Induction Of Sox9 Research Articles

Cyclin G1 Expands Liver Tumor-Initiating Cells by Sox2 Induction via Akt/mTOR Signaling

Recurrence and chemoresistance of liver cancer has been attributed to the existence of liver tumor-initiating cells (T-ICs). It is important to decipher the molecular mechanism for acquisition of drug resistance and to design combinatorial therapeutic strategies. Cyclin G1 has been shown to play a pivotal role in initiation and metastasis of hepatocellular carcinoma. In this study, we found that enhanced cyclin G1 expression was associated with drug resistance of hepatoma cells and higher recurrence rate in hepatocellular carcinoma patients. Expression of cyclin G1 was elevated in liver T-ICs and closely correlated with the expression of liver T-IC markers. Forced cyclin G1 expression remarkably enhanced self-renewal and tumorigenicity of hepatoma cells. Cyclin G1 overexpression dramatically upregulated the expression of Sox2 both in vitro and in vivo, which was impaired by chemical inhibitors of Akt/mTOR signaling. Furthermore, blockade of Akt/mTOR signaling or interference of Sox2 expression suppressed cyclin G1-enhanced self-renewal, chemoresistance, and tumorigenicity of hepatoma cells, indicating that cyclin G1 expands liver T-ICs through Sox2 induction via Akt/mTOR signaling pathway. These results suggest that cyclin G1-induced liver T-IC expansion contributes to the recurrence and chemoresistance of hepatoma, and cyclin G1 may be a promising biomarker for individualized therapy of hepatocellular carcinoma patients.

SOX2 Expression Associates with Stem Cell State in Human Ovarian Carcinoma

The SRY-related HMG-box family of transcription factors member SOX2 regulates stemness and pluripotency in embryonic stem cells and plays important roles during early embryogenesis. More recently, SOX2 expression was documented in several tumor types including ovarian carcinoma, suggesting an involvement of SOX2 in regulation of cancer stem cells (CSC). Intriguingly, however, studies exploring the predictive value of SOX2 protein expression with respect to histopathologic and clinical parameters report contradictory results in individual tumors, indicating that SOX2 may play tumor-specific roles. In this report, we analyze the functional relevance of SOX2 expression in human ovarian carcinoma. We report that in human serous ovarian carcinoma (SOC) cells, SOX2 expression increases the expression of CSC markers, the potential to form tumor spheres, and the in vivo tumor-initiating capacity, while leaving cellular proliferation unaltered. Moreover, SOX2-expressing cells display enhanced apoptosis resistance in response to conventional chemotherapies and TRAIL. Hence, our data show that SOX2 associates with stem cell state in ovarian carcinoma and induction of SOX2 imposes CSC properties on SOC cells. We propose the existence of SOX2-expressing ovarian CSCs as a mechanism of tumor aggressiveness and therapy resistance in human SOC.

Plastic Fantastic: Schwann Cells and Repair of the Peripheral Nervous System

Repair in the peripheral nervous system (PNS) depends upon the plasticity of the myelinating cells, Schwann cells, and their ability to dedifferentiate, direct axonal regrowth, remyelinate, and allow functional recovery. The ability of such an exquisitely specialized myelinating cell to revert to an immature dedifferentiated cell that can direct repair is remarkable, making Schwann cells one of the very few regenerative cell types in our bodies. However, the idea that the PNS always repairs after injury, in contrast to the central nervous system, is not true. Repair in patients after nerve trauma can be incredibly variable, depending on the site and type of injury, and only a relatively small number of axons may fully regrow and reinnervate their targets. Recent research has shown that it is an active process that drives Schwann cells back to an immature state after injury and that this requires activity of the p38 and extracellular-regulated kinase 1/2 mitogen-activated protein kinases, as well as the transcription factor cJun. Analysis of the events after peripheral nerve transection has shown how signaling from nerve fibroblasts forms Schwann cells into cords in the newly generated nerve bridge, via Sox2 induction, to allow the regenerating axons to cross the gap. Understanding these pathways and identifying additional mechanisms involved in these processes raises the possibility of both boosting repair after PNS trauma and even, possibly, blocking the inappropriate demyelination seen in some disorders of the peripheral nervous system.

Sox9 Induction, Ectopic Paneth Cells, and Mitotic Spindle Axis Defects in Mouse Colon Adenomatous Epithelium Arising From Conditional Biallelic Apc Inactivation

We generated transgenic mice in which human CDX2 gene elements control expression of a tamoxifen-regulated Cre protein (CDX2P-CreER(T2)) to allow for inducible gene targeting in intestinal epithelium. After tamoxifen dosing of CDX2P-CreER(T2) mice, Cre activity was detected in the distal ileal, cecal, colonic, and rectal epithelium, with selected crypt base, transit amplifying, and surface cells all capable of activating Cre function. Four weeks after tamoxifen dosing of CDX2P-CreER(T2) mice carrying a Cre-activated fluorescent reporter, single crypts were uniformly fluorescence positive or negative, reflecting Cre activation in crypt stem cells. Biallelic inactivation of the Apc tumor suppressor gene via the CDX2P-CreER(T2) transgene in colon epithelium led to acute alterations in cell proliferation, apoptosis, and morphology, along with mitotic spindle misorientation, β-catenin nuclear localization, and induction of the intestinal stem cell markers Lgr5 and Musashi-1 and the Sox9 transcription factor. Normal mouse colon epithelium lacks Paneth cells, a key small intestine niche cell type, and Paneth cell differentiation is dependent on Sox9 function. In Apc-deficient colon epithelium, ectopic Paneth-like cells were seen outside the crypt base, such as new crypt budding sites. Our data indicate Apc inactivation via CDX2P-CreER(T2) targeting in mouse colon epithelium is sufficient to induce adenomatous changes and the generation of Paneth-like cells from neoplastic progenitors, with potentially significant roles in colon adenoma development and progression.

Transcriptional regulation of the alpha-1 type II collagen gene by nuclear factor κB/p65 and Sox9 in the chondrocytic phenotype of uterine carcinosarcomas

Uterine carcinosarcomas (U-CSs) are considered monoclonal in origin, but little is known about the mechanisms for establishment of heterologous sarcomatous components. Here, we examine the functional roles of nuclear factor κB (NF-κB)/p65 and Sox9 in the transcriptional regulation of alpha-1 type II collagen (COL2A1), a hallmark of chondrogenesis, during morphologic change in the direction of the chondrocytic phenotype. In 32 cases of U-CS, both phosphorylated p65 and Sox9 expression were colocalized in Col2A1-positive sarcomatous components, particularly in cartilaginous elements, with strongly positive correlation (ρ = 0.72, P = .005). A positive association of Col2A1 expression between protein (immunohistochemistry) and messenger RNA (in situ hybridization) assays was evident in sarcomatous components, whereas 9 cases also showed distinct positive signals for the messenger RNA without protein expression in carcinomatous elements, probably through a posttranscriptional and/or posttranslational modulation mechanism. In the Ishikawa endometrial cancer line, overexpression of p65 could activate transcription of COL2A1 promoter-intron reporters through binding to specific NF-κB sites in the first intron, along with up-regulation of Sox9. Exogenous induction of Sox9 also caused an increase in transcription of COL2A1, in contrast to a repression of the p65-mediated COL2A1 transcription, suggesting the existence of a negative feedback loop. These data, therefore, suggest that NF-κB/p65 signaling, as well as Sox9, may contribute to changes in the morphology of U-CS cells toward the chondrocytic phenotype through modulation of COL2A1 transcription.

SOX9 and myocardin counteract each other in regulating vascular smooth muscle cell differentiation

Transdifferentiation of vascular smooth muscle cells (VSMC) into chondrogenic cells contributes significantly to vascular calcification during the pathogenesis of atherosclerosis. However, the transcriptional mechanisms that control such phenotypic switch remain unclear. This process is characterized by the induction of Sox9 and Col2a1 genes accompanied by the repression of myocardin (Myocd) and SMC differentiation markers such as SM22, SM α-actin and SM-MHC. Here we explore the regulatory role of SOX9, the master regulator for chondrogenesis, in modulating SMC marker gene expression. qRT-PCR and luciferase assays show that over-expression of SOX9 inhibits SMC gene transcription and promoter activities induced by myocardin, the master regulator of smooth muscle differentiation. Such suppression is independent of the CArG box in the SMC promoters but dependent on myocardin. EMSA assay further shows that SOX9 neither participates in SRF (serum response factor) binding to the CArG box nor interacts with SRF, while co-immunoprecipitation demonstrates an association of SOX9 with myocardin. Conversely, myocardin suppresses SOX9-mediated chondrogenic gene Col2a1 expression. These findings provide the first mechanistic insights into the important regulatory role of SOX9 and myocardin in controlling the transcription program during SMC transdifferentiation into chondrocytes.

Notch1 signaling regulates chondrogenic lineage determination through Sox9 activation

Notch signaling is involved in several cell lineage determination processes during embryonic development. Recently, we have shown that Sox9 is most likely a primary target gene of Notch1 signaling in embryonic stem cells (ESCs). By using our in vitro differentiation protocol for chondrogenesis from ESCs through embryoid bodies (EBs) together with our tamoxifen-inducible system to activate Notch1, we analyzed the function of Notch signaling and its induction of Sox9 during EB differentiation towards the chondrogenic lineage. Temporary activation of Notch1 during early stages of EB, when lineage determination occurs, was accompanied by rapid and transient Sox9 upregulation and resulted in induction of chondrogenic differentiation during later stages of EB cultivation. Using siRNA targeting Sox9, we knocked down and adjusted this early Notch1-induced Sox9 expression peak to non-induced levels, which led to reversion of Notch1-induced chondrogenic differentiation. In contrast, continuous Notch1 activation during EB cultivation resulted in complete inhibition of chondrogenic differentiation. Furthermore, a reduction and delay of cardiac differentiation observed in EBs after early Notch1 activation was not reversed by siRNA-mediated Sox9 knockdown. Our data indicate that Notch1 signaling has an important role during early stages of chondrogenic lineage determination by regulation of Sox9 expression.

An EGFR-ERK-SOX9 Signaling Cascade Links Urothelial Development and Regeneration to Cancer

Like many carcinomas, urothelial carcinoma (UroCa) is associated with chronic injury. A better understanding of this association could inform improved strategies for preventing and treating this disease. We investigated the expression, regulation, and function of the transcriptional regulator SRY-related high-mobility group box 9 (Sox9) in urothelial development, injury repair, and cancer. In mouse bladders, Sox9 levels were high during periods of prenatal urothelial development and diminished with maturation after birth. In adult urothelial cells, Sox9 was quiescent but was rapidly induced by a variety of injuries, including exposure to the carcinogen cyclophosphamide, culture with hydrogen peroxide, and osmotic stress. Activation of extracellular signal-regulated kinases 1/2 (ERK1/2) was required for Sox9 induction in urothelial injury and resulted from activation of the epidermal growth factor receptor (Egfr) by several Egfr ligands that were dramatically induced by injury. In UroCa cell lines, SOX9 expression was constitutively upregulated and could be suppressed by EGFR or ERK1/2 blockade. Gene knockdown showed a role for SOX9 in cell migration and invasion. Accordingly, SOX9 protein levels were preferentially induced in invasive human UroCa tissue samples (n = 84) compared with noninvasive cancers (n = 56) or benign adjacent urothelium (n = 49). These results identify a novel, potentially oncogenic signaling axis linking urothelial injury to UroCa. Inhibiting this axis is feasible through a variety of pharmacologic approaches and may have clinical utility.

ID4 Imparts Chemoresistance and Cancer Stemness to Glioma Cells by Derepressing miR-9*–Mediated Suppression of SOX2

Glioma stem cells (GSC) possess tumor-initiating potential and are relatively resistant to conventional chemotherapy and irradiation. Thus, they are considered to be major drivers for glioma initiation, progression, and recurrence. However, the precise mechanism governing acquisition of their drug resistance remains to be elucidated. Our previous study has shown that inhibitor of differentiation 4 (ID4) dedifferentiates Ink4a/Arf(-/-) mouse astrocytes and human glioma cells to glioma stem-like cells (induced GSCs or iGSCs). In this article, we report that ID4-driven iGSCs exhibit chemoresistant behavior to anticancer drugs through activation of ATP-binding cassette (ABC) transporters. We found that ID4 enhanced SOX2 protein expression by suppressing microRNA-9* (miR-9*), which can repress SOX2 by targeting its 3'-untranslated region. Consequently, ID4-mediated SOX2 induction enhanced ABCC3 and ABCC6 expression through direct transcriptional regulation, indicating that ID4 regulates the chemoresistance of iGSCs by promoting SOX2-mediated induction of ABC transporters. Furthermore, we found that short hairpin RNA-mediated knockdown of SOX2 in ID4-driven iGSCs resulted in loss of cancer stemness. Moreover, ectopic expression of SOX2 could dedifferentiate Ink4a/Arf(-/-) astrocytes and glioma cells to iGSCs, indicating a crucial role of SOX2 in genesis and maintenance of GSCs. Finally, we found that the significance of the ID4-miR-9*-SOX2-ABCC3/ABCC6 regulatory pathway is recapitulated in GSCs derived from patients with glioma. Together, our results reveal a novel regulatory mechanism by which ID4-driven suppression of miR-9* induces SOX2, which imparts stemness potential and chemoresistance to glioma cells and GSCs.

Modulation of transforming growth factor beta signalling pathway genes by transforming growth factor beta in human osteoarthritic chondrocytes: involvement of Sp1 in both early and late response cells to transforming growth factor beta

IntroductionTransforming growth factor beta (TGFβ) plays a central role in morphogenesis, growth, and cell differentiation. This cytokine is particularly important in cartilage where it regulates cell proliferation and extracellular matrix synthesis. While the action of TGFβ on chondrocyte metabolism has been extensively catalogued, the modulation of specific genes that function as mediators of TGFβ signalling is poorly defined. In the current study, elements of the Smad component of the TGFβ intracellular signalling system and TGFβ receptors were characterised in human chondrocytes upon TGFβ1 treatment.MethodsHuman articular chondrocytes were incubated with TGFβ1. Then, mRNA and protein levels of TGFβ receptors and Smads were analysed by RT-PCR and western blot analysis. The role of specific protein 1 (Sp1) was investigated by gain and loss of function (inhibitor, siRNA, expression vector).ResultsWe showed that TGFβ1 regulates mRNA levels of its own receptors, and of Smad3 and Smad7. It modulates TGFβ receptors post-transcriptionally by affecting their mRNA stability, but does not change the Smad-3 and Smad-7 mRNA half-life span, suggesting a potential transcriptional effect on these genes. Moreover, the transcriptional factor Sp1, which is downregulated by TGFβ1, is involved in the repression of both TGFβ receptors but not in the modulation of Smad3 and Smad7. Interestingly, Sp1 ectopic expression permitted also to maintain a similar expression pattern to early response to TGFβ at 24 hours of treatment. It restored the induction of Sox9 and COL2A1 and blocked the late response (repression of aggrecan, induction of COL1A1 and COL10A1).ConclusionsThese data help to better understand the negative feedback loop in the TGFβ signalling system, and enlighten an interesting role of Sp1 to regulate TGFβ response.

Sox9 Expression during Fracture Repair

The molecular and cellular mechanisms involved in bone development provide an insight into the nature of bone regeneration. Sox9 is a key transcription factor for chondrogenesis and is also expressed in osteochondroprogenitors during embryonic bone development. However, it has not been determined whether Sox9-expressing cells appear during fracture repair other than in the cartilaginous callus. On the other hand, the difference between bone development and repair is that the motion of the fractured segments is associated with the subsequent fate decision of osteochondrogenic precursors between osteogenesis or chondrogenesis, but the underlying mechanism of this still has to be elucidated. We herein evaluate whether Sox9-expressing cells appear during osseous regeneration in the initial stages of fracture healing in vivo. We also investigated the association between Sox9 induction and mechanical stress and the role of Runx1 expression. As a result, Sox9- and Runx1-expressing cells were detected in the periosteal callus together with Runx2 expression. Their expression levels were significantly downregulated during its ossification, as observed in embryonic bone development. The application of cyclic tension to isolated and cultured stromal cells resulted in the upregulation and maintenance of Sox9 mRNA expression in vitro. These results showed that as in early skeletal development, Sox9- and Runx1-expressing precursor cells first appear in the periosteal callus as an early fracture repair response. Our findings also suggested that the mechanical environment modulates Sox9 expression levels in osteochondrogenic precursors and consequently influences their fate decision between osteogenic and chondrogenic lineage commitment.

SOX9 induces and maintains neural stem cells

Neural stem cells (NSCs) are uncommitted cells of the CNS defined by their multipotentiality and ability to self renew. We found these cells to not be present in substantial numbers in the CNS until after embryonic day (E) 10.5 in mouse and E5 in chick. This coincides with the induction of SOX9 in neural cells. Gain- and loss-of-function studies indicated that SOX9 was essential for multipotent NSC formation. Moreover, Sonic Hedgehog was able to stimulate precocious generation of NSCs by inducing Sox9 expression. SOX9 was also necessary for the maintenance of multipotent NSCs, as shown by in vivo fate mapping experiments in the adult subependymal zone and olfactory bulbs. In addition, loss of SOX9 led ependymal cells to adopt a neuroblast identity. These data identify a functional link between extrinsic and intrinsic mechanisms of NSCs specification and maintenance, and establish a central role for SOX9 in the process.

WNT5A Regulates Chondrocyte Differentiation through Differential Use of the CaN/NFAT and IKK/NF-κB Pathways

Although genetic evidence demonstrated a requirement for Wnt5a during cartilage development, little is known about the mechanisms underlying Wnt5a-regulated chondrocyte growth and differentiation. We therefore investigated the signaling pathways by which Wnt5a influences chondrogenesis and differentiation to hypertrophy. Wnt5a treatment of chondroprogenitor cells increased chondrocyte hypertrophy and was associated with an increase in nuclear factor of activated T cells (NFAT) and a decrease in nuclear factor-kappaB (NF-kappaB) activation. In contrast, Wnt5a inhibited chondrocyte hypertrophy. This inhibition of hypertrophy occurred with the reciprocal signaling activation, in that a decrease in NFAT and an increase in NF-kappaB activation was observed. Furthermore, the increase in chondroprogenitor cell differentiation with Wnt5a treatment was blocked by calmodulin kinase or NFAT loss of function. In addition, the repression of chondrocyte hypertrophy observed was abrogated by NF-kappaB loss of function. Activation of the NFAT pathway downstream of Wnt5a also negatively regulated NF-kappaB activity, providing evidence of antagonism between these two pathways. Mechanistically, Wnt5a acts to increase chondrocyte differentiation at an early stage through calmodulin kinase /NFAT-dependent induction of Sox9. Conversely, Wnt5a represses chondrocyte hypertrophy via NF-kappaB-dependent inhibition of Runx2 expression. These data indicate that Wnt5a regulates chondrogenesis and chondrocyte hypertrophy in a stage-dependent manner through differential utilization of NFAT- and NF-kappaB-dependent signal transduction.

Abstract 4029: Sox9 functions downstream of Hedgehog-Gli1 in epithelial transformation

Abstract The Sonic Hedgehog (Shh) signaling pathway plays critical roles in cell fate specification during embryonic and fetal development and in adult tissues. The extracellular morphogen, Shh, signals through Gli family zinc finger transcription factors to regulate the expression of downstream target genes. Constitutive Shh-Gli signaling is implicated in the pathogenesis of several human cancers, including cutaneous basal cell carcinoma (BCC), prostate cancer and medulloblastoma. How Gli can signal through downstream genes to induce malignant transformation remains poorly understood. In this work, we performed microarray analysis to reveal the gene expression profile after tetracycline-regulated induction of Gli1 for 3 or 6 hours in cultured epithelial cells, identifying multiple known Shh target genes. Among the most rapidly induced genes was Sox9, a member of SRY family of transcription factors. Sox9 is essential for male sex determination and is a master regulator of chondrogenesis. Sox9 is also well established as a Shh-Gli target gene, but how it functions in Shh-Gli signaling is not well understood. We found that Sox9 mRNA and protein levels are greatly increased after short-term or long-term Gli1 expression in a rat culture model of epithelial cells, termed RK3E, and in mouse skin. As shown by reporter assays, Sox9 transcriptional activity was increased by approximately 18-fold in RK3E cells transformed by Gli1. To enable knockdown studies in rat cells, we defined the full-length rat Sox9 coding sequence. Subsequently, suppression of rat Sox9 by siRNA indicated an essential role for this Gli-regulated gene in malignant transformation of RK3E in vitro. Specifically, shRNA plasmids that suppress Sox9 could dramatically reduced the transforming activity of Gli1. In contrast, there was little effect on other transforming oncoproteins including H-Ras and ErbB2. These results establish Sox9 induction as an early response to Gli1, and demonstrate that induction of Sox9 is essential for transformation by Gli1. Further characterization of the Sox9 knockdown phenotype is in progress and will be presented. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4029.

Abstract 5171: EGFR induction of SOX9 is required in a cellular migration program induced by urothelial injury and maintained in cancer

Abstract Data from a variety of tissue types and experimental systems indicate that the transcriptional regulator SRY-related HMG box 9 (SOX9) can be induced by injury and promote migration as well as tumor growth. We hypothesize that in cancers associated with chronic injury, such as urothelial carcinoma (UroCa), SOX9 may mediate epithelial injury repair. We found that urothelial SOX9 was induced during times of rapid proliferation during bladder organogenesis and injury repair. High levels of epidermal growth factor (EGF) ligands have been noted in urine and represent a potential trigger for urothelial injury repair programs. Using specific antagonists, we found that EGF receptor activation by cognate ligands heparain binding EGF-like growth factor (HB-EGF) and/or amphiregulin was responsible for Sox9 induction in urothelial cells and tissues. As expected, EGFR activation occurred through the mitogen associated protein kinase (MAPK) pathway. With chronic breaches of urothelial integrity, EGFR-Sox9 stimulation may promote urothelial carcinogenesis, as Sox9 expression was significantly upregulated in invasive human UroCa samples and cell lines. When expressed in established tumors, SOX9 may confer a selective advantage to cancer cells by promoting their ability to invade and colonize new sites. As support for this idea, small interfering RNA inhibition of SOX9 levels abrogated in vitro wound healing and invasion, suggesting a role for SOX9 in tumor spread. These results indicate a potential mechanism for urothelial carcinogenesis through an EGFR-MAPK-SOX9 cascade, and a further function for this axis in established cancers. Future studies will examine the potential mechanisms supporting perseverative SOX9 expression in cancer and opportunities for disrupting this pathway as a therapeutic strategy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5171.

Helicobacter pyloriinduces gastric mucosal intestinal metaplasia through the inhibition of interleukin-4-mediated HMG box protein Sox2 expression

Helicobacter pylori is a major cause of the transdifferentiation into intestinal metaplasia that may develop gastric cancer. However, the molecular pathogenesis of this transdifferentiation is poorly understood. A SRY-related HMG box protein Sox2 is an essential transcription factor of organ development in brain, lung, and stomach. Our aim of this study was to investigate the mechanism responsible for regulation of Sox2 in host Th1-dominant response to H. pylori. Sox2 protein was immunohistochemically expressed in both human oxyntic and pyloric glands with H. pylori infection, but not in intestinal metaplasia. Western immunoblotting of gastric epithelial cell lines showed that IL-4, a Th2-related cytokine, dose dependently enhanced Sox2 expression among H. pylori infection-mediated cytokines. Small changes of Sox2 expression were observed after each treatment with IFN-gamma, IL-1beta, or TNF-alpha. IL-4-mediated Sox2 induction was suppressed by the inhibition of STAT6 activation with STAT6 RNA interference, and electrophoretic mobility shift assay indicated that activation of the Sox2 promoter by IL-4 occurred through the action of STAT6. Furthermore, H. pylori and IFN-gamma inhibited the phosphorylation of STAT6, resulting in the suppression of IL-4-mediated Sox2 expression. Immunohistochemical analyses showed significantly the suppressed STAT6 activity in H. pylori-infected human gastric mucosa. Additionally, downregulation of Sox2 by knockdown experiments led to intestinal phenotype with expressions of Cdx2 and MUC2. These results suggest that H. pylori and IFN-gamma interfere with the differentiation into oxyntic and pyloric glands by the downregulation of Sox2 on IL-4/STAT6 signaling, which may contribute to the transdifferentiation into intestinal metaplasia.

Transcriptional induction of SOX9 by NF-κB family member RelA in chondrogenic cells

Although SOX9 is a key molecule for chondrogenic differentiation, little is known about the upstream signal. The present study attempted to identify transcription factors to induce SOX9 expression and examined the mechanism. Sequences of about 1 kb of 5'-end flanking regions were compared between human and mouse SOX9 genes. In vivo localization was examined by immunohistochemistry in the limb cartilage of fetal mice. Promoter activities of the SOX9, SOX6, and type II collagen (COL2A1) genes were determined in human non-chondrogenic HeLa cells and mouse chondrogenic ATDC5 cells transfected with a luciferase-reporter gene containing the promoter fragments. Protein-DNA binding was examined by electrophoretic mobility shift and chromatin immunoprecipitation assays. The chondrogenic differentiation was assessed by endogenous SOX9, SOX6, and COL2A1 mRNA levels, and by Alcian blue staining and alkaline phosphatase activity. Among transcription factors whose binding motifs were identified in the highly-conserved regions between human and mouse SOX9 promoters, a nuclear factor kappa B (NF-kappaB) member RelA strongly activated the promoter activity. RelA and SOX9 were co-localized in the limb cartilage. Deletion, mutagenesis, and tandem-repeat analyses identified the core region responsive to RelA at the NF-kappaB binding motif to be around -250bp of the human SOX9 promoter, and this was confirmed to show specific binding to RelA. RelA induced the chondrogenic differentiation parameters in HeLa and ATDC5 cells. We have identified RelA as a transcriptional factor for SOX9 induction and chondrogenic differentiation via binding to an NF-kappaB binding motif in the SOX9 promoter.

Distinct mechanisms drive the induction of Sox2 and Sox3 expression in neuroectoderm

Distinct mechanisms drive the induction of Sox2 and Sox3 expression in neuroectoderm

SOX9 and the tanning response: something new under the sun

SOX9 and the tanning response: something new under the sun

Hypoxia Promotes the Differentiated Human Articular Chondrocyte Phenotype through SOX9-dependent and -independent Pathways

The chondrocyte is solely responsible for synthesis and maintenance of the resilient articular cartilage matrix that gives this load-bearing tissue its mechanical integrity. When the differentiated cell phenotype is lost, the matrix becomes compromised and cartilage function begins to fail. We have recently shown that hypoxia promotes the differentiated phenotype through hypoxia-inducible factor 2alpha (HIF-2alpha)-mediated SOX9 induction of the main matrix genes. However, to date, only a few genes have been shown to be SOX9 targets, while little is known about SOX9-independent regulators. We therefore performed a detailed microarray study to address these issues. Analysis involved 35 arrays on chondrocytes obtained from seven healthy, non-elderly human cartilage samples. Genes were selected that were down-regulated with serial passage in culture (as this causes loss of the differentiated phenotype) and subsequently up-regulated in hypoxia. The importance of key findings was further probed using the technique of RNA interference on these human articular chondrocytes. Our results show that hypoxia has a broader beneficial effect on the chondrocyte phenotype than has been previously described. Of special note, we report new hypoxia-inducible and SOX9-regulated genes, Gdf10 and Chm-I. In addition, Mig6 and InhbA were induced by hypoxia, predominantly via HIF-2alpha, but were not regulated by SOX9. Therefore, hypoxia, and more specifically HIF-2alpha, promotes both SOX9-dependent and -independent factors important for cartilage homeostasis. HIF-2alpha may therefore represent a new and promising therapeutic target for cartilage repair.