Upregulation of c-MYC in WT1-mutant tumors: assessment of WT1 putative transcriptional targets using cDNA microarray expression profiling of genetically defined Wilms' tumors.

The Wilms' tumor suppressor gene, WT1, functions as a transcriptional regulator that represses or activates the expression of a variety of putative target genes. However, it is not clear which genes are the biological targets of WT1, nor which cellular pathway(s) is critically altered in tumors as a result of WT1 mutation. To investigate in vivo the role of WT1 as a transcription factor in Wilms' tumors, we used cDNA microarrays to compare the expression of putative WT1 target genes in a set of 15 primary Wilmstumors carrying WT1-inactivating mutations versus a set of 16 tumors with no WT1 mutations. We hypothesized that the expression of direct downstream targets of WT1 that are relevant to tumor development would differ between these two genetically distinct sets of tumors. Using the Atlas Human Cancer 1.2 cDNA arrays to quantitate gene expression in the 31 tumors, we found that the expression of one WT1 putative target gene, c-MYC, statistically significantly differed between the two sets of tumors and was upregulated in WT1-mutant tumors. This increase of relative gene expression for c-MYC was confirmed using real-time reverse transcription-polymerase chain reaction. The differential expression of another putative target gene, EGR1, approached significance and was also upregulated in WT1-mutant tumors. These data, in addition to the coexpression of c-MYC and WT1 in embryonic renal mesenchyme, strongly suggest that c-MYC is a biologically relevant target of WT1 in Wilmstumors.