The Wilms Tumor Suppressor-1 Target Gene Podocalyxin Is Transcriptionally Repressed by p53

Abstract

Wilms tumor is a pediatric kidney cancer that affects 1 in 10,000 children. The Wilms tumor suppressor-1 (WT1) 1 gene was identified as a tumor suppressor gene based upon the presence of WT1 mutations in a subset (ϳ10 -15%) of Wilms tumor samples (reviewed in Ref. 1). However, the majority of Wilms tumor cases cannot be explained by genetic alteration of the WT1 locus. There may be disruption of biological pathways either upstream or downstream of WT1, or there may be pathways independent of WT1 leading to this type of neoplasm. Several lines of evidence suggest that p53 also plays an important role in the development and/or progression of Wilms tumors. The p53 and WT1 tumor suppressor genes encode transcription factors that have been shown to interact physically and to modulate each other's function in some experimental situations (2). p53 can alter the transcription regulatory activity of WT1. In addition, WT1 stabilizes the p53 protein, alters its activity as a transcription factor, and prevents p53-induced apoptosis (2, 3). Physical and functional interaction has also been observed between the p53 family members p73 and p63 and WT1 (4). Further evidence for biologically relevant interaction between WT1 and p53 includes the fact that the majority of Wilms tumors develop in the presence of wild-type p53 (5). This is in contrast to adult onset human tumors, in which p53 mutations are frequently observed (ϳ50%). The small subset of Wilms tumors that do harbor p53 mutations develop into much more aggressive anaplastic tumors (between 3 and 7% of the total) that are characterized by unfavorable histology, increased metastasis, chemoresistance, and poor prognosis (6 -9). Moreover, Li-Fraumeni patients carrying germ-line p53 mutations are predisposed to development of Wilms tumors (10), and Wilms tumors are one of a small number of cancers that are specifically associated with such mutations (11). To better understand the involvement of both p53 and WT1 in pathways leading to Wilms tumorigenesis, we have used cDNA microarrays to profile gene expression changes dependent upon the activity of these two factors.To accomplish this, we developed strategies to alter the function of WT1 and p53 in a Wilms tumor cell line, WiT49. This cell line is characteristic of anaplastic Wilms tumors in that it expresses wild-type WT1 and mutant p53. We have previously shown that WT1 activity can be effectively abrogated in WiT49 cells by expression of a naturally occurring dominant-negative mutant version of the protein (DDS5) (12). To restore wild-type p53 function in WiT49 cells, we made use of the small molecule compound CP-31398 developed by Pfizer. CP-31398 was originally shown to stabilize the p53 protein with mutation at codon 173, 175, 249, or 273 in the wild-type conformation and to allow its transcriptional and tumor suppressor functions (13). More recently, it has been shown that CP-31398 can stabilize the wild-type p53 protein as well (14 -16). We found here that CP-31398 restores activity to the codon 248 mutant p53 prese...

Transcript profiling of Wilms tumors reveals connections to kidney morphogenesis and expression patterns associated with anaplasia

“…The classic p53 target gene p21 was downregulated in the anaplastic Wilms tumors, indicating a deficiency in p53 activity in these tumors. Additional evidence comes from our recent work where we have demonstrated that Podocalyxin, a gene upregulated in anaplastic Wilms tumors, was transcriptionally repressed by p53 in a Wilms tumor cell line (Stanhope-Baker et al, 2004). The molecular bases underlying the anaplastic nuclear morphology remain unknown.…”

ST7-mediated suppression of tumorigenicity of prostate cancer cells is characterized by remodeling of the extracellular matrix

“…It was identified as an endogenous downstream target of the WT1 TSG, mediating glomerular differentiation (Palmer et al, 2001). PODXL is a target of p53-mediated transcriptional repression in a Wilm's tumor cell line (Stanhope-Baker et al, 2004).…”

Podocalyxin in the Diagnosis and Treatment of Cancer

“…Unlike most of the cancers discussed in this review, PC expression (transcript) is significantly reduced in 64 patient nephroblastoma samples (relative mean 0.29) compared to pooled normal fetal kidney (Stanhope-Baker et al, 2004). Although WT1 is a positive regulator of PODXL expression (Palmer et al, 2001), and loss of WT1 expression is associated with some Wilms' tumours, there was no evidence of a correlation between PODXL and WT1 expression in this study (Stanhope-Baker et al, 2004). However, perhaps of diagnostic value, this same study showed that PODXL expression was increased in more aggressive, anaplastic tumours compared to 40 non-anaplastic tumors (StanhopeBaker et al, 2004).…”

“…Notably, functional loss of p53 is associated with the most aggressive, anaplastic nephroblastomas with poor prognosis. As p53 negatively regulates PODXL expression (Stanhope-Baker et al, 2004), enhanced PODXL expression in anaplastic nephroblastomas may be explained directly by this genetic pathway. Although more study is required to know if enhanced PODXL expression in anaplastic nephroblastoma has a direct role in promoting tumour aggressiveness, expression of PODXL in nephroblastoma may be useful as a marker of poorly differentiated, anaplastic tumours.…”

“…For example, with respect to the pathogenesis of carcinomas (especially prostate and breast cancers) STAT5 activation downstream of the prolactin receptor activation is one possible route to enhanced PC expression (Jacobson et al, 2010). Transcriptional repressors of PODXL include the ubiquitously expressed tumour suppressor transcription factor p53 (TP53) and the integrin-associated adaptor protein PINCH1 (LIMS1) (Stanhope-Baker et al, 2004;Wang et al, 2011). PINCH1 is normally associated with focal adhesion complexes in podocytes but becomes dissociated from these in response to transforming growth factor beta (TGF) stimulation (Wang et al, 2011).…”