Deletions on chromosome 9q are seen in a subset of acute myeloid leukemia (AML) cases and are specifically associated with t(8;21) AML. We previously defined the commonly deleted region in del(9q) AML and characterized the genes in this interval. To determine the critical lost gene(s) that might cooperate with the AML1-ETO fusion gene produced by t(8;21), we developed a set of shRNAs directed against each gene in this region. Within this library, shRNAs to TLE1 and TLE4 were the only shRNAs capable of rescuing AML1-ETO expressing U937T-A/E cells from AML1-ETO-induced cell-cycle arrest and apoptosis. Knockdown of TLE1 or TLE4 levels increased the rate of cell division of the AML1-ETO-expressing Kasumi-1 cell line, whereas forced expression of either TLE1 or TLE4 caused apoptosis and cell death. Knockdown of Gro3, a TLE homolog in zebrafish, cooperated with AML1-ETO to cause an accumulation of noncirculating hematopoietic blast cells.
IntroductionOne of the most common genetic aberrations in acute myeloid leukemia (AML) is the balanced chromosomal translocation t(8;21). This translocation, seen in 8% to 13% of de novo AML cases, 1-3 creates the RUNX1-MTG8/AML1-ETO fusion gene. AML1-ETO is insufficient for leukemogenesis as evidenced by mouse models, 4-7 the detection of fusion gene transcripts in AML patients in long-term remission, 8,9 as well as the finding of transcripts in newborns who did not develop t(8;21) AML for more than 10 years. 10 Although AML1-ETO expression promotes the maintenance of early hematopoietic precursors, 11,12 it markedly inhibits short-term expansion of primary human bone marrow cells and the proliferation of committed progenitors and CD34 ϩ cells. 13 This suggests a model in which secondary mutations are required to further transform preleukemic stem cells and allow their progeny to expand.Deletion of a portion of the long arm of chromosome 9, del(9q), is a recurring abnormality in malignant myeloid diseases reported in approximately 2% of AML cases and is nonrandomly associated with t(8;21). Approximately 36% to 50% of samples with del(9q) have t(8;21); conversely, 7% to 14% of pediatric AML samples with t(8;21) have del(9q). 1,[14][15][16] After numerical abnormalities, del(9q) is the single most common associated structural chromosomal abnormality seen with t(8;21) AML, indicating loss of function of a gene or genes on chromosome 9q may be one of the most important cooperating genes in t(8;21) AML.In a search for this cooperating gene(s), we recently narrowed the commonly deleted region (CDR) in 43 del(9q) AML samples to less than 2.4 Mb at 9q21.32-9q21.33. There are 10 known genes within, or immediately adjacent to, this region -TLE (transducin like enhancer of split)-1, FRMD3, UBQLN1, GKAP42, KIF27, HNRPK, SLC28A3, RMI1 (Q9H9A7), and NTRK2, and 3 novel or potential genes, RASEF, C9orf103 (ENSG00000148057), and C9orf64 (Q8N2B1). 17 Sequence analysis of the coding regions of these genes failed to identify clearly inactivating mutations in the remaining allele in del(9q) AML sampl...