SOX9 directly Regulates CTGF/CCN2 Transcription in Growth Plate Chondrocytes and in Nucleus Pulposus Cells of Intervertebral Disc.
ABSTRACT: Several lines of evidence indicate that connective tissue growth factor (CTGF/CCN2) stimulates chondrocyte proliferation and maturation. Given the fact that SOX9 is essential for several steps of the chondrocyte differentiation pathway, we asked whether Ctgf (Ccn2) is the direct target gene of SOX9. We found that Ctgf mRNA was down-regulated in primary sternal chondrocytes from Sox9(flox/flox) mice infected with Ad-CMV-Cre. We performed ChIP-on-chip assay using anti-SOX9 antibody, covering the Ctgf gene from 15?kb upstream of its 5'-end to 10?kb downstream of its 3'-end to determine SOX9 interaction site. One high-affinity interaction site was identified in the Ctgf proximal promoter by ChIP-on-chip assay. An important SOX9 regulatory element was found to be located in -70/-64 region of the Ctgf promoter. We found the same site for SOX9 binding to the Ctgf promoter in nucleus pulposus (NP) cells. The loss of Sox9 in growth plate chondrocytes in knee joint and in NP cells in intervertebral disc led to the decrease in CTGF expression. We suggest that Ctgf is the direct target gene of SOX9 in chondrocytes and NP cells. Our study establishes a strong link between two regulatory molecules that have a major role in cartilaginous tissues.
Project description:CCN2/connective tissue growth factor is highly expressed in hypertrophic chondrocytes and is required for chondrogenesis. However, the transcriptional mechanisms controlling its expression in cartilage are largely unknown. The activity of the Ccn2 promoter was, therefore, investigated in osteochondro-progenitor cells and hypertrophic chondrocytes to ascertain these mechanisms. Sox9 and T-cell factor (TCF) x lymphoid enhancer factor (LEF) factors contain HMG domains and bind to related consensus sites. TCF x LEF factors are normally repressive but when bound to DNA in a complex with beta-catenin become activators of gene expression. In silico analysis of the Ccn2 proximal promoter identified multiple consensus TCF x LEF elements, one of which was also a consensus binding site for Sox9. Using luciferase reporter constructs, the TCF x LEF x Sox9 site was found to be involved in stage-specific expression of Ccn2. Luciferase, electrophoretic mobility shift assay (EMSA), and ChIP analysis revealed that Sox9 represses Ccn2 expression by binding to the consensus TCF x LEF x Sox9 site. On the other hand, the same assays showed that in hypertrophic chondrocytes, TCF x LEF x beta-catenin complexes occupy the consensus TCF x LEF x Sox9 site and activate Ccn2 expression. Furthermore, transgenic mice in which lacZ expression is driven under the control of the proximal Ccn2 promoter revealed that the proximal Ccn2 promoter responded to Wnt signaling in cartilage. Hence, we propose that differential occupancy of the TCF x LEF x Sox9 site by Sox9 versus beta-catenin restricts high levels of Ccn2 expression to hypertrophic chondrocytes.
Project description:CCN2 (connective tissue growth factor (CTGF/CCN2)) is a matricellular protein that utilizes integrins to regulate cell proliferation, migration and survival. The loss of CCN2 leads to perinatal lethality resulting from a severe chondrodysplasia. Upon closer inspection of Ccn2 mutant mice, we observed defects in extracellular matrix (ECM) organization and hypothesized that the severe chondrodysplasia caused by loss of CCN2 might be associated with defective chondrocyte survival. Ccn2 mutant growth plate chondrocytes exhibited enlarged endoplasmic reticula (ER), suggesting cellular stress. Immunofluorescence analysis confirmed elevated stress in Ccn2 mutants, with reduced stress observed in Ccn2 overexpressing transgenic mice. In vitro studies revealed that Ccn2 is a stress responsive gene in chondrocytes. The elevated stress observed in Ccn2-/- chondrocytes is direct and mediated in part through integrin ?5. The expression of the survival marker NF?B and components of the autophagy pathway were decreased in Ccn2 mutant growth plates, suggesting that CCN2 may be involved in mediating chondrocyte survival. These data demonstrate that absence of a matricellular protein can result in increased cellular stress and highlight a novel protective role for CCN2 in chondrocyte survival. The severe chondrodysplasia caused by the loss of CCN2 may be due to increased chondrocyte stress and defective activation of autophagy pathways, leading to decreased cellular survival. These effects may be mediated through nuclear factor ?B (NF?B) as part of a CCN2/integrin/NF?B signaling cascade.
Project description:We have recently demonstrated that overexpression of Smurf2 under the control of type II collagen alpha 1 (Col2a1) promoter induces an intervertebral disc degeneration phenotype in Col2a1-Smurf2 transgenic mice. The chondrocyte-like cells that express type II collagen and Smurf2 in the transgenic mouse discs are prone to degenerate. However, how the chondrocyte-like cells contribute to disc degeneration is not known. Here, we utilized primary old bovine nucleus pulposus (NP) cells as substitutes for the chondrocyte-like cells in Col2a1-Smurf2 transgenic mouse discs to identify mechanism. We found that 35% of the cells were senescent; TGF-β treatment of the cells induced a rapid moderate accumulation of β-catenin, which interacted with connective tissue growth factor (CTGF/CCN2) in the cytoplasm and recruited it to the membrane for secretion. The TGF-β-initiated β-catenin-mediated CTGF secretory cascade did not occur in primary young bovine NP cells; however, when Smurf2 was overexpressed in young bovine NP cells, the cells became senescent and allowed this cascade to occur. These results suggest that Smurf2-induced disc degeneration in Col2a1-Smurf2 transgenic mice occurs through activation of CTGF secretory pathway in senescent disc cells.
Project description:Matrix metalloproteinase 3 (MMP3) is well known as a secretory endopeptidase that degrades extracellular matrices. Recent reports indicated the presence of MMPs in the nucleus (A. J. Kwon et al., FASEB J. 18:690-692, 2004); however, its function has not been well investigated. Here, we report a novel function of human nuclear MMP3 as a trans regulator of connective tissue growth factor (CCN2/CTGF). Initially, we cloned MMP3 cDNA as a DNA-binding factor for the CCN2/CTGF gene. An interaction between MMP3 and transcription enhancer dominant in chondrocytes (TRENDIC) in the CCN2/CTGF promoter was confirmed by a gel shift assay and chromatin immunoprecipitation. The CCN2/CTGF promoter was activated by overexpressed MMP3, whereas a TRENDIC mutant promoter lost the response. Also, the knocking down of MMP3 suppressed CCN2/CTGF expression. By cytochemical and histochemical analyses, MMP3 was detected in the nuclei of chondrocytic cells in culture and also in the nuclei of normal and osteoarthritic chondrocytes in vivo. The nuclear translocation of externally added recombinant MMP3 and six putative nuclear localization signals in MMP3 also were shown. Furthermore, we determined that heterochromatin protein gamma coordinately regulates CCN2/CTGF by interacting with MMP3. The involvement of this novel role of MMP3 in the development, tissue remodeling, and pathology of arthritic diseases through CCN2/CTGF regulation thus is suggested.
Project description:Vascular endothelial growth factor (VEGF) is essential for establishing vascularization and regulating chondrocyte development and survival. We have demonstrated that VEGF regulates the expression of CCN2/connective tissue growth factor (CCN2/CTGF) an essential mediator of cartilage development and angiogenesis, suggesting that CCN2 functions in down-stream of VEGF, and that VEGF function is mediated in part by CCN2. On the other hand, the phenotype of Ccn2 mutant growth plates, which exhibit decreased expression of VEGF in the hypertrophic zone, indicates that Vegf expression is dependent on Ccn2 expression as well. Therefore, we investigated the molecular mechanisms underlying the induction of VEGF by CCN2 using a human chondrocytic cell line, HCS-2/8. Hypoxic stimulation (5% O(2)) of HCS-2/8 cells increased VEGF mRNA levels by approximately 8 fold within 6 h as compared with the cells cultured under normoxia. In addition, VEGF expression was further up-regulated under hypoxia in HCS-2/8 cells transfected with a Ccn2 expression plasmid. Hypoxia-inducible factor (HIF)-1alpha mRNA and protein levels were increased by stimulation with recombinant CCN2 (rCCN2). Furthermore, the activity of a VEGF promoter that contained a HIF-1 binding site was increased in HCS-2/8, when the cells were stimulated by rCCN2. These results suggest that CCN2 regulates the expression of VEGF at a transcriptional level by promoting HIF-1alpha activity. In fact, HIF-1alpha was detected in the nuclei of proliferative and pre-hypertrophic chondrocytes of wild-type mice, whereas it was not detected in Ccn2 mutant chondrocytes in vivo. This activation cascade from CCN2 to VEGF may therefore play a critical role in chondrocyte development and survival.
Project description:The transcription factor SOX9 plays an essential role in determining the fate of several cell types and is a master factor in regulation of chondrocyte development. Our aim was to determine which genes in the genome of chondrocytes are either directly or indirectly controlled by SOX9. We used RNA-Seq to identify genes whose expression levels were affected by SOX9 and used SOX9 ChIP-Seq to identify those genes that harbor SOX9-interaction sites. For RNA-Seq, the RNA expression profile of primary Sox9flox/flox mouse chondrocytes infected with Ad-CMV-Cre was compared with that of the same cells infected with a control adenovirus. Analysis of RNA-Seq data indicated that, when the levels of Sox9 mRNA were decreased more than 8-fold by infection with Ad-CMV-Cre, 196 genes showed a decrease in expression of at least 4-fold. These included many cartilage extracellular matrix (ECM) genes and a number of genes for ECM modification enzymes (transferases), membrane receptors, transporters, and others. In ChIP-Seq, 75% of the SOX9-interaction sites had a canonical inverted repeat motif within 100 bp of the top of the peak. SOX9-interaction sites were found in 55% of the genes whose expression was decreased more than 8-fold in SOX9-depleted cells and in somewhat fewer of the genes whose expression was reduced more than 4-fold, suggesting that these are direct targets of SOX9. The combination of RNA-Seq and ChIP-Seq has provided a fuller understanding of the SOX9-controlled genetic program of chondrocytes.
Project description:CCN2/CTGF is a multifunctional factor that plays a crucial role in the growth and differentiation of chondrocytes. The chicken ccn2 gene is regulated not only at the transcriptional level but also by the interaction between a posttranscriptional element in the 3' untranslated region (3'-UTR) and a cofactor. In the present study, we identified a nucleophosmin (NPM) (also called B23) as this cofactor. Binding of NPM to the element was confirmed, and subsequent analysis revealed a significant correlation between the decrease in cytosolic NPM and the increased stability of the ccn2 mRNA during chondrocyte differentiation in vivo. Furthermore, recombinant chicken NPM enhanced the degradation of chimeric RNAs containing the posttranscriptional cis elements in a chicken embryonic fibroblast extract in vitro. It is noteworthy that the RNA destabilization effect by NPM was far more prominent in the cytosolic extract of chondrocytes than in that of fibroblasts, representing a chondrocyte-specific action of NPM. Stimulation by growth factors to promote differentiation changed the subcellular distribution of NPM in chondrocytes, which followed the expected patterns from the resultant change in the ccn2 mRNA stability. Therefore, the present study reveals a novel aspect of NPM as a key player in the posttranscriptional regulation of ccn2 mRNA during the differentiation of chondrocytes.
Project description:A comprehensive analysis of Sox9 binding profiles in developing chondrocytes identified marked enrichment of an AP-1-like motif (Ohba et al. 2015). Here, we have explored the functional interplay between Sox9 and AP-1 in mammalian chondrocyte development. Among AP-1 family members, Jun and Fosl2 were highly expressed within prehypertrophic and early hypertrophic chondrocytes. Chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq) showed a striking overlap in Jun- and Sox9-bound regions throughout the chondrocyte genome, a reflection of direct binding of each factor to target motifs in shared enhancers, and physical interactions of AP-1 with Sox9. In vitro expression analysis indicates that direct co-binding of Sox9 and AP-1 at target motifs enhanced target gene expression, while protein-protein interactions suppressed AP-1- and Sox9-driven transcription. Analysis of prehypertrophic chondrocyte removal of Sox9 demonstrated Sox9 was essential for hypertrophic chondrocyte development, while in vitro and ex vivo analyses showed AP-1 promotes chondrocyte hypertrophy. Sox9 and Jun co-bound and co-activated a Col10a1 enhancer in Sox9 and AP-1 motif-dependent manners consistent with their combined action promoting hypertrophic gene expression. Together, the data support a model where AP-1-family members promote Sox9-action in the transition of chondrocytes to a terminal hypertrophic program. Intersection of ChIP-seq data from Sox9 and AP-1 factor Jun, RNA-seq data from developing rib chondrocytes and Col10a1mCherry positive hypertrophic chondrocytes in neonatal mice to uncover regulation of Sox9 by AP-1 factors during chondrocyte hypertrophy.
Project description:To examine the role of connective tissue growth factor CCN2/CTGF (CCN2) in the maintenance of the articular cartilaginous phenotype, we analyzed knee joints from aging transgenic mice (TG) overexpressing CCN2 driven by the Col2a1 promoter. Knee joints from 3-, 14-, 40-, and 60-day-old and 5-, 12-, 18-, 21-, and 24-month-old littermates were analyzed. Ccn2-LacZ transgene expression in articular cartilage was followed by X-gal staining until 5 months of age. Overexpression of CCN2 protein was confirmed through all ages in TG articular cartilage and in growth plates. Radiographic analysis of knee joints showed a narrowing joint space and other features of osteoarthritis in 50% of WT, but not in any of the TG mice. Transgenic articular cartilage showed enhanced toluidine blue and safranin-O staining as well as chondrocyte proliferation but reduced staining for type X and I collagen and MMP-13 as compared with those parameters for WT cartilage. Staining for aggrecan neoepitope, a marker of aggrecan degradation in WT articular cartilage, increased at 5 and 12 months, but disappeared at 24 months due to loss of cartilage; whereas it was reduced in TG articular cartilage after 12 months. Expression of cartilage genes and MMPs under cyclic tension stress (CTS) was measured by using primary cultures of chondrocytes obtained from wild-type (WT) rib cartilage and TG or WT epiphyseal cartilage. CTS applied to primary cultures of mock-transfected rib chondrocytes from WT cartilage and WT epiphyseal cartilage induced expression of Col1a1, ColXa1, Mmp-13, and Mmp-9 mRNAs; however, their levels were not affected in CCN2-overexpressing chondrocytes and TG epiphyseal cartilage. In conclusion, cartilage-specific overexpression of CCN2 during the developmental and growth periods reduced age-related changes in articular cartilage. Thus CCN2 may play a role as an anti-aging factor by stabilizing articular cartilage.
Project description:Previously we showed that CCN family member 2/connective tissue growth factor (CCN2) promotes the proliferation, differentiation, and maturation of growth cartilage cells in vitro. To elucidate the specific role and molecular mechanism of CCN2 in cartilage development in vivo, in the present study we generated transgenic mice overexpressing CCN2 and analyzed them with respect to cartilage and bone development. Transgenic mice were generated expressing a ccn2/lacZ fusion gene in cartilage under the control of the 6 kb-Col2a1-enhancer/promoter. Changes in cartilage and bone development were analyzed histologically and immunohistologically and also by micro CT. Primary chondrocytes as well as limb bud mesenchymal cells were cultured and analyzed for changes in expression of cartilage-related genes, and non-transgenic chondrocytes were treated in culture with recombinant CCN2. Newborn transgenic mice showed extended length of their long bones, increased content of proteoglycans and collagen II accumulation. Micro-CT analysis of transgenic bones indicated increases in bone thickness and mineral density. Chondrocyte proliferation was enhanced in the transgenic cartilage. In in vitro short-term cultures of transgenic chondrocytes, the expression of col2a1, aggrecan and ccn2 genes was substantially enhanced; and in long-term cultures the expression levels of these genes were further enhanced. Also, in vitro chondrogenesis was strongly enhanced. IGF-I and IGF-II mRNA levels were elevated in transgenic chondrocytes, and treatment of non-transgenic chondrocytes with recombinant CCN2 stimulated the expression of these mRNA. The addition of CCN2 to non-transgenic chondrocytes induced the phosphorylation of IGFR, and ccn2-overexpressing chondrocytes showed enhanced phosphorylation of IGFR. Our data indicates that the observed effects of CCN2 may be mediated in part by CCN2-induced overexpression of IGF-I and IGF-II. These findings indicate that CCN2-overexpression in transgenic mice accelerated the endochondral ossification processes, resulting in increased length of their long bones. Our results also indicate the possible involvement of locally enhanced IGF-I or IGF-II in this extended bone growth.