Isolation and sequence of a cDNA for human pro-(cathepsin L)

A Cathepsin-Targeted Quenched Activity-Based Probe Facilitates Enhanced Detection of Human Tumors during Resection

PURPOSE

Fluorescence-guided surgery using tumor-targeted contrast agents has been developed to improve the completeness of oncologic resections. Quenched activity-based probes that fluoresce after covalently binding to tumor-specific enzymes have been proposed to improve specificity, but none have been tested in humans. Here, we report the successful clinical translation of a cathepsin activity-based probe (VGT-309) for fluorescence-guided surgery.

EXPERIMENTAL DESIGN

We optimized the specificity, dosing, and timing of VGT-309 in preclinical models of lung cancer. To evaluate clinical feasibility, we conducted a canine study of VGT-309 during pulmonary tumor resection. We then conducted a randomized, double-blind, dose-escalation study in healthy human volunteers receiving VGT-309 to evaluate safety. Finally, we tested VGT-309 in humans undergoing lung cancer surgery.

RESULTS

In preclinical models, we found highly specific tumor cell labeling that was blocked by a broad spectrum cathepsin inhibitor. When evaluating VGT-309 for guidance during resection of canine tumors, we found that the probe selectively labeled tumors and demonstrated high tumor-to-background ratio (TBR; range: 2.15-3.71). In the Phase I human study, we found that VGT-309 was safe at all doses studied. In the ongoing Phase II trial, we report two cases in which VGT-309 localized visually occult, non-palpable tumors (TBRs = 2.83 and 7.18) in real time to illustrate its successful clinical translation and potential to improve surgical management.

CONCLUSIONS

This first-in-human study demonstrates the safety and feasibility of VGT-309 to label human pulmonary tumors during resection. These results may be generalizable to other cancers due to cathepsin overexpression in many solid tumors.

Preventing Cleavage of the Respiratory Syncytial Virus Attachment Protein in Vero Cells Rescues the Infectivity of Progeny Virus for Primary Human Airway Cultures

All live attenuated respiratory syncytial virus (RSV) vaccines that have advanced to clinical trials have been produced in Vero cells. The attachment (G) glycoprotein in virions produced in these cells is smaller than that produced in other immortalized cells due to cleavage. These virions are 5-fold less infectious for primary well-differentiated human airway epithelial (HAE) cell cultures. Because HAE cells are isolated directly from human airways, Vero cell-grown vaccine virus would very likely be similarly inefficient at initiating infection of the nasal epithelium following vaccination, and therefore, a larger inoculum would be required for effective vaccination. We hypothesized that Vero cell-derived virus containing an intact G protein would be more infectious for HAE cell cultures. Using protease inhibitors with increasing specificity, we identified cathepsin L to be the protease responsible for cleavage. Our evidence suggests that cleavage occurs in the late endosome or lysosome during endocytic recycling. Cathepsin L activity was 100-fold greater in Vero cells than in HeLa cells. In addition, cathepsin L was able to cleave the G protein in Vero cell-grown virions but not in HeLa cell-grown virions, suggesting a difference in G-protein posttranslational modification in the two cell lines. We identified by mutagenesis amino acids important for cleavage, and these amino acids included a likely cathepsin L cleavage site. Virus containing a modified, noncleavable G protein produced in Vero cells was 5-fold more infectious for HAE cells in culture, confirming our hypothesis and indicating the value of including such a mutation in future live attenuated RSV vaccines.

IMPORTANCE

Worldwide, RSV is the second leading infectious cause of infant death, but no vaccine is available. Experimental live attenuated RSV vaccines are grown in Vero cells, but during production the virion attachment (G) glycoprotein is cleaved. Virions containing a cleaved G protein are less infectious for primary airway epithelial cells, the natural RSV target. In the study described here we identified the protease responsible, located the cleavage site, and demonstrated that cleavage likely occurs during endocytic recycling. Moreover, we showed that the infectivity of Vero cell-derived virus for primary airway epithelial cells is increased 5-fold if the virus contains a mutation in the G protein that prevents cleavage. The blocking of cleavage should improve RSV vaccine yield, consequently reducing production costs. Posttranslational cleavage of the fusion glycoprotein of many viruses plays an essential role in activation; however, cleavage of the RSV G protein is a novel example of a detrimental effect of cleavage on virus infectivity.

Cathepsin L targeting in cancer treatment

Proteolytic enzymes may serve as promising targets for novel therapeutic treatment strategies seeking to impede cancer progression and metastasis. One such enzyme is cathepsin L (CTSL), a lysosomal cysteine protease. CTSL upregulation, a common occurrence in a variety of human cancers, has been widely correlated with metastatic aggressiveness and poor patient prognosis. In addition, CTSL has been implicated to contribute to cancer-associated osteolysis, a debilitating morbidity affecting both life expectancy and the quality of life. In this review, we highlight the mechanisms by which CTSL contributes to tumor progression and dissemination and discuss the therapeutic utility of CTSL intervention strategies aimed at impeding metastatic progression and bone resorption.

Functional analysis of C1 family cysteine peptidases in the larval gut of Тenebrio molitor and Tribolium castaneum

BACKGROUND

Larvae of the tenebrionids Tenebrio molitor and Tribolium castaneum have highly compartmentalized guts, with primarily cysteine peptidases in the acidic anterior midgut that contribute to the early stages of protein digestion.

RESULTS

High throughput sequencing was used to quantify and characterize transcripts encoding cysteine peptidases from the C1 papain family in the gut of tenebrionid larvae. For T. castaneum, 25 genes and one questionable pseudogene encoding cysteine peptidases were identified, including 11 cathepsin L or L-like, 11 cathepsin B or B-like, and one each F, K, and O. The majority of transcript expression was from two cathepsin L genes on chromosome 10 (LOC659441 and LOC659502). For cathepsin B, the major expression was from genes on chromosome 3 (LOC663145 and LOC663117). Some transcripts were expressed at lower levels or not at all in the larval gut, including cathepsins F, K, and O. For T. molitor, there were 29 predicted cysteine peptidase genes, including 14 cathepsin L or L-like, 13 cathepsin B or B-like, and one each cathepsin O and F. One cathepsin L and one cathepsin B were also highly expressed, orthologous to those in T. castaneum. Peptidases lacking conservation in active site residues were identified in both insects, and sequence analysis of orthologs indicated that changes in these residues occurred prior to evolutionary divergence. Sequences from both insects have a high degree of variability in the substrate binding regions, consistent with the ability of these enzymes to degrade a variety of cereal seed storage proteins and inhibitors. Predicted cathepsin B peptidases from both insects included some with a shortened occluding loop without active site residues in the middle, apparently lacking exopeptidase activity and unique to tenebrionid insects. Docking of specific substrates with models of T. molitor cysteine peptidases indicated that some insect cathepsins B and L bind substrates with affinities similar to human cathepsin L, while others do not and have presumably different substrate specificity.

CONCLUSIONS

These studies have refined our model of protein digestion in the larval gut of tenebrionid insects, and suggest genes that may be targeted by inhibitors or RNA interference for the control of cereal pests in storage areas.

Macrobrachium rosenbergii cathepsin L: molecular characterization and gene expression in response to viral and bacterial infections

Cathepsin L (MrCathL) was identified from a constructed cDNA library of freshwater prawn Macrobrachium rosenbergii. MrCathL full-length cDNA is 1161 base pairs (bp) with an ORF of 1026bp which encodes a polypeptide of 342 amino acid (aa) long. The eukaryotic cysteine proteases, histidine and asparagine active site residues were identified in the aa sequence of MrCathL at 143-154, 286-296 and 304-323, respectively. The pair wise clustalW analysis of MrCathL showed the highest similarity (97%) with the homologous cathepsin L from Macrobrachium nipponense and the lowest similarity (70%) from human. Phylogenetic analysis revealed two distinct clusters of the invertebrates and vertebrates cathepsin L in the phylogenetic tree. MrCathL and cathepsin L from M. nipponense were clustered together, formed a sister group to cathepsin L of Penaeus monodon, and finally clustered to Lepeophtheirus salmonis. High level of (P<0.05) MrCathL gene expression was noticed in haemocyte and lowest in eyestalk. Furthermore, the MrCathL gene expression in M. rosenbergii was up-regulated in haemocyte by virus [M. rosenbergii nodovirus (MrNV) and white spot syndrome baculovirus (WSBV)] and bacteria (Vibrio harveyi and Aeromonas hydrophila). The recombinant MrCathL exhibited a wide range of activity in various pH between 3 and 10 and highest at pH 7.5. Cysteine proteinase (stefin A, stefin B and antipain) showed significant influence (100%) on recombinant MrCathL enzyme activity. The relative activity and residual activity of recombinant MrCathL against various metal ions or salts and detergent tested at different concentrations. These results indicated that the metal ions, salts and detergent had an influence on the proteinase activity of recombinant MrCathL. Conclusively, the results of this study imply that MrCathL has high pH stability and is fascinating object for further research on the function of cathepsin L in prawn innate immune system.

Procathepsin L secretion, which triggers tumour progression, is regulated by Rab4a in human melanoma cells

The switch of human melanoma cell phenotype from non to highly tumorigenic and metastatic is triggered by the increase of procathepsin L secretion, which modifies the tumour microenvironment. The aim of the present study was to identify components involved in the regulation of procathepsin L secretion in melanoma cells. We focused on Rab family members, i.e. Rab3A, Rab4A, Rab4B, Rab5A, Rab8A, Rab11A, Rab27A and Rab33A, which are involved in distinct regulatory pathways. From analysis of mRNA and protein expression of these Rab components and their knockdown by specific siRNAs (small interfering RNAs) it emerged that Rab4A protein is involved in the regulation of procathepsin L secretion. This result was strengthened as procathepsin L secretion was either inhibited by expression of a Rab4A dominant-negative mutant or increased by overexpression of the wild-type Rab4A. Rab4A regulation: (i) discriminates between procathepsin L secretion and expression of intracellular cathepsin L forms; (ii) did not modify other Rab proteins and GAPDH (glyceraldehyde-3-phosphate dehydrogenase) expression, or IL-8 (interleukin-8) and MMP-2 (matrix metalloproteinase-2) secretion; and (iii) was still efficient during unglycosylated procathepsin L secretion. Thus down- or up-regulation of Rab4A expression or Rab4A function triggered inhibition or increase of procathepsin L secretion respectively. Furthermore, Rab4A regulation, by modifying procathepsin L secretion, switches the tumorigenic phenotype of human melanoma cells in nude mice.

Post-transcriptional regulation of human cathepsin L expression

The expression of cathepsin L, a lysosomal protease, is known to be elevated in cancer and other pathologies. Multiple splice variants of human cathepsin L with variable 5'UTRs exist, which encode for the same protein. Previously we have observed that variant hCATL A (bearing the longest 5'UTR) was translated in vitro with significantly lower efficiency than variant hCATL AIII (bearing the shortest 5'UTR). Contrary to these findings, results of the present study reveal that in cancer cells, hCATL A mRNA exhibits higher translatability in spite of having lower stability than AIII. This is the first report demonstrating a highly contrasting trend in translation efficiencies of hCATL variants in rabbit reticulocytes and live cells. Expression from chimeric mRNAs containing 5'UTRs of A or AIII upstream to luciferase reporter cDNA established the A UTR to be the sole determinant for this effect. Transient transfections of bicistronic plasmids and mRNAs confirmed the presence of a functional Internal Ribosome Entry Site in this UTR. Our data suggest that differential stability and translation initiation modes mediated by the 5'UTRs of human cathepsin L variants are involved in regulating its expression.

Protein C inhibitor regulates both cathepsin L activity and cell-mediated tumor cell migration

BACKGROUND

Protein C inhibitor (PCI) is a plasma serine protease inhibitor (serpin) that regulates several serine proteases in coagulation including thrombin and activated protein C. However, the physiological role of PCI remains under investigation. The cysteine protease, cathepsin L, has a role in many physiological processes including cardiovascular diseases, blood vessel remodeling, and cancer.

METHODS AND RESULTS

We found that PCI inhibits cathepsin L with an inhibition rate (k(2)) of 3.0x10(5)M(-)(1)s(-)(1). Whereas, the PCI P1 mutant (R354A) inhibits cathepsin L at rates similar to wild-type PCI, mutating the P2 residue results in a slight decrease in the rate of inhibition. We then assessed the effect of PCI and cathepsin L on the migration of human breast cancer (MDA-MB-231) cells. Cathepsin L was expressed in both the cell lysates and conditioned media of MDA-MB-231 cells. Wound-induced and transwell migration of MDA-MB-231 cells was inhibited by exogenously administered wtPCI and PCI P1 but not PCI P14 mutant. In addition, migration of MDA-MB-231 cells expressing wtPCI was significantly decreased compared to non-expressing MDA-MB-231 cells or MDA-MB-231 cells expressing the PCI P14 mutant. Downregulation of cathepsin L by either a specific cathepsin L inhibitor or siRNA technology also resulted in a decrease in the migration of MDA-MB-231 cells.

CONCLUSIONS

Overall, our data show that PCI regulates tumor cell migration partly by inhibiting cathepsin L.

GENERAL SIGNIFICANCE

Consequently, inhibiting cathepsin L by serpins like PCI may be a new pathway of regulating hemostasis, cardiovascular and metastatic diseases.

Molecular cloning of cDNA for SPase, a monkey cathepsin L orthologue

SPase is a cysteine protease isolated from an African green monkey kidney cell line, CV-1, and has selective cleavage activity toward transcription factor SP-1 and retinoblastoma susceptibility gene product RB. In this study, a cDNA encoding SPase was cloned from a cDNA library prepared from CV-1 cells. The cDNA clone encodes 333 amino acids and is 96.5% identical to human cathepsin L at the nucleotide and amino acid sequence levels. SPase appears to be translated as a preproenzyme based on the comparison between the deduced amino acid sequence and the N-terminal sequence of the purified enzyme. Northern blot analysis exhibited the considerably higher expression of SPase in CV-1 cells compared with COS-1 cells, showing a good correlation with enzymatic activity in these cell lines. Bacterially expressed SPase protein exhibited proteolytic activity toward SP-1 and RB proteins. These observations suggest that SPase is a monkey cathepsin L orthologue.

Enzymatic production of biosilica glass using enzymes from sponges: basic aspects and application in nanobiotechnology (material sciences and medicine)

Biomineralization, biosilicification in particular (i.e. the formation of biogenic silica, SiO2), has become an exciting source of inspiration for the development of novel bionic approaches following "nature as model". Siliceous sponges are unique among silica forming organisms in their ability to catalyze silica formation using a specific enzyme termed silicatein. In this study, we review the present state of knowledge on silicatein-mediated "biosilica" formation in marine sponges, the involvement of further molecules in silica metabolism and their potential application in nanobiotechnology and medicine.

Phylogenetic relationships and gene expression pattern of three different cathepsin L (Ctsl) isoforms in zebrafish: Ctsla is the putative yolk processing enzyme

Certain cysteine proteases, such as cathepsin L (Ctsl), have been involved in yolk processing mechanisms in oocytes and embryos of lower vertebrates. In zebrafish (Danio rerio), three different ctsl genes, ctsla, ctslb and ctslc, have been found in the genome, but their pattern of expression, as well as information on which the encoded enzymes are potentially involved in yolk absorption during embryogenesis, is unknown. Here, phylogenetic and gene structure analysis revealed that zebrafish ctsla and ctslb genes are similar, showing a highly conserved structure in comparison with human ctsl, while ctslc presents different exon organization together with an earlier evolution. Thus, ctslc appears to be evolved from a common ancestral ctsl-like gene, possibly through an early duplication event, whereas ctsla and ctslb may be originated from a second duplication mechanism. Zebrafish ctsla, ctslb and ctslc also showed different patterns of mRNA expression during embryogenesis and in adult tissues. While Ctsla transcripts were accumulated in embryos throughout development and in the adult ovary, those encoding Ctslb were detected only in embryos around the time of hatching as previously reported, and those for Ctslc appeared only in larvae and in some adult tissues, but not in the ovary. In zebrafish and killifish (Fundulus heteroclitus) embryos, Ctsla mRNA was first detected in blastomers, and later in development it was localized in cells of the yolk syncytial layer, an embryonic structure involved in yolk absorption. These data therefore suggested that Ctsla is most likely the putative protease involved in yolk processing in fish embryos, while Ctslc seems not to be required during early embryogenesis in zebrafish.

Identification of Sites of Mannose 6-Phosphorylation on Lysosomal Proteins

Most newly synthesized soluble lysosomal proteins contain mannose 6-phosphate (Man-6-P), a specific carbohydrate modification that is recognized by Man-6-P receptors (MPRs) that direct targeting to the lysosome. A number of proteomic studies have focused on lysosomal proteins, exploiting the fact that Man-6-P-containing forms can be purified by affinity chromatography on immobilized MPRs. These studies have identified many known lysosomal proteins as well as many proteins not previously classified as lysosomal. The latter are of considerable biological interest with potential implications for lysosomal function and as candidates for lysosomal storage diseases of unknown etiology. However, a significant problem in interpreting the biological relevance of such proteins has been in distinguishing true Man-6-P glycoproteins from simple contaminants and from proteins associated with true Man-6-P glycoproteins (e.g. protease inhibitors and lectins). In this report, we describe a mass spectrometric approach to the verification of Man-6-phosphorylation based upon LC-MS of MPR-purified proteolytic glycopeptides. This provided a useful tool in validating novel MPR-purified proteins as true Man-6-P glycoproteins and also allowed identification of low abundance components not observed in the analysis of the total Man-6-P glycoprotein mixture. In addition, this approach allowed the global mapping of 99 Man-6-phosphorylation sites from 44 known lysosomal proteins purified from mouse and human brain. This information is likely to provide useful insights into protein determinants for this modification and may be of significant value in protein engineering approaches designed to optimize protein delivery to the lysosome in therapeutic applications such as gene and enzyme replacement therapies.

Formation of siliceous spicules in the marine demosponge Suberites domuncula

The siliceous skeleton of demosponges is constructed of spicules. We have studied the formation of spicules in primmorphs from Suberites domuncula. Scanning electron microscopy and transmission electron-microscopical (TEM) analyses have revealed, in the center of the spicules, an axial canal that is 0.3-1.6 microm wide and filled with an axial filament. This filament is composed of the enzyme silicatein, which synthesizes the spicules. TEM analysis has shown that spicule formation starts intracellularly and ends extracellularly in the mesohyl. At the initial stage, the axial canal is composed only of silicatein, whereas membranous structures and fibrils (10-15 nm in width) can later also be identified, suggesting that intracellular components protrude into the axial canal. Antibodies against silicatein have been applied for Western blotting; intracellularly, silicatein is processed to the mature form (24 kDa), whereas the pro-enzyme with the propeptide (33 kDa) is detected extracellularly. Silicatein undergoes phosphorylation at five sites. Immunohistological analysis has shown that silicatein exists in the axial canal (axial filament) and on the surface of the spicules, suggesting that they grow by apposition. Finally, we have demonstrated that the enzymic reaction of silicatein is inhibited by anti-silicatein antibodies. These data provide, for the first time, a comprehensive outline of spicule formation.

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.

Prognostic impact of cysteine proteases cathepsin B and cathepsin L in pancreatic adenocarcinoma

OBJECTIVES

The cysteine proteases cathepsin B (CTSB) and L (CTSL) have been implicated in tumor spread and metastatic formation. In pancreatic adenocarcinoma, the role of these proteases is not very well defined. To find out which cell types produce CTSB and CTSL and to evaluate the prognostic impact of these proteases, 70 specimens from curatively resected patients with pancreatic adenocarcinoma were examined by in situ hybridization and immunohisto-chemistry.

METHODS

Seventy patients with ductal adenocarcinoma of the pancreas were studied after R0 resection with a follow-up of at least 3 years. CTSB and CTSL expression was performed immunohisto-chemically using polyclonal anti-CTSB and CTSL antibodies. To detect cell types involved in producing CTSB and CTSL as well as the intracellular localization of specific mRNA sequences, nonisotopic in situ hybridization was performed. The correlations among CTSB and CTSL expression, clinicopathologic parameters, and clinical outcome were analyzed.

RESULTS

The immunoreactivity was 96% for CTSB and 90% for CTSL. Positive mRNA signals were obtained in the cytoplasm tumor cells, macrophages, and fibroblasts in 77% for CTSB and 81% for CTSL, respectively. Statistical analysis showed a significant correlation between CTSB/CTSL expression and tumor grading (P < 0.05) and between CTSB and lymphatic invasion (P = 0.05). Kaplan-Meier analyses revealed statistical significance for CTSB/CTSL expression with the survival after curative resection (P < 0.05). Both proteases are strong prognostic markers in multivariate analysis (P = 0.0001) beside UICC stage, nodal status, tumor size, and grading (P < 0.05). Furthermore, CTSB expression is an independent prognostic marker for cancer recurrence within 6 months after curative surgery in multivariate analysis (P = 0.0001).

CONCLUSIONS

CTSB and CTSL are strong and independent prognostic markers in resectable pancreatic adenocarcinoma rather than UICC stage, TNM classification, or tumor grading. Furthermore, CTSB is a predictor for early recurrence after curative resection. These data underline the significance of tumor-associated proteolysis for cancer invasion and metastasis and may lead to defining subgroups of patients with early recurrence and poor outcome.

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.

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.

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.

Cloning and characterization of anti-cathepsin L single chain variable fragment whose expression inhibits procathepsin L secretion in human melanoma cells

We previously demonstrated that increase of procathepsin L secretion by human melanoma cells strongly increased their tumourigenicity and switched their phenotype from low to highly metastatic. Thus, we herein analysed whether it was possible to inhibit procathepsin L secretion using anti-cathepsin L ScFv. For this purpose, we produced different forms of fusion cathepsin L in prokaryotic or eukaryotic expression systems. An anti-cathepsin L monoclonal antibody (mAb), named 3D8, was isolated from mice immunized with purified procathepsin L-His. This 3D8 mAb interacted with an epitope localized on the 156-197 amino acid sequence of cathepsin L and recognized recombinant or native forms of cathepsin L synthesized by human melanoma cells. An active anti-cathepsin L ScFv was generated and characterized from 3D8 mAb heavy and light variable chains. Then, human melanoma cells were transiently co-transfected with 3D8 ScFv and cathepsin L cDNAs. Data demonstrated that increase of 3D8 ScFv expression in human melanoma cells totally inhibited procathepsin L secretion and induced accumulation of intracellular procathepsin L. Our results constitute the first demonstration that anti-cathepsin L ScFv could be used in human melanoma cells to inhibit procathepsin L secretion. This ScFv represents a new molecular tool to explore cell therapy of human melanomas.

Mouse testin: complementary DNA cloning, genomic organization, and characterization of its proximal promoter region

Testin is a secretory protein that was initially identified from rat Sertoli cell-enriched cultures and has been suggested to be a sensitive marker to monitor the integrity of Sertoli-germ cell junctions. However, the expression of the testin gene in other species and the molecular mechanisms that govern its transcription are unknown. To address these issues, we cloned and characterized the mouse testin gene. A full-length mouse testin cDNA encoding a polypeptide of 333 amino acid residues was isolated by library screening. Sequence analysis revealed that mouse testin shares 90.1%, 58.9%, 62.2%, and 64.6% identity with rat testin and cathepsin L of mouse, rat, and human, respectively, at the amino acid level. Reverse transcription-polymerase chain reaction and Southern blot analysis demonstrated that mouse testin transcripts were predominantly expressed in the gonads. The mouse testin gene spans over 21 kilobases (kb) and contains eight exons interrupted by seven introns. Primer extension analysis and 5' rapid amplification of cDNA ends identified a major transcription start site located 134 base pairs upstream from the translation initiation codon. Analysis of a 2.3-kb mouse testin 5'-flanking region revealed that it lacked TATA and CAAT boxes, and the region was not GC rich. By the use of deletion analysis, in vitro DNase I footprinting, and site-directed mutagenesis, we identified within the proximal promoter region three closely spaced putative binding sites for GATA, sex-determining factor, and steroidogenic factor 1 that are important for testin gene transcription in mouse Sertoli (MSC-1) cells. These cis-acting elements are also present in the conserved Mullerian-inhibiting substance (MIS) proximal promoters, raising a possibility that the transcriptions of testin and MIS genes are controlled by similar mechanisms.

Cowpea bruchid Callosobruchus maculatus uses a three-component strategy to overcome a plant defensive cysteine protease inhibitor

The soybean cysteine protease inhibitor, soyacystatin N (scN), negatively impacts growth and development of the cowpea bruchid, Callosobruchus maculatus[Koiwa et al. (1998) Plant J 14: 371-379]. However, the developmental delay and feeding inhibition caused by dietary scN occurred only during the early developmental stages (the 1st, 2nd and 3rd instars) of the cowpea bruchid. The 4th instar larvae reared on scN diet (adapted) exhibited rates of feeding and development which were comparable to those feeding on an scN-free diet (unadapted) prior to pupation. Total gut proteolytic capacity at this larval stage significantly increased in the scN-adapted insects. The elevated enzymatic activity was attributed to a differential expression of insect gut cysteine proteases (representing the major digestive enzymes), and of aspartic proteases. scN degradation by the gut extract was observed only in adapted bruchids, and this activity appeared to be a combined effect of scN-induced cysteine and aspartic proteases. Thirty cDNAs encoding cathepsin L-like cysteine proteases were isolated from insect guts, and they were differentially regulated by dietary scN. Our results suggest that the cowpea bruchid adapts to the challenge of scN by qualitative and quantitative remodelling of its digestive protease complement, and by activating scN-degrading protease activity.

Identification and characterization of a novel human cathepsin L splice variant

Human cathepsin L (hCATL) has been implicated in a variety of physiological and pathological processes. It was hitherto known to be encoded by four mRNA species, namely hCATL A, AI, AII and hCATL B, differing in their 5' untranslated regions (UTRs). Of these, hCATL A, AI and AII are produced by the alternative splicing of the same primary transcript. HCATL AI and hCATL AII, lack 27 and 90 bases, respectively, from the 3' end of exon 1 of hCATL A. The present study describes the identification of a new splice variant hCATL AIII, which similarly lacks 145 bases from the 3' end of exon 1 of hCATL A. It is produced by the splicing out of 136-280 bases of the first exon in addition to intron 1 of hCATL A, which together serve as an intron for hCATL AIII. HCATL AIII was observed to be the most abundant splice variant in five different human cell lines. In vitro transcription coupled translation studies revealed that hCATL AIII is translated with 4.4-, 3.9- and 1.6-fold higher efficiency as compared to hCATL A, AI and AII, respectively. These results were further confirmed by measuring the enzymatic activities of the in vitro translated products. Cloning of hCATL AIII UTR upstream to luciferase reporter gene resulted in a 3.75-fold higher expression of the reporter gene as compared to the luciferase construct containing UTR of hCATL A. Thus, we have identified a novel human cathepsin L splice variant, hCATL AIII, which is most abundant in human cell lines and is translated with highest efficiency. Our results demonstrate either the presence of a positive or absence of a negative cis-acting regulatory element(s) in the UTR of hCATL AIII that is sufficient to confer translational advantage to a heterologous mRNA. The predominance of this most efficiently translated splice variant in malignant cells suggests that it plays a key role in the over-expression of human cathepsin L in cancer.

A cathepsin L protease essential for Caenorhabditis elegans embryogenesis is functionally conserved in parasitic nematodes

Proteolytic enzymes are involved in processes important to development and survival of many organisms. Parasite proteases are considered potential targets of parasite control yet, for most, their precise physiological functions are unknown. Validation of potential targets requires analysis of function. We have recently identified a cathepsin L (CPL) cysteine protease, Ce-CPL-1, which is essential for embryonic development of the free-living nematode Caenorhabditis elegans. We now show that CPL genes closely related to Ce-cpl-1 are expressed in the animal parasitic nematodes Haemonchus contortus, Dictyocaulus viviparus, Teladorsagia circumcincta, Ancylostoma caninum and Ascaris suum, as well as in plant parasitic nematodes. The similarities in gene structure and encoded amino acid sequence indicate that the parasite and C. elegans CPLs are homologous enzymes. We demonstrate functional compensation of the loss of C. elegans cpl-1 by transgenic expression of the H. contortus cpl-1 gene, rescuing the embryonic lethality. These genes may therefore be orthologues, sharing the same function in both species. Targeting of this enzyme has potential in inhibiting development and transmission of parasitic nematodes. In addition, the role of CPL is important to our understanding of nematode development.

Characterization of human cathepsin L promoter and identification of binding sites for NF-Y, Sp1 and Sp3 that are essential for its activity

Cathepsin L is a cysteine protease whose overexpression in human melanoma cells increases their tumorigenicity and switches their phenotype from non-metastatic to highly metastatic. Regulation of the transcription of the gene encoding human cathepsin L has not been yet studied and only preliminary data exist on the promoter regulation of the gene encoding rodent cathepsin L. In the present study we identified molecular elements involved in the transcriptional regulation of human cathepsin L in melanoma cells. The sequence of the 5'-flanking region of the gene encoding human cathepsin L was determined up to 3263 bp upstream of the translation start site. The major transcription intiation site was located. Three mRNA splice variants, differing in their 5' untranslated ends, were identified. Regulatory regions crucial for cathepsin L promoter activity were characterized between -1489 and -1646 bp. In this region, two GC boxes (-1590/-1595 and -1545/-1550) and a CCAAT motif (-1571/-1575) were involved in specific DNA-protein interactions. An electrophoretic mobility-shift assay demonstrated that Sp1 and Sp3 transcription factors bound to these GC boxes, and only the transcription factor nuclear factor Y (NF-Y) bound to the CCAAT motif. Mutagenesis studies demonstrated that these binding sites contributed at least 85% of cathepsin L promoter activity. Thus structural and functional analysis demonstrated that binding sites for NF-Y, Sp1 and Sp3 are essential for transcription of the gene encoding human cathepsin L in melanoma cells.

Molecular characterization of putative yolk processing enzymes and their expression during oogenesis and embryogenesis in rainbow trout (Oncorhynchus mykiss)

Vitellogenin is the major yolk protein precursor in fish, but little is known about its processing pathway in the oocyte, nor about mobilization of yolk proteins during embryogenesis. In this study we cloned three putative yolk processing enzymes; specifically, cathepsin B and L, and lipoprotein lipase (LPL), from the rainbow trout ovary and determined their patterns of gene expression, together with cathepsin D, during oogenesis and embryogenesis using reverse transcription-polymerase chain reaction. The approximate sizes of both cathepsin B and cathepsin L transcripts were estimated as 1.7-1.8 kilobases by Northern blot analysis. Cathepsin D mRNA and cathepsin L mRNA were expressed constitutively throughout vitellogenesis and embryogenesis, showing the highest levels of expression at around fertilization. Cathepsin B and LPL were expressed exclusively during oogenesis. Quantitatively, expression of cathepsin D mRNA was higher than cathepsin B, cathepsin L, and LPL mRNA throughout the period studied. The different patterns of expression for these genes during oogenesis and embryogenesis signify specific temporal roles in yolk protein processing.

Cloning and characterization of human cathepsin L promoter

Cathepsin L is a lysosomal cysteine protease, which is over-expressed and secreted by malignant cells. 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. The structural portion of the human cathepsin L (hCATL) gene was cloned to elucidate its genomic organization (Chauhan et al., J. Biol. Chem. 218 (1993) 1039). In the present study, a 1.90 kb DNA fragment, containing 1825 bp of the 5' upstream region of hCATL and 75 bases of the first exon of the hCATL, was amplified by PCR from an adaptor ligated placental genomic library. This fragment has been demonstrated to exhibit promoter activity by luciferase reporter assays. Sequence analysis of this fragment revealed the presence of approximately 29 different putative transcription factor binding sites. Several of them like AP-4, GATA-1, Lmo2, CEBPB, MZF-1, NF-AT, etc. were present more than once in this region. However, a consensus CAAT box but no consensus TATA box was found within the 1.0 kb upstream of exon 1. The transcription initiation site of hCATL, using placental total RNA, was mapped to a single adenine residue 289 bases upstream of the ATG codon.

Comparative molecular modelling identifies a common putative IgE epitope on cysteine protease allergens of diverse sources

BACKGROUND

Previous approaches for studying common allergenic epitopes have mainly focused on sequence comparisons, which unfortunately yield little or no information on the shape of the epitope which is the most important determinant of cross-reactivity.

OBJECTIVES

The aim of this study was to investigate the structural basis for cross-reactivity between a previously identified immunodominant epitope of the house dust mite allergen Der p 1 (Leu147-Gln160) and the corresponding epitopes on other allergens that are either taxonomically closely related (i.e. cysteine proteases of other mite species) or representing evolutionary conserved structures (i.e. plant, human and parasite cysteine proteases).

METHODS

We carried out comparative molecular modelling on a range of cysteine proteases, including those of other mite species (Der f 1 and Eur m 1), human (cathepsins B, K, L, S and O), plants (papain, chymopapain and actinidin) and parasites (cruzain, cathepsin L-like Leishmania protease, Entamoeba ACP1 protease and Schistosoma Q26534, Q11003 and cathepsin L proteases).

RESULTS

Our study shows that all the cysteine proteases investigated here display an epitope corresponding to that previously identified on Der p 1, but with varying shapes and degree of accessibility. It appears that the core of the epitope on these homologous cysteine proteases consists of a centrally located conserved Tyr residue flanked on either sides by accessible amino acids.

CONCLUSION

Therefore, these cysteine proteases seem to use similar accessible structures, which may form the basis for the rational design of generic epitope-directed treatment strategies for controlling allergic diseases.

Mouse cathepsin M, a placenta-specific lysosomal cysteine protease related to cathepsins L and P

The complete nucleotide sequence of a novel cathepsin cDNA derived from mouse placenta was determined and is termed cathepsin M. The predicted protein of 333 amino acid is a member of the family C1A proteases and is related to mouse cathepsins L and P. Mouse cathepsin M is highly expressed in placenta, whereas no detectable levels were found in lung, spleen, heart, brain, kidney, thymus, testicle, liver, or embryo. Phylogenic analyses of the sequences of human and mouse cathepsins show that cathepsin M is most closely related to cathepsins P and L. However, the differences are sufficiently large to indicate that the enzymes will be found in other species. This is in contrast to human cathepsins L and V, which probably resulted from a gene duplication after divergence of mammalian species.

Expression and characterization of a recombinant cysteine proteinase of Leishmania mexicana

A major cysteine proteinase (CPB) of Leishmania mexicana, that is predominantly expressed in the form of the parasite that causes disease in mammals, has been overexpressed in Escherichia coli and purified from inclusion bodies to apparent homogeneity. The CPB enzyme, CPB2.8, was expressed as an inactive pro-form lacking the characteristic C-terminal extension (CPB2.8DeltaCTE). Pro-region processing was initiated during protein refolding and proceeded through several intermediate stages. Maximum enzyme activity accompanied removal of the entire pro-region. This was facilitated by acidification. Purified mature enzyme gave a single band on SDS/PAGE and gelatin SDS/PAGE gels, co-migrated with native enzyme in L. mexicana lysates, and had the same N-terminal sequence as the native enzyme. The procedure yielded >3.5 mg of active enzyme per litre of E. coli culture.

A plant defensive cystatin (soyacystatin) targets cathepsin L-like digestive cysteine proteinases (DvCALs) in the larval midgut of western corn rootworm (Diabrotica virgifera virgifera)

Feeding bioassay results established that the soybean cysteine proteinase inhibitor N (soyacystatin N, scN) substantially inhibits growth and development of western corn rootworm (WCR), by attenuating digestive proteolysis [Zhao, Y. et al. (1996) Plant Physiol. 111, 1299-1306]. Recombinant scN was more inhibitory than the potent and broad specificity cysteine proteinase inhibitor E-64. WCR digestive proteolytic activity was separated by mildly denaturing SDS-PAGE into two fractions and in-gel assays confirmed that the proteinase activities of each were largely scN-sensitive. Since binding affinity to the target proteinase [Koiwa, H. et al. (1998) Plant J. 14, 371-380] governs the effectiveness of scN as a proteinase inhibitor and an insecticide, five peptides (28-33 kDa) were isolated from WCR gut extracts by scN affinity chromatographic separation. Analysis of the N-terminal sequence of these peptides revealed similarity to a cathepsin L-like cysteine proteinase (DvCAL1, Diabrotica virgifera virgifera cathepsin L) encoded by a WCR cDNA. Our results indicate that cathepsin L orthologs are pivotal digestive proteinases of WCR larvae, and are targets of plant defensive cystatins (phytocystatins), like scN.

Molecular cloning and structural and functional characterization of human cathepsin F, a new cysteine proteinase of the papain family with a long propeptide domain

A cDNA encoding a new cysteine proteinase belonging to the papain family and called cathepsin F has been cloned from a human prostate cDNA library. This cDNA encodes a polypeptide of 484 amino acids, with the same domain organization as other cysteine proteinases, including a hydrophobic signal sequence, a prodomain, and a catalytic region. However, this propeptide domain is unusually long and distinguishes cathepsin F from other proteinases of the papain family. Cathepsin F also shows all structural motifs characteristic of these proteinases, including the essential cysteine residue of the active site. Consistent with these structural features, cathepsin F produced in Escherichia coli as a fusion protein with glutathione S-transferase degrades the synthetic peptide benzyloxycarbonyl-Phe-Arg-7-amido-4-methylcoumarin, a substrate commonly used for functional characterization of cysteine proteinases. Furthermore, this proteolytic activity is blocked by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane, an inhibitor of cysteine proteinases. The gene encoding cathepsin F maps to chromosome 11q13, close to that encoding cathepsin W. Cathepsin F is widely expressed in human tissues, suggesting a role in normal protein catabolism. Northern blot analysis also revealed a significant level of expression in some cancer cell lines opening the possibility that this enzyme could be involved in degradative processes occurring during tumor progression.

Structure and functions of proteases which cleave human C3 and are expressed on normal or tumor human cells: some are involved in tumorigenic and metastatic properties of human melanoma cells

Human C3 is a multipotent molecule which participates to different events involved in immune response as complement activation, antigen presentation, cell-cell interactions and cell proliferation. Thus, proteinases which cleave C3 may modify C3-dependent cellular functions. This led us to identify two membrane-associated proteinases which cleave human C3: (a) A p57 serine proteinase expressed on human erythrocyte membranes--This p57 proteinase shared antigenic determinants with ankyrine and may be involved in clearance of immune complexes; (b) A p41 cysteine proteinase, which shares antigenic determinants, amino-acid sequence and specific activity with procathepsin-L--This p41 C3-cleaving cyteine proteinase is also involved in tumorigenic and metastatic properties of human melanoma in nude mice. Indeed, pretreatment of highly tumorigenic and metastatic melanoma cells with anti-p39 Ab totally abolished their tumorigenicity and significantly decreased the number of experimental lung metastases in nude mice. Furthermore, overexpression of procathepsin-L in nonmetastatic melanoma cells increased their tumorigenicity and switched their phenotype to highly metastatic cells in nude mice. Altogether, these data support that expression and secretion of procathepsin-L, which cleaves human C3, might be one of the multiple mechanisms by which tumor cells escape the immune surveillance.

Acidic pH as a physiological regulator of human cathepsin L activity

Human cysteine protease cathepsin L was inactivated at acid pH by a first-order process. The inactivation rate decreased with increasing concentrations of a small synthetic substrate, suggesting that substrates stabilize the active conformation. The substrate-independent inactivation rate constant increased with organic solvent content of the buffer, consistent with internal hydrophobic interactions, disrupted by the organic solvent, also stabilizing the enzyme. Circular dichroism showed that the inactivation is accompanied by large structural changes, a decrease in alpha-helix content being especially pronounced. The high activation energy of the reaction at pH 3.0 (200 kJ.mol-1) supported such a major conformational change occurring. The acid inactivation of cathepsin L was irreversible, consistent with the propeptide being needed for proper folding of the enzyme. Aspartic protease cathepsin D was shown to cleave denatured, but not active cathepsin L, suggesting a potential mechanism for in-vivo regulation and turnover of cathepsin L inside lysosomes.

Cathepsin Z, a novel human cysteine proteinase with a short propeptide domain and a unique chromosomal location

We have identified and characterized a novel human cysteine proteinase of the papain family. A full-length cDNA for this enzyme was cloned from a human brain cDNA library. Nucleotide sequence analysis revealed that the isolated cDNA codes for a polypeptide of 303 amino acids, tentatively called cathepsin Z, that exhibits structural features characteristic of cysteine proteinases. Fluorescent in situ hybridization experiments revealed that the human cathepsin Z gene maps to chromosome 20q13, a location that differs from all cysteine proteinase genes mapped to date. The cDNA encoding cathepsin Z was expressed in Escherichia coli as a fusion protein with glutathione S-transferase, and after purification, the recombinant protein was able to degrade the synthetic peptide benzyloxycarbonyl-Phe-Arg-7-amido-4-methylcoumarin, used as a substrate for cysteine proteinases. Northern blot analysis demonstrated that cathepsin Z is widely expressed in human tissues, suggesting that this enzyme could be involved in the normal intracellular protein degradation taking place in all cell types. Cathepsin Z is also ubiquitously distributed in cancer cell lines and in primary tumors from different sources, suggesting that this enzyme may participate in tumor progression as reported for other cathepsins. Finally, on the basis of a series of distinctive structural features, including diverse peptide insertions and an unusual short propeptide, together with its unique chromosomal location among cysteine proteinases, we propose that cathepsin Z may be the first representative of a novel subfamily of this class of proteolytic enzymes.

Effect of carbohydrate position on lysosomal transport of procathepsin L

To study the role of carbohydrate in lysosomal protein transport, we engineered two novel glycosylation signals (Asn-X-Ser/Thr) into the cDNA of human procathepsin L, a lysosomal acid protease. We constructed six mutant cDNAs encoding glycosylation signals at mutant sites Asn-138, Asn-175, or both sites together, in the presence or absence of the wild-type Asn-204 site. We stably transfected wild-type and mutant cDNAs into NIH3T3 mouse fibroblasts and then used species-specific antibodies to determine the glycosylation status, phosphorylation, localization, and transport kinetics of recombinant human procathepsin L containing one, two, or three glycosylation sites. Both novel glycosylation sites were capable of being glycosylated, although Asn-175 was utilized only 30-50% of the time. Like the wild-type glycosylation at Asn-204, carbohydrates at Asn-138 and Asn-175 were completely sensitive to endoglycosidase H, and they were phosphorylated. Mutant proteins containing two carbohydrates were capable of being delivered to lysosomes, but there was not a consistent relationship between the efficiency of lysosomal delivery and carbohydrate content of the protein. Pulse-chase labeling revealed a unique biosynthetic pattern for proteins carrying the Asn-175 glycosylation sequence. Whereas wild-type procathepsin L and mutants bearing carbohydrate at Asn-138 appeared in lysosomes by about 60 min, proteins with carbohydrate at Asn-175 were processed to a lysosome-like polypeptide within 15 min. Temperature shift, brefeldin A, and NH4Cl experiments suggested that the rapid processing did not occur in the endoplasmic reticulum and that Asn-175 mutants could interact with the mannose 6-phosphate receptor. Taken together, our results are consistent with the interpretation that Asn-175 carbohydrate confers rapid transport to lysosomes. We may have identified a recognition domain in procathepsin L that is important for its interactions with the cellular transport machinery.

Characterisation of a Trypanosoma cruzi acidic 30 kDa cysteine protease

A novel proteolytic activity was identified in epimastigote, amastigote and trypomastigote forms of Trypanosoma cruzi using the fluorogenic substrate N-Succinyl-Leu-Leu-Val-Tyr-7-amido-4-methylcoumarin. Epimastigotes showed enzyme activity to be 2-fold higher than amastigotes and trypomastigotes. The protease that displays this activity was purified from epimastigote forms by a four step chromatographic procedure: Diethylaminoethyl-Sephacel, Phenyl-Sepharose, Phenyl-Superose, and Concanavalin A Sepharose columns. The purified enzyme is a glycoprotein that migrates as a 30 kDa protein in 12.5% SDS-polyacrylamide gel electrophoresis (PAGE), under reducing conditions. Its optimal enzymatic activity on both fluorogenic and protein substrates was found to occur at an acidic pH. The inhibition pattern of the purified 30 kDa protease showed that it belongs to the cysteine-protease class. In addition to the synthetic substrate, the purified protease hydrolysed bovine serum albumin (BSA) and human type I collagen. The N-terminal amino acid sequence of the protease shows similarity to the mammalian cathepsin B protease.

Functional expression of Fasciola hepatica cathepsin L1 in Saccharomyces cerevisiae

A cDNA encoding the complete precursor of a Fasciola hepatica cathepsin L protease was isolated and sequenced. Functionally active enzyme was expressed and secreted by Saccharomyces cerevisiae transformed with a plasmid carrying the complete gene. Experiments with temperature-sensitive yeast mutants showed that the enzyme is trafficked through the yeast secretory pathway. Yeast transformed with a truncated gene, which lacked the pre-peptide-encoding and most of the pro-peptide-encoding sequences, did not express funtionally active enzyme. The yeast-expressed enzyme exhibited physicochemical properties in common with the native enzyme including, pH optimum for activity, stability at 37 degrees C and ability to cleave gelatin and immunoglobulin. Enzyme kinetic data showed that the native and yeast-expressed cathepsin L1 have similar specificities for substrates with hydrophobic residues in the P2 position. This is the first report of the functional expression of a cathepsin L proteinase in S. cerevisiae that did not require the use of yeast secretory signal sequences.

The genes of the lysosomal cysteine proteinases cathepsin B, H, L, and S map to different mouse chromosomes

The mouse genes for the lysosomal cysteine proteinases cathepsin B, H, L, and S were mapped to Chromosomes (Chrs) 14, 9, 13, and 3, respectively. Two of the DNA probes used in this study detected an additional, independently segregating locus. The cathepsin B-specific probe hybridized to a locus on Chr 2, and the cathepsin H probe to a locus on the X Chr. These loci either correspond to pseudogenes or to cathepsin B- and cathepsin H-related genes. The four cysteine proteinases mapped in this study lie within known regions of conserved synteny between mouse and human chromosomes, when compared with the corresponding positions of their human homologs. Assuming that the genes of the cysteine proteinase gene family arose from a common ancestral gene, our results suggest that these four cysteine proteinases had been dispersed over different chromosomes before separation of mouse and human in evolution.

The cysteine proteinase gene cprG in Dictyostelium discoideum has a serine-rich domain that contains GlcNAc-1-P

A lysosomal cysteine proteinase called proteinase-1 is the major proteolytic enzyme in vegetative cells of Dictyostelium discoideum. This phosphoglycosylated protein contains multiple residues of GlcNAc-1-P linked to peptidyl serines. Here we report the cloning, structure, and expression of its cDNA (cprG). Another cDNA (cprF) closely related to cprG was also cloned and characterized. mRNAs of both genes are present during the vegetative phase and decrease in developing cells. However, the level of cprG mRNA is about 100-fold higher than that of cprF. The predicted protein products of both genes contain a unique serine-rich domain that was previously found only in two Dictyostelium proteinases (CP4 and CP5) that also carry a GlcNAc-1-P-Ser modification. The cprG product, renamed CP7, was tagged with the FLAG-epitope (FLAG-CP7) and shown to bind to cystatin, a highly specific inhibitor of cysteine proteinases. The FLAG-CP7 product also contained both N-linked oligosaccharides and GlcNAc-1-P. Deletion of the serine-rich domain from FLAG-CP7 yields a product that still binds to cystatin, but no longer carries GlcNAc-1-P. This finding supports the idea that the GlcNAc-1-P residues are normally added to the serine-rich domain, found only in vegetative Dictyostelium cysteine proteinases.

Biosynthesis, processing, and intracellular transport of GM2 activator protein in human epidermal keratinocytes. The lysosomal targeting of the GM2 activator is independent of a mannose-6-phosphate signal

The processing, intracellular transport, and endocytosis of the GM2 activator protein (GM2AP), an essential cofactor of beta-hexosaminidase A for the degradation of ganglioside GM2, was investigated in human epidermal keratinocytes. The GM2AP precursor is synthesized as an 18-kDa peptide, which is singly glycosylated, resulting in 22-kDa high mannose and 24-27-kDa complex glycoforms. A small portion of the 22-kDa form bears phosphomannosyl residues. About 30% of the GM2AP precursor is secreted during 12 h after synthesis, consisting almost exclusively of complex glycoforms. In a post-Golgi compartment, the intracellular remainder is converted to a 20-kDa mature form within 24 h, bearing a heavily trimmed N-glycan on a 17-kDa backbone. Interestingly, even nonglycosylated GM2AP is delivered to the lysosome, as shown by tunicamycin treatment and subcellular fractionation. Also, its endocytosis is independent of carbohydrate-linked signals and is even more effective for nonglycosylated GM2AP. We conclude that a mannose-6-phosphate-independent pathway for the lysosomal delivery of GM2AP exists in cultured human keratinocytes.

Leishmania major: comparison of the cathepsin L- and B-like cysteine protease genes with those of other trypanosomatids

Cysteine proteases play important roles in the pathogenesis of several parasitic infections and have been proposed as targets for the structure-based strategy of drug design. As a first step toward applying this strategy to design inhibitors as antiparasitic agents for leishmaniasis, we have isolated and sequenced the full-length clones of two cysteine protease genes from Leishmania major. One of the genes is structurally similar to the cathepsin L-like family and the other is similar to the cathepsin B-like family of cysteine proteases. The L. major cathepsin L-like sequence has a proregion that shares high sequence similarity with other cathepsin L sequences but not cathepsin B sequences and has a proline/threonine-rich C-terminal extension. The cathepsin L-like gene occurs in multiple copies, whereas there may be only one copy of the cathepsin B-like gene. Northern blot analyses show that both genes are expressed in the promastigote and amastigote stages, and pulse field gel electrophoresis revealed that the cathepsin L- and B-like genes are each found on two nonhomologous chromosomes. The L. major L-like amino acid sequence is 75% identical to the L. mexicana sequence, 74% identical to the L. pifanoi sequence, 47% identical with the Trypanosoma cruzi sequence, 47% identical with the T. congolense sequence, and 45% identical with the T. brucei sequence. L. major is one of two trypanosomatid species for which a cathepsin B-like gene has been identified and sequenced; its amino acid sequence is 82% identical to the one from L. mexicana. Tree inference based on distance and parsimony methods of kinetoplastid cathepsin L proteins yielded independent support for phylogenetic hypotheses inferred from analyses of ribosomal RNA genes. Because the cathepsin L locus has a high level of phylogenetic signal with respect to trypanosomatid taxa, this locus has great potential utility for investigating the evolutionary history of trypanosomatids and related organisms.

Sequence analysis and distribution of two new human cathepsin L splice variants

Despite elevated cathepsin L mRNA levels in kidney tumors, cathepsin L protein/activity was scarcely detectable in these tumors. As a possible reason, we detected two new splice variants of human cathepsin L mRNAs not identical to those previously reported. Besides the normal 'full-length' mRNA (hCATL-A) there is one form lacking 27 nucleotides (hCATL-A I) and another form lacking 90 nucleotides (hCATL-A II) in exon I. The splice variants do not influence the amino acid sequence of the translational product. hCATL-A and hCATL-A I probably form a secondary structure at the 5' non-coding sequence not present in hCATL-A II.

Characterization of intestinally active proteinases of cyst-nematodes

Cryostat sections of juvenile and adult female stages of the soybean cyst-nematode, Heterodera glycines, were incubated with 4 different naphthylamide-linked peptide substrates to localize and characterize proteinase activity within the animal. Detected activity was restricted to the intestine and 2 distinct classes of proteinase were identified on the basis of substrate specificity and sensitivity to plant proteinase inhibitors. A cathepsin L-like cysteine proteinase activity capable of hydrolysing the synthetic substrates Z-Ala-Arg-Arg-MNA and Z-Phe-Arg-MNA but not Z-Arg-Arg-MNA or L-Arg-NA was inhibited by an engineered variant of a cysteine proteinase inhibitor from rice (Oc-I delta D86). The cleavage of Z-Phe-Arg-MNA was sensitive to inhibition by a combination of Oc-I delta D86 and cowpea trypsin inhibitor (CpTI). Degenerate oligonucleotide primers were used to amplify fragments of cysteine proteinase genes from 2 cyst-nematodes, H. glycines and Globodera pallida. Comparison of the H. glycines fragment with known genes established highest homology to cathepsin L-like genes. In contrast, the amplified G. pallida fragment displayed greatest homology to cathepsin B-like genes from Caenorhabditis elegans.

Identification and characterization of the v-cath gene of the baculovirus, CfMNPV

The v-cath gene of the Autographa californica multi-nucleocapsid nuclear polyhedrosis virus (AcMNPV) encodes a cathepsin L-like proteinase which plays a role in the liquefaction of host tissues during a viral infection [1]. We have identified a homologous gene in the spruce budworm virus, Choristoneura fumiferana MNPV (CfMNPV). The CfMNPV v-cath gene is 74% identical to AcMNPV v-cath at the nucleotide sequence level and 80% identical at the level of predicted amino acid sequence. Transcription analysis of the CfMNPV v-cath gene revealed that it is expressed late in infection and that transcription initiates within the consensus baculovirus late-promoter motif.

The identification of two novel ligands of the FGF receptor by a yeast screening method and their activity in Xenopus development

We have developed a functional screen in yeast to identify ligands for receptor tyrosine kinases. Using this method, we cloned two Xenopus genes that activate the fibroblast growth factor (FGF) receptor. These encode novel secreted proteins, designated FRL1 and FRL2, distantly related to the epidermal growth factor and angiogenin/ribonuclease families, respectively. Both genes activate the FGF receptor in Xenopus oocytes as well as in yeast. Overexpression induces mesoderm and neural-specific genes in Xenopus explants; induction is blocked by a dominant negative inhibitor of the FGF receptor. FRL1 is broadly expressed during gastrulation and neurulation, while FRL2 is expressed principally in the axial mesoderm and brain at later stages. Our results indicate that despite their lack of similarity with FGF, FRL1 and FRL2 are ligands for the FGF receptor that play distinct roles in development.