Inhibitor Of Eukaryotic Protein Synthesis Research Articles

Trichodermin inhibits the growth of oral cancer through apoptosis-induced mitochondrial dysfunction and HDAC-2-mediated signaling

Trichodermin (TCD), a trichothecene first isolated from marine Trichoderma viride, is an inhibitor of eukaryotic protein synthesis. However, the potential effects of TCD on human oral squamous cell carcinoma (OSCC) cells and the underlying molecular mechanisms remain unknown. In this study, the exposure of OSCC cells (Ca922 and HSC-3 cells) to TCD suppressed cell proliferation assessed using MTT assays and colony formation assays. TCD inhibited the migration and invasion of OSCC cells (Ca922 and HSC-3 cells) through the downregulation of matrix metalloproteinase 9. After treatment of OSCC cells with TCD, the G2/M phase was arrested, caspase-related apoptosis (cleaved caspase-3 and PARP expression) was induced, and the protein level of x-linked inhibitor of apoptosis was reduced. Meanwhile, the TCD-induced cell death was reversed by the pan-caspase inhibitor Z-VAD-FMK. Furthermore, TCD diminished mitochondrial membrane potential, mitochondrial oxidative phosphorylation and glycolytic function in OSCC cells. In addition, TCD decreased the levels of histone deacetylase 2 (HDAC-2) and downstream signaling proteins, including phosphorylated STAT3 and NF-κB. Finally, TCD significantly suppressed tumor growth in a zebrafish OSCC xenotransplantation model. Overall, this evidence demonstrates that TCD is a novel promising strategy for the treatment of OSCCs.

Trichodermin Induces G0/G1 Cell Cycle Arrest by Inhibiting c-Myc in Ovarian Cancer Cells and Tumor Xenograft-Bearing Mice.

Ovarian cancer is a fatal gynecological cancer because of a lack of early diagnosis, which often relapses as chemoresistant. Trichodermin, a trichothecene first isolated from Trichoderma viride, is an inhibitor of eukaryotic protein synthesis. However, whether trichodermin is able to suppress ovarian cancer or not was unclear. In this study, trichodermin (0.5 µM or greater) significantly decreased the proliferation of two ovarian cancer cell lines A2780/CP70 and OVCAR-3. Normal ovarian IOSE 346 cells were much less susceptible to trichodermin than the cancer cell lines. Trichodermin predominantly inhibited ovarian cancer cells by inducing G0/G1 cell cycle arrest rather than apoptosis. Trichodermin decreased the expression of cyclin D1, CDK4, CDK2, retinoblastoma protein, Cdc25A, and c-Myc but showed little effect on the expression of p21Waf1/Cip1, p27Kip1, or p16Ink4a. c-Myc was a key target of trichodermin. Trichodermin regulated the expression of Cdc25A and its downstream proteins via c-Myc. Overexpression of c-Myc attenuated trichodermin’s anti-ovarian cancer activity. In addition, trichodermin decelerated tumor growth in BALB/c nude mice, proving its effectiveness in vivo. These findings suggested that trichodermin has the potential to contribute to the treatment of ovarian cancer.

Trichothecenes in Cereal Grains - An Update.

Trichothecenes are sesquiterpenoid mycotoxins produced by fungi from the order Hypocreales, including members of the Fusarium genus that infect cereal grain crops. Different trichothecene-producing Fusarium species and strains have different trichothecene chemotypes belonging to the Type A and B class. These fungi cause a disease of small grain cereals, called Fusarium head blight, and their toxins contaminate host tissues. As potent inhibitors of eukaryotic protein synthesis, trichothecenes pose a health risk to human and animal consumers of infected cereal grains. In 2009, Foroud and Eudes published a review of trichothecenes in cereal grains for human consumption. As an update to this review, the work herein provides a comprehensive and multi-disciplinary review of the Fusarium trichothecenes covering topics in chemistry and biochemistry, pathogen biology, trichothecene toxicity, molecular mechanisms of resistance or detoxification, genetics of resistance and breeding strategies to reduce their contamination of wheat and barley.

Molecular Basis for Olefin Rearrangement in the Gephyronic Acid Polyketide Synthase.

Polyketide synthases (PKS) are a rich source of natural products of varied chemical composition and biological significance. Here, we report the characterization of an atypical dehydratase (DH) domain from the PKS pathway for gephyronic acid, an inhibitor of eukaryotic protein synthesis. Using a library of synthetic substrate mimics, the reaction course, stereospecificity, and tolerance to non-native substrates of GphF DH1 are probed via LC-MS analysis. Taken together, the studies establish GphF DH1 as a dual-function dehydratase/isomerase that installs an odd-to-even double bond and yields a product consistent with the isobutenyl terminus of gephyronic acid. The studies also reveal an unexpected C2 epimerase function in catalytic turnover with the native substrate. A 1.55-Å crystal structure of GphF DH1 guided mutagenesis experiments to elucidate the roles of key amino acids in the multistep DH1 catalysis, identifying critical functions for leucine and tyrosine side chains. The mutagenesis results were applied to add a secondary isomerase functionality to a nonisomerizing DH in the first successful gain-of-function engineering of a PKS DH. Our studies of GphF DH1 catalysis highlight the versatility of the DH active site and adaptation for a specific catalytic outcome with a specific substrate.

MFS Transporters and GABA Metabolism Are Involved in the Self-Defense Against DON in Fusarium graminearum.

Trichothecene mycotoxins, such as deoxynivalenol (DON) produced by the fungal pathogen, Fusarium graminearum, are not only important for plant infection but are also harmful to human and animal health. Trichothecene targets the ribosomal protein Rpl3 that is conserved in eukaryotes. Hence, a self-defense mechanism must exist in DON-producing fungi. It is reported that TRI (trichothecene biosynthesis) 101 and TRI12 are two genes responsible for self-defense against trichothecene toxins in Fusarium. In this study, however, we found that simultaneous disruption of TRI101 and TRI12 has no obvious influence on DON resistance upon exogenous DON treatment in F. graminearum, suggesting that other mechanisms may be involved in self-defense. By using RNA-seq, we identified 253 genes specifically induced in DON-treated cultures compared with samples from cultures treated or untreated with cycloheximide, a commonly used inhibitor of eukaryotic protein synthesis. We found that transporter genes are significantly enriched in this group of DON-induced genes. Of those genes, 15 encode major facilitator superfamily transporters likely involved in mycotoxin efflux. Significantly, we found that genes involved in the metabolism of gamma-aminobutyric acid (GABA), a known inducer of DON production in F. graminearum, are significantly enriched among the DON-induced genes. The GABA biosynthesis gene PROLINE UTILIZATION 2-2 (PUT2-2) is downregulated, while GABA degradation genes are upregulated at least twofold upon treatment with DON, resulting in decreased levels of GABA. Taken together, our results suggest that transporters influencing DON efflux are important for self-defense and that GABA mediates the balance of DON production and self-defense in F. graminearum.

Impact of capsaicin, an active component of chili pepper, on pathogenic chlamydial growth ( Chlamydia trachomatis and Chlamydia pneumoniae ) in immortal human epithelial HeLa cells

Chlamydia trachomatis is the leading cause of sexually transmitted infections worldwide. Capsaicin, a component of chili pepper, which can stimulate actin remodeling via capsaicin receptor TRPV1 (transient receptor potential vanilloid 1) and anti-inflammatory effects via PPARγ (peroxisome proliferator-activated receptor-γ) and LXRα (liver X receptor α), is a potential candidate to control chlamydial growth in host cells. We examined whether capsaicin could inhibit C.trachomatis growth in immortal human epithelial HeLa cells. Inclusion forming unit and quantitative PCR assays showed that capsaicin significantly inhibited bacterial growth in cells in a dose-dependent manner, even in the presence of cycloheximide, a eukaryotic protein synthesis inhibitor. Confocal microscopic and transmission electron microscopic observations revealed an obvious decrease in bacterial numbers to inclusions bodies formed in the cells. Although capsaicin can stimulate the apoptosis of cells, no increase in cleaved PARP (poly (ADP-ribose) polymerase), an apoptotic indicator, was observed at a working concentration. All of the drugs tested (capsazepine, a TRPV1 antagonist; 5CPPSS-50, an LXRα inhibitor; and T0070907, a PPARγ inhibitor) had no effect on chlamydial inhibition in the presence of capsaicin. In addition, we also confirmed that capsaicin inhibited Chlamydia pneumoniae growth, indicating a phenomena not specific to C.trachomatis. Thus, we conclude that capsaicin can block chlamydial growth without the requirement of host cell protein synthesis, but by another, yet to be defined, mechanism.

Use of Antibiotics for Maintenance of Axenic Cultures of Amphidinium carterae for the Analysis of Translation.

Most dinoflagellates in culture are bacterized, complicating the quantification of protein synthesis, as well as the analysis of its regulation. In bacterized cultures of Amphidinium carterae Hulbert, up to 80% of protein synthetic activity appears to be predominantly bacterial based on responses to inhibitors of protein synthesis. To circumvent this, axenic cultures of A. carterae were obtained and shown to respond to inhibitors of protein synthesis in a manner characteristic of eukaryotes. However, these responses changed with time in culture correlating with the reappearance of bacteria. Here we show that culture with kanamycin (50 μg/mL), carbenicillin (100 μg/mL), and streptomycin sulfate (50 μg/mL) (KCS), but not 100 units/mL of penicillin and streptomycin (PS), prevents the reappearance of bacteria and allows A. carterae protein synthesis to be quantified without the contribution of an associated bacterial community. We demonstrate that A. carterae can grow in the absence of a bacterial community. Furthermore, maintenance in KCS does not inhibit the growth of A. carterae cultures but slightly extends the growth phase and allows accumulation to somewhat higher saturation densities. We also show that cultures of A. carterae maintained in KCS respond to the eukaryotic protein synthesis inhibitors cycloheximide, emetine, and harringtonine. Establishment of these culture conditions will facilitate our ability to use polysome fractionation and ribosome profiling to study mRNA recruitment. Furthermore, this study shows that a simple and fast appraisal of the presence of a bacterial community in A. carterae cultures can be made by comparing responses to cycloheximide and chloramphenicol rather than depending on lengthier culture-based assessments.

Cellular Effects of Cylindrospermopsin (Cyanobacterial Alkaloid Toxin) and its Potential Medical Consequences.

Cylindrospermopsin (CYN) is a tricyclic guanidino alkaloid toxin produced by several cyanobacterial genera. It alters cellular functioning in eukaryotes, including animal and plant organisms. Over the past decades, more and more evidence shows its potential hazardous effects on animal and human health. In this review, we give a critical survey and interpretation of data currently available on its biochemical and consequently, cellular effects. CYN is considered to be a cytotoxin. Several reports suggest that it is a potent inhibitor of eukaryotic protein synthesis, though the exact mechanisms are not completely understood. Here we show that the biochemical changes induced by CYN are complex, possibly involving multiple modes of action. Glutathione metabolism and pyrimidine nucleotide synthesis is affected besides the proposed protein synthesis inhibition. Biochemical alterations lead to the following cellular/subcellular alterations both in animals and plants: (i) changes in cell division rates due to perturbations in chromatin and cytoskeleton; (ii) perturbations of structure and functioning of endomembranes including endoplasmic reticulum; (iii) general metabolic alterations leading to genotoxicity and programmed cell death/apoptosis. The underlying mechanisms and possible health consequences are discussed.

Ribosome quality control is a central protection mechanism for yeast exposed to deoxynivalenol and trichothecin

BackgroundThe trichothecene mycotoxins deoxynivalenol (DON) and trichothecin (TTC) are inhibitors of eukaryotic protein synthesis. Their effect on cellular homeostasis is poorly understood. We report a systematic functional investigation of the effect of DON and TTC on the yeast Saccharomyces cerevisiae using genetic array, network and microarray analysis. To focus the genetic analysis on intracellular consequences of toxin action we eliminated the PDR5 gene coding for a potent pleiotropic drug efflux protein potentially confounding results. We therefore used a knockout library with a pdr5Δ strain background.ResultsDON or TTC treatment creates a fitness bottleneck connected to ribosome efficiency. Genes isolated by systematic genetic array analysis as contributing to toxin resistance function in ribosome quality control, translation fidelity, and in transcription. Mutants in the E3 ligase Hel2, involved in ribosome quality control, and several members of the Rpd3 histone deacetylase complex were highly sensitive to DON. DON and TTC have similar genetic profiles despite their different toxic potency. Network analysis shows a coherent and tight network of genetic interactions among the DON and TTC resistance conferring gene products. The networks exhibited topological properties commonly associated with efficient processing of information. Many sensitive mutants have a "slow growth" gene expression signature. DON-exposed yeast cells increase transcripts of ribosomal protein and histone genes indicating an internal signal for growth enhancement.ConclusionsThe combination of gene expression profiling and analysis of mutants reveals cellular pathways which become bottlenecks under DON and TTC stress. These are generally directly or indirectly connected to ribosome biosynthesis such as the general secretory pathway, cytoskeleton, cell cycle delay, ribosome synthesis and translation quality control. Gene expression profiling points to an increased demand of ribosomal components and does not reveal activation of stress pathways. Our analysis highlights ribosome quality control and a contribution of a histone deacetylase complex as main sources of resistance against DON and TTC.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2718-y) contains supplementary material, which is available to authorized users.

Purification and partial characterization of a ribosome-inactivating protein from the latex of Euphorbia trigona Miller with cytotoxic activity toward human cancer cell lines

BackgroundThe objective of this study is to investigate the cytotoxic activity of three isolectins purified from the latex of Euphorbia trigona Miller. HypothesisAmong lectins are the ribosome-inactivating proteins (RIPs), which are potent inhibitors of protein synthesis in cells and in cell-free systems. ResultsThree isolectins, ETR1, ETR2 and ETR3, were purified by anion exchange chromatography. Both ETR1 and ETR3 yielded a single band on SDS–PAGE under reducing conditions, corresponding to a molecular weight of 32 g mol−1, while ETR2 yielded two bands corresponding to 31 and 33 g mol−1. When non-reducing conditions were used molecular weight decreased, indicating the presence of intrachain disulfide bonds. Size-exclusion chromatography revealed proteins of apparent molecular weight of 59–63 g mol−1, suggesting a dimeric nature, with subunits not being held together by disulfide linkage. ETR1, ETR2 and ETR3 hemagglutinated human, sheep and rat erythrocytes and this hemagglutination was specifically inhibited by galactose and its derivatives. The lectins studied were thermostable up to 60 °C and their observed activity was maintained across pH range 5–12. These lectins, from the latex of Euphorbia trigona, are potent inhibitors of eukaryotic protein synthesis in a cell-free system. Flow cytometry analysis revealed the antiproliferative activity of them toward A549, HeLa, H116, HL-60 cell lines. ConclusionEuphorbia trigona isolectins are RIPs with cytotoxic activity toward human cancer cell lines.

Draft Genome Sequence of Gephyronic Acid Producer Cystobacter violaceus Strain Cb vi76.

A draft genome sequence of Cystobacter violaceus strain Cb vi76, which produces the eukaryotic protein synthesis inhibitor gephyronic acid, has been obtained. The genome contains numerous predicted secondary metabolite clusters, including the gephyronic acid biosynthetic pathway. This genome will contribute to the investigation of secondary metabolism in other Cystobacter strains.

Cytotoxic effects of cylindrospermopsin in mitotic and non-mitotic Vicia faba cells

Cylindrospermopsin (CYN) is a cyanobacterial toxin known as a eukaryotic protein synthesis inhibitor. We aimed to study its effects on growth, stress responses and mitosis of a eukaryotic model, Vicia faba (broad bean). Growth responses depended on exposure time (3 or 6d), cyanotoxin concentration, culture conditions (dark or continuous light) and V. faba cultivar (“Standard” or “ARC Egypt Cross”). At 6d of exposure, CYN had a transient stimulatory effect on root system growth, roots being possibly capable of detoxification. The toxin induced nucleus fragmentation, blebbing and chromosomal breaks indicating double stranded DNA breaks and programmed cell death. Root necrotic tissue was observed at 0.1–20μgmL−1 CYN that probably impeded toxin uptake into vascular tissue. Growth and cell death processes observed were general stress responses. In lateral root tip meristems, lower CYN concentrations (0.01–0.1μgmL−1) induced the stimulation of mitosis and distinct mitotic phases, irrespective of culture conditions or the cultivar used. Higher cyanotoxin concentrations inhibited mitosis. Short-term exposure of hydroxylurea-synchronized roots to 5μgmL−1 CYN induced delay of mitosis that might have been related to a delay of de novo protein synthesis. CYN induced the formation of double, split and asymmetric preprophase bands (PPBs), in parallel with the alteration of cell division planes, related to the interference of cyanotoxin with protein synthesis, thus it was a plant- and CYN specific alteration.

Cycloheximide prevents thede novopolypeptide synthesis required to recover from acetylene inhibition inNitrosopumilus maritimus

Developing methods to differentiate the relative contributions of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) to ammonia (NH3) oxidation has been challenging due to the lack of compounds that selectively inhibit AOA. In this study, we investigated the effects of specific bacteria- and eukaryote-selective protein synthesis inhibitors on the recovery of acetylene (C2H2)-inactivated NH3 oxidation in the marine AOA Nitrosopumilus maritimus and compared the results with recovery of the AOB Nitrosomonas europaea. C2 H2 irreversibly inhibited N. maritimus NH3 oxidation in a similar manner to what was observed previously with N. europaea. However, cycloheximide (CHX), a widely used eukaryotic protein synthesis inhibitor, but not bacteria-specific protein synthesis inhibitors (kanamycin and gentamycin), inhibited the recovery of NH3-oxidizing activity in N. maritimus. CHX prevented the incorporation of (14)CO2 -labeling into cellular proteins, providing further evidence that CHX acts as a protein synthesis inhibitor in N. maritimus. If the effect of CHX on protein synthesis can be confirmed among other isolates of AOA, the combination of C2H2 inactivation followed by recovery of NH3 oxidation either in the presence of bacteria-selective protein synthesis inhibitors or CHX might be used to estimate the relative contributions of AOB and AOA to NH3 oxidation in natural environments.

Elucidation of Gephyronic Acid Biosynthetic Pathway Revealed Unexpected SAM-Dependent Methylations

Gephyronic acid, a cytostatic polyketide produced by the myxobacterium Cystobacter violaceus Cb vi76, exhibits potent and selective eukaryotic protein synthesis inhibition. Next-generation sequencing of the C. violaceus genome revealed five type I polyketide synthases and post-PKS tailoring enzymes including an O-methyltransferase and a cytochrome P450 monooxygenase. Seven methyltransferase (MT) domains embedded within the PKS subunits were found to install the methyl branches throughout the gephyronic acid skeleton. A rare loading domain from the GNAT superfamily also contains an embedded MT domain that catalyzes the in situ production of an isobutyryl starter unit. Phylogenetic analysis identified new motifs that distinguish MT domains located in PKS pathways with in cis acyltransferase (AT) domains from MT domains located in PKS pathways with trans AT enzymes. The identification of the gene cluster sets the stage for the generation of a heterologous expression system, which will allow further investigation of selective eukaryotic protein synthesis inhibitors through the generation of gephyronic acid analogues.

Translation of viral mRNAs that do not require eIF4E is blocked by the inhibitor 4EGI-1

High throughput screening has rendered new inhibitors of eukaryotic protein synthesis. One such molecule, 4EGI-1 has been reported to selectively block the initiation factor eIF4E. We have investigated the action of this inhibitor on translation directed by several viral mRNAs which, in principle, do not utilize eIF4E. We found that 4EGI-1 inhibits translation directed by poliovirus IRES, in rabbit reticulocyte lysates, to a similar extent as capped mRNA. Moreover, 4EGI-1 inhibits translation driven by poliovirus IRES, both in vitro and in cultured cells, despite cleavage of eIF4G by picornavirus proteases. Finally, translation of vesicular stomatitis virus mRNAs and Sindbis virus subgenomic mRNA is blocked by 4EGI-1 in infected cells to a similar extent as cellular mRNAs. These findings cast doubt on the selective action of this inhibitor, and suggest that this molecule may affect other steps in protein synthesis unrelated to cap recognition by eIF4E.

Synthesis and Biological Evaluation of Gephyronic Acid Derivatives: Initial Steps towards the Identification of the Biological Target of Polyketide Inhibitors of Eukaryotic Protein Synthesis

AbstractCoupled to the development of a total synthesis of gephyronic acid, a series of diastereomeric analogues and their precursors have been prepared by employing complementary aldol strategies for the key coupling step of fragments 4 and 5. A biological evaluation revealed the importance of the epoxide for the cytotoxicity against L‐929 (mouse fibroblast) and KB‐3‐1 (HeLa clone, human cervix carcinoma derived) cell lines. Moreover, variation of the configuration of the C3–C5 stereotriad and the C1 carboxylic acid were found to be important features. Improved activities compared with the natural product were observed when the carboxy terminus at C1 was replaced by a methyl ester or PMB‐protected alcohol. Surprisingly, the derivatives (8R)‐17d and (8S)‐16a showed antibacterial activity against Pseudomonas aeruginosa.

Abstract C67: Gene expression profiling with human breast cancer cell lines exposed to gephyronic acid

Abstract Gephyronic acid is an antibiotic natural product isolated at the HZI (Helmholtz-Zentrum für Infektionsforschung) by Sasse and Höfle from the myxobacterium Archangium gephyra in 1995. Gephyronic acid has been shown to inhibit the growth of yeast and mold in the micromolar range; it also exhibits a cytostatic effect on mammalian cell cultures (human cervix, human leukemia, hamster kidney, hamster ovary, mouse connective tissue, and monkey kidney cancer cells) in the nanomolar range. An in vitro translation assay demonstrated that gephyronic acid is a specific inhibitor of eukaryotic protein synthesis. Interdisciplinary efforts within our laboratory are directed to the evaluation of gephyronic acid as a potential anticancer agent and its structural and biological relationship to the myriaporones and tedanolides. Our recent structural assignment and total synthesis of gephyronic acid incorporates a synthetic route that provides a means by which to access significant quantities of gephyronic acid efficiently and selectively, thus facilitating further biological evaluation. Additionally, we seek to identify the mode of action for gephyronic acid by screening various cancer cell lines through transcriptome and proteome profiling. Our proposed method will analyze mRNA expression levels of cells treated with gephyronic acid, or without for control, through the application of cDNA microarrays. Transcript profiling will then be coupled to proteomic profiling utilizing a method of protein labeling called iTRAQ. Identifying specific genes and their associated proteins will secure the mode of action of gephyronic acid selective activity and further defines potential as a chemotherapeutic lead. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr C67.

ChemInform Abstract: Cycloheximide and Congeners as Inhibitors of Eukaryotic Protein Synthesis from Endophytic Actinomycetes Streptomyces sps. YIM56132 and YIM56141.

Abstract[isolation, structure and activity of two new cycloheximide congeners, i.e.

ChemInform Abstract: Gephyronic Acid, a Missing Link between Polyketide Inhibitors of Eukaryotic Protein Synthesis. Part 1. Structural Revision and Stereochemical Assignment of Gephyronic Acid.

AbstractThe structure of the title compound, a constituent of the myxobacterium Archangium gephyra (Ar 3895) which exists as a separable mixture of keto and hemiketal isomers, is unambiguously confirmed as (I).

ChemInform Abstract: Gephyronic Acid, a Missing Link between Polyketide Inhibitors of Eukaryotic Protein Synthesis. Part 2. Total Synthesis of Gephyronic Acid.

ChemInform Abstract: Gephyronic Acid, a Missing Link between Polyketide Inhibitors of Eukaryotic Protein Synthesis. Part 2. Total Synthesis of Gephyronic Acid.