NMDAR-dependent Argonaute 2 phosphorylation regulates miRNA activity and dendritic spine plasticity.

Dipen Rajgor,Mascia Amici,Thomas M Sanderson,Jonathan G Hanley,Graham L Collingridge

doi:10.15252/embj.201797943

Abstract

MicroRNAs (miRNAs) repress translation of target mRNAs by associating with Argonaute (Ago) proteins to form the RNA‐induced silencing complex (RISC), underpinning a powerful mechanism for fine‐tuning protein expression. Specific miRNAs are required for NMDA receptor (NMDAR)‐dependent synaptic plasticity by modulating the translation of proteins involved in dendritic spine morphogenesis or synaptic transmission. However, it is unknown how NMDAR stimulation stimulates RISC activity to rapidly repress translation of synaptic proteins. We show that NMDAR stimulation transiently increases Akt‐dependent phosphorylation of Ago2 at S387, which causes an increase in binding to GW182 and a rapid increase in translational repression of LIMK1 via miR‐134. Furthermore, NMDAR‐dependent down‐regulation of endogenous LIMK1 translation in dendrites and dendritic spine shrinkage requires phospho‐regulation of Ago2 at S387. AMPAR trafficking and hippocampal LTD do not involve S387 phosphorylation, defining this mechanism as a specific pathway for structural plasticity. This work defines a novel mechanism for the rapid transduction of NMDAR stimulation into miRNA‐mediated translational repression to control dendritic spine morphology.

Highlights

MicroRNAs are small non-coding endogenous RNA molecules that repress the translation of target mRNAs through complementary binding in the transcript 30-untranslated region (30UTR), a process that has emerged in the past decade as being fundamentally important for fine-tuning protein synthesis in a wide range of cellular processes
To investigate the regulation of RNA-induced silencing complex (RISC) in response to NMDA receptor (NMDAR) stimulation, we focussed on the interaction between Ago2 and GW182, because this interaction is a critical regulator of RISC function (Pfaff & Meister, 2013; Jonas & Izaurralde, 2015)
We analysed the association of Ago2 with the RNA helicase DDX6, which associates with Ago2 via GW182, and MOV10, which is recruited to RISC by an unknown mechanism (Meister et al, 2005; Chen et al, 2014)

Summary

Introduction

MicroRNAs (miRNAs) are small non-coding endogenous RNA molecules that repress the translation of target mRNAs through complementary binding in the transcript 30-untranslated region (30UTR), a process that has emerged in the past decade as being fundamentally important for fine-tuning protein synthesis in a wide range of cellular processes. A large proportion of neuronal miRNAs are enriched in dendrites, and several have been assigned roles in modulating the local translation of specific proteins involved in excitatory synaptic transmission or in regulating the actin cytoskeleton to control the morphology of dendritic spines, which house excitatory synapses (Lippi et al, 2011; Bicker et al, 2014; Hu et al, 2014, 2015; Gu et al, 2015). Long-term plasticity of dendritic spines is thought to be an important cellular mechanism for information storage in the brain and to play an essential role in learning and memory and the fine-tuning of neural circuitry during development (Kasai et al, 2010; Caroni et al, 2012)

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Conclusion