The Wilms tumor suppressor-1 target gene podocalyxin is transcriptionally repressed by p53.

Wilms tumors are a heterogeneous class of tumors in which Wilms tumor suppressor-1 (WT1) and the p53 tumor suppressor may be variously inactivated by mutation, reduced in expression, or even overexpressed in the wild-type state. The downstream transcriptional targets of WT1 and p53 that are critical for mediating their roles in Wilms tumorigenesis are not well defined. The WiT49 cell line is characteristic of anaplastic Wilms tumors that are refractory to treatment and expresses wild-type WT1 and mutant p53. We have used the small molecule compound CP-31398 (Pfizer) to restore wild-type p53 function to the codon 248 mutant p53 present in WiT49 cells. In these cells, CP-31398 activated transcription of p53-regulated promoters and enhanced UV light-induced apoptosis without altering the overall p53 protein level. These phenotypes were accompanied by restored binding of the p53 protein to promoter sequences in vivo. Gene expression profiling of CP-31398-treated WiT49 cells revealed subsets of putative p53 target genes that were up- or down-regulated. A preferred target of p53-mediated repression in this system is the podocalyxin (PODXL) gene. PODXL is also transcriptionally regulated by WT1 and has roles in cell adhesion and anti-adhesion. Our results show that PODXL is a bona fide target of p53-mediated transcriptional repression while being positively regulated by WT1. We propose that inappropriate expression of PODXL due to changes in WT1 and/or p53 activity may contribute to Wilms tumorigenesis.