Cytotrienin A, a translation inhibitor that induces ectodomain shedding of TNF receptor 1 via activation of ERK and p38 MAP kinase

(Homo-)harringtonine prevents endothelial inflammation through IRF-1 dependent downregulation of VCAM1 mRNA expression and inhibition of cell adhesion molecule protein biosynthesis

The plant alkaloid homoharringtonine (HHT) is a Food and Drug Administration (FDA)-approved drug for the treatment of hematologic malignancies. In addition to its well-established antitumor activity, accumulating evidence attributes anti-inflammatory effects to HHT, which have mainly been studied in leukocytes to date. However, a potential influence of HHT on inflammatory activation processes in endothelial cells, which are a key feature of inflammation and a prerequisite for the leukocyte-endothelial cell interaction and leukocyte extravasation, remains poorly understood. In this study, the anti-inflammatory potential of HHT and its derivative harringtonine (HT) on the TNF-induced leukocyte-endothelial cell interaction was assessed, and the underlying mechanistic basis of these effects was elucidated. HHT affected inflammation in vivo in a murine peritonitis model by reducing leukocyte infiltration and proinflammatory cytokine expression as well as ameliorating abdominal pain behavior. In vitro, HT and HHT impaired the leukocyte-endothelial cell interaction by decreasing the expression of the endothelial cell adhesion molecules intracellular adhesion molecule -1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). This effect was mediated by a bipartite mechanism. While HHT did not affect the prominent TNF-induced pro-inflammatory NF-ĸB signaling cascade, the compound downregulated the VCAM1 mRNA expression in an IRF-1-dependent manner and diminished active ICAM1 mRNA translation as determined by polysome profiling. This study highlights HHT as an anti-inflammatory compound that efficiently hampers the leukocyte-endothelial cell interaction by targeting endothelial activation processes.

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.

Anticancer Small-Molecule Agents Targeting Eukaryotic Elongation Factor 1A: State of the Art

Eukaryotic elongation factor 1A (eEF1A) canonically delivers amino acyl tRNA to the ribosomal A site during the elongation stage of protein biosynthesis. Yet paradoxically, the oncogenic nature of this instrumental protein has long been recognized. Consistently, eEF1A has proven to be targeted by a wide assortment of small molecules with excellent anticancer activity, among which plitidepsin has been granted approval for the treatment of multiple myeloma. Meanwhile, metarrestin is currently under clinical development for metastatic cancers. Bearing these exciting advances in mind, it would be desirable to present a systematic up-to-date account of the title topic, which, to the best of our knowledge, has thus far been unavailable in the literature. The present review summarizes recent advances in eEF1A-targeting anticancer agents, both naturally occurring and synthetically crafted, with regard to their discovery or design, target identification, structure–activity relationship, and mode of action. Their structural diversity and differential eEF1A-targeting mechanisms warrant continuing research in pursuit of curing eEF1A-driven malignancy.

Small Molecule Inhibitors Targeting Nuclear Factor κB Activation Markedly Reduce Expression of Interleukin-2, but Not Interferon-γ, Induced by Phorbol Esters and Calcium Ionophores

The T-box transcription factor Eomesodermin (Eomes) promotes the expression of interferon-γ (IFN-γ). We recently reported that the small molecule inhibitors, TPCA-1 and IKK-16, which target nuclear factor κB (NF-κB) activation, moderately reduced Eomes-dependent IFN-γ expression in mouse lymphoma BW5147 cells stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin (IM). In the present study, we investigated the direct effects of NF-κB on IFN-γ expression in mouse lymphoma EL4 cells and primary effector T cells. Eomes strongly promoted IFN-γ expression and the binding of RelA and NFATc2 to the IFN-γ promoter when EL4 cells were stimulated with PMA and IM. Neither TPCA-1 nor IKK-16 reduced IFN-γ expression; however, they markedly decreased interleukin (IL)-2 expression in Eomes-transfected EL4 cells. Moreover, TPCA-1 markedly inhibited the binding of RelA, but not that of Eomes or NFATc2 to the IFN-γ promoter. In effector CD4⁺ and CD8⁺ T cells activated with anti-CD3 and anti-CD28 antibodies, IFN-γ expression induced by PMA and A23187 was not markedly decreased by TPCA-1 or IKK-16 under conditions where IL-2 expression was markedly reduced. Therefore, the present results revealed that NF-κB is dispensable for IFN-γ expression induced by PMA and calcium ionophores in EL4 cells expressing Eomes and primary effector T cells.

The natural product vioprolide A exerts anti-inflammatory actions through inhibition of its cellular target NOP14 and downregulation of importin-dependent NF-ĸB p65 nuclear translocation

Chronic inflammation is characterized by persisting leukocyte infiltration of the affected tissue, which is enabled by activated endothelial cells (ECs). Chronic inflammatory diseases remain a major pharmacotherapeutic challenge, and thus the search for novel drugs and drug targets is an ongoing demand. We have identified the natural product vioprolide A (vioA) to exert anti-inflammatory actions in vivo and in ECs in vitro through inhibition of its cellular target nucleolar protein 14 (NOP14). VioA attenuated the infiltration of microglia and macrophages during laser-induced murine choroidal neovascularization and the leukocyte trafficking through the vascular endothelium in the murine cremaster muscle. Mechanistic studies revealed that vioA downregulates EC adhesion molecules and the tumor necrosis factor receptor (TNFR) 1 by decreasing the de novo protein synthesis in ECs. Most importantly, we found that inhibition of importin-dependent NF-ĸB p65 nuclear translocation is a crucial part of the action of vioA leading to reduced NF-ĸB promotor activity and inflammatory gene expression. Knockdown experiments revealed a causal link between the cellular target NOP14 and the anti-inflammatory action of vioA, classifying the natural product as unique drug lead for anti-inflammatory therapeutics.

A Quick Guide to Small-Molecule Inhibitors of Eukaryotic Protein Synthesis

Eukaryotic ribosome and cap-dependent translation are attractive targets in the antitumor, antiviral, anti-inflammatory, and antiparasitic therapies. Currently, a broad array of small-molecule drugs is known that specifically inhibit protein synthesis in eukaryotic cells. Many of them are well-studied ribosome-targeting antibiotics that block translocation, the peptidyl transferase center or the polypeptide exit tunnel, modulate the binding of translation machinery components to the ribosome, and induce miscoding, premature termination or stop codon readthrough. Such inhibitors are widely used as anticancer, anthelmintic and antifungal agents in medicine, as well as fungicides in agriculture. Chemicals that affect the accuracy of stop codon recognition are promising drugs for the nonsense suppression therapy of hereditary diseases and restoration of tumor suppressor function in cancer cells. Other compounds inhibit aminoacyl-tRNA synthetases, translation factors, and components of translation-associated signaling pathways, including mTOR kinase. Some of them have antidepressant, immunosuppressive and geroprotective properties. Translation inhibitors are also used in research for gene expression analysis by ribosome profiling, as well as in cell culture techniques. In this article, we review well-studied and less known inhibitors of eukaryotic protein synthesis (with the exception of mitochondrial and plastid translation) classified by their targets and briefly describe the action mechanisms of these compounds. We also present a continuously updated database (http://eupsic.belozersky.msu.ru/) that currently contains information on 370 inhibitors of eukaryotic protein synthesis.

Natural products as drugs and tools for influencing core processes of eukaryotic mRNA translation

Eukaryotic protein synthesis is the highly conserved, complex mechanism of translating genetic information into proteins. Although this process is essential for cellular homoeostasis, dysregulations are associated with cellular malfunctions and diseases including cancer and diabetes. In the challenging and ongoing search for adequate treatment possibilities, natural products represent excellent research tools and drug leads for new interactions with the translational machinery and for influencing mRNA translation. In this review, bacterial-, marine- and plant-derived natural compounds that interact with different steps of mRNA translation, comprising ribosomal assembly, translation initiation and elongation, are highlighted. Thereby, the exact binding and interacting partners are unveiled in order to accurately understand the mode of action of each natural product. The pharmacological relevance of these compounds is furthermore assessed by evaluating the observed biological activities in the light of translational inhibition and by enlightening potential obstacles and undesired side-effects, e.g. in clinical trials. As many of the natural products presented here possess the potential to serve as drug leads for synthetic derivatives, structural motifs, which are indispensable for both mode of action and biological activities, are discussed. Evaluating the natural products emphasises the strong diversity of their points of attack. Especially the fact that selected binding partners can be set in direct relation to different diseases emphasises the indispensability of natural products in the field of drug development. Discovery of new, unique and unusual interacting partners again renders them promising tools for future research in the field of eukaryotic mRNA translation.

α-Conidendrin inhibits the expression of intercellular adhesion molecule-1 induced by tumor necrosis factor-α in human lung adenocarcinoma A549 cells

α-Conidendrin is a lignan isolated from Taxus wallichiana and other species. In the present study, we demonstrated that α-conidendrin inhibited the cell-surface expression of intercellular adhesion molecule-1 (ICAM-1) induced by tumor necrosis factor-α (TNF-α) at an IC₅₀ value of 40-60 μM in human lung adenocarcinoma A549 cells. α-Conidendrin decreased ICAM-1 protein and mRNA expression levels at concentrations of 40-100 μM in TNF-α-stimulated A549 cells. The TNF-α-induced mRNA expression of vascular cell adhesion molecule-1, E-selectin, and cyclooxygenase-2 was also reduced by α-conidendrin. In the TNF-α-induced nuclear factor κB (NF-κB) signaling pathway, α-conidendrin did not influence the translocation of the NF-κB subunit RelA from the cytoplasm to the nucleus at concentrations up to 100 μM. A chromatin immunoprecipitation assay revealed that α-conidendrin at 100 μM reduced the binding of RelA to the ICAM-1 promoter in response to a stimulation with TNF-α. Collectively, these results indicated that α-conidendrin interfered with the DNA binding of RelA to the ICAM-1 promoter, thereby reducing ICAM-1 transcription.

Eudesmane-Type Sesquiterpene Lactones Inhibit Nuclear Translocation of the Nuclear Factor κB Subunit RelB in Response to a Lymphotoxin β Stimulation

The transcription factor nuclear factor κB (NF-κB) regulates various biological processes, including inflammatory responses. We previously reported that eudesmane-type sesquiterpene lactones inhibited multiple steps in the canonical NF-κB signaling pathway induced by tumor necrosis factor-α and interleukin-1α. In contrast, the biological activities of eudesmane-type sesquiterpene lactones on the non-canonical NF-κB signaling pathway remain unclear. In the present study, we found that (11S)-2α-bromo-3-oxoeudesmano-12,6α-lactone, designated santonin-related compound 2 (SRC2), inhibited NF-κB luciferase reporter activity induced by lymphotoxin β (LTβ) in human lung carcinoma A549 cells. Although SRC2 did not prevent the processing of the NF-κB subunit p100 induced by LTβ, it inhibited the nuclear translocation of RelB and p52 in response to the LTβ stimulation. In contrast to (-)-dehydroxymethylepoxyquinomicin, SRC2 inhibited the LTβ-induced nuclear translocation of the RelB (C144S) mutant in a manner similar to wild-type RelB. While eudesmane derivatives possessing an α-bromoketone moiety or α,β-unsaturated carbonyl moieties inhibited LTβ-induced NF-κB luciferase reporter activity, eudesmane derivatives possessing an α-bromoketone moiety exhibited stronger inhibitory activity on the LTβ-induced nuclear translocation of RelB than those possessing a single α-methylene-γ-lactone moiety. The results of the present study revealed that SRC2 inhibits the nuclear translocation of RelB in the non-canonical NF-κB signaling pathway induced by LTβ.

Quinacrine Inhibits ICAM-1 Transcription by Blocking DNA Binding of the NF-κB Subunit p65 and Sensitizes Human Lung Adenocarcinoma A549 Cells to TNF-α and the Fas Ligand

Quinacrine has been used for therapeutic drugs in some clinical settings. In the present study, we demonstrated that quinacrine decreased the expression of intercellular adhesion molecule-1 (ICAM-1) induced by tumor necrosis factor (TNF)-α and interleukin-1 (IL-1) α in human lung adenocarcinoma A549 cells. Quinacrine inhibited ICAM-1 mRNA expression and nuclear factor κB (NF-κB)-responsive luciferase reporter activity following a treatment with TNF-α and IL-1α. In the NF-κB signaling pathway, quinacrine did not markedly affect the TNF-α-induced degradation of the inhibitor of NF-κB or the TNF-α-induced phosphorylation of the NF-κB subunit, p65, at Ser-536 and its subsequent translocation to the nucleus. In contrast, a chromatin immunoprecipitation assay showed that quinacrine prevented the binding of p65 to the ICAM-1 promoter following TNF-α stimulation. Moreover, TNF-α and the Fas ligand effectively reduced the viability of A549 cells in the presence of quinacrine only. Quinacrine down-regulated the constitutive and TNF-α-induced expression of c-FLIP and Mcl-1 in A549 cells. These results revealed that quinacrine inhibits ICAM-1 transcription by blocking the DNA binding of p65 and sensitizes A549 cells to TNF-α and the Fas ligand.

Cardenolide aglycones inhibit tumor necrosis factor α-induced expression of intercellular adhesion molecule-1 at the translation step by blocking Na⁺/K⁺-ATPase

Cardiac glycosides, which are inhibitors of Na(+)/K(+)-ATPase, are classified into cardenolides and bufadienolides. We have recently shown that two cardenolide glycosides, ouabain and odoroside A, inhibit Na(+)/K(+)-ATPase, thereby preventing nuclear factor κB-inducible protein expression by blocking Na(+)-dependent amino acid transport. In this study, we investigated the mechanism of action of cardenolide aglycones in tumor necrosis factor α (TNF-α)-induced gene expression. Ouabagenin, digitoxigenin, and digoxigenin were found to inhibit the TNF-α-induced cell-surface expression of intercellular adhesion molecule-1 (ICAM-1) in human lung carcinoma A549 cells. Those cardenolide aglycones did not inhibit the TNF-α-induced expression of ICAM-1 mRNA, but strongly inhibited the TNF-α-induced expression of ICAM-1 as translation product. The inhibition of the TNF-α-induced ICAM-1 expression by ouabagenin, digitoxigenin, and digoxigenin was significantly reversed by the ectopic expression of ouabain-resistant rat Na(+)/K(+)-ATPase α1 isoform. Moreover, knockdown of Na(+)/K(+)-ATPase α1 isoform augmented the inhibition of the TNF-α-induced ICAM-1 expression by ouabagenin or ouabain. These results clearly indicate that cardenolide aglycones inhibit the TNF-α-induced ICAM-1 expression at the translation step by blocking Na(+)/K(+)-ATPase.

Ribosomal alteration-derived signals for cytokine induction in mucosal and systemic inflammation: noncanonical pathways by ribosomal inactivation

Ribosomal inactivation damages 28S ribosomal RNA by interfering with its functioning during gene translation, leading to stress responses linked to a variety of inflammatory disease processes. Although the primary effect of ribosomal inactivation in cells is the functional inhibition of global protein synthesis, early responsive gene products including proinflammatory cytokines are exclusively induced by toxic stress in highly dividing tissues such as lymphoid tissue and epithelia. In the present study, ribosomal inactivation-related modulation of cytokine production was reviewed in leukocyte and epithelial pathogenesis models to characterize mechanistic evidence of ribosome-derived cytokine induction and its implications for potent therapeutic targets of mucosal and systemic inflammatory illness, particularly those triggered by organellar dysfunctions.

Cycloheximide inhibits follicle-stimulating hormone β subunit transcription by blocking de novo synthesis of the labile activin type II receptor in gonadotrope cells

The pituitary gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), play essential roles in the regulation of vertebrate reproduction. Activins and inhibins have opposing actions on FSH (but not LH) synthesis, either inducing or inhibiting transcription of the FSHβ subunit gene (Fshb). The translational inhibitor cycloheximide (CHX) produces inhibin-like effects in cultured pituitary cells, selectively suppressing FSH production. Using the murine gonadotrope-like cell line, LβT2, as a model, we tested the hypothesis that a component of the activin pathway is highly labile in gonadotrope cells and that its rapid loss following CHX treatment impairs activin-stimulated Fshb transcription. Treatment of cells with CHX for 6h, but not 1h, blocked activin A-stimulated Fshb transcription. Pre-treatment of LβT2 cells with CHX for as few as 2-3h inhibited activin A-stimulated SMAD2/3 phosphorylation without altering total SMAD2/3 protein levels. These data indicated that CHX affects activin signalling upstream of SMAD proteins, most likely at the receptor level. Indeed, CHX rapidly reduced activin A binding to LβT2 cells. We went on to show that activin A signals via the type II receptor ACVR2, rather than ACVR2B, to regulate Fshb transcription and that the receptor has a half life of ~2h in LβT2 cells. The mechanism of ACVR2 turnover remains undefined, but appears to be ligand-, proteasome-, and lysosome-independent. Collectively, these data indicate that CHX produces inhibin-like effects in gonadotropes by preventing de novo synthesis of the highly labile ACVR2, thereby blocking activin signaling to the Fshb promoter.

Deoxynivalenol induces ectodomain shedding of TNF receptor 1 and thereby inhibits the TNF-α-induced NF-κB signaling pathway

Trichothecene mycotoxins are known to inhibit eukaryotic translation and to trigger the ribotoxic stress response, which regulates gene expression via the activation of the mitogen-activated protein (MAP) kinase superfamily. In this study, we found that deoxynivalenol induced the ectodomain shedding of tumor necrosis factor (TNF) receptor 1 (TNFRSF1A) and thereby inhibited the TNF-α-induced signaling pathway. In human lung carcinoma A549 cells, deoxynivalenol and 3-acetyldeoxynivalenol inhibited the expression of intercellular adhesion molecule-1 (ICAM-1) induced by TNF-α more strongly than that induced by interleukin 1α (IL-1α), whereas T-2 toxin and verrucarin A exerted nonselective inhibitory effects. Deoxynivalenol and 3-acetyldeoxynivalenol also inhibited the nuclear factor κB (NF-κB) signaling pathway induced by TNF-α, but not that induced by IL-1α. Consistent with these findings, deoxynivalenol and 3-acetyldeoxynivalenol induced the ectodomain shedding of TNF receptor 1 by TNF-α-converting enzyme (TACE), also known as a disintegrin and metalloproteinase 17 (ADAM17). In addition to the TACE inhibitor TAPI-2, the MAP kinase or extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126 and the p38 MAP kinase inhibitor SB203580, but not the c-Jun N-terminal kinase (JNK) inhibitor SP600125, suppressed the ectodomain shedding of TNF receptor 1 induced by deoxynivalenol and reversed its selective inhibition of TNF-α-induced ICAM-1 expression. Our results demonstrate that deoxynivalenol induces the TACE-dependent ectodomain shedding of TNF receptor 1 via the activation of ERK and p38 MAP kinase, and thereby inhibits the TNF-α-induced NF-κB signaling pathway.

Identification of new therapeutic targets by genome-wide analysis of gene expression in the ipsilateral cortex of aged rats after stroke

Background

Because most human stroke victims are elderly, studies of experimental stroke in the aged rather than the young rat model may be optimal for identifying clinically relevant cellular responses, as well for pinpointing beneficial interventions.

Methodology/Principal Findings

We employed the Affymetrix platform to analyze the whole-gene transcriptome following temporary ligation of the middle cerebral artery in aged and young rats. The correspondence, heat map, and dendrogram analyses independently suggest a differential, age-group-specific behaviour of major gene clusters after stroke. Overall, the pattern of gene expression strongly suggests that the response of the aged rat brain is qualitatively rather than quantitatively different from the young, i.e. the total number of regulated genes is comparable in the two age groups, but the aged rats had great difficulty in mounting a timely response to stroke. Our study indicates that four genes related to neuropathic syndrome, stress, anxiety disorders and depression (Acvr1c, Cort, Htr2b and Pnoc) may have impaired response to stroke in aged rats. New therapeutic options in aged rats may also include Calcrl, Cyp11b1, Prcp, Cebpa, Cfd, Gpnmb, Fcgr2b, Fcgr3a, Tnfrsf26, Adam 17 and Mmp14. An unexpected target is the enzyme 3-hydroxy-3-methylglutaryl-Coenzyme A synthase 1 in aged rats, a key enzyme in the cholesterol synthesis pathway. Post-stroke axonal growth was compromised in both age groups.

Conclusion/Significance

We suggest that a multi-stage, multimodal treatment in aged animals may be more likely to produce positive results. Such a therapeutic approach should be focused on tissue restoration but should also address other aspects of patient post-stroke therapy such as neuropathic syndrome, stress, anxiety disorders, depression, neurotransmission and blood pressure.

Translation inhibitors and their unique biological properties

In eukaryotes, many translation inhibitors have been widely used as bioprobes to evaluate the contribution of translation to signaling pathways and cellular functions. Several types of translation inhibitors are also known to trigger the activation of the mitogen-activated protein kinase superfamily in an intracellular mechanism called ribotoxic stress response. This perspective focuses on the biological properties of recently identified translation inhibitors that trigger ribotoxic stress response, particularly glutarimides as well as triene-ansamycins.