Daxx Is a Transcriptional Repressor of CCAAT/Enhancer-binding Protein β
Daxx Is a Transcriptional Repressor of CCAAT/Enhancer-binding Protein β
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DOI：
10.1074/jbc.m109.041186
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发表时间：
2009-10-16
影响因子：
4.8
通讯作者：
Klempnauer, Karl-Heinz
中科院分区：
文献类型：
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作者：
Wethkamp, Nils;Klempnauer, Karl-Heinz
CCAAT/增强子结合蛋白β (C/EBP β)是bZIP转录因子家族的一员，在包括造血系统细胞在内的多种组织中表达。C/EBP β参与组织特异性基因表达，从而参与增殖和分化等基本细胞过程。在这里，我们发现C/EBP β的活性受到转录共抑制因子Daxx的负调控。发现C/EBP β在过表达后和内源性水平上与Daxx直接相互作用。谷胱甘肽s -转移酶下拉实验表明，Daxx通过氨基酸190-400结合到C/EBP β的C端。C/EBP β的共表达改变了亚核Daxx分布模式，从主要定位于pod到核质。Daxx抑制基础和p300增强的C/EBP β转录活性。此外，Daxx降低了C/EBP β依赖的p300磷酸化，这反过来又与p300介导的C/EBP β乙酰化水平降低有关。早幼粒细胞白血病蛋白的共表达消除了Daxx对C/EBP β的抑制作用以及Daxx与C/EBP β的直接相互作用，可能是通过将Daxx重新招募到pml致癌结构域。在急性早幼粒细胞白血病（APL）细胞中，已知C/EBP β活性是全反式维甲酸诱导的细胞分化和疾病缓解所必需的。我们发现，全反式维甲酸和三氧化二砷处理导致与Daxx相关的C/EBP β分数降低，这表明Daxx依赖性C/EBP β抑制的缓解是导致APL细胞分化的重要分子事件。总的来说，我们的数据确定Daxx是一种新的C/EBP β负调节因子，并为消除Daxx-C/EBP β复合物形成与APL缓解之间的联系提供了第一个线索。
CCAAT/enhancer-binding Protein beta (C/EBP beta) is a member of the bZIP transcription factor family that is expressed in various tissues, including cells of the hematopoietic system. C/EBP beta is involved in tissue-specific gene expression and thereby takes part in fundamental cellular processes such as proliferation and differentiation. Here, we show that the activity of C/EBP beta is negatively regulated by the transcriptional co-repressor Daxx. C/EBP beta was found to directly interact with Daxx after overexpression as well as on the endogenous level. Glutathione S-transferase pulldown assays showed that Daxx binds via amino acids 190-400 to the C-terminal part of C/EBP beta. Coexpression of C/EBP beta changed the sub-nuclear Daxx distribution pattern from predominantly POD-localized to nucleoplasmic. Daxx suppressed basal and p300-enhanced transcriptional activity of C/EBP beta. Furthermore, Daxx decreased the C/EBP beta dependent phosphorylation of p300, which in turn was associated with a diminished level of p300-mediated C/EBP beta acetylation. Co-expression of promyelocytic leukemia protein abrogated the repressive effect of Daxx on C/EBP beta as well as the direct interaction of Daxx and C/EBP beta, presumably by re-recruiting Daxx to PML-oncogenic domains. In acute promyelocytic leukemia (APL) cells, C/EBP beta activity is known to be required for all-trans-retinoic acid-induced cell differentiation and disease remission. We show that all-trans-retinoic acid as well as arsenic trioxide treatment leads to a reduced C/EBP beta fraction associated with Daxx suggesting a relief of Daxx-dependent C/EBP beta repression as an important molecular event leading to APL cell differentiation. Overall, our data identify Daxx as a new negative regulator of C/EBP beta and provide first clues for a link between abrogation of Daxx-C/EBP beta complex formation and APL remission.