3 LEVELS OF FUNCTIONAL INTERACTION DETERMINE THE ACTIVITY OF CCAAT/ENHANCER BINDING PROTEIN-ALPHA ON THE SERUM-ALBUMIN PROMOTER
3 LEVELS OF FUNCTIONAL INTERACTION DETERMINE THE ACTIVITY OF CCAAT/ENHANCER BINDING PROTEIN-ALPHA ON THE SERUM-ALBUMIN PROMOTER
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DOI：
10.1101/gad.8.3.350
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发表时间：
1994-02-01
影响因子：
10.5
通讯作者：
ZIFF, EB
中科院分区：
文献类型：
--
作者：
NERLOV, C;ZIFF, EB
我们研究了HepG 2肝癌细胞系中转录因子CCAAT/增强子结合蛋白α（C/EBP α）对血清白蛋白启动子的激活。我们发现，三种不同的机制决定了C/EBP α激活该启动子的能力，在细胞类型特异性和合作的方式。首先，C/EBP α的反式激活功能是通过该蛋白质的三个独立结构域之间的合作产生的，我们将其命名为反式激活元件（TE-I至TE-III）。TE本身几乎没有或没有激活转录的能力，但任何两个TE都可以在C/EBP α蛋白中以及当连接到GAL 4 DNA结合结构域时合作这样做。第二，TE-III被发现含有一个负调节亚结构域，当C/EBP α结合在白蛋白启动子的环境中时，其功能被减轻。这形成了C/EBP α协同激活该启动子的基础。最后，我们证明了C/EBP α的亮氨酸拉链参与确定白蛋白启动子激活的细胞类型特异性，因为它在非肝HeLa细胞系中对白蛋白启动子激活产生强烈的负面影响，但在HepG 2细胞中没有。这些发现揭示了C/EBP α的作用模式，并显示了亮氨酸拉链在细胞类型特异性基因表达中的新功能。
We have studied the activation of the serum albumin promoter by transcription factor CCAAT/enhancer binding protein a (C/EBP alpha) in the HepG2 hepatoma cell line. We find that three distinct mechanisms determine the ability of C/EBP alpha to activate this promoter in a cell-type-specific and cooperative manner. First, the trans-activating function of C/EBP alpha is generated through cooperation between three separate domains of the protein that we have named trans-activation elements (TE-I through TE-III). The TEs have little or no ability to activate transcription by themselves, but any two can cooperate to do so, both in the C/EBP alpha protein and when linked to the GAL4 DNA-binding domain. Second, TE-III was found to contain a negative regulatory subdomain, the function of which was alleviated when C/EBP alpha was bound in the environment of the albumin promoter. This formed the basis for cooperative activation of this promoter by C/EBP alpha. Finally, we demonstrate that the leucine zipper of C/EBP alpha participates in determining the cell type specificity of albumin promoter activation, as it exerts a strong negative effect on albumin promoter activation in the nonhepatic HeLa cell line but not in HepG2 cells. These findings shed new light on the mode of action of C/EBP alpha and show a novel function for a leucine zipper in cell-type-specific gene expression.