The Wilms' tumor gene product, WT1, represses transcription of the platelet-derived growth factor A-chain gene

The -KTS splice variant of WT1 is essential for ovarian determination in mice

Sex determination in mammals depends on the differentiation of the supporting lineage of the gonads into Sertoli or pregranulosa cells that govern testis and ovary development, respectively. Although the Y-linked testis-determining gene Sry has been identified, the ovarian-determining factor remains unknown. In this study, we identified -KTS, a major, alternatively spliced isoform of the Wilms tumor suppressor WT1, as a key determinant of female sex determination. Loss of -KTS variants blocked gonadal differentiation in mice, whereas increased expression, as found in Frasier syndrome, induced precocious differentiation of ovaries independently of their genetic sex. In XY embryos, this antagonized Sry expression, resulting in male-to-female sex reversal. Our results identify -KTS as an ovarian-determining factor and demonstrate that its time of activation is critical in gonadal sex differentiation.

G-quadruplexes in cancer-related gene promoters: from identification to therapeutic targeting

INTRODUCTION

Guanine-rich DNA sequences can fold into four-stranded noncanonical secondary structures called G-quadruplexes (G4s) which are widely distributed in functional regions of the human genome, such as telomeres and gene promoter regions. Compelling evidence suggests their involvement in key genome functions such as gene expression and genome stability. Notably, the abundance of G4-forming sequences near transcription start sites suggests their potential involvement in regulating oncogenes.

AREAS COVERED

This review provides an overview of current knowledge on G4s in human oncogene promoters. The most representative G4-binding ligands have also been documented. The objective of this work is to present a comprehensive overview of the most promising targets for the development of novel and highly specific anticancer drugs capable of selectively impacting the expression of individual or a limited number of genes.

EXPERT OPINION

Modulation of G4 formation by specific ligands has been proposed as a powerful new tool to treat cancer through the control of oncogene expression. Actually, most of G4-binding small molecules seem to simultaneously target a range of gene promoter G4s, potentially influencing several critical driver genes in cancer, thus producing significant therapeutic benefits.

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.

CMIP interacts with WT1 and targets it on the proteasome degradation pathway

BACKGROUND

The Wilms tumor 1 suppressor gene, WT1, is expressed throughout life in podocytes and is essential for their function. Downregulation of WT1 has been reported in podocyte diseases but the underlying mechanisms remain unclear. Podocyte injury is the hallmark of idiopathic nephrotic syndrome (INS), the most frequent glomerular disease in children and young adults. An increase in the abundance of Cmaf-inducing protein (CMIP) has been found to alter podocyte function, but it is not known whether CMIP affects WT1 expression.

METHODS

Transcriptional and post-transcriptional regulation of WT1in the presence of CMIP was studied using transient transfection, mouse models, and siRNA handling.

RESULTS

We showed that overproduction of CMIP in the podocyte was consistently associated with a downregulation of WT1 according to two mechanisms. We found that CMIP prevented the NF-kB-mediated transcriptional activation of WT1. We demonstrated that CMIP interacts directly with WT1 through its leucine-rich repeat domain. Overexpression of CMIP in the M15 cell line induced a downregulation of WT1, which was prevented by lactacystin, a potent proteasome inhibitor. We showed that CMIP exhibits an E3 ligase activity and targets WT1 to proteasome degradation. Intravenous injection of Cmip-siRNA specifically prevented the repression of Wt1 in lipopolysaccharides-induced proteinuria in mice.

CONCLUSIONS

These data suggest that CMIP is a repressor of WT1 and might be a critical player in the pathophysiology of some podocyte diseases. Because WT1 is required for podocyte integrity, CMIP could be considered a therapeutic target in podocyte diseases.

Role for Egr1 in the Transcriptional Program Associated with Neuronal Differentiation of PC12 Cells

PC12 cells are a well-established model to study how differences in signal transduction duration can elicit distinct cell behaviors. Epidermal growth factor (EGF) activates transient ERK signaling in PC12 cells that lasts 30–60 min, which in turn promotes proliferation; nerve growth factor (NGF) activates more sustained ERK signaling that lasts 4–6 h, which in turns induces neuronal differentiation. Data presented here extend a previous study by Mullenbrock et al. (2011) that demonstrated that sustained ERK signaling in response to NGF induces preferential expression of a 69-member gene set compared to transient ERK signaling in response to EGF and that the transcription factors AP-1 and CREB play a major role in the preferential expression of several genes within the set. Here, we examined whether the Egr family of transcription factors also contributes to the preferential expression of the gene set in response to NGF. Our data demonstrate that NGF causes transient induction of all Egr family member transcripts, but a corresponding induction of protein was detected for only Egr1 and 2. Chromatin immunoprecipitation experiments provided clearest evidence that, after induction, Egr1 binds 12 of the 69 genes that are preferentially expressed during sustained ERK signaling. In addition, Egr1 expression and binding upstream of its target genes were both sustained in response to NGF versus EGF within the same timeframe that its targets are preferentially expressed. These data thus provide evidence that Egr1 contributes to the transcriptional program activated by sustained ERK signaling in response to NGF, specifically by contributing to the preferential expression of its target genes identified here.

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.

Prognostic significance of WT1 expression in soft tissue sarcoma

Background

Soft tissue sarcomas (STS) are rare. We evaluated the WT1 protein expression level in various types of STS and elucidated the value of WT1 as a prognostic factor and a possible therapeutic target.

Methods

Immunohistochemical staining for WT1 was performed in 87 cases of STS using formalin-fixed, paraffin-embedded blocks. The correlation between WT1 expression and clinicopathological factors was analyzed. Survival analysis was conducted in 67 patients. We assessed the validity of WT1 immunohistochemistry as an index of WT1 protein expression using Western blot analysis.

Results

WT1 expression was noted in 47 cases (54.0%). Most rhabdomyosarcomas and malignant peripheral nerve sheath tumors showed WT1 expression (91.7% and 71.4%, respectively; P = 0.005). WT1 expression was related to higher FNCLCC histologic grade and AJCC tumor stage. In the group with high grade STS, strong WT1 expression was correlated with better survival (P = 0.025). The immunohistochemical results were correlated quantitatively with the staining score and the concentration of the Western blot band.

Conclusions

This study demonstrates that various types of STS show positive immunostaining for WT1 and that WT1 expression has a prognostic significance. So STS should be considered candidates for WT1 peptide--based immunotherapy.

Expression of inhibin-alpha is regulated synergistically by Wilms' tumor gene 1 (Wt1) and steroidogenic factor-1 (Sf1) in sertoli cells

Wt1 encodes a zinc finger nuclear transcriptional factor, which is specifically expressed in testicular Sertoli cells and knockdown of Wt1 in Sertoli cells causes male mice subfertility. However, the underlying mechanism is still unclear. In this study, we found that expression of inhibin-α is significantly reduced in Wt1-deficient Sertoli cells. Luciferase assays using the inhibin-α promoter indicated that the inhibin-α promoter is transactivated by the Wt1 A, and B isoforms (−KTS), but not the C, and D isoforms (+KTS). Analysis of the Wt1 responsive element of the inhibin-α promoter region using site-directed mutagenesis showed that the nucleotides between −58 and −49 are essential for Wt1-dependent transactivation of the inhibin-α promoter. ChIP assays indicated that Wt1 directly interacts with the inhibin-α promoter. In addition, the inhibin-α promoter is activated synergistically by Wt1 and Sf1. Mutation of the ligand binding domain (LBD) of Sf1 (residues 235–238) completely abolished the synergistic action between Wt1 and Sf1, but did not affect the physical interaction between these two proteins, suggesting that other factor(s) may also be involved in the regulation of inhibin-α in Sertoli cells. Further studies demonstrated that β-catenin enhances the synergistic activation of Wt1 and Sf1 on the inhibin-α promoter. Given the fact that inhibin-α, a subunit of inhibin, is known to be involved in the regulation of spermatogenesis and testicular steroidogenesis, this study reveals a new regulatory mechanism of inhibin-α in Sertoli cells and also sheds light on the physiological functions of Wt1 in gonad development and spermatogenesis.

Low Wilms' tumor gene expression in tumor tissues predicts poor prognosis in patients with non-small-cell lung cancer

We elucidated the relationship between prognosis of non-small-cell lung cancer (NSCLC) and Wilms' tumor gene (WT1) mRNA expression in tumor tissue. The WT1 mRNA expression levels of the fatal cases were lower as compared with those of the survival cases. Overall survival (OS) and disease-free survival (DFS) of the high WT1 expression group were longer than of the low expression group. As for squamous cell lung cancer (SQLC), low WT1 expression was significantly associated with lymph node metastasis. Cox analysis revealed that the gene level was a significant prognostic factor in OS and DFS. Low WT1 expression predicted poor prognosis in patients with NSCLC.

Wilms tumor suppressor 1 (WT1) and early growth response 1 (EGR1) are regulators of STIM1 expression

Store-operated calcium entry (SOCE) is a key evolutionarily conserved process whereby decreases in endoplasmic reticulum Ca(2+) content lead to the influx of Ca(2+) across the plasma membrane. How this process is regulated in specific tumor cell types is poorly understood. In an effort to address this concern, we obtained and tested primary Wilms tumor cells, finding no detectable SOCE in this cell type. Analysis of the expression levels of STIM1 and ORAI1 (the molecular mediators of SOC) revealed poor STIM1 expression. Analysis of the STIM1 promoter using the TESS search system (University of Pennsylvania) revealed four putative response elements to the zinc-finger proteins WT1 (Wilms tumor suppressor 1) and EGR1 (early growth response 1). Either overexpression of WT1 or knockdown of EGR1 resulted in loss of STIM1 expression and a resultant decrease in SOCE. Furthermore, examination of Egr1 knock-out animals revealed loss of STIM1 expression in multiple tissues. Finally, using chromatin immunoprecipitation, we reveal direct binding of both WT1 and EGR1 to putative response elements located within 500 bp of the transcriptional start site of STIM1. Considering that WT1 and EGR1 are well described oncogenes and tumor suppressors, these observations may reveal new mechanisms responsible for distinct Ca(2+) signals in cancer cells.

WT-1 expression in gastrointestinal stromal tumours

AIMS

Wilms' tumour-1 (WT-1) encodes a transcription factor originally identified as a tumour suppressor gene, whose mutations are responsible for tumorigenesis of Wilms' tumour. The overexpression of WT-1 has been demonstrated in variable tumours. In this study, WT-1 immunoreactivity was explored in 97 gastrointestinal stromal tumours (GISTs).

METHODS

The expression of WT-1 was compared with other immunohistochemical markers of GIST and the association with clinicopathological features was also evaluated. For comparison, six melanomas and 71 soft tissue tumours were used.

RESULTS

All 97 GISTs were positive for WT-1 and the staining intensity was strong in 59 (60.8%), moderate in 28 (28.9%) and weak in 10 cases (10.3%). Cytoplasmic staining with moderate to strong intensity was more frequent in GISTs positive for platelet-derived growth factor receptor-alpha (PDGFRA) (p = 0.04). However, WT-1 immunoreactivity was not related to the clinicopathological variables, including tumour location, histological subtype, risk of progression and recurrence status. Leiomyosarcomas, schwannomas, malignant peripheral nerve sheath tumours (MPNSTs) and melanomas showed cytoplasmic staining, whereas leiomyomas and mesenteric fibromatoses were totally negative for WT-1.

CONCLUSIONS

Although the biological roles of WT-1 in GIST are still unknown, our findings might provide a rationale for immunotherapy targeting WT-1 and a therapeutic solution to the challenge of imatinib-resistant GISTs.

Dynamic interaction between WT1 and BASP1 in transcriptional regulation during differentiation

The Wilms' tumour suppressor protein WT1 plays a central role in the development of the kidney and also other organs. WT1 can act as a transcription factor with highly context-specific activator and repressor functions. We previously identified Brain Acid Soluble Protein 1 (BASP1) as a transcriptional cosuppressor that can block the transcriptional activation function of WT1. WT1 and BASP1 are co-expressed during nephrogenesis and both proteins ultimately become restricted to the podocyte cells of the adult kidney. Here, we have analysed the WT1/BASP1 complex in a podocyte precursor cell line that can be induced to differentiate. Chromatin immunoprecipitation revealed that WT1 and BASP1 occupy the promoters of the Bak, c-myc and podocalyxin genes in podocyte precursor cells. During differentiation-dependent upregulation of podocalyxin expression BASP1 occupancy of the podocalyxin promoter is reduced compared to that of WT1. In contrast, the repressive WT1/BASP1 occupancy of the c-myc and Bak promoters is maintained and these genes are downregulated during the differentiation process. We provide evidence that the regulation of BASP1 promoter occupancy involves the sumoylation of BASP1. Our results reveal a dynamic cooperation between WT1 and BASP1 in the regulation of gene expression during differentiation.

PDGF-A promoter and enhancer elements provide efficient and selective antineoplastic gene therapy in multiple cancer types

Development of antineoplastic gene therapies is impaired by a paucity of transcription control elements with efficient, cancer cell-specific activity. We investigated the utility of promoter (AChP) and 5'-distal enhancer (ACE66) elements from the platelet-derived growth factor-A (PDGF-A) gene, which are hyperactive in many human cancers. Efficacy of these elements was tested in multiple tumor cell lines, both in cell culture and as tumor explants in athymic nude mice. Plasmid and viral vectors were constructed with the AChP promoter alone or in fusion with three copies of the ACE66 enhancer for expression of the prototype suicide gene, thymidine kinase (TK). ACE/AChP and AChP cassettes elicited ganciclovir (GCV)-induced cytotoxicity in multiple tumor cell lines. The ACE enhancer element also exhibited synergism with placental and liver-specific promoter elements. An adenovirus containing the AChP-TK cassette produced striking increases in GCV sensitivity in cultured tumor cell lines, as well as GCV-induced regression of U87 MG glioblastoma explants in vivo. TK expression was distributed throughout tumors receiving the therapeutic virus, whereas TdT-mediated dUTP nick end labeling (TUNEL) analysis revealed numerous regions undergoing apoptosis. Vascularization and reticulin fiber networks were less pronounced in virus-GCV-treated tumors, suggesting that both primary and stromal cell types may have been targeted. These studies provide proof-of-principle for utility of the PDGF-A promoter and ACE66 enhancer in antineoplastic gene therapy for a diverse group of human cancers.

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.

Wilms' tumour 1 gene expression is increased in hepatocellular carcinoma and associated with poor prognosis

BACKGROUND/AIMS

Wilms' tumour 1 gene (WT1) was originally isolated as a tumour-suppressor gene. We investigated the expression of WT1 in hepatocellular carcinoma (HCC; T) and in non-cancerous hepatic tissues (non-tumour: NT) from patients with chronic liver diseases, and then examined the role of WT1 in the carcinogenesis or prognosis of HCC.

METHODS

The expression of WT1 in T and NT from 50 patients with HCC was investigated using Western blotting, immunohistochemistry and real-time reverse transcriptase-polymerase chain reaction (RT-PCR). We also examined whether WT1 expression was related to clinicopathological factors in individual patients in addition to prognostic factors in 50 patients with HCC and in 26 without HCC.

RESULTS

Western blotting and immunohistochemical staining showed that WT1 was overexpressed in T compared with NT (P<0.001) and real-time reverse transcriptase-polymerase chain reaction (RT-PCR) showed that WT1 mRNA expression was similarly increased. Overexpressed WT1 in HCC was significantly associated with T factors at the TNM stage, and short doubling time of HCC. Univariate and multivariate analyses revealed that WT1 overexpression was an independent prognostic factor for HCC. The disease-free survival period in patients with overexpressed WT1 in NT tissues was significantly reduced.

CONCLUSION

The expression of WT1 is increased more in HCC than in non-tumour tissues. Moreover, overexpressed WT1 was associated with tumour growth, and resulted in a worsening prognosis of HCC. Our findings from NT tissues revealed that WT1 overexpression might contribute to oncogenic potential.

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 transcription factor Wilms tumor 1 regulates matrix metalloproteinase-9 through a nitric oxide-mediated pathway

Matrix metalloproteinase-9 (MMP-9) is released by human lung epithelial cells (LEC) in conditions such as asthma and chronic obstructive pulmonary disease and expression of MMP-9 correlates with the severity of these disorders. MMP-9 production has been reported to be regulated by a NO/soluble guanylate cyclase-dependent pathway. Transcriptional regulation of this enzyme, however, is poorly understood. Using phylogenetic analysis, we observed a highly conserved sequence in the 5' flanking region of the MMP-9 gene containing binding sites for the transcription factor Wilms tumor 1 (WT1). We confirmed the presence of WT1 in human LEC and that treatment with TNF or a mixture containing LPS, PMA, and IFN-gamma resulted in translocation of WT1 from the nucleus to the cytosol. This translocation coincided with increased expression of MMP-9 and could be blocked by inhibitors of the NO/soluble guanylate cyclase pathway. WT1 knockdown using small-interfering RNA up-regulated MMP-9 expression in the presence of the NO synthase inhibitor 1400W. Using either WT1 pulldown with probes for the conserved region of the MMP-9 promoter or chromatin immunoprecipitation, we confirmed WT1 binding to the MMP-9 promoter. These findings indicate WT1 is a repressor of MMP-9, regulated by a NO-mediated pathway in human LEC. To our knowledge, this is the first report of WT1 regulating MMP-9 expression. Further study is needed to determine whether clinical conditions exhibiting tissue remodeling, such as asthma and/or chronic obstructive pulmonary disease, demonstrate reduced levels of WT1 or its repressor activity.

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.

High WT1 expression is associated with very poor survival of patients with osteogenic sarcoma metastasis

PURPOSE

Although metastasis is the primary determinant of poor survival of patients with osteogenic sarcoma, some patients live much longer than others, indicating metastatic heterogeneity underlying survival outcome. The purpose of the investigation was to identify genes underlying survival outcome of patients with osteogenic sarcoma metastasis.

EXPERIMENTAL DESIGN

We have used microarray to first compare mRNA expression between normal bone and osteogenic sarcoma specimens, identified genes overexpressed in osteogenic sarcoma, and compared expression of the selected gene between a poorly metastatic (SAOS) and two highly metastatic cell lines (LM8 and 143B). Finally, expression of the selected gene was assessed by immunostaining of osteogenic sarcoma samples with known survival outcome.

RESULTS

Microarray analysis revealed 5.3-fold more expression of WT1 mRNA in osteogenic sarcoma compared with normal bone and >2-fold overexpression in 143B and LM8 cells compared with SAOS. Furthermore, WT1 mRNA was absent in normal bone (10 of 10) by reverse transcription-PCR but present in osteogenic sarcoma-derived cell lines (5 of 8). One hundred percent (42 of 42) of low-grade osteogenic sarcoma specimens expressed no WT1 as determined by immunostaining; however, 24% (12 of 49) of the high-grade specimens showed intense staining. Mean survival of patients with high-grade metastatic osteogenic sarcoma but low WT1 staining (27 of 37) was 96.5 +/- 129.3 months, whereas mean survival of patients with high-grade metastatic osteogenic sarcoma having intense staining (10 of 37) was 18.3 +/- 12.3 months (P > 0.0143). All splice variants of WT1 mRNA, including a hitherto unknown variant (lacking exons 4 and 5), were found to be expressed in osteogenic sarcoma.

CONCLUSION

WT1 seems to be associated with very poor survival of patients with osteogenic sarcoma metastasis.

The WT1 Wilms' tumor suppressor gene is a downstream target for insulin-like growth factor-I (IGF-I) action in PC12 cells

The biological actions of the insulin-like growth factors, IGF-I and IGF-II, are mediated by the ligand-induced activation of the IGF-I receptor (IGF-IR), a transmembrane heterotetramer linked to the ras-raf-mitogen-activated protein kinase (MAPK) and phosphatidyl inositol 3 kinase (PI3K)-protein kinase B (PKB)/Akt signal transduction cascades. The Wilms' tumor suppressor gene (wt1) encodes a zinc finger transcription factor, WT1, which has been implicated in various cellular processes including proliferation, differentiation and apoptosis. In the present study we demonstrated that IGF-I modulates the WT1 gene expression in neurally derived PC12 cells in a dose- and time-dependent manner. This effect was mediated through both the MAPK and PI3-kinase signaling pathways, as shown by the ability of the specific inhibitors UO126 and LY294002 to abrogate IGF-I action. Moreover, using RT-PCR and transient transfection assays, we demonstrated that the IGF-I effect was associated with corresponding changes in WT1 mRNA levels and WT1 promoter activity. In addition, the results of the present study revealed that high WT1 levels were associated with the induction of apoptosis, whereas low WT1 levels were correlated with the inhibition of apoptosis, as demonstrated by poly ADP ribose polymerase (PARP) cleavage, Bax expression, Annexin V-FITC staining, and by the use of antisense oligonucleotides against WT1. In summary, our results show that the wt1 gene is a novel target for IGF-I action in neurally derived cells.

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.

Single chain antibody against the common epitope of mutant p53 restores wild-type activity to mutant p53 protein

Here, we describe the biological activity of ME1, a mouse single chain Fv fragment (scFv) against the common epitope of mutant p53, which is efficiently expressed in mammalian cells. We found that in vivo interaction of the conformational p53 mutant R175H protein with the scFv resulted in the acquisition of wild-type p53 characteristics, manifested in trans-activation of p21, as well as induction of apoptosis. Moreover, antibody binding leads to abrogation of the mutant p53 mediated "gain of function" as estimated by downregulation of EGR-1, a transcriptional target of mutant p53. These findings suggest that the scFv restores wild-type properties to mutant p53.

A 5'-distal enhanceosome in the PDGF-A gene is activated in choriocarcinoma cells via ligand-independent binding of vitamin D receptor and constitutive jun kinase signaling

Overexpression of platelet-derived growth factor A-chain (PDGF-A) is clearly linked to autocrine and paracrine stimulation of malignant growth in many human cancers. We have shown previously that PDGF-A overexpression in choriocarcinoma, hepatoma and lung carcinoma cell lines is driven by the activity of a 66 bp enhancer element (ACE66) located approximately 7 kb upstream of the PDGF-A transcription start site. In this study, the ACE66 element is shown to be activated in JEG-3 choriocarcinoma cells through synergistic interactions between consensus DNA motifs for binding of vitamin D receptor, AP1 and ELK1. Binding of the vitamin D/retinoid-X receptor (VDR/RXRalpha) heterodimer to the ACE66 element was reconstituted in vitro with recombinant VDR/RXRalpha and with JEG-3 nuclear extract, and was verified in living JEG-3 cells by chromatin immunoprecipitation analysis. Transcriptional activity of the ACE66 element, as well as occupancy of the element by VDR/RXRalpha, was shown to be independent of stimulation with the hormonal VDR ligand, 1,25-dihydroxyvitamin D3. The jun kinase pathway of mitogen-activated protein kinase (MAPK) signaling was shown to activate the ACE66 enhancer, most likely through activation of factors binding to the AP1 element. These results identify a novel mechanism of transcriptional enhancement involving ligand-independent activity of the VDR/RXR heterodimer and MAPK signaling pathways that appears to play an important role in the overexpression of PDGF in many different settings of human malignancy.

PDGF-A, PDGF-Rbeta, TGFbeta3 and bone morphogenic protein-4 in desmoplastic small round cell tumors with EWS-WT1 gene fusion product and their role in stromal desmoplasia: an immunohistochemical study

Histologically, desmoplastic small round cell tumor is composed of the characteristic neoplastic small round cells with divergent differentiation, and distinct desmoplastic stroma. Genetically, the tumor shows a characteristic 11;22 translocation, involving the EWS gene on chromosome 22 and the WT1gene on chromosome 11 to produce an EWS-WT1 fusion gene which generates a chimeric protein functioning as a novel transcription factor that activates expression of target genes such as PDGF-A. Expression of PDGF-A, a potent growth factor for fibroblasts, has been detected in desmoplastic small round cell tumors and has been linked to the characteristic desmoplasia in these tumors. Bone morphogenic proteins, which are members of the TGFbeta superfamily play a complex role in regulating cell growth and differentiation and bone formation but have not been evaluated in desmoplastic small round cell tumors. In all, 24 desmoplastic small round cell tumors with EWS-WT1 fusion product confirmed by RT-PCR analysis were evaluated for expression of PDGF-A, PDGF-Rbeta, TGFbeta3 and bone morphogenic protein-4 by standard immunohistochemical methods with antigen retrieval on paraffin sections. Immunoreactivity was evaluated semiquantitively. Tumor-associated desmoplasia was quantified using a three-tier scale on hematoxylin- and eosin-stained sections. Desmoplastic small round cell tumors showed variable immunoreactivity with TGFbeta3 (21/24), BMP4 (14/21), PDGF-A (19/24) and PDGF-Rbeta (16/22). Less frequently, the stromal cells showed reactivity with TGFbeta3, PDGF-Rbeta and PDGF-A. Tumor-associated desmoplasia was prominent in eight, intermediate in seven and weak in nine cases. There was no correlation between tumor-associated desmoplasia and the markers tested except PDGF-A. In contrast to a previous study, our study showed that the level of PDGF-A expression inversely correlated with tumor-associated desmoplasia. Other targets of the EWS-WT1 transcription factor other than PDGF-A may be directly responsible for the prominent tumor-associated desmoplasia seen in desmoplastic small round cell tumor.

Transactivation of the EGR1 gene contributes to mutant p53 gain of function

Tumor-associated mutants of the p53 tumor suppressor protein exert biological activities compatible with an oncogenic gain of function. To explore the underlying molecular mechanism, we performed microarray analysis, comparing p53-null cells to mutant p53-expressing cells. One of the genes up-regulated in the presence of mutant p53 was EGR1, a transcription factor implicated in growth control, apoptosis, and cancer. EGR1 induction by various types of stress is markedly augmented in cells expressing mutant p53. Moreover, chromatin immunoprecipitation analysis indicates that mutant p53 is physically associated with the EGR1 promoter. Functional assays indicate that induction of EGR1 by mutant p53 contributes to enhanced transformed properties and resistance to apoptosis. We propose that EGR1 is a significant contributor to mutant p53 gain of function.

Ets-1 stimulates platelet-derived growth factor A-chain gene transcription and vascular smooth muscle cell growth via cooperative interactions with Sp1

The platelet-derived growth factor (PDGF) family of ligands (composed of A-, B-, C-, and D-chains), potent mitogens, and chemoattractants for cells of mesenchymal origin has been implicated in numerous vascular pathologies involving smooth muscle cell (SMC) hyperplasia. Understanding the molecular mechanisms mediating PDGF transcription would provide new insights into strategies to control PDGF-dependent pathophysiologic processes. We demonstrated previously that PDGF-A expression is under the positive regulatory influence of Sp1, Sp3, and Egr-1 and is negatively controlled by GCF2, NF-1(X), and WT-1. In this article, we demonstrate that Ets-1 induces PDGF-A expression in primary rat aortic SMCs at the level of transcription and mRNA expression. Electrophoretic mobility shift, supershift, and mutational analyses revealed a functional role for the (-555)TTCC(-552) motif in the PDGF-A promoter that binds endogenous Ets-1. Chromatin immunoprecipitation analysis showed the interaction of endogenous and exogenous Ets-1 or glutathione S-transferase-tagged Ets-1, bearing only the DNA-binding domain with the authentic PDGF-A promoter. Conversely, dominant-negative mutant of Ets-1 blocked the promoter interaction of endogenous Ets-1. Overexpression of Ets-1 but not the mutant form of Ets-1 activates the PDGF-A promoter cooperatively with Sp1. Sp1, which interacts with Ets-1, failed to induce PDGF-A promoter-dependent expression if the promoter contained a site-specific mutation in this novel Ets-binding site. Small interfering RNA to Ets-1 and Sp1 blocked PDGF-BB- and serum-inducible PDGF-A expression. SMC growth was stimulated by Ets-1 and Sp1 separately and further increased by both factors together. Ets-1-inducible mitogenesis is blocked by antibodies neutralizing PDGF-A and involves activation of the PDGF alpha-receptor, which binds PDGF-A. These findings identify a functional cis-acting element for Ets-1 in the PDGF-A promoter and demonstrate that Sp1 and Ets-1 cooperatively activate PDGF-A transcription in vascular SMCs.

WT1 is a tumor-associated antigen in colon cancer that can be recognized by in vitro stimulated cytotoxic T cells

The Wilms' tumor suppressor gene (WT1) has been shown to be overexpressed in acute and chronic leukemias and in a variety of solid human malignancies, including cancers of the breast and lung. In our present study, we investigated the potential role of WT1 gene in human colon cancer. WT1 mRNA and protein expression was analyzed in a panel of human colon cancer cell lines and primary colon carcinomas by RT-PCR and Western blot analysis, respectively. A mutational screen of WT1' zinc-finger region was carried out by sequence analysis. Finally, using peptide-stimulated cytotoxic T cells it was investigated whether WT1-expressing colon tumor cells are a potential target for antigen-specific immunotherapy. Medium to high abundant levels of WT1 mRNA were detected by RT-PCR in 10 of 12 (83%) colon cell lines and by quantitative, real-time RT-PCR in 13 of 15 (87%) primary tumors, whereas only very low levels of expression were found in 2 primary tumors. Interestingly, however, low levels of WT1 mRNA were also detected in all samples derived from normal colon mucosa. When RT-PCR products were examined by sequence analysis, both +KTS and -KTS splice isoforms but no zinc-finger mutations were found, suggesting that the wild-type form of the WT1 gene is expressed. To determine whether the WT1 protein can serve as a target antigen for immunotherapy, 2 HLA-A2.1-restricted WT1 peptides (Db126 and WH187) were used for the in vitro induction of WT1-specific cytotoxic T lymphocytes (CTLs). The WH187-specific CTLs not only lysed target cells pulsed exogenously with cognate peptide but also WT1-expressing colon tumor cells in a HLA-restricted manner. These findings identify the WT1 protein as an attractive target for the development of antigen-specific immunotherapy in human colon cancer.

Transcription of the platelet-derived growth factor A-chain gene

The molecular mechanisms which control the transcription of growth factor genes underlie such diverse biological processes as embryonic development, cellular differentiation and wound healing. Moreover, disruption of these controls is implicated in the development and progression of a wide variety of human diseases, including cancer, atherosclerosis and fibrotic disease. This review highlights progress made in the study of the gene encoding platelet-derived growth factor A-chain (PDGF-A) from the perspective of its normal patterns of expression, as well as possible mechanisms leading to dysregulation and disease. A particular focus has been placed on the identification and characterization of specific DNA elements, DNA-binding proteins and other aspects of transcriptional regulation involved in activation and repression of the human PDGF-A promoter.

Wilms' tumor suppressor (WT1) is a mediator of neuronal degeneration associated with the pathogenesis of Alzheimer's disease

Wilms' tumor suppressor (WT1), a 52- to 54-kda transcription factor, is the gene product of Wilms' tumor 1 (wt1), one of at least three genes involved in the development of a pediatric kidney cancer. Expression patterns of WT1 indicate that it is not restricted to the kidney but may play a role in the development and homeostasis of other tissues as well. WT1 has been implicated in various cellular processes including proliferation, differentiation, and apoptosis. High levels of WT1 induce apoptosis independent of p53, whereas low levels of WT1 inhibit apoptosis. Because apoptosis has been suggested to play a role in neurodegeneration in Alzheimer's disease (AD), immunohistochemistry of WT1 and paired helical filament (PHF) in serial sections was carried out. Immunohistochemical localization of WT1 and PHF showed the presence of WT1 in approximately 42% of PHF-positive neurofibrillary tangle containing-neurons. Laser confocal microscopy of hippocampal neuron cultures undergoing apoptosis induced by amyloid beta peptide (Abeta) or staurosporine demonstrated significant time-dependent elevations of WT1 correlating with increased levels of apoptosis. Blockade of WT1 transcription by antisense oligonucleotide reduced WT1 expression and prevented neuronal apoptosis in both Abeta- and staurosporine-treated cultures. Together, these data suggest a role for WT1 in the neurodegeneration observed in AD brain.

Upregulation of c-MYC in WT1-mutant tumors: assessment of WT1 putative transcriptional targets using cDNA microarray expression profiling of genetically defined Wilms' tumors

The Wilms' tumor suppressor gene, WT1, functions as a transcriptional regulator that represses or activates the expression of a variety of putative target genes. However, it is not clear which genes are the biological targets of WT1, nor which cellular pathway(s) is critically altered in tumors as a result of WT1 mutation. To investigate in vivo the role of WT1 as a transcription factor in Wilms' tumors, we used cDNA microarrays to compare the expression of putative WT1 target genes in a set of 15 primary Wilmstumors carrying WT1-inactivating mutations versus a set of 16 tumors with no WT1 mutations. We hypothesized that the expression of direct downstream targets of WT1 that are relevant to tumor development would differ between these two genetically distinct sets of tumors. Using the Atlas Human Cancer 1.2 cDNA arrays to quantitate gene expression in the 31 tumors, we found that the expression of one WT1 putative target gene, c-MYC, statistically significantly differed between the two sets of tumors and was upregulated in WT1-mutant tumors. This increase of relative gene expression for c-MYC was confirmed using real-time reverse transcription-polymerase chain reaction. The differential expression of another putative target gene, EGR1, approached significance and was also upregulated in WT1-mutant tumors. These data, in addition to the coexpression of c-MYC and WT1 in embryonic renal mesenchyme, strongly suggest that c-MYC is a biologically relevant target of WT1 in Wilmstumors.

Ligand-activated Ahr signaling leads to disruption of nephrogenesis and altered Wilms' tumor suppressor mRNA splicing

The aryl hydrocarbon receptor (Ahr), a member of the large basic helix-loop-helix (bHLH) and PAS homology domain superfamily, is a highly conserved transcriptional regulator involved in mammalian development. In the present study, a murine metanephros organ culture system was employed to evaluate the role of the Ahr signaling in nephrogenesis in vitro. Ahr and Wilms' tumor suppressor (wt1) mRNAs were detected by in situ hybridization and RT-PCR during the course of renal development. Treatment with 3 microM BaP, a hydrocarbon ligand of Ahr, inhibited glomerulogenesis and branching morphogenesis of metanephric kidneys. Deficits in the epithelialization of mesenchymal cells were evidenced by inhibition of the formation of podocyte foot processes and glomerular basement membranes. Hydrocarbon treatment markedly induced -KTS wt1 splice variants, although total wt1 mRNA levels remained unchanged. A significant decrease in total WT1 protein was observed by both immunocytochemistry and Western analysis in cultures challenged with BaP compared to controls. Comparison of metanephric cultures from Ahr+/+ and Ahr-/- mice showed that Ahr is involved in kidney development, and required for BaP-induced deficits in nephrogenesis. These results indicate that ligand activation of Ahr signaling disrupts nephrogenesis in vitro, and that this response involves modulation of wt1 alternative splicing and post-transcriptional control.

Overexpression of the Wilms' tumor gene WT1 in human bone and soft-tissue sarcomas

The expression levels of the Wilms' tumor gene WT1 were examined in 36 cases of various types of human bone and soft-tissue sarcomas using quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). They included 12 malignant fibrous histiocytomas (MFH), 3 malignant peripheral nerve sheath tumors (MPNST), 6 synovial sarcomas (SyS), 4 myxoid liposarcomas (MyLS), one angiosarcoma (AGS), one clear cell sarcoma (CCS), and 9 osteosarcomas (OS). Eleven (92%) of 12 MFH, 2 (67%) of 3 MPNST, all (100%) of 6 SyS, 2 (50%) of 4 MyLS, one AGS, one CCS, and 5 (56%) of 9 OS cases overexpressed WT1 in the range of 1.4 x 10(-3)-3.9 x 10(-1) levels (WT1 expression level in K562 leukemic cells was defined as 1.0). Thus, 28 (78%) out of 36 various types of human bone and soft-tissue sarcomas overexpressed the WT1 gene. Immunohistochemical analysis showed positive staining for WT1 protein in all of 4 cases (one case each of MFH, MyLS, AGS and OS) with WT1 gene overexpression detected by RT-PCR analysis, demonstrating clearly that WT1 was expressed at the protein level in various types of human bone and soft-tissue sarcomas. The direct sequencing analysis of the WT1 genomic DNA showed no mutations in any of 10 exons of the WT1 gene in 8 different sarcoma samples (3 MFH, one SyS, one MyLS, one AGS, and 2 OS). The present study demonstrates that various types of human bone and soft-tissue sarcomas frequently overexpress the wild-type WT1 gene, suggesting an important role of the wild-type WT1 gene in tumorigenesis of various types of human bone and soft-tissue sarcomas.

Interaction of early growth response protein 1 (Egr-1), specificity protein 1 (Sp1), and cyclic adenosine 3'5'-monophosphate response element binding protein (CREB) at a proximal response element is critical for gastrin-dependent activation of the chromogranin A promoter

Recently, binding of specific protein 1 (Sp1) and cAMP response element binding protein (CREB) to a GC-rich element at -92/-62 has been identified as a critical step in gastrin-dependent regulation of the chromogranin A (CgA) gene in gastric epithelial cells. Here we demonstrate that binding of early growth response protein 1 (Egr-1) to the distal part of the -92/-62 site is also required for gastrin-dependent CgA transactivation. Gastrin elevated cellular and nuclear Egr-1 levels in a time-dependent manner and also increased Egr-1 binding to the CgA -92/-73 region. Disruption of this site reduced gastrin responsiveness without influencing basal promoter activity, while loss of Sp1 and/or CREB binding sites diminished basal and gastrin-stimulated CgA promoter activity. Ectopic Egr-1 overexpression potently stimulated the CgA promoter, whereas coexpression of Egr-1 with Sp1 and/or CREB resulted in additive effects. Functional analysis of Sp1-, Egr-1-, or CREB-specific promoter mutations in transfection studies confirmed the tripartite organization of the CgA -92/-62 element. Signaling studies revealed that MAPK kinase 1 (MEK1)/ERK1/2 cascades are critical for gastrin-dependent Egr-1 protein accumulation as well as Egr-1 binding to the CgA promoter. Our studies for the first time identify Egr-1 as a nuclear target of gastrin and show that functional interplay of Egr-1, Sp1, and CREB is indispensable for gastrin-dependent CgA transactivation in gastric epithelial cells.

Wilms tumor gene (WT1) expression as a panleukemic marker

The Wilms tumor gene (WT1) is expressed in blasts of patients with acute leukemia, irrespective of lineage, and WT1 nuclear protein is detectable in the majority of such blasts. Only very few physiologic hematopoietic progenitors express WT1, but the WT1 expression level of these progenitors and that of leukemic blasts are comparable. Although not specific for acute hematologic malignant diseases, continuous WT1 expression in almost all leukemic blasts strikingly contrasts to its rather transient expression in very few physiologic hematopoietic progenitors. Quantitative and semiquantitative WT1 reverse transcriptase polymerase chain reaction (RT-PCR) protocols have limitations in discriminating physiologic from pathologic overall WT1 expression levels in mononuclear cell preparations. Because of these limitations, reports conflict on the usefulness of long-term monitoring of WT1 expression in patients with acute leukemia. Real-time quantitative WT1 RT-PCR protocols, however, have been developed and tested in small series of patients with acute leukemia. Such protocols hold promise to enable evaluation of the individual treatment response (short-term monitoring) and early diagnosis of imminent relapse through the detection and long-term monitoring of minimal residual disease in patients with acute leukemia. These protocols also should facilitate the notoriously difficult distinction between eosinophilic leukemia and hypereosinophilic syndromes. Data on WT1 expression in leukemic blasts and their physiologic counterparts are discussed in light of clinical relevance.

A review of the Wilms' tumor 1 gene (WT1) and its role in hematopoiesis and leukemia

One of the first clones of the Wilms tumor 1 (WT1) gene, WT33, was isolated from a B cell leukemia cell line in 1990. Now, 12 years on, WT1 has emerged as a potentially important target for antileukemic therapies. Our understanding of the role that WT1 plays during normal hematopoiesis is still limited, and there is a large amount of conflicting data concerning the precise manner in which WT1 gene expression contributes to leukemogenesis. However, interest in this field has intensified in the past 5 years. This review surveys the progress made in this area.

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.

Tumor suppressor genes in normal and malignant hematopoiesis

Over the last decade, a growing number of tumor suppressor genes have been discovered to play a role in tumorigenesis. Mutations of p53 have been found in hematological malignant diseases, but the frequency of these alterations is much lower than in solid tumors. These mutations occur especially as hematopoietic abnormalities become more malignant such as going from the chronic phase to the blast crisis of chronic myeloid leukemia. A broad spectrum of tumor suppressor gene alterations do occur in hematological malignancies, especially structural alterations of p15(INK4A), p15(INK4B) and p14(ARF) in acute lymphoblastic leukemia as well as methylation of these genes in several myeloproliferative disorders. Tumor suppressor genes are altered via different mechanisms, including deletions and point mutations, which may result in an inactive or dominant negative protein. Methylation of the promoter of the tumor suppressor gene can blunt its expression. Chimeric proteins formed by chromosomal translocations (i.e. AML1-ETO, PML-RARalpha, PLZF-RARalpha) can produce a dominant negative transcription factor that can decrease expression of tumor suppressor genes. This review provides an overview of the current knowledge about the involvement of tumor suppressor genes in hematopoietic malignancies including those involved in cell cycle control, apoptosis and transcriptional control.

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.

NF1/X represses PDGF A-chain transcription by interacting with Sp1 and antagonizing Sp1 occupancy of the promoter

The regulatory mechanisms mediating basal and inducible platelet-derived growth factor (PDGF)-A expression have been the focus of intense recent investigation, but repression of PDGF-A expression is largely unexplored. Here we isolated a nuclear factor that interacts with the proximal region of the PDGF-A promoter using bulk binding assays and chromatography techniques. Peptide mass fingerprint and supershift analysis revealed this DNA-binding protein to be NF1/X. NF1/X repressed PDGF-A promoter-dependent transcription and endogenous mRNA expression, which was reversible by oligonucleotide decoys bearing an NF1/X-binding site. Mutation in the DNA-binding domain of NF1/X abolished its repression of PDGF-A promoter. NF1/X antagonized the activity of a known activator of the PDGF-A chain, Sp1, by inhibiting its occupancy of the proximal PDGF-A promoter. NF1/X physically and specifically interacts with Sp1 via its subtype-specific domain and blocks Sp1 induction of the promoter. NF1/X residues 311-416 mediated NF1/X suppression of basal PDGF-A transcription, whereas residues 243-416 were required for NF1/X repression of Sp1-inducible promoter activity. These findings demonstrate that repression of PDGF-A gene transcription is governed by interplay between NF1/X and Sp1.

NM23-H1 and NM23-H2 repress transcriptional activities of nuclease-hypersensitive elements in the platelet-derived growth factor-A promoter

The platelet-derived growth factor (PDGF)-A promoter is regulated by a number of GC-rich regulatory elements that possess non-B-form DNA structures. Screening of a HeLa cDNA expression library with the C-rich strand of a PDGF-A silencer sequence (5'-S1 nuclease-hypersensitive site (SHS)) yielded three cDNA clones encoding NM23-H1, a protein implicated as a suppressor of metastasis in melanoma and breast carcinoma. Recombinant human NM23-H1 cleaved within the 3'-portions of both 5'-SHS strands in either single-stranded or duplex forms. In contrast, NM23-H2, known as a transcriptional activator with a DNA cleavage function, cleaved within the 5'-portions of both strands, revealing that NM23-H1 and NM23-H2 cleave at distinct sites of the 5'-SHS and by different mechanisms. NM23-H1 and NM23-H2 also cleaved within the PDGF-A basal promoter region, again exhibiting preferences for cleavage within the 5'- and 3'-portions of the element, respectively. Transient transfection analyses in HepG2 cells revealed that both NM23-H1 and -H2 repressed transcriptional activity driven by the PDGF-A basal promoter (-82 to +8). Activity of the negative regulatory region (-1853 to -883), which contains the 5'-SHS, was also inhibited modestly by NM23-H1 and NM23-H2. These studies demonstrate for the first time that NM23-H1 interacts both structurally and functionally with DNA. They also indicate a role for NM23 proteins in repressing transcription of a growth factor oncogene, providing a possible molecular mechanism to explain their metastasis-suppressing effects.

PDGF and the testis

Testicular development is controlled by a complex hierarchy of gene regulatory proteins, growth factors, cell adhesion molecules, signaling molecules and hormones that interact, often acting within short time windows, via reciprocal control relationships. The identification in the testis of platelet-derived growth factor (PDGF), a key regulator of connective tissue cells in embryogenesis and pathogenesis, has focused attention on the role of this growth factor in testicular pathophysiology. This review summarizes recent advances in the study of the actions of PDGF in the male gonad, and attempts to incorporate complex in vitro and in vivo experimental data into a model that might clarify the role played by PDGF in the mammalian testis.

WT1 proteins: functions in growth and differentiation

The Wilms' tumor 1 gene (WT1) has been identified as a tumor suppressor gene involved in the etiology of Wilms' tumor. Approximately 10% of all Wilms' tumors carry mutations in the WT1 gene. Alterations in the WT1 gene have also been observed in other tumor types, such as leukemia, mesothelioma and desmoplastic small round cell tumor. Dependent on the tumor type, WT1 proteins might either function as tumor suppressor proteins or as survival factors. Mutations in the WT1 gene can also result in congenital abnormalities as observed in Denys-Drash and Frasier syndrome patients. Mouse models have proven the critical importance of WT1 expression for the development of several organs, including the kidneys, the gonads and the spleen. The WT1 proteins seem to perform two main functions. They regulate the transcription of a variety of target genes and may be involved in post-transcriptional processing of RNA. The WT1 gene encodes at least 24 protein forms. These isoforms have partially distinct biological functions and effects, which in many cases are also specific for the model system in which WT1 is studied. This review discusses the molecular mechanisms by which the various WT1 isoforms exert their functions in normal development and how alterations in WT1 may lead to developmental abnormalities and tumor growth.

A functional interaction with CBP contributes to transcriptional activation by the Wilms tumor suppressor WT1

The Wilms tumor gene WT1 encodes a zinc finger transcription factor that is required for normal kidney development. WT1 was identified as a transcriptional repressor, based on its suppression of promoter reporters, but analysis of native transcripts using high density microarrays has uncovered transcriptional activation, rather than repression, of potential target genes. We report here that WT1 binds to the transcriptional coactivator CBP, leading to synergistic activation of a physiologically relevant promoter. The physical interaction between WT1 and CBP is evident in vitro and in vivo, and the two proteins are co-immunoprecipitated from embryonic rat kidney cells. The WT1-CBP association requires the first two zinc fingers of WT1 and the adenovirus 5 E1A-binding domain of CBP. Overexpression of this domain of CBP is sufficient to inhibit WT1-mediated transcriptional activation of a promoter reporter, as is co-transfection of E1A. Retrovirally driven expression of either the CBP fragment or of E1A in human hematopoietic cells suppresses the induction by WT1 of its endogenous target gene, p21(Cip1). These observations support a model of WT1 as a transcriptional activator of genes required for cellular differentiation.