DKK3 Research Articles

Wnt/β-catenin signaling of cartilage canal and osteochondral junction chondrocytes and full thickness cartilage in early equine osteochondrosis.

The objective of this study was to elucidate gene and protein expression of Wnt signaling molecules in chondrocytes of foals having early osteochondrosis (OC) versus normal controls. The hypothesis was that increased expression of components of Wnt signaling pathway in osteochondral junction (OCJ) and cartilage canal (CC) chondrocytes would be found in early OC when compared to controls. Paraffin-embedded osteochondral samples (7 OC, 8 normal) and cDNA from whole cartilage (7 OC, 10 normal) and chondrocytes surrounding cartilage canals and osteochondral junctions captured with laser capture microdissection (4 OC, 6 normal) were obtained from femoropatellar joints of 17 immature horses. Equine-specific Wnt signaling molecule mRNA expression levels were evaluated by two-step real-time qPCR. Spatial tissue protein expression of β-catenin, Wnt-11, Wnt-4, and Dkk-1 was determined by immunohistochemistry. There was significantly decreased Wnt-11 and increased β-catenin, Wnt-5b, Dkk-1, Lrp6, Wif-1, Axin1, and SC-PEP gene expression in early OC cartilage canal chondrocytes compared to controls. There was also significantly increased β-catenin gene expression in early OC osteochondral junction chondrocytes compared to controls. Based on this study, abundant gene expression differences in OC chondrocytes surrounding cartilage canals suggest pathways associated with catabolism and inhibition of chondrocyte maturation are targeted in early OC pathogenesis.

P-192 DNA methylation profile of APC and DKK2 genes as biomarkers in colorectal cancer patients

P-192 DNA methylation profile of APC and DKK2 genes as biomarkers in colorectal cancer patients

Tet3 mediates stable glucocorticoid-induced alterations in DNA methylation and Dnmt3a/Dkk1 expression in neural progenitors.

Developmental exposure to excess glucocorticoids (GCs) has harmful neurodevelopmental effects, which include persistent alterations in the differentiation potential of embryonic neural stem cells (NSCs). The mechanisms, however, are largely unknown. Here, we investigated the effects of dexamethasone (Dex, a synthetic GC analog) by MeDIP-like genome-wide analysis of differentially methylated DNA regions (DMRs) in NSCs isolated from embryonic rat cortices. We found that Dex-induced genome-wide DNA hypomethylation in the NSCs in vitro. Similarly, in utero exposure to Dex resulted in global DNA hypomethylation in the cerebral cortex of 3-day-old mouse pups. Dex-exposed NSCs displayed stable changes in the expression of the DNA methyltransferase Dnmt3a, and Dkk1, an essential factor for neuronal differentiation. These alterations were dependent on Tet3 upregulation. In conclusion, we propose that GCs elicit strong and persistent effects on DNA methylation in NSCs with Tet3 playing an essential role in the regulation of Dnmt3a and Dkk1. Noteworthy is the occurrence of similar changes in Dnmt3a and Dkk1 gene expression after exposure to excess GC in vivo.

Cellular processes involved in human epidermal cells exposed to extremely low frequency electric fields

We observed on different tissues and organisms a biological response after exposure to pulsed low frequency and low amplitude electric or electromagnetic fields but the precise mechanism of cell response remains unknown. The aim of this publication is to understand, using bioinformatics, the biological relevance of processes involved in the modification of gene expression. The list of genes analyzed was obtained after microarray protocol realized on cultures of human epidermal explants growing on deepidermized human skin exposed to a pulsed low frequency electric field. The directed acyclic graph on a WebGestalt Gene Ontology module shows six categories under the biological process root: “biological regulation”, “cellular process”, “cell proliferation”, “death”, “metabolic process” and “response to stimulus”. Enriched derived categories are coherent with the type of in vitro culture, the stimulation protocol or with the previous results showing a decrease of cell proliferation and an increase of differentiation. The Kegg module on WebGestalt has highlighted “cell cycle” and “p53 signaling pathway” as significantly involved. The Kegg website brings out interactions between FoxO, MAPK, JNK, p53, p38, PI3K/Akt, Wnt, mTor or NF-KappaB. Some genes expressed by the stimulation are known to have an exclusive function on these pathways. Analyses performed with Pathway Studio linked cell proliferation, cell differentiation, apoptosis, cell cycle, mitosis, cell death etc. with our microarrays results. Medline citation generated by the software and the fold change variation confirms a diminution of the proliferation, activation of the differentiation and a less well-defined role of apoptosis or wound healing. Wnt and DKK functional classes, DKK1, MACF1, ATF3, MME, TXNRD1, and BMP-2 genes proposed in previous publications after a manual analysis are also highlighted with other genes after Pathway Studio automatic procedure. Finally, an analysis conducted on a list of genes characterized by an accelerated regulation after extremely low frequency pulsed stimulation also confirms their role in the processes of cell proliferation and differentiation. Bioinformatics approach allows in-depth research, without the bias of pre-selection, on cellular processes involved in a huge gene list.

Sequencing of the DKK1 gene in patients with anorectal malformations and hypospadias.

Anorectal malformations (ARM) are rare congenital malformations of the gastrointestinal tract. Approximately 60% of the patients have additional congenital malformations, such as hypospadias. A recently published article showed that deletion of one single gene, dickkopf WNT signaling pathway inhibitor-1 (Dkk1), resulted in an imperforate anus with rectourinary fistula and preputial hypospadias in mice. To determine whether DKK1 also plays a role in the etiology of ARM and hypospadias in humans, we sequenced the four exons of the DKK1 gene in 17 patients affected with both ARM and hypospadias. No new potential disease-causing variant was identified. However, we detected a known non-synonymous variant in one patient, which was predicted in silico to be damaging, and the corresponding unaffected amino acid is highly conserved. In this human study, a potential interesting non-synonymous variant was found in the DKK1 gene. Whether this variant plays a contributory role in the genesis of ARM or hypospadias would require a much larger study.

Pax6 regulates the expression of Dkk3 in murine and human cell lines, and altered responses to Wnt signaling are shown in FlpIn-3T3 cells stably expressing either the Pax6 or the Pax6(5a) isoform.

Pax6 is a transcription factor important for early embryo development. It is expressed in several cancer cell lines and tumors. In glioblastoma, PAX6 has been shown to function as a tumor suppressor. Dickkopf 3 (Dkk3) is well established as a tumor suppressor in several tumor types, but not much is known about the regulation of its expression. We have previously found that Pax6 and Pax6(5a) increase the expression of the Dkk3 gene in two stably transfected mouse fibroblast cell lines. In this study the molecular mechanism behind this regulation is looked at. Western blot and reverse transcriptase quantitative PCR (RT-qPCR) confirmed higher level of Dkk3 expression in both Pax6 and Pax6(5a) expressing cell lines compared to the control cell line. By the use of bioinformatics and electrophoretic mobility shift assay (EMSA) we have mapped a functional Pax6 binding site in the mouse Dkk3 promoter. The minimal Dkk3 promoter fragment required for transcriptional activation by Pax6 and Pax6(5a) was a 200 bp region just upstream of the transcriptional start site. Mutation of the evolutionary conserved binding site in this region abrogated transcriptional activation and binding of Pax6/Pax6(5a) to the mouse Dkk3 promoter. Since the identified Pax6 binding site in this promoter is conserved, RT-qPCR and Western blot were used to look for regulation of Dkk3/REIC expression in human cell lines. Six of eight cell lines tested showed changes in Dkk3/REIC expression after PAX6 siRNA knockdown. Interestingly, we observed that the Pax6/Pax6(5a) expressing mouse fibroblast cell lines were less responsive to canonical Wnt pathway stimulation than the control cell line when TOP/FOP activity and the levels of active β-catenin and GSK3-β Ser9 phosphorylation were measured after LiCl stimulation.

Potential of adenovirus‐mediated REIC/Dkk‐3 gene therapy for use in the treatment of pancreatic cancer

The reduced expression in immortalized cells REIC/the dickkopf 3 (Dkk-3) gene, tumor suppressor gene, is downregulated in various malignant tumors. In a prostate cancer study, an adenovirus vector carrying the REIC/Dkk-3 gene (Ad-REIC) induces apoptosis. In the current study, we examined the effects of REIC/Dkk-3 gene therapy in pancreatic cancer. REIC/Dkk-3 expression was assessed by immunoblotting and immunohistochemistry in the pancreatic cancer cell lines (ASPC1, MIAPaCa2, Panc1, BxPC3, SUIT-2, KLM1, and T3M4) and pancreatic cancer tissues. The Ad-REIC agent was used to investigate the apoptotic effect in vitro and antitumor effects in vivo. We also assessed the therapeutic effects of Ad-REIC therapy with gemcitabine. The REIC/Dkk-3 expression was lost in the pancreatic cancer cell lines and decreased in pancreatic cancer tissues. Ad-REIC induced apoptosis and inhibited cell growth in the ASPC1 and MIAPaCa2 lines in vitro, and Ad-REIC inhibited tumor growth in the mouse xenograft model using ASPC1 cells. The antitumor effect was further enhanced in combination with gemcitabine. This synergistic effect may be caused by the suppression of autophagy via the enhancement of mammalian target of rapamycin signaling. Ad-REIC induces apoptosis and inhibits tumor growth in pancreatic cancer cell lines. REIC/Dkk-3 gene therapy is an attractive therapeutic tool for pancreatic cancer.

SHH, WNT, and NOTCH pathways in medulloblastoma: when cancer stem cells maintain self-renewal and differentiation properties

Infant medulloblastoma (MB) is a malignant neuroepithelial embryonal tumor of the cerebellum, believed to derive from precursor granule cells with stem or progenitor cells appearance, and caused by a change in expression profile of genes related to the development. This work aims to study the expression profile of these genes in MB tumors, correlating with clinicopathological characteristics. We quantified, by qPCR in 40 MB tumor samples, the expression of genes in HH (PTCH1, PTCH2, and GLI1), WNT (APC, CTNNB1, WIF1, and DKK2), and NOTCH pathways (NOTCH2 and HES1), which have a crucial role in development, and genes as MYCC, MYCN, and TERT, correlating this findings to patient's clinicopathological characteristics. Considering the universal RNA as our control sample, and considering the median of gene expression in the control samples as our cutoff, we observed that HES1 gene showed decreased expression compared to control (p = 0.0059), but patients with HES1 overexpression were directly related to a shorter survival (p = 0.0165). Individuals with higher GLI1 gene expression had significant shorter survival (p = 0.0469), and high expression was prevalent in patients up to 5years old (p = 0.0479). Patients showing high PTCH2 expression were related to worse survival (p = 0.0426), and it was correlated with GLI1 high expression (p = 0.0094). We also observed a concomitant overexpression of WIF1 and DKK2 genes in a subgroup of MB samples (n = 11, p = 0.0118). Our results suggest the presence of activated developmental signaling pathways in MB, which are important for cell proliferation and maintenance, and that may be targeted for novel therapeutic options.

Magnesium Inhibits Wnt/β-Catenin Activity and Reverses the Osteogenic Transformation of Vascular Smooth Muscle Cells

Magnesium reduces vascular smooth muscle cell (VSMC) calcification in vitro but the mechanism has not been revealed so far. This work used only slightly increased magnesium levels and aimed at determining: a) whether inhibition of magnesium transport into the cell influences VSMC calcification, b) whether Wnt/β-catenin signaling, a key mediator of osteogenic differentiation, is modified by magnesium and c) whether magnesium can influence already established vascular calcification. Human VSMC incubated with high phosphate (3.3 mM) and moderately elevated magnesium (1.4 mM) significantly reduced VSMC calcification and expression of the osteogenic transcription factors Cbfa-1 and osterix, and up-regulated expression of the natural calcification inhibitors matrix Gla protein (MGP) and osteoprotegerin (OPG). The protective effects of magnesium on calcification and expression of osteogenic markers were no longer observed in VSMC cultured with an inhibitor of cellular magnesium transport (2-aminoethoxy-diphenylborate [2-APB]). High phosphate induced activation of Wnt/β-catenin pathway as demonstrated by the translocation of β-catenin into the nucleus, increased expression of the frizzled-3 gene, and downregulation of Dkk-1 gene, a specific antagonist of the Wnt/β-catenin signaling pathway. The addition of magnesium however inhibited phosphate-induced activation of Wnt/β-catenin signaling pathway. Furthermore, TRPM7 silencing using siRNA resulted in activation of Wnt/β-catenin signaling pathway. Additional experiments were performed to test the ability of magnesium to halt the progression of already established VSMC calcification in vitro. The delayed addition of magnesium decreased calcium content, down-regulated Cbfa-1 and osterix and up-regulated MGP and OPG, when compared with a control group. This effect was not observed when 2-APB was added. In conclusion, magnesium transport through the cell membrane is important to inhibit VSMC calcification in vitro. Inhibition of Wnt/β-catenin by magnesium is one potential intracellular mechanism by which this anti-calcifying effect is achieved.

The Novel Long Noncoding RNA linc00467 Promotes Cell Survival but Is Down-Regulated by N-Myc

The worst subtype of neuroblastoma is caused by MYCN oncogene amplification and N-Myc oncoprotein over-expression. Long noncoding RNAs (lncRNAs) are emerging as critical regulators of gene expression and tumourigenesis. While Myc oncoproteins are well-known to exert tumourigenic effects by regulating the expression of protein-coding genes and microRNAs, little is known about which lncRNAs are Myc targets and whether the Myc target lncRNAs play a role in Myc-induced oncogenesis. Here we performed differential gene expression studies using lncRNA microarray in neuroblastoma cells after transfection with control or N-Myc-specific small interfering RNA (siRNA), and identified N-Myc target lncRNAs including the novel lncRNA linc00467, the expression and function of which were completely unknown. RT-PCR, chromatin immunoprecipitation and luciferase assays showed that N-Myc suppressed linc00467 gene expression through direct binding to the linc00467 gene promoter and reducing linc00467 promoter activity. While N-Myc suppressed the expression of RD3, the protein-coding gene immediately down-stream of linc00467 gene, through direct binding to the RD3 gene promoter and reducing RD3 promoter activity, linc00467 reduced RD3 mRNA expression. Moreover, Affymetrix microarray analysis revealed that one of genes significantly up-regulated by linc00467 siRNA was the tumour suppressor gene DKK1. Importantly, knocking-down linc00467 expression with siRNA in neuroblastoma cells reduced the number of viable cells and increased the percentage of apoptotic cells, and co-transfection with DKK1 siRNA blocked the effects. These findings therefore demonstrate that N-Myc-mediated suppression of linc00467 gene transcription counterintuitively blocks N-Myc-mediated reduction in RD3 mRNA expression, and reduces neuroblastoma cell survival by inducing DKK1 expression.

A4.3 Differences of bone WNT regulators expression between fragility fractures and osteoarthritis patients

IntroductionThe importance of Wnt signalling, a crucial pathway for osteoblast differentiation and a master bone mass regulator as been recently highlighted. With this study, we aim to compare bone expression...

A4.11 Combination of TNF-α and IL-17a promotes osteogenic differentiation, but increases schnurri 3 in isolated human mesenchymal stem cells

Background and ObjectivesRheumatoid arthritis (RA) is characterised by defective bone repair and excessive bone destruction, and ankylosing spondylitis (AS) by increased ectopic bone formation. Since TNF-α and IL-17A are involved...

Molecular simulation analysis of the structure complex of C2 domains of DKK family members and β-propeller domains of LRP5/6: explaining why DKK3 does not bind to LRP5/6.

Dickkopf (DKK) proteins interact with low-density lipoprotein receptor-related protein 5/6 (LRP5/6) to modulate WNT signaling. The interaction is mediated by a cysteine-rich domain (C2) in the DKK protein and beta-propeller domains (PD) of LRP5/6. However, the third member of the DKK family (DKK3) does not bind to LRP5/6. To determine why DKK3 does not bind to the receptor domains, we performed a molecular modeling simulation study including homology modeling, protein-protein docking and molecular dynamics (MD). The computed affinities (ΔGbinding) between the C2 and PD models were consistent with the previously reported experimental results. The C2 model of DKK3 showed the lowest affinity for PD models. Multiple sequence alignment of C2 domains revealed that the DKK3 genes have a unique 7-amino-acid insertion (L249-E255 in human DKK3) and P258 in a finger loop 1 (FL1). Interestingly, the insertion sequence is evolutionally conserved. MD simulations of high-affinity complex models of C2 and PD showed that FL1 directly interacts with the PD models and stabilizes the complex models. We also built a 7-amino-acid-deletion/P258G mutant model of DKK3C2 and estimated its affinities for the PD models. The affinity for human LRP5PD2 was increased by the substitution (ΔGbinding＝－48.9kcal/mol) and the affinity was compatible with that of high-affinity ligands. The results suggested that the lack of affinity between human DKK3 and human LRP5/6 results from: i) insertion of the 7 amino acids, and ii) P258 in human DKK3. The sequence differences thus suggest an explanation for this unique property of DKK3.

CER1gene variations associated with bone mineral density, bone markers, and early menopause in postmenopausal women

BackgroundOsteoporosis has a multifactorial pathogenesis characterized by a combination of low bone mass and increased fragility. In our study, we focused on the effects of polymorphisms in CER1 and DKK1 genes, recently reported as important susceptibility genes for osteoporosis, on bone mineral density (BMD) and bone markers in osteoporotic women. Our objective was to evaluate the effect of CER1 and DKK1 variations in 607 postmenopausal women. The entire DKK1 gene sequence and five selected CER1 SNPs were amplified and resequenced to assess whether there is a correlation between these genes and BMD, early menopause, and bone turnover markers in osteoporotic patients.ResultsOsteoporotic women seem to suffer menopause 2 years earlier than the control group. The entire DKK1 gene sequence analysis revealed six variations. There was no correlation between the six DKK1 variations and osteoporosis, in contrast to the five common CER1 variations that were significantly associated with BMD. Additionally, osteoporotic patients with rs3747532 and rs7022304 CER1 variations had significantly higher serum levels of parathyroid hormone and calcitonin and lower serum levels of osteocalcin and IGF-1.ConclusionsNo significant association between the studied DKK1 variations and osteoporosis was found, while CER1 variations seem to play a significant role in the determination of osteoporosis and a potential predictive role, combined with bone markers, in postmenopausal osteoporotic women.

Genetic Association Study of Dickkopf-1 and Sclerostin Genes with Paget Disease of Bone

Increased expression of DKK1 gene was reported in pagetic osteoblasts and stromal cells, and increased serum levels of DKK1 and SOST proteins were reported in patients with Paget disease of bone (PDB). This study aimed at identifying rare genetic variants of the DKK1 and SOST genes and at testing for genetic association with PDB in the French-Canadian population. Exons, promoters, and exon-intron junctions of these genes were sequenced in patients with PDB and healthy controls. An association study of Tag SNPs of both genes was also performed in 239 pagetic patients and 297 healthy individuals. Three rare variants were identified in this study, all located in the DKK1 gene: one variant in the second exon leading to alteration in a highly conserved amino acid (p.R120L), one in the 5'-untranslated region (-50 C/A), and one in a splice site of intron 1 (IVS1 184 T/C), although none of these rare variants were associated with PDB. A genetic association of a Tag SNP of the DKK1 gene was found: the G allele of rs1569198 was significantly decreased in patients in comparison to controls (42 vs. 49 %, uncorrected P = 0.03, OR = 0.77, 95 % CI 0.61-0.98). In conclusion, this study identified three rare genetic variants in DKK1 in the French-Canadian population. In addition, a weak genetic association of a common variant of DKK1, rs1569198, which is located on a predicted new acceptor site for splicing of this gene, was observed in PDB, whereas no rare variant or genetic association was found in the SOST gene.

RNA interference-mediated targeting of DKK1 gene expression in Ishikawa endometrial carcinoma cells causes increased tumor cell invasion and migration

The Wnt signaling pathway plays an essential role in tumor invasion and migration. DKK1 functions as an important inhibitor of the pathway and represents a promising target for cancer therapy. The aim of the present study was to determine the role of DKK1 in endometrial carcinoma (EC) cell invasion and migration using RNA interference (RNAi) technology. Ishikawa EC cells were transfected at high efficiency with specific DKK1 siRNA. RT-PCR and western blot analysis were used to determine the mRNA and protein levels of DKK1, β-catenin and metalloproteinase 14 (MMP14) in siRNA-treated and -untreated cells. In addition, the invasion and migration of the EC cells were detected by invasion and migration assays. Transient transfection of DKK1 siRNA significantly inhibited the mRNA and protein levels of DKK1. Markedly increased cell invasion and migration was observed following treatment with DKK1 siRNA when compared with the negative control siRNA-treated and siRNA-untreated cells. The knockdown of DKK1 also elevated the mRNA and protein levels of β-catenin and MMP14 involved in the Wnt signaling pathway, indicating that targeting this gene may promote intracellular Wnt signal transduction and thus, accelerate EC cell invasion and migration in vitro. The RNAi-mediated targeting of DKK1 gene expression in Ishikawa EC cells resulted in increased tumor cell invasion and migration. DKK1 was identified as an inhibitor of EC cell invasion and migration via its novel role in the Wnt signaling pathway. Targeting DKK1 may therefore represent an effective anti-invasion and -migration strategy for the treatment of EC.

Association of common gene variants in the WNT/β-catenin pathway with colon cancer recurrence

Wnt/β-catenin signaling has a central role in the development and progression of most colon cancers (CCs). Germline variants in Wnt/β-catenin pathway genes may result in altered gene function and/or activity, thereby causing inter-individual differences in relation to tumor recurrence capacity and chemoresistance. We investigated germline polymorphisms in a comprehensive panel of Wnt/β-catenin pathway genes to predict time to tumor recurrence (TTR) in patients with stage III and high-risk stage II CC. A total of 234 patients treated with 5-fluorouracil-based chemotherapy were included in this study. Whole-blood samples were analyzed for putative functional germline polymorphisms in SFRP3, SFRP4, DKK2, DKK3, Axin2, APC, TCF7L2, WNT5B, CXXC4, NOTCH2 and GLI1 genes by PCR-based restriction fragment-length polymorphism or direct DNA sequencing. Polymorphisms with statistical significance were validated in an independent study cohort. The minor allele of WNT5B rs2010851 T>G was significantly associated with a shorter TTR (10.7 vs 4.9 years; hazard ratio: 2.48; 95% CI, 0.96-6.38; P=0.04) in high-risk stage II CC patients. This result remained significant in multivariate Cox's regression analysis. This study shows that the WNT5B germline variant rs2010851 was significantly identified as a stage-dependent prognostic marker for CC patients after 5-fluorouracil-based adjuvant therapy.

Abstract 5360: Targeting H3K27 Methylation by 3-Deazaneplanocin A (DZNep) in lung and esophageal cancers.

Abstract Polycomb repressor complex-2 (PRC-2) is aberrantly expressed in a variety of human malignancies including lung and esophageal cancers. PRC-2 contains three main core proteins, enhancer of zeste 2 (EZH2), suppressor of zeste 12 (SUZ12), and embryonic ectoderm development (EED). In the present study, we sought to examine the effects of PRC-2 expression in lung and esophageal cancers, and to determine if PRC-2 is a potential therapeutic target in these malignancies. qRT-PCR analysis demonstrated significant over-expression of EZH2, SUZ12, and EED in cultured lung and esophageal cancer cells as well as primary tumors relative to normal or immortalized aerodigestive tract epithelial cells, or normal lung or esophageal tissues. Over-expression of individual PRC-2 components appeared to coincide with tumor histology; for example EZH2 was particularly over-expressed in small cell lung cancers, whereas EED appeared to be over-expressed primarily in esophageal cancers. DZNep mediated dose-dependent depletion of EZH2, EED and SUZ12, with corresponding decreases in global H3K27Me3 levels in cultured lung and esophageal cancer cells. Depletion of PRC-2 expression/activity coincided with growth arrest in these cancer cells. The growth inhibitory effects of DZNep in lung cancer cells were recapitulated byshRNA-mediated knock-down of EZH2 in these cells. DZNep induced expression of Dkk-1, a putative tumor suppressor that we have previously reported to be repressed by polycomb-mediated mechanisms in lung cancer cells and cultured normal respiratory epithelia following exposure to cigarette smoke condensate (CSC). Chromatin immunoprecipitation (ChIP) experiments demonstrated that DZNep-mediated activation of Dkk-1 coincided with decreased levels of H3K27Me3 within the Dkk-1 promoter. qRT-PCR and immunoblot experiments revealed that exposure of lung cancer cells to DZNep before or concurrent with CSC abrogated tobacco-mediated repression of Dkk-1 in vitro. Subsequent experiments demonstrated that daily intra-peritoneal (IP) injections of CSC significantly decreased Dkk-1 gene expression in subcutaneous A549 and Calu-6 xenografts, and enhanced growth of these tumors in nude mice. IP administration of DZNep (2.5 mg/kg BID q4 days every 7 days) significantly abrogated the enhancement effect of cigarette smoke on growth of lung cancer xenografts; this phenomenon coincided with decreased EZH2 and increased Dkk-1 expression in these xenografts. Collectively, these findings support development of DZNep for inhibiting PRC-2 expression in thoracic malignancies. Citation Format: Mahadev Rao, Young Hong, Scott Atay, Trevor Upham, Julie Hong, Nicole Datrice, Mary Zhang, Enrique Zudaire, Victor Marquez, David Schrump. Targeting H3K27 Methylation by 3-Deazaneplanocin A (DZNep) in lung and esophageal cancers. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5360. doi:10.1158/1538-7445.AM2013-5360

Rheumatoid Arthritis Bone Fragility Is Associated With Upregulation of IL17 and DKK1 Gene Expression

Our aim was to compare bone gene expression in rheumatoid arthritis (RA) and primary osteoporosis (OP) patients. Secondary aims were to determine the association of gene expression of the Wnt/β-catenin signaling pathway with inflammatory cytokines in the bone microenvironment and to assess the serum levels of Wnt/β-catenin proteins in both groups. RA patients referred for hip replacement surgery were recruited. Primary OP patients were used as controls. Gene expression of Wnt pathway mediators, matrix proteins, and pro-inflammatory cytokines were analyzed in bone samples. Bone turnover markers, inflammatory cytokines, and Wnt mediators were measured in serum. Twenty-two patients were included: 10 with RA and 12 with primary OP. The expressions of Wnt10b (p = 0.034), its co-receptor LRP6 (p = 0.041), and its negative regulator DKK1 (p = 0.008) were upregulated in RA bone. IL17 gene expression in bone was upregulated in RA patients (p = 0.031) and correlated positively with Wnt10b (r = 0.810, p = 0.015), DKK2 (r = 0.800, p = 0.010), and RANKL/OPG ratio (r = 0.762, p = 0.028). DKK2 (p = 0.04) was significantly decreased in RA serum compared with primary OP. In conclusion, bone fragility in RA patients is induced by an unbalanced bone microenvironment and is associated with a specific gene expression pattern, namely, the upregulation of IL17 and DKK1, suggesting that the modulation of these two pathways might prevent RA systemic bone loss.

P3: iNOS/NO upregulates Wnt/β-catenin signaling through dickkopf-1 (DKK1) inhibition

Wnt signaling contributes to carcinogenesis and tumor progression but the detailed mechanism of constitutive activation or silencing of Wnt signaling is not well-established. We have shown that human iNOS (hiNOS) gene is a target of Wnt/ β -catenin signaling pathway, and Wnt/ β -catenin signaling regulates hiNOS by inhibiting NF- κ B activity in cancer cells. DKK1 is a potent secreted Wnt antagonist that plays a key role in the negative regulation of the canonical Wnt system, by interacting with Wnt co-receptor proteins in the LRP family to inhibit Wnt signaling. However, the relationship between induced NO synthesis and DKK1-mediated inhibition of Wnt signaling has not been examined. The purpose of this study was to determine if iNOS expression and NO influence Wnt/ β -catenin activity, and if so whether this was mediated by an effect on DKK1 expression. Stable cell lines transfected with human iNOS (hiNOS) or DKK-1genes were established in the SW480 colon cancer cell line. Stable cell lines transfected with shRNA-iNOS were established in SW480 colon and MCF7 breast cancer cell lines. A Wnt signaling pathway microarray analysis (SuperArray) was employed to study the global transcriptional response to hiNOS gene expression. The Greiss reaction was used for the detection of NO production. RT-PCR and Western blotting were used for gene expression analysis. Banked cancer tissues were examined for hiNOS and DKK1 expression. Human iNOS (hiNOS) gene expression was inversely correlated with DKK1 expression in human colon and breast cancer tumor samples and intestinal adenoma tumors from Min ( APC min /+ ) mice. HiNOS gene expression promoted canonical Wnt signaling in cancer cells. HiNOS expression transcriptionally downregulated DKK1 gene expression in the Wnt-related gene superarray, and in cancer cell lines stably expressing hiNOS. Cytokines that induced iNOS expression in cancer cells and primary human hepatocytes decreased constitutive DKK1 protein levels. Knocking down hiNOS gene by shRNA restored DKK1 expression and inhibitory effect on Wnt signaling. These findings demonstrate that iNOS/NO down-regulate DKK1 gene expression at the transcriptional level in vitro, and are consistent with the in vivo findings in cancer tissues where iNOS and DKK1 expression are inversely correlated. These data identify a previously unrecognized mechanism by which the iNOS/NO pathway promotes cancer by inhibiting DKK1 which unleashes Wnt/ β -catenin signaling leading to enhanced β -catenin target gene activation. The findings provide new insight into the complex control mechanisms of iNOS/NO, DKK1, and Wnt/ β -catenin during carcinogenesis. Nothing to disclose.