Myogenesis in Wilms' Tumors is Associated with Mutations of the WT1 Gene and Activation of Bcl-2 and the Wnt Signaling Pathway

Abstract

Wilms tumors with WT1 mutations [ WT1(-)] have a stromal-predominant histology with varying extents of rhabdomyogenesis. These tumors also frequently have mutations in the beta-catenin gene ( CTNNB1). We have investigated the molecular events that may explain the origins of rhabdomyogenesis in WT1(-) tumors. Of 35 Wilms tumors, we identified 12 with WT1 mutations, of which 9 carried CTNNB1 mutations. We compared WT1 wild-type tumors [ WT1(+)] with WT1(-) tumors for histological features, localization of beta-catenin, Bcl-2 expression, and apoptosis using an in-situ end-labeling technique. WT1(+) tumors showed triphasic and blastemal- and epithelial predominant-histology. Expression of WT1, beta-catenin, and Bcl-2 recapitulated those of normal kidney epithelial development. Localization of beta-catenin was observed in the cytoplasm and cytoplasmic membrane of early glomerular epithelial structures. Bcl-2 is also expressed in condensing blastema and early glomerular epithelial structures which had little apoptosis. WT1(-) tumors, regardless of whether CTNNB1 mutations were detected or not, showed a stromal-rich phenotype with abundant expression of beta-catenin in the nucleus of the rhabdomyoblasts. Bcl-2 was expressed in rhabdomyoblasts, but not in blastemal cells undergoing apoptosis, suggesting that WT1 regulates Bcl-2 positively in the epithelial pathway, but negatively in the myogenic pathway. These data indicate that mutations in WT1 might alter the Wnt signaling pathway and Bcl-2 related-apoptosis. In WT1(-) tumors, the nuclear accumulation of beta-catenin and Bcl-2 expression are associated with rhabdomyogenesis, and dysregulation of Bcl-2 may be a mechanism by which the histogenesis (loss of blastemal component, muscle differentiation) may be explained.

Canonical WNT signalling determines lineage specificity in Wilms tumour

“…We next examined 53 tumours by immunohistochemistry (IHC) for nuclear accumulation of b-catenin. The intensity and distribution of nuclear staining of b-catenin were variable both within and between tumours as we and other groups have previously reported (Koesters et al, 2003;Fukuzawa et al, 2004a;Li et al, 2004;Fukuzawa et al, 2007). Nuclear immunostaining of b-catenin was detected predominantly in the undifferentiated mesenchymal cells and sometimes in the blastemal cells in 17 tumours (T2-4, 6-14, 16-20) (Table 1a).…”

“…Consistent with the histological features of ILNR-derived WTs that often have various ectopic mesenchymal elements, the Figure 6) are in the second column from the right. WT1 and CTNNB1 mutations were previously examined in tumours (Fukuzawa et al, 2004a) referred to as reference 1. CTNNB1 mutations have been identified in tumours with IGF2 LOI (Fukuzawa et al, 2008) referred to as reference 2.…”

“…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).…”