NMDA receptor–dependent dephosphorylation of serine 387 in Argonaute 2 increases its degradation and affects dendritic spine density and maturation

Abstract

Argonaute (AGO) proteins are essential components of the microRNA (miRNA) pathway. AGO proteins are loaded with miRNAs to target mRNAs and thereby regulate mRNA stability and protein translation. As such, AGO proteins are important actors in controlling local protein synthesis, for instance, at dendritic spines and synapses. Although miRNA-mediated regulation of dendritic mRNAs has become a focus of intense interest over the past years, the mechanisms regulating neuronal AGO proteins remain largely unknown. Here, using rat hippocampal neurons, we report that dendritic Ago2 is down-regulated by the proteasome upon NMDA receptor activation. We found that Ser-387 in Ago2 is dephosphorylated upon NMDA treatment and that this dephosphorylation precedes Ago2 degradation. Expressing Ser-387 phosphorylation-deficient or phosphomimetic Ago2 in neurons, we observed that this phosphorylation site is involved in modulating dendritic spine morphology and postsynaptic density protein 95 (PSD-95) expression in spines. Collectively, our results point toward a signaling pathway linking NMDA receptor-dependent Ago2 dephosphorylation and turnover to postsynaptic structural changes. They support a model in which NMDA receptor-mediated dephosphorylation of Ago2 and Ago2 turnover contributes to the de-repression of mRNAs involved in spine growth and maturation.

E-cadherin Interacts With Posttranslationally-Modified AGO2 to Enhance miRISC Activity

“…EGFR interacts with AGO2 under hypoxia leading to elevated Y393 phosphorylation and inhibit miRNA biogenesis ( Shen et al, 2013 ). Having observed the accumulated AGO2 in E-cadherin-expressing cells, we proposed that E-cadherin interacts with phosphorylated AGO2, even though the shift caused by phosphorylation itself may not result in such an obvious molecular weight change, which was also observed by Nicolas et al demonstrating a ∼30 kDa increase of AGO2 protein ( Paradis-Isler and Boehm, 2018 ). Thus, we used anti-phosphoserine antibody and observed phosphoserine signal at the same molecular weight of E-cadherin-interacting AGO2 ( Figure 2B ).…”

“…Phosphorylation at S387 by AKT pathway alters AGO2 cellular localization and promotes miRISC activity ( Bridge et al, 2017 ). The ERK-mediated S387 phosphorylation enhances AGO2 protein stability in neuron cells ( Paradis-Isler and Boehm, 2018 ) and prevents AGO2 secretion into exosome ( McKenzie et al, 2016 ). In addition, multi-site phosphorylation (S824-S834) by CSNK1A1 is necessary for efficient silencing of endogenous miRNA targets and fully efficient miRNA-mediated silencing ( Golden et al, 2017 ).…”

AGO2 localizes to cytokinetic protrusions in a p38-dependent manner and is needed for accurate cell division

“…Human cellular protrusions are known to be involved in intercellular trafficking of cytoplasmic or genetic material 35 , 36 , pathogen transmission 37 , 38 , mitochondria, calcium, and other cargoes transportation 35 , 39 , and miRNA and protein communication 40 . In dendritic spines, AGO2 constitutes an important element for derepression of dendritic mRNAs and local protein synthesis triggered by synaptic activity, thus introducing the concept of spatio-temporal participation of AGO2 in local protein regulation 41 . Our findings support a similar AGO2-dictated local regulation in other cell types such as epithelial cells.…”

The Role of Dynamic miRISC During Neuronal Development

“…The increased interaction was mediated by S387 phosphorylation of AGO2 via the AKT pathway and was essential for NMDAR induced spine shrinkage. On the contrary, another study has reported that NMDAR activation leads to the dephosphorylation of AGO2 at S387 (Paradis-Isler and Boehm, 2018). This dephosphorylation was shown to induce degradation of AGO2 resulting in de-repression of miRNA mediated silencing and subsequent spine growth and maturation.…”