Petrovick M S, Hiebert S W, Friedman A D, Hetherington C J, Tenen D G, Zhang D E
Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA.
Mol Cell Biol. 1998 Jul;18(7):3915-25. doi: 10.1128/MCB.18.7.3915.
Control elements of many genes are regulated by multiple activators working in concert to confer the maximal level of expression, but the mechanism of such synergy is not completely understood. The promoter of the human macrophage colony-stimulating factor (M-CSF) receptor presents an excellent model with which we can study synergistic, tissue-specific activation for two reasons. First, myeloid-specific expression of the M-CSF receptor is regulated transcriptionally by three factors which are crucial for normal hematopoiesis: PU.1, AML1, and C/EBPalpha. Second, these proteins interact in such a way as to demonstrate at least two examples of synergistic activation. We have shown that AML1 and C/EBPalpha activate the M-CSF receptor promoter in a synergistic manner. As we report here, AML1 also synergizes, and interacts physically, with PU. 1. Detailed analysis of the physical and functional interaction of AML1 with PU.1 and C/EBPalpha has revealed that the proteins contact one another through their DNA-binding domains and that AML1 exhibits cooperative DNA binding with C/EBPalpha but not with PU.1. This difference in DNA-binding abilities may explain, in part, the differences observed in synergistic activation. Furthermore, the activation domains of all three factors are required for synergistic activation, and the region of AML1 required for synergy with PU.1 is distinct from that required for synergy with C/EBPalpha. These observations present the possibility that synergistic activation is mediated by secondary proteins contacted through the activation domains of AML1, C/EBPalpha, and PU.1.
许多基因的调控元件受多种激活因子协同作用来调控，以实现最高水平的表达，但这种协同作用的机制尚未完全明确。人类巨噬细胞集落刺激因子（M-CSF）受体的启动子是一个很好的模型，基于两个原因我们可以用它来研究协同的、组织特异性的激活作用。其一，M-CSF受体的髓系特异性表达受三个对正常造血至关重要的因子转录调控：PU.1、AML1和C/EBPα。其二，这些蛋白质相互作用，至少展示了两个协同激活的例子。我们已经表明，AML1和C/EBPα以协同方式激活M-CSF受体启动子。正如我们在此报道的，AML1也与PU.1协同作用并发生物理相互作用。对AML1与PU.1和C/EBPα的物理及功能相互作用的详细分析表明，这些蛋白质通过它们的DNA结合结构域相互接触，并且AML1与C/EBPα表现出协同DNA结合，但与PU.1没有。这种DNA结合能力的差异可能部分解释了在协同激活中观察到的差异。此外，所有三个因子的激活结构域对于协同激活都是必需的，并且AML1与PU.1协同所需的区域与AML1与C/EBPα协同所需的区域不同。这些观察结果表明，协同激活可能是由通过AML1、C/EBPα和PU.1的激活结构域接触的二级蛋白质介导的。
