SREBPs in Regulation of Lipid Metabolism

项目描述（申请人提供）：我们的研究项目集中于营养输入和代谢需求调节脂质代谢基因的机制。在哺乳动物中，有三种SREBP是脂质代谢基因的主要调节因子。SREBP-1a和1c由来自单个基因的重叠mRNA编码，SREBP-2由不同基因转录。SREBP通过它们的bHLHLZ结构域结合DMA作为二聚体，并且它们具有彼此同源和异源二聚化的潜力。在这个建议中，我们评估的特定功能的个人同源和异源二聚体的SREBP靶基因的激活相结合的细胞培养和动物模型，以获得一个多层次的观点，这些复杂的转录因子的脂质调控。在目的1中，我们设计了同时表达两种不同SREBP同种型（每种都在单独的调节诱导物的控制下）的转化细胞，以检查单个SREBP同源和异源二聚体在结合和激活靶基因中的功能作用。在目标2中，我们不再对单个SREBP进行人工操作，而是专注于小鼠模型中饮食波动和药理学挑战对SREBP结合和靶基因激活的影响。在目标3中，我们联合收割机结合SREBP人工操作和动物模型的优势来研究同时过表达1a和1c的小鼠。这是特别感兴趣的，因为它将允许我们在动物模型中测试我们的假设，即1c减弱1a活性（基于细胞培养研究）。这些研究非常重要，原因有两个：1）了解单个SREBP的功能将预测其表达的生理或药理学变化如何改变动物的脂质代谢，2）人类基因组仅包含30，000个单独的基因，因此基因数量不足以解释个体人类令人难以置信的复杂性。从重叠mRNA（如SREBP-1a和-1c）表达多种蛋白质以及蛋白质单体差异结合成具有独特功能特性（也是SREBP的特性）的不同二聚体/复合物是显著增加基因组编码潜力的两种机制。因此，SREBP系统提供了一个定义明确的实验模型，以评估有助于从DNA到蛋白质水平的基因组复杂性扩展的分子机制。

DESCRIPTION (provided by applicant): Our research program is focused on mechanisms by which nutritional input and metabolic demand regulate genes of lipid metabolism. In mammals there are three SREBPs that are major regulators of genes in lipid metabolism. SREBP-1a and 1c are encoded by overlapping mRNAs from a single gene and SREBP-2 is transcribed from a distinct gene. SREBPs bind DMA as dimers through their bHLHLZ domains and they have the potential to homo and heterodimerize with one another. In this proposal, we evaluate the specific functions of the individual homo and heterodimers in activation of SREBP target genes by combining cell culture and animal models to obtain a multi-level perspective on lipid regulation by these complex transcription factors. In Aim 1 we engineer transformed cells that simultaneously express only two different SREBP isoforms (each under the control of a separate regulatory inducer) in order to examine the functional roles of the individual SREBP homo and heterodimers in binding to and activation of target genes. In Aim 2 we move away from artificial manipulation of the individual SREBPs and instead focus on the consequences of dietary fluctuation and pharmacologic challenge to SREBP binding and activation of target genes in a mouse model. In Aim 3 we combine the strengths of artificial manipulation of SREBPs and animal models to study mice that over-express both 1a and 1c simultaneously. This is of particular interest because it will allow us to test our hypothesis that 1c attenuates 1 a activity (based on cell culture studies) in an animal model. These studies are highly significant for two reasons: 1) understanding the function of the individual SREBPs will predict how physiologic or pharmacologic changes in their expression alter lipid metabolism in animals, 2) The human genome contains only 30,000 individual genes, so gene number is insufficient to account for the incredible complexity of an individual human being. Expression of multiple proteins from overlapping mRNAs (like SREBP-1a and -1c) and differential association of protein monomers into distinct dimers/complexes with unique functional properties (also a property of SREBPs) are two mechanisms that significantly increase genomic coding potential. Thus, the SREBP system provides a well-defined experimental model to evaluate molecular mechanisms that contribute to the expansion of genome complexity from the DNA to protein level.