Eukaryotic translation elongation factor 1A induces anoikis by triggering cell detachment

The eEF1A protein in cancer: Clinical significance, oncogenic mechanisms, and targeted therapeutic strategies

Eukaryotic elongation factor 1A (eEF1A) is among the most abundant proteins in eukaryotic cells. Evolutionarily conserved across species, eEF1A is in charge of translation elongation for protein biosynthesis as well as a plethora of non-translational moonlighting functions for cellular homeostasis. In malignant cells, however, eEF1A becomes a pleiotropic driver of cancer progression via a broad diversity of pathways, which are not limited to hyperactive translational output. In the past decades, mounting studies have demonstrated the causal link between eEF1A and carcinogenesis, gaining deeper insights into its multifaceted mechanisms and corroborating its value as a prognostic marker in various cancers. On the other hand, an increasing number of natural and synthetic compounds were discovered as anticancer eEF1A-targeting inhibitors. Among them, plitidepsin was approved for the treatment of multiple myeloma whereas metarrestin was currently under clinical development. Despite significant achievements in these two interrelated fields, hitherto there lacks a systematic examination of the eEF1A protein in the context of cancer research. Therefore, the present work aims to delineate its clinical implications, molecular oncogenic mechanisms, and targeted therapeutic strategies as reflected in the ever expanding body of literature, so as to deepen mechanistic understanding of eEF1A-involved tumorigenesis and inspire the development of eEF1A-targeted chemotherapeutics and biologics.

Immunogens in Balamuthia mandrillaris: a proteomic exploration

Balamuthia mandrillaris is the causative agent of granulomatous amoebic encephalitis, a rare and often fatal infection affecting the central nervous system. The amoeba is isolated from diverse environmental sources and can cause severe infections in both immunocompromised and immunocompetent individuals. Given the limited understanding of B. mandrillaris, our research aimed to explore its protein profile, identifying potential immunogens crucial for early granulomatous amoebic encephalitis diagnosis. Cultures of B. mandrillaris and other amoebas were grown under axenic conditions, and total amoebic extracts were obtained. Proteomic analyses, including two-dimensional electrophoresis and mass spectrometry, were performed. A 50-kDa band showed a robust recognition of antibodies from immunized BALB/c mice; peptides contained in this band were matched with elongation factor-1 alpha, which emerged as a putative key immunogen. Besides, lectin blotting revealed the presence of glycoproteins in B. mandrillaris, and confocal microscopy demonstrated the focal distribution of the 50-kDa band throughout trophozoites. Cumulatively, these observations suggest the participation of the 50-kDa band in adhesion and recognition mechanisms. Thus, these collective findings demonstrate some protein characteristics of B. mandrillaris, opening avenues for understanding its pathogenicity and developing diagnostic and therapeutic strategies.

Proximity extracellular protein-protein interaction analysis of EGFR using AirID-conjugated fragment of antigen binding

Receptor proteins, such as epidermal growth factor receptor (EGFR), interact with other proteins in the extracellular region of the cell membrane to drive intracellular signalling. Therefore, analysis of extracellular protein-protein interactions (exPPIs) is important for understanding the biological function of receptor proteins. Here, we present an approach using a proximity biotinylation enzyme (AirID) fusion fragment of antigen binding (FabID) to analyse the proximity exPPIs of EGFR. AirID was C-terminally fused to the Fab fragment against EGFR (EGFR-FabID), which could then biotinylate the extracellular region of EGFR in several cell lines. Liquid Chromatography-Mass Spectrometry (LC-MS/MS) analysis indicated that many known EGFR interactors were identified as proximity exPPIs, along with many unknown candidate interactors, using EGFR-FabID. Interestingly, these proximity exPPIs were influenced by treatment with EGF ligand and its specific kinase inhibitor, gefitinib. These results indicate that FabID provides accurate proximity exPPI analysis of target receptor proteins on cell membranes with ligand and drug responses.

Mouse skin peptidomic analysis of the hemorrhage induced by a snake venom metalloprotease

Hemorrhage induced by snake venom metalloproteases (SVMPs) results from proteolysis, capillary disruption, and blood extravasation. HF3, a potent SVMP of Bothrops jararaca, induces hemorrhage at pmol doses in the mouse skin. To gain insight into the hemorrhagic process, the main goal of this study was to analyze changes in the skin peptidome generated by injection of HF3, using approaches of mass spectrometry-based untargeted peptidomics. The results revealed that the sets of peptides found in the control and HF3-treated skin samples were distinct and derived from the cleavage of different proteins. Peptide bond cleavage site identification in the HF3-treated skin showed compatibility with trypsin-like serine proteases and cathepsins, suggesting the activation of host proteinases. Acetylated peptides, which originated from the cleavage at positions in the N-terminal region of proteins in both samples, were identified for the first time in the mouse skin peptidome. The number of peptides acetylated at the residue after the first Met residue, mostly Ser and Ala, was higher than that of peptides acetylated at the initial Met. Proteins cleaved in the hemorrhagic skin participate in cholesterol metabolism, PPAR signaling, and in the complement and coagulation cascades, indicating the impairment of these biological processes. The peptidomic analysis also indicated the emergence of peptides with potential biological activities, including pheromone, cell penetrating, quorum sensing, defense, and cell-cell communication in the mouse skin. Interestingly, peptides generated in the hemorrhagic skin promoted the inhibition of collagen-induced platelet aggregation and could act synergistically in the local tissue damage induced by HF3.

A Biomolecular Toolbox for Precision Nanomotors

The application of nanomotors for cancer diagnosis and therapy is a new and exciting area of research, which when combined with precision nanomedicine, promises to solve many of the issues encountered by previous development of passive nanoparticles. The goal of this article is to introduce nanomotor and nanomedicine researchers to the deep pool of knowledge available regarding cancer cell biology and biochemistry, as well as provide a greater appreciation of the complexity of cell membrane compositions, extracellular surfaces, and their functional consequences. A short description of the nanomotor state-of-art for cancer therapy and diagnosis is first provided, as well as recommendations for future directions of the field. Then, a biomolecular targeting toolbox has been collated for researchers looking to apply their nanomaterial of choice to a biological setting, as well as providing a glimpse into currently available clinical therapies and technologies. This toolbox contains an overview of different classes of targeting molecules available for high affinity and specific targeting and cell surface targets to aid researchers in the selection of a clinical disease model and targeting methodology. It is hoped that this review will provide biological context, inspiration, and direction to future nanomotor and nanomedicine research.

On the Need to Tell Apart Fraternal Twins eEF1A1 and eEF1A2, and Their Respective Outfits

eEF1A1 and eEF1A2 are paralogous proteins whose presence in most normal eukaryotic cells is mutually exclusive and developmentally regulated. Often described in the scientific literature under the collective name eEF1A, which stands for eukaryotic elongation factor 1A, their best known activity (in a monomeric, GTP-bound conformation) is to bind aminoacyl-tRNAs and deliver them to the A-site of the 80S ribosome. However, both eEF1A1 and eEF1A2 are endowed with multitasking abilities (sometimes performed by homo- and heterodimers) and can be located in different subcellular compartments, from the plasma membrane to the nucleus. Given the high sequence identity of these two sister proteins and the large number of post-translational modifications they can undergo, we are often confronted with the dilemma of discerning which is the particular proteoform that is actually responsible for the ascribed biochemical or cellular effects. We argue in this review that acquiring this knowledge is essential to help clarify, in molecular and structural terms, the mechanistic involvement of these two ancestral and abundant G proteins in a variety of fundamental cellular processes other than translation elongation. Of particular importance for this special issue is the fact that several de novo heterozygous missense mutations in the human EEF1A2 gene are associated with a subset of rare but severe neurological syndromes and cardiomyopathies.

Biologically Active TNIIIA2 Region in Tenascin-C Molecule: A Major Contributor to Elicit Aggressive Malignant Phenotypes From Tumors/Tumor Stroma

Tenascin (TN)-C is highly expressed specifically in the lesions of inflammation-related diseases, including tumors. The expression level of TN-C in tumors and the tumor stroma is positively correlated with poor prognosis. However, no drugs targeting TN-C are currently clinically available, partly because the role of TN-C in tumor progression remains controversial. TN-C harbors an alternative splicing site in its fibronectin type III repeat domain, and its splicing variants including the type III-A2 domain are frequently detected in malignant tumors. We previously identified a biologically active region termed TNIIIA2 in the fibronectin type III-A2 domain of TN-C molecule and showed that this region is involved in promoting firm and persistent cell adhesion to fibronectin. In the past decade, through the exposure of various cell lines to peptides containing the TNIIIA2 region, we have published reports demonstrating the ability of the TNIIIA2 region to modulate distinct cellular activities, including survival/growth, migration, and invasion. Recently, we reported that the signals derived from TNIIIA2-mediated β1 integrin activation might play a crucial role for inducing malignant behavior of glioblastoma (GBM). GBM cells exposed to the TNIIIA2 region showed not only exacerbation of PDGF-dependent proliferation, but also acceleration of disseminative migration. On the other hand, we also found that the pro-inflammatory phenotypic changes were promoted when macrophages are stimulated with TNIIIA2 region in relatively low concentration and resulting MMP-9 upregulation is needed to release of the TNIIIA2 region from TN-C molecule. With the contribution of TNIIIA2-stimulated macrophages, the positive feedback spiral loop, which consists of the expression of TN-C, PDGF, and β1 integrin, and TNIIIA2 release, seemed to be activated in GBM with aggressive malignancy. Actually, the growth of transplanted GBM grafts in mice was significantly suppressed via the attenuation of β1 integrin activation. In this review, we thus introduce that the TNIIIA2 region has a significant impact on malignant progression of tumors by regulating cell adhesion. Importantly, it has been demonstrated that the TNIIIA2 region exerts unique biological functions through the extremely strong activation of β1-integrins and their long-lasting duration. These findings prompt us to develop new therapeutic agents targeting the TNIIIA2 region.

Exposure of the cryptic de-adhesive site FNIII14 in fibronectin molecule and its binding to membrane-type eEF1A induce migration and invasion of cancer cells via β1-integrin inactivation

Cell migration is a highly coordinated process that involves not only integrin-mediated adhesion but also de-adhesion. We previously found that a cryptic de-adhesive site within fibronectin molecule, termed FNIII14, weakens cell adhesion to the extracellular matrix by inactivating β1-integrins. Surprisingly, eukaryotic translation elongation factor-1A (eEF1A), an essential factor during protein biosynthesis, was identified as a membrane receptor that mediates the de-adhesive effect of FNIII14. Here, we demonstrate that FNIII14-mediated de-adhesion causes enhanced migration and invasion in two types of highly invasive/metastatic cancer cells, resulting in the initiation of metastasis. Both in vitro migration and invasion of highly invasive human melanoma cell line, Mum2B, were inhibited by a matrix metalloproteinase (MMP)-2/9 inhibitor or a function-blocking antibody against FNIII14 (anti-FNIII14 Ab), suggesting that MMP-mediated exposure of the cryptic de-adhesive site FNIII14 was responsible for Mum2B cell migration and invasion. The MMP-induced FNIII14 exposure was also shown to be functional in the migration and invasion of highly metastatic mouse breast cancer cell line 4T1. Overexpression and knockdown experiments of eEF1A in Mum2B cells revealed that the migration and invasion were dependent on the membrane levels of eEF1A. In vivo experiments using tumor xenograft mouse models derived from Mum2B and 4T1 cell lines showed that the anti-FNIII14 Ab has a significant anti-metastatic effect. Thus, these results provide novel insights into the regulation of cancer cell migration and invasion and suggest promising targets for anti-metastasis strategies.

Involvement of Integrin-Activating Peptides Derived from Tenascin-C in Cancer Aggression and New Anticancer Strategy Using the Fibronectin-Derived Integrin-Inactivating Peptide

Matricellular proteins, which exist in association with the extracellular matrix (ECM) and ECM protein molecules, harbor functional sites within their molecular structures. These functional sites are released through proteolytic cleavage by inflammatory proteinases, such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS), and the peptides containing these functional sites have unique biological activities that are often not detected in the parent molecules. We previously showed that tenascin-C (TNC) and plasma fibronectin (pFN), examples of matricellular proteins, have cryptic bioactive sites that have opposite effects on cell adhesion to the ECM. A peptide containing the bioactive site of TNC, termed TNIIIA2, which is highly released at sites of inflammation and in the tumor microenvironment (TME), has the ability to potently and persistently activate β1-integrins. In the opposite manner, the peptide FNIII14 containing the bioactive site of pFN has the ability to inactivate β1-integrins. This review highlights that peptide TNIIIA2 can act as a procancer factor and peptide FNIII14 can act as an anticancer agent, based on the regulation on β1-integrin activation. Notably, the detrimental effects of TNIIIA2 can be inhibited by FNIII14. These findings open the possibility for new therapeutic strategies based on the inactivation of β1-integrin by FNIII14.

Inactivation of beta1 integrin induces proteasomal degradation of Myc oncoproteins

The MYC family oncogenes (MYC, MYCN, and MYCL) contribute to the genesis of many human cancers. Among them, amplification of the MYCN gene and over-expression of N-Myc protein are the most reliable risk factors in neuroblastoma patients. On the other hand, we previously found that a peptide derived from fibronectin, termed FNIII14, is capable of inducing functional inactivation in β1-integrins. Here, we demonstrate that inactivation of β1-integrin by FNIII14 induced proteasomal degradation in N-Myc of neuroblastoma cells with MYCN amplification. This N-Myc degradation by FNIII14 reduced the malignant properties, including the anchorage-independent proliferation and invasive migration, of neuroblastoma cells. An in vivo experiment using a mouse xenograft model showed that the administration of FNIII14 can inhibit tumor growth, and concomitantly a remarkable decrease in N-Myc levels in tumor tissues. Of note, the activation of proteasomal degradation based on β1-integrin inactivation is applicable to another Myc family oncoprotein, c-myc, which also reverses cancer-associated properties in pancreatic cancer cells. Collectively, β1-integrin inactivation could be a new chemotherapeutic strategy for cancers with highly expressed Myc. FNIII14, which is a unique pharmacological agent able to induce β1-integrin inactivation, may be a promising drug targeting Myc oncoproteins for cancer chemotherapy.

Biotin-transfer from a trifunctional crosslinker for identification of cell surface receptors of soluble protein ligands

Here we describe a novel crosslinker and its application as a biotin-transfer reagent to identify cell surface receptors of soluble protein ligands on live cells. This crosslinker contains three functional groups: an aldehyde-reactive aminooxy group, a sulfhydryl, and a biotin (ASB). It is readily synthesized via a 3-step addition reaction using standard solid-phase peptide synthesis methods and commercially available intermediates, allowing access to laboratories without specialized synthetic chemistry capabilities. For the biotin-transfer method, ASB is linked to a protein ligand through the sulfhydryl group in a two-step process that allows the introduction of a disulfide bond between the ligand and the crosslinker. Incubation of the labelled ligand with oxidized live cells leads to the formation of crosslinks with aldehyde-containing glycans on the cell surface receptor. Subsequent reduction of the disulfide bond results in biotin transfer from the ligand to the cell surface receptor. Protein biotinylation that is mediated by ligand binding to its receptor is differentiated from background biotinylation events by comparison with a similarly labelled control protein using comparative proteomic mass spectrometry to quantify streptavidin-bound proteins. Using this method, we successfully identified the cell surface receptors of a peptide hormone, a monoclonal antibody, and a single-domain antibody-Fc fusion construct.

New Type of Antitumor Agent Targeting the Cell Adhesion Molecule, Integrin

The extracellular matrix (ECM) provides a variety of biological signals for cell regulation. It is apparent that some of these signals are derived from functional sites, which are concealed in the higher structure of ECM protein molecules. Previously, we found that fibronectin, a ubiquitous cell adhesive ECM protein, harbors a cryptic functional site termed FNIII14, which can be exposed through the processing of fibronectin by inflammatory proteinases, including matrix metalloproteinase-2 (MMP-2). FNIII14, once exposed, induces a conformational change in beta1-integrins necessary for their functional inactivation, resulting in weakened cell adhesion to the ECM. Interestingly, eukaryotic peptide elongation factor 1A (eEF1A) was recently identified as a membrane receptor mediating this anti-adhesive effect of FNIII14. Here, we show that exposure of FNIII14 from the fibronectin matrix, and its interaction with the membrane receptor eEF1A, contributes to the migration and invasion of cancer cells. Furthermore, an in vivo experiment using a mouse xenograft model shows that FNIII14 could be a promising target for preventing lung metastasis of melanoma.

Rapid Preparation of a Plasma Membrane Fraction: Western Blot Detection of Translocated Glucose Transporter 4 from Plasma Membrane of Muscle and Adipose Cells and Tissues

Membrane proteins account for 70% to 80% of all pharmaceutical targets, indicating their clinical relevance and underscoring the importance of identifying differentially expressed membrane proteins that reflect distinct disease properties. The translocation of proteins from the bulk of the cytosol to the plasma membrane is a critical step in the transfer of information from membrane-embedded receptors or transporters to the cell interior. To understand how membrane proteins work, it is important to separate the membrane fraction of cells. This unit provides a protocol for rapidly obtaining plasma membrane fractions for western blot analysis. © 2016 by John Wiley & Sons, Inc.

eEF1A1 binds and enriches protoporphyrin IX in cancer cells in 5-aminolevulinic acid based photodynamic therapy

Photodynamic therapy (PDT) with protoporphyrin IX (PpIX), which is endogenously derived from 5-aminolevulinic acid (5-ALA) or its derivatives, is a promising modality for the treatment of both pre-malignant and malignant lesions. However, the mechanisms of how ALA-induced PpIX selectively accumulated in the tumors are not fully elucidated. Here we discovered that eukaryotic translation elongation factor 1 alpha 1 (eEF1A1) interacted with PpIX (with an affinity constant of 2.96 × 10(6) M(-1)). Microscopy imaging showed that ALA-induced PpIX was co-localized with eEF1A1 in cancer cells. eEF1A1 was found to enrich ALA-induced PpIX in cells by competitively blocking the downstream bioavailability of PpIX. Taken together, our study discovered eEF1A1 as a novel photosensitizer binding protein, which may play an essential role in the enrichment of ALA-induced PpIX in cancer cells during PDT. These suggested eEF1A1 as a molecular marker to predict the selectivity and efficiency of 5-ALA based PDT in cancer therapy.

Elongation factor-1A1 is a novel substrate of the protein phosphatase 1-TIMAP complex

TIMAP (TGF-β inhibited membrane associated protein) is a protein phosphatase 1 (PP1) regulatory subunit highly abundant in endothelial cells and it is involved in the maintenance of pulmonary endothelial barrier function. It localizes mainly in the plasma membrane, but it is also present in the nuclei and cytoplasm. Direct interaction of TIMAP with the eukaryotic elongation factor 1 A1 (eEF1A1) is shown by pull-down, LC-MS/MS, Far-Western and immunoprecipitations. In connection with the so called moonlighting functions of the elongation factor, eEF1A is thought to establish protein-protein interactions through a transcription-dependent nuclear export motif, TD-NEM, and to aid nuclear export of TD-NEM containing proteins. We found that a TD-NEM-like motif of TIMAP has a critical role in its specific binding to eEF1A1. However, eEF1A1 is not or not exclusively responsible for the nuclear export of TIMAP. On the contrary, TIMAP seems to regulate membrane localization of eEF1A1 as the elongation factor co-localized with TIMAP in the plasma membrane fraction of control endothelial cells, but it has disappeared from the membrane in TIMAP depleted cells. It is demonstrated that membrane localization of eEF1A1 depends on the phosphorylation state of its Thr residue(s); and ROCK phosphorylated eEF1A1 is a novel substrate for TIMAP-PP1 underlining the complex regulatory role of TIMAP in the endothelium. The elongation factor seems to be involved in the regulation of endothelial cell attachment and spreading as silencing of eEF1A1 positively affected these processes which were monitored by transendothelial resistance measurements.

New insights on the interaction between the isoforms 1 and 2 of human translation elongation factor 1A

The eukaryotic translation elongation factor 1A (eEF1A) is a moonlighting protein that besides to its canonical role in protein synthesis is also involved in many other cellular processes such as cell survival and apoptosis. In a previous work, we identified eEF1A Raf-mediated phosphorylation sites and defined their role in the regulation of eEF1A half-life and apoptosis of human cancer cells. We proposed that the phosphorylation of eEF1A by C-Raf required the presence of both eEF1A isoforms thus suggesting the formation of a potential eEF1A heterodimer owning regulatory properties. This study aimed at investigating the cellular localization and interaction between two eEF1A isoforms. To this end, we developed chimera proteins by adding at the N-terminal end of both eEF1A1 and eEF1A2 cyan fluorescence protein (mCerulean) and yellow fluorescence protein (mVenus), respectively. The fluorescent eEF1A1 and eEF1A2 chimeras were both addressed to COS-7 cells and found co-localized in the cytoplasm at the level of cellular membranes. We highlighted FRET between the labeled N-termini of eEF1A isoforms. The intra-molecular FRET of this chimera was about 17%. Our results provide novel information on the intracellular distribution and interaction of eEF1A isoforms.

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.

Tenascin-C-derived peptide TNIIIA2 highly enhances cell survival and platelet-derived growth factor (PDGF)-dependent cell proliferation through potentiated and sustained activation of integrin α5β1

Tenascin-C is an adhesion modulatory matrix protein that is highly expressed in tumors; however, its biochemical activity involved in tumorigenesis is not fully understood. On the other hand, increasing evidence indicates the importance of integrin α5β1 in cancer development. We previously demonstrated that tenascin-C harbors a functional site that can be released as a proadhesive peptide such as TNIIIA2. Peptide TNIIIA2 is capable of inducing activation of β1-integrins including α5β1 via syndecan-4. In this study the proadhesive effect of TNIIIA2 was characterized by potentiated and sustained activation of integrin α5β1. Based on this effect, TNIIIA2 rendered nontransformed fibroblasts (NIH3T3) resistant to serum deprivation-elicited anoikis through activation of the Akt/Bcl-2 pathway. Moreover, TNIIIA2 hyperstimulated PDGF-dependent proliferation of NIH3T3 by activating integrin α5β1. Tenascin-C, a parental protein of TNIIIA2, also stimulated PDGF-dependent proliferation, which was blocked by a matrix metalloproteinase-2/9 inhibitor and an anti-TNIIIA2 function-blocking antibody, suggesting proteolytic exposure of the proadhesive effect of TNIIIA2. Mechanistic analyses revealed that TNIIIA2 induced a lateral association of PDGF receptor β with the molecular complex of activated integrin α5β1 and syndecan-4 in the membrane microdomains enriched with cholesterol/caveolin-1, resulting in prolonged activation of PDGF receptor β and the subsequent Ras/mitogen-activated protein kinase pathway in a PDGF-dependent manner. Of note, TNIIIA2 induced continuous proliferation in NIH3T3 in an integrin α5β1-dependent manner even after they formed a confluent monolayer. Thus, it was proposed that tenascin-C might be involved in deregulated cell growth through potentiated and sustained activation of integrin α5β1 after exposure of the proadhesive effect of TNIIIA2.