TRANSCRIPTIONAL REGULATION OF THE HUMAN WILMS-TUMOR GENE (WT1) - CELL-TYPE-SPECIFIC ENHANCER AND PROMISCUOUS PROMOTER

The Wilms' tumor gene, WT1, is expressed in few tissues, mainly the de veloping kidney, genitourinary system, and mesothelium, and in immatur e hematopoietic cells. To develop an understanding of the role of WT1 in development and tumorigenesis, we have identified transcriptional r egulatory elements that function in transient reporter gene constructs transfected into kid ney and hematopoietic cell lines. We found three transcription start sites of the WT1 gene and have identified an esse ntial promoter region by deletion analysis. The WT1 promoter is a memb er of the GC-rich, TATA-less, and CCAAT-less class of polymerase II pr omoters. Whereas the WT1 promoter is similar to other tumor suppressor gene promoters, the WT1 expression pattern (unlike Rb and p53) is tis sue-restricted. The WT1 GC-rich promoter is promiscuous, functioning i n all cell lines tested, independent of WT1 expression. This finding s uggests that the promoter is not tissue-specific, but that tissue-spec ific expression of WT1 is modulated by additional regulatory elements. Indeed, we have identified a transcriptional enhancer located 3' of t he WT1 gene >50 kilobases downstream from the promoter. This orientati on-independent enhancer increases the basal transcription rate of the WT1 promoter in the human erythroleukemia cell line K562, but not in a ny of the other cell lines tested.