Loss Of WT1 Research Articles

High-grade Anaplastic Transformation of Ovarian Serous Borderline Tumor: A Distinctive Morphology With Abundant Dense Eosinophilic Cytoplasm and Dismal Prognosis.

Ovarian serous borderline tumors (SBTs) have a generally favorable prognosis. Although the risk of progression to low-grade serous carcinoma is well documented, progression to high-grade carcinoma is rare. We report the clinicopathologic features of seven SBTs, each associated with the presence of a morphologically unique high-grade component with an extremely dismal prognosis. All of the SBTs exhibited typical hierarchical branching and scattered eosinophilic cells, whereas the high-grade component consisted of a profuse proliferation of epithelioid cells with abundant dense, eosinophilic cytoplasm, variable nuclear pleomorphism, and evident loss of WT1, estrogen receptor, and p16 positivity. In most cases, the SBT demonstrated an abrupt transition to the high-grade component, but one patient initially presented with the usual SBT and developed a recurrent disease that was composed entirely of the high-grade component. Targeted next-generation sequencing revealed identical driver mutations in both the SBT and high-grade components (BRAF in 3, KRAS in 1), confirming clonality. Three cases, in addition, harbored telomerase reverse transcriptase promoter mutations in both components. One case, despite insufficient material for sequencing, was BRAF V600E-positive by immunohistochemistry. Most patients with available follow-up data died within 9 months of diagnosis. This study confirms prior reports of ovarian SBT transformation to high-grade carcinoma and further characterizes a distinct subset with abundant dense eosinophilic cytoplasm and an extremely dismal prognosis. The presence of BRAF mutations in a major subset of these tumors questions the notion that BRAF is associated with senescent eosinophilic cells and improved outcomes in SBT. The role of the additional telomerase reverse transcriptase promoter mutations merits further investigation.

GDF-15 Suppresses Puromycin Aminonucleoside-Induced Podocyte Injury by Reducing Endoplasmic Reticulum Stress and Glomerular Inflammation.

GDF15, also known as MIC1, is a member of the TGF-beta superfamily. Previous studies reported elevated serum levels of GDF15 in patients with kidney disorder, and its association with kidney disease progression, while other studies identified GDF15 to have protective effects. To investigate the potential protective role of GDF15 on podocytes, we first performed in vitro studies using a Gdf15-deficient podocyte cell line. The lack of GDF15 intensified puromycin aminonucleoside (PAN)-triggered endoplasmic reticulum stress and induced cell death in cultivated podocytes. This was evidenced by elevated expressions of Xbp1 and ER-associated chaperones, alongside AnnexinV/PI staining and LDH release. Additionally, we subjected mice to nephrotoxic PAN treatment. Our observations revealed a noteworthy increase in both GDF15 expression and secretion subsequent to PAN administration. Gdf15 knockout mice displayed a moderate loss of WT1+ cells (podocytes) in the glomeruli compared to wild-type controls. However, this finding could not be substantiated through digital evaluation. The parameters of kidney function, including serum BUN, creatinine, and albumin-creatinine ratio (ACR), were increased in Gdf15 knockout mice as compared to wild-type mice upon PAN treatment. This was associated with an increase in the number of glomerular macrophages, neutrophils, inflammatory cytokines, and chemokines in Gdf15-deficient mice. In summary, our findings unveil a novel renoprotective effect of GDF15 during kidney injury and inflammation by promoting podocyte survival and regulating endoplasmic reticulum stress in podocytes, and, subsequently, the infiltration of inflammatory cells via paracrine effects on surrounding glomerular cells.

Wilms' tumor gene 1: lessons from the interface between kidney development and cancer.

In 1990, mutations of the Wilms' tumor-1 gene (WT1), encoding a transcription factor in the embryonic kidney, were found in 10-15% of Wilms' tumors; germline WT1 mutations were associated with hereditary syndromes involving glomerular and reproductive tract dysplasia. For more than three decades, these discoveries prompted investigators to explore the embryonic role of WT1 and the mechanisms by which loss of WT1 leads to malignant transformation. Here, we discuss how alternative splicing of WT1 generates isoforms that act in a context-specific manner to activate or repress target gene transcription. WT1 also regulates posttranscriptional regulation, alters the epigenetic landscape, and activates miRNA expression. WT1 functions at multiple stages of kidney development, including the transition from resting stem cells to committed nephron progenitor, which it primes to respond to WNT9b signals from the ureteric bud. WT1 then drives nephrogenesis by activating WNT4 expression and directing the development of glomerular podocytes. We review the WT1 mutations that account for Denys-Drash syndrome, Frasier syndrome, and WAGR syndrome. Although the WT1 story began with Wilms' tumors, an understanding of the pathways that link aberrant kidney development to malignant transformation still has some important gaps. Loss of WT1 in nephrogenic rests may leave these premalignant clones with inadequate DNA repair enzymes and may disturb the epigenetic landscape. Yet none of these observations provide a complete picture of Wilms' tumor pathogenesis. It appears that the WT1 odyssey is unfinished and still holds a great deal of untilled ground to be explored.

Recurrent noncoding somatic and germline WT1 variants converge to disrupt MYB binding in acute promyelocytic leukemia

AbstractGenetic alternations can occur at noncoding regions, but how they contribute to cancer pathogenesis is poorly understood. Here, we established a mutational landscape of cis-regulatory regions (CREs) in acute promyelocytic leukemia (APL) based on whole-genome sequencing analysis of paired tumor and germline samples from 24 patients and epigenetic profiling of 16 patients. Mutations occurring in CREs occur preferentially in active enhancers bound by the complex of master transcription factors in APL. Among significantly enriched mutated CREs, we found a recurrently mutated region located within the third intron of WT1, an essential regulator of normal and malignant hematopoiesis. Focusing on noncoding mutations within this WT1 intron, an analysis on 169 APL patients revealed that somatic mutations were clustered into a focal hotspot region, including one site identified as a germline polymorphism contributing to APL risk. Significantly decreased WT1 expression was observed in APL patients bearing somatic and/or germline noncoding WT1 variants. Furthermore, biallelic WT1 inactivation was recurrently found in APL patients with noncoding WT1 variants, which resulted in the complete loss of WT1. The high incidence of biallelic inactivation suggested the tumor suppressor activity of WT1 in APL. Mechanistically, noncoding WT1 variants disrupted MYB binding on chromatin and suppressed the enhancer activity and WT1 expression through destroying the chromatin looping formation. Our study highlights the important role of noncoding variants in the leukemogenesis of APL.

Wt1 Haploinsufficiency Induces an Age-Dependent Enhancement in Stem Cell Self-Renewal and Cooperates with FLT3-ITD to Drives Leukemogenesis

Genetic studies have identified recurrent somatic mutations in Acute Myeloid Leukemia (AML) patients, including in WT1 (Wilms' tumor gene 1). WT1 encodes for a zinc finger transcription factor that can be either targeted by nonsense/frameshift mutations or, alternatively, overexpressed in AML patients. The molecular mechanisms by which WT1 mutations contribute to leukemogenesis have not been fully elucidated. We recently showed that WT1 acts as a co-factor for TET2-mediated enzymatic function and placement of 5-hydroxymethylcytosine. Here, we show that with time Wt1 haploinsufficiency enhances stem cell self-renewal and cooperates with FLT3-ITD mutations to induce leukemogenesis.In order to assess the impact of Wt1 loss/haploinsufficiency on hematopoiesis and leukemogenesis in vivo, we generated a hematopoietic-specific conditional Wt1 knockout mice model (Mx1-Cre+ Wt1fl/fl). Studies of steady state hematopoiesis showed that Wt1 loss or haploinsufficiency was not associated with any significant differences in blood parameters compared to control counterparts. Lineage-Sca-1+c-Kit+ from Wt1fl/fl or Wt1fl/+ animals were not able to serially replate in CFU assays compare to control. We did note that homozygous Wt1-deletion induces an increase absolute number of GM colonies. Wt1-deletion led to a reduction in the proportion of ST-HSC percentage and an increase in GMP and MPPs in BM of primary non-competitive transplanted animals (Figure 1). These results showed loss of Wt1 alters myeloid differentiation but does not markedly impact steady state hematopoiesis.However, when we transplanted Wt1fl/+, but not Wt1fl/fl cells into secondary recipients, we enhanced engraftment of BM cells over control counterparts (Figure 2) and progression to T-ALL. This disease was transplantable and characterized by increased percentages of LT-HSC and MP in the BM of the recipient mice. This led us to hypothesize that WT1 haploinsufficiency, could induce age-dependent changes in hematopoietic stem cell function. Consistent with this proposal, a subset of WT1-haploinsufficient primary elderly mice (18-22 months old) developed hepatomegaly due to liver-specific myeloproliferation and extramedullary hematopoiesis. Moreover, we observed that Wt1fl/+, but not Wt1fl/fl cells, from mice 6-8 months after initial deletion showed a competitive advantage in transplantation assays and increased serial replating. By contrast, loss of one copy of Wt1 did not induce these phenotypes in young mice analyzed 4-6 weeks post deletion (Figure 3) or in mice in which we deleted one copy of Wt1 at 6-8 months of age. These data suggest that Wt1 haploinsufficiency can induce a progressive increase in self-renewal consistent with progressive remodeling of the Wt1-mutant clone.Given this observation, we hypothesized additional genetic events were required to induce leukemogenesis. Activating mutations in the FLT3 (Fms- like tyrosine kinase 3) gene commonly co-occur with WT1 mutations. To assess if these genes cooperate in leukemogenesis, we crossed Wt1fl/fl mice with Flt3-ITD knock-in mice and induced Wt1-deletion. In vivo competitive assays and serial transplantation experiments showed that Flt3-ITD-Wt1-depleted cells engrafted better in recipient mice than Flt3-ITD cells (Figure 4). Wt1fl/+ FLT3m/m mice developed fully penetrant AML with short latency (5-7 weeks post birth). This disease was characterized by increased percentages of MP and GMP in the BM of these mice compared to controls (Figure 5). Prompted by the known influence of genetic background on the phenotypes resulting from gene-targeting experiments, we bred Wt1fl/+ FLT3m/+ into the mouse strain 129S1/SvImJ. Wt1fl/+ FLT3m/m mouse developed a similar AML with a similar penetrance but a longer latency (7-9 weeks). We also noticed that Wt1fl/+ FLT3m/+ micedeveloped AML in this strain (6-7 months post birth) compare to mice with a C57BL/6 background.Taken together, our results demonstrate that alterations in WT1 function have a dose- and time-dependent impact on hematopoiesis. We hypothesize that Wt1-haploinsufficiency allows for hematopoietic stem/progenitor cells to accumulate epigenetic changes and secondary mutations (such as FLT3-ITD), which then promote leukemic transformation. This work also demonstrates that AML mutations can induce age-dependent, progressive alterations in hematopoiesis, which contribute to transformation. [Display omitted] DisclosuresLevine:Qiagen: Equity Ownership; Roche: Research Funding; Roche: Research Funding; Celgene: Research Funding; Qiagen: Equity Ownership; Celgene: Research Funding.

Defective mesothelium and limited physical space are drivers of dysregulated lung development in a genetic model of congenital diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) is a developmental disorder associated with diaphragm defects and lung hypoplasia. The etiology of CDH is complex and its clinical presentation is variable. We investigated the role of the pulmonary mesothelium in dysregulated lung growth noted in the Wt1 knockout mouse model of CDH. Loss of WT1 leads to intrafetal effusions, altered lung growth, and branching defects prior to normal closure of the diaphragm. We found significant differences in key genes; however, when Wt1 null lungs were cultured ex vivo, growth and branching were indistinguishable from wild-type littermates. Micro-CT imaging of embryos in situ within the uterus revealed a near absence of space in the dorsal chest cavity, but no difference in total chest cavity volume in Wt1 null embryos, indicating a redistribution of pleural space. The altered space and normal ex vivo growth suggest that physical constraints are contributing to the CDH lung phenotype observed in this mouse model. These studies emphasize the importance of examining the mesothelium and chest cavity as a whole, rather than focusing on single organs in isolation to understand early CDH etiology.

Expansion of the renal capsular stroma, ureteric bud branching defects and cryptorchidism in mice with Wilms tumor 1 gene deletion in the stromal compartment of the developing kidney.

Development of the mammalian kidney is orchestrated by reciprocal interactions of stromal and nephrogenic mesenchymal cells with the ureteric bud epithelium. Previous work showed that the transcription factor Wilms tumor 1 (WT1) acts in the nephrogenic lineage to maintain precursor cells, to drive the epithelial transition of aggregating precursors into a renal vesicle and to specify and maintain the podocyte fate. However, WT1 is expressed not only in the nephrogenic lineage but also transiently in stromal progenitors in the renal cortex. Here we report that specific deletion of Wt1 in the stromal lineage using the Foxd1cre driver line results at birth in cryptorchidism and hypoplastic kidneys that harbour fewer and enlarged ureteric bud tips and display an expansion of capsular stroma into the cortical region. In vivo and ex vivo analysis at earlier stages revealed that stromal loss of Wt1 reduces stromal proliferation, and delays and alters branching morphogenesis, resulting in a variant architecture of the collecting duct tree with an increase of single at the expense of bifurcated ureteric bud tips. Molecular analysis identified a transient reduction of Aldh1a2 expression and of retinoic acid signalling activity in stromal progenitors, and of Ret in ureteric bud tips. Administration of retinoic acid partly rescued the branching defects of mutant kidneys in culture. We propose that WT1 maintains retinoic acid signalling in the cortical stroma, which, in turn, assures proper levels and dynamics of Ret expression in the ureteric bud tips, and thus normal ramification of the ureteric tree. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Abstract 2980: Single cell RNA sequencing reveals AML immunoediting under pressure from engineered T cell therapy

Abstract Targeting relapsed acute myeloid leukemia (AML) with engineered T cells holds exceptional promise, but obstacles to efficacy exist. Understanding resistance mechanisms is essential to improve therapy and may broadly inform cancer immune escape. We and others have developed transgenic T cell receptor (TCR) therapies targeting the intracellular WT1 oncoprotein that promotes growth of most high-risk AMLs. TCR therapies generally target epitopes processed by the proteasome for Class I presentation. As mutation or loss of WT1 or loss of HLA expression is infrequent in AML, we hypothesized resistant clones may have defective antigen processing. A 25-year-old man with AML recurrent after a 2nd allogeneic stem cell transplant received reinduction chemotherapy and transgenic donor-derived T cells recognizing the HLA-A2 restricted WT1126-134 epitope (NCT01640301). The patient experienced a 12-month remission followed by relapse despite robust T cell persistence (>6% of CD8+ T cells). The relapsed leukemia expressed WT1 and HLA-A2 but was refractory to retreatment with additional WT1126-134-restricted T cells. Single cell RNA sequencing (scRNAseq) was performed on cryopreserved PBMCs from remission (n=4976 cells) and relapsed (n=2780) time points (10x Genomics platform). During apparent remission, transgenic T cells had a transcriptome distinct from native CD8s, expressing activation markers including HLA-DR, IL32, CD69 and CTLA4, suggesting recent TCR triggering from antigen encounter. However, at the time AML progression was observed, transgenic cells clustered with native quiescent CD8s, implying they were no longer encountering the targeted epitope. Transcriptome analysis of relapsed AML demonstrated downregulation of a single subunit of the immune proteasome (β1i), which we recently demonstrated in cell lines to be critical for processing the targeted WT1126-134 epitope. This patient's refractory AML was killed by T cells restricted to an alternate HLA-A2 epitope of WT1 processed independently of β1i, confirming the functional impact of immune proteasome downregulation. At an early responding timepoint, scRNAseq detected clinically unrecognized rare circulating AML cells already β1i-low, suggesting β1i loss represented immunoediting/outgrowth of a pre-existing clone as a consequence of T cell immunotherapy pressure. ScRNAseq is poised to become an important diagnostic in immunotherapy, with sufficient depth to profile both transgenic T cells and low burden/minimal residual AML, and, in our case, successfully identified a potentially targetable mechanism of immune escape. Our data suggest T cell therapy in AML and other tumors may be improved by in depth analysis of individual leukemic cells, and from selecting target epitopes processed by both standard and immunoproteasomes and/or early combination therapy combining TCRs recognizing differentially processed epitopes. Citation Format: Kelly G. Paulson, Thomas M. Schmitt, Daniel Egan, Valentin Voillet, Miranda C. Lahman, Felecia D. Wagener, Daniel S. Hunter, Petri R. Muhlhauser, Paul C. Hendrie, Cecilia Yeung, Nathalie Vigneron, Benoit Van den Eynde, Jason H. Bielas, Merav Bar, Raphael Gottardo, Aude G. Chapuis, Philip D. Greenberg. Single cell RNA sequencing reveals AML immunoediting under pressure from engineered T cell therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2980.

Activation of podocyte Notch mediates early Wt1 glomerulopathy

The Wilms' tumor suppressor gene, WT1, encodes a zinc finger protein that regulates podocyte development and is highly expressed in mature podocytes. Mutations in the WT1 gene are associated with the development of renal failure due to the formation of scar tissue within glomeruli, the mechanisms of which are poorly understood. Here, we used a tamoxifen-based CRE-LoxP system to induce deletion of Wt1 in adult mice to investigate the mechanisms underlying evolution of glomerulosclerosis. Podocyte apoptosis was evident as early as the fourth day post-induction and increased during disease progression, supporting a role for Wt1 in mature podocyte survival. Podocyte Notch activation was evident at disease onset with upregulation of Notch1 and its transcriptional targets, including Nrarp. There was repression of podocyte FoxC2 and upregulation of Hey2 supporting a role for a Wt1/FoxC2/Notch transcriptional network in mature podocyte injury. The expression of cleaved Notch1 and HES1 proteins in podocytes of mutant mice was confirmed in early disease. Furthermore, induction of podocyte HES1 expression was associated with upregulation of genes implicated in epithelial mesenchymal transition, thereby suggesting that HES1 mediates podocyte EMT. Lastly, early pharmacological inhibition of Notch signaling ameliorated glomerular scarring and albuminuria. Thus, loss of Wt1 in mature podocytes modulates podocyte Notch activation, which could mediate early events in WT1-related glomerulosclerosis.

Wilms Tumor Suppressor, WT1, Cooperates with MicroRNA-26a and MicroRNA-101 to Suppress Translation of the Polycomb Protein, EZH2, in Mesenchymal Stem Cells

Hereditary forms of Wilms arise from developmentally arrested clones of renal progenitor cells with biallelic mutations of WT1; recently, it has been found that Wilms tumors may also be associated with biallelic mutations in DICER1 or DROSHA, crucial for miRNA biogenesis. We have previously shown that a critical role for WT1 during normal nephrogenesis is to suppress transcription of the Polycomb group protein, EZH2, thereby de-repressing genes in the differentiation cascade. Here we show that WT1 also suppresses translation of EZH2. All major WT1 isoforms induce an array of miRNAs, which target the 3' UTR of EZH2 and other Polycomb-associated transcripts. We show that the WT1(+KTS) isoform binds to the 5' UTR of EZH2 and interacts directly with the miRNA-containing RISC to enhance post-transcriptional inhibition. These observations suggest a novel mechanism through which WT1 regulates the transition from resting stem cell to activated progenitor cell during nephrogenesis. Our findings also offer a plausible explanation for the fact that Wilms tumors can arise either from loss of WT1 or loss of miRNA processing enzymes.

Deducing the stage of origin of Wilms' tumours from a developmental series of Wt1-mutant mice

Wilms’ tumours, paediatric kidney cancers, are the archetypal example of tumours caused through the disruption of normal development. The genetically best defined subgroup of Wilms’ tumours is the group caused by biallelic loss of the WT1 tumour suppressor gene. Here we describe a developmental series of mouse models with conditional loss of Wt1 in different stages of nephron development before and after the mesenchymal to epithelial transition (MET). We demonstrate that Wt1 is essential for normal development at all kidney developmental stages under study. Comparison of genome-wide expression data from the mutant mouse models to human tumour material of WT1-mutant and WT1 wild-type datasets identifies the stage of origin of human WT1-mutant tumours, and emphasizes fundamental differences between the two human tumour groups due to different developmental stages of

Wilms Tumor Suppressor, WT1, Suppresses Epigenetic Silencing of the β-Catenin Gene

The mammalian kidney is derived from progenitor cells in intermediate mesoderm. During embryogenesis, progenitor cells expressing the Wilms tumor suppressor gene, WT1, are induced to differentiate in response to WNT signals from the ureteric bud. In hereditary Wilms tumors, clonal loss of WT1 precludes the β-catenin pathway response and leads to precancerous nephrogenic rests. We hypothesized that WT1 normally primes progenitor cells for differentiation by suppressing the enhancer of zeste2 gene (EZH2), involved in epigenetic silencing of differentiation genes. In human amniotic fluid-derived mesenchymal stem cells, we show that exogenous WT1B represses EZH2 transcription. This leads to a dramatic decrease in the repressive lysine 27 trimethylation mark on histone H3 that silences β-catenin gene expression. As a result, amniotic fluid mesenchymal stem cells acquire responsiveness to WNT9b and increase expression of genes that mark the onset of nephron differentiation. Our observations suggest that biallelic loss of WT1 sustains the inhibitory histone methylation state that characterizes Wilms tumors.

Deducing the stage of origin of Wilms' tumours from a developmental series of Wt1-mutant mice.

ABSTRACTWilms' tumours, paediatric kidney cancers, are the archetypal example of tumours caused through the disruption of normal development. The genetically best-defined subgroup of Wilms' tumours is the group caused by biallelic loss of the WT1 tumour suppressor gene. Here, we describe a developmental series of mouse models with conditional loss of Wt1 in different stages of nephron development before and after the mesenchymal-to-epithelial transition (MET). We demonstrate that Wt1 is essential for normal development at all kidney developmental stages under study. Comparison of genome-wide expression data from the mutant mouse models with human tumour material of mutant or wild-type WT1 datasets identified the stage of origin of human WT1-mutant tumours, and emphasizes fundamental differences between the two human tumour groups due to different developmental stages of origin.

WT1 Protects Leukemic Cells from Cytotoxic Replicative Stress

BACKGROUND:The transcription factor WT1 is a “pan-leukemic marker”. WT1 is overexpressed in a significant number of AML, CML, ALL, and MDS cells. Moreover, the persistence of WT1 expression after chemotherapy indicates residual leukemic stem cells. Hydroxyurea can decrease the white blood cell count in leukemic patients. Hydroxyurea inhibits ribonucleotide reductase and consequently depletes the cellular dNTP pool. This process induces replicative stress and activates the intra-S phase checkpoint. The prolonged arrest of DNA replication leads to double strand DNA breaks and apoptosis. The aim of our study was to investigate whether WT1 has an impact on the survival of AML and CML cells treated with hydroxyurea. Furthermore, we analyzed whether replicative stress affects WT1 expression. We also addressed whether clinically relevant drugs modulating WT1 influence apoptosis, autophagy, and DNA damage signaling in leukemic cells.METHODS:We used human AML and CML cells (MV4-11, RS4-11, NB4, HEL, K562) and primary AML cells with various genetic lesions (FLT3-ITD, MLL-AF4, PML-RARα, JAK2V617F, BCR-ABL; p53 mutant or null) or a complex karyotype. Cells were exposed to 0,5 mM hydroxyurea and analyzed by FACS, Western Blot and mRNA expression analyses. RNAi with morpholinos targeting the WT1 mRNA as well as the tyrosine kinase inhibitor imatinib (0,1-1 µM) and epigenetic modifiers of the histone deacetylase inhibitor family (HDACi: 1,5-5 µM entinostat and 10-100 nM panobinostat) were used to decrease WT1 levels.RESULTS:1.The stability of WT1 is causally linked to the survival of leukemic cells undergoing replicative stress. Hydroxyurea-treated leukemic cells retaining WT1 (K562 and RS4-11 cells) accumulate in S phase and survive. However, cells that lose WT1 (NB4, MV4-11, HEL, and primary AML cells) succumb to apoptosis (57-70% apoptosis after 24 h; p<0,001).2.The specific elimination of WT1 in K562 cells with morpholino antisense nucleotides (10 nM) significantly sensitizes the cells to hydroxyurea-induced apoptosis (26-30% increased apoptosis rates after 24 h; p<0,005).3.The hydroxyurea-induced loss of WT1 in sensitive cells is caspase-dependent but does not require the p53 tumor suppressor. The pan-caspase inhibitor ZVAD-FMK (20-50 µM) and the ectopic overexpression of mitochondrial anti-apoptotic proteins (BCL-XL/BCL2) prevents the hydroxyurea-induced depletion of WT1 and apoptosis in NB4 cells (from 62-69% to 9-14%; p<0,001).4.Moreover, our data reveal that hydroxyurea promotes the occurrence of previously unrecognized WT1 cleavage products. These are different from the known HTRA2-induced WT1 fragments, as they contain the WT1 zinc fingers required for DNA binding. These novel cleavage products also contain the domain for transcriptional activation, but lack the domain for transcriptional repression. We demonstrate that caspases cleave the full-length WT1 protein into such fragments, which accumulate in the nucleus of hydroxyurea-treated NB4 cells.5.Resistance of BCR-ABL-positive K562 CML cells to pro-apoptotic effects of hydroxyurea can be overcome with the tyrosine kinase inhibitor imatinib. This drug inhibits the WT1 promoter and sensitizes the cells to hydroxyurea (22-48% increased apoptosis rate after 24 h; p<0,005).6.The HDACi entinostat and panobinostat suppress the WT1 gene and accelerate the proteasomal degradation of WT1 by an increased expression of the E2 ubiquitin conjugase UBCH8. The depletion of WT1 by HDACi renders K562 cells sensitive towards hydroxyurea-induced killing and causes a synergistic activation of cell death (apoptosis increased by 43-55% after 24 h; p<0,001).7.In K562 cells hydroxyurea/entinostat combinations lead to a caspase-dependent cleavage of the DNA repair enzyme PARP-1 and to the accumulation of double-strand DNA breaks.8.We further show that entinostat significantly shifts the balance from a hydroxyurea-induced autophagy program to apoptosis (from 60% to 16% autophagy; p<0,001) in K562 cells. We reveal that entinostat depletes proteins critical for autophagy and autophagosome-lysosome fusion (Beclin-1 and HDAC6) in these cells.CONCLUSIONS:Our data illustrate that WT1 is a novel biological target of hydroxyurea, independent of a specific genetic lesion and irrespective of a functional p53 pathway. The inhibition of WT1 might be therapeutically exploitable for targeting approaches against leukemic cells. DisclosuresNo relevant conflicts of interest to declare.

DNA Hydroxymethylation Profiling Reveals that WT1 Mutations Result in Loss of TET2 Function in Acute Myeloid Leukemia

Somatic mutations in IDH1/IDH2 and TET2 result in impaired TET2-mediated conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). The observation that WT1 inactivating mutations anticorrelate with TET2/IDH1/IDH2 mutations in acute myeloid leukemia (AML) led us to hypothesize that WT1 mutations may impact TET2 function. WT1 mutant AML patients have reduced 5hmC levels similar to TET2/IDH1/IDH2 mutant AML. These mutations are characterized by convergent, site-specific alterations in DNA hydroxymethylation, which drive differential gene expression more than alterations inDNA promoter methylation. WT1 overexpression increases global levels of 5hmC, and WT1 silencing reduced 5hmC levels. WT1 physically interacts with TET2 and TET3, and WT1 loss of function results in a similar hematopoietic differentiation phenotype as observed with TET2 deficiency. These data provide a role for WT1 in regulating DNA hydroxymethylation and suggest that TET2 IDH1/IDH2 and WT1 mutations define an AML subtype defined by dysregulated DNA hydroxymethylation.

WT1 controls antagonistic FGF and BMP-pSMAD pathways in early renal progenitors.

Kidney organogenesis requires the tight control of proliferation, differentiation and apoptosis of renal progenitor cells. How the balance between these cellular decisions is achieved remains elusive. The Wilms' tumour suppressor Wt1 is required for progenitor survival, but the molecular cause for renal agenesis in mutants is poorly understood. Here we demonstrate that lack of Wt1 abolishes fibroblast growth factor (FGF) and induces BMP/pSMAD signalling within the metanephric mesenchyme. Addition of recombinant FGFs or inhibition of pSMAD signalling rescues progenitor cell apoptosis induced by the loss of Wt1. We further show that recombinant BMP4, but not BMP7, induces an apoptotic response within the early kidney that can be suppressed by simultaneous addition of FGFs. These data reveal a hitherto unknown sensitivity of early renal progenitors to pSMAD signalling, establishes FGF and pSMAD signalling as antagonistic forces in early kidney development and places WT1 as a key regulator of pro-survival FGF signalling pathway genes.

Wt1 Is Involved in Leydig Cell Steroid Hormone Biosynthesis by Regulating Paracrine Factor Expression in Mice1

Wilms tumor gene, Wt1, is abundantly expressed in testis Sertoli cells. Our recent study demonstrated that Wt1 is involved in spermatogenesis by regulating Sertoli cell polarity. In the present study, we found that Wt1 is also required for steroidogenesis in Leydig cells and that deletion of the Wt1 gene resulted in defects in testosterone biosynthesis and downregulation of steroidogenic gene expression, including cytochrome P450 side-chain cleavage (P450scc), steroidogenic acute regulatory protein (StAR), 3beta-hydroxysteroid dehydrogenase I (3beta-HSD), and cytochrome P450 17A1 (Cyp17a1). The expression of LHR was significantly decreased in Wt1(-/flox); Cre-ER(TM) testes after tamoxifen induction, whereas the luteinizing hormone level in serum was unchanged. Further studies revealed that desert hedgehog (Dhh) expression was regulated by Wt1 in Sertoli cells and that its expression was significantly reduced in Wt1-deficient testes. In vitro study demonstrated that the defect in testosterone production and decreased expression of several steroidogenic genes in Wt1-deficient testis explants was partially rescued by smoothened agonist (SAG), a hedgehog pathway agonist. These results indicate that Wt1 is most likely involved in Leydig cell steroidogenesis by regulating the expression of paracrine factors in seminiferous tubules. Dhh probably had important roles in this process, but we could not exclude the possibility that other factors were also required for Leydig cell steroidogenesis. Loss of Wt1 leads to downregulation of paracrine factors, which in turn causes a decrease in steroidogenic enzyme expression and reduces testosterone production in Leydig cells. The results of this study further confirm that the cross talk between Sertoli cells and Leydig cells has important roles in Leydig cell steroidogenesis.

MP23-12 GENOME-WIDE MAPPING OF WT1 TARGET GENES REVEALS MOLECULAR MECHANISMS OF WT1 IN NEPHROGENESIS AND WILMS’ TUMOR

You have accessJournal of UrologyKidney Cancer: Basic Research I1 Apr 2014MP23-12 GENOME-WIDE MAPPING OF WT1 TARGET GENES REVEALS MOLECULAR MECHANISMS OF WT1 IN NEPHROGENESIS AND WILMS’ TUMOR Eunah Chung and Joo-Seop Park Eunah ChungEunah Chung More articles by this author and Joo-Seop ParkJoo-Seop Park More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2014.02.880AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES The Wt1 gene encodes a transcription factor that not only prevents Wilms’ tumor formation but also plays an important role in nephrogenesis. At an early step in nephrogenesis, mesenchymal nephron progenitors become epithelialized to form a renal vesicle, which then undergoes complex morphogenesis and develops into a mature nephron. Wt1 is expressed in both undifferentiated mesenchymal nephron progenitors and differentiating epithelialized nephron progenitors. It was previously reported that conditional deletion of Wt1 arrests differentiation of nephron progenitors. Expression of Wnt4 and Lhx1, two pivotal genes required for differentiation of nephron progenitors, is downregulated in the Wt1 mutant kidney. Loss-of-function mutations of Wt1 are often found in Wilms’ tumor. It was previously reported that, in Wilms’ tumor, phosphorylation of Erk1/2 (MAP kinases) and IRS (insulin receptor substrate), both of which are downstream of IGF signaling pathway, is increased. Identification of direct target genes regulated by Wt1 is essential in understanding how Wt1 regulates differentiation of nephron progenitors and prevents Wilms’ tumor formation. METHODS We performed Wt1 chromatin immunoprecipitation coupled with next-generation sequencing (ChIP-seq) in embryonic kidneys at E16.5. Sequencing libraries were generated by ligation-mediated PCR following a standard protocol and sequencing was performed on Illumina HiSeq 2000. The sequences were aligned to mouse genome (mm9) by using Bowtie and the data were analyzed by using HOMER and GREAT software. RESULTS We identified over 14,000 genomic target sites of Wt1. Our data show that both Wnt4 and Lhx1 are direct targets of Wt1. In addition, our data show that multiple components of IGF-MAP kinase pathways, such as Irs1, Irs2, Igf1r, Mapk1 (Erk2), and Mapk6 (Erk3), are among the top ranked direct targets of Wt1. De novo motif analysis of our Wt1 ChIP-seq data suggest that Wt1 may interact with Foxc2 and Hox proteins to regulate its target genes. CONCLUSIONS Given that expression of Wnt4 and Lhx1 is downregulated in the Wt1 mutant kidney, our Wt1 ChIP-seq data suggest that Wt1 acts as a transcriptional activator for Wnt4 and Lhx1. Considering that a mouse model of Wilms’ tumor requires both the loss of Wt1 and upregulation of Igf2, our data suggest that Wt1 represses expression of multiple components of IGF-MAP kinase pathways. Loss of Wt1 may cause nephron progenitors to become hypersensitive to IGF signaling. Our results provide new insights into how Wt1 regulates nephrogenesis and prevents Wilms’ tumor formation. © 2014FiguresReferencesRelatedDetails Volume 191Issue 4SApril 2014Page: e247-e248 Advertisement Copyright & Permissions© 2014MetricsAuthor Information Eunah Chung More articles by this author Joo-Seop Park More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Wilms' tumor 1 (Wt1) regulates pleural mesothelial cell plasticity and transition into myofibroblasts in idiopathic pulmonary fibrosis

Pleural mesothelial cells (PMCs), which are derived from the mesoderm, exhibit an extraordinary capacity to undergo phenotypic changes during development and disease. PMC transformation and trafficking has a newly defined role in idiopathic pulmonary fibrosis (IPF); however, the contribution of Wilms' tumor 1 (Wt1)-positive PMCs to the generation of pathognomonic myofibroblasts remains unclear. PMCs were obtained from IPF lung explants and healthy donor lungs that were not used for transplantation. Short hairpin Wt1-knockdown PMCs (sh Wt1) were generated with Wt1 shRNA, and morphologic and functional assays were performed in vitro. Loss of Wt1 abrogated the PMC phenotype and showed evidence of mesothelial-to-mesenchymal transition (MMT), with a reduced expression of E-cadherin and an increase in the profibrotic markers α-smooth muscle actin (α-SMA) and fibronectin, along with increased migration and contractility, compared with that of the control. Migration of PMCs in response to active transforming growth factor (TGF)-β1 was assessed by live-cell imaging with 2-photon microscopy and 3D imaging, of Wt1-EGFP transgenic mice. Lineage-tracing experiments to map the fate of Wt1(+) PMCs in mouse lung in response to TGF-β1 were also performed by using a Cre-loxP system. Our results, for the first time, demonstrate that Wt1 is necessary for the morphologic integrity of pleural membrane and that loss of Wt1 contributes to IPF via MMT of PMCs into a myofibroblast phenotype.

Activation of Rac-1 and RhoA Contributes to Podocyte Injury in Chronic Kidney Disease

Rho-family GTPases like RhoA and Rac-1 are potent regulators of cellular signaling that control gene expression, migration and inflammation. Activation of Rho-GTPases has been linked to podocyte dysfunction, a feature of chronic kidney diseases (CKD). We investigated the effect of Rac-1 and Rho kinase (ROCK) inhibition on progressive renal failure in mice and studied the underlying mechanisms in podocytes. SV129 mice were subjected to 5/6-nephrectomy which resulted in arterial hypertension and albuminuria. Subgroups of animals were treated with the Rac-1 inhibitor EHT1846, the ROCK inhibitor SAR407899 and the ACE inhibitor Ramipril. Only Ramipril reduced hypertension. In contrast, all inhibitors markedly attenuated albumin excretion as well as glomerular and tubulo-interstitial damage. The combination of SAR407899 and Ramipril was more effective in preventing albuminuria than Ramipril alone. To study the involved mechanisms, podocytes were cultured from SV129 mice and exposed to static stretch in the Flexcell device. This activated RhoA and Rac-1 and led via TGFβ to apoptosis and a switch of the cells into a more mesenchymal phenotype, as evident from loss of WT-1 and nephrin and induction of α-SMA and fibronectin expression. Rac-1 and ROCK inhibition as well as blockade of TGFβ dramatically attenuated all these responses. This suggests that Rac-1 and RhoA are mediators of podocyte dysfunction in CKD. Inhibition of Rho-GTPases may be a novel approach for the treatment of CKD.