Manfred Beier

Twenty-four new cases of WT1 germline mutations and review of the literature: Genotype/phenotype correlations for Wilms tumor development

We report here 24 new Wilms tumor (WT) patients with germline WT1 alterations and a synopsis of our own previously described and literature cases in whom age of tumor‐onset, gender, and laterality were known. This combined database contains 282 patients, 117 patients with and 165 without WT1 germline alterations. Using this information we have determined the median age of tumor‐onset for patients with (12.5 months) and without WT1 gene alterations (36 months). The earliest onset was in patients with truncation (12 mo, 66 patients), followed by missense mutations (18 mo, 30 patients) and deletions (22 mo, 21 patients). Patients with the two most frequent nonsense mutations R362X and R390X and the Denys–Drash syndrome (DDS) hot spot mutation R394W/Q/L had a very early onset (9, 12, and 18 mo, respectively). The highest number of bilateral tumors was observed in the group of truncation mutations, with a higher percentage of bilateral tumors when truncations occurred in the 5′ half of the WT1 gene. In addition to genital tract anomalies (GU), early onset nephrotic syndrome with diffuse mesangial sclerosis and stromal‐predominant histology, tumor bilaterality, and early age of onset can now be added to the list of risk factors for carrying a germline WT1 mutation.

Hyperactivation of the Insulin-like Growth Factor Receptor I Signaling Pathway Is an Essential Event for Cisplatin Resistance of Ovarian Cancer Cells

Platinum plays a central role in the therapy of ovarian cancer, and the emergence of platinum resistance is a major obstacle for clinical management of the disease. We treated A2780 ovarian cancer cells by weekly cycles of cisplatin over a period of 6 months and unveiled that enhanced insulin-like growth factor I receptor (IGF-IR) expression and autocrine IGF-I are associated with hyperactivation of the IGF-IR and phosphatidylinositol-3-OH kinase (PI3K) pathways in cisplatin-resistant cells. IGF-IR expression levels increased during treatment cycles and correlated with cisplatin resistance. Purified IGF-I induced cisplatin resistance in diverse ovarian cancer cell lines, and small molecule inhibitors proved that IGF-IR and PI3K are essential for cisplatin resistance. Similar results were obtained with BG-1 ovarian cancer cells. Cytogenetic and array comparative genomic hybridization analyses revealed selection and de novo formation of chromosomal alterations during resistance development. An analysis of gene expression profiles of primary ovarian carcinomas identified the regulatory subunit PIK3R2 of PI3-kinase as a significant negative prognosis factor for ovarian cancer. We conclude that targeting the IGF-IR and the PI3K pathways is a promising new strategy to treat cisplatin-resistant ovarian carcinomas.

Molecular definition of chromosome arm 5q deletion end points and detection of hidden aberrations in patients with myelodysplastic syndromes and isolated del(5q) using oligonucleotide array CGH

Isolated deletions of the long arm of chromosome 5, del(5q), are observed in 10% of myelodysplastic syndromes (MDS) and are associated with a more favorable prognosis, although the clinical course varies considerably. If one or more additional chromosomal aberrations are present, this correlates with a significantly shorter overall survival. To assess the frequency of hidden abnormalities in cases with an isolated cytogenetic del(5q), we have performed a genome wide high resolution 44 K 60mer oligonucleotide array comparative genomic hybridization (aCGH) study using DNA from bone marrow cells of 12 MDS and one AML patient. In one case a single additional hidden 5.6 Mb deletion of 13q14 and in another case multiple larger aberrations involving many chromosomes were found. Fluorescence in situ hybridization demonstrated that aberrations present in 35% of the bone marrow cells can be detected by aCGH. Furthermore with oligonucleotide aCGH the deletion end points in 5q were mapped precisely, revealing a cluster of proximal breakpoints in band q14.3 (n = 8) and a distal cluster between bands q33.2 and q34 (n = 11). This study shows the high resolution of oligonucleotide CGH arrays for precisely mapping genomic alterations and for refinement of deletion end points. In addition, the high sensitivity of this method enables the study of whole bone marrow cells from MDS patients, a disease with a low blast count.

Wilms tumor cells with WT1 mutations have characteristic features of mesenchymal stem cells and express molecular markers of paraxial mesoderm

Wilms tumors (WTs) are genetically heterogeneous kidney tumors whose cells of origin are unknown. Tumors with WT1 mutations and concomitant loss of the wild-type allele represent a distinct subgroup, frequently associated with mutations in CTNNB1. Here, we describe the establishment and characterization of long-term cell cultures derived from five individual WTs with WT1 mutations. Three of these tumor cell lines also had CTNNB1 mutations and an activated canonical Wnt signaling pathway as measured by beta-catenin/T cell-specific transcription factor (TCF) transcriptional activity. Four of the five Wilms cell lines had a stable normal karyotype for at least 25 passages, and four lines showed loss of heterozygosity of chromosome 11p due to mitotic recombination in 11p11. Gene expression profiling revealed that the WT cell lines are highly similar to human mesenchymal stem cells (MSCs) and FACS analysis demonstrated the expression of MSC-specific surface proteins CD105, CD90 and CD73. The stem cell like nature of the WT cells is further supported by their adipogenic, chondrogenic, osteogenic and myogenic differentiation potentials. By generating multipotent mesenchymal precursors from paraxial mesoderm (PAM) in tissue culture using embryonal stem cells, gene expression profiles of PAM and MSCs were described. Using these published gene sets, we found coexpression of a large number of genes in WT cell lines, PAM and MSCs. Lineage plasticity is indicated by the simultaneous expression of genes from the mesendodermal and neuroectodermal lineages. We conclude that WTs with WT1 mutations have specific traits of PAM, which is the source of kidney stromal cells.

Clinical relevance of mutations in the Wilms tumor suppressor 1 gene WT1 and the cadherin‐associated protein β1 gene CTNNB1 for patients with Wilms tumors

Mutations in the Wilms tumor (WT) suppressor 1 gene (WT1) and the cadherin‐associated protein β1 gene (CTNNB1) are found predominantly in stromal type WT, defining a genetic subgroup. The clinical relevance of these mutations remains to be determined.

Overcoming chemotherapy resistance of ovarian cancer cells by liposomal cisplatin: Molecular mechanisms unveiled by gene expression profiling

Previously we reported that liposomal cisplatin (CDDP) overcomes CDDP resistance of ovarian A2780cis cancer cells (Krieger et al., Int. J. Pharm. 389, 2010, 10-17). Here we find that the cytotoxic activity of liposomal CDDP is not associated with detectable DNA platination in resistant ovarian cancer cells. This suggests that the mode of action of liposomal CDDP is different from the free drug. To gain insight into mechanisms of liposomal CDDP activity, we performed a transcriptome analysis of untreated A2780cis cells, and A2780cis cells in response to exposure with IC50 values of free or liposomal CDDP. A process network analysis of upregulated genes showed that liposomal CDDP induced a highly different gene expression profile in comparison to the free drug. p53 was identified as a key player directing transcriptional responses to free or liposomal CDDP. The free drug induced expression of essential genes of the intrinsic (mitochondrial) apoptosis pathway (BAX, BID, CASP9) most likely through p38MAPK activation. In contrast, liposomal CDDP induced expression of genes from DNA damage pathways and several genes of the extrinsic pathway of apoptosis (TNFRSF10B-DR5, CD70-TNFSF7). It thus appears that liposomal CDDP overcomes CDDP resistance by inducing DNA damage and in consequence programmed cell death by the extrinsic pathway. Predictions from gene expression data with respect to apoptosis activation were confirmed at the protein level by an apoptosis antibody array. This sheds new light on liposomal drug carrier approaches in cancer and suggests liposomal CDDP as promising strategy for the treatment of CDDP resistant ovarian carcinomas.

Classification of a frameshift/extended and a stop mutation in WT1 as gain of function mutations that activate cell cycle genes and promote Wilms tumour cell proliferation

The WT1 gene encodes a zinc finger transcription factor important for normal kidney development. WT1 is a suppressor for Wilms tumour development and an oncogene for diverse malignant tumours. We recently established cell lines from primary Wilms tumours with different WT1 mutations. To investigate the function of mutant WT1 proteins, we performed WT1 knockdown experiments in cell lines with a frameshift/extension (p.V432fsX87 = Wilms3) and a stop mutation (p.P362X = Wilms2) of WT1, followed by genome-wide gene expression analysis. We also expressed wild-type and mutant WT1 proteins in human mesenchymal stem cells and established gene expression profiles. A detailed analysis of gene expression data enabled us to classify the WT1 mutations as gain-of-function mutations. The mutant WT1Wilms2 and WT1Wilms3 proteins acquired an ability to modulate the expression of a highly significant number of genes from the G2/M phase of the cell cycle, and WT1 knockdown experiments showed that they are required for Wilms tumour cell proliferation. p53 negatively regulates the activity of a large number of these genes that are also part of a core proliferation cluster in diverse human cancers. Our data strongly suggest that mutant WT1 proteins facilitate expression of these cell cycle genes by antagonizing transcriptional repression mediated by p53. We show that mutant WT1 can physically interact with p53. Together the findings show for the first time that mutant WT1 proteins have a gain-of-function and act as oncogenes for Wilms tumour development by regulating Wilms tumour cell proliferation.

Reduction of the tumorigenic potential of human retinoblastoma cell lines by TFF1 overexpression involves p53/caspase signaling and miR-18a regulation

Trefoil factor family (TFF) peptides have been shown to play a pivotal role in oncogenic transformation, tumorigenesis and metastasis by changing cell proliferation, apoptosis, migration and invasion behavior of various cancer cell lines. In the study presented, we investigated the effect of TFF1 overexpression on cell growth, viability, migration and tumorigenicity of different retinoblastoma (RB) cell lines. Transient TFF1 overexpression significantly increases RB cell apoptosis levels. Stable, lentiviral TFF1 overexpression likewise decreases RB cell viability, proliferation and growth and significantly increases apoptosis as revealed by WST‐1 assays, BrdU and DAPI cell counts. TFF1‐induced apoptosis is executed via cleaved caspase‐3 activation as revealed by caspase blockage experiments and caspase‐3 immunocytochemistry. Results from pG13‐luciferase reporter assays and Western blot analyses indicate that TFF1‐induced apoptosis is mediated through transcriptional activity of p53 with concurrently downregulated miR‐18a expression. In ovo chicken chorioallantoic membrane (CAM) assays revealed that TFF1 overexpression significantly decreases the size of tumors forming from Y79 and RB355 cells and reduces the migration potential of RB355 cells. Differentially expressed genes and pathways involved in cancer progression were identified after TFF1 overexpression in Y79 cells by gene expression array analysis, underlining the effects on reduced tumorigenicity. TFF1 knockdown in RBL30 cells revealed caspase‐3/7‐independent apoptosis induction, but no changes on cell proliferation level. In summary, the in vitro and in vivo data demonstrate for the first time a tumor suppressor function of TFF1 in RB cells which is at least partly mediated by p53 activation and miR‐18a downregulation.

Chemotherapy and terminal skeletal muscle differentiation in WT1-mutant Wilms tumors

Wilms tumors (WT) with WT1 mutations do not respond well to preoperative chemotherapy by volume reduction, suggesting resistance to chemotherapy. The histologic pattern of this tumor subtype indicates an intrinsic mesenchymal differentiation potential. Currently, it is unknown whether cytotoxic treatments can induce a terminal differentiation state as a direct comparison of untreated and chemotherapy‐treated tumor samples has not been reported so far. We conducted gene expression profiling of 11 chemotherapy and seven untreated WT1‐mutant Wilms tumors and analyzed up‐ and down‐regulated genes with bioinformatic methods. Cell culture experiments were performed from primary Wilms tumors and genetic alterations in WT1 and CTNNB1 analyzed. Chemotherapy induced MYF6 165‐fold and several MYL and MYH genes more than 20‐fold and repressed many genes from cell cycle process networks. Viable tumor cells could be cultivated when patients received less than 8 weeks of chemotherapy but not in two cases with longer treatments. In one case, viable cells could be extracted from a lung metastasis occurring after 6 months of intensive chemotherapy and radiation. Comparison of primary tumor and metastasis cells from the same patient revealed up‐regulation of RELN and TBX2, TBX4 and TBX5 genes and down‐regulation of several HOXD genes. Our analyses demonstrate that >8 weeks of chemotherapy can induce terminal myogenic differentiation in WT1‐mutant tumors, but this is not associated with volume reduction. The time needed for all tumor cells to achieve the terminal differentiation state needs to be evaluated. In contrast, prolonged treatments can result in genetic alterations leading to resistance.

Establishment of a Conditionally Immortalized Wilms Tumor Cell Line with a Homozygous WT1 Deletion within a Heterozygous 11p13 Deletion and UPD Limited to 11p15

We describe a stromal predominant Wilms tumor with focal anaplasia and a complex, tumor specific chromosome 11 aberration: a homozygous deletion of the entire WT1 gene within a heterozygous 11p13 deletion and an additional region of uniparental disomy (UPD) limited to 11p15.5-p15.2 including the IGF2 gene. The tumor carried a heterozygous p.T41A mutation in CTNNB1. Cells established from the tumor carried the same chromosome 11 aberration, but a different, homozygous p.S45Δ CTNNB1 mutation. Uniparental disomy (UPD) 3p21.3pter lead to the homozygous CTNNB1 mutation. The tumor cell line was immortalized using the catalytic subunit of human telomerase (hTERT) in conjunction with a novel thermolabile mutant (U19dl89-97tsA58) of SV40 large T antigen (LT). This cell line is cytogenetically stable and can be grown indefinitely representing a valuable tool to study the effect of a complete lack of WT1 in tumor cells. The origin/fate of Wilms tumors with WT1 mutations is currently poorly defined. Here we studied the expression of several genes expressed in early kidney development, e.g. FOXD1, PAX3, SIX1, OSR1, OSR2 and MEIS1 and show that these are expressed at similar levels in the parental and the immortalized Wilms10 cells. In addition the limited potential for muscle/ osteogenic/ adipogenic differentiation similar to all other WT1 mutant cell lines is also observed in the Wilms10 tumor cell line and this is retained in the immortalized cells. In summary these Wilms10 cells are a valuable model system for functional studies of WT1 mutant cells.