Evidence for the role of matrix metalloproteinase-13 in bone resorption by giant cell tumor of bone

Visfatin alters the cytokine and matrix-degrading enzyme profile during osteogenic and adipogenic MSC differentiation

OBJECTIVES

Age-related bone loss is associated with bone marrow adiposity. Adipokines (e.g., visfatin, resistin, leptin) are adipocyte-derived factors with immunomodulatory properties and might influence differentiation of bone marrow-derived mesenchymal stem cells (MSC) in osteoarthritis (OA) and osteoporosis (OP). Thus, the presence of adipokines and MMPs in bone marrow and their effects on MSC differentiation were analyzed.

METHODS

MSC and ribonucleic acid (RNA) were isolated from femoral heads after hip replacement surgery of OA or osteoporotic femoral neck fracture (FF) patients. Bone structural parameters were evaluated by microcomputed tomography (μCT). MSC were differentiated towards adipocytes or osteoblasts with/without adipokines. Gene expression (adipokines, bone marker genes, MMPs, TIMPs) and cytokine production was evaluated by realtime-polymerase chain reaction (realtime-PCR) and enzyme-linked immunosorbent assay (ELISA). Matrix mineralization was quantified using Alizarin red S staining.

RESULTS

μCT showed an osteoporotic phenotype of FF compared to OA bone (reduced trabecular thickness and increased ratio of bone surface vs volume of solid bone). Visfatin and leptin were increased in FF vs OA. Visfatin induced the secretion of IL-6, IL-8, and MCP-1 during osteogenic and adipogenic differentiation. In contrast to resistin and leptin, visfatin increased MMP2 and MMP13 during adipogenesis. In osteogenically differentiated cells, MMPs and TIMPs were reduced by visfatin. Visfatin significantly increased matrix mineralization during osteogenesis, whereas collagen type I expression was reduced.

CONCLUSION

Visfatin-mediated increase of matrix mineralization and reduced collagen type I expression could contribute to bone fragility. Visfatin is involved in impaired bone remodeling at the adipose tissue/bone interface through induction of proinflammatory factors and dysregulated MMP/TIMP balance during MSC differentiation.

Giant-cell tumor of bone with pathological evidence of blood vessel invasion

Giant cell tumor of bone is a rare but aggressive benign tumor that arises at the end of long tubular bones. The tumor rarely metastasizes; however, we report a case in which a giant cell tumor of bone presented with progressive pulmonary metastases. There has been no clear pathologic evidence of the definitive cause or route of metastasis. In our case, the primary tumor site was located in the left femur with pathological evidence of blood vessel invasion. The histological and pathological features of this entity are discussed in this letter to the editor.

Genome-Wide Transcriptome Profiling of the Neoplastic Giant Cell Tumor of Bone Stromal Cells by RNA Sequencing

Giant cell tumor of bone (GCTB) is the most common non-malignant primary bone tumor reported in Hong Kong. Failure of treatment in advanced GCTB with aggressive local recurrence remains a clinical challenge. In order to reveal the molecular mechanism underlying the pathogenesis of this tumor, we aimed to examine the transcriptome profiling of the neoplastic stromal cells of GCTB in this study. RNA-sequencing was performed on three GCTB stromal cell samples and one bone marrow-derived MSC sample and 174 differentially expressed genes (DEGs) were identified between these two cell types. The top five up-regulated genes are SPP1, F3, TSPAN12, MMP13, and LGALS3BP and further validated by qPCR and Western Blotting. Knockdown of SPP1 was found to induce RUNX2 and OPG expression in GCTB stromal cells but not the MSCs. Ingenuity pathway analysis (IPA) of the 174 DEGs revealed significant alternations in 23 pathways; variant calling analysis revealed 1915 somatic variants of 384 genes with high or moderate impacts. Interestingly, four canonical pathways were found overlapping in both analyses; from which VEGFA, CSF1, PLAUR, and F3 genes with somatic mutation were found up-regulated in GCTB stromal cells. The STRING diagram showed two main clusters of the DEGs; one cluster of histone genes that are down-regulated in GCTB samples and another related to osteoblast differentiation, angiogenesis, cell cycle progression, and tumor growth. The DEGs and somatic mutations found in our study warrant further investigation and validation, nevertheless, our study add new insights in the search for new therapeutic targets in treating GCTB. J. Cell. Biochem. 118: 1349-1360, 2017. © 2016 Wiley Periodicals, Inc.

Multiple myeloma-derived MMP-13 mediates osteoclast fusogenesis and osteolytic disease

Multiple myeloma (MM) cells secrete osteoclastogenic factors that promote osteolytic lesions; however, the identity of these factors is largely unknown. Here, we performed a screen of human myeloma cells to identify pro-osteoclastogenic agents that could potentially serve as therapeutic targets for ameliorating MM-associated bone disease. We found that myeloma cells express high levels of the matrix metalloproteinase MMP-13 and determined that MMP-13 directly enhances osteoclast multinucleation and bone-resorptive activity by triggering upregulation of the cell fusogen DC-STAMP. Moreover, this effect was independent of the proteolytic activity of the enzyme. Further, in mouse xenograft models, silencing MMP-13 expression in myeloma cells inhibited the development of osteolytic lesions. In patient cohorts, MMP-13 expression was localized to BM-associated myeloma cells, while elevated MMP-13 serum levels were able to correctly predict the presence of active bone disease. Together, these data demonstrate that MMP-13 is critical for the development of osteolytic lesions in MM and that targeting the MMP-13 protein - rather than its catalytic activity - constitutes a potential approach to mitigating bone disease in affected patients.

Bortezomib Inhibits Giant Cell Tumor of Bone through Induction of Cell Apoptosis and Inhibition of Osteoclast Recruitment, Giant Cell Formation, and Bone Resorption

Giant cell tumor of bone (GCTB) is a rare and highly osteolytic bone tumor that usually leads to an extensive bone lesion. The purpose of this study was to discover novel therapeutic targets and identify potential agents for treating GCTB. After screening the serum cytokine profiles in 52 GCTB patients and 10 normal individuals using the ELISA assay, we found that NF-κB signaling-related cytokines, including TNFα, MCP-1, IL1α, and IL17A, were significantly increased in GCTB patients. The results were confirmed by IHC that the expression and activity of p65 were significantly increased in GCTB patients. Moreover, all of the NF-κB inhibitors tested suppressed GCTB cell growth, and bortezomib (Velcade), a well-known proteasome inhibitor, was the most potent inhibitor in blocking GCTB cells growth. Our results showed that bortezomib not only induced GCTB neoplastic stromal cell (NSC) apoptosis, but also suppressed GCTB NSC-induced giant cell differentiation, formation, and resorption. Moreover, bortezomib specifically suppressed GCTB NSC-induced preosteoclast recruitment. Furthermore, bortezomib ameliorated GCTB cell-induced bone destruction in vivo As a result, bortezomib suppressed NF-κB-regulated gene expression in GCTB NSC apoptosis, monocyte migration, angiogenesis, and osteoclastogenesis. Particularly, the inhibitory effects of bortezomib were much better than zoledronic acid, a drug currently used in treating GCTB, in our in vitro experimental paradigms. Together, our results demonstrated that NF-κB signaling pathway is highly activated in GCTB, and bortezomib could suppress GCTB and osteolysis in vivo and in vitro, indicating that bortezomib is a potential agent in the treatment of GCTB. Mol Cancer Ther; 15(5); 854-65. ©2016 AACR.

Identification of differentially expressed genes and their subpathways in recurrent versus primary bone giant cell tumors

Giant cell tumor (GCT) of the bone is a benign but locally aggressive bone neoplasm with a strong tendency to develop local recurrent and metastatic disease. Thus, it provides a useful model system for the identification of biological mechanisms involved in bone tumor progression and metastasis. This study profiled 24 cases of recurrent versus primary bone GCT tissues using QuantiGene 2.0 Multiplex Arrays that included Human p53 80-Plex Panels and Human Stem Cell 80-Plex Panels. A total of 32 differentially expressed genes were identified, including the 20 most upregulated genes and the 12 most downregulated genes in recurrent GCT. The genes identified are related to cell growth, adhesion, apoptosis, signal transduction and bone formation. Furthermore, iSubpathwayMiner analyses were performed to identify significant biological pathway regions (subpathway) associated with this disease. The pathway analysis identified 11 statistically significant enriched subpathways, including pathways in cancer, p53 signaling pathway, osteoclast differentiation pathway and Wnt signaling pathway. Among these subpathways, four genes (IGF1, MDM2, STAT1 and RAC1) were presumed to play an important role in bone GCT recurrence. The differentially expressed MDM2 protein was immunohistochemically confirmed in the recurrent versus primary bone GCT tissues. This study identified differentially expressed genes and their subpathways in recurrent GCT, which may serve as potential biomarkers for the prediction of GCT recurrence.

MiR-126-5p regulates osteoclast differentiation and bone resorption in giant cell tumor through inhibition of MMP-13

Giant cell tumor (GCT) of bone is an aggressive skeletal tumor characterized by localized bone resorption. Matrix metalloproteinase-13 (MMP-13) is the principal proteinase expressed by the stromal cells of GCT (GCTSCs) and also considered to play a crucial role in formation of the osteolytic lesion in GCT. However, the exact mechanism of the regulation of MMP-13 expression in GCTSCs was unknown. In this study, we identified miR-126-5p was significantly downregulated in GCTSCs and affect osteoclast (OC) differentiation and bone resorption by repressing MMP-13 expression at the post-transcriptional level. Thus, our studies show that miR-126-5p plays an important physiological role in multinucleated giant cell formation and osteolytic lesion in GCT.

Parathyroid hormone-related protein (PTHrP) modulates adhesion, migration and invasion in bone tumor cells

Parathyroid-hormone-related protein (PTHrP) has been shown to be an important factor in osteolysis in the setting of metastatic carcinoma to the bone. However, PTHrP may also be central in the setting of primary bone tumors. Giant cell tumor of bone (GCT) is an aggressive osteolytic bone tumor characterized by osteoclast-like giant cells that are recruited by osteoblast-like stromal cells. The stromal cells of GCT are well established as the only neoplastic element of the tumor, and we have previously shown that PTHrP is highly expressed by these cells both in vitro and in vivo. We have also found that the stromal cells exposed to a monoclonal antibody to PTHrP exhibited rapid plate detachment and quickly died in vitro. Therefore, PTHrP may serve in an autocrine manner to increase cell proliferation and promote invasive properties in GCT. The purpose of this study was to use transcriptomic microarrays and functional assays to examine the effects of PTHrP neutralization on cell adhesion, migration and invasion. Microarray and proteomics data identified genes that were differentially expressed in GCT stromal cells under various PTHrP treatment conditions. Treatment of GCT stromal cells with anti-PTHrP antibodies showed a change in the expression of 13 genes from the integrin family relative to the IgG control. Neutralization of PTHrP reduced cell migration and invasion as evidenced by functional assays. Adhesion and anoikis assays demonstrated that although PTHrP neutralization inhibits cell adhesion properties, cell detachment related to PTHrP neutralization did not result in associated cell death, as expected in mesenchymal stromal cells. Based on the data presented herein, we conclude that PTHrP excreted by GCT stromal cells increases bone tumor cell local invasiveness and migration.

Myofibroblastic differentiation of stromal cells in giant cell tumor of bone: an immunohistochemical and ultrastructural study

The nature of the mononuclear stromal cells (MSCs) in giant cell tumor of bone (GCTB) has not been thoroughly investigated. The purpose of this study was to evaluate the degree and significance of myofibroblastic differentiation in 18 cases of GCTB by immunohistochemistry (IH) and/or electron microscopy (EM). All immunostained cases were found positive for smooth muscle actin (SMA) and/or muscle specific actin (MSA), most in 1-33% of the MSCs. Ultrastructurally, most MSCs were fibroblasts, and a significant number of cells displayed myofibroblastic differentiation. Myofibroblasts are an important component of MSCs in GCTB. The myofibroblastic population may be responsible in part for the production of matrix metalloproteinases (MMPs), which probably play a role in bone destruction, tumor aggression, and recurrence.

ETV5 as a regulator of matrix metalloproteinase 2 in human chondrosarcoma

Chondrosarcoma is a unique type of bone cancer in that it does not respond to chemotherapy or radiation therapy, and therefore many affected patients die from metastatic disease. Metastasis has been correlated with the upregulation of the matrix metalloproteinase (MMP) family of proteases, which can degrade extracellular components. ETV5 is a transcription factor which has shown to be overexpressed in various types of invasive tumors. We hypothesized that ETV5 regulates MMP2 in human chondrosarcoma with the protease acting as a downstream effector. Gene knock-down of ETV5 in human chondrosarcoma cells reduces MMP2 mRNA expression as well as decreased protein production and significantly decreased MMP2 activity. With plasmid transfected ETV5 upregulation, MMP2 expression is similarly upregulated at the gene expression and protein levels. Data from our bone resorption studies revealed that when a matrix metalloproteinase-2 inhibitor is added to the growth media of chondrosarcoma cells, collagen released from bone chips incubated with the cells decreased by 27%. This data suggests that ETV5 has a significant role in regulating MMP2 expression and therefore matrix resorption in human chondrosarcoma, and thus may be a targetable upstream effector of the metastatic cascade in this cancer.

Giant cell tumor of bone: a basic science perspective

Comprehending the pathogenesis of giant cell tumor of bone (GCT) is of critical importance for developing novel targeted treatments for this locally-aggressive primary bone tumor. GCT is characterized by the presence of large multinucleated osteoclast-like giant cells distributed amongst mononuclear spindle-like stromal cells and other monocytes. The giant cells are principally responsible for the extensive bone resorption by the tumor. However, the spindle-like stromal cells chiefly direct the pathology of the tumor by recruiting monocytes and promoting their fusion into giant cells. The stromal cells also enhance the resorptive ability of the giant cells. This review encompasses many of the attributes of GCT, including the process of giant cell formation and the mechanisms of bone resorption. The significance of the receptor activator of nuclear factor-κB ligand (RANKL) in the development of GCT and the importance of proteases, including numerous matrix metalloproteinases, are highlighted. The mesenchymal lineage of the stromal cells and the origin of the hematopoietic monocytes are also discussed. Several aspects of GCT that require further understanding, including the etiology of the tumor, the mechanisms of metastases, and the development of an appropriate animal model, are also considered. By exploring the current status of GCT research, this review accentuates the significant progress made in understanding the biology of the tumor, and discusses important areas for future investigation.

Investigation of FGFR2-IIIC signaling via FGF-2 ligand for advancing GCT stromal cell differentiation

Giant cell tumor of bone (GCT) is an aggressive bone tumor consisting of multinucleated osteoclast-like giant cells and proliferating osteoblast-like stromal cells. The signaling mechanism involved in GCT stromal cell osteoblastic differentiation is not fully understood. Previous work in our lab reported that GCT stromal cells express high levels of TWIST1, a master transcription factor in skeletal development, which in turn down-regulates Runx2 expression and prevents terminal osteoblastic differentiation in these cells. The purpose of this study was to determine the upstream regulation of TWIST1 in GCT cells. Using GCT stromal cells obtained from patient specimens, we demonstrated that fibroblast growth factor receptor (FGFR)-2 signaling plays an essential role in bone development and promotes differentiation of immature osteoblastic cells. Fibroblast growth factor (FGF)-2 stimulates FGFR-2 expression, resulting in decreased TWIST1 expression and increased Runx2, alkaline phosphastase (ALP) and osteopontin (OPN) expression. Inhibition of FGFR-2 through siRNA decreased the expression of ALP, Runx2 and OPN in GCT stromal cells. Our study also confirmed that FGF-2 ligand activates downstream ERK1/2 signaling and pharmacological inhibition of the ERK1/2 signaling pathway suppresses FGF-2 stimulated osteogenic differentiation in these cells. Our results indicate a significant role of FGFR-2 signaling in osteoblastic differentiation in GCT stromal cells.

Transcriptomic and proteomic analyses in bone tumor cells: Deciphering parathyroid hormone-related protein regulation of the cell cycle and apoptosis

Giant cell tumor of bone (GCT) is an aggressive skeletal tumor characterized by local bone destruction, high recurrence rates, and metastatic potential. Previous works in our laboratory, including functional assays, have shown that neutralization of parathyroid hormone-related protein (PTHrP) in the cell environment inhibits cell proliferation and induces cell death in GCT stromal cells, indicating a role for PTHrP in cell propagation and survival. The objective of this study was to investigate the global gene and protein expression patterns of GCT cells in order to identify the underlying pathways and mechanisms of neoplastic proliferation provided by PTHrP in the bone microenvironment. Primary stromal cell cultures from 10 patients with GCT were used in this study. Cells were exposed to optimized concentrations of either PTHrP peptide or anti-PTHrP neutralizing antiserum and were analyzed with both cDNA microarray and proteomic microarray assays in triplicate. Hierarchical clustering and principal component analyses confirmed that counteraction of PTHrP in GCT stromal cells results in a clear-cut gene expression pattern distinct from all other treatment groups and the control cell line human fetal osteoblast (hFOB). Multiple bioinformatics tools were used to analyze changes in gene/protein expression and identify important gene ontologies and pathways common to this anti-PTHrP-induced regulatory gene network. PTHrP neutralization interferes with multiple cell survival and apoptosis signaling pathways by triggering both death receptors and cell cycle-mediated apoptosis, particularly via the caspase pathway, TRAIL pathway, JAK-STAT signaling pathway, and cyclin E/CDK2-associated G1/S cell cycle progression. These findings indicate that PTHrP neutralization exhibits anticancer potential by regulating cell-cycle progression and apoptosis in bone tumor cells, with the corollary being that PTHrP is a pro-neoplastic factor that can be targeted in the treatment of bone tumors.

Stro-1(+) stromal cells have stem-like features in giant cell tumor of bone

BACKGROUND

Giant cell tumor of bone (GCTB) is an aggressive benign bone tumor with poor prognosis whose neoplastic component is stromal cells (SCs). Tumor stem-like cells (TSCs) have been demonstrated as precursors for tumor genesis and growth. The aim of this study is to identify TSCs in GCTB.

METHODS

Stro-1(+) and Stro-1(-) cells were isolated by fluorescence-activated cell sorting (FACS). Stem-like properties of both Stro-1(+) and Stro-1(-) subpopulations were assessed using MTT colorimetric assays, cell cycle analyses, sphere formation assays, and differentiation assays. Molecular profiles were analyzed by flow cytometry, immunofluorescence, and qRT-PCR.

RESULTS

The existence of rare Stro-1(+) cells was confirmed in vitro using FACS and in vivo by immunohistochemistry. These Stro-1(+) cells exhibited higher proliferative and cisplatin-resistant potentials than Stro-1(-) cells. In serum-free suspension cultures, Stro-1(+) SCs could form cell spheres and maintain self-renewal. Furthermore, Stro-1(+) SCs could differentiate into two mesenchymal lineage cells: osteoblasts and adipocytes. Cell surface markers CD44, CD117, and CD133 and stem cell-associated genes OCT3/4, NANOG, and ABCG2 were significantly higher in the Stro-1(+) subpopulation.

CONCLUSIONS

This study demonstrates that Stro-1(+) SCs in GCTB possess stem-like biological and molecular phenotypes, indicating that they are the TSCs of GCTB.

The role of TWIST as a regulator in giant cell tumor of bone

Giant cell tumor of bone (GCT) is an aggressive tumor consisting of multinucleated osteoclast-like giant cells and proliferating osteoblast-like stromal cells. Our group has reported that the stromal cells express high levels of the bone resorbing matrix metalloproteinase (MMP)-13, and that this expression is regulated by the osteoblast transcription factor Runx2. The purpose of this study was to determine the upstream regulation of Runx2 in GCT cells. Using GCT stromal cells obtained from patient specimens, we demonstrated that TWIST, a master osteogenic regulator, was highly expressed in all GCT specimens. TWIST overexpression downregulated Runx2 expression whereas TWIST siRNA knockdown resulted in Runx2 and MMP-13 upregulation. Interestingly, cells obtained from a GCT lung metastasis showed a reverse regulatory pattern between TWIST and Runx2. In mutational analysis, we revealed a point mutation (R154S) at the Helix2 domain of TWIST. This TWIST mutation may be an essential underlying factor in the development and pathophysiology of these tumors in that they lead to inappropriate TWIST downregulation of Runx2, arrested osteoblastic differentiation, and the maintenance of an immature and neoplastic phenotype.

PTHrP induces autocrine/paracrine proliferation of bone tumor cells through inhibition of apoptosis

Giant Cell Tumor of Bone (GCT) is an aggressive skeletal tumor characterized by local bone destruction, high recurrence rates and metastatic potential. Previous work in our lab has shown that the neoplastic cell of GCT is a proliferating pre-osteoblastic stromal cell in which the transcription factor Runx2 plays a role in regulating protein expression. One of the proteins expressed by these cells is parathryroid hormone-related protein (PTHrP). The objectives of this study were to determine the role played by PTHrP in GCT of bone with a focus on cell proliferation and apoptosis. Primary stromal cell cultures from 5 patients with GCT of bone and one lung metastsis were used for cell-based experiments. Control cell lines included a renal cell carcinoma (RCC) cell line and a human fetal osteoblast cell line. Cells were exposed to optimized concentrations of a PTHrP neutralizing antibody and were analyzed with the use of cell proliferation and apoptosis assays including mitochondrial dehydrogenase assays, crystal violet assays, APO-1 ELISAs, caspase activity assays, flow cytometry and immunofluorescent immunohistochemistry. Neutralization of PTHrP in the cell environment inhibited cell proliferation in a consistent manner and induced apoptosis in the GCT stromal cells, with the exception of those obtained from a lung metastasis. Cell cycle progression was not significantly affected by PTHrP neutralization. These findings indicate that PTHrP plays an autocrine/paracrine neoplastic role in GCT by allowing the proliferating stromal cells to evade apoptosis, possibly through non-traditional caspase-independent pathways. Thus PTHrP neutralizing immunotherapy is an intriguing potential therapeutic strategy for this tumor.

AP-1 as a Regulator of MMP-13 in the Stromal Cell of Giant Cell Tumor of Bone

Matrix-metalloproteinase-13 (MMP-13) has been shown to be an important protease in inflammatory and neoplastic conditions of the skeletal system. In particular, the stromal cells of giant cell tumor of bone (GCT) express very high levels of MMP-13 in response to the cytokine-rich environment of the tumor. We have previously shown that MMP-13 expression in these cells is regulated, at least in part, by the RUNX2 transcription factor. In the current study, we identify the expression of the c-Fos and c-Jun elements of the AP-1 transcription factor in these cells by protein screening assays and real-time PCR. We then used siRNA gene knockdown to determine that these elements, in particular c-Jun, are upstream regulators of MMP-13 expression and activity in GCT stromal cells. We conclude that there was no synergy found between RUNX2 and AP-1 in the regulation of the MMP13 expression and that these transcription factors may be independently regulated in these cells.