Sp7/Osterix up-regulates the mouse pro-α3(V) collagen gene (Col5a3) during the osteoblast differentiation

Roles of SP/KLF transcription factors in odontoblast differentiation: From development to diseases

OBJECTIVES

A zinc-finger transcription factor family comprising specificity proteins (SPs) and Krüppel-like factor proteins (KLFs) plays an important role in dentin development and regeneration. However, a systematic regulatory network involving SPs/KLFs in odontoblast differentiation has not yet been described. This review examined the expression patterns of SP/KLF gene family members and their current known functions and mechanisms in odontoblast differentiation, and discussed prospective research directions for further exploration of mechanisms involving the SP/KLF gene family in dentin development.

MATERIALS AND METHODS

Relevant literature on SP/KLF gene family members and dentin development was acquired from PubMed and Web of Science.

RESULTS

We discuss the expression patterns, functions, and related mechanisms of eight members of the SP/KLF gene family in dentin development and genetic disorders with dental problems. We also summarize current knowledge about their complementary or synergistic actions. Finally, we propose future research directions for investigating the mechanisms of dentin development.

CONCLUSIONS

The SP/KLF gene family plays a vital role in tooth development. Studying the complex complementary or synergistic interactions between SPs/KLFs is helpful for understanding the process of odontoblast differentiation. Applications of single-cell and spatial multi-omics may provide a more complete investigation of the mechanism involved in dentin development.

The bone transcription factor Osterix controls extracellular matrix- and node of Ranvier-related gene expression in oligodendrocytes

Oligodendrocytes are the primary producers of many extracellular matrix (ECM)-related proteins found in the CNS. Therefore, oligodendrocytes play a critical role in the determination of brain stiffness, node of Ranvier formation, perinodal ECM deposition, and perineuronal net formation, all of which depend on the ECM. Nevertheless, the transcription factors that control ECM-related gene expression in oligodendrocytes remain unknown. Here, we found that the transcription factor Osterix (also known as Sp7) binds in proximity to genes important for CNS ECM and node of Ranvier formation and mediates their expression. Oligodendrocyte-specific ablation of Sp7 changes ECM composition and brain stiffness and results in aberrant node of Ranvier formation. Sp7 is known to control osteoblast maturation and bone formation. Our comparative analyses suggest that Sp7 plays a conserved biological role in oligodendrocytes and in bone-forming cells, where it mediates brain and bone tissue stiffness by controlling expression of ECM components.

Exploring Omega-3's Impact on the Expression of Bone-Related Genes in Meagre (Argyrosomus regius)

Dietary supplementation with Omega-3 fatty acids seems to promote skeletal health. Therefore, their consumption at imbalanced or excessive levels has offered less beneficial or even prejudicial effects. Fish produced in aquaculture regimes are prone to develop abnormal skeletons. Although larval cultures are usually fed with diets supplemented with Omega-3 Long Chain Polyunsaturated fatty acids (LC-PUFAs), the lack of knowledge about the optimal requirements for fatty acids or about their impact on mechanisms that regulate skeletal development has impeded the design of diets that could improve bone formation during larval stages when the majority of skeletal anomalies appear. In this study, Argyrosomus regius larvae were fed different levels of Omega-3s (2.6% and 3.6% DW on diet) compared to a commercial diet. At 28 days after hatching (DAH), their transcriptomes were analyzed to study the modulation exerted in gene expression dynamics during larval development and identify impacted genes that can contribute to skeletal formation. Mainly, both levels of supplementation modulated bone-cell proliferation, the synthesis of bone components such as the extracellular matrix, and molecules involved in the interaction and signaling between bone components or in important cellular processes. The 2.6% level impacted several genes related to cartilage development, denoting a special impact on endochondral ossification, delaying this process. However, the 3.6% level seemed to accelerate this process by enhancing skeletal development. These results offered important insights into the impact of dietary Omega-3 LC-PUFAs on genes involved in the main molecular mechanism and cellular processes involved in skeletal development.

Sp7 Action in the Skeleton: Its Mode of Action, Functions, and Relevance to Skeletal Diseases

Osteoblast differentiation is a tightly regulated process in which key transcription factors (TFs) and their target genes constitute gene regulatory networks (GRNs) under the control of osteogenic signaling pathways. Among these TFs, Sp7 works as an osteoblast determinant critical for osteoblast differentiation. Following the identification of Sp7 and a large number of its functional studies, recent genome-scale analyses have made a major contribution to the identification of a "non-canonical" mode of Sp7 action as well as "canonical" ones. The analyses have not only confirmed known Sp7 targets but have also uncovered its additional targets and upstream factors. In addition, biochemical analyses have demonstrated that Sp7 actions are regulated by chemical modifications and protein-protein interaction with other transcriptional regulators. Sp7 is also involved in chondrocyte differentiation and osteocyte biology as well as postnatal bone metabolism. The critical role of SP7 in the skeleton is supported by its relevance to human skeletal diseases. This review aims to overview the Sp7 actions in skeletal development and maintenance, particularly focusing on recent advances in our understanding of how Sp7 functions in the skeleton under physiological and pathological conditions.

A neomorphic variant in SP7 alters sequence specificity and causes a high-turnover bone disorder

SP7/Osterix is a transcription factor critical for osteoblast maturation and bone formation. Homozygous loss-of-function mutations in SP7 cause osteogenesis imperfecta type XII, but neomorphic (gain-of-new-function) mutations of SP7 have not been reported in humans. Here we describe a de novo dominant neomorphic missense variant (c.926 C > G:p.S309W) in SP7 in a patient with craniosynostosis, cranial hyperostosis, and long bone fragility. Histomorphometry shows increased osteoblasts but decreased bone mineralization. Mice with the corresponding variant also show a complex skeletal phenotype distinct from that of Sp7-null mice. The mutation alters the binding specificity of SP7 from AT-rich motifs to a GC-consensus sequence (typical of other SP family members) and produces an aberrant gene expression profile, including increased expression of Col1a1 and endogenous Sp7, but decreased expression of genes involved in matrix mineralization. Our study identifies a pathogenic mechanism in which a mutation in a transcription factor shifts DNA binding specificity and provides important in vivo evidence that the affinity of SP7 for AT-rich motifs, unique among SP proteins, is critical for normal osteoblast differentiation.

Recent Advances of Osterix Transcription Factor in Osteoblast Differentiation and Bone Formation

With increasing life expectations, more and more patients suffer from fractures either induced by intensive sports or other bone-related diseases. The balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption is the basis for maintaining bone health. Osterix (Osx) has long been known to be an essential transcription factor for the osteoblast differentiation and bone mineralization. Emerging evidence suggests that Osx not only plays an important role in intramembranous bone formation, but also affects endochondral ossification by participating in the terminal cartilage differentiation. Given its essentiality in skeletal development and bone formation, Osx has become a new research hotspot in recent years. In this review, we focus on the progress of Osx's function and its regulation in osteoblast differentiation and bone mass. And the potential role of Osx in developing new therapeutic strategies for osteolytic diseases was discussed.

Extracellular Vesicle microRNAs Contribute to the Osteogenic Inhibition of Mesenchymal Stem Cells in Multiple Myeloma

Osteolytic bone disease is the major complication associated with the progression of multiple myeloma (MM). Recently, extracellular vesicles (EVs) have emerged as mediators of MM-associated bone disease by inhibiting the osteogenic differentiation of human mesenchymal stem cells (hMSCs). Here, we investigated a correlation between the EV-mediated osteogenic inhibition and MM vesicle content, focusing on miRNAs. By the use of a MicroRNA Card, we identified a pool of miRNAs, highly expressed in EVs, from MM cell line (MM1.S EVs), expression of which was confirmed in EVs from bone marrow (BM) plasma of patients affected by smoldering myeloma (SMM) and MM. Notably, we found that miR-129-5p, which targets different osteoblast (OBs) differentiation markers, is enriched in MM-EVs compared to SMM-EVs, thus suggesting a selective packaging correlated with pathological grade. We found that miR-129-5p can be transported to hMSCs by MM-EVs and, by the use of miRNA mimics, we investigated its role in recipient cells. Our data demonstrated that the increase of miR-129-5p levels in hMSCs under osteoblastic differentiation stimuli inhibited the expression of the transcription factor Sp1, previously described as a positive modulator of osteoblastic differentiation, and of its target the Alkaline phosphatase (ALPL), thus identifying miR-129-5p among the players of vesicle-mediated bone disease.

The pro-α1(V) collagen gene (Col5a1) is coordinately regulated by miR-29b with core promoter in cultured cells

AIMS

Col5a1 encodes the α1 chain of type V collagen, a quantitatively minor fibrillar collagen that is critical for the formation and function of the organs in the body. MicroRNAs (miRNAs) are small noncoding RNAs that posttranscriptionally regulate biological functions by binding to the 3'-untranslated region (3'UTR) of specific target mRNA. In this study, we investigated the posttranscriptional regulation of miRNAs on the Col5a1 gene expression.

MATERIALS AND METHODS

We cultured osteoblasts and fibroblasts of cell lines. To examine the 3'UTR activity of the Col5a1 gene, chimeric plasmids constructs containing the core promoter and 3'UTR of Col5a1 were generated and luciferase assays were performed. We also evaluated the role of miRNA using constructs that were mutated at the putative binding sites of miRNA. In addition, we evaluated the endogenous mRNA and protein, and luciferase activity of the Col5a1 gene after miRNA overexpression/knockdown or CRISPR/Cas9-induced knockout.

RESULTS

The luciferase assay showed a decreased activity of the 3'UTR of Col5a1 gene. However, the expression of the mutant constructs of miRNA-binding sites was restored. The overexpression of miRNA inhibited the Col5a1 gene not only with regard to the luciferase activity and endogenous mRNA but also at the protein level. In contrast, the RNAi-mediated knockdown or CRISPR/Cas9 system increased the expression of the Col5a1 gene.

CONCLUSION

These results provided evidence that miR-29b regulates the Col5a1 gene expression through binding to the 3'UTR, which might play an important role in the pathogenesis of disease related to bone metabolism and fibrogenic reactions.

Manifestation of osteoblastic phenotypes in the sarcomatous component of epithelial carcinoma and sarcomatoid carcinoma

Epithelial carcinomas occasionally have sarcomatous components that consist primarily of spindle and cuboidal cells, which often resemble osteoblasts. Sarcomatoid carcinomas consist of similar cells. Recent studies have characterized these phenomena as a manifestation of epithelial-mesenchymal transition in carcinoma cells, but the mesenchymal phenotypes that manifest in sarcomatous cells of epithelial carcinomas are not well understood. Here, we examined the expression profiles of four osteoblastic differentiation biomarkers in the sarcomatous components of multiple carcinoma types, including five renal clear cell, four breast invasive ductal, two esophageal, one maxillary squamous cell, three larynx, three lung, one liver, and one skin sarcomatoid carcinoma. Expression was analyzed by immunohistochemistry using antibodies against cell adhesion molecule 1, a member of the IgCAM superfamily, osterix transcription factor (Osterix), cluster of differentiation 151, a transmembrane 4 superfamily member, and alkaline phosphatase. Immunostaining intensity was rated in scale 0 (negative), 0.5 (weak), and 1 (strong) for each marker, and the four scale values were summed to calculate osteoblastic scores. In all, 10 cases had a osteoblastic score ≥3, and all of these 10 cases were cell adhesion molecule 1- and Osterix-positive. Eight and five of the nine samples with a osteoblastic score <3 were negative for cell adhesion molecule 1 ( p < 0.0001) and Osterix ( p = 0.006), respectively. The other markers showed no statistical significance. These results indicate that osteoblastic differentiation can occur in carcinoma cells and that cell adhesion molecule 1 could be a useful marker for identifying this phenomenon in carcinoma tissues.

Zinc finger transcription factor Sp7/Osterix acts on bone formation and regulates col10a1a expression in zebrafish

Sp7/Osterix as a zinc finger transcription factor is expressed specifically in osteoblasts. Embryonic lethality of Sp7 knockout mice, however, has prevented from examining the functions of Sp7 in osteoblast and bone formation in live animals. Here we used TALEN, a versatile genome-editing tool, to generate one zebrafish sp7 mutant line. Homozygous sp7-/- mutant zebrafish are able to survive to adulthood. Alizarin Red staining and Micro-CT analysis showed that sp7-/- larvae and adult fish fail to develop normal opercula, and display curved tail fins and severe craniofacial malformation, while Alcian Blue staining showed no obvious cartilage defects in sp7-/- fish. Quantitative RT-PCR showed that a number of osteoblast markers including spp1, phex, col1ala, and col1a1b are significantly down-regulated in sp7-/- fish. Furthermore, col10a1a, whose ortholog is the cartilage marker in mice, was shown to be a novel downstream gene of Sp7 as an osteoblast marker in zebrafish. Together, these results suggest that Sp7 is required for zebrafish bone development and zebrafish sp7 mutants provide animal models for investigating novel aspects of bone development.

Osterix plays a critical role in BMP4-induced promoter activity of connexin43

Osterix is an essential transcription factor for osteogenesis and is expressed in osteoblasts. Although Osterix has been shown to be induced by bone morphogenetic protein 4, the molecular mechanism underlying Osterix function during osteoblast differentiation remains unclear. Connexin43 (Cx43) is the most abundant gap junction protein in bone cells and plays a critical role in osteoblast differentiation. However, little is known about the functional interactions between Osterix and the Cx43 promoter. In the present study, we investigated the relationship between Osterix and Cx43 in HEK293 and C2C12 cells. Cx43 expression was significantly repressed by the addition of shRNA against Osterix, whereas overexpression of Osterix resulted in enhanced Cx43 expression. Furthermore, Osterix directly occupied the promoter region of Cx43 and subsequently increased Cx43 promoter activity in a dose-dependent manner. In addition, phosphorylation of the Ser76 and Ser80 residues in Osterix were found to be critical for its activity on the Cx43 promoter. Our results suggest that Osterix plays an important role in increasing bone morphogenetic protein 4-induced Cx43 activity.

Role of Osterix and MicroRNAs in Bone Formation and Tooth Development

Osterix (Osx) is an osteoblast-specific transcription factor that is essential for bone formation. MicroRNAs (miRNAs) are ~22-nucleotide-long noncoding RNAs that play important regulatory roles in animals and plants by targeting mRNAs for cleavage or translational repression. They can also control osteoblast-mediated bone formation and osteoclast-related bone remodeling. The vital roles of Osx and miRNAs during bone formation have been well studied, but very few studies have discussed their co-functions and the relationships between them. In this review, we outline the significant functions of Osx and miRNAs on certain cell types during osteogenesis and illustrate their roles during tooth development. More importantly, we discuss the relationship between Osx and miRNAs, which we believe could lead to a new treatment for skeletal and periodontal diseases.

Enhanced osteoprogenitor elongated collagen fiber matrix formation by bioactive glass ionic silicon dependent on Sp7 (osterix) transcription

Bioactive glasses release ions, those enhance osteoblast collagen matrix synthesis and osteogenic marker expression during bone healing. Collagen matrix density and osteogenic marker expression depend on osteogenic transcription factors, (e.g., Osterix (OSX)). We hypothesize that enhanced expression and formation of collagen by Si(4+) depends on enhanced expression of OSX transcription. Experimental bioactive glass (6P53-b) and commercial Bioglass(TM) (45S5) were dissolved in basal medium to make glass conditioned medium (GCM). ICP-MS analysis was used to measure bioactive glass ion release rates. MC3T3-E1 cells were cultured for 20 days, and gene expression and extracellular matrix collagen formation was analyzed. In a separate study, siRNA was used to determine the effect of OSX knockdown on impacting the effect of Si(4+) on osteogenic markers and matrix collagen formation. Each bioactive glass exhibited similar ion release rates for all ions, except Mg(2+) released by 6P53-b. Gene expression results showed that GCM markedly enhanced many osteogenic markers, and 45S5 GCM showed higher levels of expression and collagen matrix fiber bundle density than 6P53-b GCM. Upon knockdown of OSX transcription, collagen type 5, alkaline phosphatase, and matrix density were not enhanced as compared to wild type cells. This study illustrates that the enhancement of elongated collagen fiber matrix formation by Si(±) depends on OSX transcription. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2604-2615, 2016.

Sp7/Osterix Is Restricted to Bone-Forming Vertebrates where It Acts as a Dlx Co-factor in Osteoblast Specification

In extant species, bone formation is restricted to vertebrate species. Sp7/Osterix is a key transcriptional determinant of bone-secreting osteoblasts. We performed Sp7 chromatin immunoprecipitation sequencing analysis identifying a large set of predicted osteoblast enhancers and validated a subset of these in cell culture and transgenic mouse assays. Sp family members bind GC-rich target sequences through their zinc finger domain. Several lines of evidence suggest that Sp7 acts differently, engaging osteoblast targets in Dlx-containing regulatory complexes bound to AT-rich motifs. Amino acid differences in the Sp7 zinc finger domain reduce Sp7's affinity for the Sp family consensus GC-box target; Dlx5 binding maps to this domain of Sp7. The data support a model in which Dlx recruitment of Sp7 to osteoblast enhancers underlies Sp7-directed osteoblast specification. Because an Sp7-like zinc finger variant is restricted to vertebrates, the emergence of an Sp7 member within the Sp family was likely closely coupled to the evolution of bone-forming vertebrates.

Sp1 upregulates the proximal promoter activity of the mouse collagen α1(XI) gene (Col11a1) in chondrocytes

Type XI collagen is a cartilage-specific extracellular matrix, and is important for collagen fibril formation and skeletal morphogenesis. We have previously reported that NF-Y regulated the proximal promoter activity of the mouse collagen α1(XI) gene (Col11a1) in chondrocytes (Hida et. al. In Vitro Cell. Dev. Biol. Anim. 2014). However, the mechanism of the Col11a1 gene regulation in chondrocytes has not been fully elucidated. In this study, we further characterized the proximal promoter activity of the mouse Col11a1 gene in chondrocytes. Cell transfection experiments with deletion and mutation constructs indicated that the downstream region of the NF-Y binding site (-116 to +1) is also necessary to regulate the proximal promoter activity of the mouse Col11a1 gene. This minimal promoter region has no TATA box and GC-rich sequence; we therefore examined whether the GC-rich sequence (-96 to -67) is necessary for the transcription regulation of the Col11a1 gene. Luciferase assays using a series of mutation constructs exhibited that the GC-rich sequence is a critical element of Col11a1 promoter activity in chondrocytes. Moreover, in silico analysis of this region suggested that one of the most effective candidates was transcription factor Sp1. Consistent with the prediction, overexpression of Sp1 significantly increased the promoter activity. Furthermore, knockdown of Sp1 expression by siRNA transfection suppressed the proximal promoter activity and the expression of endogenous transcript of the mouse Col11a1 gene. Taken together, these results indicate that the transcription factor Sp1 upregulates the proximal promoter activity of the mouse Col11a1 gene in chondrocytes.

Microarray meta-analysis identifies evolutionarily conserved BMP signaling targets in developing long bones

In vertebrates, BMP signaling has been demonstrated to be sufficient for bone formation in several tissue contexts. This suggests that genes necessary for bone formation are expressed in a BMP signaling dependent manner. However, till date no gene has been reported to be expressed in a BMP signaling dependent manner in bone. Our aim was to identify such genes. On searching the literature we found that several microarray experiments have been conducted where the transcriptome of osteogenic cells in absence and presence of BMP signaling activation have been compared. However, till date, there is no evidence to suggest that any of the genes found to be upregulated in presence of BMP signaling in these microarray analyses is indeed a target of BMP signaling in bone. We wanted to utilize this publicly available information to identify candidate BMP signaling target genes in vivo. We performed a meta-analysis of six such comparable microarray datasets. This analysis and subsequent experiments led to the identification of five targets of BMP signaling in bone that are conserved both in mouse and chick. Of these Lox, Klf10 and Gpr97 are likely to be direct transcriptional targets of BMP signaling pathway. Dpysl3, is a novel BMP signaling target identified in our study. Our data demonstrate that Dpysl3 is important for osteogenic differentiation of mesenchymal cells and is involved in cell secretion. We have demonstrated that the expression of Dpysl3 is co-operatively regulated by BMP signaling and Runx2. Based on our experimental data, in silico analysis of the putative promoter-enhancer regions of Bmp target genes and existing literature, we hypothesize that BMP signaling collaborates with multiple signaling pathways to regulate the expression of a unique set of genes involved in endochondral ossification.

Immunomodulatory drugs thalidomide and lenalidomide affect osteoblast differentiation of human bone marrow stromal cells in vitro

Osteoblastic activity is severely impaired in active myeloma, contributing to the development of myeloma bone disease. Although several drugs reducing osteoclast-mediated bone degradation are in clinical use, approaches to specifically augment bone formation are at an early stage of development. Novel antimyeloma drugs not only directly act on myeloma cells, but impact on the microenvironment as well. Proteasome inhibitors were previously shown to have bone anabolic properties. Here we investigated the impact of immunomodulatory drugs (IMiDs) on bone formation. Treatment with thalidomide and lenalidomide significantly inhibited osteoblast development in vitro, as reflected by a reduction of alkaline phosphatase activity and matrix mineralization. The effects were upheld in combination with bortezomib. The IMiDs upregulated Dickkopf-1 (DKK1) and inhibin beta A, but blocking these molecules was not able to restore regular osteoblast development. We therefore performed gene expression profiling to reveal other osteoblast regulatory factors that might be involved in the IMiD-mediated effect on osteoblast development. Our data indicate that osteoblast inhibition is possibly an IMiD-class effect mediated by downregulation of major osteoblast regulators (e.g., runt-related transcription factor 2, distal-less homeobox 5, pleiotrophin) and concurrent induction of secreted inhibitors of osteoblast formation (e.g. DKK1, activin A, gremlin 1). Our results highlight the need for bone anabolic therapeutics in myeloma, counteracting the negative impact of prolonged IMiD exposure on bone metabolism.

Control of Fiat (factor inhibiting ATF4-mediated transcription) expression by Sp family transcription factors in osteoblasts

FIAT (factor inhibiting ATF4-mediated transcription) represses Osteocalcin gene transcription and inhibits osteoblast activity by heterodimerizing with ATF4 to prevent it from binding DNA. It thus appears important to identify and characterize the molecular mechanisms that control Fiat gene expression in osteoblasts. In silico sequence analysis identified a canonical GC-box within a 1,400 bp region of the proximal Fiat gene promoter. Electrophoretic mobility shift assays (EMSA) with MC3T3-E1 osteoblastic cells nuclear extracts indicated that the transcription factors Sp1 and Sp3, but not Sp7/OSTERIX, bound this proximal GC-box. Chromatin immunoprecipitation confirmed interaction of the two transcription factors with the Fiat promoter GC-element in living osteoblasts. Transient transfection studies showed that Sp1 dose-dependently activated the expression of a Fiat-luciferase reporter construct while both the long or short isoforms of Sp3 dose-dependently inhibited transcription from the Fiat reporter construct. Transfection of an Sp7/OSTERIX expression vector did not affect expression of the Fiat-luciferase reporter. Co-transfection of increasing amounts of the Sp3 expression vector in the context of maximal Sp1-dependent Fiat-luciferase activation led to dose-dependent repression of the expression of the reporter. Using RNA knockdown, we measured a reduction in steady-state Fiat expression when Sp1 was inhibited, and a reciprocal increase upon Sp3 knockdown. In parallel, treatment of osteoblasts with WP631, which prevents Sp1/DNA interactions, strongly inhibited the expression of Fiat and reduced the occupancy of the Fiat promoter proximal GC-box by Sp1. Taken together, our results suggest an interplay between Sp1 and Sp3 as a mechanism involved in the control of Fiat gene expression in osteoblasts.

Cell adhesion molecule 1 is a new osteoblastic cell adhesion molecule and a diagnostic marker for osteosarcoma

AIMS

An immunohistochemical screen for mouse embryos showed that cell adhesion molecule 1 (CADM1), which is an immunoglobulin superfamily member, was expressed in developing bones. Here, we determined the cell types expressing CADM1 and examined its usefulness in the differential diagnosis of osteosarcoma.

MAIN METHODS

Serial sections of murine developing mandibles were stained with anti-CADM1 antibody, by a coloring substrate reactive to alkaline phosphatase (ALP), a broad osteoblastic marker for preosteoblasts to osteoblasts, and by in situ hybridization for osteopontin (OPN), a marker for mature osteoblasts. CADM1 immunohistochemistry was also performed on human remodeling bones, osteosarcomas and other soft tissue tumors.

KEY FINDINGS

CADM1 immunohistochemistry for the mandible revealed that morphologically identifiable osteoblasts expressed CADM1 on their plasma membranes, but neither osteocytes nor bone lining cells did. At the mandibular margin, not only OPN-positive cells but also OPN-negative, ALP-positive cells were CADM1-positive, whereas inside the mandible, OPN-positive cells were often CADM1-negative. Clear membranous staining was detected in the majority of osteosarcomas (46/57), whereas only 13% (6/46) of the other soft tissue tumors were CADM1-positive (P<0.001).

SIGNIFICANCE

These results indicated that CADM1 was a novel osteoblastic adhesion molecule that is expressed transiently during osteoblastic maturation, and a useful diagnostic marker for osteosarcoma cells.