Tet1 plays an essential oncogenic role in MLL-rearranged leukemia

TET1, the founding member of the TET family of enzymes (TET1/2/3) that convert 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), was first identified as a partner gene in MLL-rearranged leukemia, but its definitive pathological role in leukemia is unclear. The down-regulation of all three TET genes and loss-of-function mutations of TET2 have been frequently observed in various cancers, and it was thought that they all play tumor-suppressor roles in tumorigenesis. Here we show that TET1 is likely a direct target of MLL and significantly up-regulated in MLL-rearranged leukemia, associated with an increased level of 5hmC. Our further in vitro and in vivo studies demonstrate that Tet1 plays an indispensable oncogenic role in MLL-rearranged leukemia, through cooperating with MLL fusion proteins in regulating their co-targets including the Hoxa/Meis1/Pbx3/Flt3 genes. Our data delineate a MLL-fusion/Tet1/Hoxa/Meis1/Pbx3/Flt3 signaling axis in MLL-rearranged leukemia, and highlight TET1 as a potential therapeutic target in treating this presently therapy-resistant disease. We report genome-wide 5hmC enrichment profiles and RNA-Seq gene expression in MLL-AF9 transformed and control mouse bone marrow mononuclear cells. These 5hmC profiles are derived from selctive chemical labeling and enrichment of 5hmC containing genomic DNA fragments, while the RNA-Seq expression profiles are generated from polyA enriched RNA