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

Endothelial Twist1-PDGFB signaling mediates hypoxia-induced proliferation and migration of αSMA-positive cells

Remodeling of distal pulmonary arterioles (PAs) associated with marked accumulation of pulmonary artery smooth muscle cells (PASMCs) represents one of the major pathologic features of pulmonary hypertension (PH). We have reported that the transcription factor Twist1 mediates hypoxia-induced PH. However, the mechanism by which endothelial Twist1 stimulates SMC accumulation to distal PAs in PH remains unclear. Here, we have demonstrated that Twist1 overexpression increases the expression of platelet-derived growth factor (PDGFB) in human pulmonary arterial endothelial (HPAE) cells. Hypoxia upregulates the levels of Twist1 and PDGFB in HPAE cells. When we implant hydrogel supplemented with endothelial cells (ECs) on the mouse lung, these ECs form vascular lumen structures and hypoxia upregulates PDGFB expression and stimulates accumulation of αSMA–positive cells in the gel, while knockdown of endothelial Twist1 suppresses the effects. The levels of Twist1 and PDGFB are higher in PAE cells isolated from idiopathic pulmonary arterial hypertension (IPAH) patients compared to those from healthy controls. IPAH patient-derived PAE cells stimulate accumulation of αSMA–positive cells in the implanted gel, while Twist1 knockdown in PAE cells inhibits the effects. Endothelial Twist1-PDGFB signaling plays a key role in αSMA–positive cell proliferation and migration in PH.

Functions of Exogenous RUNX2 in Giant Cell Tumor of Bone In Vitro

OBJECTIVES

This research aimed to investigate the relative level of Runt-related transcription factor 2 (RUNX2) in giant cell tumor of bone (GCTB). Through the histopathological similarities between osteoporosis and GCTB, the biological functions of exogenous RUNXS were demonstrated in GCTB cell lines. This generated awareness of the molecular mechanism of the biogenesis and metastasis of GCTB, as well as showing the pathways and processes involved in this study. This research also expected to provide hints for the clinical treatment of patients with GCTB, to release the tumor burden and reduce the recurrence rate and metastasis of patients with this condition.

METHODS

The expression of RUNX2 in the tumors was verified by Western Blot, qRT-PCR and immunohistochemistry, compared with the normal tissues' adjacent tumors. Subsequently, the plasmids expressing RUNX2 were constructed, amplified and transfected into the 0404 cell line through transfection kits (0.4, 0.8, 1.6, 2.4 ng/μl). After that, the proliferation, migration, invasion, cellular viability and apoptosis of 0404 cell lines were examined by EDU assay, wound healing assay, transwell assay, annexin v staining, and CCK8 assay, respectively.

RESULTS

The messenger RNA (mRNA) level of RUNX2 in tumors was over 100 folds more than the normal tissues. The protein level of tumors upregulated 8.32(±4.41) folds relatively. After the transfection of RUNX2 overexpressed plasmids into the 0404 cell line, the mRNA level of RUNX2 increased approximately 530.11(±24.87), 1117.96(±77.68), 2835.09(±45.22) and 4781.51(±79.37) folds respectively, and the protein level was upregulated about 4.12(±1.15), 16.73(±1.63), 21.53(±2.41) and 23.39(±0.85) folds respectively. The proliferation of 0404 cells was inhibited by 2.13(±1.02)% of 1.6 ng/μl group and 3.03(±1.76)% of 2.4 ng/μl group. And the migration was inhibited about 45.56(±6.13)%, 50.79(±5.27)%, 63.15(±8.62)% and 93.90(±3.65)% respectively. The invasion was decreased about 14.49(±5.4)%, 37.02(±6.52)%, 42.24(±2.59)% and 48.97(±10.61)% respectively. Meanwhile, FITC Annexin V/PI apoptosis assay demonstrated that RUNX2 plasmids could promote apoptosis rate around 4.15(±0.27)%, 5.07(±0.27)%, 7.61(±0.45)% and 11.32(±1.02)% respectively, and CCK8 proved these plasmids could weaken cellular viability in a concentration-dependent manner with the time passing.

CONCLUSIONS

RUNX2 is highly expressed in giant cell tumors of bone. The RUNX2 overexpressed plasmids we constructed could be successfully transfected into 0404 cell line. Far more importantly, the exogenous RUNX2 can seriously block the biological functions of 0404 cell line in a concentration-dependent manner, including proliferation, translocation, invasion, cellular viability, and apoptosis. Meanwhile, the mechanism was hypothesized and discussed in the article.

MicroRNA-106b inhibits osteoclastogenesis and osteolysis by targeting RANKL in giant cell tumor of bone

Giant cell tumor (GCT) of bone consists of three major cell types: giant cells, monocytic cells, and stromal cells. From microarray analysis, we found that miR-106b was down-regulated in GCT clinical samples and further determined by fluorescence in situ hybridization. In addition, the expression of novel potential target of miR-106b, RANKL, was elevated in GCT along with previously determined targets in other tumors such as IL-8, MMP2 and TWIST. In a RANKL 3′UTR luciferase reporter assays, agomiR-106b repressed the luciferase activity and the effect was eliminated when the targeting site in the reporter was mutated, suggesting a direct regulation of miR-106b on RANKL mRNA. Moreover, overexpression of miR-106b in GCTSCs through TALEN-mediated site-specific knockin clearly inhibited osteoclastogenesis and osteolysis. By grafting the GCT onto the chick CAM, we confirmed the inhibitory effect of miR-106b on RANKL expression and giant cell formation. Furthermore, in an OVX mouse model, silencing of miR-106b increased RANKL protein expression and promoted bone resorption, while up-regulation of miR-106b inhibited bone resorption. These results suggest that miR-106b is a novel suppressor of osteolysis by targeting RANKL and some other cytokines, which indicates that miR-106b may be a potential therapeutic target for the treatment of GCT.

Epithelial to mesenchymal transition inducing transcription factors and metastatic cancer

The epithelial to mesenchymal transition (EMT) is an important step for the developmental process. Recent evidences support that EMT allows the tumor cells to acquire invasive properties and to develop metastatic growth characteristics. Some of the transcription factors, which are actively involved in EMT process, have a significant role in the EMT-metastasis linkage. A number of studies have reported that EMT-inducing transcription factors (EMT-TFs), such as Twist, Snail, Slug, and Zeb, are directly or indirectly involved in cancer cell metastasis through a different signaling cascades, including the Akt, signal transducer and activator of transcription 3 (STAT3), mitogen-activated protein kinase (MAPK) and Wnt pathways, with the ultimate consequence of the downregulation of E-cadherin and upregulation of metastatic proteins, such as N-cadherin, vimentin, matrix metalloproteinase (MMP)-2, etc. This review summarizes the update information on the association of EMT-TFs with cancer metastasis and the possible cancer therapeutics via targeting the EMT-TFs.

Twist: a molecular target in cancer therapeutics

Twist, the basic helix-loop-helix transcription factor, is involved in the process of epithelial to mesenchymal transitions (EMTs), which play an essential role in cancer metastasis. Overexpression of Twist or its promoter methylation is a common scenario in metastatic carcinomas. Twist is activated by a variety of signal transduction pathways, including Akt, signal transducer and activator of transcription 3, mitogen-activated protein kinase, Ras, and Wnt signaling. Activated Twist upregulates N-cadherin and downregulates E-cadherin, which are the hallmarks of EMT. Moreover, Twist plays an important role in some physiological processes involved in metastasis, like angiogenesis, invadopodia, extravasation, and chromosomal instability. Twist also protects cancer cells from apoptotic cell death. In addition, Twist is responsible for the stemness of cancer cells and the generation of drug resistance. Recently, targeting Twist has gained significant interests in cancer therapeutics. The inactivation of Twist by small RNA technology or chemotherapeutic approach has been proved successful. Moreover, several inhibitors which are antagonistic to the upstream or downstream molecules of Twist signaling pathways have also been identified. Development of potential treatment strategies by targeting Twist has a great promise in cancer therapeutics.

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.

Interleukin-27 expression modifies prostate cancer cell crosstalk with bone and immune cells in vitro

Prostate cancer is frequently associated with bone metastases, where the crosstalk between tumor cells and key cells of the bone microenvironment (osteoblasts, osteoclasts, immune cells) amplifies tumor growth. We have explored the potential of a novel cytokine, interleukin-27 (IL-27), for inhibiting this malignant crosstalk, and have examined the effect of autocrine IL-27 on prostate cancer cell gene expression, as well as the effect of paracrine IL-27 on gene expression in bone and T cells. In prostate tumor cells, IL-27 upregulated genes related to its signaling pathway while downregulating malignancy-related receptors and cytokine genes involved in gp130 signaling, as well as several protease genes. In both undifferentiated and differentiated osteoblasts, IL-27 modulated upregulation of genes related to its own signaling pathway as well as pro-osteogenic genes. In osteoclasts, IL-27 downregulated several genes typically involved in malignancy and also downregulated osteoclastogenesis-related genes. Furthermore, an osteogenesis-focused real-time PCR array revealed a more extensive profile of pro-osteogenic gene changes in both osteoblasts and osteoclasts. In T-lymphocyte cells, IL-27 upregulated several activation-related genes and also genes related to the IL-27 signaling pathway and downregulated several genes that could modulate osteoclastogenesis. Overall, our results suggest that IL-27 may be able to modify interactions between prostate tumor and bone microenvironment cells and thus could be used as a multifunctional therapeutic for restoring bone homeostasis while treating metastatic prostate tumors.

Regulators of skeletal development: a cluster analysis of 206 bone tumors reveals diagnostically useful markers

The molecules Indian hedgehog (IHH), SP7 (also known as osterix), sex-determining region Y-box 9 (SOX9), runt-related transcription factor 2 (RUNX2) and TWIST1 regulate the normal differentiation of osteo- and chondrogenic cells from precursors during skeletal development and remodeling. The aberrant function of the same molecules has been implicated in the pathogenesis of bone tumors. Preliminary studies suggest that antibodies against these molecules have practical, diagnostic or prognostic utility in tumors. However, a comprehensive analysis of the expression of these molecules in a large, diverse set of bone tumors has yet to be reported. The goals of this study were to compare the immunohistochemical profiles of IHH, SP7, SOX9, RUNX2 and TWIST1 among bone tumors and to determine the optimum panel for diagnostic utility. Tissue microarrays prepared from 206 undecalcified tumors (71 osteosarcomas, 26 osteoblastomas/osteoid osteomas, 50 giant cell tumors, 5 chondromyxoid fibromas and 54 chondroblastomas) were stained with antibodies to IHH, SP7, SOX9, RUNX2 and TWIST1. The stains were scored for intensity (0-3+) and distribution. The results were analyzed by cluster analysis. Optimum antibody panels for diagnostic sensitivity and specificity were calculated. Analysis revealed six main clusters that corresponded well to tumor types and suggested a close relationship between the stromal cells of giant cell tumor and the osteoblasts of osteosarcoma. The expression profile of chondromyxoid fibroma and chondroblastoma also suggested related differentiation. The distribution of osteoblastomas and osteoid osteomas was more heterogeneous. RUNX2, SOX9 and TWIST1 represented the most sensitive and specific immunohistochemical panel to distinguish among these diagnoses with the limitation that no result could discriminate between chondroblastoma and chondromyxoid fibroma. IHH and SP7 did not yield additional utility.

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.

A microRNA signature differentiates between giant cell tumor derived neoplastic stromal cells and mesenchymal stem cells

Giant cell tumor (GCT) derived stromal cells (GCTSCs) have been identified as the neoplastic cell population of GCTs. Within these stromal cells a subpopulation has been identified that shares several features with mesenchymal stem cells (MSCs) indicating that these neoplastic cells develop from MSCs. Although spontaneous transformations of MSC have already been observed in vitro and in vivo the underlying molecular mechanisms are poorly understood. As microRNAs are crucially involved in tumorigenesis and the modulation of stem cell fate and behavior, they represent promising candidates for the regulation of this process. Therefore, the aim of this study was the comparative analysis of the microRNA expression profiles of GCTSCs and MSCs in order to identify differentially expressed microRNAs and their target genes. We could identify a microRNA signature consisting of 26 differentially expressed microRNAs that perfectly separates these two cell types. One of the microRNAs with the most pronounced differences in expression levels was miR-224. We could confirm the already known regulation of the apoptosis inhibitor API5 by miR-224 and could further identify three novel miR-224 target genes (SMAD5, SLMAP, H3.3B). The involvement of these genes in the regulation of apoptosis resistance, proliferation, differentiation and the regulation of gene transcription suggests pivotal roles of these genes in the neoplastic transformation of MSCs during GCT development.