DIFFERENTIAL-EFFECTS OF WILMS-TUMOR WT1 SPLICE VARIANTS ON THE INSULIN-RECEPTOR PROMOTER

The Wilms tumor gene WT1 has been implicated in the early development of the kidney. Mutations in WT1 are found in a small fraction of Wilms tumor, a pediatric nephroblastoma, and Denys-Drash syndrome, characte rized by genitourinary abnormalities. The WT1 gene product functions a s a transcriptional repressor of growth factor-related genes. The kidn ey is one of the major sites of insulin action in vivo and expresses h igh levels of insulin receptors (IR). IR expression has been detected during early embryogenesis, suggesting that it may play a role in deve lopment. We investigated whether two WT1 splice variants lacking or in cluding a three-amino-acid (KTS) insertion between the third and fourt h zinc finger in the DNA-binding domain could repress the IR promoter in vitro. We show that the +KTS variant effectively represses promoter activity under all conditions tested but the -KTS variant was only ab le to repress in the presence of cotransfected C/EBP beta or a dominan t-negative p53 mutation. Deletional mapping indicated that distinct re gions of the IR promoter mediated the effects of the two isoforms and DNaseI footprint analysis identified potential WT1 binding sites withi n these regions. (C) 1997 Academic Press.