Biomedical subjects

Hyun-Mo Ryoo

Publications and source records attributed to Hyun-Mo Ryoo.

At least 19 recordsLinked to original sources

PubMed2007

The suppressive effect of myeloid Elf-1-like factor (MEF) in osteogenic differentiation.

Myeloid Elf-1 like factor (MEF) is a member of the Ets transcription factor family. Ets family proteins control the expression of genes that are critical for biological processes such as proliferation, differentiation, and cell death. Some of Ets factors are also known to regulate bone development. In this study, we investigated the role of MEF in osteoblast differentiation. MEF expression was highest early in the differentiation of MC3T3-E1 osteoblasts and was reduced by treatment with BMP-2. The expression of MEF suppressed the alkaline phosphatase activity and expression induced by BMP-2 stimulation and mediated by Runx2. The expression of MEF also reduces osteocalcin mRNA levels, and mineralization in MC3T3-E1 cells. We found that the MEF-mediated suppression of osteogenic differentiation was critically related to Runx2 regulation. The MEF and Runx2 proteins physically interact to form a complex, and this interaction interferes with Runx2 binding to the cis-acting element OSE2 derived from the osteocalcin promoter. Co-transfection of MEF inhibited the 6xOSE2-luciferase reporter activity induced by Runx2. In addition, MEF stimulated the transcription of a negative mediator Msx2, and a transcriptional repressor, Mab21L1, and suppressed the transcription of a positive mediator, Dlx5 in osteoblast differentiation. MEF overexpression stimulated C2C12 cell proliferation. Together, our findings suggest that MEF promotes cell proliferation and functions as a negative regulator of osteogenic differentiation by directly interacting with Runx2 and suppressing its transcriptional activity.

Alkaline Phosphatase↗

PubMed2006

Nano-fibrous scaffolding promotes osteoblast differentiation and biomineralization.

Nano-fibrous poly(L-lactic acid) (PLLA) scaffolds with interconnected pores were developed under the hypothesis that nano-fibrous scaffolding would mimic a morphological function of collagen fibrils to create a more favorable microenvironment for cells versus solid-walled scaffolds. In this study, an in vitro system was used to examine biological properties of the nano-fibrous scaffolds compared with those of solid-walled scaffolds for their potential use in bone tissue engineering. Biomineralization was enhanced substantially on the nano-fibrous scaffolds compared to solid-walled scaffolds, and this was confirmed by von Kossa staining, measurement of calcium contents, and transmission electron microscopy. In support of this finding, osteoblasts cultured on the nano-fibrous scaffolds exhibited higher alkaline phosphatase activity and an earlier and enhanced expression of the osteoblast phenotype versus solid-walled scaffolds. Most notable were the increases in runx2 protein and in bone sialoprotein mRNA in cells cultured on nano-fibrous scaffolds versus solid-walled scaffolds. At the day 1 of culture, alpha2 and beta1 integrins as well as alphav and beta3 integrins were highly expressed on the surface of cells seeded on nano-fibrous scaffolds, and linked to this were higher levels of phospho-Paxillin and phospho-FAK in cell lysates. In contrast, cells seeded on solid-walled scaffolds expressed significantly lower levels of these integrins, phospho-Paxillin, and phospho-FAK. To further examine the role of nano-fibrous architecture, we inhibited the formation of collagen fibrils by adding 3,4-dehydroproline to cultures and then assayed cells for expression of alpha2 integrin. Cells seeded on nano-fibrous scaffolds sustained expression of alpha2 integrin in the presence of dehydroproline, while suppression of alpha2 integrin was evident in cells seeded on solid-walled scaffolds. These results provide initial evidence that synthetic nano fibers may exhibit certain properties that are comparable to natural collagen fibers, and thus, the nano-fibrous architecture may serve as a superior scaffolding versus solid-walled architecture for promoting osteoblast differentiation and biomineralization.

Animals↗

PubMed2006

TGF-beta2 stimulates cranial suture closure through activation of the Erk-MAPK pathway.

Cranial sutures are important growth sites of the skull. During suture closure, the dura mater is one of the most important sources of various positive and negative regulatory signals. Previous results indicate that TGF-beta2 from dura mater strongly accelerates suture closure, however, its exact regulatory mechanism is still unclear. In this study, we confirmed that removal of dura mater in calvarial organ culture strongly accelerates sagittal suture closure and that this effect is further enhanced by TGF-beta2 treatment. TGF-beta2 stimulated cell proliferation in the MC3T3-E1 cell line. Similarly, it stimulated the proliferation of cells in the sutural space in calvarial organ culture. Furthermore, TGF-beta2-mediated enhanced cell proliferation and suture closure were almost completely inhibited by an Erk-MAPK blocker, PD98059. These results indicate that TGF-beta2-induced activation of Erk-MAPK is an important signaling component that stimulates cell proliferation to enrich osteoprogenitor cells, thereby promoting their differentiation into osteoblasts to achieve a rapid calvarial bone expansion.

Animals↗

PubMed2006

Tetraspanin CD9 regulates osteoclastogenesis via regulation of p44/42 MAPK activity.

Tetraspanin CD9 has been shown to regulate cell-cell fusion in sperm-egg fusion and myotube formation. However, the role of CD9 in osteoclast, another multinucleated cell type, is not still clear. Therefore, we investigated the role of CD9 in osteoclast differentiation. CD9 was expressed in osteoclast lineage cells and its expression level increased during the progression of RANKL-induced osteoclastogenesis. KMC8, a neutralizing antibody specific to CD9, significantly suppressed RANKL-induced multinucleated osteoclast formation and the mRNA expression of osteoclast differentiation marker genes. To define CD9-regulated osteoclastogenic signaling pathway, MAPK pathways were examined. KMC8 induced long-term phosphorylation of p44/42 MAPK, but not of p38 MAPK. Constitutive activation of p44/42 MAPK by overexpressing constitutive-active mutant of MEK1 almost completely blocked osteoclast differentiation. Taken together, these results suggest that CD9 expressed on osteoclast lineage cells might positively regulate osteoclastogenesis via the regulation of p44/42 MAPK activity.

Animals↗

PubMed2006

Bone morphogenetic protein-2 stimulates Runx2 acetylation.

Runx2/Cbfa1/Pebp2aA is a global regulator of osteogenesis and is crucial for regulating the expression of bone-specific genes. Runx2 is a major target of the bone morphogenetic protein (BMP) pathway. Genetic analysis has revealed that Runx2 is degraded through a Smurf-mediated ubiquitination pathway, and its activity is inhibited by HDAC4. Here, we demonstrate the molecular link between Smurf, HDACs and Runx2, in BMP signaling. BMP-2 signaling stimulates p300-mediated Runx2 acetylation, increasing transactivation activity and inhibiting Smurf1-mediated degradation of Runx2. HDAC4 and HDAC5 dea-cetylate Runx2, allowing the protein to undergo Smurf-mediated degradation. Inhibition of HDAC increases Runx2 acetylation, and potentiates BMP-2-stimulated osteoblast differentiation and increases bone formation. These results demonstrate that the level of Runx2 is controlled by a dynamic equilibrium of acetylation, deacetylation, and ubiquitination. These findings have important medical implications because BMPs and Runx2 are of tremendous interest with regard to the development of therapeutic agents against bone diseases.

Animals↗

PubMed2006

Bone-related gene profiles in developing calvaria.

Generating a comprehensive understanding of osteogenesis-related gene profiles is very important in the development of new treatments for osteopenic conditions. Developing calvaria undergoes a typical intramembranous bone-forming process. To identify genes associated with osteoblast differentiation, we isolated total RNAs from parietal bones, that represent active osteoblasts, and sutural mesenchyme, that represents osteoprogenitor cells, and comprehensively analyzed their gene expression profiles using an oligo-based Affymetrix microarray chip containing 22,690 probes. About 2100 genes with "Present" calls had more than 2-fold higher expression in bone compared to sutures while 73 of these genes had more than 8-fold expression. Some of these genes are already known to be bone-related biomarkers: VitD receptor, bone sialoprotein, osteocalcin, osteopontin, MMP13, etc. Eight genes were selected and subjected to confirmation by quantitative real-time RT-PCR analyses. All the genes tested showed higher expression in bones, ranging from 5- to 140-fold. Several of these genes are ESTs while others are already known but their functions in osteogenesis were not previously known. Most genes of the BMP and FGF families probed in the Genechip analysis were more highly expressed in bone tissues compared to suture. All differentially-expressed Runx and Dlx family genes also showed higher expression in bone. These results imply that our data is valid and can be used as a good standard for the mining of osteogenesis-related genes.

Animals↗

PubMed2006

Four novel RUNX2 mutations including a splice donor site result in the cleidocranial dysplasia phenotype.

Cleidocranial dysplasia (CCD) is an autosomal dominant disorder caused by haploinsufficiency of the RUNX2 gene. In this study, we analyzed by direct sequencing RUNX2 mutations from eleven CCD patients. Four of seven mutations were novel: two nonsense mutations resulted in a translational stop at codon 50 (Q50X) and 112 (E112X); a missense mutation converted arginine to glycine at codon 131 (R131G); and an exon 1 splice donor site mutation (donor splice site GT/AT, IVS1 + 1G > A) at exon 1-intron junction resulted in the deletion of QA stretch contained in exon 1 of RUNX2. We focused on the functional analysis of the IVS1 + 1G > A mutation. A full-length cDNA of this mutation was cloned (RUNX2Deltae1) and expressed in Chinese hamster ovary (CHO) and HeLa cells. Functional analysis of RUNX2Deltae1 was performed with respect to protein stability, nuclear localization, DNA binding, and transactivation activity of a downstream RUNX2 target gene. Protein stability of RUNX2Deltae1 is similar to wild-type RUNX2 as determined by Western blot analysis. Subcellular localization of RUNX2Deltae1, assessed by in situ immunofluorescent staining, was observed with partial retention in both the nucleus and cytoplasm. This finding is in contrast to RUNX2 wild-type, which is detected exclusively in the nucleus. DNA binding activity was also compromised by the RUNX2Deltae1 in gel shift assay. Finally, RUNX2Deltae1 blocked transactivation of the osteocalcin gene determined by transient transfection assay. Our findings demonstrate for the first time that the CCD phenotype can be caused by a splice site mutation, which results in the deletion of N-terminus amino acids containing the QA stretch in RUNX2 that contains a previously unidentified second nuclear localization signal (NLS). We postulate that the QA sequence unique to RUNX2 contributes to a competent structure of RUNX2 that is required for nuclear localization, DNA binding, and transactivation function.

Adolescent↗

PubMed2006

Runx2 phosphorylation induced by fibroblast growth factor-2/protein kinase C pathways.

Runx2 is a key transcription factor in osteoblast differentiation, and its activity is regulated by fibroblast growth factors (FGFs). Craniosynostosis, characterized by premature suture closure, results from mutations that generate constitutively active FGF receptors (FGFRs). We previously showed that FGF/FGFR-activated protein kinase C (PKC) is involved in the expression and activity of Runx2. Activated PKCdelta physically interacts with Runx2 in FGF2-stimulated MC3T3-E1 preosteoblastic cells. Immunopurified Runx2 protein reacted with PKCdelta kinase, and a phosphorylated 1460-Da peptide fragment (amino acids 241-252, 1380-Da) derived from Runx2 was also detected in MS analysis. Computer analysis predicted that Ser247 in this Runx2 can be a possible phosphorylation site by PKCdelta. We also showed that Runx2 activity after FGF stimulation correlates with the presence of the Runx2 Ser247 residue. The S247A (Ser --> Ala) mutation confers decreased transcriptional activity on a Runx2-responsive promoter after FGF treatment.

Animals↗

PubMed2006

Dexamethasone inhibits the formation of multinucleated osteoclasts via down-regulation of beta3 integrin expression.

Although glucocorticoids are known to affect osteoclast differentiation and function, there have been conflicting reports about the effect of glucocorticoids on osteoclast formation, leading to the assumption that microenvironment and cell type influence their action. We explored the effect of the synthetic glucocorticoid analog dexamethasone on the formation of osteoclasts. Dexamethasone inhibited the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated osteoclasts without affecting the formation of TRAP-positive mononuclear cells in a coculture of mouse osteoblasts and bone marrow cells. Dexamethasone did not inhibit mRNA expression levels of the receptor activator of nuclear factor-kappaB ligand and osteoprotegerin, the essential regulators of osteoclastogenesis. Dexamethasone down-regulated the expression of beta3 integrin mRNA and protein but did not alter expression of other osteoclast differentiation marker genes. Both dexamethasone and echistatin, a beta3 integrin function blocker, inhibited TRAP-positive multinucleated osteoclast formation but not TRAP-positive mononuclear cell formation. These results suggest that dexamethasone inhibits the formation of multinucleated osteoclasts, at least in part, through the down-regulation of beta3 integrin, which plays an important role in the formation of multinucleated osteoclasts.

Animals↗

PubMed2006

Control of tooth morphogenesis by Runx2.

Odontogenesis is a complex process in which the interplay of signaling cascades of the epithelium and mesenchyme is critical. Evidence for the involvement of Runx2--a well-known osteogenic master transcription factor--in odontogenesis, has been accumulating. Haploinsufficiency of Runx2 in humans results in cleido-cranial dysplasia (CCD), characterized by supernumerary teeth; in Runx2-/- mice, molar odontogenesis does not proceed beyond the late bud stage. In this article, we discuss the role of Runx2 in tooth development, specifically in the signaling interplay of the epithelium and mesenchyme during the transition from bud stage to cap stage. Runx2 is an important molecule of the dental mesenchyme; its expression is induced by epithelial fibroblast growth factor (FGF), and it is involved in regulating the induction of mesenchymal signaling back to the dental epithelium for epithelial morphogenesis. In addition, we discuss the role of the two major isoforms of Runx2, and other Runx family genes, in odontogenic processes.

Animals↗

PubMed2005

The bone-related Zn finger transcription factor Osterix promotes proliferation of mesenchymal cells.

Osterix is a bone-related transcription factor that functions genetically downstream of Runx2, which controls both growth and differentiation in osteoblasts. Here we assessed the biological function of Osterix in mesenchymal cells that are not normally committed to the osteogenic lineage. Stably transfected NIH3T3 fibroblasts that express exogenous Osterix were examined for their ability to convert into osteoblastic cells by analyzing gene expression profiles of bone phenotype related markers, as well as by measuring bone nodule formation and cell proliferation. Forced expression of Osterix stimulates osteopontin gene expression but not the expression or activity of other bone-related markers, including collagen type I, alkaline phosphatase, osteocalcin, or osteonectin. Moreover, cells stably expressing Osterix do not induce bone nodule formation. Strikingly, both polyclonal and monoclonal cells expressing Osterix exhibit enhanced proliferation. Collectively, these results indicate that Osterix is insufficient to establish osteogenic lineage commitment, perhaps due to the ability of Osterix to promote cell growth. We propose that regulatory pathways operating upstream of or in parallel with Osterix are required for osteogenic conversion of uncommitted mesenchymal cells.

Animals↗

PubMed2005

Critical molecular switches involved in BMP-2-induced osteogenic differentiation of mesenchymal cells.

Bone morphogenetic protein (BMP)-2 strongly induces bone formation. Introduction of the protein in muscle tissue results in ectopic bone formation. Similarly, BMP-2 treatment also stimulates the in vitro transdifferentiation of myogenic cells to osteogenic cells. The establishment of an in vitro model system has enabled the investigation of intracellular events including BMP receptor activation, BMP-2-induced R-Smad activation, and kinase activation, and the role of osteogenic transcription factors, such as Runx2, Osx, Dlx5, and Msx2. Many reviews have addressed events downstream of BMP-receptor binding but few deal with molecular cascades involved in BMP-2-induced osteogenesis. We focus on critical molecular switches, especially transcription factors, and several kinase pathways involved in osteogenic differentiation.

Animals↗

PubMed2005

Dlx5 specifically regulates Runx2 type II expression by binding to homeodomain-response elements in the Runx2 distal promoter.

Two major isoforms of the Runx2 gene are expressed by alternative promoter usage: Runx2 type I (Runx2-I) is derived from the proximal promoter (P2), and Runx2 type II (Runx2-II) is produced by the distal promoter (P1). Our previous results indicate that Dlx5 mediates BMP-2-induced Runx2 expression and osteoblast differentiation (Lee, M.-H., Kim, Y-J., Kim, H-J., Park, H-D., Kang, A-R., Kyung, H.-M., Sung, J-H., Wozney, J. M., Kim, H-J., and Ryoo, H-M. (2003) J. Biol. Chem. 278, 34387-34394). However, little is known of the molecular mechanisms by which Dlx5 up-regulates Runx2 expression in BMP-2 signaling. Here, Runx2-II expression was found to be specifically stimulated by BMP-2 treatment or by Dlx5 overexpression. In addition, BMP-2, Dlx5, and Runx2-II were found to be expressed in osteogenic fronts and parietal bones of the developing cranial vault and Runx2-I and Msx2 in the sutural mesenchyme. Furthermore, Runx2 P1 promoter activity was strongly stimulated by Dlx5 overexpression, whereas Runx2 P2 promoter activity was not. Runx2 P1 promoter deletion analysis indicated that the Dlx5-specific response is due to sequences between -756 and -342 bp of the P1 promoter, where three Dlx5-response elements are located. Dlx5 responsiveness to these elements was confirmed by gel mobility shift assay and site-directed mutagenesis. Moreover, Msx2 specifically suppressed the Runx2 P1 promoter, and the responsible region overlaps with that recognized by Dlx5. In summary, Dlx5 specifically transactivates the Runx2 P1 promoter, and its action on the P1 promoter is antagonized by Msx2.

Animals↗

PubMed2005

Runx2 regulates FGF2-induced Bmp2 expression during cranial bone development.

Calvarial bone is formed by the intramembranous bone-forming process, which involves many signaling molecules. The constitutive activation of the fibroblast growth factor (FGF) signaling pathway accelerates osteoblast differentiation and results in premature cranial suture closure. Bone morphogenetic protein (BMP) signaling pathways, which involve the downstream transcription factors Dlx5 and Msx2, are also involved in the bone-forming processes. However, the relationships between these two main signaling cascades are still unclear. We found that FGF2 treatment of developing bone fronts stimulated Bmp2 gene expression but that BMP2 treatment could not induce Fgf2 expression. Moreover, the disruption of the Runx2 gene completely eliminated the expression of Bmp2 and its downstream genes Dlx5 and Msx2 in the developing primordium of bone, while the expression of Fgf2 was maintained. In addition, cultured Runx2-/- cells expressed very low baseline levels of Bmp2 that were up-regulated by transfection with a Runx2-expressing plasmid. These levels in turn were markedly elevated by FGF2 treatment. FGF2 treatment also strongly enhanced the Bmp2 expression in MC3T3-E1 cells, whose endogenous Runx2 gene is intact and which express Bmp2 at low baseline levels as well. These results indicate that Runx2 is an important mediator of the expression of Bmp2 in response to FGF stimulation in cranial bone development.

Animals↗

PubMed2004

Bone morphogenetic protein-2-induced alkaline phosphatase expression is stimulated by Dlx5 and repressed by Msx2.

Alkaline phosphatase (ALP) is a widely accepted bone marker. Its expression is stimulated by bone morphogenetic protein (BMP)-2 treatment, the activation of BMP receptors and R-Smads, and the expression of Dlx5 and Runx2. However, how BMP-2 induces ALP expression is not clearly understood. We dissected the murine ALP promoter and found within it a Dlx5-binding cis-acting element by electrophoretic mobility shift assays and site-directed mutagenesis of the element. Dlx5 and the product of its target gene, Runx2, stimulated ALP promoter activity in an additive manner. However, because Dlx5 continued to stimulate ALP expression in Runx2(-/-) cells, the ALP stimulatory activity of Dlx5 is independent of Runx2. We also found that overexpression of Msx2 suppressed the mRNA level and enzyme activity of ALP that were induced by BMP-2 stimulation, and suppressed the Dlx5-stimulated ALP promoter activity by competing with Dlx5 for the cis-acting element in the ALP promoter. Moreover, Msx2 levels are constitutively high in C2C12 myogenic cells but decrease over time after BMP-2 treatment. This may explain why BMP-2 treatment of these cells results in immediate Dlx5 expression yet ALP expression commences only 1-2 days later. In other words, Msx2 in high levels counteracts initially the transcriptional activity of Dlx5 in low levels until a threshold Dlx5:Msx2 ratio is reached to the levels that allow the ALP stimulatory activity of Dlx5 to prevail. Thus, Dlx5 transactivates ALP expression, directly by binding to its cognate response element and/or indirectly by stimulating Runx2 expression, and Msx2 counteracts the direct transactivation of Dlx5.

Alkaline Phosphatase↗

PubMed2004

Runx2 mediates FGF signaling from epithelium to mesenchyme during tooth morphogenesis.

Runx2 (Cbfa1) is a runt domain transcription factor that is essential for bone development and tooth morphogenesis. Teeth form as ectodermal appendages and their development is regulated by interactions between the epithelium and mesenchyme. We have shown previously that Runx2 is expressed in the dental mesenchyme and regulated by FGF signals from the epithelium, and that tooth development arrests at late bud stage in Runx2 knockout mice [Development 126 (1999) 2911]. In the present study, we have continued to clarify the role of Runx2 in tooth development and searched for downstream targets of Runx2 by extensive in situ hybridization analysis. The expression of Fgf3 was downregulated in the mesenchyme of Runx2 mutant teeth. FGF-soaked beads failed to induce Fgf3 expression in Runx2 mutant dental mesenchyme whereas in wild-type mesenchyme they induced Fgf3 in all explants indicating a requirement of Runx2 for transduction of FGF signals. Fgf3 was absent also in cultured Runx2-/- calvarial cells and it was induced by overexpression of Runx2. Furthermore, Runx2 was downregulated in Msx1 mutant tooth germs, indicating that it functions in the dental mesenchyme between Msx1 and Fgf3. Shh expression was absent from the epithelial enamel knot in lower molars of Runx2 mutant and reduced in upper molars. However, other enamel knot marker genes were expressed normally in mutant upper molars, while reduced or missing in lower molars. These differences between mutant upper and lower molars may be explained by the substitution of Runx2 function by Runx3, another member of the runt gene family that was upregulated in upper but not lower molars of Runx2 mutants. Shh expression in mutant enamel knots was not rescued by FGFs in vitro, indicating that in addition to Fgf3, Runx2 regulates other mesenchymal genes required for early tooth morphogenesis. Also, exogenous FGF and SHH did not rescue the morphogenesis of Runx2 mutant molars. We conclude that Runx2 mediates the functions of epithelial FGF signals regulating Fgf3 expression in the dental mesenchyme and that Fgf3 may be a direct target gene of Runx2.

Animals↗

PubMed2004

Establishment and characterization of a stable cell line to evaluate cellular Runx2 activity.

Runx2 is an essential transcription factor for osteoblast differentiation from early commitment step to final differentiation. Based on its crucial role in osteoblast differentiation, the transcriptional activity of Runx2 protein implies more valuable information for osteoblast differentiation than any other parameters, such as Runx2 mRNA or protein level. Thus, a sensitive, specific, and consistent method to determine the Runx2 transcriptional activity has long been expected. Here we suggest a stable cell line that carries 6xOSE2-Luciferase reporter vector would be a good evaluation system to determine biological Runx2 transcriptional activity. The proliferation rate, cell shape, and the myogenic differentiation potential of the cloned cell line were similar to those of parental premyoblastic C2C12 cells. The cells specifically responded to Runx2 modulating agent such as FGF2. The stable cell line responded 5-6 folds more sensitively than the transiently transfected cells with Runx2. Though overexpression of any Runx gene stimulated the luciferase activity, Runx2 enhanced the reporter activity the highest. Collectively, the 6xOSE2-luc stable cells would be a good biological evaluation system to assess the activity of extracellular Runx2 modulating stimulations as well as the signal transduction pathways involved in the stimulations.

Animals↗

PubMed2004

Gene expression profile of human chondrocyte HCS-2/8 cell line by EST sequencing analysis.

Large-scale single-pass sequencing of randomly selected cDNA clones from cell type specific libraries has proven to be a powerful approach for the discovery of novel gene functions, identification of novel gene family members, and definition of gene expression profiles. HCS-2/8 chondrocyte has been used as a cell culture model to study chondrocyte differentiation. Here we performed 3350 single-pass sequencing reactions obtained from the 5' ends of cDNAs from HCS-2/8 cells. To define the expression profiles of HCS-2/8 chondrocytes, we analyzed the identity of these representative cDNA sequences using database searches (BLAST). The sequences represent 1927 unique genes with known function (i.e., unigene clusters), 38 transcripts that are similar to genes with known function, 739 expressed genes with unknown function (i.e., expressed sequence tags), and 18 cDNAs which have not previously been sequenced. Interestingly, many transcripts were expressed from chromosome 12 compared with total genes, while the fewer numbers of cDNAs were derived from genes on chromosomes 14, 18 and Y. The chondrocytic phenotype of HCS-2/8 cells is reflected by abundant expression of genes related to cell structure and motility and the 20 most frequently expressed unigenes reflect a chondrocyte-related gene expression signature. Thus, our data establish a representative set of more than 2000 genes expressed in a chondrocytic cell line. This finding provides a framework for understanding cell growth and differentiation of chondrocytes and their metabolic function in the formation and remodeling of cartilage.

Cell Line, Tumor↗