eEF1A: thinking outside the ribosome

Translational control in aging and neurodegeneration

Protein metabolism plays central roles in age-related decline and neurodegeneration. While a large body of research has explored age-related changes in protein degradation, alterations in the efficiency and fidelity of protein synthesis with aging are less well understood. Age-associated changes occur in both the protein synthetic machinery (ribosomal proteins and rRNA) and within regulatory factors controlling translation. At the same time, many of the interventions that prolong lifespan do so in part by pre-emptively decreasing protein synthesis rates to allow better harmonization to age-related declines in protein catabolism. Here we review the roles of translation regulation in aging, with a specific focus on factors implicated in age-related neurodegeneration. We discuss how emerging technologies such as ribosome profiling and superior mass spectrometric approaches are illuminating age-dependent mRNA-specific changes in translation rates across tissues to reveal a critical interplay between catabolic and anabolic pathways that likely contribute to functional decline. These new findings point to nodes in posttranscriptional gene regulation that both contribute to aging and offer targets for therapy. This article is categorized under: Translation > Translation Regulation Translation > Ribosome Biogenesis Translation > Translation Mechanisms.

Evaluation on Elongation Factor 1 Alpha of Entamoeba histolytica Interaction with the Intermediate Subunit of the Gal/GalNAc Lectin and Actin in Phagocytosis

Entamoeba histolytica is the causative agent of amoebiasis. This disease results in 40,000 to 100,000 deaths annually. The pathogenic molecules involved in the invasion of trophozoites had been constantly being clarified. This study explored the role of elongation factor 1 alpha (EF1a) in E. histolytica pathogenicity. Biolayer interferometry binding and pull-down assays suggest that EF1a and intermediate subunit of lectin (Igl) binding are specific. Submembranous distribution of EF1a closely aligns with the localization of Igl, which appear in abundance on membranes of trophozoites. Messenger RNA (mRNA) expression of EF1a is positively correlated with trends in Igl levels after co-incubation with Chinese hamster ovary (CHO) cells in vitro, suggesting a regulatory linkage between these proteins. Erythrophagocytosis assays also imply a role for EF1a in phagocytosis. Finally, EF1a and actin are collocated in trophozoites. These results indicated elongation factor 1a is associated with E. histolytica phagocytosis, and the relationships between EF1a, Igl, and actin are worth further study to better understand the pathogenic process.

Precursors of thymic peptides as stress sensors

INTRODUCTION

A large volume of data indicates that the known thymic hormones, thymulin, thymopoietin, thymosin-α, thymosin-β, and thymic humoral factor-y2, exhibit different spectra of activities. Although large in volume, available data are rather fragmented, resulting in a lack of understanding of the role played by thymic hormones in immune homeostasis.

AREA COVERED

Existing data compartmentalizes the effect of thymic peptides into 2 categories: influence on immune cells and interconnection with neuroendocrine systems. The current study draws attention to a third aspect of the thymic peptide effect that has not been clarified yet, wherein ubiquitous and highly abundant intranuclear precursors of so called 'thymic peptides' play a fundamental role in all somatic cells.

EXPERT OPINION

Our analysis indicated that, under certain stress-related conditions, these precursors are cleaved to form immunologically active peptides that rapidly leave the nucleus and intracellular spaces, to send 'distress signals' to the immune system, thereby acting as stress sensors. We propose that these peptides may form a link between somatic cells and immune as well as neuroendocrine systems. This model may provide a better understanding of the mechanisms underlying immune homeostasis, leading thereby to the development of new therapeutic regimes utilizing the characteristics of thymic peptides.

Host Epigenetics in Intracellular Pathogen Infections

Some intracellular pathogens are able to avoid the defense mechanisms contributing to host epigenetic modifications. These changes trigger alterations tothe chromatin structure and on the transcriptional level of genes involved in the pathogenesis of many bacterial diseases. In this way, pathogens manipulate the host cell for their own survival. The better understanding of epigenetic consequences in bacterial infection may open the door for designing new vaccine approaches and therapeutic implications. This article characterizes selected intracellular bacterial pathogens, including Mycobacterium spp., Listeria spp., Chlamydia spp., Mycoplasma spp., Rickettsia spp., Legionella spp. and Yersinia spp., which can modulate and reprogram of defense genes in host innate immune cells.

Domain II of the translation elongation factor eEF1A is required for Gcn2 kinase inhibition

The signalling pathway governing general control nonderepressible (Gcn)2 kinase allows cells to cope with amino acid shortage. Under starvation, Gcn2 phosphorylates the translation initiation factor eukaryotic translation initiation factor (eIF)2α, triggering downstream events that ultimately allow cells to cope with starvation. Under nutrient-replete conditions, the translation elongation factor eEF1A binds Gcn2 to contribute to keeping Gcn2 inactive. Here, we aimed to map the regions in eEF1A involved in binding and/or regulating Gcn2. We find that eEF1A amino acids 1-221 and 222-315, containing most of domains I and II, respectively, bind Gcn2 in vitro. Overexpression of eEF1A lacking or containing domain III impairs eIF2α phosphorylation. While the latter reduces growth under starvation similarly to eEF1A lacking domain I, the former enhances growth in a Gcn2-dependent manner. Our studies suggest that domain II is required for Gcn2 inhibition and that eEF1A lacking domain III mainly affects the Gcn2 response pathway downstream of Gcn2.

Crystal structure of the metaeffector MesI (Lpg2505) from Legionella pneumophila

Persistence and replication of the gram-negative bacterium Legionella pneumophila in the human host cell depend on so-called effector proteins that target diverse cellular functions and modulate them in favor of the pathogen. We solved the crystal structure of the L. pneumophila effector protein MesI de novo to a resolution of 2.2 Å. The 34 kDa polypeptide chain folds into two distinct α-helical domains. The larger C-terminal domain shows similarity to tetratricopeptide repeat proteins. Using size-exclusion chromatography, we confirmed that MesI binds tightly to full-length SidI and that deletion of either the N- or the C-terminus weakens the interaction. Based on the three-dimensional structure of MesI we suggest a possible binding mode for SidI and identified two homologs of MesI within the proteome of L. pneumophila that do not bind to SidI, but may act as specific inhibitors of other yet to be identified effectors.

LreEF1A4, a Translation Elongation Factor from Lilium regale, Is Pivotal for Cucumber Mosaic Virus and Tobacco Rattle Virus Infections and Tolerance to Salt and Drought

Eukaryotic translation elongation factors are implicated in protein synthesis across different living organisms, but their biological functions in the pathogenesis of cucumber mosaic virus (CMV) and tobacco rattle virus (TRV) infections are poorly understood. Here, we isolated and characterized a cDNA clone, LreEF1A4, encoding the alpha subunit of elongation factor 1, from a CMV-elicited suppression subtractive hybridization library of Lilium regale. The infection tests using CMV remarkably increased transcript abundance of LreEF1A4; however, it also led to inconsistent expression profiles of three other LreEF1A homologs (LreEF1A1-3). Protein modelling analysis revealed that the amino acid substitutions among four LreEF1As may not affect their enzymatic functions. LreEF1A4 was ectopically overexpressed in petunia (Petunia hybrida), and transgenic plants exhibited delayed leaf and flower senescence, concomitant with increased transcription of photosynthesis-related genes and reduced expression of senescence-associated genes, respectively. A compromised resistance to CMV and TRV infections was found in transgenic petunia plants overexpressing LreEF1A4, whereas its overexpression resulted in an enhanced tolerance to salt and drought stresses. Taken together, our data demonstrate that LreEF1A4 functions as a positive regulator in viral multiplication and plant adaption to high salinity and dehydration.

Yeast as a Model to Understand Actin-Mediated Cellular Functions in Mammals-Illustrated with Four Actin Cytoskeleton Proteins

The budding yeast Saccharomyces cerevisiae has an actin cytoskeleton that comprises a set of protein components analogous to those found in the actin cytoskeletons of higher eukaryotes. Furthermore, the actin cytoskeletons of S. cerevisiae and of higher eukaryotes have some similar physiological roles. The genetic tractability of budding yeast and the availability of a stable haploid cell type facilitates the application of molecular genetic approaches to assign functions to the various actin cytoskeleton components. This has provided information that is in general complementary to that provided by studies of the equivalent proteins of higher eukaryotes and hence has enabled a more complete view of the role of these proteins. Several human functional homologues of yeast actin effectors are implicated in diseases. A better understanding of the molecular mechanisms underpinning the functions of these proteins is critical to develop improved therapeutic strategies. In this article we chose as examples four evolutionarily conserved proteins that associate with the actin cytoskeleton: (1) yeast Hof1p/mammalian PSTPIP1, (2) yeast Rvs167p/mammalian BIN1, (3) yeast eEF1A/eEF1A1 and eEF1A2 and (4) yeast Yih1p/mammalian IMPACT. We compare the knowledge on the functions of these actin cytoskeleton-associated proteins that has arisen from studies of their homologues in yeast with information that has been obtained from in vivo studies using live animals or in vitro studies using cultured animal cell lines.

Chicken eEF1α is a Critical Factor for the Polymerase Complex Activity of Very Virulent Infectious Bursal Disease Virus

Infectious bursal disease (IBD) is an immunosuppressive, highly contagious, and lethal disease of young chickens caused by IBD virus (IBDV). It results in huge economic loss to the poultry industry worldwide. Infection caused by very virulent IBDV (vvIBDV) strains results in high mortality in young chicken flocks. However, the replication characteristics of vvIBDV are not well studied. Publications have shown that virus protein 3 (VP3) binds to VP1 and viral double-stranded RNA, and together they form a ribonucleoprotein complex that plays a key role in virus replication. In this study, vvIBDV VP3 was used to identify host proteins potentially involved in modulating vvIBDV replication. Chicken eukaryotic translation elongation factor 1α (cheEF1α) was chosen to further investigate effects on vvIBDV replication. By small interfering RNA-mediated cheEF1α knockdown, we demonstrated the possibility of significantly reducing viral polymerase activity, with a subsequent reduction in virus yields. Conversely, over-expression of cheEF1α significantly increased viral polymerase activity and virus replication. Further study confirmed that cheEF1α interacted only with vvIBDV VP3 but not with attenuated IBDV (aIBDV) VP3. Furthermore, the amino acids at the N- and C-termini were important in the interaction between vvIBDV VP3 and cheEF1α. Domain III was essential for interactions between cheEF1α and vvIBDV VP3. In summary, cheEF1α enhances vvIBDV replication by promoting the activity of virus polymerase. Our study indicates cheEF1α is a potential target for limiting vvIBDV infection.

Mycobacterium tuberculosis Uses Mce Proteins to Interfere With Host Cell Signaling

Tuberculosis continues to be the main cause for mortality by an infectious agent, making Mycobacterium tuberculosis one of the most successful pathogens to survive for long durations within human cells. In order to survive against host defenses, M. tuberculosis modulates host cell signaling. It employs many proteins to achieve this and the Mce proteins are emerging as one group that play a role in host cell signaling in addition to their primary role as lipid/sterol transporters. Mce proteins belong to the conserved Mce/MlaD superfamily ubiquitous in diderm bacteria and chloroplasts. In mycobacteria, mce operons, encode for six different Mce proteins that assemble with inner membrane permeases into complexes that span across the mycobacterial cell wall. Their involvement in signaling modulation is varied and they have been shown to bind ERK1/2 to alter host cytokine expression; eEF1A1 to promote host cell proliferation and integrins for host cell adherence and entry. Recently, structures of prokaryotic Mce/MlaD proteins have been determined, giving an insight into the conserved domain. In this mini-review, we discuss current evidence for the role of mycobacterial Mce proteins in host cell signaling and structural characteristics of the protein-protein interactions coordinated by the human proteins to modulate the host signaling.

Enriching cancer pharmacology with drugs of marine origin

Marine natural products have proven, over the last half-century, to be effective biological modulators. These molecules have revealed new targets for cancer therapy as well as dissimilar modes of action within typical classes of drugs. In this scenario, innovation from marine-based pharmaceuticals has helped advance cancer chemotherapy in many aspects, as most of these are designated as first-in-class drugs. Here, by examining the path from discovery to development of clinically approved drugs of marine origin for cancer treatment-cytarabine (Cytosar-U®), trabectedin (Yondelis®), eribulin (Halaven®), brentuximab vedotin (Adcetris®), and plitidepsin (Aplidin®)- together with those in late clinical trial phases-lurbinectedin, plinabulin, marizomib, and plocabulin-the present review offers a critical analysis of the contributions given by these new compounds to cancer pharmacotherapy.

Junction Mapper is a novel computer vision tool to decipher cell-cell contact phenotypes

Stable cell–cell contacts underpin tissue architecture and organization. Quantification of junctions of mammalian epithelia requires laborious manual measurements that are a major roadblock for mechanistic studies. We designed Junction Mapper as an open access, semi-automated software that defines the status of adhesiveness via the simultaneous measurement of pre-defined parameters at cell–cell contacts. It identifies contacting interfaces and corners with minimal user input and quantifies length, area and intensity of junction markers. Its ability to measure fragmented junctions is unique. Importantly, junctions that considerably deviate from the contiguous staining and straight contact phenotype seen in epithelia are also successfully quantified (i.e. cardiomyocytes or endothelia). Distinct phenotypes of junction disruption can be clearly differentiated among various oncogenes, depletion of actin regulators or stimulation with other agents. Junction Mapper is thus a powerful, unbiased and highly applicable software for profiling cell–cell adhesion phenotypes and facilitate studies on junction dynamics in health and disease.

Protein Methylation and Translation: Role of Lysine Modification on the Function of Yeast Elongation Factor 1A

To date, 12 protein lysine methyltransferases that modify translational elongation factors and ribosomal proteins (Efm1-7 and Rkm 1-5) have been identified in the yeast Saccharomyces cerevisiae. Of these 12, five (Efm1 and Efm4-7) appear to be specific to elongation factor 1A (EF1A), the protein responsible for bringing aminoacyl-tRNAs to the ribosome. In S. cerevisiae, the functional implications of lysine methylation in translation are mostly unknown. In this work, we assessed the physiological impact of disrupting EF1A methylation in a strain where four of the most conserved methylated lysine sites are mutated to arginine residues and in strains lacking either four or five of the Efm lysine methyltransferases specific to EF1A. We found that loss of EF1A methylation was not lethal but resulted in reduced growth rates, particularly under caffeine and rapamycin stress conditions, suggesting EF1A interacts with the TORC1 pathway, as well as altered sensitivities to ribosomal inhibitors. We also detected reduced cellular levels of the EF1A protein, which surprisingly was not reflected in its stability in vivo. We present evidence that these Efm methyltransferases appear to be largely devoted to the modification of EF1A, finding no evidence of the methylation of other substrates in the yeast cell. This work starts to illuminate why one protein can need five different methyltransferases for its functions and highlights the resilience of yeast to alterations in their posttranslational modifications.

Early defects in translation elongation factor 1α levels at excitatory synapses in α-synucleinopathy

Cognitive decline and dementia in neurodegenerative diseases are associated with synapse dysfunction and loss, which may precede neuron loss by several years. While misfolded and aggregated α-synuclein is recognized in the disease progression of synucleinopathies, the nature of glutamatergic synapse dysfunction and loss remains incompletely understood. Using fluorescence-activated synaptosome sorting (FASS), we enriched excitatory glutamatergic synaptosomes from mice overexpressing human alpha-synuclein (h-αS) and wild-type littermates to unprecedented purity. Subsequent label-free proteomic quantification revealed a set of proteins differentially expressed upon human alpha-synuclein overexpression. These include overrepresented proteins involved in the synaptic vesicle cycle, ER-Golgi trafficking, metabolism and cytoskeleton. Unexpectedly, we found and validated a steep reduction of eukaryotic translation elongation factor 1 alpha (eEF1A1) levels in excitatory synapses at early stages of h-αS mouse model pathology. While eEF1A1 reduction correlated with the loss of postsynapses, its immunoreactivity was found on both sides of excitatory synapses. Moreover, we observed a reduction in eEF1A1 immunoreactivity in the cingulate gyrus neuropil of patients with Lewy body disease along with a reduction in PSD95 levels. Altogether, our results suggest a link between structural impairments underlying cognitive decline in neurodegenerative disorders and local synaptic defects. eEF1A1 may therefore represent a limiting factor to synapse maintenance.

Dark side of the epididymis: tails of sperm maturation

BACKGROUND

The Hermes body (HB) previously called the cytoplasmic droplet is a focal distension of the flagellar cytoplasm of epididymal spermatozoa consisting mainly of isolated flattened Golgi cisternae.

OBJECTIVE

To define a functional role for the HB of epididymal spermatozoa.

METHODS

Isolated fractions of HBs of epididymal spermatozoa were prepared and by quantitative tandem mass spectrometry revealed 1511 proteins.

RESULTS

The glucose transporter GLUT-3 was the most abundant protein followed by hexokinase 1, which along with the presence of all glycolytic enzymes suggested a role for the HB in glycolysis. Several TMED/p24 Golgi trafficking proteins were abundant with TMED7/p27 and TMED2/p24 defining the identity of the flattened cisternae within the HB as Golgi, along with the known Golgi proteins, GBF1, GOLPH3, Man2α1, and ManIIX. The Golgi trafficking protein TMED7/p27 via small 50-nm vesicles emanating from the Golgi cisternae was proposed to transport GLUT-3 to the plasma membrane for ATP production related to sperm motility. The internal membranes revealed abundant proteins not only of Golgi cisternae, but also of endoplasmic reticulum and endosomes. COPI and COPII coats, clathrin, SNAREs, annexins, atlastins, and GTPases were identified for vesicular trafficking and membrane fusion, in addition to ribosomes, stress proteins for protection, proteasome proteins involved in degradation, and cytoskeletal elements for migration of the HB along the flagellum. The biogenesis of the HB occurring at step 19 spermatids of the testis just prior to their release was uncovered as a key step in germ cell differentiation, where several proteins were expressed, some for the first time.

CONCLUSION

As epididymal spermatozoa undergo remodeling of their protein makeup through selective degradation of sperm proteins during epididymal transit, then remodeling as a consequence of new protein synthesis is not excluded by our observations.

In Silico Structural Modeling and Analysis of Elongation Factor-1 Alpha and Elongation Factor-like Protein

Translation elongation factor-1alpha (EF-1α) or its paralog elongation factor-like proteins (EFL) interact with an aminoacyl-transfer RNA (aa-tRNA) to play its essential role in elongation of peptide-chain during protein synthesis. Species usually have either an EF-1α or EFL protein; however, some species have both EF-1α and EFL (dual-EF-containing species). In the dual-EF-containing species, EF-1α appeared to be highly divergent in the sequence. Homology modeling and surface analysis of EF-1α and EFL were performed to examine the hypothesis that the divergent EF-1α in the dual-EF-containing eukaryotes does not strongly interact with aa-tRNA compared to the canonical EF-1α and EFL. The subsequent molecular dynamics simulations were carried out to confirm the validity of modeled structures and to analyze their stability. It was found that the molecular surfaces of the divergent EF-1α proteins were negatively charged partly, and thus they might not interact with negatively charged aa-tRNA as strongly as the canonical ones. The molecular docking simulations between EF-1α/EFL and aa-tRNA also support the hypothesis.

Single-Molecule Real-Time (SMRT) Full-Length RNA-Sequencing Reveals Novel and Distinct mRNA Isoforms in Human Bone Marrow Cell Subpopulations

Hematopoietic cells are continuously replenished from progenitor cells that reside in the bone marrow. To evaluate molecular changes during this process, we analyzed the transcriptomes of freshly harvested human bone marrow progenitor (lineage-negative) and differentiated (lineage-positive) cells by single-molecule real-time (SMRT) full-length RNA-sequencing. This analysis revealed a ~5-fold higher number of transcript isoforms than previously detected and showed a distinct composition of individual transcript isoforms characteristic for bone marrow subpopulations. A detailed analysis of messenger RNA (mRNA) isoforms transcribed from the ANXA1 and EEF1A1 loci confirmed their distinct composition. The expression of proteins predicted from the transcriptome analysis was evaluated by mass spectrometry and validated previously unknown protein isoforms predicted e.g., for EEF1A1. These protein isoforms distinguished the lineage negative cell population from the lineage positive cell population. Finally, transcript isoforms expressed from paralogous gene loci (e.g., CFD, GATA2, HLA-A, B, and C) also distinguished cell subpopulations but were only detectable by full-length RNA sequencing. Thus, qualitatively distinct transcript isoforms from individual genomic loci separate bone marrow cell subpopulations indicating complex transcriptional regulation and protein isoform generation during hematopoiesis.

Pharmacokinetic evaluation of the PNC disassembler metarrestin in wild-type and Pdx1-Cre;LSL-KrasG12D/+;Tp53R172H/+ (KPC) mice, a genetically engineered model of pancreatic cancer

PURPOSE

Metarrestin is a first-in-class small molecule clinical candidate capable of disrupting the perinucleolar compartment, a subnuclear structure unique to metastatic cancer cells. This study aims to define the pharmacokinetic (PK) profile of metarrestin and the pharmacokinetic/pharmacodynamic relationship of metarrestin-regulated markers.

METHODS

PK studies included the administration of single or multiple dose of metarrestin at 3, 10, or 25 mg/kg via intravenous (IV) injection, gavage (PO) or with chow to wild-type C57BL/6 mice and KPC mice bearing autochthonous pancreatic tumors. Metarrestin concentrations were analyzed by UPLC-MS/MS. Pharmacodynamic assays included mRNA expression profiling by RNA-seq and qRT-PCR for KPC mice.

RESULTS

Metarrestin had a moderate plasma clearance of 48 mL/min/kg and a large volume of distribution of 17 L/kg at 3 mg/kg IV in C57BL/6 mice. The oral bioavailability after single-dose (SD) treatment was > 80%. In KPC mice treated with SD 25 mg/kg PO, plasma AUC0-∞ of 14400 ng h/mL, Cmax of 810 ng/mL and half-life (t1/2) of 8.5 h were observed. At 24 h after SD of 25 mg/kg PO, the intratumor concentration of metarrestin was high with a mean value of 6.2 µg/g tissue (or 13 µM), well above the cell-based IC50 of 0.4 µM. At multiple dose (MD) 25 mg/kg/day PO in KPC mice, mean tissue/plasma AUC0-24h ratio for tumor, spleen and liver was 37, 30 and 31, respectively. There was a good linear relationship of dosage to AUC0-24h and C24h. AUC0-24h MD to AUC0-24h SD ratios ranged from two for liver to five for tumor indicating additional accumulation in tumors. Dose-dependent normalization of FOXA1 and FOXO6 mRNA expression was observed in KPC tumors.

CONCLUSIONS

Metarrestin is an effective therapeutic candidate with a favorable PK profile achieving excellent intratumor tissue levels in a disease with known poor drug delivery.

The eukaryotic translation elongation factor 1A regulation of actin stress fibers is important for infectious RSV production

Cellular protein eukaryotic translation elongation factor 1A (eEF1A) is an actin binding protein that plays a role in the formation of filamentous actin (F-actin) bundles. F-Actin regulates multiple stages of respiratory syncytial virus (RSV) replication including assembly and budding. Our previous study demonstrated that eEF1A knock-down significantly reduced RSV replication. Here we investigated if the eEF1A function in actin bundle formation was important for RSV replication and release. To investigate this, eEF1A function was impaired in HEp-2 cells by either knock-down of eEF1A with siRNA, or treatment with an eEF1A inhibitor, didemnin B (Did B). Cell staining and confocal microscopy analysis showed that both eEF1A knock-down and treatment with Did B resulted in disruption of cellular stress fiber formation and elevated accumulation of F-actin near the plasma membrane. When treated cells were then infected with RSV, there was also reduced formation of virus-induced cellular filopodia. Did B treatment, similarly to eEF1A knock-down, reduced the release of infectious RSV, but unlike eEF1A knock-down, did not significantly affect RSV genome replication. The lower infectious virus production in Did B treated cells also reduced RSV-induced cell death. In conclusion, the cellular factor eEF1A plays an important role in the regulation of F-actin stress fiber formation required for RSV assembly and release.

The role of translation elongation factor eEF1 subunits in neurodevelopmental disorders

The multi-subunit eEF1 complex plays a crucial role in de novo protein synthesis. The central functional component of the complex is eEF1A, which occurs as two independently encoded variants with reciprocal expression patterns: whilst eEF1A1 is widely expressed, eEF1A2 is found only in neurons and muscle. Heterozygous mutations in the gene encoding eEF1A2, EEF1A2, have recently been shown to cause epilepsy, autism, and intellectual disability. The remaining subunits of the eEF1 complex, eEF1Bα, eEF1Bδ, eEF1Bγ, and valyl-tRNA synthetase (VARS), together form the GTP exchange factor for eEF1A and are ubiquitously expressed, in keeping with their housekeeping role. However, mutations in the genes encoding these subunits EEF1B2 (eEF1Bα), EEF1D (eEF1Bδ), and VARS (valyl-tRNA synthetase) have also now been identified as causes of neurodevelopmental disorders. In this review, we describe the mutations identified so far in comparison with the degree of normal variation in each gene, and the predicted consequences of the mutations on the functions of the proteins and their isoforms. We discuss the likely effects of the mutations in the context of the role of protein synthesis in neuronal development.

Binding of eEF1A2 to the RNA-dependent protein kinase PKR modulates its activity and promotes tumour cell survival

Background

Through several not-fully-characterised moonlighting functions, translation elongation factor eEF1A2 is known to provide a fitness boost to cancer cells. Furthermore, eEF1A2 has been demonstrated to confer neoplastic characteristics on preneoplastic, nontumourigenic precursor cells. We have previously shown that eEF1A2 is the target of plitidepsin, a marine drug currently in development for cancer treatment. Herein, we characterised a new signalling pathway through which eEF1A2 promotes tumour cell survival.

Methods

Previously unknown binding partners of eEF1A2 were identified through co-immunoprecipitation, high-performance liquid chromatography-mass spectrometry and proximity ligation assay. Using plitidepsin to release eEF1A2 from those protein complexes, their effects on cancer cell survival were analysed in vitro.

Results

We uncovered that double-stranded RNA-activated protein kinase (PKR) is a novel eEF1A2-interacting partner whose pro-apoptotic effect is hindered by the translation factor, most likely through sequestration and inhibition of its kinase activity. Targeting eEF1A2 with plitidepsin releases PKR from the complex, facilitating its activation and triggering a mitogen-activated protein kinase signalling cascade together with a nuclear factor-κB-dependent activation of the extrinsic apoptotic pathway, which lead to tumour cell death.

Conclusions

Through its binding to PKR, eEF1A2 provides a survival boost to cancer cells, constituting an Achilles heel that can be exploited in anticancer therapy.

Metarrestin, a perinucleolar compartment inhibitor, effectively suppresses metastasis

Metastasis remains a leading cause of cancer mortality due to the lack of specific inhibitors against this complex process. To identify compounds selectively targeting the metastatic state, we used the perinucleolar compartment (PNC), a complex nuclear structure associated with metastatic behaviors of cancer cells, as a phenotypic marker for a high-content screen of over 140,000 structurally diverse compounds. Metarrestin, obtained through optimization of a screening hit, disassembles PNCs in multiple cancer cell lines, inhibits invasion in vitro, suppresses metastatic development in three mouse models of human cancer, and extends survival of mice in a metastatic pancreatic cancer xenograft model with no organ toxicity or discernable adverse effects. Metarrestin disrupts the nucleolar structure and inhibits RNA polymerase (Pol) I transcription, at least in part by interacting with the translation elongation factor eEF1A2. Thus, metarrestin represents a potential therapeutic approach for the treatment of metastatic cancer.

Evaluation of Reference Genes for Real-Time Quantitative PCR Analysis in Larvae of Spodoptera litura Exposed to Azadirachtin Stress Conditions

Azadirachtin is an efficient and broad-spectrum botanical insecticide against more than 150 kinds of agricultural pests with the effects of mortality, antifeedant and growth regulation. Real-time quantitative polymerase chain reaction (RT-qPCR) could be one of the powerful tools to analyze the gene expression level and investigate the mechanism of azadirachtin at transcriptional level, however, the ideal reference genes are needed to normalize the expression profiling of target genes. In this present study, the fragments of eight candidate reference genes were cloned and identified from the pest Spodoptera litura. In addition, the expression stability of these genes in different samples from larvae of control and azadirachtin treatments were evaluated by the computational methods of NormFinder, BestKeeper, Delta CT, geNorm, and RefFinder. According to our results, two of the reference genes should be the optimal number for RT-qPCR analysis. Furthermore, the best reference genes for different samples were showed as followed: EF-1α and EF2 for cuticle, β-Tubulin and RPL7A for fat body, EF2 and Actin for midgut, EF2 and RPL13A for larva and RPL13A and RPL7A for all the samples. Our results established a reliable normalization for RT-qPCR experiments in S. litura and ensure the data more accurate for the mechanism analysis of azadirachtin.

An Update on Host-Pathogen Interplay and Modulation of Immune Responses during Orientia tsutsugamushi Infection

The obligate intracellular bacterium Orientia tsutsugamushi is the causative agent of scrub typhus in humans, a serious mite-borne disease present in a widespread area of endemicity, which affects an estimated 1 million people every year. This disease may exhibit a broad range of presentations, ranging from asymptomatic to fatal conditions, with the latter being due to disseminated endothelial infection and organ injury. Unique characteristics of the biology and host-pathogen interactions of O. tsutsugamushi, including the high antigenic diversity among strains and the highly variable, short-lived memory responses developed by the host, underlie difficulties faced in the pursuit of an effective vaccine, which is an imperative need. Other factors that have hindered scientific progress relative to the infectious mechanisms of and the immune response triggered by this bacterium in vertebrate hosts include the limited number of mechanistic studies performed on animal models and the lack of genetic tools currently available for this pathogen. However, recent advances in animal model development are promising to improve our understanding of host-pathogen interactions. Here, we comprehensively discuss the recent advances in and future perspectives on host-pathogen interactions and the modulation of immune responses related to this reemerging disease, highlighting the role of animal models.

Mycobacterium tuberculosis Mce2E suppresses the macrophage innate immune response and promotes epithelial cell proliferation

The intracellular pathogen Mycobacterium tuberculosis (Mtb) can survive in the host and cause disease by interfering with a variety of cellular functions. The mammalian cell entry 2 (mce2) operon of Mtb has been shown to contribute to tuberculosis pathogenicity. However, little is known about the regulatory roles of Mtb Mce2 family proteins towards host cellular functions. Here we show that the Mce2 family protein Mce2E suppressed the macrophage innate immune response and promoted epithelial cell proliferation. Mce2E inhibited activation of the extracellular signal-regulated kinase (ERK) and Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) signaling pathways in a non-canonical D motif (a MAPK-docking motif)-dependent manner, leading to reduced expression of TNF and IL-6 in macrophages. Furthermore, Mce2E promoted proliferation of human lung epithelium-derived lung adenoma A549 cells by inhibiting K48-linked polyubiquitination of eEF1A1 in a β strand region-dependent manner. In summary, Mce2E is a novel multifunctional Mtb virulence factor that regulates host cellular functions in a niche-dependent manner. Our data suggest a potential novel target for TB therapy.

Regulation of eukaryotic elongation factor 1 alpha (eEF1A) by dynamic lysine methylation

Lysine methylation is a frequent post-translational protein modification, which has been intensively studied in the case of histone proteins. Lysine methylations are also found on many non-histone proteins, and one prominent example is eukaryotic elongation factor 1 alpha (eEF1A). Besides its essential role in the protein synthesis machinery, a number of non-canonical functions have also been described for eEF1A, such as regulation of the actin cytoskeleton and the promotion of viral replication. The functional significance of the extensive lysine methylations on eEF1A, as well as the identity of the responsible lysine methyltransferases (KMTs), have until recently remained largely elusive. However, recent discoveries and characterizations of human eEF1A-specific KMTs indicate that lysine methylation of eEF1A can be dynamic and inducible, and modulates mRNA translation in a codon-specific fashion. Here, we give a general overview of eEF1A lysine methylation and discuss its possible functional and regulatory significance, with particular emphasis on newly discovered human KMTs.

Methylation of Elongation Factor 1A: Where, Who, and Why?

Eukaryotic elongation factor 1A (eEF1A) is an essential and highly conserved protein involved in diverse cellular processes, including translation, cytoskeleton organisation, nuclear export, and proteasomal degradation. Recently, nine novel and site-specific methyltransferases were discovered that target eEF1A, five in yeast and four in human, making it the eukaryotic protein with the highest number of independent methyltransferases. Some of these methyltransferases show striking evolutionary conservation. Yet, they come from diverse methyltransferase families, indicating they confer competitive advantage through independent origins. As might be expected, the first functional studies of specific methylation sites found them to have distinct effects, notably on eEF1A-related processes of translation and tRNA aminoacylation. Further functional studies of sites will likely reveal other unique roles for this interesting modification.

Dysregulation of Elongation Factor 1A Expression is Correlated with Synaptic Plasticity Impairments in Alzheimer's Disease

Synaptic dysfunction may represent an early and crucial pathophysiology in Alzheimer's disease (AD). Recent studies implicate a connection between synaptic plasticity deficits and compromised capacity of de novo protein synthesis in AD. The mRNA translational factor eukaryotic elongation factor 1A (eEF1A) is critically involved in several forms of long-lasting synaptic plasticity. By examining postmortem human brain samples, a transgenic mouse model, and application of synthetic human Aβ42 on mouse hippocampal slices, we demonstrated that eEF1A protein levels were significantly decreased in AD, particularly in the hippocampus. In contrast, brain levels of eukaryotic elongation factor 2 were unaltered in AD. Further, upregulation of eEF1A expression by the adenylyl cyclase activator forskolin, which induces long-lasting synaptic plasticity, was blunted in hippocampal slices derived from Tg2576 AD model mice. Finally, Aβ-induced hippocampal long-term potentiation defects were alleviated by upregulation of eEF1A signaling via brain-specific knockdown of the gene encoding tuberous sclerosis 2. In summary, our findings suggest a strong correlation between the dysregulation of eEF1A synthesis and AD-associated synaptic failure. These findings provide insights into the understanding of molecular mechanisms underlying AD etiology and may aid in identification of novel biomarkers and therapeutic targets.

mRNA Translation Gone Awry: Translation Fidelity and Neurological Disease

Errors during mRNA translation can lead to a reduction in the levels of functional proteins and an increase in deleterious molecules. Advances in next-generation sequencing have led to the discovery of rare genetic disorders, many caused by mutations in genes encoding the mRNA translation machinery, as well as to a better understanding of translational dynamics through ribosome profiling. We discuss here multiple neurological disorders that are linked to errors in tRNA aminoacylation and ribosome decoding. We draw on studies from genetic models, including yeast and mice, to enhance our understanding of the translational defects observed in these diseases. Finally, we emphasize the importance of tRNA, their associated enzymes, and the inextricable link between accuracy and efficiency in the maintenance of translational fidelity.

Regulation of mRNA Translation in Neurons-A Matter of Life and Death

Dynamic regulation of mRNA translation initiation and elongation is essential for the survival and function of neural cells. Global reductions in translation initiation resulting from mutations in the translational machinery or inappropriate activation of the integrated stress response may contribute to pathogenesis in a subset of neurodegenerative disorders. Aberrant proteins generated by non-canonical translation initiation may be a factor in the neuron death observed in the nucleotide repeat expansion diseases. Dysfunction of central components of the elongation machinery, such as the tRNAs and their associated enzymes, can cause translational infidelity and ribosome stalling, resulting in neurodegeneration. Taken together, dysregulation of mRNA translation is emerging as a unifying mechanism underlying the pathogenesis of many neurodegenerative disorders.

Treatment with didemnin B, an elongation factor 1A inhibitor, improves hepatic lipotoxicity in obese mice

Eukaryotic elongation factor EEF1A1 is induced by oxidative and ER stress, and contributes to subsequent cell death in many cell types, including hepatocytes. We recently showed that blocking the protein synthesis activity of EEF1A1 with the peptide inhibitor, didemnin B, decreases saturated fatty acid overload-induced cell death in HepG2 cells. In light of this and other recent work suggesting that limiting protein synthesis may be beneficial in treating ER stress-related disease, we hypothesized that acute intervention with didemnin B would decrease hepatic ER stress and lipotoxicity in obese mice with nonalcoholic fatty liver disease (NAFLD). Hyperphagic male ob/ob mice were fed semipurified diet for 4 weeks, and during week 5 received i.p. injections of didemnin B or vehicle on days 1, 4, and 7. Interestingly, we observed that administration of this compound modestly decreased food intake without evidence of illness or distress, and thus included an additional control group matched for food consumption with didemnin B-treated animals. Treatment with didemnin B improved several characteristics of hepatic lipotoxicity to a greater extent than the effects of caloric restriction alone, including hepatic steatosis, and some hepatic markers of ER stress and inflammation (GRP78, Xbp1s, and Mcp1). Plasma lipid and lipoprotein profiles and histopathological measures of NAFLD, including lobular inflammation, and total NAFLD activity score were also improved by didemnin B. These data indicate that acute intervention with the EEF1A inhibitor, didemnin B, improves hepatic lipotoxicity in obese mice with NAFLD through mechanisms not entirely dependent on decreased food intake, suggesting a potential therapeutic strategy for this ER stress-related disease.

Methylation of human eukaryotic elongation factor alpha (eEF1A) by a member of a novel protein lysine methyltransferase family modulates mRNA translation

Many cellular proteins are methylated on lysine residues and this has been most intensively studied for histone proteins. Lysine methylations on non-histone proteins are also frequent, but in most cases the functional significance of the methylation event, as well as the identity of the responsible lysine (K) specific methyltransferase (KMT), remain unknown. Several recently discovered KMTs belong to the so-called seven-β-strand (7BS) class of MTases and we have here investigated an uncharacterized human 7BS MTase currently annotated as part of the endothelin converting enzyme 2, but which should be considered a separate enzyme. Combining in vitro enzymology and analyzes of knockout cells, we demonstrate that this MTase efficiently methylates K36 in eukaryotic translation elongation factor 1 alpha (eEF1A) in vitro and in vivo. We suggest that this novel KMT is named eEF1A-KMT4 (gene name EEF1AKMT4), in agreement with the recently established nomenclature. Furthermore, by ribosome profiling we show that the absence of K36 methylation affects translation dynamics and changes translation speed of distinct codons. Finally, we show that eEF1A-KMT4 is part of a novel family of human KMTs, defined by a shared sequence motif in the active site and we demonstrate the importance of this motif for catalytic activity.

The novel lysine specific methyltransferase METTL21B affects mRNA translation through inducible and dynamic methylation of Lys-165 in human eukaryotic elongation factor 1 alpha (eEF1A)

Lysine methylation is abundant on histone proteins, representing a dynamic regulator of chromatin state and gene activity, but is also frequent on many non-histone proteins, including eukaryotic elongation factor 1 alpha (eEF1A). However, the functional significance of eEF1A methylation remains obscure and it has remained unclear whether eEF1A methylation is dynamic and subject to active regulation. We here demonstrate, using a wide range of in vitro and in vivo approaches, that the previously uncharacterized human methyltransferase METTL21B specifically targets Lys-165 in eEF1A in an aminoacyl-tRNA- and GTP-dependent manner. Interestingly, METTL21B-mediated eEF1A methylation showed strong variation across different tissues and cell lines, and was induced by altering growth conditions or by treatment with certain ER-stress-inducing drugs, concomitant with an increase in METTL21B gene expression. Moreover, genetic ablation of METTL21B function in mammalian cells caused substantial alterations in mRNA translation, as measured by ribosomal profiling. A non-canonical function for eEF1A in organization of the cellular cytoskeleton has been reported, and interestingly, METTL21B accumulated in centrosomes, in addition to the expected cytosolic localization. In summary, the present study identifies METTL21B as the enzyme responsible for methylation of eEF1A on Lys-165 and shows that this modification is dynamic, inducible and likely of regulatory importance.

Elongation factor Tu is a multifunctional and processed moonlighting protein

Many bacterial moonlighting proteins were originally described in medically, agriculturally, and commercially important members of the low G + C Firmicutes. We show Elongation factor Tu (Ef-Tu) moonlights on the surface of the human pathogens Staphylococcus aureus (Sa_Ef-Tu) and Mycoplasma pneumoniae (Mpn_Ef-Tu), and the porcine pathogen Mycoplasma hyopneumoniae (Mhp_Ef-Tu). Ef-Tu is also a target of multiple processing events on the cell surface and these were characterised using an N-terminomics pipeline. Recombinant Mpn_Ef-Tu bound strongly to a diverse range of host molecules, and when bound to plasminogen, was able to convert plasminogen to plasmin in the presence of plasminogen activators. Fragments of Ef-Tu retain binding capabilities to host proteins. Bioinformatics and structural modelling studies indicate that the accumulation of positively charged amino acids in short linear motifs (SLiMs), and protein processing promote multifunctional behaviour. Codon bias engendered by an A + T rich genome may influence how positively-charged residues accumulate in SLiMs.

Protein glutaminylation is a yeast-specific posttranslational modification of elongation factor 1A

Ribosomal translation factors are fundamental for protein synthesis and highly conserved in all kingdoms of life. The essential eukaryotic elongation factor 1A (eEF1A) delivers aminoacyl tRNAs to the A-site of the translating 80S ribosome. Several studies have revealed that eEF1A is posttranslationally modified. Using MS analysis, site-directed mutagenesis, and X-ray structural data analysis of Saccharomyces cerevisiae eEF1A, we identified a posttranslational modification in which the α amino group of mono-l-glutamine is covalently linked to the side chain of glutamate 45 in eEF1A. The MS analysis suggested that all eEF1A molecules are modified by this glutaminylation and that this posttranslational modification occurs at all stages of yeast growth. The mutational studies revealed that this glutaminylation is not essential for the normal functions of eEF1A in S. cerevisiae However, eEF1A glutaminylation slightly reduced growth under antibiotic-induced translational stress conditions. Moreover, we identified the same posttranslational modification in eEF1A from Schizosaccharomyces pombe but not in various other eukaryotic organisms tested despite strict conservation of the Glu⁴⁵ residue among these organisms. We therefore conclude that eEF1A glutaminylation is a yeast-specific posttranslational modification that appears to influence protein translation.

Proteomic analyses of nucleus laminaris identified candidate targets of the fragile X mental retardation protein

The avian nucleus laminaris (NL) is a brainstem nucleus necessary for binaural processing, analogous in structure and function to the mammalian medial superior olive. In chickens (Gallus gallus), NL is a well-studied model system for activity-dependent neural plasticity. Its neurons have bipolar extension of dendrites, which receive segregated inputs from two ears and display rapid and compartment-specific reorganization in response to unilateral changes in auditory input. More recently, fragile X mental retardation protein (FMRP), an RNA-binding protein that regulates local protein translation, has been shown to be enriched in NL dendrites, suggesting its potential role in the structural dynamics of these dendrites. To explore the molecular role of FMRP in this nucleus, we performed proteomic analysis of NL, using micro laser capture and liquid chromatography tandem mass spectrometry. We identified 657 proteins, greatly represented in pathways involved in mitochondria, translation and metabolism, consistent with high levels of activity of NL neurons. Of these, 94 are potential FMRP targets, by comparative analysis with previously proposed FMRP targets in mammals. These proteins are enriched in pathways involved in cellular growth, cellular trafficking and transmembrane transport. Immunocytochemistry verified the dendritic localization of several proteins in NL. Furthermore, we confirmed the direct interaction of FMRP with one candidate, RhoC, by in vitro RNA binding assays. In summary, we provide a database of highly expressed proteins in NL and in particular a list of potential FMRP targets, with the goal of facilitating molecular characterization of FMRP signaling in future studies.

METTL21B Is a Novel Human Lysine Methyltransferase of Translation Elongation Factor 1A: Discovery by CRISPR/Cas9 Knockout

Lysine methylation is widespread on human proteins, however the enzymes that catalyze its addition remain largely unknown. This limits our capacity to study the function and regulation of this modification. Here we used the CRISPR/Cas9 system to knockout putative protein methyltransferases METTL21B and METTL23 in K562 cells, to determine if they methylate elongation factor eEF1A. The known eEF1A methyltransferase EEF1AKMT1 was also knocked out as a control. Targeted mass spectrometry revealed the loss of lysine 165 methylation upon knockout of METTL21B, and the expected loss of lysine 79 methylation on knockout of EEF1AKMT1 No loss of eEF1A methylation was seen in the METTL23 knockout. Recombinant METTL21B was shown in vitro to catalyze methylation on lysine 165 in eEF1A1 and eEF1A2, confirming it as the methyltransferase responsible for this methylation site. Proteomic analysis by SILAC revealed specific upregulation of large ribosomal subunit proteins in the METTL21B knockout, and changes to further processes related to eEF1A function in knockouts of both METTL21B and EEF1AKMT1 This indicates that the methylation of lysine 165 in human eEF1A has a very specific role. METTL21B exists only in vertebrates, with its target lysine showing similar evolutionary conservation. We suggest METTL21B be renamed eEF1A-KMT3. This is the first study to specifically generate CRISPR/Cas9 knockouts of putative protein methyltransferase genes, for substrate discovery and site mapping. Our approach should prove useful for the discovery of further novel methyltransferases, and more generally for the discovery of sites for other protein-modifying enzymes.

Lys48 ubiquitination during the intraerythrocytic cycle of the rodent malaria parasite, Plasmodium chabaudi

Ubiquitination tags proteins for different functions within the cell. One of the most abundant and studied ubiquitin modification is the Lys48 polyubiquitin chain that modifies proteins for their destruction by proteasome. In Plasmodium is proposed that post-translational regulation is fundamental for parasite development during its complex life-cycle; thus, the objective of this work was to analyze the ubiquitination during Plasmodium chabaudi intraerythrocytic stages. Ubiquitinated proteins were detected during intraerythrocytic stages of Plasmodium chabaudi by immunofluorescent microscopy, bidimensional electrophoresis (2-DE) combined with immunoblotting and mass spectrometry. All the studied stages presented protein ubiquitination and Lys48 polyubiquitination with more abundance during the schizont stage. Three ubiquitinated proteins were identified for rings, five for trophozoites and twenty for schizonts. Only proteins detected with a specific anti- Lys48 polyubiquitin antibody were selected for Mass Spectrometry analysis and two of these identified proteins were selected in order to detect the specific amino acid residues where ubiquitin is placed. Ubiquitinated proteins during the ring and trophozoite stages were related with the invasion process and in schizont proteins were related with nucleic acid metabolism, glycolysis and protein biosynthesis. Most of the ubiquitin detection was during the schizont stage and the Lys48 polyubiquitination during this stage was related to proteins that are expected to be abundant during the trophozoite stage. The evidence that these Lys48 polyubiquitinated proteins are tagged for destruction by the proteasome complex suggests that this type of post-translational modification is important in the regulation of protein abundance during the life-cycle and may also contribute to the parasite cell-cycle progression.

Extract of Syzygium aromaticum suppress eEF1A protein expression and fungal growth

AIMS

Clove extract has therapeutic potential as an antifungal drug, yet the mechanism of action remains ambiguous. Current study aimed to address the molecular process of the antifungal activity exerted by clove extract.

METHODS AND RESULTS

The antifungal assay results showed that clove extract had some effects on all of the tested yeast. Propidium iodide staining assay showed cell membrane damage in Saccharomyces cerevisiae after treatment of clove extract for 30 h. Interestingly, SDS-polyacrylamide gel electrophoresis assays revealed that the protein expression of eukaryotic elongation factor 1 alpha (eEF1A) was suppressed significantly after treatment with clove extract (not pure eugenol). Transcriptional analyses revealed that the TEF1 and TEF2 genes (translation elongation factor EF-1 alpha) encoding eEF1A were not disturbed with the addition of clove extract; however, the expression of related genes EFB1 (translation elongation factor 1 subunit beta), ENO2 (phosphopyruvate hydratase ENO2), GSP1 (Ran GTPase GSP1), RPP0 (ribosomal protein P0), YEF3 (translation elongation factor EF-3), TEF4 (translation elongation factor EF1B gamma), and RPS2 (ribosomal 40S subunit protein S2) increased significantly.

CONCLUSIONS

These results suggest that clove extract plays a role in disrupting growth and affecting yeast metabolism. eEF1A was affected by clove extract at the protein level but not at the transcriptional level.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is based on a detailed study of antifungal action exerted by clove extract, and proposed that down-regulation of eEF1A protein expression may contribute to its antifungal activity. These results may have clinical significance for future application of clove extract as a natural antifungal agent.

Heterozygous mutation of eEF1A1b resulted in spermatogenesis arrest and infertility in male tilapia, Oreochromis niloticus

Eukaryotic elongation factor 1 alpha (eEF1A) is an essential component of the translational apparatus. In the present study, eEF1A1b was isolated from the Nile tilapia. Real-time PCR and Western blot revealed that eEF1A1b was expressed highly in the testis from 90 dah (days after hatching) onwards. In situ hybridization and immunohistochemistry analyses showed that eEF1A1b was highly expressed in the spermatogonia of the testis. CRISPR/Cas9 mediated mutation of eEF1A1b resulted in spermatogenesis arrest and infertility in the F0 XY fish. Consistently, heterozygous mutation of eEF1A1b (eEF1A1b+/-) resulted in an absence of spermatocytes at 90 dah, very few spermatocytes, spermatids and spermatozoa at 180 dah, and decreased Cyp11b2 and serum 11-ketotestosterone level at both stages. Further examination of the fertilization capacity of the sperm indicated that the eEF1A1b+/- XY fish were infertile due to abnormal spermiogenesis. Transcriptomic analyses of the eEF1A1b+/- testis from 180 dah XY fish revealed that key elements involved in spermatogenesis, steroidogenesis and sperm motility were significantly down-regulated compared with the control XY. Transgenic overexpression of eEF1A1b rescued the spermatogenesis arrest phenotype of the eEF1A1b+/- testis. Taken together, our data suggested that eEF1A1b is crucial for spermatogenesis and male fertility in the Nile tilapia.

Expanded polyalanine tracts function as nuclear export signals and promote protein mislocalization via eEF1A1 factor

Polyalanine (poly(A)) diseases are caused by the expansion of translated GCN triplet nucleotide sequences encoding poly(A) tracts in proteins. To date, nine human disorders have been found to be associated with poly(A) tract expansions, including congenital central hypoventilation syndrome and oculopharyngeal muscular dystrophy. Previous studies have demonstrated that unexpanded wild-type poly(A)-containing proteins localize to the cell nucleus, whereas expanded poly(A)-containing proteins primarily localize to the cytoplasm. Because most of these poly(A) disease proteins are transcription factors, this mislocalization causes cellular transcriptional dysregulation leading to cellular dysfunction. Correcting this faulty localization could potentially point to strategies to treat the aforementioned disorders, so there is a pressing need to identify the mechanisms underlying the mislocalization of expanded poly(A) protein. Here, we performed a glutathione S-transferase pulldown assay followed by mass spectrometry and identified eukaryotic translation elongation factor 1 α1 (eEF1A1) as an interacting partner with expanded poly(A)-containing proteins. Strikingly, knockdown of eEF1A1 expression partially corrected the mislocalization of the expanded poly(A) proteins in the cytoplasm and restored their functions in the nucleus. We further demonstrated that the expanded poly(A) domain itself can serve as a nuclear export signal. Taken together, this study demonstrates that eEF1A1 regulates the subcellular location of expanded poly(A) proteins and is therefore a potential therapeutic target for combating the pathogenesis of poly(A) diseases.

Mechanism and Regulation of Protein Synthesis in Saccharomyces cerevisiae

In this review, we provide an overview of protein synthesis in the yeast Saccharomyces cerevisiae The mechanism of protein synthesis is well conserved between yeast and other eukaryotes, and molecular genetic studies in budding yeast have provided critical insights into the fundamental process of translation as well as its regulation. The review focuses on the initiation and elongation phases of protein synthesis with descriptions of the roles of translation initiation and elongation factors that assist the ribosome in binding the messenger RNA (mRNA), selecting the start codon, and synthesizing the polypeptide. We also examine mechanisms of translational control highlighting the mRNA cap-binding proteins and the regulation of GCN4 and CPA1 mRNAs.

SPL33, encoding an eEF1A-like protein, negatively regulates cell death and defense responses in rice

Lesion-mimic mutants are useful to dissect programmed cell death and defense-related pathways in plants. Here we identified a new rice lesion-mimic mutant, spotted leaf 33 (spl33) and cloned the causal gene by a map-based cloning strategy. SPL33 encodes a eukaryotic translation elongation factor 1 alpha (eEF1A)-like protein consisting of a non-functional zinc finger domain and three functional EF-Tu domains. spl33 exhibited programmed cell death-mediated cell death and early leaf senescence, as evidenced by analyses of four histochemical markers, namely H2O2 accumulation, cell death, callose accumulation and TUNEL-positive nuclei, and by four indicators, namely loss of chlorophyll, breakdown of chloroplasts, down-regulation of photosynthesis-related genes, and up-regulation of senescence-associated genes. Defense responses were induced in the spl33 mutant, as shown by enhanced resistance to both the fungal pathogen Magnaporthe oryzae and the bacterial pathogen Xanthomonas oryzae pv. oryzae and by up-regulation of defense response genes. Transcriptome analysis of the spl33 mutant and its wild type provided further evidence for the biological effects of loss of SPL33 function in cell death, leaf senescence and defense responses in rice. Detailed analyses showed that reactive oxygen species accumulation may be the cause of cell death in the spl33 mutant, whereas uncontrolled activation of multiple innate immunity-related receptor genes and signaling molecules may be responsible for the enhanced disease resistance observed in spl33. Thus, we have demonstrated involvement of an eEF1A-like protein in programmed cell death and provided a link to defense responses in rice.

Comprehensive Identification of mRNA-Binding Proteins of Leishmania donovani by Interactome Capture

Leishmania are unicellular eukaryotes responsible for leishmaniasis in humans. Like other trypanosomatids, leishmania regulate protein coding gene expression almost exclusively at the post-transcriptional level with the help of RNA binding proteins (RBPs). Due to the presence of polycystronic transcription units, leishmania do not regulate RNA polymerase II-dependent transcription initiation. Recent evidence suggests that the main control points in gene expression are mRNA degradation and translation. Protein-RNA interactions are involved in every aspect of RNA biology, such as mRNA splicing, polyadenylation, localization, degradation, and translation. A detailed picture of these interactions would likely prove to be highly informative in understanding leishmania biology and virulence. We developed a strategy involving covalent UV cross-linking of RBPs to mRNA in vivo, followed by interactome capture using oligo(dT) magnetic beads to define comprehensively the mRNA interactome of growing L. donovani amastigotes. The protein mass spectrometry analysis of captured proteins identified 79 mRNA interacting proteins which withstood very stringent washing conditions. Strikingly, we found that 49 of these mRNA interacting proteins had no orthologs or homologs in the human genome. Consequently, these may represent high quality candidates for selective drug targeting leading to novel therapeutics. These results show that this unbiased, systematic strategy has the promise to be applicable to study the mRNA interactome during various biological settings such as metabolic changes, stress (low pH environment, oxidative stress and nutrient deprivation) or drug treatment.