E-cadherin is a WT1 target gene

A Simple and Versatile Strategy for Oriented Immobilization of His-Tagged Proteins on Magnetic Nanoparticles

Oriented and covalent immobilization of proteins on magnetic nanoparticles (MNPs) is particularly challenging as it requires both the functionality of the protein and the colloidal stability of the MNPs to be preserved. Here, we describe a simple, straightforward, and efficient strategy for MNP functionalization with proteins using metal affinity binding. Our method involves a single-step process where MNPs are functionalized using a preformed, ready-to-use nitrilotriacetic acid-divalent metal cation (NTA-M2+) complex and polyethylene glycol (PEG) molecules. As a proof-of-concept, we demonstrate the oriented immobilization of a recombinant cadherin fragment engineered with a hexahistidine tag (6His-tag) onto the MNPs. Our developed methodology is simple and direct, enabling the oriented bioconjugation of His-tagged cadherins to MNPs while preserving protein functionality and the colloidal stability of the MNPs, and could be extended to other proteins expressing a polyhistidine tag. When compared to the traditional method where NTA is first conjugated to the MNPs and afterward free metal ions are added to form the complex, this novel strategy results in a higher functionalization efficiency while avoiding MNP aggregation. Additionally, our method allows for covalent bonding of the cadherin fragments to the MNP surface while preserving functionality, making it highly versatile. Finally, our strategy not only ensures the correct orientation of the protein fragments on the MNPs but also allows for the precise control of their density. This feature enables the selective targeting of E-cadherin-expressing cells only when MNPs are decorated with a high density of cadherin fragments.

Declining levels of miR-382-3p at puberty trigger the onset of spermatogenesis

A major change in the transcriptome of testicular Sertoli cells (Scs) at the onset of puberty enables them to induce robust spermatogenesis. Through comprehensive literature mining, we generated a list of genes crucial for Sc functioning and computationally predicted the microRNAs regulating them. Differential expression analysis of microRNAs in infant and pubertal rat Scs showed that miR-382-3p levels decline significantly in pubertal Scs. Interestingly, miR-382-3p was found to regulate genes like Ar and Wt1, which are crucial for functional competence of Scs. We generated a transgenic (Tg) mouse model in which pubertal decline of miR-382-3p was prevented by its overexpression in pubertal Scs. Elevated miR-382-3p restricted the functional maturation of Scs at puberty, leading to infertility. Prevention of decline in miR-382-3p expression in pubertal Scs was responsible for defective blood-testis barrier (BTB) formation, severe testicular defects, low epididymal sperm counts and loss of fertility in these mice. This provided substantial evidence that decline in levels of miR-382-3p at puberty is the essential trigger for onset of robust spermatogenesis at puberty. Hence, sustained high levels of miR-382-3p in pubertal Scs could be one of the underlying causes of idiopathic male infertility and should be considered for diagnosis and treatment of infertility.

Every Beat You Take-The Wilms' Tumor Suppressor WT1 and the Heart

Nearly three decades ago, the Wilms’ tumor suppressor Wt1 was identified as a crucial regulator of heart development. Wt1 is a zinc finger transcription factor with multiple biological functions, implicated in the development of several organ systems, among them cardiovascular structures. This review summarizes the results from many research groups which allowed to establish a relevant function for Wt1 in cardiac development and disease. During development, Wt1 is involved in fundamental processes as the formation of the epicardium, epicardial epithelial-mesenchymal transition, coronary vessel development, valve formation, organization of the cardiac autonomous nervous system, and formation of the cardiac ventricles. Wt1 is further implicated in cardiac disease and repair in adult life. We summarize here the current knowledge about expression and function of Wt1 in heart development and disease and point out controversies to further stimulate additional research in the areas of cardiac development and pathophysiology. As re-activation of developmental programs is considered as paradigm for regeneration in response to injury, understanding of these processes and the molecules involved therein is essential for the development of therapeutic strategies, which we discuss on the example of WT1.

Alteration of N6-methyladenosine epitranscriptome profile in unilateral ureteral obstructive nephropathy

Aim: To reveal the alterations of N⁶-methyladenosine (m⁶A) epitranscriptome profile in kidney after unilateral ureteral obstruction in mice. Materials & methods: Total renal m⁶A and expressions of methyltransferases and demethylases were detected by colorimetric quantification method, real-time PCR and western blot, respectively. Methylated RNA immunoprecipitation sequencing was performed to map epitranscriptome-wide m⁶A profile. Results: Total m⁶A levels were time-dependent decreased within 1 week, with the lowest level detected at day 7. A total of 823 differentially methylated transcripts in 507 genes were identified. Specifically, demethylated mRNAs selectively acted on multiple pathways, including TGF-β and WNT. Conclusion: m⁶A modification has a functional importance in renal interstitial fibrosis during obstructive nephropathy and might be a promising therapeutic target.

Deubiquitinase inhibitor degrasyn suppresses metastasis by targeting USP5-WT1-E-cadherin signalling pathway in pancreatic ductal adenocarcinoma

Wilm's tumour-1 (WT1) is overexpressed in pancreatic ductal adenocarcinoma (PDAC) and enhances metastasis. Deubiquitination stabilizes target proteins, and inhibiting deubiquitination facilitates the degradation of target proteins. However, whether inhibiting deubiquitination of WT1 facilitates its degradation and presents anti-cancer ability in PDAC is unknown. Here, we found that deubiquitinase inhibitor degrasyn rapidly induced the degradation of endogenous and exogenous WT1 through enhancing ubiquitination of WT1 followed by the up-regulation of E-cadherin. Knockdown of WT1 by short hairpin RNAs (shRNAs) inhibited metastasis and overexpression of WT1 partially prevented degrasyn-induced anti-metastasis activity, suggesting that degrasyn presents anti-metastasis activity partially through degrading WT1 protein. We further identified that USP5 deubiquitinated WT1 and stabilized its expression. The higher expressions of USP5 and WT1 are associated with tumour metastasis. More importantly, degrasyn inhibited the activity of USP5 and overexpression of USP5 partially prevented degrasyn-induced degradation of WT1 protein, suggesting that degrasyn degraded WT1 protein through inhibiting the activity of USP5. Finally, degrasyn reduced the tumorigenicity in a xenograft mouse model and reduced the metastasis in vivo. Our results indicate that degrasyn presents strong anti-cancer activity through USP5-WT1-E-cadherin signalling in PDAC. Therefore, degrasyn holds promise as cancer therapeutic agent in PDAC with high expressions of USP5 and WT1.

Influence of Wilms' tumor suppressor gene WT1 on bovine Sertoli cells polarity and tight junctions via non-canonical WNT signaling pathway

Sertoli cells (SCs) are polarized epithelial cells and provide a microenvironment for the development of germ cells (GCs). The Wilms' tumor suppressor gene WT1 which support spermatogenesis is expressed explicitly in SCs. This study investigated the effect of WT1 on the polarity and blood-testis barrier (BTB) formation of bovine SCs in order to provide theoretical and practical bases for the spermatogenic process in mammals. In this study, newborn calf SCs were used as research material, and the RNAi technique was used to knockdown the endogenous WT1. The results show that WT1 knockdown did not affect the proliferation ability of SCs, but down-regulated the expression of polarity-associated proteins (Par3, Par6b, and E-cadherin), junction-associated protein (occludin) and inhibits transcription of downstream genes (WNT4, JNK, αPKC, and CDC42) in non-canonical WNT signaling pathway. WT1 also altered ZO-1 and occludin protein distribution. Overexpression of WNT1 did not affect the expression of Par6b, E-cadherin, and occludin, whereas the non-canonical WNT signaling pathway inhibitors wnt-c59, CCG-1423, and GO-6983 down-regulated the expression of Par6b, E-cadherin, and occludin respectively. This study indicates that WT1 mediates the regulation of several proteins involved in bovine SCs polarity maintenance and intercellular tight junctions (TJ) by non-canonical WNT signaling pathway.

Reversible interconversion and maintenance of mammary epithelial cell characteristics by the ligand-regulated EGFR system

Epithelial cell plasticity is controlled by extracellular cues, but the underlying mechanisms remain to be fully understood. Epidermal growth factor (EGF) and amphiregulin (AREG) are high- and low-affinity ligands for EGF receptor (EGFR), respectively. EGFR signaling is known to promote epithelial-mesenchymal transition (EMT) by the activation of ERK and the induction of an EMT transcription factor, ZEB1. Here, we demonstrate that ligand-switching between EGF and AREG at equivalent molarity reversibly interconverts epithelial and mesenchymal-like states of EGFR signal-dependent mammary epithelial cells. The EGF- and AREG-cultured cells also differ in their epithelial characteristics, including the expression of cell surface markers, the mode of migration and the ability for acinus-formation. The ligand-switching between EGF and AREG temporally alters strength of the shared EGFR-ERK signaling. This alteration inverts relative expression levels of ZEB1 and its antagonizing microRNAs, miR-205 and miR-200c, those are critical determinants of the epithelial phenotype. Further, AREG-induced EGFR accumulation on the plasma membrane compensates for the weak association between AREG and EGFR. The EGFR dynamics enables AREG to support proliferation as efficiently as EGF at equivalent molarity and to maintain epithelial characteristics. Our findings reveal a role of EGFR ligands-generated signal strength in the regulation of mammary epithelial cell plasticity.

ABCG2 localizes to the nucleus and modulates CDH1 expression in lung cancer cells

Breast cancer resistance protein [BCRP/ATP-binding cassette subfamily G member 2 (ABCG2)] is a member of the ATP-binding cassette transporter family. The presence of ABCG2 on the plasma membrane in many kinds of human cancer cells contributes to multidrug resistance during chemotherapy, and it has been used as the side population marker for identifying cancer stem cells in lung cancers. We report here that, in addition to the membranous form, ABCG2 proteins are also found inside the nucleus, where they bind to the E-box of CDH1 (E-cadherin) promoter and regulate transcription of this gene. Increased expression of ABCG2 causes an increase of E-cadherin and attenuates cell migration, whereas knockdown of ABCG2 downregulates E-cadherin and enhances cell motility. In mice, xenografted A549 cells that have less ABCG2 are more likely to metastasize from the subcutaneous inoculation site to the internal organs. However, for the cancer cells that have already entered the blood circulation, an increased level of ABCG2, and correspondingly increased E-cadherin, may facilitate circulating cancer cells to colonize at a distant site and form a metastatic tumor. We propose a novel role for nuclear ABCG2 that functions as a transcription regulator and participates in modulation of cancer metastasis.

CUGBP1 and HuR regulate E-cadherin translation by altering recruitment of E-cadherin mRNA to processing bodies and modulate epithelial barrier function

The effectiveness and stability of epithelial barrier depend on apical junctional complexes, which consist of tight junctions (TJs) and adherens junctions (AJs). E-cadherin is the primary component of AJs, and it is essential for maintenance of cell-to-cell interactions and regulates the epithelial barrier. However, the exact mechanism underlying E-cadherin expression, particularly at the posttranscriptional level, remains largely unknown. RNA-binding proteins CUG-binding protein 1 (CUGBP1) and HU antigen R (HuR) are highly expressed in the intestinal epithelial tissues and modulate the stability and translation of target mRNAs. Here, we present evidence that CUGBP1 and HuR interact directly with the 3'-untranslated region of E-cadherin mRNA and regulate E-cadherin translation. CUGBP1 overexpression in Caco-2 cells inhibited E-cadherin translation by increasing the recruitment of E-cadherin mRNA to processing bodies (PBs), thus resulting in an increase in paracellular permeability. Overexpression of HuR exhibited an opposite effect on E-cadherin expression by preventing the translocation of E-cadherin mRNA to PBs and therefore prevented CUGBP1-induced repression of E-cadherin expression. Elevation of HuR also abolished the CUGBP1-induced epithelial barrier dysfunction. These findings indicate that CUGBP1 and HuR negate each other's effects in regulating E-cadherin translation by altering the recruitment of E-cadherin mRNA to PBs and play an important role in the regulation of intestinal barrier integrity under various pathophysiological conditions.

Nuclear signaling from cadherin adhesion complexes

The arrival of multicellularity in evolution facilitated cell-cell signaling in conjunction with adhesion. As the ectodomains of cadherins interact with each other directly in trans (as well as in cis), spanning the plasma membrane and associating with multiple other entities, cadherins enable the transduction of "outside-in" or "inside-out" signals. We focus this review on signals that originate from the larger family of cadherins that are inwardly directed to the nucleus, and thus have roles in gene control or nuclear structure-function. The nature of cadherin complexes varies considerably depending on the type of cadherin and its context, and we will address some of these variables for classical cadherins versus other family members. Substantial but still fragmentary progress has been made in understanding the signaling mediators used by varied cadherin complexes to coordinate the state of cell-cell adhesion with gene expression. Evidence that cadherin intracellular binding partners also localize to the nucleus is a major point of interest. In some models, catenins show reduced binding to cadherin cytoplasmic tails favoring their engagement in gene control. When bound, cadherins may serve as stoichiometric competitors of nuclear signals. Cadherins also directly or indirectly affect numerous signaling pathways (e.g., Wnt, receptor tyrosine kinase, Hippo, NFκB, and JAK/STAT), enabling cell-cell contacts to touch upon multiple biological outcomes in embryonic development and tissue homeostasis.

Mechanisms of transcriptional regulation by WT1 (Wilms' tumour 1)

The WT1 (Wilms' tumour 1) gene encodes a zinc finger transcription factor and RNA-binding protein that direct the development of several organs and tissues. WT1 manifests both tumour suppressor and oncogenic activities, but the reasons behind these opposing functions are still not clear. As a transcriptional regulator, WT1 can either activate or repress numerous target genes resulting in disparate biological effects such as growth, differentiation and apoptosis. The complex nature of WT1 is exemplified by a plethora of isoforms, post-translational modifications and multiple binding partners. How WT1 achieves specificity to regulate a large number of target genes involved in diverse physiological processes is the focus of the present review. We discuss the wealth of the growing molecular information that defines our current understanding of the versatility and utility of WT1 as a master regulator of organ development, a tumour suppressor and an oncogene.

Wilms' tumor protein induces an epithelial-mesenchymal hybrid differentiation state in clear cell renal cell carcinoma

The Wilms' tumor transcription factor (WT1) was originally classified as a tumor suppressor, but it is now known to also be associated with cancer progression and poor prognosis in several malignancies. WT1 plays an essential role in orchestrating a developmental process known as mesenchymal-to-epithelial transition (MET) during kidney development, but also induces the reverse process, epithelial-to-mesenchymal transition (EMT) during heart development. WT1 is not expressed in the adult kidney, but shows elevated expression in clear cell renal cell carcinoma (ccRCC). However, the role of WT1 in this disease has not been characterized. In this study, we demonstrate that WT1 is upregulated in ccRCC cells that are deficient in the expression of the von Hippel-Lindau tumor suppressor protein (VHL). We found that WT1 transcriptionally activated Snail, a master transcriptional repressor that is known to induce EMT. Although Snail represses E-cadherin and induces mesenchymal characteristics, we found partial maintenance of E-cadherin and associated epithelial characteristics in kidney cells and ccRCC cells that express WT1, since WT1 upregulates E-cadherin expression and competes with Snail repression. These findings support a novel paradigm in which WT1 induces an epithelial-mesenchymal hybrid transition (EMHT), characterized by Snail up-regulation with E-cadherin maintenance, a tumor cell differentiation state in which cancer cells keep both EMT and MET characteristics which may promote tumor cell plasticity and tumor progression.

Exogenous expression of WT1 gene influences U937 cell biological behaviors and activates MAPK and JAK-STAT signaling pathways

Wilms' tumor 1 (WT1) gene plays important roles in leukemogenesis. To further explore its underlying mechanisms, we transfected two WT1 isoforms, WT1(+17AA/-KTS) and WT1(+17AA/+KTS) into U937, a WT1-null monoblastic cell line, studied their effects on migration, colony formation, apoptosis, gene expression and pertinent signaling pathways of U937 cells. The results showed that WT1(+17AA/-KTS), but not WT1(+17AA/+KTS), enhanced migration and colony forming abilities of U937 cells, and suppressed etoposide-induced U937 cell apoptosis. Transfection of WT1 isoforms activated gene expressions of chemokine, and induced up-regulation of signaling molecules involved in JAK-STAT and MAPK signaling pathways. This study showed that exogenous expression of WT1 gene remarkably affected biological behaviors of U937 cells, and these effects are possibly mediated by up-regulation of genes related to chemokine, JAK-STAT and MAPK signaling pathways.

Wilms' tumor 1 (Wt1) regulates pleural mesothelial cell plasticity and transition into myofibroblasts in idiopathic pulmonary fibrosis

Pleural mesothelial cells (PMCs), which are derived from the mesoderm, exhibit an extraordinary capacity to undergo phenotypic changes during development and disease. PMC transformation and trafficking has a newly defined role in idiopathic pulmonary fibrosis (IPF); however, the contribution of Wilms' tumor 1 (Wt1)-positive PMCs to the generation of pathognomonic myofibroblasts remains unclear. PMCs were obtained from IPF lung explants and healthy donor lungs that were not used for transplantation. Short hairpin Wt1-knockdown PMCs (sh Wt1) were generated with Wt1 shRNA, and morphologic and functional assays were performed in vitro. Loss of Wt1 abrogated the PMC phenotype and showed evidence of mesothelial-to-mesenchymal transition (MMT), with a reduced expression of E-cadherin and an increase in the profibrotic markers α-smooth muscle actin (α-SMA) and fibronectin, along with increased migration and contractility, compared with that of the control. Migration of PMCs in response to active transforming growth factor (TGF)-β1 was assessed by live-cell imaging with 2-photon microscopy and 3D imaging, of Wt1-EGFP transgenic mice. Lineage-tracing experiments to map the fate of Wt1(+) PMCs in mouse lung in response to TGF-β1 were also performed by using a Cre-loxP system. Our results, for the first time, demonstrate that Wt1 is necessary for the morphologic integrity of pleural membrane and that loss of Wt1 contributes to IPF via MMT of PMCs into a myofibroblast phenotype.

Signaling and mechanical roles of E-cadherin

The epithelium comprises an important tissue that lines the internal and external surfaces of metazoan organs. In order to organize sheets of epithelial cells into three-dimensional tissues, it requires the coordination of basic cellular processes such as polarity, adhesion, growth, and differentiation. Moreover, as a primary barrier to the external environment, epithelial tissues are often subjected to physical forces and damage. This critical barrier function dictates that these fundamental cellular processes are continually operational in order to maintain tissue homeostasis in the face of almost constant trauma and stress. A protein that is largely responsible for the organization and maintenance of epithelial tissues is the transmembrane protein, E-cadherin, found at the surface of epithelial cells. Though originally investigated for its essential role in mediating intercellular cohesion, its impact on a wide array of physiological processes underscores its fundamental contributions to tissue development and its perturbation in a variety of common diseases.

The Wilms tumor gene, Wt1, is critical for mouse spermatogenesis via regulation of sertoli cell polarity and is associated with non-obstructive azoospermia in humans

Azoospermia is one of the major reproductive disorders which cause male infertility in humans; however, the etiology of this disease is largely unknown. In the present study, six missense mutations of WT1 gene were detected in 529 human patients with non-obstructive azoospermia (NOA), indicating a strong association between WT1 mutation and NOA. The Wilms tumor gene, Wt1, is specifically expressed in Sertoli cells (SCs) which support spermatogenesis. To examine the functions of this gene in spermatogenesis, Wt1 was deleted in adult testis using Wt1^flox and Cre-ER^TM mice strains. We found that inactivation of Wt1 resulted in massive germ cell death and only SCs were present in most of the seminiferous tubules which was very similar to NOA in humans. In investigating the potential mechanism for this, histological studies revealed that the blood–testis barrier (BTB) was disrupted in Wt1 deficient testes. In vitro studies demonstrated that Wt1 was essential for cell polarity maintenance in SCs. Further studies found that the expression of cell polarity associated genes (Par6b and E-cadherin) and Wnt signaling genes (Wnt4, Wnt11) were downregulated in Wt1 deficient SCs, and that the expression of Par6b and E-cadherin was regulated by Wnt4. Our findings suggest that Wt1 is important in spermatogenesis by regulating the polarity of SCs via Wnt signaling pathway and that WT1 mutation is one of the genetic causes of NOA in humans.

Infertility is one of the most common health problems, affecting about 15% of the couples in the world. In about half of these couples, infertility is related to male reproductive defect. Azoospermia is one of the major causes of male infertility in humans. Previous studies have found that the mutation or deletion of some genes is associated with azoospermia; however, the genetic cause of this remains largely unknown. In the present study, we detected Wt1 missense mutations in men with non-obstructive azoospermia (NOA). An essential function for WT1 in male spermatogenesis was confirmed by the use of a Wt1 conditional knockout mouse strain. Inactivation of Wt1 resulted in germ cell loss in mice, which was similar to NOA in human patients. Our data indicate that WT1 mutation is one genetic cause of male infertility and suggest that WT1 mutational analysis will be useful for diagnosis in a clinical setting.

The Wilms' tumor gene (WT1) regulates E-cadherin expression and migration of prostate cancer cells

Background

One key step in the development of prostate cancer (PCa) metastasis is the loss of E-cadherin expression associated with increased cellular motility and tumor invasion. This loss of E-cadherin expression is also required during normal embryogenesis and similar transcriptional repressors have been identified in both processes. We have previously reported the presence of one such transcription factor, WT1 in high Gleason grade prostate tumor tissues, and its absence in non-neoplastic or benign prostatic hyperplasia tissues.

Results

To better understand the effect of WT1 on E-cadherin expression and migration of PCa cells we quantified WT1 and E-cadherin mRNA levels in normal prostate epithelial and PCa cell lines with varying migratory potential. In WT1 transfected cells E-cadherin transcript levels were decreased, while they were increased in siWT1-RNA transfected PCa cells, suggesting that elevated WT1 expression was sufficient to dampen E-cadherin levels and potentially enhance migratory ability. To delineate the mechanism of WT1-mediated repression of E-cadherin, potential WT1 binding sites were tested in vitro and in vivo binding of WT1 to the E-cadherin promoter in the chromatin of LNCaP and PC3 cells was assessed by Chromatin Immunoprecipitation. The effect of WT1 binding was measured in reporter assays; in PC3 and DU145 cells WT1 decreased the activity of the proximal E-cadherin promoter. Using site-directed mutagenesis, a newly identified WT1 binding site located 146 bp from the transcription start site was shown to be required for this repression by WT1. Transwell migration and wound healing assays revealed that in LNCaP cells with low migratory potential, over-expression of WT1 was sufficient to enhance migration, conversely, in the highly migratory PC3 cells silencing of WT1 decreased migration.

Conclusions

These findings suggested that WT1 expression in high grade prostate cancer may contribute to migration and metastasis. Thus, in prostate cancer WT1 may function as a novel oncogene facilitating development of the lethal metastatic phenotype.

E-cadherin dysfunction in gastric cancer--cellular consequences, clinical applications and open questions

E-cadherin plays a major role in cell-cell adhesion and inactivating germline mutations in its encoding gene predispose to hereditary diffuse gastric cancer. Evidence indicates that aside from its recognized role in early tumourigenesis, E-cadherin is also pivotal for tumour progression, including invasion and metastization. Herein, we discuss E-cadherin alterations found in a cancer context, associated cellular effects and signalling pathways, and we raise new key questions that will impact in the management of GC patients and families.

Epithelial E- and P-cadherins: role and clinical significance in cancer

E-cadherin and P-cadherin are major contributors to cell-cell adhesion in epithelial tissues, playing pivotal roles in important morphogenetic and differentiation processes during development, and in maintaining integrity and homeostasis in adult tissues. It is now generally accepted that alterations in these two molecules are observed during tumour progression of most carcinomas. Genetic or epigenetic alterations in E- and P-cadherin-encoding genes (CDH1 and CDH3, respectively), or alterations in their proteins expression, often result in tissue disorder, cellular de-differentiation, increased invasiveness of tumour cells and ultimately in metastasis. In this review, we will discuss the major properties of E- and P-cadherin molecules, its regulation in normal tissue, and their alterations and role in cancer, with a specific focus on gastric and breast cancer models.

Signaling from the adherens junction

The cadherin/catenin complex organizes to form a structural Velcro that joins the cytoskeletal networks of adjacent cells. Functional loss of this complex arrests the development of normal tissue organization, and years of research have gone into teasing out how the physical structure of adhesions conveys information to the cell interior. Evidence that most cadherin-binding partners also localize to the nucleus to regulate transcription supports the view that cadherins serve as simple stoichiometric inhibitors of nuclear signals. However, it is also clear that cadherin-based adhesion initiates a variety of molecular events that can ultimately impact nuclear signaling. This chapter discusses these two modes of cadherin signaling in the context of tissue growth and differentiation.

Rosuvastatin preserves renal structure following unilateral ureteric obstruction in the neonatal rat

BACKGROUND/AIMS

Unilateral ureteric obstruction (UUO) in neonatal rodents can be used as a paradigm for in utero obstruction in humans and a platform for studying the potential of novel therapies for congenital obstructive nephropathy. The present study examined the effect of rosuvastatin (Ros) on key morphometric measures of renal injury and corresponding gene expression correlates following neonatal UUO in the rat.

METHODS

Neonatal rats subjected to UUO and controls were treated daily with vehicle or Ros for 14 days. Quantification of tubular dilatation, glomerular size and number and tubulointerstitial fibrotic area was performed and changes validated by reference to appropriate renal gene expression correlates.

RESULTS

UUO increased tubular diameter and interstitial fibrosis by 2.7- and 7-fold, respectively, in parallel with increases in renal transforming growth factor-β(1) (TGF-β(1)) and tumor necrosis factor-α (TNF-α) mRNA levels. Glomerular number and size were reduced by 52 and 33%, respectively. Reductions in WT-1 mRNA and protein expression were noted following obstruction occurring in tandem with reduced mRNA levels for BMP-7 and E-cadherin. Ros attenuated tubular dilatation (33%) and interstitial fibrosis (72%) in association with the normalization of renal TGF-β(1) and TNF-α mRNA levels. Ros improved glomerular number and size (30 and 50%), and preserved mRNA and protein expression levels of WT-1 and normalized mRNA levels for BMP-7 and E-cadherin.

CONCLUSIONS

Ros treatment attenuated all changes, most notably the increase in interstitial fibrosis. Notably, Ros treatment was unable to completely salvage glomerular development. Together these data highlight the therapeutic potential and limitations of Ros in neonatal obstruction.

AHR regulates WT1 genetic programming during murine nephrogenesis

Mounting evidence suggests that the blueprint of chronic renal disease is established during early development by environmental cues that dictate alterations in differentiation programming. Here we show that aryl hydrocarbon receptor (AHR), a lig-and-activated basic helix-loop-helix-PAS homology domain transcription factor, disrupts murine renal differentiation by interfering with Wilms tumor suppressor gene (WT1) signaling in the developing kidney. Embryonic kidneys of C57BL/6J Ahr⁻/⁻ mice at gestation d (GD) 14 showed reduced condensation in the nephrogenic zone and decreased numbers of differentiated structures compared with wild-type mice. These deficits correlated with increased expression of the (+) 17aa Wt1 splice variant, decreased mRNA levels of Igf-1 rec., Wnt-4 and E-cadherin, and reduced levels of 52 kDa WT1 protein. AHR knockdown in wild-type embryonic kidney cells mimicked these alterations with notable increases in (+) 17aa Wt1 mRNA, reduced levels of 52 kDa WT1 protein, and increased (+) 17aa 40-kDa protein. AHR downregulation also reduced Igf-1 rec., Wnt-4, secreted frizzled receptor binding protein-1 (sfrbp-1) and E-cadherin mRNAs. In the case of Igf-1 rec. and Wnt-4, genetic disruption was fully reversed upon restoration of cellular Wt1 protein levels, confirming that functional interactions between AHR and Wt1 represent a likely molecular target for renal developmental interference.

Tissue organization by cadherin adhesion molecules: dynamic molecular and cellular mechanisms of morphogenetic regulation

This review addresses the cellular and molecular mechanisms of cadherin-based tissue morphogenesis. Tissue physiology is profoundly influenced by the distinctive organizations of cells in organs and tissues. In metazoa, adhesion receptors of the classical cadherin family play important roles in establishing and maintaining such tissue organization. Indeed, it is apparent that cadherins participate in a range of morphogenetic events that range from support of tissue integrity to dynamic cellular rearrangements. A comprehensive understanding of cadherin-based morphogenesis must then define the molecular and cellular mechanisms that support these distinct cadherin biologies. Here we focus on four key mechanistic elements: the molecular basis for adhesion through cadherin ectodomains, the regulation of cadherin expression at the cell surface, cooperation between cadherins and the actin cytoskeleton, and regulation by cell signaling. We discuss current progress and outline issues for further research in these fields.

Candidate genes and potential targets for therapeutics in Wilms' tumour

Wilms' tumour (WT) is the most common malignant renal tumour of childhood. During the past two decades or so, molecular studies carried out on biopsy specimens and tumour-derived cell lines have identified a multitude of chromosomal and epigenetic alterations in WT. In addition, a significant amount of evidence has been gathered to identify the genes and signalling pathways that play a defining role in its genesis, growth, survival and treatment responsiveness. As such, these molecules and mechanisms constitute potential targets for novel therapeutic strategies for refractory WT. In this report we aim to review some of the many candidate genes and intersecting pathways that underlie the complexities of WT biology.

Differentiation of murine embryonic stem cells toward renal lineages by conditioned medium from ureteric bud cells in vitro

The kidney is formed from two tissue populations derived from the intermediate mesoderm, the ureteric bud, and the metanephric mesenchyme. Metanephric mesenchyme is a pluripotent renal stem population, and conversion of renal mesenchyme into epithelia depends on the ureteric bud in vivo and in vitro. Embryonic stem (ES) cells have been induced to differentiate into a broad spectrum of specialized cell types in vitro, including hematopoietic, pancreatic, and neuronal cells. Such ES-derived cells can provide a valuable source of progenitor cells. However, whether ES cells can be stimulated by factors secreted from the fetal renal cells to differentiate into renal precursor cells in vitro has not been reported. In this study, we showed that murine ES cells can give rise to embryoid bodies in the absence of leukemia inhibitory factor. Culture conditions were optimized [6 days, 10 ng/ml activin and 10(-7) M retinoic acid (RA)] to generate maximal mesoderm populations specifically expressing Pax2 and brachyury. Results showed that 72% of the cells were brachyury positive by fluorescent activated cell sorter on Day 6 of EB cell differentiation. Conditioned medium collected from cultures of ureteric bud cells from renal cells of a 13-day-old fetus was added to the culture medium. Mesoderm cells were cultured for up to 10 days before showing expression of renal markers, initiation of nephrogenesis (WT-1 and Pax2), and terminally differentiated renal cell types (POD-1 and E-cadherin). This study suggests that ES cells pre-treated by RA and activin can interact with secreted molecules of the fetal renal cells to specifically differentiate into renal precursor cells. Our results provide an experimental basis for the development of in vitro assays to steer differentiation of ES cells toward renal lineages.

Effect of WT1 gene silencing on the tumorigenicity of human glioblastoma multiforme cells

OBJECT

Wilms tumor 1 (WT1) is overexpressed in many human cancers, including glioblastoma multiforme (GBM). In another study, the authors showed that transient WT1 silencing increases the radiosensitivity of glioma cells. Studies of nonglioma cell lines have demonstrated that WT1 promotes cell proliferation and survival; however, this ability has not been rigorously analyzed in human GBM.

METHODS

The authors tested the efficacy of 2 sequences of short hairpin RNA (shRNA) directed against WT1 in U251MG human GBM cells and found that 1 sequence was capable of stably silencing WT1 expression. They then evaluated the effect of WT1 silencing on cellular proliferation, invasion, and in vivo tumor formation.

RESULTS

Stable WT1-shRNA expression significantly decreased the proliferation of U251MG cells in vitro as demonstrated by both an adenosine 5'-triphosphate-based viability assay and tritiated thymidine uptake. Furthermore, stable WT1 silencing caused significantly slower growth after the subcutaneous inoculation of tumor cells in the flanks of athymic nude mice and was associated with an increased latency period.

CONCLUSIONS

Data in this study provide proof of the principle that downregulation of WT1 causes decreased tumorigenicity of a GBM cell line in vitro and in vivo and suggest that WT1 is a promising target for novel molecular GBM therapies, perhaps in combination with standard treatment modalities.

Wt1 is required for cardiovascular progenitor cell formation through transcriptional control of Snail and E-cadherin

The epicardial epithelial-mesenchymal transition (EMT) is hypothesized to generate cardiovascular progenitor cells that differentiate into various cell types, including coronary smooth muscle and endothelial cells, perivascular and cardiac interstitial fibroblasts and cardiomyocytes. Here we show that an epicardial-specific knockout of the gene encoding Wilms' tumor-1 (Wt1) leads to a reduction in mesenchymal progenitor cells and their derivatives. We show that Wt1 is essential for repression of the epithelial phenotype in epicardial cells and during embryonic stem cell differentiation through direct transcriptional regulation of the genes encoding Snail (Snai1) and E-cadherin (Cdh1), two of the major mediators of EMT. Some mesodermal lineages do not form in Wt1-null embryoid bodies, but this effect is rescued by the expression of Snai1, underscoring the importance of EMT in generating these differentiated cells. These new insights into the molecular mechanisms regulating cardiovascular progenitor cells and EMT will shed light on the pathogenesis of heart diseases and may help the development of cell-based therapies.

Serine threonine receptor-associated protein (STRAP) plays a role in the maintenance of mesenchymal morphology

The stromal tissue, made of extracellular matrix and mesenchymal cells, is vital for the functional design of all complex tissues. Fibroblasts are key components of stromal tissue and play a crucial role during organ development, wound repair, angiogenesis and fibrosis. We have previously reported the identification of a novel WD-domain protein, STRAP(1) that inhibits transforming growth factor-beta (TGF-beta) signaling and enhances tumorigenicity via TGF-beta-dependent and TGF-beta-independent mechanisms. Here, we report, for the first time, that deletion of STRAP from Mouse Embryonic Fibroblasts (MEFs) results in a loss of mesenchymal morphology. These cells lose their spindle shape and exhibit features of an epithelial morphology. Gene expression profiling has confirmed that deletion of STRAP affects expression of sets of genes important for diverse functions including cell-cell adhesion and cell polarization, and upregulates E-cadherin expression leading to the formation of adherens junctions, subsequent localization of beta-catenin to the cell membrane and downregulation of the mesenchymal markers like LEF1 (lymphoid enhancer-binding factor 1). Upregulation of WT1 (Wilms tumor homolog 1) in STRAP null MEFs plays a role in E-cadherin induction. Finally, stable expression of STRAP in these cells results in a loss of WT1 and E-cadherin expressions, and a reversal from epithelial to the mesenchymal morphology. Thus, these results provide a novel TGF-beta-independent function of STRAP and describe a mechanism for the role of STRAP in the maintenance of mesenchymal morphology.

Genetic regulatory networks of nephrogenesis: deregulation of WT1 splicing by benzo(a)pyrene

Recent studies have identified AHR as a master regulator of Wilms' tumor suppressor gene (WT1) signaling in the developing kidney. Activation of AHR signaling by environmental chemical is associated with proteasome-mediated degradation of AHR protein, disruption of WT1 alternative splicing, and marked alterations in the regulation of genetic programs of developmental progression in the developing kidney. The complexity of genetic regulatory networks of nephrogenesis controlled by AHR-WT1 interactions will be discussed here with particular emphasis given to the biological and medical consequences that may result from deficits in nephrogenesis that compromise reserve capacity and renal function later in life. Understanding the impact of early-life environmental exposures to chemicals that disrupt AHR signaling can help minimize negative health consequences to pregnant women and their offspring.

Comparison of different clones (WT49 versus 6F-H2) of WT-1 antibodies for immunohistochemical diagnosis of malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is known to mimic the morphology of a number of diverse neoplastic conditions. WT-1 protein is conventionally used as a positive mesothelioma marker. Recently, a new monoclonal antibody clone WT49 has recently become commercially available. To compare specificity and sensitivity of the conventionally used clone 6F-H2 for the diagnosis of MPM to those of the new clone WT49. Forty cases of MPM, and 55 cases of lung carcinoma, 10 cases of synovial sarcoma of the intrathoracic region were analyzed. Of the 40 cases of MPM tested, clone WT49 and 6F-H2 stained 30 (75.0%) and 26 (65.0%) cases, respectively. Nuclear staining of clone WT49 was observed in 4 (7.2%) cases of lung carcinomas and in 1 (10.0%) case of synovial sarcoma. However, there was no nuclear staining of clone 6F-H2 in lesions other than MPM. There was no cytoplasmic staining of clone WT49 in any tumor. However, cytoplasmic staining of clone 6F-H2 was observed in 7 (17.5%) cases of MPM, 17 (30.1%) cases of lung carcinomas, and 5 (50.0%) cases of synovial sarcoma. The main advantage of WT49 is its higher reactivity with the sarcomatoid area of biphasic mesothelioma, but the results also indicate 1 drawback, that this clone was seen to react with a small percentage of lung carcinomas when it is used to distinguish epithelioid mesotheliomas from lung carcinomas. Furthermore, the positive reaction of clone WT49 was restricted to nucleus without cytoplasmic staining, which is seen in conventionally used WT-1 antibodies.

Polyamines regulate E-cadherin transcription through c-Myc modulating intestinal epithelial barrier function

The integrity of the intestinal epithelial barrier depends on intercellular junctions that are highly regulated by numerous extracellular and intracellular factors. E-cadherin is found primarily at the adherens junctions in the intestinal mucosa and mediates strong cell-cell contacts that have a functional role in forming and regulating the epithelial barrier. Polyamines are necessary for E-cadherin expression, but the exact mechanism underlying polyamines remains elusive. The current study was performed to determine whether polyamines induce E-cadherin expression through the transcription factor c-Myc and whether polyamine-regulated E-cadherin plays a role in maintenance of the epithelial barrier integrity. Decreasing cellular polyamines reduced c-Myc and repressed E-cadherin transcription as indicated by a decrease in levels of E-cadherin promoter activity and its mRNA. Forced expression of the c-myc gene by infection with adenoviral vector containing c-Myc cDNA stimulated E-cadherin promoter activity and increased E-cadherin mRNA and protein levels in polyamine-deficient cells. Experiments using different E-cadherin promoter mutants revealed that induction of E-cadherin transcription by c-Myc was mediated through the E-Pal box located at the proximal region of the E-cadherin promoter. Decreased levels of E-cadherin in polyamine-deficient cells marginally increased basal levels of paracellular permeability but, remarkably, potentiated H(2)O(2)-induced epithelial barrier dysfunction. E-cadherin silencing by transfection with its specific small interfering RNA also increased vulnerability of the epithelial barrier to H(2)O(2). These results indicate that polyamines enhance E-cadherin transcription by activating c-Myc, thus promoting function of the epithelial barrier.

Suppression of transcription factor early growth response 1 reduces herpes simplex virus lethality in mice

Herpes simplex virus type 1 (HSV-1) infection is the most common cause of sporadic, fatal encephalitis, but current understanding of how the virus interacts with cellular factors to regulate disease progression is limited. Here, we show that HSV-1 infection induced the expression of the cellular transcription factor early growth response 1 (Egr-1) in a human neuronal cell line. Egr-1 increased viral replication by activating promoters of viral productive cycle genes through binding to its corresponding sequences in the viral promoters. Mouse studies confirmed that Egr-1 expression was enhanced in HSV-1-infected brains and that Egr-1 functions to promote viral replication in embryonic fibroblasts. Furthermore, Egr-1 deficiency or knockdown of Egr-1 by a DNA-based enzyme greatly reduced the mortality of HSV-1-infected mice by decreasing viral loads in tissues. This study provides what we believe is the first evidence that Egr-1 increases the mortality of HSV-1 encephalitis by enhancing viral replication. Moreover, blocking this cellular machinery exploited by the virus could prevent host mortality.

WT1 induction of mitogen-activated protein kinase phosphatase 3 represents a novel mechanism of growth suppression

In its role as a tumor suppressor, WT1 transactivates several genes that are regulators of cell growth and differentiation pathways. For instance, WT1 induces the expression of the cell cycle regulator p21, the growth-regulating glycoprotein amphiregulin, the proapoptotic gene Bak, and the Ras/mitogen-activated protein kinase (MAPK) inhibitor Sprouty1. Here, we show that WT1 transactivates another important negative regulator of the Ras/MAPK pathway, MAPK phosphatase 3 (MKP3). In a WT1-inducible cell line that exhibits decreased cell growth and increased apoptosis on expression of WT1, microarray analysis showed that MKP3 is the most highly induced gene. This was confirmed by real-time PCR where MKP3 and other members of the fibroblast growth factor 8 syn expression group, which includes Sprouty 1 and the Ets family of transcription factors, were induced rapidly following WT1 expression. WT1 induction was associated with a block in the phosphorylation of extracellular signal-regulated kinase in response to epidermal growth factor stimulation, an effect mediated by MKP3. In the presence of a dominant-negative MKP3, WT1 could no longer block phosphorylation of extracellular signal-regulated kinase. Lastly, when MKP3 expression is down-regulated by short hairpin RNA, WT1 is less able to block Ras-mediated transformation of 3T3 cells.

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.

Evolutionary conservation of zinc finger transcription factor binding sites in promoters of genes co-expressed with WT1 in prostate cancer

BACKGROUND

Gene expression analyses have led to a better understanding of growth control of prostate cancer cells. We and others have identified the presence of several zinc finger transcription factors in the neoplastic prostate, suggesting a potential role for these genes in the regulation of the prostate cancer transcriptome. One of the transcription factors (TFs) identified in the prostate cancer epithelial cells was the Wilms tumor gene (WT1). To rapidly identify coordinately expressed prostate cancer growth control genes that may be regulated by WT1, we used an in silico approach.

RESULTS

Evolutionary conserved transcription factor binding sites (TFBS) recognized by WT1, EGR1, SP1, SP2, AP2 and GATA1 were identified in the promoters of 24 differentially expressed prostate cancer genes from eight mammalian species. To test the relationship between sequence conservation and function, chromatin of LNCaP prostate cancer and kidney 293 cells were tested for TF binding using chromatin immunoprecipitation (ChIP). Multiple putative TFBS in gene promoters of placental mammals were found to be shared with those in human gene promoters and some were conserved between genomes that diverged about 170 million years ago (i.e., primates and marsupials), therefore implicating these sites as candidate binding sites. Among those genes coordinately expressed with WT1 was the kallikrein-related peptidase 3 (KLK3) gene commonly known as the prostate specific antigen (PSA) gene. This analysis located several potential WT1 TFBS in the PSA gene promoter and led to the rapid identification of a novel putative binding site confirmed in vivo by ChIP. Conversely for two prostate growth control genes, androgen receptor (AR) and vascular endothelial growth factor (VEGF), known to be transcriptionally regulated by WT1, regulatory sequence conservation was observed and TF binding in vivo was confirmed by ChIP.

CONCLUSION

Overall, this targeted approach rapidly identified important candidate WT1-binding elements in genes coordinately expressed with WT1 in prostate cancer cells, thus enabling a more focused functional analysis of the most likely target genes in prostate cancer progression. Identifying these genes will help to better understand how gene regulation is altered in these tumor cells.

In silico regulatory analysis for exploring human disease progression

Background

An important goal in bioinformatics is to unravel the network of transcription factors (TFs) and their targets. This is important in the human genome, where many TFs are involved in disease progression. Here, classification methods are applied to identify new targets for 152 transcriptional regulators using publicly-available targets as training examples. Three types of sequence information are used: composition, conservation, and overrepresentation.

Results

Starting with 8817 TF-target interactions we predict an additional 9333 targets for 152 TFs. Randomized classifiers make few predictions (~2/18660) indicating that our predictions for many TFs are significantly enriched for true targets. An enrichment score is calculated and used to filter new predictions.

Two case-studies for the TFs OCT4 and WT1 illustrate the usefulness of our predictions:

• Many predicted OCT4 targets fall into the Wnt-pathway. This is consistent with known biology as OCT4 is developmentally related and Wnt pathway plays a role in early development.

• Beginning with 15 known targets, 354 predictions are made for WT1. WT1 has a role in formation of Wilms' tumor. Chromosomal regions previously implicated in Wilms' tumor by cytological evidence are statistically enriched in predicted WT1 targets. These findings may shed light on Wilms' tumor progression, suggesting that the tumor progresses either by loss of WT1 or by loss of regions harbouring its targets.

• Targets of WT1 are statistically enriched for cancer related functions including metastasis and apoptosis. Among new targets are BAX and PDE4B, which may help mediate the established anti-apoptotic effects of WT1.

• Of the thirteen TFs found which co-regulate genes with WT1 (p ≤ 0.02), 8 have been previously implicated in cancer. The regulatory-network for WT1 targets in genomic regions relevant to Wilms' tumor is provided.

Conclusion

We have assembled a set of features for the targets of human TFs and used them to develop classifiers for the determination of new regulatory targets. Many predicted targets are consistent with the known biology of their regulators, and new targets for the Wilms' tumor regulator, WT1, are proposed. We speculate that Wilms' tumor development is mediated by chromosomal rearrangements in the location of WT1 targets.

Reviewers

This article was reviewed by Trey Ideker, Vladimir A. Kuznetsov(nominated by Frank Eisenhaber), and Tzachi Pilpel.

Diagnostic value of WT1 in neuroepithelial tumours

AIMS

Currently, clinical trials using WT1 (Wilms tumour gene) peptide vaccines are conducted in haematopoietic malignancies and solid cancers. Single reports showed that the Wilms tumour gene product WT1 is also expressed in astrocytic neoplasms. Our aim was to investigate WT1 expression in a large cohort of various neuroepithelial tumours of different World Health Organization (WHO) grades and in normal central nervous system (CNS) tissue specimens to test its potential value as a diagnostic marker.

METHODS

Specimens were assessed by RT-PCR, Western blotting and immunohistochemistry. The samples investigated in our study consisted of 334 human neuroepithelial tumours, among those 33 oligodendrogliomas, 219 astrocytomas (including 105 glioblastomas) and 47 ependymomas.

RESULTS

Our results showed a de novo WT1 expression in neuroepithelial tumours. In diffuse astrocytomas and ependymomas, WT1 expression increased significantly with the grade of malignancy. In contrast, no significant difference was seen between WHO grade-II and -III oligodendrogliomas. Controlling for WHO grade, the comparison of oligodendrogliomas with ependymal and astrocytic tumours showed higher expression values for the latter.

CONCLUSIONS

Our study shows that WT1 is expressed de novo in numerous neuroepithelial tumours and increases with the grade of malignancy. These results suggest an important role of WT1 in tumourigenesis and progression in human brain tumours.

A GATA4/WT1 cooperation regulates transcription of genes required for mammalian sex determination and differentiation

Background

In mammals, sex determination is genetically controlled. The SRY gene, located on Y chromosome, functions as the dominant genetic switch for testis development. The SRY gene is specifically expressed in a subpopulation of somatic cells (pre-Sertoli cells) of the developing urogenital ridge for a brief period during gonadal differentiation. Despite this tight spatiotemporal expression pattern, the molecular mechanisms that regulate SRY transcription remain poorly understood. Sry expression has been shown to be markedly reduced in transgenic mice harboring a mutant GATA4 protein (a member of the GATA family of transcription factors) disrupted in its ability to interact with its transcriptional partner FOG2, suggesting that GATA4 is involved in SRY gene transcription.

Results

Although our results show that GATA4 directly targets the pig SRY promoter, we did not observe similar action on the mouse and human SRY promoters. In the mouse, Wilms' tumor 1 (WT1) is an important regulator of both Sry and Müllerian inhibiting substance (Amh/Mis) expression and in humans, WT1 mutations are associated with abnormalities of sex differentiation. GATA4 transcriptionally cooperated with WT1 on the mouse, pig, and human SRY promoters. Maximal GATA4/WT1 synergism was dependent on WT1 but not GATA4 binding to their consensus regulatory elements in the SRY promoter and required both the zinc finger and C-terminal regions of the GATA4 protein. Although both isoforms of WT1 synergized with GATA4, synergism was stronger with the +KTS rather than the -KTS isoform. WT1/GATA4 synergism was also observed on the AMH promoter. In contrast to SRY, WT1/GATA4 action on the mouse Amh promoter was specific for the -KTS isoform and required both WT1 and GATA4 binding.

Conclusion

Our data therefore provide new insights into the molecular mechanisms that contribute to the tissue-specific expression of the SRY and AMH genes in both normal development and certain syndromes of abnormal sex differentiation.

A pathologic link between Wilms tumor suppressor gene, WT1, and IFI16

The Wilms tumor gene (WT1) is mutated or deleted in patients with heredofamilial syndromes associated with the development of Wilms tumors, but is infrequently mutated in sporadic Wilms tumors. By comparing the microarray profiles of syndromic versus sporadic Wilms tumors and WT1-inducible Saos-2 osteosarcoma cells, we identified interferon-inducible protein 16 (IFI16), a transcriptional modulator, as a differentially expressed gene and a candidate WT1 target gene. WT1 induction in Saos-2 osteosarcoma cells led to strong induction of IFI16 expression and its promoter activity was responsive to the WT1 protein. Immunohistochemical analysis showed that IFI16 and WT1 colocalized in WT1-replete Wilms tumors, but not in normal human midgestation fetal kidneys, suggesting that the ability of WT1 to regulate IFI16 in tumors represented an aberrant pathologic relationship. In addition, endogenous IFI16 and WT1 interacted in vivo in two Wilms tumor cell lines. Furthermore, IFI16 augmented the transcriptional activity of WT1 on both synthetic and physiological promoters. Strikingly, short hairpin RNA (shRNA)-mediated knockdown of either IFI16 or WT1 led to decreased growth of Wilms tumor cells. These data suggest that IFI16 and WT1, in certain cellular context including sporadic Wilms tumors, may support cell survival.

Immunohistochemical analysis of gamma catenin in Wilms' tumors

The aim of our study was to investigate the expression of gamma-catenin in normal kidney and in Wilms' tumor by immunohistochemistry and to correlate the results with tumor stage, histological type, and prognostic group. We investigated 28 cases of Wilms' tumor, 2 Wilms' tumor metastases in lungs, and 1 specimen of normal renal tissue. Expression of gamma-catenin was detected in 14 cases. There was a weak inverse relationship between gamma-catenin expression and tumor stage. Expression of gamma-catenin was detected in various histologic types of Wilms' tumor, but there was no statistically significant correlation, except in cases with diffuse anaplasia that were negative. In 2 metastatic cases and in the case of bilateral Wilms' tumor gamma-catenin immunostaining was not observed Our findings suggest an absence of strong correlation between the loss of gamma-catenin and unfavorable outcome.

The Wilms tumor genes wt1a and wt1b control different steps during formation of the zebrafish pronephros

The Wilms tumor protein WT1 is an essential factor for kidney development. In humans, mutations in WT1 lead to Wilms tumor, a pediatric kidney cancer as well as to developmental anomalies concerning the urogenital tract. Inactivation of Wt1 in mice causes multiple organ defects most notably agenesis of the kidneys. In zebrafish, two paralogous wt1 genes exist, wt1a and wt1b. The wt1 genes are expressed in a similar and overlapping but not identical pattern. Here, we have examined the role of both wt1 genes in early kidney development employing a transgenic line with pronephros specific GFP expression and morpholino knockdown experiments. Inactivation of wt1a led to failure of glomerular differentiation and morphogenesis resulting in a rapidly expanding general body edema. In contrast, knockdown of wt1b was compatible with early glomerular development. After 48 h, however, wt1b morphant embryos developed cysts in the region of the glomeruli and tubules and subsequent pericardial edema at 4 days post-fertilization. Thus, our data suggest different functions for wt1a and wt1b in zebrafish nephrogenesis. While wt1a has a more fundamental and early role in pronephros development and is essential for the formation of glomerular structures, wt1b functions at later stages of nephrogenesis.

Oncogenic signaling pathways and deregulated target genes

A limited number of somatic mutations are known to trigger malignancy via chronic activation of cellular signaling pathways. High-throughput analysis of gene expression in cancer cells has revealed a plethora of deregulated genes by far exceeding the number of known genetic alterations. Targeted tumor therapy takes advantage of deregulated signaling in cancer. However, cancer cells may evade successful therapy, e.g., targeting oncogenic kinases, due to mutation of the target protein or to resistance mechanisms acting downstream of or parallel to the therapeutic block. To improve therapy and molecular diagnostics, we need detailed information on the wiring of pathway components and targets that ultimately execute the malignant properties of advanced tumors. Here we review work on Ras-mediated signal transduction and Ras pathway-responsive targets. We introduce the concept of signal-regulated transcriptional modules comprising groups of target genes responding to individual branches of the pathway network. Furthermore, we discuss functional approaches based on RNA interference for elucidating critical nodes in oncogenic signaling and the targets essential for malignancy.

Identification of Novel Wilms' Tumor Suppressor Gene Target Genes Implicated in Kidney Development

The Wilms' tumor suppressor gene (WT1) encodes a zinc finger transcription factor that is vital during development of several organs including metanephric kidneys. Despite the critical regulatory role of WT1, the pathways and mechanisms by which WT1 orchestrates development remain elusive. To identify WT1 target genes, we performed a genome-wide expression profiling analysis in cells expressing inducible WT1. We identified a number of direct WT1 target genes, including the epidermal growth factor (EGF)-family ligands epiregulin and HB-EGF, the chemokine CX3CL1, and the transcription factors SLUG and JUNB. The target genes were validated using quantitative reverse transcriptase-polymerase chain reaction, small interfering RNA knockdowns, chromatin immunoprecipitation, and luciferase reporter analyses. Immunohistochemistry of fetal kidneys confirmed that a number of the WT1 target genes had overlapping expression patterns with the highly restricted spatiotemporal expression of WT1. Finally, using an in vitro embryonic kidney culture assay, we found that the addition of recombinant epiregulin, amphiregulin, CX3CL1, and interleukin-11 significantly enhanced ureteric bud branching morphogenesis. Our genome-wide screen implicates WT1 in the transcriptional regulation of the EGF-family of growth factors as well as the CX3CL1 chemokine during nephrogenesis.

The role of the Wilms tumour gene (WT1) in normal and malignant haematopoiesis

In addition to its loss playing a pivotal role in the development of a childhood kidney malignancy, the Wilms tumour 1 gene (WT1) has emerged as an important factor in normal and malignant haematopoiesis. Preferentially expressed in CD34+ haematopoietic progenitors and down-regulated in more-differentiated cells, the WT1 transcription factor has been implicated in regulation of apoptosis, proliferation and differentiation. Putative target genes, such as BCL2, MYC, A1 and cyclin E, may cooperate with WT1 to modulate cell growth. However, the effects of WT1 on target gene expression appear to be isoform-specific. Certain WT1 isoforms are over-represented in leukaemia, but the exact mechanisms underlying the role of WT1 in transformation remain unclear. The ubiquity of WT1 in haematological malignancies has led to efforts to exploit it as a marker for minimal residual disease and as a prognostic factor, with conflicting results. In vitro killing of tumour cells by WT1-specific CD8+ cytotoxic T lymphocytes facilitated design of Phase I vaccine trials that showed clinical regression of WT1-positive tumours. Alternative methods employing WT1-specific immunotherapy are being investigated and might ultimately be used to optimise multimodal therapy of haematological malignancies.

A tumor suppressor and oncogene: the WT1 story

The Wilms' tumor 1 (WT1) gene encodes a transcription factor important for normal cellular development and cell survival. The initial discovery of WT1 as the causative gene in an autosomal-recessive condition identified it as a tumor suppressor gene whose mutations are associated with urogenital disease and the development of kidney tumors. However, this view is not in keeping with the frequent finding of wild-type, full-length WT1 in human leukemia, breast cancer and several other cancers including the majority of Wilms' tumors. Rather, these observations suggest that in those conditions, WT1 has an oncogenic role in tumor formation. In this review, we explore the literature supporting both views of WT1 in human cancer and in particular human leukemias. To understand the mechanism by which WT1 can do this, we will also examine its functional activity as a transcription factor and the influence of protein partners on its dual behavior.

The Wilms tumor suppressor Wt1 promotes cell adhesion through transcriptional activation of the alpha4integrin gene

Cell-matrix interaction through specific adhesion molecules is a critical step during organ development. In addition, down-regulation of cell adhesion receptors may promote tumor invasion and metastasis. We show here that the Wilms tumor suppressor Wt1, which is necessary for normal development of the epicardium, coronary vessels, genitourinary system, and other tissues, activates transcription of the alpha4integrin gene. Binding of the Wt1(-KTS) form, which is transcriptionally active, to the proximal alpha4integrin promoter was demonstrated by electrophoretic mobility shift assay and chromatin immunoprecipitation. A reporter construct harboring approximately 1.9 kb of the human alpha4integrin gene promoter was activated significantly by transient co-transfection of a Wt1(-KTS) expression plasmid. Introducing mutations in two identified Wt1(-KTS) binding motifs in the proximal promoter of the alpha4integrin gene abrogated this stimulatory effect. Endogenous alpha4integrin transcripts were increased more than 3-fold in human embryonic kidney 293 cells with stable expression of the Wt1(-KTS) protein. Wt1-overexpressing cells showed augmented adhesion to the alpha4integrin ligand vascular cell adhesion molecule-1 that was abolished upon incubation with an inhibitory alpha4integrin antibody. Double immunofluorescent staining revealed co-localization of Wt1 and alpha4integrin in the developing epicardium of mouse embryos. Cardiac expression of alpha4integrin was reduced significantly in embryos with a homozygous Wt1 defect (Wt1-/-). These findings demonstrate that Wt1 can support cell adhesion through enhanced expression of alpha4integrin. This transcriptional activation of the alpha4integrin gene by Wt1(-KTS) might contribute to normal formation of the epicardium and other tissues in the developing embryo.