DIFFERENTIAL REGULATION OF THE HUMAN WILMS-TUMOR SUPPRESSOR GENE (WTI) PROMOTER BY 2 ISOFORMS OF PAX2

PAX2 is a member of the paired box family of genes with an important r ole in kidney, genital tract and eye development. Another gene essenti al for kidney and genital tract development is the Wilms tumour gene, WT1. PAX2 and WT1 encode transcription factors expressed during fetal kidney development in patterns that overlap both spatially and tempora lly. The overlap of PAX2 and WT1 expression in fetal kidney prompted u s to determine whether PAX2 regulates the WT1 gene. To investigate thi s possibility, the WT1 promoter and a series of WT1 promoter deletion fragments were cloned into a luciferase reporter vector, and used in c otransfection experiments with PAX2 expression constructs. PAX2 transa ctivated the WT1 promoter up to 35-fold in CHO-K1 cells, and from four - to sevenfold in 293 cells. Two regions of the WT1 promoter were requ ired in the same promoter construct for efficient transactivation by P AX2 in CHO-K1 cells, and purified recombinant PAX2 protein was found t o bind to two sites in the WT1 promoter, at -205/-230 and +377/ +402. Removal of WT1 promoter sequences containing the -205/-230, or + 377/ + 402 binding sites abolished transactivation of the WT1 promoter by P AX2 in CHO-K1 cells, and had a differential effect on transactivation of the WT1 promoter in 293 cells, depending on the PAX2 isoform used. A fragment containing the -205/ -230 site alone could be transactivate d by PAX2. These findings suggest that PAX2 is a tissue-specific modul ator of WT1 expression, and is involved in cell growth control via WT1 .