Vascular endothelial growth factor (VEGF) is suppressed in WT1-transfected LNCaP cells

WT1 mutants reveal SRPK1 to be a downstream angiogenesis target by altering VEGF splicing

Angiogenesis is regulated by the balance of proangiogenic VEGF(165) and antiangiogenic VEGF(165)b splice isoforms. Mutations in WT1, the Wilms' tumor suppressor gene, suppress VEGF(165)b and cause abnormal gonadogenesis, renal failure, and Wilms' tumors. In WT1 mutant cells, reduced VEGF(165)b was due to lack of WT1-mediated transcriptional repression of the splicing-factor kinase SRPK1. WT1 bound to the SRPK1 promoter, and repressed expression through a specific WT1 binding site. In WT1 mutant cells SRPK1-mediated hyperphosphorylation of the oncogenic RNA binding protein SRSF1 regulated splicing of VEGF and rendered WT1 mutant cells proangiogenic. Altered VEGF splicing was reversed by wild-type WT1, knockdown of SRSF1, or SRPK1 and inhibition of SRPK1, which prevented in vitro and in vivo angiogenesis and associated tumor growth.

WT1 protein directly regulates expression of vascular endothelial growth factor and is a mediator of tumor response to hypoxia

WT1 is a zinc finger transcription factor expressed at high levels in many types of solid tumors, and high WT1 expression is an adverse prognostic factor. How WT1 contributes to tumor growth and influences prognosis remains unclear. We investigated the hypothesis that WT1 up-regulates VEGF in solid tumors, augmenting the response to hypoxia. We found a correlation between levels of WT1 expression and VEGF expression in Ewing sarcoma cell lines. Transfecting WT1-null SK-ES-1 cells with WT1 up-regulated VEGF mRNA expression and resulted in increased angiogenic activity in vitro. Conversely, diminishing WT1 expression in WT1-positive cell lines using WT1-specific shRNA down-regulated VEGF mRNA expression and decreased angiogenic activity in vitro. Transient transfection assays demonstrated that WT1 can regulate the activity of the VEGF promoter, and chromatin immunoprecipitation assays showed that WT1 can bind directly to the VEGF promoter in intact cells. WT1 expression in Ewing sarcoma cells is up-regulated by hypoxia. Importantly, using shRNA to inhibit this up-regulation blunted the hypoxia-mediated increase in VEGF expression. Taken together, these data demonstrate that VEGF is a direct, bona fide WT1 target gene in sarcoma and that WT1 plays a key role in optimizing the response of tumor cells to hypoxia.

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

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

WT1 induction of mitogen-activated protein kinase phosphatase 3 represents a novel mechanism of growth suppression

In its role as a tumor suppressor, WT1 transactivates several genes that are regulators of cell growth and differentiation pathways. For instance, WT1 induces the expression of the cell cycle regulator p21, the growth-regulating glycoprotein amphiregulin, the proapoptotic gene Bak, and the Ras/mitogen-activated protein kinase (MAPK) inhibitor Sprouty1. Here, we show that WT1 transactivates another important negative regulator of the Ras/MAPK pathway, MAPK phosphatase 3 (MKP3). In a WT1-inducible cell line that exhibits decreased cell growth and increased apoptosis on expression of WT1, microarray analysis showed that MKP3 is the most highly induced gene. This was confirmed by real-time PCR where MKP3 and other members of the fibroblast growth factor 8 syn expression group, which includes Sprouty 1 and the Ets family of transcription factors, were induced rapidly following WT1 expression. WT1 induction was associated with a block in the phosphorylation of extracellular signal-regulated kinase in response to epidermal growth factor stimulation, an effect mediated by MKP3. In the presence of a dominant-negative MKP3, WT1 could no longer block phosphorylation of extracellular signal-regulated kinase. Lastly, when MKP3 expression is down-regulated by short hairpin RNA, WT1 is less able to block Ras-mediated transformation of 3T3 cells.

Diagnostic value of WT1 in neuroepithelial tumours

AIMS

Currently, clinical trials using WT1 (Wilms tumour gene) peptide vaccines are conducted in haematopoietic malignancies and solid cancers. Single reports showed that the Wilms tumour gene product WT1 is also expressed in astrocytic neoplasms. Our aim was to investigate WT1 expression in a large cohort of various neuroepithelial tumours of different World Health Organization (WHO) grades and in normal central nervous system (CNS) tissue specimens to test its potential value as a diagnostic marker.

METHODS

Specimens were assessed by RT-PCR, Western blotting and immunohistochemistry. The samples investigated in our study consisted of 334 human neuroepithelial tumours, among those 33 oligodendrogliomas, 219 astrocytomas (including 105 glioblastomas) and 47 ependymomas.

RESULTS

Our results showed a de novo WT1 expression in neuroepithelial tumours. In diffuse astrocytomas and ependymomas, WT1 expression increased significantly with the grade of malignancy. In contrast, no significant difference was seen between WHO grade-II and -III oligodendrogliomas. Controlling for WHO grade, the comparison of oligodendrogliomas with ependymal and astrocytic tumours showed higher expression values for the latter.

CONCLUSIONS

Our study shows that WT1 is expressed de novo in numerous neuroepithelial tumours and increases with the grade of malignancy. These results suggest an important role of WT1 in tumourigenesis and progression in human brain tumours.

WT1 expression distinguishes astrocytic tumor cells from normal and reactive astrocytes

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

Vascular endothelial growth factor expression in rat skin incision wound

Vascular endothelial growth factor (VEGF) is a glycoprotein that enhances vascular permeability, induces chemotaxis and activation of monocytes/macrophages, and promotes growth of vascular endothelial cells. We report that infiltrating polymorphonuclear leukocytes in an incision wound in rat skin express VEGF from 1 day after the injury, as shown by immunohistochemistry. VEGF is also present in macrophages, fibroblast-like cells, and endothelial cells 3 and 7 days after the injury. mRNA for VEGF is statistically significantly increased in the wound area in the tissue 1 day after the skin incision compared with 3 and 7 days after the incision. The VEGF protein content in the wound tissue is statistically significantly higher in the wound than in control skin at 1 and 3 days after skin incision. Our results indicate that VEGF is produced by inflammatory cells to induce vascularization in the early stage of the wound healing process.

Identification of Novel Wilms' Tumor Suppressor Gene Target Genes Implicated in Kidney Development

The Wilms' tumor suppressor gene (WT1) encodes a zinc finger transcription factor that is vital during development of several organs including metanephric kidneys. Despite the critical regulatory role of WT1, the pathways and mechanisms by which WT1 orchestrates development remain elusive. To identify WT1 target genes, we performed a genome-wide expression profiling analysis in cells expressing inducible WT1. We identified a number of direct WT1 target genes, including the epidermal growth factor (EGF)-family ligands epiregulin and HB-EGF, the chemokine CX3CL1, and the transcription factors SLUG and JUNB. The target genes were validated using quantitative reverse transcriptase-polymerase chain reaction, small interfering RNA knockdowns, chromatin immunoprecipitation, and luciferase reporter analyses. Immunohistochemistry of fetal kidneys confirmed that a number of the WT1 target genes had overlapping expression patterns with the highly restricted spatiotemporal expression of WT1. Finally, using an in vitro embryonic kidney culture assay, we found that the addition of recombinant epiregulin, amphiregulin, CX3CL1, and interleukin-11 significantly enhanced ureteric bud branching morphogenesis. Our genome-wide screen implicates WT1 in the transcriptional regulation of the EGF-family of growth factors as well as the CX3CL1 chemokine during nephrogenesis.

Inhibition of fibroblast to myofibroblast transition by halofuginone contributes to the chemotherapy-mediated antitumoral effect

Stromal myofibroblasts play an important role in tumor progression. The transition of fibroblasts to myofibroblasts is characterized by expression of smooth muscle genes and profuse synthesis of extracellular matrix proteins. We evaluated the efficacy of targeting fibroblast-to-myofibroblast transition with halofuginone on tumor progression in prostate cancer and Wilms' tumor xenografts. In both xenografts, low doses of halofuginone treatment, independent of the route of administration, resulted in a trend toward inhibition in tumor development. Moreover, halofuginone synergizes with low dose of docetaxel in prostate cancer and vincristine and dactinomycin in Wilms' tumor xenografts, resulting in significant reduction in tumor volume and weight comparable to the effect observed by high doses of the respective chemotherapies. In prostate cancer and Wilms' tumor xenografts, halofuginone, but not the respective chemotherapies, inhibited the synthesis of collagen type I, alpha-smooth muscle actin, transgelin, and cytoglobin, all of which are characteristics of activated myofibroblasts. Halofuginone, as the respective chemotherapies, increased the synthesis of Wilms' tumor suppressor gene product (WT-1) and prostate apoptosis response gene-4 (Par-4), resulting in apoptosis/necrosis. These results suggest that targeting the fibroblast-to-myofibroblast transition with halofuginone may synergize with low doses of chemotherapy in achieving a significant antitumoral effect, avoiding the need of high-dose chemotherapy and its toxicity without impairing treatment efficacy.