Kinetic analysis reveals successive steps leading to miRNA‐mediated silencing in mammalian cells

Béthune, Julien; Artus‐Revel, Caroline G; Filipowicz, Witold

doi:10.1038/embor.2012.82

Cited by 185 publications

(186 citation statements)

References 30 publications

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“…Several recent studies demonstrated translational repression as an early step of miRNA-mediated silencing, which is followed by mRNA deadenylation and decay (4,42,43). Multiple studies now have shown that miRNAs interfere with translation initiation, specifically with cap recognition by eIF4E (3)(4)(5), and may induce the dissociation of eIF4E and eIF4G from target mRNAs (44).…”

Section: Discussionmentioning

confidence: 99%

Cap-binding protein 4EHP effects translation silencing by microRNAs

Chapat

Jafarnejad

Matta‐Camacho

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

111

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MicroRNAs (miRNAs) play critical roles in a broad variety of biological processes by inhibiting translation initiation and by destabilizing target mRNAs. The CCR4-NOT complex effects miRNA-mediated silencing, at least in part through interactions with 4E-T (eIF4E transporter) protein, but the precise mechanism is unknown. Here we show that the cap-binding eIF4E-homologous protein 4EHP is an integral component of the miRNA-mediated silencing machinery. We demonstrate that the cap-binding activity of 4EHP contributes to the translational silencing by miRNAs through the CCR4-NOT complex. Our results show that 4EHP competes with eIF4E for binding to 4E-T, and this interaction increases the affinity of 4EHP for the cap. We propose a model wherein the 4E-T/4EHP interaction engenders a closed-loop mRNA conformation that blocks translational initiation of miRNA targets.M icroRNAs (miRNAs) are short, ∼22-nucleotide noncoding RNAs that affect gene expression in most eukaryotes. miRNAs mediate posttranscriptional silencing by guiding the miRNA-induced silencing complex (miRISC), an assembly of Argonautes and GW182/TNRC6 proteins, to target mRNAs. Target recognition initiates a succession of events: mRNA translational repression, deadenylation, and mRNA decay (1). miRNAs impair the function of eIF4F, a three-subunit complex composed of eIF4E, the m 7 GTP (cap)-interacting factor; eIF4G, a scaffolding protein; and eIF4A, a DEAD-box RNA helicase (2-5). The silencing activity of miRISC is mediated by the CCR4-NOT deadenylase complex through the scaffolding subunit, CNOT1 (6-8). CNOT1 recruits the DDX6 and 4E-T (eIF4E transporter, also known as EIF4ENIF1) proteins, which are important for miRNA-mediated silencing (9-16). The 4E-T protein is a conserved eIF4E-binding protein, which directly binds to the dorsal surface of eIF4E through its canonical eIF4E-binding YX 4 LL (Y 30 TKEELL) motif and impairs the eIF4E/eIF4G interaction and translation initiation (17). The 4E-T protein also facilitates the decay of CCR4-NOT-targeted mRNAs by linking the 3′-terminal mRNA decay machinery to the cap via its interaction with eIF4E (13).In mammals, eIF4E is the best-studied member of a family of proteins composed of eIF4E (eIF4E1), 4EHP (4E-homologous protein; eIF4E2), and eIF4E3. The 4EHP and eIF4E proteins share 28% sequence identity (18,19). The 4EHP protein is ubiquitously expressed, and it is 5-10 times less abundant than eIF4E in a number of mammalian cell lines (18)(19)(20). Like eIF4E, 4EHP binds to 4E-T, but in sharp contrast to eIF4E, it does not associate with eIF4G (18, 21). The 4EHP protein has a 30-to 100-fold weaker affinity for the cap than eIF4E due to a twoamino acid substitution in its cap-binding pocket (22).The 4EHP protein has primarily been documented as a translation repressor. In the Drosophila embryo, 4EHP associates with the RNA binding protein Bicoid to repress caudal mRNA translation (23). Similarly, 4EHP also represses the hunchback mRNA by binding to the nanos repressive element complex, which consists of nanos...

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Section: Discussionmentioning

confidence: 99%

Cap-binding protein 4EHP effects translation silencing by microRNAs

Chapat

Jafarnejad

Matta‐Camacho

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

111

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“…There is now accumulating evidence that translational repression of miRNA targets is the primary event in the mechanism; several groups have demonstrated that repression can be seen without the necessity for mRNA degradation. [58][59][60][61][62][63][64][65] In vitro studies showed that miRNA-mediated repression is a two-step process, the first of which affects translation of the target mRNA. 59,66 These were followed by a series of reports that employed temporal studies to demonstrate that translational repression of miRNA targets precedes deadenylation and degradation in Drosophila, zebrafish and mammalian cells.…”

Section: Steps To Repressionmentioning

confidence: 99%

The complexity of miRNA-mediated repression

2014

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Since their discovery 20 years ago, miRNAs have attracted much attention from all areas of biology. These short (B22 nt) non-coding RNA molecules are highly conserved in evolution and are present in nearly all eukaryotes. They have critical roles in virtually every cellular process, particularly determination of cell fate in development and regulation of the cell cycle. Although it has long been known that miRNAs bind to mRNAs to trigger translational repression and degradation, there had been much debate regarding their precise mode of action. It is now believed that translational control is the primary event, only later followed by mRNA destabilisation. This review will discuss the most recent advances in our understanding of the molecular underpinnings of miRNA-mediated repression. Moreover, we highlight the multitude of regulatory mechanisms that modulate miRNA function.

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“…While miRNA guides are typically complementary with their target along the seed sequence (nt 2-8) they base pair imperfectly along the remainder of the guide sequence [68]. As a result, miRISCs remain engaged with their target strands and induce silencing by translational repression and/or target deadenylation/destabilization mechanisms [69][70][71] (Box 2); however, the relative contributions of these non-slicing mechanisms remains hotly debated [72][73][74][75]. In addition to guide RNA considerations, different Ago subfamily members also serve as molecular determinants for silencing output.…”

Section: Rnai Effector Machinerymentioning

confidence: 99%

“…Once bound, Ago (purple) recruits GW182 (teal), which mediates interactions with additional silencing machinery. The interaction of GW182 with PABP (fuchsia) is believed to interfere with PABP stimulation of translation initiation [73][74][75]. Alternatively, as a result of PABP displacement, mRNA is made more sensitive to deadenylation, leading to destabilization [72].…”

Section: Overview Of Effector Step Mechanismsmentioning

confidence: 99%

From guide to target: molecular insights into eukaryotic RNA-interference machinery

Ipsaro

Joshua‐Tor

2015

Nat Struct Mol Biol

210

144

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Since its relatively recent discovery, RNA interference (RNAi) has emerged as a potent, specific, and ubiquitous means of gene regulation. Through a number of pathways that are conserved from yeast to humans, small non-coding RNAs direct molecular machinery to silence gene expression. In this review, we focus on mechanisms and structures that govern RNA silencing in higher organisms. In addition to highlighting recent advances, parallels and differences between RNAi pathways are discussed. Together, the studies reviewed herein reveal the versatility and programmability of RNA-induced Silencing Complexes (RISCs) and emphasize the importance of both upstream biogenesis and downstream silencing factors. Discovery and Biological Perspectives of RNA interferenceRNAi was first described by Fire and Mello in the 1990s when, in an attempt to use antisense RNA to down-regulate gene expression, they observed that double-stranded RNA (dsRNA) was more potent than sense or anti-sense RNA alone [1]. This seminal work boasted robust and specific gene knock down in addition to coining the term "RNA interference" (RNAi). Shortly beforehand, the discovery of individual regulatory RNAs in C. elegans hinted that small, non-coding RNAs might be a pervasive means of gene regulation in higher organisms [2,3]. In the following decade, with the mechanistic insight of Fire and Mello's work in hand, this idea was confirmed and it is now accepted that wellover 1,000 small RNAs are encoded in the human genome that may regulate over 60% of our genes [4,5]. It also became apparent that several seemingly disconnected phenomena are variations of RNAi-type pathways including co-suppression in plants, DNA elimination in Tetrahymena, and quelling in Neurospora [6]. The prevalence of RNAi is impressive and its importance is underscored by the fact that RNAi dysfunction is associated with numerous diseases and disorders including neurological maladies, cancers, and infertility.Shortly after the initial description of RNAi phenomenology, a burst of genetic, biochemical, biophysical, and bioinformatic efforts laid a strong foundation for identifying the molecular pathways, players, and parameters that govern silencing via RNAi. Work from Reprints and permissions information is available online at http://www.nature.com/reprints/index.html. HHMI Author ManuscriptHHMI Author Manuscript HHMI Author Manuscript numerous groups defined the molecular apparatus of RNAi as RISC (RNA-induced Silencing Complex), a ribonucleoprotein complex minimally comprised of a small singlestranded RNA (~20-31 nucleotides) and an Argonaute protein which serves as the effector molecule (reviewed in [7]). In this configuration, the loaded "guide" RNA acts as a specificity determinant that directs Argonaute and any other associated machinery to the target. The guide-loaded Argonaute platform underlies every example in the expansive array of known RNAi pathways in eukaryotes regardless of the source of the guide (structured loci, transposons, viral, etc.), the machinery ...

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Kinetic analysis reveals successive steps leading to miRNA‐mediated silencing in mammalian cells

Cited by 185 publications

References 30 publications

Cap-binding protein 4EHP effects translation silencing by microRNAs

Cap-binding protein 4EHP effects translation silencing by microRNAs

The complexity of miRNA-mediated repression

From guide to target: molecular insights into eukaryotic RNA-interference machinery

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