scholarly journals Circadian Clock Control of Translation Initiation Factor eIF2α Activity Requires eIF2γ-Dependent Recruitment of Rhythmic PPP-1 Phosphatase in Neurospora crassa

mBio ◽  
2021 ◽  
Vol 12 (3) ◽  
Author(s):  
Zhaolan Ding ◽  
Teresa M. Lamb ◽  
Ahmad Boukhris ◽  
Rachel Porter ◽  
Deborah Bell-Pedersen
Keyword(s):  
Protein Synthesis ◽  
Circadian Clock ◽  
Neurospora Crassa ◽  
Translation Initiation ◽  
Significant Proportion ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Cellular Growth ◽  
Initiation Factor ◽  
Content Type

ABSTRACT The circadian clock controls the phosphorylation and activity of eukaryotic translation initiation factor 2α (eIF2α). In Neurospora crassa, the clock drives a daytime peak in the activity of the eIF2α kinase CPC-3, the homolog of yeast and mammalian GCN2 kinase. This leads to increased levels of phosphorylated eIF2α (P-eIF2α) and reduced mRNA translation initiation during the day. We hypothesized that rhythmic eIF2α activity also requires dephosphorylation of P-eIF2α at night by phosphatases. In support of this hypothesis, we show that mutation of N. crassa PPP-1, a homolog of the yeast eIF2α phosphatase GLC7, leads to high and arrhythmic P-eIF2α levels, while maintaining core circadian oscillator function. PPP-1 levels are clock-controlled, peaking in the early evening, and rhythmic PPP-1 levels are necessary for rhythmic P-eIF2α accumulation. Deletion of the N terminus of N. crassa eIF2γ, the region necessary for eIF2γ interaction with GLC7 in yeast, led to high and arrhythmic P-eIF2α levels. These data supported that N. crassa eIF2γ functions to recruit PPP-1 to dephosphorylate eIF2α at night. Thus, in addition to the activity of CPC-3 kinase, circadian clock regulation of eIF2α activity requires dephosphorylation by PPP-1 phosphatase at night. These data show how the circadian clock controls the activity a central regulator of translation, critical for cellular metabolism and growth control, through the temporal coordination of phosphorylation and dephosphorylation events. IMPORTANCE Circadian clock control of mRNA translation contributes to the daily cycling of a significant proportion of the cellular protein synthesis, but how this is accomplished is not understood. We discovered that the clock in the model fungus Neurospora crassa regulates rhythms in protein synthesis by controlling the phosphorylation and dephosphorylation of a conserved translation initiation factor eIF2α. During the day, N. crassa eIF2α is phosphorylated and inactivated by CPC-3 kinase. At night, a clock-controlled phosphatase, PPP-1, dephosphorylates and activates eIF2α, leading to increased nighttime protein synthesis. Translation requires significant cellular energy; thus, partitioning translation to the night by the clock provides a mechanism to coordinate energy metabolism with protein synthesis and cellular growth.

scholarly journals Correction of eIF2-dependent defects in brain protein synthesis, synaptic plasticity, and memory in mouse models of Alzheimer’s disease

2021 ◽  
Vol 14 (668) ◽  
pp. eabc5429
Author(s):  
Mauricio M. Oliveira ◽  
Mychael V. Lourenco ◽  
Francesco Longo ◽  
Nicole P. Kasica ◽  
Wenzhong Yang ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Protein Synthesis ◽  
Synaptic Plasticity ◽  
Translation Initiation ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Postmortem Brain Tissue ◽  
Phosphorylated Eif2α

Neuronal protein synthesis is essential for long-term memory consolidation, and its dysregulation is implicated in various neurodegenerative disorders, including Alzheimer’s disease (AD). Cellular stress triggers the activation of protein kinases that converge on the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α), which attenuates mRNA translation. This translational inhibition is one aspect of the integrated stress response (ISR). We found that postmortem brain tissue from AD patients showed increased phosphorylation of eIF2α and reduced abundance of eIF2B, another key component of the translation initiation complex. Systemic administration of the small-molecule compound ISRIB (which blocks the ISR downstream of phosphorylated eIF2α) rescued protein synthesis in the hippocampus, measures of synaptic plasticity, and performance on memory-associated behavior tests in wild-type mice cotreated with salubrinal (which inhibits translation by inducing eIF2α phosphorylation) and in both β-amyloid-treated and transgenic AD model mice. Thus, attenuating the ISR downstream of phosphorylated eIF2α may restore hippocampal protein synthesis and delay cognitive decline in AD patients.

scholarly journals mTORC1 signalling and eIF4E/4E-BP1 translation initiation factor stoichiometry influence recombinant protein productivity from GS-CHOK1 cells

2016 ◽  
Vol 473 (24) ◽  
pp. 4651-4664 ◽  
Author(s):  
Lyne Jossé ◽  
Jianling Xie ◽  
Christopher G. Proud ◽  
C. Mark Smales
Keyword(s):  
Protein Synthesis ◽  
Cell Growth ◽  
Recombinant Protein ◽  
Cell Lines ◽  
Translation Initiation ◽  
Mammalian Cells ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Cho Cell

Many protein-based biotherapeutics are produced in cultured Chinese hamster ovary (CHO) cell lines. Recent reports have demonstrated that translation of recombinant mRNAs and global control of the translation machinery via mammalian target of rapamycin (mTOR) signalling are important determinants of the amount and quality of recombinant protein such cells can produce. mTOR complex 1 (mTORC1) is a master regulator of cell growth/division, ribosome biogenesis and protein synthesis, but the relationship between mTORC1 signalling, cell growth and proliferation and recombinant protein yields from mammalian cells, and whether this master regulating signalling pathway can be manipulated to enhance cell biomass and recombinant protein production (rPP) are not well explored. We have investigated mTORC1 signalling and activity throughout batch culture of a panel of sister recombinant glutamine synthetase-CHO cell lines expressing different amounts of a model monoclonal IgG4, to evaluate the links between mTORC1 signalling and cell proliferation, autophagy, recombinant protein expression, global protein synthesis and mRNA translation initiation. We find that the expression of the mTORC1 substrate 4E-binding protein 1 (4E-BP1) fluctuates throughout the course of cell culture and, as expected, that the 4E-BP1 phosphorylation profiles change across the culture. Importantly, we find that the eIF4E/4E-BP1 stoichiometry positively correlates with cell productivity. Furthermore, eIF4E amounts appear to be co-regulated with 4E-BP1 amounts. This may reflect a sensing of either change at the mRNA level as opposed to the protein level or the fact that the phosphorylation status, as well as the amount of 4E-BP1 present, is important in the co-regulation of eIF4E and 4E-BP1.

scholarly journals Correction of eIF2-dependent defects in brain protein synthesis, synaptic plasticity and memory in mouse models of Alzheimer’s disease

2020 ◽  
Author(s):  
Mauricio M. Oliveira ◽  
Mychael V. Lourenco ◽  
Francesco Longo ◽  
Nicole P. Kasica ◽  
Wenzhong Yang ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Protein Synthesis ◽  
Synaptic Plasticity ◽  
Mouse Models ◽  
Translation Initiation ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Long Term Memory

AbstractNeuronal protein synthesis is essential for long-term memory consolidation. Conversely, dysregulation of protein synthesis has been implicated in a number of neurodegenerative disorders, including Alzheimer’s disease (AD). Several types of cellular stress trigger the activation of protein kinases that converge on the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α-P). This leads to attenuation of cap-dependent mRNA translation, a component of the integrated stress response (ISR). We show that AD brains exhibit increased eIF2α-P and reduced eIF2B, key components of the eIF2 translation initiation complex. We further demonstrate that attenuating the ISR with the small molecule compound ISRIB (ISR Inhibitor) rescues hippocampal protein synthesis and corrects impaired synaptic plasticity and memory in mouse models of AD. Our findings suggest that attenuating eIF2α-P-mediated translational inhibition may comprise an effective approach to alleviate cognitive decline in AD.

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.

Protein synthesis and its control in neuronal cells with a focus on vanishing white matter disease

2009 ◽  
Vol 37 (6) ◽  
pp. 1298-1310 ◽  
Author(s):  
Graham D. Pavitt ◽  
Christopher G. Proud
Keyword(s):  
Protein Synthesis ◽  
White Matter ◽  
Translation Initiation ◽  
Neuronal Cells ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Coding Region ◽  
The Right ◽  
Vanishing White Matter

Protein synthesis (also termed mRNA translation) is a key step in the expression of a cell's genetic information, in which the information contained within the coding region of the mRNA is used to direct the synthesis of the new protein, a process that is catalysed by the ribosome. Protein synthesis must be tightly controlled, to ensure the right proteins are made in the right amounts at the right time, and must be accurate, to avoid errors that could lead to the production of defective and potentially damaging proteins. In addition to the ribosome, protein synthesis also requires proteins termed translation factors, which mediate specific steps of the process. The first major stage of mRNA translation is termed ‘initiation’ and involves the recruitment of the ribosome to the mRNA and the identification of the correct start codon to commence translation. In eukaryotic cells, this process requires a set of eIFs (eukaryotic initiation factors). During the second main stage of translation, ‘elongation’, the ribosome traverses the coding region of the mRNA, assembling the new polypeptide: this process requires eEFs (eukaryotic elongation factors). Control of eEF2 is important in certain neurological processes. It is now clear that defects in eIFs or in their control can give rise to a number of diseases. This paper provides an overview of translation initiation and its control mechanisms, particularly those examined in neuronal cells. A major focus concerns an inherited neurological condition termed VHM (vanishing white matter) or CACH (childhood ataxia with central nervous system hypomyelination). VWM/CACH is caused by mutations in the translation initiation factor, eIF2B, a component of the basal translational machinery in all cells.

scholarly journals Circadian clock control of eIF2α phosphorylation is necessary for rhythmic translation initiation

2020 ◽  
Vol 117 (20) ◽  
pp. 10935-10945 ◽  
Author(s):  
Shanta Karki ◽  
Kathrina Castillo ◽  
Zhaolan Ding ◽  
Olivia Kerr ◽  
Teresa M. Lamb ◽  
...  
Keyword(s):  
Circadian Clock ◽  
Translation Initiation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Nutrient Metabolism ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase ◽  
The Impact

The circadian clock in eukaryotes controls transcriptional and posttranscriptional events, including regulation of the levels and phosphorylation state of translation factors. However, the mechanisms underlying clock control of translation initiation, and the impact of this potential regulation on rhythmic protein synthesis, were not known. We show that inhibitory phosphorylation of eIF2α (P-eIF2α), a conserved translation initiation factor, is clock controlled in Neurospora crassa, peaking during the subjective day. Cycling P-eIF2α levels required rhythmic activation of the eIF2α kinase CPC-3 (the homolog of yeast and mammalian GCN2), and rhythmic activation of CPC-3 was abolished under conditions in which the levels of charged tRNAs were altered. Clock-controlled accumulation of P-eIF2α led to reduced translation during the day in vitro and was necessary for the rhythmic synthesis of select proteins in vivo. Finally, loss of rhythmic P-eIF2α levels led to reduced linear growth rates, supporting the idea that partitioning translation to specific times of day provides a growth advantage to the organism. Together, these results reveal a fundamental mechanism by which the clock regulates rhythmic protein production, and provide key insights into how rhythmic translation, cellular energy, stress, and nutrient metabolism are linked through the levels of charged versus uncharged tRNAs.

scholarly journals Caspase-mediated cleavage of eukaryotic translation initiation factor subunit 2α

1999 ◽  
Vol 342 (1) ◽  
pp. 65-70 ◽  
Author(s):  
Shinya SATOH ◽  
Makoto HIJIKATA ◽  
Hiroshi HANDA ◽  
Kunitada SHIMOTOHNO
Keyword(s):  
Protein Synthesis ◽  
Translation Initiation ◽  
Caspase 3 ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Eukaryotic Translation Initiation Factor ◽  
Α Subunit ◽  
Eukaryotic Translation ◽  
Initiation Of Translation ◽  
Eukaryotic Translation Initiation

Eukaryotic translation initiation factor 2α (eIF-2α), a target molecule of the interferon-inducible double-stranded-RNA-dependent protein kinase (PKR), was cleaved in apoptotic Saos-2 cells on treatment with poly(I)˙poly(C) or tumour necrosis factor α. This cleavage occurred with a time course similar to that of poly(ADP-ribose) polymerase, a well-known caspase substrate. In addition, eIF-2α was cleaved by recombinant active caspase-3 in vitro. By site-directed mutagenesis, the cleavage site was mapped to an Ala-Glu-Val-Asp300 ↓ Gly301 sequence located in the C-terminal portion of eIF-2α. PKR phosphorylates eIF-2α on Ser51, resulting in the suppression of protein synthesis. PKR-mediated translational suppression was repressed when the C-terminally cleaved product of eIF-2α was overexpressed in Saos-2 cells, even though PKR can phosphorylate this cleaved product. These results suggest that caspase-3 or related protease(s) can modulate the efficiency of protein synthesis by cleaving the α subunit of eIF-2, a key component in the initiation of translation.

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