Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan; Department of Medical Genome Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Institute of Molecular and Cellular Biosciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-0032, Japan.
Mol Cell. 2014 Oct 2;56(1):67-78. doi: 10.1016/j.molcel.2014.09.004.
miRNAs silence their complementary target mRNAs by translational repression as well as by poly(A) shortening and mRNA decay. In Drosophila, miRNAs are typically incorporated into Argonaute1 (Ago1) to form the effector complex called RNA-induced silencing complex (RISC). Ago1-RISC associates with a scaffold protein GW182, which recruits additional silencing factors. We have previously shown that miRNAs repress translation initiation by blocking formation of the 48S and 80S ribosomal complexes. However, it remains unclear how ribosome recruitment is impeded. Here, we examined the assembly of translation initiation factors on the target mRNA under repression. We show that Ago1-RISC induces dissociation of eIF4A, a DEAD-box RNA helicase, from the target mRNA without affecting 5' cap recognition by eIF4E in a manner independent of GW182. In contrast, direct tethering of GW182 promotes dissociation of both eIF4E and eIF4A. We propose that miRNAs act to block the assembly of the eIF4F complex during translation initiation.
miRNAs 通过翻译抑制以及 poly(A) 缩短和 mRNA 降解来使它们的互补靶 mRNA 沉默。在果蝇中，miRNAs 通常被整合到 Argonaute1 (Ago1) 中，形成称为 RNA 诱导沉默复合物 (RISC) 的效应复合物。Ago1-RISC 与支架蛋白 GW182 结合，后者招募额外的沉默因子。我们之前已经表明，miRNAs 通过阻止 48S 和 80S 核糖体复合物的形成来抑制翻译起始。然而，核糖体募集如何受到阻碍仍不清楚。在这里，我们研究了在抑制下靶 mRNA 上翻译起始因子的组装。我们表明，Ago1-RISC 诱导 DEAD-box RNA 解旋酶 eIF4A 从靶 mRNA 上解离，而不影响 eIF4E 对 5' 帽的识别，这种方式不依赖于 GW182。相比之下，GW182 的直接连接促进了 eIF4E 和 eIF4A 的解离。我们提出，miRNAs 作用是在翻译起始时阻止 eIF4F 复合物的组装。
