β-Catenin and K-RAS synergize to form primitive renal epithelial tumors with features of epithelial Wilms' tumors

Mice with renal-specific alterations of stem cell-associated signaling develop symptoms of chronic kidney disease but surprisingly no tumors

Previously, we found that Wnt and Notch signaling govern stem cells of clear cell kidney cancer (ccRCC) in patients. To mimic stem cell responses in the normal kidney in vitro in a marker-unbiased fashion, we have established tubular organoids (tubuloids) from total single adult mouse kidney epithelial cells in Matrigel and serum-free conditions. Deep proteomic and phosphoproteomic analyses revealed that tubuloids resembled renewal of adult kidney tubular epithelia, since tubuloid cells displayed activity of Wnt and Notch signaling, long-term proliferation and expression of markers of proximal and distal nephron lineages. In our wish to model stem cell-derived human ccRCC, we have generated two types of genetic double kidney mutants in mice: Wnt-β-catenin-GOF together with Notch-GOF and Wnt-β-catenin-GOF together with a most common alteration in ccRCC, Vhl-LOF. An inducible Pax8-rtTA-LC1-Cre was used to drive recombination specifically in adult kidney epithelial cells. We confirmed mutagenesis of β-catenin, Notch and Vhl alleles on DNA, protein and mRNA target gene levels. Surprisingly, we observed symptoms of chronic kidney disease (CKD) in mutant mice, but no increased proliferation and tumorigenesis. Thus, the responses of kidney stem cells in the tubuloid and genetic systems produced different phenotypes, i.e. enhanced renewal versus CKD.

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.

Novel findings and expansion of phenotype in a mosaic RASopathy caused by somatic KRAS variants

Mosaic KRAS variants and other RASopathy genes cause oculoectodermal, encephalo-cranio-cutaneous lipomatosis, and Schimmelpenning-Feuerstein-Mims syndromes, and a spectrum of vascular malformations, overgrowth and other associated anomalies, the latter of which are only recently being characterized. We describe eight individuals in total (six unreported cases and two previously reported cases) with somatic KRAS variants and variably associated features. Given the findings of somatic overgrowth (in seven individuals) and vascular or lymphatic malformations (in eight individuals), we suggest mosaic RASopathies (mosaic KRAS variants) be considered in the differential diagnosis for individuals presenting with asymmetric overgrowth and lymphatic or vascular anomalies. We expand the association with embryonal tumors, including the third report of embryonal rhabdomyosarcoma, as well as novel findings of Wilms tumor and nephroblastomatosis in two individuals. Rare or novel findings in our series include the presence of epilepsy, polycystic kidneys, and T-cell deficiency in one individual, and multifocal lytic bone lesions in two individuals. Finally, we describe the first use of targeted therapy with a MEK inhibitor for an individual with a mosaic KRAS variant. The purposes of this report are to expand the phenotypic spectrum of mosaic KRAS-related disorders, and to propose possible mechanisms of pathogenesis, and surveillance of its associated findings.

Non-coding RNAs in Wilms' tumor: biological function, mechanism, and clinical implications

Non-coding RNAs are involved with maintenance and regulation of physiological mechanisms and are involved in pathological processes, such as cancer. Among the small ncRNAs, miRNAs are the most explored in tumorigenesis, metastasis development, and resistance to chemotherapy. These small molecules of ~ 22 nucleotides are modulated during early renal development, involved in the regulation of gene expression and Wilms' tumor progression. Wilms' tumors are embryonic tumors with few mutations and complex epigenetic dysregulation. In recent years, the small ncRNAs have been explored as potentially related both in physiological development and in the tumorigenesis of several types of cancer. Besides, genes regulated by miRNAs are related to biological pathways as PI3K, Wnt, TGF-β, and Hippo signaling pathways, among others, which may be involved with the underlying mechanisms of resistance to chemotherapy, and in this way, it has emerged as potential targets for cancer therapies, including for Wilms' tumors.

Bilateral Nephroblastic Tumors and a Complex Renal Vascular Anomaly in a Patient With a Mosaic RASopathy: Novel Histopathologic Features and Molecular Insights

Mosaic RASopathies are an emerging group of disorders characterized by mosaic or post-zygotic activating mutations in genes of the RAS/MAPKinase signaling pathway. The phenotype is highly variable, ranging from limited or localized forms to cases with a syndromic presentation with extensive or multiorgan involvement, and also overlaps with other mosaic disorders. While there are several reports of malignancies in patients with mosaic RASopathies, specifically rhabdomyosarcoma and transitional urothelial carcinoma, the lifetime risk and molecular mechanisms that lead to the development of malignancies remain unclear. We report a 22-month-old boy with a somatic RASopathy due to an underlying KRAS p.G12D mutation who presented with a large unilateral epidermal nevus, asymmetric lower limb overgrowth with lytic and sclerotic bone lesions, capillary malformation, bilateral nephrogenic rests and Wilms tumors, and a novel complex renal vascular anomaly that resembles Fibro-Adipose Vascular Anomaly (FAVA). This report further expands the phenotypic spectrum of somatic RASopathies, and discusses the potential phenotypic and pathogenetic overlap with PIK3CA-related overgrowth disorders, specifically CLOVES. The occurrence of a secondary cancer hotspot mutation (FBXW7 p.R479G) in the Wilms tumor, but not the associated nephrogenic rest, moreover suggests that additional driver mutations are involved in the development of Wilms tumor in somatic overgrowth disorders.

The Vanderbilt O'Brien Kidney Center

The Vanderbilt O'Brien Kidney Center (VOKC) is one of the eight National Institutes of Health P30-funded centers in the United States. The mission of these core-based centers is to provide technical and conceptual support to enhance and facilitate research in the field of kidney diseases. The goal of the VOKC is to provide support to understand mechanisms and identify potential therapies for acute and chronic kidney disease. The services provided by the VOKC are meant to help the scientific community to have the right support and tools as well as to select the right animal model, statistical analysis, and clinical study design to perform innovative research and translate discoveries into personalized care to prevent, diagnose, and cure kidney disease. To achieve these goals, the VOKC has in place a program to foster collaborative investigation into critical questions of kidney disease, to personalize diagnosis and treatment of kidney disease, and to disseminate information about kidney disease and the benefits of VOKC services and research. The VOKC is complemented by state-of-the-art cores and an education and outreach program whose goals are to provide an educational platform to enhance the study of kidney disease, to publicize information about services available through the VOKC, and to provide information about kidney disease to patients and other interested members of the community. In this review, we highlight the major services and contributions of the VOKC.

Wilms tumor-suppressing peptide inhibits proliferation and induces apoptosis of Wilms tumor cells in vitro and in vivo

BACKGROUND

Our previous study identified a Wilms tumor-suppressing peptide (WTSP) that was upregulated in healthy children, but downregulated in children with Wilms tumor (WT). This study aimed to investigate the effect of WTSP on WT growth in vivo and in vitro.

METHODS

WTSP was synthesized by solid-phase synthesis of FOMC-protected amino acids. Cell growth curve, cytotoxicity, and apoptosis of WTSP-treated human WT cell line (SK-NEP-1) were determined by cell count, Cell Counting Kit-8 assay, and flow cytometry. The expression of key proteins of four WT-associated signaling pathways was determined by real-time PCR and western blotting. The WT xenograft mouse model was established by the armpit injection of SK-NEP-1 cells. The TUNEL assay was used to detect apoptosis in mouse tumor cells.

RESULTS

WTSP inhibited the proliferation of SK-NEP-1 cells in a dose- and time-dependent manner, and it arrested SK-NEP-1 cells in G2/M phase. WTSP-treated cells exhibited a low expression of PCNA and Bcl-2 and high expression of Bax. The expression of β-catenin was markedly changed after WTSP treatment. WTSP-treated mice had significantly smaller tumors than untreated mice.

CONCLUSION

Our findings indicated an anti-tumor effect of WTSP, which is correlated with Wnt/β-catenin pathway. This newly identified peptide may exert a therapeutic effect of WT in the future.

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.

The genetic changes of Wilms tumour

Wilms tumour is the most common renal malignancy of childhood. The disease is curable in the majority of cases, albeit at considerable cost in terms of late treatment-related effects in some children. However, one in ten children with Wilms tumour will die of their disease despite modern treatment approaches. The genetic changes that underpin Wilms tumour have been defined by studies of familial cases and by unbiased DNA sequencing of tumour genomes. Together, these approaches have defined the landscape of cancer genes that are operative in Wilms tumour, many of which are intricately linked to the control of fetal nephrogenesis. Advances in our understanding of the germline and somatic genetic changes that underlie Wilms tumour may translate into better patient outcomes. Improvements in risk stratification have already been seen through the introduction of molecular biomarkers into clinical practice. A host of additional biomarkers are due to undergo clinical validation. Identifying actionable mutations has led to potential new targets, with some novel compounds undergoing testing in early phase trials. Avenues that warrant further exploration include targeting Wilms tumour cancer genes with a non-redundant role in nephrogenesis and targeting the fetal renal transcriptome.

Association of KRAS and NRAS gene polymorphisms with Wilms tumor risk: a four-center case-control study

Wilms tumor is a type of pediatric solid tumor that arises partly due to somatic and germline mutations. Single-nucleotide polymorphisms (SNPs) in the RAS gene reportedly modify the risk for several types of human malignancies. We conducted a multicenter study to investigate whether RAS gene variants predispose individuals to Wilms tumor. Four SNPs in RAS were genotyped in 355 Wilms tumor cases and 1070 controls. The SNPs included rs12587 G>T, rs7973450 A>G and rs7312175 G>A in KRAS, and rs2273267 A>T in NRAS. Individuals harboring the rs12587 GT genotype were more likely to develop Wilms tumor than those carrying the GG genotype (adjusted odds ratio [OR]=1.30, 95% confidence interval [CI]=1.004-1.68, P=0.046). However, the other three SNPs seemed not to influence the risk for Wilms tumor. Compared to individuals without a risk genotype, those harboring one to three KRAS risk genotypes had an adjusted OR of 1.28 for developing Wilms tumor (95% CI=1.002-1.64, P=0.048). Stratification analysis revealed that rs12587 GT/TT was associated with Wilms tumor risk in children >18 months old (adjusted OR=1.39, 95% CI=1.02-1.89, P=0.037). Our findings indicate that the rs12587 G>T polymorphism in KRAS is associated with increased Wilms tumor susceptibility.

β-Catenin directs the transformation of testis Sertoli cells to ovarian granulosa-like cells by inducing Foxl2 expression

Sertoli and granulosa cells are two major types of somatic cells in male and female gonads, respectively. Previous studies have shown that Sertoli and granulosa cells are derived from common progenitor cells and that differentiation of these two cell types is regulated by sex differentiation genes. The signaling pathway including the adhesion and transcription factor Ctnnb1 (cadherin-associated protein, β1, also known as β-catenin) regulates differentiation of granulosa cells in the absence of the transcription factor Sry, and overactivation of β-catenin in the presence of Sry leads to granulosa prior to sex determination. Surprisingly, our previous study found that β-catenin overactivation in Sertoli cells after sex determination can also cause disruption of the testicular cord and aberrant testis development. However, the underlying molecular mechanism was unclear. In this study, we found that constitutive activation of Ctnnb1 in Sertoli cells led to ectopic expression of the granulosa cell-specific marker FOXL2 in testes. Co-staining experiments revealed that FOXL2-positive cells were derived from Sertoli cells, and Sertoli cells were transformed into granulosa-like cells after Ctnnb1 overactivation. Further studies demonstrated that CTNNB1 induced Foxl2 expression by directly binding to transcription factor Tcf/Lef-binding sites in the FOXL2 promoter region. We also found that direct overexpression of Foxl2 decreased the expression of Sertoli cell-specific genes in primary Sertoli cells. Taken together, these results demonstrate that repression of β-catenin (CTNNB1) signaling is required for lineage maintenance of Sertoli cells. Our study provides a new mechanism for Sertoli cell lineage maintenance during gonad development.

Bilateral Wilms tumour: a review of clinical and molecular features

Wilms tumour (WT) is the most common paediatric kidney cancer and affects approximately one in 10 000 children. The tumour is associated with undifferentiated embryonic lesions called nephrogenic rests (NRs) or, when diffuse, nephroblastomatosis. WT or NRs can occur in both kidneys, termed bilateral disease, found in only 5-8% of cases. Management of bilateral WT presents a major clinical challenge in terms of maximising survival, preserving renal function and understanding underlying genetic risk. In this review, we compile clinical data from 545 published cases of bilateral WT and discuss recent progress in understanding the molecular basis of bilateral WT and its associated precursor NRs in the context of the latest radiological, surgical and epidemiological features.

Pharmacologic Inhibition of β-Catenin With Pyrvinium Inhibits Murine and Human Models of Wilms Tumor

Wilms tumor (WT) is the most common renal malignancy in children and the fourth most common pediatric solid malignancy in the US. Although the mechanisms underlying the WT biology are complex, these tumors most often demonstrate activation of the canonical Wnt/β-catenin pathway. We and others have shown that constitutive activation of β-catenin restricted to the renal epithelium is sufficient to induce primitive renal epithelial tumors, which resemble human WT. Here we demonstrate that pharmacologic inhibition of β-catenin gene transcription with pyrvinium inhibits tumor growth and metastatic progression in a murine model of WT. Cellular invasion is significantly inhibited in both murine WT-like and human WT cells and is accompanied by downregulation of the oncogenes Myc and Birc5 (survivin). Our studies provide proof of the concept that the canonical Wnt/β-catenin pathway may be a novel therapeutic target in the management of WT.

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.

Nephron Progenitor But Not Stromal Progenitor Cells Give Rise to Wilms Tumors in Mouse Models with β-Catenin Activation or Wt1 Ablation and Igf2 Upregulation

Wilms tumor, a common childhood tumor of the kidney, is thought to arise from undifferentiated renal mesenchyme. Variable tumor histology and the identification of tumor subsets displaying different gene expression profiles suggest that tumors may arise at different stages of mesenchyme differentiation and that this ontogenic variability impacts tumor pathology, biology, and clinical outcome. To test the tumorigenic potential of different cell types in the developing kidney, we used kidney progenitor-specific Cre recombinase alleles to introduce Wt1 and Ctnnb1 mutations, two alterations observed in Wilms tumor, into embryonic mouse kidney, with and without biallelic Igf2 expression, another alteration that is observed in a majority of tumors. Use of a Cre allele that targets nephron progenitors to introduce a Ctnnb1 mutation that stabilizes β-catenin resulted in the development of tumors with a predominant epithelial histology and a gene expression profile in which genes characteristic of early renal mesenchyme were not expressed. Nephron progenitors with Wt1 ablation and Igf2 biallelic expression were also tumorigenic but displayed a more triphasic histology and expressed early metanephric mesenchyme genes. In contrast, the targeting of these genetic alterations to stromal progenitors did not result in tumors. These data demonstrate that committed nephron progenitors can give rise to Wilms tumors and that committed stromal progenitors are less tumorigenic, suggesting that human Wilms tumors that display a predominantly stromal histology arise from mesenchyme before commitment to a stromal lineage.

K-Ras, H-Ras, N-Ras and B-Raf mutation and expression analysis in Wilms tumors: association with tumor growth

Nephroblastoma (Wilms tumor) is a kidney neoplasia, predominately occurring at very young age, resulting from the malignant transformation of renal stem cells. The Ras proto-oncogenes and B-Raf are members of an intracellular cascade pathway, which regulates cell growth and differentiation, and ultimately cancer development. Our objective was to determine the mutation rate and to measure the mRNA levels of the three Ras genes and of B-Raf in formalin-fixed paraffin-embedded tissue samples from 32 patients with nephroblastoma and 10 controls. No mutations were detected in the four studied genes among our Wilms tumors cases, while Ras and B-Raf expression was higher in malignant samples versus controls. Statistical analysis revealed a positive correlation of K-Ras (p < 0.001) and B-Raf (p = 0.006) with tumor size, a negative correlation of K-Ras (p = 0.041) and H-Ras (p = 0.033) with the percentage of tissue necrosis, and an association of N-Ras (p = 0.047) and B-Raf (p = 0.044) with tissue histology. From the above, we deduce that although Ras and B-Raf mutations are rare events in Wilms tumors, their expression pattern suggests that they play an important role in the development and progression of this malignancy.

Senescence Process in Primary Wilms' Tumor Cell Culture Induced by p53 Independent p21 Expression

Wilms tumor (WT) is an embryonal tumor occurring in developing kidney tissue. WT cells showing invasive cancer characteristics, also retain renal stem cell behaviours. In-vitro culture of WT is hampered by limited replicative potential. This study aimed to establish a longterm culture of WT cells to enable the study of molecular events to attempt to explain its cellular senescence.

METHODS

Primary cell cultures from fresh WT tumor specimen were established. Of 5 cultures tried, only 1 could be propagated for more than 7 passages. One culture, identified as PSU-SK-1, could be maintained > 35 passages and was then subjected to molecular characterization and evaluation for cancer characteristics. The cells consistently harbored concomitant mutations of CTNNB1 (Ser45Pro) and WT1 (Arg413Stop) thorough the cultivation. On Transwell invasion assays, the cells exhibited migration and invasion at 55% and 27% capability of the lung cancer cells, A549. On gelatin zymography, PSU-SK-1 showed high expression of the matrix metaloproteinase. The cells exhibited continuous proliferation with 24-hour doubling time until passages 28-30 when the growth slowed, showing increased cell size, retention of cells in G1/S proportion and positive β-galactosidase staining. As with those evidence of senescence in advanced cell passages, expression of p21 and cyclin D1 increased when the expression of β-catenin and its downstream protein, TCF, declined. There was also loss-of-expression of p53 in this cell line. In conclusion, cellular senescence was responsible for limited proliferation in the primary culture of WT, which was also associated with increased expression of p21 and was independent of p53 expression. Decreased activation of the Wnt signalling might explain the induction of p21 expression.

Multi-organ Mapping of Cancer Risk

Cancers are distributed unevenly across the body, but the importance of cell intrinsic factors such as stem cell function in determining organ cancer risk is unknown. Therefore, we used Cre-recombination of conditional lineage tracing, oncogene, and tumor suppressor alleles to define populations of stem and non-stem cells in mouse organs and test their life-long susceptibility to tumorigenesis. We show that tumor incidence is determined by the life-long generative capacity of mutated cells. This relationship held true in the presence of multiple genotypes and regardless of developmental stage, strongly supporting the notion that stem cells dictate organ cancer risk. Using the liver as a model system, we further show that damage-induced activation of stem cell function markedly increases cancer risk. Therefore, we propose that a combination of stem cell mutagenesis and extrinsic factors that enhance the proliferation of these cell populations, creates a "perfect storm" that ultimately determines organ cancer risk. VIDEO ABSTRACT.

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.

Acute Inhibition of MEK Suppresses Congenital Melanocytic Nevus Syndrome in a Murine Model Driven by Activated NRAS and Wnt Signaling

Congenital melanocytic nevus (CMN) syndrome is the association of pigmented melanocytic nevi with extra-cutaneous features, classically melanotic cells within the central nervous system, most frequently caused by a mutation of NRAS codon 61. This condition is currently untreatable and carries a significant risk of melanoma within the skin, brain, or leptomeninges. We have previously proposed a key role for Wnt signaling in the formation of melanocytic nevi, suggesting that activated Wnt signaling may be synergistic with activated NRAS in the pathogenesis of CMN syndrome. Some familial pre-disposition suggests a germ-line contribution to CMN syndrome, as does variability of neurological phenotypes in individuals with similar cutaneous phenotypes. Accordingly, we performed exome sequencing of germ-line DNA from patients with CMN to reveal rare or undescribed Wnt-signaling alterations. A murine model harboring activated NRAS(Q61K) and Wnt signaling in melanocytes exhibited striking features of CMN syndrome, in particular neurological involvement. In the first model of treatment for this condition, these congenital, and previously assumed permanent, features were profoundly suppressed by acute post-natal treatment with a MEK inhibitor. These data suggest that activated NRAS and aberrant Wnt signaling conspire to drive CMN syndrome. Post-natal MEK inhibition is a potential candidate therapy for patients with this debilitating condition.

Hyperglycemia in the absence of cilia accelerates cystogenesis and induces renal damage

In polycystic kidney disease (PKD), the rate of cyst formation and disease progression is highly variable. The lack of predictability in disease progression may be due to additional environmental factors or pathophysiological processes called "third hits." Diabetes is a growing epidemic, and recent studies suggest that PKD patients may be at an increased risk for this disease. We sought to determine if hyperglycemia enhances the initiation and rate of cystogenesis. Tamoxifen was administered to adult Ift88 conditional floxed allele mice to induce cilia loss in the presence of Cre. Subsequent administration of streptozotocin resulted in equivalent hyperglycemia in cilia(+) and cilia(-) mice. Hyperglycemia with loss of cilia increased the rate of cyst formation and cell proliferation. Structural and functional alterations in the kidney, including focal glomerular foot process effacement, interstitial inflammation, formation of primitive renal tubules, polyuria, and increased proteinuria, were also observed in hyperglycemic cilia(-) mice. Gene array analysis indicated enhanced Wnt and epithelial-to-mesenchymal transition signaling in the kidney of hyperglycemic cilia(-) mice. These data show that hyperglycemia, in the absence of cilia, results in renal structural and functional damage and accelerates cystogenesis, suggesting that diabetes is a risk factor in the progression of PKD.

The yin and yang of kidney development and Wilms' tumors

Wilms' tumor, or nephroblastoma, is the most common pediatric renal cancer. The tumors morphologically resemble embryonic kidneys with a disrupted architecture and are associated with undifferentiated metanephric precursors. Here, we discuss genetic and epigenetic findings in Wilms' tumor in the context of renal development. Many of the genes implicated in Wilms' tumorigenesis are involved in the control of nephron progenitors or the microRNA (miRNA) processing pathway. Whereas the first group of genes has been extensively studied in normal development, the second finding suggests important roles for miRNAs in general-and specific miRNAs in particular-in normal kidney development that still await further analysis. The recent identification of Wilms' tumor cancer stem cells could provide a framework to integrate these pathways and translate them into new or improved therapeutic interventions.

N -Methyl- N -nitrosourea-induced Renal Tumors in Rats: Immunohistochemical Comparison to Human Wilms Tumors

N-Methyl-N-nitrosourea (MNU)-induced renal tumors in rats and Wilms tumors in humans were compared. Renal mesenchymal tumors (RMTs) and nephroblastomas (blastemal and epithelial components) in female Lewis rats treated with a single intraperitoneal injection of 50 mg/kg MNU at birth and Wilms tumors (blastemal, epithelial and mesenchymal components) in humans were analyzed for the expression of pancytokeratin (CK), vimentin, p63, α-smooth muscle actin (SMA), desmin, S-100, CD57, CD117/c-kit, Wilms tumor 1 protein (WT1) and β-catenin. The mesenchymal components of rat RMTs and human Wilms tumors expressed vimentin, SMA and β-catenin. The blastemal components of rat nephroblastomas and human Wilms tumors expressed vimentin, CD117/c-kit and β-catenin. The epithelial components of rat nephroblastomas and human Wilms tumors expressed vimentin and β-catenin. WT1 was expressed in different cellular components of rat tumors as compared with human Wilms tumors; the expression was seen in mesenchymal tumors and blastemal components of nephroblastomas in rats and epithelial components in human Wilms tumors. CK, p63 and CD57 were not expressed in rat RMTs or nephroblastomas, while CK and WT1 were expressed in epithelial components and CD57 was expressed in blastemal and epithelial components of human Wilms tumors. Rat and human tumors were universally negative for the expression of desmin and S-100. The immunohistochemical characteristics of rat renal tumors and human Wilms tumors may provide valuable information on the differences in renal oncogenesis and biology between the two species.

An anti-apoptotic protein human survivin is a direct inhibitor of caspase-3 and -7

Survivin, an apoptosis inhibitor/cell-cycle regulator, is critically required for suppression of apoptosis and ensuring normal cell division in the G2/M phase of the cell cycle. It is highly expressed in a cell cycle-regulated manner and localizes together with caspase-3 on microtubules within centrosomes. Whether survivin is a physiologically relevant caspase inhibitor has been unclear due to the difficulties with obtaining correctly folded survivin and finding the right conditions for inhibition assay. In this study, recombinant, active human survivin was expressed in Escherichia coli and purified to homogeneity. The protein, existing as a homodimer in solution, binds caspase-3 and -7 tightly with dissociation constants of 20.9 and 11.5 nM, respectively, when evaluated by surface plasmon resonance spectroscopy. Consistently, survivin potently inhibits the cleavage of a physiological substrate poly(ADP-ribose) polymerase and an artificial tetrapeptide by caspase-3 and -7 in vitro with apparent inhibition constants of 36.0 and 16.5 nM, respectively. The data suggest that sequestering caspase-3 and -7 in inhibited states on microtubules is at least one mechanism of survivin in the suppression of default apoptosis in the G2/M phase. The localization of survivin on microtubules, which is essential for its function, should increase the protective activity at the action site.