The Wilms tumor suppressor gene wt1 encodes a zinc finger DNA binding protein, WT1, that functions as a transcriptional repressor. The fetal mitogen insulin-like growth factor II (IGF-II) is overexpressed in Wilms tumors and may have autocrine effects in tumor progression. The major fetal IGF-II promoter was defined in transient transfection assays as a region spanning from nucleotides -295 to +135, relative to the transcription start site. WT1 bound to multiple sites in this region and functioned as a potent repressor of IGF-II transcription in vivo. Maximal repression was dependent on the presence of WT1 binding sites on each side of the transcriptional initiation site. These findings provide a molecular basis for overexpression of IGF-II in Wilms tumors and suggest that WT1 negatively regulates blastemal cell proliferation by limiting the production of a fetal growth factor in the developing vertebrate kidney.

No abstract

The Wilms' tumor suppressor, WT1, is a zinc finger transcriptional regulator which exists as multiple forms owing to alternative mRNA splicing. The most abundant splicing variants contain a nine-nucleotide insertion encoding lysine, threonine, and serine (KTS) in the H-C link region between the third and fourth WT1 zinc fingers which disrupts binding to a previously defined WT1-EGR1 binding site. We have identified WT1[+KTS] binding sites in the insulin-like growth factor II gene and show that WT1[+KTS] represses transcription from the insulin-like growth factor II P3 promoter. The highest affinity WT1[+KTS] DNA binding sites included nucleotide contacts involving all four WT1 zinc fingers. We also found that different subsets of three WT1 zinc fingers could bind to distinct DNA recognition elements. A tumor-associated, WT1 finger 3 deletion mutant was shown to bind to juxtaposed nucleotide triplets for the remaining zinc fingers 1, 2, and 4. The characterization of novel WT1 DNA recognition elements adds a new level of complexity to the potential gene regulatory activity of WT1. The results also present the possibility that altered DNA recognition by the dominant WT1 zinc finger 3 deletion mutant may contribute to tumorigenesis.