Dickkopf-1 is down-regulated by MYCN and inhibits neuroblastoma cell proliferation

Extrachromosomal circular DNA and their roles in cancer progression

Extrachromosomal circular DNA (eccDNA), a chromosome-independent circular DNA, has garnered significant attention due to its widespread distribution and intricate biogenesis in carcinoma. Existing research findings propose that multiple eccDNAs contribute to drug resistance in cancer treatments through complex and interrelated regulatory mechanisms. The unique structure and genetic properties of eccDNA increase tumor heterogeneity. This increased diversity is a result of eccDNA's ability to stimulate oncogene remodeling and participate in anomalous splicing processes through chimeric cyclization and the reintegration of loop DNA back into the linear genome. Such actions promote oncogene amplification and silencing. eccDNA orchestrates protein interactions and modulates protein degradation by acting as a regulatory messenger. Moreover, it plays a pivotal role in modeling the tumor microenvironment and intensifying the stemness characteristics of tumor cells. This review presented detailed information about the biogenesis, distinguishing features, and functions of eccDNA, emphasized the role and mechanisms of eccDNA during cancer treatment, and further proposed the great potential of eccDNA in inspiring novel strategies for precision cancer therapy and facilitating the discovery of prognostic biomarkers for cancer.

Dickopff 1 inhibits cancer stem cell properties and promotes neuronal differentiation of human neuroblastoma cell line SH-SY5Y

Neuroblastomas are pediatric tumors arising from undifferentiated cells of neural crest origin with stem cell-like characteristics. Dysregulation of Wnt/β-catenin signaling has been shown to be linked to the development of various tumors. Activated Wnt signaling results in β-catenin accumulation in the nucleus to support pro-neoplastic traits. DKK1, a secreted glycoprotein, is an inhibitor of Wnt signaling, and the addition of DKKI to the culture medium has been used to suppress the Wnt pathway. This study aimed to analyze the role of Dickopff-1 as a potential differentiating agent for the neuroblastoma cell line SH-SY5Y and neurospheres derived from it. The treatment of SH-5Y5Y derived neurospheres by DKK1 resulted in their disintegration and reduced proliferation markers like Ki67, PCNA. DKK1 treatment to the neurospheres also resulted in the loss of cancer stem cell markers like CD133, KIT and pluripotency markers like SOX2, OCT4, NANOG. DKK1 treatment caused reduction in mRNA expression of β-catenin and TCF genes like TCF4, TCF12. When the SH-SY5Y cancer cells were grown under differentiating conditions, DKKI caused neuronal differentiation by itself, and in synergy with retinoic acid. This was verified by the expression of markers like MAPT, DCX, GAP43, ENO2 and also with changes in neurite length. We concluded that Wnt inhibition, as exemplified by DKK1 treatment, is therefore a possible differentiating condition and also suppresses the proliferative and cancer stemness related properties of SH-SY5Y neuroblastoma cells.

Role of non-coding RNAs in neuroblastoma

Neuroblastoma is known as the most prevalent extracranial malignancy in childhood with a neural crest origin. It has been widely accepted that non-coding RNAs (ncRNAs) play important roles in many types of cancer, including glioma and gastrointestinal cancers. They may regulate the cancer gene network. According to recent sequencing and profiling studies, ncRNAs genes are deregulated in human cancers via deletion, amplification, abnormal epigenetic, or transcriptional regulation. Disturbances in the expression of ncRNAs may act either as oncogenes or as anti-tumor suppressor genes, and can lead to the induction of cancer hallmarks. ncRNAs can be secreted from tumor cells inside exosomes, where they can be transferred to other cells to affect their function. However, these topics still need more study to clarify their exact roles, so the present review addresses different roles and functions of ncRNAs in neuroblastoma.

Synaptopodin-2: a potential tumor suppressor

Initially identified as an actin-binding protein containing a PSD95-DLG-ZO1 Domain (PZD domain), Synaptopodin 2 (SYNPO2) has long been considered a structural protein ubiquitously expressed in muscular tissues. However, emerging evidence suggests that SYNPO2 performs diverse functions in cancers in addition to its role in microfilament assembly. In most cancers, high SYNPO2 expression is positively correlated with a good prognosis, suggesting its role as a novel tumor suppressor. Abnormal SYNPO2 expression affects autophagy generation, particularly mitophagy induced by low oxidation or viral infection, as well as chaperone-mediated autophagy triggered by microfilament damage. Mechanically, SYNPO2 regulates tumor growth, metastasis, and invasion via activating the PI3K/AKT/mTOR signal and Hippo signaling pathways. Moreover, the subcellular localization, promoter methylation and single nucleotide polymorphism (SNP) of SYNPO2 have been associated with cancer progression and clinical outcomes, highlighting its potential as a prognostic or diagnostic target for this patient population. This review focuses on the role of SYNPO2 in cancer, including its generation, epigenetic modification, subcellular localization, and biological function.

Neural crest cells development and neuroblastoma progression: Role of Wnt signaling

Neuroblastoma (NB) is one of the most common heterogeneous extracranial cancers in infancy that arises from neural crest (NC) cells of the sympathetic nervous system. The Wnt signaling pathway, both canonical and noncanonical pathway, is a highly conserved signaling pathway that regulates the development and differentiation of the NC cells during embryogenesis. Reports suggest that aberrant activation of Wnt ligands/receptors in Wnt signaling pathways promote progression and relapse of NB. Wnt signaling pathways regulate NC induction and migration in a similar manner; it regulates proliferation and metastasis of NB. Inhibiting the Wnt signaling pathway or its ligands/receptors induces apoptosis and abrogates proliferation and tumorigenicity in all major types of NB cells. Here, we comprehensively discuss the Wnt signaling pathway and its mechanisms in regulating the development of NC and NB pathogenesis. This review highlights the implications of aberrant Wnt signaling in the context of etiology, progression, and relapse of NB. We have also described emerging strategies for Wnt-based therapies against the progression of NB that will provide new insights into the development of Wnt-based therapeutic strategies for NB.

Dickkopf-1 Inhibition Reactivates Wnt/β-Catenin Signaling in Rhabdomyosarcoma, Induces Myogenic Markers In Vitro and Impairs Tumor Cell Survival In Vivo

The Wnt/β-catenin signaling pathway plays a pivotal role during embryogenesis and its deregulation is a key mechanism in the origin and progression of several tumors. Wnt antagonists have been described as key modulators of Wnt/β-catenin signaling in cancer, with Dickkopf-1 (DKK-1) being the most studied member of the DKK family. Although the therapeutic potential of DKK-1 inhibition has been evaluated in several diseases and malignancies, little is known in pediatric tumors. Only a few works have studied the genetic inhibition and function of DKK-1 in rhabdomyosarcoma. Here, for the first time, we report the analysis of the therapeutic potential of DKK-1 pharmaceutical inhibition in rhabdomyosarcoma, the most common soft tissue sarcoma in children. We performed DKK-1 inhibition via shRNA technology and via the chemical inhibitor WAY-2626211. Its inhibition led to β-catenin activation and the modulation of focal adhesion kinase (FAK), with positive effects on in vitro expression of myogenic markers and a reduction in proliferation and invasion. In addition, WAY-262611 was able to impair survival of tumor cells in vivo. Therefore, DKK-1 could constitute a molecular target, which could lead to novel therapeutic strategies in RMS, especially in those patients with high DKK-1 expression.

Dickkopf Proteins and Their Role in Cancer: A Family of Wnt Antagonists with a Dual Role

The Wnt signaling pathway regulates crucial aspects such as cell fate determination, cell polarity and organogenesis during embryonic development. Wnt pathway deregulation is a hallmark of several cancers such as lung, gastric and liver cancer, and has been reported to be altered in others. Despite the general agreement reached by the scientific community on the oncogenic potential of the central components of the pathway, the role of the antagonist proteins remains less clear. Deregulation of the pathway may be caused by overexpression or downregulation of a wide range of antagonist proteins. Although there is growing information related to function and regulation of Dickkopf (DKK) proteins, their pharmacological potential as cancer therapeutics still has not been fully developed. This review provides an update on the role of DKK proteins in cancer and possible potential as therapeutic targets for the treatment of cancer; available compounds in pre-clinical or clinical trials are also reviewed.

LncRNA XIST facilitates cell growth, migration and invasion via modulating H3 histone methylation of DKK1 in neuroblastoma

Long non-coding RNAs (lncRNAs) have been confirmed to be aberrantly expressed and involved in the progression of neuroblastoma. This study aimed to explore the expression profile of lncRNA X-inactive specific transcript (XIST) and its functional involvement in neuroblastoma. In this study, the relative level of XIST in neuroblastoma tissues and cell lines was detected by qPCR, and DKK1 protein expression was determined using western blot. The effect of XIST on cell growth, invasion and migration in vitro and in tumorigenesis of neuroblastoma was assessed. The level of H3K27me3 in DKK1 promoter was analyzed with ChIP-qPCR. Interaction between XIST and EZH2 was verified by RNA immunoprecipitation (RIP) and RNA pull-down assay. XIST was significantly upregulated in neuroblastoma tissues (n = 30) and cells lines, and it was statistically associated with the age and International Neuroblastoma Staging System (INSS) staging in neuroblastoma patients. Downregulation of XIST suppressed the growth, migration and invasion of neuroblastoma cells. EZH2 inhibited DKK1 expression through inducing H3 histone methylation in its promoter. XIST increased the level of H3K27me3 in DKK1 promoter via interacting with EZH2. Downregulation of XIST increased DKK1 expression to suppress neuroblastoma cell growth, invasion, and migration, which markedly restrained the tumor progression. In conclusion, XIST downregulated DKK1 by inducing H3 histone methylation via EZH2, thereby facilitating the growth, migration and invasion of neuroblastoma cells and retarding tumor progression.

WNT Signaling in Neuroblastoma

The term WNT (wingless-type MMTV integration site family) signaling comprises a complex molecular pathway consisting of ligands, receptors, coreceptors, signal transducers and transcriptional modulators with crucial functions during embryonic development, including all aspects of proliferation, morphogenesis and differentiation. Its involvement in cancer biology is well documented. Even though WNT signaling has been divided into mainly three distinct branches in the past, increasing evidence shows that some molecular hubs can act in various branches by exchanging interaction partners. Here we discuss developmental and clinical aspects of WNT signaling in neuroblastoma (NB), an embryonic tumor with an extremely broad clinical spectrum, ranging from spontaneous differentiation to fatal outcome. We discuss implications of WNT molecules in NB onset, progression, and relapse due to chemoresistance. In the light of the still too high number of NB deaths, new pathways must be considered.

Downregulation of N‑Myc inhibits neuroblastoma cell growth via the Wnt/β‑catenin signaling pathway

Neuroblastoma, one of the most common types of cancer in childhood, is commonly treated with surgery, radiation and chemotherapy. However, prognosis and survival remain poor for children with high‑risk neuroblastoma. Therefore, the identification of novel, effective therapeutic targets is necessary. N‑Myc, a proto‑oncogene protein encoded by the v‑myc avial myelocytomatosis viral oncogene neuroblastoma derived homolog (MYCN) gene, is associated with tumorigenesis. In the present study, the effect of N‑Myc silencing on MYCN‑amplified CHP134 and BE‑2C neuroblastoma cells was evaluated, and the underlying molecular mechanism was investigated. N‑Myc was successfully knocked down using an N‑Myc‑specific small interfering RNA, the efficacy of interference efficiency confirmed by reverse transcription‑quantitative polymerase chain reaction and western blotting. Cell viability was evaluated by MTT assay and apoptosis was measured by ELISA assay. The results indicated that MYCN silencing significantly decreased cell viability and promoted apoptosis. Subsequently, the expression levels of key Wnt/β‑catenin signaling pathway proteins were detected by western blotting, and MYCN silencing was demonstrated to inhibit Wnt/β‑catenin signaling, decreasing the expression ofanti‑apoptosis proteins and increasing the expression of pro‑apoptosis protein. This suggested that N‑Myc regulated survival and growth of CHP134 and BE‑2C neuroblastoma cells, potentially through Wnt/β‑catenin signaling. Furthermore, associated proteins, N‑Myc and STAT interactor and dickkopf Wnt signaling pathway inhibitor 1, were demonstrated to be involved in this regulation. Therefore, N‑Myc and its downstream targets may provide novel therapeutic targets for the treatment of neuroblastoma.

WNT signaling, the development of the sympathoadrenal-paraganglionic system and neuroblastoma

Neuroblastoma (NB) is a tumor of the sympathoadrenal system arising in children under 15 years of age. In Germany, NB accounts for 7% of childhood cancer cases, but 11% of cancer deaths. It originates from highly migratory progenitor cells that leave the dorsal neural tube and contribute neurons and glial cells to sympathetic ganglia, and chromaffin and supportive cells to the adrenal medulla and paraganglia. Clinically, histologically and molecularly, NBs present as extremely heterogeneous, ranging from very good to very poor prognosis. The etiology of NB still remains unclear and needs to be elucidated, however, aberrant auto- and paracrine embryonic cell communications seem to be likely candidates to initiate or facilitate the emergence, progression and regression of NB. The wingless-type MMTV integration site (WNT) family of proteins represents an evolutionary highly conserved signaling system that orchestrates embryogenesis. At least 19 ligands in the human, numerous receptors and co-receptors are known, which control not only proliferation, but also cell polarity, migration and differentiation. Here we seek to interconnect aspects of WNT signaling with sympathoadrenal and paraganglionic development to define new WNT signaling cues in the etiology and progression of NB.

Cinacalcet inhibits neuroblastoma tumor growth and upregulates cancer-testis antigens

The calcium–sensing receptor is a G protein-coupled receptor that exerts cell-type specific functions in numerous tissues and some cancers. We have previously reported that this receptor exhibits tumor suppressor properties in neuroblastoma. We have now assessed cinacalcet, an allosteric activator of the CaSR approved for clinical use, as targeted therapy for this developmental tumor using neuroblastoma cell lines and patient-derived xenografts (PDX) with different MYCN and TP53 status. In vitro, acute exposure to cinacalcet induced endoplasmic reticulum stress coupled to apoptosis via ATF4-CHOP-TRB3 in CaSR-positive, MYCN-amplified cells. Both phenotypes were partially abrogated by phospholipase C inhibitor U73122. Prolonged in vitro treatment also promoted dose- and time-dependent apoptosis in CaSR-positive, MYCN-amplified cells and, irrespective of MYCN status, differentiation in surviving cells. Cinacalcet significantly inhibited tumor growth in MYCN-amplified xenografts and reduced that of MYCN-non amplified PDX. Morphology assessment showed fibrosis in MYCN-amplified xenografts exposed to the drug. Microarrays analyses revealed up-regulation of cancer-testis antigens (CTAs) in cinacalcet-treated MYCN-amplified tumors. These were predominantly CTAs encoded by genes mapping on chromosome X, which are the most immunogenic. Other modulated genes upon prolonged exposure to cinacalcet were involved in differentiation, cell cycle exit, microenvironment remodeling and calcium signaling pathways. CTAs were up-regulated in PDX and in vitro models as well. Moreover, progressive increase of CaSR expression upon cinacalcet treatment was seen both in vitro and in vivo. In summary, cinacalcet reduces neuroblastoma tumor growth and up-regulates CTAs. This effect represents a therapeutic opportunity and provides surrogate circulating markers of neuroblastoma response to this treatment.

DKK1 inhibits proliferation and migration in human retinal pigment epithelial cells via the Wnt/β-catenin signaling pathway

Retinal pigment epithelial (RPE) cells play important roles in diabetic retinopathy (DR). Dickkopf 1 (DKK1) has been reported to be important in the regulation of cell proliferation and migration. However, there are few previous studies regarding DKK1 in RPE cells. Therefore, in the present study, we investigated the effect of DKK1 on the proliferation and migration of human RPE cells, and the signaling mechanisms underlying these effects. The results showed that the overexpression of DKK1 significantly inhibited the proliferation and migration of ARPE-19 cells. In addition, overexpression of DKK1 markedly inhibited the expression of β-catenin and cyclin D1 in ARPE-19 cells. Collectively, the present findings suggest that the overexpression of DKK1 inhibited the proliferation and migration of RPE cells by suppressing the Wnt/β-catenin signaling pathway. Therefore, DKK1 are able to augment the growth of human RPE, and further studies are warranted to investigate the effects of DKK1 effects on DR.

TWIST1 is a direct transcriptional target of MYCN and MYC in neuroblastoma

In neuroblastoma, MYCN amplification is associated with a worse prognosis and is a criterion used in the clinic to provide intensive treatments to children even with localized disease. In correlation with MYCN amplification, upregulation of TWIST1, a transcription factor playing a crucial role in inhibition of apoptosis and differentiation, was previously reported. Clinical data set analysis of MYCN, MYC and TWIST1 expression permits us to confirm that TWIST1 expression is upregulated in MYCN amplified neuroblastoma but also in a subset of neuroblastoma harboring high expression of MYCN or MYC without gene amplification. In silico analyses reveal the presence of several MYC regulatory motifs (E-Boxes and INR) within the TWIST1 promoter. Using gel shift assay and reporter activity assays, we demonstrate that both N-Myc and c-Myc proteins can bind and activate the TWIST1 promoter. Therefore, we propose TWIST1 as a direct MYC transcriptional target.

Serum level of DKK-1 and its prognostic potential in non-small cell lung cancer

Background

The aim of the present study was to measure the serum level of dickkopf-1(DKK-1) in patients with non-small cell lung cancer (NSCLC), and to determine the prognostic potential of serum DKK-1 in NSCLC.

Material and methods

The present study included a total of 150 patients with NSCLC and 150 healthy controls. Serum level of DKK-1 was measured by enzyme-linked immunosorbent assay (ELISA). Numerical variables were recorded as means ± standard deviation (SD) and analyzed by independent t-tests. Categorical variables were presented as rates and analyzed by using the chi-square test or Fisher’s exact test. The overall survival was analyzed by log-rank test, and survival curves were plotted according to Kaplan–Meier.

Results

We found that serum DKK-1 level was significantly higher in patients with NSCLC than healthy controls. Mean serum DKK-1 level was 31.42 ± 6.32 ng/ml in the NSCLC group and 14.12 ± 3.29 ng/ml in the healthy control group (p <0.01). Serum DKK-1 level expression level was significantly positively correlated with TNM stage (p = 0.009), lymph node involvement(p = 0.001), and distant metastases(p < 0.001).

In the multivariate Cox proportional hazards analysis, high DKK-1 expression was independently associated with poor survival (P < 0.001; HR = 3.98; 95% CI =2.19-4.83).

Conclusions

In conclusion, our results showed that DKK-1 was overexpressed in NSCLC, and DKK-1 in serum was a good predictor of poor prognosis in patients with NSCLC. More researches are needed in the future to clarify the detailed mechanism of DKK-1 in the carcinogenesis and metastasis of NSCLC.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1471414150119415.

Neuroblastoma and MYCN

Neuroblastoma, the most common extracranial solid tumor of childhood, is thought to originate from undifferentiated neural crest cells. Amplification of the MYC family member, MYCN, is found in ∼25% of cases and correlates with high-risk disease and poor prognosis. Currently, amplification of MYCN remains the best-characterized genetic marker of risk in neuroblastoma. This article reviews roles for MYCN in neuroblastoma and highlights recent identification of other driver mutations. Strategies to target MYCN at the level of protein stability and transcription are also reviewed.

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.

DKK-1 in serum as a clinical and prognostic factor in patients with cervical cancer

OBJECTIVES

Dickkopf-1 (DKK-1) is involved in osteoporosis, arthritis, and cancer development and can become a potential therapeutic target of these diseases. The different expression of DKK-1 in different cancers shows that the function of DKK-1 depends on the histological type of the cancer cells and the tissue microenvironment. Because DKK-1 is a secreted protein, we investigated whether it could be found in the serum of patients with cervical cancer.

STUDY DESIGN

The expression of DKK-1 was measured by enzyme-linked immunosorbent assay (ELISA) in the serum of 60 healthy women, 60 patients with cervical intraepithelial neoplasia (CIN) and 156 patients with cervical cancer. Detailed treatment information of all 156 patients with cervical cancer and exhaustive follow-up data of 138 patients were collected.

RESULTS

The levels of serum DKK-1 were significantly increased in patients with cervical cancer (11.90 [SD, 17.28] μg/mL) compared with healthy women (1.48 [SD, 1.86] μg/mL) and patients with CIN (4.77 [SD, 10.24] μg/mL) (p=0.00, p=0.00). The expression of DKK-1 in serum was correlated with lymphatic metastasis and tumor diameter in cervical carcinoma and associated with the prognosis of patients with cervical cancer.

CONCLUSIONS

DKK-1 detection with ELISA as a biological marker can be used for the detection and diagnosis of cervical carcinoma. DKK-1 in serum is a good predictor of poor prognosis in patients with cervical cancer.

Parathyroid hormone-related protein inhibits DKK1 expression through c-Jun-mediated inhibition of β-catenin activation of the DKK1 promoter in prostate cancer

Prostate cancer (PCa)bone metastases are unique in that majority of them induce excessive mineralized bone matrix, through undefined mechanisms, as opposed to most other cancers that induce bone resorption. Parathyroid hormone-related protein (PTHrP) is produced by PCa cells and intermittent PTHrP exposure has bone anabolic effects, suggesting that PTHrP could contribute to the excess bone mineralization. Wnts are bone-productive factors produced by PCa cells, and the Wnt inhibitor Dickkopfs-1 (DKK1) has been shown to promote PCa progression. These findings, in conjunction with the observation that PTHrP expression increases and DKK1 expression decreases as PCa progresses, led to the hypothesis that PTHrP could be a negative regulator of DKK1 expression in PCa cells and, hence, allow the osteoblastic activity of Wnts to be realized. To test this, we first demonstrated that PTHrP downregulated DKK1 mRNA and protein expression. We then found through multiple mutated DKK1 promoter assays that PTHrP, through c-Jun activation, downregulated the DKK1 promoter through a transcription factor (TCF) response element site. Furthermore, chromatin immunoprecipitation (ChIP) and re-ChIP assays revealed that PTHrP mediated this effect through inducing c-Jun to bind to a transcriptional activator complex consisting of β-catenin, which binds the most proximal DKK1 promoter, the TCF response element. Together, these results demonstrate a novel signaling linkage between PTHrP and Wnt signaling pathways that results in downregulation of a Wnt inhibitor allowing for Wnt activity that could contribute the osteoblastic nature of PCa.

MYCN-mediated transcriptional repression in neuroblastoma: the other side of the coin

Neuroblastoma is the most common extra cranial solid tumor in childhood and the most frequently diagnosed neoplasm during the infancy. MYCN amplification and overexpression occur in about 25% of total neuroblastoma cases and this percentage increases at 30% in advanced stage neuroblastoma. So far, MYCN expression profile is still one of the most robust and significant prognostic markers for neuroblastoma outcome. MYCN is a transcription factor that belongs to the family of MYC oncoproteins, comprising c-MYC and MYCL genes. Deregulation of MYC oncoprotein expression is a crucial event involved in the occurrence of different types of malignant tumors. MYCN, as well as c-MYC, can heterodimerize with its partner MAX and activate the transcription of several target genes containing E-Box sites in their promoter regions. However, recent several lines of evidence have revealed that MYCN can repress at least as many genes as it activates, thus proposing a novel function of this protein in neuroblastoma biology. Whereas the mechanism by which MYCN can act as a transcriptional activator is relatively well known, very few studies has been done in the attempt to explain how MYCN can exert its transcription repression function. Here, we will review current knowledge about the mechanism of MYCN-mediated transcriptional repression and will emphasize its role as a repressor in the recruitment of a precise set of proteins to form complexes capable of down-regulating specific subsets of genes whose function is actively involved in apoptosis, cell differentiation, chemosensitivity, and cell motility. The finding that MYCN can also act as a repressor has widen our view on its role in oncogenesis and has posed the bases to search for novel therapeutic drugs that can specifically target its transcriptional repression function.

MYCN is recruited to the RASSF1A promoter but is not critical for DNA hypermethylation in neuroblastoma

Tumor suppressor genes such as RASSF1A are often epigenetically repressed by DNA hypermethylation in neuroblastoma, where the MYCN proto-oncogene is frequently amplified. MYC has been shown to associate with DNA methyltransferases, thereby inducing transcriptional repression of target genes, which suggested that MYCN might play a similar mechanistic role in the hypermethylation of tumor suppressor genes in neuroblastoma. This study tested that hypothesis by using co-immunoprecipitation and ChIP to investigate MYCN-DNA methyltransferase interactions, together with MYCN knock-down and over-expression systems to examine the effect of MYCN expression changes on gene methylation, employing both candidate gene and genome-wide assays. We show that MYCN interacts with DNA methyltransferases and is recruited to the promoter region of RASSF1A. However, using four model systems, we showed that long-term silencing of MYCN induces only a small loss of DNA methylation at the RASSF1A promoter in MYCN amplified neuroblastoma cell lines and over-expression of MYCN does not induce any DNA methylation, suggesting that MYCN is not critical for DNA hypermethylation in neuroblastoma.

p53, SKP2, and DKK3 as MYCN Target Genes and Their Potential Therapeutic Significance

Neuroblastoma is the most common extra-cranial solid tumor of childhood. Despite significant advances, it currently still remains one of the most difficult childhood cancers to cure, with less than 40% of patients with high-risk disease being long-term survivors. MYCN is a proto-oncogene implicated to be directly involved in neuroblastoma development. Amplification of MYCN is associated with rapid tumor progression and poor prognosis. Novel therapeutic strategies which can improve the survival rates whilst reducing the toxicity in these patients are therefore required. Here we discuss genes regulated by MYCN in neuroblastoma, with particular reference to p53, SKP2, and DKK3 and strategies that may be employed to target them.

Wnt and Wnt inhibitors in bone metastasis

Bone metastasis is a clinically devastating development of progressive cancers including prostate carcinoma, breast carcinoma and multiple myeloma. Bone metastases are typically painful, lead to adverse skeletal-related events, such as fracture, and are highly resistant to therapy. A major contribution to the ability of cancers to successfully establish bone metastases is their ability to exploit mechanisms of normal bone remodeling. Wnts are a large family of morphogenic proteins that are critical for bone development and contribute to maintaining bone mass in the mature organism. Wnt function is balanced by the presence of a variety of endogenous inhibitors, such as the dickkopf family members, secreted frizzled related proteins and sclerostin. Together, these factors contribute to normal bone homeostasis, allowing for dynamic changes in bone to withstand alterations in physical forces and physiological needs. In this review, we describe the role that Wnts and their inhibitors have in normal bone biology and cancer-related bone pathology. An overview of Wnt signaling pathways is discussed and key bone microenvironment cellular players, as they pertain to Wnt biology, are examined. Finally, we describe clinical trials of several Wnt inhibitor antagonists for patients with tumor-related bone disease. As few options currently exist for the treatment of bone-metastatic disease, Wnt proteins and their inhibitors offer promise for the development of novel therapeutics.

NEU4L sialidase overexpression promotes β-catenin signaling in neuroblastoma cells, enhancing stem-like malignant cell growth

Neuroblastoma (NB) is a frequently lethal tumor that occurs in childhood and originates from embryonic neural crest cells. The malignant and aggressive phenotype of NB is strictly related to the deregulation of pivotal pathways governing the proliferation/differentiation status of neural crest precursor cells, such as MYCN, Delta/Notch and Wnt/β-catenin (CTNNB1) signaling. In this article, we demonstrate that sialidase NEU4 long (NEU4L) influences the differentiation/proliferation behavior of NB SK-N-BE cells by determining hyperactivation of the Wnt/β-catenin signaling pathway. NEU4L overexpression in SK-N-BE cells induced significant increases in active, nonphosphorylated β-catenin content, β-catenin/TCF transcriptional activity and β-catenin gene target expression including MYCN, MYC, CCND2 (cyclin D2) and CDC25A. In turn, these molecular features strongly modified the behavior of NEU4L SK-N-BE overexpressing cells, promoting the following: (1) an enhanced proliferation rate, mainly due to a faster transition from G1 to S phase in the cell cycle; (2) a more undifferentiated cell phenotype, which was similar to stem-like NB cells and possibly mediated by an increase of the expression of the pluripotency genes, MYC, NANOG, OCT-4, CD133 and NES (nestin); (3) the failure of NB cell differentiation after serum withdrawal. The molecular link between NEU4L and Wnt/β-catenin signaling appeared to rely most likely on the capability of the enzyme to modify the sialylation level of cell glycoproteins. These findings could provide a new candidate for therapeutic treatment.

Activated β-catenin forces N2A cell-derived neurons back to tumor-like neuroblasts and positively correlates with a risk for human neuroblastoma

Neuroblastoma is an embryonic malignancy arising from neuroblasts. The mechanisms that regulate the origination of neuroblastoma are still not very clear. In this study, we revealed that 6-bromoindirubin 3'-oxime (BIO), a specific GSK-3β inhibitor, promoted N2A cells-derived neurons to become tumor-like neuroblasts. Moreover, constitutively activated β-catenin (S33Y) also promoted this process, whereas, silencing endogenous expression of β-catenin abolished BIO-induced effects. These results implicated the potential relationship between the Wnt/β-catenin signaling and neuroblastoma formation. Indeed, we found that the amount of β-catenin in nucleus, which indicated the activation of Wnt/β-catnin signaling, was accumulated in human neuroblastoma specimens and positively correlated with clinical risk of neuroblastoma. These results give us a new sight into the neuroblastoma initiation and progression, and provide a potential drug target for neuroblastoma treatment.

Dickkopf1: a tumor suppressor or metastasis promoter?

Dickkopf1 (DKK1), a secreted inhibitor of the Wnt/β-catenin pathway, is a negative regulator of bone formation. DKK1 acts as a switch that transitions prostate cancer bone metastases from osteolytic to osteoblastic and also is an active indicator of poor outcome for multiple myeloma. However, in other tumor types, DKK1 upregulation or overexpression suppresses tumor growth. Thus, the role of DKK1 in cancer appears to be diverse. This raises a question: Could the increased levels of DKK1 still be tumor protective when observed in high levels in the serum of patients? Here, we summarize the diverse, seemingly contradicting roles of DKK1 and attempt to explain the apparent dichotomy in its activity. We propose that DKK1 is a critical secreted factor that modulates microenvironment. Based on the location and components of the microenvironment DKK1 will support different outcomes.

Neuroblastoma and bone metastases: clinical significance and prognostic value of Dickkopf 1 plasma levels

The critical role of the Wnt pathway inhibition in sustaining the onset of bone lesions has been demonstrated in a variety of bone diseases and tumors, and it has been associated with cancer aggressiveness. We have previously demonstrated that neuroblastoma cells express Dickkopf 1 (Dkk1), an inhibitor of the canonical Wnt pathway which prevents the differentiation of bone-forming cells. Since Dkk1 is a secreted factor, it could have potential clinical application as tumor marker for detecting bone metastasis and monitoring of disease. In this study, we investigated the diagnostic and prognostic value of Dkk1 plasma levels in 92 children affected by neuroblastoma, including 32 with bone metastases. Fifty-seven children hospitalized for minor surgical problems served as control group. Circulating levels of Dkk1 were higher in healthy children than in normal adults and were comparable to those found in adult patients with aggressive tumors. No significant differences were found between neuroblastoma patients and controls and between patients with and without bone metastases. However, when only patients with metastatic neuroblastoma were considered, the highest Dkk1 levels were detected in patients that poorly responded to induction chemotherapy and in subjects with unamplified MYCN and three or more different metastatic sites. The 'Receiver Operating Characteristic' curve enabled us to identify a threshold value to distinguish patients who were unresponsive to induction treatment. The relationship between Dkk1 and drug resistance was supported by in vitro experiments, since an increased sensitivity to doxorubicin was found in neuroblastoma cells releasing low Dkk1 levels, either constitutively or experimentally following the treatment with specific siRNA. In conclusion, Dkk1 is released by neuroblastoma cells and is able to affect the balance between osteoblastogenesis and osteoclastogenesis, thus favoring the onset of osteolytic metastases. Nevertheless, Dkk1 plasma levels do not allow the detection of bone lesions in neuroblastoma but seem to have a predictive value with regard to the severity and the prognosis of the disease in a subset of patients with metastatic tumor. New knowledge on the biological role of Dkk1 in driving the natural history of neuroblastoma has to be further investigated and could help to establish specific therapeutic strategies able to target key factors of tumor progression.

Cooperative action of multiple cis-acting elements is required for N-myc expression in branchial arches: specific contribution of GATA3

The precise expression of the N-myc proto-oncogene is essential for normal mammalian development, whereas altered N-myc gene regulation is known to be a determinant factor in tumor formation. Using transgenic mouse embryos, we show that N-myc sequences from kb -8.7 to kb +7.2 are sufficient to reproduce the N-myc embryonic expression profile in developing branchial arches and limb buds. These sequences encompass several regulatory elements dispersed throughout the N-myc locus, including an upstream limb bud enhancer, a downstream somite enhancer, a branchial arch enhancer in the second intron, and a negative regulatory element in the first intron. N-myc expression in the limb buds is under the dominant control of the limb bud enhancer. The expression in the branchial arches necessitates the interplay of three regulatory domains. The branchial arch enhancer cooperates with the somite enhancer region to prevent an inhibitory activity contained in the first intron. The characterization of the branchial arch enhancer has revealed a specific role of the transcription factor GATA3 in the regulation of N-myc expression. Together, these data demonstrate that correct N-myc developmental expression is achieved via cooperation of multiple positive and negative regulatory elements.

MYCN oncoprotein targets and their therapeutic potential

The MYCN oncogene encodes a transcription factor which is amplified in up to 40% of high risk neuroblastomas. MYCN amplification is a well-established poor prognostic marker in neuroblastoma, however the role of MYCN expression and the mechanisms by which it acts to promote an aggressive phenotype remain largely unknown. This review discusses the current evidence identifying the direct and indirect downstream transcriptional targets of MYCN from recent studies, with particular reference to how MYCN affects the cell cycle, DNA damage response, differentiation and apoptosis in neuroblastoma.

Myc proteins as therapeutic targets

Myc proteins (c-myc, Mycn and Mycl) target proliferative and apoptotic pathways vital for progression in cancer. Amplification of the MYCN gene has emerged as one of the clearest indicators of aggressive and chemotherapy-refractory disease in children with neuroblastoma, the most common extracranial solid tumor of childhood. Phosphorylation and ubiquitin-mediated modulation of Myc protein influence stability and represent potential targets for therapeutic intervention. Phosphorylation of Myc proteins is controlled in-part by the receptor tyrosine kinase/phosphatidylinositol 3-kinase/Akt/mTOR signaling, with additional contributions from Aurora A kinase. Myc proteins regulate apoptosis in part through interactions with the p53/Mdm2/Arf signaling pathway. Mutation in p53 is commonly observed in patients with relapsed neuroblastoma, contributing to both biology and therapeutic resistance. This review examines Myc function and regulation in neuroblastoma, and discusses emerging therapies that target Mycn.

Global MYCN transcription factor binding analysis in neuroblastoma reveals association with distinct E-box motifs and regions of DNA hypermethylation

Background

Neuroblastoma, a cancer derived from precursor cells of the sympathetic nervous system, is a major cause of childhood cancer related deaths. The single most important prognostic indicator of poor clinical outcome in this disease is genomic amplification of MYCN, a member of a family of oncogenic transcription factors.

Methodology

We applied MYCN chromatin immunoprecipitation to microarrays (ChIP-chip) using MYCN amplified/non-amplified cell lines as well as a conditional knockdown cell line to determine the distribution of MYCN binding sites within all annotated promoter regions.

Conclusion

Assessment of E-box usage within consistently positive MYCN binding sites revealed a predominance for the CATGTG motif (p<0.0016), with significant enrichment of additional motifs CATTTG, CATCTG, CAACTG in the MYCN amplified state. For cell lines over-expressing MYCN, gene ontology analysis revealed enrichment for the binding of MYCN at promoter regions of numerous molecular functional groups including DNA helicases and mRNA transcriptional regulation. In order to evaluate MYCN binding with respect to other genomic features, we determined the methylation status of all annotated CpG islands and promoter sequences using methylated DNA immunoprecipitation (MeDIP). The integration of MYCN ChIP-chip and MeDIP data revealed a highly significant positive correlation between MYCN binding and DNA hypermethylation. This association was also detected in regions of hemizygous loss, indicating that the observed association occurs on the same homologue. In summary, these findings suggest that MYCN binding occurs more commonly at CATGTG as opposed to the classic CACGTG E-box motif, and that disease associated over expression of MYCN leads to aberrant binding to additional weaker affinity E-box motifs in neuroblastoma. The co-localization of MYCN binding and DNA hypermethylation further supports the dual role of MYCN, namely that of a classical transcription factor affecting the activity of individual genes, and that of a mediator of global chromatin structure.

MSX1 induces the Wnt pathway antagonist genes DKK1, DKK2, DKK3, and SFRP1 in neuroblastoma cells, but does not block Wnt3 and Wnt5A signalling to DVL3

Neuroblastoma is the most common extra-cranial solid childhood cancer; it arises from neural crest-derived cells of the sympathetic nervous system. The anomalous regulation of embryonic developmental pathways like Delta-Notch and Wnt has been implicated in aberrant cell growth and differentiation in many (childhood) tumours. We have previously found regulation of Delta-Notch pathway genes by the MSX1 neural crest development gene in a neuroblastoma cell line, and significant correlations between these genes in neuroblastic tumours. However, a clear role for the Wnt pathway in neuroblastic tumours has not yet been determined. We now analyze the complete spectrum of genes regulated by inducible expression of MSX1 in the SJNB8 neuroblastoma cell line using Affymetrix expression profiling. We show that MSX1 induces the expression of four different Wnt pathway inhibitor genes: Dickkopf 1-3 (DKK1-3) and secreted frizzled-related protein 1 (SFRP1), and provide evidence that high expression of two of these genes correlates with good prognosis. We were able to demonstrate that both the canonical Wnt3 and the alternative Wnt5A ligands are highly expressed in neuroblastic tumours and cell lines, and specifically activate the DVL3 Wnt co-receptor protein in SJNB8 neuroblastoma cells. These results suggest involvement of MSX1 in Wnt signalling and demonstrate activity of the more upstream Wnt pathway in neuroblastic cells.

Clinical significance of serum DKK-1 in patients with gynecological cancer

Dickkopf-1 (DKK-1) is a secreted protein involved in embryonic development. Dickkopf-1 is also implicated in osteoporosis, arthritis, and cancer and represents a potential therapeutic target for the treatment of these diseases. Because DKK-1 encodes a secreted protein, we investigated whether the DKK-1 protein is secreted into the sera of patients with gynecological cancer. The levels of DKK-1 protein were assessed by enzyme-linked immunosorbent assay in the sera of 104 patients with gynecological cancer including 36 with ovarian, 40 with cervical, and 28 with endometrial cancers. The serum levels of DKK-1 protein were higher in patients with cervical (314.13 [385.02] pg/mL, P = 0.000) and endometrial (46.95 [21.62] pg/mL, P = 0.000) cancers than in healthy individuals (29.45 [11.86] pg/mL). The serum levels of DKK-1 protein were associated with clinical stage in all patients with gynecological cancer. In patients with cervical cancer, the serum levels of DKK-1 protein were also associated with histological type and lymphatic metastasis. Dickkopf-1 protein detection using enzyme-linked immunosorbent assay as a molecular marker can contribute to the detection and the diagnosis of cervical and endometrial cancers, especially for cervical squamous cell cancer.

Musashi1 modulates cell proliferation genes in the medulloblastoma cell line Daoy

BACKGROUND

Musashi1 (Msi1) is an RNA binding protein with a central role during nervous system development and stem cell maintenance. High levels of Msi1 have been reported in several malignancies including brain tumors thereby associating Msi1 and cancer.

METHODS

We used the human medulloblastoma cell line Daoy as model system in this study to knock down the expression of Msi1 and determine the effects upon soft agar growth and neurophere formation. Quantitative RT-PCR was conducted to evaluate the expression of cell proliferation, differentiation and survival genes in Msi1 depleted Daoy cells.

RESULTS

We observed that MSI1 expression was elevated in Daoy cells cultured as neurospheres compared to those grown as monolayer. These data indicated that Msi1 might be involved in regulating proliferation in cancer cells. Here we show that shRNA mediated Msi1 depletion in Daoy cells notably impaired their ability to form colonies in soft agar and to grow as neurospheres in culture. Moreover, differential expression of a group of Notch, Hedgehog and Wnt pathway related genes including MYCN, FOS, NOTCH2, SMO, CDKN1A, CCND2, CCND1, and DKK1, was also found in the Msi1 knockdown, demonstrating that Msi1 modulated the expression of a subset of cell proliferation, differentiation and survival genes in Daoy.

CONCLUSION

Our data suggested that Msi1 may promote cancer cell proliferation and survival as its loss seems to have a detrimental effect in the maintenance of medulloblastoma cancer cells. In this regard, Msi1 might be a positive regulator of tumor progression and a potential target for therapy.

High Myc pathway activity and low stage of neuronal differentiation associate with poor outcome in neuroblastoma

The childhood cancer neuroblastoma arises in the developing sympathetic nervous system and is a genotypically and phenotypically heterogeneous disease. Prognostic markers of poor survival probability include amplification of the MYCN oncogene and an undifferentiated morphology. Whereas these features discriminate high- from low-risk patients with precision, identification of poor outcome low- and intermediate-risk patients is more challenging. In this study, we analyze two large neuroblastoma microarray datasets using a priori-defined gene expression signatures. We show that differential overexpression of Myc transcriptional targets and low expression of genes involved in sympathetic neuronal differentiation predicts relapse and death from disease. This was evident not only for high-risk patients but was also robust in identifying groups of poor prognosis patients who were otherwise judged to be at low- or intermediate-risk for adverse outcome. These data suggest that pathway-specific gene expression profiling might be useful in the clinic to adjust treatment strategies for children with neuroblastoma.