Tumor promoters and Kirsten sarcoma virus increase synthesis of a secreted glycoprotein by regulating levels of translatable mRNA

Cancer-associated mutations reveal a novel role for EpCAM as an inhibitor of cathepsin-L and tumor cell invasion

Background

EpCAM (Epithelial cell adhesion molecule) is often dysregulated in epithelial cancers. Prior studies implicate EpCAM in the regulation of oncogenic signaling pathways and epithelial-to-mesenchymal transition. It was recently demonstrated that EpCAM contains a thyroglobulin type-1 (TY-1) domain. Multiple proteins with TY-1 domains are known to inhibit cathepsin-L (CTSL), a cysteine protease that promotes tumor cell invasion and metastasis. Analysis of human cancer sequencing studies reveals that somatic EpCAM mutations are present in up to 5.1% of tested tumors.

Methods

The Catalogue of Somatic Mutations in Cancer (COSMIC) database was queried to tabulate the position and amino acid changes of cancer associated EpCAM mutations. To determine how EpCAM mutations affect cancer biology we studied C66Y, a damaging TY-1 domain mutation identified in liver cancer, as well as 13 other cancer-associated EpCAM mutations. In vitro and in vivo models were used to determine the effect of wild type (WT) and mutant EpCAM on CTSL activity and invasion. Immunoprecipitation and localization studies tested EpCAM and CTSL protein binding and determined compartmental expression patterns of EpCAM mutants.

Results

We demonstrate that WT EpCAM, but not C66Y EpCAM, inhibits CTSL activity in vitro, and the TY-1 domain of EpCAM is responsible for this inhibition. WT EpCAM, but not C66Y EpCAM, inhibits tumor cell invasion in vitro and lung metastases in vivo. In an extended panel of human cancer cell lines, EpCAM expression is inversely correlated with CTSL activity. Previous studies have demonstrated that EpCAM germline mutations can prevent EpCAM from being expressed at the cell surface. We demonstrate that C66Y and multiple other EpCAM cancer-associated mutations prevent surface expression of EpCAM. Cancer-associated mutations that prevent EpCAM cell surface expression abrogate the ability of EpCAM to inhibit CTSL activity and tumor cell invasion.

Conclusions

These studies reveal a novel role for EpCAM as a CTSL inhibitor, confirm the functional relevance of multiple cancer-associated EpCAM mutations, and suggest a therapeutic vulnerability in cancers harboring EpCAM mutations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08239-z.

Cathepsin L in tumor angiogenesis and its therapeutic intervention by the small molecule inhibitor KGP94

A significant proportion of breast cancer patients harbor clinically undetectable micrometastases at the time of diagnosis. If left untreated, these micro-metastases may lead to disease relapse and possibly death. Hence, there is significant interest in the development of novel anti-metastatic agents that could also curb the growth of pre-established micrometastases. Like primary tumor, the growth of metastases also is driven by angiogenesis. Although the role of cysteine protease Cathepsin L (CTSL) in metastasis associated tumor cell functions such as migration and invasion is well recognized, its role in tumor angiogenesis remains less explored. The present study examines the contribution of CTSL to breast cancer angiogenesis and evaluates the anti-angiogenic efficacy of CTSL inhibitor KGP94. CTSL semi-quantitative RT-PCR analysis on breast tissue panels revealed significant upregulation of CTSL in breast cancer patients which strongly correlated with increased relapse and metastatic incidence and poor overall survival. Preclinically, CTSL ablation using shRNA or KGP94 treatment led to a significant reduction in MDA-MB-231 tumor cell induced angiogenesis in vivo. In-vitro assessments demonstrated a significant decrease in various angiogenic properties such as endothelial cell sprouting, migration, invasion, tube formation and proliferation in the presence of KGP94. Microarray analyses revealed a significant upregulation of cell cycle related genes by CTSL. Western blot analyses further confirmed upregulation of members of the cyclin family by CTSL. Collectively, these data indicate that CTSL is an important contributor to tumor angiogenesis and that the CTSL inhibition may have therapeutic utility in the treatment of breast cancer patients.

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.

Comparative genomic of the teleost cathepsin B and H and involvement in bacterial induced immunity of miiuy croaker

Cathepsins are a family of lysosomal proteases play different roles at physiological and pathological states and present in almost all animals as well as other organisms. Cathepsins B and H are both cysteine proteases of cathepsins. Cathepsin B and H have been studied playing parts in protein degradation/turnover, antigen presentation/processing and hormone maturation in mammals. However, little is known about the structures and functions of cathepsin B and H in teleosts. In the present study, we identified and characterized the full-length miiuy croaker (Miichthys miiuy) cathepsin B and H genes. The sequence analysis results showed that both cathepsin B and H contain the characteristics of papain family with a signal peptide, propeptide and mature peptide regions. The comparison of the genomic organizations and locations indicated the conserved synteny and mild evolution in the cathepsin B and H genes adjacent regions. In addition, the gene synteny analysis showed that miiuy croaker cathepsin B has a closer relationship to stickleback and fugu than to cave fish and zebrafish, and cathepsin H was most similar with the 2 subtype in tilapia and fugu. By phylogenetic analysis, miiuy croaker cathepsin B and H were all assigned to cysteine proteases, and with a close relationship to Salmo salar cathepsin B and Oplegnathus fasciatus cathepsin H, respectively. Quantitative real-time RT-PCR analysis results confirmed that cathepsin B and H genes expressed ubiquitously in all tested healthy tissues from miiuy croaker. Furthermore, up-regulated expression of the cathepsin B and H transcripts in liver, spleen and kidney after exposure upon Vibrio anguillarum suggested that they may play important roles in innate immune response and antigen processing of miiuy croaker.

Cathepsin L inhibition by the small molecule KGP94 suppresses tumor microenvironment enhanced metastasis associated cell functions of prostate and breast cancer cells

Metastasis remains the major cause of therapeutic failure, poor prognosis and high mortality in breast and prostate cancer patients. Aberrant microenvironments including hypoxia and acidic pH are common features of most solid tumors that have been long associated with enhanced metastasis and poor patient outcomes. Novel approaches to reduce metastatic incidences and improve overall survival of cancer patients clearly are needed. The crucial role of Cathepsin L (CTSL) in the dissemination of tumor cells has led to the development of novel cathepsin L inhibition strategies. The present study evaluated the ability of KGP94, a small molecule inhibitor of CTSL, to impair the metastatic phenotype of prostate (PC-3ML) and breast (MDA-MB-231) cancer cells both under normal and aberrant microenvironmental conditions. To assess the role of CTSL in hypoxia and acidosis triggered metastasis associated cell functions, secreted CTSL levels were determined under conditions pertinent to the tumor microenvironment. Acute exposures to hypoxic or acidic conditions significantly elevated secreted CTSL levels either through an increase in intracellular CTSL levels or through activation of lysosomal exocytosis or both, depending on the tumor type. Increases in CTSL secretion closely paralleled enhanced tumor cell migration and invasion suggesting that CTSL could be an essential factor in tumor microenvironment triggered metastasis. Importantly, KGP94 treatment led to marked attenuation of tumor cell invasion and migration under both normal and aberrant microenvironmental conditions suggesting that it may have significant utility as an anti-metastatic agent.

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.

Reovirus receptors, cell entry, and proapoptotic signaling

Mammalian orthoreoviruses (reoviruses) are members of the Reoviridae. Reoviruses contain 10 double-stranded (ds) RNA gene segments enclosed in two concentric protein shells, called outer capsid and core. These viruses serve as a versatile experimental system for studies of viral replication events at the virus-cell interface, including engagement of cell-surface receptors, internalization and disassembly, and activation of the innate immune response, including NF-κB-dependent cellular signaling pathways. Reoviruses also provide a model system for studies of virus-induced apoptosis and organ-specific disease in vivo.Reoviruses attach to host cells via the filamentous attachment protein, σ1. The σ1 protein of all reovirus serotypes engages junctional adhesion molecule-A (JAM-A), an integral component of intercellular tight junctions. The σ1 protein also binds to cell-surface carbohydrate, with the type of carbohydrate bound varying by serotype. Following attachment to JAM-A and carbohydrate, reovirus internalization is mediated by β1 integrins, most likely via clathrin-dependent endocytosis. In the endocytic compartment, reovirus outer-capsid protein σ3 is removed by acid-dependent cysteine proteases in most cell types. Removal of σ3 results in the exposure of a hydrophobic conformer of the viral membrane-penetration protein, μ1, which pierces the endosomal membrane and delivers transcriptionally active reovirus core particles into the cytoplasm.Reoviruses induce apoptosis in both cultured cells and infected mice. Perturbation of reovirus disassembly using inhibitors of endosomal acidification or protease activity abrogates apoptosis. The μ1-encoding M2 gene is genetically linked to strain-specific differences in apoptosis-inducing capacity, suggesting a function for μ1 in induction of death signaling. Reovirus disassembly leads to activation of transcription factor NF-κB, which modulates apoptotic signaling in numerous types of cells. Inhibition of NF-κB nuclear translocation using either pharmacologic agents or expression of transdominant forms of IκB blocks reovirus-induced apoptosis, suggesting an essential role for NF-κB activation in the death response. Multiple effector pathway s downstream of NF-κB-directed gene expression execute reovirus-induced cell death. This chapter will focus on the mechanisms by which reovirus attachment and disassembly activate NF-κB and stimulate the cellular proapoptotic machinery.

CUX1 transcription factors: from biochemical activities and cell-based assays to mouse models and human diseases

ChIP-chip and expression analyses indicated that CUX1 transcription factors regulate a large number of genes and microRNAs involved in multiple cellular processes. Indeed, in proliferating cells CUX1 was shown to regulate several genes involved in DNA replication, progression into S phase and later, the spindle assembly checkpoint that controls progression through mitosis. siRNA-mediated knockdown established that CUX1 is required for cell motility. Moreover, higher expression of short CUX1 isoforms, as observed in many cancers, was shown to stimulate cell migration and invasion. In parallel, elevated expression particularly in higher grade tumors of breast and pancreatic cancers implicated CUX1 in tumor initiation and progression. Indeed, transgenic mouse models demonstrated a causal role of CUX1 in cancers originating from various cell types. These studies revealed that higher CUX1 expression or activity not only stimulates cell proliferation and motility, but also promotes genetic instability. CUX1 has also been implicated in the etiology of polycystic kidney diseases, both from a transgenic approach and the analysis of CUX1 activity in multiple mouse models of this disease. Studies in neurobiology have uncovered a potential implication of CUX1 in cognitive disorders, neurodegeneration and obesity. CUX1 was shown to be expressed specifically in pyramidal neurons of the neocortex upper layers where it regulates dendrite branching, spine development, and synapse formation. In addition, modulation of CUX1 expression in neurons of the hypothalamus has been associated with changes in leptin receptor trafficking in the vicinity of the primary cilium resulting in altered leptin signaling and ultimately, eating behavior. Overall, studies in various fields have allowed the development of several cell-based assays to monitor CUX1 function and have extended the range of organs in which CUX1 plays an important role in development and tissue homeostasis.

Epigenetic regulation of cathepsin L expression in chronic myeloid leukaemia

The expression and significance of cathepsin L (CTSL) has been extensively studied in solid tumours. However no such information in chronic myeloid leukaemia (CML) was available. We investigated the activity and expression of this protease in peripheral blood mononuclear cells (PBMCs) of 47 adult CML patients. Thirty adults suffering from systemic diseases and 50 healthy volunteers served as controls. The mRNA levels of CTSL, its specific endogenous inhibitor cystatin C and transcriptional up-regulator vascular endothelial growth factor (VEGF) were quantitated by real-time qPCR. CTSL protease activity and its mRNA expression were significantly higher in CML chronic phase (CP) patients compared to CML accelerated phase/blast crisis (AP/BC) patients and controls (P≤ 0.001). VEGF whose expression was most pronounced in CP and declined (P≤ 0.001) in the advanced phases of the malignancy exhibited a strong positive correlation with CTSL expression (r= 0.97; P≤ 0.001). Cystatin C expression was significantly lower (P≤ 0.001) in CML and displayed inverse correlation with CTSL (r=−0.713; P≤ 0.001) activity. CTSL promoter was significantly hypomethylated in CML CP compared to CML AP/BC patients as well as controls. K562, a BC CML cell line displayed CTSL activity, expression and methylation status of CTSL promoter that was comparable to CML AP/BC patients. Treatment of these cells or PBMCs isolated from CML AP/BC patients with 5′-aza-cytidine resulted in a dramatic increase in CSTL activity and/or expression thereby demonstrating the role of promoter methylation in the stage specific expression of CTSL in CML. Differential expression of CTSL in CML at various stages of malignancy may prove useful in identification of the high-risk patients thereby facilitating better management of disease.

Molecular characterization and expression analysis of Cathepsin B and L cysteine proteases from rock bream (Oplegnathus fasciatus)

Cathepsins are lysosomal cysteine proteases of the papain family that play an important role in intracellular protein degradation and turn over within the lysosomal system. In the present study, full-length sequences of cathepsin B (RbCathepsin B) and L (RbCathepsin L) were identified after transcriptome sequencing of rock bream Oplegnathus fasciatus mixed tissue cDNA. Cathepsin B was composed of 330 amino acid residues with 36 kDa predicted molecular mass. RbCathepsin L contained 336 amino acid residues encoding for a 38 kDa predicted molecular mass protein. The sequencing analysis results showed that both cathepsin B and L contain the characteristic papain family cysteine protease signature and active sites for the eukaryotic thiol proteases of cysteine, asparagine and histidine. In addition, RbCathepsin L contained EF hand Ca(2+) binding and cathepsin propeptide inhibitor domains. The rock bream cathepsin B and L showed the highest amino acid identity of 90 and 95% to Lutjanus argentimaculatus cathepsin B and Lates calcarifer cathepsin L, respectively. By phylogenetic analysis, cathepsin B and L exhibited a high degree of evolutionary relationship to respective cathepsin family members of the papain superfamily. Quantitative real-time RT-PCR analysis results confirmed that the expression of cathepsin B and L genes was constitutive in all examined tissues isolated from un-induced rock bream. Moreover, activation of RbCathepsin B and L mRNA was observed in both lipopolysaccharide (LPS) and Edwardsiella tarda challenged liver and blood cells, indicating a role of immune response in rock bream.

Cathepsins B and L in peripheral blood mononuclear cells of pediatric acute myeloid leukemia: potential poor prognostic markers

The diagnostic and prognostic significance of cathepsin B (CTSB) and L (CTSL) is well documented for solid tumors. However, their significance in acute leukemias is lacking. This study was planned to investigate expression and significance of these proteases in peripheral blood mononuclear cells (PBMCs) of patients with pediatric acute myeloid leukemia (AML). CTSL and CTSB activities were assayed in PBMCs of 24 children with AML and ten healthy controls by spectrofluorimetry. The mRNA levels of these proteases and their specific endogenous inhibitor cystatin C and transcriptional upregulator vascular endothelial growth factor (VEGF) were quantitated by real-time PCR. Correlation analysis of CTSL and CTSB activities/expression with their inhibitor/upregulator and event-free survival (EFS) was done using appropriate statistical tools. CTSL and CTSB protease activity and their mRNA expression were significantly higher in AML patients compared to controls (p ≤ 0.001). A strong positive correlation was observed between VEGF expression and CTSL (r = 0.812; p ≤ 0.001). Similarly, VEGF exhibited a strong positive correlation with CTSB (r = 0.501; p = 0.013). Cystatin expression though significantly high (p ≤ 0.001) in AML was negatively correlated with CTSL (r = -0.920; p ≤ 0.001) and CTSB (r = -0.580, p ≤ 0.001) expression. AML patients with higher CTSL and CTSB activity exhibited an inferior EFS (CTSL: p = 0.045; CTSB: p = 0.002) and overall survival (OS; CTSL: p = 0.05; CTSB: p = 0.004) compared to patients with lower levels of these proteases. This is the first report demonstrating increased expression of CTSL and CTSB in AML, mechanism of their increased expression in relation to VEGF, and their association with poor EFS and OS. These results suggest a potential utility of these proteases as prognostic markers for this malignancy.

Transcriptional upregulation of human cathepsin L by VEGF in glioblastoma cells

The role of vascular endothelial growth factor (VEGF) on cathepsin L expression was investigated in human glioblastoma cells (U87MG). Our results demonstrate the transcriptional upregulation of cathepsin L expression by VEGF. Transient transfection of U87MG cells with VEGF expression vector significantly increased cathepsin L activity. These results were further corroborated by a parallel increase in the mRNA levels and promoter activity of cathepsin L by VEGF. By deletion analysis, we identified a 47 base pair VEGF response element (VRE) in human cathepsin L promoter. Site directed mutagenesis studies demonstrated that both SP-1 and AP-4 motifs present in this region contribute to VEGF responsiveness. These results prove for the first time that over-expression of VEGF in human glioblastoma cells induces cathepsin L expression at the transcriptional level. This mechanism could be involved in the enhanced tumorogenic potential of these cells.

Attachment and cell entry of mammalian orthoreovirus

Mammalian orthoreoviruses (reoviruses) serve as a tractable model system for studies of viral pathogenesis. Reoviruses infect virtually all mammals, but cause disease only in the very young. Prototype strains of the three reovirus serotypes differ in pathogenesis following infection of newborn mice. Reoviruses are nonenveloped, icosahedral particles that consist of ten segments of double-stranded RNA encapsidated within two protein shells, the inner core and outer capsid. High-resolution structures of individual components of the reovirus outer capsid and a single viral receptor have been solved and provide insight into the functions of these molecules in viral attachment, entry, and pathogenesis. Attachment of reovirus to target cells is mediated by the reovirus sigma1 protein, a filamentous trimer that projects from the outer capsid. Junctional adhesion molecule-A is a serotype-independent receptor for reovirus, and sialic acid is a coreceptor for serotype 3 strains. After binding to receptors on the cell surface, reovirus is internalized via receptor-mediated endocytosis. Internalization is followed by stepwise disassembly of the viral outer capsid in the endocytic compartment. Uncoating events, which require acidic pH and endocytic proteases, lead to removal of major outer-capsid protein sigma3, resulting in exposure of membrane-penetration mediator micro1 and a conformational change in attachment protein sigma1. After penetration of endosomes by uncoated particles, the transcriptionally active viral core is released into the cytoplasm, where replication proceeds. Despite major advances in defining reovirus attachment and entry mechanisms, many questions remain. Ongoing research is aimed at understanding serotype-dependent differences in reovirus tropism, viral cell-entry pathways, the individual and corporate roles of acidic pH and proteases in viral entry, and micro1 function in membrane penetration.

Characterization and expression of AmphiCL encoding cathepsin l proteinase from amphioxus Branchiostoma belcheri tsingtauense

An amphioxus complementary DNA, AmphiCL, encoding cathepsin L proteinase was isolated from the gut cDNA library of Branchiostoma belcheri tsingtauense. It is 1480 bp long, and its longest open reading frame codes for a precursor protein, which consists of 327 amino acid residues including a signal peptide (preregion), a propeptide, and a mature proteinase. Northern blot showed that AmphiCL was expressed in the gill, testis, hepatic cecum, and hind-gut with a molecular size of about 1480 bp. AmphiCL was also expressed at low level in the muscle, notochord, and ovary as revealed by the more sensitive reverse transcriptase polymerase chain reaction techniques. Semiquantitative RT-PCR also showed that although AmphiCL expression in the gut was significantly downregulated by feeding Arthrospira platensis powder, a protein-rich food, its expression in the same tissue was upregulated by exposure to lipopolysaccharide, an integral component of the outer membrane of gram-negative bacteria. This suggests that although the involvement of AmphiCL in food digestion remains to be confirmed, AmphiCL may play a role in inflammatory reaction in amphioxus.

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.

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.

Cathepsin B Is Inhibited in Mutant Cells Selected during Persistent Reovirus Infection

Persistent reovirus infections of murine L929 (L) fibroblast cells select mutant (LX) cells that do not support proteolytic disassembly of reovirus virions within the endocytic pathway. To better understand the function and regulation of endocytic proteases, we conducted experiments to define the block to reovirus disassembly displayed by LX cells. In contrast to parental L cells, mutant LX cells harbor defects that interfere with the maturation and activity of cathepsin B and cathepsin L but not cathepsin H. The cDNAs encoding cathepsin B and cathepsin L in L cells are identical to those in LX cells, indicating that LX cells manifest an extrinsic block to the function of these enzymes. Mixed lysates of L cells and LX cells lack activity of both cathepsin B and cathepsin L, suggesting the presence of an inhibitor of cathepsin function in LX cells. A cathepsin B-green fluorescent protein (GFP) fusion protein expressed in L cells and purified by immunoprecipitation retains cathepsin B activity, whereas cathepsin B-GFP expressed in LX cells does not. However, activity of cathepsin B-GFP expressed in LX cells can be recovered by incubating the immunoprecipitate with L cell lysate followed by immunoprecipitation, providing further evidence that LX cells express a cathepsin inhibitor. Native-gel electrophoresis and gel filtration chromatography demonstrate that, in both cell lines, the double-chain form of cathepsin B is sequestered in a large molecular weight complex that renders this form of the enzyme inactive. Alteration of this sequestration complex appears to be responsible for inhibition of cathepsin B in LX cells. These findings suggest that cathepsins can be regulated within the endocytic pathway. Moreover, this regulation influences host cell susceptibility to intracellular pathogens.

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.

Cathepsin-L, a key molecule in the pathogenesis of drug-induced and I-cell disease-mediated gingival overgrowth: a study with cathepsin-L-deficient mice

Drug-induced gingival overgrowth, the chronic side effect of calcium antagonists, is frequently seen due to the increase in patients with hypertension, although the etiology of the disease is largely unknown. I-cell disease, which accompanies gingival overgrowth, is characterized by a deficiency in UDP-N-acetyl-glucosamine and is classified as one of the lysosomal storage diseases. Here, we hypothesized that a common mechanism may underlie the etiology of gingival overgrowth seen in patients treated with calcium antagonist and in patients with I-cell disease. A calcium antagonist, nifedipine, specifically suppressed cathepsin-L activity and mRNA expression, but not that of cathepsin-B in cultured gingival fibroblasts. The activity of cathepsin-L was suppressed up to 50% at 24 hours after treatment of the cells with the reagent. The selective suppression of cathepsin-L activity appeared not to be dependent on Ca(2+), since treatment of the cells with thapsigargin suppressed both cathepsin-B and -L activity. Mice deficient in the cathepsin-L gene manifested enlarged gingivae. Histological observation of the gingivae demonstrated typical features of acanthosis, a phenotype very similar to that of experimentally induced gingival overgrowth. Since cathepsin-L deficiency was reported to be associated with thickening of the skin, impaired cathepsin-L activity may play a key role in the establishment of skin and gingival abnormalities seen in I-cell disease. In addition, reduced cathepsin-L activity may play an important role in inducing drug-induced gingival overgrowth.

Chondroitin sulfate proteoglycan is a potent enhancer in the processing of procathepsin L

The acceleration effect of chondroitin-4-sulfate(CS-) proteoglycan on the processing of procathepsin L in vitro was investigated using enzyme purified from the culture medium of MLC cells. Procathepsin L was slightly processed even when it was incubated without CS-proteoglycan for 60 min in 50 mm acetate buffer, pH 5.5, and trace amounts of the 31 kDa mature form and 35-38 kDa intermediates of cathepsin L were formed. On the other hand, in the presence of CS-proteoglycan, procathepsin L was completely converted to the mature form within the same 60 minute time period. Moreover, Z-Phe-Arg-MCA hydrolyzing activity was increased significantly by the incubation with CS-proteoglycan, while no considerable increase in the activity was observed during the incubation without CS-proteoglycan. Since the specific cathepsin L inhibitor, CLIK-195, inhibited the processing of procathepsin L accelerated by CS-proteoglycan, the trace amount of cathepsin L activity may participate in the processing. These results suggest that CS-proteoglycan may play a role in accelerating the processing of procathepsin L as an endogenous enhancer in the extracellular environment in vivo.

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.

An alternate targeting pathway for procathepsin L in mouse fibroblasts

In transformed mouse fibroblasts, a significant proportion of the lysosomal cysteine protease cathepsin L remains in cells as an inactive precursor which associates with membranes by a mannose phosphate-independent interaction. When microsomes prepared from these cells were resolved on sucrose gradients, this procathepsin L was localized in dense vesicles distinct from those enriched for growth hormone, which is secreted constitutively when expressed in fibroblasts. Ultrastructural studies using antibodies directed against the propeptide to avoid detection of the mature enzyme in lysosomes revealed that the proenzyme was concentrated in dense cores within small vesicles and multivesicular endosomes which labeled with antibodies specific for CD63. Consistent with the resemblance of these cores to those of regulated secretory granules, secretion of procathepsin L from fibroblasts was modestly stimulated by phorbol, 12-myristate, 13-acetate. When protein synthesis was blocked with cycloheximide and lysosomal proteolysis inhibited with leupeptin, procathepsin L was found to gradually convert to the active single-chain protease. The data suggest that when synthesis levels are high, a portion of the procathepsin L is packaged in dense cores within multivesicular endosomes localized near the plasma membrane. Gradual activation of this proenzyme achieves targeting of the proenzyme to lysosomes by a mannose phosphate receptor-independent pathway.

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.

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.

Mutant cells selected during persistent reovirus infection do not express mature cathepsin L and do not support reovirus disassembly

Persistent reovirus infections of murine L929 cells select cellular mutations that inhibit viral disassembly within the endocytic pathway. Mutant cells support reovirus growth when infection is initiated with infectious subvirion particles (ISVPs), which are intermediates in reovirus disassembly formed following proteolysis of viral outer-capsid proteins. However, mutant cells do not support growth of virions, indicating that these cells have a defect in virion-to-ISVP processing. To better understand mechanisms by which viruses use the endocytic pathway to enter cells, we defined steps in reovirus replication blocked in mutant cells selected during persistent infection. Subcellular localization of reovirus after adsorption to parental and mutant cells was assessed using confocal microscopy and virions conjugated to a fluorescent probe. Parental and mutant cells did not differ in the capacity to internalize virions or distribute them to perinuclear compartments. Using pH-sensitive probes, the intravesicular pH was determined and found to be equivalent in parental and mutant cells. In both cell types, virions localized to acidified intracellular organelles. The capacity of parental and mutant cells to support proteolysis of reovirus virions was assessed by monitoring the appearance of disassembly intermediates following adsorption of radiolabeled viral particles. Within 2 h after adsorption to parental cells, proteolysis of viral outer-capsid proteins was observed, consistent with formation of ISVPs. However, in mutant cells, no proteolysis of viral proteins was detected up to 8 h postadsorption. Since treatment of cells with E64, an inhibitor of cysteine-containing proteases, blocks reovirus disassembly, we used immunoblot analysis to assess the expression of cathepsin L, a lysosomal cysteine protease. In contrast to parental cells, mutant cells did not express the mature, proteolytically active form of the enzyme. The defect in cathepsin L maturation was not associated with mutations in procathepsin L mRNA, was not complemented by procathepsin L overexpression, and did not affect the maturation of cathepsin B, another lysosomal cysteine protease. These findings indicate that persistent reovirus infections select cellular mutations that affect the maturation of cathepsin L and suggest that alterations in the expression of lysosomal proteases can modulate viral cytopathicity.

A unique cathepsin-like protease isolated from CV-1 cells is involved in rapid degradation of retinoblastoma susceptibility gene product, RB, and transcription factor SP1

The regulation of transcription factors by kinase or phosphatase has been well-described. However, little is known about the inactivation of transcription factors or the nuclear regulators by proteolytic degradation. In this report, we purified a specific protease, SPase, from nuclear extracts of the green monkey kidney cell line, CV-1. Studies of biochemical characteristics and substrate specificity indicated that SPase is a cathepsin B-like cysteinyl protease. However, the two tryptic peptide sequences derived from the purified SPase are either identical or highly homologous to those of human cathepsin L, and furthermore, SPase shares immunoreactivity with both anti-human cathepsin L and anti-mouse cathepsin L antibody. The SPase was shown to be localized in both cytoplasm and nucleus when subcellular compartments of CV-1 cells were fractionated. Transcription factor, SP1, and retinoblastoma susceptible gene product, RB, are substrates of SPase while other nuclear factors such as c-Jun and c-Fos are not. These results implied that SPase plays an integral role in regulating a set of proteins in the nuclei. In vivo treatment of CV-1 cells with cysteinyl protease inhibitor, E-64d, protected RB from degradation. SPase failed to degrade underphosphorylated RB present in TPA induced terminally differentiated HL-60 or U937 cells. Phosphorylation of RB may cause conformational changes, thus facilitating proteolytic digestion. These observations suggest that an alternative pathway inactivates the function of RB in controlling cell growth. Therefore, a possible role of SPase may be to affect the stability of important regulators involved in controlling cellular proliferation and differentiation.

Processing properties of recombinant human procathepsin L

Human procathepsin L is highly expressed in mouse myeloma cells and processed into the mature enzyme under the acidic condition below pH 5.5. Different from the mature enzyme, it is stable at a neutral pH. To examine whether or not procathepsin L is autoprocessed intramolecularly, we constructed a mutant procathepsin L cDNA in which the codon for Cys138 proposed as the active site was mutated to encode Ser by PCR-mutagenesis. The mutant procathepsin L (C138S) was secreted into the culture medium from mouse myeloma cells expressing this mutant cDNA, but not processed into the mature form under the acidic condition. In addition, the mutant C138S was not processed by the incubation at 37 degrees C with wild-type procathepsin L or mature cathepsin L under the acidic condition. These findings showed that Cys138 is the active site of cathepsin L and that the autocatalytic processing occurs intramolecularly.

Nuclear localization of procathepsin L/MEP in ras-transformed mouse fibroblasts

It has been well-documented that secretion of procathepsin L is enhanced in ras-oncogene-transformed cells. In the present study, intracellular localization of cathepsin L was investigated by cell fractionation using Nonidet P-40 followed by immunoblot analysis. The results showed that a significant amount of procathepsin L was detectable in the nuclear fraction of Ha-ras, Ki-ras- and erbB2-transformed NIH3T3 mouse fibroblasts while procathepsin L was detected only in the cytoplasmic fraction of NIH3T3 cells and v-mos-transformed cells. These results suggest that the processing and translocation of cathepsin L are seriously impeded in ras- and erbB2-transformed cells.

Expression and immunohistochemical localization of cathepsin L during the progression of human gliomas

Recent studies suggest that cysteine proteinase cathepsin L is involved in the process of tumor invasion and metastasis. We examined cathepsin L activity in brain tumor tissue samples by an enzymatic assay, and cathepsin L protein content by enzyme-linked immunoadsorbent assays and Western blotting to determine whether increased levels of cathepsin L correlate with the progression of human gliomas. Native and acid-activatable cathepsin L activities were highest in glioblastomas followed by anaplastic astrocytomas and were lowest in low-grade gliomas and normal brain tissues. Significantly higher amounts of an M(r) 29,000 cathepsin L were present in glioblastomas and anaplastic astrocytomas than in normal brain tissues and low-grade glioma tissue extracts. Using specific antibodies to cathepsin L, we also studied its cellular distribution by immunohistochemical procedures. Higher diffuse cathepsin L immunoreactivity was found in glioblastomas than in low-grade gliomas and normal brain tissue samples. Finally, the addition of cathepsin L antibody inhibits the invasion of glioblastoma cell lines through Matrigel invasion assay. These results suggest the expression of cathepsin L is dramatically upregulated in malignant gliomas and correlates with the malignant progression of human gliomas in vivo.

Direct evidence for the elevated synthesis and secretion of procathepsin L in the distal caput epididymis of boar

The proteins which are secreted from the restricted part of the epididymis are suggested to sustain sperm maturation. In porcine species, as the potential abilities of sperm for movement and fertilization greatly increase in the corpus epididymis, the secretions in both the caput and corpus epididymis seem to be very important for the sperm maturation. In this study, we have directed our attention to the 40 kDa protein which is detected in the fluid of the distal caput epididymis of boar. It was purified from the porcine cauda epididymal fluid and its cDNA was cloned from the cDNA library of the distal caput epididymis. According to the deduced amino acid sequence, the 40 kDa protein has been identified as procathepsin L. Northern blot analysis showed that the procathepsin L mRNA was most abundant in the distal caput epididymis among the tissues as examined. Consistent with the distribution of the procathepsin L mRNA in the epididymis, the activity of procathepsin L was absent in the fluid of the proximal and mid caput epididymis and first appeared in the distal caput epididymal fluid, whose contents gradually decreased with the passage through the epididymis. These results first appeared in the first distal caput epididymis expresses very high levels of procathepsin L and unusually secretes it into the luminal fluid instead of targeting it to lysosomes. It has been also found that the mRNA of PDGF, which is known to enhance cathepsin L expression in the culture cells, is very high in the mid caput epididymis, which just precedes the site of procathepsin L secretion. This result indicates that PDGF directly regulates the locally restricted expression and secretion of procathepsin L in the epididymis, which is one of the possible mechanisms involved in the functional differentiation in the epididymis.

Cloning and expression of a rat placental cDNA encoding a novel cathepsin L-related protein

Cathepsin L is a major lysosomal cysteine protease produced by mouse placenta and fibroblasts. This study characterizes a novel cathepsin L-related mRNA expressed in rat placenta. Immunological and nucleotide screening of a rat placenta library identified six positive clones, the largest, pCLRP-9, being 924 base pairs in length. The combined sequences of all the clones contain an open reading frame of 711 nucleotides, a termination codon, a polyadenylation site, and 197 nucleotides of 3' untranslated region, but lack the 5' translation initiation codon. The pCLRP nucleotide sequence showed 60-64% identity to those of mouse, rat, and human cathepsin L. The deduced amino acid sequence of pCLRP codes for 237 amino acids, which align with the carboxy-terminal sequence of cathepsin L and has the active site residues characteristic of the cysteine protease family. Northern blot analysis showed hybridization of pCLRP with a major mRNA transcript of 1.3 kilobases expressed in placenta, but not kidney or liver. In contrast, a cDNA for mouse pro-cathepsin L hybridized with a transcript of 1.7 kilobases expressed in rat kidney, as well as placenta. During late gestation, steady-state levels of rat placental pCLRP mRNA were highest on day 18, whereas those of mouse procathepsin L were greatest on day 20 of gestation. Antiserum to mouse cathepsin L cross-reacted with four proteins of molecular weights 36,000 to 42,000 in rat placental culture medium, of which two were absent in the kidney. These data indicate that rat placenta expresses several species of cathepsin L-type proteins, which may be involved in placental function and nutrient supply.

Constitutive expression of c-fos gene inhibits type 1 collagen synthesis in transfected osteoblasts

To clarify the contribution of c-fos DNA to bone formation, the effect of constitutive expression of the c-fos gene in collagen synthesis was examined by introducing c-fos DNA into osteoblastic MC3T3-E1 cells. The [3H] proline incorporation into the collagenase digestible protein(CDP) and the percent collagen synthesis were significantly decreased in the c-fos transfectants which constitutively express c-fos mRNA as compared with control transfectants. Transcription of type 1(alpha 1) collagen gene was also specifically decreased in the c-fos transfectants. This indicates that constitutive expression of c-fos DNA interferes with bone formation by inhibiting collagen synthesis in osteoblasts.

Mannose 6-phosphate receptors: potential mediators of germ cell-Sertoli cell interactions

These studies have demonstrated that mouse pachytene spermatocytes, round spermatids, and Sertoli cells synthesize mannose 6-phosphate receptors and that the proportions of the CI- and CD-MPRs vary markedly between cell types. Isolated spermatogenic cells synthesize predominantly the CD-MPR and lower levels of the CI-MPR. In contrast, cultured Sertoli cells selectively synthesize the CI-MPR, even though transcripts for the CD-MPR have been detected in these cells. These striking differences in the expression of MPRs suggest that these receptors may serve multiple roles during germ cell differentiation. We have hypothesized that MPRs in the seminiferous epithelium mediate interactions between germ cells and Sertoli cells, and participate in the targeting of hydrolytic enzymes to the acrosome. In support of the first hypothesis, we have shown that functional MPRs are localized on the surface of spermatogenic cells and Sertoli cells where they mediate the endocytosis of M6P-containing ligands. As in other somatic cells, the CI-MPR is likely to be responsible for M6P receptor-mediated endocytosis in the seminiferous epithelium. Recent studies have shown that Sertoli cells in culture synthesize and secrete at least ten M6P-containing glycoproteins. Furthermore, pachytene spermatocytes and round spermatids endocytose these Sertoli M6P-glycoproteins and process them to lower molecular weight forms that persist during 17 h culture periods. The identification of relevant ligands for mannose 6-phosphate receptors in the seminiferous epithelium may help define new regulatory mechanisms in cell differentiation. Current efforts to determine if Sertoli M6P-glycoproteins modulate germ cell function should confirm the significance of surface MPRs and clarify their roles in signal transduction and/or the endocytosis of Sertoli cell products.

The structure of the mouse cathepsin B gene and its putative promoter

The mouse cathepsin B gene and its flanking regions were cloned and characterized. The gene contains 10 exons and 9 introns spanning about 20 kb. Although the exon-intron organization of the mouse cathepsin B gene showed some similarity to the rat cathepsin H and L genes, significant differences were found. In particular, the highly conserved sequence that contains the catalytically active cysteine in these genes is split at different sites by an intron. As with other thiol proteinases, there is no obvious correspondence between the coding exons and structural or functional units within preprocathepsin B. These results suggest that the lysosomal thiol proteinase genes are evolutionarily ancient and that intron shifting has occurred subsequent to their divergence from a common ancestral form. The 5'-flanking region and exon 1 sequences in the mouse cathepsin B gene have a high GC content of approximately 72%. The 5'-flanking region also contains several potential Sp1 binding sites, but lacks TATA and CAAT motifs. These characteristics suggest that cathepsin B is a "housekeeping" gene and its transcription may be controlled by multiple transcription factors, including Sp1.

Regulation of collagen gene expression by transformed human fibroblasts: decreased type I and type III collagen RNA transcription

The regulation of collagen gene expression in normal diploid human fetal fibroblasts (KMS-6 cells), and fibroblasts immortally transformed by treatment of KMS-6 with Co-60 gamma rays (KMST-6 cells) was compared to that of ones tumorigenically transformed by treatment of KMST-6 cells with Harvey murine sarcoma virus (KMST-6-Ras cells). Synthesized collagenous protein decreased to approximately 30% of that of normal fetal fibroblasts in both transformed cell lines, and the relative rate of collagen synthesis to total protein synthesis decreased about sixfold in KMST-6 cells and twelvefold in KMST-6-Ras cells. The m-RNA levels of type I collagen in both of these cell lines decreased to approximately 20% of that of the control fibroblasts, whereas type III collagen m-RNA levels decreased to only 9% of that of the control. The copy number of the collagen gene in both transformed cell lines was unaltered. The transcriptional rates of collagen alpha 1(I) and collagen alpha 1(III) in both cell lines decreased to 20% and 7% respectively of that of control. These data indicate that collagen synthesis was reduced at the transcriptional level in these transformed human fibroblasts.

Comparison of cathepsin L synthesized by normal and transformed cells at the gene, message, protein, and oligosaccharide levels

The major excreted protein of transformed mouse fibroblasts (MEP) has recently been identified as the lysosomal cysteine protease, cathepsin L. The synthesis and intracellular trafficking of this protein in mouse fibroblasts are regulated by growth factors and malignant transformation. To further define the basis for this regulation, a cDNA encoding MEP/cathepsin L was isolated from a mouse liver cDNA library and used to compare cathepsin L of normal and Kirsten sarcoma virus-transformed NIH 3T3 fibroblasts. Although cathepsin L message levels were elevated 20-fold in the transformed fibroblasts, normal and transformed cells displayed similar cathepsin L genomic DNA digest patterns and gene copy numbers, and cathepsin L mRNA sequences appeared identical by RNase protection analysis. These findings indicate that (i) cathepsin L is synthesized from the same gene in normal and transformed cells and (ii) cathepsin L polypeptides made by these cells are translated with the same primary sequence. Cathepsin L polypeptides synthesized by quiescent, growing, and transformed cells displayed similar isoelectric focusing patterns, suggesting similar post-translational modification. Site-directed mutagenesis of the mouse liver cDNA and expression in COS monkey cells was used to examine the glycosylation of mouse cathepsin L. The results indicated that only one of the two potential N-linked glycosylation sites (the one at Asn221) is glycosylated. Analysis by ion exchange chromatography on QAE-Sephadex, and affinity chromatography on mannose 6-phosphate receptor-Affi-Gel 10, indicated that the cathepsin L oligosaccharide was phosphorylated similarly in normal and transformed cells. Although several phosphorylated oligosaccharide species were observed, the major species contained two phosphomonoester moieties and bound efficiently to the receptor. These findings suggest that cathepsin L made by normal and transformed mouse fibroblasts are identical and substantiate the hypothesis that trafficking of cathepsin L in these cells is regulated by growth-induced changes in the lysosomal protein transport system.

Expression of the collagenolytic and Ras-induced cysteine proteinase cathepsin L and proliferation-associated oncogenes in synovial cells of MRL/I mice and patients with rheumatoid arthritis

Based on the observation that rheumatoid joint destruction is related to the presence of transformed-appearing proliferating synovial lining cells attached to cartilage and bone at the site of early destruction, we searched for the expression of proliferation- and transformation-associated oncoproteins in synovial tissues from patients with early destructive rheumatoid arthritis (RA). Immunolocalization of Ras and Myc proteins was found in about 70% of the RA cases and was restricted to the proliferating synovial lining cells. The cysteine proteinase, cathepsin L, which has been shown to be the major ras-induced protein in ras-transformed murine NIH 3T3 cells, was detected in 50% of the RA cases, predominantly in synovial cells attached to cartilage and bone at the site of joint destruction. Moreover, utilizing cytoplastic dot hybridization analysis, we demonstrated the presence of RNA sequences complementary to human cathepsin L in primary cultures of human synovial cells from RA joints and complementary to murine cathepsin L in synovial lining cells derived from MRL/l mice developing spontaneously a RA-like disease. Significant levels of ras oncogene transcripts and products in human RA synovial cells associated with an increased expression of the cathepsin L gene indicate that this collagen-degrading enzyme may contribute to the destruction of cartilage and bone in RA.

Nuclear pp64 is phosphorylated in both serine/threonine and tyrosine through complex pathways regulated by 12-O-tetradecanoylphorbol-13-acetate and platelet-derived growth factor

Platelet-derived growth factor (PDGF) induces the time and dose dependent serine/threonine phosphorylation of pp64, a nuclear protein in normal rat kidney (NRK) cells. pp64 is phosphorylated additionally on tyrosine in SSV-transformed NRK cells. To further characterize the regulation of phosphorylation of pp64, other mitogens and inhibitors were studied. 12-O-tetradecanoylphorbol-13-acetate (TPA) but not epidermal growth factor (EGF) or insulin induced the phosphorylation of nuclear pp64. Addition of the inhibitor H7 to TPA-treated NRK cells resulted in a striking further increase in phosphorylation of pp64 and, to a lesser extent, in NRK cells treated with PDGF and H7. When cells were treated with PDGF and H7, pp64 was recognized by anti-phosphotyrosine antisera. The increased phosphorylation induced by H7 was inhibited when forskolin was included. This loss of phosphorylation in pp64 with forskolin treatment paralleled a loss of immunoreactivity of pp64 to anti-phosphosphotyrosine. Complex and independent pathways thus appear to signal the growth factor dependent nuclear phosphorylation of pp64, involving phosphorylations both on serine/threonine and on tyrosine.

Induction of a mitogen-responsive gene after expression of the Ha-ras oncogene in NIH 3T3 fibroblasts

A cDNA clone, T1, has been isolated whose corresponding mRNA was transiently expressed at highly elevated levels after conditional expression of the Ha-ras(EJ) gene and after mitogenic activation of quiescent NIH 3T3 cells. Glucocorticoid hormone stimulated substantial T1 expression as well but only in proliferating cells. At least two different signaling pathways participate in the regulation of the T1 gene: a protein kinase C-dependent signal is involved in the response of proliferating NIH 3T3 cells to glucocorticoid in the absence but not the presence of p21ras, whereas a protein kinase C-independent mechanism mediates the response to serum factors. Treatment of cells with the protein kinase inhibitor 2-aminopurine blocked induction of expression of the T1 gene. T1 mRNA accumulation is regulated at the transcriptional level.

Modulation of the transport of a lysosomal enzyme by PDGF

The major excreted protein (MEP) of transformed mouse fibroblasts is the lysosomal protease, cathepsin L. MEP is also secreted by untransformed mouse cells in response to growth factors and tumor promoters, and is thought to play a role in cell growth and transformation. To determine the relationship between MEP synthesis and MEP secretion, we have examined these events in PDGF-treated NIH 3T3 cells. PDGF enhanced MEP synthesis and caused the diversion of MEP from the lysosomal delivery pathway to a secretory pathway. These two effects were found to be regulated independently at various times after growth factor addition. Short PDGF treatments (0.5 or 1 h) resulted in quantitative secretion of MEP although synthesis was near the control level. High levels of both synthesis and secretion occurred between 2 and 14 h of PDGF treatment. Between 18 and 30 h, the amount of secreted MEP returned to the low control level even though synthesis remained elevated. The secretion was specific for MEP; other lysosomal enzymes were not found in the media from PDGF-treated cells. PDGF-induced secretion of MEP was inhibited 84% by cycloheximide, suggesting that protein synthesis is required to elicit this effect. PDGF also caused a time-dependent increase in mannose 6-phosphate (Man-6-P) receptor-mediated endocytosis. These data support a model in which PDGF alters the distribution of Man-6-P receptors such that the Golgi concentration of receptors becomes limiting, thereby causing the selective secretion of the low affinity ligand, MEP.

Conditioned medium from ras oncogene-transformed NIH 3T3 cells induces bone resorption in vitro

Tumor-associated hypercalcemia is due, in part, to enhanced osteoclastic bone resorption induced by soluble factors elaborated from malignant cells. ras transformation of NIH 3T3 cells results in a 50-fold induction of cathepsin L mRNA and secretion of the corresponding protein. Since cathepsin L is an acid proteinase we asked whether conditioned medium from these cells would directly increase calcium release from bone in vitro. We tested conditioned medium obtained after 72 h culture of NIH 3T3 ras-transformed cells (DT) or nontransformed NIH 3T3 cells (3T3) and identical medium not exposed to cells (Ctl). Incubation of either live or dead neonatal mouse calvaria for 48 h in DT-conditioned medium increased calcium release compared to bones incubated with 3T3 medium. In both states the increased calcium release with DT medium was blocked by 0.25 mM E-64, a general cysteine proteinase inhibitor, and 1 microM Z-Phe-Ala-CH2F, a specific inhibitor of cathepsin L activity. Thus, conditioned medium from ras-transformed cells enhances calcium release in both live and dead bone. Since cathepsin L is the major protein secreted by these cells and the effect of DT-conditioned medium is blocked by a specific inhibitor of cathepsin L, these studies suggest that this acid proteinase acts directly on bone mineral to enhance net calcium release.

Molecular oncogenetics of metastasis

Metastasis is a complex non-stochastic process that is most likely the result of genetic and epigenetic interactions of a wide variety of genes. The search for a single gene which can encompass such a pleiotropic response as to account for the observed phenotypic characteristics of metastatic tumour populations has been unsuccessful. Particular studies involving gene transfection, subtractive hybridisation and cell fusion are beginning to identify specific genes which contribute to metastasis in some cell types. However, such analyses are complicated by the inherent genetic instability and phenotypic heterogeneity present in tumour populations. A more detailed understanding of the metastatic process may require an abandoning of current generalised approaches to metastasis in favour of concentrating on key components of the metastatic cascade such as adhesion and invasion.

Gene structure and 5'-upstream sequence of rat cathepsin L

The structure of rat cathepsin L gene has been determined. The gene spans 8.5 kilobase pairs comprising 8 exons, and has an intron located near the active site cysteine residue. The gene structure does not correspond well to the functional units of the proteinase. These characteristics are found to be in common with the cysteine proteinase gene family. In the 5'-upstream region, one CAAT-box and four SP-1 binding sites, together with two AP-2 binding sites and CRE, but no typical TATA-box are found. Further, SP-1 and AP-2 binding sites and an octamer motif are also found in the 1st intron, suggesting a complex regulatory mechanism for the expression of the cathepsin L gene.

Induction of a mitogen-responsive gene after expression of the Ha-ras oncogene in NIH 3T3 fibroblasts

A cDNA clone, T1, has been isolated whose corresponding mRNA was transiently expressed at highly elevated levels after conditional expression of the Ha-ras(EJ) gene and after mitogenic activation of quiescent NIH 3T3 cells. Glucocorticoid hormone stimulated substantial T1 expression as well but only in proliferating cells. At least two different signaling pathways participate in the regulation of the T1 gene: a protein kinase C-dependent signal is involved in the response of proliferating NIH 3T3 cells to glucocorticoid in the absence but not the presence of p21ras, whereas a protein kinase C-independent mechanism mediates the response to serum factors. Treatment of cells with the protein kinase inhibitor 2-aminopurine blocked induction of expression of the T1 gene. T1 mRNA accumulation is regulated at the transcriptional level.