Human platelet-derived growth factor A chain is transcriptionally repressed by the Wilms tumor suppressor WT1

G-quadruplexes in cancer-related gene promoters: from identification to therapeutic targeting

INTRODUCTION

Guanine-rich DNA sequences can fold into four-stranded noncanonical secondary structures called G-quadruplexes (G4s) which are widely distributed in functional regions of the human genome, such as telomeres and gene promoter regions. Compelling evidence suggests their involvement in key genome functions such as gene expression and genome stability. Notably, the abundance of G4-forming sequences near transcription start sites suggests their potential involvement in regulating oncogenes.

AREAS COVERED

This review provides an overview of current knowledge on G4s in human oncogene promoters. The most representative G4-binding ligands have also been documented. The objective of this work is to present a comprehensive overview of the most promising targets for the development of novel and highly specific anticancer drugs capable of selectively impacting the expression of individual or a limited number of genes.

EXPERT OPINION

Modulation of G4 formation by specific ligands has been proposed as a powerful new tool to treat cancer through the control of oncogene expression. Actually, most of G4-binding small molecules seem to simultaneously target a range of gene promoter G4s, potentially influencing several critical driver genes in cancer, thus producing significant therapeutic benefits.

The Role of Wilms' Tumor Gene (WT1) Expression as a Marker of Minimal Residual Disease in Acute Myeloid Leukemia

The Minimal Residual Disease(MRD) monitoring in acute myeloid leukemia (AML) is crucial to guide treatment after morphologic complete remission, to define the need for consolidation with allogeneic stem cell transplantation (Allo-SCT), and to detect impending relapse allowing early intervention. However, more than 50% of patients with AML lack a specific or measurable molecular marker to monitor MRD. We reviewed the key studies on WT1 overexpression as a marker of MRD in AML patients undergoing an intensive chemotherapy program, including Allo-SCT. In addition, we provided some practical considerations on how to properly use WT1 expression as an MRD marker, considering its strengths and weaknesses. In order to achieve the best sensitivity and specificity, it is recommended to refer to the standardized method of European LeukemiaNet and its defined threshold (250 WT1 copies/10⁴ Abelson (ABL) on Bone Marrow-BM and 50 WT1 copies/10⁴ ABL on Peripheral Blood-PB), which has been validated in a large and multicenter cohort of patients and normal controls.

Origins of DNA methylation defects in Wilms tumors

Wilms tumor is an embryonic renal cancer that typically presents in early childhood and accounts for 7% of all paediatric cancers. Different genetic alterations have been described in this malignancy, however, only a few of them are associated with a majority of Wilms tumors. Alterations in DNA methylation, in contrast, are frequent molecular defects observed in most cases of Wilms tumors. How these epimutations are established in this tumor is not yet completely clear. The recent identification of the molecular actors required for the epigenetic reprogramming during embryogenesis suggests novel possible mechanisms responsible for the DNA methylation defects in Wilms tumor. Here, we provide an overview of the DNA methylation alterations observed in this malignancy and discuss the distinct molecular mechanisms by which these epimutations can arise.

Genomic regions associated with susceptibility to Barrett's esophagus and esophageal adenocarcinoma in African Americans: The cross BETRNet admixture study

Background

Barrett’s esophagus (BE) and esophageal adenocarcinoma (EAC) are far more prevalent in European Americans than in African Americans. Hypothesizing that this racial disparity in prevalence might represent a genetic susceptibility, we used an admixture mapping approach to interrogate disease association with genomic differences between European and African ancestry.

Methods

Formalin fixed paraffin embedded samples were identified from 54 African Americans with BE or EAC through review of surgical pathology databases at participating Barrett’s Esophagus Translational Research Network (BETRNet) institutions. DNA was extracted from normal tissue, and genotyped on the Illumina OmniQuad SNP chip. Case-only admixture mapping analysis was performed on the data from both all 54 cases and also on a subset of 28 cases with high genotyping quality. Haplotype phases were inferred with Beagle 3.3.2, and local African and European ancestries were inferred with SABER plus. Disease association was tested by estimating and testing excess European ancestry and contrasting it to excess African ancestry.

Results

Both datasets, the 54 cases and the 28 cases, identified two admixture regions. An association of excess European ancestry on chromosome 11p reached a 5% genome-wide significance threshold, corresponding to -log₁₀(P) = 4.28. A second peak on chromosome 8q reached -log₁₀(P) = 2.73. The converse analysis examining excess African ancestry found no genetic regions with significant excess African ancestry associated with BE and EAC. On average, the regions on chromosomes 8q and 11p showed excess European ancestry of 15% and 20%, respectively.

Conclusions

Chromosomal regions on 11p15 and 8q22-24 are associated with excess European ancestry in African Americans with BE and EAC. Because GWAS have not reported any variants in these two regions, low frequency and/or rare disease associated variants that confer susceptibility to developing BE and EAC may be driving the observed European ancestry association evidence.

The stress-response molecule NR4A1 resists ROS-induced pancreatic β-cells apoptosis via WT1

Pancreatic β-cells often face endoplasmic reticulum stress and/or ROS-associated oxidative stress under adverse conditions. Our previous work has verified that NR4A1 protects pancreatic β-cells from ER-stress induced apoptosis. However, It remains unknown whether NR4A1 is able to protect pancreatic β-cells against ROS-associated oxidative stress. In the present study, our data showed that NR4A1 protein expression rapidly increased in MIN6 cells upon H₂O₂ treatment, and overexpression of NR4A1 in MIN6 cells conferred resistance to cell apoptosis induced by H₂O₂. These results were further substantiated in isolated islets from mice infected with an adenovirus overexpressing NR4A1. 8-hydroxy-2'-deoxyguanosine (8-OHdG) was used as a biomarker for oxidative stress or a marker for ROS damage. We found that the 8-OHdG level in the islets from NR4A1 knockout mice fed with high-fat diet was much higher than that in the islets from parental control mice; and higher apoptotic rate was observed in the islets from NR4A1 KO mice compared to control mice. Further investigation of underlying mechanisms of NR4A1's protective effects showed that NR4A1 overexpression in MIN6 cells reduced Caspase 3 activation caused by H₂O₂, and increased expression of WT1 and SOD1. There is a putative NR4A1 binding site (-1118bp to -1111bp) in WT1 promoter; our data demonstrated that NR4A1 protein physically associates with the WT1 promoter, and enhanced WT1 promoter transactivation and knockdown of WT1 in MIN6 cells induced apoptosis. These findings suggest that NR4A1 protects pancreatic β-cells against H₂O₂ mediated apoptosis by up-regulating WT1 expression.

Role for Egr1 in the Transcriptional Program Associated with Neuronal Differentiation of PC12 Cells

PC12 cells are a well-established model to study how differences in signal transduction duration can elicit distinct cell behaviors. Epidermal growth factor (EGF) activates transient ERK signaling in PC12 cells that lasts 30–60 min, which in turn promotes proliferation; nerve growth factor (NGF) activates more sustained ERK signaling that lasts 4–6 h, which in turns induces neuronal differentiation. Data presented here extend a previous study by Mullenbrock et al. (2011) that demonstrated that sustained ERK signaling in response to NGF induces preferential expression of a 69-member gene set compared to transient ERK signaling in response to EGF and that the transcription factors AP-1 and CREB play a major role in the preferential expression of several genes within the set. Here, we examined whether the Egr family of transcription factors also contributes to the preferential expression of the gene set in response to NGF. Our data demonstrate that NGF causes transient induction of all Egr family member transcripts, but a corresponding induction of protein was detected for only Egr1 and 2. Chromatin immunoprecipitation experiments provided clearest evidence that, after induction, Egr1 binds 12 of the 69 genes that are preferentially expressed during sustained ERK signaling. In addition, Egr1 expression and binding upstream of its target genes were both sustained in response to NGF versus EGF within the same timeframe that its targets are preferentially expressed. These data thus provide evidence that Egr1 contributes to the transcriptional program activated by sustained ERK signaling in response to NGF, specifically by contributing to the preferential expression of its target genes identified here.

Distinct global binding patterns of the Wilms tumor gene 1 (WT1) -KTS and +KTS isoforms in leukemic cells

The zinc finger transcription factor Wilms tumor gene 1 (WT1) acts as an oncogene in acute myeloid leukemia. A naturally occurring alternative splice event between zinc fingers three and four, removing or retaining three amino acids (±KTS), is believed to change the DNA binding affinity of WT1, although there are conflicting data regarding the binding affinity and motifs of the different isoforms. Increased expression of the WT1 -KTS isoform at the expense of the WT1 +KTS isoform is associated with poor prognosis in acute myeloid leukemia. We determined the genome-wide binding pattern of WT1 -KTS and WT1 +KTS in leukemic K562 cells by chromatin immunoprecipitation and deep sequencing. We discovered that the WT1 -KTS isoform predominantly binds close to transcription start sites and to enhancers, in a similar fashion to other transcription factors, whereas WT1 +KTS binding is enriched within gene bodies. We observed a significant overlap between WT1 -KTS and WT1 +KTS target genes, despite the binding sites being distinct. Motif discovery revealed distinct binding motifs for the isoforms, some of which have been previously reported as WT1 binding sites. Additional analyses showed that both WT1 -KTS and WT1 +KTS target genes are more likely to be transcribed than non-targets, and are involved in cell proliferation, cell death, and development. Our study provides evidence that WT1 -KTS and WT1 +KTS share target genes yet still bind distinct locations, indicating isoform-specific regulation in transcription of genes related to cell proliferation and differentiation, consistent with the involvement of WT1 in acute myeloid leukemia.

Transcriptome analysis reveals differentially expressed genes associated with germ cell and gonad development in the Southern bluefin tuna (Thunnus maccoyii)

BACKGROUND

Controlling and managing the breeding of bluefin tuna (Thunnus spp.) in captivity is an imperative step towards obtaining a sustainable supply of these fish in aquaculture production systems. Germ cell transplantation (GCT) is an innovative technology for the production of inter-species surrogates, by transplanting undifferentiated germ cells derived from a donor species into larvae of a host species. The transplanted surrogates will then grow and mature to produce donor-derived seed, thus providing a simpler alternative to maintaining large-bodied broodstock such as the bluefin tuna. Implementation of GCT for new species requires the development of molecular tools to follow the fate of the transplanted germ cells. These tools are based on key reproductive and germ cell-specific genes. RNA-Sequencing (RNA-Seq) provides a rapid, cost-effective method for high throughput gene identification in non-model species. This study utilized RNA-Seq to identify key genes expressed in the gonads of Southern bluefin tuna (Thunnus maccoyii, SBT) and their specific expression patterns in male and female gonad cells.

RESULTS

Key genes involved in the reproductive molecular pathway and specifically, germ cell development in gonads, were identified using analysis of RNA-Seq transcriptomes of male and female SBT gonad cells. Expression profiles of transcripts from ovary and testis cells were compared, as well as testis germ cell-enriched fraction prepared with Percoll gradient, as used in GCT studies. Ovary cells demonstrated over-expression of genes related to stem cell maintenance, while in testis cells, transcripts encoding for reproduction-associated receptors, sex steroids and hormone synthesis and signaling genes were over-expressed. Within the testis cells, the Percoll-enriched fraction showed over-expression of genes that are related to post-meiosis germ cell populations.

CONCLUSIONS

Gonad development and germ cell related genes were identified from SBT gonads and their expression patterns in ovary and testis cells were determined. These expression patterns correlate with the reproductive developmental stage of the sampled fish. The majority of the genes described in this study were sequenced for the first time in T. maccoyii. The wealth of SBT gonadal and germ cell-related gene sequences made publicly available by this study provides an extensive resource for further GCT and reproductive molecular biology studies of this commercially valuable fish.

Phase I pilot study of Wilms tumor gene 1 peptide-pulsed dendritic cell vaccination combined with gemcitabine in pancreatic cancer

This study aimed to evaluate the feasibility of and immune response to Wilms tumor gene 1 (WT1) peptide-pulsed dendritic cell vaccination combined with gemcitabine (DCGEM) as a first-line therapy among patients with advanced pancreatic cancer. Ten HLA-A*2402 patients were treated with WT1 peptide-pulsed DC vaccination (1 × 10(7) cells) on days 8 and 22 and gemcitabine (1000 mg/m(2) ) on days 1, 8 and 15. Induction of a WT1-specific immune response was evaluated using the delayed-type hypersensitivity (DTH) skin test, interferon-γ enzyme-linked immunospot and HLA tetramer assays, along with assays for various immunological factors. DCGEM was well-tolerated, and the relative dose intensity of gemcitabine was 87%. Disease control associated with a low neutrophil/lymphocyte ratio was observed in all three patients with DTH positivity; it was also correlated with a low percentage of granulocytic myeloid derived suppressor cells in the pretreatment peripheral blood (P = 0.017). Patients with liver metastases and high levels of inflammatory markers such as C-reactive protein and interleukin-8 (IL-8) showed poor survival even though a WT1-specific immune response was induced in them. WT1 peptide-pulsed DCGEM is feasible and effective for inducing anti-tumor T-cell responses. Our results support future investigations for pancreatic cancer patients with non-liver metastases and favorable immunological conditions. This trial was registered with the University hospital Medical Information Network (UMIN) Clinical Trials Registry (http://www.umin.ac.jp/ctr/ number: UMIN-000004855).

A new role for wilms tumor protein 1: differential activities of + KTS and -KTS variants to regulate LHβ transcription

Luteinizing hormone (LH) is synthesized and secreted throughout the reproductive cycle from gonadotrope cells in the anterior pituitary, and is required for steroidogenesis and ovulation. LH contains an α-subunit common with FSH, and a unique LHβ subunit that defines biological activity. Basal LHβ transcription is low and stimulated by hypothalamic GnRH, which induces synthesis of early growth response protein-1 (Egr1), and stimulates binding of transcription factors Egr1 and steroidogenic factor-1 (SF1) on the promoter. WT1 (Wilms tumor protein1) is a zinc finger transcription factor with an essential role in urogenital system development, and which regulates several reproductive genes via interactions with SF1 or binding to GC-rich elements such as Egr1 binding sites. We investigated a potential role for WT1 in LHβ transcription in clonal mouse gonadotrope LβT2 cells. WT1 was present in LβT2 and mouse pituitary cells, and protein bound to the endogenous LHβ promoter. Interestingly, mRNAs for WT1(+KTS), which contains a three amino-acid insertion between the 3rd and 4th zinc fingers, and the WT1 (-KTS) variant were both expressed at significant levels. WT1 mRNAs and protein were decreased approximately 50% by GnRH treatment, under conditions where Egr1 mRNA and protein, and LHβ transcription, were stimulated. Decreasing expression of mRNA for WT1 (-KTS) decreased stimulation of LHβ and Egr1 by GnRH, whereas decreasing both WT1 (-KTS) and (+KTS) increased endogenous LHβ transcription, and prevented LHβ but not Egr1 stimulation by GnRH, suggesting differing biological activities for the WT1 isoforms. Overexpression of WT1 showed that WT1(-KTS) enhanced LHβ promoter GnRH stimulation 2-to-3-fold and required the 3'Egr1 site, but WT1(+KTS) repressed both basal and GnRH-stimulated LHβ promoter activity by approximately 70%. Our data suggest that WT1 can modulate LHβ transcription, with differential roles for the two WT1 variants; WT1 (-KTS) enhances and WT1 (+KTS) suppresses transcription.

Wilms' tumor gene WT1 promotes homologous recombination-mediated DNA damage repair

The Wilms' tumor gene WT1 is overexpressed in leukemia and various types of solid tumors and plays an oncogenic role in these malignancies. Alternative splicing at two sites yields four major isoforms, 17AA(+)KTS(+), 17AA(+)KTS(-), 17AA(-)KTS(+), and 17AA(-)KTS(-), and all the isoforms are expressed in the malignancies. However, among the four isoforms, function of WT1[17AA(-)KTS(+)] isoform still remains undetermined. In the present study, we showed that forced expression of WT1[17AA(-)KTS(+)] isoform significantly inhibited apoptosis by DNA-damaging agents such as Doxorubicin, Mitomycin, Camptothesisn, and Bleomycin in immortalized fibroblast MRC5SV and cervical cancer HeLa cells. Knockdown of Rad51, an essential factor for homologous recombination (HR)-mediated DNA repair canceled the resistance to Doxorubicin induced by WT1[17AA(-)KTS(+)] isoform. GFP recombination assay showed that WT1[17AA(-)KTS(+)] isoform alone promoted HR, but that three other WT1 isoforms did not. WT1[17AA(-)KTS(+)] isoform significantly upregulated the expression of HR genes, XRCC2, Rad51D, and Rad54. Knockdown of XRCC2, Rad51D, and Rad54 inhibited the HR activity and canceled resistance to Doxorubicin in MRC5SV cells with forced expression of WT1[17AA(-)KTS(+)] isoform. Furthermore, chromatin immunoprecipitation (ChIP) assay showed the binding of WT1[17AA(-)KTS(+)] isoform protein to promoters of XRCC2 and Rad51D. Immunohistochemical study showed that Rad54 and XRCC2 proteins were highly expressed in the majority of non-small-cell lung cancer (NSCLC) and gastric cancer, and that expression of these two proteins was significantly correlated with that of WT1 protein in NSCLCs. Our results presented here showed that WT1[17AA(-)KTS(+)] isoform had a function to promote HR-mediated DNA repair.

Mechanisms of transcriptional regulation by WT1 (Wilms' tumour 1)

The WT1 (Wilms' tumour 1) gene encodes a zinc finger transcription factor and RNA-binding protein that direct the development of several organs and tissues. WT1 manifests both tumour suppressor and oncogenic activities, but the reasons behind these opposing functions are still not clear. As a transcriptional regulator, WT1 can either activate or repress numerous target genes resulting in disparate biological effects such as growth, differentiation and apoptosis. The complex nature of WT1 is exemplified by a plethora of isoforms, post-translational modifications and multiple binding partners. How WT1 achieves specificity to regulate a large number of target genes involved in diverse physiological processes is the focus of the present review. We discuss the wealth of the growing molecular information that defines our current understanding of the versatility and utility of WT1 as a master regulator of organ development, a tumour suppressor and an oncogene.

BMP-specific SMADs function as novel repressors of PDGFA and modulate its expression in ovarian granulosa cells and tumors

Platelet-derived growth factor alpha (PDGFA) is frequently upregulated in various cancers and thought to function as a key player in the development and progression of tumor growth by regulating aspects of cell proliferation, angiogenesis and metastasis. However, the mechanism by which it is upregulated is not fully understood. Previously, we demonstrated that conditional deletion of two transcription factors that signal for the bone morphogenetic proteins (Smad1 and Smad5) in ovarian granulosa cells causes metastatic granulosa cell tumors (GCTs) in female mice and phenocopies human juvenile GCTs (JGCTs). Smad1/5 double conditional knockout tumors, as well as human JGCTs, are highly vascularized, hemorrhagic and mitotically active. Expression analysis of these tumors and their metastases revealed a significant upregulation of key proliferation and pro-angiogenic factors such as Pdgfa, Pdgfb and Vegf. We examined whether these genes were direct targets of SMAD1 and SMAD5. Knockdown of SMAD1 and SMAD5 in mouse primary granulosa cells and a human GCT-derived cell line (COV434) resulted in upregulation of PDGFA, but not PDGFB nor VEGF. We identified several putative SMAD1/5-binding sites in the PDGFA promoter, and chromatin immunoprecipitation and reporter assays demonstrated that SMAD1/5 interact with the PDGFA promoter to regulate its activity. Further, SMAD1/5 antagonize the activity of the transcription factor Sp1, a well-known positive regulator of PDGFA, by inhibiting its occupancy at a key regulatory site on the proximal PDGFA promoter. Collectively, our studies establish that loss of SMAD1/5 leads to upregulation of PDGFA in ovarian granulosa cells, and that a novel regulatory interaction exists between the BR-SMADs and Sp1 in controlling PDGFA expression during granulosa cell tumorigenesis.

Low Wilms' tumor gene expression in tumor tissues predicts poor prognosis in patients with non-small-cell lung cancer

We elucidated the relationship between prognosis of non-small-cell lung cancer (NSCLC) and Wilms' tumor gene (WT1) mRNA expression in tumor tissue. The WT1 mRNA expression levels of the fatal cases were lower as compared with those of the survival cases. Overall survival (OS) and disease-free survival (DFS) of the high WT1 expression group were longer than of the low expression group. As for squamous cell lung cancer (SQLC), low WT1 expression was significantly associated with lymph node metastasis. Cox analysis revealed that the gene level was a significant prognostic factor in OS and DFS. Low WT1 expression predicted poor prognosis in patients with NSCLC.

Wilms' tumor 1 silencing decreases the viability and chemoresistance of glioblastoma cells in vitro: a potential role for IGF-1R de-repression

Wilms' tumor 1 (WT1) is a transcription factor with a multitude of downstream targets that have wide-ranging effects in non-glioma cell lines. Though its expression in glioblastomas is now well-documented, the role of WT1 in these tumors remains poorly defined. We hypothesized that WT1 functions as an oncogene to enhance glioblastoma viability and chemoresistance. WT1's role was examined by studying the effect of WT1 silencing and overexpression on DNA damage, apoptosis and cell viability. Results indicated that WT1 silencing adversely affected glioblastoma viability, at times, in synergy with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and cisplatin. To investigate other mechanisms through which WT1 could affect viability, we measured cell cycle distribution, senescence, and autophagy. WT1 silencing had no effect on these processes. Lastly, we examined WT1 regulation of IGF-1R expression. Counterintuitively, upregulation of IGF-1R was evident after WT1 silencing. In conclusion, WT1 functions as a survival factor in glioblastomas, possibly through inhibition of IGF-1R expression.

The Wilms' tumour suppressor protein WT1 acts as a key transcriptional repressor of the human thromboxane A2 receptor gene in megakaryocytes

In humans, the TPalpha and TPbeta isoforms of the thromboxane A2 receptor are transcriptionally regulated by distinct promoters, designated Prm1 and Prm3. Previous investigations identified two upstream repressor regions (URR) 1 and URR2 within Prm1. Herein, it was sought to characterize Prm1, identifying the factor(s) regulating URR1 and URR2 in human erythroleukaemia (HEL) 92.1.7 cells. Genetic reporter assays and 5' deletions confirmed the presence of URR1 and URR2 but also identified a third repressor, designated RR3, within the proximal 'core' promoter. Bioinformatic analysis revealed several GC elements representing putative sites for Egr1/Sp1/Wilms tumour (WT)1 within URR1, URR2 and RR3. While mutation of three GC elements within URR1 and of an adjacent GC element suggested that repressor binding occurs through a cooperative mechanism, repressors binding to the single GC elements within URR2 and RR3 act independently to regulate Prm1. While electrophoretic mobility shift assays and supershift assays demonstrated that each of the GC elements can bind Egr1 and WT1 in vitro, chromatin immunoprecipitations established that WT1 is the factor predominantly bound to each of the repressor regions in vivo. Additionally, ectopic expression of -KTS isoforms of WT1 decreased Prm1-directed gene expression and TPalpha mRNA expression. Collectively, these data establish WT1 as a critical repressor of Prm1, suppressing TPalpha expression in the platelet progenitor megakaryoblastic HEL cells.

Dynamic interaction between WT1 and BASP1 in transcriptional regulation during differentiation

The Wilms' tumour suppressor protein WT1 plays a central role in the development of the kidney and also other organs. WT1 can act as a transcription factor with highly context-specific activator and repressor functions. We previously identified Brain Acid Soluble Protein 1 (BASP1) as a transcriptional cosuppressor that can block the transcriptional activation function of WT1. WT1 and BASP1 are co-expressed during nephrogenesis and both proteins ultimately become restricted to the podocyte cells of the adult kidney. Here, we have analysed the WT1/BASP1 complex in a podocyte precursor cell line that can be induced to differentiate. Chromatin immunoprecipitation revealed that WT1 and BASP1 occupy the promoters of the Bak, c-myc and podocalyxin genes in podocyte precursor cells. During differentiation-dependent upregulation of podocalyxin expression BASP1 occupancy of the podocalyxin promoter is reduced compared to that of WT1. In contrast, the repressive WT1/BASP1 occupancy of the c-myc and Bak promoters is maintained and these genes are downregulated during the differentiation process. We provide evidence that the regulation of BASP1 promoter occupancy involves the sumoylation of BASP1. Our results reveal a dynamic cooperation between WT1 and BASP1 in the regulation of gene expression during differentiation.

PDGF-A promoter and enhancer elements provide efficient and selective antineoplastic gene therapy in multiple cancer types

Development of antineoplastic gene therapies is impaired by a paucity of transcription control elements with efficient, cancer cell-specific activity. We investigated the utility of promoter (AChP) and 5'-distal enhancer (ACE66) elements from the platelet-derived growth factor-A (PDGF-A) gene, which are hyperactive in many human cancers. Efficacy of these elements was tested in multiple tumor cell lines, both in cell culture and as tumor explants in athymic nude mice. Plasmid and viral vectors were constructed with the AChP promoter alone or in fusion with three copies of the ACE66 enhancer for expression of the prototype suicide gene, thymidine kinase (TK). ACE/AChP and AChP cassettes elicited ganciclovir (GCV)-induced cytotoxicity in multiple tumor cell lines. The ACE enhancer element also exhibited synergism with placental and liver-specific promoter elements. An adenovirus containing the AChP-TK cassette produced striking increases in GCV sensitivity in cultured tumor cell lines, as well as GCV-induced regression of U87 MG glioblastoma explants in vivo. TK expression was distributed throughout tumors receiving the therapeutic virus, whereas TdT-mediated dUTP nick end labeling (TUNEL) analysis revealed numerous regions undergoing apoptosis. Vascularization and reticulin fiber networks were less pronounced in virus-GCV-treated tumors, suggesting that both primary and stromal cell types may have been targeted. These studies provide proof-of-principle for utility of the PDGF-A promoter and ACE66 enhancer in antineoplastic gene therapy for a diverse group of human cancers.

In silico regulatory analysis for exploring human disease progression

Background

An important goal in bioinformatics is to unravel the network of transcription factors (TFs) and their targets. This is important in the human genome, where many TFs are involved in disease progression. Here, classification methods are applied to identify new targets for 152 transcriptional regulators using publicly-available targets as training examples. Three types of sequence information are used: composition, conservation, and overrepresentation.

Results

Starting with 8817 TF-target interactions we predict an additional 9333 targets for 152 TFs. Randomized classifiers make few predictions (~2/18660) indicating that our predictions for many TFs are significantly enriched for true targets. An enrichment score is calculated and used to filter new predictions.

Two case-studies for the TFs OCT4 and WT1 illustrate the usefulness of our predictions:

• Many predicted OCT4 targets fall into the Wnt-pathway. This is consistent with known biology as OCT4 is developmentally related and Wnt pathway plays a role in early development.

• Beginning with 15 known targets, 354 predictions are made for WT1. WT1 has a role in formation of Wilms' tumor. Chromosomal regions previously implicated in Wilms' tumor by cytological evidence are statistically enriched in predicted WT1 targets. These findings may shed light on Wilms' tumor progression, suggesting that the tumor progresses either by loss of WT1 or by loss of regions harbouring its targets.

• Targets of WT1 are statistically enriched for cancer related functions including metastasis and apoptosis. Among new targets are BAX and PDE4B, which may help mediate the established anti-apoptotic effects of WT1.

• Of the thirteen TFs found which co-regulate genes with WT1 (p ≤ 0.02), 8 have been previously implicated in cancer. The regulatory-network for WT1 targets in genomic regions relevant to Wilms' tumor is provided.

Conclusion

We have assembled a set of features for the targets of human TFs and used them to develop classifiers for the determination of new regulatory targets. Many predicted targets are consistent with the known biology of their regulators, and new targets for the Wilms' tumor regulator, WT1, are proposed. We speculate that Wilms' tumor development is mediated by chromosomal rearrangements in the location of WT1 targets.

Reviewers

This article was reviewed by Trey Ideker, Vladimir A. Kuznetsov(nominated by Frank Eisenhaber), and Tzachi Pilpel.

Transcriptional regulation of human survivin by early growth response (Egr)-1 transcription factor

Survivin, a member of the inhibitor of apoptosis protein family, is involved in both, inhibition of apoptosis and regulation of cell division. Because of the tumor-specific expression of survivin, the reduction of its expression is an important therapeutic option in the treatment of malignant diseases. Thus, we analyzed the transcriptional regulation of survivin in order to establish survivin as a target gene for new therapeutic approaches. Here, we describe a novel regulatory region within the survivin promoter. After treatment with phorbol 12-myristate-13-acetate, the early growth response (Egr)-1 transcription factor binds to the sequence 5'GAGGGGGCG 3' within the human survivin promoter in vitro and in entire cells. In reporter-gene assays and overexpression experiments, survivin is downregulated following exogenous expression of wildtype Egr-1. Using p53 wildtype and mutated cell lines, we show that Egr-1 negatively regulates survivin expression and sensitizes cell lines to TRAIL-induced apoptosis.

Characterization of the G-quadruplexes in the duplex nuclease hypersensitive element of the PDGF-A promoter and modulation of PDGF-A promoter activity by TMPyP4

The proximal 5′-flanking region of the human platelet-derived growth factor A (PDGF-A) promoter contains one nuclease hypersensitive element (NHE) that is critical for PDGF-A gene transcription. On the basis of circular dichroism (CD) and electrophoretic mobility shift assay (EMSA), we have shown that the guanine-rich (G-rich) strand of the DNA in this region can form stable intramolecular parallel G-quadruplexes under physiological conditions. A Taq polymerase stop assay has shown that the G-rich strand of the NHE can form two major G-quadruplex structures, which are in dynamic equilibrium and differentially stabilized by three G-quadruplex-interactive drugs. One major parallel G-quadruplex structure of the G-rich strand DNA of NHE was identified by CD and dimethyl sulfate (DMS) footprinting. Surprisingly, CD spectroscopy shows a stable parallel G-quadruplex structure formed within the duplex DNA of the NHE at temperatures up to 100°C. This structure has been characterized by DMS footprinting in the double-stranded DNA of the NHE. In transfection experiments, 10 μM TMPyP4 reduced the activity of the basal promoter of PDGF-A ∼40%, relative to the control. On the basis of these results, we have established that ligand-mediated stabilization of G-quadruplex structures within the PDGF-A NHE can silence PDGF-A expression.

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.

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.

A tumor suppressor and oncogene: the WT1 story

The Wilms' tumor 1 (WT1) gene encodes a transcription factor important for normal cellular development and cell survival. The initial discovery of WT1 as the causative gene in an autosomal-recessive condition identified it as a tumor suppressor gene whose mutations are associated with urogenital disease and the development of kidney tumors. However, this view is not in keeping with the frequent finding of wild-type, full-length WT1 in human leukemia, breast cancer and several other cancers including the majority of Wilms' tumors. Rather, these observations suggest that in those conditions, WT1 has an oncogenic role in tumor formation. In this review, we explore the literature supporting both views of WT1 in human cancer and in particular human leukemias. To understand the mechanism by which WT1 can do this, we will also examine its functional activity as a transcription factor and the influence of protein partners on its dual behavior.

The WT1 Wilms' tumor suppressor gene is a downstream target for insulin-like growth factor-I (IGF-I) action in PC12 cells

The biological actions of the insulin-like growth factors, IGF-I and IGF-II, are mediated by the ligand-induced activation of the IGF-I receptor (IGF-IR), a transmembrane heterotetramer linked to the ras-raf-mitogen-activated protein kinase (MAPK) and phosphatidyl inositol 3 kinase (PI3K)-protein kinase B (PKB)/Akt signal transduction cascades. The Wilms' tumor suppressor gene (wt1) encodes a zinc finger transcription factor, WT1, which has been implicated in various cellular processes including proliferation, differentiation and apoptosis. In the present study we demonstrated that IGF-I modulates the WT1 gene expression in neurally derived PC12 cells in a dose- and time-dependent manner. This effect was mediated through both the MAPK and PI3-kinase signaling pathways, as shown by the ability of the specific inhibitors UO126 and LY294002 to abrogate IGF-I action. Moreover, using RT-PCR and transient transfection assays, we demonstrated that the IGF-I effect was associated with corresponding changes in WT1 mRNA levels and WT1 promoter activity. In addition, the results of the present study revealed that high WT1 levels were associated with the induction of apoptosis, whereas low WT1 levels were correlated with the inhibition of apoptosis, as demonstrated by poly ADP ribose polymerase (PARP) cleavage, Bax expression, Annexin V-FITC staining, and by the use of antisense oligonucleotides against WT1. In summary, our results show that the wt1 gene is a novel target for IGF-I action in neurally derived cells.

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.

Wilms' tumor gene WT1 17AA(-)/KTS(-) isoform induces morphological changes and promotes cell migration and invasion in vitro

The wild-type Wilms' tumor gene WT1 is overexpressed in human primary leukemia and in a wide variety of solid cancers. All of the four WT1 isoforms are expressed in primary cancers and each is considered to have a different function. However, the functions of each of the WT1 isoforms in cancer cells remain unclear. The present study demonstrated that constitutive expression of the WT1 17AA(-)/KTS(-) isoform induces morphological changes characterized by a small-sized cell shape in TYK-nu.CP-r (TYK) ovarian cancer cells. In the WT1 17AA(-)/KTS(-) isoform-transduced TYK cells, cell-substratum adhesion was suppressed, and cell migration and in vitro invasion were enhanced compared to that in mock vector-transduced TYK cells. Constitutive expression of the WT1 17AA(-)/KTS(-) isoform also induced morphological changes in five (one gastric, one esophageal, two breast and one fibrosarcoma) of eight cancer cell lines examined. No WT1 isoforms other than the WT1 17AA(-)/KTS(-) isoform induced the phenotypic changes. A decrease in alpha-actinin 1 and cofilin expression and an increase in gelsolin expression were observed in WT1 17AA(-)/KTS(-) isoform-transduced TYK cells. In contrast, co-expression of alpha-actinin 1 and cofilin or knockdown of gelsolin expression by small interfering RNA restored WT1 17AA(-)/KTS(-) isoform-transduced TYK cells to a phenotype that was comparable to that of the parent TYK cells. These results indicated that the WT1 17AA(-)/KTS(-) isoform exerted its oncogenic functions through modulation of cytoskeletal dynamics. The present results may provide a novel insight into the signaling pathway of the WT1 gene for its oncogenic functions.

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.

Regulation of Vein Graft Hyperplasia by Survivin, an Inhibitor of Apoptosis Protein

OBJECTIVE

Survivin (SVV) is an inhibitor of apoptosis protein (IAP) that is upregulated in cancer and has recently been implicated in vascular injury. We sought to investigate the role of SVV in vein graft hyperplasia.

METHODS AND RESULTS

Adenoviral constructs expressing a dominant-negative (AdT34A) and wild-type (AdWT) SVV were used. Proliferation and apoptosis were assayed on endothelial cells (ECs) and smooth muscle cells (SMCs) from human saphenous vein. A rabbit carotid interposition vein graft model (N=31) was used, with adventitial gene transfer of SVV constructs. In vitro, overexpression of SVV was associated with protection from cytokine-induced apoptosis in ECs and SMCs; conversely, AdT34A directly induced apoptosis in these cells. SMC proliferation was increased by AdWT infection, whereas AdT34A reduced proliferation; both effects were serum-dependent. Expression of platelet-derived growth factor (PDGF) in SMCs was regulated by functional SVV expression in analogous fashion. In vivo, proliferation and apoptosis (7 days), as well as wall thickness (30 days), were modified by adenoviral-mediated SVV expression. Adventitial angiogenesis was regulated by the SVV-expressing constructs in a fashion parallel to wall thickness changes.

CONCLUSIONS

SVV is a critical regulator of multiple processes, including proliferation, apoptosis, and angiogenesis, that determine the remodeling response of vein grafts following arterialization.

A 5'-distal enhanceosome in the PDGF-A gene is activated in choriocarcinoma cells via ligand-independent binding of vitamin D receptor and constitutive jun kinase signaling

Overexpression of platelet-derived growth factor A-chain (PDGF-A) is clearly linked to autocrine and paracrine stimulation of malignant growth in many human cancers. We have shown previously that PDGF-A overexpression in choriocarcinoma, hepatoma and lung carcinoma cell lines is driven by the activity of a 66 bp enhancer element (ACE66) located approximately 7 kb upstream of the PDGF-A transcription start site. In this study, the ACE66 element is shown to be activated in JEG-3 choriocarcinoma cells through synergistic interactions between consensus DNA motifs for binding of vitamin D receptor, AP1 and ELK1. Binding of the vitamin D/retinoid-X receptor (VDR/RXRalpha) heterodimer to the ACE66 element was reconstituted in vitro with recombinant VDR/RXRalpha and with JEG-3 nuclear extract, and was verified in living JEG-3 cells by chromatin immunoprecipitation analysis. Transcriptional activity of the ACE66 element, as well as occupancy of the element by VDR/RXRalpha, was shown to be independent of stimulation with the hormonal VDR ligand, 1,25-dihydroxyvitamin D3. The jun kinase pathway of mitogen-activated protein kinase (MAPK) signaling was shown to activate the ACE66 enhancer, most likely through activation of factors binding to the AP1 element. These results identify a novel mechanism of transcriptional enhancement involving ligand-independent activity of the VDR/RXR heterodimer and MAPK signaling pathways that appears to play an important role in the overexpression of PDGF in many different settings of human malignancy.

PDGF-A, PDGF-Rbeta, TGFbeta3 and bone morphogenic protein-4 in desmoplastic small round cell tumors with EWS-WT1 gene fusion product and their role in stromal desmoplasia: an immunohistochemical study

Histologically, desmoplastic small round cell tumor is composed of the characteristic neoplastic small round cells with divergent differentiation, and distinct desmoplastic stroma. Genetically, the tumor shows a characteristic 11;22 translocation, involving the EWS gene on chromosome 22 and the WT1gene on chromosome 11 to produce an EWS-WT1 fusion gene which generates a chimeric protein functioning as a novel transcription factor that activates expression of target genes such as PDGF-A. Expression of PDGF-A, a potent growth factor for fibroblasts, has been detected in desmoplastic small round cell tumors and has been linked to the characteristic desmoplasia in these tumors. Bone morphogenic proteins, which are members of the TGFbeta superfamily play a complex role in regulating cell growth and differentiation and bone formation but have not been evaluated in desmoplastic small round cell tumors. In all, 24 desmoplastic small round cell tumors with EWS-WT1 fusion product confirmed by RT-PCR analysis were evaluated for expression of PDGF-A, PDGF-Rbeta, TGFbeta3 and bone morphogenic protein-4 by standard immunohistochemical methods with antigen retrieval on paraffin sections. Immunoreactivity was evaluated semiquantitively. Tumor-associated desmoplasia was quantified using a three-tier scale on hematoxylin- and eosin-stained sections. Desmoplastic small round cell tumors showed variable immunoreactivity with TGFbeta3 (21/24), BMP4 (14/21), PDGF-A (19/24) and PDGF-Rbeta (16/22). Less frequently, the stromal cells showed reactivity with TGFbeta3, PDGF-Rbeta and PDGF-A. Tumor-associated desmoplasia was prominent in eight, intermediate in seven and weak in nine cases. There was no correlation between tumor-associated desmoplasia and the markers tested except PDGF-A. In contrast to a previous study, our study showed that the level of PDGF-A expression inversely correlated with tumor-associated desmoplasia. Other targets of the EWS-WT1 transcription factor other than PDGF-A may be directly responsible for the prominent tumor-associated desmoplasia seen in desmoplastic small round cell tumor.

Overexpression of the Wilms' tumor gene W T1 in primary astrocytic tumors

Expression of the Wilms' tumor gene W T1 in primary astrocytic tumors was examined using a quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR) or immunohistochemistry. Real-time RT-PCR showed that W T1 mRNA was expressed at various levels in all of the 25 astrocytic tumors examined. Immunohistochemical analysis showed that W T1 protein was expressed in 5 of 6 low-grade astrocytic tumors (grade I-II) and all of 18 high-grade ones (grade III-IV), and that expression levels of W T1 protein in high-grade tumors were significantly higher than those in low-grade ones. W T1 protein was not detected in the normal glial cells contained in the tumor specimens. Furthermore, treatment with W T1 antisense oligomers specifically inhibited growth of glioblastoma cell lines, U87-MG, A172, and T-98G. These results may indicate that the W T1 gene plays an important role in tumorigenesis of primary astrocytic tumors.

ZNF411, a novel KRAB-containing zinc-finger protein, suppresses MAP kinase signaling pathway

Cardiac differentiation involves a cascade of coordinated gene expression that regulates cell proliferation and matrix protein formation in a defined temporo-spatial manner. The zinc-finger-containing transcription factor has been implicated as a critical regulator of multiple cardiac-expressed genes as well as a regulator of inducible gene expression in response to hypertrophic stimulation. Mitogen-activated protein kinase (MAPK) signal transduction pathways are among the most widespread mechanisms of eukaryotic cell regulation. The MAPKs function inside the nucleus and target transcription factors that are prebound to DNA. Many transcription factors are probably important MAPK targets. Here, we have cloned a new zinc-finger gene named ZNF411 using degenerate primers from an early embryo heart cDNA library, which mapped to 19p13.11. The ZNF411 gene consists of 2360 nucleotides and encodes a protein of 499 amino acids with an amino-terminal KRAB domain and eleven carboxy-terminal C2H2 zinc-finger units. Northern blot analysis indicates that a 2.4 kb transcript specific for ZNF411 is expressed in heart, skeletal muscle, and placenta at adult stage and is expressed in most of the examined embryonic tissues, especially at a higher level in skeletal muscle, heart, and pancreas. ZNF411 protein distributes evenly in nuclei when overexpressed in the cells. Reporter gene assays show that ZNF411 is a transcriptional repressor and overexpression of ZNF411 in the COS-7 cells inhibits the transcriptional activities of AP-1 and SRE. These results indicate that ZNF411 is a member of the zinc-finger transcription factor family and may be involved in the heart development, and it probably works as a negative regulator in MAPK signaling pathway.

Ets-1 stimulates platelet-derived growth factor A-chain gene transcription and vascular smooth muscle cell growth via cooperative interactions with Sp1

The platelet-derived growth factor (PDGF) family of ligands (composed of A-, B-, C-, and D-chains), potent mitogens, and chemoattractants for cells of mesenchymal origin has been implicated in numerous vascular pathologies involving smooth muscle cell (SMC) hyperplasia. Understanding the molecular mechanisms mediating PDGF transcription would provide new insights into strategies to control PDGF-dependent pathophysiologic processes. We demonstrated previously that PDGF-A expression is under the positive regulatory influence of Sp1, Sp3, and Egr-1 and is negatively controlled by GCF2, NF-1(X), and WT-1. In this article, we demonstrate that Ets-1 induces PDGF-A expression in primary rat aortic SMCs at the level of transcription and mRNA expression. Electrophoretic mobility shift, supershift, and mutational analyses revealed a functional role for the (-555)TTCC(-552) motif in the PDGF-A promoter that binds endogenous Ets-1. Chromatin immunoprecipitation analysis showed the interaction of endogenous and exogenous Ets-1 or glutathione S-transferase-tagged Ets-1, bearing only the DNA-binding domain with the authentic PDGF-A promoter. Conversely, dominant-negative mutant of Ets-1 blocked the promoter interaction of endogenous Ets-1. Overexpression of Ets-1 but not the mutant form of Ets-1 activates the PDGF-A promoter cooperatively with Sp1. Sp1, which interacts with Ets-1, failed to induce PDGF-A promoter-dependent expression if the promoter contained a site-specific mutation in this novel Ets-binding site. Small interfering RNA to Ets-1 and Sp1 blocked PDGF-BB- and serum-inducible PDGF-A expression. SMC growth was stimulated by Ets-1 and Sp1 separately and further increased by both factors together. Ets-1-inducible mitogenesis is blocked by antibodies neutralizing PDGF-A and involves activation of the PDGF alpha-receptor, which binds PDGF-A. These findings identify a functional cis-acting element for Ets-1 in the PDGF-A promoter and demonstrate that Sp1 and Ets-1 cooperatively activate PDGF-A transcription in vascular SMCs.

Overexpression of the Wilms' tumor gene WT1 in pancreatic ductal adenocarcinoma

The expression of the Wilms' tumor gene WT1 was examined by immunohistochemistry in 40 cases of pancreatic ductal adenocarcinoma. WT1 protein was expressed in 30 (75%) of the 40 pancreatic ductal adenocarcinomas, but not in the remaining 10 (25%). In normal pancreatic ductal cells, WT1 protein was undetectable. No correlations between WT1 expression and clinicopathological parameters such as age, sex, T or N stage, tumor location, and tumor differentiation were observed. Treatment with WT1 antisense oligomers significantly inhibited the growth of five human pancreatic cancer cell lines, PSN1, MiaPaCa2, ASPC1, BxPC3, and PCI6, expressing the WT1 gene. These results indicate an important role of the WT1 gene in the tumorigenesis of pancreatic ductal adenocarcinoma expressing WT1 and provide a rationale for new treatment strategies to treat pancreatic ductal adenocarcinoma by targeting the WT1 gene and its product.

WT1 is Differentially Expressed in Serous, Endometrioid, Clear Cell, and Mucinous Carcinomas of the Peritoneum, Fallopian Tube, Ovary, and Endometrium

The Wilms' tumor gene WT1 plays complex roles in the development of the organs of the genitourinary tract and mesothelium, as well as Wilms' tumors. Although its biologic role is still unclear, most serous carcinomas of the ovary and peritoneum, mesotheliomas, and Wilms' tumor have been shown to express WT1. A recent study, however, found no WT1 expression in serous carcinomas of the endometrium, suggesting that WT1 could be useful in identifying the primary site of serous carcinomas. We examined the expression of WT1 and p53 by immunohistochemistry in 69 cases of endometrial carcinoma (35 endometrioid, 18 clear cell, 16 serous), 68 cases of ovarian carcinoma (28 serous, 11 endometrioid, 18 clear cell, and 11 mucinous), 14 fallopian tube carcinomas (12 serous, 2 endometrioid), and 20 primary peritoneal serous carcinomas. WT1 nuclear reactivity of any extent and intensity was considered positive. Immunohistochemical stains were evaluated semiquantitatively using a four-tiered scale. Among endometrial carcinomas, WT1 immunoreactivity was seen in 10 of 16 serous, but in none of 35 endometrioid or 18 clear cell carcinomas. Among ovarian tumors, WT1 expression was seen in 24 of 28 serous and 4 of 18 clear cell carcinomas, but in none of 11 endometrioid and 11 mucinous tumors. All 12 serous carcinomas but none of 2 endometrioid carcinomas of the fallopian tube were positive for WT1. WT1 expression was seen in 19 of 20 serous primary peritoneal carcinomas. The difference in WT1 expression was highly significant between serous and other types of tumors in all sites (p<0.0001, chi-square test), although the level of WT1 expression was significantly different among serous carcinomas arising at different sites (p<0.0001, Kruskal-Wallis test). A significant positive correlation was found between the level of p53 and WT1 expression in all carcinomas combined (r = 0.3935, p<0.0001, Spearman test), but when only serous carcinomas were analyzed, the correlation between p53 and WT1 expression levels did not reach statistical significance. Our results suggest that WT1 expression in epithelial tumors of the female genital tract may be related to cell differentiation and histologic subtypes of carcinomas, rather than to primary site of origin.

Gene expression profiles of livers from thermally injured rats

The liver plays an important role in a severe thermal injury by modulating immune function, inflammatory processes and the acute phase response, which are an orchestrated attempt to restore homeostasis. Using high-density oligonucleotide arrays, we examined the gene expression profile in the livers of rats between 2 and 240 h after a 40% total body surface area (TBSA) burn. Alterations in gene expression unique to a thermal injury were identified. Approximately 39 genes out of 8700 genes on each array across all the time points showed a significant change in expression patterns. Real time reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses verified significant changes in early growth response-1 (Egr-1) messenger RNA (mRNA) and protein levels corresponding to the array data. Significant increases in serum levels of alpha-2-macroglobulin that correspond to changes in its mRNA levels were observed at 6 and 24 h after burn, p<0.05. The genomic pattern for liver in the hypermetabolic phase after the burn injury involves transcription factors, stress and inflammatory responses, cytoskeletal and extracellular matrix modifications, and regulation of cell proliferation and differentiation. During the initial phase of thermal injury gene expression profiles in the liver may provide some insight into how cellular protection mechanisms and systemic hypermetabolism are initiated and controlled. The genome wide changes observed may provide a rational therapeutic strategy to improve burn care.

Transcription of the platelet-derived growth factor A-chain gene

The molecular mechanisms which control the transcription of growth factor genes underlie such diverse biological processes as embryonic development, cellular differentiation and wound healing. Moreover, disruption of these controls is implicated in the development and progression of a wide variety of human diseases, including cancer, atherosclerosis and fibrotic disease. This review highlights progress made in the study of the gene encoding platelet-derived growth factor A-chain (PDGF-A) from the perspective of its normal patterns of expression, as well as possible mechanisms leading to dysregulation and disease. A particular focus has been placed on the identification and characterization of specific DNA elements, DNA-binding proteins and other aspects of transcriptional regulation involved in activation and repression of the human PDGF-A promoter.

Wilms' tumor suppressor (WT1) is a mediator of neuronal degeneration associated with the pathogenesis of Alzheimer's disease

Wilms' tumor suppressor (WT1), a 52- to 54-kda transcription factor, is the gene product of Wilms' tumor 1 (wt1), one of at least three genes involved in the development of a pediatric kidney cancer. Expression patterns of WT1 indicate that it is not restricted to the kidney but may play a role in the development and homeostasis of other tissues as well. WT1 has been implicated in various cellular processes including proliferation, differentiation, and apoptosis. High levels of WT1 induce apoptosis independent of p53, whereas low levels of WT1 inhibit apoptosis. Because apoptosis has been suggested to play a role in neurodegeneration in Alzheimer's disease (AD), immunohistochemistry of WT1 and paired helical filament (PHF) in serial sections was carried out. Immunohistochemical localization of WT1 and PHF showed the presence of WT1 in approximately 42% of PHF-positive neurofibrillary tangle containing-neurons. Laser confocal microscopy of hippocampal neuron cultures undergoing apoptosis induced by amyloid beta peptide (Abeta) or staurosporine demonstrated significant time-dependent elevations of WT1 correlating with increased levels of apoptosis. Blockade of WT1 transcription by antisense oligonucleotide reduced WT1 expression and prevented neuronal apoptosis in both Abeta- and staurosporine-treated cultures. Together, these data suggest a role for WT1 in the neurodegeneration observed in AD brain.

Overexpression of the Wilms' tumor gene WT1 in colorectal adenocarcinoma

Expression of the Wilms' tumor gene WT1 was examined in 59 cases of colorectal adenocarcinoma to examine the involvement of WT1 in tumorigenesis. Quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR) showed that WT1 mRNA was expressed in the range from 7.2 x 10(-5) to 4.9 x 10(-1) levels (WT1 expression level in K562 leukemic cells was defined as 1.0) in all (100%) of the 28 cases of colorectal adenocarcinoma examined, and that the WT1 mRNA expression levels were higher in 20 (71%) of the 28 cases compared to those of normal-appearing mucosal tissues examined. Immunohistochemical analysis using an anti-WT1 antibody was performed on 46 cases of colorectal adenocarcinoma (15 of the 28 cases with WT1 mRNA expression and 31 newly collected cases), and the expression of WT1 protein was detected in 41 (89%) of the 46 cases. The direct sequencing analysis of the WT1 genomic DNA showed no mutations in any of the 10 exons of the WT1 gene in any of 5 different colorectal adenocarcinomas. These results may indicate an important role of the wild-type WT1 gene in tumorigenesis of colorectal adenocarcinoma.

Overexpression of the Wilms' tumor gene WT1 in primary thyroid cancer

The expression levels of the Wilms' tumor gene WT1 were examined in 34 primary thyroid cancers (24 papillary, 5 follicular, 1 anaplastic, and 4 medullary carcinomas), 17 thyroid follicular adenomas, and 6 normal-appearing thyroid tissues using quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR). In 33 of 34 thyroid cancers, the WT1 mRNA was expressed at levels ranging from 5.0 x 10 (-5) to 8.3 x 10 (-2) levels (WT1 expression level in K562 leukemic cells was defined as 1.0). The WT1 mRNA expression levels were significantly higher than those in either thyroid follicular adenomas (P < 0.001) or normal-appearing thyroid tissues (P < 0.01). Immunohistochemical analysis confirmed the expression of WT1 protein in 20 of 21 thyroid cancers with WT1 mRNA expression. WT1 protein was also detected in 6 of 7 follicular adenomas with WT1 mRNA expression. However, the intensity of staining of WT1 protein in adenoma cells was weaker than that in cancer cells and its expression was restricted to approximately 30-80% of adenoma cells in the tumors examined. The direct sequencing analysis of the WT1 genomic DNA showed no mutations in any of the 10 exons of the WT1 gene in all of the 9 different thyroid cancers. These findings indicate an important role of the wild-type WT1 gene in the tumorigenesis of primary thyroid cancer.

Overexpression of the Wilms' tumor gene WT1 in head and neck squamous cell carcinoma

The expression levels of the Wilms' tumor gene WT1 were examined in 56 cases of head and neck squamous cell carcinoma (HNSCC) using quantitative real-time reverse transcriptase-polymerase chain reaction (RT-PCR). They included 4 cases of floor of mouth, 9 of gingiva, 25 of tongue, 10 of oropharynx, 3 of hypopharynx, and 5 larynx squamous cell carcinoma (SCC). All (100%) of 4 cases of floor of mouth, 5 (56%) of 9 gingiva, 17 (68%) of 25 tongue, 8 (80%) of 10 oropharynx, all (100%) of 3 hypopharynx, and all (100%) of 5 larynx SCC overexpressed the WT1 gene in the range of 3.07 x 10(-4)-8.60 x 10(-1) levels (the WT1 expression level in K562 leukemic cells was defined as 1.0). Thus, 42 (75%) out of 56 cases of HNSCC overexpressed the WT1 gene. The high expression level of the WT1 gene significantly correlated with poor histological tumor differentiation and high tumor stage of HNSCC. Immunohistochemical analysis confirmed the expression of WT1 protein in 6 cases (one floor of mouth, 2 tongue, 2 oropharynx, and one larynx SCC) with overexpression of the WT1 gene. The direct sequencing analysis of the WT1 genomic DNA showed no mutations in any of 10 exons of the WT1 gene in 5 different HNSCC. These findings suggest an important role of the wild-type WT1 gene in the tumorigenesis of HNSCC.

Genetic network identification by high density, multiplexed reversed transcriptional (HD-MRT) analysis in steroidogenic axis model cell lines

Transcriptional network analysis in steroidogenic axis cell lines requires an understanding of cellular network composition and complexity. Previous studies have shown that absence of transcriptional network components in a cell line compromises that cell line's functional capacity for transcriptional regulation. Our goal was to analyze qualitatively steroidogenic axis-derived cell lines' expression of a putative transcriptional network involved in human and mouse development. To pursue this analysis we used Northern blots and a high density-multiplexed reverse transcription-polymerase chain reaction (HD-MRT-PCR) approach. Our results revealed that, while some members of this putative network were universally expressed, only a minority of the non-constitutive targeted transcripts were present in any single line. Based on our data and previously published results for contextual expression of these transcription factors, a model was constructed possessing the topology suggestive of a scale-free network: certain network members were highly connected nodes and would represent critical sites of vulnerability. The importance of these highly connected nodes for network function is supported by the severe phenotypes exhibited by human patients and animal models when these genes are mutated. We conclude that knowledge of network composition in specific cell lines is essential for their use as models to investigate functional interactions within selected subnetworks.

Wilms tumor gene (WT1) expression as a panleukemic marker

The Wilms tumor gene (WT1) is expressed in blasts of patients with acute leukemia, irrespective of lineage, and WT1 nuclear protein is detectable in the majority of such blasts. Only very few physiologic hematopoietic progenitors express WT1, but the WT1 expression level of these progenitors and that of leukemic blasts are comparable. Although not specific for acute hematologic malignant diseases, continuous WT1 expression in almost all leukemic blasts strikingly contrasts to its rather transient expression in very few physiologic hematopoietic progenitors. Quantitative and semiquantitative WT1 reverse transcriptase polymerase chain reaction (RT-PCR) protocols have limitations in discriminating physiologic from pathologic overall WT1 expression levels in mononuclear cell preparations. Because of these limitations, reports conflict on the usefulness of long-term monitoring of WT1 expression in patients with acute leukemia. Real-time quantitative WT1 RT-PCR protocols, however, have been developed and tested in small series of patients with acute leukemia. Such protocols hold promise to enable evaluation of the individual treatment response (short-term monitoring) and early diagnosis of imminent relapse through the detection and long-term monitoring of minimal residual disease in patients with acute leukemia. These protocols also should facilitate the notoriously difficult distinction between eosinophilic leukemia and hypereosinophilic syndromes. Data on WT1 expression in leukemic blasts and their physiologic counterparts are discussed in light of clinical relevance.

Cancer immunotherapy targeting WT1 protein

The Wilms tumor gene WT1 is expressed in leukemias and various kinds of solid tumors, including lung and breast cancer, and exerts an oncogenic function in these malignancies, suggesting that WT1 protein is a novel, overexpressed tumor antigen. The WT1 protein, in fact, is an attractive tumor rejection antigen in animal models. Stimulation in vitro of peripheral blood mononuclear cells with HLA-A*2402--and HLA-A*0201--restricted 9-mer WT1 peptides elicits WT1-specific cytotoxic T-lymphocytes (CTLs), and the CTLs kill endogenously WT1-expressing leukemia or solid tumor cells. Furthermore, WT1 immunoglobulin M (IgM) and IgG antibodies are detected in patients with hematopoietic malignancies such as acute myeloid leukemia, chronic myeloid leukemia, and myelodysplastic syndromes, indicating that WT1 protein overexpressed by leukemia cells is indeed immunogenic. Taken together, these results demonstrate that WT1 protein is a promising tumor antigen for cancer immunotherapy against leukemias and various kinds of solid tumors, including lung and breast cancer.

Regulation of gene expression by WT1 in development and tumorigenesis

WT1 encodes a zinc finger transcription factor implicated in normal development and tumorigenesis. Germline mutation or deletion of WT1 results in a spectrum of abnormal kidney development, male-to-female intersex disorders, and predisposition to pediatric nephroblastoma, Wilms tumor. Initially thought to encode a transcriptional repressor, WT1-dependent functions are now more clearly linked to its property as a transcriptional activator of genes involved in renal development and sex determination. WT1 is expressed in 4 isoforms as a result of 2 alternative messenger RNA splicing events, the more significant of which encodes the 3 amino acids lysine, threonine, and serine (KTS) between zinc fingers 3 and 4. Although WT1 isoforms lacking KTS act as sequence-specific DNA binding factors, a large body of evidence now implicates the KTS-containing isoforms in RNA processing. In keeping with distinct biochemical mechanisms for these isoforms, genetic data from humans and mice point to separate but partially overlapping roles for WT1 (+KTS) and (-KTS) during genitourinary development. Recently, a hematopoietic model system has been used to study functional properties of WT1 in vitro. WT1 expression in primary hematopoietic cells leads to stage-specific effects that may be relevant to WT1-mediated tumor suppression.

The role of WT1 in oncogenesis: tumor suppressor or oncogene?

Although originally identified as a tumor suppressor gene, WT1 is overexpressed in a variety of hematologic malignancies and solid tumors, including acute leukemia, breast cancer, malignant mesothelioma, renal cell carcinoma, and others. Overexpression of both wild-type and mutant WT1 has been reported. In some cases, this finding represents overexpression of a gene that should be expressed at lower levels, but in other cases, WT1 is expressed at high levels in a tissue type in which there is normally no expression at all. In this review, the mechanisms of altered WT1 expression are explored, including changes in promoter methylation. WT1 target genes that may be important for oncogenesis are discussed, as is the use of WT1 expression as a diagnostic tool. The prognostic implications of altered WT1 expression and the potential for immunotherapy aimed at WT1 are also discussed.

Downregulation of Wilms' tumor 1 protein inhibits breast cancer proliferation

High levels of Wilms' Tumor 1 (WT1) mRNA have been correlated with poor prognosis in breast cancer patients. However, the function of WT1 protein in breast cancer is not known. We observed that the levels of WT1 protein correlated with the proliferation of breast cancer cells. When the proliferation of breast cancer cells was stimulated by 17beta-estradiol, WT1 protein expression increased. But when the proliferation of breast cancer cells was inhibited by tamoxifen or all-trans retinoic acid (ATRA), WT1 protein expression decreased. We hypothesize that WT1 protein plays a role in regulating breast cancer cell proliferation. Using liposome-incorporated WT1 antisense oligodeoxynucleotides, we found that downregulation of WT1 protein expression led to breast cancer growth inhibition and reduced cyclin D1 protein levels. These results indicate that WT1 protein contributes to breast cancer progression by promoting breast cancer cell proliferation.