Protein Synthesis Initiation Factor Research Articles

Not4 and Not5 modulate translation elongation by Rps7A ubiquitination, Rli1 moonlighting, and condensates that exclude eIF5A.

In this work, we show that Not4 and Not5 from the Ccr4-Not complex modulate translation elongation dynamics and change ribosome A-site dwelling occupancy in a codon-dependent fashion. These codon-specific changes in not5Δ cells are very robust and independent of codon position within the mRNA, the overall mRNA codon composition, or changes of mRNA expression levels. They inversely correlate with codon-specific changes in cells depleted for eIF5A and positively correlate with those in cells depleted for ribosome-recycling factor Rli1. Not5 resides in punctate loci, co-purifies with ribosomes and Rli1, but not with eIF5A, and limits mRNA solubility. Overexpression of wild-type or non-complementing Rli1 and loss of Rps7A ubiquitination enable Not4 E3 ligase-dependent translation of polyarginine stretches. We propose that Not4 and Not5 modulate translation elongation dynamics to produce a soluble proteome by Rps7A ubiquitination, dynamic condensates that limit mRNA solubility and exclude eIF5A, and a moonlighting function of Rli1.

Abstract 4390: Dietary soy isoflavone equol promotes breast cancer progression via regulation of protein synthesis initiation

Abstract We previously reported that dietary daidzein, a soy isoflavone, increased breast cancer progression in a nude mouse model of breast cancer metastasis. Further studies indicated that equol, a metabolite of the soy isoflavone daidzein is responsible for the cancer promoting effects of soy isoflavones in breast cancer cells in vitro. We reported that equol increases the expression of the eukaryotic protein synthesis initiation factor eIF4G1, and the transcription factor c-Myc. Increased eIF4G in response to equol resulted in the non-canonical protein synthesis of pro-cancer molecules such as Cyclin D, Bcl-XL, p120, matrix metalloproteinases, etc., as confirmed by ribosome profiling and eIF4G1 knockdown studies. This study tested the hypothesis that equol promoted breast cancer progression via eIF4G1 upregulation. Immunocompromised nude mice were used to establish mammary fatpad tumors from human metastatic breast cancer cells expressing eIF4G1 knockdowns via a Tetracycline-inducible promoter. Oral gavage of 50 mg/kg BW Doxycycline 3X a week for 4 weeks was enough to knockdown eIF4G1 expression by ~80%. Therefore, one week following tumor establishment, the mice were treated with vehicle (90% corn oil, 10% ethanol), equol, Doxycycline or, equol and Doxycycline. Data show that as expected, equol treatment increased tumor growth relative to vehicle treatment. Moreover, eIF4G1 knockdown abolished the effect of equol on tumor growth. Interestingly, the effect of eIF4G1 knockdown on mammary tumor growth was not evident until 55 days of doxycycline treatment. Therefore, we tested the cell and tumor lysates for potential expression of the eIF4G1 isoform Dap5 when eIF4G1 is knocked out. Dap5 protein was expressed in eIF4G1 knockdown cells and was increased by equol treatment, indicating that Dap5 may compensate for eIF4G1 knockdown by inducing alternative cap-mediated protein synthesis. In conclusion, the cancer promoting effect of equol is abolished in breast tumors where eIF4G1 expression was stably knocked down, thus, validating our hypothesis that equol increases breast cancer progression via upregulation of eIF4G1 dependent protein synthesis initiation. Citation Format: Ailed M. Cruz-Collazo, Columba De la Parra, Robert Schneider, Suranganie Dharmawardhane. Dietary soy isoflavone equol promotes breast cancer progression via regulation of protein synthesis initiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4390.

Eukaryotic initiation factor 4A2 (EIF4A2) expression in colorectal cancer and prediction of prognosis.

664 Background: Eukaryotic initiation factor 4A2(EIF4A2) is a member of the eukaryotic initiation factor 4A family and it is one of the protein-synthesis initiation factors, which are involved in the binding of messenger RNA to the ribosome. The prognostic roles of EIF4A2 in breast cancer, melanoma and lung cancer have been studied. However, the clinical significance and biologic role of EIF4A2 in colorectal cancer remain unknown. Methods: We used quantitative real-time polymerase chain reaction to compare expression of eIF4A2 mRNA between 72 paired colorectal cancer tissues and non-tumor colorectal tissues. We used immunohistochemistry to study the expression of EIF4A2 in 310 colorectal cancer patients under surgical resection, 247 of them received curative surgery. We also analyzed correlation between EIF4A2 expression and clinicopathological characteristics. The biological function of EIF4A2 on colorectal cancer cells were determined in vitro by knock-downing EIF4A2 in HCT116 and DLD1 cell lines. We performed MTT tests, colony formation assays, transwell and wound healing assays. Results: EIF4A2 mRNA was significantly higher in colorectal cancer tissues compared to the paired non-tumor colorectal tissues(P = 0.0034). Over-expression of EIF4A2 was prognostic of shorter overall survival(P = 0.002) and shorter disease-free survival(P = 0.042). Over-expression of EIF4A2 was significantly correlated with more TNM stage IV(P = 0.012). Multivariate analysis suggested EIF4A2 as an independent predictor of overall survival (hazard ratio 2.041[95% CI 1.385 to 3.008], P < 0.001) and disease-free survival (hazard ratio 1.537[95% CI 1.003 to 2.355], P = 0.049). Functionally, knockdown of EIF4A2 in HCT116 and DLD1 cell lines exerted tumor-suppressive effects by significantly inhibiting cell proliferation, colony formation,migration and invasion(P < 0.05). Conclusions: EIF4A2 is highly expressed in colorectal cancer and predicts poor prognosis. EIF4A2 could be served as a potential prognostic marker for colorectal cancer patients.

Differential effects of SUMO1 and SUMO3 on PKR activation and stability

Double-stranded RNA (dsRNA)-dependent protein kinase (PKR) is a serine/threonine kinase that exerts its own phosphorylation and the phosphorylation of the α subunit of the protein synthesis initiation factor eIF-2α. PKR was identified as a target of SUMOylation and the triple PKR-SUMO deficient mutant on Lysine residues K60-K150-K440 has reduced PKR activity. We report that SUMO1 and SUMO3 expression exert differential effects on PKR localization, activation and stability. SUMO1 or SUMO3 did not alter the repartition of PKR in the cytoplasm and the nucleus. However, in SUMO3-expressing cells PKR was found more concentrated around the perinuclear membrane and was recruited from small speckles to nuclear dots. Interestingly, SUMO1 expression alone resulted in PKR and eIF-2α activation, whereas SUMO3 reduced PKR and eIF-2α activation upon viral infection or dsRNA transfection. In addition, encephalomyocarditis virus (EMCV) enhanced PKR conjugation to SUMO1 and SUMO3 but only SUMO3 expression promoted caspase-dependent EMCV-induced PKR degradation. Furthermore, the higher EMCV-induced PKR activation by SUMO1 was correlated with an inhibition of EMCV. Importantly SUMO1, by inducing PKR activation in the absence of viral infection, and SUMO3, by counteracting both PKR activation and stability upon viral infection, shed a new light on the differential effects of SUMO-modified PKR.

Simvastatin exerts anti-hepatitis B virus activity by inhibiting expression of minichromosome maintenance protein 7 in HepG2.2.15 cells.

Simvastatin (SIM), a 3-hydroxy-3-methylglutaryl coenzymeA reductase inhibitor, has been reported to inhibit the activity of hepatitisB virus (HBV), however, the mechanism underlying its antiviral function remains unknown. Minichromosome maintenance (MCM)7, a component of the MCM complex, has been reported to act as an important host factor aiding virus genome replication in host cells. The present study demonstrated that downregulation of MCM7 inhibited the expression of proteins transferred by adenoviral vectors. This suggests an association between MCM7 and viral DNA expression. Thus, the current study aimed to investigate whether SIM affected MCM7 expression. Notably, the results of the present study indicated that following exposure to SIM the protein expression levels of MCM7 in HepG2.2.15, a human HBV‑transfected liver cell line, was decreased. In addition, the HBV DNA replication in the cell line was suppressed. As quantitative polymerase chain reaction experiments demonstrated that SIM did not downregulate the mRNA expression level of MCM7, the current study further investigated whether SIM affects the translation of MCM7. Western blot experiments indicated that SIM improved the activation of eukaryotic initiation factor‑2α (eIF2α), a protein synthesis initiation factor, and upregulated the upstream factors of eIF2α, protein kinase RNA‑like endoplasmic reticulum kinase, which is regulated by the liver kinaseB1 (LKB1)‑AMP‑activated protein kinase (AMPK) signaling pathway. These results indicated that SIM induced HBV downregulation via an MCM‑dependent mechanism, and SIM may inhibit MCM7 expression by increasing the phosphorylation of eIF2α, which is mediated by the LKB1-AMPK signaling pathway.

Abstract LB-015: XIAP induction by the MAPK-eIF4G1 pathway drives NFκB activation in inflammatory breast cancer growth and therapeutic resistance

Abstract Inflammatory breast cancer (IBC) is the most lethal, distinct form of breast cancer, however, the basis for its aggressiveness and rapid acquisition of drug resistance is not fully understood. Using immunohistochemical analysis, we identified a strong correlation between high grade, high stage, and triple-negative status and elevated expression of the X-linked inhibitor of apoptosis protein (XIAP) in IBC. Molecular profiling of multiple IBC cell lines revealed that modulating XIAP expression can significantly alter the expression pattern of a 79-gene, characteristic IBC profile that was previously obtained from clinical samples. Using specific antagonists and RNAi, we determined that the mitogen activated protein kinase (MAPK) pathway and its interaction with the protein synthesis initiation factor eIF4G1, both of which are elevated in IBC, cooperate to drive XIAP induction and resistance to therapeutic apoptosis. Further, we found that XIAP expression directly correlates with activation of the transcription factor NFκB, a molecular component defining IBC. Mutational analysis revealed that the BIR1 domain of XIAP is essential for subsequent TAB1:IKKβ-dependent NFκB activation. After determining this association between XIAP and TAB1, we tested a peptide-mediated strategy used to block the BIR1:TAB1 interaction antagonized NFκB activity which led to decreased anchorage independent growth and reversed resistance to an EGFR tyrosine kinase inhibitor. Most significantly, orthotopic implantation of XIAP silenced IBC cells revealed the necessity of expression for IBC tumor growth, while overexpression of XIAP enhanced tumor growth. Our findings establish that XIAP augments the malignant properties in IBC by enhancing NFκB function, identify a druggable pathway with multiple targets, and provide feasibility for the development of novel therapeutics targeting the BIR1 domain of XIAP in IBC. Grant Support: Supported by American Cancer Society, the Duke Cancer Institute as part of the P30 Cancer Center Support Grant NIH CA014236, the Duke Department of Surgery, and DOD grant W81XWH-13-1-0047. Citation Format: Myron K. Evans, Joseph Geradts, Courtney Edwards, Arianna Price, Arjun J. Arora, Amy J. Aldrich, Adrian Ramirez, Timothy J. Robinson, Peter B. Vermeulen, Steven van Laere, Gayathri R. Devi. XIAP induction by the MAPK-eIF4G1 pathway drives NFκB activation in inflammatory breast cancer growth and therapeutic resistance. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-015.

Altered Mitochondria, Protein Synthesis Machinery, and Purine Metabolism Are Molecular Contributors to the Pathogenesis of Creutzfeldt-Jakob Disease.

Neuron loss, synaptic decline, and spongiform change are the hallmarks of sporadic Creutzfeldt-Jakob disease (sCJD), and may be related to deficiencies in mitochondria, energy metabolism, and protein synthesis. To investigate these relationships, we determined the expression levels of genes encoding subunits of the 5 protein complexes of the electron transport chain, proteins involved in energy metabolism, nucleolar and ribosomal proteins, and enzymes of purine metabolism in frontal cortex samples from 15 cases of sCJD MM1 and age-matched controls. We also assessed the protein expression levels of subunits of the respiratory chain, initiation and elongation translation factors of protein synthesis, and localization of selected mitochondrial components. We identified marked, generalized alterations of mRNA and protein expression of most subunits of all 5 mitochondrial respiratory chain complexes in sCJD cases. Expression of molecules involved in protein synthesis and purine metabolism were also altered in sCJD. These findings point to altered mRNA and protein expression of components of mitochondria, protein synthesis machinery, and purine metabolism as components of the pathogenesis of CJD.

Sperm Affects Head Sensory Neuron in Temperature Tolerance of Caenorhabditis elegans.

Tolerance to environmental temperature change is essential for the survival and proliferation of animals. The process is controlled by various body tissues, but the orchestration of activity within the tissue network has not been elucidated in detail. Here, we show that sperm affects the activity of temperature-sensing neurons (ASJ) that control cold tolerance in Caenorhabditis elegans. Genetic impairment of sperm caused abnormal cold tolerance, which was unexpectedly restored by impairment of temperature signaling in ASJ neurons. Calcium imaging revealed that ASJ neuronal activity in response to temperature was decreased in sperm mutant gsp-4 with impaired protein phosphatase 1 and rescued by expressing gsp-4 in sperm. Genetic analysis revealed a feedback network in which ASJ neuronal activity regulates the intestine through insulin and a steroid hormone, which then affects sperm and, in turn, controls ASJ neuronal activity. Thus, we propose that feedback between sperm and a sensory neuron mediating temperature tolerance.

Editing of Cellular Self-RNAs by Adenosine Deaminase ADAR1 Suppresses Innate Immune Stress Responses

Adenosine deaminases acting on double-stranded RNA (ADARs) catalyze the deamination of adenosine (A) to produce inosine (I) in double-stranded (ds) RNA structures, a process known as A-to-I RNA editing. dsRNA is an important trigger of innate immune responses, including interferon (IFN) production and action. We examined the role of A-to-I RNA editing by two ADARs, ADAR1 and ADAR2, in the sensing of self-RNA in the absence of pathogen infection, leading to activation of IFN-induced, RNA-mediated responses in mouse embryo fibroblasts. IFN treatment of Adar1(-/-) cells lacking both the p110 constitutive and p150 IFN-inducible ADAR1 proteins induced formation of stress granules, whereas neither wild-type (WT) nor Adar2(-/-) cells displayed a comparable stress granule response following IFN treatment. Phosphorylation of protein synthesis initiation factor eIF2α at serine 51 was increased in IFN-treated Adar1(-/-) cells but not in either WT or Adar2(-/-) cells following IFN treatment. Analysis by deep sequencing of mouse exonic loci containing A-to-I-editing sites revealed that the majority of editing in mouse embryo fibroblasts was carried out by ADAR1. IFN treatment increased editing in both WT and Adar2(-/-) cells but not in either Adar1(-/-) or Adar1(-/-) (p150) cells or Stat1(-/-) or Stat2(-/-) cells. Hyper-edited sites found in predicted duplex structures showed strand bias of editing for some RNAs. These results implicate ADAR1 p150 as the major A-to-I editor in mouse embryo fibroblasts, acting as a feedback suppressor of innate immune responses otherwise triggered by self-RNAs possessing regions of double-stranded character.

Protein kinase R and the inflammasome.

Protein kinase R (PKR) was first identified as a mediator of the double-stranded RNA (dsRNA)-mediated inhibition of protein synthesis in extracts from interferon-treated cells. In a physiological context, viral replication results in production of dsRNA, activation of PKR by autophosphorylation, and phosphorylation of the protein synthesis initiation factor eIF2α. Subsequent biochemical, structural, and genetic analyses have identified the dsRNA and kinase domain structure of PKR, and shown that its deletion from the germline of mice results in impaired resistance to infection by many different viruses. These studies have also opened up roles for PKR in different signaling pathways, the most recent being regulation of the inflammasome. Here we review evidence for this newly ascribed function for PKR and discuss roles in inflammasome regulation and associated diseases.

Protein phosphatase PP1/GLC7 interaction domain in yeast eIF2γ bypasses targeting subunit requirement for eIF2α dephosphorylation

Whereas the protein kinases GCN2, HRI, PKR, and PERK specifically phosphorylate eukaryotic translation initiation factor 2 (eIF2α) on Ser51 to regulate global and gene-specific mRNA translation, eIF2α is dephosphorylated by the broadly acting serine/threonine protein phosphatase 1 (PP1). In mammalian cells, the regulatory subunits GADD34 and CReP target PP1 to dephosphorylate eIF2α; however, as there are no homologs of these targeting subunits in yeast, it is unclear how GLC7, the functional homolog of PP1 in yeast, is recruited to dephosphorylate eIF2α. Here, we show that a novel N-terminal extension on yeast eIF2γ contains a PP1-binding motif (KKVAF) that enables eIF2γ to pull down GLC7 and target it to dephosphorylate eIF2α. Truncation or point mutations designed to eliminate the KKVAF motif in eIF2γ impair eIF2α dephosphorylation in vivo and in vitro and enhance expression of GCN4. Replacement of the N terminus of eIF2γ with the GLC7-binding domain from GAC1 or fusion of heterologous dimerization domains to eIF2γ and GLC7, respectively, maintained eIF2α phosphorylation at basal levels. Taken together, these results indicate that, in contrast to the paradigm of distinct PP1-targeting or regulatory subunits, the unique N terminus of yeast eIF2γ functions in cis to target GLC7 to dephosphorylate eIF2α.

A Phase 1 Study of Everolimus + Weekly Cisplatin + Intensity Modulated Radiation Therapy in Head-and-Neck Cancer

Elevated expression of eukaryotic protein synthesis initiation factor 4E (eIF4E) in histologically cancer-free margins of resected head and neck squamous cell carcinomas (HNSCCs) is mediated by mammalian target of rapamycin complex 1 (mTORC1) and has been associated with increased risk of disease recurrence. Preclinically, inhibition of mTORC1 with everolimus sensitizes cancer cells to cisplatin and radiation. This was single-institution phase 1 study to establish the maximum tolerated dose of daily everolimus given with fixed dose cisplatin (30 mg/m(2) weekly × 6) and concurrent intensity modulated radiation therapy for patients with locally and/or regionally advanced head-and-neck cancer. The study had a standard 3 + 3 dose-escalation design. Tumor primary sites were oral cavity (4), salivary gland (4), oropharynx (2), nasopharynx (1), scalp (1), and neck node with occult primary (1). In 4 of 4 cases in which resected HNSCC surgical pathology specimens were available for immunohistochemistry, elevated expression of eIF4E was observed in the cancer-free margins. The most common grade ≥3 treatment-related adverse event was lymphopenia (92%), and dose-limiting toxicities (DLTs) were mucositis (n=2) and failure to thrive (n=1). With a median follow up of 19.4 months, 2 patients have experienced recurrent disease. The maximum tolerated dose was everolimus 5 mg/day. Head-and-neck cancer patients tolerated everolimus at therapeutic doses (5 mg/day) given with weekly cisplatin and intensity modulated radiation therapy. The regimen merits further evaluation, especially among patients who are status post resection of HNSCCs that harbor mTORC1-mediated activation of eIF4E in histologically negative surgical margins.

Downregulation of EIF4A2 in Non–Small-Cell Lung Cancer Associates with Poor Prognosis

BackgroundEIF4A2, which belongs to the eukaryotic initiation factor 4A family, is a highly conserved gene for one of the protein-synthesis initiation factors involved in the binding of messenger RNA to the ribosome. The role of EIF4A2 in some cancers, eg, breast cancer and melanoma, has been studied. However, the clinical significance and biologic role of EIF4A2 in lung cancer remains unknown. Patients and MethodsA total of 170 patients with non–small-cell lung cancer who were undergoing surgical resection were studied. We applied the tissue microarray by using immunohistochemistry to study the expression of EIF4A2 in patients with non–small-cell lung cancer (NSCLC). ResultsWe found that the expression rate of EIF4A2 in NSCLC was 87.6%. The expression of EIF4A2 was significantly correlated with the histopathologic classification (P = .049) and tumor grade (P < .019). Moreover, NSCLC patients with low EIF4A2 expression survived shorter than those with high EIF4A2 expression, as indicated by overall survival (P = .023) and disease-free survival (P = .011) assessed by the Kaplan-Meier method. In addition, multivariate analysis suggested EIF4A2 as an independent predictor of disease-free survival (hazard ratio 0.543 [95% CI, 0.329-0.897]; P = .017). ConclusionCollectively, our study demonstrated that EIF4A2 was remarkably involvement in the development of NSCLC and could be served as a potential prognostic marker for patients with this deadly disease.

7-Ketocholesterol induces P-glycoprotein through PI3K/mTOR signaling in hepatoma cells

7-Ketocholesterol (7-KC) is found at an elevated level in patients with cancer and chronic liver disease. The up-regulation of an efflux pump, P-glycoprotein (P-gp) leads to drug resistance. To elucidate the effect of 7-KC on P-gp, P-gp function and expression were investigated in hepatoma cell lines Huh-7 and HepG2 and in primary hepatocyte-derived HuS-E/2 cells. At a subtoxic concentration, 48-h exposure to 7-KC reduced the intracellular accumulation and cytotoxicity of P-gp substrate doxorubicin in hepatoma cells, but not in HuS-E/2 cells. In Huh-7 cells, 7-KC elevated efflux function through the activation of phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway. 7-KC activated the downstream protein synthesis initiation factor 4E-BP1 and induced P-gp expression post-transcriptionally. The stimulation of efflux was reversible and could not be prevented by N-acetyl cysteine. Total cellular ATP content remained the same, whereas the lactate production was increased and fluorescence lifetime of protein-bound NADH was shortened. These changes suggested a metabolic shift to glycolysis, but glycolytic inhibitors did not eliminate 7-KC-mediated P-gp induction. These results demonstrate that 7-KC induces P-gp through PI3K/mTOR signaling and decreased the cell-killing efficacy of doxorubicin in hepatoma cells.

Increased protein synthesis of IRES containing mRNAs, that induce cell survival and proliferation, by the daidzein metabolite equol may contribute to breast cancer malignancy.

The effects of soy isoflavones on established breast cancer remain to be understood. We recently reported that dietary daidzein increased primary mammary tumor growth and metastasis, and upregulated eukaryotic protein synthesis initiation factors (eIF) eIF4G and eIF4E. The increased eIF expression in tumor extracts of mice after daidzein diets was associated with protein expression of mRNAs with internal ribosome entry sites (IRES). Results with metastatic cancer cell lines show that the effects of daidzein in vivo can be recapitulated by its metabolite equol. Equol increased metastatic cancer cell viability and up‐regulated gene and protein expression of the transcription factor c‐Myc. In vitro, equol, but not daidzein, up‐regulated eIF4G without affecting eIF4E or its regulator, 4E‐BP, levels. This elevated eIF4G was not associated with eIF4E or 4E‐BP in cap affinity chromatography assays or co‐immunoprecipitations. In dual luciferase assays, IRES‐dependent protein synthesis was increased by equol. As shown by western blotting and polysomal associations, equol specifically increased the expression of IRES‐containing mRNAs of cancer promoting molecules. Therefore, upregulation of eIF4G by equol may result in increased translation of pro‐cancer mRNAs with IRESs and, thus, promote cancer malignancy. Supported by US Army/BCRP W81XWH‐11–1‐0199 to CD and NIH/NIGMS SC3GM084824 to SD.

The Soy Isoflavone Equol May Increase Cancer Malignancy via Up-regulation of Eukaryotic Protein Synthesis Initiation Factor eIF4G

Dietary soy is thought to be cancer-preventive; however, the beneficial effects of soy on established breast cancer is controversial. We recently demonstrated that dietary daidzein or combined soy isoflavones (genistein, daidzein, and glycitein) increased primary mammary tumor growth and metastasis. Cancer-promoting molecules, including eukaryotic protein synthesis initiation factors (eIF) eIF4G and eIF4E, were up-regulated in mammary tumors from mice that received dietary daidzein. Herein, we show that increased eIF expression in tumor extracts of mice after daidzein diets is associated with protein expression of mRNAs with internal ribosome entry sites (IRES) that are sensitive to eIF4E and eIF4G levels. Results with metastatic cancer cell lines show that some of the effects of daidzein in vivo can be recapitulated by the daidzein metabolite equol. In vitro, equol, but not daidzein, up-regulated eIF4G without affecting eIF4E or its regulator, 4E-binding protein (4E-BP), levels. Equol also increased metastatic cancer cell viability. Equol specifically increased the protein expression of IRES containing cell survival and proliferation-promoting molecules and up-regulated gene and protein expression of the transcription factor c-Myc. Moreover, equol increased the polysomal association of mRNAs for p 120 catenin and eIF4G. The elevated eIF4G in response to equol was not associated with eIF4E or 4E-binding protein in 5' cap co-capture assays or co-immunoprecipitations. In dual luciferase assays, IRES-dependent protein synthesis was increased by equol. Therefore, up-regulation of eIF4G by equol may result in increased translation of pro-cancer mRNAs with IRESs and, thus, promote cancer malignancy.

Towards functional repertoire of the earliest proteins

The conserved protein sequence motifs present in all prokaryotic proteomes, “omnipresent motifs,” presumably, correspond to the earliest proteins of the Last Universal Cellular Ancestor, from which all the proteomes have descended. Fifteen proteomes, each representing one of the total 15 diverse phyla of 131 Eubacteria and Archea, from which the omnipresent elements have been originally derived, are exhaustively screened. All those proteins which harbor the omnipresent motifs are identified. Six “omnipresent” protein types are revealed which are located in all 15 proteomes: ABC cassettes, FtsH proteases, translation initiation factors, translation elongation factors, isoleucyl-tRNA synthases, and RNA polymerases β’. In addition to the omnipresent motifs, these proteins also contain other highly conserved motifs, standing for additional modules of the proteins. Remarkably, the identified tentative earliest proteins are responsible for only three basic functions: supply of monomers (ABC transporters and proteases), protein synthesis (initiation and elongation factors, aminoacyl-tRNA synthases), and RNA synthesis (polymerases). No enzymes involved in metabolic activities are present in the list of the earliest proteins derived by this approach. Some of the omnipresent sequence motifs are found, indeed, in the metabolic enzymes (e.g. NTP binding motifs), but these enzymes do not make a sequence matching collection of 15 sequences, i.e. they are not omnipresent. Future analysis of less conserved sequence motifs may reveal at what degree of conservation (stage of evolution) the metabolic enzymes could have entered the scene.

Protein Kinase PKR Amplification of Interferon β Induction Occurs through Initiation Factor eIF-2α-mediated Translational Control

The protein kinase PKR is activated by RNA with double-stranded (ds) structure and subsequently impairs translation through phosphorylation of protein synthesis initiation factor eIF-2α. PKR also mediates activation of signal transduction pathways leading to interferon beta (IFN-β) gene induction following virus-infection or RNA transfection. We previously demonstrated in measles virus-infected cells that PKR is required for the maximal induction of IFN-β gene expression by the interferon promoter stimulator gene 1 (IPS-1) adaptor-dependent cytosolic RNA sensor pathway. While both IPS-1 and PKR are important mediators of IFN-β induction, with PKR contributing to an enhanced NF-κB activation, the mechanism by which PKR enhances NF-κB activity and amplifies IFN-β induction is unresolved. Herein we tested the possibility that PKR could activate signal transduction pathways indirectly through translational control responses. Following transfection with synthetic or natural dsRNAs or infection with measles virus, we observed increased mRNA but decreased protein levels for the inhibitor of NF-κB signaling, IκB-α, that correlated with PKR activation and eIF-2α phosphorylation. Importantly, knockdown of PKR increased IκB-α protein levels and impaired IFN-β induction. Additionally, inhibition of translation by cycloheximide treatment rescued IFN-β induction following PKR knockdown but not IPS-1 knockdown. Mutation of eIF-2α to prevent phosphorylation also impaired IFN-β induction in PKR-sufficient virus-infected cells. These results suggest that an eIF-2α-dependent translation inhibition mechanism is sufficient to explain the PKR-mediated amplification of IPS-1-dependent IFN-β induction by foreign RNA.

Specific Domains in Yeast Translation Initiation Factor eIF4G Strongly Bias RNA Unwinding Activity of the eIF4F Complex toward Duplexes with 5′-Overhangs

During eukaryotic translation initiation, the 43 S ribosomal pre-initiation complex is recruited to the 5'-end of an mRNA through its interaction with the 7-methylguanosine cap, and it subsequently scans along the mRNA to locate the start codon. Both mRNA recruitment and scanning require the removal of secondary structure within the mRNA. Eukaryotic translation initiation factor 4A is an essential component of the translational machinery thought to participate in the clearing of secondary structural elements in the 5'-untranslated regions of mRNAs. eIF4A is part of the 5'-7-methylguanosine cap-binding complex, eIF4F, along with eIF4E, the cap-binding protein, and the scaffolding protein eIF4G. Here, we show that Saccharomyces cerevisiae eIF4F has a strong preference for unwinding an RNA duplex with a single-stranded 5'-overhang versus the same duplex with a 3'-overhang or without an overhang. In contrast, eIF4A on its own has little RNA substrate specificity. Using a series of deletion constructs of eIF4G, we demonstrate that its three previously elucidated RNA binding domains work together to provide eIF4F with its 5'-end specificity, both by promoting unwinding of substrates with 5'-overhangs and inhibiting unwinding of substrates with 3'-overhangs. Our data suggest that the RNA binding domains of eIF4G provide the S. cerevisiae eIF4F complex with a second mechanism, in addition to the eIF4E-cap interaction, for directing the binding of pre-initiation complexes to the 5'-ends of mRNAs and for biasing scanning in the 5' to 3' direction.

Abstract 1988: Increased expression of eukaryotic protein synthesis initiation factor eIF4G by the daidzein metabolite equol may contribute to breast cancer malignancy

Abstract The role of dietary soy in cancer has been the subject of intense investigation and is thought to be cancer preventive. However, the beneficial effects of soy on established breast cancer is controversial. We recently demonstrated that dietary daidzein and combined soy isoflavones (genistein, daidzein, and glycitein) promoted breast cancer progression in a nude mouse model by increasing both primary mammary tumor growth and metastasis. Dietary daidzein significantly upregulated cancer promoting molecules including eukaryotic protein synthesis initiation factors (eIF) eIF4G and eIF4E. Herein, using tumors from mice treated orally with daidzein, we show that increased eIF expression is associated with expression of mRNAs with long structured 5′ untranslated regions and internal ribosomal entry sites (IRES) that are sensitive to eIF4E and eIF4G levels. We then tested the hypothesis that daidzein upregulates protein synthesis initiation in breast cancer, but found that daidzein treatment did not affect the levels of eIFs in the same MDA-MB-435 cell line in vitro. Therefore, we tested the effect of equol that is metabolized from daidzein by the gut bacteria in mice and humans. Results show that equol specifically upregulated eIF4G, but not eIF4E, in MDA-MB-435 and MDA-MB-231 human breast cancer cells. Equol treatment also increased gene and protein expression of c-MYC and protein expression of other cell survival and proliferation promoting molecules with IRES sites. The elevated eIF4G in response to equol was not associated with eIF4E in a cap binding co-capture assay. Therefore, upregulation of eIF4G by equol may regulate cap-independent protein synthesis initiation resulting in cancer cell survival, proliferation, and thus, tumor progression. This research was supported by grant numbers US Army/BCRP W81XWH-11-1-0199 to CD, to NIH/NIGMS SC3GM084824 to SD Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1988. doi:1538-7445.AM2012-1988