Enhanced expression of cathepsin L in metastatic bone tumors

CTSL, a prognostic marker of breast cancer, that promotes proliferation, migration, and invasion in cells in triple-negative breast cancer

Introduction

In the world, the incidence of breast cancer has surpassed that of lung cancer, and it has become the first malignant tumor among women. Triple-negative breast cancer (TNBC) shows an extremely heterogeneous malignancy toward high recurrence, metastasis, and mortality, but there is a lack of effective targeted therapy. It is urgent to develop novel molecular targets in the occurrence and therapeutics for TNBC, and novel therapeutic strategies to block the recurrence and metastasis of TNBC.

Methods

In this study, CTSL (cathepsin L) expression in tissues and adjacent tissues of TNBC patients was monitored by immunohistochemistry and western blots. The correlations between CTSL expressions and clinicopathological characteristics in the patient tissues for TNBC were analyzed. Cell proliferation, migration, and invasion assay were also performed when over-expressed or knocked-down CTSL.

Results

We found that the level of CTSL in TNBC is significantly higher than that in the matched adjacent tissues, and associated with differentiated degree, TNM Stage, tumor size, and lymph node metastatic status in TNBC patients. The high level of CTSL was correlated with a short RFS (p<0.001), OS (p<0.001), DMFS (p<0.001), PPS (p= 0.0025) in breast cancer from online databases; while in breast cancer with lymph node-positive, high level of CTSL was correlated with a short DMFS (p<0.001) and RFS (p<0.001). Moreover, in vitro experiments showed that CTSL overexpression promotes the abilities for proliferation, migration, and invasion in MCF-7 and MDA-MB-231 cell lines, while knocking-down CTSL decreases its characteristics in MDA-MB-231 cell lines.

Conclusion

CTSL might involve into the regulation of the proliferation, invasion, and metastasis of TNBC. Thus, CTSL would be a novel, potential therapeutic, and prognostic target of TNBC.

Identification of Factors Driving Doxorubicin-Resistant Ewing Tumor Cells to Survival

BACKGROUND

Ewing sarcoma (ES) cells exhibit extreme plasticity that contributes to the cell's survival and recurrence. Although multiple studies reveal various signaling pathways mediated by the EWSR1/FLI1 fusion, the specific transcriptional control of tumor cell resistance to doxorubicin is unknown. Understanding the molecular hubs that contribute to this behavior provides a new perspective on valuable therapeutic options against tumor cells.

METHODS

Single-cell RNA sequencing and LC-MS/MS-based quantitative proteomics were used.

RESULTS

A goal of this study was to identify protein hubs that would help elucidate tumor resistance which prompted ES to relapse or metastasize. Several differentially expressed genes and proteins, including adhesion, cytoskeletal, and signaling molecules, were observed between embryonic fibroblasts and control and doxorubicin-treated tumor cell lines. While several cancer-associated genes/proteins exhibited similar expression across fibroblasts and non-treated cells, upregulation of some proteins belonging to metabolic, stress response, and growth pathway activation was uniquely observed in doxorubicin-treated sarcoma cells, respectively. The novel information on differentially expressed genes/proteins provides insights into the biology of ES cells, which could help elucidate mechanisms of their recurrence.

CONCLUSIONS

Collectively, our results identify a novel role of cellular proteins in contributing to tumor cell resistance and escape from doxorubicin therapy and contributing to ES progression.

Structural Dynamics Investigation of Human Family 1 & 2 Cystatin-Cathepsin L1 Interaction: A Comparison of Binding Modes

Cystatin superfamily is a large group of evolutionarily related proteins involved in numerous physiological activities through their inhibitory activity towards cysteine proteases. Despite sharing the same cystatin fold, and inhibiting cysteine proteases through the same tripartite edge involving highly conserved N-terminal region, L1 and L2 loop; cystatins differ widely in their inhibitory affinity towards C1 family of cysteine proteases and molecular details of these interactions are still elusive. In this study, inhibitory interactions of human family 1 & 2 cystatins with cathepsin L1 are predicted and their stability and viability are verified through protein docking & comparative molecular dynamics. An overall stabilization effect is observed in all cystatins on complex formation. Complexes are mostly dominated by van der Waals interaction but the relative participation of the conserved regions varied extensively. While van der Waals contacts prevail in L1 and L2 loop, N-terminal segment chiefly acts as electrostatic interaction site. In fact the comparative dynamics study points towards the instrumental role of L1 loop in directing the total interaction profile of the complex either towards electrostatic or van der Waals contacts. The key amino acid residues surfaced via interaction energy, hydrogen bonding and solvent accessible surface area analysis for each cystatin-cathepsin L1 complex influence the mode of binding and thus control the diverse inhibitory affinity of cystatins towards cysteine proteases.

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.

Cathepsin L in metastatic bone disease: therapeutic implications

Cathepsin L is a lysosomal cysteine proteinase primarily devoted to the metabolic turnover of intracellular proteins. However, accumulating evidence suggests that this endopeptidase might also be implicated in the regulation of other important biological functions, including bone resorption in normal and pathological conditions. These findings support the concept that cathepsin L, in concert with other proteolytic enzymes involved in bone remodeling processes, could contribute to facilitate bone metastasis formation. In support of this hypothesis, recent studies indicate that cathepsin L can foster this process by triggering multiple mechanisms which, in part, differ from those of the major cysteine proteinase of osteoclasts, namely cathepsin K. Therefore, cathepsin L can be regarded as an additional target in the treatment of patients with metastatic bone disease. This review discusses the clinical and therapeutic implications related to these findings.

Cathepsins and osteosarcoma: Expression analysis identifies cathepsin K as an indicator of metastasis

Osteosarcoma is the most frequent malignant bone tumor with a poor survival rate for patients with metastasis. Previous studies have shown that beside other proteases, distinct sets of cathepsins are involved in the process of metastasis of different tumors. In this study we investigated the expression of cathepsin proteases in human osteosarcoma metastasis. First, the mRNA expression of 14 human cathepsins was studied in SAOS-2 osteosarcoma cells and the highly metastatic LM5 and LM7 sublines by reverse transcriptase (RT)-polymerase chain reaction (PCR). The expression of cathepsin D, K, and L mRNA was found upregulated and that of cathepsin F, H, and V downregulated in the highly metastatic LM5 and LM7 cells. A subgroup of the cathepsin proteases was further studied at the protein level by Western blot analysis of cell extracts. The expression of cathepsin B and H was decreased and that of cathepsin D, K, and L was increased in the highly metastatic cell lines as compared to the SAOS-2 cell line. Diagnostic relevance of cathepsin K expression in osteosarcoma was revealed upon correlation of survival and metastasis with immunohistochemical cathepsin K staining of biopsies collected from 92 patients prior to chemotherapy. Patients with metastatic high-grade osteosarcoma and low cathepsin K expression at diagnosis had a better prognosis than those with high expression. Thus, it appears that cathepsin K expression is of predictive prognostic value for patients with high-grade tumors and metastasis at diagnosis.

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.

Cysteine cathepsins are central contributors of invasion by cultured adenosylmethionine decarboxylase-transformed rodent fibroblasts

Adenosylmethionine decarboxylase (AdoMetDC), a key enzyme in the biosynthesis of polyamines, is often up-regulated in cancers. We have demonstrated previously that overexpression of AdoMetDC alone is sufficient to transform NIH 3T3 cells and induce highly invasive tumors in nude mice. Here, we studied the transformation-specific alterations in gene expression induced by AdoMetDC by using cDNA microarray and two-dimensional electrophoresis technologies. We specifically tried to identify the secreted proteins contributing to the high invasive activity of the AdoMetDC-transformed cells. We found a significant increase in the expression and secretion of procathepsin L, which was cleaved and activated in the presence of glycosaminoglycans (heparin), and a smaller increase in cathepsin B. Inhibition of the cathepsin L and B activity by specific peptide inhibitors abrogated the invasive capacity of the AdoMetDC transformants in Matrigel. The transformed cells also showed a small increase in the activity of gelatin-degrading matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator activities, neither of which was sensitive to the inhibitors of cathepsin L and B. Furthermore, the invasive potency of the transformed cells remained unaffected by specific inhibitors of MMPs. The results suggest that cysteine cathepsins are the main proteases contributing to the high invasiveness of the AdoMetDC-transformed cells and that the invasion potential is largely independent of activation of the MMPs.

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.

Cathepsin L antisense oligonucleotides in a human osteosarcoma cell line: effects on the invasive phenotype

Alterations in cathepsin L expression and trafficking have been associated with the progression and metastasis of several tumor entities. In the present study, we examined the effects of various cathepsin L antisense (as) phosphorothioate oligonucleotides on both the expression of cathepsin L and the invasive potential of the human osteosarcoma cell line MNNG/HOS. Seven oligonucleotides of 20-bp length each and one random control oligonucleotide were chosen to block cathepsin L expression. Northern blot analysis demonstrated a significant reduction in cathepsin L mRNA expression by the six antisense oligonucleotides at a concentration of 10 microM. Cathepsin L protein expression was reduced significantly (50-85%) by the antisense oligonucleotides, as compared with the controls. Adhesion to matrices of collagen I and matrigel was not affected. In in vitro motility and invasion assays performed in uncoated and precoated transwell chambers, the ability of cells to migrate through the filters was inhibited by 35-75% using antisense oligonucleotides. The random control did not show any inhibitory effect. These data demonstrate that in MNNG/HOS cells cathepsin L influences cellular malignancy by promoting migration and basement membrane degradation.

Cysteine protease production by human osteosarcoma cells (MG63, SAOS2) and its modulation by soluble factors

The production of cysteine protease by two human osteosarcoma cell lines (MG-63 and SaOS2) was analyzed, as well as their modulation by interleukin 1beta (hIL-1 beta), interleukin 6 (hIL-6), insulin growth factor-1 (hIGF-1), oncostatin M (hOSM), leukemia inhibitory factor (hLIF) and growth hormone (hGH). Cysteine protease activities were detected using a synthetic substrate. The protease activities (especially cathepsin L activity) of both cell lines were increased significantly in the presence of hIL-1 beta, hIL-6 and hOSM. In contrast, hIGF-1 and hGH decreased these activities, and no effect was detectable in the presence of hLIF. The addition of antibodies against the gp-130 chain of the hIL-6 and hOSM receptors totally inhibited the stimulating effect of these two cytokines on cysteine protease activities. In increasing collagen type I degradation, hIL-1beta, hIL-6 and hOSM could be involved in bone resorption, whereas the inhibitory action of hIGF-1 and hGH on collagen type I degradation suggest that this factor could play a role in bone formation.

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

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