Retrograde trafficking of Argonaute 2 acts as a rate-limiting step for de novo miRNP formation on endoplasmic reticulum-attached polysomes in mammalian cells.

Mainak Bose,Susanta Chatterjee,Bahnisikha Barman,Suvendra N Bhattacharyya,Yogaditya Chakrabarty

doi:10.26508/lsa.201800161

Mainak Bose, Susanta Chatterjee + Show 3 more

Open Access

https://doi.org/10.26508/lsa.201800161

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Abstract

microRNAs are short regulatory RNAs in metazoan cells. Regulation of miRNA activity and abundance is evident in human cells where availability of target messages can influence miRNA biogenesis by augmenting the Dicer1-dependent processing of precursors to mature microRNAs. Requirement of subcellular compartmentalization of Ago2, the key component of miRNA repression machineries, for the controlled biogenesis of miRNPs is reported here. The process predominantly happens on the polysomes attached with the endoplasmic reticulum for which the subcellular Ago2 trafficking is found to be essential. Mitochondrial tethering of endoplasmic reticulum and its interaction with endosomes controls Ago2 availability. In cells with depolarized mitochondria, miRNA biogenesis gets impaired, which results in lowering of de novo-formed mature miRNA levels and accumulation of miRNA-free Ago2 on endosomes that fails to interact with Dicer1 and to traffic back to endoplasmic reticulum for de novo miRNA loading. Thus, mitochondria by sensing the cellular context regulates Ago2 trafficking at the subcellular level, which acts as a rate-limiting step in miRNA biogenesis process in mammalian cells.

Highlights

Introduction miRNAs constitute an extensive class of small regulatory RNAs that are ~22 nucleotides long and control the expression of more than half of protein-coding genes in humans [1]. miRNAs are endogenously transcribed from their respective genes as pri-miRNAs that are processed inside the nucleus by the microprocessor (DroshaDGCR8) complex to generate a ~60–70-nt pre-miRNA [2, 3, 4]
Targetdriven miRNA biogenesis is ensured by increased processivity of the enzyme Dicer1 that in the presence of cognate mRNAs go through higher number of successful Ago-loading cycles for respective miRNAs
We have shown the importance of organelles in controlling the miRNP biogenesis process

Summary

Introduction

MiRNAs constitute an extensive class of small regulatory RNAs that are ~22 nucleotides long and control the expression of more than half of protein-coding genes in humans [1]. miRNAs are endogenously transcribed from their respective genes as pri-miRNAs that are processed inside the nucleus by the microprocessor (DroshaDGCR8) complex to generate a ~60–70-nt pre-miRNA [2, 3, 4]. MiRNAs are endogenously transcribed from their respective genes as pri-miRNAs that are processed inside the nucleus by the microprocessor (DroshaDGCR8) complex to generate a ~60–70-nt pre-miRNA [2, 3, 4]. Mature miRNAs form complex with effector Argonaute proteins to form miRNPs that usually bind to 39-UTRs of target mRNAs having imperfect complementarities to the respective miRNAs. Binding of miRNAs induces translation repression that is usually accompanied by exonucleolytic degradation of target messages [7]. Corresponding target mRNAs can act as a key player in regulating miRNA biogenesis and stability [9, 10, 11, 12, 13, 14]. It has been reported of late that a target mRNA induces increased activity of Ago-associated Dicer to enhance biogenesis of their cognate miRNAs [15]. Information on the exact subcellular sites of target-driven biogenesis and its regulation has remained unidentified

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