Biological Function of Iron Responsive Elements

说明(申请人提供)：铁是几乎所有生物体的必需但具有潜在毒性的营养物质。缺铁是人类最常见的营养缺乏症，根据年龄和性别的不同，2%到22%的美国人患有这种疾病。与此同时，过量的铁储存与神经紊乱和某些癌症有关。哺乳动物铁代谢受两种调节RNA结合蛋白--铁调节蛋白1(Irp1)和IRP2的调节。IRPS与多达七种不同的mRNA中的铁反应元件(IRE)结合，编码对维持铁的稳态或对缺铁的适应性反应所需的其他途径至关重要的蛋白质。这包括与铁的运输、使用和储存有关的蛋白质以及TCA循环酶线粒体乌头酸酶。显然，为了满足不同细胞类型的生理需求，IRP对含有IRE的mRNA进行了差异调节，但对于IRPS如何区分不同的mRNA却知之甚少。由于IRPS是铁代谢的关键调节因子，而含有IRE的mRNA编码的蛋白质表达失调会导致神经退行性变、铁超载等疾病，因此阐明含IRE的mRNA被选择性调控的机制是非常重要的。 我们的总体目标是了解铁代谢是如何通过含有IRE的信使核糖核酸的分级调节来控制的。我们证明了5‘非翻译区有一个IRE的mRNA受IRP的差异调控；我们提出了几个新的假说来解释这种分级调控，我们建议：1)确定线粒体乌头酸酶(Macon)5’IRE区的结构，以及IRP和特定的翻译因子以及侧翼序列在该区域的结构和/或热力学稳定性中的作用；2)确定特定的翻译因子、细胞蛋白质合成能力和单个IRP在选择性调控含IRE的mRNA的使用中的作用；3)阐明IRE及其侧翼序列在5‘非编码区含有功能强或弱IRE区的mRNA体内翻译的分级调控中的作用。我们的研究提供了一种从分子到细胞水平的综合方法，将：a)描述定义IRP调控谱宽度的机制；b)展示RNA调控元件之间的靶点多样性如何控制mRNA的命运；以及c)作为理解组合mRNA调控如何控制基本生物过程的范例。

DESCRIPTION (provided by applicant): Iron is an essential but potentially toxic nutrient for nearly all organisms. Iron deficiency is the most common human nutritional deficiency disease with 2 to 22% of Americans suffering from it depending on age and gender. At the same time excessive iron stores are associated with neurological disorders and certain cancers. Mammalian iron metabolism is modulated by two regulatory RNA binding proteins, iron regulatory protein 1 (IRP1) and IRP2. IRPs bind to iron responsive elements (IRE) in up to seven different mRNA encoding proteins critical for the maintenance of iron homeostasis or for other pathways needed during the adaptive response to iron deficiency. This includes proteins involved in the transport, use and storage of iron as well as the TCA cycle enzyme mitochondrial aconitase. It is clear that IRE-containing mRNA are differentially regulated by IRP in order to meet the physiological demands of various cell types yet relatively little is known as to how IRPs discriminate between different mRNA. Because IRPs are pivotal regulators of iron metabolism, and dysregulation of the expression of proteins encoded by IRE-containing mRNA contributes to neurodegenerative, iron overload and other diseases, it is important to elucidate the mechanisms through which IRE-containing mRNA are selectively regulated. Our overall goal is to understand how iron metabolism is controlled through the hierarchical regulation of IRE-containing mRNA. We demonstrate that mRNA with one IRE in their 5' untranslated region are differentially regulated by IRP; we propose several novel hypotheses to explain this hierarchical regulation and we propose to: 1) determine the structure of the 5' IRE region of mitochondrial aconitase (macon) mRNA and the role of IRP and specific translation factors as well as flanking sequences in the structure and/or thermodynamic stability of this region; 2) determine the role of specific translation factors, cellular protein synthetic capacity and individual IRP in the selective regulation of the use of IRE-containing mRNA; 3) elucidate the role of IRE and flanking sequences in the hierarchical regulation of the translation in vivo of mRNA containing functionally strong or weak IRE-regions in the 5' UTR. Our studies provide a comprehensive approach from the molecular to the cellular level that will: a) delineate the mechanisms that define the breadth of the IRP regulatory spectrum; b) demonstrate how target site diversity amongst RNA regulatory elements controls mRNA fate; and c) serve as a paradigm for understanding how combinatorial mRNA regulation controls fundamental biological processes.