Selective association of sterol regulatory element-binding protein isoforms with target promoters in vivo
Selective association of sterol regulatory element-binding protein isoforms with target promoters in vivo
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DOI：
10.1074/jbc.m404693200
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发表时间：
2004-09-03
影响因子：
4.8
通讯作者：
Osborne, TF
中科院分区：
文献类型：
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作者：
Bennett, MK;Toth, JI;Osborne, TF
固醇调节元件结合蛋白(SREBP)家族的所有三个成员的mRNAs都广泛表达，并且蛋白质高度相似。它们具有通过其bHLHLZ结构域进行异源和同源二聚的潜力，因此很难明确地研究除其他两个以外的每一个的作用。在目前的研究中，我们利用只表达一个功能SREBP的细胞系和染色质免疫沉淀技术来分析单个SREBP与三个特定靶基因的结合：羟甲基戊二酰辅酶A还原酶(Red)、脂肪酸合成酶(FAS)和角鲨烯合成酶(SQS)。我们的研究表明，SREBP-2与所有三个基因的启动子结合，并且与使用这些细胞的原始报告一致，所有三个mRNAs也被诱导。在只表达SREBP-1a的品系中，Red和Fas的mRNAs被诱导，而SQS没有被诱导。染色质免疫沉淀也表明SREBP-1a能有效地招募到Red和Fas启动子，但不能招募到SQS。这表明SREBP-2选择性地结合了SQS启动子，并足以解释在表达SREBP-1a的细胞中缺乏SQS mRNA诱导的原因。SREBP-1c蛋白从相应细胞的提取液中纯化后，尽管在DNA结合中完全活跃，但不能稳定地招募到任何SREBP靶启动子。这也足以解释为什么SREBP-1c的单一表达缺乏SREBP靶基因的诱导。我们还表明，虽然SREBP-1a和-2蛋白有效地与改变细胞染色质的转录共激活子相互作用，但SREBP-1c不能。综上所述，我们的数据支持一个模型，即在体内天然染色质中，SREBPs在特定位置识别的初始阶段需要进行染色质修饰。
The mRNAs for all three members of the sterol regulatory element-binding protein ( SREBP) family are widely expressed, and the proteins are highly similar. They have potential to both hetero- and homodimerize through their bHLHLZ domains, so it has been difficult to definitively study the role of each one apart from the other two. In the current study, we have utilized cell lines that express only one functional SREBP and the chromatin immunoprecipitation technique to analyze individual SREBP binding to three specific target genes: hydroxymethylglutaryl-CoA reductase ( Red), fatty acid synthase (FAS), and squalene synthase (SQS). Our studies show that SREBP-2 binds to promoters for all three genes, and in agreement with the original report using these cells, all three mRNAs are also induced. In the line expressing only SREBP-1a, mRNAs for Red and FAS are induced, but SQS is not. Chromatin immunoprecipitation also shows that SREBP-1a is recruited efficiently to Red and FAS promoters but not to SQS. This observation indicates SREBP-2 selectively binds the SQS promoter and is sufficient to explain the lack of SQS mRNA induction in the SREBP-1a-expressing cells. SREBP-1c protein was not stably recruited to any SREBP target promoter despite being fully active in DNA binding when purified from extracts of the corresponding cells. This is also sufficient to explain the lack of SREBP target gene induction by the singular expression of SREBP-1c. We also show that whereas SREBP-1a and -2 proteins interact efficiently with transcriptional co-activators that modify cellular chromatin, SREBP-1c does not. Taken together, our data support a model suggesting that chromatin modification is required during the initial stage of specific site recognition by SREBPs in native chromatin in vivo.