RUNX1/EVI1, which blocks myeloid differentiation, inhibits CCAAT-enhancer binding protein alpha function.
The RUNX1/EVI1 chimeric transcription factor produced by t(3;21) causes leukemic transformation in hematopoietic stem cell tumors, possibly through a differentiation block of malignant myeloid progenitors. A dominant negative effect over wild-type RUNX1 has been shown to constitute one of the underlying molecular mechanisms. We introduced RUNX1/EVI1 cDNA into LG-3 cells that differentiate along the myeloid lineage upon exposure to granulocyte colony stimulating factor, and confirmed that RUNX1/EVI1 suppressed the differentiation. To further investigate the molecular mechanisms of RUNX1/EVI1-mediated differentiation block, we analyzed RUNX1/EVI1's effect on the functions of CCAAT-enhancer binding protein alpha (C/EBPalpha), a key transcriptional regulator that induces granulocytic differentiation. RUNX1/EVI1 was found to associate with C/EBPalpha. By using a reporter assay with the CEBPA promoter, we observed a dominant negative effect of RUNX1/EVI1 over C/EBPalpha-mediated transcriptional activation via the carboxyl terminal-binding protein (CtBP)-binding site in the EVI1 portion. In a gel-shift assay, RUNX1/EVI1 downregulated the DNA-binding activity of C/EBPalpha. Therefore, recruitment of histone deacetylase via CtBP and disruption of DNA binding could be likely scenarios for the RUNX1/EVI1-induced dominant repression on C/EBPalpha. Importantly, coexpression of C/EBPalpha restored the differentiation ability of the RUNX1/EVI1-expressing LG-3 cells. All of these data argue that inhibition of C/EBPalpha function may be causatively related to the leukemogenic potential of RUNX1/EVI1.
Tokita
Katsuya
K
Department of Hematology, Dokkyo Medical University School of Medicine, 880 Kitakobayashi, Mibu-machi, Shimotsuga-gun, Tochigi 321-0293, Japan.
Maki
Kazuhiro
K
Mitani
Kinuko
K
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000037:antagonists & inhibitors / Q000502:physiology*; D019556:COS Cells; D002454:Cell Differentiation; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D002522:Chlorocebus aethiops; D002891:Chromosomes, Human, Pair 21; D002893:Chromosomes, Human, Pair 3; D050676:Core Binding Factor Alpha 2 Subunit / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000502:physiology*; D016179:Granulocyte Colony-Stimulating Factor / Q000235:genetics; D006098:Granulocytes / Q000166:cytology / Q000502:physiology; D000882:Haplorhini; D006801:Humans; D007938:Leukemia / Q000235:genetics*; D000074008:MDS1 and EVI1 Complex Locus Protein; D050506:Mutant Chimeric Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011519:Proto-Oncogenes / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014162:Transfection; D014178:Translocation, Genetic
D022763:CCAAT-Enhancer-Binding Protein-alpha; D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins; D000074008:MDS1 and EVI1 Complex Locus Protein; C063575:MECOM protein, human; D050506:Mutant Chimeric Proteins; D014157:Transcription Factors; D016179:Granulocyte Colony-Stimulating Factor