Differential regulation of the human Wilms tumour suppressor gene (WT1) promoter by two isoforms of PAX2

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.

Deletion of an intronic HIF-2α binding site suppresses hypoxia-induced WT1 expression

Hypoxia-inducible factors (HIFs) play a key role in the adaptation to low oxygen by interacting with hypoxia response elements (HREs) in the genome. Cellular levels of the HIF-2α transcription factor subunit influence the histopathology and clinical outcome of neuroblastoma, a malignant childhood tumor of the sympathetic ganglia. Expression of the Wilms tumor gene, WT1, marks a group of high-risk neuroblastoma. Here, we identify WT1 as a downstream target of HIF-2α in Kelly neuroblastoma cells. In chromatin immunoprecipitation assays, HIF-2α bound to a HRE in intron 3 of the WT1 gene, but not to another predicted HIF binding site (HBS) in the first intron. The identified element conferred oxygen sensitivity to otherwise hypoxia-resistant WT1 and SV40 promoter constructs. Deletion of the HBS in the intronic HRE by genome editing abolished WT1 expression in hypoxic neuroblastoma cells. Physical interaction between the HRE and the WT1 promoter in normoxic and hypoxic Kelly cells was shown by chromosome conformation capture assays. These findings demonstrate that binding of HIF-2α to an oxygen-sensitive enhancer in intron 3 stimulates transcription of the WT1 gene in neuroblastoma cells by hypoxia-independent chromatin looping. This novel regulatory mechanism may have implications for the biology and prognosis of neuroblastoma.

Paired box 2 promotes progression of endometrial cancer via regulating cell cycle pathway

Background: Human paired box 2 (PAX2) plays a key role in cell fate, early patterning and organogenesis.

Methods: We investigated the function of PAX2 on the biological behavior of endometrial cancer in vitro and in vivo and to explore the regulation mechanism, stable knocking-down and over-expression PAX2 endometrial cancer cell lines were established. CCK-8 and transwell assays were applied to determine proliferation, invasion and migration ability. Cell cycle distribution was analyzed by flow cytometry. Affymetrix GeneChip® human Exon 1.0 ST arrays was used to screen the downstream target genes of PAX2.

Results: PAX2 significantly enhanced proliferation and invasiveness. In addition, PAX2 influenced the expression of cyclin-dependent kinase 1(CDK1), which play pivotal roles in cell cycle pathway. When CDK1 was knocked down, and the cell proliferation promotion role of PAX2 was attenuated dramatically to a level comparable with the control groups.

Conclusions: PAX2, though influencing the expression of CDK1, promotes the proliferation, enhances the mobility of endometrial cancer cells, thus exerts an important role in the carcinogenesis of endometrial cancer. PAX2 may be a potential therapeutic target for endometrial cancer.

SMAD proteins directly suppress PAX2 transcription downstream of transforming growth factor-beta 1 (TGF-β1) signalling in renal cell carcinoma

Canonical TGF-β1 signalling promotes tumor progression by facilitating invasion and metastasis, whereby release of TGF-β1, by (for example) infiltrating immune cells, induces epithelial to mesenchymal transition (EMT). PAX2, a member of the Paired box family of transcriptional regulators, is normally expressed during embryonic development, including in the kidney, where it promotes mesenchymal to epithelial transition (MET). PAX2 expression is silenced in many normal adult tissues. However, in contrast, PAX2 is expressed in several cancer types, including kidney, prostate, breast, and ovarian cancer. While multiple studies have implicated TGF-β superfamily members in modulating expression of Pax genes during embryonic development, few have investigated direct regulation of Pax gene expression by TGF-β1. Here we have investigated direct regulation of PAX2 expression by TGF-β1 in clear cell renal cell carcinoma (CC-RCC) cell lines. Treatment of PAX2-expressing 786-O and A498 CC-RCC cell lines with TGF-β1 resulted in inhibition of endogenous PAX2 mRNA and protein expression, as well as expression from transiently transfected PAX2 promoter constructs; this inhibition was abolished in the presence of expression of the inhibitory SMAD, SMAD7. Using ChIP-PCR we showed TGF-β1 treatment induced SMAD3 protein phosphorylation in 786-O cells, and direct SMAD3 binding to the human PAX2 promoter, which was inhibited by SMAD7 over-expression. Overall, these data suggest that canonical TGF-β signalling suppresses PAX2 transcription in CC-RCC cells due to the direct binding of SMAD proteins to the PAX2 promoter. These studies improve our understanding of tumor progression and epithelial to mesenchyme transition (EMT) in CC-RCC and in other PAX2-expressing cancer types.

Repression of CMIP transcription by WT1 is relevant to podocyte health

The WT1 (Wilm's tumor suppressor) gene is expressed throughout life in podocytes and is essential for the functional integrity of the glomerular filtration barrier. We have previously shown that CMIP (C-Maf inducing protein) is overproduced in podocyte diseases and alters intracellular signaling. Here we isolated the proximal region of the human CMIP promoter and showed by chromatin immunoprecipitation assays and electrophoretic-mobility shift that Wilm's tumor protein (WT1) bound to 2 WT1 response elements, located at positions -290/-274 and -57/-41 relative to transcription start site. Unlike the human CMIP gene, only one Wt1 response element was identified in the mouse Cmip proximal promoter located at position -217/-206. Luciferase reporter assays indicated that WT1 dose-dependently inhibited the transcriptional induction of the CMIP promoter. Transfection of decoy oligonucleotides mimicking the WT1 response elements prevented the inhibition of WT1 on CMIP promoter activity. Furthermore, WT1 silencing promoted Cmip expression. In line with these findings, the abundance of Cmip was early and significantly increased at the transcript and protein level in podocytes displaying a primary defect in Wt1, including Denys-Drash syndrome and Frasier syndrome. Thus, WT1 is a major repressor of the CMIP gene in physiological situations, while conditional deletion of CMIP in the developing kidney did not affect the development of mature glomeruli.

A Boolean network model of human gonadal sex determination

BACKGROUND

Gonadal sex determination (GSD) in humans is a complex biological process that takes place in early stages of embryonic development when the bipotential gonadal primordium (BGP) differentiates towards testes or ovaries. This decision is directed by one of two distinct pathways embedded in a GSD network activated in a population of coelomic epithelial cells, the Sertoli progenitor cells (SPC) and the granulosa progenitor cells (GPC). In males, the pathway is activated when the Sex-Determining Region Y (SRY) gene starts to be expressed, whereas in females the WNT4/ β-catenin pathway promotes the differentiation of the GPCs towards ovaries. The interactions and dynamics of the elements that constitute the GSD network are poorly understood, thus our group is interested in inferring the general architecture of this network as well as modeling the dynamic behavior of a set of genes associated to this process under wild-type and mutant conditions.

METHODS

We reconstructed the regulatory network of GSD with a set of genes directly associated with the process of differentiation from SPC and GPC towards Sertoli and granulosa cells, respectively. These genes are experimentally well-characterized and the effects of their deficiency have been clinically reported. We modeled this GSD network as a synchronous Boolean network model (BNM) and characterized its attractors under wild-type and mutant conditions.

RESULTS

Three attractors with a clear biological meaning were found; one of them corresponding to the currently known gene expression pattern of Sertoli cells, the second correlating to the granulosa cells and, the third resembling a disgenetic gonad.

CONCLUSIONS

The BNM of GSD that we present summarizes the experimental data on the pathways for Sertoli and granulosa establishment and sheds light on the overall behavior of a population of cells that differentiate within the developing gonad. With this model we propose a set of regulatory interactions needed to activate either the SRY or the WNT4/ β-catenin pathway as well as their downstream targets, which are critical for further sex differentiation. In addition, we observed a pattern of altered regulatory interactions and their dynamics that lead to some disorders of sex development (DSD).

PAX2 promoted prostate cancer cell invasion through transcriptional regulation of HGF in an in vitro model

Elucidating the mechanism of prostate cancer cell invasion may lead to the identification of novel therapeutic strategies for its treatment. Paired box 2 (PAX2) and hepatocyte growth factor (HGF) proteins are promoters of prostate cancer cell invasion. We found that PAX2 protein activated the HGF gene promoter through histone H3 acetylation and upregulated HGF gene expression. Deletion analysis revealed that the region from -637 to -314 of the HGF gene was indispensable for HGF promoter activation by PAX2. This region contains consensus PAX2 binding sequences and mutations of the sequences attenuated HGF promoter activation. Using an in vitro invasion model, we found that PAX2 and HGF promoted prostate cancer cell invasion in the same pathway. Knockdown of HGF expression attenuated the cells' invasive capacity. Moreover, in tissue samples of human prostate cancers, HGF and PAX2 expression levels were positively correlated. These results suggested that upregulation of HGF gene expression by PAX2 enhanced the invasive properties of prostate cancer cells. The PAX2/HGF pathway in prostate cancer cells may be a novel therapeutic target in prostate cancer patients.

Hyper-expression of PAX2 in human metastatic prostate tumors and its role as a cancer promoter in an in vitro invasion model

BACKGROUND

Metastasis is a consequence of many biological events, during which cancer stem cells are shifted into a malignant state. Among these events, invasion of prostate cancer cells into host tissues is possible to be assessed by means of an in vitro invasion model, and is thought to be coupled to altered expression of membrane proteins. Dysregulated functions of the factors regulating organogenesis during embryogenesis are known to facilitate metastasis of many types of cancers. PAX2 (paired box 2) is a member of the PAX transcription factor family, which regulates prostatic ductal growth and branching in organogenesis of mammalian prostates. However, the role of PAX2 in prostate cancer development remains to be determined.

METHODS

PAX2 expression in human prostate cancers and normal prostate epithelium were examined by quantitative RT-PCR and immunohistochemistry. Matrigel invasion assay and a gene array analysis were performed using prostate cancer cell lines transfected with either control or PAX2 siRNA.

RESULTS

In human prostate cancers, PAX2 was hyper-expressed in metastatic cancers, but was expressed at lower levels in non-metastatic cancers. Consistent with this, PAX2 knockdown repressed cell growth and invasion in a Matrigel invasion assay. Gene ontology analysis revealed that many cell membrane proteins were downregulated after PAX2 knockdown.

CONCLUSIONS

Our data suggested that PAX2 hyper-expression promotes the development of the metastatic state in prostate cancer cells, presumably through upregulating the expression of cell membrane proteins.

Typical renal-coloboma syndrome phenotype in a patient with a submicroscopic deletion of the PAX2 gene

We present a patient with optic nerve hypoplasia, secondary strabismus, mild deafness, abnormal external ear helices, and renal hypoplasia. The clinical phenotype was consistent with renal-coloboma syndrome, but no point mutation in the PAX2 gene could be identified. High-resolution array comparative genomic hybridization (aCGH) analysis showed that this patient has a submicroscopic deletion on chromosome 10, affecting the entire coding region of the PAX2 gene. This finding provided the molecular confirmation of the patient's clinical diagnosis and showed that, in addition to point mutations, deletions of the PAX2 gene contribute to the etiology of the renal-coloboma syndrome.

A novel interstitial deletion of 10q24.2q24.32 in a patient with renal coloboma syndrome

Renal coloboma syndrome (RCS) is considered to be a rare autosomal dominant inherited disorder characterized by renal malformations and optic disc coloboma. Ocular anomalies range from asymptomatic abnormalities in retinal blood vessel patterning to large excavations of the optic nerve associated with reduced visual acuity. Commonly observed manifestations of the kidney are renal hypoplasia and vesicoureteric reflux leading to end-stage renal disease. Mutations in the PAX2 gene on chromosome 10 have been identified in patients with RCS. Up to date, nucleotide substitutions, insertions, small deletions, one de novo translocation, and one 240 kb deletion of the coding region of the PAX2 gene have been described to be responsible for RCS. We report here a new case of a patient with RCS due to a deletion of 3.8 Mb on chromosome 10q. Deletions on the long arm of chromosome 10 harboring the PAX2 gene seem to be a rare cause for RCS. Nevertheless, array-CGH testing should represent an important and valuable addition to PAX2 gene sequencing in diagnostic of RCS.

Semaphorin3a regulates endothelial cell number and podocyte differentiation during glomerular development

Semaphorin3a (Sema3a), a chemorepellant guidance protein, plays crucial roles in neural, cardiac and peripheral vascular patterning. Sema3a is expressed in the developing nephron, mature podocytes and collecting tubules. Sema3a acts as a negative regulator of ureteric bud branching, but its function in glomerular development has not been examined. Here we tested the hypothesis that Sema3a regulates glomerular vascular development using loss- and gain-of-function mouse models. Sema3a deletion resulted in defects in renal vascular patterning, excess endothelial cells within glomerular capillaries, effaced podocytes with extremely wide foot processes and albuminuria. Podocyte Sema3a overexpression during organogenesis resulted in glomerular hypoplasia, characterized by glomerular endothelial cell apoptosis, delayed and abnormal podocyte foot process development, a complete absence of slit diaphragms and congenital proteinuria. Nephrin, WT1 and VEGFR2 were downregulated in Sema3a-overexpressing kidneys. We conclude that Sema3a is an essential negative regulator of endothelial cell survival in developing glomeruli and plays a crucial role in podocyte differentiation in vivo. Hence, a tight regulation of Sema3a dosage is required for the establishment of a normal glomerular filtration barrier.

Angiotensin II up-regulates PAX2 oncogene expression and activity in prostate cancer via the angiotensin II type I receptor

BACKGROUND

Paired homeobox 2 gene (PAX2) is a transcriptional regulator, aberrantly expressed in prostate cancer cells and its down-regulation promotes cell death in these cells. The molecular mechanisms of tumor progression by PAX2 over-expression are still unclear. However, it has been reported that angiotensin-II (A-II) induces cell growth in prostate cancer via A-II type 1 receptor (AT1R) and is mediated by the phosphorylation of mitogen activated protein kinase (MAPK) as well as signal transducer and activator of transcription 3 (STAT3).

METHODS

Here we have demonstrated that A-II up-regulates PAX2 expression in prostate epithelial cells and prostate cancer cell lines resulting in increased cell growth. Furthermore, AT1R receptor antagonist losartan was shown to inhibit A-II induced PAX2 expression in prostate cancer. Moreover, analysis using pharmacological inhibitors against MEK1/2, ERK1/2, JAK-II, and phospho-STAT3 demonstrated that AT1R-mediated stimulatory effect of A-II on PAX2 expression was regulated in part by the phosphorylation of ERK1/2, JAK II, and STAT3 pathways. In addition, we have showed that down-regulation of PAX2 by an AT1R antagonist as well as JAK-II and STAT3 inhibitors suppress prostate cancer cell growth.

RESULTS

Collectively, these findings show for the first time that the renin-angiotensin system (RAS) may promote prostate tumorigenesis via up-regulation of PAX2 expression.

CONCLUSIONS

Therefore, PAX2 may be a novel therapeutic target for the treatment of carcinomas such as prostate cancer via the down-regulation of its expression by targeting the AT1R signaling pathways.

Identification of an immunogenic HLA-A*0201-binding T-cell epitope of the transcription factor PAX2

PAX2 is a transcription factor and member of the highly conserved family of paired box genes. PAX2 is aberrantly expressed in a variety of solid and hematologic malignancies. PAX2 regulates the transcription factor Wilms tumor gene 1, which is a promising target of cancer immunotherapy. The aim of this study was to apply a modified reverse immunology strategy to identify immunogenic epitopes of PAX2 which could be useful for cancer immunotherapy. Thirteen potential HLA-A*0201 epitopes were predicted by a major histocompatibility complex binding algorithm (SYFPEITHI) and a proteasome cleavage algorithm (PAProC) and screened for recognition by T cells from HLA-A*02-positive cancer patients using intracellular cytokine cytometry. Epitope-specific T cells were generated from CD4CD25 regulatory T-cell-depleted peripheral blood mononuclear cell. Nine of 20 colorectal cancer patients, 1 of 13 renal cell carcinoma patients, and 2 of 17 lymphoma patients had a spontaneous CD8 T-cell response toward at least 1 of 6 PAX2 peptide pools. None of the 20 healthy subjects showed reactivity toward PAX2. PAX2.337-345 (TLPGYPPHV)-specific T cells could repeatedly be generated, which specifically lysed the PAX2 expressing colorectal tumor cell line SW480. In this study, a modified reverse immunology strategy was employed to identify a first immunogenic HLA-A*0201 restricted T-cell epitope and natural ligand of the tumor antigen PAX2. Thus, PAX2 is another embryonic transcription factor, which is of potential interest as immunotherapy target antigen.

The zinc finger domain of Wilms' tumor 1 suppressor gene (WT1) behaves as a dominant negative, leading to abrogation of WT1 oncogenic potential in breast cancer cells

Introduction

There is growing evidence that the Wilms' tumor 1 suppressor gene (WT1) behaves as an oncogene in some forms of breast cancer. Previous studies have demonstrated that the N-terminal domain of WT1 can act as a dominant negative through self-association. In the studies presented here we have explored the potential for the zinc finger domain (ZF) of WT1 to also have dominant-negative effects, and thus further our understanding of this protein.

Methods

Using full-length and ZF-only forms of WT1 we assessed their effect on the WT1 and c-myc promoter using luciferase and chromatin immunoprecipitation assays. The gene expression levels were determined by quantitative real-time RT-PCR, northern blot and western blot. We also assessed the effect of the ZF-only form on the growth of breast cancer cell lines in culture.

Results

Transfection with WT1–ZF plasmids resulted in a stronger inhibition of WT1 promoter than full-length WT1 in breast cancer cells. The WT1–ZF form lacking the lysine–threonine–serine (KTS) insert (ZF - KTS) can bind to the majority of WT1 consensus sites throughout the WT1 promoter region, while the ZF containing the insert (ZF + KTS) form only binds to sites in the proximal promoter. The abundances of endogenous WT1 mRNA and protein were markedly decreased following the stable expression of ZF - KTS in breast cancer cells. The expressions of WT1 target genes, including c-myc, Bcl-2, amphiregulin and TERT, were similarly suppressed by ZF - KTS. Moreover, WT1–ZF - KTS abrogated the transcriptional activation of c-myc mediated by all four predominant isoforms of WT1 (including or lacking alternatively spliced exons 5 and 9). Finally, WT1–ZF - KTS inhibited colony formation and cell division, but induced apoptosis in MCF-7 cells.

Conclusion

Our observations strongly argue that the WT1–ZF plasmid behaves as a dominant-negative regulator of the endogenous WT1 in breast cancer cells. The inhibition on proliferation of breast cancer cells by WT1–ZF - KTS provides a potential candidate of gene therapy for breast cancer.

A Hox-Eya-Pax complex regulates early kidney developmental gene expression

During embryonic development, the anterior-posterior body axis is specified in part by the combinatorial activities of Hox genes. Given the poor DNA binding specificity of Hox proteins, their interaction with cofactors to regulate target genes is critical. However, few regulatory partners or downstream target genes have been identified. Herein, we demonstrate that Hox11 paralogous proteins form a complex with Pax2 and Eya1 to directly activate expression of Six2 and Gdnf in the metanephric mesenchyme. We have identified the binding site within the Six2 enhancer necessary for Hox11-Eya1-Pax2-mediated activation and demonstrate that this site is essential for Six2 expression in vivo. Furthermore, genetic interactions between Hox11 and Eya1 are consistent with their participation in the same pathway. Thus, anterior-posterior-patterning Hox proteins interact with Pax2 and Eya1, factors important for nephrogenic mesoderm specification, to directly regulate the activation of downstream target genes during early kidney development.

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.

Regulation of c-Ret in the developing kidney is responsive to Pax2 gene dosage

During kidney development, Pax2 and Pax8 are expressed very early in the mammalian nephric duct and both precede the expression of receptor tyrosine kinase, c-Ret. However, in Pax2-/- mutant mice, expression of c-Ret is lost after embryonic day 10.5. As the Ret/Gdnf pathway is necessary for renal development and there is a temporal and spatial relationship of Pax2 and c-Ret expression in the developing genito-urinary system, we postulate that Pax2 is necessary for c-Ret expression in the developing kidney. In vitro, Pax2 protein is capable of physically interacting with a c-RET promoter, and both Pax2 and Pax8 can activate the expression of a reporter gene driven by the c-RET promoter. Compound heterozygous null mice (Pax2+/-: Ret+/-) display an increased incidence of unilateral and bilateral renal agenesis, and smaller kidneys with fewer nephrons. Furthermore, the expression of Gdnf is reduced 2-3-fold, whereas c-Ret expression is reduced 9-47-fold in Pax2 heterozygous embryonic kidneys as detected by real-time quantitative RT (QRT)-PCR. The data demonstrate that Pax2 plays an integral role in the initiation and maintenance of the Ret/Gdnf pathway by not only activating the ligand of the pathway, but by also enhancing the expression of the pathway receptor Ret. The effects of reduced Pax2 gene dosage are thus amplified resulting in a haploinsufficient phenotype.

Inhibition of PAX2 expression results in alternate cell death pathways in prostate cancer cells differing in p53 status

Inhibition of apoptosis is a critical pathophysiological factor that contributes to the development of prostate cancer. Recently, PAX2, a transcriptional regulator implicated in oncogenesis, has been demonstrated to be expressed by prostate cancer. However, its downstream molecular pathways for suppression of apoptosis, other than the tumor suppressor gene p53, have yet to be elucidated. Here, we examine the effects of inhibiting PAX2 expression by prostate cancer cells that differ in p53 gene status. These data collectively demonstrate that PAX2 inhibition results in cell death independent of p53, and that additional tumor suppressors or cell death pathways may be inhibited by PAX2 in prostate cancer cells.

Molecular mechanisms of oestrogen and SERMs in endometrial carcinogenesis

Endometrial cancer is the most common gynaecological cancer, and is associated with endometrial hyperplasia, unopposed oestrogen exposure and adjuvant therapy for breast cancer using selective oestrogen-receptor modulators (SERMs), particularly tamoxifen. Oestrogen and SERMs are thought to be involved in endometrial carcinogenesis through their effects on transcriptional regulation. Ultimately, oestrogen and SERMs affect the transduction of cellular signalling pathways that govern cell growth and proliferation, through downstream effectors such as PAX2 (paired box 2).

WT1 gene expression as a prognostic marker in advanced serous epithelial ovarian carcinoma: an immunohistochemical study

BACKGROUND

WT1 is a tumor suppressor gene responsible for Wilms' tumor. WT1 reactivity is limited to ovarian serous carcinomas. Recent studies have shown that WT1 plays an important role in the progression of disease and indicates a poorer prognosis of human malignancies such as acute myeloid leukemia and breast cancer. The aims of this study were to determine the survival and recurrence-free survival of women with advanced serous epithelial ovarian carcinoma in relation to WT1 gene expression.

METHODS

The study accrued women over an 18-year period, from 1987-2004. During the study period, 163 patients were diagnosed with advanced serous epithelial ovarian carcinoma and had undergone complete post-operative chemotherapy, but the final study group comprised 99 patients. The records of these women were reviewed and the paraffin-embedded tissue of these women stained with WT1 immunostaining. Survival analysis was performed using Kaplan-Meier and Cox regression methods.

RESULTS

Fifty patients showed WT1 staining and forty-nine did not. Five-year survival of non-staining and staining groups were 39.4% and 10.7% (p < 0.00005); five-year recurrence-free survival of these groups were 29.8% and < or = 7.5% (p < 0.00005), respectively. For survival the HR of WT1 staining, adjusted for residual tumor and chemotherapy response, was 1.98 (95% CI 1.28-3.79), and for recurrence-free survival the HR was 3.36 (95% CI 1.60-7.03). The HR for recurrence-free survival was not confounded by any other variables.

CONCLUSION

This study suggests that expression of WT1 gene may be indicative of an unfavorable prognosis in patients with advanced serous epithelial ovarian carcinoma.

Multicystic dysplastic kidney and variable phenotype in a family with a novel deletion mutation of PAX2

The renal coloboma syndrome (OMIM 120330) is caused by mutations in the PAX2 gene. Typical findings in these patients include renal hypoplasia, renal insufficiency, vesicoureteric reflux, and optic disc coloboma. A family with a novel heterozygous 10-bp deletion in exon 2 of the PAX2 gene leading to a truncating mutation and variable phenotype across three generations is reported. The first presentation of multicystic dysplastic kidney in this syndrome is reported. The possibility that abnormal PAX2 protein in this case may cause a dominant negative effect also is discussed. The finding of multicystic dysplastic kidney in renal coloboma syndrome could suggest that PAX2 may play a role in early ureteric obstruction and subsequent renal maldevelopment.

Upregulation of Wilms' tumor gene 1 (WT1) in desmoid tumors

Desmoid tumors (aggressive fibromatosis) are locally invasive soft tissue tumors in which beta-catenin/TCF3 mediated Wnt signaling is activated. More than 80% of desmoid tumors contain activating mutations in beta-catenin. It has been shown that the Wnt signaling pathway interacts with Wilms' tumor gene 1 (WT1) in normal kidney development and plays a role in the genesis of some Wilms' tumors. About 15% of Wilms' tumors contain WT1 mutations and of these, about 50% contain beta-catenin mutations. This overlap in mutation pattern of WT1 and beta-catenin in Wilms' tumor suggests that these 2 genes may collaborate in the genesis of a subset of Wilms' tumors. To investigate whether this hypothesis could be extended to other Wnt-dependent tumor types, we searched for WT1 mutations and studied WT1 expression in beta-catenin mutant desmoid tumors. We investigated the expression of WT1 mRNA and protein in desmoid tumors. Medium to high abundant levels of WT1 mRNA were detected by TaqMan quantitative PCR in all tested desmoid cells, whereas adjacent normal fibroblasts showed less expression of WT1. Western blot analysis and immunohistochemistry confirmed this overexpression at the protein level. A mutational screen of the WT1 zinc-finger region by sequence analysis did not identify any mutations. Finally, we investigated a possible role of beta-catenin on WT1 regulation and vice versa. Overexpression of different beta-catenin mutants in the HEK293T cell line did not modulate WT1 promoter activity and WT1 did not affect beta-catenin /TCF transcriptional activity in this cell line. These results show that the wild-type WT1 gene is strongly overexpressed in beta-catenin mutant desmoid tumors and may play a role in tumorigenesis of desmoid tumors, similar to what has been suggested in some epithelial malignancies.

Ataxia-telangiectasia mutated gene controls insulin-like growth factor I receptor gene expression in a deoxyribonucleic acid damage response pathway via mechanisms involving zinc-finger transcription factors Sp1 and WT1

The IGF-I receptor (IGF-IR) has a central role in cell cycle progression as well as in the establishment of the transformed phenotype. Increased expression of the IGF-IR gene, in addition, is correlated with acquisition of radioresistance for cell killing. The ataxia-telangiectasia mutated (ATM) gene product has a pivotal role in coordinating the cellular response to DNA damage. The present study was aimed at testing the hypothesis that the ability of ATM to coordinate the DNA damage response that will lead to cell survival or, alternatively, to apoptosis depends, to a significant extent, on its capacity to control IGF-IR gene expression. The potential involvement of ATM in regulation of IGF-IR expression and function was investigated in isogenic cells with and without ATM function [AT22IJE-T/pEBS7 (ATM -/-) and ATM-corrected AT22IJE-T/YZ5 (ATM +/+) cells and 293 human embryonic kidney cells transfected with small interfering RNAs targeted to ATM]. In addition, the effect of ATM on IGF-IR expression was assessed in nonisogenic cells with ATM function (HFF + human telomerase reverse transcriptase) and without ATM function (GM5823 + human telomerase reverse transcriptase). Results obtained showed that IGF-IR gene expression and IGF-IR promoter activity were largely reduced in ATM -/- cells. Addition of the radiomimetic agent neocarzinostatin for 4 h, however, induced a significant increase in IGF-IR levels in cells without ATM function. In addition, IGF-I-induced IGF-IR and insulin receptor substrate-1 phosphorylation were greatly impaired in ATM-deficient cells. Furthermore, we identified zinc-finger transcription factors Sp1 and WT1 as potential mediators of the effect of ATM on IGF-IR gene expression. The present data suggests that the IGF-IR gene is a novel downstream target in an ATM-mediated DNA damage response pathway. Deregulated expression of the IGF-IR gene after ionizing radiation may be linked to genomic instability and enhanced transforming capacity.

Activation of the WT1 tumor suppressor gene promoter by Pea3

Gene array profiling of RNA from cells engineered to express a dominant-negative version of the ETS family member transcription factor Pea3 (polyomavirus enhancer activator 3) identified WT1 as a candidate downstream gene. Given the co-expression of WT1 and Pea3 in developing kidney and breast tissue undergoing mesenchymal to epithelial transitions, we further characterized this potential gene hierarchy. Analysis of the human WT1 promoter revealed several potential binding sites for Pea3. Pea3 transactivated the WT1 promoter in transient transfection assays and bound to specific sites within the WT1 promoter in vitro. Our results position Pea3 upstream of WT1 and define a gene hierarchy important for mesenchymal-epithelial transitions.

Insights into the physiological role of WT1 from studies of genetically modified mice

Discenza, Maria Teresa, and Jerry Pelletier. Insights into the physiological role of WT1 from studies of genetically modified mice. Physiol Genomics 16: 287-300, 2004; 10.1152/physiolgenomics.00164.2003.—The identification of WT1 gene mutations in children with WAGR and Denys-Drash syndromes pointed toward a role for WT1 in genitourinary system development. Biochemical analysis of the different WT1 protein isoforms showed that WT1 is a transcription factor and also has the ability to bind RNA. Analysis of WT1 complexes identified several target genes and protein partners capable of interacting with WT1. Some of these studies placed WT1, its downstream targets, and protein partners in a transcriptional regulatory network that controls urogenital system development. We review herein studies on WT1 knockout and transgenic models that have been instrumental in defining a physiological role for WT1 in normal and abnormal urogenital development.

WT1 is a modifier of the Pax2 mutant phenotype: cooperation and interaction between WT1 and Pax2

Metanephric kidney development requires an inductive interaction between the ureteric bud and progenitor mesenchyme, where the early expression of two genes, Wilms' tumour 1 (WT1) and paired box 2 (Pax2), establishes critical but unknown developmental pathways. Indeed, transgenic mice with deregulated overexpression of Pax2 exhibit structural kidney defects and impaired renal function, as do mice harboring targeted disruptions and/or spontaneous mutations of either the Pax2 or WT1 genes. WT1 and Pax2 are thought to regulate each other's expression during renal development. To better define the relationship between WT1 and Pax2, we generated mouse embryos containing heterozygous mutations in both genes. WT1(+/-)/Pax2(1Neu/+) kidneys were 50% smaller than wild-type kidneys. They were characterized by severe attenuation of the renal medulla, and reduced development of calyces and the renal pelvis. Renal cortex development in compound heterozygotes culminated in fewer nephrons than in WT1(+/-), Pax2(1Neu/+) or wild-type mice. Only minor variations in the mesenchymal expression pattern of Pax2 protein, and the mRNA expression levels of Pax2 and WT1, were noted in mutant kidneys. We show that WT1 and Pax2 proteins interact in vitro and in vivo, demonstrating that WT1 and Pax2 can form a molecular complex. Our data suggest that WT1 is a modifier of the Pax2 mutant phenotype.

The Secreted Frizzled Related Protein 2 (SFRP2) Gene Is a Target of the Pax2 Transcription Factor

Despite their essential role in vertebrate development, the function of Pax proteins in gene regulation is not well understood. To identify potential genes regulated by the Pax2 protein, we screened embryonic kidney cells transformed with Pax2-expressing retroviruses for genes activated in response to Pax2 expression. In this system, the gene encoding the secreted frizzled related protein, Sfrp2, was strongly activated in all Pax2b-expressing cells. This activation of Sfrp2 expression correlated with changes in chromatin structure at the Sfrp2 locus, particularly in and around regions of Pax2 binding. Although the amount of Pax2-dependent transactivation was low in transient assays, the data suggests that local alterations of chromatin structure by Pax proteins can greatly enhance expression when presented in the right cellular context.

The WT1 Wilms' tumor suppressor gene: a novel target for insulin-like growth factor-I action

IGF-I stimulates cell division in numerous cell types after activation of the IGF-I receptor, a transmembrane heterotetramer linked to the ras-raf-MAPK and phosphatidylinositol 3-kinase signaling pathways. The WT1 Wilms' tumor suppressor is a zinc finger-containing transcription factor that is involved in a number of developmental processes, as well as in the etiology of certain neoplasias. In the present study, we demonstrated that IGF-I reduced WT1 expression in osteosarcoma-derived Saos-2 cells in a time- and dose-dependent manner. This effect was mediated through the MAPK signaling pathway, as shown by the ability of the specific inhibitor UO126 to abrogate IGF-I action. Furthermore, the effect of IGF-I involved repression of transcription from the WT1 gene promoter, as demonstrated using transient transfection assays. Taken together, our results suggest that the WT1 gene is a novel downstream target for IGF-I action. Reduced levels of WT1 may facilitate IGF-I-stimulated cell cycle progression. Most importantly, inhibition of WT1 gene expression by IGF-I may have significant implications in terms of cancer initiation and/or progression.

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.

Gene expression in Wilms' tumor mimics the earliest committed stage in the metanephric mesenchymal-epithelial transition

Wilms' tumor (WT) has been considered a prototype for arrested cellular differentiation in cancer, but previous studies have relied on selected markers. We have now performed an unbiased survey of gene expression in WTs using oligonucleotide microarrays. Statistical criteria identified 357 genes as differentially expressed between WTs and fetal kidneys. This set contained 124 matches to genes on a microarray used by Stuart and colleagues (Stuart RO, Bush KT, Nigam SK: Changes in global gene expression patterns during development and maturation of the rat kidney. Proc Natl Acad Sci USA 2001, 98:5649-5654) to establish genes with stage-specific expression in the developing rat kidney. Mapping between the two data sets showed that WTs systematically overexpressed genes corresponding to the earliest stage of metanephric development, and underexpressed genes corresponding to later stages. Automated clustering identified a smaller group of 27 genes that were highly expressed in WTs compared to fetal kidney and heterologous tumor and normal tissues. This signature set was enriched in genes encoding transcription factors. Four of these, PAX2, EYA1, HBF2, and HOXA11, are essential for cell survival and proliferation in early metanephric development, whereas others, including SIX1, MOX1, and SALL2, are predicted to act at this stage. SIX1 and SALL2 proteins were expressed in the condensing mesenchyme in normal human fetal kidneys, but were absent (SIX1) or reduced (SALL2) in cells at other developmental stages. These data imply that the blastema in WTs has progressed to the committed stage in the mesenchymal-epithelial transition, where it is partially arrested in differentiation. The WT-signature set also contained the Wnt receptor FZD7, the tumor antigen PRAME, the imprinted gene NNAT and the metastasis-associated transcription factor E1AF.

Regulation of ureteric bud outgrowth by Pax2-dependent activation of the glial derived neurotrophic factor gene

The outgrowth of the ureteric bud from the posterior nephric duct epithelium and the subsequent invasion of the bud into the metanephric mesenchyme initiate the process of metanephric, or adult kidney, development. The receptor tyrosine kinase RET and glial cell-derived neurotrophic factor (GDNF) form a signaling complex that is essential for ureteric bud growth and branching morphogenesis of the ureteric bud epithelium. We demonstrate that Pax2 expression in the metanephric mesenchyme is independent of induction by the ureteric bud. Pax2 mutants are deficient in ureteric bud outgrowth and do not express GDNF in the uninduced metanephric mesenchyme. Furthermore, Pax2 mutant mesenchyme is unresponsive to induction by wild-type heterologous inducers. In normal embryos, GDNF is sufficient to induce ectopic ureter buds in the posterior nephric duct, a process inhibited by bone morphogenetic protein 4. However, GDNF replacement in organ culture is not sufficient to stimulate ureteric bud outgrowth from Pax2 mutant nephric ducts, indicating additional defects in the nephric duct epithelium of Pax2 mutants. Pax2 can activate expression of GDNF in cell lines derived from embryonic metanephroi. Furthermore, Pax2 protein can bind to upstream regulatory elements within the GDNF promoter region and can transactivate expression of reporter genes. Thus, activation of GDNF by Pax2 coordinates the position and outgrowth of the ureteric bud such that kidney development can begin.

Immunohistochemical localization of Pax2 and associated proteins in the developing kidney of mice with renal hypoplasia

Pax2 has been identified as a key regulatory protein associated with renal developmental malformations. The purpose of this study was to determine whether Pax2 protein expression, and that of other proteins important for normal renal development, is abnormally distributed in the prenatal kidney of the Brachyrrhine (Br) mouse that displays heritable renal hypoplasia. Embryonic 3H1 +/+ and Br/Br mice were collected between E11.0 and E18.0. Routine light microscopy and immunohistochemical analysis using antibodies to Pax2, E-cadherin, fibronectin, laminin, and Type IV collagen were applied to sequential tissue sections. E-cadherin stained consistently in the renal tubules of both normal and mutant animals. Whereas the initial expression of Pax2 corresponded between normal and mutant kidneys, it became progressively limited to the nephrogenic zone in +/+ animals, while distributing erratically in the Br/Br kidney. Fibronectin was not expressed in the normal nephrogenic zone but remained abundantly distributed throughout the Br/Br kidney. Luminin and Type IV collagen staining revealed a deficiency in renal vasculature formation in Br/Br kidneys. Results suggest that initial morphological differentiation occurs normally in the Br kidney but that subsequent nephric formation is associated with abnormal distribution of Pax2 and ECM proteins. (J Histochem Cytochem 49:1081-1097, 2001)

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.

Genes and proteins involved in mesenchymal to epithelial transition

It has been known for many years that the epithelia of the urogenital system derive from mesenchyme. Essential regulators of this conversion have recently been discovered, and cellular changes have been described. However, we do not have a coherent view of how these dramatic changes are integrated, nor do we know the source or identity of extracellular signals that must regulate epithelialization of mesenchymal precursors. The metanephric kidney, Wolffian duct, and the Drosophila midgut are the leading model systems to describe how epithelia derive from mesenchyme.

Wilms tumor and the WT1 gene

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

Wilms' Tumor Suppressor GeneWT1

Abstract.Normal development of the kidney is a highly complex process that requires precise orchestration of proliferation, differentiation, and apoptosis. In the past few years, a number of genes that regulate these processes, and hence play pivotal roles in kidney development, have been identified. The Wilms' tumor suppressor geneWT1has been shown to be one of these essential regulators of kidney development, and mutations in this gene result in the formation of tumors and developmental abnormalities such as the Denys-Drash and Frasier syndromes. A fascinating aspect of theWT1gene is the multitude of isoforms produced from its genomic locus. In this review, our current understanding of the structural features ofWT1, how they modulate the transcriptional and post-transcriptional activities of the protein, and how mutations affecting individual isoforms can lead to diseased kidneys is summarized. In addition, results from transgenic experiments, which have yielded important findings regarding the function of WT1in vivo, are discussed. Finally, data on the unusual feature of RNA editing ofWT1transcripts are presented, and the relevance of RNA editing for the normal functioning of the WT1 protein in the kidney is discussed.

The paired homeodomain transcription factor Pax-2 is expressed in the endocrine pancreas and transactivates the glucagon gene promoter

Glucagon gene expression is controlled by at least four DNA elements within the promoter; G2, G3, and G4 confer islet-specific expression, while G1 restricts glucagon transcription to alpha cells. Two islet-specific complexes are formed on G3, the insulin-responsive element of the glucagon gene; one of these corresponds to the paired homeodomain protein Pax-6, a major glucagon gene transactivator that plays a crucial role in alpha cell development. We describe here the identification of the second complex as Pax-2, another member of the paired box family. Pax-2 is known to be crucial for the development of the urogenital tract and of the central nervous system, but its presence in the endocrine pancreas has not been reported. We detected Pax-2 gene expression by RT-PCR; in islets, Pax-2 is present as two alternative splicing isoforms, Pax-2A and Pax-2B, whereas in the glucagon- and insulin-producing cell lines alphaTC1 and Min6, a distinct isoform, Pax-2D2, is found in addition to Pax-2B. Both islet-specific isoforms bind to the enhancer element G3 and to the alpha-specific promoter element G1 that also interacts with Pax-6. Pax-2A and Pax-2B dose-dependently activate transcription from the G3 and the G1 elements both in heterologous and in glucagon-producing cells. Our data indicate that Pax-2 is the third paired domain protein present in the endocrine pancreas and that one of its roles may be the regulation of glucagon gene expression.

Cross-talk in kidney development

As in most organs, the emerging theme in kidney development is the importance of cross-talk between several tissues and cell lineages to allow morphogenesis to proceed in a complex but highly regulated way. Over the past few years, knock-out and transgenic analyses in mice and evolutionary comparison with non-mammalian species have been particularly instrumental in identifying molecules with crucial functions for tissue-tissue interactions. The transcription factors Wt1 and Eya1, the signalling molecules Gdnf and LIF and the receptors c-Ret and GdnfRalpha have been demonstrated to fulfil fundamental roles in the first step of metanephric induction, the outgrowth of the ureter. Signalling by members of the Wnt, BMP and FGF families, regulated by transcription factors such as Pax2, mediates nephrogenesis by adjusting the balance between the ureteric bud epithelium, stromal and nephrogenic tissues. The stromal tissue, neglected for many years, has been shown to serve important functions in regulating the growth of nephrons. Finally, we have also begun to gain insight into the molecular events underlying patterning of the nephron into distinct functional units including glomerulus, proximal and distal tubule.

Kidney development: regulatory molecules crucial to both mice and men

Although the study of embryonic kidney development began in the 1950s, three decades passed until scientists began identifying the molecular controls of renal organogenesis. Most of these advances have come from mouse gene targeting and rodent kidney explant manipulation. Translation of the rodent data to human congenital kidney disease has only just begun. The activities of those regulatory molecules proven to be used in common appear remarkably similar in mouse and human renal development. Examples of these genes include glial cell line-derived neurotrophic factor (GDNF), RET, PAX2, Wilms tumor suppressor (WT1), and components in the renin-angiotensin pathway. Other factors that participate in mouse renal organogenesis, such as N-Myc, may later be proven important in human kidney development.

Analysis of Wilms tumor gene (WT1) expression in acute leukemia patients with special reference to the differential diagnosis between eosinophilic leukemia and idiopathic hypereosinophilic syndromes

Continuous Wilms' tumor gene (WT1) expression is a typical feature of leukemic blasts in AML, ALL, and blast crisis CML patients. It is easily detectable by a variety of RT-PCR protocols, which differ mainly in their sensitivity. The nuclear WT1 protein can be found in blasts of approximately 50-60% of acute leukemia patients at diagnosis. Conversely, WT1 is only transiently expressed in normal hemopoiesis. Early CD34+ hemopoietic progenitors express WT1, whereas no WT1 mRNA transcripts can be found in mature blood cells and differentiation-induced committed CD34- progenitors. As a powerful complementary diagnostic tool, testing for WT1 expression can be helpful to discriminate between eosinophilic leukemia (EoL) patients and patients with idiopathic hypereosinophilic syndromes. Conflicting data about the usefulness of testing for WT1 expression to monitor minimal residual disease (MRD) in treated leukemia patients will be discussed. Finally, research strategies to circumvent shortcomings in detecting leukemia-associated WT1 expression will be outlined.

Embryonic renal epithelia: induction, nephrogenesis, and cell differentiation

Embryonic metanephroi, differentiating into the adult kidney, have come to be a generally accepted model system for organogenesis. Nephrogenesis implies a highly controlled series of morphogenetic and differentiation events that starts with reciprocal inductive interactions between two different primordial tissues and leads, in one of two mainstream processes, to the formation of mesenchymal condensations and aggregates. These go through the intricate process of mesenchyme-to-epithelium transition by which epithelial cell polarization is initiated, and they continue to differentiate into the highly specialized epithelial cell populations of the nephron. Each step along the developmental metanephrogenic pathway is initiated and organized by signaling molecules that are locally secreted polypeptides encoded by different gene families and regulated by transcription factors. Nephrogenesis proceeds from the deep to the outer cortex, and it is directed by a second, entirely different developmental process, the ductal branching of the ureteric bud-derived collecting tubule. Both systems, the nephrogenic (mesenchymal) and the ductogenic (ureteric), undergo a repeat series of inductive signaling that serves to organize the architecture and differentiated cell functions in a cascade of developmental gene programs. The aim of this review is to present a coherent picture of principles and mechanisms in embryonic renal epithelia.

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

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

Advances in the molecular basis of renal neoplasia

The past 2 years have provided exciting progress in elucidating the molecular basis of renal cancer. Work on the von Hippel-Lindau tumor suppressor, pVHL, in clear-cell renal cancer is already suggesting new potential therapies, and should have important implications in the pathogenesis of renal cystic disease and tumor angiogenesis. In addition, study of the Wilms' tumor suppressor, WT1, is revealing much about the pathogenesis of Wilms' tumor, urogenital development, and glomerular podocyte biology. c-met, the gene encoding the hepatocyte growth factor receptor, has recently been identified as a causative gene for hereditary papillary renal cancer. This review will highlight these and other new molecular advances in the renal cancer field.

Gene expression in the epididymis

The epididymis is a tubular organ exhibiting vectorial functions of sperm concentration, maturation, transport, and storage. The molecular basis for these functions is poorly understood. However, it has become increasingly clear that regional differences along the length of the duct play a role in epididymal physiology and that region-specific gene expression is involved in the formation of these differences. Although not an overtly segmented organ, the epididymis consists of a series of highly coiled "zones," separated by connective tissue septulae and distinct by cell morphology and their pattern of gene expression. Thus, it constitutes an interesting mammalian model to study how pattern formation is achieved by differential gene activity. A large number of epididymis-expressed genes have been cloned and analyzed at the molecular level, most of them have been characterized by a distinct temporal and spatial expression pattern within the organ. Only recently have theories been developed about how and when during ontogenesis this pattern formation takes place and what its significance might be. This review summarizes the current knowledge on regionalized gene expression in the epididymis and presents hypotheses concerning its ontogenetic origin and regulation in the adult.

WT1: what has the last decade told us?

When positionally cloned in late 1989, it was anticipated that mutations within the Wilms' tumour suppressor gene (WT1) would prove responsible for this common solid kidney cancer of childhood. Characterisation of the WT1 expression pattern and of the structure of the encoded protein isoforms and their mode of action has now spanned almost a decade. WT1 proteins act as nucleic acid-binding zinc finger-containing transcription factors involved in both transactivation and repression. These activities are facilitated and constrained by interactions with other proteins. Expression analyses and knockout mice indicate that WT1 protein plays a critical role in normal kidney and gonad development. Specific constitutional WT1 mutations results in several urogenital anomaly syndromes. While only 10% of sporadic Wilms' tumours do display WT1 mutation, WT1 is mutated in other cancers, including acute myeloid leukaemia. Much is still to be determined in WT1 biology. The next decade will see at least three streams of attention. The first two, elucidation of the role of WT1 in RNA metabolism and the characterisation of further protein partners, may together explain the distinct tissue-specific functions of WT1. Finally, further research into the role of WT1 in haematopoiesis will improve our understanding of WT1 in leukaemia.

YAC transgenic analysis reveals Wilms' tumour 1 gene activity in the proliferating coelomic epithelium, developing diaphragm and limb

Wilms' Tumour 1 gene (WT1) is required for the correct development of the urogenital system. To examine its regulation and expression, we created several transgenic mouse lines containing a beta-galactosidase reporter driven by the human WT1 promoter. A 5 kb promoter weakly recapitulated a subset of the endogenous Wt1 expression pattern. In contrast, 470 and 280 kb YAC transgenes reproduced the correct pattern with high activity and highlighted new expression sites. Wt1 is expressed in the septum transversum revealing how its mutation causes diaphragmatic defects. Wt1 expression in the limb demarcates a zone between chondrogenic and apoptotic domains. Finally, Wt1 is expressed in mesenchymal cells derived from the coelomic epithelium. Based upon these and further data we discuss a Wt1 role in epithelial<-->mesenchymal transitions.

Xenopus Pax-2 displays multiple splice forms during embryogenesis and pronephric kidney development

Kidney organogenesis is initiated with the formation of the pronephric kidney and requires Pax-2 gene function. We report here the cloning and characterization of Pax-2 cDNAs from the frog Xenopus laevis, a model system suitable for the study of early kidney organogenesis. We show that expression of Xenopus Pax-2 (XPax-2) genes was confined to the nervous system, sensory organs, the visceral arches, and the developing excretory system. DNA sequencing of XPax-2 cDNAs isolated from head and pronephric kidney libraries revealed seven novel alternatively spliced Pax-2 isoforms. They all retain DNA-binding domains, but can differ significantly in their C termini with some isoforms containing a novel Pax-2 exon. We investigated the spectrum of XPax-2 splice events in pronephric kidneys, animal cap cultures and in whole embryos. Splicing of XPax-2 transcripts was found to be extensive and temporally regulated during Xenopus embryogenesis. Since all investigated tissues expressed essentially the full spectrum of XPax-2 splice variants, we conclude that splicing of XPax-2 transcripts does not occur in a tissue-specific manner.