The Wilms' tumor gene product WT1 mediates the down-regulation of the rat epidermal growth factor receptor by nerve growth factor in PC12 cells.

Recently, we characterized the rat epidermal growth factor receptor (EGFR) promoter and demonstrated that TCC repeat sequences are required for the down-regulation of EGFR by nerve growth factor (NGF) in PC12 cells. In this study, we report that the Wilms' tumor gene product WT1, a zinc finger transcription factor, is able to enhance the activity of the rat EGFR promoter in cotransfection assays. Gel mobility shift assays demonstrate that WT1 binds to the TCC repeat sequences of the rat EGFR promoter. Overexpression of WT1 resulted in up-regulation of the expression levels of endogenous EGFR in PC12 cells. Interestingly, NGF down-regulated the expression levels of WT1 and EGFR in PC12 cells, but not in the p140(trk)-deficient variant PC12nnr5 cells or in cells expressing either dominant-negative Ras or dominant-negative Src. Most importantly, we evaluated the inhibitory effect of antisense WT1 RNA on EGFR expression, and we found that antisense WT1 RNA could substantially reduce EGFR repression in either histochemical staining study or immunoblot analysis. These results indicate that NGF-induced down-regulation of the EGFR in PC12 cells is mediated through WT1 and that WT1 may play an important role in the differentiation of nerve cells.