Coordinate occupancy of AP-1 sites in the vitamin D-responsive and CCAAT box elements by Fos-Jun in the osteocalcin gene: model for phenotype suppression of transcription

Genetic response to low‑intensity ultrasound on mouse ST2 bone marrow stromal cells

Although low‑intensity ultrasound (LIUS) is a clinically established procedure, the early cellular effect of LIUS on a genetic level has not yet been studied. The current study investigated the early response genes elicited by LIUS in bone marrow stromal cells (BMSCs) using global‑scale microarrays and computational gene expression analysis tools. Mouse ST2 BMSCs were treated with LIUS [I_SATA, 25 mW/cm² for 20 min with a frequency of 1.11 MHz in a pulsed‑wave mode (0.2‑s burst sine waves repeated at 1 kHz)], then cultured for 0.5, 1 and 3 h at 37˚C. The time course of changes in gene expression was evaluated using GeneChip^® high‑density oligonucleotide microarrays and Ingenuity^® Pathway Analysis tools. The results were verified by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR). A single exposure of LIUS did not affect cell morphology, cell growth or alkaline phosphatase activity. However, 61 upregulated and 103 downregulated genes were identified from 0.5 to 3 h after LIUS treatment. Two significant gene networks, labeled E and H, were identified from the upregulated genes, while a third network, labeled T, was identified from the downregulated genes. Gene network E or H containing the immediate‑early genes FBJ osteosarcoma oncogene and early growth response 1 or the heat shock proteins heat shock protein 1a/b was associated mainly with the biological functions of bone physiology and protein folding or apoptosis, respectively. Gene network T containing transcription factors fos‑like antigen 1 and serum response factor was also associated with the biological functions of the gene expression. RT‑qPCR indicated that the expression of several genes in the gene networks E and H were elevated in LIUS‑treated cells. LIUS was demonstrated to induce gene expression after short application in mouse ST2 BMSCs. The results of the present study provide a basis for the elucidation of the detailed molecular mechanisms underlying the cellular effects of LIUS.

In vitro evaluation of osteoblast adhesion, proliferation and differentiation on chitosan-TiO2 nanotubes scaffolds with Ca2+ ions

Hydrothermally synthesized TiO₂ nanotubes (TNTs) were first used as a filler for chitosan scaffold for reinforcement purpose. Chitosan-TNTs (CTNTs) scaffolds prepared via direct blending and freeze drying retained cylindrical structure and showed enhanced compressive modulus and reduced degradation rate compared to chitosan membrane which experienced severe shrinkage after rehydration with ethanol. Macroporous interconnectivity with pore size of 70-230μm and porosity of 88% were found in CTNTs scaffolds. Subsequently, the functionalization of CTNTs scaffolds with CaCl₂ solutions (0.5mM-40.5mM) was conducted at physiological pH. The adsorption isotherm of Ca²⁺ ions onto CTNTs scaffolds fitted well with Freundlich isotherm. CTNTs scaffolds with Ca²⁺ ions showed high biocompatibility by promoting adhesion, proliferation and early differentiation of MG63 in a non-dose dependent manner. CTNTs scaffolds with Ca²⁺ ions can be an alternative for bone regeneration.

Demineralized bone matrix used for direct pulp capping in rats

Objectives

To evaluate the wound healing process following direct pulp capping with demineralized bone matrix (DBM) and calcium hydroxide (Ca(OH)₂).

Methods

Fifty 8-weeks-old SPF Wistar male rats were divided into two groups: one was the DBM treated group, and the other was the Ca(OH)₂ treated group. Pulpotomy was performed on the maxillary first molar of one side of each rat, and the another side was left as the blank control. Rats were sacrificed after each observation period (1, 3, 7, 14 and 28 days) and specimen slices were made. Hematoxylin-Eosin (HE) staining was used for observing the changes of pulp tissue, and immunohistochemical staining was used for observing the expression of reparative dentinogenesis-related factors runt transcription factor 2 (Runx2), type I collagen (COL I), osteocalcin (OCN) and dentin sialoprotein (DSP).

Results

Inflammatory cell infiltration (ICI) and pulp tissue disorganization (PTD) could be observed in both the DBM and Ca(OH)₂ groups at all observation periods. The DBM group showed slighter ICI on 1 and 28 days and milder PTD on 28 days, with a significant difference (P<0.05). Reparative dentin formation (RDF) could initially be observed on 14 days postoperatively, and the DBM group showed more regular and thinner RDF with significant differences on 14 and 28 days compared with the Ca(OH)₂ group (P<0.05). In both groups, the expression of Runx2, COL I, DSP and OCN were positive. Generally, the expression of these four factors in the DBM group was stronger than the Ca(OH)₂ group on the same observation periods.

Conclusions

DBM had the ability of inducing odontoblast differentiation and promoting dentinogenesis. DBM could initiate physiologic wound healing in pulp and had the ability to promote reparative dentin formation. Consequently, DBM may be an acceptable alternative for direct pulp capping.

Activation of Mechanosensitive Transcription Factors in Murine C2C12 Mesenchymal Precursors by Focused Low-Intensity Pulsed Ultrasound (FLIPUS)

In this paper, we investigated the mechanoresponse of C2C12 mesenchymal precursor cells to focused low-intensity pulsed ultrasound (FLIPUS). The setup has been developed for in vitro stimulation of adherent cells in the defocused far field of the ultrasound propagating through the bottom of the well plate. Twenty-four-well tissue culture plates, carrying the cell monolayers, were incubated in a temperature-controlled water tank. The ultrasound was applied at 3.6-MHz frequency, pulsed at 100-Hz repetition frequency with a 27.8% duty cycle, and calibrated at an output intensity of I_SATA = 44.5 ±7.1 mW/cm². Numerical sound propagation simulations showed no generation of standing waves in the well plate. The response of murine C2C12 cells to FLIPUS was evaluated by measuring activation of mechanosensitive transcription factors, i.e., activator protein-1 (AP-1), specificity protein 1 (Sp1), and transcriptional enhancer factor (TEAD), and expression of mechanosensitive genes, i.e., c-fos, c-jun, heparin binding growth associated molecule (HB-GAM), and Cyr-61. FLIPUS induced 50% ( p ≤ 0.05 ) and 70% ( p ≤ 0.05 ) increases in AP-1 and TEAD promoter activities, respectively, when stimulated for 5 min. The Sp1 activity was enhanced by about 20% ( p ≤ 0.05 ) after 5-min FLIPUS exposure and the trend persisted for 30-min ( p ≤ 0.05 ) and 1-h ( p ≤ 0.05 ) stimulation times. Expressions of mechanosensitive genes c-fos ( p ≤ 0.05 ), c-jun ( p ≤ 0.05 ), HB-GAM ( p ≤ 0.05 ), and cystein-rich protein 61 ( p ≤ 0.05 ) were enhanced in response to 5-min FLIPUS stimulation. The increase in proliferation of C2C12s occurred after the FLIPUS stimulation ( p ≤ 0.05 ), with AP-1, Sp1, and TEAD possibly regulating the observed cellular activities.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

Endocrinology of bone/brain crosstalk

Bone metabolism is regulated by the action of two skeletal cells: osteoblasts and osteoclasts. This process is controlled by many genetic, hormonal and lifestyle factors, but today more and more studies have allowed us to identify a neuronal regulation system termed 'bone-brain crosstalk', which highlights a direct relationship between bone tissue and the nervous system. The first documentation of an anatomic relationship between nerves and bone was made via a wood cut by Charles Estienne in Paris in 1545. His diagram demonstrated nerves entering and leaving the bones of a skeleton. Later, several studies were conducted on bone innervation and, as of today, many observations on the regulation of bone remodeling by neurons and neuropeptides that reside in the CNS have created a new research field, that is, neuroskeletal research.

An integrated understanding of the physiological response to elevated extracellular phosphate

Recent studies have suggested that changes in serum phosphate levels influence pathological states associated with aging such as cancer, bone metabolism, and cardiovascular function, even in individuals with normal renal function. The causes are only beginning to be elucidated but are likely a combination of endocrine, paracrine, autocrine, and cell autonomous effects. We have used an integrated quantitative biology approach, combining transcriptomics and proteomics to define a multi-phase, extracellular phosphate-induced, signaling network in pre-osteoblasts as well as primary human and mouse mesenchymal stromal cells. We identified a rapid mitogenic response stimulated by elevated phosphate that results in the induction of immediate early genes including c-fos. The mechanism of activation requires FGF receptor signaling followed by stimulation of N-Ras and activation of AP-1 and serum response elements. A distinct long-term response also requires FGF receptor signaling and results in N-Ras activation and expression of genes and secretion of proteins involved in matrix regulation, calcification, and angiogenesis. The late response is synergistically enhanced by addition of FGF23 peptide. The intermediate phase results in increased oxidative phosphorylation and ATP production and is necessary for the late response providing a functional link between the phases. Collectively, the results define elevated phosphate, as a mitogen and define specific mechanisms by which phosphate stimulates proliferation and matrix regulation. Our approach provides a comprehensive understanding of the cellular response to elevated extracellular phosphate, functionally connecting temporally coordinated signaling, transcriptional, and metabolic events with changes in long-term cell behavior.

The biology and pathology of vitamin D control in bone

Vitamin D is a steroid pro-hormone, whose active metabolite binds the vitamin D receptor (VDR) which, in turn, binds to DNA sequences on target genes as a heterodimer with the retinoid-X receptor, resulting in regulation of gene expression. The vitamin D pro-hormone can be synthesized in the skin, in response to ultraviolet radiation; however, dietary sources have become increasingly important as a result of cultural changes over the past few centuries. Based on its initial discovery as an anti-rachitic factor, studies of the role of vitamin D and its receptor have largely focused on the skeleton. Investigations into the pathophysiologic basis and therapeutic responses of skeletal disorders associated with impaired vitamin D action have led to the identification of the molecular pathways involved in hormone activation and regulation of gene expression by the liganded VDR. These studies have also demonstrated that the skeletal actions of the VDR and its ligand are largely redundant if normal mineral ion homeostasis can be maintained by other means. However, investigations in animal models with tissue-specific ablation of the VDR or the enzyme required for hormone activation have demonstrated novel actions in skeletal tissues. The active vitamin D metabolite has been shown to have both paracrine and endocrine actions in other tissues as well.

Regulation of gene expression in osteoblasts

In recent years, much progress has been made in understanding the factors that regulate the gene expression program that underlies the induction, proliferation, differentiation, and maturation of osteoblasts. A large and growing number of transcription factors make important contributions to the precise control of osteoblast formation and function. It has become increasingly clear that these diverse transcription factors and the signals that regulate their activity cannot be viewed as discrete, separate signaling pathways. Rather, they form a highly interconnected, cooperative network that permits gene expression to be closely regulated. There has also been a substantial increase in our understanding of the mechanistic control of gene expression by cofactors such as acetyltransferases and histone deacetylases. The purpose of this review is to highlight recent progress in understanding the major transcription factors and epigenetic coregulators, including histone deacetylases and microRNAs, involved in osteoblastogenesis and the mechanisms that determine their functions as regulators of gene expression.

Transcription factor and microRNA regulation in androgen-dependent and -independent prostate cancer cells

Background

Prostate cancer is one of the leading causes of cancer death in men. Androgen ablation, the most commonly-used therapy for progressive prostate cancer, is ineffective once the cancer cells become androgen-independent. The regulatory mechanisms that cause this transition (from androgen-dependent to androgen-independent) remain unknown. In this study, based on the microarray data comparing global gene expression patterns in the prostate tissue between androgen-dependent and -independent prostate cancer patients, we indentify a set of transcription factors and microRNAs that potentially cause such difference, using a model-based computational approach.

Results

From 335 position weight matrices in the TRANSFAC database and 564 microRNAs in the microRNA registry, our model identify 5 transcription factors and 7 microRNAs to be potentially responsible for the level of androgen dependency. Of these transcription factors and microRNAs, the estimated function of all the 5 transcription factors are predicted to be inhibiting transcription in androgen-independent samples comparing with the dependent ones. Six out of 7 microRNAs, however, demonstrated stimulatory effects. We also find that the expression levels of three predicted transcription factors, including AP-1, STAT3 (signal transducers and activators of transcription 3), and DBP (albumin D-box) are significantly different between androgen-dependent and -independent patients. In addition, microRNA microarray data from other studies confirm that several predicted microRNAs, including miR-21, miR-135a, and miR-135b, demonstrate differential expression in prostate cancer cells, comparing with normal tissues.

Conclusion

We present a model-based computational approach to identify transcription factors and microRNAs influencing the progression of androgen-dependent prostate cancer to androgen-independent prostate cancer. This result suggests that the capability of transcription factors to initiate transcription and microRNAs to facilitate mRNA degradation are both decreased in androgen-independent prostate cancer. The proposed model-based approach indicates that considering combinatorial effects of transcription factors and microRNAs in a unified model provides additional transcriptional and post-transcriptional regulatory mechanisms on global gene expression in the prostate cancer with different hormone-dependency.

Effects of continuous activation of vitamin D and Wnt response pathways on osteoblastic proliferation and differentiation

The Wnt pathway regulates cell proliferation and differentiation in development and disease, with a number of recent reports linking Wnt to control of osteoblast differentiation and bone mass. There is also accumulating evidence for interaction between the Wnt and nuclear receptor (NR)-mediated control pathways in non-osseous tissues. Calcitriol (1,25D(3)), which is the active hormonal ligand for the vitamin D receptor (VDR), a member of the NR superfamily, induces osteoblastic cell cycle arrest and expression of genes involved in matrix mineralization in vitro, with over-expression of VDR in mature osteoblasts increasing bone mass in mice. To determine whether the vitamin D and Wnt control pathways interact in osteoblastic regulation, we investigated the treatment effects of 1,25D(3) and/or lithium chloride (LiCl), which mimics canonical Wnt pathway activation, on osteoblast proliferation and differentiation. Treatments were initiated at various stages in differentiating cultures of the MC3T3-E1 osteoprogenitor cell line. Treatment of subconfluent cultures (day 1) with either agent transiently increased cell proliferation but decreased viable cell number, with additive inhibition after combined treatment. Interestingly, although early response patterns of alkaline phosphatase activity to 1,25D(3) and LiCl were opposite, mineralized nodule formation was virtually abolished by either treatment initiated at day 1 and remained very low after initiating treatments at matrix-formation stage (day 6). By contrast, mineralized nodule formation was substantial but reduced if 1,25D(3) and/or LiCl treatment was initiated at mineralization onset (day 13). Osteocalcin production was reduced by all treatments at all time points. Thus, vitamin D and/or canonical Wnt pathway activation markedly reduced mineralization, with additive inhibitory effects on viable cell number. The strength of the response was dependent on the stage of differentiation at treatment initiation. Importantly, the inhibitory effect of LiCl in this committed osteoblastic cell line contrasts with the stimulatory effects of genetic Wnt pathway activation in human and mouse bone tissue. This is consistent with the anabolic Wnt response occurring at a stage prior to the mature osteoprogenitor in the intact skeleton and suggests that prolonged or repeated activation of the canonical Wnt response in committed cells may have an inhibitory effect on osteoblast differentiation and function.

Differential mechanisms of transcriptional regulation of the mouse osteocalcin gene by Jun family members

The osteocalcin gene encodes an osteoblast-specific protein that is induced with the onset of mineralization at late stages of differentiation. Several transcriptional regulators have been characterized that control the transcription of osteocalcin, including activator protein 1 (AP-1) family members such as the Fra2/JunD heterodimer. We have previously shown that the c-Jun homodimer activates transcription from the murine osteocalcin proximal promoter and that this response is potentiated by the alpha chain of the nascent polypeptide-associated complex (alphaNAC) transcriptional coactivator. We now further explore the mechanisms involved and show that c-Jun binds two cryptic AP-1 sites within the proximal promoter of osteocalcin and that this binding is strictly alphaNAC-dependent. Chromatin immunoprecipitation (ChIP) confirmed that c-Jun occupies its binding sites within the osteocalcin 5'-flanking region in living osteoblasts. Interestingly, the ChIP assay revealed that both JunB and JunD also bind the osteocalcin promoter. JunD, but not JunB, stimulated osteocalcin gene transcription in transient transfection assays, but this effect was not potentiated by alphaNAC. Thus, the c-Jun and JunD family members utilize distinct mechanisms that implicate differential interaction with transcriptional coactivators to regulate osteocalcin expression.

Sequential expression of endothelial nitric oxide synthase, inducible nitric oxide synthase, and nitrotyrosine in odontoblasts and pulp cells during dentin repair after tooth preparation in rat molars

Nitric oxide (NO) stimulates osteoblast differentiation, but whether NO contributes to odontoblast differentiation during dentin repair is unknown. By using reverse transcription/polymerase chain reaction and immunostaining, we investigated the gene expression and/or immunolocalization of endothelial NO synthase (eNOS), inducible NOS (iNOS), and nitrotyrosine (a biomarker for NO-derived peroxinitrite), and alkaline phosphatase (ALP) and osteocalcin (early and terminal differentiation markers of odontoblasts, respectively) in dental pulp tissue after rat tooth preparation. At the early stage (1-3 days) post-preparation, markedly increased expression of iNOS and nitrotyrosine was found in odontoblasts and pulp cells beneath the cavity, whereas eNOS expression was significantly decreased. ALP mRNA expression was significantly increased after 1 day but decreased after 3 days, whereas ALP activity was weak in the dentin-pulp interface under the cavity after 1 day but strong after 3 days. Osteocalcin mRNA expression was significantly increased at this stage. At 7 days post-preparation, tertiary dentin was formed under the cavity. All the molecules studied were expressed at control levels in odontoblasts/pulp cells beneath the cavity. These findings show that abundant NO is released from odontoblasts and pulp cells at an early stage after tooth preparation and indicate that, after tooth preparation, the up-regulation of iNOS and nitrotyrosine in odontoblasts is synchronized with increased cellular expression of ALP and osteocalcin. Therefore, the NO synthesized by iNOS after tooth preparation probably participates in regulating odontoblast differentiation during tertiary dentinogenesis.

Preventing polyglutamine-induced activation of c-Jun delays neuronal dysfunction in a mouse model of SCA7 retinopathy

We have approached the role of cellular stress in neurodegenerative diseases caused by polyglutamine expansion (polyQ) in the context of Spinocerebellar ataxia type 7 (SCA7) that includes retinal degeneration. Using the R7E mouse, in which polyQ-ataxin-7 is specifically over-expressed in rod photoreceptors, we previously showed that rod dysfunction correlated to moderate and prolonged activation of the JNK/c-Jun stress pathway. SCA7 retinopathy was also associated with reduced expression of rod-specific genes, including the transcription factor Nrl, which is essential for rod differentiation and function. Here, we report that R7E retinopathy is improved upon breeding with the JunAA knock-in mice, in which JNK-mediated activation of c-Jun is compromised. Expression of Nrl and its downstream targets, which are involved in phototranduction, are partially restored in the JunAA-R7E mice. We further show that c-Jun can directly repress the transcription of Nrl. Our studies suggest that polyQ-induced cellular stress leads to repression of genes necessary for neuronal fate and function.

Transforming growth factor-beta1 to the bone

TGF-beta1 is a ubiquitous growth factor that is implicated in the control of proliferation, migration, differentiation, and survival of many different cell types. It influences such diverse processes as embryogenesis, angiogenesis, inflammation, and wound healing. In skeletal tissue, TGF-beta1 plays a major role in development and maintenance, affecting both cartilage and bone metabolism, the latter being the subject of this review. Because it affects both cells of the osteoblast and osteoclast lineage, TGF-beta1 is one of the most important factors in the bone environment, helping to retain the balance between the dynamic processes of bone resorption and bone formation. Many seemingly contradictory reports have been published on the exact functioning of TGF-beta1 in the bone milieu. This review provides an overall picture of the bone-specific actions of TGF-beta1 and reconciles experimental discrepancies that have been reported for this multifunctional cytokine.

Sequence-specific DNA binding by the alphaNAC coactivator is required for potentiation of c-Jun-dependent transcription of the osteocalcin gene

Since the c-Jun coactivator alphaNAC was initially identified in a differential screen for genes expressed in differentiated osteoblasts, we examined whether the osteocalcin gene, a specific marker of terminal osteoblastic differentiation, could be a natural target for the coactivating function of alphaNAC. We had also previously shown that alphaNAC can specifically bind DNA in vitro, but it remained unclear whether the DNA-binding function of alphaNAC is expressed in vivo or if it is required for coactivation. We have identified an alphaNAC binding site within the murine osteocalcin gene proximal promoter region and demonstrated that recombinant alphaNAC or alphaNAC from ROS17/2.8 nuclear extracts can specifically bind this element. Using transient transfection assays, we have shown that alphaNAC specifically potentiated the c-Jun-dependent transcription of the osteocalcin promoter and that this activity specifically required the DNA-binding domain of alphaNAC. Chromatin immunoprecipitation confirmed that alphaNAC occupies its binding site on the osteocalcin promoter in living osteoblastic cells expressing osteocalcin. Inhibition of the expression of endogenous alphaNAC in osteoblastic cells by use of RNA interference provoked a decrease in osteocalcin gene transcription. Our results show that the osteocalcin gene is a target for the alphaNAC coactivating function, and we propose that alphaNAC is specifically targeted to the osteocalcin promoter through its DNA-binding activity as a means to achieve increased specificity in gene transcription.

Expression of osteocalcin and Jun D in the early period during reactionary dentin formation after tooth preparation in rat molars

We examined, in rats, the expression of osteocalcin and Jun D in the early stage of reactionary dentin formation after tooth preparation and the accompanying morphological changes. Reverse transcription/polymerase chain reaction analysis revealed strong expression of osteocalcin mRNA in pulp tissue at 2 and 3 days post-preparation compared with that in control teeth. Light microscopy demonstrated that, at the dentin-pulp interface, damaged odontoblasts were detached from the dentin matrix immediately after preparation, with neutrophils lining the dental surface after 1 day. After 2-3 days, differentiated odontoblasts appeared at the interface. Reactionary dentin with tubular structures was formed under the cavity after 10 days. Immunoelectron microscopy showed that trace amounts of osteocalcin were expressed in odontoblasts at 2 days post-preparation, and abundant osteocalcin was found in the highly developed Golgi apparatus and granules at 3 days post-preparation. Osteocalcin was also found on type I collagen fibrils in newly formed predentin. The existing dentinal tubules were filled with osteocalcin-coated type I collagen fibrils. We observed, by immunohistochemistry, that Jun D was temporally expressed in the nuclei of the odontoblasts at 1 and 2 days post-preparation. However, no Jun D was found in the dental pulp cells at any other time or in control teeth. Thus, osteocalcin expression is correlated with reactionary dentin formation, and Jun D is associated with osteocalcin expression in odontoblasts. Osteocalcin may also serve as an obturator of the dentinal tubules to protect dental pulp vitality against external irritants after preparation.

Transient increase in anti-p-ATF2 immunoreactivity in the late secretion ameloblasts apical to the transition zone of rat incisors

Activating transcription factor 2 (ATF2) was localized in the ameloblasts of rat incisors by immunohistochemistry. A specific antibody against phosphorylated ATF2 (p-ATF2), which is an activated form of ATF2, was detected from the proliferation zone to maturation ameloblasts just after the transition. In the secretion zone, a transient increase in p-ATF2 was observed in the late secretion ameloblast nuclei, where a stronger reactivity of p-ATF2 extended from 1 mm apical to the transition to the transition zone, whereas ameloblast nuclei in most of the maturation zone exhibited either weak or no reactivity. A similar pattern was also observed in the case of c-Jun immunohistochemistry, except for in most of the maturation zone, where strong c-Jun reactivity was detected. Thus, ATF-2 and c-Jun are deeply involved in amelogenesis and, in particular, ATF2 is related to the proliferation, differentiation, secretion and transition zones.

Different effects of BMP-2 on marrow stromal cells from human and rat bone

Bone morphogenetic proteins (BMPs) promote the differentiation of osteoprogenitor cells, and also induce osteogenesis in bone marrow stromal cells (MSC) from rats and mice. However, compared to results with animal models, BMPs are relatively inefficient in inducing human MSC to undergo osteogenesis, and are much less effective in promoting bone formation in human clinical trials. Previous studies indicated that, while human MSC respond to dexamethasone with elevated levels of the osteoblast marker alkaline phosphatase, most isolates of human MSC fail to show alkaline phosphatase induction in response to BMP-2, BMP-4, or BMP-7. Several other genes known to be induced by BMPs are appropriately regulated; thus, human MSC are capable of some BMP-activated signaling. Analysis of the BMP receptors ALK-3 and ALK-6 indicated that, although ALK-6 mRNA was not expressed in human MSC, overexpressing a constitutively active ALK-6 receptor did not induce elevated alkaline phosphatase. Real-time RT-PCR was used to investigate expression of several osteoblast-related transcription factors in MSC after 6 days' exposure to BMP2 or dexamethasone. Msx-2, a transcription factor that has been reported to inhibit differentiation of osteoprogenitor cells, showed 10-fold elevation in BMP-2-treated human MSC, but not in BMP-2-treated rat MSC. Overexpression of Msx-2 in human and rat MSC, however, did not alter alkaline phosphatase levels, which suggests that absence of BMP-stimulated alkaline phosphatase was not caused by the BMP-2-induced increase in Msx-2. Although Runx2 isoforms have been implicated in control of osteoblast differentiation, levels of this transcription factor were unaffected by BMP treatment. Expression of the FKHR transcription factor, which has been reported to regulate alkaline phosphatase transcription in mouse cells, showed a modest increase in response to BMP-2, but a much greater increase in dexamethasone-treated cells. We propose that BMP regulation of the bone/liver/kidney alkaline phosphatase gene is indirect, requiring expression of new transcription factor(s) that behave differently in rodent and human MSC.

Integration of hormone signaling in the regulation of human 25(OH)D3 24-hydroxylase transcription

The current study sought to define the molecular mechanisms involved in the cross talk between 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] and activators of PKC in the regulation of 25(OH)D(3) 24-hydroxlyase [24(OH)ase]. Transfection of the h24(OH)ase promoter construct [-5,500/-22 luciferase; vitamin D response elements at -294/-274 and -174/-151; AP-1 site at -1,167/-1,160] in vitamin D receptor (VDR)-transfected COS-7 cells resulted in strong activation by 1,25(OH)(2)D(3). In these cells, cotreatment with the PKC activator TPA and 1,25(OH)(2)D(3) yielded a 27-fold increase in luciferase activity, which was 2- to 3-fold greater than activation obtained with 1,25(OH)(2)D(3) alone (P < 0.05). Similar results were observed using LLCPK-1 kidney cells, suggesting that the previously observed enhancement of 1,25(OH)(2)D(3)-induced renal 24(OH)ase mRNA and activity by PKC activation occurs at the level of transcription. The functional cooperation between PKC activation and VDR was not found to be mediated by the AP-1 site in the h24(OH)ase promoter or by enhanced binding of GRIP or DRIP205 to VDR and was also not due to PKC-mediated phosphorylation of VDR on Ser(51). Our study demonstrates that, in LLCPK-1 kidney cells, the PKC enhancement of 1,25(OH)(2)D(3)-stimulated transcription may be due, in part, to an increase in VDR concentration. In addition, inhibitors of the MAPK pathway were found to decrease the TPA enhancement (P < 0.05). Because activation of MAPK has been reported to result in the phosphorylation of SRC-1 and in functional cooperation between SRC-1 and CREB binding protein, we propose that the potentiation of VDR-mediated transcription may also be mediated through changes in the phosphorylation of specific VDR coregulators.

Parathyroid hormone induction of the osteocalcin gene. Requirement for an osteoblast-specific element 1 sequence in the promoter and involvement of multiple-signaling pathways

Parathyroid hormone (PTH) is an important peptide hormone regulator of bone formation and osteoblast activity. However, its mechanism of action in bone cells is largely unknown. This study examined the effect of PTH on mouse osteocalcin gene expression in MC3T3-E1 preosteoblastic cells and primary cultures of bone marrow stromal cells. PTH increased the levels of osteocalcin mRNA 4-5-fold in both cell types. PTH also stimulated transcriptional activity of a 1.3-kb fragment of the mouse osteocalcin gene 2 (mOG2) promoter. Inhibitor studies revealed a requirement for protein kinase A, protein kinase C, and mitogen-activated protein kinase pathways in the PTH response. Deletion of the mOG2 promoter sequence from -1316 to -116 caused no loss in PTH responsiveness whereas deletion from -116 to -34 completely prevented PTH stimulation. Interestingly, this promoter region does not contain the RUNX2 binding site shown to be necessary for PTH responsiveness in other systems. Nuclear extracts from PTH-treated MC3T3-E1 cells exhibited increased binding to OSE1, a previously described osteoblast-specific enhancer in the mOG2 promoter. Furthermore, mutation of OSE1 in DNA transfection assays established the requirement for this element in the PTH response. Collectively, these studies establish that actions of PTH on the osteocalcin gene are mediated by multiple signaling pathways and require OSE1 and associated nuclear proteins.

Mechanisms for the enhancement of fracture healing in rats treated with intermittent low-dose human parathyroid hormone (1-34)

Recent reports have demonstrated that intermittent treatment with parathyroid hormone (1-34) [PTH(1-34)] increases callus formation and mechanical strength in experimental fracture healing. However, little is known about the optimal dose required for enhancement of fracture repair or the molecular mechanisms by which PTH regulates the healing process. In this study, we analyzed the underlying molecular mechanisms by which PTH affects fracture healing and tested the hypothesis that intermittent low-dose treatment with human PTH(1-34) can increase callus formation and mechanical strength. Unilateral femoral fractures were produced and a daily subcutaneous injection of 10 microg/kg of PTH(1-34) was administered during the entire healing period. Control animals were injected with vehicle solution alone. The results showed that on day 28 and day 42 after fracture, bone mineral content (BMC), bone mineral density (BMD), and ultimate load to failure of the calluses were significantly increased in the PTH-treated group compared with controls (day 28, 61, 46, and 32%; day 42, 119, 74, and 55%, respectively). The number of proliferating cell nuclear antigen (PCNA)-positive subperiosteal osteoprogenitor cells was significantly increased in the calluses of the PTH-treated group on day 2, and TRAP+ multinucleated cells were significantly increased in areas of callus cancellous bone on day 7. The levels of expression of type I collagen (COLlA1), osteonectin (ON), ALP, and osteocalcin (OC) mRNA were increased markedly in the PTH-treated group and accompanied by enhanced expression of insulin-like growth factor (IGF)-I mRNA during the early stages of healing (days 4-7). The increased expression of COL1A1, ON, ALP, and OC mRNA continued during the later stages of healing (days 14-21) despite a lack of up-regulation of IGF-I mRNA. These results suggest that treatment of fractures with intermittent low dose PTH(1-34) enhances callus formation by the early stimulation of proliferation and differentiation of osteoprogenitor cells, increases production of bone matrix proteins, and enhances osteoclastogenesis during the phase of callus remodeling. The resultant effect to increase callus mechanical strength supports the concept that clinical investigations on the ability of injectable low-dose PTH(1-34) to enhance fracture healing are indicated.

Enhancement of osteogenesis in vitro by a novel osteoblast differentiation-promoting compound, TAK-778, partly through the expression of Msx2

TAK-778 [(2R,4S)-(-)-N-(4-Diethoxyphosphorylmethylphenyl)-1,2,4,5-tetrahydro-4-methyl-7,8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxamide: mw 505.52], a novel compound promoting osteoblast differentiation, promotes osteogenesis in vitro and enhances bone formation during skeletal repair in vivo. In this study, we further evaluated the effects of TAK-778 on the differentiation of cultured bone marrow stromal cells into osteoblasts in the presence of dexamethasone, paying particular attention to the expression of transcription factors involved in regulating osteoblast differentiation. Treatment of TAK-778 (10(-7)-10(-5) M) for 4 h resulted in an increase in the mRNA expression of Msx2, but not Cbfa1 or Dlx5. This transcriptional alteration preceded the changes in other markers related to the osteoblast phenotype, such as alkaline phosphatase and osteocalcin mRNA. The transfection of Msx2-antisense in the cells caused a significant reduction in the levels of alkaline phosphatase mRNA expression induced by TAK-778. These results suggest that TAK-778 promotes osteoblast differentiation partly through the expression of Msx2, a homeobox-related gene.

The induction of c-fos mRNA expression by mechanical stress in human periodontal ligament cells

The periodontal ligament is subjected to mechanical loading during occlusion and mastication. Although internuclear transcription factors are associated with the regulatory pathway that converts these extracellular mechanical stimuli into a cellular response, there are no reports on these in human periodontal ligament fibroblasts. In this study, the amounts of c-fos mRNA in human periodontal ligament fibroblasts were investigated shortly after subjecting them to a cyclic tension force in vitro. The mRNA of alkaline phosphatase and the matrix proteins type I collagen, type III collagen, matrix Gla-protein, osteonectin, osteopontin, and osteocalcin were also examined. A significant, rapid, transient increase in c-fos mRNA was detected, which peaked 30 min after the application of mechanical force. However, there was no significant change in the mRNA for alkaline phosphatase or the matrix proteins. These results provide evidence that periodontal ligament fibroblasts and c-fos may play a critical part in the response of periodontal tissue to mechanical stimulation.

Signal transduction system for interleukin-6 synthesis stimulated by lipopolysaccharide in human osteoblasts

Lipopolysaccharide (LPS) is a bacterial cell component that plays multifunctional roles in inflammatory reactions, and one of the roles is as a powerful stimulator of bone resorption. LPS stimulated bone resorption via CD14 in mouse calvaria and was reported to function as a receptor for bacterial LPS complexed with serum proteins. Interleukin-6 (IL-6) is capable of stimulating the differentiation of osteoclasts from their hematopoietic precursors, and LPS elevates IL-6 synthesis in human osteoblastic cells. However, the signaling pathway of LPS-induced IL-6 synthesis in osteoblasts is unknown. In the present study, we could detect the existence of CD14 in human osteoblastic cells by RT-PCR analysis and show that LPS increased IL-6 mRNA and synthesis via CD14 in human osteoblastic cells. In human osteoblasts (SaM-1 cells) treated with 10 microg/ml LPS, increases in IL-6 mRNA and synthesis were inhibited by anti-CD14 antibody (MEM-18), PD98059 (an inhibitor of classic mitogen-activated protein kinase [MAPK]), or SB203580 (an inhibitor of p38 MAPK) but were not inhibited by H-89 (an inhibitor of protein kinase A [PKA]) and calphostin C (an inhibitor of protein kinase C [PKC]). Furthermore, LPS-induced IL-6 synthesis was inhibited by curcumin (an inhibitor of activating protein-1 [AP-1]) but not by pyrrolidine dithiocarbamate (PDTC) (an inhibitor of nuclear factor kappa B [NF-kappaB]). The findings of the present study suggest that the LPS receptor CD14, existent in human osteoblastic cells, and IL-6 synthesis in response to LPS probably occur via CD14, p38 MAPK, and MAP kinase/extracellular-regulated kinase kinase (MEK), leading to the transcriptional activation of AP-1 in human osteoblastic cells.

Signal transduction system for interleukin-6 and interleukin-11 synthesis stimulated by epinephrine in human osteoblasts and human osteogenic sarcoma cells

Epinephrine increased gene- and protein-expression of interleukin-6 (IL-6) and interleukin-11 (IL-11), which are capable of stimulating the development of osteoclasts from their hematopoietic precursors, in human osteoblast (SaM-1) and human osteosarcoma (SaOS-2, HOS, and MG-63) cell lines. An increase in IL-6 and IL-11 synthesis in response to epinephrine appeared to be a common feature in osteoblastic cells, but the magnitude of expression was different in these cell lines. In HOS cells treated with epinephrine, increases of IL-6 and IL-11 synthesis were inhibited by timolol (a beta-blocker), H-89 (N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide; an inhibitor of protein kinase A (PKA)) and SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole; an inhibitor of p38 mitogen-activated protein kinase (MAPK)], but not by phentolamine (an alpha-blocker), calphostin C [an inhibitor of protein kinase C (PKC)], or PD98059 (2'-amino-3'-methoxyflavone; an inhibitor of classic MAPK), suggesting a common pathway mediated by beta-adrenergic receptors in the PKA and p38 systems involved in the signal transduction of IL-6 and IL-11. Furthermore, expression of both genes was inhibited by curcumin [an inhibitor of activating protein-1 (AP-1) activation], but not by pyrrolidine dithiocarbamate (PDTC) [an inhibitor of nuclear factor (NF)-kappaB]. The pharmacological study suggested that coinduction of the two genes in response to epinephrine occurred via activation of AP-1. The findings of the present study suggest that coinduction of IL-6 and IL-11 in response to epinephrine probably occurs via the PKA and p38 MAPK systems, leading to the transcriptional activation of AP-1 in human osteoblastic cells.

Integrin-mediated signaling in osteoblasts on titanium implant materials

The intracellular signaling pathway for osteoblast adhesion to the orthopedic implant material Ti6Al4V (TIV) was investigated and compared to integrin-mediated adhesion to extracellular matrix proteins. Primary osteoblasts from fetal rat calvaria were plated onto TIV, fibronectin (FN), and poly-L-lysine (PLL) and the levels of focal adhesion kinase (FAK), mitogen-activated protein kinase (MAPK), and AP-1 transcription factors, c-fos and c-jun, were compared by Western and Northern blots. Cells on all substrates showed maximum FAK phosphorylation within 60 min and then a decrease at 2 and 24 h. However, the subsequent signal transduction pathway differed on PLL compared to TIV and FN. MAPK was phosphorylated similarly in osteoblasts attached to FN and TIV, whereas cells on PLL demonstrated no MAPK phosphorylation. On TIV and FN, c-fos and c-jun mRNA levels were maximal within 1 h and then plateaued or declined by 2 h. On PLL, they increased at 2 h. Within 1 h, c-fos protein was stimulated in cells attached to TIV and FN and decreased in cells on PLL. c-jun protein increased on all substrates compared to unplated cells. Cytoskeletal changes visualized by phalloidin fluorescence microscopy at 4 h of culture were delayed on TIV compared to FN. In addition, approximately 50% fewer cells adhered to TIV compared to FN or PLL. By 24 h, a well-spread cytoskeleton with focal adhesion sites was apparent on TIV and FN, but cells on PLL were rounded with minimal cell spreading. During 6 days of culture, cells on FN and TIV proliferated, whereas the number of cells on PLL remained the same or decreased, depending on the initial plating density. We conclude that osteoblast adhesion to TIV implants is similar to osteoblast adhesion to FN and leads to osteoblast proliferation. These data provide evidence for the biocompatibility of TIV at a molecular level.

Integrin-mediated signaling regulates AP-1 transcription factors and proliferation in osteoblasts

Since osteoblast proliferation is critical for bone development, the effect of bone extracellular matrix (ECM) proteins on osteoblast signaling and proliferation in serum-free medium was investigated. Proliferation was highest in primary rat calvarial osteoblasts cells grown on fibronectin but less on type I collagen; osteonectin and poly-L-lysine did not support early proliferation. Fibronectin and type I collagen binding requires integrins, whereas cell adhesion to osteonectin or poly-L-lysine does not involve integrins. Therefore, the role of integrins in osteoblast signaling, leading to the induction of AP-1 transcription factors (c-fos and c-jun) which are important in cell proliferation, was studied. c-fos and c-jun message levels were increased at 60 min in osteoblasts plated onto fibronectin or collagen, but not in cells on osteonectin or poly-L-lysine. Protein synthesis was not required for c-fos mRNA expression; however, kinase activity was necessary for c-fos induction. In cells plated onto fibronectin, c-fos mRNA levels were controlled by protein kinase C and phosphotyrosine kinase signaling pathways. In contrast, c-fos levels in collagen-adhering cells may involve protein kinase A. The signaling pathway involving the phosphorylation of focal adhesion kinase and mitogen-activated kinases was also shown to be transiently increased in osteoblasts on fibronectin and type I collagen, but not in cells on poly-L-lysine. These results demonstrate that osteoblast binding to the extracellular matrix through integrins induces c-fos and c-jun, and that both fibronectin and collagen affect these AP-1 transcription factors through protein kinase-sensitive pathways. Thus, osteoblast proliferation is modulated differentially by specific ECM components.

Role of activator protein 1 transcriptional activity in the regulation of gene expression by transforming growth factor beta1 and bone morphogenetic protein 2 in ROS 17/2.8 osteoblast-like cells

In osteoblastic cells, transforming growth factor beta1 (TGF-beta1) has been found to regulate the expression of a variety of proto-oncogenes including c-fos, c-jun, and junB. The c-fos in particular has been implicated in the mitogenic effect of TGF-beta1. Here, we examined the role of these early response genes in the regulation of osteoblast (OB) gene expression by two members of the TGF-beta superfamily, TGF-beta1 and bone morphogenetic protein 2 (BMP-2). In ROS 17/2.8 cells, TGF-beta1 as well as BMP-2 up-regulated the expression of junB and c-fos messenger RNAs (mRNAs), and this increase was correlated in both cases with an increase in activator protein 1 (AP-1) DNA-binding activity involving JunB and c-Fos proteins. Protein kinase C (PKC)- and protein tyrosine kinase (PTK)-dependent pathways have been implicated in both TGF-beta1 signaling and AP-1 gene regulation. Therefore, using the kinase inhibitors chelerythrine chloride and genistein, we showed that PKC and PTK activities, respectively, participated in TGF-beta1- and BMP-2-induced increases in junB mRNA levels. Similarly, these kinase activities were involved in the stimulatory effect of BMP-2 on c-fos mRNA expression. Using a natural dominant negative for AP-1 transcriptional activity in ROS 17/2.8 cells, we then showed that AP-1 transcription factors mediated TGF-beta1- and BMP-2-regulated expression of the (alpha1) collagen I gene as well as TGF-beta1-regulated expression of the parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor. Our data emphasize the role of the AP-1 transcription factor in TGF-beta1 and BMP-2 signaling and highlight the importance of this transcription factor family in the expression of OB genes.

Overexpression of DeltaFosB transcription factor(s) increases bone formation and inhibits adipogenesis

Members of the AP-1 family of transcription factors participate in the regulation of bone cell proliferation and differentiation. We report here a potent AP-1-related regulator of osteoblast function: DeltaFosB, a naturally occurring truncated form of FosB that arises from alternative splicing of the fosB transcript and is expressed in osteoblasts. Overexpression of DeltaFosB in transgenic mice leads to increased bone formation throughout the skeleton and a continuous post-developmental increase in bone mass, leading to osteosclerosis. In contrast, DeltaFosB inhibits adipogenesis both in vivo and in vitro, and downregulates the expression of early markers of adipocyte differentiation. Because osteoblasts and adipocytes are thought to share a common precursor, it is concluded that DeltaFosB transcriptionally regulates osteoblastogenesis, possibly at the expense of adipogenesis.

Developmental regulation of collagenase-3 mRNA in normal, differentiating osteoblasts through the activator protein-1 and the runt domain binding sites

Collagenase-3 mRNA is initially detectable when osteoblasts cease proliferation, increasing during differentiation and mineralization. We showed that this developmental expression is due to an increase in collagenase-3 gene transcription. Mutation of either the activator protein-1 or the runt domain binding site decreased collagenase-3 promoter activity, demonstrating that these sites are responsible for collagenase-3 gene transcription. The activator protein-1 and runt domain binding sites bind members of the activator protein-1 and core-binding factor family of transcription factors, respectively. We identified core-binding factor a1 binding to the runt domain binding site and JunD in addition to a Fos-related antigen binding to the activator protein-1 site. Overexpression of both c-Fos and c-Jun in osteoblasts or core-binding factor a1 increased collagenase-3 promoter activity. Furthermore, overexpression of c-Fos, c-Jun, and core-binding factor a1 synergistically increased collagenase-3 promoter activity. Mutation of either the activator protein-1 or the runt domain binding site resulted in the inability of c-Fos and c-Jun or core-binding factor a1 to increase collagenase-3 promoter activity, suggesting that there is cooperative interaction between the sites and the proteins. Overexpression of Fra-2 and JunD repressed core-binding factor a1-induced collagenase-3 promoter activity. Our results suggest that members of the activator protein-1 and core-binding factor families, binding to the activator protein-1 and runt domain binding sites are responsible for the developmental regulation of collagenase-3 gene expression in osteoblasts.

Thiazide diuretics affect osteocalcin production in human osteoblasts at the transcription level without affecting vitamin D3 receptors

Besides their natriuretic and calciuretic effect, thiazide diuretics have been shown to decrease bone loss rate and improve bone mineral density. Clinical evidence suggests a specific role of thiazides on osteoblasts, because it reduces serum osteocalcin (OC), an osteoblast-specific protein, yet the mechanisms implicated are unknown. We therefore investigated the role of hydrochlorothiazide (HCTZ) on OC production by the human osteoblast-like cell line MG-63. HCTZ dose-dependently (1-100 microM) inhibited 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]-induced OC release by these cells (maximal effect, -40-50% and p < 0.005 by analysis of variance [ANOVA]) as measured by ELISA. This effect of HCTZ on OC release was caused by a direct effect on OC gene expression because Northern blot analysis revealed that OC messenger RNA (mRNA) levels were reduced in the presence of increasing doses of the diuretic (-47.2+/-4.0%; p < 0.0001 by paired ANOVA with 100 microM 13.6+/-0.49 pmol/mg protein/15 minutes; p < 0.05) in MG-63 cells. Reducing extracellular Ca2+ concentration with 0.5 mM EDTA or 0.5 mM ethylene glycol-bis(beta-amino ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) only partly prevented the inhibitory effect of the diuretic on OC secretion (maximal effect, -22.5+/-6.9%), suggesting that thiazide-dependent Ca2+ influx is not sufficient to elicit the inhibition of OC secretion. Because OC production is strictly dependent on the presence of 1,25(OH)2D3 in human osteoblasts, we next evaluated the possible role of HCTZ on vitamin D3 receptors (VDR) at the mRNA and protein levels. Both Northern and Western blot analyses showed no effect of HCTZ (1-100 microM) on VDR levels. The presence of EGTA in the culture media reduced slightly the VDR mRNA levels under basal condition but this was not modified in the presence of increasing levels of HCTZ. The OC gene promoter also is under the control of transcription factors such as Yin Yang 1 (YY1) and cFOS. Western blot analysis revealed no changes in YY1 levels in response to HCTZ either in the presence or in the absence of 0.5 mM EGTA in the culture media. In contrast, HCTZ induced a dose-dependent increase in cFOS levels (p < 0.002 by ANOVA), a situation prevented by incubation with EGTA. These studies indicate that HCTZ inhibits OC mRNA expression independently of an effect on VDR, YY1, or extracellular Ca2+ levels but involves changes in cFOS levels. As OC retards bone formation/mineralization, the inhibition of OC production by HCTZ could explain its preventive role in bone loss rate.

Isolation and characterization of the distal promoter region of mouse Cbfa1

Cbfa1 is an essential transcription factor for bone formation, and as such little is known about the region responsible for the transcriptional regulation of this gene. Here we report the determination of the transcription start sites, isolation and partial characterization of distal promoter region of this gene. Three transcription start sites were identified by the 5'-Cap site method, recently invented for rapid examination of the 5'-end of genes of interest. A reporter construct containing 1.8 kb of 5' of transcription start sites had approximately 25-fold more luciferase activity than the promoter-less vector in osteoblastic cell lines. Deletion analysis of the reporter construct demonstrated that the minimal region to express promoter activity lies between bp -168 and -99, taking the most downstream transcription start site as +1. By Northern blot analysis, mRNA expression from the distal promoter was detected in the differentiated osteoblastic cell lines, UMR-106, ROS17/2.8 and MC3T3-E1, but not in cell lines of immature phenotype or originated from other organs. Luciferase activity was strongest in UMR-106 and ROS17/2.8, and weakest in COS-1 and HepG2, which are cell lines originating from other organs, corresponding to the level of mRNA expression. These results demonstrated that the distal promoter region examined here is important for tissue- and cell-type-specific gene expression of Cbfa1.

Adenovirus-mediated gene therapy of osteoblasts in vitro and in vivo

Modulation of biological pathways governing osteogenesis may accelerate osseous regeneration and reduce the incidence of complications associated with fracture healing. Transforming growth factor beta1 (TGF-beta1) is a potent growth factor implicated in the regulation of osteogenesis and fracture repair. The use of recombinant proteins, however, has significant disadvantages and has limited the clinical utility of these molecules. Targeted gene therapy using adenovirus vectors is a technique that may circumvent difficulties associated with growth factor delivery. In this study, we investigate the efficacy of replication-deficient adenoviruses containing the human TGF-beta1 and the bacterial lacZ genes in transfecting osteoblasts in vitro and osseous tissues in vivo. We demonstrate that adenovirus-mediated gene therapy efficiently transfects osteoblasts in vitro with the TGF-beta1 virus causing a marked up-regulation in TGF-beta1 mRNA expression even 7 days after transfection. Increased TGF-beta1 mRNA expression was efficiently translated into protein production and resulted in approximately a 46-fold increase in TGF-beta1 synthesis as compared with control cells (vehicle- or B-galactosidase-transfected). Moreover, virally produced TGF-beta1 was functionally active and regulated the expression of collagen IalphaI (5-fold increase) and the vascular endothelial growth factor (2.5-fold increase). Using an adenovirus vector encoding the Escherichia coli LacZ gene, we demonstrated that adenovirus-mediated gene transfer efficiently transfects osteoblasts and osteocytes in vivo and that transfection can be performed by a simple percutaneous injection. Finally, we show that delivery of the hTGF-beta1 gene to osseous tissues in vivo results in significant changes in the epiphyseal plate primarily as a result of increased thickness of the provisional calcification zone.

Increased AP-1 activity in drug resistant human breast cancer MCF-7 cells

The expression, DNA binding, and transactivating activity of activator protein 1 (AP-1) was examined in a series of multidrug resistant (MDR) MCF-7 human breast cancer cells that have increasing levels of MDR1 gene expression. We observed an increase in the amount of both c-jun and c-fos mRNA in cells with 12-, 65-, or 200-fold higher resistance to adriamycin when compared to drug-sensitive MCF-7 wild type (WT) cells. Electrophoretic mobility shift assays (EMSA) demonstrated an increase in the DNA binding activity of an AP-1 complex in nuclear extracts from MDR MCF-7 cells when compared to extracts from WT cells. We observed a proportional increase in luciferase expression from a reporter vector containing consensus AP-1 binding sites in transiently transfected MDR cells when compared to WT cells, indicating that AP-1 mediated gene expression is increased in drug-resistant MCF-7 cells. Since the MDR1 promoter contains a putative AP-1 binding site, we used EMSA to examine AP-1 binding activity to an oligonucleotide probe that contained the relevant MDR1 promoter sequences (-123 to -108). Nuclear extracts from resistant MCF-7 cells displayed an increased level of DNA binding of Jun/Jun dimers to the probe, indicating that AP-1 was capable of binding to this promoter site. A luciferase reporter construct containing triplicate copies of the MDR1 promoter sequence was expressed at higher levels in transiently transfected MDR cells when compared to expression in WT cells. Co-transfection of WT cells with a c-jun expression vector and either of the AP-1 luciferase constructs demonstrated that c-jun could activate gene expression from both the consensus and the MDR1 AP-1 sites in a dose dependent manner. In addition, RT-PCR and western blot analysis showed that levels of MDR1 mRNA and Pgp were increased in c-jun transfected WT cells. Taken together, these data indicate that increased AP-1 activity may be an important mediator of MDR by regulating the expression of MDR1.

AP-1 and vitamin D receptor (VDR) signaling pathways converge at the rat osteocalcin VDR element: requirement for the internal activating protein-1 site for vitamin D-mediated trans-activation

Responsiveness of genes to steroid hormones is a complex process involving synergistic and/or antagonistic interactions between specific receptors and other nonreceptor transcription factors. Thus, DNA recognition elements for steroid hormone receptors are often located among binding sites for other trans-acting factors. The hormonal form of vitamin D, 1,25-dihydroxyvitamin D3, stimulates transcription of the tissue-specific osteocalcin (OC) gene in osteoblastic cells. The rat OC vitamin D response element contains an internal acitvating protein-1 (AP-1) site. Here, we report for the first time that this AP-1 site is critical for the transcriptional enhancement of rat osteocalcin gene expression mediated by vitamin D. Precise mutations were introduced either in the steroid half-elements or in the internal AP-1 sequences. One mutation within the internal AP-1 site retained vitamin D receptor/retinoid X receptor binding equivalent to that of the wild-type sequence, but resulted in complete loss of vitamin D inducibility of the OC promoter. These results suggest a functional interaction between the hormone receptor and nuclear oncoproteins at the rat OC vitamin D response element. This cooperation of activities may have important consequences in physiological regulation of osteocalcin transcription during osteoblast differentiation and bone tissue development in vivo.

Inhibition of proliferation and induction of differentiation of osteoblastic cells by a novel 1,25-dihydroxyvitamin D3 analog with an extensively modified side chain (CB1093)

1,25-Dihydroxyvitamin D3 (1,25D) is involved in the regulation of proliferation and differentiation of a variety of cell types including cancer cells. In recent years, numerous new vitamin D3 analogs have been developed in order to obtain favorable therapeutic properties. The effects of a new 20-epi analog, CB1093 (20-epi-22-ethoxy-23-yne-24a,26a,27a-trihomo+ ++-1alpha,25(OH)2D3), on the proliferation and differentiation of human MG-63 osteosarcoma cell line were compared here with those of the parent compound 1,25D. Proliferation of the MG-63 cells was inhibited similarly by 22%, 50% and 59% after treatment with 0.1 microM 1,25D or CB1093 for 48 h, 96 h, and 144 h, respectively. In transfection experiments, the compounds were equipotent in stimulating reporter gene activity under the control of human osteocalcin gene promoter. In cell culture experiments, however, CB1093 was more potent than 1,25D at low concentrations and more effective for a longer period of time in activating the osteocalcin gene expression at mRNA and protein levels. Also, a 6-h pretreatment and subsequent culture for up to 120 h without 1,25D or CB1093 yielded higher osteocalcin mRNA and protein levels with analog-treated cells than with 1,25D-treated cells. The electrophoretic mobility shift assay (EMSA) revealed stronger VDR-VDRE binding with analog-treated MG-63 cells than with 1,25D-treated cells. The differences in the DNA binding of 1,25D-bound vs. analog-bound VDR, however, largely disappeared when the binding reactions were performed with recombinant hVDR and hRXRbeta proteins. These results demonstrate that the new analog CB1093 was equally or even more effective than 1,25D in regulating all human osteosarcoma cell functions ranging from growth inhibition to marker gene expression and that the differences in effectivity most probably resulted from interactions of the hVDR:hRXRbeta-complex with additional nuclear proteins.

1alpha,25-dehydroxyvitamin D3 synergism toward transforming growth factor-beta1-induced AP-1 transcriptional activity in mouse osteoblastic cells via its nuclear receptor

The present study demonstrates 1alpha,25-dehydroxyvitamin D3 (1alpha-25-(OH)2D3) synergism toward transforming growth factor (TGF)-beta1-induced activation protein-1 (AP-1) activity in mouse osteoblastic MC3T3-E1 cells via the nuclear receptor of the vitamin. 1alpha-25-(OH)2D3 synergistically stimulated TGF-beta1-induced expression of the c-jun gene in the cells but not that of the c-fos gene. We actually showed by a gel mobility shift assay 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced AP-1 binding to the 12-(O-tetradecanoylphorbol-13-acetate response element (TRE). 1alpha-25-(OH)2D3 markedly stimulated the transient activity of TGF-beta1-induced AP-1 in the cells transfected with a TRE-chloramphenicol acetyltransferase (CAT) reporter gene. Also, a synergistic increase in TGF-beta1-induced CAT activity was observed in the cells cotransfected with an expression vector encoding vitamin D3 receptor (VDR) and the reporter gene. However, the synergistic CAT activity was inhibited by pretreatment with VDR antisense oligonucleotides. In addition, in a Northern blot assay, we observed 1alpha-25-(OH)2D3 synergism of TGF-beta1-induced expression of the c-jun gene in the cells transfected with the VDR expression vector and also found that the synergistic action was clearly blocked by VDR antisense oligonucleotide pretreatment. The present study strongly suggests a novel positive regulation by 1alpha-25-(OH)2D3 of TGF-beta1-induced AP-1 activity in osteoblasts via "genomic action."

Heterogeneous pattern of gene expression in cloned cell lines established from a rat transplantable osteosarcoma lung metastatic nodule

We have established three cloned cell lines (COS1NR, COS2NR and COS4NR) from the lung metastatic nodule of a highly metastatic variant of rat transplantable osteosarcoma, C-SLM. All three clones shared the same morphological characteristics and tumorigenicity, but their growth rates in vitro and metastatic ability in vivo differed from each other. Single-strand conformation polymorphism (SSCP) analysis revealed all three clones to have the same p53 gene mutation and parent C-SLM tumor. On the other hand, Northern blot analysis showed a different pattern of expression for the genes, c-fos, c-jun, c-Ha-ras, transin (rat stromelysin), bone Gla protein (osteocalsin) and nm23/NDP kinase. These results indicate the presence of a heterogeneous cell population in terms of the different pattern of gene expression in a lung metastatic nodule of rat osteosarcoma and the present newly established cell lines will be useful for further investigation of the biological behavior of osteosarcomas.

Formoterol and isoproterenol induce c-fos gene expression in osteoblast-like cells by activating beta2-adrenergic receptors

Formoterol, a beta2-adrenergic agonist has been shown in ovariectomized rat models to have anabolic effects on bone. However, those studies did not determine whether the effect of formoterol was by a direct action on bone cells themselves or indirectly via anabolic action on muscle. To address the question of whether formoterol could directly affect osteoblast function we investigated the expression patterns of beta3-adrenergic receptors (betaARs) in human osteoblast-like cells and functional coupling to gene expression. Northern blot analysis showed that betaAR subtypes are expressed at different levels in the osteoblast-like cell lines TE-85, SaOS-2, MG-63, and OHS-4. beta1AR expression was found in SaOS-2, OHS-4, and TE-85, but not MG-63 cells. beta2ARs are expressed at higher levels in MG-63 cells than in TE-85 and SaOS-2 cells, but were not detected in OHS-4 cells. PCR analysis paralleled the northern blot analysis except that beta3AR expression was found in one of three human primary osteoblast cDNAs tested. beta3AR expression was not found in any of the osteoblast-like cell lines. The nonspecific betaAR agonist, isoproterenol, and the beta2AR-specific agonist, formoterol, induced c-fos gene expression in cultured SaOS-2 cells in an immediate early fashion. This effect was inhibited by the beta2AR-specific antagonist, ICI 118551, but not by the beta1AR-specific antagonist, CGP 20712, indicating that induction of c-fos gene expression is specifically mediated by beta2ARs. c-fos gene expression was induced by both isoproterenol and formoterol via increases in cAMP, which in turn activated the cAMP/PKA pathway; the PKA inhibitor, H89, inhibited c-fos gene expression. Thus, betaARs are expressed in osteoblast-like cells and are coupled to c-fos gene expression via the beta2AR, increases in cAMP levels and activation of a PKA-dependent pathway.