title: The t(8;21) fusion product, AML-1-ETO, associates with C/EBP-alpha, inhibits C/EBP-alpha-dependent transcription, and blocks granulocytic differentiation.
abstract: AML-1B is a hematopoietic transcription factor that is functionally inactivated by multiple chromosomal translocations in human acute myeloblastic and B-cell lymphocytic leukemias. The t(8;21)(q22;q22) translocation replaces the C terminus, including the transactivation domain of AML-1B, with ETO, a nuclear protein of unknown function. We previously showed that AML-1-ETO is a dominant inhibitor of AML-1B-dependent transcriptional activation. Here we demonstrate that AML-1-ETO also inhibits C/EBP-alpha-dependent activation of the myeloid cell-specific, rat defensin NP-3 promoter. AML-1B bound the core enhancer motifs present in the NP-3 promoter and activated transcription approximately sixfold. Similarly, C/EBP-alpha bound NP-3 promoter sequences and activated transcription approximately sixfold. Coexpression of C/EBP-alpha with AML-1B or its family members, AML-2 and murine AML-3, synergistically activated the NP-3 promoter up to 60-fold. The t(8;21) product, AML-1-ETO, repressed AML-1B-dependent activation of NP-3 and completely inhibited C/EBP-alpha-dependent activity as well as the synergistic activation. In contrast, the inv(16) product, which indirectly targets AML family members by fusing their heterodimeric DNA binding partner, CBF-beta, to the myosin heavy chain, inhibited AML-1B but not C/EBP-alpha activation or the synergistic activation. AML-1-ETO and C/EBP-alpha were coimmunoprecipitated and thus physically interact in vivo. Deletion mutants demonstrated that the C terminus of ETO was required for AML-1-ETO-mediated repression of the synergistic activation but not for association with C/EBP-alpha. Finally, overexpression of AML-1-ETO in myeloid progenitor cells prevented granulocyte colony-stimulating factor-induced differentiation. Thus, AML-1-ETO may contribute to leukemogenesis by specifically inhibiting C/EBP-alpha- and AML-1B-dependent activation of myeloid promoters and blocking differentiation.
authors.affiliation: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors.forename: J J
authors.initials: JJ
authors.lastname: Westendorf
authors.forename: C M
authors.initials: CM
authors.lastname: Yamamoto
authors.forename: N
authors.initials: N
authors.lastname: Lenny
authors.forename: J R
authors.initials: JR
authors.lastname: Downing
authors.forename: M E
authors.initials: ME
authors.lastname: Selsted
authors.forename: S W
authors.initials: SW
authors.lastname: Hiebert
mesh_terms: D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D019556:COS Cells; D002454:Cell Differentiation / Q000235:genetics; D002891:Chromosomes, Human, Pair 21; D002898:Chromosomes, Human, Pair 8; D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D006098:Granulocytes / Q000166:cytology / Q000378:metabolism*; D006410:Hematopoiesis / Q000235:genetics; D006801:Humans; D007938:Leukemia / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics*; D015514:Oncogene Proteins, Fusion; D011401:Promoter Regions, Genetic / Q000235:genetics; D000075142:RUNX1 Translocation Partner 1 Protein; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D014178:Translocation, Genetic
chemical_list: C107844:AML1-ETO fusion protein, human; D022762:CCAAT-Enhancer-Binding Proteins; D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D015514:Oncogene Proteins, Fusion; D000075142:RUNX1 Translocation Partner 1 Protein; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors