Transcriptional activities of nuclear SREBP-1a,-1c, and-2 to different target promoters of lipogenic and cholesterogenic genes
Transcriptional activities of nuclear SREBP-1a,-1c, and-2 to different target promoters of lipogenic and cholesterogenic genes
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DOI：
10.1194/jlr.m100417-jlr200
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发表时间：
2002-08-01
影响因子：
6.5
通讯作者：
Yamada, N
中科院分区：
文献类型：
--
作者：
Amemiya-Kudo, M;Shimano, H;Yamada, N
对甾醇调节元件结合蛋白（SREBP）家族在体内作用的近期研究表明，SREBP - 2对胆固醇生成基因的表达更具特异性，而SREBP - 1则针对脂肪生成基因。为了确定这种差异调节所涉及的分子机制，在HepG2细胞中进行了荧光素酶报告基因检测，以比较核SREBP - 1a、- 1c和- 2对一系列含有甾醇调节元件（SRE）、类SRE或E - 盒序列的SREBP靶启动子的转录活性。结果首先表明，其启动子中含有经典SRE的胆固醇生成基因可被SREBP - 1a和SREBP - 2强烈且有效地激活，但不被SREBP - 1c激活。其次，含有E - 盒的报告基因被SREBP - 1a和- 1c激活的效率要低得多，尽管SREBP - 2能够与E - 盒结合，但它没有活性。第三，含有SRE变体（类SRE序列）的脂肪生成酶的启动子可被SREBP - 1a强烈激活，而被SREBP - 1c和- 2适度且同等程度地激活。最后，将核SREBPs的碱性螺旋 - 环 - 螺旋（bHLH）部分内独特的酪氨酸残基替换为精氨酸（在所有其他bHLH蛋白中发现的保守残基），会消除所有SREBPs对SRE的转录活性，相反，会导致SREBP - 1对E - 盒的活性显著增加，但SREBP - 2对E - 盒的活性没有增加。（《脂质研究杂志》）这些数据表明核SREBP - 1和- 2对不同靶DNA具有不同的特异性和亲和力，分别解释了SREBP - 1和- 2在体内对胆固醇生成酶和脂肪生成酶差异调节背后的部分机制。
Recent studies on the in vivo roles of the sterol regulatory element binding protein (SREBP) family indicate that SREBP-2 is more specific to cholesterogenic gene expression whereas SRFBP-1 targets lipogenic genes. To define the molecular mechanism involved in this differential regulation, luciferase-reporter gene assays were performed in HepG2 cells to compare the transactivities of nuclear SR-EBP-1a, -1c, and -2 on a battery of SR-EBP-target promoters containing sterol regulatory element (SRE), SRE-Iike, or E-box sequences. The results show first that cholesterogenic genes containing classic SREs in their promoters are strongly and efficiently activated by both SREBP-1a and SREBP-2, but not by SREBP-1c. Second, an E-box containing reporter gene is much less efficiently activated by SREBP-1a and -1c, and SREBP-2 was inactive in spite of its ability to bind to the E-box. Third, promoters of lipogenic enzymes containing variations of SRE (SRE-like sequences) are strongly activated by SREBP-1a, and only modestly and equally by both SREBP-1c and -2. Finally, substitution of the unique tyrosine residue within the basic helix-loop-helix (bHLH) portion of nuclear SREBPs with arginine, the conserved residue found in all other bHLH proteins, abolishes the transactivity of all SREBPs for SRE, and conversely results in markedly increased activity of SREBP-1 but not activity of SREBP-2 for E-boxes.(jlr) These data demonstrate the different specificity and affinity of nuclear SREBP-1 and -2 for different target DNAs, explaining a part of the mechanism behind the differential in vivo regulation of cholesterogenic and lipogenic enzymes by SREBP-1 and -2, respectively.