PRODUCTS OF ALTERNATIVELY SPLICED TRANSCRIPTS OF THE WILMS-TUMOR SUPPRESSOR GENE, WT1, HAVE ALTERED DNA-BINDING SPECIFICITY AND REGULATE TRANSCRIPTION IN DIFFERENT WAYS

The Wilms' tumor susceptibility gene, wt1, encodes a transcription fac tor of the zinc finger protein family. Mutations in the WT1 gene produ ct have been detected in both sporadic and familial Wilms' tumors, sug gesting that alterations in WT1 may disrupt its normal function as a t ranscriptional regulator. The transcripts of wt1 are alternatively spl iced; however, roles of the alternatively spliced forms have not been defined. The major transcript of wt1 encodes a WT1 protein [WT1(+KTS)17AA] that contains three amino acids (+KTS) between the third and fou rth zinc fingers and a serine-rich, 17 amino acid (+17AA) domain N-ter minal to the zinc finger region. We now show that the WT1(+KTS) forms functionally bind to a unique G + C-rich sequence within the PDGF A-ch ain promoter. We also show that WT1 (+KTS)+17AA functions as a strong transciptional repressor and that +17AA alone fused to the zinc-finger domain of WT1 or to the heterologous DNA binding domain of GAL4 funct ions independently as a repressor. Deletion of four serine residues wi thin +17AA abolishes the repressor activity of +17AA. These results in dicate that wt1 products with +17AA contain an additional dominant rep ressor domain and that the presence or absence of +KTS determines alte rnative DNA binding specificity.