Cancer. Converging on beta-catenin in Wilms tumor

Tumor Suppressive Role of MUC6 in Wilms Tumor via Autophagy-Dependent β-Catenin Degradation

Wilms tumor is the most common renal malignancy in children. Known gene mutations account for about 40% of all wilms tumor cases, but the full map of genetic mutations in wilms tumor is far from clear. Whole genome sequencing and RNA sequencing were performed in 5 pairs of wilms tumor tissues and adjacent normal tissues to figure out important genetic mutations. Gene knock-down, CRISPR-induced mutations were used to investigate their potential effects in cell lines and in-vivo xenografted model. Mutations in seven novel genes (MUC6, GOLGA6L2, GPRIN2, MDN1, MUC4, OR4L1 and PDE4DIP) occurred in more than one patient. The most prevalent mutation was found in MUC6, which had 7 somatic exonic variants in 4 patients. In addition, TaqMan assay and immunoblot confirmed that MUC6 expression was reduced in WT tissues when compared with control tissues. Moreover, the results of MUC6 knock-down assay and CRISPR-induced MUC6 mutations showed that MUC6 inhibited tumor aggression via autophagy-dependent β-catenin degradation while its mutations attenuated tumor-suppressive effects of MUC6. Seven novel mutated genes (MUC6, GOLGA6L2, GPRIN2, MDN1, MUC4, OR4L1 and PDE4DIP) were found in WT, among which MUC6 was the most prevalent one. MUC6 acted as a tumor suppressive gene through autophagy dependent β-catenin pathway.

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.

The Glucose-Regulated MiR-483-3p Influences Key Signaling Pathways in Cancer

The hsa-mir-483 gene, located within the IGF2 locus, transcribes for two mature microRNAs, miR-483-5p and miR-483-3p. This gene, whose regulation is mediated by the the CTNNB1/USF1 complex, shows an independent expression from its host gene IGF2. The miR-483-3p affects the Wnt/β-catenin, the TGF-β, and the TP53 signaling pathways by targeting several genes as CTNNB1, SMAD4, IGF1, and BBC3. Accordingly, miR-483-3p is associated with various tissues specific physiological properties as insulin and melanin production, as well as with cellular physiological functions such as wounding, differentiation, proliferation, and survival. Deregulation of miR-483-3p is observed in different types of cancer, and its overexpression can inhibit the pro-apoptotic pathway induced by the TP53 target effectors. As a result, the oncogenic characteristics of miR-483-3p are linked to the effect of some of the most relevant cancer-related genes, TP53 and CTNNB1, as well as to one of the most important cancer hallmark: the aberrant glucose metabolism of tumor cells. In this review, we summarize the recent findings regarding the miR-483-3p, to elucidate its functional role in physiological and pathological contexts, focusing overall on its involvement in cancer and in the TP53 pathway.

Effects of mutations in Wnt/β-catenin, hedgehog, Notch and PI3K pathways on GSK-3 activity-Diverse effects on cell growth, metabolism and cancer

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase that participates in an array of critical cellular processes. GSK-3 was first characterized as an enzyme that phosphorylated and inactivated glycogen synthase. However, subsequent studies have revealed that this moon-lighting protein is involved in numerous signaling pathways that regulate not only metabolism but also have roles in: apoptosis, cell cycle progression, cell renewal, differentiation, embryogenesis, migration, regulation of gene transcription, stem cell biology and survival. In this review, we will discuss the roles that GSK-3 plays in various diseases as well as how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTOR, Ras/Raf/MEK/ERK, Wnt/beta-catenin, hedgehog, Notch and TP53. Mutations that occur in these and other pathways can alter the effects that natural GSK-3 activity has on regulating these signaling circuits that can lead to cancer as well as other diseases. The novel roles that microRNAs play in regulation of the effects of GSK-3 will also be evaluated. Targeting GSK-3 and these other pathways may improve therapy and overcome therapeutic resistance.

SIX2 Effects on Wilms Tumor Biology

Wilms tumor (WT) blastema retains gene expression profiles characteristic of the multipotent nephron progenitor pool, or cap mesenchyme (CM), in the developing kidney. As a result, WT blastema and the CM are believed to represent contextual analogues of one another. Sine oculis homeobox 2 (SIX2) is a transcription factor expressed specifically in the CM, provides a critical mechanism for CM self-renewal, and remains persistently active in WT blastema, although its purpose in this childhood malignancy remains unclear. We hypothesized that SIX2, analogous to its function in development, confers a survival pathway to blastema, the putative WT stem cell. To test its functional significance in WT biology, wild-type SIX2 was overexpressed in the human WT cell line, WiT49. After validating this model, SIX2 effects on anchorage-independent growth, proliferation, invasiveness, canonical WNT pathway signaling, and gene expression of specific WNT pathway participants were evaluated. Relative to controls, WiT49 cells overexpressing SIX2 showed significantly enhanced anchorage-independent growth and early-passage proliferation representing surrogates of cell survival. Interestingly, overexpression of SIX2 generally repressed TCF/LEF-dependent canonical WNT signaling, which activates and coordinates both differentiation and stem pathways, but significantly heightened canonical WNT signaling through the survivin promoter, a mechanism that exclusively maintains the stem state. In summary, when overexpressed in a human WT cell line, SIX2 enhances cell survival and appears to shift the balance in WNT/β-catenin signaling away from a differentiation path and toward a stem cell survival path.

Molecular characterization of Wilms' tumor from a resource-constrained region of sub-Saharan Africa

Sub-Saharan African children have an increased incidence of Wilms' tumor (WT) and experience alarmingly poor outcomes. Although these outcomes are largely due to inadequate therapy, we hypothesized that WT from this region exhibits features of biological aggressiveness that may warrant broader implementation of high-risk therapeutic protocols. We evaluated 15 Kenyan WT (KWT) for features of aggressive disease (blastemal predominance and Ki67/cellular proliferation) and treatment resistance (anaplasia and p53 immunopositivity). To explore the additional biological features of KWT, we determined the mutational status of the CTNNB1/β-catenin and WT1 genes and performed immunostaining for markers of Wnt pathway activation (β-catenin) and nephronic progenitor cell self-renewal (WT1, CITED1 and SIX2). We characterized the proteome of KWT using imaging mass spectrometry (IMS). The results were compared to histology- and age-matched North American WT (NAWT) controls. For patients with KWT, blastemal predominance was noted in 53.3% and anaplasia in 13%. We detected increased loss to follow-up (p = 0.028), disease relapse (p = 0.044), mortality (p = 0.001) and nuclear unrest (p = 0.001) in patients with KWT compared to controls. KWT and NAWT showed similar Ki67/cellular proliferation. We detected an increased proportion of epithelial nuclear β-catenin in KWT (p = 0.013). All 15 KWT specimens were found to harbor wild-type CTNNB1/β-catenin, and one contained a WT1 nonsense mutation. WT1 was detected by immunostaining in 100% of KWT, CITED1 in 80% and SIX2 in 80%. IMS revealed a molecular signature unique to KWT that was distinct from NAWT. The African WT specimens appear to express markers of adverse clinical behavior and treatment resistance and may require alternative therapies or implementation of high-risk treatment protocols.

Mutated beta-catenin evades a microRNA-dependent regulatory loop

hsa-mir-483 is located within intron 2 of the IGF2 gene. We have previously shown oncogenic features of miR-483-3p through cooperation with IGF2 or by independently targeting the proapoptotic gene BBC3/PUMA. Here we demonstrate that expression of miR-483 can be induced independently of IGF2 by the oncoprotein β-catenin through an interaction with the basic helix-loop-helix protein upstream stimulatory transcription factor 1. We also show that β-catenin itself is a target of miR-483-3p, triggering a negative regulatory loop that becomes ineffective in cells harboring an activating mutation of β-catenin. These results provide insights into the complex regulation of the IGF2/miR-483 locus, revealing players in the β-catenin pathway.

Mutations in the WTX-gene are found in some high-grade microsatellite instable (MSI-H) colorectal cancers

BACKGROUND

Genetically, colorectal cancers (CRCs) can be subdivided into tumors with chromosomal instability (CIN) or microsatellite instability (MSI). In both types of CRCs genes that are involved in the degradation of beta-CATENIN are frequently mutated. Whereas in CIN CRCs APC (Adenomatous Polyposis Coli) is affected in most cases, high grade MSI (MSI-H) CRCs frequently display mutations in various genes, like the APC-, AXIN2- or CTNNBI (beta-CATENIN) gene itself. Recently in Wilms tumors, WTX (Wilms tumor gene on the X-chromosome) was discovered as another gene involved in the destruction of beta-CATENIN. As the WTX-gene harbors a short T6-microsatellite in its N-terminal coding region, we hypothesized that frameshift-mutations might occur in MSI-H CRCs in the WTX gene, thus additionally contributing to the stabilization of beta-CATENIN in human CRCs.

METHODS

DNA was extracted from 632 formalin-fixed, paraffin-embedded metastatic CRCs (UICCIV) and analyzed for MSI-H by investigating the stability of the highly sensitive microsatellite markers BAT25 and BAT26 applying fluorescence capillary electrophoresis (FCE). Then, in the MSI-H cases, well described mutational hot spot regions from the APC-, AXIN2- and CTNNBI genes were analyzed for genomic alterations by didesoxy-sequencing while the WTX T6-microsatellite was analyzed by fragment analysis. Additionally, the PCR products of T5-repeats were subcloned and mutations were validated using didesoxy-sequencing. Furthermore, the KRAS and the BRAF proto-oncogenes were analyzed for the most common activating mutations applying pyro-sequencing. mRNA expression of WTX from MSI-H and MSS cases and a panel of colorectal cancer cell lines was investigated using reverse transcription (RT-) PCR and FCE.

RESULTS

In our cohort of 632 metastatic CRCs (UICCIV) we identified 41 MSI-H cases (6.5%). Two of the 41 MSI-H cases (4.8%) displayed a frameshift mutation in the T6-repeat resulting in a T5 sequence. Only one case, a male patient, expressed the mutated WTX gene while being wild type for all other investigated genes.

CONCLUSION

Mutations in the WTX-gene might compromise the function of the beta-CATENIN destruction complex in only a small fraction of MSI-H CRCs thus contributing to the process of carcinogenesis.

A novel role for Wnt/Ca2+ signaling in actin cytoskeleton remodeling and cell motility in prostate cancer

Wnt signaling is a critical regulatory pathway in development and disease. Very little is known about the mechanisms of Wnt signaling in prostate cancer, a leading cause of death in men. A quantitative analysis of the expression of Wnt5A protein in human tissue arrays, containing 600 prostate tissue cores, showed >50% increase in malignant compared to benign cores (p<0.0001). In a matched pair of prostate cancer and normal cell line, expression of Wnt5A protein was also increased. Calcium waves were induced in prostate cells in response to Wnt5A with a 3 fold increase in Flou-4 intensity. The activity of Ca²⁺/calmodulin dependent protein kinase (CaMKII), a transducer of the non-canonical Wnt/Ca²⁺ signaling, increased by 8 fold in cancer cells; no change was observed in β-catenin expression, known to activate the canonical Wnt/β-catenin pathway. Mining of publicly available human prostate cancer oligoarray datasets revealed that the expression of numerous genes (e.g., CCND1, CD44) under the control of β-catenin transcription is down-regulated. Confocal and quantitative electron microscopy showed that specific inhibition of CaMKII in cancer cells causes remodeling of the actin cytoskeleton, irregular wound edges and loose intercellular architecture and a 6 and 8 fold increase in the frequency and length of filopodia, respectively. Conversely, untreated normal prostate cells showed an irregular wound edge and loose intercellular architecture; incubation of normal prostate cells with recombinant Wnt5A protein induced actin remodeling with a regular wound edge and increased wound healing capacity. Live cell imaging showed that a functional consequence of CaMKII inhibition was 80% decrease in wound healing capacity and reduced cell motility in cancer cells. We propose that non-canonical Wnt/Ca²⁺ signaling via CaMKII acts as a novel regulator of structural plasticity and cell motility in prostate cancer.

A novel Wilms tumor 1 (WT1) target gene negatively regulates the WNT signaling pathway

Mammalian kidney development requires the functions of the Wilms tumor gene WT1 and the WNT/beta-catenin signaling pathway. Recent studies have shown that WT1 negatively regulates WNT/beta-catenin signaling, but the molecular mechanisms by which WT1 inhibits WNT/beta-catenin signaling are not completely understood. In this study, we identified a gene, CXXC5, which we have renamed WID (WT1-induced Inhibitor of Dishevelled), as a novel WT1 transcriptional target that negatively regulates WNT/beta-catenin signaling. WT1 activates WID transcription through the upstream enhancer region. In the developing kidney, Wid and Wt1 are coexpressed in podocytes of maturing nephrons. Structure-function analysis demonstrated that WID interacts with Dishevelled via its C-terminal CXXC zinc finger and Dishevelled binding domains and potently inhibits WNT/beta-catenin signaling in vitro and in vivo. WID is evolutionarily conserved, and ablation of wid in zebrafish embryos with antisense morpholino oligonucleotides perturbs embryonic kidney development. Taken together, our results demonstrate that the WT1 negatively regulates WNT/beta-catenin pathway via its target gene WID and further suggest a role for WID in nephrogenesis.

GSK3: a multifaceted kinase in Wnt signaling

GSK3 is one of the few signaling mediators that play central roles in a diverse range of signaling pathways, including those activated by Wnts, hedgehog, growth factors, cytokines, and G protein-coupled ligands. Although the inhibition of GSK3-mediated beta-catenin phosphorylation is known to be the key event in Wnt-beta-catenin signaling, the mechanisms that underlie this event remain incompletely understood. The recent demonstration of GSK3 involvement in Wnt receptor phosphorylation illustrates the multifaceted roles that GSK3 plays in Wnt-beta-catenin signaling. In this review, we will summarize these recent results and offer explanations, hypotheses, and models to reconcile some of these observations.

An integrated genome screen identifies the Wnt signaling pathway as a major target of WT1

WT1, a critical regulator of kidney development, is a tumor suppressor for nephroblastoma but in some contexts functions as an oncogene. A limited number of direct transcriptional targets of WT1 have been identified to explain its complex roles in tumorigenesis and organogenesis. In this study we performed genome-wide screening for direct WT1 targets, using a combination of ChIP-ChIP and expression arrays. Promoter regions bound by WT1 were highly G-rich and resembled the sites for a number of other widely expressed transcription factors such as SP1, MAZ, and ZNF219. Genes directly regulated by WT1 were implicated in MAPK signaling, axon guidance, and Wnt pathways. Among directly bound and regulated genes by WT1, nine were identified in the Wnt signaling pathway, suggesting that WT1 modulates a subset of Wnt components and responsive genes by direct binding. To prove the biological importance of the interplay between WT1 and Wnt signaling, we showed that WT1 blocked the ability of Wnt8 to induce a secondary body axis during Xenopus embryonic development. WT1 inhibited TCF-mediated transcription activated by Wnt ligand, wild type and mutant, stabilized beta-catenin by preventing TCF4 loading onto a promoter. This was neither due to direct binding of WT1 to the TCF binding site nor to interaction between WT1 and TCF4, but by competition of WT1 and TCF4 for CBP. WT1 interference with Wnt signaling represents an important mode of its action relevant to the suppression of tumor growth and guidance of development.

Pediatric genitourinary tumors

PURPOSE OF REVIEW

We will review the 2007/2008 literature on pediatric genitourinary tumors.

RECENT FINDINGS

Newly identified constitutional epigenetic defects in Wilms tumor genes extend the understanding of Wilms tumor risk in children lacking syndromic features, and add to the complexity of the pathogenesis of these tumor suppressor genes. Pediatric renal cell carcinoma has distinct molecular characteristics and clinical associations from the adult counterpart. The pathway from PAX3-FKHR translocation to the development of rhabdomyosarcoma tumors has been further elucidated.

SUMMARY

Therapeutic strategies continue to be driven by developments in molecular diagnostics in pediatric genitourinary tumors.

Wilms' tumour: a complex enigma to decipher

Wilms' tumour (WT) is the most common solid tumour of childhood. The molecular signalling pathways determining the origin and behaviour of WT are very complex and several genes in several loci may participate. This review tries to briefly compile recent works on the histology and on the molecular alterations that promote the genesis, development and behaviour of WT. Some molecular alterations seem to be associated with specific histological types and particular clinical outcomes, suggesting that they might be utilised to determine the prognosis and to identify poor prognostic subgroups that can be targeted for more individualised treatments.

Functional inactivation of the WTX gene is not a frequent event in Wilms' tumors

For many years the precise genetic etiology of the majority of Wilms' tumors has remained unexplained. Recently, the WTX gene, mapped to chromosome Xq11.1, has been reported to be lost or mutated in approximately one-third of Wilms' tumors. Moreover, in female cases, the somatically inactivated alleles were found to invariantly derive from the active chromosome X. Consequently, WTX has been proposed as a 'one-hit' tumor suppressor gene. To provide further insights on the contribution of WTX to the development of the disease, we have examined 102 Wilms' tumors, obtained from 43 male and 57 female patients. Quantitative PCR analyses detected WTX deletions in 5 of 45 (11%) tumors from males, whereas loss of heterozygosity at WTX-linked microsatellites was observed in 9 tumors from 50 informative females (19%). However, in the latter group, using a combination of HUMARA assay and bisulfite-modified DNA sequencing, we found that the deletion affected the active chromosome X only in two cases (4%). Sequence analyses detected an inactivating somatic mutation of WTX in a single tumor, in which a strongly reduced expression of the mutant allele respect to the wild-type allele was observed, a finding not consistent with its localization on the active chromosome X. Overall, a functional somatic nullizygosity of the WTX gene was ascertained only in seven of the Wilms' tumors included in the study (approximately 7%). Our findings indicate that previously reported estimates on the proportion of Wilms' tumors due to WTX alterations should be reconsidered.