Upregulation of Wilms' tumor gene 1 (WT1) in desmoid tumors

Abstract

Desmoid tumors (aggressive fibromatosis) are locally invasive soft tissue tumors in which β-catenin/TCF3 mediated Wnt signaling is activated. More than 80% of desmoid tumors contain activating mutations in β-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 β-catenin mutations. This overlap in mutation pattern of WT1 and β-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 β-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 desmoids 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 β-catenin on WT1 regulation and vice versa. Overexpression of different β-catenin mutants in the HEK293T cell line did not modulate WT1 promoter activity and WT1 did not affect β-catenin /TCF transcriptional activity in this cell line. These results show that the wild-type WT1 gene is strongly overexpressed in β-catenin mutant desmoid tumors and may play a role in tumorigenesis of desmoid tumors, similar to what has been suggested in some epithelial malignancies. © 2004 Wiley-Liss, Inc.