Identification of a novel response element in the rat bone sialoprotein (BSP) gene promoter that mediates constitutive and fibroblast growth factor 2-induced expression of BSP

Nuclear action of FGF members in endocrine-related tissues and cancer: Interplay with steroid receptor pathways

Dysregulation of the fibroblast growth factors/fibroblast growth factor receptor (FGF/FGFR) pathway has been implicated in a wide range of human disorders and several members have been localized in the nuclear compartment. Hormone-activated steroid receptors or ligand independent activated receptors form nuclear complexes that activate gene transcription. This review aims to highlight the interplay between the steroid receptor and the FGF/FGFR pathways and focuses on the current knowledge on nuclear action of FGF members in endocrine-related tissues and cancer. The nuclear trafficking and targets of FGF/FGFR members and the available evidence on the interplay with steroid hormones and receptors is described. Finally, the data on aberrant FGF/FGFR signaling is summarized and the nuclear action of FGF members on endocrine resistant breast cancer is highlighted. Identifying the mechanisms underlying FGF-induced endocrine resistance will be important to understand how to efficiently target endocrine-related diseases and even enhance or restore endocrine sensitivity in hormone receptor positive tumors.

Canonical FGFs Prevent Osteogenic Lineage Commitment and Differentiation of Human Bone Marrow Stromal Cells Via ERK1/2 Signaling

Controlling the adipo-osteogenic lineage decision of trabecular human bone marrow stromal cells (hBMSCs) in favor of osteogenesis represents a promising approach for osteoporosis therapy and prevention. Previously, Fibroblast Growth Factor 1 (FGF1) and its subfamily member FGF2 were scored as leading candidates to exercise control over skeletal precursor commitment and lineage decision albeit literature results are highly inconsistent. We show here that FGF1 and 2 strongly prevent the osteogenic commitment and differentiation of hBMSCs. Mineralization of extracellular matrix (ECM) and mRNA expression of osteogenic marker genes Alkaline Phosphatase (ALP), Collagen 1A1 (COL1A1), and Integrin-Binding Sialoprotein (IBSP) were significantly reduced. Furthermore, master regulators of osteogenic commitment like Runt-Related Transcription Factor 2 (RUNX2) and Bone Morphogenetic Protein 4 (BMP4) were downregulated. When administered under adipogenic culture conditions, canonical FGFs did not support osteogenic marker expression. Moreover despite the presence of osteogenic differentiation factors, FGFs even disabled the pro-osteogenic lineage decision of pre-differentiated adipocytic cells. In contrast to FGF Receptor 2 (FGFR2), FGFR1 was stably expressed throughout osteogenic and adipogenic differentiation and FGF addition. Moreover, FGFR1 and Extracellular Signal-Regulated Kinases 1 and 2 (ERK1/2) were found to be responsible for underlying signal transduction using respective inhibitors. Taken together, we present new findings indicating that canonical FGFR-ERK1/2 signaling entrapped hBMSCs in a pre-committed state and arrested further maturation of committed precursors. Our results might aid in unraveling and controlling check points relevant for ageing-associated aberrant adipogenesis with consequences for the treatment of degenerative diseases such as osteoporosis and for skeletal tissue engineering strategies. J. Cell. Biochem. 118: 263-275, 2017. © 2016 Wiley Periodicals, Inc.

Activation of intracellular calcium signaling in osteoblasts colocalizes with the formation of post-yield diffuse microdamage in bone matrix

Previous studies demonstrated that extracellular calcium efflux ([Ca(2+)]E) originates from the regions of bone extracellular matrix that are undergoing microdamage. Such [Ca(2+)]E is reported to induce the activation of intracellular calcium signaling ([Ca(2+)]I) in MC3T3-E1 cells. The current study investigated the association between microdamage and local activation of intracellular calcium signaling quantifiably in MC3T3-E1 cells. Cells were seeded on devitalized notched bovine bone samples to induce damage controllably within the field of observation. A sequential staining procedure was implemented to stain for intracellular calcium activation followed by staining for microdamage on the same sample. The increase in [Ca(2+)]I fluorescence in cells of mechanically loaded samples was greater than that of unloaded negative control cells. The results showed that more than 80% of the cells with increased [Ca(2+)]I fluorescence were located within the damage zone. In conclusion, the findings demonstrate that there are spatial proximity between diffuse microdamage induction and the activation of intracellular calcium ([Ca(2+)]I) signaling in MC3T3-E1 cells. The downstream responses to the observed activation in future research may help understand how bone cells repair microdamage.

A Clinical Indications Prediction Scale Based on TWIST1 for Human Mesenchymal Stem Cells

In addition to their stem/progenitor properties, mesenchymal stem cells (MSCs) also exhibit potent effector (angiogenic, antiinflammatory, immuno-modulatory) functions that are largely paracrine in nature. It is widely believed that effector functions underlie most of the therapeutic potential of MSCs and are independent of their stem/progenitor properties. Here we demonstrate that stem/progenitor and effector functions are coordinately regulated at the cellular level by the transcription factor Twist1 and specified within populations according to a hierarchical model. We further show that manipulation of Twist1 levels by genetic approaches or by exposure to widely used culture supplements including fibroblast growth factor 2 (Ffg2) and interferon gamma (IFN-gamma) alters MSC efficacy in cell-based and in vivo assays in a predictable manner. Thus, by mechanistically linking stem/progenitor and effector functions our studies provide a unifying framework in the form of an MSC hierarchy that models the functional complexity of populations. Using this framework, we developed a CLinical Indications Prediction (CLIP) scale that predicts how donor-to-donor heterogeneity and culture conditions impact the therapeutic efficacy of MSC populations for different disease indications.

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Mesenchymal stem cells exhibit stem/progenitor and effector (angiogenic, anti-inflammatory, immuno-modulatory) functions.

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Twist1 coordinately regulates stem/progenitor and effector functions, which are specified hierarchically in populations.

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Twist1 levels predict inter-population differences in therapeutic efficacy of mesenchymal stem cells for different disease indications.

Mesenchymal stem cells are being evaluated in human clinical trials for treating ischemic, inflammatory, and immunological diseases. However, most completed trials have yielded suboptimal outcomes due to the inability to predict the potency of different donor populations, which are functionally heterogeneous. We demonstrate that clinically relevant biological activities of MSCs are coordinately regulated by the transcription factor Twist1. Furthermore, we showed that TWIST1 levels reliably predict differences in the angiogenic, anti-inflammatory, and immuno-modulatory activity of populations and as such used it to develop a Clinical Indications Prediction (CLIP) scale. By predicting potency of MSC populations for different disease indications the CLIP scale is expected to dramatically improve MSC-based clinical trial outcomes.

Expression of osterix Is Regulated by FGF and Wnt/β-Catenin Signalling during Osteoblast Differentiation

Osteoblast differentiation from mesenchymal cells is regulated by multiple signalling pathways. Here we have analysed the roles of Fibroblast Growth Factor (FGF) and canonical Wingless-type MMTV integration site (Wnt/β-Catenin) signalling pathways on zebrafish osteogenesis. We have used transgenic and chemical interference approaches to manipulate these pathways and have found that both pathways are required for osteoblast differentiation in vivo. Our analysis of bone markers suggests that these pathways act at the same stage of differentiation to initiate expression of the osteoblast master regulatory gene osterix (osx). We use two independent approaches that suggest that osx is a direct target of these pathways. Firstly, we manipulate signalling and show that osx gene expression responds with similar kinetics to that of known transcriptional targets of the FGF and Wnt pathways. Secondly, we have performed ChIP with transcription factors for both pathways and our data suggest that a genomic region in the first intron of osx mediates transcriptional activation. Based upon these data, we propose that FGF and Wnt/β-Catenin pathways act in part by directing transcription of osx to promote osteoblast differentiation at sites of bone formation.

Poly(L-Lactide)/Poly(ε-Caprolactone) and Collagen/β-Tricalcium Phosphate Scaffolds for the Treatment of Critical-Sized Rat Alveolar Defects: A Microtomographic, Molecular-Biological, and Histological Study

OBJECTIVE

To determine the efficacy of a newly developed scaffold (col/β-TCP) in a preclinical rat model as compared with the gold standard treatment (autograft) and control scaffolds (PLLA/PCL).

DESIGN

Fifty-six Sprague-Dawley rats were randomized into four experimental groups, and critical-sized alveolar defects (7 × 4 × 3 mm) were created in each animal. Group A was the blank defect group, group B received autograft, group C received col/β-TCP scaffolds, and group D received PLLA/PCL blend scaffolds to fill the bone defects. New bone formation was assessed radiomorphometrically, histomorphometrically, and molecular-biologically at 1 and 4 months following surgery.

RESULTS

Radiomorphometrically, the best new bone volume rate at 1 month (43.7%) and 4 months (45.4%) was observed in the autograft group, and the difference was significantly higher than in the other three groups (P < .005, P < .001, P < .001 for 1 month and P = .004, P < .001, P < .001 for 4 months). Even though the new bone volume rate in the col/β-TCP group (21.5%) was higher than that of the PLLA/PCL group (18.2%), the difference was not significant (P = .08). Molecular-genetic analysis revealed significantly higher BSP and ALP gene expression levels in the autograft and col/β-TCP groups than in the blank defect group (P = .002 and P = .004).

CONCLUSION

The engineered tissue scaffolds described herein have great potential as an alternative treatment option when cost, donor region morbidity, and duration of hospitalization are considered.

Osteogenic transcription factors and proto-oncogene regulate bone sialoprotein gene transcription

Runt homeodomain protein 2 (Runx2), distalless 5 (Dlx5) and Smad1 are transcription factors that play critical roles in controlling the differentiation of osteoblasts and mineralization of bone. Proto-oncogene tyrosine-protein kinase, Src, is an enzyme encoded by the Src gene. The normal cellular gene is called cellular-Src (c-Src). Bone sialoprotein (BSP), a protein implicated in the initial mineralization of newly formed bone, is an early phenotypic marker of differentiated osteoblasts. In this study, we used overexpression plasmids with Runx2, Dlx5, Smad1 or c-Src inserts to search for the effects of these transcription factors and proto-oncogene on BSP gene expression using rat osteoblast-like ROS 17/2.8. When we used Runx2, Dlx5 or c-Src overexpression plasmids for the transfection, BSP and Runx2 mRNA levels were increased in ROS 17/2.8 cells. However, overexpression of Smad1 did not induce BSP and Runx2 mRNA. Transient transfection analyses were performed using chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene. Transfection of ROS 17/2.8 cells with Runx2, Dlx5 or c-Src overexpression plasmid increased the luciferase activities of the constructs, pLUC3 (-116 to +60), pLUC4 (-425 to +60) and pLUC5 (-801 to +60). However, Smad1 overexpression had no effect on the luciferase activities. These results demonstrate that overexpression of Runx2, Dlx5 or c-Src stimulates BSP transcription, and suggest that Runx2, Dlx5 and c-Src might be crucial transcriptional regulators of mineralization and bone formation.

Insulin-like growth factor-II regulates bone sialoprotein gene transcription

Insulin-like growth factor-I and -II (IGF-I and IGF-II) have been found in bone extracts of several different species, and IGF-II is the most abundant growth factor stored in bone. Bone sialoprotein (BSP) is a noncollagenous extracellular matrix glycoprotein associated with mineralized connective tissues. In this study, we have investigated the regulation of BSP transcription by IGF-II in rat osteoblast-like ROS17/2.8 cells. IGF-II (50 ng/ml) increased BSP mRNA and protein levels after 6-h stimulation, and enhanced luciferase activities of the constructs pLUC3 (-116 to +60), pLUC4 (-425 to +60), pLUC5 (-801 to +60) and pLUC6 (-938 to +60). Effects of IGF-II were inhibited by tyrosine kinase, extracellular signal-regulated kinase1/2 and phosphatidylinositol 3-kinase inhibitors, and abrogated by 2-bp mutations in cAMP response element (CRE), FGF2 response element (FRE) and homeodomain protein-binding site (HOX). The results of gel shift assays showed that nuclear proteins binding to CRE, FRE and HOX sites were increased by IGF-II (50 ng/ml) at 3 and 6 h. CREB1, phospho-CREB1, c-Fos and c-Jun antibodies disrupted the formation of the CRE-protein complexes. Dlx5 and Runx2 antibodies disrupted the FRE- and HOX-protein complex formations. These studies therefore demonstrated that IGF-II increased BSP transcription by targeting CRE, FRE and HOX elements in the proximal promoter of the rat BSP gene. Moreover, phospho-CREB1, c-Fos, c-Jun, Dlx5 and Runx2 transcription factors appear to be key regulators of IGF-II effects on BSP transcription.

Effects of interleukin-11 on the expression of human bone sialoprotein gene

Interleukin-11 (IL-11) is a bone marrow stromal fibroblast-derived cytokine with a wide spectrum of activities in different biological systems. IL-11 and IL-6 are two cytokines known to rely on osteoblast-osteoclast communication for their effects on osteoclast differentiation. Bone sialoprotein (BSP) is a mineralized connective tissue-specific protein expressed in differentiated osteoblasts, odontoblasts, and cementoblasts. To determine the molecular basis of the transcriptional regulation of the human BSP gene by IL-11, we conducted real-time polymerase chain reactions (PCR), transient transfection analyses with chimeric constructs of the human BSP gene promoter linked to a luciferase reporter gene, gel mobility shift assays, and a chromatin immunoprecipitation assay using human osteoblast-like Saos2 cells. IL-11 (20 ng/ml) increased BSP, Runx2, and Osterix mRNA levels at 6 h and the alkaline phosphatase (ALP) mRNA level at 12 h in osteoblast-like Saos2 cells. In a transient transfection assay, IL-11 (20 ng/ml, 12 h) increased luciferase activities of constructs between -60LUC and -868LUC including the human BSP gene promoter. Transcriptional stimulations by IL-11 were partially inhibited in the constructs that included 2-bp mutations in the cAMP response element 1 (CRE1, -72 to -79) and CRE2 (-667 to -674). When mutations were made in pairs of CRE1 and CRE2 in -868LUC, the effect of IL-11 on luciferase activity was almost totally abrogated. Transcriptional activities induced by IL-11 were inhibited by protein kinase A, tyrosine kinase, ERK1/2, and PI3-kinase inhibitors. Gel mobility shift analyses showed that IL-11 increased nuclear proteins binding to CRE1 and CRE2. CREB1, phospho-CREB1, c-Fos, and c-Jun antibodies disrupted the formation of CRE1 and CRE2 protein complexes. These data demonstrate that IL-11 stimulates BSP gene transcription via CRE1 and CRE2 elements in the human BSP gene promoter.

Lipopolysaccharide-regulated production of bone sialoprotein and interleukin-8 in human periodontal ligament fibroblasts: the role of toll-like receptors 2 and 4 and the MAPK pathway

BACKGROUND AND OBJECTIVE

Lipopolysaccharide (LPS) on the cell wall of periodontal pathogens is a major mediator of the inflammatory response and can enhance alveolar bone resorption in periodontitis. Bone sialoprotein is an early marker of osteoblast differentiation. The proinflammatory cytokine, interleukin-8 (IL-8), induces osteoclast differentiation, maturation and maintenance of bone resorption activity. However, the effects of LPS from periodontal pathogens on the expression of bone sialoprotein and IL-8 in human osteoblasts and the mechanism of periodontal bone metabolism regulation are rather unclear. The objectives of this study were to determine the effects of Porphyromonas gingivalis LPS on the production of bone sialoprotein and IL-8 in human periodontal ligament fibroblasts (hPDLFs), and to investigate whether toll-like receptor (TLR) 2, TLR4 and MAPKs pathways are involved in the regulation of production of bone sialoprotein and IL-8 by P. gingivalis LPS.

MATERIAL AND METHODS

The third-generation of hPDLFs were cultured with mineralization-inducing culture medium. After hPDLFs were treated with P. gingivalis LPS, bone sialoprotein and IL-8 mRNA expression were detected using Real time PCR. Then hPDLFs were transiently transfected with siTLR2 or siTLR4 (20 nm) or inhibited by MAPK signaling pathways inhibitors, and then bone sialoprotein and IL-8 mRNA and protein expression were also detected using Real time PCR and western blotting.

RESULTS

Treatments with 0.01 and 0.1 mg/L of P. gingivalis LPS for 8 h up-regulated bone sialoprotein mRNA expression, whereas 10 and 100 mg/L of P. gingivalis LPS induced a significant decrease in the expression of bone sialoprotein mRNA. In contrast, IL8 mRNA levels were increased significantly by 10 mg/L of P. gingivalis LPS. Interestingly, small interfering RNA (siRNA) knock down of the TLR2 and ERK1/2 inhibitor, PD98059, abolished the effects of P. gingivalis LPS on the bone sialoprotein mRNA level, whereas siRNA knock down of the TLR2 and p38 MAPK inhibitor, SB203580, blocked the effect of P. gingivalis LPS on IL-8 in hPDLFs.

CONCLUSION

This study suggests that in hPDLFs, P. gingivalis LPS suppresses bone sialoprotein and enhances IL-8 gene and protein expression via TLR2 and ERK1/2 or the p38 MAPK signaling pathway, respectively.

Melatonin regulates human bone sialoprotein gene transcription

Melatonin is produced by the pineal gland and regulates various physiological processes including osteoblast differentiation and bone formation. Bone sialoprotein (BSP) is a mineralized connective tissue-specific protein expressed in the early stage of cementum and bone mineralization. To elucidate the effects of melatonin on human BSP gene expression, we utilized human Saos2 osteoblast-like cells. Melatonin (100 nM) increased the level of BSP mRNA at 3 h, and the level became maximal at 12 and 24 h. We then investigated the melatonin-induced transcriptional activity of luciferase constructs (between -84LUC and -868LUC) including different lengths of the human BSP gene promoter transfected into Saos2 cells. The effects of melatonin abrogated in constructs included 2-bp mutations in the two cAMP response elements (CRE1 and CRE2). The effects of melatonin were suppressed by protein kinase A, tyrosine kinase, ERK1/2 and phosphatidylinositol 3-kinase inhibitors. Gel mobility shift assays showed that melatonin increased the binding of nuclear proteins to CRE1 and CRE2, and antibodies against CRE binding protein 1 (CREB1), phospho-CREB1, c-Fos, c-Jun, JunD and Fra2 disrupted CRE1 and CRE2 protein complex formation. These data indicate that melatonin induces BSP transcription via the CRE1 and CRE2 elements in the human BSP gene promoter. (J Oral Sci 56, 67-76, 2014).

Transcriptional regulation of the human bone sialoprotein gene by fibroblast growth factor 2

Fibroblast growth factor 2 (FGF2), a member of the FGF family, positively regulates bone formation and osteoblast differentiation. Bone sialoprotein (BSP) is highly expressed during early bone formation and may play a role in primary mineralization of bone. In the present study, FGF2 (10 ng/mL) was found to increase the levels of Runx2 and BSP mRNA at 3 and 12 h in human osteoblast-like Saos2 cells. Transient transfection assays were performed using chimeric constructs of the human BSP gene promoter ligated with a luciferase reporter gene. FGF2 (10 ng/mL, 12 h) induced the luciferase activities of the -84LUC and -927LUC constructs in Saos2 cells. The results of gel shift assays showed that FGF2 (10 ng/mL) increased the binding of nuclear protein to the FGF2 response element (FRE) and the activator protein 1 (AP1) binding site. Antibodies against Dlx5, Msx2, Runx2 and Smad1 blocked FRE-protein complex formation, and antibodies against CREB1, c-Jun and Fra2 interrupted AP1-protein complex formation. These results indicate that FGF2 increases BSP transcription by targeting the FRE and AP1 elements in the proximal promoter of the human BSP gene. Moreover, the transcription factors Dlx5, Msx2, Runx2, Smad1, CREB1, c-Jun and Fra2 could be key regulators of the effects of FGF2 on human BSP transcription.

Transcriptional regulation of bone sialoprotein gene by CO(2) laser irradiation

Bone sialoprotein (BSP), an early marker of osteoblast differentiation, has been implicated in the nucleation of hydroxyapatite during de novo bone formation. Low-power laser irradiation has a stimulating effect on cells and tissues. Although the carbon dioxide (CO(2)) laser is a hard surgical laser, we have attempted to use it at low energy density to achieve biological alterations. To investigate the effects of CO(2) laser irradiation on BSP gene transcription, we used rat osteoblast-like ROS17/2.8 cells. BSP mRNA levels were increased at 12 h after irradiation with the CO(2) laser (2 W, 20 s). Transient transfection assays using various sizes of the rat BSP gene promoter linked to the luciferase reporter gene showed that CO(2) laser irradiation induced luciferase activity of a -116 to +60 BSP promoter construct (pLUC3) at 12 h in the cells. Transcriptional stimulation by CO(2) laser irradiation was abrogated in the pLUC3 construct containing a 2-bp mutation in the fibroblast growth factor 2 response element (FRE). Gel shift analyses showed that CO(2) laser irradiation increased the binding of nuclear protein to FRE. These studies demonstrate that CO(2) laser irradiation increases BSP transcription via FRE in the rat BSP gene promoter.

Calcium hydroxide regulates bone sialoprotein gene transcription in human osteoblast-like Saos2 cells

Bone sialoprotein (BSP) is a mineralized tissue-specific protein expressed in differentiated osteoblasts that appears to function in the initial mineralization of bone. Calcium hydroxide (Ca(OH)(2)) is a basic salt that has been widely used for a variety of applications in dentistry, due to its antimicrobial effects and its capability of inducing hard tissue formation. However, details of the mechanism involved in the mineralization induced by Ca(OH)(2) are still unclear. In the present study, Ca(OH)(2) (0.4 mM) was found to increase the levels of BSP and Runx2 mRNA at 3 h in human osteoblast-like Saos2 cells. Transient transfection assays were performed using chimeric constructs of the human BSP gene promoter linked to a luciferase reporter gene. Treatment of Saos2 cells with Ca(OH)(2) (0.4 mM) increased the luciferase activities of the constructs between -60LUC and -927LUC at 12 h. Gel shift analysis showed that Ca(OH)(2) (0.4 mM) increased the binding of nuclear protein to CRE1, CRE2 and FRE. Antibodies against CREB1, c-Fos, c-Jun, JunD, Fra2 and P300 disrupted the formation of the CRE1- and CRE2-protein complexes, and antibodies against Dlx5, Msx2, Runx2 and Smad1 disrupted the formation of the FRE-protein complex. These findings demonstrate that Ca(OH)(2) stimulates BSP transcription by targeting the CRE1, CRE2 and FRE elements in the human BSP gene promoter.

Transcriptional regulation of bone sialoprotein gene by interleukin-11

Interleukin-11 (IL-11) is a stromal cell-derived cytokine that belongs to the interleukin-6 family of cytokines. IL-11 has many biological activities and has roles in hematopoiesis, immune responses, the nervous system and bone metabolism. Bone sialoprotein (BSP) is a mineralized tissue-specific protein expressed in differentiated osteoblasts that appears to function in the initial mineralization of bone. IL-11 (20 ng/ml) increased BSP mRNA and protein levels at 12h in osteoblast-like ROS 17/2.8 cells. In a transient transfection assay, IL-11 (20 ng/ml) increased luciferase activity of the construct (-116 to +60) in ROS 17/2.8 cells and rat bone marrow stromal cells. Introduction of 2 bp mutations to the luciferase constructs showed that the effects of IL-11 were mediated by a cAMP response element (CRE), a fibroblast growth factor 2 response element (FRE) and a homeodomain protein-binding site (HOX). Luciferase activities induced by IL-11 were blocked by protein kinase A inhibitor, tyrosine kinase inhibitor and ERK1/2 inhibitor. Gel shift analyses showed that IL-11 (20 ng/ml) increased nuclear protein binding to CRE, FRE and HOX. CREB1, phospho-CREB1, c-Fos, c-Jun, JunD and Fra2 antibodies disrupted the formation of CRE-protein complexes. Dlx5, Msx2, Runx2 and Smad1 antibodies disrupted FRE- and HOX-protein complex formations. These studies demonstrate that IL-11 stimulates BSP transcription by targeting CRE, FRE and HOX sites in the proximal promoter of the rat BSP gene. Moreover, phospho-CREB1, c-Fos, c-Jun, JunD, Fra2, Dlx5, Msx2, Runx2 and Smadl transcription factors appear to be key regulators of IL-11 effects on BSP transcription.

Transcriptional regulation of bone sialoprotein gene by Porphyromonas gingivalis lipopolysaccharide

Lipopolysaccharide (LPS) is a major mediator of inflammatory response. Periodontopathic bacterium Porphyromonas gingivalis LPS has quite different character from Escherichia coli LPS. E. coli LPS is agonist for Toll-like receptor 4 (TLR4), whereas P. gingivalis LPS worked as antagonist for TLR4. Bone sialoprotein (BSP) is an early marker of osteoblast differentiation. To investigate the effects of P. gingivalis LPS on BSP transcription, we used rat osteoblast-like ROS17/2.8 cells. BSP mRNA levels were decreased by 0.1 microg/ml and increased by 0.01 microg/ml P. gingivalis LPS at 12 h. Results of luciferase assays showed that 0.1 microg/ml decreased and 0.01 microg/ml P. gingivalis LPS increased BSP transcription in -116 to +60 BSP construct. The effects of P. gingivalis LPS were abrogated by double mutations in cAMP response element (CRE) and FGF2 response element (FRE). Tyrosine kinase inhibitor herbimycin A, ERK1/2 inhibitor and antioxidant N-acetylcystein inhibited effects of P. gingivalis LPS. Protein kinase A inhibitor and PI3-kinase/Akt inhibitor only abolished the effect of 0.01 microg/ml P. gingivalis LPS. Furthermore, 0.1 microg/ml LPS decreased the CRE- and FRE-protein complexes formation, whereas 0.01 microg/ml P. gingivalis LPS increased the nuclear protein binding to CRE and FRE. ChIP assays revealed increased binding of CREB1, JunD, Fra2, Runx2, Dlx5, and Smad1 to a chromatin fragment containing the CRE and FRE by 0.01 microg/ml P. gingivalis LPS. These studies therefore indicated that 0.1 microg/ml suppressed, and 0.01 microg/ml P. gingivalis LPS increased BSP gene transcription mediated through CRE and FRE elements in the rat BSP gene promoter.

Kaempferol stimulates bone sialoprotein gene transcription and new bone formation

Kaempferol is a typical flavonol-type flavonoid that is present in a variety of vegetables and fruits, and has a protective effect on postmenopausal bone loss. Bone sialoprotein (BSP) is thought to function in the initial mineralization of bone and could be crucial for osteoblast differentiation, bone matrix mineralization and tumor metastasis. In the present study we investigated the regulation of BSP transcription by kaempferol in rat osteoblast-like UMR106 cells, and the effect of kaempferol on new bone formation. Kaempferol (5 microM) increased BSP and Osterix mRNA levels at 12 h and up-regulated Runx2 mRNA expression at 6 h. Kaempferol increased luciferase activity of the construct pLUC3, which including the promoter sequence between nucleotides -116 to +60. Transcriptional stimulation by kaempferol abrogated in constructs included 2 bp mutations in the inverted CCAAT, CRE, and FRE elements. Gel shift analyses showed that kaempferol increased nuclear protein binding to CRE and FRE elements, whereas the CCAAT-protein complex did not change after kaempferol stimulation. Twelve daily injections of 5 microM kaempferol directly into the periosteum of parietal bones of newborn rats increased new bone formation. These data suggest that kaempferol increased BSP gene transcription mediated through inverted CCAAT, CRE, and FRE elements in the rat BSP gene promoter, and could induce osteoblast activities in the early stage of bone formation.

cAMP and fibroblast growth factor 2 regulate bone sialoprotein gene expression in human prostate cancer cells

Bone sialoprotein (BSP) is a noncollagenous protein of the extracellular matrix in mineralized connective tissues that has been implicated in the nucleation of hydroxyapatite. Forskolin (FSK), an activator of adenylate cyclase, increased the intracellular cAMP level, which stimulates the proliferation and differentiation of osteoblasts. Fibroblast growth factor 2 (FGF2) is a potent mitogen in many cell types, including osteoblasts. In human prostate cancer DU145 cells, FSK (1 μM) and FGF2 (10 ng/ml) increased BSP and Runx2 mRNA and protein levels at 3 and 12h, respectively. Transient transfection analyses were performed using chimeric constructs of the human BSP gene promoter linked to a luciferase reporter gene. Treatment of DU145 cells with FSK (1 μM) and FGF2 (10 ng/ml) increased the luciferase activities of constructs between -60LUC to -927LUC and -108LUC to -927LUC, including the human BSP gene promoter. Effects of FSK and FGF2 abrogated in constructs included 2bp mutations in the two cAMP response elements (CRE1 and CRE2). Luciferase activities induced by FSK and FGF2 were blocked by protein kinase A and tyrosine kinase inhibitors. Gel mobility shift analyses showed that FSK and FGF2 increased the binding of CRE1 and CRE2. CRE1-protein complexes were supershifted by phospho-CREB1 and c-Fos antibodies, and disrupted by CREB1, c-Jun, JunD, Fra2, p300, Runx2, Dlx5 and Smad1 antibodies. CRE2-protein complexes were disrupted by CREB1, phospho-CREB1, c-Fos, c-Jun, JunD, Fra2, p300, Runx2, Dlx5 and Smad1 antibodies. These studies demonstrate that FSK and FGF2 stimulate BSP transcription in DU145 human prostate cancer cells by targeting the CRE1 and CRE2 elements in the human BSP gene promoter.

Butyric acid stimulates bone sialoprotein gene transcription

Butyric acid (sodium butyrate; BA) is an extracellular metabolite secreted from periodontopathic bacteria present in subgingival plaque. BA induces apoptosis of T and B cells, and acts as a potent inhibitor of histone deacetylases. Bone sialoprotein (BSP) is thought to function in the initial mineralization of bone, and may be crucial for osteoblast differentiation, bone matrix mineralization and tumor metastasis. In the present study we investigated the regulation of BSP transcription by BA in rat osteoblast-like ROS17/2.8 cells. At 12 h, BA (10(-4) M) increased the level of BSP mRNA, and enhanced the luciferase activity of the construct pLUC3, which includes the promoter sequence between nucleotides -116 and +60. Transcriptional stimulation by BA was abrogated in the pLUC3 construct which containing a 2-bp mutation in the fibroblast growth factor 2 response element (FRE). Gel shift analyses showed that BA increased the binding of nuclear protein to FRE. These data suggest that BA increases the transcription of the BSP gene mediated through FRE in the rat BSP gene promoter, and induces osteoblast activity in the early stage of bone formation.

Fibroblast growth factor 2 regulates bone sialoprotein gene transcription in human breast cancer cells

Bone sialoprotein (BSP) is a major non-collagenous, extracellular matrix glycoprotein associated with mineralized tissues. Fibroblast growth factor 2 (FGF2) is recognized as a potent mitogen for a variety of mesenchymal cells. FGF2 produced by osteoblasts accumulates in the bone matrix and acts as an autocrine/paracrine regulator of osteoblasts. We previously reported that FGF2 regulates BSP gene transcription through the FGF2 response element (FRE) and activator protein 1 (AP1) binding site overlapping with the glucocorticoid response element in the rat BSP gene promoter. In the present study, FGF2 (10 ng/ml) increased BSP and Runx2 mRNA levels at 6 h in MCF7 human breast cancer cells. Transient transfection analyses were performed using chimeric constructs of the human BSP gene promoter linked to a luciferase reporter gene. Treatment of MCF7 cells with FGF2 (10 ng/ml) increased the luciferase activity of the constructs between -84LUC and -927LUC. Gel mobility shift analyses showed that FGF2 increased the binding of AP1 and CRE2. The CRE2- and AP1-protein complexes were disrupted by antibodies against CREB1, c-Fos, c-Jun, Fra2, p300 and Runx2. These studies demonstrate that FGF2 stimulates BSP transcription in MCF7 human breast cancer cells by targeting the AP1 and CRE2 elements in the human BSP gene promoter.

Effects of porcine 25 kDa amelogenin and its proteolytic derivatives on bone sialoprotein expression

BACKGROUND AND OBJECTIVE

Amelogenins are hydrophobic proteins that are the major component of developing enamel. Enamel matrix derivative has been used for periodontal regeneration. Bone sialoprotein is an early phenotypic marker of osteoblast differentiation. In this study, we examined the ability of porcine amelogenins to regulate bone sialoprotein transcription.

MATERIAL AND METHODS

To determine the molecular basis of the transcriptional regulation of the bone sialoprotein gene by amelogenins, we conducted northern hybridization, transient transfection analyses and gel mobility shift assays using the osteoblast-like ROS 17/2.8 cells.

RESULTS

Amelogenins (100 ng/mL) up-regulated bone sialoprotein mRNA at 3 h, with maximal mRNA expression occurring at 12 h (25 and 20 kDa) and 6 h (13 and 6 kDa). Amelogenins (100 ng/mL, 12 h) increased luciferase activities in pLUC3 (nucleotides -116 to +60), and 6 kDa amelogenin up-regulated pLUC4 (nucleotides -425 to +60) activity. The tyrosine kinase inhibitor inhibited amelogenin-induced luciferase activities, whereas the protein kinase A inhibitor abolished 25 kDa amelogenin-induced bone sialoprotein transcription. The effects of amelogenins were abrogated by 2-bp mutations in the fibroblast growth factor 2 response element (FRE). Gel-shift assays with radiolabeled FRE, homeodomain-protein binding site (HOX) and transforming growth factor-beta1 activation element (TAE) double-strand oligonucleotides revealed increased binding of nuclear proteins from amelogenin-stimulated ROS 17/2.8 cells at 3 h (25 and 13 kDa) and 6 h (20 and 6 kDa).

CONCLUSION

These results demonstrate that porcine 25 kDa amelogenin and its proteolytic derivatives stimulate bone sialoprotein transcription by targeting FRE, HOX and TAE in the bone sialoprotein gene promoter, and that full-length amelogenin and amelogenin cleavage products are able to regulate bone sialoprotein transcription via different signaling pathways.

Endothelin-1 regulates rat bone sialoprotein gene transcription

Endothelin-1 (ET-1) was originally discovered as a vasoconstrictor protein excreted by vascular endothelial cells. Recently, tumor-produced ET-1 has been considered to stimulate osteoblasts to form new bone, and to be an important mediator of osteoblastic bone metastasis. ET-1 has high affinity for two different membrane receptors, ET(A)R and ET(B)R, which are expressed by many types of cells including osteoblasts. Bone sialoprotein (BSP) is a phosphorylated and sulfated glycoprotein associated with mineralized connective tissues. To investigate the effects of ET-1 on BSP transcription, we used rat osteoblast-like ROS17/2.8 cells. Levels of BSP and osteopontin mRNA were increased at 12 h after treatment with ET-1 (10 ng/ml), and ET-1 at the same concentration induced luciferase activity of a -116 to +60 BSP promoter construct at 6 h. Transcriptional activity of -84BSPLUC, which contains the cAMP response element (CRE), was increased by ET-1. Furthermore, at 6 h, ET-1 (10 ng/ml) increased the binding of nuclear protein to CRE, the FGF2 response element (FRE) and the homeodomain protein-binding site (HOX). Antibodies against CREB1, JunD and Fra2 disrupted the formation of CRE-protein complexes, while antibodies against Runx2 and Dlx5 reduced the formation of FRE- and HOX-protein complexes. These findings indicate that ET-1 increases BSP transcription via the CRE, FRE and HOX sites in the rat BSP gene promoter.

Effects of inorganic polyphosphate on bone sialoprotein gene expression

Inorganic polyphosphate (poly(P)) is a biopolymer existing in almost all cells and tissues. The biological functions of poly(P) in micro-organisms have been extensively investigated in studies of poly(P) in eukaryotic cells, especially osteoblasts, and are increasing. Bone sialoprotein (BSP) is thought to function in bone mineralization, and is selectively expressed by differentiated osteoblasts. In this study, application of sodium phosphate glass type 25 (SPG25, 12.5 and 125 microM) increased BSP mRNA levels at 12 h in osteoblast-like ROS 17/2.8 cells. In transient transfection assay, 12.5 and 125 microM SPG25 increased luciferase activities of the constructs pLUC3 (-116 to +60), pLUC4 (-425 to +60), pLUC5 (-801 to +60) and pLUC6 (-938 to +60). Introduction of 2 bp mutations to the luciferase constructs showed that the effects of SPG25 were mediated by a FGF2 response element (FRE) and a homeodomain protein binding site (HOX). Luciferase activities induced by SPG25 were blocked by tyrosine kinase inhibitor herbimycine A, MAP kinase kinase inhibitor U0126, PI3-kinase/Akt inhibitor LY249002 and inorganic phosphate transport inhibitor foscarnet. Gel shift analyses showed that both 12.5 and 125 microM SPG25 increased nuclear protein binding to FRE and HOX elements. These studies demonstrate that SPG25 stimulates BSP transcription by targeting FRE and HOX elements in the proximal promoter of the rat BSP gene.

The osteogenic transcription factor Runx2 regulates components of the fibroblast growth factor/proteoglycan signaling axis in osteoblasts

Heparan sulfate proteoglycans cooperate with basic fibroblast growth factor (bFGF/FGF2) signaling to control osteoblast growth and differentiation, as well as metabolic functions of osteoblasts. FGF2 signaling modulates the expression and activity of Runt-related transcription factor 2 (Runx2/Cbfa1), a key regulator of osteoblast proliferation and maturation. Here, we have characterized novel Runx2 target genes in osteoprogenitors under conditions that promote growth arrest while not yet permitting sustained phenotypic maturation. Runx2 enhances expression of genes related to proteoglycan-mediated signaling, including FGF receptors (e.g., FGFR2 and FGFR3) and proteoglycans (e.g., syndecans [Sdc1, Sdc2, Sdc3], glypicans [Gpc1], versican [Vcan]). Runx2 increases expression of the glycosyltransferase Exostosin-1 (Ext1) and heparanase, as well as alters the relative expression of N-linked sulfotransferases (Ndst1 = Ndst2 > Ndst3) and enzymes mediating O-linked sulfation of heparan sulfate (Hs2st > Hs6st) or chondroitin sulfate (Cs4st > Cs6st). Runx2 cooperates with FGF2 to induce expression of Sdc4 and the sulfatase Galns, but Runx2 and FGF2 suppress Gpc6, thus suggesting intricate Runx2 and FGF2 dependent changes in proteoglycan utilization. One functional consequence of Runx2 mediated modulations in proteoglycan-related gene expression is a change in the responsiveness of bone markers to FGF2 stimulation. Runx2 and FGF2 synergistically enhance osteopontin expression (>100 fold), while FGF2 blocks Runx2 induction of alkaline phosphatase. Our data suggest that Runx2 and the FGF/proteoglycan axis may form an extracellular matrix (ECM)-related regulatory feed-back loop that controls osteoblast proliferation and execution of the osteogenic program.

Parathyroid hormone regulation of the human bone sialoprotein gene transcription is mediated through two cAMP response elements

Parathyroid hormone (PTH) regulates serum calcium and inorganic phosphate levels through its actions on kidney and bone. Bone sialoprotein (BSP) is an early marker of osteoblast differentiation and bone metabolism. We here report that two cAMP response elements (CRE) in the human BSP gene promoter are target of PTH. In human osteoblast-like Saos2 cells, PTH (human 1-34 PTH, 10 nM) increased BSP mRNA and protein levels at 3 h. From transient transfection assays, 2- to 2.5-fold increase in transcription by PTH was observed at 3 and 6 h in -184, -211, -428, -868, and -927 luciferase constructs that included the human BSP gene promoter. Effect of PTH was abrogated by 2 bp mutations in either the CRE1 (-79 to -72) or CRE2 (-674 to -667). Luciferase activities induced by PTH were blocked by protein kinase A inhibitor H89 and tyrosine kinase inhibitor herbimycin A. Gel shift analyses showed that PTH increased binding of nuclear proteins to the CRE1 and CRE2 elements. The CRE1-protein and CRE2-protein complexes were disrupted by CRE binding protein 1 (CREB1) antibodies and supershifted by phospho-CREB1 antibody. ChIP assays detected binding of CREB1 and phospho-CREB1 to a chromatin fragment containing CRE1 and CRE2, and increased binding of phospho-CREB1 to the both sites. These studies demonstrate that PTH stimulates human BSP gene transcription by targeting the two CREs in the promoter of the human BSP gene.

Regulation of human bone sialoprotein gene transcription by platelet-derived growth factor-BB

Platelet-derived growth factor (PDGF) is produced by mesenchymal cells and released by platelets following aggregation and is synthesized by osteoblasts. In bone, PDGF stimulates proliferation and differentiation of osteoblasts. PDGF also increases bone resorption, most likely by increasing the number of osteoclasts. Bone sialoprotein (BSP) is thought to function in the initial mineralization of bone, selectively expressed by differentiated osteoblast. To determine the molecular mechanisms PDGF regulation of human BSP gene transcription, we have analyzed the effects of PDGF-BB on osteoblast-like Saos2 and ROS17/2.8 cells. PDGF-BB (5 ng/ml) increased BSP mRNA and protein levels at 12 h in Saos2 cells, and induced BSP mRNA expression at 3 h, reached maximal at 12 h in ROS17/2.8 cells. Transient transfection analyses were performed using chimeric constructs of the human BSP gene promoter linked to a luciferase reporter gene. Treatment of Saos2 cells with PDGF-BB (5 ng/ml, 12 h) increased luciferase activities of all constructs between -184LUC to -2672LUC including the human BSP gene promoter. Effects of PDGF-BB abrogated in constructs included 2 bp mutations in the two cAMP response elements (CRE1 and CRE2), activator protein 1(3) (AP1(3)) and shear stress response element 1 (SSRE1). Luciferase activities induced by PDGF-BB were blocked by protein kinase A inhibitor H89 and tyrosine kinase inhibitor herbimycin A. Gel mobility shift analyses showed that PDGF-BB increased binding of CRE1, CRE2, AP1(3) and SSRE1 elements. CRE1- and CRE2-protein complexes were supershifted by CREB1 and phospho-CREB1 antibodies. Notably, AP1(3)-protein complexes were supershifted by c-Fos and JunD, and disrupted by CREB1, phospho-CREB1, c-Jun and Fra2 antibodies. These studies, therefore, demonstrate that PDGF-BB stimulates human BSP transcription by targeting the CRE1, CRE2, AP1(3) and SSRE1 elements in the human BSP gene promoter.

Nicotine suppresses bone sialoprotein gene expression

BACKGROUND AND OBJECTIVE

Tobacco smoking is a risk factor for periodontitis and osteoporosis. Nicotine is a major component of tobacco, and has been reported to inhibit proliferation and differentiation of osteoblasts. Bone sialoprotein (BSP) is a mineralized tissue-specific protein expressed by differentiated osteoblasts that appears to function in the initial mineralization of bone. The purpose of this study was to determine the effects of nicotine on bone metabolism.

MATERIAL AND METHODS

We used rat osteobast-like UMR106 and ROS 17/2.8 cells and rat stromal bone marrow RBMC-D8 cells. To determine the molecular basis of the transcriptional regulation of the BSP gene by nicotine, we conducted Northern hybridization, transient transfection analyses with chimeric constructs of the BSP gene promoter linked to a luciferase reporter gene and gel mobility shift assays.

RESULTS

Nicotine (250 microg/mL) decreased the BSP mRNA levels at 12 and 24 h in UMR106 and ROS 17/2.8 cells. From transient transfection assays using various sized BSP promoter-luciferase constructs, nicotine decreased the luciferase activities of the construct, including the promoter sequence nucleotides -116 to +60, in UMR106 and RBMC-D8 cells. Nicotine decreased the nuclear protein binding to the cAMP response element (CRE), fibroblast growth factor 2 response element (FRE) and homeodomain protein-binding site (HOX) at 12 and 24 h.

CONCLUSION

This study indicates that nicotine suppresses BSP transcription mediated through CRE, FRE and HOX elements in the proximal promoter of the rat BSP gene.

Bone sialoprotein and its transcriptional regulatory mechanism

BACKGROUND AND OBJECTIVE

Bone sialoprotein is a mineralized tissue-specific noncollagenous protein that is glycosylated, phosphorylated and sulfated. The temporo-spatial deposition of bone sialoprotein into the extracellular matrix of bone, and the ability of bone sialoprotein to nucleate hydroxyapatite crystal formation, indicates a potential role for bone sialoprotein in the initial mineralization of bone, dentin and cementum. Bone sialoprotein is also expressed in breast, lung, thyroid and prostate cancers.

MATERIAL AND METHODS

We used osteoblast-like cells (rat osteosarcoma cell lines ROS17/2.8 and UMR106, rat stromal bone marrow RBMC-D8 cells and human osteosarcoma Saos2 cells), and breast and prostate cancer cells to investigate the transcriptional regulation of bone sialoprotein. To determine the molecular basis of the transcriptional regulation of the bone sialoprotein gene, we conducted northern hybridization, transient transfection analyses with chimeric constructs of the bone sialoprotein gene promoter linked to a luciferase reporter gene and gel mobility shift assays.

RESULTS

Bone sialoprotein transcription is regulated by hormones, growth factors and cytokines through tyrosine kinase, mitogen-activated protein kinase and cAMP-dependent pathways. Microcalcifications are often associated with human mammary lesions, particularly with breast carcinomas. Expression of bone sialoprotein by cancer cells could play a major role in the mineral deposition and in preferred bone homing of breast cancer cells.

CONCLUSION

Bone sialoprotein protects cells from complement-mediated cellular lysis, activates matrix metalloproteinase 2 and has an angiogenic capacity. Therefore, regulation of the bone sialoprotein gene is potentially important in the differentiation of osteoblasts, bone matrix mineralization and tumor metastasis. This review highlights the function and transcriptional regulation of bone sialoprotein.

CREB-1 and AP-1 transcription factors JunD and Fra-2 regulate bone sialoprotein gene expression in human breast cancer cells

Bone sialoprotein (BSP) expression is detected in a variety of human osteotropic cancers. High expression of BSP in breast and prostate primary carcinomas is associated with progression and bone metastases development. In this study, we examined the transcriptional regulation of BSP gene expression in MDA-MB-231 and MCF-7 human breast cancer cells compared with Saos-2 human osteoblast-like cells. BSP human promoter deletion analyses delineated a -56/-84 region, which comprises a cAMP response element (CRE) that was sufficient for maximal promoter activity in breast cancer cell lines. We found that the basic fibroblast growth factor response element (FRE) also located in the proximal promoter was a crucial regulator of human BSP promoter activity in Saos-2 but not in breast cancer cells. Promoter activity experiments in combination with DNA mobility shift assays demonstrated that BSP promoter activity is under the control of the CRE element, through CREB-1, JunD and Fra-2 binding, in MDA-MB-231, MCF-7 and in Saos-2 cells. Forskolin, a protein kinase A pathway activator, failed to enhance BSP transcriptional activity suggesting that CRE site behaves as a constitutive rather than an inducible element in these cell lines. Over-expression of JunD and Fra-2 increased BSP promoter activity and upregulated endogenous BSP protein expression in MCF-7 and Saos-2 cells while siRNA-mediated inhibition of both factors expression significantly reduced BSP protein level in MDA-MB-231. Collectively, these data provide with new transcriptional mechanisms, implicating CREB and AP-1 factors, that control BSP gene expression in breast cancer cells.

AP1 binding site is another target of FGF2 regulation of bone sialoprotein gene transcription

Bone sialoprotein (BSP) is an early marker of osteoblast differentiation. We previously reported that fibroblast growth factor 2 (FGF2) regulates BSP gene transcription via FGF2 response element (FRE) in the proximal promoter of rat BSP gene. We here report that activator protein 1 (AP1) binding site overlapping with glucocorticoid response element (GRE) AP1/GRE in the rat BSP gene promoter is another target of FGF2. Using the osteoblastic cell line ROS17/2.8, we determined that BSP mRNA levels increased by 10 ng/ml FGF2 at 6 and 12 h. Runx2 protein levels increased by FGF2 (10 ng/ml) at 3 h. Treatment of ROS17/2.8 cells with FGF2 (10 ng/ml, 12 h) increased luciferase activities of constructs including -116 to +60 and -938 to +60 of the rat BSP gene promoter. Effects of FGF2 abrogated in constructs included 2 bp mutations in the FRE and AP1/GRE elements. Luciferase activities induced by FGF2 were blocked by tyrosine kinase inhibitor herbimycin A, src-tyrosine kinase inhibitor PP1 and MAP kinase kinase inhibitor U0126. Gel shift analyses showed that FGF2 increased binding of FRE and AP1/GRE elements. Notably, the AP1/GRE-protein complexes were supershifted by Smad1 and c-Fos antibodies, c-Jun and Dlx5 antibodies disrupted the complexes formation, on the other hand AP1/GRE-protein complexes did not change by Runx2 antibody. These studies demonstrate that FGF2 stimulates BSP gene transcription by targeting the FRE and AP1/GRE elements in the rat BSP gene promoter.

Androgen receptor stimulates bone sialoprotein (BSP) gene transcription via cAMP response element and activator protein 1/glucocorticoid response elements

Bone sialoprotein (BSP) is an early marker of osteoblast differentiation. Androgens are steroid hormones that are essential for skeletal development. The androgen receptor (AR) is a transcription factor and a member of the steroid receptor superfamily that plays an important role in male sexual differentiation and prostate cell proliferation. To determine the molecular mechanism involved in the stimulation of bone formation, we have analyzed the effects of androgens and AR effects on BSP gene transcription. AR protein levels were increased after AR overexpression in ROS17/2.8 cells. BSP mRNA levels were increased by AR overexpression. However, the endogenous and overexpressed BSP mRNA levels were not changed by DHT (10(-8) M, 24 h). Whereas luciferase (LUC) activities in all constructs, including a short construct (nts -116 to +60), were increased by AR overexpression, the basal and LUC activities enhanced by AR overexpression were not induced by DHT (10(-8)M, 24 h). The effect of AR overexpression was abrogated by 2 bp mutations in either the cAMP response element (CRE) or activator protein 1 (AP1)/glucocorticoid response element (GRE). Gel shift analyses showed that AR overexpression increased binding to the CRE and AP1/GRE elements. Notably, the CRE-protein complexes were supershifted by phospho-CREB antibody, and CREB, c-Fos, c-Jun, and AR antibodies disrupted the complexes formation. The AP1/GRE-protein complexes were supershifted by c-Fos antibody and c-Jun, and AR antibodies disrupted the complexes formation. These studies demonstrate that AR stimulates BSP gene transcription by targeting the CRE and AP1/GRE elements in the promoter of the rat BSP gene.

Effects of quercetin and quercetin 3-glucuronide on the expression of bone sialoprotein gene

Quercetin is a typical flavonol-type flavonoid and is present in a variety of vegetables, and their antioxidant effect implies their possible role in the prevention of oxidative stress related chronic diseases. Bone sialoprotein (BSP) is a noncollagenous protein of the extracellular matrix in the mineralized connective tissues that has been implicated in the nucleation of hydroxyapatite crystals. Previously, we reported that isoflavone (genistein) activated BSP gene transcription is mediated through an inverted CCAAT box in the proximal BSP gene promoter. The present study investigates the regulation of BSP transcription in a rat osteoblast-like cell line, ROS 17/2.8 cells, by quercetin and its conjugated metabolite quercetin 3-glucuronide. Quercetin and quercetin 3-glucuronide (5 microM) increased the BSP mRNA levels at 12 h and quercetin upregulated the Cbfa1/Runx2 mRNA expression at 12 h. From transient transfection assays using various sized BSP promoter-luciferase constructs, quercetin increased the luciferase activity of the construct (pLUC3), including the promoter sequence nucleotides -116 to -43. Transcriptional stimulations by quercetin were almost completely abrogated in the constructs that included 2 bp mutations in the inverted CCAAT and FRE elements whereas the CCAAT-protein complex did not change after stimulation by quercetin according to gel shift assays. Quercetin increased the nuclear protein binding to the FRE and 3'-FRE. These data suggest that quercetin and quercetin 3-glucuronide increased the BSP mRNA expression, and that the inverted CCAAT and FRE elements in the promoter of the BSP gene are required for quercetin induced BSP transcription.

Insulin-like growth factor-I increases bone sialoprotein (BSP) expression through fibroblast growth factor-2 response element and homeodomain protein-binding site in the proximal promoter of the BSP gene

Insulin-like growth factor-I (IGF-I) promotes bone formation by stimulating proliferation and differentiation of osteoblasts. Bone sialoprotein (BSP), is thought to function in the initial mineralization of bone, is selectively expressed by differentiated osteoblast. To determine the molecular mechanism of IGF-I regulation of osteogenesis, we analyzed the effects of IGF-I on the expression of BSP in osteoblast-like Saos2 and in rat stromal bone marrow (RBMC-D8) cells. IGF-I (50 ng/ml) increased BSP mRNA levels at 12 h in Saos2 cells. In RBMC-D8 cells, IGF-I increased BSP mRNA levels at 3 h. From transient transfection assays, a twofold increase in transcription by IGF-I was observed at 12 h in pLUC3 construct that included the promoter sequence from -116 to +60. Effect of IGF-I was abrogated by 2-bp mutations in either the FGF2 response element (FRE) or homeodomain protein-binding site (HOX). Gel shift analyses showed that IGF-I increased binding of nuclear proteins to the FRE and HOX elements. Notably, the HOX-protein complex was supershifted by Smad1 antibody, while the FRE-protein complex was shifted by Smad1 and Cbfa1 antibodies. Dlx2 and Dlx5 antibodies disrupted the formation of the FRE- and HOX-protein complexes. The IGF-I effects on the formation of FRE-protein complexes were abolished by tyrosine kinase inhibitor herbimycin A (HA), PI3-kinase/Akt inhibitor LY249002, and MAP kinase kinase inhibitor U0126, while IGF-I effects on HOX-protein complexes were abolished by HA and LY249002. These studies demonstrate that IGF-I stimulates BSP transcription by targeting the FRE and HOX elements in the proximal promoter of BSP gene.

Effect of chlorpromazine on bone sialoprotein (BSP) gene transcription

Bone sialoprotein (BSP), an early marker of osteoblast differentiation. Whereas physical forces may play an important role in the regulation of bone cell function, little is known about how cells are able to sense mechanical loads. Chlorpromazine, a tranquilizing agent for treatments of psychiatric disorders, mimics hypotonic stress and causes membrane deformation. Application of 10 microg/ml of chlorpromazine suppressed BSP mRNA levels after 12 and 24 h in osteoblast-like ROS17/2.8 cells and rat stromal bone marrow cells (SBMC-D8). Chlorpromazine (10 microg/ml) decreased luciferase activity of the construct (pLUC3; -116 to +60 of the rat BSP gene promoter) after 12 h, the effect was inhibited by the tyrosine kinase inhibitor herbimycin A (HA) and MAP kinase kinase inhibitor U0126. Introduction of 2-bp mutation in the pLUC3 construct showed that the chlorpromazine effects were mediated by cAMP response element (CRE) and FGF2 response element (FRE). In gel shift assays, using radiolabeled double-stranded CRE and FRE oligonucleotides, which revealed decreased binding of nuclear proteins from chlorpromazine-stimulated cells. These studies, therefore, show that chlorpromazine suppresses BSP gene transcription through tyrosine and MAP kinases-dependent pathways and that the chlorpromazine effects are mediated by CRE and FRE elements in the proximal promoter of the BSP gene.

Fibroblast growth factor 2 and cyclic AMP synergistically regulate bone sialoprotein gene expression

Bone sialoprotein (BSP) is a noncollagenous protein of the mineralized bone extracellular matrix. We here report that FGF2 and cAMP act synergistically to stimulate BSP gene expression. Treatment of ROS 17/2.8 cells with either 10 ng/ml FGF2 or 1 microM FSK for 6 h resulted in 5.4- and 8.2-fold increases, respectively, in the levels of BSP mRNA. However, in the presence of both FGF2 and forskolin (FGF/FSK), BSP mRNA levels were increased synergistically by 20.4-fold. Using a luciferase reporter construct, encompassing BSP promoter nucleotides -116 to +60, transcription was also increased synergistically by 15.0-fold with FGF/FSK, compared to stimulations of 2.6- and 5.3-fold, respectively, for FGF2 and FSK alone. Transcriptional stimulation by FGF/FSK abrogated in constructs included 2 bp mutations in the inverted CCAAT, CRE, FRE and Pit-1 elements. Whereas the FRE-protein complex was increased by FGF2 and FGF/FSK, the Pit-1-protein complex was decreased by FSK and FGF/FSK. Notably, transcriptional activity induced by FGF/FSK was blocked by protein kinase A, tyrosine kinase and MEK inhibitors. These studies indicate that the combinatorial effects of FGF and FSK act through PKA, tyrosine kinase and MAP-kinase-dependent pathways, which target the inverted CCAAT, CRE, FRE and Pit-1 elements in the BSP gene to synergistically increase BSP expression.

Regulation of bone sialoprotein (BSP) gene transcription by lipopolysaccharide

Lipopolysaccharide (LPS) is a major mediator of inflammatory responses in periodontal disease that inhibits bone formation and stimulates bone resorption. To determine the molecular mechanisms involved in the suppression of bone formation, we have analyzed the effects of LPS on BSP gene expression. Bone sialoprotein (BSP) is a mineralized tissue-specific protein that appears to function in the initial mineralization of bone. Treatment of osteoblast-like ROS 17/2.8 cells with LPS (1 microg/ml) for 12 h caused a marked reduction in BSP mRNA levels. The addition of antioxidant N-acetylcysteine (NAC; 20 mM) 30 min prior to stimulation with LPS attenuated the inhibition of BSP mRNA levels. Transient transfection analyses, using chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene, revealed that LPS (1 microg/ml) suppressed expression of luciferase construct, encompassing BSP promoter nucleotides -108 to +60, transfected into ROS17/2.8 cells. The effects of LPS were inhibited by protein kinase A (PKA) inhibitor, H89 and the tyrosine kinase inhibitor, herbimycin A (HA). Introduction of 2 bp mutations in the inverted CCAAT box (ATTGG; nts -50 and -46), a cAMP response element (CRE; nts -75 to -68), a FGF response element (FRE; nts -92 to -85), and a pituitary specific transcription factor binding element (Pit-1; nts -111 to -105) showed that the LPS effects were mediated by the CRE and FRE. Whereas the FRE and 3'-FRE DNA-protein complexes were decreased by LPS, CRE DNA-protein complex did not change after LPS treatment. These studies, therefore, show that LPS suppresses BSP gene transcription through PKA and tyrosine kinase-dependent pathways and that the LPS effects are mediated through CRE and FRE elements in the proximal BSP gene promoter.

Amelogenin stimulates bone sialoprotein (BSP) expression through fibroblast growth factor 2 response element and transforming growth factor-beta1 activation element in the promoter of the BSP gene

BACKGROUND

Amelogenins are a complex mixture of hydrophobic proteins that are the major organic component of developing enamel. The principal function of the amelogenins and their degradation products has been assigned to structural roles in creating the space and milieu for promoting enamel mineralization. Enamel matrix derivative (EMD) has been used clinically for periodontal regeneration and its therapeutic effectiveness has been attributed to amelogenin, non-amelogenin enamel matrix proteins, and growth factors. While EMD is believed to induce periodontal regeneration, the precise mechanism is not known. Bone sialoprotein (BSP), an early phenotypic marker of osteoblast and cementoblast differentiation, has been implicated in the nucleation of hydroxyapatite during bone formation. In this study, we examined the ability of amelogenin to regulate BSP gene transcription in osteoblast like cells.

METHODS

We conducted Northern hybridization, transient transfection analyses, and gel mobility shift assays using full-length recombinant amelogenin to determine the molecular basis of the transcriptional regulation of BSP gene by amelogenin.

RESULTS

Recombinant amelogenin (1 microg/ml, 12 hours) increased BSP mRNA levels approximately 2.4-fold. In transient transfection analyses, amelogenin (1 microg/ml, 12 hours) increased luciferase activity approximately 1.5-fold in pLUC3 (nucleotides -116 to +60) and further increased pLUC5 (nucleotides -801 to +60) activity approximately 2.3-fold transfected into ROS 17/2.8 cells. Amelogenin also increased luciferase activities in rat stromal bone marrow cells. The effect of amelogenin was inhibited by the tyrosine kinase inhibitor herbimycin A. Transcriptional stimulation by amelogenin was almost completely abrogated in cells expressing a BSP promoter construct with a mutation in the fibroblast growth factor 2 (FGF2) response element (FRE). Gel mobility shift assays with radiolabeled FRE and transforming growth factor-beta1 (TGF-beta1) activation element (TAE) ds-oligonucleotides revealed increased binding of nuclear proteins from amelogenin-stimulated ROS 17/2.8 cells.

CONCLUSION

Amelogenin stimulation alters BSP gene transcription by inducing nuclear proteins that bind to the FRE and TAE in the rat BSP gene promoter.

In vivo and in vitro comparison of the effects of FGF-2 null and haplo-insufficiency on bone formation in mice

We previously reported that deletion of the Fgf2 gene (Fgf2-/-) resulted in decreased bone mass in adult mice. This study examines the effect of haplo-insuffiency (Fgf2+/-) on bone loss in vertebrae from these mutant mice. Fgf2+/+ mice attained peak bone mass at 8-9 months of age. In contrast BMD was significantly reduced in vertebrae from adult (8-9) Fgf2+/- mice. Exogenous FGF-2 rescued reduced bone nodule formation in Fgf2+/- and Fgf2-/- cultures. Runx2 mRNA was reduced in cultures from Fgf2+/- and Fgf2-/- mice. FGF receptor2 mRNA and protein were markedly reduced in Fgf2+/- and Fgf2-/- mice. Decreased bone formation in Fgf2 mutant mice may correlate with impaired FGFR signaling, decreased Runx2 gene expression.

Over-expression of fibroblast growth factor-2 causes defective bone mineralization and osteopenia in transgenic mice

Over-expression of human FGF-2 cDNA linked to the phosphoglycerate kinase promoter in transgenic (TgFGF2) mice resulted in a dwarf mouse with premature closure of the growth plate and shortening of bone length. This study was designed to further characterize bone structure and remodeling in these mice. Bones of 1-6 month-old wild (NTg) and TgFGF2 mice were studied. FGF-2 protein levels were higher in bones of TgFGF2 mice. Bone mineral density was significantly decreased as early as 1 month in femurs from TgFGF2 mice compared with NTg mice. Micro-CT of trabecular bone of the distal femurs from 6-month-old TgFGF2 mice revealed significant reduction in trabecular bone volume, trabecular number (Tb.N), and increased trabecular separation (Tb.Sp). Osteoblast surface/bone surface, double-labeled surface, mineral apposition rate, and bone formation rates were all significantly reduced in TgFGF2 mice. There were fewer TRAP positive osteoclasts in calvaria from TgFGF2 mice. Quantitative histomorphometry showed that total bone area was similar in both genotypes, however percent osteoclast surface, and osteoclast number/bone surface were significantly reduced in TgFGF2 mice. Increased replication of TgFGF2 calvarial osteoblasts was observed and primary cultures of bone marrow stromal cells from TgFGF2 expressed markers of mature osteoblasts but formed fewer mineralized nodules. The data presented indicate that non-targeted over-expression of FGF-2 protein resulted in decreased endochondral and intramembranous bone formation. These results are consistent with FGF-2 functioning as a negative regulator of postnatal bone growth and remodeling in this animal model.

Human osteocalcin and bone sialoprotein mediating osteomimicry of prostate cancer cells: role of cAMP-dependent protein kinase A signaling pathway

Osteocalcin and bone sialoprotein are the most abundant noncollagenous bone matrix proteins expressed by osteoblasts. Surprisingly, osteocalcin and bone sialoprotein are also expressed by malignant but not normal prostate epithelial cells. The purpose of this study is to investigate how osteocalcin and bone sialoprotein expression is regulated in prostate cancer cells. Our investigation revealed that (a) human osteocalcin and bone sialoprotein promoter activities in an androgen-independent prostate cancer cell line of LNCaP lineage, C4-2B, were markedly enhanced 7- to 12-fold in a concentration-dependent manner by conditioned medium collected from prostate cancer and bone stromal cells. (b) Deletion analysis of human osteocalcin and bone sialoprotein promoter regions identified cyclic AMP (cAMP)-responsive elements (CRE) as the critical determinants for conditioned medium-mediated osteocalcin and bone sialoprotein gene expression in prostate cancer cells. Consistent with these results, the protein kinase A (PKA) pathway activators forskolin and dibutyryl cAMP and the PKA pathway inhibitor H-89, respectively, increased or repressed human osteocalcin and bone sialoprotein promoter activities. (c) Electrophoretic mobility shift assay showed that conditioned medium-mediated stimulation of human osteocalcin and bone sialoprotein promoter activities occurs through increased interaction between CRE and CRE-binding protein. (d) Conditioned medium was found to induce human osteocalcin and bone sialoprotein promoter activities via increased CRE/CRE-binding protein interaction in a cell background-dependent manner, with marked stimulation in selected prostate cancer but not bone stromal cells. Collectively, these results suggest that osteocalcin and bone sialoprotein expression is coordinated and regulated through cAMP-dependent PKA signaling, which may define the molecular basis of the osteomimicry exhibited by prostate cancer cells.

TNF-alpha suppresses bone sialoprotein (BSP) expression in ROS17/2.8 cells

Tumor necrosis factor-alpha (TNF-alpha) is a major mediator of inflammatory responses in many diseases that inhibits bone formation and stimulates bone resorption. To determine molecular mechanisms involved in the suppression of bone formation we have analyzed the effects of TNF-alpha on BSP gene expression. Bone sialoprotein (BSP) is a mineralized tissue-specific protein that appears to function in the initial mineralization of bone. Previous studies have demonstrated that BSP mRNA expression is essentially restricted to fully-differentiated cells of mineralized connective tissues and that the expression of BSP is developmentally regulated. Treatment of rat osteosarcoma ROS 17/2.8 cells with TNF-alpha (10 ng/ml) for 24 h caused a marked reduction in BSP mRNA levels. The addition of antioxidant N-acetylcysteine (NAC; 20 mM) 30 min prior to stimulation with TNF-alpha attenuated the inhibition of BSP mRNA levels. Transient transfection analyses, using chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene, revealed that TNF-alpha (10 ng/ml) suppressed expression in all constructs, including a short construct (pLUC3; nts -116 to +60), transfected into ROS17/2.8 cells. Further deletion analysis of the BSP promoter showed that a region within nts -84 to -60 was targeted by TNF-alpha, the effects which were inhibited by NAC and the tyrosine kinase inhibitor, herbimycin A (HA). Introduction of 2bp mutations in the inverted CCAAT box (ATTGG; nts -50 and -46), a putative cAMP response element (CRE; nts -75 to -68), and a FGF response element (FRE; nts -92 to -85) showed that the TNF-alpha effects were mediated by the CRE. These results were supported by gel mobility shift assays, using a radiolabeled double-stranded CRE oligonucleotide, which revealed decreased binding of a nuclear protein from TNF-alpha-stimulated ROS 17/2.8 cells. Further, the inhibitory effect of TNF-alpha on CRE DNA-protein complex was completely abolished by NAC or HA treatment. These studies, therefore, show that TNF-alpha suppresses BSP gene transcription through a tyrosine kinase-dependent pathway that generates reactive oxygen species and that the TNF-alpha effects are mediated by a CRE element in the proximal BSP gene promoter.

Regulation of Rat Bone Sialoprotein Gene Transcription by Enamel Matrix Derivative

BACKGROUND

Enamel matrix derivative (EMD) has recently been developed for use as a periodontal regenerative treatment. While EMD is believed to induce regeneration of periodontal tissue, the precise mechanism is not known. Bone sialoprotein (BSP), an early phenotypic marker of osteoblast differentiation, has been implicated in the nucleation of hydroxyapatite during bone formation. In this study, we examined the ability of EMD to regulate BSP gene transcription in osteoblast-like cells.

METHODS

To determine the molecular basis of the transcriptional regulation of BSP gene transcription by EMD, we conducted Northern hybridization, transient transfection analyses with chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene, and gel mobility shift assays.

RESULTS

Using the osteoblastic cell line ROS 17/2.8, we determined that BSP mRNA levels increased approximately 2.8-fold by EMD. In transient transfection analyses, EMD (50 microg/ml, 12 hours) increased luciferase activities of pLUC4 (nt -425 to +60) and pLUC5 (nt -801 to +60), transfected into ROS 17/2.8 cells. Within the pLUC4 and 5, a homeodomain binding element (HOX) and a transforming growth factor (TGF)-beta activation element (TAE) are present. Gel mobility shift assays with radiolabeled HOX and TAE ds-oligonucleotides revealed increased binding of nuclear proteins from EMD stimulated ROS 17/2.8 cells.

CONCLUSION

These studies have, therefore, identified EMD response elements in the rat BSP gene promoter that may mediates the effects of EMD on BSP gene transcription.

Static magnetic fields-induced bone sialoprotein (BSP) expression is mediated through FGF2 response element and pituitary-specific transcription factor-1 motif

Bone sialoprotein (BSP) is a sulfated and phosphorylated glycoprotein found almost exclusively in mineralized connective tissues. Recent studies on the developmental expression of BSP mRNA and temporo-spatial appearance of the protein during bone formation in vivo and in vitro have demonstrated that BSP is expressed by differentiated osteoblasts, and that it may function in the initial nucleation of hydroxyapatite crystals in de novo bone formation. Physical forces may play a fundamental role in the regulation of cell function in bone, but little is known about how cells are able to sense mechanical loads and signal transduction. Magnetic fields of sufficient magnitude have been shown to affect various biologic systems at organ, tissue, cellular, and subcellular levels. In the present study, rat osteosarcoma-derived osteoblast-like cells, UMR 106, were used to assess the effect of static magnetic fields (SMF) on gene transcription of BSP. In our culture system, application of 300 and 800 Gauss SMF increased BSP mRNA levels after 24 h stimulation. To determine the molecular basis of the transcriptional regulation of BSP gene transcription by SMF, we conducted transient transfection analyses with chimeric constructs of the rat BSP gene promoter linked to a luciferase (LUC) reporter gene. SMF (300 and 800 Gauss) increased expression of the construct (pLUC3; -116 to +60) after 24 h treatment. Further deletion analysis of the BSP promoter showed that a region within nt -116 to -84 was targeted by SMF, the effect of which was inhibited by the tyrosine kinase inhibitor herbimycin A (HA). Mutations (2 bp) were made in an inverted CCAAT box between nt -50 and -46, a cyclicAMP response element (CRE; between nt -75 and -68), a fibroblast growth factor-2 response element (FRE; -92 to -85), and a pituitary-specific transcription factor-1 motif (Pit-1; nt -111 to -105) within the pLUC3 construct. Transcriptional stimulation by SMF was almost completely abrogated in constructs that included 2-bp mutations in the FRE and Pit-1. Binding of nuclear proteins to a radiolabeled FRE was increased and that to a Pit-1 was decreased in nuclear extracts prepared from SMF-stimulated UMR 106 cells. Further, the stimulatory and inhibitory effects of SMF on FRE and Pit-1 DNA-protein complexes were completely abolished by HA treatment. These studies, therefore, show that SMF increases BSP transcription through a tyrosine kinase-dependent pathway and that the SMF effects are mediated through juxtaposed FRE and Pit-1elements in the proximal promoter of the BSP gene.