eEF1A2 exacerbated insulin resistance in male skeletal muscle via PKCβ and ER stress

Recent studies raise the possibility that eukaryotic translation elongation factor 1 alpha (eEF1A) may play a role in metabolism. One isoform, eEF1A2, is specifically expressed in skeletal muscle, heart and brain. It regulates translation elongation and signal transduction. Nonetheless, eEF1A2's function in skeletal muscle glucose metabolism remains unclear. In the present study, suppression subtractive hybridisation showed a decrease in Eef1a2 transcripts in the skeletal muscle of diabetic Mongolian gerbils. This was confirmed at mRNA and protein levels in hyperglycaemic gerbils, and in db/db and high-fat diet-fed mice. Further, this downregulation was independent of Eef1a2 promoter methylation. Interestingly, adeno-associated virus-mediated eEF1A2 overexpression in skeletal muscle aggravated fasting hyperglycaemia, hyperinsulinaemia and glucose intolerance in male diabetic gerbils but not in female gerbil models. The overexpression of eEF1A2 in skeletal muscle also resulted in promoted serum glucose levels and insulin resistance in male db/db mice. Up- and downregulation of eEF1A2 by lentiviral vector transfection confirmed its inhibitory effect on insulin-stimulated glucose uptake and signalling transduction in C2C12 myotubes with palmitate (PA)-induced insulin resistance. Furthermore, eEF1A2 bound PKCβ and increased its activation in the cytoplasm, whereas suppression of PKCβ by an inhibitor attenuated eEF1A2-mediated impairment of insulin sensitivity in insulin-resistant myotubes. Endoplasmic reticulum (ER) stress was elevated by eEF1A2, whereas suppression of ER stress or JNK partially restored insulin sensitivity in PA-treated myotubes. Additionally, eEF1A2 inhibited lipogenesis and lipid utilisation in insulin-resistant skeletal muscle. Collectively, we demonstrated that eEF1A2 exacerbates insulin resistance in male murine skeletal muscle via PKCβ and ER stress.

Elongation Factor 1A-1 Is a Mediator of Hepatocyte Lipotoxicity Partly through Its Canonical Function in Protein Synthesis

Elongation factor 1A-1 (eEF1A-1) has non-canonical functions in regulation of the actin cytoskeleton and apoptosis. It was previously identified through a promoter-trap screen as a mediator of fatty acid-induced cell death (lipotoxicity), and was found to participate in this process downstream of ER stress. Since ER stress is implicated in the pathogenesis of nonalcoholic fatty liver disease (NAFLD), we investigated the mechanism of action of eEF1A-1 in hepatocyte lipotoxicity. HepG2 cells were exposed to excess fatty acids, followed by assessments of ER stress, subcellular localization of eEF1A-1, and cell death. A specific inhibitor of eEF1A-1 elongation activity, didemnin B, was used to determine whether its function in protein synthesis is involved in lipotoxicity. Within 6 h, eEF1A-1 protein was modestly induced by high palmitate, and partially re-localized from its predominant location at the ER to polymerized actin at the cell periphery. This early induction and subcellular redistribution of eEF1A-1 coincided with the onset of ER stress, and was later followed by cell death. Didemnin B did not prevent the initiation of ER stress by high palmitate, as indicated by eIF2α phosphorylation. However, consistent with sustained inhibition of eEF1A-1-dependent elongation activity, didemnin B prevented the recovery of protein synthesis and increase in GRP78 protein that are normally associated with later phases of the response to ongoing ER stress. This resulted in decreased palmitate-induced cell death. Our data implicate eEF1A-1, and its function in protein synthesis, in hepatocyte lipotoxicity.

Eukaryotic translation elongation factor 1-alpha 1 inhibits p53 and p73 dependent apoptosis and chemotherapy sensitivity

The p53 family of transcription factors is a key regulator of cell proliferation and death. In this report we identify the eukaryotic translation elongation factor 1-alpha 1 (eEF1A1) to be a novel p53 and p73 interacting protein. Previous studies have demonstrated that eEF1A1 has translation-independent roles in cancer. We report that overexpression of eEF1A1 specifically inhibits p53-, p73- and chemotherapy-induced apoptosis resulting in chemoresistance. Short-interfering RNA-mediated silencing of eEF1A1 increases chemosensitivity in cell lines bearing wild type p53, but not in p53 null cells. Furthermore, silencing of eEF1A1 partially rescues the chemoresistance observed in response to p53 or p73 knockdown, suggesting that eEF1A1 is a negative regulator of the pro-apoptotic function of p53 and p73. Thus, in the context of p53-family signaling, eEF1A1 has anti-apoptotic properties. These findings identify a novel mechanism of regulation of the p53 family of proteins by eEF1A1 providing additional insight into potential targets to sensitize tumors to chemotherapy.

The yeast rapid tRNA decay pathway competes with elongation factor 1A for substrate tRNAs and acts on tRNAs lacking one or more of several modifications

The structural and functional integrity of tRNA is crucial for translation. In the yeast Saccharomyces cerevisiae, certain aberrant pre-tRNA species are subject to nuclear surveillance, leading to 3' exonucleolytic degradation, and certain mature tRNA species are subject to rapid tRNA decay (RTD) if they are appropriately hypomodified or bear specific destabilizing mutations, leading to 5'-3' exonucleolytic degradation by Rat1 and Xrn1. Thus, trm8-Δ trm4-Δ strains are temperature sensitive due to lack of m(7)G(46) and m(5)C and the consequent RTD of tRNA(Val(AAC)), and tan1-Δ trm44-Δ strains are temperature sensitive due to lack of ac(4)C(12) and Um(44) and the consequent RTD of tRNA(Ser(CGA)) and tRNA(Ser(UGA)). It is unknown how the RTD pathway interacts with translation and other cellular processes, and how generally this pathway acts on hypomodified tRNAs. We provide evidence here that elongation factor 1A (EF-1A) competes with the RTD pathway for substrate tRNAs, since its overexpression suppresses the tRNA degradation and the growth defect of strains subject to RTD, whereas reduced levels of EF-1A have the opposite effect. We also provide evidence that RTD acts on a variety of tRNAs lacking one or more different modifications, since trm1-Δ trm4-Δ mutants are subject to RTD of tRNA(Ser(CGA)) and tRNA(Ser(UGA)) due to lack of m(2,2)G(26) and m(5)C, and since trm8-Δ, tan1-Δ, and trm1-Δ single mutants are each subject to RTD. These results demonstrate that RTD interacts with the translation machinery and acts widely on hypomodified tRNAs.

Prostate-tumor-inducing gene-1 analysis in human prostate cancer cells and tissue in relation to Mycoplasma infection

The potential role of PTI-1, in the natural story of prostate adenocarcinoma remains to be fully determined. PTI-1 expression was evaluated in human prostate cancer cell lines and in paraffin-embedded archive tissues. PTI-1 expression was found in Mycoplasma infected but not in non-infected cells. The lack of PTI-1 expression was also confirmed in fixed and paraffin-embedded human cancer prostate biopsies. The overall data indicate that, in prostate tumor cell lines, PTI-1 presence parallels Mycoplasma infection suggesting that PTI-1 might not necessarily play a major role in the onset of prostate tumorigenesis.

Eukaryotic elongation factor 1A interacts with Turnip mosaic virus RNA-dependent RNA polymerase and VPg-Pro in virus-induced vesicles

Eukaryotic elongation factor 1-alpha (eEF1A) was identified as an interactor of Turnip mosaic virus (TuMV) RNA-dependent RNA polymerase (RdRp) and VPg-protease (VPg-Pro) using tandem affinity purification and/or in vitro assays. Subcellular fractionation experiments revealed that the level of eEF1A substantially increased in membrane fractions upon TuMV infection. Replication of TuMV occurs in cytoplasmic membrane vesicles, which are induced by 6K-VPg-Pro. Confocal microscopy indicated that eEF1A was included in these vesicles. To confirm that eEF1A was found in replication vesicles, we constructed an infectious recombinant TuMV that contains an additional copy of the 6K protein fused to the green fluorescent protein (GFP). In cells infected with this recombinant TuMV, fluorescence emitted by 6KGFP was associated with cytoplasmic membrane vesicles that contained VPg-Pro, the eukaryotic initiation factor (iso) 4E, the poly(A)-binding protein, the heat shock cognate 70-3 protein, and eEF1A. These results suggest that TuMV-induced membrane vesicles host at least three plant translation factors in addition to the viral replication proteins.

Characterization of a Putative Ovarian Oncogene, Elongation Factor 1α, Isolated by Panning a Synthetic Phage Display Single-Chain Variable Fragment Library with Cultured Human Ovarian Cancer Cells

PURPOSE

In an effort to identify cell surface targets and single short-chain antibody (scFv) for ovarian cancer therapy, we used a phage display approach to isolate an antibody with high reactivity against ovarian cancer.

EXPERIMENTAL DESIGN

A phage scFv library was subjected to panning against human SK-OV-3 ovarian cancer cells. A clone with high reactivity was selected and tested in immunoperoxidase staining on a panel of normal tissues and ovarian carcinoma. Using immunoprecipitation, a differentially expressed band was analyzed by mass spectrometry. The antigen subclass was characterized with reverse transcription-PCR on cDNA library of normal tissues, and 91 ovarian cancer specimens, and correlated with clinicohistopathologic characteristics.

RESULTS

Ninety-six individual scFv clones were screened in ELISA following panning. scFv F7 revealed high reactivity with ovarian cancer cell lines and showed intense staining of 15 fresh ovarian cancer specimens and no staining of a panel of normal tissues. A 40-kDa protein was identified to be translation elongation factor 1alpha1 (EEF1A1; P < 0.05). The expression of EEF1A2, a highly homologous and functionally similar oncogene, was found to be restricted only to the normal tissues of the heart, brain, and skeletal muscle. Aberrant EEF1A2 mRNA expression was found in 21 of 91 (23%) of ovarian cancer specimens and significantly correlated with increased likelihood of recurrence (P = 0.021).

CONCLUSIONS

scFv F7 may represent an ovarian cancer-specific antibody against translation EEF1A family of translational factors. We propose that EEF1A2 may be a useful target for therapy of human ovarian cancer.

Elongation factor 1a mediates the specificity of mitochondrial tRNA import in T. brucei

Mitochondrial tRNA import is widespread in eukaryotes. Yet, the mechanism that determines its specificity is unknown. Previous in vivo experiments using the tRNAs(Met), tRNA(Ile) and tRNA(Lys) have suggested that the T-stem nucleotide pair 51:63 is the main localization determinant of tRNAs in Trypanosoma brucei. In the cytosol-specific initiator tRNA(Met), this nucleotide pair is identical to the main antideterminant that prevents interaction with cytosolic elongation factor (eEF1a). Here we show that ablation of cytosolic eEF1a, but not of initiation factor 2, inhibits mitochondrial import of newly synthesized tRNAs well before translation or growth is affected. tRNA(Sec) is the only other cytosol-specific tRNA in T. brucei. It has its own elongation factor and does not bind eEF1a. However, a mutant of the tRNA(Sec) expected to bind to eEF1a is imported into mitochondria. This import requires eEF1a and aminoacylation of the tRNA. Thus, for a tRNA to be imported into the mitochondrion of T. brucei, it needs to bind eEF1a, and it is this interaction that mediates the import specificity.

The elongation factor 1A: a novel regulator in the DNA replication/repair protein network in wheat cells?

Proliferating cell nuclear antigen (PCNA) is a DNA sliding clamp interacting with multiple partners in DNA transactions such as DNA replication/repair and recombination as well as chromatin assembly. We previously detected and purified by chromatographic procedures a 31 kDa PCNA from cultured wheat cells (Triticum monococcum L). Here we report the complete sequence of the wheat 31 kDa PCNA showing a very high aminoacid identity with its plant counterparts (maize and rice). This recombinant PCNA has been used as a bait in an affinity chromatography procedure, in order to capture PCNA interacting proteins. We detected by liquid chromatography, tandem mass spectrometry and search in plant protein databases, several specific bands from wheat cell lysates in fractions bound to wheat PCNA-affinity column. One of them is the wheat elongation factor 1A. Its putative regulatory role in DNA replication/repair is discussed.

eEF1A2 activates Akt and stimulates Akt-dependent actin remodeling, invasion and migration

eEF1A2 (eukaryotic protein elongation factor 1 alpha 2) is a protein translation factor that is likely a human oncogene by virtue of its capacity to transform mammalian cells and its high expression in tumors of the ovary, breast and lung. Here, we show that expression of eEF1A2 is sufficient to stimulate the formation of filopodia in BT549 human breast cancer cells and non-transformed Rat2 cells. Filopodia formation in eEF1A2-expressing cells is dependent on the activity of phosphatidylinositol-3 kinase (PI3K), and the ROCK and Akt kinases. Furthermore, eEF1A2 expression is sufficient to activate Akt in a PI3K-dependent fashion and inactivation of eEF1A2 by short interfering RNA reduces Akt activity. Using breast cancer cell line BT 549, we show that eEF1A2 expression stimulates cell migration and invasion in a largely PI3K- and Akt-dependent manner. These results suggest that eEF1A2 regulates oncogenesis through Akt and PI3K-dependent cytoskeletal remodeling.

Elongation factor 1A family regulates the recycling of the M4 muscarinic acetylcholine receptor

In this study, we tested the hypothesis that the elongation 1A (eEF1A) family regulates the cell surface density of the M4 subtype of the muscarinic acetylcholine receptors (mAChR) following agonist-induced internalization. Here, we show that mouse brains lacking eEF1A2 have no detectable changes in M4 expression or localization. We, however, did discover that eEF1A1, the other eEF1A isoform, is expressed in adult neurons contrary to previous reports. This novel finding suggested that the lack of change in M4 expression and distribution in brains lacking eEF1A2 might be due to compensatory effects of eEF1A1. Supporting this theory, we demonstrate that the overexpression of either eEF1A1 or eEF1A2 inhibits M4 recovery to the cell surface after agonist-induced internalization in PC12 cells. Furthermore, eEF1A1 or eEF1A2 had no effect on the recovery of the M1 subtype in PC12 cells. These results demonstrate the novel ability of the eEF1A family to specifically regulate the M4 mAChR.

eEF1B: At the dawn of the 21st century

Translational regulation of gene expression in eukaryotes can rapidly and accurately control cell activity in response to stimuli or when rapidly dividing. There is increasing evidence for a key role of the elongation step in this process. Elongation factor-1 (eEF1), which is responsible for aminoacyl-tRNA transfer on the ribosome, is comprised of two entities: a G-protein named eEF1A and a nucleotide exchange factor, eEF1B. The multifunctional nature of eEF1A, as well as its oncogenic potential, is currently the subject of a number of studies. Until recently, less work has been done on eEF1B. This review describes the macromolecular complexity of eEF1B, its multiple phosphorylation sites and numerous cellular partners, which lead us to suggest an essential role for the factor in the control of gene expression, particularly during the cell cycle.

A critical role for eukaryotic elongation factor 1A-1 in lipotoxic cell death

The deleterious consequences of fatty acid (FA) and neutral lipid accumulation in nonadipose tissues, such as the heart, contribute to the pathogenesis of type 2 diabetes. To elucidate mechanisms of FA-induced cell death, or lipotoxicity, we generated Chinese hamster ovary (CHO) cell mutants resistant to palmitate-induced death and isolated a clone with disruption of eukaryotic elongation factor (eEF) 1A-1. eEF1A-1 involvement in lipotoxicity was confirmed in H9c2 cardiomyoblasts, in which small interfering RNA-mediated knockdown also conferred palmitate resistance. In wild-type CHO and H9c2 cells, palmitate increased reactive oxygen species and induced endoplasmic reticulum (ER) stress, changes accompanied by increased eEF1A-1 expression. Disruption of eEF1A-1 expression rendered these cells resistant to hydrogen peroxide- and ER stress-induced death, indicating that eEF1A-1 plays a critical role in the cell death response to these stressors downstream of lipid overload. Disruption of eEF1A-1 also resulted in actin cytoskeleton defects under basal conditions and in response to palmitate, suggesting that eEF1A-1 mediates lipotoxic cell death, secondary to oxidative and ER stress, by regulating cytoskeletal changes critical for this process. Furthermore, our observations of oxidative stress, ER stress, and induction of eEF1A-1 expression in a mouse model of lipotoxic cardiomyopathy implicate this cellular response in the pathophysiology of metabolic disease.

Plasmid vectors harboring cellular promoters can induce prolonged gene expression in hematopoietic and mesenchymal progenitor cells

Although prolonged transgene expression in progenitor cells might be desirable for modified cell therapy, the viral promoter-based expression vector tends to promote transgene expression only for a limited period. Here, we examined the ability of cellular promoters from elongation factor-1alpha (EF-1alpha) and ubiquitin C to drive gene expression in hematopoietic TF-1 and mesenchymal progenitor cells. We compared the expression levels and duration of a model gene, interleukin-2, generated by the cellular promoters to those by the cytomegalovirus (CMV) promoter. The EF-1alpha and ubiquitin C promoters drove prolonged gene expression in hematopoietic TF-1 and mesenchymal progenitor cells, whereas the CMV promoter did not. At day 7 after transfection in TF-1 cells, the mRNA expression levels of interleukin-2 driven by the EF-1alpha and ubiquitin C promoters were 118- and 56-fold higher, respectively, than those driven by the CMV promoter. Similarly, in mesenchymal progenitor cells, the expression levels of interleukin-2 driven by the EF-1alpha and ubiquitin C promoters were 98- and 20-fold higher, respectively, than that driven by the CMV promoter-encoding plasmid. Moreover, the ubiquitin C promoter directed higher levels of green fluorescence protein expression in mesenchymal progenitor cells than did the CMV promoter. These results indicate that the use of cellular promoters such as those for EF-1alpha and ubiquitin C might direct prolonged gene expression in hematopoietic and mesenchymal progenitor cells.

Leishmania donovani engages in regulatory interference by targeting macrophage protein tyrosine phosphatase SHP-1

Protozoan parasites of the genus leishmania are obligate intracellular parasites of monocytes and macrophages. These pathogens have evolved to invade the mammalian immune system and typically survive for long periods of time. Leishmania have developed a variety of remarkable strategies to prevent their elimination by both innate and acquired immune effector mechanisms. One particular strategy of interest involves manipulation of host cell regulatory pathways so as to prevent macrophage activation required for efficient microbicidal activity. These interference mechanisms are the main focus of this review. Several lines of evidence have been developed to show that the Src homology-2 domain containing tyrosine phosphatase-1 (SHP-1) becomes activated in leishmania-infected cells and that this contributes to disease pathogenesis. Recent studies aimed at understanding the mechanism responsible for the change in activation state of SHP-1 led to the identification of leishmania EF-1alpha as an SHP-1 binding protein and SHP-1 activator. This was a surprising finding given that this ubiquitous and highly conserved protein plays an essential role in protein translation in both prokaryotic and eukaryotic cells. The role of leishmania EF-1alpha as an SHP-1 activator and its contribution to pathogenesis are reviewed with particular attention to the properties that distinguish it from host EF-1alpha.

Proteasome-mediated degradation of cotranslationally damaged proteins involves translation elongation factor 1A

Rad23 and Rpn10 play synergistic roles in the recognition of ubiquitinated proteins by the proteasome, and loss of both proteins causes growth and proteolytic defects. However, the physiological targets of Rad23 and Rpn10 have not been well defined. We report that rad23Delta rpn10Delta is unable to grow in the presence of translation inhibitors, and this sensitivity was suppressed by translation elongation factor 1A (eEF1A). This discovery suggested that Rad23 and Rpn10 perform a role in translation quality control. Certain inhibitors increase translation errors during protein synthesis and cause the release of truncated polypeptide chains. This effect can also be mimicked by ATP depletion. We determined that eEF1A interacted with ubiquitinated proteins and the proteasome following ATP depletion. eEF1A interacted with the proteasome subunit Rpt1, and the turnover of nascent damaged proteins was deficient in rpt1. An eEF1A mutant (eEF1A(D156N)) that conferred hyperresistance to translation inhibitors was much more effective at eliminating damaged proteins and was detected in proteasomes in untreated cells. We propose that eEF1A is well suited to detect and promote degradation of damaged proteins because of its central role in translation elongation. Our findings provide a mechanistic foundation for defining how cellular proteins are degraded cotranslationally.

The translation elongation factor eEF1B plays a role in the oxidative stress response pathway

The multi-subunit guanine nucleotide exchange factor eEF1B for Saccharomyces cerevisiae Translation Elongation Factor 1A (eEF1A) has catalytic (eEF1Balpha) and noncatalytic (eEF1Bgamma) subunits. Deletion of the two nonessential genes encoding eEF1Bgamma has no dramatic effects on total protein synthesis or translational fidelity. Instead, loss of each gene gives resistance to oxidative stress, and loss of both is additive. The level of stress resistance is similar to overexpression of the Yap1p stress transcription factor and is dependent on the presence of the YAP1gene. Cells lacking the catalytic eEF1Balpha subunit show even greater resistance to CdSO(4), with or without eEF1Bgamma present. Thus, the loss of guanine nucleotide exchange activity promotes the resistance. As nucleotide exchange is a critical regulator of most G-proteins, these results indicate a new mechanism in the growing list of examples of post-transcriptional responses to cellular stress.

eEF1A binding to aminoacylated viral RNA represses minus strand synthesis by TYMV RNA-dependent RNA polymerase

The genomic RNA of Turnip yellow mosaic virus (TYMV) has an 82-nucleotide-long tRNA-like structure at its 3'-end that can be valylated and then form a stable complex with translation elongation factor eEF1A.GTP. Transcription of this RNA by TYMV RNA-dependent RNA polymerase (RdRp) to yield minus strands has previously been shown to initiate within the 3'-CCA sequence. We have now demonstrated that minus strand synthesis is strongly repressed upon the binding of eEF1A.GTP to the valylated viral RNA. eEF1A.GTP had no effect on RNA synthesis templated by non-aminoacylated RNA. Higher eEF1A.GTP levels were needed to repress minus strand synthesis templated by valyl-EMV TLS RNA, which binds eEF1A.GTP with lower affinity than does valyl-TYMV RNA. Repression by eEF1A.GTP was also observed with a methionylated variant of TYMV RNA and with aminoacylated tRNAHis, tRNAAla, and tRNAPhe transcripts. It is proposed that minus strand repression by eEF1A.GTP binding occurs early during infection to help coordinate the competing translation and replication functions of the genomic RNA.

Axonal transport of eukaryotic translation elongation factor 1alpha mRNA couples transcription in the nucleus to long-term facilitation at the synapse

Long-term synaptic plasticity requires both gene expression in the nucleus and local protein synthesis at synapses. The effector proteins that link molecular events in the cell body with local maintenance of synaptic strength are not known. We now show that treatment with serotonin (5-HT) that produces long-term facilitation induces the Aplysia eukaryotic translation elongation factor 1alpha (Ap-eEF1A) as a late gene that might serve this coupling function in sensory neurons. Although the translation factor is induced, it is not transported into axon processes when the stimulation with 5-HT was restricted to the cell body. In contrast, its mRNA is transported when 5-HT was applied to both cell body and synapses. Intracellular injection of antisense oligonucleotides or antibodies that block the induction and expression of Ap-eEF1A do not affect the initial expression of long-term facilitation but do block its maintenance beyond 24 h. The transport of eEF1A protein and its mRNA to nerve terminals suggests that the translation factor plays a role in the local protein synthesis that is essential for maintaining newly formed synapses.

The role of protein elongation factor eEF1A2 in ovarian cancer

Frequent gains of chromosome 20q12-13 in ovarian tumors indicate that at least one important oncogene is found at that locus. One of the genes there is EEF1A2, which maps to 20q13.3 and encodes protein elongation factor eEF1A2. This review will focus on recent evidence indicating that EEF1A2 is an important ovarian oncogene and that the protein elongation network can activate tumorigenesis and inhibit apoptosis.

Efficient transduction of primary human B lymphocytes and nondividing myeloma B cells with HIV-1-derived lentiviral vectors

We studied the transduction of primary human B lymphocytes and myeloma cells with lentiviral vectors. In peripheral blood B cells that had been activated with helper T cells (murine thymoma EL-4 B5) and cytokines, multiply attenuated HIV-1-derived vectors pseudotyped with vesicular stomatitis virus (VSV) G-envelope protein achieved the expression of green fluorescence protein (GFP) in 27% +/- 12% (mean +/- 1 SD; median, 27%) of B cells in different experiments. When compared in parallel cultures, the transducibility of B cells from different donors exhibited little variation. The human cytomegalovirus (CMV) promoter gave 4- to 6-fold higher GFP expression than did the human elongation factor-1alpha promoter. A murine retroviral vector pseudotyped with VSV G protein proved inefficient even in mitotically active primary B cells. B cells freshly stimulated with Epstein-Barr virus were also transducible by HIV vectors (24% +/- 9%), but B cells activated with CD40 ligand and cytokines resisted transduction. Thus, different culture systems gave different results. Freshly isolated, nondividing myeloma cells were efficiently transduced by HIV vectors; for 6 myelomas the range was 14% to 77% (median, 28%) GFP(+) cells. HIV vectors with a mutant integrase led to no significant GFP signal in primary B or myeloma cells, suggesting that vector integration was required for high transduction. In conclusion, HIV vectors are promising tools for studies of gene functions in primary human B cells and myeloma cells for the purposes of research and the development of gene therapies.

Extended conformation of mammalian translation elongation factor 1A in solution

The conformation of mammalian elongation factor eEF1A in solution was examined by the small angle neutron scattering and scanning microcalorimetry. We have found that in contrast to the bacterial analogue the eEF1A molecule has no fixed rigid structure in solution. The radius of gyration of the eEF1A molecule (5.2 nm) is much greater than that of prokaryotic EF1A. The specific heat of denaturation is considerably lower for eEF1A than for EF1A, suggesting that the eEF1A conformation is significantly more disordered. Despite its flexible conformation, eEF1A is found to be highly active in different functional tests. According to the neutron scattering data, eEF1A becomes much more compact in the complex with uncharged tRNA. The absence of a rigid structure and the possibility of large conformational change upon interaction with a partner molecule could be important for eEF1A functioning in channeled protein synthesis and/or for the well-known capability of the protein to interact with different ligands besides the translational components.

Translation elongation-3-like factors: are they rational antifungal targets?

The occurrence of fungal infection has escalated significantly in recent years and is expected to continue to increase for the foreseeable future. Unfortunately, only a limited number of antifungal drugs are currently available partially due to a lack of suitable targets. The most commonly used antifungals target the same molecule in the cell membrane and, while efficacious, are either extremely toxic or susceptible to resistance. This article examines elongation factor-3, which is unique to fungi and essential for fungal cell survival and, thus, an attractive antifungal target. A search for inhibitors of this 'perfect target' led to identification of compounds (sordarins) which inhibited elongation factor-2, a protein with a mammalian homologue. Molecular analysis demonstrated why sordarins can specifically act against fungal elongation factor-2. This data questions the validity of pursuing genes as targets only if they are unique to fungi. Proteins that are homologous to elongation factor-3 are also discussed. The advances in molecular techniques and bioinformatics will allow the re-evaluation of targets previously thought to be unattractive. In addition, molecular genetics provides new and novel information on cellular processes that can potentially introduce new targets.

Interaction of the eukaryotic elongation factor 1A with newly synthesized polypeptides

eEF1A, the eukaryotic homologue of bacterial elongation factor Tu, is a well characterized translation elongation factor responsible for delivering aminoacyl-tRNAs to the A-site at the ribosome. Here we show for the first time that eEF1A also associates with the nascent chain distal to the peptidyltransferase center. This is demonstrated for a variety of nascent chains of different lengths and sequences. Interestingly, unlike other ribosome-associated factors, eEF1A also interacts with polypeptides after their release from the ribosome. We demonstrate that eEF1A does not bind to correctly folded full-length proteins but interacts specifically with proteins that are unable to fold correctly in a cytosolic environment. This association was demonstrated both by photo-cross-linking and by a functional refolding assay.

G13A substitution affects the biochemical and physical properties of the elongation factor 1 alpha. A reduced intrinsic GTPase activity is partially restored by kirromycin

The G13A substitution in the G13XXXXGK[T,S] consensus sequence of the elongation factor 1 alpha from the archaeon Sulfolobus solfataricus (SsEF-1 alpha) was introduced in order to study the reasons for selective differences found in the homologous consensus element AXXXXGK[T,S] of the other elongation factor EF-2 or EF-G. In a previous work, it was shown that the main effect of the A26G mutation was the activation of the intrinsic GTPase of SsEF-2 [De Vendittis, E., Adinolfi, B. S., Amatruda, M. R., Raimo, G., Masullo, M., and Bocchini, V. (1994) Eur. J. Biochem. 262, 600-605]. In this work, we found that, compared to the wild-type factor (SsEF-1 alpha wt), G13ASsEF-1 alpha shows (i) a reduced rate of [(3)H]Phe polymerization that was probably due to its reduced ability to form a ternary complex with heterologous aa-tRNA and (ii) a reduced intrinsic GTPase activity that was stimulated by high concentrations of NaCl (GTPase(Na)) [Masullo, M., De Vendittis, E., and Bocchini, V. (1994) J. Biol. Chem. 269, 20376-20379]. In addition, G13ASsEF-1 alpha showed an increased affinity for GDP and GTP. Surprisingly, the decreased intrinsic GTPase(Na) of G13ASsEF-1 alpha can be partially restored by kirromycin, an effect not found for SsEF-1 alpha wt. The temperature inducing a 50% denaturation of G13ASsEF-1 alpha was somewhat lower (-5 degrees C) than that of SsEF-1 alpha wt, and the decrease in its thermophilicity was slightly more accentuated (-10 degrees C). These results indicate that the nature of the residue in position 13 is important for the functional and physical properties of SsEF-1 alpha.

Deletion and dosage modulation of the eEF1A gene in Podospora anserina: effect on the life cycle

eEF1A is encoded by a unique gene in the filamentous fungus Podospora anserina. We show here that (1) this gene is essential for vegetative growth, (2) readthrough at UGA stop codon level is positively correlated with eEF1A level, (3) eEF1A level is regulated in P. anserina. (4) Increasing eEF1A gene dosage does not modify P. anserina life cycle parameters, especially longevity is not changed. These data confirm and extend those previously obtained in yeast and Drosophila.

Moonlighting functions of polypeptide elongation factor 1: from actin bundling to zinc finger protein R1-associated nuclear localization

Eukaryotic polypeptide elongation factor EF-1 is not only a major translational factor, but also one of the most important multifunctional (moonlighting) proteins. EF-1 consists of four different subunits collectively termed EF-1alphabeta beta'gamma and EF-1alphabeta gammadelta in plants and animals, respectively. EF-1alpha x GTP catalyzes the binding of aminoacyl-tRNA to the A-site of the ribosome. EF-1beta beta'gamma (EF-1beta and EF-1beta'), catalyzes GDP/GTP exchange on EF-1alpha x GDP to regenerate EF-1alpha x GTP. EF-1gamma has recently been shown to have glutathione S-transferase activity. EF-2 catalyzes the translocation of peptidyl-tRNA from the A-site to the P-site on the ribosome. Recently, molecular mimicry among tRNA, elongation factors, releasing factor (RF), and ribosome recycling factor (RRF) has been demonstrated and greatly improved our understanding of the mechanism of translation. Moreover, eukaryotic elongation factors have been shown to be concerned or likely to be concerned in various important cellular processes or serious diseases, including translational control, signal transduction, cytoskeletal organization, apoptosis, adult atopic dermatitis, oncogenic transformation, nutrition, and nuclear processes such as RNA synthesis and mitosis. This article aims to overview the recent advances in protein biosynthesis, concentrating on the moonlighting functions of EF-1.

eEF1A Controls ascospore differentiation through elevated accuracy, but controls longevity and fruiting body formation through another mechanism in Podospora anserina

Antisuppressor mutations in the eEF1A gene of Podospora anserina were previously shown to impair ascospore formation, to drastically increase life span, and to permit the development of the Crippled Growth degenerative process. Here, we show that eEF1A controls ascospore formation through accuracy level maintenance. Examination of antisuppressor mutant perithecia reveals two main cytological defects, mislocalization of spindle and nuclei and nuclear death. Antisuppression levels are shown to be highly dependent upon both the mutation site and the suppressor used, precluding any correlation between antisuppression efficiency and severity of the sporulation impairment. Nevertheless, severity of ascospore differentiation defect is correlated with resistance to paromomycin. We also show that eEF1A controls fruiting body formation and longevity through a mechanism(s) different from accuracy control. In vivo, GFP tagging of the protein in a way that partly retains its function confirmed earlier cytological observation; i.e., this factor is mainly diffuse within the cytosol, but may transiently accumulate within nuclei or in defined regions of the cytoplasm. These data emphasize the fact that the translation apparatus exerts a global regulatory control over cell physiology and that eEF1A is one of the key factors involved in this monitoring.

Function-structure analysis of proteins using covarion-based evolutionary approaches: Elongation factors

The divergent evolution of protein sequences from genomic databases can be analyzed by the use of different mathematical models. The most common treat all sites in a protein sequence as equally variable. More sophisticated models acknowledge the fact that purifying selection generally tolerates variable amounts of amino acid replacement at different positions in a protein sequence. In their "stationary" versions, such models assume that the replacement rate at individual positions remains constant throughout evolutionary history. "Nonstationary" covarion versions, however, allow the replacement rate at a position to vary in different branches of the evolutionary tree. Recently, statistical methods have been developed that highlight this type of variation in replacement rates. Here, we show how positions that have variable rates of divergence in different regions of a tree ("covarion behavior"), coupled with analyses of experimental three-dimensional structures, can provide experimentally testable hypotheses that relate individual amino acid residues to specific functional differences in those branches. We illustrate this in the elongation factor family of proteins as a paradigm for applications of this type of analysis in functional genomics generally.

Modulation of molecular mechanisms involved in protein synthesis machinery as a new tool for the control of cell proliferation

In the past years, the attention of scientists has focused mainly on the study of the genetic information and alterations that regulate eukaryotic cell proliferation and that lead to neoplastic transformation. All therapeutic strategies against cancer are, to date, directed at DNA either with cytotoxic drugs or gene therapy. Little or no interest has been aroused by protein synthesis mechanisms. However, an increasing body of data is emerging about the involvement of translational processes and factors in control of cell proliferation, indicating that protein synthesis can be an additional target for anticancer strategies. In this paper we review the novel insights on the biochemical and molecular events leading to protein biosynthesis and we describe their involvement in cell proliferation and tumorigenesis. A possible mechanistic explanation is given by the interactions that occur between protein synthesis machinery and the proliferative signal transduction pathways and that are therefore suitable targets for indirect modulation of protein synthesis. We briefly describe the molecular tools used to block protein synthesis and the attempts made at increasing their efficacy. Finally, we propose a new multimodal strategy against cancer based on the simultaneous intervention on protein synthesis and signal transduction.