SREBPs in Regulation of Lipid Metabolism

描述(申请人提供)：我们的研究计划集中在营养输入和代谢需求调节脂肪代谢基因的机制上。在哺乳动物中，有三个SREBPs是脂代谢基因的主要调节者。SREBP-1a和1c由单个基因的重叠mRNA编码，SREBP-2由不同的基因转录而成。SREBPs通过它们的bHLHLZ结构域以二聚体的形式与DMA结合，它们有可能相互同质和异质二聚。在这项建议中，我们通过结合细胞培养和动物模型来评估单个同源和异源二聚体在SREBP靶基因激活中的特定功能，以获得这些复杂转录因子调节脂质的多水平视角。在目标1中，我们设计了只同时表达两种不同SREBP亚型的转化细胞(每一种都在单独的调控诱导剂的控制下)，以检测单独的SREBP同源和异源二聚体在与靶基因结合和激活中的功能作用。在目标2中，我们不再人为地操纵单个SREBPs，而是专注于饮食波动和药物挑战对SREBP结合和靶基因激活的影响。在目标3中，我们结合了SREBPs人工操作和动物模型的优势，研究同时过度表达1a和1c的小鼠。这一点特别令人感兴趣，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活动(基于细胞培养研究)。这些研究具有非常重要的意义，原因有两个：1)了解单个SREBPs的功能将预测其表达的生理或药物变化如何改变动物的脂肪代谢；2)人类基因组只包含30,000个单独的基因，因此基因数量不足以解释单个人类令人难以置信的复杂性。从重叠的mRNA(如SREBP-1a和-1c)表达多个蛋白质和将蛋白质单体差异结合成具有独特功能特性(也是SREBPs的特性)的不同二聚体/复合体是显著提高基因组编码潜力的两种机制。因此，SREBP系统提供了一个明确的实验模型来评估导致基因组复杂性从DNA水平扩展到蛋白质水平的分子机制。

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.