THE WT1 GENE-PRODUCT STABILIZES P53 AND INHIBITS P53-MEDIATED APOPTOSIS

The Wilms' tumor-suppressor gene product WT1 coimmunoprecipitates with p53 from baby rat kidney (BRK) cells and Wilms' tumor specimens, and expression of WT1 in BRK cells is associated with increased levels of endogenous wild-type p53 protein. To study the effect of WT1 on p53 fu nction, we cotransfected expression constructs into Saos-2 cells, an o steosarcoma cell line without endogenous expression of either gene. Ex pression of WT1 resulted in increased steady-state levels of p53, attr ibutable to a prolongation in protein half-life, and associated with p rotection against papillomavirus Eb-mediated degradation of p53. This effect mapped to zinc fingers 1 and 2 of WT1 and was not observed with the closely related EGR1 protein. The stabilized p53 demonstrated enh anced binding to its target DNA sequence and increased trans-activatio n of a promoter containing this RGC site, but reduced transcriptional repression of a TATA-containing promoter lacking this site. Expression of WT1 inhibited p53-mediated apoptosis triggered by UV irradiation o r by expression of temperature-sensitive p53 in the wild-type conforma tion, but did not affect p53-mediated cell cycle arrest. We conclude t hat WT1 protein can stabilize p53, modulate its hans-activational prop erties, and inhibit its ability to induce apoptosis. This effect may c ontribute to the elevated levels of wild-type p53 protein that are obs erved in Wilms' tumors.