TEL-AML1 regulation of survivin and apoptosis via miRNA-494 and miRNA-320a

Abstract

There is increasing evidence that miRNA and transcription factors interact in an instructive fashion in normal and malignant hematopoiesis. We explored the impact of TEL-AML1 (ETV6-RUNX1), the most common fusion protein in childhood leukemia, on miRNA expression and the leukemic phenotype. Using RNA interference, miRNA expression arrays, and quantitative polymerase chain reaction, we identified miRNA-494 and miRNA-320a to be up-regulated upon TEL-AML1 silencing independently of TEL expression. Chromatin immunoprecipitation analysis identified miRNA-494 as a direct miRNA target of the fusion protein TEL-AML1. Using bioinformatic analysis as well as functional luciferase experiments, we demonstrate that survivin is a target of the 2 miRNAs. miRNA-494 and miRNA-320a were introduced to the cells by transfection and survivin expression determined by Western blot analysis. These miRNAs blocked survivin expression and resulted in apoptosis in a similar manner as TEL-AML1 silencing by itself; this silencing was also shown to be Dicer-dependent. miRNAs-494 and -320a are expressed at lower levels in TEL-AML1؉ leukemias compared with immunophenotype-matched nonTEL-AML1 acute lymphoblastic leukemia subtypes, and within TEL-AML1؉ leukemias their expression is correlated to survivin levels. In summary our data suggest that TEL-AML1 might exert its antiapoptotic action at least in part by suppressing miRNA-494 and miRNA320a, lowering their expression causing enhanced survivin expression. IntroductionThe t(12;21) is the most frequent chromosomal lesion in childhood B-cell precursor acute lymphoblastic leukemia, occurring with an incidence of 25% overall and generating the TEL-AML1 fusion gene. 1 The t(12;21) translocation is present at birth in most children who contract the disease and thus represents presumably an initiating event in leukemogenesis in utero. [2][3][4] The encoded protein contains the 336 amino-terminal region of the TEL Ets protein, fused to the residues 21 to 480 of the tissue-specific transcription factor, AML1. TEL and AML1 are both transcription factors with an important role in hematopoiesis. The resulting fusion protein has the AML1 DNA binding domain and the TEL protein interaction domain and has been shown to maintain transcription factor properties and bind DNA. 5-7 TEL-AML1 has been shown to also interfere with apoptosis as its expression affects vigorous antiapoptotic genes, among these survivin. 8,9 Together with other chimeric proteins, TEL-AML1 may act as a dominant negative transcription factor that may reduce the expression of tumor suppressor and increase antiapoptotic genes. 10 In particular, the frequent inactivation of the AML1 transactivation functions in leukemias, for AML1-ETO and TEL-AML1 chimeric proteins, suggests that AML1 regulates one or more critical genes and miRNAs that when repressed, might promote the development of leukemias. 11 miRNAs are single-stranded RNA molecules approximately 21 to 23 nucleotides in length that have the ability to control gene expression; a single mi...

Correlation of miR-494 expression with tumor progression and patient survival in pancreatic cancer

“…Varied expression of miRNAs in normal tissues compared with cancerous tissues and the significant correlation between specific expression and prognosis imply that miRNAs are determinants of certain clinical outcomes (Lu et al, 2005;Volinia et al, 2006). miR-494 has been found to be downregulated in different types of cancer tissues and is a tumor suppressor, as it induced cell cycle arrest, cell senescence, and apoptosis and suppresses cell proliferation (Diakos et al 2010;Ohdaira et al 2012;Yamanaka et al 2012). Ohdaira et al found that miR-494 suppressed cell proliferation and induced senescence in A549 lung cancer cells (Ohdaira et al 2012).…”

“…A particular type of miRNA-miR-494-is downregulated in different types of cancer tissues. Moreover, it is a tumor suppressor and induces cell cycle arrest, cell senescence, and apoptosis, but suppresses cell proliferation (Diakos et al, 2010;Ohdaira et al, 2012;Yamanaka et al, 2012). Li et al found that downregulation of miR-494 via loss of SMAD4 increased FOXM1 and β-catenin signaling in pancreatic cancer cells.…”

Integration of High-Resolution Methylome and Transcriptome Analyses to Dissect Epigenomic Changes in Childhood Acute Lymphoblastic Leukemia

“…TEL-AML1), and the chimeric protein is assumed to act as regulation-resistant transcriptional repressor of RUNX1 target genes (33). However, recent studies investigating fusion protein-dependent genome-wide expression changes report gene repression and activation in similar amounts for proteincoding (34) and miRNA (35) genes.…”

MicroRNAs in acute leukemia: from biological players to clinical contributors

“…61,66 Interestingly, miR-494 and miR-320a were downregulated by the TEL-AML1 fusion protein derived from the t(12;21)/(p13;q22) translocation found in B25% of children with ALL (Table 1). 27 As both miRNAs were shown to target the anti-apoptosis protein survivin this may facilitate the survival and proliferation of TEL-AML1-positive ALL cells. 27 Also genomic deletions may dysregulate the expression of miRNAs.…”

“…27 As both miRNAs were shown to target the anti-apoptosis protein survivin this may facilitate the survival and proliferation of TEL-AML1-positive ALL cells. 27 Also genomic deletions may dysregulate the expression of miRNAs. The chromosome 13q14 deletion is responsible for the inactivation of miR-15/16-cluster in CLL patients 13 and a deletion of 7 Mb on chromosome 12 reduced the expression of miR-203 in murine T-cell leukemias/lymphomas.…”