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

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.

C2H2-Type Zinc Finger Proteins: Evolutionarily Old and New Partners of the Nuclear Hormone Receptors

Nuclear hormone receptors (NRs) are evolutionarily conserved ligand-dependent transcription factors. They are essential for human life, mediating the actions of lipophilic molecules, such as steroid hormones and metabolites of fatty acid, cholesterol, and external toxic compounds. The C2H2-type zinc finger proteins (ZNFs) form the largest family of the transcription factors in humans and are characterized by multiple, tandemly arranged zinc fingers. Many of the C2H2-type ZNFs are conserved throughout evolution, suggesting their involvement in preserved biological activities, such as general transcriptional regulation and development/differentiation of organs/tissues observed in the early embryonic phase. However, some C2H2-type ZNFs, such as those with the Krüppel-associated box (KRAB) domain, appeared relatively late in evolution and have significantly increased family members in mammals including humans, possibly modulating their complicated transcriptional network and/or supporting the morphological development/functions specific to them. Such evolutional characteristics of the C2H2-type ZNFs indicate that these molecules influence the NR functions conserved through evolution, whereas some also adjust them to meet with specific needs of higher organisms. We review the interaction between NRs and C2H2-type ZNFs by focusing on some of the latter molecules.

Genetic susceptibility to infectious diseases: Current status and future perspectives from genome-wide approaches

Genome-wide association studies (GWASs) have been widely applied to identify genetic factors that affect complex diseases or traits. Presently, the GWAS Catalog includes > 2800 human studies. Of these, only a minority have investigated the susceptibility to infectious diseases or the response to therapies for the treatment or prevention of infections. Despite their limited application in the field, GWASs have provided valuable insights by pinpointing associations to both innate and adaptive immune response loci, as well as novel unexpected risk factors for infection susceptibility. Herein, we discuss some issues and caveats of GWASs for infectious diseases, we review the most recent findings ensuing from these studies, and we provide a brief summary of selected GWASs for infections in non-human mammals. We conclude that, although the general trend in the field of complex traits is to shift from GWAS to next-generation sequencing, important knowledge on infectious disease-related traits can be still gained by GWASs, especially for those conditions that have never been investigated using this approach. We suggest that future studies will benefit from the leveraging of information from the host's and pathogen's genomes, as well as from the exploration of models that incorporate heterogeneity across populations and phenotypes. Interactions within HLA genes or among HLA variants and polymorphisms located outside the major histocompatibility complex may also play an important role in shaping the susceptibility and response to invading pathogens.

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Relatively few GWASs for infectious diseases were performed.

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Phenotype heterogeneity and case/control misclassification can affect GWAS power.

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Adaptive and innate immunity loci were identified in several infectious disease GWASs.

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Unexpected loci (e.g., lncRNAs) were also associated with infection susceptibility.

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GWASs should integrate host and pathogen diversity and use complex association models.

The transcriptional coregulator NAB2 is a target gene for the Wilms' tumor gene 1 protein (WT1) in leukemic cells

The Wilms’ tumor gene 1 (WT1) is recurrently mutated in acute myeloid leukemia. Mutations and high expression of WT1 associate with a poor prognosis. In mice, WT1 cooperates with the RUNX1/RUNX1T1 (AML1/ETO) fusion gene in the induction of acute leukemia, further emphasizing a role for WT1 in leukemia development. Molecular mechanisms for WT1 are, however, incompletely understood. Here, we identify the transcriptional coregulator NAB2 as a target gene of WT1. Analysis of gene expression profiles of leukemic samples revealed a positive correlation between the expression of WT1 and NAB2, as well as a non-zero partial correlation. Overexpression of WT1 in hematopoietic cells resulted in increased NAB2 levels, while suppression of WT1 decreased NAB2 expression. WT1 bound and transactivated the proximal NAB2 promoter, as shown by ChIP and reporter experiments, respectively. ChIP experiments also revealed that WT1 can recruit NAB2 to the IRF8 promoter, thus modulating the transcriptional activity of WT1, as shown by reporter experiments. Our results implicate NAB2 as a previously unreported target gene of WT1 and that NAB2 acts as a transcriptional cofactor of WT1.

The Incidence of and Factors Associated with Vitamin D Deficiency in Newly Diagnosed Children with Cancer

This retrospective chart review study aimed to assess vitamin D status and identify risk factors associated with vitamin D deficiency and bone parameters in children with cancer at admission. The data of 86 (50 males and 36 females) patients between April 2013 and June 2015 were analyzed. Calcium, phosphorus, alkaline phosphatase (ALP), 25(OH)D, age, gender, diagnostic category, body mass index, duration of complaints, and season of blood sampling were recorded. Median age was 7.17 years (range 0.31-17.40) in 29 hematological malignancy and 57 solid tumor patients. According to cut-off level of 20 ng/ml, 63% of children with cancer had vitamin D deficiency at diagnosis with a median 25(OH)D of 16.75 ng/ml. The mean vitamin D value of children >10 years was significantly low in comparison to that observed in younger children [11.83, 95% confidence interval (CI) = = 8.85-14.81 ng/ml vs. 19.81, 95% CI = = 17.02-22.60 ng/ml]. Vitamin D measurement between November and May was a risk factor for vitamin D deficiency (P < 0.05). The frequency of hypocalcemia and hypophosphatemia was not different between two groups of vitamin D. Further longitudinal studies are needed to investigate whether monitoring vitamin D status and supplementation in children with cancer might prevent future complications related to vitamin D deficiency.

WT1 and interferon-β-vitamin D association in MS: a longitudinal study

BACKGROUND

It has been suggested that polymorphisms in the WT1 gene modulate the effect of IFN-β treatment in multiple sclerosis (MS) through regulation of the relationship between IFN-β and vitamin D.

OBJECTIVE

To examine whether WT1 modulates the relationship between IFN-β and vitamin D in a longitudinal study with repeated assessment of vitamin D before and after initiation of IFN-β.

METHODS

In a prospective study of 85 patients with relapsing remitting MS, 25-hydroxyvitamin D was measured at month 0, 1, 3, 6, 7, 9, 12, 18 and 24. None of the patients used any immunomodulatory treatment at inclusion, and all started IFN-β treatment at month 6.

RESULTS

The mean concentrations of seasonally adjusted 25-hydroxyvitamin increased slightly (3.1 ± 1.2 nmol/l, P = 0.008) after initiation of IFN-β. The association between IFN-β treatment and 25-hydroxyvitamin D was similar in patients carrying any of the two alleles in the WT1 SNPs (rs10767935 and rs5030244) recently reported to modulate this relationship.

CONCLUSIONS

In this prospective study with repeated measurements of 25-hydroxyvitamin D before and during treatment with IFN-β, we did not find that genetic variation in WT1 plays any role in regulating the relationship between IFN-β and serum 25-hydroxyvitamin D.

WT1 expression in the human fetus during development

Wilms’ Tumor 1 (WT1) is a transcription factor involved in the development of the urogenital system. The purpose of this study was to analyze the immunoreactivity for WT1 protein in different tissues and organs in human fetuses in early phases of gestation. To this end, samples from multiple organs were obtained from 4 human fetuses, ranging from 7 up to 12 weeks of gestation. Each sample was formalin-fixed, paraffin embedded and immunostained for WT1. Our data show that WT1 is involved in development of multiple human organs in a more vast series of cells types than previously reported. Immunostaining for WT1 was characterized by a predominant cytoplasmic reactivity in the vast majority of cell types. Mesenchimal progenitors in the fetal lung, ductal plate progenitors in fetal liver, cap mesenchimal cells in the developing kidney, fetal zone cells in adrenal glands, atrial and ventricular cardiomyocytes in the fetal heart, radial glial cells in the fetal cerebral cortex and skeletal muscle cell precursors showed the highest levels of WT1 immunoreactivity. Future studies will be needed to detect differences in the expression of WT1 in various organs at different gestational ages, in order to better evaluate the role of WT1 in cell proliferation and differentiation during intrauterine human development.

Modulating effects of WT1 on interferon-β-vitamin D association in MS

OBJECTIVE

To investigate whether those genes involved in the vitamin D pathway modulate the relationship between 25-hydroxyvitamin D (25(OH)D) and IFN-β, the relationship between IFN-β and sun in predicting 25(OH)D, and the interaction between IFN-β and 25(OH)D in modulating relapse risk in patients with MS.

METHODS

Prospective cohort study of 169 participants with MS and genotype data followed 2002-2005. Gene-IFN-β and gene-IFN-β-sun interactions predicting 25(OH)D evaluated by multilevel mixed-effects linear regression. Gene-IFN-β interactions with 25(OH)D in modulating in relapse risk assessed using survival analysis.

RESULTS

The cohort was 71.6% female and of mean age 47.8. Two-independent intronic genotyped SNPs (rs10767935 and rs5030244) in WT1 significantly modified the IFN-β-25(OH)D association after adjustment (P(interaction) = 0.001, 0.0002; P(adj) = 0.003, 0.006, respectively). There was a marked difference in the interaction between self-reported sun exposure and IFN-β in predicting 25(OH)D by level of rs10767935, although this did not reach statistical significance. No SNPs modified the interaction between IFN-β and 25(OH)D in predicting relapse.

CONCLUSIONS

We have demonstrated that two-independent SNPs (rs10767935 and rs5030244) in WT1 modified the IFN-β-25(OH)D association in patients with MS. Some evidence was shown for a difference in the sun-IFN-β-25(OH)D association by level of rs10767935. These findings indicate that WT1 variants may play a role in altering the effects of IFN-β on vitamin D in MS.

Calcitriol restores antiestrogen responsiveness in estrogen receptor negative breast cancer cells: a potential new therapeutic approach

BACKGROUND

Approximately 30% of breast tumors do not express the estrogen receptor (ER) α, which is necessary for endocrine therapy approaches. Studies are ongoing in order to restore ERα expression in ERα-negative breast cancer. The aim of the present study was to determine if calcitriol induces ERα expression in ER-negative breast cancer cells, thus restoring antiestrogen responses.

METHODS

Cultured cells derived from ERα-negative breast tumors and an ERα-negative breast cancer cell line (SUM-229PE) were treated with calcitriol and ERα expression was assessed by real time PCR and western blots. The ERα functionality was evaluated by prolactin gene expression analysis. In addition, the effects of antiestrogens were assessed by growth assay using the XTT method. Gene expression of cyclin D1 (CCND1), and Ether-à-go-go 1 (EAG1) was also evaluated in cells treated with calcitriol alone or in combination with estradiol or ICI-182,780. Statistical analyses were determined by one-way ANOVA.

RESULTS

Calcitriol was able to induce the expression of a functional ERα in ER-negative breast cancer cells. This effect was mediated through the vitamin D receptor (VDR), since it was abrogated by a VDR antagonist. Interestingly, the calcitriol-induced ERα restored the response to antiestrogens by inhibiting cell proliferation. In addition, calcitriol-treated cells in the presence of ICI-182,780 resulted in a significant reduction of two important cell proliferation regulators CCND1 and EAG1.

CONCLUSIONS

Calcitriol induced the expression of ERα and restored the response to antiestrogens in ERα-negative breast cancer cells. The combined treatment with calcitriol and antiestrogens could represent a new therapeutic strategy in ERα-negative breast cancer patients.

Common variants at 11p13 are associated with susceptibility to tuberculosis

After imputation of data from the 1000 Genomes Project into a genome-wide dataset of Ghanaian individuals with tuberculosis and controls, we identified a resistance locus on chromosome 11p13 downstream of the WT1 gene (encoding Wilms tumor 1). The strongest signal was obtained at the rs2057178 SNP (P = 2.63 × 10(-9)). Replication in Gambian, Indonesian and Russian tuberculosis case-control study cohorts increased the significance level for the association with this SNP to P = 2.57 × 10(-11).

Biochemical and functional interaction between ZNF224 and ZNF255, two members of the Kruppel-like zinc-finger protein family and WT1 protein isoforms

Wilms' tumour suppressor gene, WT1, is mutated/deleted in approximately 15% of Wilms' tumours, highly expressed in the majority of other cancers and is essential for normal embryonic development. The gene encodes multiple isoforms of a zinc-finger (ZF) protein with diverse cellular functions, in particular participating in both transcriptional and post-transcriptional gene regulation. Physical interactions of other cellular proteins with WT1 are known to modulate its function. However, despite the isolation of several WT1-binding proteins, the mechanisms involved in regulating WT1 activities are not clearly understood. In this study, we report the identification of the Krüppel-like ZF protein, ZNF224, as a novel human WT1-associating protein and demonstrate that ZNF224 and its isoform ZNF255 show a specific pattern of interaction with the WT1 splicing variants WT1(-KTS) and WT1(+KTS). These interactions occur in different subcellular compartments and are devoted to control different cellular pathways. The nuclear interaction between ZNF224 and WT1(-KTS) results in an increase in trascriptional activation mediated by WT1, implying that ZNF224 acts as a co-regulator of WT1, whereas, on the contrary, the results obtained for ZNF255 suggest a role for this protein in RNA processing together with WT1. Moreover, our data give the first functional information about the involvement of ZNF255 in a specific molecular pathway, RNA maturation and processing.

CCAAT enhancer-binding protein alpha is a molecular target of 1,25-dihydroxyvitamin D3 in MCF-7 breast cancer cells

Numerous studies have shown that the active form of vitamin D, 1,25(OH)(2)D(3), can exert growth inhibitory effects on human breast cancer cells and mammary tumor growth. However, the molecular mechanisms remain to be fully delineated. This study demonstrates for the first time that CCAAT enhancer-binding protein alpha (C/EBPalpha), a member of the C/EBP family of transcription factors, is induced by 1,25(OH)(2)D(3) and is a potent enhancer of VDR transcription in MCF-7 breast cancer cells. 1,25(OH)(2)D(3) was found to induce C/EBPalpha as well as VDR expression in MCF-7 cells. C/EBPalpha was not detected in MDA-MB-231 cells that are poorly responsive to 1,25(OH)(2)D(3). Antiproliferative effects of 1,25(OH)(2)D(3) and induction of VDR were observed in MDA-MB-231 cells transfected with C/EBPalpha, and knockdown of C/EBPalpha suppressed VDR and antiproliferative effects of 1,25(OH)(2)D(3) in MCF-7 cells. Transfection of C/EBPalpha in MCF-7 cells resulted in a dose-dependent enhancement of hVDR transcription. Our studies show that C/EBPalpha can bind to Brahma (Brm), an ATPase that is a component of the SWI/SNF complex, and cooperate with Brm in the regulation of hVDR transcription in MCF-7 cells. Because the levels of VDR in MCF-7 breast cancer cells correlate with the antiproliferative effects of 1,25(OH)(2)D(3) and because C/EBPalpha has been suggested as a potential tumor suppressor in breast cancer, these findings provide important mechanisms whereby 1,25(OH)(2)D(3) may act to inhibit growth of breast cancer cells. These findings also identify C/EBPalpha as a 1,25(OH)(2)D(3) target in breast cancer cells and provide evidence for C/EBPalpha as a candidate for breast cancer treatment.

Synergistic antileukemic activity of carnosic acid-rich rosemary extract and the 19-nor Gemini vitamin D analogue in a mouse model of systemic acute myeloid leukemia

OBJECTIVE

Differentiation therapy with the hormonal form of vitamin D, 1alpha,25-dihydroxyvitamin D(3) (1,25D(3)), is a promising approach to treatment of acute myeloid leukemia (AML); however, 1,25D(3) induces hypercalcemia at pharmacologically active doses. We investigated the in vitro and in vivoantileukemic efficacy of combined treatment with non-toxic doses of a low-calcemic 1,25D(3) analogue, 1,25-dihydroxy-21(3-hydroxy-3-methyl-butyl)-19-nor-cholecalciferol (19-nor-Gemini; Ro27-5646), and rosemary plant agents in a mouse model of AML.

METHODS

Proliferation and differentiation of WEHI-3B D- (WEHI) murine myelomonocytic leukemia cellsin vitro were determined by standard assays. Reactive oxygen species, glutathione and protein expression levels were measured by flow cytometry, enzymatic assay and Western blotting, respectively. Systemic AML was developed by intravenous injection of WEHI cells in syngeneic Balb/c mice.

RESULTS

19-nor-Gemini had a higher potency than its parent compounds, Gemini (Ro27-2310) and 1,25D(3), in the induction of differentiation (EC(50) = 0.059 +/- 0.011, 0.275 +/- 0.093 and 0.652 +/- 0.085 nM, respectively) and growth arrest (IC(50) = 0.072 +/- 0.018, 0.165 +/- 0.061 and 0.895 +/- 0.144 nM, respectively) in WEHI cells in vitro, and lower in vivo toxicity. Combined treatment of leukemia-bearing mice with 19-nor-Gemini (injected intraperitoneally) and standardized rosemary extract (mixed with food) resulted in a synergistic increase in survival (from 42.2 +/- 2.5 days in untreated mice to 66.5 +/- 4.2 days, n = 3) and normalization of white blood cell and differential counts. This was consistent with strong cooperative antiproliferative and differentiation effects of low concentrations of 19-nor-Gemini or 1,25D(3) combined with rosemary extract or its major polyphenolic component, carnosic acid, as well as with the antioxidant action of rosemary agents and vitamin D derivatives in WEHI cell cultures.

CONCLUSION

Combined effectiveness of 1,25D(3) analogues and rosemary agents against mouse AML warrants further exploration of this therapeutic approach in translational models of human leukemia.

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.

Effective treatment of leukemic cell lines with wt1 siRNA

The expression of wt1 and bcl-2 is considered to have a proliferating and survival supporting effect in leukemia blast cells. Here we describe the use of siRNA against wt1 and bcl-2 in leukemic cell lines for successful growth inhibition. We have used two different sequences designated as siRNA-A and siRNA-B corresponding to positions within the wt1 coding sequence to downregulate wt1 and a commercially available siRNA kit to downregulate bcl-2. WT1 and bcl-2 gene expression in transfected leukemic cell lines were evaluated with RT-PCR and western blot analyses. MTT assay was used to measure the cell viability and flow cytometry using annexin V/PI-staining for apoptosis. K562 and HL-60 cell lines transfected with siRNA-A targeted to wt1 had greatly decreased levels of both wt1 mRNA and protein expression. In contrast, siRNA-B and control siRNA led almost to no effect on wt1 mRNA and protein expression. siRNA-A-reduced wt1 mRNA expression was associated with a decreased cell proliferation and increased number of apoptotic cells in K562 and HL-60 cells by 24 and 48 h after transfection. Combined treatment with wt1 siRNA and bcl-2 siRNA simultaneously was not able to override the cell growth and apoptosis effects compared to single treatment with wt1 siRNA. siRNAs targeted against human wt1 might be a valuable tool as antiproliferative agent against wt1 expressing leukemic cells.

VDR-mediated gene expression patterns in resting human coronary artery smooth muscle cells

Vitamin D analogs such as paricalcitol and calcitriol that activate the vitamin D receptor (VDR) provide survival benefit for Stage 5 chronic kidney disease (CKD) patients, possibly associated with a decrease in cardiovascular (CV)-related incidents. Phenotypic changes of smooth muscle cells play an important role in CV disease. The role of vitamin D analogs in modulating gene expression in smooth muscle cells is still not well understood. In this study, DNA microarray analysis of approximately 22,000 different human genes was used to characterize the VDR-mediated gene expression profile in human coronary artery smooth muscle cells (CASMC) at rest. Cells in serum free medium were treated with 0.1 microM calcitriol (1alpha,25-dihydroxyvitamin D(3)) or paricalcitol (19-nor-1alpha,25-(OH)(2)D(2)) for 30 h. A total of 181 target genes were identified, with 103 genes upregulated and 78 downregulated (>two fold changes in either drug treatment group with P < 0.01). No significant difference was observed between calcitriol and paricalcitol. Target genes fell into various categories with the top five in cellular process, cell communication, signal transduction, development, and morphogenesis. Twenty-two selected genes linked to the CV system were also impacted. Real-time RT-PCR and/or Western blotting analysis were employed to confirm the expression patterns of selected genes such as 25-hydroxyvitamin D-24-hydroxylase, Wilms' tumor gene 1, transforming growth factorbeta3, plasminogen activator inhibitor-1, thrombospondin-1 (THBS1), and thrombomodulin (TM). This study provides insight into understanding the role of VDR in regulating gene expression in resting smooth muscle cells.

Cellular Expression Levels of the Vitamin D Receptor Are Critical to Its Transcriptional Regulation by the Pituitary Transcription Factor Pit-1

The biological role of 1,25-dihydroxyvitamin D3 has generally been related to calcium homeostasis, but this hormone also has fundamental effects on processes of cellular proliferation and differentiation. The genomic actions of 1,25-dihydroxyvitamin D3 are mediated by the vitamin D receptor (VDR) present in target cells. However, VDR transcriptional regulation is not well understood, probably attributable to the complexity of the VDR gene and its promoter. In the present study, it is demonstrated that administration of the pituitary transcription factor Pit-1 (originally found in the pituitary gland but also present in other nonpituitary cell types and tissues) to the MCF-7 (human breast adenocarcinoma) cell line induces a significant increase in VDR mRNA and protein levels. Conversely, Pit-1-targeted small interference RNA markedly reduced expression of VDR in MCF-7 cells. Reporter gene assays demonstrated that the effect of Pit-1 is mediated by its binding to a region located between −254 and −246 bp from the VDR transcription start site. Selective mutations of this site completely abolished VDR transcription. Chromatin immunoprecipitation analysis showed that binding of Pit-1 to the VDR promoter leads additionally to recruitment of cAMP response element-binding protein binding protein, acetylated histone H4, and RNA polymerase II. Surprisingly, Pit-1 binding also recruits VDR protein to the VDR promoter. Using several cell lines with different levels of VDR expression, it was demonstrated that up-regulation of VDR transcription by Pit-1 is dependent on the presence of VDR protein, suggesting that transcriptional expression of VDR in a given cell type is dependent on, among other factors, its own expression levels.

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.

Exons and functional regions of the human vitamin D receptor gene around and within the main 1a promoter are well conserved among mammals

The human vitamin D receptor (hVDR) gene encompasses eight exons (2-9) in the so-called coding region and six more exons (1a-1f) in the so-called regulatory region, which contains several reported promoters. Evolutionary comparison performed on the VDR promoter sequences of a dozen of mammalian species shows a very high conservation of numerous regions around and in the 1a promoter, including exons 1e, 1a and 1d, and the Sp1 site region. This suggests that the so-called 1a promoter is well conserved among mammals. Homology among mammals also concerns three functional SNP site regions of the hVDR 1a promoter, the 1e-G-1739A SNP region (a Cdx-2 binding site), and both 1a-G-1521C and 1a-A-1012G sites, the 1a-1012A being located within a GATA site. Interestingly, the 1521G and 1012A nucleotides are being evolutionary conserved, suggesting that the 1521C/1012G haplotype, which is found in human chromosomes (43% of Caucasians), is a human specificity.

Comparative Genome Analysis Identifies the Vitamin D Receptor Gene as a Direct Target of p53-Mediated Transcriptional Activation

p53 is the most frequently mutated tumor suppressor gene in human neoplasia and encodes a transcriptional coactivator. Identification of p53 target genes is therefore key to understanding the role of p53 in tumorigenesis. To identify novel p53 target genes, we first used a comparative genomics approach to identify p53 binding sequences conserved in the human and mouse genome. We hypothesized that potential p53 binding sequences that are conserved are more likely to be functional. Using stringent filtering procedures, 32 genes were newly identified as putative p53 targets, and their responsiveness to p53 in human cancer cells was confirmed by reverse transcription-PCR and real-time PCR. Among them, we focused on the vitamin D receptor (VDR) gene because vitamin D3 has recently been used for chemoprevention of human tumors. VDR is induced by p53 as well as several other p53 family members, and analysis of chromatin immunoprecipitation showed that p53 protein binds to conserved intronic sequences of the VDR gene in vivo. Introduction of VDR into cells resulted in induction of several genes known to be p53 targets and suppression of colorectal cancer cell growth. In addition, p53 induced VDR target genes in a vitamin D3-dependent manner. Our in silico approach is a powerful method for identification of functional p53 binding sites and p53 target genes that are conserved among humans and other organisms and for further understanding the function of p53 in tumorigenesis.

Coronary vessel development requires activation of the TrkB neurotrophin receptor by the Wilms' tumor transcription factor Wt1

The formation of intramyocardial blood vessels is critical for normal heart development and tissue repair after infarction. We report here expression of the Wilms' tumor gene-1, Wt1, in coronary vessels, which could contribute to the defective cardiac vascularization in Wt1-/- mice. Furthermore, the high-affinity neurotrophin receptor TrkB, which is expressed in the epicardium and subepicardial blood vessels, was nearly absent from Wt1-deficient hearts. Activation of Wt1 in an inducible cell line significantly enhanced TrkB expression. The promoter of NTRK2, the gene encoding TrkB, was stimulated approximately 10-fold by transient cotransfection of a Wt1 expression construct. The critical DNA-binding site for activation of the NTRK2 promoter by Wt1 was delineated by DNase I footprint analysis and electrophoretic mobility shift assay. Transgenic experiments revealed that the identified Wt1 consensus motif in the NTRK2 promoter was necessary to direct expression of a reporter gene to the epicardium and the developing vasculature of embryonic mouse hearts. Finally, mice with a disrupted Ntrk2 gene lacked a significant proportion of their intramyocardial blood vessels. These findings demonstrate that transcriptional activation of the TrkB neurotrophin receptor gene by the Wilms' tumor suppressor Wt1 is a crucial mechanism for normal vascularization of the developing heart.

Suppression of death receptor-mediated apoptosis by 1,25-dihydroxyvitamin D3 revealed by microarray analysis

Recent studies suggest that growth inhibition by 1,25-dihydroxyvitamin D3 represents an innovative approach to ovarian cancer therapy. To understand the molecular mechanism of 1,25-dihydroxyvitamin D3 action, we profiled the hormone-induced changes in the transcriptome of ovarian cancer cells using microarray technology. More than 200 genes were identified to be regulated by 1,25-dihydroxyvitamin D3. Reverse transcription-PCR analyses confirmed the regulation of a group of apoptosis-related genes, including the up-regulation of the decoy receptor that inhibits tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) action, TRAIL receptor 4, and the down-regulation of Fas, the receptor that mediates the action of Fas ligand. The regulation was further confirmed at the protein level. Consistent with the regulation of the death receptors, pretreatment with 1,25-dihydroxyvitamin D3 decreased apoptosis induced by TRAIL and Fas ligand. Because persistent 1,25-dihydroxyvitamin D3 treatment has been shown to induce apoptosis in ovarian cancer, the hormone appears to exert a dual effect on the death of ovarian cancer cells. Knockdown of TRAIL receptor 4 by RNA interference or ectopic expression of Fas relieved the suppressive effect of 1,25-dihydroxyvitamin D3, showing that molecular manipulation of death receptors is a viable approach to overcome the protective effect of 1,25-dihydroxyvitamin D3 on the apoptosis of ovarian cancer. These strategies may allow ovarian cancer patients to benefit from therapy with both 1,25-dihydroxyvitamin D3 and ligands for death receptors, such as TRAIL, shown to selectively induce apoptosis in cancer but not normal cells.

Effects of Vitamin D analogs on gene expression profiling in human coronary artery smooth muscle cells

Vitamin D analogs provide survival benefit for chronic kidney disease patients with cardiovascular complications. Activation of smooth muscle cells plays a role in cardiovascular diseases. It is not known how Vitamin D analogs modulate gene expression in smooth muscle cells. In this study, DNA microarray technology was used to assess the gene expression profile in human coronary artery smooth muscle cells treated with 0.1microM 1alpha,25-dihydroxyvitamin D3 (calcitriol) or paricalcitol (an analog of calcitriol) for 30 h. The effects of calcitriol and paricalcitol were similar. A total of 176 target genes were identified with 115 up-regulated and 61 down-regulated genes in the paricalcitol group. Target genes fall into various categories including cell differentiation/proliferation. Real-time RT-PCR analysis demonstrated that paricalcitol dose- and time-dependently regulated the expression of IGF1, WT1 and TGFbeta3, three genes known to modulate cell proliferation. Paricalcitol also down-regulated the expression of natriuretic peptide precursor B and thrombospondin 1. Both drugs inhibited cell proliferation in a dose-dependent manner. This study identified genes not previously known to be regulated by VDR, providing insight into understanding the role of VDR on regulating smooth muscle cell growth, thrombogenicity, fibrinolysis and endothelial regeneration.

Ras activation is associated with vitamin D receptor mRNA instability in HC11 mammary cells

HC11, a spontaneously immortalized murine mammary lineage maintains features of normal cells while HC11 H-ras transformed cells (HC11 ras) are tumorigenic. Ras transformation is associated with a lower Vitamin D receptor (VDR) mRNA content. Our goal was to investigate the mechanism underlying VDR mRNA differences between these cells. Although the VDR transcriptional rate measured by run-on assays did not differ between the cells, our data suggested a pos transcriptional mechanism involving higher VDR mRNA degradation in HC11 ras cells which was not due to mutations in its 3'-UTR region since sequences of mRNA obtained from HC11 and HC11 ras cells were identical. Treatment of HC11 ras cells with a farnesyltransferase inhibitor, which prevents ras activation, causing an enhancement of VDR mRNA levels, indicating an association between the ras signaling pathway and VDR mRNA instability. The present work suggests that the decreased mRNA levels in HC11 ras cells might in part be due to an early loss of stability.

The Wilms' tumor suppressor Wt1 encodes a transcriptional activator of the class IV POU-domain factor Pou4f2 (Brn-3b)

The Wilms' tumor gene Wt1 encodes a zinc finger protein, which is required for normal formation of the genitourinary system and mesothelial tissues. Our recent findings indicate that Wt1 also plays a critical role in the development of ganglion cells in the vertebrate retina. Here we show that the POU-domain factor Pou4f2 (formerly Brn-3b), which is necessary for retinal ganglion cell survival, is up-regulated in human embryonic kidney (HEK)293 cells with stable Wt1 expression. Consistent with our previous observations of increased Pou4f2 mRNA in stably Wt1-transfeced HEK293 cells [EMBO J. 21 (2002) 1398], endogenous Pou4f2 was also elevated at the protein level in the HEK293 transfectants as well as in U2OS osteosarcoma cells that expressed an inducible Wt1 isoform. Transient co-transfection of a Wt1 expression construct activated a Pou4f2 promoter-reporter construct approximately 4-fold. Stimulation of the Pou4f2 promoter required a Wt1 binding element that was similar to a degenerative consensus site previously identified in other Wt1 responsive genes. Double-immunofluorescent labeling revealed co-expression of Pou4f2 and Wt1 in glomerular podocytes of adult kidney and in developing retinal ganglion cells of mouse embryos. Pou4f2 immunoreactivity was absent from the retinas of Wt1(-/-) embryos. In conclusion, we identified Pou4f2 as a novel downstream target gene of Wt1. Co-localization of both proteins in glomerular podocytes of the kidney and in developing retinal ganglion cells suggests a role for Wt1-Pou4f2 interaction in these tissues.

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.

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 is expressed in the coronary vasculature after myocardial infarction

Expression of the Wilms' tumor gene Wt1 in the epicardium is critical for normal heart development. Mouse embryos with inactivated Wt1 gene have extremely thin ventricles, which can result in heart failure and death. Here, we demonstrate that Wt1 can be activated in adult hearts by local ischemia. Wt1 mRNA was increased more than twofold in the left ventricular myocardium of rats between 1 day and 9 wk after infarction. Wt1 expression was localized by means of mRNA in situ hybridization and immunohistochemistry to vascular endothelial and vascular smooth muscle cells in the border zone of the infarcted tissue. A strikingly similar distribution was seen for vascular endothelial growth factor and two different cell proliferation markers in the coronary vessels of the ischemic heart. No Wt1 could be detected in the vasculature of the noninfarcted right ventricles. Wt1 expression in the coronary vessels of the ischemic heart was mimicked by exposure of rats to normobaric hypoxia (8% O2) and 0.1% CO, respectively. These findings demonstrate that Wt1 is expressed in the vasculature of the heart in response to local ischemia and hypoxia. They suggest that Wt1 has a role in the growth of coronary vessels after myocardial infarction.

The Wilms' tumor gene Wt1 is required for normal development of the retina

The Wilms' tumor gene Wt1 is known for its important functions during genitourinary and mesothelial formation. Here we show that Wt1 is necessary for neuronal development in the vertebrate retina. Mouse embryos with targeted disruption of Wt1 exhibit remarkably thinner retinas than age-matched wild-type animals. A large fraction of retinal ganglion cells is lost by apoptosis, and the growth of optic nerve fibers is severely disturbed. Strikingly, expression of the class IV POU-domain transcription factor Pou4f2 (formerly Brn-3b), which is critical for the survival of most retinal ganglion cells, is lost in Wt1(-/-) retinas. Forced expression of Wt1 in cultured cells causes an up-regulation of Pou4f2 mRNA. Moreover, the Wt1(-KTS) splice variant can activate a reporter construct carrying 5'-regulatory sequences of the human POU4F2. The lack of Pou4f2 and the ocular defects in Wt1(-/-) embryos are rescued by transgenic expression of a 280 kb yeast artificial chromosome carrying the human WT1 gene. Taken together, our findings demonstrate a continuous requirement for Wt1 in normal retina formation with a critical role in Pou4f2-dependent ganglion cell differentiation.

Recent advances in Wilms tumor genetics

The past decade has witnessed substantial growth in our knowledge of the genes and loci that are altered in Wilms tumor. Although Wilms tumor was one of the original paradigms of Knudson's two-hit model of cancer formation, it has become apparent that several genetic events contribute to Wilms tumorigenesis. Recent research has identified targets and regulators of the first Wilms tumor gene, WT1, has uncovered several candidate genes at the second Wilms tumor locus, WT2, and has identified two familial Wilms tumor loci, FWT1 and FWT2. The recent discovery of activating beta-catenin mutations in some Wilms tumors has also implicated the Wnt signaling pathway in this neoplasm. Recurrent abnormalities of other loci, including 16q, 1p, and 7p, have indicated that these sites may harbor Wilms tumor genes. An enhanced understanding of these and other genetic lesions will provide the foundation for novel targeted Wilms tumor therapies.

Functional characterization of WT1 binding sites within the human vitamin D receptor gene promoter

The Wilms' tumor suppressor gene, wt1, encodes a zinc finger transcription factor that can regulate gene expression. It plays an essential role in tumorigenesis, kidney differentiation, and urogenital development. To identify WT1 downstream targets, gene expression profiling was conducted using a cDNA array hybridization approach. We confirm herein that the human vitamin D receptor (VDR), a ligand-activated transcription factor, is a WT1 downstream target. Nuclear run on experiments demonstrated that the effect of WT1 on VDR expression is at the transcriptional level. Transient transfection assays, deletion mutagenesis, electrophoretic mobility shift assays, and chromatin immunoprecipitation assays suggest that, although WT1 is presented with a possibility of three binding sites within the VDR promoter, activation of the human VDR gene appears to occur through a single site. This site differs from a previously identified WT1-responsive site in the murine VDR promoter (Maurer U, Jehan F, Englert C, Hübinger G, Weidmann E, DeLucas HF, and Bergmann L. J Biol Chem 276: 3727-3732, 2001). We also show that the products of a Denys-Drash syndrome allele of wt1 inhibit WT1-mediated transactivation of the human VDR promoter. Our results indicate that the human VDR gene is a downstream target of WT1 and may be regulated differently than its murine counterpart.

Wilms' tumor (nephroblastoma)

Wilms' tumor (nephroblastoma) is a subject which continues to challenge clinicians in their attempts to achieve the best survival of their patients, while minimizing morbidity. Overall survival of over 85% of all children can now be achieved using combination therapy with chemotherapy, surgery, and in some cases radiotherapy. Recent reviews of two multi-institutional, multinational trials (the International Society of Pediatric Oncology and the National Wilms' Tumor Study Group) are discussed in this article, in which their current approaches to therapy are presented. In addition to these clinical advances, the genetic and molecular features of Wilms' tumor continue to provide insight into the biology of nephroblastoma and into neoplasia in general. A recent review of these aspects of the field is provided.

Ribozyme-mediated cleavage of wt1 transcripts suppresses growth of leukemia cells

OBJECTIVE

The Wilms' tumor gene product (WT1) was identified as a tumor suppressor in pediatric kidney tumors. Conversely, acute leukemias express WT1 at a high frequency, and leukemias with high levels of WT1 expressed by leukemic blast cells have a significantly worse prognosis, suggesting an oncogenic function of WT1 in leukemic cells. To address this issue, we developed five hammerhead ribozymes (RZ1-RZ5) designed to cleave various wt1-mRNA GUC-recognition sites and thus suppress wt1 expression.

METHODS

Using in vitro transcribed ribozymes and truncated wt1 target RNAs as substrates, we performed in vitro cleavage assays. The sequence of two ribozymes was then cloned into the pCDNA3 expression vector containing a self-processing ribozyme cassette. Downregulation of wt1 due to ribozyme expression was analyzed in the human 293 embryonic kidney and the K562 chronic myeloid leukemia cell line by Western blotting and RT-PCR. Growth of stable transfected K562 cells was determined by proliferation analysis and 3H-thymidine incorporation.

RESULTS

In vitro, the anti-wt1 ribozymes were able to recognize and cleave the target RNA in a highly sequence-specific and time-dependent manner. The ribozymes showed different catalytic activity. Coexpression of wt1 and the self-processing ribozymes pRZ3 and pRZ5, respectively, resulted in a significantly downregulated WT1 protein level when transiently transfected in 293 cells. Furthermore, stable transfection of pRZ3 and pRZ5 resulted in considerably reduced expression of endogenous wt1 in K562 cells, correlating with the inhibition of cell proliferation and the induction of cell death.

CONCLUSION

Our data suggest that anti-wt1 ribozymes are a potent inhibitor of wt1 expression with possible implications for the inhibition of cell proliferation in leukemic cells.