SIX2 Effects on Wilms Tumor Biology

Hallmark discoveries in the biology of Wilms tumour

The modern study of Wilms tumour was prompted nearly 50 years ago, when Alfred Knudson proposed the 'two-hit' model of tumour development. Since then, the efforts of researchers worldwide have substantially expanded our knowledge of Wilms tumour biology, including major advances in genetics - from cloning the first Wilms tumour gene to high-throughput studies that have revealed the genetic landscape of this tumour. These discoveries improve understanding of the embryonal origin of Wilms tumour, familial occurrences and associated syndromic conditions. Many efforts have been made to find and clinically apply prognostic biomarkers to Wilms tumour, for which outcomes are generally favourable, but treatment of some affected individuals remains challenging. Challenges are also posed by the intratumoural heterogeneity of biomarkers. Furthermore, preclinical models of Wilms tumour, from cell lines to organoid cultures, have evolved. Despite these many achievements, much still remains to be discovered: further molecular understanding of relapse in Wilms tumour and of the multiple origins of bilateral Wilms tumour are two examples of areas under active investigation. International collaboration, especially when large tumour series are required to obtain robust data, will help to answer some of the remaining unresolved questions.

NIK-mediated reactivation of SIX2 enhanced the CSC-like traits of hepatocellular carcinoma cells through suppressing ubiquitin-proteasome system

The critical roles of NF-κB Inducing Kinase (NIK) in tumor progression have been elucidated in various tumors; however, its effects on hepatocellular carcinoma (HCC) progression are still confusing. Here, we found that NIK level was upregulated in HCC tissues compared to that of normal tissues, and positively correlated with the levels of cancer stem cell (CSC) markers. Then we established HCC cells with NIK-stable knockdown and found that NIK knockdown suppressed the CSC-like traits of HCC cells through in vivo and in vitro experiments. Mechanistically, we revealed that SIX2 protein level, but not its mRNA level, was significantly reduced in HCC cells with NIK knockdown, which was rescued by MG132 treatment. Furthermore, NIK knockdown promoted the ubiquitination level of SIX2 and decreased its protein stability. Moreover, Six2 overexpression partially reversed the inhibition of NIK knockdown on the CSC-like traits of HCC cells. This study identified a novel NIK/SIX2 axis conferring HCC stemness.

Identification and Characterization of the Wilms Tumor Cancer Stem Cell

A nephrogenic progenitor cell (NP) with cancer stem cell characteristics driving Wilms tumor (WT) using spatial transcriptomics, bulk and single cell RNA sequencing, and complementary in vitro and transplantation experiments is identified and characterized. NP from WT samples with NP from the developing human kidney is compared. Cells expressing SIX2 and CITED1 fulfill cancer stem cell criteria by reliably recapitulating WT in transplantation studies. It is shown that self-renewal versus differentiation in SIX2+CITED1+ cells is regulated by the interplay between integrins ITGβ1 and ITGβ4. The spatial transcriptomic analysis defines gene expression maps of SIX2+CITED1+ cells in WT samples and identifies the interactive gene networks involved in WT development. These studies define SIX2+CITED1+ cells as the nephrogenic-like cancer stem cells of WT and points to the renal developmental transcriptome changes as a possible driver in regulating WT formation and progression.

Retinoic acid promotes differentiation of WiT49- but not of CCG99-11 Wilms tumour cells

BACKGROUND

Most children with Wilms tumour are successfully treated with multidrug chemotherapy and surgery. These treatments cause severe side effects for the patients, an issue that needs to be addressed by exploring other treatment options with less or no side effects. One option is to complement current therapies with agents that could potentially induce tumour cell differentiation, for example retinoic acid (RA).

AIMS

To facilitate quick assessment of an agent's effect on Wilms tumour differentiation by a rapid in vitro model system.

METHODS AND RESULTS

Here WiT49 and CCG99-11 Wilms tumour cells were treated with 10 μM RA for 72 h or 9 days. Cultured cells were scraped off from Petri dishes, pelleted and embedded in paraffin in the same way as clinical tumour specimens are preserved. Cell morphology and differentiation were evaluated by analyses of haematoxylin eosin (H&E) and immunohistochemical stainings. Based on H&E, WT1 and CKAE1/3 stainings, RA treatment induced further epithelial differentiation of WiT49 cells, whereas there was no sign of induced maturation in CCG99-11 cells. Ki67 staining showed that RA inhibited cell proliferation in both cell lines.

CONCLUSIONS

Our study shows that in vitro culturing of WiT49 and CCG99-11 cells, followed by pelleting and paraffin embedding of cell pellets, could aid in a quick evaluation of potential differentiating agents against Wilms tumour. In addition, our results strengthen previous results that retinoic acid could be a potential complement to regular Wilms tumour treatment.

Exploiting embryonic niche conditions to grow Wilms tumor blastema in culture

Introduction

Wilms Tumor (WT), or nephroblastoma, is the most common pediatric kidney cancer. Most WTs display a “favorable” triphasic histology, in which the tumor is comprised of blastemal, stromal, and epithelial cell types. Blastemal predominance after neoadjuvant chemotherapy or diffuse anaplasia (“unfavorable” histology; 5-8%) portend a worse prognosis. Blastema likely provide the putative cancer stem cells (CSCs), which retain molecular and histologic features characteristic of nephron progenitor cells (NPCs), within WTs. NPCs arise in the metanephric mesenchyme (MM) and populate the cap mesenchyme (CM) in the developing kidney. WT blastemal cells, like NPCs, similarly express markers, SIX2 and CITED1. Tumor xenotransplantation is currently the only dependable method to propagate tumor tissue for research or therapeutic screening, since efforts to culture tumors in vitro as monolayers have invariably failed. Therefore, a critical need exists to propagate WT stem cells rapidly and efficiently for high-throughput, real-time drug screening.

Methods

Previously, our lab developed niche conditions that support the propagation of murine NPCs in culture. Applying similar conditions to WTs, we assessed our ability to maintain key NPC "stemness" markers, SIX2, NCAM, and YAP1, and CSC marker ALDHI in cells from five distinct untreated patient tumors.

Results

Accordingly, our culture conditions maintained the expression of these markers in cultured WT cells through multiple passages of rapidly dividing cells.

Discussion

These findings suggest that our culture conditions sustain the WT blastemal population, as previously shown for normal NPCs. As a result, we have developed new WT cell lines and a multi-passage in vitro model for studying the blastemal lineage/CSCs in WTs. Furthermore, this system supports growth of heterogeneous WT cells, upon which potential drug therapies could be tested for efficacy and resistance.

Fgf8 promotes survival of nephron progenitors by regulating BAX/BAK-mediated apoptosis

Fibroblast growth factors (Fgfs) have long been implicated in processes critical to embryonic development, such as cell survival, migration, and differentiation. Several mouse models of organ development ascribe a prosurvival requirement specifically to FGF8. Here, we explore the potential role of prosurvival FGF8 signaling in kidney development. We have previously demonstrated that conditional deletion of Fgf8 in the mesodermal progenitors that give rise to the kidney leads to renal aplasia in the mutant neonate. Deleterious consequences caused by loss of FGF8 begin to manifest by E14.5 when massive aberrant cell death occurs in the cortical nephrogenic zone in the rudimentary kidney as well as in the renal vesicles that give rise to the nephrons. To rescue cell death in the Fgf8 mutant kidney, we inactivate the genes encoding the pro-apoptotic factors BAK and BAX. In a wild-type background, the loss of Bak and Bax abrogates normal cell death and has minimal effect on renal development. However, in Fgf8 mutants, the combined loss of Bak and Bax rescues aberrant cell death in the kidneys and restores some measure of kidney development: 1) the nephron progenitor population is greatly increased; 2) some glomeruli form, which are rarely observed in Fgf8 mutants; and 3) kidney size is rescued by about 50% at E18.5. The development of functional nephrons, however, is not rescued. Thus, FGF8 signaling is required for nephron progenitor survival by regulating BAK/BAX and for subsequent steps involving, as yet, undefined roles in kidney development.

The SIX Family of Transcription Factors: Common Themes Integrating Developmental and Cancer Biology

The sine oculis (SIX) family of transcription factors are key regulators of developmental processes during embryogenesis. Members of this family control gene expression to promote self-renewal of progenitor cell populations and govern mechanisms of cell differentiation. When the function of SIX genes becomes disrupted, distinct congenital defects develops both in animal models and humans. In addition to the embryonic setting, members of the SIX family have been found to be critical regulators of tumorigenesis, promoting cell proliferation, epithelial-to-mesenchymal transition, and metastasis. Research in both the fields of developmental biology and cancer research have provided an extensive understanding of SIX family transcription factor functions. Here we review recent progress in elucidating the role of SIX family genes in congenital disease as well as in the promotion of cancer. Common themes arise when comparing SIX transcription factor function during embryonic and cancer development. We highlight the complementary nature of these two fields and how knowledge in one area can open new aspects of experimentation in the other.

Circular RNA 0007255 regulates the progression of breast cancer through miR-335-5p/SIX2 axis

Background

Breast cancer (BC) is a common cancer in women worldwide. Emerging evidence has indicated that circular RNA hsa‐circ_0007255 (circ_0007255) is a prognostic mediator in BC progression. However, the functional role of circ_0007255 needs to be determined.

Methods

The expression of circ_0007255, microRNA (miR)‐335‐5p, and SIX Homeobox 2 (SIX2) was evaluated using quantitative real‐time polymerase chain reaction (qRT‐PCR) or western blot assay. Actinomycin D and RNase R treatment was performed to analyze the stability of circ_0007255. Additionally, Seahorse extracellular flux, colony formation and transwell analyses were carried out to detect oxygen consumption ratio (OCR), colony formation and cell mobility, respectively. The interaction between miR‐335‐5p and circ_0007255 or SIX2 was confirmed via dual‐luciferase reporter assay. A xenograft tumor model was established to explore the role of circ_0007255 in vivo.

Results

Circ_0007255 and SIX2 were overexpressed, but miR‐335‐5p was diminished in BC tissues and cells. Circ_0007255 absence inhibited oxygen consumption, colony formation, cell migration and invasion, and these effects were particularly abrogated via miR‐335‐5p upregulation in BC cells. Moreover, SIX2 deficiency eliminated the promotion effects of miR‐335‐5p inhibitor on oxygen consumption, colony formation, and cell mobility in BC cells. Importantly, circ_0007255 inhibited tumor growth in vivo. Mechanically, circ_0007255 was a sponge of miR‐335‐5p to regulate SIX2 expression in BC progression.

Conclusion

Circ_0007255 functioned as a novel oncogene in the progression of BC by regulating miR‐335‐5p/SIX2 axis, and might be a promising biomarker for BC treatment.

Key points

Significant findings of the study: Levels of circ_0007255 and SIX2 were upregulated, but miR‐335‐5p was diminished in BC tissues and cells. Circ_0007255 was an oncogene in BC development and exerted its function via miR‐335‐5p/SIX2 axis in BC. Tumor growth was reduced by circ_0007255 absence.

What this study adds: Circ_0007255 functioned as a novel oncogene in the progression of BC by regulating miR‐335‐5p/SIX2 axis, and might be a promising biomarker for BC treatment.

Identification of key genes and microRNAs involved in kidney Wilms tumor by integrated bioinformatics analysis

Wilms tumor (WT) is one of the most common types of pediatric solid tumors; however, its molecular mechanisms remain unclear. The present study aimed to identify key genes and microRNAs (miRNAs), and to predict the underlying molecular mechanisms of WT using integrated bioinformatics analysis. Original gene expression profiles were downloaded from the Gene Expression Omnibus (GEO; accession, GSE66405) and The Cancer Genome Atlas (TCGA) databases. Similarly, miRNA expression patterns were downloaded from GEO (accession, GSE57370) and TCGA. R version 3.5.0 software was used to identify differentially expressed genes (DEGs) and differentially expressed miRNAs (DEMs) using the limma and edgeR packages. Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology analyses were performed to examine the biological functions of the DEGs. Additionally, a protein-protein interaction (PPI) network was constructed to screen hub gene modules using Cytoscape software. By predicting target genes of the DEMs and integrating them with DEGs, the present study constructed a miRNA-mRNA regulatory network to predict the possible molecular mechanism of WT. Expression of hub genes was validated using the Oncomine database. A total of 613 genes and 29 miRNAs were identified to be differentially expressed in WT. By constructing a PPI network and screening hub gene modules, 5 upregulated genes, including BUB1 mitotic checkpoint serine/threonine kinase, BUB1B mitotic checkpoint serine/threonine kinase B, cell division cycle protein 45, cyclin B2 and pituitary tumor-transforming 1. These genes were identified to be associated with the cell cycle pathway, which suggested that these genes may serve important roles in WT. In addition, a miRNA-mRNA regulatory network was constructed and comprised 16 DEMs and 19 DEGs. In conclusion, key genes, miRNAs and the mRNA-miRNA regulatory network identified in the present study may improve understanding of the underlying molecular mechanisms in the occurrence and development of WT, and may aid the identification of potential biomarkers and therapeutic targets.

Blastemal NCAM+ALDH1+ Wilms' tumor cancer stem cells correlate with disease progression and poor clinical outcome: A pilot study

BACKGROUND

Cancer Stem Cells (CSCs) have been suggested as the culprit responsible for tumor resistance to treatment and disease recurrence. Wilms' tumor (WT) is a paradigm for studying the relation between development and tumorigenesis, showing three main histological elements: undifferentiated blastema, epithelia and stroma, mimicking human kidney development. NCAM + ALDH1+ cells were previously found to contain the cancer stem like-cell population in WT. Thus far, the correlation between histologic characterization of this cell population, clinicopathologic parameters and prognostic outcome has yet been investigated in WT.

PROCEDURES

Paraffin-imbedded primary WT specimens from twenty-four patients were immunostained for NCAM and ALDH1. Positivity and histologic compartment localization were determined by two independent observers, blinded to the clinical outcome. Clinicopathologic parameters and prognostic outcomes were determined based on the patients' medical records. The association of NCAM and ALDH1 co-localization with clinicopathologic characteristics was analyzed byχ²-test. Survival analysis was carried out by the log-rank test using Kaplan-Meier method.

RESULTS

Blastemal co-localization of NCAM and ALDH1 was observed in 33% of WTs. Metastases, ICE chemotherapy protocol, blastemal predominance following preoperative chemotherapy, recurrence and patient demise were found to significantly correlate with blastemal NCAM + ALDH1+ cell staining (p < 0.05). A significant inverse correlation between blastemal double positive cells, disease-free survival and overall survival was also observed.

CONCLUSIONS

WT blastemal NCAM + ALDH1+ CSCs significantly correlate with adverse clinicopathologic parameters and poorer prognosis. These results underscore the role of CSCs in disease progression. Additionally, this pilot study supports the addition of these markers for risk stratification of WTs.

FXR1 expression domain in Wilms tumor

BACKGROUND/PURPOSE

Wilms tumor (WT) is the most common childhood kidney cancer globally. Our prior unbiased proteomic screen of WT disparities revealed increased expression of Fragile X-Related 1 (FXR1) in Kenyan specimens where survival is dismal. FXR1 is an RNA-binding protein that associates with poor outcomes in multiple adult cancers. The aim of this study therefore was to validate and characterize the FXR1 expression domain in WT.

METHODS

Quantitative FXR1 gene expression was compared between WT, adjacent, adult, and fetal kidney specimens. The cellular and subcellular expression domain of FXR1 was characterized across these tissues using immunoperoxidase staining. RNA-sequencing of FXR1 was performed from WT and other pediatric malignancies to examine its broader target potential.

RESULTS

FXR1 was detected in all clinical WT specimens evaluated (n = 82), and as a result appeared independent of demographic, histology, or adverse event. Specific cytosolic staining was strongest in blastema, intermediate and variable in epithelia, and weakest in stroma. When present, areas of skeletal muscle differentiation stained strongly for FXR1. qPCR revealed increased FXR1 expression in WT compared to adult and adjacent kidney (p < 0.0002) but was similar to fetal kidney (p = 0.648). RNA-sequencing revealed expression of FXR1 in multiple pediatric tumors, greatest in rhabdomyosarcoma and WT.

CONCLUSIONS

FXR1 was expressed consistently across this broad sampling of WT and most robustly in the primitive blastema. Notably, FXR1 labeled a specific self-renewing progenitor population of the fetal kidney.

PPARG Negatively Modulates Six2 in Tumor Formation of Clear Cell Renal Cell Carcinoma

Substantial research has revealed that peroxisome proliferator-activated receptor-gamma (PPARG) plays a critical role in glucose homeostasis and lipid metabolism, and recent studies have shown different effects in the progression of different tumors. However, the role of PPARG and its target gene in clear cell renal cell carcinoma (ccRCC) are incompletely understood. Clinical data revealed abnormal glucolipid metabolism in primary ccRCC samples. In addition, transcriptional profiling indicated that PPARG expression was positively correlated, whereas Six2 expression was negatively correlated with the overall survival of ccRCC patients. Staining showed that PPARG was mainly expressed in tumor cell cytoplasm, and Six2 was localized to the nuclei. In a ccRCC cell line, PPARG activation promoted cell apoptosis, inhibited cell migration and proliferation, and reduced Six2 expression. Mechanistically, overexpressing Six2 downregulated E-cadherin expression and cell apoptosis, but PPARG activation reversed those effects. Taken together, PPARG promotes apoptosis and suppresses the migration and proliferation of ccRCC cells by inhibiting Six2. These findings reveal that the PPARG/Six2 axis acts as a central pathobiological mediator of ccRCC formation and as a potential therapeutic target for the treatment of patients with ccRCC.

Tumor-suppressive activity of Hnf1β in Wilms' tumor

Hepatocyte nuclear factor 1β (HNF1β) is a transcription factor belonging to the HNF-1 family and has been implicated in a number of cancers, but its role in Wilms' tumor (nephroblastoma) has not been addressed. Here, we compared its expression between Wilms' tumor patient kidney tissue and adjacent tissue based on the Oncomine database ( www.oncomine.com ). Cell proliferation, apoptosis, migration, and HNF1β expression level were analyzed in Wilms' tumor-derived G401 cells. Using a variety of mouse tissues (lung, heart, kidney, etc.), we found that HNF1β is the highest expression in the kidneys. Oncomine analysis further demonstrated that HNF1β has a lower expression in Wilms' tumor tissue than in paracancerous tissues. Overexpression of HNF1β decreased cell proliferation and migration, but promoted cell apoptosis. Knockdown of HNF1β produced the opposite results. These results indicated that HNF1β may play important roles in kidney development and function, and its activation may negatively regulate Wilms' tumor progression.

SIX2 Mediates Late-Stage Metastasis via Direct Regulation of SOX2 and Induction of a Cancer Stem Cell Program

The capacity for tumor cells to metastasize efficiently is directly linked to their ability to colonize secondary sites. Here we identify Six2, a developmental transcription factor, as a critical regulator of a breast cancer stem cell program that enables metastatic colonization. In several triple-negative breast cancer (TNBC) models, Six2 enhanced the expression of genes associated with embryonic stem cell programs. Six2 directly bound the Sox2 Srr2 enhancer, promoting Sox2 expression and downstream expression of Nanog, which are both key pluripotency factors. Regulation of Sox2 by Six2 enhanced cancer stem cell properties and increased metastatic colonization. Six2 and Sox2 expression correlated highly in breast cancers including TNBC, where a Six2 expression signature was predictive of metastatic burden and poor clinical outcome. Our findings demonstrate that a SIX2/SOX2 axis is required for efficient metastatic colonization, underscoring a key role for stemness factors in outgrowth at secondary sites. SIGNIFICANCE: These findings provide novel mechanistic insight into stemness and the metastatic outgrowth of triple-negative breast cancer cells.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/4/720/F1.large.jpg.

Molecular and epidemiologic characterization of Wilms tumor from Baghdad, Iraq

BACKGROUND

Wilms tumor (WT) is the most common childhood kidney cancer worldwide, yet its incidence and clinical behavior vary according to race and access to adequate healthcare resources. To guide and streamline therapy in the war-torn and resource-constrained city of Baghdad, Iraq, we conducted a first-ever molecular analysis of 20 WT specimens to characterize the biological features of this lethal disease within this challenged population.

METHODS

Next-generation sequencing of ten target genes associated with WT development and treatment resistance (WT1, CTNNB1, WTX, IGF2, CITED1, SIX2, p53, N-MYC, CRABP2, and TOP2A) was completed. Immunohistochemistry was performed for 6 marker proteins of WT (WT1, CTNNB1, NCAM, CITED1, SIX2, and p53). Patient outcomes were compiled.

RESULTS

Mutations were detected in previously described WT "hot spots" (e.g., WT1 and CTNNB1) as well as novel loci that may be unique to the Iraqi population. Immunohistochemistry showed expression domains most typical of blastemal-predominant WT. Remarkably, despite the challenges facing families and care providers, only one child, with combined WT1 and CTNNB1 mutations, was confirmed dead from disease. Median clinical follow-up was 40.5 months (range 6-78 months).

CONCLUSIONS

These data suggest that WT biology within a population of Iraqi children manifests features both similar to and unique from disease variants in other regions of the world. These observations will help to risk stratify WT patients living in this difficult environment to more or less intensive therapies and to focus treatment on cell-specific targets.

Six2 is involved in GATA1-mediated cell apoptosis in mouse embryonic kidney-derived cell lines

Six2 (Sine oculis homeobox 2), a homeodomain transcription factor, plays a crucial role in the regulation of mammalian nephrogenesis. It is also implicated in numerous biological functions, such as cell proliferation, apoptosis, and migration. However, the underlying regulatory mechanisms of Six2 remain largely unknown. In this study, we predicted that CRX, GATA1, HOXD8, and POU2F2 might target, binding to the promoter region of Six2 (~2000 bp) by bioinformatics analysis. Among the four genes, the predicted binding sequence of GATA1 is most highly conserved across species. Luciferase assays demonstrated that knockdown of GATA1 decreased the activity of Six2 promoter and qPCR result of Six2 expression was in consistent with this in 293T cells. Mutation of GATA1 binding sites of mSix2 promoter led to obvious decrease of the mSix2 promoter activity. Furthermore, knockdown of GATA1 decreased Six2 expression in mk3 cells and increased cell apoptosis of mk3 and mk4 compared with corresponding control cells, but this up-regulation can be rescued by Six2 overexpression. Our findings indicated that GATA1 may be a potential regulator of Six2-maintained population of nephron progenitor cells.

Functional KRAS mutations and a potential role for PI3K/AKT activation in Wilms tumors

Wilms tumor (WT) is the most common renal neoplasm of childhood and affects 1 in 10 000 children aged less than 15 years. These embryonal tumors are thought to arise from primitive nephrogenic rests that derive from the metanephric mesenchyme during kidney development and are characterized partly by increased Wnt/β-catenin signaling. We previously showed that coordinate activation of Ras and β-catenin accelerates the growth and metastatic progression of a murine WT model. Here, we show that activating KRAS mutations can be found in human WT. In addition, high levels of phosphorylated AKT are present in the majority of WT. We further show in a mouse model and in renal epithelial cells that Ras cooperates with β-catenin to drive metastatic disease progression and promotes in vitro tumor cell growth, migration, and colony formation in soft agar. Cellular transformation and metastatic disease progression of WT cells are in part dependent on PI3K/AKT activation and are inhibited via pharmacological inhibition of this pathway. Our studies suggest both KRAS mutations and AKT activation are present in WT and may represent novel therapeutic targets for this disease.

Biology and treatment of renal tumours in childhood

In Europe, almost 1000 children are diagnosed with a malignant renal tumour each year. The vast majority of cases are nephroblastoma, also known as Wilms' tumour (WT). Most children are treated according to Société Internationale d'Oncologie Pédiatrique Renal Tumour Study Group (SIOP-RTSG) protocols with pre-operative chemotherapy, surgery, and post-operative treatment dependent on stage and histology. Overall survival approaches 90%, but a subgroup of WT, with high-risk histology and/or relapsed disease, still have a much poorer prognosis. Outcome is similarly poor for the rare non-WT, particularly for malignant rhabdoid tumour of the kidney, metastatic clear cell sarcoma of the kidney (CCSK), and metastatic renal cell carcinoma (RCC). Improving outcome and long-term quality of life requires more accurate risk stratification through biological insights. Biomarkers are also needed to signpost potential targeted therapies for high-risk subgroups. Our understanding of Wilms' tumourigenesis is evolving and several signalling pathways, microRNA processing and epigenetics are now known to play pivotal roles. Most rhabdoid tumours display somatic and/or germline mutations in the SMARCB1 gene, whereas CCSK and paediatric RCC reveal a more varied genetic basis, including characteristic translocations. Conducting early-phase trials of targeted therapies is challenging due to the scarcity of patients with refractory or relapsed disease, the rapid progression of relapse and the genetic heterogeneity of the tumours with a low prevalence of individual somatic mutations. A further consideration in improving population survival rates is the geographical variation in outcomes across Europe. This review provides a comprehensive overview of the current biological knowledge of childhood renal tumours alongside the progress achieved through international collaboration. Ongoing collaboration is needed to ensure consistency of outcomes through standardised diagnostics and treatment and incorporation of biomarker research. Together, these objectives constitute the rationale for the forthcoming SIOP-RTSG 'UMBRELLA' study.

Genetic variation frequencies in Wilms' tumor: A meta-analysis and systematic review

Over the last few decades, numerous biomarkers in Wilms' tumor have been confirmed and shown variations in prevalence. Most of these studies were based on small sample sizes. We carried out a meta-analysis of the research published from 1992 to 2015 to obtain more precise and comprehensive outcomes for genetic tests. In the present study, 70 out of 5175 published reports were eligible for the meta-analysis, which was carried out using Stata 12.0 software. Pooled prevalence for gene mutations WT1, WTX, CTNNB1, TP53, MYCN, DROSHA, and DGCR8 was 0.141 (0.104, 0.178), 0.147 (0.110, 0.184), 0.140 (0.100, 0.190), 0.410 (0.214, 0.605), 0.071 (0.041, 0.100), 0.082 (0.048, 0.116), and 0.036 (0.026, 0.046), respectively. Pooled prevalence of loss of heterozygosity at 1p, 11p, 11q, 16q, and 22q was 0.109 (0.084, 0.133), 0.334 (0.295, 0.373), 0.199 (0.146, 0.252), 0.151 (0.129, 0.172), and 0.148 (0.108, 0.189), respectively. Pooled prevalence of 1q and chromosome 12 gain was 0.218 (0.161, 0.275) and 0.273 (0.195, 0.350), respectively. The limited prevalence of currently known genetic alterations in Wilms' tumors indicates that significant drivers of initiation and progression remain to be discovered. Subgroup analyses indicated that ethnicity may be one of the sources of heterogeneity. However, in meta-regression analyses, no study-level characteristics of indicators were found to be significant. In addition, the findings of our sensitivity analysis and possible publication bias remind us to interpret results with caution.

A Murine Model of K-RAS and β-Catenin Induced Renal Tumors Expresses High Levels of E2F1 and Resembles Human Wilms Tumor

PURPOSE

Wilms tumor is the most common renal neoplasm of childhood. We previously found that restricted activation of the WNT/β-catenin pathway in renal epithelium late in kidney development is sufficient to induce small primitive neoplasms with features of epithelial Wilms tumor. Metastatic disease progression required simultaneous addition of an activating mutation of the oncogene K-RAS. We sought to define the molecular pathways activated in this process and their relationship to human renal malignancies.

MATERIALS AND METHODS

Affymetrix® expression microarray data from murine kidneys with activation of K-ras and/or Ctnnb1 (β-catenin) restricted to renal epithelium were analyzed and compared to publicly available expression data on normal and neoplastic human renal tissue. Target genes were verified by immunoblot and immunohistochemistry.

RESULTS

Mouse kidney tumors with activation of K-ras and Ctnnb1, and human renal malignancies had similar mRNA expression signatures and were associated with activation of networks centered on β-catenin and TP53. Up-regulation of WNT/β-catenin targets (MYC, Survivin, FOXA2, Axin2 and Cyclin D1) was confirmed by immunoblot. K-RAS/β-catenin murine kidney tumors were more similar to human Wilms tumor than to other renal malignancies and demonstrated activation of a TP53 dependent network of genes, including the transcription factor E2F1. Up-regulation of E2F1 was confirmed in murine and human Wilms tumor samples.

CONCLUSIONS

Simultaneous activation of K-RAS and β-catenin in embryonic renal epithelium leads to neoplasms similar to human Wilms tumor and associated with activation of TP53 and up-regulation of E2F1. Further studies are warranted to evaluate the role of TP53 and E2F1 in human Wilms tumor.

Genetic and chromosomal alterations in Kenyan Wilms Tumor

Wilms tumor (WT) is the most common childhood kidney cancer worldwide and poses a cancer health disparity to black children of sub-Saharan African ancestry. Although overall survival from WT at 5 years exceeds 90% in developed countries, this pediatric cancer is alarmingly lethal in sub-Saharan Africa and specifically in Kenya (36% survival at 2 years). Although multiple barriers to adequate WT therapy contribute to this dismal outcome, we hypothesized that a uniquely aggressive and treatment-resistant biology compromises survival further. To explore the biologic composition of Kenyan WT (KWT), we completed a next generation sequencing analysis targeting 10 WT-associated genes and evaluated whole-genome copy number variation. The study cohort was comprised of 44 KWT patients and their specimens. Fourteen children are confirmed dead at 2 years and 11 remain lost to follow-up despite multiple tracing attempts. TP53 was mutated most commonly in 11 KWT specimens (25%), CTNNB1 in 10 (23%), MYCN in 8 (18%), AMER1 in 5 (11%), WT1 and TOP2A in 4 (9%), and IGF2 in 3 (7%). Loss of heterozygosity (LOH) at 17p, which covers TP53, was detected in 18% of specimens examined. Copy number gain at 1q, a poor prognostic indicator of WT biology in developed countries, was detected in 32% of KWT analyzed, and 89% of these children are deceased. Similarly, LOH at 11q was detected in 32% of KWT, and 80% of these patients are deceased. From this genomic analysis, KWT biology appears uniquely aggressive and treatment-resistant.

Assessment of promoter methylation and expression of SIX2 as a diagnostic and prognostic biomarker in Wilms' tumor

This study was designed to evaluate the utility of expression and DNA methylation patterns of the sine oculis homeobox homolog 2 (SIX2) gene in early diagnosis and prognosis of Wilms' tumor (WT). Methylation-specific polymerase chain reaction (MSP), real-time quantitative polymerase chain reaction (qRT-PCR), receiver operating characteristic (ROC), and survival curve analyses were utilized to measure the expression and DNA methylation patterns of SIX2 in a cohort of WT tissues, with a view to assessing their diagnostic and prognostic value. Relative expression of SIX2 mRNA was higher, while the promoter methylation level was lower in the WT than control group (P < 0.05) and closely associated with poor survival prognosis of WT children (P < 0.05). Increased expression and decreased methylation of SIX2 were correlated with increasing tumor size, clinical stage, vascular invasion, and unfavorable histological differentiation (P < 0.05). ROC curve analysis showed areas under the curve (AUCs) of 0.579 for methylation and 0.917 for expression in WT venous blood, indicating higher diagnostic yield of preoperative SIX2 expression. The preoperative venous blood SIX2 expression level serves as an underlying biomarker for early diagnosis of WT. SIX2 overexpression and concomitantly decreased promoter methylation are significantly associated with poor survival of WT children.