Increased expression of cathepsins L and B and decreased activity of their inhibitors in metastatic, ras-transformed NIH 3T3 cells

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 Induces Proangiogenic Changes in Human Omental Microvascular Endothelial Cells via Activation of the ERK1/2 Pathway

BACKGROUND

Metastasis still remains the major cause of therapeutic failure, poor prognosis and high mortality in epithelial ovarian cancer (EOC) patients. Previously, we showed that EOC cells secrete a range of factors with potential pro-angiogenic activity, in disease-relevant human omental microvascular endothelial cells (HOMECs), including the lysosomal protease cathepsin L (CathL). Thus, the aim of this study was to examine potential pro-proliferative and pro-migratory effects of CathL in HOMECs and the activated signalling pathways, and whether these proangiogenic responses are dependent on CathL-catalytic activity.

METHODS

HOMECs proliferation was investigated using WST-1, BrdU and CyQUANT assays. Cell migration was examined using a Cultrex Cell 96 transwell migration assay. Enzyme activity was assayed at various pHs using the CathL-specific fluorogenic substrate FY-CHO. Activation of cell signalling pathways was tested using a commercially available phosphokinase array and intact cellbased ELISAs.

RESULTS

We showed for the first time that CathL has a potent pro-proliferative and pro-migratory effect on HOMECs. For instance, CathL significantly increases HOMEC proliferation (134.8±14.7% vs control 100%) and migration (146.6±17.3% vs control 100%). Our data strongly suggest that these proangiogenic effects of CathL are mediated via a non-proteolytic mechanism. Finally, we show that CathL-induced activation of the ERK1/2 pathway is involved in inducing these cellular effects in HOMECs.

CONCLUSION

These data suggest that CathL acts as an extracellular ligand and plays an important pro-angiogenic, and thus pro-metastatic, role during EOC metastasis to the omentum, by activating the omental microvasculature, and thus can potentially be targeted therapeutically in the future.

The Potential Role of the Proteases Cathepsin D and Cathepsin L in the Progression and Metastasis of Epithelial Ovarian Cancer

Epithelial ovarian cancer (EOC) is the leading cause of death from gynecologic malignancies and has a poor prognosis due to relatively unspecific early symptoms, and thus often advanced stage, metastasized cancer at presentation. Metastasis of EOC occurs primarily through the transcoelomic route whereby exfoliated tumor cells disseminate within the abdominal cavity, particularly to the omentum. Primary and metastatic tumor growth requires a pool of proangiogenic factors in the microenvironment which propagate new vasculature in the growing cancer. Recent evidence suggests that proangiogenic factors other than the widely known, potent angiogenic factor vascular endothelial growth factor may mediate growth and metastasis of ovarian cancer. In this review we examine the role of some of these alternative factors, specifically cathepsin D and cathepsin L.

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.

Downregulation of cathepsin L suppresses cancer invasion and migration by inhibiting transforming growth factor‑β‑mediated epithelial‑mesenchymal transition

Cathepsin L, a lysosomal acid cysteine protease, was found to be overexpressed in several types of human carcinomas. However, its functional roles in tumor progression and the underlying mechanisms remain largely unclear. In the present study, we investigated a novel functional aspect of cathepsin L in regulating transforming growth factor‑β (TGF‑β)‑induced epithelial‑mesenchymal transition (EMT) in A549 and MCF‑7 cells and examined its possible mechanisms. We found that TGF‑β‑induced cell morphologic changes of EMT were associated with the increased protein level of cathepsin L in A549 and MCF‑7 cells, suggesting that cathepsin L may be involved in the regulation of EMT. Furthermore, we showed that silencing of cathepsin L blocked TGF‑β‑induced cell migration, invasion and actin remodeling and inhibited TGF‑β‑mediated EMT. We also demonstrated that the mechanism of how cathepsin L knockdown regulates EMT may be explained by the suppression of EMT‑inducing molecules, such as Snail, which is associated with the phosphatidylinositol 3‑kinase (PI3K)‑AKT and Wnt signaling pathways. Moreover, we proved that cathepsin L knockdown in A549 cells significantly inhibited xenograft tumor growth and EMT in vivo. The results showed a new mechanism to determine cathepsin L involvement in the regulation of cancer invasion and migration. These results showed that cathepsin L knockdown is important in regulating EMT and suggest that cathepsin L may be utilized as a new target for enhancing the efficacy of chemotherapeutics against epithelial cancer.

Activated ras signaling pathways and reovirus oncolysis: an update on the mechanism of preferential reovirus replication in cancer cells

The development of wild-type, unmodified Type 3 Dearing strain reovirus as an anticancer agent has currently expanded to 32 clinical trials (both completed and ongoing) involving reovirus in the treatment of cancer. It has been more than 30 years since the potential of reovirus as an anticancer agent was first identified in studies that demonstrated the preferential replication of reovirus in transformed cell lines but not in normal cells. Later investigations have revealed the involvement of activated Ras signaling pathways (both upstream and downstream) and key steps of the reovirus infectious cycle in promoting preferential replication in cancer cells with reovirus-induced cancer cell death occurring through necrotic, apoptotic, and autophagic pathways. There is increasing evidence that reovirus-induced antitumor immunity involving both innate and adaptive responses also contributes to therapeutic efficacy though this discussion is beyond the scope of this article. Here, we review our current understanding of the mechanism of oncolysis contributing to the broad anticancer activity of reovirus. Further understanding of reovirus oncolysis is critical in enhancing the clinical development and efficacy of reovirus.

RAS transformation requires CUX1-dependent repair of oxidative DNA damage

The base excision repair (BER) that repairs oxidative damage is upregulated as an adaptive response in maintaining tumorigenesis of RAS-transformed cancer cells.

The Cut homeobox 1 (CUX1) gene is a target of loss-of-heterozygosity in many cancers, yet elevated CUX1 expression is frequently observed and is associated with shorter disease-free survival. The dual role of CUX1 in cancer is illustrated by the fact that most cell lines with CUX1 LOH display amplification of the remaining allele, suggesting that decreased CUX1 expression facilitates tumor development while increased CUX1 expression is needed in tumorigenic cells. Indeed, CUX1 was found in a genome-wide RNAi screen to identify synthetic lethal interactions with oncogenic RAS. Here we show that CUX1 functions in base excision repair as an ancillary factor for the 8-oxoG-DNA glycosylase, OGG1. Single cell gel electrophoresis (comet assay) reveals that Cux1^+/− MEFs are haploinsufficient for the repair of oxidative DNA damage, whereas elevated CUX1 levels accelerate DNA repair. In vitro base excision repair assays with purified components demonstrate that CUX1 directly stimulates OGG1's enzymatic activity. Elevated reactive oxygen species (ROS) levels in cells with sustained RAS pathway activation can cause cellular senescence. We show that elevated expression of either CUX1 or OGG1 prevents RAS-induced senescence in primary cells, and that CUX1 knockdown is synthetic lethal with oncogenic RAS in human cancer cells. Elevated CUX1 expression in a transgenic mouse model enables the emergence of mammary tumors with spontaneous activating Kras mutations. We confirmed cooperation between Kras^G12V and CUX1 in a lung tumor model. Cancer cells can overcome the antiproliferative effects of excessive DNA damage by inactivating a DNA damage response pathway such as ATM or p53 signaling. Our findings reveal an alternate mechanism to allow sustained proliferation in RAS-transformed cells through increased DNA base excision repair capability. The heightened dependency of RAS-transformed cells on base excision repair may provide a therapeutic window that could be exploited with drugs that specifically target this pathway.

In the context of tumor development and progression, mutations are believed to accumulate owing to compromised DNA repair. Such mutations promote oncogenic growth. Yet cancer cells also need to sustain a certain level of DNA repair in order to replicate their DNA and successfully proliferate. Here we show that cancer cells that harbor an activated RAS oncogene exhibit heightened DNA repair capability, specifically in the base excision repair (BER) pathway that repairs oxidative DNA damage. RAS oncogenes alone do not transform primary cells but rather cause their senescence—that is, they stop dividing. As such, cellular senescence in this context is proposed to function as a tumor-suppressive mechanism. We show that CUX1, a protein that accelerates oxidative DNA damage repair, prevents cells from senescing and enables proliferation in the presence of a RAS oncogene. Consistent with this, RAS-induced senescence is also prevented by ectopic expression of OGG1, the DNA glycosylase that removes 8-oxoguanine, the most abundant oxidized base. Strikingly, CUX1 expression in transgenic mice enables the emergence of tumors with spontaneous activating Kras mutations. Conversely, knockdown of CUX1 is synthetic lethal for RAS-transformed cells, thereby revealing a potential Achilles' heel of these cancer cells. Overall, the work provides insight into understanding the role of DNA repair in cancer progression, showing that while DNA damage-induced mutations promote tumorigenesis, sustained RAS-dependent tumorigenesis requires suppression of DNA damage. The heightened dependency of RAS-transformed cells on base excision repair may provide a therapeutic window that could be exploited with drugs that specifically target this pathway.

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.

Cathepsin L increased level upon Ras mutants expression: the role of p38 and p44/42 MAPK signaling pathways

The involvement of Ras and three major Ras effectors, Raf, phosphatidylinositol 3-kinase (PI3K) and Ral guanine nucleotide exchange factor in the regulation of lysosomal proteases cathepsin L and B in human fibroblasts was compared. We found that cathepsin L cell content was increased by active Ras overexpression through Raf- and PI3K-mediated signaling pathways, while cathepsin B processing was altered by active Ras overexpression. Cathepsin L increased level following active Ras overexpression correlates with an increase of p38 MAPK activation and content and with an increase of p44/42 MAPK activation, so we investigated the role of these signaling pathways using pharmacological inhibitors. Unexpectedly, the p38 MAPK inhibitor SB203580 produced an increase of cathepsin L content, while the p44/42 MAPK signaling cascade inhibitor U0126 produced a remarkable shift of cathepsin L processing in favor of procathepsin L. In both cases, cathepsin B level and processing were not affected. The analysis of CTSL1 gene transcript demonstrated that cathepsin L protein and transcript correlate both in fibroblasts expressing Ras mutants and in pharmacologically treated cells, thus indicating a transcriptional up-regulation.

Cathepsin L is required for ecotropic murine leukemia virus infection in NIH3T3 cells

Recently it has been reported that a cathepsin B inhibitor, CA-074Me, attenuates ecotropic murine leukemia virus (Eco-MLV) infection in NIH3T3 cells, suggesting that cathepsin B is required for the Eco-MLV infection. However, cathepsin B activity was negative or extremely low in NIH3T3 cells. How did CA-074Me attenuate the Eco-MLV infection? The CA-074Me treatment of NIH3T3 cells inhibited cathepsin L activity, and a cathepsin L specific inhibitor, CLIK148, attenuated the Eco-MLV vector infection. These results indicate that the suppression of cathepsin L activity by CA-074Me induces the inhibition of Eco-MLV infection, suggesting that cathepsin L is required for the Eco-MLV infection in NIH3T3 cells. The CA-074Me treatment inhibited the Eco-MLV infection in human cells expressing the exogenous mouse ecotropic receptor and endogenous cathepsins B and L, but the CLIK148 treatment did not, showing that only the cathepsin L suppression by CLIK148 is not enough to prevent the Eco-MLV infection in cells expressing both of cathepsins B and L, and CA-074Me inhibits the Eco-MLV infection by suppressing both of cathepsins B and L. These results suggest that either cathepsin B or L is sufficient for the Eco-MLV infection.

Reovirus-based therapy for cancer

Reovirus is an oncolytic virus that is not associated with significant disease in humans, but is selectively able to replicate in cancer cells through exploitation of abnormal Ras signaling. Pre-clinical studies have demonstrated that treatment with reovirus is associated with significant anticancer activity across a range of tumor types. Reolysin is a proprietary formulation of the human reovirus developed by Oncolytics Biotech. Clinical evaluation of reovirus therapy has shown that it is well tolerated when administered locally or systemically. Encouraging anticancer efficacy has been observed with single-agent treatment and in combination with chemotherapy and radiotherapy. Phase II studies are currently evaluating reovirus alone and in combination with standard therapy in an array of tumor types. While immune sensitization hinders the anticancer efficacy of reovirus, it is important in preventing systemic toxicity. Immunosuppressive strategies are being developed that reduce immune neutralization of the virus to allow for improved tumor penetration, but retain sufficient antibody levels to protect normal tissues. The lack of toxicity and promising efficacy of reovirus has raised hopes that it will become an established anticancer agent.

Loss of responsiveness to IGF-I in cells with reduced cathepsin L expression levels

The lysosomal cysteine proteinase cathepsin L is involved in proteolytic processing of internalized proteins. In transformed cells, where it is frequently overexpressed, its intracellular localization and functions can be altered. Previously, we reported that treatment of highly metastatic, murine carcinoma H-59 cells with small molecule cysteine proteinase inhibitors altered the responsiveness of the type I insulin-like growth factor (IGF-I) receptor and consequently reduced cell invasion and metastasis. To assess more specifically the role of cathepsin L in IGF-I-induced signaling and tumorigenicity, we generated H-59 subclones with reduced cathepsin L expression levels. These clonal lines showed an altered responsiveness to IGF-I in vitro, as evidenced by (i) loss of IGF-I-induced receptor phosphorylation and Shc recruitment, (ii) reduced IGF-I (but not IGF-II)-induced cellular proliferation and migration, (iii) decreased anchorage-independent growth and (iv) reduced plasma membrane levels of IGF-IR. These changes resulted in increased apoptosis in vivo and an impaired ability of the cells to form liver metastases. The results demonstrate that cathepsin L expression levels regulate cell responsiveness to IGF-I and thereby identify a novel function for cathepsin L in the control of the tumorigenic/metastatic phenotype.

Inhibition of Ulmus davidiana Planch (Ulmaceae) on bone resorption mediated by processing of cathepsin K in cultured mouse osteoclasts

Ulmus davidiana Planch (Ulmaceae) (UD) has long been known to be antiinflammatory in traditional Korean medicine. This experiment investigated the effects of UD on bone resorption using bone cell culture. Different concentrations of crude extract of UD were added to mouse bone cell culture. The mitochondrial activity of the bone cells after exposure of UD was determined by colorimetric 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT). It was demonstrated that UD has potential effects on bone cell culture without cytotoxicity. The most effective concentration of UD in bone cells was 100 microg/mL. Cathepsin K (Cat K) is the major cysteine protease expressed in osteoclasts and is thought to play a key role in matrix degradation during bone resorption. When mouse long bone cells including osteoclasts and osteoblasts were treated with UD, UD prevented the osteoclast-mediated intracellular processing of Cat K, suggesting that UD may disrupt the intracellular transport of pro Cat K. Since secreted proenzymes have the potential to reenter the cell via the mannose-6-phosphate (M6P) receptor, to prevent this possibility, UD was tested in the absence or presence of M6P. Inhibition of Cat K processing by UD was observed in a dose-dependent manner. Furthermore, the addition of M6P resulted in enhanced potency of UD. UD dose-dependently inhibited in vitro bone resorption with a potency similar to that observed for inhibition of Cat K processing.

Increased expression and activity of nuclear cathepsin L in cancer cells suggests a novel mechanism of cell transformation

It is generally accepted that the role of cathepsin L in cancer involves its activities outside the cells once it has been secreted. However, cathepsin L isoforms that are devoid of a signal peptide were recently shown to be present in the nucleus where they proteolytically process the CCAAT-displacement protein/cut homeobox (CDP/Cux) transcription factor. A role for nuclear cathepsin L in cell proliferation could be inferred from the observation that the CDP/Cux processed isoform can accelerate entry into S phase. Here, we report that in many transformed cells the proteolytic processing of CDP/Cux is augmented and correlates with increased cysteine protease expression and activity in the nucleus. Taking advantage of an antibody that recognizes the prodomain of human cathepsin L, we showed that human cells express short cathepsin L species that do not contain a signal peptide, do not transit through the endoplasmic reticulum, are not glycosylated, and localize to the nucleus. We also showed that transformation by the ras oncogene causes rapid increases both in the production of short nuclear cathepsin L isoforms and in the processing of CDP/Cux. Using a cell-based assay, we showed that a cell-permeable inhibitor of cysteine proteases is able to delay the progression into S phase and the proliferation in soft agar of ras-transformed cells, whereas the non-cell-permeable inhibitor had no effect. Taken together, these results suggest that the role of cathepsin L in cancer might not be limited to its extracellular activities but may also involve its processing function in the nucleus.

Proteolytic disassembly is a critical determinant for reovirus oncolysis

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Mammalian ortheoreoviruses are currently being investigated as novel cancer therapeutics, but the cellular mechanisms that regulate susceptibility to reovirus oncolysis remain poorly understood. In this study, we present evidence that virion disassembly is a key determinant of reovirus oncolysis. To penetrate cell membranes and initiate infection, the outermost capsid proteins of reovirus must be proteolyzed to generate a disassembled particle called an infectious subviral particle (ISVP). In fibroblasts, this process is mediated by the endo/lysosomal proteases cathepsins B and L. We have analyzed the early events of infection in reovirus-susceptible and -resistant cells. We find that, in contrast to susceptible glioma cells and Ras-transformed NIH3T3 cells, reovirus-resistant cancer cells and untransformed NIH3T3 cells restrict virion uncoating and subsequent gene expression. Disassembly-restrictive cells support reovirus infection, as in vitro-generated ISVPs establish productive infection, and pretreatment with poly(I:C) does not prevent infection in cancer cells. We find that the level of active cathepsin B and L is increased in tumors and that disassembly-restrictive glioma cells support reovirus oncolysis when grown as a tumor in vivo. Together, these results provide a model in which proteolytic disassembly of reovirus is a critical determinant of susceptibility to reovirus oncolysis.

Cathepsin L increases invasion and migration of B16 melanoma

Background

Most cancers express elevated protease levels which contribute to certain aspects of tumor behavior such as growth, metastatic spread, and angiogenesis. Elevation of the cathepsins of the cysteine protease family correlates with increased invasion of tumor cells. Cysteine proteases such as cathepsins B, H and L type participate in tumor cell invasion as extracellular proteases, yet are enzymes whose exact roles in metastasis are still being elucidated.

Methods

We have examined the role of cathepsin L in highly metastatic B16F10 murine melanoma cells through genetic antisense constructs of cathepsin L. The effects of cathepsin L antisense were examined for melanoma cell proliferation, invasion, migration and adhesion.

Results

Antisense expression of cathepsin L, while decreasing enzyme activity in cell lysates, did not influence cell proliferation. Cathepsin L contributed to melanoma cell invasion and also augmented melanoma cell migration. Further, we demonstrated the adhesion of cathepsin L down-regulated clones was unaltered to fibronectin, laminin, and collagen. Finally, the inhibition of melanoma cell migration via down-regulation of cathepsin L appears to be independent of cystatin C expression.

Conclusion

This study shows that cathepsin L facilitates high metastatic B16 melanoma cell invasion and migration. The mechanism of migration inhibition by decreased cathepsin L is independent of cystatin C levels. Since metastasis depends upon both the invasiveness and migration of tumor cells, cathepsin L may be a therapeutic target of strong clinical interest.

Ras transformation mediates reovirus oncolysis by enhancing virus uncoating, particle infectivity, and apoptosis-dependent release

Reovirus, a potential cancer therapy, replicates more efficiently in Ras-transformed cells than in non-transformed cells. It was presumed that increased translation was the mechanistic basis of reovirus oncolysis. Analyses of each step of the reovirus life cycle now show that cellular processes deregulated by Ras transformation promote not one but three viral replication steps. First, in Ras-transformed cells, proteolytic disassembly (uncoating) of the incoming virions, required for onset of infection, occurs more efficiently. Consequently, threefold more Ras-transformed cells become productively infected with reovirus than non-transformed cells, which accounts for the observed increase of reovirus proteins in Ras-transformed cells. Second, Ras transformation increases the infectious-to-noninfectious virus particle ratio, as virions purified from Ras-transformed cells are fourfold more infectious than those purified from non-transformed cells. Progeny assembled in non- and Ras-transformed cells appear similar by electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, suggesting that Ras transformation introduces a subtle change necessary for virus infectivity. Finally, reovirus release, mediated by caspase-induced apoptosis, is ninefold more efficient in Ras-transformed cells. The combined effects of enhanced virus uncoating, infectivity, and release result in >100-fold differences in virus titers within one round of replication. Our analysis reveals previously unrecognized mechanisms by which Ras transformation mediates selective viral oncolysis.

The oncolytic effect in vivo of reovirus on tumour cells that have survived reovirus cell killing in vitro

The use of oncolytic viruses has received considerable attention in recent years and many viruses have proved to be effective against a variety of cancer models and a few are currently being used in clinical trials. However, the possible emergence and outcome of virus-resistant tumour cells has not been addressed. We previously reported the effective use of reovirus against lymphoid malignancies, including the Burkitt's lymphoma cell line Raji. Here we isolated in vitro persistently infected (PI) Raji cells, and cells ‘cured’ of persistent reovirus infection (‘cured’ cells). Both PI and cured Raji cells resisted reovirus infection and cell killing in vitro. In vivo, the PI cells were non-tumorigenic in SCID mice, but cured cells regained the parental cells' ability to form tumours. Tumour xenografts from the cured cells, however, were highly susceptible to reovirus oncolysis in vivo. This susceptibility was due to the proteolytic environment within tumours that facilitates reovirus infection and cell killing. Our results show that persistent infection by reovirus impedes tumour development and that although PI cells cleared of reovirus are tumorigenic, they are killed upon rechallenge with reovirus. Both the PI and cured states are therefore not likely to be significant barriers to reovirus oncolytic therapy.

cAMP-PKA signaling pathway regulates bone resorption mediated by processing of cathepsin K in cultured mouse osteoclasts

Cathepsin K (Cat K) is the major cysteine protease expressed in osteoclast and is thought to play a key role in matrix degradation during bone resorption. It is shown that the intracellular maturation of Cat K was prevented by the cAMP antagonist, Rp-cAMP, and the protein kinase A (PKA) inhibitors of KT5720 and H89. In contrast, forskolin, an adenylate cyclase agonist, rather induced Cat K processing and maturation in osteoclast. Furthermore, to determine whether Cat K processing and maturation signaling involves protein kinase C (PKC), mouse total bone cells were treated with calphostin C, a specific inhibitor of PKC, however, no effect was observed, indicating that PKC calphostin C did not affect to osteoclast-mediated Cat K processing and maturation in osteoclast. Thus, it is indicated that the cAMP-PKA signaling pathway regulate Cat K maturation in osteoclast. Since secreted proenzymes have the potential to reenter the cell via M6P receptor, to prevent this possibility, we tested cAMP antagonist Rp-cAMP and the PKA inhibitors KT5720 and H89 in the absence or presence of M6P. Inhibition of Cat K processing by Rp-cAMP, KT5720 or H89 was observed in a dose-dependent manner. Furthermore, the addition of M6P resulted in enhanced potency of Rp-cAMP, KT5720 and H89, which dose-dependently inhibited in vitro bone resorption with potency similar to that observed for inhibition of Cat K processing.

Late stage inhibition of hematogenous melanoma metastasis by cystatin C over-expression

Background

Tumor metastasis is a frequent cause of treatment failure for cancer patients. A key feature of metastatic cancer cells is their invasive ability. Cysteine proteases contribute to invasive properties of many cancer cell types. To analyze the contribution of cysteine proteases to metastasis we have over-expressed in B16 melanoma cells the natural cysteine protease inhibitor, cystatin C. We measured in vitro invasion of cystatin over-expression clones with Boyden chamber type assays. Tail-vein injections of cells were used to compare lung tumor colonization. Subcutaneous tumor growth and tumor cell metastasis from primary tumors were also analyzed. Apoptosis of tumor cells was measured in lung tissues following melanoma cell injection.

Results

Results show the in vitro invasion of cystatin C over-expressing cells was dramatically inhibited. Lung tumor colonization was also reduced. Increased tumor cell apoptosis was found to be an important factor and may be related to the reduced tumor burden noted in this system of melanoma metastasis.

Conclusion

Cysteine proteases therefore, may be a target for future anti-metastatic therapies.

Oncogenic Ras and its role in tumor cell invasion and metastasis

The processes by which cancer cells leave the tumor and enter adjacent tissue is known as invasion, whereas metastasis refers to secondary tumor colonization of tissue at a distance from the primary lesion. These two events are the most lethal of cancer phenomena and the signaling mechanisms that govern them are complex. The Ras signaling pathways are well represented in their involvement in tumor initiation, but considerably less is known about their contribution to invasion and metastasis. In this review, we discuss the current evidence for mutant Ras proteins as significant players in these aspects of cancer progression.

Enhanced cathepsin L expression is mediated by different Ras effector pathways in fibroblasts and epithelial cells

Ras expression induces increased expression and altered targeting of lysosomal proteases in multiple cell types, but the specific downstream cytoplasmic signaling pathways mediating these changes have not been identified. In this study, we compared the involvement of 3 major Ras effectors, Raf, phosphatidylinositol 3-kinase (PI3K) and Ral guanine nucleotide exchange factor (RalGEF) in the Ras-mediated alteration of lysosomal protease protein expression and targeting in rat 208F fibroblasts and rat ovarian surface epithelial (ROSE) cells. Effector domain mutants of Ras, constitutively activated variants of Raf, PI3K and RalGEF and pharmacologic inhibitors of MEK and PI3K were utilized to determine the role of these downstream pathways in mediating fibroblast transformation and lysosomal protease regulation in the fibroblasts and epithelial cells. We found that Raf activation of the ERK mitogen-activated protein kinase pathway alone was sufficient to cause morphologic and growth transformation of the fibroblasts and was necessary and sufficient to alter cathepsin L expression and targeting. In contrast, transformation and upregulation of cathepsin L expression in the epithelial cells required the activity of all 3 Ras effectors. Increased protease secretion from the epithelial cells was not observed on ectopic expression of Ras, as it was from the fibroblasts, consistent with the utilization of different signaling pathways in the 2 cell types. In neither cell type did Ras expression increase the expression, processing or secretion of 2 other major lysosomal proteases, cathepsin B and cathepsin D. Thus, Ras utilizes different effectors to mediate transformation and to deregulate cathepsin L expression and secretion in fibroblast and epithelial cells.

Inhibition of Drynariae Rhizoma extracts on bone resorption mediated by processing of cathepsin K in cultured mouse osteoclasts

In the traditional Korean medicine, Drynariae Rhizoma (DR) [Drynaria fortunei (kunze) J. Sm] has been reported as a good enhancer for bone healing. In this experiment, we investigate the effects of DR on bone resorption using the bone cells culture. Different concentrations of crude extract of DR were added to mouse bone cells culture. The mitochondria activity of the bone cells after exposure was determined by colorimetric MTT assay. It was demonstrated that DR has potential effects on the bone cells culture without any cytotoxicity. The most effective concentration of DR on bone cells was 100 micro g/ml. On the other hand, cathepsin K (Cat K) is the major cysteine protease expressed in osteoclasts and is thought to play a key role in matrix degradation during bone resorption. In this study, Mouse long bone cells including osteoclasts and osteoblast were treated with the PI3-kinase inhibitor, wortmannin (WT), and a specific inhibitor of protein kinase C (PKC), calphostin C. Although WT prevented the osteoclast-mediated intracellular processing of Cat K, calphostin C did not. Similarly, treatment of osteoclasts-containing long bone cells with Drynariae Rhizoma (DR) extracts prevented the intracellular maturation of Cat K, suggesting that DR may disrupt the intracellular trafficking of pro Cat K. This is similar to that of WT. Since secreted proenzymes have the potential to reenter the cell via mannose-6-phosphate (M6P) receptor, to prevent this possibility, we tested WT and DR in the absence or presence of M6P. Inhibition of Cat K processing by WT or DR was observed in a dose-dependent manner. Furthermore, the addition of M6P resulted in enhanced potency of WT and DR. DR dose-dependently inhibited in vitro bone resorption with a potency similar to that observed for inhibition of Cat K processing.

Increased cell density decreases cysteine proteinase inhibitor activity and increases invasive ability of two prostate tumor cell lines

The ability of a cancer cell to metastasis to a distant site is partly dependent on the secretion of matrix degrading enzymes. The lysosomal cysteine proteinases, cathepsins B and L, have been shown to be secreted by a number of cancer cells and have been implicated in metastasis. Cathepsins B and L are regulated by a class of inhibitors known as the cystatins; aberrant cystatin activity has also been shown in a number of cancer cells. Two prostate cancer cell lines, PC3 and DU145, and a normal prostate epithelial cell (NPC) culture were used to determine the importance of cathepsins L+B and cysteine proteinase inhibitor (CPI) activity in the ability of each cell line to invade the reconstituted basement membrane, Matrigel. Cathepsin L+B and CPI activities were evident in the cell extract and conditioned media of PC3, DU145 and NPC; however, only the cancer cell lines PC3 and DU145 exhibited invasive ability. Invasive ability was partially inhibited following exposure of PC3 and DU145 cells to the CPI, E-64. Since environmental factors such as cell-cell interactions are responsible for mediating the expression of a number of genes involved in metastasis, the effects of cell density on cathepsin and CPI activities and invasive ability were also determined. CPI activity decreased and invasive ability increased with increasing cell density. We conclude that cathepsin L+B plays a significant role in the invasive ability of the two prostate cancer cell lines, PC3 and DU145. This may be due to decreased regulation by endogenous CPIs whose activity diminishes at high cell densities.

Addition of exogenous protease facilitates reovirus infection in many restrictive cells

Virion uncoating is a critical step in the life cycle of mammalian orthoreoviruses. In cell culture, and probably in extraintestinal tissues in vivo, reovirus virions undergo partial proteolysis within endosomal or/or lysosomal compartments. This process converts the virion into a form referred to as an intermediate subvirion particle (ISVP). In natural enteric reovirus infections, proteolytic uncoating takes place extracellularly within the intestinal lumen. The resultant proteolyzed particles, unlike intact virions, have the capacity to penetrate cell membranes and thereby gain access to cytoplasmic components required for viral gene expression. We hypothesized that the capacity of reovirus outer capsid proteins to be proteolyzed is a determinant of cellular host range. To investigate this hypothesis, we asked if the addition of protease to cell culture medium would expand the range of cultured mammalian cell lines that can be productively infected by reoviruses. We identified many transformed and nontransformed cell lines, as well as primary cells, that restrict viral infection. In several of these restrictive cells, virion uncoating is inefficient or blocked. Addition of proteases to the cell culture medium generates ISVP-like particles and promotes viral growth in nearly all cell lines tested. Interestingly, we found that some cell lines that restrict reovirus uncoating still express mature cathepsin L, a lysosomal protease required for virion disassembly in murine L929 cells. This finding suggests that factors in addition to cathepsin L are required for efficient intracellular proteolysis of reovirus virions. Our results demonstrate that virion uncoating is a critical determinant of reovirus cellular host range and that many cells which otherwise support productive reovirus infection cannot efficiently mediate this essential early step in the virus life cycle.

Mannose-6-phosphate receptors as a molecular indicator of maturation of epididymal sperm

This review discusses some of the changes in sperm during maturation within the context of current concepts of membrane structure and fertilization. Mammalian sperm are surrounded by a limiting plasma membrane that undergoes remodeling during passage through the epididymis. This process confers on the gamete vigorous motility and the ability to fertilize the egg. The repositioning of some surface proteins may follow redistribution of lipids in the plasmalemma, and thus represent a critical step in the maturation of the gametes. Among the various affected proteins of the sperm plasmalemma, mannose-6-phosphate receptors undergo redistribution as the gametes transit through the epididymal duct. The authors summarize their studies of the redistribution of phosphomannosyl receptors during maturation of sperm and discuss possible roles of these glycoproteins in the fertilizing capability of sperm.

Biosynthesis and processing of cathepsin K in cultured human osteoclasts

Cathepsin K (cat K) is the major cysteine protease expressed in osteoclasts and is thought to play a key role in matrix degradation during bone resorption. However, little is known regarding the synthesis, activation, or turnover of the endogenous enzyme in osteoclasts. In this study, we show that mature cat K protein and enzyme activity are localized within osteoclasts. Pulse-chase experiments revealed that, following the synthesis of pro cat K, intracellular conversion to the mature enzyme occurred in a time-dependent manner. Subsequently, the level of mature enzyme decreased. Little or no cat K was observed in the culture media at any timepoint. Pretreatment of osteoclasts with either chloroquine or monensin resulted in complete inhibition of the processing of newly synthesized cat K. In addition, pro cat K demonstrated susceptibility to treatment with N-glycosidase F, suggesting the presence of high-mannose-containing oligosaccharides. Treatment of osteoclasts with the PI3-kinase inhibitor, Wortmannin (WT), not only prevented the intracellular processing of cat K but also resulted in the secretion of proenzyme into the culture media. Taken together, these results suggest that the biosynthesis, processing, and turnover of cat K in human osteoclasts is constitutive and occurs in a manner similar to that of other known cysteine proteases. Furthermore, cat K is not secreted as a proenzyme, but is processed intracellularly, presumably in lysosomal compartments prior to the release of active enzyme into the resorption lacunae.

The Expression of Lysosomal Proteinases and Their Inhibitors in Breast Cancer: Possible Relationship to Prognosis of the Disease

Proteolytic enzymes have been proposed as new biological prognostic indicators to facilitate decisions about treatment of breast cancer patients following surgery. We reported earlier that the activities of cysteine proteinases (CP), cathepsin (Cat) B and cathepsin (Cat) L and the expression of stefin A might be associated with breast tumor progression and prognosis. Here, the protein concentrations of Cats D, B and L and stefin A have been measured in a series of 60 matched pairs of breast tumours and control adjacent tissues, using ELISAs developed in our laboratory. Median tumor concentrations of Cat D (47 pm/mg), Cat B (222 ng/mg) and Cat L (88 ng/mg) were significantly (p<0.0005) increased by 7 fold, 27 fold and 6 fold, respectively. Much greater increases in the activities of Cat B (63 fold) and of Cat L (274 fold) were found, indicating activation of proCat B and proCat L and/or to a decrease in specific endogenous cystatins. However, the 1.6-fold decreased (p<0.0001) levels of inhibition by cystatins could not be entirely responsible for more than 100-fold increased ratio of CP:cystatins activity. Moreover, stefin A was either increased or decreased in tumor samples, resulting in a 1.4-fold median increase in tumors. Comparing the biological parameters with the established histo-pathological prognosticators, we found that the increased protein concentration of Cat B was associated with lymph node involvement (p<0.009) and higher stage (p<0.003), and both Cat B and Cat L activities were more increased in high grade tumours (p<0.05). Survival analysis revealed that stefin A was the most significant prognostic factor for disease-free (p<0.008) and overall survival (p<0.02), followed by increased Cat B activity and protein concentration. Cat L was of borderline significance while Cat D was not significant for prognosis. We conclude that enhanced activation of CP, due partially to an imbalance between cysteine proteinases and inhibitors is linked to the progression of breast cancer. Larger sample size is needed to confirm the prognostic significance of stefin A, Cat B and Cat L.

Rac1-induced endocytosis is associated with intracellular proteolysis during migration through a three-dimensional matrix

Transfection of Rat1 fibroblasts with an activated form of rac1 (V12rac1) stimulated cell migration in vitro compared to transfection of Rat1 fibroblasts with vector only or with dominant negative rac1 (N17rac1). To investigate the involvement of proteases in this migration, we used a novel confocal assay to evaluate the ability of the Rat1 transfectants to degrade a quenched fluorescent protein substrate (DQ-green bovine serum albumin) embedded in a three-dimensional gelatin matrix. Cleavage of the substrate results in fluorescence, thus enabling one to image extracellular and intracellular proteolysis by living cells. The Rat1 transfectants accumulated degraded substrate intracellularly. V12rac1 increased accumulation of the fluorescent product in vesicles that also labeled with the lysosomal marker LysoTracker. Treatment of the V12rac1-transfected cells with membrane-permeable inhibitors of lysosomal cysteine proteases and a membrane-permeable selective inhibitor of the cysteine protease cathepsin B significantly reduced intracellular accumulation of degraded substrate, indicating that degradation occurred intracellularly. V12rac1 stimulated uptake of dextran 70 (a marker of macropinocytosis) and polystyrene beads (markers of phagocytosis) into vesicles that also labeled for cathepsin B. Thus, stimulation of the endocytic pathways of macropinocytosis and phagocytosis by activated Rac1 may be responsible for the increased internalization and subsequent degradation of extracellular proteins.

Insulin-like growth factor-II/cation-independent mannose 6-phosphate receptor mediates paracrine interactions during spermatogonial development

The insulin-like growth factor-II/cation-independent mannose 6-phosphate (IGF-II/M6P) receptor transduces signals after binding IGF-II or M6P-bearing growth factors. We hypothesized that this receptor relays paracrine signals between Sertoli cells and spermatogonia in the basal compartment of the seminiferous epithelium. For these studies spermatogonia were isolated from 8-day-old mice with purity >95% and viability >85% after overnight culture. The IGF-II/M6P receptors were present on the surface of spermatogonia, as detected by indirect immunofluorescence. We determined that both IGF-II and M6P-glycoproteins in Sertoli cell conditioned medium (SCM) modulate gene expression in isolated spermatogonia. The IGF-II produced dose-dependent increases in both rRNA and c-fos mRNA. These effects were mediated specifically by IGF-II/M6P receptors, as shown by studies using IGF-II analogues that are specific agonists for either IGF-I or IGF-II receptors. The SCM treatment also induced dose-dependent increases in rRNA levels, and M6P competition showed that this response required interaction with IGF-II/M6P receptors. The M6P-glycoproteins isolated from SCM by IGF-II/M6P receptor affinity chromatography increased spermatogonial rRNA levels at much lower concentrations than required by SCM treatment, providing further evidence for the paracrine activity of Sertoli M6P-glycoproteins. These results demonstrate that Sertoli cells secrete paracrine factors that modulate spermatogonial gene expression after interacting with cell-surface IGF-II/M6P receptors.

Involvement of cystatin C in oxidative stress-induced apoptosis of cultured rat CNS neurons

Oxidative stress is involved in neuronal degeneration in cerebrovascular injury, neuropathology and aging. When rat CNS neurons were cultured in a high (50%) oxygen atmosphere, the neurons died. This high oxygen-induced cell death showed features of apoptotic cell death, characterized by DNA fragmentation, and was blocked by inhibitor of protein synthesis. We found that cystatin C and HuC mRNA, the products of which are an inhibitor of cysteine proteases and an RNA binding protein, respectively, were up-regulated in neurons cultured in the high oxygen atmosphere. In the present study, we focused on cystatin C. Cystatin C protein levels were also increased in neurons cultured in the high oxygen atmosphere. In situ hybridization with an RNA probe for rat cystatin C and immunocytochemistry with anti-human cystatin C antibody showed that microtubule-associated protein 2 (MAP2)-positive neurons expressed cystatin C mRNA and protein, respectively, in the high oxygen atmosphere. These results indicated that oxidative stress stimulates an increase in cystatin C expression in cultured neurons, and that cystatin C might have important roles in regulation of apoptosis elicited by oxidative stress.

Osteopontin is required for full expression of the transformed phenotype by the ras oncogene

The secreted phosphoprotein osteopontin (OPN) is strongly associated with the process of neoplastic transformation, based both on its pattern of expression in vivo and in vitro and on functional analyses. We have used 3T3 cells derived from wildtype and OPN-deficient mice and transformed by transfection with oncogenic ras to assess the role of OPN in transformation in vitro and in tumorigenesis in vivo. There was no effect of an absence of OPN on the ability of the cells to undergo immortalization or to form morphologically transformed foci following ras transfection. Wildtype and OPN-deficient cell lines were established from such foci, and lines with similar ras mRNA levels selected for further analysis. Ras-transformed cell lines from both wildtype and OPN-deficient mice could form colonies in soft agar indicating that this process can occur in the absence of OPN. However, the ability of the OPN-deficient cell lines to form colonies was reduced as compared to wildtype cell lines. Tumorigenesis in syngeneic and nude mice was assessed for a subset of cell lines that formed colonies efficiently in soft agar. Cell lines unable to make OPN formed tumors in these mice much more slowly than wildtype cells, despite similar growth of the cells on plastic and in soft agar. Taken together, these results indicate that maximal transformation by ras requires OPN expression, and implicate increased OPN expression as an important effector of the transforming activity of the ras oncogene.

Decreased metastatic spread in mice homozygous for a null allele of the cystatin C protease inhibitor gene

AIMS

Increased or altered activities of cysteine proteases have been implicated in serious human disorders such as cancer, rheumatoid arthritis, sepsis, and osteoporosis. To improve the current knowledge of the regulatory role of a major mammalian cysteine protease inhibitor, cystatin C, in such disease processes, a cystatin C deficient mouse was generated and characterized.

METHODS

The mouse cystatin C gene was inactivated by insertion of a bacterial neo gene through homologous recombination in 129/Sv embryonic stem cells. Embryonic stem cell clones were injected into C57BL/6J blastocysts followed by injection of the blastocysts into pseudopregnant female mice. F1 offspring with agouti coat colour after mating of chimaeric males with C57BL/6J females were examined by DNA analysis, and mice carrying the targeted mutation were intercrossed to obtain homozygous cystatin C deficient (CysC-/-) mice. To study the role of cysteine proteases and their inhibitors in metastasis, the spread of B16-F10 melanoma cells in CysC-/- and wild-type mice was compared. Analysis of the formation of remote metastases was carried out by intravenous injection of beta-galactosidase transfected B16-F10 cells and subsequent determination of cancer cell colonies in the lungs.

RESULTS

Cystatin C deficient mice were fertile and showed no gross pathological abnormality up to 6 months of age. Compared with wild-type mice, seven times fewer large metastatic colonies were counted by means of a dissecting microscope in CysC-/- mice two weeks after tail vein injection of B16-F10 cells. At all of eight time points from 15 minutes to two weeks after intravenous injection of tumour cells, the CysC-/- mice had significantly fewer lung metastases. The observed differences were smaller when beta-galactosidase transfected cells were used to allow counting of small colonies. Subcutaneous and intracerebral tumour growth was not different in the CysC-/- mice.

CONCLUSIONS

Cystatin C concentrations in vivo might influence metastasis in some tissues. The decreased metastatic spread of B16-F10 cells in CysC-/- mice is the result of both reduced seeding and reduced growth of tumour cells in their lungs.

Glucose controls cathepsin expression in Ras-transformed fibroblasts

Overexpression and altered trafficking of cathepsins have been associated with the malignant properties of tumors and transformed cells. A characteristic phenotype of transformed cells is also a profound deviation in their metabolism (aerobic glycolysis, glutaminolysis) which enables them to adapt to extreme nutritional conditions. However, whether the altered metabolism may change the expression of proteinases involved in malignancy has not been determined. Herein we present evidences in Kirsten-virus-transformed 3T3 fibroblasts (KBALB) that D-glucose selectively increases active forms of cathepsins L, B, and D, without altering other lysosomal nonproteolytic hydrolases (beta-D-glucosaminidase, acid phosphatase, beta-D-glucuronidase, and beta-D-galactosidase). D-Glucose did not modify mRNA levels for cathepsin B or L and did not affect secretion of pro-cathepsin L. However, D-glucose enhanced strongly the amount of the mature forms of cathepsins B and L, without altering their preferential distribution to light endosomal fractions. Induction by d-glucose of intracellular mature cathepsins B and L required a high growth density of KBALB cells and was reproduced in BALB/3T3 fibroblasts stably transfected with a constitutively activated form of Ras. d-Glucose induction of active cathepsins however was not observed in nontransformed BALB/3T3. D-Mannose, in contrast to nonmetabolized sugars (D-galactose, or L-glucose), caused a similar increase in lysosomal cathepsin activities in dense KBALB cells. The D-glucose analogue, 3-O-methyl-D-glucose, which is transported but not further metabolized, did not reproduce the d-glucose effects. Our findings indicate that, dependent on the nutrient supply and as a consequence of their altered metabolism, transformed cells may modulate the production of active proteinases implicated in malignant progression.

Differential expression of cathepsins B and L compared with matrix metalloproteinases and their respective inhibitors in rheumatoid arthritis and osteoarthritis: a parallel investigation by semiquantitative reverse transcriptase-polymerase chain reaction and immunohistochemistry

OBJECTIVE

To study the expression of the cysteine proteinases cathepsin B and L and their most potent inhibitor cystatin C in the synovial membrane of patients with rheumatoid arthritis (RA) and osteoarthritis (OA) on both the messenger RNA (mRNA) level and the protein level.

METHODS

The expression of both cysteine proteinases and cystatin C was investigated in synovial tissue from 15 RA and 11 OA patients and compared with the expression of matrix metalloproteinase 1 (MMP-1; collagenase), MMP-3 (stromelysin), and tissue inhibitor of metalloproteinases 1 (TIMP-1). Expression of mRNA was analyzed by semiquantitative reverse transcriptase-polymerase chain reaction. Protein expression was evaluated by immunohistochemistry. The results were correlated with the histologic evidence of inflammatory activity.

RESULTS

A significantly more pronounced expression of MMP mRNA was observed in RA synovium compared with OA. In contrast, the mRNA expression of cysteine proteinases, as well as TIMP-1 and cystatin C, did not differ between the patient groups. However, the protein expression of both MMP and cysteine proteinases was significantly more prominent in RA synovial lining compared with OA, whereas cystatin C and TIMP-1 protein were expressed equally.

CONCLUSION

The data indicate a more pronounced expression of MMP mRNA compared with cysteine proteinases in RA. The higher levels of cathepsin B and L proteins in RA synovial lining cells compared with OA are consistent with previous studies that assert a post-transcriptional up-regulation of these enzymes in RA.

SV40 Tag transformation of the normal invasive trophoblast results in a premalignant phenotype. I. Mechanisms responsible for hyperinvasiveness and resistance to anti-invasive action of TGFbeta

Invasion of the uterus by first trimester human placental extravillous trophoblast (EVT) cells depends on mechanisms shared by malignant cells. However, unlike tumor invasion, trophoblast invasion of the uterus is stringently controlled in situ by local molecules such as transforming growth factor (TGF)beta. Since EVT cells possess active invasion-associated genes but are nontumorigenic, our objective was to induce premalignant and then malignant phenotype into a normal EVT cell line in order to identify the molecular basis of tumor progression. Simian virus 40 large T antigen (SV40 Tag) was introduced into a normal human first trimester invasive EVT cell line, HTR8, established in our laboratory. Since the HTR8 line has a limited in vitro lifespan of 12-15 passages, SV40 Tag-transformed cells were selected on the basis of extended lifespan. A long-lived line, RSVT-2, was produced and an immortalized subclone, RSVT2/C, was further derived under a forced crisis regimen. We examined transformation-induced alterations in proliferative and invasive abilities, responses to the invasion and proliferation-regulating growth factor TGFbeta and changes in gene expression for invasion-associated enzymes or enzyme inhibitors. RSVT-2 and RSVT2/C cell lines were hyperproliferative and hyperinvasive when compared with the parental HTR8 cell line. They were also variably resistant to the anti-proliferative and anti-invasive signals from TGFbeta. Since both cell lines remained non-tumorigenic in nude mice, these properties indicate that they attained a premalignant phenotype. Both cell lines showed reduced expression of tissue inhibitor of metalloproteases (TIMP)-1, while TIMP-2 and plasminogen activator inhibitor (PAI)-I expression was was also reduced in RSVT2/C cells, thus contributing to their hyperinvasiveness. Their resistance to the anti-invasive action of TGFbeta was explained by the failure of TGFbeta to upregulate TIMPs and PAI-I, in contrast to the TGFbeta-induced upregulation noted in parental HTR8 cells.

Expression of genes that contribute to proliferative and metastatic ability in breast cancer resected during various menstrual phases

BACKGROUND

Retrospective studies show significant improvements in survival among women who had breast cancer resected during the luteal phase of their menstrual cycle compared with the follicular phase. We hypothesised that tumour tissue would show cyclical changes in expression of genes whose products might contribute to metastatic potential.

METHODS

We studied 32 premenopausal women with operable breast cancer. We assayed hormones to define more accurately the menstrual phase during which surgery was done. We used northern blot analysis of RNA from fresh-frozen tumour specimens to study the patterns of expression of genes for proteolytic enzymes (cysteine proteinase cathepsin L and aspartyl proteinase cathepsin D; matrix metalloproteinases MMP-9 and MMP-2), tissue inhibitors of metalloproteinases TIMP-1 and TIMP-2, and TP53.

RESULTS

There was a significantly higher level of expression of RNA for cathepsin L, MMP-9, and TP53 (p=0.005, 0.03, 0.03, respectively) in tumours that were resected during the follicular and periovulatory phases of the menstrual cycle than at other times in the cycle. A similar but non-significant trend was seen for MMP-2 and cathepsin D. A non-significant trend in the opposite direction was seen for TIMP-1 and TIMP-2.

INTERPRETATION

We found that tumour expression of genes that may contribute to proliferative capacity and metastatic potential can change in breast cancer during the course of the menstrual cycle. The finding could provide a molecular explanation for the reports of improved survival in some breast-cancer patients whose tumours were removed during the luteal phase of the menstrual cycle. Larger studies are required to extend our study, assess mechanisms of gene regulation, and verify any relevant influence in long-term survival.

Proteases and protease inhibitors in tumor progression

Our understanding of the role of matrix degrading proteases in cancer has dramatically expanded over the last two decades. From correlative observations linking proteases to cancer progression, we have accumulated evidence supporting a causal role for proteases in various steps of tumor progression and have become increasingly aware of the complex interactions that exist among proteases. Specific natural inhibitors of these proteases have also been identified and their role as potent cytostatic agents in cancer has been suggested. In this article some of the concepts on the role of proteases in cancer are discussed and examples of cooperation between matrix metalloproteinases and the plasmin/plasminogen activators system are presented. The role of protease inhibitors such as tissue inhibitor of metalloproteinases-2 (TIMP-2) and plasminogen activator inhibitor-2 (PAI-2) as inhibitors of tumor growth, invasion and metastasis is discussed.

ras mutation and expression of the ras-regulated genes osteopontin and cathepsin L in human esophageal cancer

As part of our ongoing studies to characterize molecular alterations in a well-defined series of surgically resected esophageal cancers, we examined the expression of 2 ras-regulated genes, whose products (osteopontin and cathepsin L) previously were shown to be associated with tumor invasion and metastasis. RNA was extracted from primary esophageal tumors (adenocarcinomas, 19; squamous-cell carcinomas, 6) and matched histologically normal esophageal mucosa from the distant resection margin. Northern analysis was used to quantitate RNA, relative to an 18S rRNA control, and immunohistochemistry to assess the tissue distribution of osteopontin. In addition, H-, K- and N-ras mutations were studied in the same tissues using PCR and hybridization with allele (mutant)-specific oligonucleotide probes. We demonstrated a K-ras mutation (codon 12, GTT) in one esophageal adenocarcinoma. The ras-regulated gene osteopontin was over-expressed in 100% of squamous-cell carcinomas and in 58% of adenocarcinomas relative to matched normal esophageal mucosa. Patterns of immunoreactivity for osteopontin protein also varied between squamous-cell carcinomas (tumor cell staining) and adenocarcinomas (predominantly tumor-infiltrating macrophages). Expression of cathepsin L also varied with esophageal tumor histology, with over-expression in 58% of primary esophageal adenocarcinomas and 33% of squamous-cell cancers.

The expression and function of cystatin C and cathepsin B and cathepsin L during mouse embryo implantation and placentation

The implantation of the mouse embryo requires the controlled invasion of the uterine stroma by the embryonic trophoblast. This event is dependent, in part, on the secretion of matrix metalloproteinases and serine proteinases for the extracellular degradation of the uterine matrix. Proteinase activity is controlled by stromal decidualization and specific proteinase inhibitors. This work adds to our understanding of implantation and placentation by reporting the expression and function of another class of proteinases/inhibitors closely related to invasive cell behavior. We focused on the cysteine proteinases, cathepsins B and L, and their inhibitor cystatin C. Northern blots showed that trophoblast expressed cathepsin B throughout the invasive period (days 5.5-10.5). Both cathepsin B message and cathepsin L protein were localized to the mature, invasive trophoblast giant cells. Substrate gel electrophoresis showed an increase in giant cell cathepsin activity with enzyme profiles changing at the end of the invasive period. Northern and western blotting showed that cystatin C, the main inhibitor of cathepsins, was a major product of the decidualizing stroma. Message levels first increased in peripheral decidualizing cells, with the protein localizing close to the embryo during implantation (days 5.5-8.5). With the regression of the decidua beginning on day 9.5, a coordinated upregulation of both cathepsin B and cystatin C was observed implying a role for controlled cathepsin expression during apoptosis. E-64, a synthetic inhibitor of cathepsins B and L, was injected into pregnant females at the stage of blastocyst attachment (days 4.5-5.5). High doses resulted in the complete failure of implantation while lower doses resulted in stunted embryos and a reduced decidual reaction. These results suggested that cathepsins B and L are necessary for normal embryo development and uterine decidualization, and that decidua contributes to their control by a coordinated expression of cystatin C within the implantation site.

Cathepsin B and cysteine proteinase inhibitors in human lung cancer cell lines

Cell lines derived from human squamous cell (EPCL), large cell (LCLC), and small cell lung cancer (SCLC) lines were investigated for the expression of cathepsin B (Cat B) and cysteine proteinase inhibitors (CPIs). The EPLC and LCLC lines expressed 5- to 50-fold more Cat B activity and contained more mature Cat B of M(r) 27-29 kDa (> 2.5 microg/mg total protein) than the SCLC lines (< 1.0 microg/mg total protein). The LPLC lines also secreted the highest amounts of Cat B precursor of M(r) about 46 kDa. Inhibitory activities against Cat B and papain were associated with high molecular mass (HMM) and low molecular mass (LMM) inhibitory proteins, both in cell extracts and in media. About 75% of the inhibitory activity was associated with HMM inhibitors, the majority of which were kininogens (M(r) > or = 67 kDa). The LMM inhibitors of M(r) 10-15 kDa were cystatin C and stefins A and B, which were quantitated by ELISA: stefins A and B were present in cell extracts and medium in similar concentrations (5-200 ng/10(6) cells), while 80-99% of the cystatin C was released in the medium (10-195 ng/10(6) cells). Phorbol ester (PMA), which induces protein-kinase C mediated signal transduction and enhances cellular differentiation in many non-small cell lung cancer (NSCLC) cell lines, increased intracellular Cat B activity and Cat B protein as well as its secretion in some cell lines but not in others, regardless of their histological type. PMA significantly (P < 0.049) decreased intracellular stefin A concentrations in two EPLC lines and non-significantly in two LCLC lines. PMA decreased secretion of stefin A in all EPLC lines, but not in LCLC lines, while IGF-I significantly increased stefin B secretion in both SCLC lines. These data showed that lung tumor cells produce both cysteine proteinases and cystatins. As the antagonistic molecules are regulated differently in histologically different types of lung tumor cells, it is possible that an imbalance between the proteinases and their specific inhibitors plays a role in progression of certain types of lung tumors in vivo.

Immunohistochemical and clinical evaluation of cathepsin expression in soft tissue sarcomas

Lysosomal proteases are known to enhance the spread of epithelial tumour cells, but little is known of the possible role of proteases in the growth of soft tissue sarcomas (STS). We investigated the expression of cathepsins D, B, S, H, L and procathepsin L in frozen sections of 34 STS from 34 patients by immunohistochemistry (IHC). Cathepsins D, B and H were relatively highly expressed in STS (77-91%). The expression rate of cathepsins S and L and of procathepsin L was lower (40-66%). Cathepsin S and L expression showed a moderate (P = 0.078 and P = 0.019) and procathepsin L a strong (P = 0.00001) correlation with the survival rate of STS patients. Cathepsin S expression is also correlated with the local recurrence rate (P < 0.01). Lysosomal proteases may play a role in STS progression, and cathepsin expression may also have significance as a prognostic factor in STS.

Exposure to hypoxia, glucose starvation and acidosis: effect on invasive capacity of murine tumor cells and correlation with cathepsin (L + B) secretion

Cells in tumors may be exposed to adverse conditions such as nutrient deprivation, acidic pH and hypoxia. It has been shown previously that exposure to hypoxia, acidosis and glucose starvation in vitro increases the experimental metastatic ability of murine KHT-LP1 sarcoma, SCC-VII squamous carcinoma and B16 melanoma cells. This effect was most marked when cells were allowed to recover under normal in vitro growth conditions before injection. In the present study we examined whether the invasive capacity of the cells could be influenced by these modifications of the cell microenvironment. We used Matrigel, a basement membrane-like preparation in a two-chamber invasion assay to address this issue. Both KHT-LP1 and SCC-VII murine cell lines showed an increased ability to invade through Matrigel after hypoxia, and glucose starvation, but there was no consistent change in invasive capacity following acidosis exposure. The results for hypoxia and glucose starvation are in agreement with our previous studies of metastatic ability for these cell lines and we confirmed this for KHT-LP1 cells exposed to hypoxia in the current study. In parallel with the invasion assays, we compared cathepsin (L + B) content of the cells in treated and control suspensions. The effect observed varied according to the cell line and the treatment received (hypoxia, glucose starvation). There was an increase of cathepsin content for KHT-LP1 cells exposed to hypoxia and this increase correlated well with the increase of the invasion ability through Matrigel. We did not observe any increase of cathepsin for hypoxia-treated SCC-VII or for KHT-LP1 and SCC-VII cells treated with glucose starvation. These results suggest that transient hypoxia and glucose starvation can increase the invasive ability of tumor cell lines and thus may cause tumor progression by facilitating the invasive step of the metastatic process. The increased levels of cathepsin (L + B) in the KHT-LP1 cells treated with hypoxia, compared to control non-treated cells, may play a part in this increased invasive capacity.

The biochemistry of cancer dissemination

The progression of a tumor cell from one of benign delimited proliferation to invasive and metastatic growth is the major cause of poor clinical outcome of cancer patients. Recent research has revealed that this complex process requires many components for successful dissemination and growth of the tumor cell at secondary sites. These include angiogenesis, enhanced extracellular matrix degradation via tumor and host-secreted proteases, tumor cell migration, and modulation of tumor cell adhesion. Each individual component is multifaceted and is discussed within this review with respect to historical and recent findings. The identification of components and their interrelationship have yielded new therapeutic targets leading to the development of agents that may prove effective in the treatment of cancer and its metastatic progression.

Expression of cysteine protease inhibitors in human gliomas and meningiomas

Increased levels of human cysteine proteases have been implicated in the progression of tumors from the premalignant to the malignant state. The physiological activities of these proteases are regulated by their interactions with specific inhibitors. To our knowledge there have been no previous reports about the cysteine protease inhibitors (CPIs) in human brain tumors. In the study reported here, we determined CPI activity during glioma progression and compared that with normal human brain tissue. We also determined CPI activities in meningioma and glioblastoma cell lines in vitro. This activity was significantly higher in normal brain tissue and low-grade glioma than in anaplastic astrocytoma and glioblastoma. CPI activity was significantly higher in benign and atypical meningioma cell extracts in comparison with those from malignant meningiomas and with those from glioblastoma cell lines. After several passages, one benign meningioma cell line showed reduced levels of CPI and increased levels of cathepsin. Our results suggest that decreases in the activities of CPI may contribute to the malignant properties of brain tumors.