Analysis of WT1 target gene expression in stably transfected cell lines

Biomarker Expression Profiling in Cervix Carcinoma Biopsies Unravels WT1 as a Target of Artesunate

BACKGROUND/AIM

Artemisinin and its derivatives are not only approved antimalarial drugs but also exert strong anticancer activity. Based on the clinical activity of artesunate (ART) that has been previously reported in cervix carcinoma, we investigated a panel of 12 different biomarkers and identified the Wilms Tumor 1 (WT1) protein as a potential target of ART.

PATIENTS AND METHODS

Matched biopsies of cervical carcinoma before, during, and after therapy from patients treated with ART were investigated for induction of apoptosis (TUNEL assay) and expression of Wilms Tumor protein 1 (WT1), 14-3-3 ζ, cluster of differentiation markers (CD4, CD8, CD56), ATP-binding cassette transporter B5 (ABCB5), glutathione S-transferase P1 (GSTP1), inducible nitric oxide synthase (iNOS), translationally controlled tumor protein (TCTP), eukaryotic elongation factor 3 (eIF3), and ADP/ATP translocase by immunohistochemistry. WT1 has been selected for more detailed analyses using molecular docking in silico, microscale thermophoresis using recombinant WT1, and cytotoxicity testing (resazurin assay) using HEK293 cells transfected with four different WT1 splice variants.

RESULTS

The fraction of apoptotic cells and the expression of WT1, 14-3-3 ζ, and CD4 increased upon ART treatment in tumors of patients. ART was bound in silico to a domain located at the DNA-binding site of WT1, while dihydroartemisinin (DHA) was bound with low affinity to a different site of WT1 not related to DNA-binding. The results were verified using microscale thermophoresis, where ART but not DHA bound to recombinant WT1. Transfectants overexpressing different WT1 splice variants exerted low but significant resistance to ART (≈2-fold).

CONCLUSION

WT1 may represent a novel target of ART in cancer cells that contribute to the response of tumor cells to this drug.

Genomic characterization of Wilms' tumor suppressor 1 targets in nephron progenitor cells during kidney development

The Wilms' tumor suppressor 1 (WT1) gene encodes a DNA- and RNA-binding protein that plays an essential role in nephron progenitor differentiation during renal development. To identify WT1 target genes that might regulate nephron progenitor differentiation in vivo, we performed chromatin immunoprecipitation (ChIP) coupled to mouse promoter microarray (ChIP-chip) using chromatin prepared from embryonic mouse kidney tissue. We identified 1663 genes bound by WT1, 86% of which contain a previously identified, conserved, high-affinity WT1 binding site. To investigate functional interactions between WT1 and candidate target genes in nephron progenitors, we used a novel, modified WT1 morpholino loss-of-function model in embryonic mouse kidney explants to knock down WT1 expression in nephron progenitors ex vivo. Low doses of WT1 morpholino resulted in reduced WT1 target gene expression specifically in nephron progenitors, whereas high doses of WT1 morpholino arrested kidney explant development and were associated with increased nephron progenitor cell apoptosis, reminiscent of the phenotype observed in Wt1(-/-) embryos. Collectively, our results provide a comprehensive description of endogenous WT1 target genes in nephron progenitor cells in vivo, as well as insights into the transcriptional signaling networks controlled by WT1 that might direct nephron progenitor fate during renal development.

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.

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.

Isolation, expression, and characterization of the human ZCRB1 gene mapped to 12q12

While isolating morphine-dependence-related genes with differential display, we cloned a novel human gene, zinc finger CCHC-type and RNA-binding motif 1 (ZCRB1, alias MADP-1) encoding a nuclear protein (217 residues). The ZCRB1 gene consists of eight exons and seven introns. It is mapped to 12q12, which is within a locus reported for Parkinson disease (M. Funayama et al., Ann. Neurol. 51 (2002) 296-301). The 5'-flanking region contains an enhancer core motif and binding sites for AP-1, AP-2, and LF-A1. ZCRB1 is characterized by an RNA-binding motif and a CCHC zinc finger motif. The latter overlaps the C..C...GH....C core nucleocapsid motif. ZCRB1 is conserved from zebrafish to human and shares homology with cold-inducible RNA-binding protein. Transfection assay showed that ZCRB1 is located in the nucleoplasm, but outside the nucleolus. ZCRB1 gene expression was stimulated by morphine, inhibited by 30-36 degrees C, and up-regulated by 39 degrees C incubation in SH-SY5Y neural cells. Zcrb1 gene expression is highest in the heart and testes, lower in the cerebellum, and lowest in the liver in mice. ZCRB1 mRNA expression is specifically elevated in hepatocarcinoma HepG2 cells. These data provide new clues for further understanding of morphine dependence, heat shock, and hepatocarcinoma.

The Wilms' tumor 1 (WT1) gene (+KTS isoform) functions with a CTE to enhance translation from an unspliced RNA with a retained intron

The Wilms' tumor 1 (WT1) gene plays an important role in mammalian urogenital development, and dysregulation of this gene is observed in many human cancers. Alternative splicing of WT1 RNA leads to the expression of two major protein isoforms, WT1(+KTS) and WT1(-KTS). Whereas WT1(-KTS) acts as a transcriptional regulator, no clear function has been ascribed to WT1(+KTS), despite the fact that this protein is crucial for normal development. Here we show that WT1(+KTS) functions to enhance expression from RNA possessing a retained intron and containing either a cellular or viral constitutive transport element (CTE). WT1(+KTS) expression increases the levels of unspliced RNA containing a CTE and specifically promotes the association of this RNA with polyribosomes. These studies provide further support for links between different steps in RNA metabolism and for the existence of post-transcriptional operons.

Anlaysis of complementary expression profiles following WT1 induction versus repression reveals the cholesterol/fatty acid synthetic pathways as a possible major target of WT1

The Wilms' tumour suppressor gene, WT1, encodes a zinc-finger protein that is mutated in Wilms' tumours and other malignancies. WT1 is one of the earliest genes expressed during kidney development. WT1 proteins can activate and repress putative target genes in vitro, although the in vivo relevance of such target genes often remains unverified. To better understand the role of WT1 in tumorigenesis and kidney development, we need to identify downstream target genes. In this study, we have expression profiled human embryonic kidney 293 cells stably transfected to allow inducible WT1 expression and mouse mesonephric M15 cells transfected with a WT1 antisense construct to abolish endogenous expression of all WT1 isoforms to identify WT1-responsive genes. The complementary overlap between the two cell lines revealed a pronounced repression of genes involved in cholesterol biosynthesis by WT1. This pathway is transcriptionally regulated by the sterol responsive element-binding proteins (SREBPs). Here, we provide evidence that the C-terminal end of the WT1 protein can directly interact with SREBP, suggesting that WT1 may modify the transcriptional function of SREBPs via a direct protein-protein interaction. Therefore, the tumour suppressor activities of WT1 may be achieved by repressing the mevalonate pathway, thereby controlling cellular proliferation and promoting terminal differentiation.

The Wilms' tumour suppressor protein, WT1, undergoes CRM1-independent nucleocytoplasmic shuttling

The Wilms' tumour suppressor gene (WT1) encodes a zinc finger-containing nuclear protein essential for kidney and urogenital development. Initially considered a transcription factor, there is mounting evidence that WT1 has a role in post-transcriptional processing. Using the interspecies heterokaryon assay, we have demonstrated that WT1 can undergo nucleocytoplasmic shuttling. We have also mapped the region responsible for nuclear export to residues 182-324. Our data add further complexity to the role of WT1 in transcriptional and post-transcriptional regulation.

The receptor tyrosine kinase regulator Sprouty1 is a target of the tumor suppressor WT1 and important for kidney development

WT1 encodes a transcription factor involved in kidney development and tumorigenesis. Using representational difference analysis, we identified a new set of WT1 targets, including a homologue of the Drosophila receptor tyrosine kinase regulator, sprouty. Sprouty1 was up-regulated in cell lines expressing wild-type but not mutant WT1. WT1 bound to the endogenous sprouty1 promoter in vivo and directly regulated sprouty1 through an early growth response gene-1 binding site. Expression of Sprouty1 and WT1 overlapped in the developing metanephric mesenchyme, and Sprouty1, like WT1, plays a key role in the early steps of glomerulus formation. Disruption of Sprouty1 expression in embryonic kidney explants by antisense oligonucleotides reduced condensation of the metanephric mesenchyme, leading to a decreased number of glomeruli. In addition, sprouty1 was expressed in the ureteric tree and antisense-treated ureteric trees had cystic lumens. Therefore, sprouty1 represents a physiologically relevant target gene of WT1 during kidney development.

The LIM-only coactivator FHL2 modulates WT1 transcriptional activity during gonadal differentiation

An essential step during sex determination is the maintenance of the Müllerian duct in females and its regression in males caused by the expression of Müllerian inhibiting substance (MIS). In testes, the Wilms' tumor suppressor and the orphan nuclear receptor SF1 cooperatively bind to the promoter and activate transcription of MIS. In the ovaries, on the other hand, the orphan nuclear receptor DAX1 binds to SF1, inhibits transactivation by WT1/SF1 and thereby suppresses the induction of MIS expression. In addition, WT1 itself is responsible for the upregulation of DAX1 transcription. So far, little is known on which protein-protein interactions or cofactors elicit the spatiotemporal control of WT1-mediated transcription. Here we demonstrate coexpression of the LIM-only coactivator FHL2 and WT1. FHL2 and WT1 functionally interact both in vitro and in vivo. The importance of this interaction is revealed by the ability of FHL2 to potentiate the synergistic induction of MIS gene expression by WT1/SF1. Moreover, FHL2 coactivates transactivation of the DAX1 promoter by WT1. Hence, we present FHL2 as a novel transcriptional coactivator of WT1. The ability to modulate both DAX1 and MIS expression might allow FHL2 to act in the molecular fine tuning of WT1-dependent control mechanisms in the reproductive organs.

Regulation of gene expression by WT1 in development and tumorigenesis

WT1 encodes a zinc finger transcription factor implicated in normal development and tumorigenesis. Germline mutation or deletion of WT1 results in a spectrum of abnormal kidney development, male-to-female intersex disorders, and predisposition to pediatric nephroblastoma, Wilms tumor. Initially thought to encode a transcriptional repressor, WT1-dependent functions are now more clearly linked to its property as a transcriptional activator of genes involved in renal development and sex determination. WT1 is expressed in 4 isoforms as a result of 2 alternative messenger RNA splicing events, the more significant of which encodes the 3 amino acids lysine, threonine, and serine (KTS) between zinc fingers 3 and 4. Although WT1 isoforms lacking KTS act as sequence-specific DNA binding factors, a large body of evidence now implicates the KTS-containing isoforms in RNA processing. In keeping with distinct biochemical mechanisms for these isoforms, genetic data from humans and mice point to separate but partially overlapping roles for WT1 (+KTS) and (-KTS) during genitourinary development. Recently, a hematopoietic model system has been used to study functional properties of WT1 in vitro. WT1 expression in primary hematopoietic cells leads to stage-specific effects that may be relevant to WT1-mediated tumor suppression.

The role of WT1 in oncogenesis: tumor suppressor or oncogene?

Although originally identified as a tumor suppressor gene, WT1 is overexpressed in a variety of hematologic malignancies and solid tumors, including acute leukemia, breast cancer, malignant mesothelioma, renal cell carcinoma, and others. Overexpression of both wild-type and mutant WT1 has been reported. In some cases, this finding represents overexpression of a gene that should be expressed at lower levels, but in other cases, WT1 is expressed at high levels in a tissue type in which there is normally no expression at all. In this review, the mechanisms of altered WT1 expression are explored, including changes in promoter methylation. WT1 target genes that may be important for oncogenesis are discussed, as is the use of WT1 expression as a diagnostic tool. The prognostic implications of altered WT1 expression and the potential for immunotherapy aimed at WT1 are also discussed.

The Wilms tumor suppressor WT1 regulates early gonad development by activation of Sf1

In mammals, several genes including the Wilms tumor suppressor gene Wt1, the Lim homeobox gene Lhx9, and the gene encoding steroidogenic factor 1 (Sf1) have been implicated in the development of the indifferent gonad prior to sexual differentiation. Interactions among these genes have not yet been elucidated. Using biochemical and genetic experiments, we demonstrate here that WT1 and LHX9 function as direct activators of the Sf1 gene. Interestingly, only the -KTS form of WT1 is able to bind to and transactivate the Sf1 promoter. This observation is consistent with differential roles for the -KTS and +KTS variants of WT1 which have been postulated on the basis of human disorders such as the Frasier syndrome. Our data suggest a pathway in which the products of the Wt1 and Lhx9 genes activate expression of Sf1 and thus mediate early gonadogenesis.

Wnt-4 regulation by the Wilms' tumour suppressor gene, WT1

The Wilms' tumour suppressor gene, WT1, encodes multiple nuclear protein isoforms, all containing four C-terminal zinc finger motifs. WT1 proteins can both activate and repress putative target genes in vitro, although the in vivo relevance of these putative target genes is often unverified. WT1 mutations can result in Wilms' tumour and the Denys-Drash Syndrome (DDS) of infantile nephropathy, XY pseudohermaphroditism and predisposition to Wilms' tumour. We have established stable transfectants of the mouse mesonephric cell line, M15, which express WT1 harbouring a common DDS point mutation (R394W). A comparison of the expression profiles of M15 and transfectant C2A was performed using Nylon-based arrays. Very few genes showed differential expression. However Wnt-4, a member of the Wnt gene family of secreted glycoproteins, was downregulated in C2A and other similar clones. Doxycycline induction of WT1-A or WT1-D expression in HEK293 stable transfectants also elicited an elevation in Wnt4 expression. Wnt4 is critical for the mesenchyme-to-epithelial transition during kidney development, making it an attractive putative WT1 target. We have mapped human Wnt-4 gene to chromosome 1p35-36, a region of frequent LOH in WT, have characterized the genomic structure of the human Wnt-4 gene and isolated 9 kb of immediate promoter. While several potential WT1 binding sites exist within this promoter, reporter analysis does not strongly support the direct regulation of Wnt4 by WT1. We propose that Wnt-4 regulation by WT1 occurs at a more distant promoter or enhancer site, or is indirect.

Activation of Vitamin D Receptor by the Wilms' Tumor GeneProduct Mediates Apoptosis of Renal Cells

Abstract. The Wilms' tumor transcription factor WT1 is required for kidney development, but little is known about WT1 downstream signaling in renal cells. This study reported an approximately fivefold upregulation of vitamin D receptor (VDR) mRNA and protein in human embryonic kidney (HEK) 293 cells that stably expressed WT1 at a level comparable to the developing kidney in vivo. Co-transfection of HEK 293 cells with expression plasmids encoding four different WT1 splicing variants stimulated mouse vdr promoter activity more than fourfold. A 201-bp fragment was identified in the proximal vdr promoter that was required for transactivation by WT1. This critical sequence contained a predicted WT1 consensus site, which bound to recombinant WT1 protein. Temporal changes of vdr and wt1 mRNA levels in developing rat kidneys were correlated closely. The active metabolite 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) strongly inhibited the proliferation of wt1-transfected HEK 293 cells. Exposure to 1,25-(OH)2D3 caused apoptosis of cultured wt1 immunopositive cells from mouse embryonic kidney cortex. These findings suggest that transcriptional activation of the VDR by WT1 can mediate programmed death of renal embryonic cells in response to 1,25-(OH)2D3. The results provide the first evidence for a role of the vitamin D endocrine system in renal cell growth and differentiation during development.

Wilms tumor and the WT1 gene

Wilms tumor or nephroblastoma is a pediatric kidney cancer arising from pluripotent embryonic renal precursors. Multiple genetic loci have been linked to Wilms tumorigenesis; positional cloning strategies have led to the identification of the WT1 tumor suppressor gene at chromosome 11p13. WT1 encodes a zinc finger transcription factor that is inactivated in the germline of children with genetic predisposition to Wilms tumor and in a subset of sporadic cancers. When present in the germline, specific heterozygous dominant-negative mutations are associated with severe abnormalities of renal and sexual differentiation, pointing to the essential role of WT1 for normal genitourinary development. The role of this tumor suppressor in normal organ-specific differentiation is also supported by the highly restricted temporal and spatial expression of WT1 in glomerular precursors of the developing kidney and by the failure of kidney development in wt1-null mice. Of two major alternative splicing products encoded by WT1, the (-KTS) isoform appears to mediate transcriptional activation of genes implicated in cellular differentiation, possibly also repressing proliferation-associated genes. The (+KTS) isoform, whose DNA-binding domain is disrupted by the insertion of three amino acids, may be involved in some aspect of mRNA processing. In addition to its function in genitourinary development, a role for WT1 in hematopoiesis is suggested by its aberrant expression and/or mutation in a subset of acute human leukemias. WT1 is also expressed in mesothelial cells; a specific oncogenic chromosomal translocation fusing the N-terminal domain of the Ewing sarcoma gene EWS to the three C-terminal zinc fingers of WT1 underlies desmoplastic small round cell tumor, an abdominal tumor thought to arise from the peritoneal lining. Understanding the distinct functional properties of WT1 isoforms and tumor-associated variants will provide unique insight into the link between normal organ-specific differentiation and malignancy.

The Wilms' tumor gene product (WT1) modulates the response to 1,25-dihydroxyvitamin D3 by induction of the vitamin D receptor

The Wilms' tumor gene (wt1) encodes a transcription factor involved in urogenital development, in particular in renal differentiation, and in hematopoietic differentiation. Differentiation of a number of solid tumor and leukemic cells lines can be mediated by 1,25-dihydroxyvitamin D(3). This is predominantly mediated by the nuclear receptor for 1,25-dihydroxyvitamin D(3), the vitamin D receptor (VDR). In initial experiments addressing a possible link between WT1 and VDR, we observed a correlated expression of WT1 and VDR mRNA in samples from renal tissues. HT29 colon carcinoma cells, stably transfected to express WT1, exhibited elevated endogenous VDR levels compared with control cells transfected with a control construct. Elevated VDR expression was found in wt1-transfected human embryonic kidney 293 cells, as well. In transient cotransfection experiments, we observed an activation of a vdr promoter reporter by WT1 through a WT1 recognition element, indicating transcriptional regulation of the vdr gene expression by WT1. The responsive sequence element was specifically bound by wild-type, but not by mutated WT1, in electrophoretic mobility shift assays. HT29 colon carcinoma cells, which respond to 1,25-dihydroxyvitamin D(3) with slow induction of growth arrest, were investigated for the influence of WT1 on 1,25-dihydroxyvitamin D(3)-mediated growth suppression. Although HT29 cells transfected with a control construct responded moderately to 1,25-dihydroxyvitamin D(3), the response of HT29 cells expressing WT1 was strikingly enhanced. Stimulation with dihydroxyvitamin D(3) caused an up to 3-fold reduction in the growth rate of different HT29 clones expressing WT1 as compared with control cells lacking WT1 expression. Thus, induction of VDR by WT1 leads to an enhanced response to 1,25-dihydroxyvitamin D(3). We conclude that the vitamin D receptor gene is a target for transcriptional activation by WT1, suggesting a possible physiological role of this regulatory pathway.

Par4 is a coactivator for a splice isoform-specific transcriptional activation domain in WT1

The Wilms' tumor suppressor protein WT1 is a transcriptional regulator involved in differentiation and the regulation of cell growth. WT1 is subject to alternative splicing, one isoform including a 17-amino acid region that is specific to mammals. The function of this 17-amino acid insertion is not clear, however. Here, we describe a transcriptional activation domain in WT1 that is specific to the WT1 splice isoform that contains the 17-amino acid insertion. We show that the function of this domain in transcriptional activation is dependent on a specific interaction with the prostate apoptosis response factor par4. A mutation in WT1 found in Wilms' tumor disturbs the interaction with par4 and disrupts the function of the activation domain. Analysis of WT1 derivatives in cells treated to induce par4 expression showed a strong correlation between the transcription function of the WT1 17-amino acid insertion and the ability of WT1 to regulate cell survival and proliferation. Our results provide a molecular mechanism by which alternative splicing of WT1 can regulate cell growth in development and disease.

Transcriptional regulation of insulin-like growth factor-I receptor gene expression in prostate cancer cells

A marked decrease in the type 1 insulin-like growth factor (IGF) receptor (IGF-IR) occurs in prostate epithelial cells during transformation from the benign to the metastatic state. One of the principal regulators of IGF-IR gene expression, the WT1 tumor suppressor, is expressed in prostate cancer and in prostate cancer cell lines. The purpose of this study was to determine whether the decrease in IGF-IR expression was transcriptionally regulated, and whether WT1 action may be involved in the repression of the IGF-IR gene in prostate cancer cells. The P69 cell line was derived by immortalization of human primary prostate epithelial cells with simian virus-40 T antigen and is rarely tumorigenic. The M12 line was derived from the P69 line by selection for tumor formation in nude mice and is tumorigeneic and metastatic. P69 cells express 20,000 IGF-IR/cell, whereas M12 cells express 3,500 IGF-IR/cell. These differences in receptor number are reflected in proportional differences in IGF-IR mRNA levels. To assess IGF-IR promoter activity in these cell lines, each was transiently transfected with luciferase reporter vectors containing the IGF-IR gene transcription start site and 476 bp of 5'-flanking sequence, 640 bp of 5'-untranslated region sequence, or both regions. The promoter activity of the full-length construct was 50% lower (P < 0.01) in M12 cells compared with P69 cells, the activity of the 5'-flanking region construct was 53% lower (P < 0.0001), and that of the 5'-untranslated region construct was 36% lower (P = 0.01). P69 clones stably transfected with a WT1 expression vector exhibited decreased expression of the endogenous IGF-IR gene and decreased promoter activity in transient transfection assays with IGF-IR promoter constructs containing multiple WT1 binding sites. The observed reduction in endogenous IGF-IR expression was sufficient to inhibit IGF-I-stimulated cell proliferation. These data suggest that most of the decreased expression of the IGF-IR seen in malignant prostate epithelium is the result of transcriptional repression of the IGF-IR gene, and that this repression may be due in part to the increased expression of the WT1 tumor suppressor in metastatic prostate cancer.

Screen for genes regulated during early kidney morphogenesis

Kidney development starts with the reciprocal induction of mesenchymal and ureteric bud cells which leads to condensation, epithelialization, and nephron formation in the mesenchyme. To identify changes in gene expression during these processes, we compared differential display polymerase chain reaction (PCR) profiles of uninduced and induced mesenchymal cells. In vitro kidney development in the form of the transfilter organ culture system was used to generate homogeneous cell populations for this type of comparison. Here we describe the isolation of known and novel genetags from this screening. Among the known genes the ufo receptor tyrosine kinase, sFRP2, and the groucho related gene (grg) were verified as being upregulated upon induction. With four of eight novel genes tested, Northern blot analysis proved to be sensitive enough to confirm differential expression. To improve sensitivity and gain additional spatial information, in situ hybridization was performed. Expression analysis of two differential display PCR products, designated C0-5 and M2-4, demonstrated the cell-specific and dynamic expression of these novel genetags in the developing kidney and other tissues. C0-5 transcripts were expressed in the ureteric bud, S-shaped bodies, and in the collecting system. Signals for M2-4, a gene not detectable by Northern blot analysis, were only found in condensing mesenchymal cells and early differentiation stages, but not in the collecting ducts. The large fraction of novel genetags from the present screening that have not yet been analyzed provides a rich resource to clone genetic networks regulating early nephrogenesis.

E-cadherin is a WT1 target gene

The WT1 tumor suppressor gene encodes a transcription factor that can activate and repress gene expression. Transcriptional targets relevant for the growth suppression functions of WT1 are poorly understood. We found that mesenchymal NIH 3T3 fibroblasts stably expressing WT1 exhibit growth suppression and features of epithelial differentiation including up-regulation of E-cadherin mRNA. Acute expression of WT1 in NIH 3T3 fibroblasts after retroviral infection induced murine E-cadherin expression. In transient transfection experiments, the human and murine E-cadherin promoters were activated by co-expression of WT1. E-cadherin promoter activity was increased in cells overexpressing WT1 and was blocked by a dominant negative form of WT1. WT1 activated the murine E-cadherin promoter through a conserved GC-rich sequence similar to an EGR-1 binding site as well as through a CAAT box sequence. WT1 produced in vitro or derived from nuclear extracts bound to the WT1-response element within the murine E-cadherin promoter, but not the CAAT box. E-cadherin, a gene important in epithelial differentiation and neoplastic transformation, represents a downstream target gene that links the roles of the WT1 in differentiation and growth control.

Regulation of the Wilms' tumour suppressor protein transcriptional activation domain

The Wilms' tumour suppressor protein WT1 contains a transcriptional regulatory domain that can either activate or repress transcription depending upon its cellular environment. The mechanistic basis for this dichotomy is unclear however. Here, we dissect the transcriptional regulatory domains of WT1. We find that a region within the domain of WT1 attributed to transcriptional repression is a potent suppressor of the activation domain at several promoters and in different cell types. In vitro transcription analysis suggests that the mechanism of suppression of the activation domain occurs at the level of transcription initiation. Furthermore we find that the WT1 suppression domain is able to inhibit a heterologous activation domain when fused in cis. Dissection of this domain resulted in the delineation of a 30 amino acid region that was sufficient to confer suppression of a transcriptional activation domain both in vivo and in vitro. Additionally, we find that the WT1 transcriptional activation domain interacts with the general transcription factor TFIIB and that this interaction is not affected by the suppression domain. Taken together, these studies suggest that the suppression domain of WT1 interacts with a cosuppressor protein to mediate inhibition of the WT1 transcriptional activation domain.

Tumor-associated WT1 missense mutants indicate that transcriptional activation by WT1 is critical for growth control

The WT1 gene encodes a zinc finger DNA binding transcription factor and is mutated in up to 15% of Wilms tumor cases. The WT1 protein binds to the promoters of many genes through GC- or TC-rich sequences and can function both as a transcriptional repressor and an activator in co-transfection assays depending on the cell type, the structure of the test promoter, and even the expression vectors used. Engineered expression of WT1 can lead to growth suppression by both cell cycle arrest and induction of apoptosis. However, the transcriptional activity of WT1 that is required for growth control was not defined. We found that three N-terminal tumor-associated missense mutations of WT1 were defective for activation of both a synthetic reporter containing WT1-binding sites as well as the promoter of a WT1 responsive gene, p21. These mutants failed to inhibit cell growth but still retain their ability to repress several putative WT1 target promoters. These results indicate that activation and not repression by WT1 is the critical transcriptional activity of the protein responsible for its growth suppressing properties.

A zinc finger truncation of murine WT1 results in the characteristic urogenital abnormalities of Denys-Drash syndrome

The Wilms tumor-suppressor gene, WT1, plays a key role in urogenital development, and WT1 dysfunction is implicated in both neoplastic (Wilms tumor, mesothelioma, leukemias, and breast cancer) and nonneoplastic (glomerulosclerosis) disease. The analysis of diseases linked specifically with WT1 mutations, such as Denys-Drash syndrome (DDS), can provide valuable insight concerning the role of WT1 in development and disease. DDS is a rare childhood disease characterized by a nephropathy involving mesangial sclerosis, XY pseudohermaphroditism, and/or Wilms tumor (WT). DDS patients are constitutionally heterozygous for exonic point mutations in WT1, which include mutations predicted to truncate the protein within the C-terminal zinc finger (ZF) region. We report that heterozygosity for a targeted murine Wt1 allele, Wt1(tmT396), which truncates ZF3 at codon 396, induces mesangial sclerosis characteristic of DDS in adult heterozygous and chimeric mice. Male genital defects also were evident and there was a single case of Wilms tumor in which the transcript of the nontargeted allele showed an exon 9 skipping event, implying a causal link between Wt1 dysfunction and Wilms tumorigenesis in mice. However, the mutant WT1(tmT396) protein accounted for only 5% of WT1 in both heterozygous embryonic stem cells and the WT. This has implications regarding the mechanism by which the mutant allele exerts its effect.

Developmental expression patterns of mouse sFRP genes encoding members of the secreted frizzled related protein family

Development of the metanephric kidney is an experimental model system to analyze interactions between mesenchymal and epithelial cells and mesenchymal-epithelial transition. To study the underlying genetic mechanisms we employed organ culture and differential display PCR to identify genes regulated upon induction of mesenchymal cells. One of the genes found encodes the secreted frizzled related protein 2 (sFRP2) that is upregulated within 2 days of in vitro development. In vivo sFRP2 expression was likewise found in mesenchymal condensates and subsequent epithelial structures. Detailed in situ hybridization analysis revealed sFRP2 expression during development of the eye, brain, neural tube, craniofacial mesenchyme, joints, testis, pancreas and below the epithelia of oesophagus, aorta and ureter where smooth muscles develop. In a comparative analysis transcripts of the related sFRP1 and sFRP4 genes were frequently found in the same tissues as sFRP2 with their expression domains overlapping in some instances, but mutually exclusive in others. While sFRP1 is specifically expressed in the embryonic metanephros, eye, brain, teeth, salivary gland and small intestine, there is only weak expression of sFRP4 except for the developing teeth, eye and salivary gland. The interpretation of the highly specific spatial and temporal expression patterns of sFRP genes will partly depend on a better functional understanding of the interaction between wnt, fz and sFRP family members. Nevertheless, sFRP genes must play quite distinct roles in the morphogenesis of several organ systems.