ABSTRACT
Desmoid tumors (aggressive fibromatosis) are locally invasive soft tissue tumors in which beta-catenin/TCF3 mediated Wnt signaling is activated. More than 80% of desmoid tumors contain activating mutations in beta-catenin. It has been shown that the Wnt signaling pathway interacts with Wilms' tumor gene 1 (WT1) in normal kidney development and plays a role in the genesis of some Wilms' tumors. About 15% of Wilms' tumors contain WT1 mutations and of these, about 50% contain beta-catenin mutations. This overlap in mutation pattern of WT1 and beta-catenin in Wilms' tumor suggests that these 2 genes may collaborate in the genesis of a subset of Wilms' tumors. To investigate whether this hypothesis could be extended to other Wnt-dependent tumor types, we searched for WT1 mutations and studied WT1 expression in beta-catenin mutant desmoid tumors. We investigated the expression of WT1 mRNA and protein in desmoid tumors. Medium to high abundant levels of WT1 mRNA were detected by TaqMan quantitative PCR in all tested desmoid cells, whereas adjacent normal fibroblasts showed less expression of WT1. Western blot analysis and immunohistochemistry confirmed this overexpression at the protein level. A mutational screen of the WT1 zinc-finger region by sequence analysis did not identify any mutations. Finally, we investigated a possible role of beta-catenin on WT1 regulation and vice versa. Overexpression of different beta-catenin mutants in the HEK293T cell line did not modulate WT1 promoter activity and WT1 did not affect beta-catenin /TCF transcriptional activity in this cell line. These results show that the wild-type WT1 gene is strongly overexpressed in beta-catenin mutant desmoid tumors and may play a role in tumorigenesis of desmoid tumors, similar to what has been suggested in some epithelial malignancies.
Subject(s)
Fibroma/genetics , Gene Expression Regulation, Neoplastic , WT1 Proteins/genetics , Alternative Splicing , Cell Line, Tumor , Cytoskeletal Proteins/genetics , Exons , Fibroma/pathology , Humans , Kidney , Plasmids , Polymerase Chain Reaction , RNA, Messenger/genetics , Recombinant Proteins/analysis , Reverse Transcriptase Polymerase Chain Reaction , Trans-Activators/genetics , Transcription, Genetic , Transfection , WT1 Proteins/deficiency , beta CateninABSTRACT
Desmoid tumors (aggressive fibromatosis) are locally invasive soft tissue tumors in which beta-catenin-mediated TCF-3-dependent transcription is activated. To provide more insight into the pathophysiology of these tumors, expression profiles were generated using oligonucleotide arrays (Affymetrix). In total, 69 differentially expressed genes were identified in desmoids compared to normal fibroblasts (fascia) from the same patients. The differential expression of a selection of genes was confirmed using RT-PCR and Northern blotting. We further evaluated the insulin-like growth factor-binding protein 6 (IGFBP-6), a gene that was consistently downregulated in all desmoids tested. Promotor studies and electromobility shift assays revealed two functional beta-catenin/TCF-responsive elements in the human IGFBP-6 promoter. These findings suggest that IGFBP-6 is directly downregulated by the beta-catenin/TCF complex in desmoid tumors, and imply a role for the IGF axis in the proliferation of desmoid tumors.