The Mechanism Of The Expression Of WT1 Gene In Leukemic Cells

Wilm's tumor suppressor 1 (WT1) in 11p13 encodes a transcriptional regulatory protein that binds DNA via four zinc fingers. Lack of expression has been observed in some Wilms' tumors, leading to its classification as a tumor suppressor gene. However, WT1 is over expressed in 80% of cases of acute leukemia, ia not expresses in chronic lymphocytic leukemia and chronic myeloid leukemia in chronic phase and is up-regulated as chronic myeloid leukemia progresses into blast crisis.Gene silencing via DNA methylation has been shown for several tumor suppressor genes. DNA methylation are believed to define an 'open' chromatin conformation and activestate for these genes when unmethylated and acondensed chromatin structure which is 'inactive' when methylated. The promoter DNA methylation of WT1, which didn't block the gene expression, was found in some solid tumors. So far there is no report about the WT1 methylation in leukemia cells yet.There are three parts in the present study. First we evaluated the expression of WT1 in a panel of normal peripheral blood and bone marrow mononuclear cells (PBMNC) some leukemia cell lines. Our results reveal some misunderstands on the WT1 expression.Second, we investigated the state of methylation of WT1 promoter in the above cells. WT1 promoter is methylated in leukemia cell line U937, K562 cells and normal PBMNC, and not in HL60 cells. Nevertheless WT1 was expressed in HL60, K562 cells, and not expressed in U937 and PBMNC. Our results demonstrate that WT1 promoter methylation didn't affect itsexpression. Other transcriptional mechanisms appear to supercede the effects of promoter methylation.Finally, we studied the role of demethylation agent 5-azadeoxycytosine (5-aza-dC) and DHACs inhibitor trichostatin (TSA) on the expression of WT1 in the U937 cells. The results show that the cooperation of 5-aza-dC and TSA may reactivate the WT1 expression hi U937 cells. We can include that the level of histone acetylation and DNA methylation together regulate the expression of WT1.