Zdanowicz Agnieszka, Thermann Rolf, Kowalska Joanna, Jemielity Jacek, Duncan Kent, Preiss Thomas, Darzynkiewicz Edward, Hentze Matthias W
European Molecular Biology Laboratory, Meyerhofstrasse 1, Heidelberg 69117, Germany.
Mol Cell. 2009 Sep 24;35(6):881-8. doi: 10.1016/j.molcel.2009.09.009.
Understanding the molecular mechanism(s) of how miRNAs repress mRNA translation is a fundamental challenge in RNA biology. Here we use a validated cell-free system from Drosophila embryos to investigate how miR2 inhibits translation initiation. By screening a library of chemical m7GpppN cap structure analogs, we identified defined modifications of the triphosphate backbone that augment miRNA-mediated inhibition of translation initiation but are "neutral" toward general cap-dependent translation. Interestingly, these caps also augment inhibition by 4E-BP. Kinetic dissection of translational repression and miR2-induced deadenylation shows that both processes proceed largely independently, with establishment of the repressed state involving a slow step. Our data demonstrate a primary role for the m7GpppN cap structure in miRNA-mediated translational inhibition, implicate structural determinants outside the core eIF4E-binding region in this process, and suggest that miRNAs may target cap-dependent translation through a mechanism related to the 4E-BP class of translational regulators.
了解微小RNA（miRNA）抑制信使核糖核酸（mRNA）翻译的分子机制是RNA生物学中的一项基本挑战。在此，我们使用经过验证的果蝇胚胎无细胞系统来研究miR2如何抑制翻译起始。通过筛选化学m7GpppN帽结构类似物文库，我们确定了三磷酸骨架的特定修饰，这些修饰增强了miRNA介导的翻译起始抑制作用，但对一般的帽依赖性翻译“中性”。有趣的是，这些帽也增强了4E结合蛋白（4E-BP）的抑制作用。对翻译抑制和miR2诱导的去腺苷酸化的动力学分析表明，这两个过程在很大程度上是独立进行的，建立抑制状态涉及一个缓慢步骤。我们的数据证明了m7GpppN帽结构在miRNA介导的翻译抑制中的主要作用，表明在此过程中核心真核翻译起始因子4E（eIF4E）结合区域之外的结构决定因素，并表明miRNA可能通过与4E-BP类翻译调节因子相关的机制靶向帽依赖性翻译。
