Major efforts have gone into identifying the targets of oncogenic transcription factors, but data from tissue culture experiments have seldom been vetted in primary cancers. Here we address this problem, using Wilms tumor as an experimental system. Wilms tumors occurring in Denys-Drash and WAGR syndromes carry inactivating mutations of the WT1 tumor suppressor gene. In contrast, WT1 mutations are rare in sporadic Wilms tumors. We have confirmed previous data indicating that mutations in beta-catenin (CTNNB1), a component of the Wnt signaling pathway that acts as an oncogene in many of the most common human malignancies, are restricted to the WT1-null tumors. We also find that these mutations are strikingly clustered at codon Ser45. By expression profiling we have identified a panel of genes that distinguish the WT1-null from WT1-positive tumors. This dataset should be a powerful tool to identify downstream targets of WT1 and beta-catenin/TCF, which we hypothesize are enriched among these differentially expressed genes.
Aim 1. We will determine whether the Wnt/beta-catenin signaling axis is universally activated in the WT1- null class of Wilms tumors.
Aim 2. To narrow the list of WT1 and beta-catenin target genes, we will manipulate WT1 levels, and components of the beta-catenin pathway in tissue culture, and compare the results with our """"""""gold standard"""""""" data from the primary Wilms tumors.
Aim 3. To validate the candidate beta-catenin target genes in vivo, we will express mutant beta-catenin to the developing kidney, using a gene knock-in approach. By creating an isogenic series, these mice will also allow us to assay for the relative potency of mutation at Ser45 vs. other phosphorylation sites in affecting the proliferative/oncogenic potency of beta-catenin. We will subsequently cross these mice with Wt1-mutant heterozygotes, possibly generating a mouse model for Wilms tumor.
