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-3: An Update on a Potential Regulator of the Tumor Microenvironment

Dickkopf-3 (Dkk-3) is a member of the Dickkopf family protein of secreted Wingless-related integration site (Wnt) antagonists that appears to modulate regulators of the host microenvironment. In contrast to the clear anti-tumorigenic effects of Dkk-3-based gene therapies, the role of endogenous Dkk-3 in cancer is context-dependent, with elevated expression associated with tumor promotion and suppression in different settings. The receptors and effectors that mediate the diverse effects of Dkk-3 have not been characterized in detail, contributing to an ongoing mystery of its mechanism of action. This review compares the various functions of Dkk-3 in the tumor microenvironment, where Dkk-3 has been found to be expressed by subpopulations of fibroblasts, endothelial, and immune cells, in addition to epithelial cells. We also discuss how the activation or inhibition of Dkk-3, depending on tumor type and context, might be used to treat different types of cancers.

Key Genes Regulating Skeletal Muscle Development and Growth in Farm Animals

Simple Summary

Skeletal muscle mass is an important economic trait, and muscle development and growth is a crucial factor to supply enough meat for human consumption. Thus, understanding (candidate) genes regulating skeletal muscle development is crucial for understanding molecular genetic regulation of muscle growth and can be benefit the meat industry toward the goal of increasing meat yields. During the past years, significant progress has been made for understanding these mechanisms, and thus, we decided to write a comprehensive review covering regulators and (candidate) genes crucial for muscle development and growth in farm animals. Detection of these genes and factors increases our understanding of muscle growth and development and is a great help for breeders to satisfy demands for meat production on a global scale.

Abstract

Farm-animal species play crucial roles in satisfying demands for meat on a global scale, and they are genetically being developed to enhance the efficiency of meat production. In particular, one of the important breeders’ aims is to increase skeletal muscle growth in farm animals. The enhancement of muscle development and growth is crucial to meet consumers’ demands regarding meat quality. Fetal skeletal muscle development involves myogenesis (with myoblast proliferation, differentiation, and fusion), fibrogenesis, and adipogenesis. Typically, myogenesis is regulated by a convoluted network of intrinsic and extrinsic factors monitored by myogenic regulatory factor genes in two or three phases, as well as genes that code for kinases. Marker-assisted selection relies on candidate genes related positively or negatively to muscle development and can be a strong supplement to classical selection strategies in farm animals. This comprehensive review covers important (candidate) genes that regulate muscle development and growth in farm animals (cattle, sheep, chicken, and pig). The identification of these genes is an important step toward the goal of increasing meat yields and improves meat quality.

MYCN Function in Neuroblastoma Development

Dysregulated expression of the transcription factor MYCN is frequently detected in nervous system tumors such as childhood neuroblastoma. Here, gene amplification of MYCN is a single oncogenic driver inducing neoplastic transformation in neural crest-derived cells. This abnormal MYCN expression is one of the strongest predictors of poor prognosis. It is present at diagnosis and is never acquired during later tumorigenesis of MYCN non-amplified neuroblastoma. This suggests that increased MYCN expression is an early event in these cancers leading to a peculiar dysregulation of cells that results in embryonal or cancer stem-like qualities, such as increased self-renewal, apoptotic resistance, and metabolic flexibility.

miR-15a-5p, miR-15b-5p, and miR-16-5p inhibit tumor progression by directly targeting MYCN in neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid malignancy in children. Despite current aggressive treatment regimens, the prognosis for high-risk NB patients remains poor, with the survival of less than 40%. Amplification/stabilization of MYCN oncogene, in NB is associated with a high risk of recurrence. Thus, there is an urgent need for novel therapeutics. The deregulated expression of microRNA (miR) is reported in NB; nonetheless, its effect on MYCN regulation is poorly understood. First, we identified that miR-15a-5p, miR-15b-5p, and miR-16-5p (hereafter miR-15a, miR-15b or miR-16) were down-regulated in patient-derived xenografts (PDX) with high MYCN expression. MiR targeting sequences on MYCN mRNA were predicted using online databases such as TargetScan and miR database. The R2 database, containing 105 NB patients, showed an inverse correlation between MYCN mRNA and deleted in lymphocytic leukemia (DLEU) 2, a host gene of miR-15. Moreover, overexpression of miR-15a, miR-15b or miR-16 significantly reduced the levels of MYCN mRNA and N-Myc protein. Conversely, inhibiting miR dramatically enhanced MYCN mRNA and N-Myc protein levels, as well as increasing mRNA half-life in NB cells. By performing immunoprecipitation assays of argonaute-2 (Ago2), a core component of the RNA-induced silencing complex, we showed that miR-15a, miR-15b and miR-16 interact with MYCN mRNA. Luciferase reporter assays showed that miR-15a, miR-15b and miR-16 bind with 3'UTR of MYCN mRNA, resulting in MYCN suppression. Moreover, induced expression of miR-15a, miR-15b and miR-16 significantly reduced the proliferation, migration, and invasion of NB cells. Finally, transplanting miR-15a-, miR-15b- and miR-16-expressing NB cells into NSG mice repressed tumor formation and MYCN expression. These data suggest that miR-15a, miR-15b and miR-16 exert a tumor-suppressive function in NB by targeting MYCN. Therefore, these miRs could be considered as potential targets for NB treatment.

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.

MYCN is a novel oncogenic target in adult B-ALL that activates the Wnt/β-catenin pathway by suppressing DKK3

Dickkopf‐3 (DKK3) is frequently down‐regulated by promoter hypermethylation and is closely associated with a poor prognosis in many cancers. Our previous studies have shown that miR‐708 down‐regulates DKK3 at the post‐transcriptional level in B‐ALL. However, whether transcriptional mechanisms lead to DKK3 silencing remains unclear. Here, we analysed the promoter regions of DKK3 by bioinformatics and found binding sites for MYCN. A dual‐luciferase reporter gene assay and ChIP experiments revealed that MYCN negatively regulates DKK3 at the transcriptional level in B‐ALL cell lines, and using bisulphite sequencing PCR, we affirmed that MYCN has no effect on the methylation of the DKK3 promoter. MYCN silencing in B‐ALL cells resulted in reduced cell proliferation, increased apoptosis and G1 phase arrest. Treatment with MYCN siRNA or 5‐aza‐2′‐deoxycytidine (5‐AdC), a demethylating agent, significantly increased the levels of DKK3 mRNA and protein and decreased the protein levels of p‐GSK3β and nuclear β‐catenin, which indicates inhibition of the Wnt/β‐catenin pathway in vitro. MYCN knockdown significantly decreased the tumorigenic capacity of Nalm6 cells, which restored DKK3 levels and inhibited the Wnt/β‐catenin pathway in vivo. Our study provides an increased understanding of adult B‐ALL pathogenesis, which may be beneficial to the development of effective prognostic markers or therapeutic targets.

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.

Dickkopf 3 attenuates xanthine dehydrogenase expression to prevent oxidative stress-induced apoptosis

Dickkopf (DKK) 3 is a DKK glycoprotein family member that controls cell fate during embryogenesis and exerts opposing effects on survival in a cell type-dependent manner; however, the mechanisms governing its pro-apoptosis versus pro-survival functions remain unclear. Here, we investigated DKK3 function in Li21 hepatoma cells and tPH5CH immortalized hepatocytes. DKK3 knockdown by siRNA resulted in reactive oxygen species accumulation and subsequent apoptosis, which were abrogated by administration of the antioxidant N-acetyl-cysteine. Moreover, forced DKK3 over-expression induced resistance to hydrogen peroxide (H₂ O₂ )-induced apoptosis. Expression analysis by cDNA microarray showed that xanthine dehydrogenase (XDH) expression was significantly lower in Li21 and tPH5CHDKK3-over-expressing cells in response to H₂ O₂ treatment when compared to that in their respective mock-transfected controls, whereas a marked increase was observed in H₂ O₂ -treated DKK3 knockdown cells. Thus, these data suggest that DKK3 promotes cell survival during oxidative stress by suppressing the expression of the superoxide-producing enzyme XDH.

Dkk3 prevents familial dilated cardiomyopathy development through Wnt pathway

To date, the role of Dickkopf 3 (Dkk3) on the pathogenesis of familial dilated cardiomyopathy (FDCM), and whether and how Dkk3 interferes with Wnt signaling in heart tissues remains unknown. Here, we demonstrate that strong Dkk3 expression was markedly downregulated in adult hearts from WT mice, and Dkk3 expression was upregulated suddenly in hearts from DCM mouse models. Using Dkk3 transgenic and knockout mice, as well as cTnT(R141W) transgenic mice, which manifests progressive chamber dilation and contractile dysfunction and has pathologic phenotypes similar to human DCM patients, we determined that transgenic expression of Dkk3 increased survival rate, improved cardiac morphology breakage and dysfunction, and ameliorated cardiac pathological changes in the cTnT(R141W) mice. In contrast, Dkk3 knockout reduced the survival rate and aggravated the pathological phenotypes of the cTnT(R141W) mice. The protective effects of Dkk3 appeared clearly at 3 months of age, peaked at 6 months of age, and decreased at 10 months of age in the cTnT(R141W) mice. Furthermore, we determined that Dkk3 upregulated Dvl1 (Dishevelled 1) and key proteins of the canonical Wnt pathway (cytoplasmic and nuclear β-catenin, c-Myc, and Axin2) and downregulated key proteins of the noncanonical Wnt pathway (c-Jun N-terminal kinase (JNK), Ca(2+)/calmodulin-dependent protein kinase II (CAMKII), and histone deacetylase 4 (HDAC4)). In contrast, Dkk3 knockout reversed these changes in the cTnT(R141W) mice. In summary, Dkk3 could prevent FDCM development in mice, especially in the compensatory stage, and probably through activation of the canonical and inhibition of the noncanonical Wnt pathway, which suggested that Dkk3 could serve as a therapeutic target for the treatment of cardiomyopathy and heart failure.

Decreased expression of Dkk1 and Dkk3 in human clear cell renal cell carcinoma

The expression patterns of the Dickkopf (Dkk) family of proteins varies in different cancers. In the present study, the expression levels of Dkk1 and Dkk3 were investigated in clear cell renal cell carcinoma (ccRCC) tissues. Dkk1 and Dkk3 serum levels were also examined in patients with ccRCC, and the association between clinicopathological features and Dkk levels was investigated. Serum Dkk1 and Dkk3 were quantified using ELISA in 64 patients with ccRCC and in 30 healthy individuals (controls). The expression levels of Dkk1 and Dkk3 were analyzed in tumor and adjacent normal tissues obtained from patients with ccRCC (n=20) using quantitative polymerase chain reaction (qPCR), western blot analysis and immunohistochemistry. The mean serum levels of Dkk1 and Dkk3 in the patients with ccRCC were significantly lower than those in the healthy controls. Furthermore, the serum Dkk1 levels were significantly lower at higher tumor‑node‑metastasis stages and tumor grades. qPCR, western blot analysis and immunohistochemistry revealed a significant decrease in the Dkk1 and Dkk3 mRNA and protein levels in the tumor tissues compared with the adjacent normal tissues. Consequently, Dkk1 and Dkk3 may present a novel molecular target for the diagnosis and therapeutic treatment of ccRCC.

Dickkopf-3 attenuates pressure overload-induced cardiac remodelling

AIMS

Dickkopf-3 (DKK3), a secreted protein in the Dickkopf family, is expressed in various tissues, including the heart, and has been shown to play an important role in tissue development. However, the biological function of DKK3 in the heart remains largely unexplored. This study aimed to examine the role of DKK3 in pathological cardiac hypertrophy.

METHODS AND RESULTS

We performed gain-of-function and loss-of-function studies using DKK3 cardiac-specific transgenic (TG) mice and DKK3 knockout (KO) mice (C57BL/6J background). Cardiac hypertrophy was induced by aortic banding. Cardiac hypertrophy was evaluated by echocardiographic, haemodynamic, pathological, and molecular analyses. Our results demonstrated that the loss of DKK3 exaggerated pressure overload-induced cardiac hypertrophy, fibrosis, and dysfunction, whereas the overexpression of DKK3 protected the heart against pressure overload-induced cardiac remodelling. These beneficial effects were associated with the inhibition of the ASK1-JNK/p38 (apoptosis signal-regulating kinase 1-c-Jun N-terminal kinase/p38) signalling cascade. Parallel in vitro experiments confirmed these in vivo observations. Co-immunoprecipitation experiments suggested that physical interactions occurred between DKK3 and ASK1. Moreover, rescue experiments indicated that, in DKK3 TG mice, the activation of ASK1 using a cardiac-specific conditional ASK1 transgene reduced the functionality of DKK3 in response to pressure overload; furthermore, the inactivation of ASK1 by dominant-negative ASK1 rescued pressure overload-induced cardiac abnormalities in DKK3 KO mice.

CONCLUSION

Taken together, our findings indicate that DKK3 acts as a cardioprotective regulator of pathological cardiac hypertrophy and that this function largely occurs via the regulation of ASK1-JNK/p38 signalling.

GSK3 inhibitors regulate MYCN mRNA levels and reduce neuroblastoma cell viability through multiple mechanisms, including p53 and Wnt signaling

Neuroblastoma is an embryonal tumor accounting for approximately 15% of childhood cancer deaths. There exists a clinical need to identify novel therapeutic targets, particularly for treatment-resistant forms of neuroblastoma. Therefore, we investigated the role of the neuronal master regulator GSK3 in controlling neuroblastoma cell fate. We identified novel GSK3-mediated regulation of MYC (c-MYC and MYCN) mRNA levels, which may have implications for numerous MYC-driven cancers. In addition, we showed that certain GSK3 inhibitors induced large-scale cell death in neuroblastoma cells, primarily through activating apoptosis. mRNA-seq of GSK3 inhibitor-treated cells was performed and subsequent pathway analysis revealed that multiple signaling pathways contributed to the loss of neuroblastoma cell viability. The contribution of two of the signaling pathways highlighted by the mRNA-seq analysis was functionally validated. Inhibition of the p53 tumor suppressor partly rescued the cell death phenotype, whereas activation of canonical Wnt signaling contributed to the loss of viability, in a p53-independent manner. Two GSK3 inhibitors (BIO-acetoxime and LiCl) and one small-molecule Wnt agonist (Wnt Agonist 1) demonstrated therapeutic potential for neuroblastoma treatment. These inhibitors reduced the viability of numerous neuroblastoma cell lines, even those derived from high-risk MYCN-amplified metastatic tumors, for which effective therapeutics are currently lacking. Furthermore, although LiCl was lethal to neuroblastoma cells, it did not reduce the viability of differentiated neurons. Taken together our data suggest that these small molecules may hold potential as effective therapeutic agents for the treatment of neuroblastoma and other MYC-driven cancers.

Role of Intracellular and Extracellular MicroRNA-92a in Colorectal Cancer

Colorectal cancer is one of the leading causes of cancer-related death worldwide. Previous studies have shown that miR-92a has an oncogenic function in several cancers and that its up-regulation is correlated with malignant clinicopathologic behaviors of colorectal cancer. It also has been suggested that circulating miR-92a in patients' plasma can be a potential biomarker for colorectal cancer. However, the precise roles of intracellular and extracellular miR-92a are not yet understood. In this study, we examined the expression levels of miR-92a in colorectal tumors (38 cancer specimens and 56 adenoma specimens) and paired adjacent nontumorous tissues. Increased expression of miR-92a was frequently observed in the cancers compared with that in the adenomas and was correlated with advanced clinical stages, tumor depth, and size. We also demonstrated that the levels of miR-92a within microvesicles (MVs) in the plasma of mice bearing colon cancer xenografts were significantly increased compared with those in control mice. One of the roles of intracellular and extracellular miR-92a was shown to be down-regulation of Dickkopf-3 (Dkk-3), a presumed tumor suppressor gene. Within the colon cancer cells, suppression of Dkk-3 by miR-92a contributed to the cell proliferation. Extracellular miR-92a packed within MVs secreted by colon cancer cells was delivered into endothelial cells and contributed to the proliferation and motility of these cells through down-regulation of the same target gene, Dkk-3. These data suggest that intracellular and extracellular miR-92a had important roles in tumor growth and the tumor microenvironment in colorectal cancer.

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.

Targeting the hedgehog signal transduction pathway at the level of GLI inhibits neuroblastoma cell growth in vitro and in vivo

Hedgehog (HH) signaling is an important regulator of embryogenesis that has been associated with the development of several types of cancer. HH signaling is characterized by Smoothened (SMO)-dependent activation of the GLI transcription factors, which regulate the expression of critical developmental genes. Neuroblastoma, an embryonal tumor of the sympathetic nervous system, was recently shown to express high levels of key molecules in this signaling cascade. Using compounds blocking SMO (cyclopamine and SANT1) or GLI1/GLI2 (GANT61) activity revealed that inhibition of HH signaling at the level of GLI was most effective in reducing neuroblastoma growth. GANT61 sensitivity positively correlated to GLI1 and negatively to MYCN expression in the neuroblastoma cell lines tested. GANT61 downregulated GLI1, c-MYC, MYCN and Cyclin D1 expression and induced apoptosis of neuroblastoma cells. The effects produced by GANT61 were mimicked by GLI knockdown but not by SMO knockdown. Furthermore, GANT61 enhanced the effects of chemotherapeutic drugs used in the treatment of neuroblastoma in an additive or synergistic manner and reduced the growth of established neuroblastoma xenografts in nude mice. Taken together this study suggests that inhibition of HH signaling is a highly relevant therapeutic target for high-risk neuroblastoma lacking MYCN amplification and should be considered for clinical testing.

Autocrine prostaglandin E2 signaling promotes tumor cell survival and proliferation in childhood neuroblastoma

BACKGROUND

Prostaglandin E(2) (PGE(2)) is an important mediator in tumor-promoting inflammation. High expression of cyclooxygenase-2 (COX-2) has been detected in the embryonic childhood tumor neuroblastoma, and treatment with COX inhibitors significantly reduces tumor growth. Here, we have investigated the significance of a high COX-2 expression in neuroblastoma by analysis of PGE(2) production, the expression pattern and localization of PGE(2) receptors and intracellular signal transduction pathways activated by PGE(2).

PRINCIPAL FINDINGS

A high expression of the PGE(2) receptors, EP1, EP2, EP3 and EP4 in primary neuroblastomas, independent of biological and clinical characteristics, was detected using immunohistochemistry. In addition, mRNA and protein corresponding to each of the receptors were detected in neuroblastoma cell lines. Immunofluorescent staining revealed localization of the receptors to the cellular membrane, in the cytoplasm, and in the nuclear compartment. Neuroblastoma cells produced PGE(2) and stimulation of serum-starved neuroblastoma cells with PGE(2) increased the intracellular concentration of calcium and cyclic AMP with subsequent phosphorylation of Akt. Addition of 16,16-dimethyl PGE(2) (dmPGE(2)) increased cell viability in a time, dose- and cell line-dependent manner. Treatment of neuroblastoma cells with a COX-2 inhibitor resulted in a diminished cell growth and viability that was reversed by the addition of dmPGE(2). Similarly, PGE(2) receptor antagonists caused a decrease in neuroblastoma cell viability in a dose-dependent manner.

CONCLUSIONS

These findings demonstrate that PGE(2) acts as an autocrine and/or paracrine survival factor for neuroblastoma cells. Hence, specific targeting of PGE(2) signaling provides a novel strategy for the treatment of childhood neuroblastoma through the inhibition of important mediators of tumor-promoting inflammation.

Stability of PCR targets for monitoring minimal residual disease in neuroblastoma

In neuroblastoma (NB) patients, minimal residual disease (MRD) can be detected by real-time quantitative PCR (qPCR) using NB-specific target genes, such as PHOX2B and TH. However, it is unknown whether the mRNA levels of these targets vary either during treatment or at relapse. If marker genes are not stably expressed, estimation of MRD levels in bone marrow (BM) or peripheral blood will be hampered. We studied the stability of a panel of qPCR markers in primary tumors at diagnosis compared with i) paired metastasis (n = 7), ii) treated (n = 10), and iii) relapse (n = 6) tumors. We also compared relative expression of the targets in iv) primary tumors and BM at diagnosis (n = 17), v) BM and peripheral blood at diagnosis (n = 20), vi) BM at diagnosis and during treatment (n = 26), and vii) BM from different puncture sides (n = 110). Especially at diagnosis, PCR target expression is quite stable. Accurate quantification is possible when expression level can be related to the primary tumor; however, PCR target expression can alter on treatment and at relapse. If the median value of relative expression of a panel of PCR targets is used, most variations due to treatment and outgrowth of subclones level out, allowing for reliable application and quantification of MRD-PCR targets in NB patients.

Targeting the Wnt pathway in cancer: the emerging role of Dickkopf-3

Aberrant activation of the Wnt signaling pathway is a major trait of many human cancers. Due to its vast implications in tumorigenesis and progression, the Wnt pathway has attracted considerable attention at several molecular levels, also with respect to developing novel cancer therapeutics. Indeed, research in Wnt biology has recently provided numerous clues, and evidence is accumulating that the secreted Wnt antagonist Dickkopf-related protein 3 (Dkk-3) and its regulators may constitute interesting therapeutic targets in the most important human cancers. Based on the currently available literature, we here review the knowledge on the biological role of Dkk-3 as an antagonist of the Wnt signaling pathway, the involvement of Dkk-3 in several stages of tumor development, the genetic and epigenetic mechanisms disrupting DKK3 gene function in cancerous cells, and the potential clinical value of Dkk-3 expression/DKK3 promoter methylation as a biomarker and molecular target in cancer diseases. In conclusion, Dkk-3 rapidly emerges as a key player in human cancer with auspicious tumor suppressive capacities, most of all affecting apoptosis and proliferation. Its gene expression is frequently downregulated by promoter methylation in almost any solid and hematological tumor entity. Clinically, evidence is accumulating of Dkk-3 being both a potential tumor biomarker and effective anti-cancer agent. Although further research is needed, re-establishing Dkk-3 expression in cancer cells holds promise as novel targeted molecular tumor therapy.

Dickkopf3 overexpression inhibits pancreatic cancer cell growth in vitro

AIM: To elucidate the role of dickkopf3 (Dkk3) in human pancreatic cancer cell growth.

METHODS: Dkk3 mRNA and protein expression in human pancreatic cancer cell lines were detected by real-time reverse transcription polymerase chain reaction (real-time RT-PCR), Western blotting and immunofluorescence. Methylation of the Dkk3 promoter sequence was examined by methylation-specific polymerase chain reaction (MSP) and Dkk3 mRNA expression was determined by real-time RT-PCR after 5-aza-2’-deoxycytidine (5-aza-dC) treatment. The effects of Dkk3 on cancer cell proliferation and in vitro sensitivity to gemcitabine were investigated by CellTiter 96^® AQueous One Solution Cell Proliferation Assay (MTS) after transfecting the Dkk3 expression plasmid into human pancreatic cancer cells. The expression of β-catenin, phosphorylated extracellular signal-regulated protein kinases (pERK) and extracellular signal-regulated protein kinases (ERK) was also examined by real-time RT-PCR and Western blotting after upregulating Dkk3 expression in human pancreatic cancer cells.

RESULTS: The results show that the expression levels of both Dkk3 mRNA and protein were low in all pancreatic cancer cell lines tested. The Dkk3 promoter sequence was methylated in the MIA PaCa-2 and AsPC-1 cell lines, which showed reduced Dkk3 expression. These two cell lines, which initially had a methylated Dkk3 promoter, showed increased Dkk3 mRNA expression that was dependent upon the dosage and timing of the DNA demethylating agent, 5-aza-dC, treatment (P < 0.05 or P < 0.01). When Dkk3 expression was upregulated following the transfection of a Dkk3 expression plasmid into MIA PaCa-2 cells, the ability of cells to proliferate decreased (P < 0.01), and the expression of β-catenin and pERK was downregulated (P < 0.01). Sensitivity to gemcitabine was enhanced in Dkk3 expression plasmid-transfected cells.

CONCLUSION: Our findings, for the first time, implicate Dkk3 as a tumor suppressor in human pancreatic cancer, through the downregulation of β-catenin expression via the ERK-mediated pathway.

Dickkopf-3 is regulated by the MYCN-induced miR-17-92 cluster in neuroblastoma

Neuroblastoma (NB) is a paediatric tumour with a remarkable diverse clinical behaviour. Approximately half of the high stage aggressive tumours are characterized by MYCN gene amplification but our understanding of the role of MYCN in NB oncogenesis is incomplete. Previous studies have shown that MYCN expression is inversely correlated with expression of Dickkopf-3 (DKK3), a gene encoding an extracellular protein with presumed tumour suppressor activity, but direct MYCN regulation of DKK3 was excluded leaving the mechanism of regulation unexplained. Given the recently established role of MYCN-regulated miRNAs in downregulation of protein-coding genes and predicted seeds for miR-17-92 cluster members within the DKK3 3'UTR, we hypothesized that this mechanism would act in MYCN regulation of DKK3. To investigate this, we used a validated miR-17-92-inducible cellular system and could demonstrate robust downregulation of DKK3 mRNA and protein levels upon miR-17-92 overexpression. Next, two of the three predicted miRNAs, miR-19b and miR-92a, were shown to lower DKK3 protein levels, in addition to measurable DKK3 mRNA knock-down by miR-92a. Direct interaction between miR-19b or miR-92a and the 3'UTR of DKK3 was validated using luciferase reporter assays. In conclusion, this study demonstrates that the MYCN-induced downregulation of DKK3 results from direct upregulation of miR-17-92 components effecting both DKK3 mRNA stability and translation which further contributes to the pleiotropic oncogenic effect of elevated MYCN levels. The strict MYCN-mediated regulation of DKK3 is suggestive for an important downstream function of the MYCN protein and thus warrants further investigations to unravel the role of DKK3 in NB.

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.

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.

Overexpression of Dickkopf 3 in hepatoblastomas and hepatocellular carcinomas

Dickkopf 3 (Dkk3) is a protein expressed at a very early stage of hepatogenesis. In this study, we examined whether Dkk3 was related to a premature or dedifferentiated nature in hepatoblastomas (HBLs) and hepatocellular carcinomas (HCCs). It was demonstrated that Dkk3 was overexpressed in HBLs and HCCs and that its expression was more frequent in the former than in the latter, being consistent with the fact that most HBLs show an embryonal or fetal hepatic histology, whereas there was no distinct relationship between Dkk3 expression and clinical data or histology. All of the HBLs expressed Dkk3, alpha-fetoprotein (AFP), or both proteins, suggesting that, similar to AFP, Dkk3 is another potentially useful biomarker detecting a wide range of HBLs. Furthermore, Dkk3 and AFP were expressed reciprocally in the tumors. These results suggest that Dkk3 may be related to the premature or dedifferentiated nature of HBLs and HCCs, whereas AFP may be related to a more differentiated nature. Thus, assessment of Dkk3 and AFP may be useful in the diagnosis of hepatic tumors.

Systematic identification of genes involved in divergent skeletal muscle growth rates of broiler and layer chickens

Background

The genetic closeness and divergent muscle growth rates of broilers and layers make them great models for myogenesis study. In order to discover the molecular mechanisms determining the divergent muscle growth rates and muscle mass control in different chicken lines, we systematically identified differentially expressed genes between broiler and layer skeletal muscle cells during different developmental stages by microarray hybridization experiment.

Results

Taken together, 543 differentially expressed genes were identified between broilers and layers across different developmental stages. We found that differential regulation of slow-type muscle gene expression, satellite cell proliferation and differentiation, protein degradation rate and genes in some metabolic pathways could give great contributions to the divergent muscle growth rates of the two chicken lines. Interestingly, the expression profiles of a few differentially expressed genes were positively or negatively correlated with the growth rates of broilers and layers, indicating that those genes may function in regulating muscle growth during development.

Conclusion

The multiple muscle cell growth regulatory processes identified by our study implied that complicated molecular networks involved in the regulation of chicken muscle growth. These findings will not only offer genetic information for identifying candidate genes for chicken breeding, but also provide new clues for deciphering mechanisms underlining muscle development in vertebrates.

Embryonal rhabdomyosarcoma as a second malignancy following multimodal therapy for advanced-stage neuroblastoma

Second malignancy as a long-term complication in survivors of advanced-stage neuroblastoma is rare, but it is becoming recognized more frequently. We report an unusual case of a soft-tissue sarcoma developing within a retroperitoneal primary following previous extensive treatment for metastatic neuroblastoma using multimodality imaging including PET/CT.