A far upstream cis-element is required for Wilms' tumor-1 (WT1) gene expression in renal cell culture

To identify novel cis-regulatory elements responsible for the tissue-restricted expression pattern of the Wilms' tumor-1 (WT1) gene, we mapped a total of 11 DNase I-hypersensitive sites in the 5'-flanking region and first intron of the human gene, six of which were specific for WT1 expressing cell lines. A 1.4-kilobase (kb) fragment from the mouse wt1 5'-flanking region contained cross-hybridizing sequence with significant homology to a region of DNase I hypersensitivity in the human WT1 gene which bound to nuclear matrix in human fetal kidney 293 cells. None of the DNase I-hypersensitive sites/matrix attachment regions, either alone or in combination, were sufficient for tissue-specific WT1 expression in transient and stably transfected cell lines. However, stable transfection of an approximately 620-kb yeast artificial chromosome (YAC) that carried the entire mouse wt1 locus into 293 cells resulted in wt1 (trans)gene expression at a level of approximately 30% of the endogenous human gene. Deletion of the 1.4-kb cross-hybridizing mouse fragment, located approximately 15 kb upstream of the transcription start site, caused complete loss of wt1 gene expression in the YAC-transfected 293 cells. In summary, we have identified a far upstream element that contains a region of DNase I hypersensitivity and that binds to nuclear matrix. This element includes phylogenetically conserved sequence and is required, although not sufficient, for mouse wt1 gene expression in human fetal kidney cells in culture.