An oxygen-regulated switch in the protein synthesis machinery

Uniacke, James; Holterman, Chet E.; Lachance, Gabriel; Franovic, Aleksandra; Jacob, Mathieu D.; Fabian, Marc R.; Payette, Josianne; Holčı́k, Martin; Pause, Arnim; Lee, Stephen

doi:10.1038/nature11055

Cited by 275 publications

(398 citation statements)

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“…The specificity of eIF4E and 4EHP for their mRNA targets and their affinities for the cap are influenced by binding partners (2,26,28). Thus, we used the BioID assay (29) to identify the eIF4E and 4EHP interacting proteins.…”

Section: Resultsmentioning

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.

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110

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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: Resultsmentioning

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.

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110

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“…Elegant studies by the Maxwell group (13) and others (14) revealed that HIF-2α mRNA is absent in human kidney tubule epithelia but present in dysplastic foci of the nephron. In these incipient renal tumor cells, HIF-2α may function as an oncoprotein (15), collaborating with, or activating, multiple growth-promoting pathways including cancer stewards c-myc (16), ras (17), and EGFR (18,19). Silencing of HIF-2α suppresses tumorigenesis of various genetically diverse cancers, further highlighting its central role in malignancy (16,17,20,21), although this depends on the experimental context (22).…”

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confidence: 99%

DNMT3a epigenetic program regulates the HIF-2α oxygen-sensing pathway and the cellular response to hypoxia

Lachance

Uniacke

Audas

et al. 2014

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

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Epigenetic regulation of gene expression by DNA methylation plays a central role in the maintenance of cellular homeostasis. Here we present evidence implicating the DNA methylation program in the regulation of hypoxia-inducible factor (HIF) oxygensensing machinery and hypoxic cell metabolism. We show that DNA methyltransferase 3a (DNMT3a) methylates and silences the HIF-2α gene (EPAS1) in differentiated cells. Epigenetic silencing of EPAS1 prevents activation of the HIF-2α gene program associated with hypoxic cell growth, thereby limiting the proliferative capacity of adult cells under low oxygen tension. Naturally occurring defects in DNMT3a, observed in primary tumors and malignant cells, cause the unscheduled activation of EPAS1 in early dysplastic foci. This enables incipient cancer cells to exploit the HIF-2α pathway in the hypoxic tumor microenvironment necessary for the formation of cellular masses larger than the oxygen diffusion limit. Reintroduction of DNMT3a in DNMT3a-defective cells restores EPAS1 epigenetic silencing, prevents hypoxic cell growth, and suppresses tumorigenesis. These data support a tumor-suppressive role for DNMT3a as an epigenetic regulator of the HIF-2α oxygensensing pathway and the cellular response to hypoxia.

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“…Testing interactions with components of this complex revealed that neither HIF-2α nor RBM4 interact with eIF4E or eIF4G, but they do interact with eIF4A and the eIF4E isoform 4E2, suggesting that the HIF-2α/RBM4 complex binds to an alternative capbinding assembly. eIF4E2, also known as 4E-homologous protein (4EHP) [6], does not interact with eIF4G and binds only weakly to 4EBP1, a factor that binds and inhibits eIF4E under hypoxia [2,[7][8][9]. The low affinity of eIF4E2 for 4EBP1 explains its resistance to inactivation in this metabolic condition.…”

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confidence: 99%

“…Cell function under hypoxia, however, is maintained by a significant degree of "residual" translation. In a recent article in Nature, Lee and colleagues show that the eIF4E homologue 4E2, in complex with the transcription factor HIF-2α and the RNA-binding protein RBM4, sustains cap-dependent translation during hypoxia [2]. Thus, by using a specialized isoform of eIF4E in complex with a hypoxia-induced RNP, the translational machinery preserves selective protein synthesis during stress ( Figure 1).…”

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confidence: 99%

“…During hypoxia, however, eIF4E is inactivated by 4EBP, increasing the chances that eIF4E2 binds the cap. Increased local concentration of eIF4E2 on specific targets promoted by interactions with RNA-binding proteins [2], or posttranslational modifications of eIF4E2 [11] may contribute to translational stimulation under particular conditions. Finally, interaction of eIF4E2 with specific initiation factor isoforms could also provide versatility in translational control.…”

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Versatility of the translational machinery during stress: changing partners to keep dancing

Gebauer

2012

Cell Res

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Cap-dependent translation is initiated by the binding of eIF4E to the cap structure at the 5′ end of mRNAs. During hypoxic stress, global translation decreases because eIF4E is inactivated. In a recent article in Nature, Lee and colleagues show that residual hypoxic translation is maintained by a specialized isoform of eIF4E, which binds to target mRNAs in complex with a hypoxia-induced RNP.Translation of most messenger RNAs in the cell is initiated by binding of eukaryotic initiation factor (eIF) 4E to the m 7 GpppN cap structure at the mRNA 5′ end. Multiple eIF4E isoforms have been described in a variety of organisms along the evolutionary scale, but their functions remain for the most part obscure [1]. Translation is drastically reduced upon low oxygen tension (hypoxia) by mechanisms that inhibit the function of eIF4E. Cell function under hypoxia, however, is maintained by a significant degree of "residual" translation. In a recent article in Nature, Lee and colleagues show that the eIF4E homologue 4E2, in complex with the transcription factor HIF-2α and the RNA-binding protein RBM4, sustains cap-dependent translation during hy-. Thus, by using a specialized isoform of eIF4E in complex with a hypoxia-induced RNP, the translational machinery preserves selective protein synthesis during stress (Figure 1).The hypoxia inducible factor (HIF) family of transcription factors maintain cellular oxygen homeostasis. HIF-2α is induced under hypoxia and activates the expression of epidermal growth factor receptor (EGFR), a factor that confers growth advantage to hypoxic tumor cells. Lee and colleagues first show that the accumulation of EGFR is independent of the transcriptional activity of HIF-2α. First, EGFR protein accumulates in cells treated with transcription inhibitors; second, no changes in the steady state amounts of EGFR mRNA are detected upon hypoxia; and third, depletion of HIF-1β, a factor required for HIF transcriptional activity, has no effect on EGFR expression. These results pointed to a surprising direct role of HIF-2α in EGFR mRNA translation, a notion reinforced by the finding that HIF-2α associates with polysomes.The authors further show that HIF-2α associates to a region of EGFR 3′ UTR that is necessary and sufficient to drive translation of reporters in a HIF-2α-dependent manner. HIF-2α does not contain discernible RNA-binding motifs, raising the possibility that RNA binding is mediated by interactions with bridge RNA-binding proteins. An unbiased search for HIF-2α interactors identified RBM4, a protein involved in translational control [3,4]. RBM4 interacts with the HIF-2α-responsive region of EGFR 3′ UTR, and its depletion results in dissociation of HIF-2α from EGFR mRNA, indicating that RBM4 recruits HIF-2α to the 3′ UTR of the EGFR transcript. Furthermore, depletion of RBM4 abrogates the hypoxic translation of endogenous EGFR or EGFR reporters without affecting the levels of HIF-2α. Thus, RBM4 mediates the effects of HIF-2α in hypoxic translation of EGFR mRNA.But the HIF-2α/RBM4 complex regulate...

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An oxygen-regulated switch in the protein synthesis machinery

Cited by 275 publications

References 31 publications

Cap-binding protein 4EHP effects translation silencing by microRNAs

Cap-binding protein 4EHP effects translation silencing by microRNAs

DNMT3a epigenetic program regulates the HIF-2α oxygen-sensing pathway and the cellular response to hypoxia

Versatility of the translational machinery during stress: changing partners to keep dancing

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