Physical and functional interactions between liver X receptor/retinoid X receptor and Sp1 modulate the transcriptional induction of the human ATP binding cassette transporter A1 gene by oxysterols and retinoids
Physical and functional interactions between liver X receptor/retinoid X receptor and Sp1 modulate the transcriptional induction of the human ATP binding cassette transporter A1 gene by oxysterols and retinoids
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DOI：
10.1021/bi700994m
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发表时间：
2007-10-16
期刊：
影响因子：
2.9
通讯作者：
Kardassis, Dimitris
中科院分区：
文献类型：
--
作者：
Thymiakou, Efstathia;Zannis, Vassilis I.;Kardassis, Dimitris
脂质转运体三磷酸腺苷结合盒转运体A1(ABCA1)促进细胞内磷脂和胆固醇向无脂载脂蛋白A-I的外流，从而启动高密度脂蛋白(HDL)的生物合成。ABCA1基因的表达受肝X受体/维甲酸X受体(LXR/RXR)异源二聚体及其配体氧固醇和维甲酸的调控，与其他高密度脂蛋白代谢基因协调。在本研究中，我们证明了氧固醇/维甲酸诱导的ABCA1基因的转录受无处不在的转录因子Sp1的调控，该转录因子与ABCA1启动子近端，邻近LXR/RXR反应元件。ABCA1基因对氧化甾醇/维甲酸的反应以及配体诱导的Sp1和RXRα/LXRα异源二聚体对ABCA1启动子的募集都被广为人知的Sp1抑制剂米曲霉素A所阻断。利用缺乏内源性Sp1的SL2细胞，我们证明了LXRα/RXRα异源二聚体及其配体激活ABCA1启动子需要Sp1。利用GAL4反式激活系统证明了这些因子之间的功能相互作用。通过体外和体内实验，我们发现Sp1和LXRα之间的物理相互作用需要LXRα的N-末端区域，它包括AF1和DNA结合域以及Sp1的两个不同的结构域：反式激活结构域B和DNA结合域。总体而言，本研究揭示了一种新的调节人类ABCA1转运蛋白的机制，涉及氧固醇/维甲酸诱导的激素核受体和转录因子Sp1之间的协同作用。
The lipid transporter ATP binding cassette transporter A1 (ABCA1) promotes the efflux of cellular phospholipids and cholesterol to lipid-free apolipoprotein A-I and thus initiates the biogenesis of high-density lipoprotein (HDL). The expression of the ABCAl gene is controlled, coordinately with other genes of HDL metabolism, by liver X receptor/retinoid X receptor (LXR/RXR) heterodimers and their ligands oxysterols and retinoids. In the present study, we show that the oxysterol/retinoid-induced transcription of the ABCAl gene is modulated by the ubiquitous transcription factor Sp1 that binds to the proximal ABCA1 promoter, adjacently to the LXR/RXR responsive element. The response of the ABCA1 gene to oxysterols/retinoids as well as the ligand-inducible recruitment of Sp1 and RXR alpha/LXR alpha heterodimers to the ABCA1 promoter was blocked by mithramycin A, a well-known Sp1 inhibitor. Using SL2 cells which lack endogenous Sp1, we showed that activation of the ABCAl promoter by LXR alpha/RXR alpha heterodimers and their ligands requires Sp1. Functional interactions between these factors were demonstrated using the GAL4 transactivation system. Using both in vitro and in vivo assays, we show that physical interactions between Sp1 and LXR alpha require the N-terminal region of LXR alpha, which includes the AF1 and DNA binding domains and two different domains of Sp1: the transactivation domain B and the DNA binding domain. Overall, the present study revealed a novel mechanism of regulation of the human ABCA1 transporter which involves synergistic interactions between oxysterol/retinoid-inducible hormone nuclear receptors and the transcription factor Sp1.