Zhang D E, Hetherington C J, Meyers S, Rhoades K L, Larson C J, Chen H M, Hiebert S W, Tenen D G
Department of Medicine, Beth Israel Hospital and Harvard Medical School, Boston, Massachusetts 02215, USA.
Mol Cell Biol. 1996 Mar;16(3):1231-40. doi: 10.1128/MCB.16.3.1231.
Transcription factors play a key role in the development and differentiation of specific lineages from multipotential progenitors. Identification of these regulators and determining the mechanism of how they activate their target genes are important for understanding normal development of monocytes and macrophages and the pathogenesis of a common form of adult acute leukemia, in which the differentiation of monocytic cells is blocked. Our previous work has shown that the monocyte-specific expression of the macrophage colony-stimulating factor (M-CSF) receptor is regulated by three transcription factors interacting with critical regions of the M-CSF receptor promoter, including PU.1 and AML1.PU.1 is essential for myeloid cell development, while the AML1 gene is involved in several common leukemia-related chromosome translocations, although its role in hematopoiesis has not been fully identified. Along with AML1, a third factor, Mono A, interacts with a small region of the promoter which can function as a monocyte-specific enhancer when multimerized and linked to a heterologous basal promoter. Here, we demonstrate by electrophoretic mobility shift assays with monocytic nuclear extracts, COS-7 cell-transfected factors, and specific antibodies that the monocyte-enriched factor Mono A is CCAAT enhancer-binding protein (C/EBP). C/EBP has been shown previously to be an important transcription factor involved in hepatocyte and adipocyte differentiation; in hematopoietic cells, C/EBP is specifically expressed in myeloid cells. In vitro binding analysis reveals a physical interaction between C/EBP and AML1. Further transfection studies show that C/EBP and AML1 in concert with the AML1 heterodimer partner CBF beta synergistically activate M-CSF receptor by more then 60 fold. These results demonstrate that C/EBP and AML1 are important factors for regulating a critical hematopoietic growth factor receptor, the M-CSF receptor, suggesting a mechanism of how the AML1 fusion protein could contribute to acute myeloid leukemia. Furthermore, they demonstrate physical and functional interactions between AML1 and C/EBP transcription factor family members.
转录因子在多能祖细胞向特定谱系的发育和分化过程中发挥着关键作用。鉴定这些调节因子并确定它们激活靶基因的机制，对于理解单核细胞和巨噬细胞的正常发育以及一种常见成人急性白血病的发病机制至关重要，在这种白血病中，单核细胞的分化受阻。我们之前的研究表明，巨噬细胞集落刺激因子（M-CSF）受体的单核细胞特异性表达受三种与M-CSF受体启动子关键区域相互作用的转录因子调控，包括PU.1和AML1。PU.1对髓系细胞发育至关重要，而AML1基因参与了几种常见的白血病相关染色体易位，尽管其在造血过程中的作用尚未完全明确。与AML1一起，第三个因子Mono A与启动子的一个小区域相互作用，当该区域多聚化并与异源基础启动子相连时，可作为单核细胞特异性增强子发挥作用。在此，我们通过使用单核细胞核提取物、COS-7细胞转染因子和特异性抗体进行的电泳迁移率变动分析证明，单核细胞富集因子Mono A是CCAAT增强子结合蛋白（C/EBP）。先前已表明C/EBP是参与肝细胞和脂肪细胞分化的重要转录因子；在造血细胞中，C/EBP在髓系细胞中特异性表达。体外结合分析揭示了C/EBP与AML1之间的物理相互作用。进一步的转染研究表明，C/EBP和AML1与AML1异二聚体伙伴CBFβ协同作用，可使M-CSF受体的活性增强60倍以上。这些结果表明，C/EBP和AML1是调节关键造血生长因子受体M-CSF受体的重要因子，提示了AML1融合蛋白可能导致急性髓系白血病的机制。此外，它们还证明了AML1与C/EBP转录因子家族成员之间的物理和功能相互作用。
