Wilms' tumor 1 gene (WT1) is overexpressed and provides an oncogenic function in pediatric nephroblastomas harboring the wild-type WT1.

Wilms' tumor 1 gene (WT1) is known to be a tumor suppressor gene in the subset of nephroblastomas that harbors WT1 mutations. However, its role in nephroblastomas without mutations remains unclear. This study aimed to evaluate the expression of WT1 and its potential oncogenic role in pediatric nephroblastoma with wild-type WT1. A total of 24 nephroblastomas were studied for WT1 mRNA expression by quantitative reverse-transcription polymerase chain reaction. The expression levels were compared between nephro-blastomas with and without WT1 mutations, as well as to normal kidney tissue, other pediatric renal tumors and neuroblastomas. Immunohistochemistry was used to evaluate expression patterns at the tissue level. Post-transcriptional inhibition of WT1 was performed in primary cultures of wild-type nephroblastoma using WT1 siRNA. The average WT1 expression level in nephroblastoma tissue was significantly higher than that in normal kidney tissue and neuroblastomas. Expression at the mRNA level was not different between nephroblastomas with WT1 mutations (4 cases) and those with wild-type WT1 (20 cases). However, while WT1 immunoreactivity was positive in all of the nephroblastoma components in the tumors with wild-type WT1, the protein expression was weaker and limited to stromal components in the tumors with mutated WT1, where it co-localized with β-catenin nuclear accumulation. The post-transcriptional inhibition of WT1 resulted in growth retardation and a significantly increased apoptotic fraction. Our study found overexpression of the WT1 gene in pediatric nephroblastomas with wild-type WT1. Moreover, the study suggests an oncogenic role of WT1 in this tumor subset.