up-regulated expression of CTSB within metastatic cell populations. These results indicate that both cancer cell-derived and stroma cell-derived (i.e., macrophages) CTSB plays an important role in tumor progression and metastasis.

Towards novel anti-cancer strategies based on cystatin function

Cystatins have recently emerged as important players in a multitude of physiological and patho-physiological settings that range from cell survival and proliferation, to differentiation, cell signaling and immunomodulation. This group of cysteine protease inhibitors forms a large super-family of proteins composed of one, two, three, and, in some species, more than three cystatin domains. Over the last 20 years or so, members of the cystatin super-family have been primarily explored with respect to their capacity to inhibit intracellular cysteine proteases. Yet, this classical mode of action does not fully explain their remarkably diverse biological functions. Due to the space limitations, the author will discuss here the most recent findings that suggest that some of the single-domain, cytoplasmic and cell-secreted cystatins may play important roles in the promotion or suppression of tumor growth, invasion and metastasis. Based on the present understanding of cystatin function, novel avenues for anti-cancer strategies are proposed.

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

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSIONS

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

Lysosomes and lysosomal proteins in cancer cell death (new players of an old struggle)

Death of cancer cells influences tumor development and progression, as well as the response to anticancer therapies. This can occur through different cell death programmes which have recently been shown to implicate components of the acidic organelles, lysosomes. The role of lysosomes and lysosomal enzymes, including cathepsins and some lipid hydrolases, in programmed cell death associated with apoptotic or autophagic phenotypes is presented, as evidenced from observations on cultured cells and living animals. The possible molecular mechanisms that underlie the action of lysosomes during cell death are also described. Finally, the contribution of lysosomal proteins and lysosomes to tumor initiation and progression is discussed. Elucidation of this role and the underlying mechanisms will shed a new light on these 'old' organelles and hopefully pave the way for the development of novel anticancer strategies.

Proteome analysis of a human uveal melanoma primary cell culture by 2-DE and MS

We present here the first proteomics analysis of uveal melanoma (UM) cells. These cells represent a good model for the identification of polypeptide markers, which could be developed as diagnostic tools. UM is the most common primary intraocular tumour in adults. In contrast to other cancers, the survival rate of patients with this malignancy has changed little over the past few decades; a better understanding of the molecular biology of UM oncogenesis and metastasis is needed to build the basis for the identification of novel drug targets. In the study presented here, proteins from a UM primary cell culture were separated by 2-DE using a pI 3-10 gradient; 270 spots were analysed by LC-MS/MS, identifying 683 proteins derived from 393 different genes. Of those, 69 (18%) are related to cancer processes involving cell division, proliferation, invasion, metastasis, oncogenesis, drug resistance and others. To our knowledge, 96% of the proteins identified, including 16 hypothetical proteins, have never been reported in UM before. This study represents the first step towards the establishment of a UM protein database as a valuable resource for the study of this malignancy.

Matrigel invasion by the prostate cancer cell lines, PC3 and DU145, and cathepsin L+B activity

Cathepsins L and B are lysosomal cysteine proteinases whose activities and cellular location are altered in many types of cancers and cancer cell lines. Cathepsins L and B play an unspecified role in cancer invasion and metastasis. The purpose of our study was to determine whether cathepsins L and B are important for the ability of two prostate cancer cell lines, PC3 and DU 145, to invade the basement membrane-like preparation, Matrigel. Exposure of PC3 and DU145 to the irreversible cysteine proteinase inhibitor, E64, decreases the invasive ability of DU145, but not PC3. PC3 and DU145 were treated with the phorbol ester analogue, phorbol 12-myristate 13-acetate (PMA), a known tumor promoter that activates protein kinase C and contributes to the metastatic phenotype. PMA increased secreted cathepsin L+B activity and the invasive ability of PC3 and DU145; co-exposure to E64 and PMA decreased both cathepsin L+B activity and invasion. We conclude that DU145 requires cathepsin L+B activity more than PC3 for the invasion of the Matrigel. When the amount of secreted cathepsin L+B activity is increased by PMA treatment, however, PC3 becomes dependent on cathepsin L+B for invasion. Our study demonstrates that modulation of the amount of secreted cathepsin L+B activity influences the invasive phenotype of PC3 and DU145.

Leishmania chagasi/infantum: further investigations on Leishmania tropisms in atypical cutaneous and visceral leishmaniasis foci in Central America

In Central America, apparently genetically identical Leishmania chagasi/infantum parasites cause cutaneous (CL) and visceral leishmaniasis (VL), the latter being more frequent in young children. The present study investigated if there were pathology-related differences in virulence between Honduran CL and VL strains using Mediterranean L. infantum strains as a reference. Macrophage infectivity and serum sensitivity, properties thought to be associated with virulence, were similar between CL and VL strains from both regions. Attention focused on the genome organisation of genes for two candidate virulence factors: Leishmania mitogen activated protein kinase (LMPK) and cysteine proteinase b (Cpb). Interestingly, the Mediterranean strains exhibited restriction enzyme polymorphisms associated with tropism for both LMPK and Cpb genes whereas no differences were observed for the Honduran strains. We also report relative genetic homogeneity of the Honduran strains as compared to the Mediterranean strains and discuss it in terms of the probable origin for the Central American L. chagasi/infantum.

Cathepsin B promotes both motility and invasiveness of oral carcinoma cells

We previously demonstrated that overexpression of cathepsin B (CB) protease in oral squamous cell carcinomas correlated positively with advanced tumor stage and poor histologic malignancy grade. Here we examined whether CB contributes to the invasiveness of oral carcinoma cells. For RNA-mediated inhibition, two ribozymes that target CB mRNA were designed and stably expressed in the oral squamous cell carcinoma cell line 1386Tu. Both ribozymes diminished expression of CB mRNA, protein, and activity, without affecting cathepsin D or beta-actin, as determined by quantitative real-time PCR, Western blots, and protease activity assays. Matrigel invasion assays showed that the invasiveness of the cells was significantly reduced by the expressed ribozymes and, surprisingly, the motilities of the ribozyme-transfected cells were also diminished. Our results document a direct role for CB in promoting oral cancer spread and invasion, and open the possibility of controlling oral carcinoma malignancy and metastasis by targeting CB with RNA inhibitor strategies.

RNAi-mediated inhibition of cathepsin B and uPAR leads to decreased cell invasion, angiogenesis and tumor growth in gliomas

RNA interference (RNAi) provides a powerful method for gene silencing in eukaryotic cells, including proliferating mammalian cells. Here, we determined whether RNAi could be utilized to inhibit the expression of proteases implicated in the extracellular matrix degradation, which is characteristic of tumor progression. We have previously shown that antisense stable clones of uPAR and cathepsin B were less invasive and did not form tumors when injected intracranially ex vivo. Since antisense-mediated gene silencing does not completely inhibit the translation of target mRNA and high molar concentrations of antisense molecules are required to achieve gene silencing, we used the RNAi approach to silence uPAR and cathepsin B in this study. We found that the expression of double-stranded RNA leads to the efficient and specific inhibition of endogenous uPAR and cathepsin B protein expression in glioma cell lines as determined by Western blotting. We also found the RNAi of uPAR and cathepsin B reduces glioma cell invasion and angiogenesis in in vitro and in vivo models. Intratumoral injections of plasmid vectors expressing hpRNA for uPAR and cathepsin B resulted in the regression of pre-established intracranial tumors. Further, RNAi for uPAR and cathepsin B inhibited cell proliferation and reduced the levels of pERK and pFAK compared to controls. Taken together, our findings indicate for the first time that RNAi operates in human glioma cells with potential application for cancer gene therapy.

In vitro anti-cancer activities in Caco-2 and HCT-116 cells of recombinant cystatin C prepared by a Pichia expression system

Caco-2 and HCT-116 cells were used to access growth-inhibition and anti-invasion activity of recombinant cystatin C expressed in Pichia pastoris X33, G12W/H86V. The mutant G12W/H86V prepared by a pilot plant production system showed more than 10% growth inhibition of Caco-2 cells at 0.56-56 nM concentrations. Growth-inhibited cells had lower cathepsin L activity than the control cells that were not treated with the inhibitor. Conversely, the cathepsin B activity was not changed by treatment with G12W/H86V. The in vitro anti-invasion test using HCT-116 cells showed that G12W/H86V suppressed the cell invasion by 15%, while its wild-type cystatin, aspartic protease inhibitor pepstatin A, and matrix metalloproteinase (MMP) inhibitor MMP-2/MMP-9 inhibitor III did not suppress cell invasion. These results indicate that the recombinant cystatin C with higher protease inhibitory activity effectively retards the growth and invasiveness of human colon carcinoma cells.