Isolation, characterization, and expression of the murine Wilms' tumor gene (WT1) during kidney development

The Wilms' Tumor Suppressor WT1 in Cardiomyocytes: Implications for Cardiac Homeostasis and Repair

The Wilms' tumor suppressor WT1 is essential for the development of the heart, among other organs such as the kidneys and gonads. The Wt1 gene encodes a zinc finger transcription factor that regulates proliferation, cellular differentiation processes, and apoptosis. WT1 is also involved in cardiac homeostasis and repair. In adulthood, WT1-expression levels are lower compared to those observed through development, and WT1 expression is restricted to a few cell types. However, its systemic deletion in adult mice is lethal, demonstrating that its presence is also key for organ maintenance. In response to injury, the epicardium re-activates the expression of WT1, but little is known about the roles it plays in cardiomyocytes, which are the main cell type affected after myocardial infarction. The fact that cardiomyocytes exhibit a low proliferation rate in the adult heart in mammals highlights the need to explore new approaches for cardiac regeneration. The aim of this review is to emphasize the functions carried out by WT1 in cardiomyocytes in cardiac homeostasis and heart regeneration.

Expression of Wilm’s Tumor Gene (WT1) in Endometrium with Potential Link to Gestational Vascular Transformation

Background: Wilm’s tumor 1 gene (WT1) is a transcription factor with versatile cellular functions in embryonic development, the maintenance of adult tissue functions, and regeneration. WT1 is known to be regulated by progesterone and it is abundantly expressed in endometrium, but its function is unclear. Design: in this observational and descriptive study, WT1 expression was detected by immunohistochemical staining in endometrium of various physiological and pathological conditions. Result: WT1 was detected in endometrial stromal cells and vascular smooth muscle cells, in both proliferative and secretory phases of menstrual cycles. WT1 appeared increased in vascular smooth muscle cells in spiral artery in early pregnancy and it was also detected in regenerative endothelial cells and smooth muscle cells in decidual vasculopathy at term. WT1 expression appeared decreased in endometrial stromal cells in adenomyosis (endometriosis). Conclusion: WT1 potentially links the hormonal effects on endometrial decidualization and may play a role in gestational vascular transformation during pregnancy and restoration after pregnancy.

Physiological functions of Wilms' tumor 1-associating protein and its role in tumourigenesis

The Wilms' tumor-associated gene WT1 encodes a tumor suppressor gene, which is implicated in renal differentiation and development of adult urogenital system. Wilms' tumor 1-associating protein (WTAP) is initially identified as a nuclear protein that specifically interacts with WT1 in both in vitro and in vivo assays. WTAP is ubiquitously expressed in different tissues and various growth periods, and its expression is involved in cell cycle, RNA splicing and stabilization, N6-methyladenosine RNA modification, cell proliferation, and apoptosis as well as embryonic development. In the present review, we aimed to summarize the functions of WTAP in various physiological and pathological processes, in particular with regard to the current knowledge about the role of WTAP in tumorigenesis of different cancers.

The ontogeny, activation and function of the epicardium during heart development and regeneration

The epicardium plays a key role during cardiac development, homeostasis and repair, and has thus emerged as a potential target in the treatment of cardiovascular disease. However, therapeutically manipulating the epicardium and epicardium-derived cells (EPDCs) requires insights into their developmental origin and the mechanisms driving their activation, recruitment and contribution to both the embryonic and adult injured heart. In recent years, studies of various model systems have provided us with a deeper understanding of the microenvironment in which EPDCs reside and emerge into, of the crosstalk between the multitude of cardiovascular cell types that influence the epicardium, and of the genetic programmes that orchestrate epicardial cell behaviour. Here, we review these discoveries and discuss how technological advances could further enhance our knowledge of epicardium-based repair mechanisms and ultimately influence potential therapeutic outcomes in cardiovascular regenerative medicine.

Generation of higher affinity T cell receptors by antigen-driven differentiation of progenitor T cells in vitro

Many promising targets for T-cell-based cancer immunotherapies are self-antigens. During thymic selection, T cells bearing T cell receptors (TCRs) with high affinity for self-antigen are eliminated. The affinity of the remaining low-avidity TCRs can be improved to increase their antitumor efficacy, but conventional saturation mutagenesis approaches are labor intensive, and the resulting TCRs may be cross-reactive. Here we describe the in vitro maturation and selection of mouse and human T cells on antigen-expressing feeder cells to develop higher-affinity TCRs. The approach takes advantage of natural Tcrb gene rearrangement to generate diversity in the length and composition of CDR3β. In vitro differentiation of progenitors transduced with a known Tcra gene in the presence of antigen drives differentiation of cells with a distinct agonist-selected phenotype. We purified these cells to generate TCRβ chain libraries pre-enriched for target antigen specificity. Several TCRβ chains paired with a transgenic TCRα chain to produce a TCR with higher affinity than the parental TCR for target antigen, without evidence of cross-reactivity.

Graft Growth and Podocyte Dedifferentiation in Donor-Recipient Size Mismatch Kidney Transplants

Background

Kidney transplantation is the treatment choice for patients with end-stage renal diseases. Because of good long-term outcome, pediatric kidney grafts are also accepted for transplantation in adult recipients despite a significant mismatch in body size and age between donor and recipient. These grafts show a remarkable ability of adaptation to the recipient body and increase in size in a very short period, presumably as an adaptation to hyperfiltration.

Methods

We investigated renal graft growth as well as glomerular proliferation and differentiation markers Kiel-67, paired box gene 2 and Wilms tumor protein (WT1) expression in control biopsies from different transplant constellations: infant donor for infant recipient, infant donor for child recipient, infant donor for adult recipient, child donor for child recipient, child donor for adult recipient, and adult donor for an adult recipient.

Results

We detected a significant increase in kidney graft size after transplantation in all conditions with a body size mismatch, which was most prominent when an infant donated for a child. Podocyte WT1 expression was comparable in different transplant conditions, whereas a significant increase in WT1 expression could be detected in parietal epithelial cells, when a kidney graft from a child was transplanted into an adult. In kidney grafts that were relatively small for the recipients, we could detect reexpression of podocyte paired box gene 2. Moreover, the proliferation marker Kiel-67 was expressed in glomerular cells in grafts that increased in size after transplantation.

Conclusions

Kidney grafts rapidly adapt to the recipient size after transplantation if they are transplanted in a body size mismatch constellation. The increase in transplant size is accompanied by an upregulation of proliferation and dedifferentiation markers in podocytes. The different examined conditions exclude hormonal factors as the key trigger for this growth so that most likely hyperfiltration is the key trigger inducing the rapid growth response.

WT1-associated protein is a novel prognostic factor in pancreatic ductal adenocarcinoma

Although Wilms tumor 1 (WT1)-associated protein (WTAP) was initially found to be a specific WT1-binding protein, it has increasingly attracted attention because of its oncogenic role in various types of malignancies, including cholangiocarcinoma, glioblastoma and acute myeloid leukemia. However, the clinical impact of WTAP on pancreatic ductal adenocarcinoma (PDAC) is still unknown. A total of 145 patients who underwent surgical treatment from 2004 to 2008 were enrolled in the present study. The cytoplasmic and nuclear expression of WTAP in tumor and adjacent normal tissues was examined by immunohistochemical analysis in order to investigate the relationship between WTAP and the clinicopathological factors and prognosis of patients with PDAC. The nuclear and cytoplasmic expression of WTAP in tumor tissues was significantly higher compared with non-tumor tissues (P<0.001). High expression of WTAP in the nucleus was significantly associated with gender (P=0.010) and tumor stage (P=0.020), while high expression of WTAP in the cytoplasm was significantly associated with gender (P=0.018), histological grade (P=0.047) and perineural invasion (P=0.028). In addition, a univariate analysis revealed that high nuclear expression of WTAP in tumor tissues was significantly associated with poor overall survival (P<0.001), as well as several clinicopathological variables, including gender and N stage. In a multivariate Cox regression analysis, nuclear WTAP expression was identified as an independent prognostic indicator for PDAC (relative risk, 1.855; 95% confidence interval, 1.033–3.333; P=0.039). The results of the present study indicated that high nuclear expression of WTAP is a valuable molecular biomarker of a poor prognosis among patients with PDAC.

A Point Mutation in p190A RhoGAP Affects Ciliogenesis and Leads to Glomerulocystic Kidney Defects

Rho family GTPases act as molecular switches regulating actin cytoskeleton dynamics. Attenuation of their signaling capacity is provided by GTPase-activating proteins (GAPs), including p190A, that promote the intrinsic GTPase activity of Rho proteins. In the current study we have performed a small-scale ENU mutagenesis screen and identified a novel loss of function allele of the p190A gene Arhgap35, which introduces a Leu1396 to Gln substitution in the GAP domain. This results in decreased GAP activity for the prototypical Rho-family members, RhoA and Rac1, likely due to disrupted ordering of the Rho binding surface. Consequently, Arhgap35-deficient animals exhibit hypoplastic and glomerulocystic kidneys. Investigation into the cystic phenotype shows that p190A is required for appropriate primary cilium formation in renal nephrons. P190A specifically localizes to the base of the cilia to permit axoneme elongation, which requires a functional GAP domain. Pharmacological manipulations further reveal that inhibition of either Rho kinase (ROCK) or F-actin polymerization is able to rescue the ciliogenesis defects observed upon loss of p190A activity. We propose a model in which p190A acts as a modulator of Rho GTPases in a localized area around the cilia to permit the dynamic actin rearrangement required for cilia elongation. Together, our results establish an unexpected link between Rho GTPase regulation, ciliogenesis and glomerulocystic kidney disease.

The Role of WT1 in Embryonic Development and Normal Organ Homeostasis

The Wilms' tumor suppressor gene 1 (Wt1) is critically involved in a number of developmental processes in vertebrates, including cell differentiation, control of the epithelial/mesenchymal phenotype, proliferation, and apoptosis. Wt1 proteins act as transcriptional and post-transcriptional regulators, in mRNA splicing and in protein-protein interactions. Furthermore, Wt1 is involved in adult tissue homeostasis, kidney function, and cancer. For these reasons, Wt1 function has been extensively studied in a number of animal models to establish its spatiotemporal expression pattern and the developmental fate of the cells expressing this gene. In this chapter, we review the developmental anatomy of Wt1, collecting information about its dynamic expression in mesothelium, kidney, gonads, cardiovascular system, spleen, nervous system, lung, and liver. We also describe the adult expression of Wt1 in kidney podocytes, gonads, mesothelia, visceral adipose tissue, and a small fraction of bone marrow cells. We have reviewed the available animal models for Wt1-expressing cell lineage analysis, including direct Wt1 expression reporters and systems for permanent Wt1 lineage tracing, based on constitutive or inducible Cre recombinase expression under control of a Wt1 promoter. Finally we provide a number of laboratory protocols to be used with these animal models in order to assess reporter expression.

Sox9 expression in carcinogenesis and its clinical significance in intrahepatic cholangiocarcinoma

BACKGROUND

Intrahepatic cholangiocarcinomas develop through a multi-step carcinogenesis. Precancerous lesions are defined as biliary intraepithelial neoplasia. Sex determining region Y-box9 (Sox9) is required for the normal differentiation of the biliary tract.

AIMS

To evaluate the Sox9 expression in carcinogenesis and its correlation with clinicopathological features in intrahepatic cholangiocarcinoma.

METHODS

Sox9 expression in normal epithelium, biliary intraepithelial neoplasia, and intrahepatic cholangiocarcinoma were investigated immunohistochemically using 43 specimens of intrahepatic cholangiocarcinoma. Sox9 expression in intrahepatic cholangiocarcinoma was compared with the clinicopathological features. The molecular effects of Sox9 were investigated by gene transfection to intrahepatic cholangiocarcinoma cell lines.

RESULTS

Sox9 expression was decreased from the normal epithelium to the biliary intraepithelial neoplasia in a stepwise fashion. In 51.2% (22/43) of the patients with intrahepatic cholangiocarcinoma, Sox9 expression was positive, and Sox9 expression was significantly associated with the biliary infiltration (P=0.034) and poor overall survival (P=0.039). Upregulation of Sox9 promoted the cell migration and invasion, and decreased the E-cadherin expression and increased the vimentin and α-SMA expression in cell lines.

CONCLUSIONS

Decreased Sox9 expression may be related to the early stage of the carcinogenesis of intrahepatic cholangiocarcinoma. Sox9 overexpression in intrahepatic cholangiocarcinoma is related to biliary infiltration and poorer prognosis, and it promotes cell migration and invasion, via the epithelial-to-mesenchymal transition.

Mediators and mechanisms of heat shock protein 70 based cytoprotection in obstructive nephropathy

Urinary heat shock protein 70 (Hsp70) is rapidly increased in patients with clinical acute kidney injury, indicating that it constitutes a component of the endogenous stress response to renal injury. Moreover, experimental models have demonstrated that Hsp70 activation is associated with the cytoprotective actions of several drugs following obstruction, including nitric oxide (NO) donors, geranylgeranylacetone, vitamin D, and rosuvastatin. Discrete and synergistic effects of the biological activities of Hsp70 may explain its cytoprotective role in obstructive nephropathy. Basic studies point to a combination of effects including inhibition of apoptosis and inflammation, repair of damaged proteins, prevention of unfolded protein aggregation, targeting of damaged protein for degradation, and cytoskeletal stabilization as primary effectors of Hsp70 action. This review summarizes our understanding of how the biological actions of Hsp70 may affect renal cytoprotection in the context of obstructive injury. The potential of Hsp70 to be of central importance to the mechanism of action of various drugs that modify the genesis of experimental obstructive nephropathy is considered.

Novel WT1 Missense Mutations in Han Chinese Women with Premature Ovarian Failure

Premature ovarian failure (POF) is a heterogeneous disease. Though dozens of candidate genes have been identified for the genetic etiology of POF, it is largely unexplained in majority of patients. Recently, Wt1^+/R394W mice was found to present POF-like phenotype, which indicates that WT1 might be a plausible candidate gene for non-syndromic POF. The coding region of WT1 gene was screened in 384 patients with POF and 6 novel variations were identified, including two missense mutations (p. Pro126Ser in exon1 and p. Arg370His in exon7) and four intronic variants (c.647-27C > T, c.647-13G > C, c.647-13G > A in intron1 and c.950 + 14T > C in intron 4). In vitro experiments showed that both mutant p. Pro126Ser and p. Arg370His repressed the expression of Amh and Cdh1, and induced the expression of Fshr and Cyp19 in mRNA level (P < 0.05). The expression changes of AMH, FSHR, CYP19 and CDH1 were confirmed by western blot. These genes (AMH, FSHR, CYP19 and CDH1) are required for granular cells (GCs) proliferation, differentiation and oocyte-GCs interaction. The novel mutant p. P126S and p. R370H in the WT1 gene potentially impaired GCs differentiation and oocyte-GCs interaction, which might result in loss of follicles prematurely. Therefore, WT1 is a plausible causal gene for POF.

Substrate-specific gene expression profiles in different kidney cell types are associated with Fabry disease

Fabry disease is an X-linked lysosomal storage disorder caused by mutations in the gene encoding the α-galactosidase A (α-Gal A) lysosomal enzyme, which results in globotriaosylceramide (Gb3) storage in vascular endothelial cells and different cell types throughout the body. Involvement of the kidney and heart is life threatening, and fibrosis of these organs is considered to be involved in the pathogenesis of Fabry disease. An increased concentration of deacylated Gb3 (lyso‑Gb3) in the plasma of symptomatic patients has also been suggested as a causative molecular event. To elucidate the molecular mechanisms involved in renal fibrosis in Fabry disease, the present analyzed the changes in global gene expression prior to and following Gb3 or lyso‑Gb3 treatment in two types of kidney cell lines, human proximal renal tubular epithelial (HK‑2) and mouse renal glomerular mesangial (SV40 MES 13) cells. Gb3 and lyso‑Gb3 treatment regulated the expression of 199 and 328 genes in each cell type, demonstrating a >2.0‑fold change. The majority of the biological functions of the regulated genes were associated with fibrogenesis or epithelial‑mesenchymal transition (EMT). The gene expression patterns of sphingolipid‑treated HK‑2 cells were distinguishable from the patterns in the SV40 MES 13 cells. Several genes associated with the EMT were selected and evaluated further in kidney cells and in Fabry mouse kidney tissues. In the SV40 MES 13 cells, the DLL1, F8, and HOXA11 genes were downregulated, and FOXP2 was upregulated by treatment with Gb3 or lyso‑Gb3. In the HK‑2 cells, the ADAMTS6, BEST1, IL4, and MYH11 genes were upregulated. Upregulation of the FOXP2, COL15A1, IL4, and MYH11 genes was also observed in the Fabry mouse kidney tissues. The gene expression profiles in kidney cells following the addition of Gb3 or lyso‑Gb3 revealed substrate‑specific and cell‑specific patterns. These findings suggested that Gb3 and lyso‑Gb3 lead to renal fibrosis in Fabry disease through different biochemical modulations.

Effects of WT1 down-regulation on oocyte maturation and preimplantation embryo development in pigs

The Wilms' tumour 1 (WT1) gene originally identified as a tumour suppressor associated with WTs encodes a zinc finger-containing transcription factor that is expressed in multiple tissues and is an important regulator of cellular and organ growth, proliferation, development, migration and survival. However, there is a deficiency of data regarding the expression and function ofWT1during oocyte maturation and preimplantation embryonic development. Herein, we sought to define the expression characteristics and functions ofWT1during oocyte maturation and preimplantation embryonic development in pigs. We show thatWT1is expressed in porcine oocytes and at all preimplantation stages in embryos generated by ICSI. We then evaluated the effects of down-regulatingWT1expression at germinal vesicle and early ICSI stages using a recombinant plasmid (pGLV3-WT1-shRNA). Down-regulation ofWT1did not affect oocyte maturation but significantly decreased preimplantation embryonic development and increased apoptosis in blastocysts. These results indicate thatWT1plays important roles in the development of porcine preimplantation embryos.

Prognostic significance of WT1 expression in soft tissue sarcoma

Background

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

Methods

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

Results

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

Conclusions

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

Wt-1 Expression Linked to Nitric Oxide Availability during Neonatal Obstructive Nephropathy

The wt-1 gene encodes a zinc finger DNA-binding protein that acts as a transcriptional activator or repressor depending on the cellular or chromosomal context. The wt-1 regulates the expression of a large number of genes that have a critical role in kidney development. Congenital obstructive nephropathy disrupts normal renal development and causes chronic progressive interstitial fibrosis, which contributes to renal growth arrest, ultimately leading to chronic renal failure. Wt-1 is downregulated during congenital obstructive nephropathy, leading to apoptosis. Of great interest, nitric oxide bioavailability associated with heat shock protein 70 (Hsp70) interaction may modulate wt-1 mRNA expression, preventing obstruction-induced cell death during neonatal unilateral ureteral obstruction. Moreover, recent genetic researches have allowed characterization of many of the complex interactions among the individual components cited, but the realization of new biochemical, molecular, and functional experiments as proposed in our and other research labs allows us to establish a deeper level of commitment among proteins involved and the potential pathogenic consequences of their imbalance.

Detection and preliminary characterization of CD8+T lymphocytes specific for Wilms' tumor antigen in patients with non-Hodgkin lymphoma

Wilms' tumor antigen (WT1) is overexpressed in many different solid tumors and hematologic malignancies. However, little is known about WT1 expression or WT1-specific immune responses in patients with non-Hodgkin lymphoma (NHL). In a cross-sectional survey study, we investigated the immune recognition of WT1 by patients with NHL. Utilizing a WT1 overlapping peptide library, we discovered that a large percentage of patients with NHL of all grades maintain WT1-specific T cells. Ex vivo frequencies of these T cells measured from unfractionated samples by the CD137 activation marker assay were high in many patients (some > 1% CD8+). Using standard in vitro techniques we discovered that they were cytotoxic to WT1 peptide library-loaded T2 cells and WT1 antigen-primed autologous Epstein-Barr virus-transformed B cell lines (EBV-LCLs) and expressed interferon gamma (IFN-γ). In addition, we detected WT1 mRNA transcripts in diseased lymph node tissues of patients with NHL utilizing real-time quantitative polymerase chain reaction (RT-qPCR) technology. These results are the first example of strong T cell reactivity against WT1 in patients with NHL which also demonstrate strong cytotoxicity against peptide-loaded tumor cells. The potential for developing WT1 as a target for immunotherapy in NHL deserves further exploration.

A Wt1-Dmrt1 transgene restores DMRT1 to sertoli cells of Dmrt1(-/-) testes: a novel model of DMRT1-deficient germ cells

DMRT1 is an evolutionarily conserved transcriptional factor expressed only in the postnatal testis, where it is produced in Sertoli cells and germ cells. While deletion of Dmrt1 in mice demonstrated it is required for postnatal testis development and fertility, much is still unknown about its temporal- and cell-specific functions. This study characterized a novel mouse model of DMRT1-deficient germ cells that was generated by breeding Dmrt1-null (Dmrt1(-/-)) mice with Wt1-Dmrt1 transgenic (Dmrt1(+/-;tg)) mice, which express a rat Dmrt1 cDNA in gonadal supporting cells by directing it from the Wilms tumor 1 locus in a yeast artificial chromosome transgene. Like Dmrt1(-/-) mice, male Dmrt1(-/-) transgenic mice (Dmrt1(-/-;tg)) were infertile, while female mice were fertile. Immunohistochemistry and Western blot analysis showed transgenic DMRT1 expressed in supporting cells of the newborn gonads of both sex and in Sertoli cells of the testis afterbirth. Sertoli cells were evaluated by electron microscopy, revealing that maturation of Dmrt1(-/-;tg) Sertoli cells was incomplete. Morphological analysis of testes from 42-day-old mice showed that, compared to Dmrt1(-/-) mice, Dmrt1(-/-;tg) mice have improved seminiferous tubule structure, with lumens present in many. Immunohistochemistry of the polarity markers ESPIN and NECTIN-2 showed that DMRT1 in Sertoli cells is required for NECTIN-2 expression and influences organization of ectoplasmic specializations. Further functional analyses of the transgene on a Dmrt1(-/-) background showed that it did not rescue the decrease in Dmrt1(-/-) testis size, but when expressed on a wild-type background, exogenous DMRT1 prevented the normal age-related decline in testis size and enhanced sperm progressive motility. The studies suggest that DMRT1 in Sertoli cells regulates tubule morphology, spermatogenesis, and sperm function via its effects on Sertoli cell maturation and polarity. Furthermore, expression and function of transgenic DMRT1 in Sertoli cells establishes a novel mouse model of DMRT1-deficient germ cells generated by breeding Dmrt1-null mice with Wt1-Dmrt1 transgenic mice (rescue; Dmrt1(-/-;tg)).

The significance of Wilms Tumor Gene (WT1) and p53 expression in curettage specimens of patients with endometrial carcinomas

In this retrospective experimental study, we assessed the immunohistochemical expression of Wilms Tumor Gene (WT1) and p53 in endometrial biopsies of patients with endometrial cancer, and correlated their expression with the final pathological findings. Sixty-two patients with primary endometrial cancer who underwent surgical treatment were investigated. Immunohistochemical expression of Wilms Tumor Gene (WT1) and p53 was assessed in curettage specimens, and the final pathology reports from hysterectomy specimens were reviewed. The expression of these markers seems to play a role in curettage specimens as they correlate with the final tumor characteristics of hysterectomy specimens. Five out of sixty-two endometrial cancer specimens (8.1%) were WT1-positive, and 21 specimens (33.9%) were P53-positive. Positive expression of WT1 and P53 was significantly associated with the non-endometrioid type (p value of 0.019 and 0.005, respectively). Positive WT1 expression was significantly associated with high grade lesions, deep myometrial invasion, and advanced stage disease. Moreover, a statistically significant inverse relationship was observed between the positivity of WT1 and P53, and the positivity of ER and PR. We think that examination for WT1 and p53 in curettage specimens might help to predict the final pathological diagnosis in patients with endometrial cancer. This might be useful for the identification of high risk groups and, therefore, of candidates for more radical surgery.

WT1-specific T-cell responses in high-risk multiple myeloma patients undergoing allogeneic T cell-depleted hematopoietic stem cell transplantation and donor lymphocyte infusions

While the emergence of WT1-specific cytotoxic T lymphocytes (WT1-CTL) has been correlated with better relapse-free survival after allogeneic stem cell transplantation in patients with myeloid leukemias, little is known about the role of these cells in multiple myeloma (MM). We examined the significance of WT1-CTL responses in patients with relapsed MM and high-risk cytogenetics who were undergoing allogeneic T cell-depleted hematopoietic stem cell transplantation (alloTCD-HSCT) followed by donor lymphocyte infusions. Of 24 patients evaluated, all exhibited WT1-CTL responses before allogeneic transplantation. These T-cell frequencies were universally correlated with pretransplantation disease load. Ten patients received low-dose donor lymphocyte infusions beginning 5 months after transplantation. All patients subsequently developed increments of WT1-CTL frequencies that were associated with reduction in specific myeloma markers, in the absence of graft-versus-host disease. Immunohistochemical analyses of WT1 and CD138 in bone marrow specimens demonstrated consistent coexpression within malignant plasma cells. WT1 expression in the bone marrow correlated with disease outcome. Our results suggest an association between the emergence of WT1-CTL and graft-versus-myeloma effect in patients treated for relapsed MM after alloTCD-HSCT and donor lymphocyte infusions, supporting the development of adoptive immunotherapeutic approaches using WT1-CTL in the treatment of MM.

Expression of Wilms' tumor 1 (WT1) in oral squamous cell carcinoma

BACKGROUND

The product of the Wilms' tumor gene, WT1 protein, is a tumor antigen for various kinds of cancer, and WT1 peptide-based cancer immunotherapy is widely anticipated as a new possibility for cancer treatment. The aim of this study was to investigate the expression of WT1 from quantitative and morphological perspectives in oral squamous cell carcinoma (OSCC), the most widespread malignant neoplasm of the oral cavity.

METHODS

Six OSCC cell lines and tissue sections from 29 OSCC patients were analyzed. To detect WT1 expression, reverse transcription-polymerase chain reaction analysis (RT-PCR), real-time PCR, Western blots, and immunofluorescence flow cytometry for WT1 were performed on the cell lines, and immunohistochemistry and fluorescence in situ hybridization (FISH) were performed on the tissue sections.

RESULTS

WT1 mRNA was found overexpressed in one of the six OSCC cell lines, with expression levels higher than that seen in human leukemia cell line (K562). Immunohistochemical analysis of tissue sections showed overexpression of WT1 protein in two patients, concentrated mainly in the cytoplasm of the outer one to three cell layers of the cancer nests. This was consistent with the expression of WT1 mRNA observed by FISH. Meanwhile, WT1 was not detected on normal oral epithelium. WT1 protein was detected on actively proliferating cancer nests and even on elongated epithelial ridge where new droplet-cancer-nests were being formed and starting infiltration toward subepithelial layer.

CONCLUSIONS

The results suggest that WT1 plays an important role in the pathogenesis of some types of OSCC, particularly in proliferation of the cancer cells.

Reactivation of Silenced WT1 Transgene by Hypomethylating Agents - Implications for in vitro Modeling of Chemoimmunotherapy

BACKGROUND

A cell line with transfected Wilms' tumor protein 1 (WT1) is has been used for the preclinical evaluation of novel treatment strategies of WT1 immunotherapy for leukemia due to the lack of appropriate murine leukemia cell line with endogenous WT1. However, silencing of the transgene occurs. Regarding the effects of hypomethylating agents (HMAs) on reactivation of silenced genes, HMAs are considered to be immune enhancers.

METHODS

We treated murine WT1- transfected C1498 (mWT1-C1498) with increasing doses of decitabine (DAC) and azacitidine (AZA) to analyze their effects on transgene reactivation.

RESULTS

DAC and AZA decreased the number of viable cells in a dose- or time-dependent manner. Quantification of WT1 mRNA level was analyzed by real-time polymerase chain reaction after mWT1-C1498 treated with increasing dose of HMA. DAC treatment for 48 h induced 1.4-, 14.6-, and 15.5-fold increment of WT1 mRNA level, compared to untreated sample, at 0.1, 1, and 10µM, respectively. Further increment of WT1 expression in the presence of 1 and 10µM DAC was evident at 72 h. AZA treatment also induced up-regulation of mRNA, but not to the same degree as with DAC treatment. The correlation between the incremental increases in WT1 mRNA by DAC was confirmed by Western blot and concomitant down-regulation of WT1 promoter methylation was revealed.

CONCLUSION

The in vitro data show that HMA can induce reactivation of WT1 transgene and that DAC is more effective, at least in mWT1-C1498 cells, which suggests that the combination of DAC and mWT1-C1498 can be used for the development of the experimental model of HMA-combined WT1 immunotherapy targeting leukemia.

SF-1 expression during adrenal development and tumourigenesis

SF-1 is a master regulator of steroidogenesis whose expression is critical for normal adrenal and gonadal organogenesis. Strict maintenance of SF-1 levels is essential, and mutations causing under- or overexpression result in congenital adrenal and gonadal defects or hyperplasia, respectively. Data from transgenic mouse models points to a network of transcription factors responsible for stringent regulation of Sf-1 expression during development, which bind to intronic enhancer elements in addition to the basal promoter to specifically modulate transcription in each Sf-1-expressing tissue. Furthermore, analysis of the role of SF-1 in adrenal tumourigenesis implies that improper developmental regulation of Sf-1 expression may have postnatal consequences separate from the well-documented developmental defects.

Wilms' tumor 1-specific cytotoxic T lymphocytes can be expanded from adult donors and cord blood

The use of WT1-specific CTL is one potential strategy to treat leukemic relapse following allogeneic stem cell transplant (SCT). Previous studies have largely focused on generating WT1-CTL from adult donors by cloning. We demonstrate that WT1-CTL can be generated from healthy adult donors and from cord blood by stimulating with an overlapping pool of peptides derived from full length WT1 and selecting antigen-specific cells based on the expression of CD137. The rapid expansion with anti-CD3 and IL-2 resulted in a 100-200-fold expansion. These CTL lysed WT1 expressing targets, including leukemia lines, in a HLA restricted manner.

Molecular analysis of WT1 and KIT mutations in patients from an Indian population with de novo acute myeloid leukemia: determination of incidence, distribution patterns, and report of a novel KIT mutation

Mutations of the WT1 gene have been reported as the most common abnormality after NPM1 and FLT3 gene mutations in acute myeloid leukemia (AML), while KIT mutations are predominantly found in core-binding factor (CBF) AMLs. We report for the first time the prevalence and distribution patterns of WT1 and KIT mutations in an Indian population of 150. Overall, 10 (6.7%) and four (2.7%) of the cases had WT1 and KIT mutations, respectively. Of the six mutations observed in exon 7, five were frameshift while the remaining one case showed a substitution mutation. In contrast to exon 7, no frameshift mutation was detected in exon 9, where all mutations were substitution mutations. Interestingly, we observed a novel mutation in exon 8 of the KIT gene resulting from the deletion of nine nucleotides and insertion of three nucleotides affecting the extracellular domain of the KIT receptor, while Asp816Tyr and Asp816His were commonly found in exon 17 of the KIT gene. The WT1 mutation was more prevalent in normal karyotype AML while KIT was associated with t(8;21). With respect to FLT3 and NPM1 mutations, WT1 was more predominant in FLT3 positive cases and less in NPM1 mutation cases, while no KIT mutation was found in FLT3/NPM1 positive cases.

WT1 mutation in 470 adult patients with acute myeloid leukemia: stability during disease evolution and implication of its incorporation into a survival scoring system

The impact of WT1 mutations in acute myeloid leukemia (AML) is not completely settled. We aimed to determine the clinical implication of WT1 mutation in 470 de novo non-M3 AML patients and its stability during the clinical course. WT1 mutations were identified in 6.8% of total patients and 8.3% of younger patients with normal karyotype (CN-AML). The WT1 mutation was closely associated with younger age (P < .001), French-American-British M6 subtype (P = .006), and t(7;11)(p15;p15) (P = .003). Multivariate analysis demonstrated that the WT1 mutation was an independent poor prognostic factor for overall survival and relapse-free survival among total patients and the CN-AML group. A scoring system incorporating WT1 mutation, NPM1/FLT3-ITD, CEBPA mutations, and age into survival analysis proved to be very useful to stratify CN-AML patients into different prognostic groups (P < .001). Sequential analyses were performed on 133 patients. WT1 mutations disappeared at complete remission in all WT1-mutated patients studied. At relapse, 3 of the 16 WT1-mutated patients who had paired samples lost the mutation and 2 acquired additional mutations, whereas 3 of 110 WT1-wild patients acquired novel mutations. In conclusion, WT1 mutations are correlated with poor prognosis in AML patients. The mutation status may be changed in some patients during AML progression.

Adoptive transfer of unselected or leukemia-reactive T-cells in the treatment of relapse following allogeneic hematopoietic cell transplantation

Adoptive transfer of in vivo generated antigen-specific donor-derived T-cells is increasingly recognized as an effective approach for the treatment or prevention of EBV lymphomas and cytomegalovirus infections complicating allogeneic hematopoietic cell transplants. This review examines evidence from preclinical experiments and initial clinical trials to critically assess both the potential and current limitations of adoptive transfer of donor T-cells sensitized to selected minor alloantigens of the host or to peptide epitopes of proteins, differentially expressed by clonogenic leukemia cells, such as the Wilms tumor protein, WT-1, as a strategy to treat or prevent recurrence of leukemia in the post-transplant period.

A novel, low-volume method for organ culture of embryonic kidneys that allows development of cortico-medullary anatomical organization

Here, we present a novel method for culturing kidneys in low volumes of medium that offers more organotypic development compared to conventional methods. Organ culture is a powerful technique for studying renal development. It recapitulates many aspects of early development very well, but the established techniques have some disadvantages: in particular, they require relatively large volumes (1–3 mls) of culture medium, which can make high-throughput screens expensive, they require porous (filter) substrates which are difficult to modify chemically, and the organs produced do not achieve good cortico-medullary zonation. Here, we present a technique of growing kidney rudiments in very low volumes of medium–around 85 microliters–using silicone chambers. In this system, kidneys grow directly on glass, grow larger than in conventional culture and develop a clear anatomical cortico-medullary zonation with extended loops of Henle.

Increasing functional avidity of TCR-redirected T cells by removing defined N-glycosylation sites in the TCR constant domain

Adoptive transfer of T lymphocytes transduced with a T cell receptor (TCR) to impart tumor reactivity has been reported as a potential strategy to redirect immune responses to target cancer cells (Schumacher, T.N. 2002. Nat. Rev. Immunol. 2:512–519). However, the affinity of most TCRs specific for shared tumor antigens that can be isolated is usually low. Thus, strategies to increase the affinity of TCRs or the functional avidity of TCR-transduced T cells might be therapeutically beneficial. Because glycosylation affects the flexibility, movement, and interactions of surface molecules, we tested if selectively removing conserved N-glycoslyation sites in the constant regions of TCR α or β chains could increase the functional avidity of T cells transduced with such modified TCRs. We observed enhanced functional avidity and improved recognition of tumor cells by T cells harboring TCR chains with reduced N-glycosylation (ΔTCR) as compared with T cells with wild-type (WT) TCR chains. T cells transduced with WT or ΔTCR chains bound tetramer equivalently at 4°C, but tetramer binding was enhanced at 37°C, predominantly as a result of reduced tetramer dissociation. This suggested a temperature-dependent mechanism such as TCR movement in the cell surface or structural changes of the TCR allowing improved multimerization. This strategy was effective with mouse and human TCRs specific for different antigens and, thus, should be readily translated to TCRs with any specificity.

No evidence for WT1 involvement in a beta-catenin-independent activation of the Wnt signaling pathway in pituitary adenomas

The overexpression of Wilms' tumor gene product WT1, which acts as a tumor suppressor or oncogene, has been reported in various malignancies. Recent studies have shown that the interaction partner Wnt-4 is upregulated in pituitary adenomas dependent on the Pit-1 lineage (somatotrophs, lactotrophs, and thyrotrophs). However, no data on WT1 expression in nontumorous pituitary tissue or pituitary adenomas is available to date. We investigated WT1 expression in 90 paraffin-embedded pituitary adenomas, including eight atypical adenomas, and in 28 nontumorous pituitary glands by immunohistochemistry. WT1 is absent in epithelial cells of all nontumorous pituitary glands and in 87 out of 90 pituitary adenomas. Only two GHomas (including one atypical adenoma) and one gonadotropin-producing adenoma expressed WT1 in the cytoplasm of single tumor cells without nuclear staining. There is no evidence that WT1 does regulate the Wnt-4/beta-catenin-independent pathway which is activated in the Pit-1-expressing subset of pituitary adenomas.

New insights into the function of the Wilms tumor suppressor gene WT1 in podocytes

The Wilms tumor suppressor gene WT1 is essential for early urogenital development: homozygous mutations in WT1 result in embryonic lethality due to a failure in the development of kidneys and gonads. In the adult kidney, WT1 expression is limited to the glomerular podocytes. Several human nephrotic diseases arise from mutations of the WT1 gene, including mutations that affect its zinc-fingers and alternative splicing of +/−KTS isoforms. These include WAGR (for Wilms tumor, aniridia, genitourinary anomalies, and mental retardation), and Frasier and Denys-Drash syndromes. Recent advances including the development of transgenic mouse models and conditionally immortalized podocyte cell lines are beginning to shed light on WT1's crucial role in podocyte function.

WT1 expression distinguishes astrocytic tumor cells from normal and reactive astrocytes

Particularly in small brain biopsies, it might be difficult to distinguish reactive astrogliosis from low-grade or infiltration zones of high-grade astrocytomas. So far no immunohistochemical marker allows a reliable distinction. Recently, the over-expression of Wilms' tumor gene product WT1 was reported in astrocytic tumor cells. However, no sufficient data on WT1 expression in normal or reactive astrocytes are available. Therefore, we investigated WT1 expression in paraffin-embedded brain sections from 28 controls, 48 cases with astrogliosis of various etiology and 219 astrocytomas [World Health Organization (WHO) grades I-IV] by immunohistochemistry. In normal brains and in astrogliosis, expression of WT1 was restricted to endothelial cells. In astrocytomas, WT1-positive tumor cells were found in pilocytic astrocytomas (66.7% of cases), diffuse astrocytomas (52.7%) WHO grade II (52.7%), anaplastic astrocytomas (83.4%) and glioblastomas (98.1%). Overall, the majority of all astrocytic neoplasms (84.5%) expressed WT1. Establishing a cut-off value of 0% immunoreactive tumor cells served to recognize neoplastic astrocytes with 100% specificity and 68% sensitivity and was associated with positive and negative predictive values of 1 and 0.68, respectively. Therefore, WT1 expression in astrocytes indicates a neoplastic origin and might represent an important diagnostic tool to differentiate reactive from neoplastic astrocytes by immunohistochemistry.

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.

Wilms tumor 1 expression in malignant gliomas and correlation of +KTS isoforms with p53 status

Object

The WT1 gene is overexpressed in many types of human cancer. It has been demonstrated that Wilms tumor 1 (WT1) promotes tumor cell proliferation and survival in some cell lines by inhibiting p53-mediated apoptosis; however, this relationship has not been investigated in gliomas. The goal in this study was to characterize the expression pattern of WT1 in human gliomas and to determine if a correlation exists between WT1 expression and p53 status.

Methods

The authors screened nine malignant glioma cell lines, 50 glioblastoma multiforme (GBM) samples, and 16 lower-grade glial tumors for WT1 expression.

Results

Five of nine cell lines, 44 of 50 GBM samples, and 13 of 16 lower-grade gliomas expressed WT1 mRNA on reverse transcriptase polymerase chain reaction (PCR) analysis. Expression of WT1 was not detected in normal astrocytes. Two WT1 isoforms, +/+ and −/+, were expressed in the majority of these samples. Real-time PCR analysis of the GBM cell lines revealed that the level of WT1 mRNA ranged from 6.33 to 214.70 ng per ng 18S ribosomal RNA. The authors screened the GBM samples for p53 mutation by using PCR and single-stranded conformational polymorphism analysis, and they demonstrated an association between WT1 expression and p53 status. Tumors that contained wild-type p53 were significantly more likely to express WT1 than tumors that contained mutant p53.

Conclusions

The presence of WT1 in glioma cell lines and the majority of primary tumor samples and its absence in normal astrocytes support the suggestion that WT1 expression is important in glioma biology.

Clinicopathological significance of WT1 expression in ovarian cancer: a possible accelerator of tumor progression in serous adenocarcinoma

Recently, oncogenic potential of the WT1 gene has been proposed in some human solid tumors and leukemias. Although previous studies have shown the frequent expression of the WT1 protein in ovarian serous adenocarcinomas (OSAs), its clinicopathologic significance is still unclear. We immunohistochemically examined the expression status of WT1 in 119 OSAs and analyzed the correlation of the intensity of WT1 immunoreactivity with the level of WT1 mRNA expression by quantitative real-time polymerase chain reaction, clinicopathologic variables, expression of p53, Bcl-2, and Ki-67 labeling index (LI). Of 119 OSAs, nuclear WT1 immunoreactivity was positive in 99 (83%), of which 44 (44%) and 55 (56%) exhibited high and low WT1 immunoreactivities, respectively. The quantitative WT1 mRNA levels were significantly correlated with the intensity of WT1 immunoreactivity (P < 0.05). In comparison with WT1-negative OSAs, the WT1-positive OSAs showed a higher grade (P = 0.007), advanced stage (P = 0.018), and higher Ki-67 LI (P < 0.001). Additionally, high WT1 immunoreactivity was correlated with a higher grade (P = 0.003), Ki-67 LI (P = 0.012), Bcl-2 expression (P = 0.003), and poorer patient outcome (5-year survival, 36.5 vs 63.8%, P = 0.008 by log-rank test). The WT1 protein may be an accelerator of the progression of OSA.

Role of transcription factors in podocytes

Despite a wealth of information on structural proteins, comparatively little is known on the transcriptional regulation of podocyte structure and function. In this review we will highlight those transcription factors which, by gene inactivation or classical transgenic experiments, have been shown to be essential for podocytes or probably will turn out to be so. The tumor suppressor protein WT1 is not only indispensable for the initial stages of kidney development, but also very likely maintains the integrity of the fully differentiated podocyte. In the kidney, the LIM homeodomain transcription factor LMX1B is specifically synthesized in podocytes, and mutations in LMX1B lead to nail-patella syndrome and the associated nephropathy. Other transcription factors such as hypoxia-inducible factors and PAX2 are likely to play a role in podocytes, whereas the significance of others, e.g. of POD1 and CITED2, is more speculative at this point.

Pax2andPax8Regulate Branching Morphogenesis and Nephron Differentiation in the Developing Kidney

Pax genes are important regulators of kidney development. In the mouse, homozygous Pax2 inactivation results in renal agenesis, a phenotype that has largely precluded the analysis of Pax gene function during metanephric kidney development. To address this later function, kidney development was analyzed in embryos that were compound heterozygous for Pax2 and for Pax8, a closely related member of the Pax gene family. Both genes are coexpressed in differentiating nephrons and collecting ducts. At the morphological level, Pax2(+/-)Pax8(+/-) metanephric kidneys are severely hypodysplastic and characterized by a reduction in ureter tips and nephron number in comparison with wild-type or Pax2(+/-) kidneys. In developing nephrons, the molecular analysis of Pax2(+/-)Pax8(+/-) kidneys reveals a strong reduction in the expression levels of Lim1, a key regulator of nephron differentiation, accompanied by an increase in apoptosis. At a more mature stage, the reduction of Pax2/8 gene dosage severely affects distal tubule formation, revealing a role for Pax genes in the differentiation of specific nephron segments. At the ureter tips, the expression of Wnt11, a target of glial cell-derived neurotrophic factor-Ret signaling, is significantly reduced, whereas the expression levels of Ret and GDNF remain normal. Together, these results demonstrate a crucial role for Pax2 and Pax8 in nephron differentiation and branching morphogenesis of the metanephros.

Dendritic Cell Immunization Induces Nonprotective WT1-specific CTL Responses in Mouse

In the present article we describe the immunogenicity in the mouse of 2 epitopes from the tumor-associated antigen Wilms tumor 1 antigen (WT1). The newly described K-restricted pWT330 epitope stimulates high-avidity allo-major histocompatibility complex restricted cytotoxic T lymphocyte (CTL) capable of killing WT1-expressing tumor cell lines. The epitope pWT126 has been previously described as a D-restricted CTL epitope. Both epitopes are weakly immunogenic as immunization with incomplete Freund adjuvant induced poor CTL responses. In contrast, when coated onto dendritic cells (DCs) both peptides readily induced CTL responses. However, these peptide-specific CTL were of low avidity and unable to recognize WT1-expressing tumor cells in vitro and to protect against tumor challenge in vivo. In contrast, vaccination with DCs coated with peptides derived from the nonself antigen ovalbumin (OVA) induced CTL that recognized OVA-expressing tumor cells and protected against tumor growth in vivo. These data show that although DC vaccination readily stimulated CTL against WT1 peptides, these CTL did not display antitumor activity in vitro and in vivo. This suggests that tolerance to the 2 WT1 epitopes interferes with the generation of protective CTL immunity in mice.

The murine Pou6f2 gene is temporally and spatially regulated during kidney embryogenesis and its human homolog is overexpressed in a subset of Wilms tumors

We have previously suggested the transcription factor gene POU6F2 as a novel tumor suppressor involved in Wilms tumor (WT) predisposition. Since WT arises from pluripotent embryonic renal precursors, in this study we analyzed the expression of the murine homolog Pou6f2 during kidney embryogenesis and compared it to that of Wt1, the homolog of WT1, a known WT related gene involved in mesenchyme to epithelium conversion. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) performed for Pou6f2 on kidney specimens from embryos, pups, and adult mice, showed that the Pou6f2 mRNA was more abundant in the earliest analyzed phase of kidney organogenesis (E13) than in more advanced fetal stages and in adult animal. In situ RT-PCR demonstrated that Pou6f2 expression parallels the centripetal differentiation of renal morphogenesis. In addition, in E18 kidney, most structures exhibiting Pou6f2 expression stained positively in immunohistochemistry for the Wt1 protein. Finally, quantitative real-time RT-PCR revealed an overexpression (>/=80 times) of POU6F2 compared with normal kidney in 5 of 22 (23%) WTs. The finding of a highly regulated temporal and spatial Pou6f2 expression during renal organogenesis, of its coexpression with Wt1 and of POU6F2 overexpression in a subset of WTs are consistent with a role of POU6F2 in kidney development and provide further support to its involvement in WT.

WT1 and glomerular diseases

The WT1 gene encodes a zinc finger transcription factor involved in kidney and gonadal development and, when mutated, in the occurrence of kidney tumor and glomerular diseases. Patients with Denys-Drash syndrome present with early nephrotic syndrome with diffuse mesangial sclerosis progressing rapidly to end-stage renal failure, male pseudohermaphroditism, and Wilms' tumor. Incomplete forms of the syndrome have been described. Germline WT1 missense mutations located in exons 8 or 9 coding for zinc fingers 2 or 3 have been detected in nearly all patients with Denys-Drash syndrome and in some patients with isolated diffuse mesangial sclerosis. Patients with Frasier syndrome present with normal female external genitalia, streak gonads, XY karyotype and progressive nephropathy with proteinuria and nephrotic syndrome with focal and segmental glomerular sclerosis progressing to end-stage renal disease in adolescence or young adulthood. They frequently develop gonadoblastoma. Germline intronic mutations leading to the loss of the +KTS isoforms have been observed in all patients with Frasier syndrome. The same mutations have been observed in genetically female patients with isolated FSGS. Transmission of the mutation is possible. Frasier mutations have also been reported in children with Denys-Drash syndrome.

Six2 is required for suppression of nephrogenesis and progenitor renewal in the developing kidney

During kidney development and in response to inductive signals, the metanephric mesenchyme aggregates, becomes polarized, and generates much of the epithelia of the nephron. As such, the metanephric mesenchyme is a renal progenitor cell population that must be replenished as epithelial derivatives are continuously generated. The molecular mechanisms that maintain the undifferentiated state of the metanephric mesenchymal precursor cells have not yet been identified. In this paper, we report that functional inactivation of the homeobox gene Six2 results in premature and ectopic differentiation of mesenchymal cells into epithelia and depletion of the progenitor cell population within the metanephric mesenchyme. Failure to renew the mesenchymal cells results in severe renal hypoplasia. Gain of Six2 function in cortical metanephric mesenchymal cells was sufficient to prevent their epithelial differentiation in an organ culture assay. We propose that in the developing kidney, Six2 activity is required for maintaining the mesenchymal progenitor population in an undifferentiated state by opposing the inductive signals emanating from the ureteric bud.

Cancer immunotherapy targeting Wilms' tumor gene WT1 product

The Wilms' tumor gene WT1 is expressed at high levels in leukemic blast cells in most acute myeloid and lymphoblastic leukemias. In myelodysplastic syndrome, WT1 mRNA expression levels increase along with disease progression; thus, WT1 mRNA is a tumor marker for leukemic blast cells. WT mRNA is also expressed at high levels in various types of solid cancers, including cancers of the lung, breast, colon and pancreas. Patients with WT1-expressing tumors produce antibodies and cytotoxic T-lymphocytes against WT1 protein, indicating that WT1 protein is highly immunogenic and a promising tumor antigen. Major histocompatibility complex class I-restricted cytotoxic T-lymphocyte and class II-restricted helper epitopes of WT1 protein were identified, and clinical studies of cancer immunotherapy using these cytotoxic T-lymphocyte epitope peptides were performed without significant adverse effect and with clinical results promising enough to encourage further clinical trials. The clinical efficacy of cancer immunotherapy targeting the WT1 protein should be clarified by a large-scale clinical study.