scholarly journals CReP mediates selective translation initiation at the endoplasmic reticulum

2020 ◽  
Vol 6 (23) ◽  
pp. eaba0745 ◽  
Author(s):  
Jonathan P. Kastan ◽  
Elena Y. Dobrikova ◽  
Jeffrey D. Bryant ◽  
Matthias Gromeier
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Stress Responses ◽  
Spatial Organization ◽  
Acute Stress ◽  
Cell Fractionation ◽  
Local Protein Synthesis ◽  
Eif2α Phosphorylation ◽  
Selective Translation

Eukaryotic protein synthesis control at multiple levels allows for dynamic, selective responses to diverse conditions, but spatial organization of translation initiation machinery as a regulatory principle has remained largely unexplored. Here we report on a role of constitutive repressor of eIF2α phosphorylation (CReP) in translation of poliovirus and the endoplasmic reticulum (ER)–resident chaperone binding immunoglobulin protein (BiP) at the ER. Functional, proximity-dependent labeling and cell fractionation studies revealed that CReP, through binding eIF2α, anchors translation initiation machinery at the ER and enables local protein synthesis in this compartment. This ER site was protected from the suppression of cytoplasmic protein synthesis by acute stress responses, e.g., phosphorylation of eIF2α(S51) or mTOR blockade. We propose that partitioning of translation initiation machinery at the ER enables cells to maintain active translation during stress conditions associated with global protein synthesis suppression.

scholarly journals Stress-Activated Protein Kinase Pathway Functions To Support Protein Synthesis and Translational Adaptation in Response to Environmental Stress in Fission Yeast

2005 ◽  
Vol 4 (11) ◽  
pp. 1785-1793 ◽  
Author(s):  
Isabelle Dunand-Sauthier ◽  
Carol A. Walker ◽  
Jana Narasimhan ◽  
Amanda K. Pearce ◽  
Ronald C. Wek ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Osmotic Stress ◽  
Environmental Stress ◽  
Fission Yeast ◽  
Translation Initiation ◽  
Mitogen Activated Protein Kinase ◽  
Wild Type ◽  
Eif2α Phosphorylation ◽  
Mitogen Activated Protein

ABSTRACT The stress-activated protein kinase (SAPK) pathway plays a central role in coordinating gene expression in response to diverse environmental stress stimuli. We examined the role of this pathway in the translational response to stress in Schizosaccharomyces pombe. Exposing wild-type cells to osmotic stress (KCl) resulted in a rapid but transient reduction in protein synthesis. Protein synthesis was further reduced in mutants disrupting the SAPK pathway, including the mitogen-activated protein kinase Wis1 or the mitogen-activated protein kinase Spc1/Sty1, suggesting a role for these stress response factors in this translational control. Further polysome analyses revealed a role for Spc1 in supporting translation initiation during osmotic stress, and additionally in facilitating translational adaptation. Exposure to oxidative stress (H2O2) resulted in a striking reduction in translation initiation in wild-type cells, which was further reduced in spc1 − cells. Reduced translation initiation correlated with phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) in wild-type cells. Disruption of Wis1 or Spc1 kinase or the downstream bZip transcription factors Atf1 and Pap1 resulted in a marked increase in eIF2α phosphorylation which was dependent on the eIF2α kinases Hri2 and Gcn2. These findings suggest a role for the SAPK pathway in supporting translation initiation and facilitating adaptation to environmental stress in part through reducing eIF2α phosphorylation in fission yeast.

scholarly journals ER-misfolded proteins become sequestered with mitochondria and impair mitochondrial function

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Adrián Cortés Sanchón ◽  
Harshitha Santhosh Kumar ◽  
Matilde Mantovani ◽  
Ivan Osinnii ◽  
José María Mateos ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Mitochondrial Dysfunction ◽  
Mitochondrial Function ◽  
Human Disease ◽  
Misfolded Proteins ◽  
Cell Fractionation ◽  
Pathological Features

AbstractProteostasis is a challenge for cellular organisms, as all known protein synthesis machineries are error-prone. Here we show by cell fractionation and microscopy studies that misfolded proteins formed in the endoplasmic reticulum can become associated with and partly transported into mitochondria, resulting in impaired mitochondrial function. Blocking the endoplasmic reticulum-mitochondria encounter structure (ERMES), but not the mitochondrial sorting and assembly machinery (SAM) or the mitochondrial surveillance pathway components Msp1 and Vms1, abrogated mitochondrial sequestration of ER-misfolded proteins. We term this mitochondria-associated proteostatic mechanism for ER-misfolded proteins ERAMS (ER-associated mitochondrial sequestration). We testify to the relevance of this pathway by using mutant α-1-antitrypsin as an example of a human disease-related misfolded ER protein, and we hypothesize that ERAMS plays a role in pathological features such as mitochondrial dysfunction.

scholarly journals PERK-dependent reciprocal crosstalk between ER and non-centrosomal microtubules coordinates ER architecture and cell shape

2021 ◽  
Author(s):  
Miguel Sánchez-Álvarez ◽  
Fidel Lolo ◽  
Heba Sailem ◽  
Patricia Pascual-Vargas ◽  
Giulio Fulgoni ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Epithelial Cells ◽  
Translation Initiation ◽  
Cell Shape ◽  
Acute Stress ◽  
Cell Morphogenesis ◽  
Unfolded Protein ◽  
Functional Relevance ◽  
The Unfolded Protein Response ◽  
Protein Response

ABSTRACTThe architecture of the endoplasmic reticulum (ER) is tightly controlled as a key determinant of its function. Its dynamics are linked to those of the cytoskeleton, but our understanding of how this coordination occurs and what its functional relevance is, is limited. We found the Unfolded Protein Response (UPR) transducer EIF2AK3/PERK is essential for acute stress-induced peripheral redistribution and remodeling of the ER, through eIF2a phosphorylation and translation initiation shutdown. PERK-mediated eIF2a phosphorylation can be bypassed by blocking ribosome activity; by depleting microtubule-anchoring ER proteins such as REEP4, p180/RRBP1 and Climp63/CKAP4; or by disrupting the microtubule cytoskeleton. Notably, specific disruption of non-centrosomal microtubules, but not centrosome depletion, relieved blockade of ER redistribution in PERK-deficient cells. Conversely, PERK deficiency stabilized non-centrosomal microtubules, promoting polarized protrusiveness in epithelial cells and neuroblasts. We propose that PERK coordinates ER architecture and homeostasis with cell morphogenesis by coupling ER remodeling and non-centrosomal MT dynamics.

scholarly journals Selective recruitment of endoplasmic reticulum-targeted and cytosolic mRNAs into membrane-associated stress granules

2021 ◽  
Author(s):  
Jessica R Child ◽  
Qiang Chen ◽  
David W Reid ◽  
Sujatha Jagannathan ◽  
Christopher V Nicchitta
Keyword(s):  
Endoplasmic Reticulum ◽  
Translation Initiation ◽  
Nuclear Export ◽  
Rna Binding ◽  
Rna Binding Proteins ◽  
Signal Sequence ◽  
Stress Granules ◽  
Cell Fractionation ◽  
Functional Link ◽  
Translational Inhibition

Stress granules (SGs) are membraneless organelles composed of mRNAs and RNA binding proteins which undergo assembly in response to stress-induced inactivation of translation initiation. The biochemical criteria for mRNA recruitment into SGs are largely unknown. In general, SG recruitment is limited to a subpopulation of a given mRNA species and RNA-seq analyses of purified SGs revealed that signal sequence-encoding (i.e. endoplasmic reticulum (ER)-targeted) transcripts are significantly under-represented, consistent with prior reports that ER-localized mRNAs are excluded from SGs. Using translational profiling, cell fractionation, and single molecule mRNA imaging, we examined SG biogenesis during the unfolded protein response (UPR) and report that UPR-elicited SG formation is gene selective. Combined immunofluorescence-smFISH studies demonstrated that UPR-induced mRNA granules co-localized with SG protein markers and were in close physical proximity to or directly associated with the ER membrane. mRNA recruitment into ER-associated SGs required stress-induced translational inhibition, though translational inhibition was not solely predictive of mRNA accumulation in SGs. SG formation in response to UPR activation or arsenite addition was blocked by the transcriptional inhibitors actinomycin D or triptolide, suggesting a functional link between gene transcriptional state and SG biogenesis. These data demonstrate that ER-targeted mRNAs can be recruited into SGs and identify the ER as a subcellular site of SG assembly. On the basis of the transcriptional inhibitor studies, we propose that newly transcribed mRNAs undergoing nuclear export during conditions of suppressed translation initiation are key substrates for SG biogenesis

scholarly journals Pharmacological brake-release of mRNA translation enhances cognitive memory

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Carmela Sidrauski ◽  
Diego Acosta-Alvear ◽  
Arkady Khoutorsky ◽  
Punitha Vedantham ◽  
Brian R Hearn ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Memory Consolidation ◽  
Cognitive Disorders ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Initiation Factor 2 ◽  
A Cell

Phosphorylation of the α-subunit of initiation factor 2 (eIF2) controls protein synthesis by a conserved mechanism. In metazoa, distinct stress conditions activate different eIF2α kinases (PERK, PKR, GCN2, and HRI) that converge on phosphorylating a unique serine in eIF2α. This collection of signaling pathways is termed the ‘integrated stress response’ (ISR). eIF2α phosphorylation diminishes protein synthesis, while allowing preferential translation of some mRNAs. Starting with a cell-based screen for inhibitors of PERK signaling, we identified a small molecule, named ISRIB, that potently (IC50 = 5 nM) reverses the effects of eIF2α phosphorylation. ISRIB reduces the viability of cells subjected to PERK-activation by chronic endoplasmic reticulum stress. eIF2α phosphorylation is implicated in memory consolidation. Remarkably, ISRIB-treated mice display significant enhancement in spatial and fear-associated learning. Thus, memory consolidation is inherently limited by the ISR, and ISRIB releases this brake. As such, ISRIB promises to contribute to our understanding and treatment of cognitive disorders.

scholarly journals Regulation of Protein Synthesis by Hypoxia via Activation of the Endoplasmic Reticulum Kinase PERK and Phosphorylation of the Translation Initiation Factor eIF2α

2002 ◽  
Vol 22 (21) ◽  
pp. 7405-7416 ◽  
Author(s):  
Constantinos Koumenis ◽  
Christine Naczki ◽  
Marianne Koritzinsky ◽  
Sally Rastani ◽  
Alan Diehl ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Prolonged Exposure ◽  
Response To Therapy ◽  
Dominant Negative ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Hypoxic Stress ◽  
Wild Type

ABSTRACT Hypoxia profoundly influences tumor development and response to therapy. While progress has been made in identifying individual gene products whose synthesis is altered under hypoxia, little is known about the mechanism by which hypoxia induces a global downregulation of protein synthesis. A critical step in the regulation of protein synthesis in response to stress is the phosphorylation of translation initiation factor eIF2α on Ser51, which leads to inhibition of new protein synthesis. Here we report that exposure of human diploid fibroblasts and transformed cells to hypoxia led to phosphorylation of eIF2α, a modification that was readily reversed upon reoxygenation. Expression of a transdominant, nonphosphorylatable mutant allele of eIF2α attenuated the repression of protein synthesis under hypoxia. The endoplasmic reticulum (ER)-resident eIF2α kinase PERK was hyperphosphorylated upon hypoxic stress, and overexpression of wild-type PERK increased the levels of hypoxia-induced phosphorylation of eIF2α. Cells stably expressing a dominant-negative PERK allele and mouse embryonic fibroblasts with a homozygous deletion of PERK exhibited attenuated phosphorylation of eIF2α and reduced inhibition of protein synthesis in response to hypoxia. PERK−/− mouse embryo fibroblasts failed to phosphorylate eIF2α and exhibited lower survival after prolonged exposure to hypoxia than did wild-type fibroblasts. These results indicate that adaptation of cells to hypoxic stress requires activation of PERK and phosphorylation of eIF2α and suggest that the mechanism of hypoxia-induced translational attenuation may be linked to ER stress and the unfolded-protein response.

scholarly journals Endurance exercise decreases protein synthesis and ER-mitochondria contacts in mouse skeletal muscle

2019 ◽  
Vol 127 (5) ◽  
pp. 1297-1306 ◽  
Author(s):  
Audrey Merle ◽  
Maxence Jollet ◽  
Florian A. Britto ◽  
Bénédicte Goustard ◽  
Nadia Bendridi ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Dna Damage ◽  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Energy Demand ◽  
Protein Translation ◽  
Strong Increase ◽  
Hindlimb Muscles

Exercise is important to maintain skeletal muscle mass through stimulation of protein synthesis, which is a major ATP-consuming process for cells. However, muscle cells have to face high energy demand during contraction. The present study aimed to investigate protein synthesis regulation during aerobic exercise in mouse hindlimb muscles. Male C57Bl/6J mice ran at 12 m/min for 45 min or at 12 m/min for the first 25 min followed by a progressive increase in velocity up to 20 m/min for the last 20 min. Animals were injected intraperitoneally with 40 nmol/g of body weight of puromycin and euthanized by cervical dislocation immediately after exercise cessation. Analysis of gastrocnemius, plantaris, quadriceps, soleus, and tibialis anterior muscles revealed a decrease in protein translation assessed by puromycin incorporation, without significant differences among muscles or running intensities. The reduction of protein synthesis was associated with a marked inhibition of mammalian target of rapamycin complex 1 (mTORC1)-dependent phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1, a mechanism consistent with reduced translation initiation. A slight activation of AMP-activated protein kinase consecutive to the running session was measured but did not correlate with mTORC1 inhibition. More importantly, exercise resulted in a strong upregulation of regulated in development and DNA damage 1 (REDD1) protein and gene expressions, whereas transcriptional regulation of other recognized exercise-induced genes ( IL-6, kruppel-like factor 15, and regulator of calcineurin 1) did not change. Consistently with the recently discovered role of REDD1 on mitochondria-associated membranes, we observed a decrease in mitochondria-endoplasmic reticulum interaction following exercise. Collectively, these data raise questions concerning the role of mitochondria-associated endoplasmic reticulum membrane disruption in the regulation of muscle proteostasis during exercise and, more generally, in cell adaptation to metabolic stress. NEW & NOTEWORTHY How muscles regulate protein synthesis to cope with the energy demand during contraction is poorly documented. Moreover, it is unknown whether protein translation is differentially affected among mouse hindlimb muscles under different physiological exercise modalities. We showed here that 45 min of running decreases puromycin incorporation similarly in 5 different mouse muscles. This decrease was associated with a strong increase in regulated in development and DNA damage 1 protein expression and a significant disruption of the mitochondria and sarcoplasmic reticulum interaction.

scholarly journals Molecular Pathways of Protein Synthesis Inhibition during Brain Reperfusion: Implications for Neuronal Survival or Death

2002 ◽  
Vol 22 (2) ◽  
pp. 127-141 ◽  
Author(s):  
Donald J. DeGracia ◽  
Rita Kumar ◽  
Cheri R. Owen ◽  
Gary S. Krause ◽  
Blaine C. White
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Translation Initiation ◽  
Open Reading Frames ◽  
Ischemia And Reperfusion ◽  
Protein Synthesis Inhibition ◽  
Messenger Rnas ◽  
Internal Ribosome Entry ◽  
Synthesis Inhibition ◽  
Brain Reperfusion

Protein synthesis inhibition occurs in neurons immediately on reperfusion after ischemia and involves at least alterations in eukaryotic initiation factors 2 (eIF2) and 4 (eIF4). Phosphorylation of the α subunit of eIF2 [eIF2(αP)] by the endoplasmic reticulum transmembrane eIF2α kinase PERK occurs immediately on reperfusion and inhibits translation initiation. PERK activation, along with depletion of endoplasmic reticulum Ca2+ and inhibition of the endoplasmic reticulum Ca2+-ATPase, SERCA2b, indicate that an endoplasmic reticulum unfolded protein response occurs as a consequence of brain ischemia and reperfusion. In mammals, the upstream unfolded protein response components PERK, IRE1, and ATF6 activate prosurvivial mechanisms (e.g., transcription of GRP78, PDI, SERCA2b) and proapoptotic mechanisms (i.e., activation of Jun N-terminal kinases, caspase-12, and CHOP transcription). Sustained eIF2(αP) is proapoptotic by inducing the synthesis of ATF4, the CHOP transcription factor, through “bypass scanning” of 5‘ upstream open-reading frames in ATF4 messenger RNA; these upstream open-reading frames normally inhibit access to the ATF4 coding sequence. Brain ischemia and reperfusion also induce μ-calpain–mediated or caspase-3–mediated proteolysis of eIF4G, which shifts message selection to m7G-cap–independent translation initiation of messenger RNAs containing internal ribosome entry sites. This internal ribosome entry site–mediated translation initiation (i.e., for apoptosis-activating factor-1 and death-associated protein-5) can also promote apoptosis. Thus, alterations in eIF2 and eIF4 have major implications for which messenger RNAs are translated by residual protein synthesis in neurons during brain reperfusion, in turn constraining protein expression of changes in gene transcription induced by ischemia and reperfusion. Therefore, our current understanding shifts the focus from protein synthesis inhibition to the molecular pathways that underlie this inhibition, and the role that these pathways play in prosurvival and proapoptotic processes that may be differentially expressed in vulnerable and resistant regions of the reperfused brain.

A critical review of translation initiation factor eIF2α kinases in plants - regulating protein synthesis during stress

2012 ◽  
Vol 39 (9) ◽  
pp. 717 ◽  
Author(s):  
Tracey M. Immanuel ◽  
David R. Greenwood ◽  
Robin M. MacDiarmid
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
Current Knowledge ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Phosphorylation Mechanism ◽  
Eif2α Kinase

Eukaryotic cells must cope with environmental stress. One type of general stress response is the downregulation of protein synthesis in order to conserve cellular resources. Protein synthesis is mainly regulated at the level of mRNA translation initiation and when the α subunit of eukaryotic translation initiation factor 2 (eIF2) is phosphorylated, protein synthesis is downregulated. Although eIF2 has the same translation initiation function in all eukaryotes, it is not known whether plants downregulate protein synthesis via eIF2α phosphorylation. Similarly, although there is evidence that plants possess eIF2α kinases, it is not known whether they operate in a similar manner to the well characterised mammalian and yeast eIF2α kinases. Two types of eIF2α kinases have been reported in plants, yet the full understanding of the plant eIF2α phosphorylation mechanism is still lacking. Here we review the current knowledge of the eIF2α phosphorylation mechanism within plants and discuss plant eIF2α, plant eIF2α kinase GCN2 and the data supporting and contradicting the hypothesis that a functional orthologue for the eIF2α kinase PKR, is present and functional in plants.

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