DNA RECOGNITION BY SPLICING VARIANTS OF THE WILMS-TUMOR SUPPRESSOR, WT1

The Wilms' tumor suppressor, WT1, is a zinc finger transcriptional reg ulator which exists as multiple forms owing to alternative mRNA splici ng. The most abundant splicing variants contain a nine-nucleotide inse rtion encoding lysine, threonine, and serine (KTS) in the H-C link reg ion between the third and fourth WT1 zinc fingers which disrupts bindi ng to a previously defined WT1-EGR1 binding site. We have identified W T1[+KTS] binding sites in the insulin-like growth factor II gene and s how that WT1[+KTS] represses transcription from the insulin-like growt h factor II P3 promoter. The highest affinity WT1[+KTS] DNA binding si tes included nucleotide contacts involving all four WT1 zinc fingers. We also found that different subsets of three WT1 zinc fingers could b ind to distinct DNA recognition elements. A tumor-associated, WT1 fing er 3 deletion mutant was shown to bind to juxtaposed nucleotide triple ts 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 presen t the possibility that altered DNA recognition by the dominant WT1 zin c finger 3 deletion mutant may contribute to tumorigenesis.