DIFFERENTIAL REGULATION OF THE WILMS-TUMOR GENE, WT1, DURING DIFFERENTIATION OF EMBRYONAL CARCINOMA AND EMBRYONIC STEM-CELLS

The expression pattern of the Wilms' tumor suppressor gene, WT1, durin g embryonal development suggests a role for the WT1 proteins in the di fferentiation of specific tissues. This notion is supported by the obs ervation that WT1 knock-out mice fail to develop kidneys and gonads, W e describe here the changes in the expression and DNA binding activity of the WT1 gene product in pig embryonal carcinoma cells and embryoni c stem cells triggered to differentiate by either retinoic acid (RA) o r DMSO. In exponentially growing P19 embryonal carcinoma (EC) cells, W T1 mRNA and proteins were undetectable, During RA-induced but not DMSO -induced differentiation of P19 EC cells, WT1 expression and DNA bindi ng are strongly activated, Treatment of embryonic stem cells with RA r esulted in a similar activation of WT1. Immunohistochemical analysis s howed that WT1 is expressed in endodermal, glial, and epithelial cell types. In addition, DNA binding by EGR-1, a transcription factor struc turally related to WT1, increased during differentiation of P19 EC and embryonic stem cells, To investigate the possible functional conseque nces of DNA binding by WT1, we examined the expression levels of two p utative transcriptional targets of WT1, the insulin-like growth factor I receptor and epidermal growth factor receptor. We found that after an initial induction, decreasing expression of the insulin-like growth factor I receptor is correlated with increasing WT1 expression. Our r esults demonstrate that expression of WT1 is induced in specific cell types during RA-induced differentiation of P19 EC cells, reflecting th e tissue-specific expression of WT1 in vivo. Therefore, we believe tha t P19 EC cells are a suitable system to study activation and function of WT1 during differentiation.