Functional characterization of the Wilms' tumor WT1 protein and identification of potential target genes
Wilms' tumor is an embryonic kidney malignancy thought to arise from loss of function of a tumor suppressor gene. The Wilms' tumor locus at chromosome 11p13 encodes a zinc finger protein (WT1) with characteristics of a transcription factor. The WT1 protein contains an amino terminus rich in proline and glutamine residues; features common to transactivation proteins. The carboxy terminus contains four contiguous zinc fingers of the C2-H2 type. WT1 is a sequence specific DNA binding protein which recognizes the DNA consensus site 5$\sp\prime$-CGCCCCCGC-3$\sp\prime,$ the same as that of EGR-1, an immediate early growth response gene product. While EGR-1 is a well-established transcriptional activator, WT1 represses transcription from promoters which contain WT1/EGR-1 consensus sequences, such as EGR-1, IGFII and PDGF-A. Thus, the product of a putative tumor suppressor gene has the ability to function as a transcriptional repressor and repress genes whose products typically promote growth. The understanding of WT1's complete physiological function depends on the identification of biologically relevant target genes active during kidney development and whose deregulation correlates with tumor formation. Two strategies were used to isolate target genes of WT1 and/or EGR-1 mediated regulation. The first relied on the combined techniques of protein affinity chromatography and whole genome PCR. Several genomic clones were isolated which bound WT1/EGR-1 proteins as well as contained contiguous transcriptional units. Unfortunately, none of these clones was responsive to WT1 or EGR-1 in a variety of functional assays. The second approach relied on identification of known genes with WT1/EGR-1 binding sites in their regulatory regions and whose temporal and spatial expression pattern was consistent with that of WT1. Using this approach, syndecan-1, which encodes a cell surface proteoglycan important in the epithelial-mesenchymal interactions during development of the kidney, was identified as a target gene of the Wilms' tumor protein. Suprisingly, WT1 transactivated the syndecan-1 promoter. These data suggest that while WT1 may repress genes whose products promote growth, it may also activate genes like syndecan-1 whose expression is necessary for kidney epithelial differentiation. Based on these studies, a model for WT1's role in kidney differentiation has been proposed.
Cook, Donna Marie, "Functional characterization of the Wilms' tumor WT1 protein and identification of potential target genes" (1996). Dissertations available from ProQuest. AAI9627905.