scholarly journals Uncoupling Stress Granule Assembly and Translation Initiation Inhibition

2009 ◽  
Vol 20 (11) ◽  
pp. 2673-2683 ◽  
Author(s):  
Sophie Mokas ◽  
John R. Mills ◽  
Cristina Garreau ◽  
Marie-Josée Fournier ◽  
Francis Robert ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Binding Protein ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Ribosomal Subunits ◽  
Initiation Factors ◽  
Eif2α Phosphorylation ◽  
Translation Initiation Factors ◽  
Dependent Pathway ◽  
Regulatory Sites

Cytoplasmic stress granules (SGs) are specialized regulatory sites of mRNA translation that form under different stress conditions known to inhibit translation initiation. The formation of SG occurs via two pathways; the eukaryotic initiation factor (eIF) 2α phosphorylation-dependent pathway mediated by stress and the eIF2α phosphorylation-independent pathway mediated by inactivation of the translation initiation factors eIF4A and eIF4G. In this study, we investigated the effects of targeting different translation initiation factors and steps in SG formation in HeLa cells. By depleting eIF2α, we demonstrate that reduced levels of the eIF2.GTP.Met-tRNAiMet ternary translation initiation complexes is sufficient to induce SGs. Likewise, reduced levels of eIF4B, eIF4H, or polyA-binding protein, also trigger SG formation. In contrast, depletion of the cap-binding protein eIF4E or preventing its assembly into eIF4F results in modest SG formation. Intriguingly, interfering with the last step of translation initiation by blocking the recruitment of 60S ribosome either with 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamideis or through depletion of the large ribosomal subunits protein L28 does not induce SG assembly. Our study identifies translation initiation steps and factors involved in SG formation as well as those that can be targeted without induction of SGs.

scholarly journals Norovirus-mediated modification of the translational landscape via virus and host-induced cleavage of translation initiation factors

2016 ◽  
Author(s):  
Edward Emmott ◽  
Frederic Sorgeloos ◽  
Sarah L. Caddy ◽  
Surender Vashist ◽  
Stanislav Sosnovtsev ◽  
...  
Keyword(s):  
Translation Initiation ◽  
Host Response ◽  
Mrna Translation ◽  
Initiation Factor ◽  
Innate Response ◽  
Viral Protease ◽  
Viral Protein Synthesis ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Covalently Linked

SummaryNoroviruses produce viral RNAs lacking a 5’ cap structure and instead use a virus-encoded VPg protein covalently linked to viral RNA to interact with translation initiation factors and drive viral protein synthesis. Norovirus infection results in the induction of the innate response leading to interferon stimulated gene (ISG) transcription. However the translation of the induced ISG mRNAs is suppressed. Using a novel mass spectrometry approach we demonstrate that diminished host mRNA translation correlates with changes to the composition of the eukaryotic initiation factor complex. The suppression of host ISG translation correlates with the activity of the viral protease (NS6) and the activation of cellular caspases leading to the establishment of an apoptotic environment. These results indicate that noroviruses exploit the differences between viral VPg-dependent and cellular cap-dependent translation in order to diminish the host response to infection.

scholarly journals Leaderless mRNAs Bind 70S Ribosomes More Strongly than 30S Ribosomal Subunits in Escherichia coli

2002 ◽  
Vol 184 (23) ◽  
pp. 6730-6733 ◽  
Author(s):  
Sean M. O'Donnell ◽  
Gary R. Janssen
Keyword(s):  
Escherichia Coli ◽  
Translation Initiation ◽  
Primer Extension ◽  
Ribosomal Subunits ◽  
Ribosome Binding ◽  
Initiation Factors ◽  
Translation Initiation Factors

ABSTRACT By primer extension inhibition assays, 70S ribosomes bound with higher affinity, or stability, than did 30S subunits to leaderless mRNAs containing AUG or GUG start codons. Addition of translation initiation factors affected ribosome binding to leaderless mRNAs. Our results suggest that translation of leaderless mRNAs might initiate through a pathway involving 70S ribosomes or 30S subunits lacking IF3.

Bidirectional RNA helicase activity of eucaryotic translation initiation factors 4A and 4F

1990 ◽  
Vol 10 (3) ◽  
pp. 1134-1144 ◽  
Author(s):  
F Rozen ◽  
I Edery ◽  
K Meerovitch ◽  
T E Dever ◽  
W C Merrick ◽  
...  
Keyword(s):  
Secondary Structure ◽  
Translation Initiation ◽  
Direct Evidence ◽  
Rna Helicase ◽  
Initiation Factor ◽  
Helicase Activity ◽  
Ribosome Binding ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Hydrolysis Of

The mechanism of ribosome binding to eucaryotic mRNAs is not well understood, but it requires the participation of eucaryotic initiation factors eIF-4A, eIF-4B, and eIF-4F and the hydrolysis of ATP. Evidence has accumulated in support of a model in which these initiation factors function to unwind the 5'-proximal secondary structure in mRNA to facilitate ribosome binding. To obtain direct evidence for initiation factor-mediated RNA unwinding, we developed a simple assay to determine RNA helicase activity, and we show that eIF-4A or eIF-4F, in combination with eIF-4B, exhibits helicase activity. A striking and unprecedented feature of this activity is that it functions in a bidirectional manner. Thus, unwinding can occur either in the 5'-to-3' or 3'-to-5' direction. Unwinding in the 5'-to-3' direction by eIF-4F (the cap-binding protein complex), in conjunction with eIF-4B, was stimulated by the presence of the RNA 5' cap structure, whereas unwinding in the 3'-to-5' direction was completely cap independent. These results are discussed with respect to cap-dependent versus cap-independent mechanisms of ribosome binding to eucaryotic mRNAs.

Plant translation initiation factors: it is not easy to be green

2004 ◽  
Vol 32 (4) ◽  
pp. 589-591 ◽  
Author(s):  
K.S. Browning
Keyword(s):  
Translation Initiation ◽  
Binding Proteins ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Translational Machinery ◽  
Initiation Factors ◽  
Translation Initiation Factors

Plants have significant differences in some of the ‘parts’ of the translational machinery. There are two forms of eukaryotic initiation factor (eIF) 4F, eIF3 has two novel subunits, eIF4B is poorly conserved, and eIF2 kinases and eIF4E binding proteins (4E-BP) are yet to be discovered. These differences suggest that plants may regulate their translation in unique ways.

scholarly journals Large G3BP-induced granules trigger eIF2α phosphorylation

2012 ◽  
Vol 23 (18) ◽  
pp. 3499-3510 ◽  
Author(s):  
Lucas C. Reineke ◽  
Jon D. Dougherty ◽  
Philippe Pierre ◽  
Richard E. Lloyd
Keyword(s):  
Stress Granules ◽  
Stress Granule ◽  
Initiation Factor ◽  
Protein Kinase R ◽  
Translational Machinery ◽  
Initiation Factors ◽  
Eif2α Phosphorylation ◽  
Translation Initiation Factors ◽  
Messenger Ribonucleoprotein ◽  
Translation Apparatus

Stress granules are large messenger ribonucleoprotein (mRNP) aggregates composed of translation initiation factors and mRNAs that appear when the cell encounters various stressors. Current dogma indicates that stress granules function as inert storage depots for translationally silenced mRNPs until the cell signals for renewed translation and stress granule disassembly. We used RasGAP SH3-binding protein (G3BP) overexpression to induce stress granules and study their assembly process and signaling to the translation apparatus. We found that assembly of large G3BP-induced stress granules, but not small granules, precedes phosphorylation of eIF2α. Using mouse embryonic fibroblasts depleted for individual eukaryotic initiation factor 2α (eIF2α) kinases, we identified protein kinase R as the principal kinase that mediates eIF2α phosphorylation by large G3BP-induced granules. These data indicate that increasing stress granule size is associated with a threshold or switch that must be triggered in order for eIF2α phosphorylation and subsequent translational repression to occur. Furthermore, these data suggest that stress granules are active in signaling to the translational machinery and may be important regulators of the innate immune response.

scholarly journals The EIF4E1-4EIP cap-binding complex of Trypanosoma brucei interacts with the terminal uridylyl transferase TUT3

PLoS ONE ◽  
2021 ◽  
Vol 16 (11) ◽  
pp. e0258903
Author(s):  
Franziska Falk ◽  
Kevin Kamanyi Marucha ◽  
Christine Clayton
Keyword(s):  
Trypanosoma Brucei ◽  
Translation Initiation ◽  
Binding Protein ◽  
Procyclic Form ◽  
Initiation Factors ◽  
Control Gene Expression ◽  
Translation Initiation Factors ◽  
Cap Binding Complex ◽  
The Stability ◽  
Reporter Mrna

Most transcription in Trypanosoma brucei is constitutive and polycistronic. Consequently, the parasite relies on post-transcriptional mechanisms, especially affecting translation initiation and mRNA decay, to control gene expression both at steady-state and for adaptation to different environments. The parasite has six isoforms of the cap-binding protein EIF4E as well as five EIF4Gs. EIF4E1 does not bind to any EIF4G, instead being associated with a 4E-binding protein, 4EIP. 4EIP represses translation and reduces the stability of a reporter mRNA when artificially tethered to the 3’-UTR, whether or not EIF4E1 is present. 4EIP is essential during the transition from the mammalian bloodstream form to the procyclic form that lives in the Tsetse vector. In contrast, EIF4E1 is dispensable during differentiation, but is required for establishment of growing procyclic forms. In Leishmania, there is some evidence that EIF4E1 might be active in translation initiation, via direct recruitment of EIF3. However in T. brucei, EIF4E1 showed no detectable association with other translation initiation factors, even in the complete absence of 4EIP. There was some evidence for interactions with NOT complex components, but if these occur they must be weak and transient. We found that EIF4E1is less abundant in the absence of 4EIP, and RNA pull-down results suggested this might occur through co-translational complex assembly. We also report that 4EIP directly recruits the cytosolic terminal uridylyl transferase TUT3 to EIF4E1/4EIP complexes. There was, however, no evidence that TUT3 is essential for 4EIP function.

scholarly journals Translation initiation mediated by RNA looping

2015 ◽  
Vol 112 (4) ◽  
pp. 1041-1046 ◽  
Author(s):  
Ki Young Paek ◽  
Ka Young Hong ◽  
Incheol Ryu ◽  
Sung Mi Park ◽  
Sun Ju Keum ◽  
...  
Keyword(s):  
Reporter Gene ◽  
Translation Initiation ◽  
Mrna Translation ◽  
Encephalomyocarditis Virus ◽  
Initiation Codon ◽  
Translation Efficiency ◽  
Upstream Gene ◽  
Translational Initiation ◽  
Initiation Factors ◽  
Translation Initiation Factors

Eukaryotic translation initiation commences at the initiation codon near the 5′ end of mRNA by a 40S ribosomal subunit, and the recruitment of a 40S ribosome to an mRNA is facilitated by translation initiation factors interacting with the m7G cap and/or poly(A) tail. The 40S ribosome recruited to an mRNA is then transferred to the AUG initiation codon with the help of translation initiation factors. To understand the mechanism by which the ribosome finds an initiation codon, we investigated the role of eIF4G in finding the translational initiation codon. An artificial polypeptide eIF4G fused with MS2 was localized downstream of the reporter gene through MS2-binding sites inserted in the 3′ UTR of the mRNA. Translation of the reporter was greatly enhanced by the eIF4G-MS2 fusion protein regardless of the presence of a cap structure. Moreover, eIF4G-MS2 tethered at the 3′ UTR enhanced translation of the second cistron of a dicistronic mRNA. The encephalomyocarditis virus internal ribosome entry site, a natural translational-enhancing element facilitating translation through an interaction with eIF4G, positioned downstream of a reporter gene, also enhanced translation of the upstream gene in a cap-independent manner. Finally, we mathematically modeled the effect of distance between the cap structure and initiation codon on the translation efficiency of mRNAs. The most plausible explanation for translational enhancement by the translational-enhancing sites is recognition of the initiation codon by the ribosome bound to the ribosome-recruiting sites through “RNA looping.” The RNA looping hypothesis provides a logical explanation for augmentation of translation by enhancing elements located upstream and/or downstream of a protein-coding region.

scholarly journals Translational Repression by RNA-Binding Protein TIAR

2006 ◽  
Vol 26 (7) ◽  
pp. 2716-2727 ◽  
Author(s):  
Krystyna Mazan-Mamczarz ◽  
Ashish Lal ◽  
Jennifer L. Martindale ◽  
Tomoko Kawai ◽  
Myriam Gorospe
Keyword(s):  
Rna Binding ◽  
Binding Protein ◽  
Protein Biosynthesis ◽  
Rna Binding Protein ◽  
Elongation Factor ◽  
Initiation Factor ◽  
Translation Elongation ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Cellular Translation

ABSTRACT The RNA-binding protein TIAR has been proposed to inhibit protein synthesis transiently by promoting the formation of translationally silent stress granules. Here, we report the selective binding of TIAR to several mRNAs encoding translation factors such as eukaryotic initiation factor 4A (eIF4A) and eIF4E (translation initiation factors), eEF1B (a translation elongation factor), and c-Myc (which transcriptionally controls the expression of numerous translation regulatory proteins). TIAR bound the 3′-untranslated regions of these mRNAs and potently suppressed their translation, particularly in response to low levels of short-wavelength UV (UVC) irradiation. The UVC-imposed global inhibition of the cellular translation machinery was significantly relieved after silencing of TIAR expression. We propose that the TIAR-mediated inhibition of translation factor expression elicits a sustained repression of protein biosynthesis in cells responding to stress.

scholarly journals The regulation of protein translation and its implications for cancer

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Ping Song ◽  
Fan Yang ◽  
Hongchuan Jin ◽  
Xian Wang
Keyword(s):  
Translation Initiation ◽  
Rna Binding ◽  
Rna Binding Proteins ◽  
Noncoding Rnas ◽  
Mrna Translation ◽  
Protein Translation ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Precision Therapy ◽  
Novel Approaches

AbstractIn addition to the deregulation of gene transcriptions and post-translational protein modifications, the aberrant translation from mRNAs to proteins plays an important role in the pathogenesis of various cancers. Targeting mRNA translation are expected to become potential approaches for anticancer treatments. Protein translation is affected by many factors including translation initiation factors and RNA-binding proteins. Recently, modifications of mRNAs mainly N6-methyladenine (m6A) modification and noncoding RNAs, such as microRNAs and long noncoding RNAs are involved. In this review, we generally summarized the recent advances on the regulation of protein translation by the interplay between mRNA modifications and ncRNAs. By doing so, we hope this review could offer some hints for the development of novel approaches in precision therapy of human cancers.

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