An isoform of the Wilms' tumor suppressor gene potentiates granulocytic differentiation

Therapeutic Effects of WT1 Silencing via Respiratory Administration of Neutral DOPC Liposomal-siRNA in a Lung Metastasis Melanoma Murine Model

The lungs represent a frequent target for metastatic melanoma as they offer a high-oxygen environment for tumor development. The overexpression of the WT1 protein has been associated with the occurrence of melanoma. In this study, we evaluated the effects of silencing the WT1 protein by siRNA in both in vitro in the B16F10 melanoma cell line and in vivo in a murine model of lung metastatic melanoma. We did this by implementing a novel respiratory delivery strategy of a neutral DOPC liposomal-siRNA system (L-siRNA). In vitro studies showed an effective silencing of the WT1 protein in the siRNAs' WT1-treated cells when compared with controls, resulting in a loss of the cell's viability and proliferation by inducing G1 arrest, the inhibition of the migration and invasion capacities of the cells, as well as the induction of apoptosis. In vivo, the respiratory administration of L-WT1 siRNA showed an efficient biodistribution on the lungs. After two weeks of treatment, the silencing of the WT1 protein resulted in an important antitumor activity that reduced the tumor weight. In the survival study, L-WT1 treatment could significantly delay the death of the animals. This work demonstrates the efficacy of the L-siRNA respiratory administration as a novel therapy to reduce pulmonary tumors and to increase survivability by silencing specific cancer oncogenes as WT1.

Acquired WT1 mutations contribute to relapse of NPM1-mutated acute myeloid leukemia following allogeneic hematopoietic stem cell transplant

The role of WT1 protein in hematopoiesis and leukemogenesisis incompletely elucidated. WT1 overexpression is common in acute myeloid leukemia (AML); however, WT1 mutations occur in only about 10% of cases, with increasing incidence in the setting of relapse. In this study, we investigated the clinical and molecular characteristics of WT1 mutations in NPM1-mutated AML, to enhance our understanding of the biology and potential therapeutic implications of WT1 mutations. Our study cohort included 67 patients with NPM1 mutated AML and a median follow-up of 13.7 months. WT1 mutations were identified in 7% (n = 5) of patients at the time of initial diagnosis. WT1 mutant clones were presumed to be present as co-dominant clones in 3/5 and in subclonal populations in 2/5 cases based on variant allelic frequency (VAF) when compared with NPM1 mutation VAF. All WT1 mutations became undetectable at time of MRD-negative (NPM1-wild type) remission. None of these patients experienced relapse at the time of last follow-up (median, 15 months; range, 4.5-20.2 months). A total of 15/67 (22%) patients relapsed; among these patient, four (27%) relapsed with WT1 mutant AML. Three of four patients had undergone allogeneic hematopoietic stem cell transplantation (HSCT). None of these patients had detectable WT1 mutations at the time of initial diagnosis. WT1 mutations were presumed clonal in two cases and subclonal in the other two cases, based on VAF. Our results indicate that WT1 mutations contribute to relapse in NPM1 mutated AML, especially in the setting of HSCT. These findings suggest that emerging WT1 mutations may serve as a conduit for relapse in NPM1-mutated AML, and that sequential molecular profiling to evaluate potential emergent WT1 mutations during surveillance and particularly at relapse likely has prognostic value in patients with NPM1 mutated AML.

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.

The role of Wt1 in regulating mesenchyme in cancer, development, and tissue homeostasis

From both the fundamental and clinical perspectives, there is growing interest in mesenchymal cells and the mechanisms that regulate the two-way switch between mesenchymal and epithelial states. Here, we review recent findings showing that the Wilms' tumor gene (Wt1) is a key regulator of mesenchyme maintenance and the mesenchyme to epithelial balance in the development of certain mesodermal organs. We summarize recent experiments demonstrating, unexpectedly, that Wt1 is also essential for the integrity or function of multiple adult tissues, mainly, we argue, through regulating mesenchymal cells. We also discuss growing evidence that implicates Wt1 in tissue repair and regeneration. Drawing on these findings, we highlight the similarities between Wt1-expressing cells in different tissues. We believe that future studies aimed at elucidating the mechanisms underlying the functions of Wt1 in adult cells will reveal key cell types, pathways, and molecules regulating adult tissue homeostasis and repair.

Transcriptional profiling of polycythemia vera identifies gene expression patterns both dependent and independent from the action of JAK2V617F

PURPOSE

To understand the changes in gene expression in polycythemia vera (PV) progenitor cells and their relationship to JAK2V617F.

EXPERIMENTAL DESIGN

Messenger RNA isolated from CD34(+) cells from nine PV patients and normal controls was profiled using Affymetrix arrays. Gene expression change mediated by JAK2V617F was determined by profiling CD34(+) cells transduced with the kinase and by analysis of leukemia cell lines harboring JAK2V617F, treated with an inhibitor.

RESULTS

A PV expression signature was enriched for genes involved in hematopoietic development, inflammatory responses, and cell proliferation. By quantitative reverse transcription-PCR, 23 genes were consistently deregulated in all patient samples. Several of these genes such as WT1 and KLF4 were regulated by JAK2, whereas others such as NFIB and EVI1 seemed to be deregulated in PV by a JAK2-independent mechanism. Using cell line models and comparing gene expression profiles of cell lines and PV CD34(+) PV specimens, we have identified panels of 14 JAK2-dependent genes and 12 JAK2-independent genes. These two 14- and 12-gene sets could separate not only PV from normal CD34(+) specimens, but also other MPN such as essential thrombocytosis and primary myelofibrosis from their normal counterparts.

CONCLUSIONS

A subset of the aberrant gene expression in PV progenitor cells can be attributed to the action of the mutant kinase, but there remain a significant number of genes characteristic of the disease but deregulated by as yet unknown mechanisms. Genes deregulated in PV as a result of the action of JAK2V617F or independent of the kinase may represent other targets for therapy.

WT1 expression at diagnosis does not predict survival in pediatric AML: a report from the Children's Oncology Group

WT1 is a transcription factor that is aberrantly overexpressed in acute and chronic leukemias. Overexpression of WT1 in pediatric acute myeloid leukemia has been reported, but the prognostic significance is unclear because sample sizes in these studies have been relatively small. WT1 expression was measured by quantitative RT-PCR in samples obtained at diagnosis from 155 pediatric AML patients treated on a cooperative group protocol. Neither overall survival nor event-free survival was correlated with WT1 expression.

WT1 protein expression in slowly proliferating myeloid leukemic cell lines is scarce throughout the cell cycle with a minimum in G0/G1 phase

Wilms' tumor gene 1 (WT1) is overexpressed in various hematological malignancies and has been proposed as a target for minimal residual disease (MRD) detection and for immunotherapy. Although WT1 is known as a key molecule for tumor cell proliferation, the expression pattern of WT1 in leukemic cells in dependency of proliferation has not yet been investigated. Furthermore, WT1 expression was mostly studied by reverse transcriptase PCR and the expression of WT1 protein has not been extensively studied. Here, we analyzed WT1 protein expression in the human myeloid leukemia cell lines K562 and HL-60 by indirect immunofluorescence and flow cytometry. Both cell lines exhibited varying nuclear WT1 immunoreactivity pointing to a cell cycle-dependent and/or proliferation-dependent WT1 expression. In rapidly proliferating cells high levels of WT1 protein were detected by flow cytometry. A reduced proliferation rate was associated with a low WT1 protein expression and an accumulation of cells in G(0)/G(1) phase. During G(0)/G(1) phase cells expressed WT1 at a lower level than in S or G(2)/M phase. Moreover, WT1 expression was diminished in all cell cycle phases in slowly proliferating cells. We conclude that WT1 protein expression is dependent on the cell cycle phase as well as on the proliferation rate. This finding might be relevant for MRD studies and immunotherapeutic strategies targeting WT1.

The Wilms' tumor suppressor Wt1 activates transcription of the erythropoietin receptor in hematopoietic progenitor cells

The Wilms' tumor protein Wt1 is required for embryonic development and has been implicated in hematologic disorders. Since Wt1 deficiency may compromise the proliferation and differentiation of erythroid progenitor cells, we analyzed the possible role of the transcriptionally active Wt1 isoform, Wt1(-KTS), in regulating the expression of the erythropoietin receptor (EpoR). Wt1 and EpoR were coexpressed in CD117(+) hematopoietic progenitor cells and in several hematopoietic cell lines. CD117(+) cells of Wt1-deficient murine embryos (Wt1(-/-)) exhibited a significantly lower proliferation response to recombinant erythropoietin than CD117(+) cells of heterozygous (Wt1(+/-)) and wild-type littermates (Wt1(+/+)). EpoR expression was significantly diminished in hematopoietic progenitors (CD117(+)) that lacked Wt1, and the erythroid colony-forming capacity was reduced by more than 50% in fetal liver cells of Wt1-deficient embryonic mice. Wt1(-KTS) significantly increased endogenous EpoR transcripts in transfected cells. The proximal EpoR promoter of human and mouse was stimulated more than 10-fold by Wt1(-KTS) in transiently cotransfeced K562 erythroleukemia cells. A responsible cis-element, which is highly conserved in the EpoR promoter of human and mouse, was identified by mutation analysis, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay. In conclusion, activation of the EpoR gene by Wt1 may represent an important mechanism in normal hematopoiesis.

The Wilms' tumor gene 1 (WT1) induces expression of the N-myc downstream regulated gene 2 (NDRG2)

The Wilms' tumor gene 1 (WT1) protein is a transcriptional regulator that is highly expressed in immature hematopoietic progenitor cells and in the majority of patients with acute and chronic myeloid leukemia. However, it is still unclear how WT1 exerts its function(s) in hematopoietic cells. The aim of this work was to investigate the function of WT1 as a transcription factor in human hematopoietic progenitor cells. To this end, an oligonucleotide array approach was used to study the gene expression in CD34(+) cells from human cord blood retrovirally transduced with WT1 or a control vector. We found that the expression of the putative tumor suppressor gene N-myc downstream regulated gene 2 (NDRG2) mRNA was induced by WT1 in CD34(+) cells and also in leukemic U937 cells. Furthermore, a novel transcription start site in the NDRG2 gene was identified in WT1-transduced cells, in addition to two previously reported transcription start sites. These results show that the expression of the NDRG2 gene is directly or indirectly induced by WT1, and provide the first insights into transcriptional regulation of the NDRG2 gene, including demonstration of a novel splice variant.

The role of the Wilms tumour gene (WT1) in normal and malignant haematopoiesis

In addition to its loss playing a pivotal role in the development of a childhood kidney malignancy, the Wilms tumour 1 gene (WT1) has emerged as an important factor in normal and malignant haematopoiesis. Preferentially expressed in CD34+ haematopoietic progenitors and down-regulated in more-differentiated cells, the WT1 transcription factor has been implicated in regulation of apoptosis, proliferation and differentiation. Putative target genes, such as BCL2, MYC, A1 and cyclin E, may cooperate with WT1 to modulate cell growth. However, the effects of WT1 on target gene expression appear to be isoform-specific. Certain WT1 isoforms are over-represented in leukaemia, but the exact mechanisms underlying the role of WT1 in transformation remain unclear. The ubiquity of WT1 in haematological malignancies has led to efforts to exploit it as a marker for minimal residual disease and as a prognostic factor, with conflicting results. In vitro killing of tumour cells by WT1-specific CD8+ cytotoxic T lymphocytes facilitated design of Phase I vaccine trials that showed clinical regression of WT1-positive tumours. Alternative methods employing WT1-specific immunotherapy are being investigated and might ultimately be used to optimise multimodal therapy of haematological malignancies.

Isoforms of Wilms' tumor suppressor gene (WT1) have distinct effects on mammary epithelial cells

The role of WT1 (Wilm's tumor suppressor gene) in breast cancer is controversial, with evidence for both tumor-promoting and tumor-suppressing activities. In order to address this question, we expressed different WT1 isoforms in the mammary epithelial cell line H16N-2, which does not express endogenous WT1. Cells were stably transfected with either WT1 (-Ex5/-KTS) or WT1 (+Ex5/+KTS) under the control of the inducible metallothionein promoter. Induction of WT1 (-Ex5/-KTS) upregulated p21, causing a slowing of proliferation and a G2-phase cell cycle arrest. In artificial basement membrane, the WT1 (-Ex5/-KTS) isoform promoted the appearance of highly organized acinar cellular aggregates. In contrast, WT1 (+Ex5/+KTS) had no effect on p21 or proliferation, but rather caused an epithelial-mesenchymal transition and a redistribution of E-cadherin from the cell membrane to the cytoplasm. This isoform also causes the cellular aggregates growing in artificial basement membrane to appear significantly less organized than control cells. Thus, different WT1 isoforms have distinct effects in this cell line, suggesting that depending on the ratio of WT1 isoform expression in mammary epithelial cells, WT1 could function to either promote or suppress a transformed phenotype.

Antiapoptotic function of 17AA(+)WT1 (Wilms' tumor gene) isoforms on the intrinsic apoptosis pathway

The WT1 gene is overexpressed in human primary leukemia and a wide variety of solid cancers. The WT1 gene is alternatively spliced at two sites, yielding four isoforms: 17AA(+)KTS(+), 17AA(+)KTS(-), 17AA(-)KTS(+), and 17AA(-)KTS(-). Here, we showed that 17AA(+)WT1-specific siRNA induced apoptosis in three WT1-expressing leukemia cell lines (K562, HL-60, and Kasumi-1), but not in WT1-non-expressing lymphoma cell line (Daudi). 17AA(+)WT1-specific siRNA activated caspase-3 and -9 in the intrinsic apoptosis pathway but not caspase-8 in the extrinsic one. On the other hand, 17AA(-)WT1-specific siRNA did not induce apoptosis in the three WT1-expressing cell lines. The apoptosis was associated with activation of proapoptotic Bax, which was activated upstream of the mitochondria. Constitutive expression of 17AA(+)WT1 isoforms inhibited apoptosis of K562 leukemia cells induced by apoptosis-inducing agents, etoposide and doxorubicin, through the protection of mitochondrial membrane damages, and DNA-binding zinc-finger region of 17AA(+)WT1 isoform was essential for the antiapoptotic functions. We further studied the gene(s) whose expression was altered by the expression of 17AA(+)WT1 isoforms and showed that the expression of proapoptotic Bak was decreased by the expression of 17AA(+)KTS(-)WT1 isoform. Taken together, these results indicated that 17AA(+)WT1 isoforms played antiapoptotic roles at some points upstream of the mitochondria in the intrinsic apoptosis pathway.

The antiapoptotic gene A1/BFL1 is a WT1 target gene that mediates granulocytic differentiation and resistance to chemotherapy

Previous work has demonstrated that WT1 (-Ex5/-KTS) potentiates granulocyte colony-stimulating factor (G-CSF)-mediated granulocytic differentiation. This WT1 isoform suppresses cyclin E, which may contribute to the prodifferentiation effect by slowing proliferation, but WT1 target genes that affect survival might also be involved. We screened a cDNA array and identified the bCL2 family member A1/BFL1 as a new WT1 target gene in 32D cl3 murine myeloblast cells. Induction of WT1 (-Ex5/-KTS) expression is accompanied by up-regulation of A1 on the cDNA array, and this up-regulation was confirmed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). Moreover, both promoter-reporter assays and chromatin immunoprecipitation assays suggest that this isoform of WT1 activates the promoter directly. Constitutive expression of A1 in 32D cl3 cells induces spontaneous granulocytic differentiation, with both morphologic and cell-surface antigen changes, as well as resistance both to chemotherapy and to withdrawal of interleukin-3 (IL-3). Finally, we note an association between WT1 expression and A1 expression in primary acute myeloid leukemia samples. Taken together, these results demonstrate that A1 is a new WT1 target gene involved in both granulocytic differentiation and resistance to cell death, and suggests that these genes might play an important role in the biology of high-risk leukemias.

Wilms' tumor gene 1 (WT1) expression in childhood acute lymphoblastic leukemia: a wide range of WT1 expression levels, its impact on prognosis and minimal residual disease monitoring

Wilms' tumor gene 1 (WT1) is overexpressed in the majority (70-90%) of acute leukemias and has been identified as an independent adverse prognostic factor, a convenient minimal residual disease (MRD) marker and potential therapeutic target in acute leukemia. We examined WT1 expression patterns in childhood acute lymphoblastic leukemia (ALL), where its clinical implication remains unclear. Using a real-time quantitative PCR designed according to Europe Against Cancer Program recommendations, we evaluated WT1 expression in 125 consecutively enrolled patients with childhood ALL (106 BCP-ALL, 19 T-ALL) and compared it with physiologic WT1 expression in normal and regenerating bone marrow (BM). In childhood B-cell precursor (BCP)-ALL, we detected a wide range of WT1 levels (5 logs) with a median WT1 expression close to that of normal BM. WT1 expression in childhood T-ALL was significantly higher than in BCP-ALL (P<0.001). Patients with MLL-AF4 translocation showed high WT1 overexpression (P<0.01) compared to patients with other or no chromosomal aberrations. Older children (> or =10 years) expressed higher WT1 levels than children under 10 years of age (P<0.001), while there was no difference in WT1 expression in patients with peripheral blood leukocyte count (WBC) > or =50 x 10(9)/l and lower. Analysis of relapsed cases (14/125) indicated that an abnormal increase or decrease in WT1 expression was associated with a significantly increased risk of relapse (P=0.0006), and this prognostic impact of WT1 was independent of other main risk factors (P=0.0012). In summary, our study suggests that WT1 expression in childhood ALL is very variable and much lower than in AML or adult ALL. WT1, thus, will not be a useful marker for MRD detection in childhood ALL, however, it does represent a potential independent risk factor in childhood ALL. Interestingly, a proportion of childhood ALL patients express WT1 at levels below the normal physiological BM WT1 expression, and this reduced WT1 expression appears to be associated with a higher risk of relapse.

In vitro Stimulation with WT1 Peptide-Loaded Epstein-Barr Virus-Positive B Cells Elicits High Frequencies of WT1 Peptide-Specific T Cells with In vitro and In vivo Tumoricidal Activity

The Wilms tumor protein (WT1) is overexpressed in most acute and chronic leukemias. To develop a practicable, clinically applicable approach for generation of WT1-specific T cells and to comparatively evaluate the immunogenicity of WT1 in normal individuals, we sensitized T cells from 13 HLA-A0201+ and 5 HLA-A2402+ donors with autologous EBV-transformed B cells or cytokine-activated monocytes, loaded with the HLA-A0201-binding WT1 peptides (126-134)RMFPNAPYL or (187-195)SLGEQQYSV or a newly identified HLA-A2402-binding WT1 peptide (301-310)RVPGVAPTL. WT1-specific T cells were regularly generated from each donor. T cells sensitized with peptide-loaded EBV-transformed B cells generated higher numbers of WT1-specific T cells than peptide-loaded cytokine-activated monocytes. Contrary to expectations, the frequencies of WT1 peptide-specific T cells were equivalent to those generated against individual highly immunogenic HLA-A0201-binding EBV peptides. Each of these T-cell lines specifically killed WT1+ leukemias and solid tumors in an HLA-restricted manner but did not lyse autologous or HLA-matched normal CD34+ hematopoietic progenitor cells or reduce their yield of colony-forming unit-granulocyte-macrophage (CFU-GM), burst-forming unit erythroid (BFU-E), or mixed colonies (CFU-mix). Furthermore, WT1 peptide-specific T cells after adoptive transfer into nonobese diabetic-severe combined immunodeficient mice bearing subcutaneous xenografts of WT1+ and WT1- HLA-A0201+ leukemias preferentially accumulated in and induced regressions of WT1+ leukemias that expressed the restricting HLA allele. Such cells are clinically applicable and may prove useful for adoptive cell therapy of WT1+ malignant diseases in humans.