Differential regulation of the human Wilms tumour suppressor gene (WTI) promoter by two isoforms of PAX2

PAX2 is a member of the paired box family of genes with an important role in kidney, genital tract and eye development. Another gene essential 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 temporally. The overlap of PAX2 and WT1 expression in fetal kidney prompted us to determine whether PAX2 regulates the WT1 gene. To investigate this possibility, the WT1 promoter and a series of WT1 promoter deletion fragments were cloned into a luciferase reporter vector, and used in cotransfection experiments with PAX2 expression constructs. PAX2 transactivated 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 required in the same promoter construct for efficient transactivation by PAX2 in CHO-K1 cells, and purified recombinant PAX2 protein was found to 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 PAX2 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 transactivated by PAX2. These findings suggest that PAX2 is a tissue-specific modulator of WT1 expression, and is involved in cell growth control via WT1.