Coexpression of bone sialoprotein (BSP) and the pivotal transcriptional regulator of osteogenesis, Cbfa1/Runx2, in malignant melanoma

Icariin stimulates osteogenesis and suppresses adipogenesis of human bone mesenchymal stem cells via miR-23a-mediated activation of the Wnt/β-catenin signaling pathway

BACKGROUND

Icariin (ICA) is a bioactive compound isolated from epimedium-derived flavonoids that modulates bone mesenchymal stem cell osteogenesis and adipogenesis. However, its precise mechanism in this process is unknown.

PURPOSE

The purpose of this study was to elucidate the role of ICA on human bone mesenchymal stem cell (hBMSC) osteogenesis and adipogenesis by focusing on miR-23a mediated activation of the Wnt/β-catenin signaling pathway.

METHODS

After ICA treatment, hBMSC osteogenesis and adipogenesis were evaluated using alkaline phosphatase staining, an alkaline phosphatase activity assay, Oil Red O staining, and cellular triglyceride levels. Moreover, the mRNA and protein expression levels of osteogenic and adipogenic markers as well as key factors of the Wnt/β-catenin signaling pathway were measured using quantitative reverse transcription polymerase chain reaction and western blotting. Lithium chloride, an activator of the Wnt/β-catenin signaling pathway, was used as a positive control. Finally, to investigate the role of miR-23a in ICA-induced activation of the Wnt/β-catenin signaling pathway, hBMSCs were transfected with miR-23a mimics or a miR-23a inhibitor.

RESULTS

ICA significantly promoted hBMSC osteogenic differentiation by upregulating alkaline phosphatase activity and the expression of bone sialoprotein II (BSPII) and runt-related transcription factor-2 (Runx-2). In contrast, ICA inhibited hBMSC adipogenic differentiation by reducing lipid droplet formation and cellular triglyceride levels as well as by downregulating the expression of peroxisome proliferator-activated receptor-γ (PPAR-γ) and CCAAT enhancer-binding protein-α (C/EBP-α). ICA mediated its effects on hBMSCs by activating the Wnt/β-catenin signaling pathway. It did so by upregulating β-catenin, low density lipoprotein receptor-related protein 5 (LRP5), and T cell factor 1 (TCF1). Notably, the up-regulation of these proteins was blocked by Dickkopf-related protein 1 (DKK1). Critically, the effects of ICA on hBMSCs were similar to that of the positive control, lithium chloride. Notably, ICA-induced activation of the Wnt/β-catenin signaling pathway was significantly attenuated following miR-23a up-regulation. Conversely, miR-23a downregulation affected hBMSCs in the same manner as ICA; i.e., it activated the Wnt/β-catenin signaling pathway.

CONCLUSION

ICA promotes and inhibits, respectively, hBMSC osteogenesis and adipogenesis via miR-23a-mediated activation of the Wnt/β-catenin signaling pathway.

Wrong place, wrong time: Runt-related transcription factor 2/SATB2 pathway in bone development and carcinogenesis

Upregulation or aberrant expression of genes such as special AT-rich sequence-binding protein 2 (SATB2) is necessary for normal cell differentiation and tissue development and is often associated with carcinogenesis and metastatic progression. SATB2 is a critical transcription factor for biological development of various specialized cell lineages, such as osteoblasts and neurons. The dysregulation of SATB2 expression has recently been associated with various types of cancer, while the mechanisms and pathways by which it mediates tumorigenesis are not well elucidated. Runt-related transcription factor 2 (RUNX2) is a master regulator for osteogenesis, and it shares common pathways with SATB2 to regulate bone development. Interestingly, these two transcription factors co-occur in several epithelial and mesenchymal cancers and are linked by multiple cancer-related proteins and microRNAs. This review examines the interactions between RUNX2 and SATB2 in a network necessary for normal bone development and the circumstances in which the expression of RUNX2 and SATB2 in the wrong place and time leads to carcinogenesis.

A Potential Role of RUNX2- RUNT Domain in Modulating the Expression of Genes Involved in Bone Metastases: An In Vitro Study with Melanoma Cells

Ectopic expression of RUNX2 has been reported in several tumors. In melanoma cells, the RUNT domain of RUNX2 increases cell proliferation and migration. Due to the strong link between RUNX2 and skeletal development, we hypothesized that the RUNT domain may be involved in the modulation of mechanisms associated with melanoma bone metastasis. Therefore, we evaluated the expression of metastatic targets in wild type (WT) and RUNT KO melanoma cells by array and real-time PCR analyses. Western blot, ELISA, immunofluorescence, migration and invasion ability assays were also performed. Our findings showed that the expression levels of bone sialoprotein (BSP) and osteopontin (SPP1) genes, which are involved in malignancy-induced hypercalcemia, were reduced in RUNT KO cells. In addition, released PTHrP levels were lower in RUNT KO cells than in WT cells. The RUNT domain also contributes to increased osteotropism and bone invasion in melanoma cells. Importantly, we found that the ERK/p-ERK and AKT/p-AKT pathways are involved in RUNT-promoted bone metastases. On the basis of our findings, we concluded that the RUNX2 RUNT domain is involved in the mechanisms promoting bone metastasis of melanoma cells via complex interactions between multiple players involved in bone remodeling.

Strontium‑containing α‑calcium sulfate hemihydrate promotes bone repair via the TGF‑β/Smad signaling pathway

Calcium phosphate-based bone substitutes have been widely used for bone repair, augmentation and reconstruction in bone implant surgery. While some of these substitutes have shown excellent biological efficacy, there remains a need to improve the performance of the current calcium phosphate-based bone substitutes. Strontium ions (Sr) can promote new osteogenesis, inhibit osteoclast formation and increase osteoconductivity. However, the therapeutic effect and mechanism of strontium-containing α-calcium sulfate hemihydrate (Sr-CaS) remains unclear. The present study created bone injuries in rats and treated the injuries with Sr-CaS. Then Cell Counting Kit-8, soft agar colony formation, flow cytometry, Transwell and Alizarin Red staining assays were performed to assess the bone cells for their proliferation, growth, apoptosis, invasion, and osteogenic differentiation abilities. The bone reconstructive states were measured by the microCT method, hematoxylin and eosin staining and Masson staining. Bone-related factors were analyzed by the reverse transcription-quantitative PCR assay; transforming growth factor (TGF)-β, mothers against decapentaplegic homolog (Smad)2/3 and β-catenin expression was measured by western blot analysis and osteocalcin (OCN) expression was assessed by immunohistochemistry. Sr-CaS did not significantly affect the proliferation and apoptosis of bone marrow stem cells (BMSCs), but did accelerate the migration and osteogenic differentiation of BMSCs in vitro. Sr-CaS promoted bone repair and significantly increased the values for bone mineral density, bone volume fraction, and trabecular thickness, but decreased trabecular spacing in vivo in a concentration-dependent manner. In addition, Sr-CaS dramatically upregulated the expression levels of genes associated with osteogenic differentiation (Runt-related transcription factor 2, Osterix, ALP, OCN and bone sialoprotein) both in vitro and in vivo. Sr-CaS also increased Smad2/3, TGF-β and phosphorylated-β-catenin protein expression in vitro and in vivo. These results indicated that materials that contain 5 or 10% Sr can improve bone defects by regulating the TGF-β/Smad signaling pathway.

Interleukin-8 promotes prostate cancer bone metastasis through upregulation of bone sialoprotein

The aim of the present study was to investigate whether interleukin-8 (IL-8) enhances the ability of prostate cancer bone metastasis by influencing the coding level of bone sialoprotein (BSP). Cultured prostate cancer cell lines LNCaP (androgen dependent) and DU145 (androgen independent) were divided into three groups: IL-8 treatment group; IL-8 receptor inhibitor (SB225002) treatment group; and control group. Western blotting and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were used to detect BSP protein and mRNA expression levels. Matrigel and bone adhesion experiments were used to detect the invasiveness of cancer cells and bone adhesion changes. Compared with the control group, western blotting and RT-qPCR results indicated that BSP protein and mRNA levels in LNCaP and DU145 were significantly upregulated following IL-8 treatment. Matrigel experiments indicated that following IL-8 treatment, the invasiveness of LNCaP and DU145 cells was significantly increased. The results of bone adhesion experiments indicated that following IL-8 treatment, the number of DU145 cells adhered to the surface of the bone was increased, compared with the control group. Following treatment of both cell lines with SB225002, western blotting and RT-qPCR results indicated that the expression levels of BSP protein and mRNA were significantly downregulated. Matrigel experiments indicated that following SB225002 treatment, the invasiveness of LNCaP and DU145 cells was significantly reduced. The number of DU145 cells adhered to the surface of the bone was reduced, compared with the untreated group. Therefore, IL-8 may promote prostate cancer bone metastasis by enhancing BSP regulation.

New Insights into the Runt Domain of RUNX2 in Melanoma Cell Proliferation and Migration

The mortality rate for malignant melanoma (MM) is very high, since it is highly invasive and resistant to chemotherapeutic treatments. The modulation of some transcription factors affects cellular processes in MM. In particular, a higher expression of the osteogenic master gene RUNX2 has been reported in melanoma cells, compared to normal melanocytes. By analyzing public databases for recurrent RUNX2 genetic and epigenetic modifications in melanoma, we found that the most common RUNX2 genetic alteration that exists in transcription upregulation is, followed by genomic amplification, nucleotide substitution and multiple changes. Additionally, altered RUNX2 is involved in unchecked pathways promoting tumor progression, Epithelial Mesenchymal Transition (EMT), and metastasis. In order to investigate further the role of RUNX2 in melanoma development and to identify a therapeutic target, we applied the CRISPR/Cas9 technique to explore the role of the RUNT domain of RUNX2 in a melanoma cell line. RUNT-deleted cells showed reduced proliferation, increased apoptosis, and reduced EMT features, suggesting the involvement of the RUNT domain in different pathways. In addition, del-RUNT cells showed a downregulation of genes involved in migration ability. In an in vivo zebrafish model, we observed that wild-type melanoma cells migrated in 81% of transplanted fishes, while del-RUNT cells migrated in 58%. All these findings strongly suggest the involvement of the RUNT domain in melanoma metastasis and cell migration and indicate RUNX2 as a prospective target in MM therapy.

Ectopic expression of the osteogenic master gene RUNX2 in melanoma Maria Teresa Valenti, Luca Dalle Carbonare, Monica Mottes

The transcription factor RUNX2 is the osteogenic master gene expressed in mesenchymal stem cells during osteogenic commitment as well as in pre-osteoblasts and early osteoblasts. However, RUNX2 is also ectopically expressed in melanoma and other cancers. Malignant melanoma (MM) is a highly metastatic skin cancer. The incidence of MM has increased considerably in the past half-century. The expression levels and mutation rates of genes such as BRAF, KIT, NRAS, PTEN, P53, TERT and MITF are higher in melanoma than in other solid malignancies. Additionally, transcription factors can affect cellular processes and induce cellular transformation since they control gene expression. Recently, several studies have identified alterations in RUNX2 expression. In particular, the regulation of KIT by RUNX2 and the increased expression of RUNX2 in melanoma specimens have been shown. Melanocytes, whose transformation results in melanoma, arise from the neural crest and therefore show “stemness” features. RUNX2 plays an important role in the re-activation of the MAPK and PI3K/AKT pathways, thus endowing melanoma cells with a high metastatic potential. In melanoma, the most frequent metastatic sites are the lung, liver, brain and lymph nodes. In addition, bone metastatic melanoma has been described. Notably, studies focusing on RUNX2 may contribute to the identification of an appropriate oncotarget in melanoma.

Cancer Secretome May Influence BSP and DSP Expression in Human Salivary Gland Cells

One of the biggest challenges in managing head and neck cancers, especially salivary gland cancers, is the identification of secreted biomarkers of the disease that can be evaluated noninvasively. A relevant source of enriched tumor markers could potentially be found in the tumor secretome. Although numerous studies have evaluated secretomes from various cancers, the influence of the cancer secretome derived from salivary gland cancers on the behavior of normal cells has not yet been elucidated. Our data indicate that secretome derived from salivary gland cancer cells can influence the expression of two potential biomarkers of oral cancer-namely, bone sialoprotein (BSP) and dentin sialoprotein (DSP)-in normal salivary gland cells. Using routine immunohistochemistry, immunofluorescence, and immunoblotting techniques, we demonstrate an enrichment of BSP and DSP in human salivary gland (HSG) cancer tissue, unique localizations of BSP and DSP in HSG cancer cells, and enriched expression of BSP and DSP in normal salivary gland cells exposed to a cancer secretome. The secretome domain of the cancer microenvironment could alter signaling cascades responsible for normal cell proliferation, migration, and invasion, thus enhancing cancer cell survival and the potential for cancer progression. The cancer secretome may be critical in maintaining and stimulating "cancer-ness," thus potentially promoting specific hallmarks of metastasis.

Different Methylation Patterns of RUNX2, OSX, DLX5 and BSP in Osteoblastic Differentiation of Mesenchymal Stem Cells

Objective

Runt-related transcription factor 2 (RUNX2) and osterix (OSX) as two specific osteoblast transcription factors and distal-less homeobox 5 (DLX5) as a non-specific one are of paramount importance in regulating osteoblast related genes including osteocalcin, bone sialoprotein (BSP), osteopontin and collagen type Iα1. The present study sets out to investigate whether epigenetic regulation of these genes is important in osteoblastic differentiation of mesenchymal stem cells (MSCs).

Materials and Methods

In this experimental study, MSCs were differentiated to osteoblasts under the influence of the osteogenic differentiation medium. DNA and RNA were extracted at days 0, 7, 14 and 21 from MSCs differentiating to osteoblasts. Promoter regions of RUNX2, OSX, DLX5 and BSP were analyzed by methylation-specific PCR (MSP). Gene expression was analyzed during osteoblastic differentiation by quantitative real-time polymerase chain reaction (PCR).

Results

MSP analysis revealed that promoter methylation status did not change in RUNX2, DLX5 and BSP during MSC osteoblastic differentiation. In contrast, OSX promoter showed a dynamic change in methylation pattern. Moreover, RUNX2, OSX, DLX5 and BSP promoter regions showed three different methylation patterns during MSC differentiation. Gene expression analyses confirmed these results.

Conclusion

The results show that in differentiation of MSCs to osteoblasts, epigenetic regulation of OSX may play a leading role.

RUNX2 is overexpressed in melanoma cells and mediates their migration and invasion

In the present study, we investigated the role of the transcription factor RUNX2 in melanomagenesis. We demonstrated that the expression of transcriptionally active RUNX2 was increased in melanoma cell lines as compared with human melanocytes. Using a melanoma tissue microarray, we showed that RUNX2 levels were higher in melanoma cells as compared with nevic melanocytes. RUNX2 knockdown in melanoma cell lines significantly decreased Focal Adhesion Kinase expression, and inhibited their cell growth, migration and invasion ability. Finally, the pro-hormone cholecalciferol reduced RUNX2 transcriptional activity and decreased migration of melanoma cells, further suggesting a role of RUNX2 in melanoma cell migration.

The role of acidic phosphoproteins in biomineralization

Biomineralization is the process by which living organisms deposit mineral in the extracellular matrix. In nature, almost 50% of biominerals are calcium-bearing minerals. In addition to calcium, we find biominerals formed from silica and magnetite. Calcium-containing biominerals could be either calcium phosphate as in apatite found in vertebrates or calcium carbonate as in calcite and aragonite found in many invertebrates. Since all biomineralization is matrix mediated, an understanding of the nature of the proteins involved is essential in elucidating its mechanism. This review will discuss some of the proteins involved in the process of biomineralization involving calcium. Two proteins, dentin matrix protein 1 and dentin phosphoprotein (Phosphophoryn) will serve as models for the vertebrate system, and two others - P16 and phosphodontin will serve as models for the invertebrate system.

The cancer-related transcription factor Runx2 modulates cell proliferation in human osteosarcoma cell lines

Runx2 regulates osteogenic differentiation and bone formation, but also suppresses pre-osteoblast proliferation by affecting cell cycle progression in the G(1) phase. The growth suppressive potential of Runx2 is normally inactivated in part by protein destabilization, which permits cell cycle progression beyond the G(1)/S phase transition, and Runx2 is again up-regulated after mitosis. Runx2 expression also correlates with metastasis and poor chemotherapy response in osteosarcoma. Here we show that six human osteosarcoma cell lines (SaOS, MG63, U2OS, HOS, G292, and 143B) have different growth rates, which is consistent with differences in the lengths of the cell cycle. Runx2 protein levels are cell cycle-regulated with respect to the G(1)/S phase transition in U2OS, HOS, G292, and 143B cells. In contrast, Runx2 protein levels are constitutively expressed during the cell cycle in SaOS and MG63 cells. Forced expression of Runx2 suppresses growth in all cell lines indicating that accumulation of Runx2 in excess of its pre-established levels in a given cell type triggers one or more anti-proliferative pathways in osteosarcoma cells. Thus, regulatory mechanisms controlling Runx2 expression in osteosarcoma cells must balance Runx2 protein levels to promote its putative oncogenic functions, while avoiding suppression of bone tumor growth.

Dentin phosphoprotein binds annexin 2 and is involved in calcium transport in rat kidney ureteric bud cells

Dentin phosphoprotein (DPP) is the most abundant noncollagenous protein in the dentin, where it plays a major role in the mineralization of dentin. However, we and others have shown that in addition to being present in the dentin, DPP is also present in nonmineralizing tissues like the kidney, lung, and salivary glands, where it conceivably has other functions such as in calcium transport. Because annexins have been implicated as calcium transporters, we examined the relationships between DPP and annexins. In this report, we show that DPP binds to annexin 2 and 6 present in a rat ureteric bud cell line (RUB1). Immunofluorescence studies show that annexin 2 and DPP colocalize in these cells. In addition, DPP and annexin 2 colocalize in the ureteric bud branches of embryonic metanephric kidney. In the RUB1 cells and ureteric bud branches of embryonic kidney, colocalization was restricted to the cell membrane. Studies on calcium influx into RUB cells show that in the presence of anti-DPP, there was a 40% reduction of calcium influx into these cells. We postulate that DPP has different functions in the kidney as compared with the odontoblasts. In the odontoblasts, its primary function is in the extracellular mineralization of dentin, whereas in the kidney it may participate in calcium transport.

High bone sialoprotein (BSP) expression correlates with increased tumor grade and predicts a poorer prognosis of high-grade glioma patients

Objectives

To investigate the expression and prognostic value of bone sialoprotein (BSP) in glioma patients.

Methods

We determined the expression of BSP using real-time RT-PCR and immunohistochemistry in tissue microarrays containing 15 normal brain and 270 glioma samples. Cumulative survival was calculated by the Kaplan-Meier method and analyzed by the log-rank test. Univariate and multivariate analyses were performed by the stepwise forward Cox regression model.

Results

Both BSP mRNA and protein levels were significantly elevated in high-grade glioma tissues compared with those of normal brain and low-grade glioma tissues, and BSP expression positively correlated with tumor grade (P<0.001). Univariate and multivariate analysis showed high BSP expression was an independent prognostic factor for a shorter progression-free survival (PFS) and overall survival (OS) in both grade III and grade IV glioma patients [hazard ratio (HR) = 2.549 and 3.154 for grade III glioma, and HR = 1.637 and 1.574 for grade IV glioma, respectively]. Patients with low BSP expression had a significantly longer median OS and PFS than those with high BSP expression. Small extent of resection and lineage of astrocyte served as independent risk factors of both shorter PFS and OS in grade III glioma patients; GBM patients without O⁶-methylguanine (O⁶-meG) DNA methyltransferase (MGMT) methylation and Karnofsky performance score (KPS) less than 70 points were related to poor prognosis. Lack of radiotherapy related to shorter OS but not affect PFS in both grade III and grade IV glioma patients.

Conclusion

High BSP expression occurs in a significant subset of high-grade glioma patients and predicts a poorer outcome. The study identifies a potentially useful molecular marker for the categorization and targeted therapy of gliomas.

SiRNA-mediated silencing of the RUNX2 gene inhibits proliferation and induces apoptosis in human gastric cancer cell line SGC7901

AIM: To detect the expression of runt-related transcription factor gene 2 (RUNX2) in human gastric cancer cell line SGC7901 and to investigate the influence of small interfering RNA (siRNA)-mediated silencing of the RUNX2 gene on the proliferation and apoptosis of SGC7901 cells.

METHODS: SGC7901 cells were divided into three groups: blank control group, negative control group (transfected with an empty vector), and experiment group (transfected with RUNX2 siRNA). After SGC7901 cells were transfected with RUNX2 siRNA, the mRNA and protein expression of RUNX2 was examined by RT-PCR and Western blot, respectively; cell proliferation was evaluated by MTT assay; and cell apoptosis was detected by flow cytometry (FCM).

RESULTS: Compared with cells of the blank control group, the expression of RUNX2 mRNA (0.27 ± 0.068 vs 0.45 ± 0.058, F = 75.6, P < 0.01) and protein (F = 123.8, P < 0.001) was down-regulated in cells transfected with RUNX2 siRNA. At 24, 48, and 72 h after transfection, the proliferation rates of SGC7901 cells transfected with RUNX2 siRNA were significantly lower than those of non-transfected cells (0.23 ± 0.039 vs 0.32 ± 0.012; 0.31 ± 0.037 vs 0.45 ± 0.074; 0.52 ± 0.021 vs 0.72 ± 0.006; F = 173.744, 14.012, 253.145; all P < 0.001). The apoptosis rate of SGC7901 cells transfected with RUNX2 siRNA was significantly higher than those of cells of the blank control group and negative control (45.65% ± 0.64% vs 4.46% ± 0.27%, 4.23% ± 0.33%, both P < 0.01).

CONCLUSION: RUNX2 expression was detected in SGC7901 cells. SiRNA-mediated silencing of the RUNX2 gene can inhibit proliferation and induce apoptosis in SGC7901 cells. RUNX2 may be a new gene therapy target for gastric cancer.

Gingival Osteogenic Melanoma in Two Dogs

Osteogenic melanoma is a rare variant of metaplastic malignant melanoma in human medicine and appears to be a similarly rare variant in dogs. Two dogs with oral malignant melanoma with neoplastic bone formation are reported in this study. Both tumors were characterized by malignant melanocytes that transitioned into neoplastic bone at the deep margins of the neoplasm. Immunohistochemical analysis revealed S100- and Melan-A–positive neoplastic cells adjacent to, and occasionally embedded within, an osteoid and chondroblastic matrix. Scattered clusters of neoplastic cells were also positive for osteocalcin. The findings indicate that in dogs, as in humans, neoplastic melanocytes have metaplastic potential and can be osteogenic.

Overexpression of bone sialoprotein leads to an uncoupling of bone formation and bone resorption in mice

The purpose of this study was to determine the effects of bone sialoprotein (BSP) overexpression in bone metabolism in vivo by using a homozygous transgenic mouse line that constitutively overexpresses mouse BSP cDNA driven by the cytomegalovirus (CMV) promoter. CMV-BSP transgenic (TG) mice and wildtype mice were weighed, and their length, BMD, and trabecular bone volume were measured. Serum levels of RANKL, osteocalcin, osteoprotegerin (OPG), TRACP5b, and PTH were determined. Bone histomorphometry, von Kossa staining, RT-PCR analysis, Western blot, MTS assay, in vitro mineralization assay, and TRACP staining were also performed to delineate phenotypes of this transgenic mouse line. Compared with wildtype mice, adult TG mice exhibit mild dwarfism, lower values of BMD, and lower trabecular bone volume. TG mice serum contained increased calcium levels and decreased PTH levels, whereas the levels of phosphorus and magnesium were within normal limits. TG mice serum also exhibited lower levels of osteoblast differentiation markers and higher levels of markers, indicating osteoclastic activity and bone resorption. H&E staining, TRACP staining, and bone histomorphometry showed that adult TG bones were thinner and the number of giant osteoclasts in TG mice was higher, whereas there were no significant alterations in osteoblast numbers between TG mice and WT mice. Furthermore, the vertical length of the hypertrophic zone in TG mice was slightly enlarged. Moreover, ex vivo experiments indicated that overexpression of BSP decreased osteoblast population and increased osteoclastic activity. Partly because of its effects in enhancing osteoclastic activity and decreasing osteoblast population, BSP overexpression leads to an uncoupling of bone formation and resorption, which in turn results in osteopenia and mild dwarfism in mice. These findings are expected to help the development of therapies to metabolic bone diseases characterized by high serum level of BSP.

Runx2 is expressed in human glioma cells and mediates the expression of galectin-3

Runx2 is a member of the Runx family of transcription factors (Runx1-3) with a restricted expression pattern. It has so far been detected predominantly in skeletal tissues where, inter alia, it regulates the expression of the beta-galactoside-specific lectin galectin-3. Here we show that, in contrast to Runx3, Runx1 and Runx2 are expressed in a variety of human glioma cells. Runx2 expression pattern in these cells correlated completely with that of galectin-3, but not with that of other galectins. A similar correlation in the expression pattern of galectin-3 and Runx2 transcripts was detected in distinct types of 70 primary neural tumors, such as glioblastoma multiforme, but not in others, such as gangliocytomas. In glioma cells, Runx2 is directly involved in the regulation of galectin-3 expression, as shown by RNAi and transcription factor binding assays demonstrating that Runx2 interacts with a Runx2-binding motif present in the human galectin-3 promoter. Knockdown of Runx2 was thus accompanied by a reduction of both galectin-3 mRNA and protein levels by at least 50%, dependent on the glial tumor cell line tested. Reverse transcriptase-polymerase chain reaction analyses, aimed at finding other potential target genes of Runx2 in glial tumor cells, revealed the presence of bone sialoprotein, osteocalcin, osteopontin, and osteoprotegerin. However, their expression patterns only partially overlap with that of Runx2. These data suggest a functional contribution of Runx-2-regulated galectin-3 expression to glial tumor malignancy.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Divergent differentiation in malignant melanomas: a review

The aim of this review was to document and discuss diagnostic problems associated with divergent differentiation ('metaplastic change') in malignant melanomas, defined as the development in these tumours of morphologically, immunohistochemically and/or ultrastructurally recognizable non-melanocytic cell or tissue components. Types of divergent differentiation reported in malignant melanoma include: fibroblastic/myofibroblastic, Schwannian and perineurial, smooth muscle, rhabdomyosarcomatous, osteocartilaginous, ganglionic and ganglioneuroblastic, neuroendocrine and probable epithelial. Divergent differentiation is certainly a rare phenomenon and, when it occurs, can be missed by unwary pathologists and lead to diagnostic uncertainty. A carefully chosen immunohistochemical panel and the input of electron microscopy can help to clarify the nature of the cellular differentiation of these tumours and lead to a correct final diagnosis. The clinical significance of such aberrations is uncertain, nor are the underlying mechanisms as yet well defined.

Regulatory roles of Runx2 in metastatic tumor and cancer cell interactions with bone

The three mammalian Runt homology domain transcription factors (Runx1, Runx2, Runx3) support biological control by functioning as master regulatory genes for the differentiation of distinct tissues. Runx proteins also function as cell context-dependent tumor suppressors or oncogenes. Abnormalities in Runx mediated gene expression are linked to cell transformation and tumor progression. Runx2 is expressed in mesenchymal linage cells committed to the osteoblast phenotype and is essential for bone formation. This skeletal transcription factor is aberrantly expressed at high levels in breast and prostate tumors and cells that aggressively metastasize to the bone environment. In cancer cells, Runx2 activates expression of bone matrix and adhesion proteins, matrix metalloproteinases and angiogenic factors that have long been associated with metastasis. In addition, Runx2 mediates the responses of cells to signaling pathways hyperactive in tumors, including BMP/TGFbeta and other growth factor signals. Runx2 forms co-regulatory complexes with Smads and other co-activator and co-repressor proteins that are organized in subnuclear domains to regulate gene transcription. These activities of Runx2 contribute to tumor growth in bone and the accompanying osteolytic disease, established by interfering with Runx2 functions in metastatic breast cancer cells. Inhibition of Runx2 in MDA-MB-231 cells transplanted to bone decreased tumorigenesis and prevented osteolysis. This review evaluates evidence that Runx2 regulates early metastatic events in breast and prostate cancers, tumor growth, and osteolytic bone disease. Consideration is given to the potential for inhibition of this transcription factor as a therapeutic strategy upstream of the regulatory events contributing to the complexity of metastasis to bone.

Expression and potential role of dentin phosphophoryn (DPP) in mouse embryonic tissues involved in epithelial-mesenchymal interactions and branching morphogenesis

Dentin sialophosphoprotein (DSPP) is synthesized in both mesenchyme and epithelium at varying stages of tooth development. At the tooth cap stage, corresponding to embryonic day (E) 13.5 of mouse embryonic life, the phosphophoryn (DPP) portion of DSPP was immunohistochemically localized to the enamel organ with intense staining of oral ectoderm but no expression in dental follicle mesenchyme. Surprisingly, DPP was also expressed in ureteric bud branches of embryonic metanephric kidney and alveolar epithelial buds of developing lung. Reverse transcriptase-polymerase chain reaction analysis verified the presence of DSPP mRNA with identical sequences in the tooth, lung, and kidney. The DSPP(-/-) mouse with ablated DPP expression in the teeth, also exhibited aberrant organogenesis in kidney and lung. In the kidney, malformed metanephric S-shaped bodies and increased mesenchymal apoptosis were observed. Inclusion of anti-DPP antibodies in organ culture of metanephroi, harvested from E13.5 wild-type mice, likewise resulted in altered ureteric bud morphogenesis, suggesting a role for DPP in epithelial-mesenchymal interactions in meristic tissues during embryonic development.

Bone sialoprotein enhances migration of bone marrow stromal cells through matrices by bridging MMP-2 to alpha(v)beta3-integrin

BMSCs migrate through matrix barriers and differentiate into osteoblasts. BSP enhances osteogenic cell migration through basement membrane and collagen matrices in vitro by localizing MMP-2 on the cell surface through alpha(v)beta(3)-integrin.

INTRODUCTION

The specific mechanisms by which bone marrow stromal cells (BMSCs) leave their primary sites, move through matrices encountered during homing to their site of final differentiation, and remove preexisting matrices in preparation for bone matrix production are not well understood.

MATERIALS AND METHODS

The enhanced migration of human osteoblast precursor cells through matrix barriers by bone sialoprotein (BSP) was studied by a modified Boyden-chamber assay. The bridging of normally soluble matrix metalloproteinase 2 (MMP-2) to the cell surface receptor, alpha(v)beta(3)-integrin, by BSP was analyzed by flow cytometry.

RESULTS

BSP enhanced the in vitro passage of BMSCs and pre-osteoblasts through matrix barriers (Matrigel and denatured type I collagen) in a dose-dependent manner. An intact ArgGlyAsp (RGD) was required in the BSP for enhanced migration through the barriers but was not sufficient, as shown by the inactivity of two other SIBLING (Small Integrin-Binding LIgand, N-linked Glycoprotein) family members, osteopontin and dentin matrix protein-1. The specificity of the BSP enhancement activity was apparently caused by this molecule's ability to bridge MMP-2 to the cell surfaces.

CONCLUSIONS

Pre-osteoblasts and their BMSC precursors may use MMP-2/BSP/integrin complexes to disrupt matrix barriers during migration to their final destinations in vivo.

Bone sialoprotein mediates the tumor cell-targeted prometastatic activity of transforming growth factor beta in a mouse model of breast cancer

Transforming growth factor betas (TGF-beta) play a dual role in carcinogenesis, functioning as tumor suppressors early in the process, and then switching to act as prometastatic factors in late-stage disease. We have previously shown that high molecular weight TGF-beta antagonists can suppress metastasis without the predicted toxicities. To address the underlying mechanisms, we have used the 4T1 syngeneic mouse model of metastatic breast cancer. Treatment of mice with a monoclonal anti-TGF-beta antibody (1D11) significantly suppressed metastasis of 4T1 cells to the lungs. When metastatic 4T1 cells were recovered from lungs of 1D11-treated and control mice, the most differentially expressed gene was found to be bone sialoprotein (Bsp). Immunostaining confirmed the loss of Bsp protein in 1D11-treated lung metastases, and TGF-beta was shown to regulate and correlate with Bsp expression in vitro. Functionally, knockdown of Bsp in 4T1 cells reduced the ability of TGF-beta to induce local collagen degradation and invasion in vitro, and treatment with recombinant Bsp protected 4T1 cells from complement-mediated lysis. Finally, suppression of Bsp in 4T1 cells reduced metastasis in vivo. We conclude that Bsp is a plausible mediator of at least some of the tumor cell-targeted prometastatic activity of TGF-beta in this model and that Bsp expression in metastases can be successfully suppressed by systemic treatment with anti-TGF-beta antibodies.

Expression of bone morphogenetic proteins and their associated molecules in ameloblastomas and adenomatoid odontogenic tumors

OBJECTIVE

To further clarify the roles of regulators of embryonic development, bone morphogenetic protein (BMPs) and their associated molecules, in oncogenesis and cytodifferentiation of odontogenic tumors, the expression of these regulator molecules were analyzed in epithelial odontogenic tumors as well as in tooth germs.

MATERIALS AND METHODS

Tooth germs, ameloblastomas, adenomatoid odontogenic tumors, and malignant ameloblastomas were examined by RT-PCR and immunohistochemistry for detection of BMP-2, -4, -7, BMP receptors I and II (BMPR-I, BMPR-II), core-binding factor alpha1 (CBFA1), and osterix.

RESULTS

mRNA expression of BMPs, BMPRs, CBFA1, and osterix was detected in all odontogenic tissues. Immunohistochemical reactivity for BMPs, BMPRs, and CBFA1 was detected in both epithelial and mesenchymal cells of tooth germs and epithelial odontogenic tumors. BMPs and BMPRs were evidently expressed in odontogenic epithelial cells in tooth germs and epithelial odontogenic tumors. Acanthomatous ameloblastomas showed increased BMP-7 reactivity in keratinizing cells. Nuclear CBFA1 expression was detected scatteredly in odontogenic epithelial cells in normal and neoplastic odontogenic tissues, as well as in some mesenchymal cells in tooth germs and in some stromal cells in epithelial odontogenic tumors. Ameloblastic carcinomas showed low reactivity for BMPs, BMPRs, and CBFA1.

CONCLUSION

BMPs and their associated molecules might play a role in cytodifferentiation of normal and neoplastic odontogenic epithelium via epithelial-mesenchymal interactions.

Cell cycle-dependent phosphorylation of the RUNX2 transcription factor by cdc2 regulates endothelial cell proliferation

RUNX2 is a member of the runt family of DNA-binding transcription factors. RUNX2 mediates endothelial cell migration and invasion during tumor angiogenesis and is expressed in metastatic breast and prostate tumors. Our published studies showed that RUNX2 DNA-binding activity is low during growth arrest, but elevated in proliferating endothelial cells. To investigate its role in cell proliferation and cell cycle regulation, RUNX2 was depleted in human bone marrow endothelial cells using RNA interference. Specific RUNX2 depletion inhibited DNA-binding activity as measured by electrophoretic mobility shift assay resulting in inhibition of cell proliferation. Cells were synchronized at the G(1)/S boundary with excess thymidine or in mitosis (M phase) with nocodazole. Endogenous or ectopic RUNX2 activity was maximal at late G(2) and during M phase. Inhibition of RUNX2 expression by RNA interference delayed entry into and exit out of the G(2)/M phases of the cell cycle. RUNX2 was coimmunoprecipitated with cyclin B1 in mitotic cells, which further supported a role for RUNX2 in cell cycle progression. Moreover, in vitro kinase assays using recombinant cdc2 kinase showed that RUNX2 was phosphorylated at Ser(451). The cdc2 inhibitor roscovitine dose dependently inhibited in vivo RUNX2 DNA-binding activity during mitosis and the RUNX2 mutant S451A exhibited lower DNA-binding activity and reduced stimulation of anchorage-independent growth relative to wild type RUNX2. These results suggest for the first time that RUNX2 phosphorylation by cdc2 may facilitate cell cycle progression possibly through regulation of G(2) and M phases, thus promoting endothelial cell proliferation required for tumor angiogenesis.

The Runx2 osteogenic transcription factor regulates matrix metalloproteinase 9 in bone metastatic cancer cells and controls cell invasion

The Runx2 (Cbfa1/AML3) transcription factor and matrix metalloproteinase 9 (MMP9) are key regulators of growth plate maturation and bone formation. The genes for both proteins are characteristic markers of breast and prostate cancer cells that metastasize to bone. Here we experimentally addressed the compelling question of whether Runx2 and MMP are functionally linked. By cDNA expression array analysis, we identified MMP9 as a novel downstream target of Runx2. Like that of MMP13, MMP9 expression is nearly depleted in Runx2 mutant mice. Chromatin immunoprecipitation and electrophoretic mobility shift assays revealed the recruitment of Runx2 to the MMP9 promoter. We show by mutational analysis that the Runx2 site mediates transactivation of the MMP9 promoter in osteoblasts (MC3T3-E1) and nonosseous (HeLa) cells. The overexpression of Runx2 by adenovirus delivery in nonmetastatic (MCF-7) and metastatic breast (MDA-MB-231) and prostate (PC3) cancer cell lines significantly increases the endogenous levels of MMP9. The knockdown of Runx2 by RNA interference decreases MMP9 expression, as well as that of other Runx2 target genes, including the genes for MMP13 and vascular endothelial growth factor. Importantly, we have demonstrated using a cell invasion assay that Runx2-regulated MMP9 levels are functionally related to the invasion properties of cancer cells. These results are consistent with Runx2 control of multiple genes that contribute to the metastatic properties of cancer cells and their activity in the bone microenvironment.

Bone marrow subendosteal microenvironment harbours functionally distinct haemosupportive stromal cell populations

In adult animals, bone marrow is the major site of blood cell production, which is controlled by interactions between the local stroma and blood cell progenitors. The endosteal/subendosteal environment comprises bone-lining and adjacent reticular cells and sustains haemopoietic stem cell (HSC) self-renewal, proliferation and differentiation. We have questioned the specific role of each of these stroma cells in controlling HSC fate. We have isolated two distinct stroma-cell populations containing subendosteal reticulocytes (F-RET) and osteoblasts (F-OST) from periosteum-free fragments of murine femurs by a two-step collagenase-digestion procedure. Both populations produce similar extracellular matrix (collagen I, laminin, fibronectin, decorin), except for collagen IV, which is low in F-OST. They also express osteogenic markers: osteopontin, osteonectin, bone sialoprotein and alkaline phosphatase (ALP). The quantity and activity of ALP are however higher in F-OST. When co-cultured with bone marrow mononuclear cells or lineage-negative haemopoietic progenitors, F-OST stroma induces low proliferation and high maintenance of early haemopoietic progenitors, whereas F-RET stroma induces high short-term proliferation and differentiation. Analysis by reverse transcription/polymerase chain reaction has revealed higher levels of Jagged-1 expression by F-OST cells than by the F-RET population. Thus, two adjacent stroma cells (subendosteal and endosteal) play distinct roles in controlling the stem-cell capacity and fate of HSC and probably contribute distinctly to HSC niche formation.

Insulin-like Growth Factor-1 Regulates Endogenous RUNX2 Activity in Endothelial Cells through a Phosphatidylinositol 3-Kinase/ERK-dependent and Akt-independent Signaling Pathway

Insulin-like growth factor-1 (IGF-1) is an angiogenic and oncogenic factor that activates signal transduction pathways involved in the expression of transcriptional regulators of tumorigenesis. RUNX2, a member of the Ig-loop family of transcription factors is expressed in vascular endothelial cells (EC) and regulates EC migration, invasion, and proliferation. Here we show that IGF-1 and its receptor regulate post-translational changes in RUNX2 to activate DNA binding in proliferating EC. The phosphatidylinositol 3-kinase (PI3K) inhibitor, LY294002, reduced both basal and IGF-1-stimulated RUNX2 DNA binding activity in the absence of changes in RUNX2 protein as did the overexpression of the phosphatidylinositol 3-phosphate phosphatase, confirming that PI3K signaling mediates RUNX2 activation. IGF-1 increased ERK1/2 activation, which was abrogated by the inhibition of PI3K, thus linking these two pathways in EC. Treatment with U0126, which inhibits ERK1/2 activation, reduced IGF-1-stimulated RUNX2 DNA binding without affecting RUNX2 protein levels. Overexpression of constitutively active MKK1 increased RUNX2 DNA binding and phosphorylation. No additive effects of PI3K or ERK inhibitors on DNA binding were evident. Surprisingly, these IGF-1-mediated effects on RUNX2 were not regulated by Akt phosphorylation, a common downstream target of PI3K, as determined by pharmacological or genetic inhibition. However, an inhibitor of the p21-activated protein kinase-1, glutathione S-transferase-Pak1-(83-149), inhibited both basal and IGF-1-stimulated RUNX2 DNA binding, suggesting that Pak1 mediates IGF-1 signaling to increase RUNX2 activity. These results indicate that the angiogenic growth factor, IGF-1, can regulate RUNX2 DNA binding through sequential activation of the PI3K/Pak1 and ERK1/2 signaling cascade.