Lysosomal cysteine proteases: more than scavengers

Carboxypeptidases cathepsins X and B display distinct protein profile in human cells and tissues

Cathepsin X, a recently discovered lysosomal cysteine protease, shares common structural features and activity properties with cysteine protease cathepsin B. Based on its widespread mRNA distribution in primary tumors and tumor cell lines, a redundant function in tumor progression has been proposed. In this study, we have shown that these two related proteases exhibit different profiles with respect to their protein distribution in cells and tissues and to their possible roles in malignancy. Protein level of cathepsin X did not differ significantly between matched pairs of lung tumor and adjacent lung tissue obtained from patients with lung cancer whereas that of cathepsin B was 9.6-fold higher in tumor compared to adjacent lung tissue. Immunohistochemical analysis of lung tumor cathepsin X revealed very faint staining in tumor cells but positive staining in infiltrated histiocytes, alveolar macrophages, bronchial epithelial cells, and alveolar type II cells. Cathepsin X stained positive also in CD68+ cells in germinal centers of secondary follicles in lymph nodes, corresponding to tingible body macrophages. Two cell lines with proven invasive behavior, MCF-10A neoT and MDA-MB 231, showed positive staining for cathepsin B, but negative for cathepsin X. We showed that the invasive potential of MCF-10A neoT cells can be impaired by specific inhibitor of cathepsin B but not by that of cathepsin X. Cathepsin X was found in large amounts in the pro-monocytic U-937 cell line, in monocytes and in dendritic cells, generated from monocytes in vitro. Our results show that cathepsin X is not involved in degradation of extracellular matrix, a proteolytic event leading to tumor cell invasion and metastasis. Its expression, restricted to immune cells suggests a role in phagocytosis and the regulation of immune response.

The use of cystatin C to inhibit epithelial-mesenchymal transition and morphological transformation stimulated by transforming growth factor-beta

Introduction

Transforming growth factor-β (TGF-β) is a potent suppressor of mammary epithelial cell (MEC) proliferation and is thus an inhibitor of mammary tumor formation. Malignant MECs typically evolve resistance to TGF-β-mediated growth arrest, enhancing their proliferation, invasion, and metastasis when stimulated by TGF-β. Recent findings suggest that therapeutics designed to antagonize TGF-β signaling may alleviate breast cancer progression, thereby improving the prognosis and treatment of breast cancer patients. We identified the cysteine protease inhibitor cystatin C (CystC) as a novel TGF-β type II receptor antagonist that inhibits TGF-β binding and signaling in normal and cancer cells. We hypothesized that the oncogenic activities of TGF-β, particularly its stimulation of mammary epithelial–mesenchymal transition (EMT), can be prevented by CystC.

Method

Retroviral infection was used to constitutively express CystC or a CystC mutant impaired in its ability to inhibit cathepsin protease activity (namely Δ14CystC) in murine NMuMG MECs and in normal rat kidney (NRK) fibroblasts. The effect of recombinant CystC administration or CystC expression on TGF-β stimulation of NMuMG cell EMT in vitro was determined with immunofluorescence to monitor rearrangements of actin cytoskeletal architecture and E-cadherin expression. Soft-agar growth assays were performed to determine the effectiveness of CystC in preventing TGF-β stimulation of morphological transformation and anchorage-independent growth in NRK fibroblasts. Matrigel invasion assays were performed to determine the ability of CystC to inhibit NMuMG and NRK motility stimulated by TGF-β.

Results

CystC and Δ14CystC both inhibited NMuMG cell EMT and invasion stimulated by TGF-β by preventing actin cytoskeletal rearrangements and E-cadherin downregulation. Moreover, both CystC molecules completely antagonized TGF-β-mediated morphological transformation and anchorage-independent growth of NRK cells, and inhibited their invasion through synthetic basement membranes. Both CystC and Δ14CystC also inhibited TGF-β signaling in two tumorigenic human breast cancer cell lines.

Conclusion

Our findings show that TGF-β stimulation of initiating metastatic events, including decreased cell polarization, reduced cell–cell contact, and elevated cell invasion and migration, are prevented by CystC treatment. Our findings also suggest that the future development of CystC or its peptide mimetics hold the potential to improve the therapeutic response of human breast cancers regulated by TGF-β.

Tumor-targeted and activated bioconjugates for improved camptothecin delivery

Earlier reports from our laboratory described bioconjugates of camptothecin (CPT) for tumor targeting. In the current work, the rate and site of CPT release from the bioconjugates were modulated using increasingly sterically hindered amino acids and cysteine proteinase-sensitive peptide linkers, respectively. Polyethylene glycol served as a spacer/scaffold between CPT and folic acid. The folic acid receptor, overexpressed on many cancer cells, was targeted using folate. The delivery system was tested in vitro for hydrolytic stability, enzyme-mediated cleavage, cytotoxicity and targeting potential. The linkers successfully modulated the hydrolysis rate (around 1--100 h) and potential site (tumor microenvironment) of CPT release. Preliminary molecular modeling approaches were utilized to assess the influence of molecular volume on hydrolysis half-life (i.e. CPT release). There was a clear, but non-linear, relationship between in vitro CPT release and increasing steric hindrance offered by the peptide linker. The efficacy of four conjugates was studied in a syngeneic rat breast cancer model. Histopathological analysis on treated tumors was performed to evaluate disease prognosis. The results demonstrate that programmed bioconjugates may provide superior efficacy and greater control over the rate and site of CPT release, resulting in higher anti-tumor efficacy and lower toxicity.

Multiple cathepsin B isoforms in schistosomula of Trichobilharzia regenti: identification, characterisation and putative role in migration and nutrition

Among schistosomatids, Trichobilharzia regenti, displays an unusual migration through the peripheral and central nervous system prior to residence in the nasal cavity of the definitive avian host. Migration causes tissue degradation and neuromotor dysfunction both in birds and experimentally infected mice. Although schistosomula have a well-developed gut, the peptidases elaborated that might facilitate nutrition and migration are unknown. This is, in large part, due to the difficulty in isolating large numbers of migrating larvae. We have identified and characterised the major 33 kDa cathepsin B-like cysteine endopeptidase in extracts of migrating schistosomula using fluorogenic peptidyl substrates with high extinction coefficients and irreversible affinity-labels. From first strand schistosomula cDNA, degenerate PCR and Rapid Amplification of cDNA End protocols were used to identify peptidase isoforms termed TrCB1.1-TrCB1.6. Highest sequence homology is to the described Schistosoma mansoni and Schistosoma japonicum cathepsins B1. Two isoforms (TrCB1.5 and 1.6) encode putatively inactive enzymes as the catalytic cysteine is substituted by glycine. Two other isoforms, TrCB1.1 and 1.4, were functionally expressed as zymogens in Pichia pastoris. Specific polyclonal antibodies localised the peptidases exclusively in the gut of schistosomula and reacted with a 33kDa protein in worm extracts. TrCB1.1 zymogen was unable to catalyse its own activation, but was trans-processed and activated by S. mansoni asparaginyl endopeptidase (SmAE aka. S. mansoni legumain). In contrast, TrCB1.4 zymogen auto-activated, but was resistant to the action of SmAE. Both activated isoforms displayed different pH-dependent specificity profiles with peptidyl substrates. Also, both isoforms degraded myelin basic protein, the major protein component of nervous tissue, but were inefficient against hemoglobin, thus supporting the adaptation of T. regenti gut peptidases to parasitism of host nervous tissue.

Cathepsin B regulates the intrinsic angiogenic threshold of endothelial cells

The lysosomal protease cathepsin B has been implicated in a variety of pathologies including pancreatitis, tumor angiogenesis, and neuronal diseases. We used a tube formation assay to investigate the role of cathepsin B in angiogenesis. When cultured between two layers of collagen I, primary endothelial cells formed tubes in response to exogenously added VEGF. Overexpressing cathepsin B reduced the VEGF-dependent tube response, whereas pharmacologically or molecularly suppressing cathepsin B eliminated the dependence on exogenous VEGF. However, tube formation still required VEGF receptor activity, which suggested that endothelial cells generated VEGF. Indeed, VEGF mRNA and protein was detectable in cells treated with cathepsin B inhibitor, which correlated with a rise in the level of HIF-1alpha. In addition to boosting the level of proangiogenic factors, blocking cathepsin B activity reduced the amount of the antiangiogenic protein endostatin. Thus endothelial cells have the intrinsic capacity to generate pro- and antiangiogenic agents. These observations complement and expand our appreciation of how endothelial cell-derived proteases regulate angiogenesis.

A Hierarchical Clustering Approach for Large Compound Libraries

A modified version of the k-means clustering algorithm was developed that is able to analyze large compound libraries. A distance threshold determined by plotting the sum of radii of leaf clusters was used as a termination criterion for the clustering process. Hierarchical trees were constructed that can be used to obtain an overview of the data distribution and inherent cluster structure. The approach is also applicable to ligand-based virtual screening with the aim to generate preferred screening collections or focused compound libraries. Retrospective analysis of two activity classes was performed: inhibitors of caspase 1 [interleukin 1 (IL1) cleaving enzyme, ICE] and glucocorticoid receptor ligands. The MDL Drug Data Report (MDDR) and Collection of Bioactive Reference Analogues (COBRA) databases served as the compound pool, for which binary trees were produced. Molecules were encoded by all Molecular Operating Environment 2D descriptors and topological pharmacophore atom types. Individual clusters were assessed for their purity and enrichment of actives belonging to the two ligand classes. Significant enrichment was observed in individual branches of the cluster tree. After clustering a combined database of MDDR, COBRA, and the SPECS catalog, it was possible to retrieve MDDR ICE inhibitors with new scaffolds using COBRA ICE inhibitors as seeds. A Java implementation of the clustering method is available via the Internet (http://www.modlab.de).

Peptidyl allyl sulfones: a new class of inhibitors for clan CA cysteine proteases

A new series of peptidyl allyl sulfone inhibitors was discovered while trying to synthesize epoxy sulfone inhibitors from vinyl sulfones using basic oxidizing conditions. The various dipeptidyl allyl sulfones were evaluated with calpain I, papain, cathepsins B and L, cruzain and rhodesain and found to be potent inhibitors. In comparison to the previously developed class of vinyl sulfone inhibitors, the novel dipeptidyl allyl sulfones were more potent inhibitors than the corresponding dipeptidyl vinyl sulfones. It was observed that the stereochemistry of the vinyl sulfone precursor played a role in the potency of the dipeptidyl allyl sulfone inhibitor.

Proteolytic-antiproteolytic balance and its regulation in carcinogenesis

Cancer development is essentially a tissue remodeling process in which normal tissue is substituted with cancer tissue. A crucial role in this process is attributed to proteolytic degradation of the extracellular matrix (ECM). Degradation of ECM is initiated by proteases, secreted by different cell types, participating in tumor cell invasion and increased expression or activity of every known class of proteases (metallo-, serine-, aspartyl-, and cysteine) has been linked to malignancy and invasion of tumor cells. Proteolytic enzymes can act directly by degrading ECM or indirectly by activating other proteases, which then degrade the ECM. They act in a determined order, resulting from the order of their activation. When proteases exert their action on other proteases, the end result is a cascade leading to proteolysis. Presumable order of events in this complicated cascade is that aspartyl protease (cathepsin D) activates cysteine proteases (e.g., cathepsin B) that can activate pro-uPA. Then active uPA can convert plasminogen into plasmin. Cathepsin B as well as plasmin are capable of degrading several components of tumor stroma and may activate zymogens of matrix metalloproteinases, the main family of ECM degrading proteases. The activities of these proteases are regulated by a complex array of activators, inhibitors and cellular receptors. In physiological conditions the balance exists between proteases and their inhibitors. Proteolytic-antiproteolytic balance may be of major significance in the cancer development. One of the reasons for such a situation is enhanced generation of free radicals observed in many pathological states. Free radicals react with main cellular components like proteins and lipids and in this way modify proteolytic-antiproteolytic balance and enable penetration damaging cellular membrane. All these lead to enhancement of proteolysis and destruction of ECM proteins and in consequence to invasion and metastasis.

Proteases and emphysema

PURPOSE OF REVIEW

The protease-antiprotease theory of emphysema is widely accepted, but exactly which cells/proteases play a role continues to be a controversial subject.

RECENT FINDINGS

Reports in humans show increased metalloproteinase activity in emphysema, but the exact role of metalloproteinases remains unclear. In laboratory animals, neutrophils turn out to be crucial, and neutrophil influx correlates well with measurements of matrix destruction. Neutrophil influx is linked to metalloproteinase activity, and in mice MMP12-induced release of tumor necrosis factor-alpha drives neutrophil infiltration. Serine elastase inhibitors, knockout of neutrophil elastase, and interference with tumor necrosis factor-alpha signaling all provide significant protection against smoke-induced emphysema, but metalloproteinase inhibitors may yield greater protection. In genetically modified mice, emphysema can be produced by overexpression of mediators such as tumor necrosis factor-alpha, interferon-gamma, or interleukin-13, and these models show evidence of metalloproteinase, cysteine protease, and serine protease attack with complicated relationships among these mediators. Collagen breakdown also appears to be important in the genesis of emphysema. Pro-apoptotic agents produce emphysema as well, possibly via an elastolytic pathway.

SUMMARY

The idea that a single protease or a single type of inflammatory cell is responsible for human emphysema is unlikely to be true; rather, there are complex interactions among proteases, and between proteases and other mediators. The problem at this time is attempting to sort out the numerous candidate effector agents and to determine which of the animal models are relevant to human disease, since there may be considerable discrepancies in the types of proteases and their roles between laboratory animals and humans. There is now good evidence from animal models that antiproteolytic therapy can be of benefit in ameliorating cigarette smoke-induced emphysema.

Targeting senescence pathways to reverse drug resistance in cancer

Irreversible proliferation arrest (also called senescence) has emerged recently as a drug-responsive program able to influence the outcome of cancer chemotherapy. Since the drug amounts required for induction of proliferation arrest are much lower than those necessitated for induction of cell death, forcing cancer cells to undergo senescence may represent a less aggressive approach to control tumor progression. However, to achieve a long-standing control of proliferation, the ability of cancer cells to escape senescence and become drug resistant must be inhibited. Therefore, a clear understanding of the mechanisms that govern drug-induced senescence is critical and can lead to discovery of novel approaches to suppress drug resistance. The present review discusses the relevance of senescence in response to chemotherapy and the onset of drug resistance development. Particular emphasis is directed toward the utilization of findings from the field of research on aging, that can be applied to induction of senescence in cancer cells and reversal of their drug resistance phenotype. Proof of principle for this relationship is represented by the identification of inhibitors of aging associated proteases such as the proteasome and cathepsin L as novel and potent cancer drug resistance reversing agents.

Effect of vitamin E and human placenta cysteine peptidase inhibitor on expression of cathepsins B and L in implanted hepatoma Morris 5123 tumor model in Wistar rats

AIM: To examine the effectiveness of human placental inhibitors, by injecting vitamin E to rats with transplanted Morris-5123 hepatoma, on the expression of cathepsins B and L in tumor, liver, lung and blood sera after transplantation of Morris 5123 hepatoma.

METHODS: Animals were divided into 10 groups receiving three different concentrations of vitamin E and inhibitors along or in combination and compared with negative control (healthy rats) and positive control (tumor rats). Effectiveness of treatment was evaluated with regard to survival time, tumor response and determination of the activities of proteolytic enzymes and their inhibitors using flurogenic substrates.

RESULTS: Cathepsins B and L activities were elevated by 16-fold in comparison with negative control tissues, and their endogenous inhibitor activity decreased by 1.2-fold before treatment. In several cases, tumors completely disappeared following vitamin E plus human placental cyteine protease inhibitor (CPI) compared with controls. The number of complete tumor responses was higher when 20 m/kg vitamin E plus 400 μg of CPI was used, i.e., 7/10 rats survived more than two mo. Cathepsins B and L were expressed significantly in tumor, liver, lung tissues and sera in parallel to the increasing of the endogenous inhibitor activity compared with the controls after treatment (P<0.0001).

CONCLUSION: The data indicate formation of metastasis significantly reduced in treated rats, which might provide a therapeutic basis for anti-cancer therapy.

Comprehensive search for cysteine cathepsins in the human genome

Our study was aimed at examinating whether or not the human genome encodes for previously unreported cysteine cathepsins. To this end, we used analyses of the genome sequence and mRNA expression levels. The program TBLASTN was employed to scan the draft sequence of the human genome for the 11 known cysteine cathepsins. The cathepsin-like segments in the genome were inspected, filtered, and annotated. In addition to the known cysteine cathepsins, the scan identified three pseudogenes, closely related to cathepsin L, on chromosome 10, as well as two remote homologs, tubulointerstitial protein antigen and tubulointerstitial protein antigen-related protein. No new members of the family were identified. mRNA expression profiles for 10 known human cysteine cathepsins showed varying expression levels in 46 different human tissues and cell lines. No expression of any of the three cathepsin L-like pseudogenes was found. Based on these results, it is likely that to date all human cysteine cathepsins are known.

Recombinant human procathepsin S is capable of autocatalytic processing at neutral pH in the presence of glycosaminoglycans

Cathepsin S is unique among mammalian cysteine cathepsins in being active and stable at neutral pH. We show that autocatalytic activation of procathepsin S at low pH is a bimolecular process that is considerably accelerated (approximately 20-fold) by glycosaminoglycans and polysaccharides such as dextran sulfate, chondroitin sulfates A and E, and dermatan sulfate through electrostatic interaction with the proenzyme. Procathepsin S is also shown to undergo autoactivation at neutral pH in the presence of dextran sulfate with t1/2 of approximately 20 min at pH 7.5. This novel property of procathepsin S may have implications in pathological conditions associated with the appearance of active cathepsins outside lysosomes.

Site-directed mutagenesis, proteolytic cleavage, and activation of human proheparanase

Heparanase is an endo-beta-D-glucuronidase that degrades heparan sulfate in the extracellular matrix and cell surfaces. Human proheparanase is produced as a latent 65-kDa polypeptide undergoing processing at two potential proteolytic cleavage sites, located at Glu109-Ser110 (site 1) and Gln157-Lys158 (site 2). Cleavage of proheparanase yields 8- and 50-kDa subunits that heterodimerize to form the active enzyme. The fate of the linker segment (Ser110-Gln157) residing between the two subunits, the mode of processing, and the protease(s) engaged in proheparanase processing are currently unknown. We applied multiple site-directed mutagenesis and deletions to study the nature of the potential cleavage sites and amino acids essential for processing of proheparanase in transfected human choriocarcinoma cells devoid of endogenous heparanase but possessing the enzymatic machinery for proper processing and activation of the proenzyme. Although mutagenesis at site 1 and its flanking sequences failed to identify critical residues for proteolytic cleavage, processing at site 2 required a bulky hydrophobic amino acid at position 156 (i.e. P2 of the cleavage site). Substitution of Tyr156 by Ala or Glu, but not Val, resulted in cleavage at an upstream site in the linker segment, yielding an improperly processed inactive enzyme. Processing of the latent 65-kDa proheparanase in transfected Jar cells was inhibited by a cell-permeable inhibitor of cathepsin L. Moreover, recombinant 65-kDa proheparanase was processed and activated by cathepsin L in a cell-free system. Altogether, these results suggest that proheparanase processing at site 2 is brought about by cathepsin L-like proteases. The involvement of other members of the cathepsin family with specificity to bulky hydrophobic residues cannot be excluded. Our results and a three-dimensional model of the enzyme are expected to accelerate the design of inhibitory molecules capable of suppressing heparanase-mediated enhancement of tumor angiogenesis and metastasis.

Inhibition of cysteine protease activity disturbs DNA replication and prevents mitosis in the early mitotic cell cycles of sea urchin embryos

Recent findings suggested that the role of cysteine proteases would not be limited to protein degradation in lysosomes but would also play regulatory functions in more specific cell mechanisms. We analyzed here the role of these enzymes in the control of cell cycle during embryogenesis. The addition of the potent cysteine protease inhibitor E64d to newly fertilized sea urchin eggs disrupted cell cycle progression, affecting nuclear as well as cytoplasmic characteristic events. Monitoring BrdU incorporation in E64d treated eggs demonstrated that DNA replication is severely disturbed. Moreover, this drug treatment inhibited male histones degradation, a step that is necessary for sperm chromatin remodeling and precedes the initiation of DNA replication in control eggs. This inhibition likely explains the DNA replication disturbance and suggests that S phase initiation requires cysteine protease activity. In turn, activation of the DNA replication checkpoint could be responsible for the consecutive block of nuclear envelope breakdown (NEB). However, in sea urchin early embryos this checkpoint doesn't control the mitotic cytoplasmic events that are not tightly coupled with NEB. Thus the fact that microtubule spindle is not assembled and cyclin B-cdk1 not activated under E64d treatment more likely rely on a distinct mechanism. Immunofluorescence experiments indicated that centrosome organization was deficient in absence of cysteine protease activity. This potentially accounts for mitotic spindle disruption and for cyclin B mis-localization in E64d treated eggs. We conclude that cysteine proteases are essential to trigger S phase and to promote M phase entry in newly fertilized sea urchin eggs.

Cathepsin L in glioma progression: Comparison with cathepsin B

OBJECTIVE

Lysosomal cysteine cathepsins have been implicated in tumor progression. This study is aimed to reveal differential expression and compare the prognostic significance of cathepsins B and L in glioma patients.

METHODS

The histological slides of 82 patients with primary astrocytic tumors were reviewed. We evaluated the immunostaining of the cathepsins in tumor and endothelial cells.

RESULTS

Cathepsins B and L stained positive in 98 and 88% of cases, respectively. The total score was significantly higher in malignant than in benign tumors, both for cathepsin B (p<0.001) and for cathepsin L (p<0.01). The IHC score in endothelial cells in the malignant group was significantly higher only for cathepsin B (p<0.0001). Survival analysis indicated that in contrast to the prognostic significance of total cathepsin B and endothelial cells associated cathepsin B for shorter patients' survival, the prognostic role of cathepsin L was not confirmed.

CONCLUSION

Cathepsin L is preferentially expressed in tumor cells, increasing with glioma progression, but is not significantly associated with new vasculature of glioblastoma. In contrast to cathepsin B, cathepsin L has no prognostic impact, suggesting different roles of the two cathepsins in glioma progression.

Crystal structure of NS-134 in complex with bovine cathepsin B: a two-headed epoxysuccinyl inhibitor extends along the entire active-site cleft

The crystal structure of the inhibitor NS-134 in complex with bovine cathepsin B reveals that functional groups attached to both sides of the epoxysuccinyl reactive group bind to the part of active-site cleft as predicted. The -Leu-Pro-OH side binds to the primed binding sites interacting with the His110 and His111 residues with its C-terminal carboxy group, whereas the -Leu-Gly-Meu (-Leu-Gly-Gly-OMe) part (Meu, methoxycarbonylmethyl) binds along the non-primed binding sites. Comparison with the propeptide structures of cathepsins revealed that the binding of the latter part is least similar to the procathepsin B structure; this result, together with the two-residue shift in positioning of the Leu-Gly-Gly part, suggests that the propeptide structures of the cognate enzymes may not be the best starting point for the design of reverse binding inhibitors.

The protein structures that shape caspase activity, specificity, activation and inhibition

The death morphology commonly known as apoptosis results from a post-translational pathway driven largely by specific limited proteolysis. In the last decade the structural basis for apoptosis regulation has moved from nothing to 'quite good', and we now know the fundamental structures of examples from the initiator phase, the pre-mitochondrial regulator phase, the executioner phase, inhibitors and their antagonists, and even the structures of some substrates. The field is as well advanced as the best known of proteolytic pathways, the coagulation cascade. Fundamentally new mechanisms in protease regulation have been disclosed. Structural evidence suggests that caspases have an unusual catalytic mechanism, and that they are activated by apparently unrelated events, depending on which position in the apoptotic pathway they occupy. Some naturally occurring caspase inhibitors have adopted classic inhibition strategies, but other have revealed completely novel mechanisms. All of the structural and mechanistic information can, and is, being applied to drive therapeutic strategies to combat overactivation of apoptosis in degenerative disease, and underactivation in neoplasia. We present a comprehensive review of the caspases, their regulators and inhibitors from a structural and mechanistic point of view, and with an aim to consolidate the many threads that define the rapid growth of this field.

Ovarian cysteine proteinases in the teleost Fundulus heteroclitus: molecular cloning and gene expression during vitellogenesis and oocyte maturation

The cysteine proteinases cathepsins B and L are members of the multigene family of lysosomal proteases that have been implicated in the processing of yolk proteins (YPs) in teleost oocytes. However, the full identification of the type of cathepsins expressed in fish ovarian follicles and embryos, as well as their regulatory mechanisms and specific function(s), are not yet elucidated. In this study, cDNAs encoding cathepsins B, L, F, K, S, Z, C, and H have been isolated from the teleost Fundulus heteroclitus, and the analysis of their deduced amino acid sequences revealed highly similar structural features to vertebrate orthologs, and confirmed in this species the existence of cathepsin L-like, cathepsin B-like, and cathepsin F-like subfamilies of cysteine proteinases. While all identified cathepsins were expressed in ovarian follicles, the corresponding mRNAs showed different temporal expression patterns. Thus, similar mRNA levels of cathepsins L, F, S, B, C, and Z were found throughout the oocyte growth or vitellogenesis period, whereas those for cathepsin H and K appeared to decrease as vitellogenesis advanced. During oocyte maturation, a transient accumulation of cathepsins L, S, H, and F mRNAs, approximately a 3-, 1.5-, 1.6-, and 6-fold increase, respectively, was detected in ovarian follicles within the 20-25 hr after hormone stimulation, coincident with the maximum proteolysis of the oocyte major YPs. The specific temporal pattern of expression of these genes may indicate a potential role of cathepsin L-like and cathepsin F proteases in the YP processing events occurring during fish oocyte maturation and/or early embryogenesis.

Potent and Selective Ketoamide-Based Inhibitors of Cysteine Protease, Cathepsin K

Cathepsin K, a lysosomal cysteine protease of the papain superfamily, is abundantly and selectively expressed in osteoclasts, suggesting that this enzyme is crucial for bone resorption. Prevention of osteoclast-mediated bone resorption via inhibition of cathepsin K could be an effective approach to prevent osteoporosis. Potent and selective reversible ketoamide-based inhibitors have been identified in the present study. Using a known crystal structure of a ketoamide-based inhibitor, information from residues that form the P2/P3 pocket was used in the design of inhibitors that could allow for gains in selectivity and potency. Further, incorporation of P' selective heterocycles, along with the P2/P3 modifications, is also described. These modifications have resulted in potent and selective cathepsin K inhibitors that allow for improvements in their physiochemical properties and represent a viable lead series for the discovery of new therapies for the prevention and treatment of osteoporosis

Mouse DESC1 is located within a cluster of seven DESC1-like genes and encodes a type II transmembrane serine protease that forms serpin inhibitory complexes

We report the identification and functional analysis of a type II transmembrane serine protease encoded by the mouse differentially expressed in squamous cell carcinoma (DESC) 1 gene, and the definition of a cluster of seven homologous DESC1-like genes within a 0.5-Mb region of mouse chromosome 5E1. This locus is syntenic to a region of human chromosome 4q13.3 containing the human orthologues of four of the mouse DESC1-like genes. Bioinformatic analysis indicated that all seven DESC1-like genes encode functional proteases. Direct cDNA cloning showed that mouse DESC1 encodes a multidomain serine protease with an N-terminal signal anchor, a SEA (sea urchin sperm protein, enterokinase, and agrin) domain, and a C-terminal serine protease domain. The mouse DESC1 mRNA was present in epidermal, oral, and male reproductive tissues and directed the translation of a membrane-associated 60-kDa N-glycosylated protein with type II topology. Mouse DESC1 was synthesized in insect cells as a zymogen that could be activated by exposure to trypsin. The purified activated DESC1 hydrolyzed synthetic peptide substrates, showing a preference for Arg in the P1 position. DESC1 proteolytic activity was abolished by generic inhibitors of serine proteases but not by other classes of protease inhibitors. Most interestingly, DESC1 formed stable inhibitory complexes with both plasminogen activator inhibitor-1 and protein C inhibitor that are expressed in the same tissues with DESC1, suggesting that type II transmembrane serine proteases may be novel targets for serpin inhibition. Together, these data show that mouse DESC1 encodes a functional cell surface serine protease that may have important functions in the epidermis, oral, and reproductive epithelium.

1,2,4-thiadiazole: a novel Cathepsin B inhibitor

A novel class of Cathepsin B inhibitors has been developed with a 1,2,4-thiadiazole heterocycle as the thiol trapping pharmacophore. Several compounds with different dipeptide recognition sequence (i.e., P1'-P2'=Leu-Pro-OH or P2-P1=Cbz-Phe-Ala) at the C5 position and with different substituents (i.e., OMe, Ph, or COOH) at the C3 position of the 1,2,4-thiadiazole ring have been synthesized and tested for their inhibitory activities. The substituted thiadiazoles 3a-h inhibit Cat B in a time dependent, irreversible manner. A mechanism based on active-site directed inactivation of the enzyme by disulfide bond formation between the active site cysteine thiol and the sulfur atom of the heterocycle is proposed. Compound 3a (K(i)=2.6 microM, k(i)K(i)=5630 M(-1)s(-1)) with a C3 methoxy moiety and a Leu-Pro-OH dipeptide recognition sequence, is found to be the most potent inhibitor in this series. The enhanced inhibitory potency of 3a is a consequence of its increased enzyme binding affinity (lower K(i)) rather than its increased intrinsic reactivity (higher k(i)). In addition, 3a is inactive against Cathepsin S, is a poor inhibitor of Cathepsin H and is >100-fold more selective for Cat B over papain.

Inhibitory Activity ofDrynariae rhizomaExtracts on Cathepsin Having Bone Resorption Activity

Effects of traditional Korean (Hanbang) medicine, Drynariae rhizoma (DR), on the protease activity of bone loss-initiation in rats and mice were investigated. Ethanol extracts-DR (EE-DR) and water extracts-DR (WE-DR) were identified as potent inhibitor of cathepsins K and L. The original WE-DR inhibits cathepsins K and L with IC50 values of 3.7 microg/ml and 4.5 microg/ml, respectively. EE-DR was more potent than that of WE-DR, because the inhibitions of cathepsin K and L increased to 0.5 microg/ml and 0.8 microg/ml, respectively. The EE-DR was proved to be the most potent. EE-DR was found to be a potent inhibitor of cathepsins K with a Ki value of 5.0 microg/ml for cathepsin K. The activity was increased by 10-fold when the assay is performed in the presence of glutathione at pH 7.0, which favors the formation of a GSH thiolate anion. Thus, it is suggested that this increase in potency is probably due to an enhanced chemical reactivity of the extract mixtures toward the thiolate of the active site of the enzyme. WE-DR exhibited time-dependet inhibition which allowed us to determine the association and dissociation rate constants with cathepsin K. Finally, EE-DR inhibits bone resorption in an in vitro assay involving mouse osteoclasts and bovine bone with an IC50 value of 70 microg/ml. WE-DR represents a new herbal formulation inhibiting cathepsin K and L activity and proteolysis of bone collagen. These results strongly suggest that DR is effective for preventing the development of bone loss induced by cathepsin K. This result also suggested that the DR is effective for bone resorptive action in bone cells.

Inhibitory selectivity of canecystatin: a recombinant cysteine peptidase inhibitor from sugarcane

The cDNA of a cystein peptidase inhibitor was isolated from sugarcane and expressed in Escherichia coli. The protein, named canecystatin, has previously been shown to exert antifungal activity on the filamentous fungus Trichoderma reesei. Herein, the inhibitory specificity of canecystatin was further characterized. It inhibits the cysteine peptidases from plant source papain (Ki =3.3nM) and baupain (Ki=2.1x10(-8)M), but no inhibitory effect was observed on ficin or bromelain. Canecystatin also inhibits lysosomal cysteine peptidases such as human cathepsin B (Ki=125nM), cathepsin K (Ki=0.76nM), cathepsin L (Ki=0.6nM), and cathepsin V (Ki=1.0nM), but not the aspartyl peptidase cathepsin D. The activity of serine peptidases such as trypsin, chymotrypsin, pancreatic, and neutrophil elastases, and human plasma kallikrein is not affected by the inhibitor, nor is the activity of the metallopeptidases angiotensin converting enzyme and neutral endopeptidase. This is the first report of inhibitory activity of a sugarcane cystatin on cysteine peptidases.

Analysis of Signal-dependent Changes in the Proteome of Drosophila Blood Cells During an Immune Response

Innate immunity is based on the recognition of cell-surface molecules of infecting agents. Microbial substances, such as peptidoglycan, lipopolysaccharide, and beta-1,3-glucans, produce functional responses in Drosophila hemocytes that contribute to innate immunity. We have used two-dimensional gel electrophoresis and MS to resolve lipopolysaccharide-induced changes in the protein profile of a Drosophila hemocytic cell line. We identified 24 intracellular proteins that were up- or down-regulated, or modified, in response to immune challenge. Several proteins with predicted immune functions, including lysosomal proteases, actin-binding/remodeling proteins, as well as proteins involved in cellular responses to oxidative stress, were affected by the immune assault. Intriguingly, a number of the proteins identified in this study have recently been implicated in phagocytosis in higher vertebrates. We suggest that phagocytosis is activated in Drosophila hemocytes by the presence of microbial substances, and that this activation constitutes an evolutionarily conserved arm of innate immunity. In addition, a number of proteins involved in calcium-regulated signaling, mRNA processing, and nuclear transport were affected, consistent with a possible role in reprogramming of gene expression. In conclusion, the present proteome analysis identified many proteins previously not linked to innate immunity, demonstrating that differential protein profiling of Drosophila hemocytes is a valuable tool for identification of new players in immune-related cellular processes.

Cysteine proteases and cell differentiation: excystment of the ciliated protist Sterkiella histriomuscorum

The process of excystment of Sterkiella histriomuscorum (Ciliophora, Oxytrichidae) leads in a few hours, through a massive influx of water and the resorption of the cyst wall, from an undifferentiated resting cyst to a highly differentiated and dividing vegetative cell. While studying the nature of the genes involved in this process, we isolated three different cysteine proteases genes, namely, a cathepsin B gene, a cathepsin L-like gene, and a calpain-like gene. Excystation was selectively inhibited at a precise differentiating stage by cysteine proteases inhibitors, suggesting that these proteins are specifically required during the excystment process. Reverse transcription-PCR experiments showed that both genes display differential expression between the cyst and the vegetative cells. A phylogenetic analysis showed for the first time that the cathepsin B tree is paraphyletic and that the diverging S. histriomuscorum cathepsin B is closely related to its Giardia homologues, which take part in the cyst wall breakdown process. The deduced cathepsin L-like protein sequence displays the structural signatures and phylogenetic relationships of cathepsin H, a protein that is known only in plants and animals and that is involved in the degradation of extracellular matrix components in cancer diseases. The deduced calpain-like protein sequence does not display the calcium-binding domain of conventional calpains; it belongs to a diverging phylogenetic cluster that includes Aspergillus palB, a protein which is involved in a signal transduction pathway that is sensitive to ambient pH.

Cathepsin B and L are involved in degradation of prions in GT1-1 neuronal cells

In scrapie-infected cells, the abnormal isoform of the prion protein, PrP(Sc), accumulates in endosomes/lysosomes. In this study, the involvement of two lysosomal proteases, cathepsin B and L, in cellular processing of PrP(Sc) was analyzed in immortalized neuronal gonadotropin-releasing hormone cells (GT1-1) infected with scrapie. Treatment with inhibitors of either cathepsin B or L resulted in accumulation of PrP(Sc). Such an increased accumulation also occurred when the activities of both cathepsins were inhibited using RNA interference. We conclude that cathepsin B and L are involved in the degradation of PrP(Sc) in scrapie-infected GT1-1 cells and that they can compensate for each other's functions. This study shows that specific proteases, abundantly present in neurons, have the capacity to degrade PrP(Sc).

Neuronal and microglial cathepsins in aging and age-related diseases

It has been long believed that cathepsins compensate for each other because of their overlapping substrate specificities. However, there is increasing evidence that disturbance of the normal balance of their enzymatic activities is the first insult in brain aging and age-related diseases. The imbalance of cathepsins may further cause age-related neuropathological changes such as accumulation of autophagic vacuoles and the formation of ceroid-lipofuscin leading to neuronal dysfunction and damage. Leakage of cathepsins due to the fragility of lysosomal membranes during aging also contributes to neurodegeneration. Furthermore, the deficiency of cathepsin D has been recently revealed to provoke a novel type of lysosomal storage disease associated with massive neurodegeneration. In these animals, microglia are activated to initiate inflammatory and cytotoxic responses by binding and phagocytosis of storage neurons. Activated microglia also release some members of cathepsins to induce neuronal death by degrading extracellular matrix proteins. Thus the microglial activation possibly through sensing neuronal storage may also be an important causative factor for neurodegeneration in lysosomal storage diseases and age-related diseases such as Alzheimer's disease. This review describes the pathological roles of neuronal and microglial cathepsins in brain aging and age-related diseases.

Structural basis of the unusual stability and substrate specificity of ervatamin C, a plant cysteine protease from Ervatamia coronaria

Ervatamin C is an unusually stable cysteine protease from the medicinal plant Ervatamia coronaria belonging to the papain family. Though it cleaves denatured natural proteins with high specific activity, its activity toward some small synthetic substrates is found to be insignificant. The three-dimensional structure and amino acid sequence of the protein have been determined from X-ray diffraction data at 1.9 A (R = 17.7% and R(free) = 19.0%). The overall structure of ervatamin C is similar to those of other homologous cysteine proteases of the family, folding into two distinct left and right domains separated by an active site cleft. However, substitution of a few amino acid residues, which are conserved in the other members of the family, has been observed in both the domains and also at the region of the interdomain cleft. Consequently, the number of intra- and interdomain hydrogen-bonding interactions is enhanced in the structure of ervatamin C. Moreover, a unique disulfide bond has been identified in the right domain of the structure, in addition to the three conserved disulfide bridges present in the papain family. All these factors contribute to an increase in the stability of ervatamin C. In this enzyme, the nature of the S2 subsite, which is the primary determinant of specificity of these proteases, is similar to that of papain, but at the S3 subsite, Ala67 replaces an aromatic residue, and has the effect of eliminating sufficient hydrophobic interactions required for S3-P3 stabilization. This provides the possible explanation for the lower activity of ervatamin C toward the small substrate/inhibitor. This substitution, however, does not affect the binding of denatured natural protein substrates to the enzyme significantly, as there exist a number of additional interactions at the enzyme-substrate interface outside the active site cleft.

Purification of bovine cathepsin B: proteomic characterization of the different forms and production of specific antibodies

Cathepsin B (EC 3.4.22.1) has been highly purified (14,225 fold) from bovine kidney by a rapid procedure that included the preparation of an enriched lysosomal extract, a selective fractionation with ammonium sulphate, size-exclusion chromatography, two cation-exchange chromatographies, and anion-exchange chromatography on diethylaminoethyl-Sephacel. After the last purification step, two hydrolytic peaks against Z-Phe-Arg-AMC were separated from each other, a minor peak corresponding to the cathepsin B single-chain form and a major one representing the double-chain form of cathepsin B. The single-chain form showed a molecular mass of 31 kDa on sodium dodecyl sulphate - polyacrylamide gel electrphoresis (PAGE) under reducing conditions, whereas the heavy chain of the double-chain form appeared as a doublet with molecular masses of 23.4 and 25 kDa, respectively. The identity of the different cathepsin B isoforms and the quality of the final enzyme preparation were confirmed by using two types of antibodies, one against a synthetic peptide sequence and one against purified cathepsin B. The proteomic study confirmed the identity of the different SDS-PAGE protein bands as cathepsin B isoforms and allowed the comparison and study of some structural differences between them at the level of their primary structures.

Cysteine protease cathepsin F is expressed in human atherosclerotic lesions, is secreted by cultured macrophages, and modifies low density lipoprotein particles in vitro

During atherogenesis, low density lipoprotein (LDL) particles in the arterial intima become modified and fuse to form extracellular lipid droplets. Proteolytic modification of apolipoprotein (apo) B-100 may be one mechanism of droplet formation from LDL. Here we studied whether the newly described acid protease cathepsin F can generate LDL-derived lipid droplets in vitro. Treatment of LDL particles with human recombinant cathepsin F led to extensive degradation of apoB-100, which, as determined by rate zonal flotation, electron microscopy, and NMR spectroscopy, triggered both aggregation and fusion of the LDL particles. Two other acid cysteine proteases, cathepsins S and K, which have been shown to be present in the arterial intima, were also capable of degrading apoB-100, albeit less efficiently. Cathepsin F treatment resulted also in enhanced retention of LDL to human arterial proteoglycans in vitro. Cultured monocyte-derived macrophages were found to secrete active cathepsin F. In addition, similarly with cathepsins S and K, cathepsin F was found to be localized mainly within the macrophage-rich areas of the human coronary atherosclerotic plaques. These results suggest that proteolytic modification of LDL by cathepsin F may be one mechanism leading to the extracellular accumulation of LDL-derived lipid droplets within the proteoglycan-rich extracellular matrix of the arterial intima during atherogenesis.

A new type of cysteine proteinase inhibitor--the salarin gene from Atlantic salmon (Salmo salar L.) and Arctic charr (Salvelinus alpinus)

Salarin is a 43 kDa glycoprotein which is found so far only in salmonid fish species. It is a strong inhibitor of cysteine proteinases. Here we characterised the salarin gene from Atlantic salmon and cDNA from Arctic charr. The salarin gene has 13 exons and 1026 bp long coding sequence. The translated amino acid sequence has four similar domains. The sequence resembles the proregion of cathepsins, known to inhibit cysteine proteinases. Salarin can be a new type of cysteine proteinase inhibitor.

A cathepsin L isoform that is devoid of a signal peptide localizes to the nucleus in S phase and processes the CDP/Cux transcription factor

The subclass of cysteine proteases termed lysosomal cathepsins has long been thought to be primarily involved in end-stage protein breakdown within lysosomal compartments. Furthermore, few specific protein substrates for these proteases have been identified. We show here that cathepsin L functions in the regulation of cell cycle progression through proteolytic processing of the CDP/Cux transcription factor. CDP/Cux processing in situ was increased following ectopic expression of cathepsin L but was reduced in Cat L(-/-) cells. Furthermore, catalytically active cathepsin L was localized to the nucleus during the G1-S transition as detected by immunofluorescence imaging and labeling using activity-based probes. Trafficking of cathepsin L to the nucleus is accomplished through a mechanism involving translation initiation at downstream AUG sites and the synthesis of proteases that are devoid of a signal peptide. Overall, these results uncover an as yet unsuspected role for cysteine proteases in the control of cell cycle progression.

Inhibitors of cysteine cathepsin and calpain do not prevent ultraviolet-B-induced apoptosis in human keratinocytes and HeLa cells

Caspases, members of the cysteine protease family, execute UVB-induced apoptosis in several cell lines and keratinocytes. Several researchers investigating UVB-induced apoptosis have demonstrated a dose-dependent protective effect of the synthetic peptide caspase inhibitor zVAD-fmk. However, zVAD-fmk displays a dose-dependent protective effect against UVB-induced apoptosis, even at doses higher than those required to block all known proapoptotic caspases. In addition, it is known that zVAD-fmk also inhibits other cysteine proteases including cathepsins and calpains, and these proteases have recently been demonstrated to play a role in the execution of programmed cell death induced by other stimuli, e.g. TNF-alpha. The purpose of the present study was therefore to investigate whether inhibitors of cysteine cathepsins and calpains could prevent UVB-induced apoptosis in HeLa cells and keratinocytes. This was done by investigating the effect of the irreversible cysteine protease inhibitor zFA-fmk, the cathepsin B inhibitor CA-074-Me and the calpain inhibitor ALLN on the viability of UVB-irradiated human keratinocytes and HeLa cells. At concentrations of 10 microM and above zVAD-fmk conferred partial dose-dependent protection against UVB-induced apoptosis in HeLa cells and keratinocytes. Moreover, caspase-3 activity was completely blocked at zVAD-fmk concentrations of 1 microM in HeLa cells. This indicates that caspase-independent mechanisms could be involved in UVB-induced apoptosis. However, the protease inhibitors zFA-fmk, CA-074-Me and ALLN all failed to prevent UVB-induced apoptosis in HeLa cells and keratinocytes. In conclusion, the protective effect of zVAD-fmk at high concentrations indicates that other proteases than caspases are active in the execution of UVB-induced apoptosis but further studies are needed to identify these proteases.

Gene expression profiling reveals multiple toxicity endpoints induced by hepatotoxicants

Microarray technology continues to gain increased acceptance in the drug development process, particularly at the stage of toxicology and safety assessment. In the current study, microarrays were used to investigate gene expression changes associated with hepatotoxicity, the most commonly reported clinical liability with pharmaceutical agents. Acetaminophen, methotrexate, methapyrilene, furan and phenytoin were used as benchmark compounds capable of inducing specific but different types of hepatotoxicity. The goal of the work was to define gene expression profiles capable of distinguishing the different subtypes of hepatotoxicity. Sprague-Dawley rats were orally dosed with acetaminophen (single dose, 4500 mg/kg for 6, 24 and 72 h), methotrexate (1mg/kg per day for 1, 7 and 14 days), methapyrilene (100mg/kg per day for 3 and 7 days), furan (40 mg/kg per day for 1, 3, 7 and 14 days) or phenytoin (300 mg/kg per day for 14 days). Hepatic gene expression was assessed using toxicology-specific gene arrays containing 684 target genes or expressed sequence tags (ESTs). Principal component analysis (PCA) of gene expression data was able to provide a clear distinction of each compound, suggesting that gene expression data can be used to discern different hepatotoxic agents and toxicity endpoints. Gene expression data were applied to the multiplicity-adjusted permutation test and significantly changed genes were categorized and correlated to hepatotoxic endpoints. Repression of enzymes involved in lipid oxidation (acyl-CoA dehydrogenase, medium chain, enoyl CoA hydratase, very long-chain acyl-CoA synthetase) were associated with microvesicular lipidosis. Likewise, subsets of genes associated with hepatotocellular necrosis, inflammation, hepatitis, bile duct hyperplasia and fibrosis have been identified. The current study illustrates that expression profiling can be used to: (1) distinguish different hepatotoxic endpoints; (2) predict the development of toxic endpoints; and (3) develop hypotheses regarding mechanisms of toxicity.

Lysosomes in cell death

For many years apoptosis research has focused on caspases and their putative role as sole executioners of programmed cell death. Accumulating information now suggests that lysosomal cathepsins are also pivotally involved in this process, especially in pathological conditions. In particular, the role of lysosomes and lysosomal enzymes in initiation and execution of the apoptotic program has become clear in several models, to the point that the existence of a 'lysosomal pathway of apoptosis' is now generally accepted. This pathway of apoptosis can be activated by death receptors, lipid mediators, and photodamage. Lysosomal proteases can be released from the lysosomes into the cytosol, where they contribute to the apoptotic cascade upstream of mitochondria. This review focuses on the players and the molecular mechanisms involved in the lysosomal pathway of apoptosis as well as on the importance of this pathway in development and pathology.

Oxidative stress inhibits ionomycin-mediated cell death in cortical neurons

Thiol-proteases play important roles in many cellular processes, including maintenance of protein homeostasis and execution of cell death. Therefore, determining how this family of enzymes is regulated is critical for our understanding of both physiological and pathological conditions. Because these proteases require a reduced cysteine residue for activity, the cellular redox state plays a crucial role in regulating the activity of thiol proteases. Importantly, increased oxidative stress can result in the direct modification of the active site cysteine, leading to enzyme inactivation. This would suggest that oxidative stress that occurs during pathological insults could prolong cell survival by preventing the execution of thiol-protease-dependent cell death pathways. To test this hypothesis, cultured rat cortical neurons were treated with the oxidizing agent diamide or doxorubicin in the presence or absence of the calcium ionophore ionomycin. Under normoxic conditions, ionomycin treatment resulted in approximately 70% cell death, which was prevented by addition of the calpain-selective inhibitor benyzloxycarbonyl-Leu-Leu-Tyr fluoromethylketone. Similarly, pretreatment of neurons with either oxidant was also protective. Protection resulting from oxidative stress was not due to new protein synthesis, insofar as cycloheximide did not affect oxidant-mediated protection. Interestingly, treatment with the antioxidant Trolox to reverse or prevent oxidative stress blocked the protective effects of both oxidants against ionomycin-induced cell death. We interpret these findings to suggest that, in diseases or conditions in which oxidative stress is increased, the ability of thiol-proteases to execute cell death pathways fully is decreased and may prolong cell survival.

Nuclear factor-kappaB mediates up-regulation of cathepsin B by doxorubicin in tumor cells

Anthracyclines such as doxorubicin remain among the most effective agents for the treatment of solid tumors and hematological malignancies. To overcome dose-limiting side effects like cardiotoxicity, an intensive effort has been undertaken to develop promising doxorubicin prodrugs that are specifically activated at the tumor site. One approach is the application of peptide prodrugs of doxorubicin. The enzyme cathepsin B catalyzes the activation of these prodrugs, and hence, the regulation of cathepsin B by antitumor agents could influence the efficacy of peptide prodrugs using this protease. In the present investigation, the effects of doxorubicin on cathepsin B expression in the human cervix carcinoma cell line HeLa were examined. Exposure to doxorubicin induced a time- and dose-dependent up-regulation of cathepsin B expression on mRNA, protein, and activity levels. In the cathepsin B gene promoter region, a potential nuclear factor kappaB (NF-kappaB) binding site could be identified. Pretreatment of HeLa cells with specific NF-kappaB inhibitors abrogated the induction of cathepsin B expression. Doxorubicin-induced degradation of the inhibitory protein IkappaB could be prevented by pretreatment with a specific proteasome inhibitor, resulting in a significant reduction of the doxorubicin-induced cathepsin B expression. Finally, binding of NF-kappaB subunits p50 and p65 to the NF-kappaB binding site in the cathepsin B gene promoter region could be demonstrated by electrophoretic mobility shift assay. In summary, our data clearly indicate that doxorubicin induces cathepsin B expression and activity via NF-kappaB. These findings contribute to a better understanding of tumor targeting with peptide prodrugs and help to define a possible mechanism of doxorubicin toxicity in tumor cells.

Identification of retinoid-modulated proteins in squamous carcinoma cells using high-throughput immunoblotting

Retinoids have shown clinical efficacy in cancer chemoprevention and therapy presumably by modulating the growth, differentiation, and apoptosis of normal, premalignant, and malignant cells. To better understand the mechanisms by which retinoids exert their effects, we used a high-throughput Western blotting method (Becton-Dickinson PowerBlot) to evaluate changes in the levels of cellular signaling proteins in head and neck squamous cell carcinoma cells treated with the cytostatic all-trans-retinoic acid or with the proapoptotic retinoids 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid or N-(4-hydroxyphenyl)retinamide. Treatments of the head and neck squamous cell carcinoma cells with these retinoids for 24 h resulted in increased levels of 14, 22, and 22 proteins and decreased levels of 5, 10, and 7 proteins, respectively. The changes in the levels of the following proteins were confirmed by conventional western immunoblotting: all-trans-retinoic acid increased ELF3, topoisomerase II alpha, RB2/p130, RIG-G, and EMAPII and decreased MEF2D and cathepsin L. N-(4-Hydroxyphenyl)retinamide up-regulated ELF3, c-Jun, Rb2/p130, JAK1, p67phox, Grb2, O(6)-methylguanine-DNA methyltransferase, and Ercc-1. 6-[3-(1-Adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid increased Rb2/p130, c-Jun, Sp1, Sin, and tomosyn and decreased cathepsin L, Mre11, and topoisomerase II alpha. Some of these proteins were also modulated by these retinoids in other human cancer cell lines. A subset of the proteins were modulated similarly by the different retinoids, whereas changes in other proteins were unique for each retinoid. These results suggest that the mechanisms by which these retinoids modulate proteins are distinct but may overlap. Some of the retinoid-modulated proteins identified in this study may be novel candidates for mediating different responses to retinoids.

Inhibition of tumorigenicity and metastasis of human melanoma cells by anti-cathepsin L single chain variable fragment

We demonstrated previously that the switch from nonmetastatic to highly metastatic phenotype of human melanoma cells is directly related to secretion of procathepsin L form. This cysteine proteinase was identified on the basis of its property to cleave human C3, the third component of complement. In an attempt to control procathepsin L secretion, we have recently generated an anti-cathepsin L single chain variable fragment (ScFv) from an anti-cathepsin L monoclonal antibody generated against recombinant cathepsin L. We herein selected clones stably transfected with this anti-cathepsin L ScFv and analyzed them for changes in tumor growth and metastasis. We show that in stably transfected clones, anti-cathepsin L ScFv strongly inhibited the secretion of procathepsin L without modifying the intracellular amount or processing pattern of cathepsin L forms. Confocal analysis demonstrated colocalization of endogenous cathepsin L and anti-cathepsin L ScFv. In addition, expression of this ScFv strongly inhibited generation of tumor and metastasis by these human melanoma clones in nude mice. In vivo, the anti-cathepsin L ScFv-transfected cells produced tumors with decreased vascularization (angiogenesis) concomitant with increased apoptosis of tumor cells. Matrigel assay also demonstrated that melanoma invasiveness was completely abolished. Thus, this is the first demonstration that anti-cathepsin L ScFv could be used to inhibit the tumorigenic and metastatic phenotype of human melanoma, depending on procathepsin L secretion, and could therefore be used as a molecular tool in a therapeutic cellular approach.

Transcriptional response to circumscribed cortical brain ischemia: spatiotemporal patterns in ischemic vs. remote non-ischemic cortex

Focal brain infarcts are surrounded by extended perilesional zones that comprise the partially ischemic penumbra but also completely non-ischemic cortex of the remote ipsilateral hemisphere. To delineate the impact of lesion-associated vs. remote processes on transcriptional programming after focal ischemia, we used cDNA array analysis, quantitative real-time polymerase chain reaction and immunohistochemistry in the photothrombosis model of circumscribed cortical ischemia in rats. At an early stage of 4 h after ischemia, gene induction occurred to a similar extent in the ischemic infarct and remote non-ischemic cortex of the ipsilateral hemisphere. Among the genes induced in non-ischemic cortex we found the NGF-inducible genes PC3, VGF and Arc, the transcriptional regulators I kappa B-alpha and Stat3, and the beta-chemokine MIP-1 alpha (CCL3). At 3 days, the spatial pattern of gene expression had changed dramatically with brain fatty acid-binding protein as the only gene significantly induced in non-ischemic ipsilateral cortex. In contrast, numerous genes were exclusively regulated at the lesion site, comprising genes involved in cell cycle regulation, proteolysis, apoptosis, lipid homeostasis and anti-inflammatory counter-regulation. Cortical spreading depression was identified as the main mechanism underlying gene induction in remote non-ischemic cortex. Our data demonstrate a dynamic spatiotemporal pattern of gene induction, which may contribute to delayed progression of damage or, alternatively, mediate neuroprotection, tissue remodeling and functional compensation.

Cystatin C Antagonizes Transforming Growth Factor β Signaling in Normal and Cancer Cells

Cystatin C (CystC) is a secreted cysteine protease inhibitor that regulates bone resorption, neutrophil chemotaxis, and tissue inflammation, as well as resistance to bacterial and viral infections. CystC is ubiquitously expressed and present in most bodily fluids where it inhibits the activities of cathepsins, a family of cysteine proteases that can promote cancer cell invasion and metastasis. Transforming growth factor β (TGF-β) is a multifunctional cytokine endowed with both tumor-suppressing and tumor-promoting activities. We show herein that TGF-β treatment up-regulated CystC transcript and protein in murine 3T3-L1 fibroblasts. Moreover, CystC mRNA expression was down-regulated in ∼50% of human malignancies, particularly cancers of the stomach, uterus, colon, and kidney. Overexpression of CystC in human HT1080 fibrosarcoma cells antagonized their invasion through synthetic basement membranes in part via a cathepsin-dependent pathway. Independent of effects on cathepsin activity, CystC also reduced HT1080 cell gene expression stimulated by TGF-β. Invasion of 3T3-L1 cells occurred through both cathepsin- and TGF-β-dependent pathways. Both pathways were blocked by CystC, but only the TGF-β-dependent pathway was blocked by a CystC mutant (i.e., Δ14CystC) that is impaired in its ability to inhibit cathepsin activity. Moreover, CystC and Δ14CystC both inhibited 3T3-L1 cell gene expression stimulated by TGF-β. We further show that CystC antagonized TGF-β binding to its cell surface receptors, doing so by interacting physically with the TGF-β type II receptor and antagonizing its binding of TGF-β. Collectively, our findings have identified CystC as a novel TGF-β receptor antagonist, as well as a novel CystC-mediated feedback loop that inhibits TGF-β signaling.

Cathepsin B mRNA and protein expression following contusion spinal cord injury in rats

We provide the first data that cathepsin B (Cath B), a lysosomal cysteine protease, is up-regulated following contusion-spinal cord injury (SCI). Following T12 laminectomy and moderate contusion, Cath B mRNA and protein expression profiles were examined from 2 to 168 h post-injury in rats using real-time PCR and immunoblots, respectively. Contusion injury significantly increased [mRNA]Cath B in the injury site and adjacent segments over sham injury levels. While the largest [mRNA]Cath B induction (20-fold over naive) was seen in the injury site, the caudal segment routinely yielded [mRNA]Cath B levels greater than 10-fold over naive. Interestingly, sham injury animals also experienced mRNA induction at several time points at the injury site and in segments rostral and caudal to the injury site. Contusion injury also significantly elevated levels of Cath B proenzyme protein (37 kDa) over sham injury in the injury site (48, 72 and 168 h post-injury). Furthermore, significant protein increases of single and double chain Cath B (both active forms) occurred at the injury site at 72 and 168 h post-injury. Similar significant increases in Cath B protein levels were seen in areas adjacent to the injury site. The induction of Cath B mRNA and protein expression following contusion injury is previously undescribed and suggests that Cath B may potentially be involved in the secondary injury cascade, perhaps for as long as 1 week post-injury.

Transcription of human cathepsin L mRNA species hCATL B from a novel alternative promoter in the first intron of its gene

Cathepsin L is a lysosomal cysteine protease over-expressed in malignancy. It is very potent in degrading collagen, elastin, laminin and other components of the basement membrane and therefore, has been implicated in tumor invasion and metastasis. Two mRNA species, hCATL A and hCATL B, which contain an identical open reading frame and different 5'UTRs, were demonstrated to be encoded by the same gene located on chromosome 9q21-22. We have previously cloned and characterized the promoter responsible for the transcription of hCATL A (hCATL A promoter). However, it was not clear whether hCATL B is a splice variant of hCATL A or transcribed from a different promoter. In the present study, we demonstrate for the first time that hCATL B is transcribed from an alternate promoter (hCATL B promoter) located in the first intron of hCATL. This TATA-less promoter initiates transcription from two cytosine nucleotides present 191 and 367 bases upstream to the translation start codon. Deletion analysis revealed that the core promoter region lies upstream to these transcription initiation sites. This region contains several putative transcription factor-binding sites like AP-1, AP-4, GATA-1, Lmo2, NF-kappa B, MZF-1, NF-AT, etc. In U-87 MG cells, hCATL B promoter exhibits at least six times less activity than our previously characterized hCATL A promoter. However, this promoter is significantly more active in malignantly transformed cells as compared to its activity in untransformed cells. Thus, our results conclusively demonstrate that hCATL B mRNA is transcribed from an alternate promoter. Increased transcriptional activity from this promoter contributes to the elevated cathepsin L expression in transformed cells.

Inhibition of dipeptidyl peptidase I in the human mast cell line HMC-1: blocked activation of tryptase, but not of the predominant chymotryptic activity

The mast cell proteases tryptase and chymase are synthesised as inactive precursors, but are stored and secreted as active enzymes. The cysteinyl protease dipeptidyl peptidase I (DPPI, cathepsin C) can activate the corresponding proenzymes in cell-free systems, but it is unknown whether it fulfils this role within the intact cell. We, therefore, tested the effect the DPPI-selective inhibitor Gly-Phe diazomethyl ketone (Gly-Phe-CHN(2)) on the tryptic and chymotryptic activity of the human mast cell-like cell line, HMC-1, and monitored any changes in the amount of immunodetectable enzymes by flow cytometry. Culture in Gly-Phe-CHN(2) produced a significant decrease in tryptase activity in cell lysates within 24hr and further decreases during continued culturing to 216 hr with periodic replenishment of Gly-Phe-CHN(2)-containing media. Flow cytometry showed no significant change in the levels of immunoreactive tryptase. In contrast, chymotryptic activity in treated cells did not differ significantly from untreated cells at any time point. Treatment of 216 hr cell lysates with DPPI revealed significant amounts of activatable protryptase in Gly-Phe-CHN(2)-treated cells, but not in controls, whereas activatable prochymotryptic activity was found in both treated and control cells. Chymase was detected immunologically, though small differences in substrate specificity and molecular mass were observed. These results strongly suggest that DPPI plays a role in the activation of tryptase, but not of the predominant chymotryptic activity of HMC-1 cells. As inhibitors of tryptase have proven efficacious in models of allergic disease, these results also indicate that inhibitors of DPPI might provide an additional point of therapeutic control.

Inhibition of the invasion capacity of carcinoma cells by WX-UK1, a novel synthetic inhibitor of the urokinase-type plasminogen activator system

The overall survival rate of patients suffering from carcinomas has remained poor and nearly unchanged over the last decades. This is mainly due to the so-called minimal residual disease, i.e., remaining tumor cells that overcome surgery and/or radiotherapy and are the cause of locoregional and distant metastases. To metastasize, tumor cells take advantage of proteases to invade and remodel surrounding tissues. Here, we analyzed the efficiency of WX-UK1, a novel 3-amidinophenylalanine-based inhibitor of the uPA system, at inhibiting the invasive capacity of carcinoma cells. First, uPAR expression was characterized in different carcinoma cell lines, including SCCHN, breast and cervical carcinoma. Thereafter, the invasive potential of these cell lines was determined using Matrigel invasion chambers and a spheroid cocultivation model with human fibroblasts. uPAR expression levels correlated positively with invasion capacity, which could be significantly inhibited by WX-UK1. A decrease of tumor cell invasion by up to 50% was achieved in both models with the SCCHN line FaDu and the cervical carcinoma line HeLa after treatment with WX-UK1. Thus, our results demonstrate the potential of WX-UK1 in vitro as a promising adjuvant antimetastatic therapy of carcinomas.

Biosynthesis and alternate targeting of the lysosomal cysteine protease cathepsin L

Upregulation of cathepsin L expression, whether during development or cell transformation, or mediated by ectopic expression from a plasmid, alters the targeting of the protease and thus its physiological function. Upregulated procathepsin L is targeted to small dense core vesicles and to the dense cores of multivesicular bodies, as well as to lysosomes and to the plasma membrane for selective secretion. The multivesicular vesicles resemble secretory lysosomes characterized in specialized cell types in that they are endosomes that stably store an upregulated protein and they possess the tetraspanin CD63. Morphologically the multivesicular endosomes also resemble late endosomes, but they store procathepsin L, not the active protease, and they are not the major site for LAMP-1 accumulation. Distinction between the lysosomal proenzyme and active protease thus identifies two populations of multivesicular endosomes in fibroblasts, one a storage compartment and one an enzymatically active compartment. A distinctive targeting pathway using aggregation is utilized to enrich the storage endosomes with a particular lysosomal protease that can potentially activate and be secreted.

Design of Potent, Selective, and Orally Bioavailable Inhibitors of Cysteine Protease Cathepsin K

Osteoclast-mediated bone matrix resorption has been attributed to cathepsin K, a cysteine protease of the papain family that is abundantly and selectively expressed in osteoclast. Inhibition of cathepsin K could potentially be an effective method to prevent osteoporosis. Structure-activity studies on a series of reversible ketoamides based inhibitors of cathepsin K have led to identification of potent and selective compounds. Crystallographic studies have given insights into the mode of binding of these inhibitors. A series of ketoamides with varying P1 moieties were first synthesized to find an optimum group that would fit into the S1 subsite of the cysteine protease, cathepsin K. With a desired P1 group in place a variety of heterocyclic analogues in the P' region were synthesized to study their steric and electronic effects. In the process of exploring these P' heterocyclic variations, excellent selectivity was gained over other highly homologous cysteine proteases, including cathepsins L, S, and V. The favorable pharmacokinetic properties of some of these cathepsin K inhibitors in rats make them suitable for evaluation in rodent osteoporosis models. A representative cathepsin K inhibitor was shown to attenuate PTH-stimulated hypercalcemia in the TPTX rat model. These inhibitors provide a viable lead series in the discovery of new therapies for the prevention and treatment of osteoporosis

Cathepsin-B and cathepsin-L expression levels do not correlate with sensitivity of tumour cells to TNF-alpha-mediated apoptosis

Recently, evidence has been accumulated that besides the caspase proteases, lysosomal cathepsins may play a role in apoptosis induction. This is especially significant as many human tumour cells express high levels of cathepsins, which might sensitise these cells to specific proapoptotic stimuli mediated by cathepsins. We found that TNF-α-mediated DNA fragmentation in tumour cells was significantly reduced in the presence of E64d and CA074Me, two inhibitors of lysosomal cysteine proteases. Transient transfection of cathepsin-B (Cath-B) and -L (Cath-L) resulting in expression levels comparable to those found in many tumours did not sensitise tumour cells to TNF-α-mediated apoptosis. As lysosomal proteases are thought to be activated by their release from this organelle into the cytosol, we used the lysosomotropic detergent N-dodecyl-imidazole-HCl (NDI-HCl) to disturb lysosomal integrity efficiently and trigger the release of its proteolytic content into the cytosol. Treatment of HeLa cells with NDI-HCl resulted in cell death, which, however, could also not be influenced by augmented Cath-B or -L expression levels. Therefore, our data do not support the hypothesis that the high Cath-B or -L expression levels frequently detected in tumour cells might be exploited to target selectively those tumours for an enhanced cell death effect induced by lysosomotropic agents.