Regulation of Mammalian mRNA Decay

项目摘要 mRNA稳定性的控制是真核生物转录后调控的关键因素， 基因表达。即使是mRNA稳定性的微小改变也会产生深远的影响， 表现为临床表型，如异常表达的原癌基因 会导致恶性肿瘤真核生物的mRNA通常被认为具有N7甲基， 鸟苷（m7G）帽在其5 ′端，以促进其稳定性和翻译。然而，我们最近 证明哺乳动物mRNAs也可以携带5 ′端烟酰胺腺嘌呤二核苷酸， (NAD)与m7G帽相反，m7G帽促进mRNA衰变，提供了一种新的mRNA 5 ′末端加工和核苷酸代谢物在mRNA周转中的贡献。我们现在 证明NAD的氧化还原状态也可以调节3 ′ RNA衰变与游离NAD功能 作为一种辅助因子来增强RNA衰变，并可能提供与细胞能量学的联系。此外，委员会认为， 黄素腺嘌呤二磷酸（FAD）也可以作为哺乳动物RNA上的5 ′帽， DXO水解酶作为蛋白质发挥功能，可在体外去除FAD帽（deFADding）。我们将 在三个具体目标下，在整个提案中以这些新的发现为基础。第一个将解决 游离NAD在体外控制3 ′端RNA衰变中的功能作用，并描述了其分子机制。 在其刺激腐烂的机制。第二个将推导出mRNA衰变的变化， 细胞中NAD水平改变的结果，并评估应激条件赋予的调节作用 通过控制NAD水平来调节RNA衰变。在最后一个目标中，我们将FAD上限设置为 一个替代的RNA帽，鉴定FAD加帽的RNA，并破译FAD帽的作用， 细胞中的去脂肪酶。总的来说，拟议的研究将提供一个迄今为止的洞察力。 未知的基本转录后调控机制，并将提供框架， 控制正常和疾病状态下基因表达的潜在新途径。

Project Summary The control of mRNA stability is a critical determinant in the post-transcriptional regulation of eukaryotic gene expression. Even minor alterations in mRNA stability can have profound consequences and may manifest as clinical phenotypes as illustrated by the ability of aberrantly expressed proto-oncogenes that can give rise to malignancies. Eukaryotic mRNAs are generally thought to possess an N7 methyl guanosine (m7G) cap at their 5¢ end to promote their stability and translation. However, our recent demonstration that mammalian mRNAs can also carry a 5´-end nicotinamide adenine dinucleotide (NAD) cap that in contrast to the m7G cap promotes mRNA decay, provides a new paradigm for mRNA 5´ end processing and the contribution of nucleotide metabolites in mRNA turnover. We now demonstrate that the redox state of NAD can also modulate 3´ RNA decay with free NAD functioning as a cofactor to enhance RNA decay and potentially providing a link to cellular energetics. Moreover, flavin adenine diphosphate (FAD) can also serve as a 5´ cap on mammalian RNAs with Nudt16 and DXO hydrolases functioning as proteins that can remove the FAD cap (deFADding) in vitro. We will build on these novel findings throughout this proposal within three specific aims. The first will address the functional role of free NAD on the control of 3´ end RNA decay in vitro and delineate the molecular mechanism involved in its stimulation of decay. The second will deduce changes in mRNA decay as a consequence of altered NAD levels in cells and assess the regulatory role imparted by stress conditions in modulating RNA decay through the control of NAD levels. In the last aim, we establish FAD cap as an alternative RNA cap, identify FAD-capped RNAs and decipher the role of FAD caps and the deFADding enzymes in cells. Collectively, the proposed studies will provide insight into a heretofore unknown fundamental post-transcriptional regulatory mechanism and will provide the framework for potential novel avenues to control gene expression in normal and disease states.