Identification of differential methylation of the WT1 antisense regulatory region and relaxation of imprinting in Wilms' tumor.

Wilms' tumor (WT) is associated with loss of heterozygosity at chromosome 11p13, the site of the Wilms' tumor suppressor gene, WT1. Although the preferential loss of maternal alleles suggested that differential allelic expression of WT1 might occur, this has not been evident in normal fetal tissues or WTs. In this study, we show that the WT1 antisense regulatory region is differentially methylated, with Southern blot analysis of four loss of heterozygosity-negative WTs and their corresponding normal kidneys indicating that allelic methylation is lost in WTs. Reverse transcription-PCR expression analysis correlates methylation with monoallelic expression of the antisense WT1 transcript (WT1-AS) in normal kidney. However, WTs display hypomethylation and biallelic expression of WT1-AS. Our findings are consistent with imprinting of WT1-AS in normal kidney and the relaxation of imprinting in Wilms' tumorigenesis. This identifies the WT1 antisense regulatory region in intron 1 as a primary site for epigenetic deregulation at chromosome 11p13 in WTs.