Bone marrow-derived cathepsin K cleaves SPARC in bone metastasis

Co-precipitating calcium phosphate as oral detoxification of cadmium

Bone-eating (also known as osteophagia), found in wild animals, is primarily recognized as a means to supplement phosphorus and calcium intake. Herein, we describe a novel function of bone-eating in detoxifying heavy metal ions through the dissolution and co-precipitation of bone minerals as they travel through the gastrointestinal (GI) tract. In this study, cadmium (Cd), a heavy metal ion, served as a toxic model. We demonstrated that hydroxyapatite (HAp), the major calcium phosphate (CaP) in bone, dissolves in the stomach and acts as a co-precipitant in the intestine for Cd detoxification. We compared HAp to a common antidote, activated charcoal (AC), which did not precipitate within the GI tract. In vitro experiments showed that HAp dissolves under acidic conditions and, upon return to a neutral environment, efficiently re-sequesters Cd. Similarly, oral administration of HAp effectively prevented Cd absorption and accumulation, resulting in enhanced Cd excretion in the feces when compared to AC. A co-precipitating CaP in the GI tract could serve as an excellent detoxification system, as it helps prevent the accumulation of toxic substances and aids in developing appropriate strategies to reduce tissue toxicity. Moreover, understanding this detoxification system would be a valuable indicator for designing efficient detoxification materials.

Proteomics study of primary and recurrent adamantinomatous craniopharyngiomas

BACKGROUND

Adamantinomatous craniopharyngiomas (ACPs) are rare benign epithelial tumours with high recurrence and poor prognosis. Biological differences between recurrent and primary ACPs that may be associated with disease recurrence and treatment have yet to be evaluated at the proteomic level. In this study, we aimed to determine the proteomic profiles of paired recurrent and primary ACP, gain biological insight into ACP recurrence, and identify potential targets for ACP treatment.

METHOD

Patients with ACP (n = 15) or Rathke's cleft cyst (RCC; n = 7) who underwent surgery at Sanbo Brain Hospital, Capital Medical University, Beijing, China and received pathological confirmation of ACP or RCC were enrolled in this study. We conducted a proteomic analysis to investigate the characteristics of primary ACP, paired recurrent ACP, and RCC. Western blotting was used to validate our proteomic results and assess the expression of key tumour-associated proteins in recurrent and primary ACPs. Flow cytometry was performed to evaluate the exhaustion of tumour-infiltrating lymphocytes (TILs) in primary and recurrent ACP tissue samples. Immunohistochemical staining for CD3 and PD-L1 was conducted to determine differences in T-cell infiltration and the expression of immunosuppressive molecules between paired primary and recurrent ACP samples.

RESULTS

The bioinformatics analysis showed that proteins differentially expressed between recurrent and primary ACPs were significantly associated with extracellular matrix organisation and interleukin signalling. Cathepsin K, which was upregulated in recurrent ACP compared with that in primary ACP, may play a role in ACP recurrence. High infiltration of T cells and exhaustion of TILs were revealed by the flow cytometry analysis of ACP.

CONCLUSIONS

This study provides a preliminary description of the proteomic differences between primary ACP, recurrent ACP, and RCC. Our findings serve as a resource for craniopharyngioma researchers and may ultimately expand existing knowledge of recurrent ACP and benefit clinical practice.

Non-Toxicological Role of Aryl Hydrocarbon Receptor in Obesity-Associated Multiple Myeloma Cell Growth and Survival

Obesity is not only a risk factor for multiple myeloma (MM) incidence, but it is also associated with an increased risk of progression from myeloma precursors-monoclonal gammopathy of undetermined significance-and smoldering myeloma. Adipocytes in the bone marrow (BMAs) microenvironment have been shown to facilitate MM cell growth via secreted factors, but the nature of these secreted factors and their mechanism of action have not been fully elucidated. The elevated expression of aryl hydrocarbon receptor (AhR) is associated with a variety of different cancers, including MM; however, the role of AhR activity in obesity-associated MM cell growth and survival has not been explored. Indeed, this is of particular interest as it has been recently shown that bone marrow adipocytes are a source of endogenous AhR ligands. Using multiple in vitro models of tumor-adipocyte crosstalk to mimic the bone microenvironment, we identified a novel, non-toxicological role of the adipocyte-secreted factors in the suppression of AhR activity in MM cells. A panel of six MM cell lines were cultured in the presence of bone marrow adipocytes in (1) a direct co-culture, (2) a transwell co-culture, or (3) an adipocyte-conditioned media to interrogate the effects of the secreted factors on MM cell AhR activity. Nuclear localization and the transcriptional activity of the AhR, as measured by CYP1A1 and CYP1B1 gene induction, were suppressed by exposure to BMA-derived factors. Additionally, decreased AhR target gene expression was associated with worse clinical outcomes. The knockdown of AhR resulted in reduced CYP1B1 expression and increased cellular growth. This tumor-suppressing role of CYP1A1 and CYP1B1 was supported by patient data which demonstrated an association between reduced target gene expression and worse overall survival. These data demonstrated a novel mechanism by which bone marrow adipocytes promote MM progression.

Adipocyte-derived kynurenine stimulates malignant transformation of mammary epithelial cells through the aryl hydrocarbon receptor

Anti-hormone therapies are not efficacious for reducing the incidence of triple negative breast cancer (TNBC), which lacks both estrogen and progesterone receptors. While the etiology of this aggressive breast cancer subtype is unclear, visceral obesity is a strong risk factor for both pre- and post-menopausal cases. The mechanism by which excessive deposition of visceral adipose tissue (VAT) promotes the malignant transformation of hormone receptor-negative mammary epithelial cells is currently unknown. We developed a novel in vitro system of malignant transformation in which non-tumorigenic human breast epithelial cells (MCF-10A) grow in soft agar when cultured with factors released from VAT. These cells, which acquire the capacity for 3D growth, show elevated aryl hydrocarbon receptor (AhR) protein and AhR target genes, suggesting that AhR activity may drive malignant transformation by VAT. AhR is a ligand-dependent transcription factor that generates biological responses to exogenous carcinogens and to the endogenous tryptophan pathway metabolite, kynurenine. The serum kynurenine to tryptophan ratio has been shown to be elevated in patients with obesity. Herein, we demonstrate that AhR inhibitors or knockdown of AhR in MCF-10A cells prevents VAT-induced malignant transformation. Specifically, VAT-induced transformation is inhibited by Kyn-101, an inhibitor for the endogenous ligand binding site of AhR. Mass spectrometry analysis demonstrates that adipocytes metabolize tryptophan and release kynurenine, which is taken up by MCF-10A cells and activates the AhR to induce CYP1B1 and promote malignant transformation. This novel hormone receptor-independent mechanism of malignant transformation suggests targeting AhR for TNBC prevention in the context of visceral adiposity.

Clinicopathological correlation of Cathepsin K expression in salivary gland carcinomas; relation to patients` outcome

BACKGROUND

Salivary gland carcinomas (SGCs) represent various groups of tumors that demonstrate marked diversity in their prognosis owing to different histology and clinical characteristics. One of the poor prognostic indicators is distant metastasis which is considered the major reason for death in SGC patients. Discovering new biomarkers is urgently required to aid in the detection of cancer onset and progression. Cathepsin K (CTSK), the lysosomal cysteine protease has a principal role in cancer invasion and progression through interaction with the tumor microenvironment, degradation of extracellular membrane proteins and destruction of the elastic lamina of blood vessels. In the English literature, little information was present about the role of CTSK in SGCs. The current study aimed to assess the immunohistochemical expression of CTSK in SGCs and correlate its expression to different clinicopathologic parameters.

METHODS

The retrospective study applied to 45 cases of SGCs categorized as high-grade (33 cases) and low-grade SGCs (12 cases) following the criteria of WHO classification (2017) of head and neck tumors. All patients` clinicopathological and follow-up records were retrieved. The following statistical tests were used to study the variance of CTSK expression in SGCs concerning different clinicopathological parameters; Pearson`s Chi-square test, unpaired two-tailed student t-test, One-way ANOVA, and Post Hoc tests. Disease-free survival (DFS) and Overall survival (OS) were calculated and displayed with the Kaplan-Meier strategy and analyzed with the log-rank test. Univariate and multivariate survival analyses were performed with Cox regression. A P-value lesser than 0.05 was considered statistically significant.

RESULTS

Strong CTSK expression was significantly related to high-grade SGCs (P = 0.000), large infiltrating carcinomas (P = 0.000), presence of nodal (P = 0.041) and distant metastasis (P = 0.009), advanced TNM clinical stage (P = 0.000), the incidence of recurrence (P = 0.009), and reduced DFS (P = 0.006). Distant metastasis was the independent predictor for DFS using Cox regression model.

CONCLUSIONS

CTSK has a great role in cancer progression by triggering many signaling pathways. Its level in cancerous tissue is considered an effective index for predicting the severity and prognosis of cancer. Therefore, we indicate its utility as a prognostic tool and therapeutic target for cancer treatment.

TRIAL REGISTRATION

Retrospectively registered.

SPARC in cancer-associated fibroblasts is an independent poor prognostic factor in non-metastatic triple-negative breast cancer and exhibits pro-tumor activity

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype and lacks specific targeted therapeutic agents. The current mechanistic evidence from cell-based studies suggests that the matricellular protein SPARC has a tumor-promoting role in TNBC; however, data on the clinical relevance of SPARC expression/secretion by tumor and stromal cells in TNBC are limited. Here, we analyzed by immunohistochemistry the prognostic value of tumor and stromal cell SPARC expression in 148 patients with non-metastatic TNBC and long follow-up (median: 5.4 years). We also quantified PD-L1 and PD-1 expression. We detected SPARC expression in tumor cells (42.4%), cancer-associated fibroblasts (CAFs; 88.1%), tumor-associated macrophages (77.1%), endothelial cells (75.2%) and tumor-infiltrating lymphocytes (9.8%). Recurrence-free survival was significantly lower in patients with SPARC-expressing CAFs. Multivariate analysis showed that SPARC expression in CAFs was an independent prognostic factor. We also detected tumor and stromal cell SPARC expression in TNBC cytosols, and in patient-derived xenografts and cell lines. Furthermore, we analyzed publicly available single-cell mRNA sequencing data and found that in TNBC, SPARC is expressed by different CAF subpopulations, including myofibroblasts and inflammatory fibroblasts that are involved in tumor-related processes. We then showed that fibroblast-secreted SPARC had a tumor-promoting role by inhibiting TNBC cell adhesion and stimulating their motility and invasiveness. Overall, our study demonstrates that SPARC expression in CAFs is an independent prognostic marker of poor outcome in TNBC. Patients with SPARC-expressing CAFs could be eligible for anti-SPARC targeted therapy.

Challenges and Opportunities Modeling the Dynamic Tumor Matrisome

We need novel strategies to target the complexity of cancer and, particularly, of metastatic disease. As an example of this complexity, certain tissues are particularly hospitable environments for metastases, whereas others do not contain fertile microenvironments to support cancer cell growth. Continuing evidence that the extracellular matrix (ECM) of tissues is one of a host of factors necessary to support cancer cell growth at both primary and secondary tissue sites is emerging. Research on cancer metastasis has largely been focused on the molecular adaptations of tumor cells in various cytokine and growth factor environments on 2-dimensional tissue culture polystyrene plates. Intravital imaging, conversely, has transformed our ability to watch, in real time, tumor cell invasion, intravasation, extravasation, and growth. Because the interstitial ECM that supports all cells in the tumor microenvironment changes over time scales outside the possible window of typical intravital imaging, bioengineers are continuously developing both simple and sophisticated in vitro controlled environments to study tumor (and other) cell interactions with this matrix. In this perspective, we focus on the cellular unit responsible for upholding the pathologic homeostasis of tumor-bearing organs, cancer-associated fibroblasts (CAFs), and their self-generated ECM. The latter, together with tumoral and other cell secreted factors, constitute the "tumor matrisome". We share the challenges and opportunities for modeling this dynamic CAF/ECM unit, the tools and techniques available, and how the tumor matrisome is remodeled (e.g., via ECM proteases). We posit that increasing information on tumor matrisome dynamics may lead the field to alternative strategies for personalized medicine outside genomics.

Cathepsin K in Pathological Conditions and New Therapeutic and Diagnostic Perspectives

Cathepsin K (CatK) is a part of the family of cysteine proteases involved in many important processes, including the degradation activity of collagen 1 and elastin in bone resorption. Changes in levels of CatK are associated with various pathological conditions, primarily related to bone and cartilage degradation, such as pycnodysostosis (associated with CatK deficiency), osteoporosis, and osteoarthritis (associated with CatK overexpression). Recently, the increased secretion of CatK is being highly correlated to vascular inflammation, hypersensitivity pneumonitis, Wegener granulomatosis, berylliosis, tuberculosis, as well as with tumor progression. Due to the wide spectrum of diseases in which CatK is involved, the design and validation of active site-specific inhibitors has been a subject of keen interest in pharmaceutical companies in recent decades. In this review, we summarized the molecular background of CatK and its involvement in various diseases, as well as its clinical significance for diagnosis and therapy.

Biomineralization of bone tissue: calcium phosphate-based inorganics in collagen fibrillar organic matrices

BACKGROUND

Bone regeneration research is currently ongoing in the scientific community. Materials approved for clinical use, and applied to patients, have been developed and produced. However, rather than directly affecting bone regeneration, these materials support bone induction, which regenerates bone. Therefore, the research community is still researching bone tissue regeneration. In the papers published so far, it is hard to find an improvement in the theory of bone regeneration. This review discusses the relationship between the existing theories on hard tissue growth and regeneration and the biomaterials developed so far for this purpose and future research directions.

MAINBODY

Highly complex nucleation and crystallization in hard tissue involves the coordinated action of ions and/or molecules that can produce different organic and inorganic composite biomaterials. In addition, the healing of bone defects is also affected by the dynamic conditions of ions and nutrients in the bone regeneration process. Inorganics in the human body, especially calcium- and/or phosphorus-based materials, play an important role in hard tissues. Inorganic crystal growth is important for treating or remodeling the bone matrix. Biomaterials used in bone tissue regeneration require expertise in various fields of the scientific community. Chemical knowledge is indispensable for interpreting the relationship between biological factors and their formation. In addition, sources of energy for the nucleation and crystallization processes of such chemical bonds and minerals that make up the bone tissue must be considered. However, the exact mechanism for this process has not yet been elucidated. Therefore, a convergence of broader scientific fields such as chemistry, materials, and biology is urgently needed to induce a distinct bone tissue regeneration mechanism.

CONCLUSION

This review provides an overview of calcium- and/or phosphorus-based inorganic properties and processes combined with organics that can be regarded as matrices of these minerals, namely collagen molecules and collagen fibrils. Furthermore, we discuss how this strategy can be applied to future bone tissue regenerative medicine in combination with other academic perspectives.

Cathepsin K: A Versatile Potential Biomarker and Therapeutic Target for Various Cancers

Cancer, a common malignant disease, is one of the predominant causes of diseases that lead to death. Additionally, cancer is often detected in advanced stages and cannot be radically cured. Consequently, there is an urgent need for reliable and easily detectable markers to identify and monitor cancer onset and progression as early as possible. Our aim was to systematically review the relevant roles of cathepsin K (CTSK) in various possible cancers in existing studies. CTSK, a well-known key enzyme in the bone resorption process and most studied for its roles in the effective degradation of the bone extracellular matrix, is expressed in various organs. Nowadays, CTSK has been involved in various cancers such as prostate cancer, breast cancer, bone cancer, renal carcinoma, lung cancer and other cancers. In addition, CTSK can promote tumor cells proliferation, invasion and migration, and its mechanism may be related to RANK/RANKL, TGF-β, mTOR and the Wnt/β-catenin signaling pathway. Clinically, some progress has been made with the use of cathepsin K inhibitors in the treatment of certain cancers. This paper reviewed our current understanding of the possible roles of CTSK in various cancers and discussed its potential as a biomarker and/or novel molecular target for various cancers.

Lysosomal peptidases – Intriguing roles in cancer progression and neurodegeneration

Lysosomal peptidases are hydrolytic enzymes capable of digesting waste proteins that are targeted to lysosomes via endocytosis and autophagy. Besides intracellular protein catabolism, they play more specific roles in several other cellular processes and pathologies, either within lysosomes, upon secretion into the cell cytoplasm or extracellular space, or bound to the plasma membrane. In cancer, lysosomal peptidases are generally associated with disease progression, as they participate in crucial processes leading to changes in cell morphology, signaling, migration, and invasion, and finally metastasis. However, they can also enhance the mechanisms resulting in cancer regression, such as apoptosis of tumor cells or antitumor immune responses. Lysosomal peptidases have also been identified as hallmarks of aging and neurodegeneration, playing roles in oxidative stress, mitochondrial dysfunction, abnormal intercellular communication, dysregulated trafficking, and the deposition of protein aggregates in neuronal cells. Furthermore, deficiencies in lysosomal peptidases may result in other pathological states, such as lysosomal storage disease. The aim of this review was to highlight the role of lysosomal peptidases in particular pathological processes of cancer and neurodegeneration and to address the potential of lysosomal peptidases in diagnosing and treating patients.

Helicobacter pylori and gastric cancer: a lysosomal protease perspective

The intimate involvement of pathogens with the heightened risk for developing certain cancers is an area of research that has captured a great deal of attention over the last 10 years. One firmly established paradigm that highlights this aspect of disease progression is in the instance of Helicobacter pylori infection and the contribution it makes in elevating the risk for developing gastric cancer. Whilst the molecular mechanisms that pinpoint the contribution that this microorganism inflicts towards host cells during gastric cancer initiation have come into greater focus, another picture that has also emerged is one that implicates the host's immune system, and the chronic inflammation that can arise therefrom, as being a central contributory factor in disease progression. Consequently, when taken with the underlying role that the extracellular matrix plays in the development of most cancers, and how this dynamic can be modulated by proteases expressed from the tumor or inflammatory cells, a complex and detailed relationship shared between the individual cellular components and their surroundings is coming into focus. In this review article, we draw attention to the emerging role played by the cathepsin proteases in modulating the stage-specific progression of Helicobacter pylori-initiated gastric cancer and the underlying immune response, while highlighting the therapeutic significance of this dynamic and how it may be amenable for novel intervention strategies within a basic research or clinical setting.

Effect of Omeprazole on Osteoblasts and Osteoclasts in vivo and in the in vitro Model Using Fish Scales

Omeprazole suppresses excessive secretion of gastric acid via irreversible inhibition of H+/K+-ATPase in the gastric parietal cells. Recent meta-analysis of data revealed an association between the use of proton pump inhibitors (PPIs) and increased risk of bone fractures, but the underlying molecular mechanism of PPI action remains unclear. In this study, we demonstrated that omeprazole directly influences bone metabolism using a unique in vitro bioassay system with teleost scales, as well as the in vivo model. The in vitro study showed that omeprazole significantly increased the activities of alkaline phosphatase and tartrate-resistant acid phosphatase after 6 h of incubation with this PPI. Expression of mRNAs for several osteoclastic markers was upregulated after 3-h incubation of fish scales with 10^-7 M omeprazole. The in vivo experiments revealed that the plasma calcium levels significantly increased in the omeprazole-treated group. The results of in vitro and in vivo studies suggest that omeprazole affects bone cells by increasing bone resorption by upregulating expression of osteoclastic genes and promoting calcium release to the circulation. The suggested in vitro bioassay in fish scales is a practical model that can be used to study the effects of drugs on bone metabolism.

Adipocyte-driven unfolded protein response is a shared transcriptomic signature of metastatic prostate carcinoma cells

A critical unknown in the field of skeletal metastases is how cancer cells find a way to thrive under harsh conditions, as exemplified by metastatic colonization of adipocyte-rich bone marrow by prostate carcinoma cells. To begin understanding molecular processes that enable tumor cells to survive and progress in difficult microenvironments such as bone, we performed unbiased examination of the transcriptome of two different prostate cancer cell lines in the absence or presence of bone marrow adipocytes. Our RNAseq analyses and subsequent quantitative PCR and protein-based assays reveal that upregulation of endoplasmic reticulum (ER) stress and unfolded protein response (UPR) genes is a shared signature between metastatic prostate carcinoma cell lines of different origin. Pathway analyses and pharmacological examinations highlight the ER chaperone BIP as an upstream coordinator of this transcriptomic signature. Additional patient-based data support our overall conclusion that ER stress and UPR induction are shared, important factors in the response and adaptation of metastatic tumor cells to their micro-environment. Our studies pave the way for additional mechanistic investigations and offer new clues towards effective therapeutic interventions in metastatic disease.

A 9-kDa matricellular SPARC fragment released by cathepsin D exhibits pro-tumor activity in the triple-negative breast cancer microenvironment

Rationale: Alternative therapeutic strategies based on tumor-specific molecular targets are urgently needed for triple-negative breast cancer (TNBC). The protease cathepsin D (cath-D) is a marker of poor prognosis in TNBC and a tumor-specific extracellular target for antibody-based therapy. The identification of cath-D substrates is crucial for the mechanistic understanding of its role in the TNBC microenvironment and future therapeutic developments.

Methods: The cath-D substrate repertoire was investigated by N-Terminal Amine Isotopic Labeling of Substrates (TAILS)-based degradome analysis in a co-culture assay of TNBC cells and breast fibroblasts. Substrates were validated by amino-terminal oriented mass spectrometry of substrates (ATOMS). Cath-D and SPARC expression in TNBC was examined using an online transcriptomic survival analysis, tissue micro-arrays, TNBC cell lines, patient-derived xenografts (PDX), human TNBC samples, and mammary tumors from MMTV-PyMT Ctsd^-/-knock-out mice. The biological role of SPARC and its fragments in TNBC were studied using immunohistochemistry and immunofluorescence analysis, gene expression knockdown, co-culture assays, western blot analysis, RT-quantitative PCR, adhesion assays, Transwell motility, trans-endothelial migration and invasion assays.

Results: TAILS analysis showed that the matricellular protein SPARC is a substrate of extracellular cath-D. In vitro, cath-D induced limited proteolysis of SPARC C-terminal extracellular Ca²⁺ binding domain at acidic pH, leading to the production of SPARC fragments (34-, 27-, 16-, 9-, and 6-kDa). Similarly, cath-D secreted by TNBC cells cleaved fibroblast- and cancer cell-derived SPARC at the tumor pericellular acidic pH. SPARC cleavage also occurred in TNBC tumors. Among these fragments, only the 9-kDa SPARC fragment inhibited TNBC cell adhesion and spreading on fibronectin, and stimulated their migration, endothelial transmigration, and invasion.

Conclusions: Our study establishes a novel crosstalk between proteases and matricellular proteins in the tumor microenvironment through limited SPARC proteolysis, revealing a novel targetable 9-kDa bioactive SPARC fragment for new TNBC treatments. Our study will pave the way for the development of strategies for targeting bioactive fragments from matricellular proteins in TNBC.

A non-immunological role for γ-interferon-inducible lysosomal thiol reductase (GILT) in osteoclastic bone resorption

The extracellular bone resorbing lacuna of the osteoclast shares many characteristics with the degradative lysosome of antigen-presenting cells. γ-Interferon-inducible lysosomal thiol reductase (GILT) enhances antigen processing within lysosomes through direct reduction of antigen disulfides and maintenance of cysteine protease activity. In this study, we found the osteoclastogenic cytokine RANKL drove expression of GILT in osteoclast precursors in a STAT1-dependent manner, resulting in high levels of GILT in mature osteoclasts, which could be further augmented by γ-interferon. GILT colocalized with the collagen-degrading cysteine protease, cathepsin K, suggesting a role for GILT inside the osteoclastic resorption lacuna. GILT-deficient osteoclasts had reduced bone-resorbing capacity, resulting in impaired bone turnover and an osteopetrotic phenotype in GILT-deficient mice. We demonstrated that GILT could directly reduce the noncollagenous bone matrix protein SPARC, and additionally, enhance collagen degradation by cathepsin K. Together, this work describes a previously unidentified, non-immunological role for GILT in osteoclast-mediated bone resorption.

Osteosarcoma Cell-Derived Small Extracellular Vesicles Enhance Osteoclastogenesis and Bone Resorption Through Transferring MicroRNA-19a-3p

Osteosarcoma (OS) is the most common primary bone cancer characterized by an aggressive phenotype with bone destruction. The prognosis of OS patients remains unoptimistic with the current treatment strategy. Recently, osteoclasts are believed to play a crucial role in cancer bone metastasis. Thus, osteoclast could be a target both in bone destruction and cancer progression in OS. However, mechanisms governing osteoclastogenesis in OS remain poorly understood. miRNA delivered by small extracellular vesicles (sEVs) could mediate cellular communications. In this study, we investigated the effects of sEVs on osteoclastogenesis and osteoclast function, also clarified the underlying mechanism. We herein found that sEVs promoted pre-osteoclast migration, osteoclastogenesis and resorption by exposing RAW264.7 cells to sEVs derived from OS cells. Bioinformatics analysis showed that phosphatase tension homologue (PTEN), and miR-19a-3p were involved in OS progression. Overexpression of miR-19a-3p or sEVs’ miR-19a-3p promoted osteoclast formation and function through PTEN/PI3K/AKT signaling pathway, while inhibition of miR-19a-3p showed the contrary results. The bone marrow macrophages (BMMs) were used to verify the results. OS mice, which were established by subcutaneous injection of OS cells, exhibited increased levels of sEVs’ miR-19a-3p in blood. Moreover, micro-computed tomography (CT) and histomorphometry analysis demonstrated that OS mice exhibited osteopenia with increased number of osteoclasts. In conclusion, miR-19a-3p delivery via OS cell-derived sEVs promotes osteoclast differentiation and bone destruction through PTEN/phosphatidylinositol 3 -kinase (PI3K)/protein kinase B (AKT) signaling pathway. These findings highlight sEVs packaging of miR-19a-3p as a potential target for prevention and treatment of bone destruction and cancer progression in OS patients. And this finding provides a novel potentially therapeutic target for the bone metastasis.

Fibronectin mediates activation of stromal fibroblasts by SPARC in endometrial cancer cells

Background

Matricellular glycoprotein, SPARC is a secreted molecule, that mediates the interaction between cells and extracellular matrix. SPARC functions as a regulator of matrix organization and modulates cell behavior. In various kinds of cancer, strong SPARC expression was observed in stromal tissues as well as in cancer epithelial cells. The function of SPARC in cancer cells is somewhat controversial and its impact on peritumoral stromal cells remains to be resolved.

Methods

We investigated the effects of SPARC expression in endometrial cancer cells on the surrounding stromal fibroblasts using in vitro co-culture system. Changes in characteristics of fibroblasts were examined by analysis of fibroblast-specific markers and in vitro contraction assay.

Results

SPARC induced AKT phosphorylation and epithelial-to-mesenchymal transition, consistent with previous reports. Cancer-associated fibroblasts of endometrial cancer expressed higher levels of mesenchymal- and fibroblast-associated factors and had a stronger contraction ability. Unexpectedly, cancer-associated fibroblasts expressed comparable levels of SPARC compared with fibroblasts from normal endometrium. However, co-culture of normal fibroblasts with SPARC-expressing Ishikawa cells resulted in activation of the fibroblasts. Immunodepletion of SPARC did not affect the activation of fibroblasts.

Conclusions

Our data indicated that SPARC activated fibroblasts only in the presence of fibronectin, which was abundantly secreted from SPARC-expressing endometrial cancer cells. These results suggested that a SPARC-fibronectin-mediated activation of fibroblasts might be involved in enhanced mobility and invasion of cancer cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07875-9.

Cathepsin-K is a potential cardiovascular risk biomarker in prevalent hemodialysis patients

PURPOSE

Cardiovascular (CV) disease remains the leading cause of mortality among end-stage kidney disease (ESKD) patients. Cathepsin-K (CatK), a small cysteine protease involved in bone and extracellular matrix remodeling, has recently emerged as a key-factor in the pathogenesis of various conditions predisposing to CV disease, including atherosclerosis, obesity, diabetes, and vascular calcification. In this pilot prospective study, we aimed at evaluating the clinical significance and the predictive power of CatK in a small cohort of hemodialysis (HD) patients.

METHODS

Cathepsin-K was measured in 54 prevalent HD patients and in 30 controls together with routine parameters. Patients were then followed up to 26 months and the time of cardiovascular death (endpoint of the study prospective phase) recorded.

RESULTS

CatK levels were increased in the HD cohort as compared with controls (p < 0.001). In HD patients, CatK was also independently correlated to PTH (β = 0.368; p = 0.001), alkaline phosphatase (β = 0.383; p < 0.001), C-reactive protein (β = 0.260; p = 0.01), and white cell count (β = - 0.219; p = 0.02). After baseline assessment, patients were followed for CV death (mean follow-up 24.8 ± 3.1 months). Kaplan-Meier analysis showed a worsen survival (log-rank p = 0.04) in HD patients with CatK levels > 440 pg/mL (best ROC-derived cut-off with 69.6% sensitivity and 79.8% specificity) with a crude HR (Mantel-Haenszel) of CV death of 3.46 (95% CI 1.89-13.44).

CONCLUSIONS

In prevalent HD patients, altered CatK levels may reflect mineral dysmetabolism and inflammation, and predict CV death in the mid-term. These preliminary findings prompt the rationale for further investigations on larger cohorts to validate CatK as a biomarker for improving CV risk stratification in ESKD.

The Role of Adipokines and Bone Marrow Adipocytes in Breast Cancer Bone Metastasis

The morbidity and mortality of breast cancer is mostly due to a distant metastasis, especially to the bone. Many factors may be responsible for bone metastasis in breast cancer, but interactions between tumor cells and other surrounding types of cells, and cytokines secreted by both, are expected to play the most important role. Bone marrow adipocyte (BMA) is one of the cell types comprising the bone, and adipokine is one of the cytokines secreted by both breast cancer cells and BMAs. These BMAs and adipokines are known to be responsible for cancer progression, and this review is focused on how BMAs and adipokines work in the process of breast cancer bone metastasis. Their potential as suppressive targets for bone metastasis is also explored in this review.

Obesity and Cathepsin K: A Complex Pathophysiological Relationship in Breast Cancer Metastases

BACKGROUND

Breast cancer appears in a strong inclination to metastasize in bone tissue. Several strategies are discussed in combating bone metastasis in breast cancer. However, therapy is only palliative and does not provide any improvement in survival to the majority of patients with advanced cancer. Obese and overweight women with breast cancer are three times more likely to develop metastatic disease compared to normal-weight women with the same treatment regimen. Overweight greatly intensify adipocytes formation in the bone marrow affecting bone metabolism by decreasing osteoblast differentiation and bone formation. Cathepsin K (CTSK), a cysteine protease, effectively degrades several components of the extracellular matrix and has the ability to differentiate adipocytes from bone marrow lineage. Therefore, the purpose of this review is to emphasize the underlying mechanism of CTSK and obesity role in breast cancer metastasis.

METHODS

Systematic review was performed using PubMed, EMBASE. The evidence of obesity and CTSK in breast cancer skeletal metastasis were analyzed, summarized and compared.

RESULTS

The present investigation argues for a specific association of CTSK with breast cancer skeletal metastasis by promoting adipocyte differentiation. The potential tumor-supporting roles of adipocytes are well documented, and in fact, suppressing adipocyte could be a new therapeutic option in the battle against lethal metastatic breast cancers.

CONCLUSION

This review emphasizes CTSK through its multifaceted role in differentiating adipocytes, inflammation, and extracellular degradation, may be a critical factor in an obesity-cancer connection. Thus, integration of CTSK targeting strategies into established traditional therapies seems to hold substantial promise.

The Matrix Revolution: Matricellular Proteins and Restructuring of the Cancer Microenvironment

The extracellular matrix (ECM) surrounding cells is indispensable for regulating their behavior. The dynamics of ECM signaling are tightly controlled throughout growth and development. During tissue remodeling, matricellular proteins (MCP) are secreted into the ECM. These factors do not serve classical structural roles, but rather regulate matrix proteins and cell-matrix interactions to influence normal cellular functions. In the tumor microenvironment, it is becoming increasingly clear that aberrantly expressed MCPs can support multiple hallmarks of carcinogenesis by interacting with various cellular components that are coupled to an array of downstream signals. Moreover, MCPs also reorganize the biomechanical properties of the ECM to accommodate metastasis and tumor colonization. This realization is stimulating new research on MCPs as reliable and accessible biomarkers in cancer, as well as effective and selective therapeutic targets.

Cysteine Cathepsins and their Extracellular Roles: Shaping the Microenvironment

For a long time, cysteine cathepsins were considered primarily as proteases crucial for nonspecific bulk proteolysis in the endolysosomal system. However, this view has dramatically changed, and cathepsins are now considered key players in many important physiological processes, including in diseases like cancer, rheumatoid arthritis, and various inflammatory diseases. Cathepsins are emerging as important players in the extracellular space, and the paradigm is shifting from the degrading enzymes to the enzymes that can also specifically modify extracellular proteins. In pathological conditions, the activity of cathepsins is often dysregulated, resulting in their overexpression and secretion into the extracellular space. This is typically observed in cancer and inflammation, and cathepsins are therefore considered valuable diagnostic and therapeutic targets. In particular, the investigation of limited proteolysis by cathepsins in the extracellular space is opening numerous possibilities for future break-through discoveries. In this review, we highlight the most important findings that establish cysteine cathepsins as important players in the extracellular space and discuss their roles that reach beyond processing and degradation of extracellular matrix (ECM) components. In addition, we discuss the recent developments in cathepsin research and the new possibilities that are opening in translational medicine.

Development of a 3D bone marrow adipose tissue model

Over the past twenty years, evidence has accumulated that biochemically and spatially defined networks of extracellular matrix, cellular components, and interactions dictate cellular differentiation, proliferation, and function in a variety of tissue and diseases. Modeling in vivo systems in vitro has been undeniably necessary, but when simplified 2D conditions rather than 3D in vitro models are used, the reliability and usefulness of the data derived from these models decreases. Thus, there is a pressing need to develop and validate reliable in vitro models to reproduce specific tissue-like structures and mimic functions and responses of cells in a more realistic manner for both drug screening/disease modeling and tissue regeneration applications. In adipose biology and cancer research, these models serve as physiologically relevant 3D platforms to bridge the divide between 2D cultures and in vivo models, bringing about more reliable and translationally useful data to accelerate benchtop to bedside research. Currently, no model has been developed for bone marrow adipose tissue (BMAT), a novel adipose depot that has previously been overlooked as "filler tissue" but has more recently been recognized as endocrine-signaling and systemically relevant. Herein we describe the development of the first 3D, BMAT model derived from either human or mouse bone marrow (BM) mesenchymal stromal cells (MSCs). We found that BMAT models can be stably cultured for at least 3 months in vitro, and that myeloma cells (5TGM1, OPM2 and MM1S cells) can be cultured on these for at least 2 weeks. Upon tumor cell co-culture, delipidation occurred in BMAT adipocytes, suggesting a bidirectional relationship between these two important cell types in the malignant BM niche. Overall, our studies suggest that 3D BMAT represents a "healthier," more realistic tissue model that may be useful for elucidating the effects of MAT on tumor cells, and tumor cells on MAT, to identify novel therapeutic targets. In addition, proteomic characterization as well as microarray data (expression of >22,000 genes) coupled with KEGG pathway analysis and gene set expression analysis (GSEA) supported our development of less-inflammatory 3D BMAT compared to 2D culture. In sum, we developed the first 3D, tissue-engineered bone marrow adipose tissue model, which is a versatile, novel model that can be used to study numerous diseases and biological processes involved with the bone marrow.

Cysteine cathepsins as a prospective target for anticancer therapies-current progress and prospects

Cysteine cathepsins (CTS), being involved in both physiological and pathological processes, play an important role in the human body. During the last 30 years, it has been shown that CTS are highly upregulated in a wide variety of cancer types although they have received a little attention as a potential therapeutic target as compared to serine or metalloproteinases. Studies on the increasing problem of neoplastic progression have revealed that secretion of cell-surface- and intracellular cysteine proteases is aberrant in tumor cells and has an impact on their growth, invasion, and metastasis by taking part in tumor angiogenesis, in apoptosis, and in events of inflammatory and immune responses. Considering the role of CTS in carcinogenesis, inhibition of these enzymes becomes an attractive strategy for cancer therapy. The downregulation of natural CTS inhibitors (CTSsis), such as cystatins, observed in various types of cancer, supports this claim. The intention of this review is to highlight the relationship of CTS with cancer and to present illustrations that explain how some of their inhibitors affect processes related to neoplastic progression.

Bone marrow adipocytes promote the Warburg phenotype in metastatic prostate tumors via HIF-1α activation

Metabolic adaptation is increasingly recognized as a key factor in tumor progression, yet its involvement in metastatic bone disease is not understood. Bone is as an adipocyte-rich organ, and a major site of metastasis from prostate cancer. Bone marrow adipocytes are metabolically active cells capable of shaping tumor metabolism via lipolysis and lipid transfer. In this study, using in vitro and in vivo models of marrow adiposity, we demonstrate that marrow fat cells promote Warburg phenotype in metastatic prostate cancer cells. We show increased expression of glycolytic enzymes, increased lactate production, and decreased mitochondrial oxidative phosphorylation in tumor cells exposed to adipocytes that require paracrine signaling between the two cell types. We also reveal that prostate cancer cells are capable of inducing adipocyte lipolysis as a postulated mechanism of sustenance. We provide evidence that adipocytes drive metabolic reprogramming of tumor cells via oxygen-independent mechanism of HIF-1α activation that can be reversed by HIF-1α downregulation. Importantly, we also demonstrate that the observed metabolic signature in tumor cells exposed to adipocytes mimics the expression patterns seen in patients with metastatic disease. Together, our data provide evidence for a functional relationship between marrow adipocytes and tumor cells in bone that has likely implications for tumor growth and survival within the metastatic niche.

Ru(ii) polypyridyl complexes as photocages for bioactive compounds containing nitriles and aromatic heterocycles

Photocaging allows for precise spatiotemporal control over the release of biologically active compounds with light. Most photocaged molecules employ organic photolabile protecting groups; however, biologically active compounds often contain functionalities such as nitriles and aromatic heterocycles that cannot be caged with organic groups. Despite their prevalence, only a few studies have reported successful caging of nitriles and aromatic heterocycles. Recently, Ru(ii)-based photocaging has emerged as a powerful method for the release of bioactive molecules containing these functional groups, in many cases providing high levels of spatial and temporal control over biological activity. This Feature Article discusses recent developments in applying Ru(ii)-based photocaging towards biological problems. Our groups designed and synthesized Ru(ii)-based platforms for the photoinduced delivery of cysteine protease and cytochrome P450 inhibitors in order to achieve selective control over enzyme inhibition. We also reported Ru(ii) photocaging groups derived from higher-denticity ancillary ligands that possess photophysical and photochemical properties distinct from more traditional Ru(ii)-based caging groups. In addition, for the first time, we are able to rapidly synthesize and screen Ru(ii) polypyridyl complexes that elicit desired properties by solid-phase synthesis. Finally, our work also defined steric and orbital mixing effects that are important factors in controlling photoinduced ligand exchange.

Oncolytic Adenovirus-Loaded Menstrual Blood Stem Cells Overcome the Blockade of Viral Activity Exerted by Ovarian Cancer Ascites

Patients with ovarian cancer present peritoneal ascites at recurrence as a marker of disseminated disease and dismal prognosis. Oncolytic immunotherapy is an emerging approach for the treatment of disseminated cancer. In the present work, we constructed a novel oncolytic adenovirus, AR2011, to target malignant ovarian tumors. AR2011 exhibited a clear lytic effect in vitro in human ovarian cancer cell lines and malignant cells obtained from ascitic fluids (AFs) of patients with ovarian cancer. AR2011 activity was neutralized by antibodies present in 31 samples of patient-derived AFs. However, this blockade was overridden by preloading menstrual blood stem cells (MenSCs) with AR2011 (MenSC-AR), since AFs exerted no in vitro inhibitory effect on viral lytic activity under these conditions. Moreover, soluble factors present in AFs act as MenSC chemoattractants. MenSC-AR treatment of nude mice carrying established peritoneal carcinomatosis following administration of human ovarian cancer cells was able to inhibit tumor growth at levels similar to those observed with AR2011 alone. This study demonstrates that MenSCs can be used to override the blockade that AFs exert on viral oncolytic effects.

Differential cathepsin responses to inhibitor-induced feedback: E-64 and cystatin C elevate active cathepsin S and suppress active cathepsin L in breast cancer cells

Cathepsins are powerful proteases, once referred to as the lysosomal cysteine proteases, that have been implicated in breast cancer invasion and metastasis, but pharmaceutical inhibitors have suffered failures in clinical trials due to adverse side effects. Scientific advancement from lysosomotropic to cell impermeable cathepsin inhibitors have improved efficacy in treating disease, but off-target effects have still been problematic, motivating a need to better understand cellular feedback and responses to treatment with cathepsin inhibitors. To address this need, we investigated effects of E-64 and cystatin C, two broad spectrum cathepsin inhibitors, on cathepsin levels intra- and extracellularly in MDA-MB-231 breast cancer cells. Cathepsins S and L had opposing responses to both E-64 and cystatin C inhibitor treatments with paradoxically elevated amounts of active cathepsin S, but decreased amounts of active cathepsin L, as determined by multiplex cathepsin zymography. This indicated cellular feedback to selectively sustain the amounts of active cathepsin S even in the presence of inhibitors with subnanomolar inhibitory constant values. These differences were identified in cellular locations of cathepsins L and S, trafficking for secretion, co-localization with endocytosed inhibitors, and longer protein turnover time for cathepsin S compared to cathepsin L. Together, this work demonstrates that previously underappreciated cellular compensation and compartmentalization mechanisms may sustain elevated amounts of some active cathepsins while diminishing others after inhibitor treatment. This can confound predictions based solely on inhibitor kinetics, and must be better understood to effectively deploy therapies and dosing strategies that target cathepsins to prevent cancer progression.

Secreted Protein Acidic and Rich in Cysteine (SPARC) Mediates Metastatic Dormancy of Prostate Cancer in Bone

Prostate cancer is known to frequently recur in bone; however, how dormant cells switch its phenotype leading to recurrent tumor remains poorly understood. We have isolated two syngeneic cell lines (indolent and aggressive) through in vivo selection by implanting PC3mm stem-like cells into tibial bones. We found that indolent cells retained the dormant phenotype, whereas aggressive cells grew rapidly in bone in vivo, and the growth rates of both cells in culture were similar, suggesting a role of the tumor microenvironment in the regulation of dormancy and recurrence. Indolent cells were found to secrete a high level of secreted protein acidic and rich in cysteine (SPARC), which significantly stimulated the expression of BMP7 in bone marrow stromal cells. The secreted BMP7 then kept cancer cells in a dormant state by inducing senescence, reducing "stemness," and activating dormancy-associated p38 MAPK signaling and p21 expression in cancer cells. Importantly, we found that SPARC was epigenetically silenced in aggressive cells by promoter methylation, but 5-azacytidine treatment reactivated the expression. Furthermore, high SPARC promoter methylation negatively correlated with disease-free survival of prostate cancer patients. We also found that the COX2 inhibitor NS398 down-regulated DNMTs and increased expression of SPARC, which led to tumor growth suppression in bone in vivo These findings suggest that SPARC plays a key role in maintaining the dormancy of prostate cancer cells in the bone microenvironment.

Photoactivated inhibition of cathepsin K in a 3D tumor model

Collagenolytic activity of cathepsin K is important for many physiological and pathological processes including osteoclast-mediated bone degradation, macrophage function and fibroblast-mediated matrix remodeling. Here, we report application of a light-activated inhibitor for controlling activity of cathepsin K in a 3D functional imaging assay. Using prostate carcinoma cell line engineered to overexpress cathepsin K, we demonstrate the utility of the proteolytic assay in living tumor spheroids for the evaluation and quantification of the inhibitor effects on cathepsin K-mediated collagen I degradation. Importantly, we also show that utilizing the ruthenium-caged version of a potent nitrile cathepsin K inhibitor (4), cis-[Ru(bpy)2(4)2](BF4)2 (5), offers significant advantage in terms of effective concentration of the inhibitor and especially its light-activated control in the 3D assay. Our results suggest that light activation provides a suitable, attractive approach for spatial and temporal control of proteolytic activity, which remains a critical, unmet need in treatment of human diseases, especially cancer.

Cathepsin K induces platelet dysfunction and affects cell signaling in breast cancer - molecularly distinct behavior of cathepsin K in breast cancer

Background

Breast cancer comprises clinically and molecularly distinct tumor subgroups that differ in cell histology and biology and show divergent clinical phenotypes that impede phase III trials, such as those utilizing cathepsin K inhibitors. Here we correlate the epithelial-mesenchymal-like transition breast cancer cells and cathepsin K secretion with activation and aggregation of platelets. Cathepsin K is up-regulated in cancer cells that proteolyze extracellular matrix and contributes to invasiveness. Although proteolytically activated receptors (PARs) are activated by proteases, the direct interaction of cysteine cathepsins with PARs is poorly understood. In human platelets, PAR-1 and −4 are highly expressed, but PAR-3 shows low expression and unclear functions.

Methods

Platelet aggregation was monitored by measuring changes in turbidity. Platelets were immunoblotted with anti-phospho and total p38, Src-Tyr-416, FAK-Tyr-397, and TGFβ monoclonal antibody. Activation was measured in a flow cytometer and calcium mobilization in a confocal microscope. Mammary epithelial cells were prepared from the primary breast cancer samples of 15 women with Luminal-B subtype to produce primary cells.

Results

We demonstrate that platelets are aggregated by cathepsin K in a dose-dependent manner, but not by other cysteine cathepsins. PARs-3 and −4 were confirmed as the cathepsin K target by immunodetection and specific antagonists using a fibroblast cell line derived from PARs deficient mice. Moreover, through co-culture experiments, we show that platelets activated by cathepsin K mediated the up-regulation of SHH, PTHrP, OPN, and TGFβ in epithelial-mesenchymal-like cells from patients with Luminal B breast cancer.

Conclusions

Cathepsin K induces platelet dysfunction and affects signaling in breast cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2203-7) contains supplementary material, which is available to authorized users.

Matricellular proteins as regulators of cancer metastasis to bone

Metastasis is the major cause of death in cancer patients, and a frequent site of metastasis for many cancers is the bone marrow. Therefore, understanding the mechanisms underlying the metastatic process is necessary for future prevention and treatment. The tumor microenvironment is now known to play a role in the metastatic cascade, both at the primary tumor and in metastatic sites, and includes both cellular and non-cellular components. The extracellular matrix (ECM) provides structural support and signaling cues to cells. One particular group of molecules associated with the ECM, known as matricellular proteins, modulate multiple aspects of tumor biology, including growth, migration, invasion, angiogenesis and metastasis. These proteins are also important for normal function in the bone by regulating bone formation and bone resorption. Recent studies have described a link between some of these proteins and metastasis of various tumors to the bone. The aim of this review is to summarize what is currently known about matricellular protein influence on bone metastasis. Particular attention to the contribution of both tumor cells and non-malignant cells in the bone has been given.

New 3D-Culture Approaches to Study Interactions of Bone Marrow Adipocytes with Metastatic Prostate Cancer Cells

Adipocytes are a major component of the bone marrow that can critically affect metastatic progression in bone. Understanding how the marrow fat cells influence growth, behavior, and survival of tumor cells requires utilization of in vitro cell systems that can closely mimic the physiological microenvironment. Herein, we present two new three-dimensional (3D) culture approaches to study adipocyte-tumor cell interactions in vitro. The first is a transwell-based system composed of the marrow-derived adipocytes in 3D collagen I gels and reconstituted basement membrane-overlayed prostate tumor cell spheroids. Tumor cells cultured under these 3D conditions are continuously exposed to adipocyte-derived factors, and their response can be evaluated by morphological and immunohistochemical analyses. We show via immunofluorescence analysis of metabolism-associated proteins that under 3D conditions tumor cells have significantly different metabolic response to adipocytes than tumor cells grown in 2D culture. We also demonstrate that this model allows for incorporation of other cell types, such as bone marrow macrophages, and utilization of dye-quenched collagen substrates for examination of proteolysis-driven responses to adipocyte- and macrophage-derived factors. Our second 3D culture system is designed to study tumor cell invasion toward the adipocytes and the consequent interaction between the two cell types. In this model, marrow adipocytes are separated from the fluorescently labeled tumor cells by a layer of collagen I. At designated time points, adipocytes are stained with BODIPY and confocal z-stacks are taken through the depth of the entire culture to determine the distance traveled between the two cell types over time. We demonstrate that this system can be utilized to study effects of candidate factors on tumor invasion toward the adipocytes. We also show that immunohistochemical analyses can be performed to evaluate the impact of direct interaction of prostate tumor cells with adipocytes. Our models underline the importance of using the appropriate culture conditions to mimic physiological interactions between marrow adipocytes and metastatic tumor cells. These systems have a potential to be utilized for analyses of various factors that may be regulated by the adipocytes in bone. Their application likely extends beyond metastatic prostate cancer to other tumors that colonize the bone marrow microenvironment.

Proteolytic Isoforms of SPARC Induce Adipose Stromal Cell Mobilization in Obesity

Adipose stromal cells (ASC) are mesenchymal adipocyte progenitors that reside in the peri-endothelium of fat tissue. ASC mobilization and migration accompany white adipose tissue (WAT) remodeling and pathological conditions. Mechanisms regulating ASC trafficking are largely unknown. We previously reported that binding of the matricellular protein secreted protein acidic and rich in cysteine (SPARC) to β1 integrin on ASC surface induces their motility. Here, we show that SPARC is required for ASC mobilization. We report two SPARC proteolytic isoforms, C-SPARC (lacking the N terminus) and N-SPARC (lacking the C terminus), generated in mesenteric WAT of obese mice. C-SPARC, but not N-SPARC, binds to β1 integrin on ASC, while N-SPARC preferentially binds to the extracellular matrix (ECM) and blocks ECM/integrin interaction. Interestingly, both C-SPARC and N-SPARC induce ASC deadhesion from the ECM, which is associated with modulation of integrin-dependent FAK-ERK signaling and integrin-independent ILK-Akt signaling. We show that these SPARC isoforms, acting on ASC through distinct mechanisms, have an additive effect in inducing ASC migration.

Marrow adipocyte-derived CXCL1 and CXCL2 contribute to osteolysis in metastatic prostate cancer

Increased bone marrow adiposity is a common feature of advanced age, obesity and associated metabolic pathologies. Augmented numbers of marrow adipocytes positively correlate with dysregulated bone remodeling, also a well-established complication of metastatic disease. We have shown previously that marrow adiposity accelerates prostate tumor progression in the skeleton and promotes extensive destruction of the bone; however, the factors behind adipocyte-driven osteolysis in the skeletal tumor microenvironment are not currently known. In this study, utilizing in vivo diet-induced models of bone marrow adiposity, we reveal evidence for positive correlation between increased marrow fat content, bone degradation by ARCaP(M) and PC3 prostate tumors, and augmented levels of host-derived CXCL1 and CXCL2, ligands of CXCR2 receptor. We show by in vitro osteoclastogenesis assays that media conditioned by bone marrow adipocytes is a significant source of CXCL1 and CXCL2 proteins. We also demonstrate that both the adipocyte-conditioned media and the recombinant CXCL1 and CXCL2 ligands efficiently accelerate osteoclast maturation, a process that can be blocked by neutralizing antibodies to each of the chemokines. We further confirm the contribution of CXCR2 signaling axis to adiposity-driven osteoclastogenesis by blocking fat cell-induced osteoclast differentiation with CXCR2 antagonist or neutralizing antibodies. Together, our results link CXCL1 and CXCL2 chemokines with bone marrow adiposity and implicate CXCR2 signaling in promoting effects of marrow fat on progression of skeletal tumors in bone.

Bone marrow adipocytes promote tumor growth in bone via FABP4-dependent mechanisms

Incidence of skeletal metastases and death from prostate cancer greatly increases with age and obesity, conditions which increase marrow adiposity. Bone marrow adipocytes are metabolically active components of bone metastatic niche that modulate the function of neighboring cells; yet the mechanisms of their involvement in tumor behavior in bone have not been explored. In this study, using experimental models of intraosseous tumor growth and diet-induced obesity, we demonstrate the promoting effects of marrow fat on growth and progression of skeletal prostate tumors. We reveal that exposure to lipids supplied by marrow adipocytes induces expression of lipid chaperone FABP4, pro-inflammatory interleukin IL-1β, and oxidative stress protein HMOX-1 in metastatic tumor cells and stimulates their growth and invasiveness. We show that FABP4 is highly overexpressed in prostate skeletal tumors from obese mice and in bone metastasis samples from prostate cancer patients. In addition, we provide results suggestive of bi-directional interaction between FABP4 and PPARγ pathways that may be driving aggressive tumor cell behavior in bone. Together, our data provide evidence for functional relationship between bone marrow adiposity and metastatic prostate cancers and unravel the FABP4/IL-1β axis as a potential therapeutic target for this presently incurable disease.

Role of SPARC in bone remodeling and cancer-related bone metastasis

There is a growing socioeconomic recognition that clinical bone diseases such as bone infections, bone tumors and osteoporotic bone loss mainly associated with ageing, are major issues in today's society. SPARC (secreted protein, acidic and rich in cysteine), a matricellular glycoprotein, may be a promising therapeutic target for preventing or treating bone-related diseases. In fact, SPARC is associated with tissue remodeling, repair, development, cell turnover, bone mineralization and may also participate in growth and progression of tumors, namely cancer-related bone metastasis. Yet, the function of SPARC in such biological processes is poorly understood and controversial. The main objective of this work is to review the current knowledge related to the activity of SPARC in bone remodeling, tumorigenesis, and bone metastasis. Progress in understanding SPARC biology may provide novel strategies for bone regeneration and the development of anti-angiogenic, anti-proliferative, or counter-adhesive treatments specifically against bone metastasis.

Inhibition of cathepsin activity in a cell-based assay by a light-activated ruthenium compound

Light-activated inhibition of cathepsin activity was demonstrated in a cell-based assay. Inhibitors of cathepsin K, Cbz-Leu-NHCH2 CN (2) and Cbz-Leu-Ser(OBn)-CN (3), were caged within the complexes cis-[Ru(bpy)2 (2)2 ]Cl2 (4) and cis-[Ru(bpy)2 (3)2 ](BF4 )2 (5) (bpy=2,2'-bipyridine) as 1:1 mixtures of Δ and Λ stereoisomers. Complexes 4 and 5 were characterized by (1) H NMR, IR, and UV/Vis spectroscopies and electrospray mass spectrometry. Photochemical experiments confirm that 4 releases two molecules of 2 upon exposure to visible light for 15 min, whereas release of 3 by 5 requires longer irradiation times. IC50 determinations against purified cathepsin K under light and dark conditions with 4 and 5 confirm that inhibition is enhanced from 35- to 88-fold, respectively, upon irradiation with visible light. No apparent toxicity was observed for 4 in the absence or presence of irradiation in bone marrow macrophage (BMM) or PC3 cells, as determined by MTT assays, at concentrations up to 10 μM. Compound 5 is well tolerated at lower concentrations (<1 μM), but does show growth-inhibitory effects at higher concentrations. Confocal microscopy experiments show that 4 decreases intracellular cathepsin activity in osteoclasts with light activation. These results support the further development of caged nitrile-based inhibitors as chemical tools for investigating spatial aspects of proteolysis within living systems.

Prostate cancer and bone: the elective affinities

The onset of metastases dramatically changes the prognosis of prostate cancer patients, determining increased morbidity and a drastic fall in survival expectancy. Bone is a common site of metastases in few types of cancer, and it represents the most frequent metastatic site in prostate cancer. Of note, the prevalence of tumor relapse to the bone appears to be increasing over the years, likely due to a longer overall survival of prostate cancer patients. Bone tropism represents an intriguing challenge for researchers also because the preference of prostate cancer cells for the bone is the result of a sequential series of targetable molecular events. Many factors have been associated with the peculiar ability of prostate cancer cells to migrate in bone marrow and to determine mixed osteoblastic/osteolytic lesions. As anticipated by the success of current targeted therapy aimed to block bone resorption, a better understanding of molecular affinity between prostate cancer and bone microenvironment will permit us to cure bone metastasis and to improve prognosis of prostate cancer patients.

Cysteine cathepsins and extracellular matrix degradation

BACKGROUND

Cysteine cathepsins are normally found in the lysosomes where they are involved in intracellular protein turnover. Their ability to degrade the components of the extracellular matrix in vitro was first reported more than 25years ago. However, cathepsins were for a long time not considered to be among the major players in ECM degradation in vivo. During the last decade it has, however, become evident that abundant secretion of cysteine cathepsins into extracellular milieu is accompanying numerous physiological and disease conditions, enabling the cathepsins to degrade extracellular proteins.

SCOPE OF VIEW

In this review we will focus on cysteine cathepsins and their extracellular functions linked with ECM degradation, including regulation of their activity, which is often enhanced by acidification of the extracellular microenvironment, such as found in the bone resorption lacunae or tumor microenvironment. We will further discuss the ECM substrates of cathepsins with a focus on collagen and elastin, including the importance of that for pathologies. Finally, we will overview the current status of cathepsin inhibitors in clinical development for treatment of ECM-linked diseases, in particular osteoporosis.

MAJOR CONCLUSIONS

Cysteine cathepsins are among the major proteases involved in ECM remodeling, and their role is not limited to degradation only. Deregulation of their activity is linked with numerous ECM-linked diseases and they are now validated targets in a number of them. Cathepsins S and K are the most attractive targets, especially cathepsin K as a major therapeutic target for osteoporosis with drugs targeting it in advanced clinical trials.

GENERAL SIGNIFICANCE

Due to their major role in ECM remodeling cysteine cathepsins have emerged as an important group of therapeutic targets for a number of ECM-related diseases, including, osteoporosis, cancer and cardiovascular diseases. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

The effect of catalase on migration and invasion of lung cancer cells by regulating the activities of cathepsin S, L, and K

Abundant clinical evidences indicate that up-regulation of several cathepsins in many human cancers is correlated with malignant progression and poor patient prognosis. In addition, a decrease in catalase activity or accumulation of hydrogen peroxide correlates with cancer metastasis. Recent studies indicate that cathepsin activation and expression can be modulated via H2O2 treatment. However, the actual relationship between catalase and cathepsins is not yet fully understood. In the present study, we found that catalase expression (or activity) was higher, while intracellular and extracellular Cat S, Cat L, and Cat K activities were lower in the non-invasive CL1-0 cells compared to the highly invasive CL1-5 cells. After CL1-0 cells were transfected with catalase-shRNA, the corresponding ROS (H2O2) level and Cat S, Cat L, or Cat K expression (or activity) was up-regulated, accompanied by an increase in cell migration and invasion. On the other hand, ROS (H2O2) level, cathepsin S, L, and K activities, cell migration and invasion were decreased in catalase-overexpressed CL1-5 cells. It is suggested that catalase may regulate cathepsin activity by controlling the production of ROS (H2O2), leading to variation in migration and invasion ability of lung cancer cells.

Effects of novel human cathepsin S inhibitors on cell migration in human cancer cells

Elevated cathepsin S (Cat S) level is correlated with higher migration ability in tumor cells. This study investigates the inhibitory effect of novel synthetic α-ketoamide compounds on cathepsin activity and cancer cell migration. The effect of several α-ketoamide compounds on the activity of recombinant cathepsins (Cat S, Cat L and Cat K) was examined. Two highly metastatic cancer cell lines were incubated with three Cat S-specific compounds (6n, 6 w and 6r) to analyze their effect on cellular Cat S activity and cell migration. At a 100 nM concentration, compounds 6n, 6r and 6 w effectively inhibited Cat S activity. Cat S activity and cell migration were significantly reduced in CL1-3 cells after treatment with either 6n or 6 w at 5 μM. Similar results were also obtained when A2058 cells were treated with 6n. These results highlight the therapeutic potential of α-ketoamide compounds, especially 6n and 6 w, to prevent or delay cancer metastasis.

Acidic extracellular microenvironment and cancer

Acidic extracellular pH is a major feature of tumor tissue, extracellular acidification being primarily considered to be due to lactate secretion from anaerobic glycolysis. Clinicopathological evidence shows that transporters and pumps contribute to H⁺ secretion, such as the Na⁺/H⁺ exchanger, the H⁺-lactate co-transporter, monocarboxylate transporters, and the proton pump (H⁺-ATPase); these may also be associated with tumor metastasis. An acidic extracellular pH not only activates secreted lysosomal enzymes that have an optimal pH in the acidic range, but induces the expression of certain genes of pro-metastatic factors through an intracellular signaling cascade that is different from hypoxia. In addition to lactate, CO₂ from the pentose phosphate pathway is an alternative source of acidity, showing that hypoxia and extracellular acidity are, while being independent from each other, deeply associated with the cellular microenvironment. In this article, the importance of an acidic extracellular pH as a microenvironmental factor participating in tumor progression is reviewed.

Osteoclast-specific cathepsin K deletion stimulates S1P-dependent bone formation

Cathepsin K (CTSK) is secreted by osteoclasts to degrade collagen and other matrix proteins during bone resorption. Global deletion of Ctsk in mice decreases bone resorption, leading to osteopetrosis, but also increases the bone formation rate (BFR). To understand how Ctsk deletion increases the BFR, we generated osteoclast- and osteoblast-targeted Ctsk knockout mice using floxed Ctsk alleles. Targeted ablation of Ctsk in hematopoietic cells, or specifically in osteoclasts and cells of the monocyte-osteoclast lineage, resulted in increased bone volume and BFR as well as osteoclast and osteoblast numbers. In contrast, targeted deletion of Ctsk in osteoblasts had no effect on bone resorption or BFR, demonstrating that the increased BFR is osteoclast dependent. Deletion of Ctsk in osteoclasts increased their sphingosine kinase 1 (Sphk1) expression. Conditioned media from Ctsk-deficient osteoclasts, which contained elevated levels of sphingosine-1-phosphate (S1P), increased alkaline phosphatase and mineralized nodules in osteoblast cultures. An S1P1,3 receptor antagonist inhibited these responses. Osteoblasts derived from mice with Ctsk-deficient osteoclasts had an increased RANKL/OPG ratio, providing a positive feedback loop that increased the number of osteoclasts. Our data provide genetic evidence that deletion of CTSK in osteoclasts enhances bone formation in vivo by increasing the generation of osteoclast-derived S1P.

Novel approaches in the pharmacotherapy of skeletal-related events in metastatic castrate-resistant prostate cancer

Biphosphonates have long been the standard of care for antiresorptive treatment of bone metastases from castrate-resistant prostate cancer (mCRPC). Although the indication has historically been mostly palliative, response rates in skeletal-related events (SRE) remain low. Denosumab has been shown to be effective in prolonging time to first SRE in clinical settings, however, critical questions remain on its ability to affect bone metastases in mCRPC. The landscape for research progress in reducing SREs using novel pharmacotherapies is growing rapidly, with several agents in clinical trials. This focused review outlines the most promising investigational drugs for treating bone metastases in mCRPC.

Macrophage cathepsin K promotes prostate tumor progression in bone

Bone marrow macrophages (BMMs) share common progenitors with osteoclasts and are critical components of bone-tumor microenvironment; however, their function in prostate tumor growth in the skeleton has not been explored. BMMs are the major source of inflammatory factors and proteases, including cysteine protease cathepsin K (CTSK). In this study, utilizing mice deficient in CTSK, we demonstrate the critical involvement of this potent collagenase in tumor progression in bone. We present the evidence that tumor growth and progression in the bone are impaired in the absence of CTSK. Most importantly, we show for the first time that BMM-supplied CTSK may be involved in CCL2- and COX-2-driven pathways that contribute to tumor progression in bone. Together, our data unravel novel roles for CTSK in macrophage-regulated processes, and provide evidence for close interplay between inflammatory, osteolytic and tumor cell-driven events in the bone-tumor microenvironment.

Bone matrix osteonectin limits prostate cancer cell growth and survival

There is considerable interest in understanding prostate cancer metastasis to bone and the interaction of these cells with the bone microenvironment. Osteonectin/SPARC/BM-40 is a collagen binding matricellular protein that is enriched in bone. Its expression is increased in prostate cancer metastases, and it stimulates the migration of prostate carcinoma cells. However, the presence of osteonectin in cancer cells and the stroma may limit prostate tumor development and progression. To determine how bone matrix osteonectin affects the behavior of prostate cancer cells, we modeled prostate cancer cell-bone interactions using the human prostate cancer cell line PC-3, and mineralized matrices synthesized by wild type and osteonectin-null osteoblasts in vitro. We developed this in vitro system because the structural complexity of collagen matrices in vivo is not mimicked by reconstituted collagen scaffolds or by more complex substrates, like basement membrane extracts. Second harmonic generation imaging demonstrated that the wild type matrices had thick collagen fibers organized into longitudinal bundles, whereas osteonectin-null matrices had thinner fibers in random networks. Importantly, a mouse model of prostate cancer metastases to bone showed a collagen fiber phenotype similar to the wild type matrix synthesized in vitro. When PC-3 cells were grown on the wild type matrices, they displayed decreased cell proliferation, increased cell spreading, and decreased resistance to radiation-induced cell death, compared to cells grown on osteonectin-null matrix. Our data support the idea that osteonectin can suppress prostate cancer pathogenesis, expanding this concept to the microenvironment of skeletal metastases.