CTNNB1 Mutations and Overexpression of Wnt/β-Catenin Target Genes in WT1-Mutant Wilms' Tumors

Abstract

Gain-of-function mutations in exon 3 of beta-catenin (CTNNB1) are specific for Wilms' tumors that have lost WT1, but 50% of WT1-mutant cases lack such "hot spot" mutations. To ask whether stabilization of beta-catenin might be essential after WT1 loss, and to identify downstream target genes, we compared expression profiles in WT1-mutant versus WT1 wild-type Wilms' tumors. Supervised and nonsupervised hierarchical clustering of the expression data separated these two classes of Wilms' tumor. The WT1-mutant tumors overexpressed genes encoding myogenic and other transcription factors (MOX2, LBX1, SIM2), signaling molecules (TGFB2, FST, BMP2A), extracellular Wnt inhibitors (WIF1, SFRP4), and known beta-catenin/TCF targets (FST, CSPG2, CMYC). Beta-Catenin/TCF target genes were overexpressed in the WT1-mutant tumors even in the absence of CTNNB1 exon 3 mutations, and complete sequencing revealed gain-of-function mutations elsewhere in the CTNNB1 gene in some of these tumors, increasing the overall mutation frequency to 75%. Lastly, we identified and validated a novel direct beta-catenin target gene, GAD1, among the WT1-mutant signature genes. These data highlight two molecular classes of Wilms' tumor, and indicate strong selection for stabilization of beta-catenin in the WT1-mutant class. Beta-Catenin stabilization can initiate tumorigenesis in other systems, and this mechanism is likely critical in tumor formation after loss of WT1.

Functional characterization of Wilms tumor-suppressor WTX and tumor-associated mutants

“…Furthermore, WTX mutations are not associated with differences in the clinical presentation or outcome of Wilms tumors (Wegert et al, 2009). Microarray experiments show distinct differences in the gene expression profile of WT1 wild-type and mutant tumors, with many of the changes in the WT1 mutant tumors due, in part, to activation of the Wnt pathway (Li et al, 2004). Gene expression profiles of WT1-replete, CTNNB1 wild-type Wilms tumors with or without WTX mutations, may clarify the role of WTX in Wilms tumorigenesis.…”

“…Sporadic Wilms tumors may be associated with bi-allelic mutation of WT1 in up to 15% of cases (reviewed in (Huff, 1998)). Loss of WT1 is frequently accompanied by gain of function mutations of CTNNB1 (Koesters et al, 1999;Maiti et al, 2000;Li et al, 2004). Sporadic Wilms tumors without WT1 mutation frequently show loss of imprinting of IGF2 locus and many genes within this region may be deregulated (Ogawa et al, 1993).…”

Canonical WNT signalling determines lineage specificity in Wilms tumour

“…WT1 mutations are strongly associated with ILNR (Beckwith, 1998) that often develop into WTs with ectopic mesenchymal elements (Beckwith et al, 1990;Beckwith, 1998). A series of immunohistochemical studies of b-catenin in WT have shown that nuclear accumulation of b-catenin is predominantly observed in mesenchymal cells irrespective of CTNNB1 mutations (Koesters et al, 2003;Li et al, 2004;Fukuzawa et al, 2004aFukuzawa et al, , 2008Zirn et al, 2006). These observations suggest a relationship between the mesenchymal lineage in WT and active WNT signalling.…”

“…The WNT-signalling pathway is known to be involved in a subset of WT (Koesters et al, 1999(Koesters et al, , 2003Maiti et al, 2000;Li et al 2004;Fukuzawa et al, 2004a). These tumours typically have WT1 mutations and/or CTNNB1 mutations (Koesters et al, 1999;Maiti et al, 2000;Li et al, 2004;Fukuzawa et al, 2004a).…”

“…These tumours typically have WT1 mutations and/or CTNNB1 mutations (Koesters et al, 1999;Maiti et al, 2000;Li et al, 2004;Fukuzawa et al, 2004a). WT1 mutations are strongly associated with ILNR (Beckwith, 1998) that often develop into WTs with ectopic mesenchymal elements (Beckwith et al, 1990;Beckwith, 1998).…”