Kim Eungseok, Yang Zhiming, Liu Ning-Chun, Chang Chawnshang
George Whipple Lab for Cancer Research, Department of Pathology, University of Rochester Medical Center, Rochester, NY 14642, USA.
Biochem Biophys Res Commun. 2005 Mar 4;328(1):85-90. doi: 10.1016/j.bbrc.2004.12.146.
While other plasma lipoproteins are exclusively expressed in liver and intestine, apoliprotein E (apoE) is ubiquitously synthesized in many tissues. To understand the molecular mechanism of non-tissue-specific apoE expression, we tested the testicular orphan receptor 4 (TR4) effect on apoE expression in different cell lines, such as HepG2, COS-1, and H1299 cells. Gel shift assay and 5' promoter activity analyses identified one distinct hormone response element (TR4RE-DR0-apoE at -303 to -292 bp) that binds to TR4 and results in full induction of apoE gene transcription. TR4 also forms a complex with Sp1 to synergistically induce apoE expression via a region containing the TR4RE-DR0-apoE and the Sp1 binding site (-169 to -140 bp). Induction of apoE expression by TR4 was also confirmed at the mRNA and protein levels in H1299 cells. Together, our data demonstrate that TR4 can enhance apoE gene expression via binding to TR4RE-DR0 in apoE 5' promoter and this TR4 binding is essential for synergistic interaction with another transcription factor, Sp1.
虽然其他血浆脂蛋白仅在肝脏和肠道中表达，但载脂蛋白E（apoE）在许多组织中广泛合成。为了解apoE非组织特异性表达的分子机制，我们检测了睾丸孤儿受体4（TR4）对不同细胞系（如HepG2、COS-1和H1299细胞）中apoE表达的影响。凝胶迁移试验和5'启动子活性分析确定了一个独特的激素反应元件（-303至-292 bp处的TR4RE-DR0-apoE），它与TR4结合并导致apoE基因转录的完全诱导。TR4还与Sp1形成复合物，通过一个包含TR4RE-DR0-apoE和Sp1结合位点（-169至-140 bp）的区域协同诱导apoE表达。在H1299细胞的mRNA和蛋白质水平上也证实了TR4对apoE表达的诱导作用。总之，我们的数据表明，TR4可以通过与apoE 5'启动子中的TR4RE-DR0结合来增强apoE基因表达，并且这种TR4结合对于与另一种转录因子Sp1的协同相互作用至关重要。
