Abstract 2193: WT1 mediated regulation of growth control genes in leukemia
Authors: Pandey Sony , Moazam Mustafa , Eisermann Kurtis , Kuerbitz Steven , Fraizer Gail 
Published: August 2012

Abstract
Prognosis and therapy of acute leukemia is influenced by leukemia-specific genetic alterations, thus highlighting the importance of identifying novel prognostic markers. One such potential marker, the Wilms’ tumor gene (WT1), a zinc finger transcription factor, is expressed in leukemic blasts and has been found to be mutated in approximately 10 percent of leukemia cases. Work in other tumor systems has shown that WT1 up-regulates expression of genes promoting cancer progression, including the angiogenic and mitogenic factor VEGF. Microarray studies have also correlated expression of JAG1 (Jagged 1) and CCNA1 (Cyclin A) with WT1 in Acute Myeloid Leukemia (AML) samples. We have identified potential WT1 binding sites within the promoters of both JAG1 and CCNA1 and have compared the expression of these genes to that of WT1, using real time quantitative PCR (QRTPCR), in pediatric leukemia and normal bone marrow. Compared to normal bone marrow, we observed lower than normal levels of WT1 in a majority of pediatric ALL samples, associated with lower than normal levels of VEGF, JAG-1 and CCNA-1. Conversely in pediatric AML(M3) we observed elevated levels of WT1 associated with elevated JAG-1 and CCNA-1. Mutations of the WT1 zinc finger (ZF) DNA binding domain have also been described in poor prognosis leukemias. To identify novel ZF mutations we sequenced WT1 in twelve pediatric acute leukemia samples. No ZF domain mutations were identified among these samples with high WT1 expression. However, a well-described SNP (rs 16754, also in exon 7), identified as a good prognostic marker in Cytogenetically Normal AML, was observed either as a homozygous or heterozygous variant of the WT1 gene. Because a majority of WT1 mutations identified in leukemias are frameshift mutations leading to a truncated protein lacking the ZF DNA binding domain, we created a truncation mutant of isoform A-WT1 lacking the ZF domain and assessed its function in K562 cells. Using QRTPCR we quantified the effect of over-expression of wild type and mutant WT1 on VEGF, JAG1 and CCNA1 expression. Compared to the vector control, wild type WT1 upregulated levels of JAG1 and CCNA1 but not VEGF mRNA. Mutant WT1 did not upregulate JAG1 or CCNA1. Our data and other studies have shown that JAG1 is elevated in AML patient samples, implicating the NOTCH 1 pathway that promotes cell proliferation and blocks differentiation. Thus, these results suggest that WT1 may act as an oncogene in K562 cells, in part by upregulating the growth promoting NOTCH-1 ligand, JAG1. Similarly, cell cycle regulation by WT1, demonstrated in other systems, may be mediated by transcriptional regulation of CCNA1. WT1 may contribute to leukemogenesis through transcriptional regulation of genes controlling cell proliferation.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2193. doi:1538-7445.AM2012-2193