FUNCTIONAL-PROPERTIES OF WT1

WT1 encodes a zinc finger transcription factor that is inactivated in a subset of Wilms' tumors. We have recently shown that introduction of wild-type WT1 into a Wilms' tumor-derived cell line, RM1, results in growth suppression, consistent with its function as a tumor suppressor gene. WT1-mediated growth suppression was also observed in other cell s derived from embryonal tumors, including two osteosarcoma cell lines , U2OS and Saos-2, notable for the respective presence or absence of w ild-type p53. To further characterize the functional properties of WT1 , multiple U2OS and Saos-2 cell lines were established, expressing eit her wild-type WT1 splicing variants or naturally occurring mutants und er control of a tightly regulated tetracycline repressable promoter. I nduction of WT1 in these cells resulted in programmed cell death. This effect was preferentially mediated by WT1 isoform B (encoding alterna tive splice 1, lacking alternative splice II ''KTS''), and it was inde pendent of p53, occurring in both U2OS and Saos-2 cells. WT1-mediated apoptosis was associated with transcriptional repression of the epider mal growth factor receptor (EGFR) and reduced synthesis of endogenous EGFR protein synthesis. Constitutive expression of EGFR abrogated WT1- mediated cell death. We conclude that wild-type WT1 can induce apoptos is in embryonal cancer cells, presumably through the withdrawal of req uired growth factor survival signals, and that EGFR is a physiological target gene for WT1. (C) 1996 Wiley-Liss, Inc.