WILMS-TUMOR-1 SPLICE VARIANTS HAVE OPPOSITE EFFECTS ON THE TUMORIGENICITY OF ADENOVIRUS-TRANSFORMED BABY-RAT KIDNEY-CELLS

The Wilms' Tumor 1 gene (WT1) encodes a transcription factor of the zi nc-finger family, As a result of alternative RNA splicing, the gene ca n be expressed as four polypeptides which differ in the presence or ab sence of two stretches of amino acids: one of 17 residues (17aa) just N-terminal of the four zinc-fingers and of three residues (K-T-S) betw een zinc finger 3 and 4. In this study, four human cDNA constructs enc oding the Wilms' tumor 1 splice variants were stably transfected into adenovirus-transformed baby rat kidney (Ad-BRK) cells. The in vivo pro duced WT1 proteins that lacked the KTS residues were found to bind eff iciently to both the Egr-1 consensus sequence and the recently describ ed WTE DNA sequence, as determined by electrophoretic mobility shift a ssays. Our studies show distinct effects of the different WT1 isoforms . Expression of the WT1 (-/+) protein, lacking the 17aa insert, strong ly suppressed the tumorigenic phenotype of the Ad-BRK cells. Intriguin gly, expression of the WT1 (-/-) protein, lacking both inserts, increa sed the tumor growth rate. In contrast to the growth in vivo, the grow th rate of the transfectants in tissue culture is not influenced by an y of the WT1 isoforms. However, the suppression of tumorigenicity appe ars to be correlated with a reduced ability of the cells to grow in se rum-free medium.