Jia Longfei, Qian Shu-Bing
Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, United States.
Acc Chem Res. 2021 Dec 7;54(23):4272-4282. doi: 10.1021/acs.accounts.1c00541. Epub 2021 Nov 10.
Synthetic messenger RNA (mRNA), once delivered into cells, can be readily translated into proteins by ribosomes, which do not distinguish exogenous mRNAs from endogenous transcripts. Until recently, the intrinsic instability and immunostimulatory property of exogenous RNAs largely hindered the therapeutic application of synthetic mRNAs. Thanks to major technological innovations, such as introduction of chemically modified nucleosides, synthetic mRNAs have become programmable therapeutic reagents. Compared to DNA or protein-based therapeutic reagents, synthetic mRNAs bear several advantages: flexible design, easy optimization, low-cost preparation, and scalable synthesis. Therapeutic mRNAs are commonly designed to encode specific antigens to elicit organismal immune response to pathogens like viruses, express functional proteins to replace defective ones inside cells, or introduce novel enzymes to achieve unique functions like genome editing. Recent years have witnessed stunning progress on the development of mRNA vaccines against SARS-Cov2. This success is built upon our fundamental understanding of mRNA metabolism and translational control, a knowledge accumulated during the past several decades. Given the astronomical number of sequence combinations of four nucleotides, sequence-dependent control of mRNA translation remains incompletely understood. Rational design of synthetic mRNAs with robust translation and optimal stability remains challenging. Massively paralleled reporter assay (MPRA) has been proven to be powerful in identifying sequence elements in controlling mRNA translatability and stability. Indeed, a completely randomized sequence in 5' untranslated region (5'UTR) drives a wide range of translational outputs. In this Account, we will discuss general principles of mRNA translation in eukaryotic cells and elucidate the role of coding and noncoding regions in the translational regulation. From the therapeutic perspective, we will highlight the unique features of 5' cap, 5'UTR, coding region (CDS), stop codon, 3'UTR, and poly(A) tail. By focusing on the design strategies in mRNA engineering, we hope this Account will contribute to the rational design of synthetic mRNAs with broad therapeutic potential.
合成信使核糖核酸（mRNA）一旦被递送至细胞内，即可被核糖体轻易地翻译成蛋白质，核糖体并不会区分外源性mRNA和内源性转录本。直到最近，外源性RNA固有的不稳定性和免疫刺激特性在很大程度上阻碍了合成mRNA的治疗应用。得益于重大技术创新，如化学修饰核苷的引入，合成mRNA已成为可编程的治疗试剂。与基于DNA或蛋白质的治疗试剂相比，合成mRNA具有多个优点：设计灵活、易于优化、制备成本低以及可规模化合成。治疗性mRNA通常被设计用于编码特定抗原，以引发机体对病毒等病原体的免疫反应；表达功能性蛋白质以替代细胞内有缺陷的蛋白质；或引入新型酶以实现诸如基因组编辑等独特功能。近年来，针对严重急性呼吸综合征冠状病毒2（SARS-CoV-2）的mRNA疫苗研发取得了惊人进展。这一成功建立在我们对mRNA代谢和翻译控制的基本理解之上，这是过去几十年积累的知识。鉴于四种核苷酸的序列组合数量庞大，mRNA翻译的序列依赖性控制仍未被完全理解。合理设计具有强大翻译能力和最佳稳定性的合成mRNA仍然具有挑战性。大规模平行报告基因检测（MPRA）已被证明在识别控制mRNA可翻译性和稳定性的序列元件方面很强大。事实上，5'非翻译区（5'UTR）中的完全随机序列会驱动广泛的翻译输出。在本综述中，我们将讨论真核细胞中mRNA翻译的一般原则，并阐明编码区和非编码区在翻译调控中的作用。从治疗角度来看，我们将重点介绍5'帽、5'UTR、编码区（CDS）终止密码子、3'UTR和聚腺苷酸（poly(A)）尾的独特特征。通过关注mRNA工程中的设计策略，我们希望本综述将有助于合理设计具有广泛治疗潜力的合成mRNA。
