Protein synthesis inhibition by flavonoids: roles of eukaryotic initiation factor 2alpha kinases

Biomacromolecules as Immunomodulators: Utilizing Nature’s Tools for Immune Regulation

Although there are numerous available immunomodulators, those of natural origin would be preferable based on their safety profile and effectiveness. The research and clinical interest in immunomodulators have increased in the last decades, especially in the immunomodulatory properties of plant-based therapies. Innovative technologies and extensive study on immunomodulatory natural products, botanicals, extracts, and active moieties with immunomodulatory potential could provide us with valuable entities to develop as novel immunomodulatory medicines to enhance current chemotherapies. This review focuses on plant-based immunomodulatory drugs that are currently in clinical studies. However, further studies in this area are of utmost importance to obtain complete information about the positive effects of medicinal plants and their chemical components and molecules as an alternative to combatting various diseases and/or prevention.

Proteostasis Perturbations and Their Roles in Causing Sterile Inflammation and Autoinflammatory Diseases

Proteostasis, a portmanteau of the words protein and homeostasis, refers to the ability of eukaryotic cells to maintain a stable proteome by acting on protein synthesis, quality control and/or degradation. Over the last two decades, an increasing number of disorders caused by proteostasis perturbations have been identified. Depending on their molecular etiology, such diseases may be classified into ribosomopathies, proteinopathies and proteasomopathies. Strikingly, most—if not all—of these syndromes exhibit an autoinflammatory component, implying a direct cause-and-effect relationship between proteostasis disruption and the initiation of innate immune responses. In this review, we provide a comprehensive overview of the molecular pathogenesis of these disorders and summarize current knowledge of the various mechanisms by which impaired proteostasis promotes autoinflammation. We particularly focus our discussion on the notion of how cells sense and integrate proteostasis perturbations as danger signals in the context of autoinflammatory diseases to provide insights into the complex and multiple facets of sterile inflammation.

Targeting translation regulators improves cancer therapy

Deregulation of protein synthesis may be involved in multiple aspects of cancer, such as gene expression, signal transduction and drive specific cell biological responses, resulting in promoting cancer growth, invasion and metastasis. Study the molecular mechanisms about translational control may help us to find more effective anti-cancer drugs and develop novel therapeutic opportunities. Recently, the researchers had focused on targeting translational machinery to overcome cancer, and various small molecular inhibitors targeting translation factors or pathways have been tested in clinical trials and exhibited improving outcomes in several cancer types. There is no doubt that an insight into the class of translation regulation protein would provide new target for pharmacologic intervention and further provide opportunities to develop novel anti-tumor therapeutic interventions. In this review, we summarized the developments of translational control in cancer survival and progression et al, and highlighted the therapeutic approach targeted translation regulation to overcome the cancer.

Glycogen synthase kinase (GSK)-3 and the double-strand RNA-dependent kinase, PKR: When two kinases for the common good turn bad

Glycogen synthase kinase (GSK)-3α/β and the double-stranded RNA-dependent kinase PKR are two sentinel kinases that carry-out multiple similar yet distinct functions in both the cytosol and the nucleus. While these kinases belong to separate signal transduction cascades, they demonstrate an uncanny propensity to regulate many of the same proteins either through direct phosphorylation or by altering transcription/translation, including: c-MYC, NF-κB, p53 and TAU, as well as each another. A significant number of studies centered on the GSK3 kinases have led to the identification of the GSK3 interactome and a number of substrates, which link GSK3 activity to metabolic control, translation, RNA splicing, ribosome biogenesis, cellular division, DNA repair and stress/inflammatory signaling. Interestingly, many of these same pathways and processes are controlled by PKR, but unlike the GSK3 kinases, a clear picture of proteins interacting with PKR and a complete listing of its substrates is still missing. In this review, we take a detailed look at what is known about the PKR and GSK3 kinases, how these kinases interact to influence common cellular processes (innate immunity, alternative splicing, translation, glucose metabolism) and how aberrant activation of these kinases leads to diseases such as Alzheimer's disease (AD), diabetes mellitus (DM) and cancer.

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GSK3α/β and PKR are major regulators of cellular homeostasis and the response to stress/inflammation and infection.

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GSK3α/β and PKR interact with and/or modify many of the same proteins and affect the expression of similar genes.

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A balance between AKT and PKR nuclear signaling may be responsible for regulating the activation of nuclear GSK3β.

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GSK3α/β- and PKR-dependent signaling influence major molecular mechanisms of the cell through similar intermediates.

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Aberrant activation of GSK3α/β and PKR is highly involved in cancer, metabolic disorders, and neurodegenerative diseases.

Profiling of Nutraceuticals and Proximates in Peanut Genotypes Differing for Seed Coat Color and Seed Size

A total of 60 genotypes of peanut comprising 46 genotypes selected from ICRISAT mini core collection and 14 elite cultivars with differing kernel color and size were used to profile the nutritional parameters such as proximates (moisture, fat, ash, crude protein, crude fiber, carbohydrate content) and nutraceuticals (total polyphenol content and total antioxidant activity). The genotypes showed varied kernel color ranging from white to purple. Kernel skin color was quantified using colorimetry, and the color parameters were expressed as CIELAB color parameters. In total, nine morphological traits, six yield related traits, eight nutritional traits and eleven color parameters were observed across 60 genotypes. The sixty genotypes were grouped into ten clusters based on the color strength. Among them, Cluster-III with dark red seeds had the maximum fat content and total polyphenol content (TPC). Cluster-VI with light pink colored seeds had high antioxidant activity (AOA) and Cluster-X with white colored seeds had highest moisture and crude protein content. Color strength (K/S) was found to be positively correlated with TPC. Another color parameter, redness/greenness (a*) was found to be positively correlated with AOA. However, seed size was positively correlated with the crude protein content, but not with any other nutritional traits under study. The population studies based on the genotypic data indicated two distinct groups pertaining to botanical types of peanut. The marker-trait association (MTA) using single marker analysis indicated 75 major MTAs for most of the nutritional traits except for moisture content. The markers associated with nutritional parameters and other important yield related traits can further be utilized for genomics-assisted breeding for nutrient-rich peanuts.

Signal Transduction in Ribosome Biogenesis: A Recipe to Avoid Disaster

Energetically speaking, ribosome biogenesis is by far the most costly process of the cell and, therefore, must be highly regulated in order to avoid unnecessary energy expenditure. Not only must ribosomal RNA (rRNA) synthesis, ribosomal protein (RP) transcription, translation, and nuclear import, as well as ribosome assembly, be tightly controlled, these events must be coordinated with other cellular events, such as cell division and differentiation. In addition, ribosome biogenesis must respond rapidly to environmental cues mediated by internal and cell surface receptors, or stress (oxidative stress, DNA damage, amino acid depletion, etc.). This review examines some of the well-studied pathways known to control ribosome biogenesis (PI3K-AKT-mTOR, RB-p53, MYC) and how they may interact with some of the less well studied pathways (eIF2α kinase and RNA editing/splicing) in higher eukaryotes to regulate ribosome biogenesis, assembly, and protein translation in a dynamic manner.

Therapeutic Opportunities in Eukaryotic Translation

The ability to block biological processes with selective small molecules provides advantages distinct from most other experimental approaches. These include rapid time to onset, swift reversibility, ability to probe activities in manners that cannot be accessed by genetic means, and the potential to be further developed as therapeutic agents. Small molecule inhibitors can also be used to alter expression and activity without affecting the stoichiometry of interacting partners. These tenets have been especially evident in the field of translation. Small molecule inhibitors were instrumental in enabling investigators to capture short-lived complexes and characterize specific steps of protein synthesis. In addition, several drugs that are the mainstay of modern antimicrobial drug therapy are potent inhibitors of prokaryotic translation. Currently, there is much interest in targeting eukaryotic translation as decades of research have revealed that deregulated protein synthesis in cancer cells represents a targetable vulnerability. In addition to being potential therapeutics, small molecules that manipulate translation have also been shown to influence cognitive processes such as memory. In this review, we focus on small molecule modulators that target the eukaryotic translation initiation apparatus and provide an update on their potential application to the treatment of disease.

Raman microspectroscopy for probing the impact of a dietary antioxidant on human breast cancer cells

Breast cancer is the second most common type of cancer worldwide and the most frequent among women, being the fifth cause of death from neoplastic disease. Since this is an oxidative-stress related neoplasia, it is largely preventable. A dietary isoflavone abundant in soybean - daidzein - is currently being investigated owing to its chemopreventive and/or chemotherapeutic properties towards the human MDA-MB-231 (metastatic, estrogen-unresponsive) and MCF-7 (estrogen-responsive) breast cancer cell lines. Biological assays for evaluation of antitumour and anti-invasive activities were combined with state-of-the-art vibrational microspectroscopy techniques. At 50 and 100 μM concentrations and 48 h incubation time, daidzein was found to induce a marked decrease in cell viability (ca. 50%) for MDA-MB-231 and MCF-7 cells (respectively ca. 50% and 42%) and 40% inhibition of cell migration. MicroRaman analysis of fixed cells upon exposure to this isoflavone unveiled its metabolic impact on both cell lines. Multivariate data analysis (unsupervised PCA) led to a clear discrimination between the control and DAID-exposed cells, with distinctive effects on their biochemical profile, particularly regarding DNA, lipids and protein components, in a cell-dependent way. This is the first reported study on the impact of dietary antioxidants on cancer cells by microRaman techniques.

Targeting translation: eIF4E as an emerging anticancer drug target

The translation initiation factor eIF4E mediates a rate-limiting process that drives selective translation of many oncongenic proteins such as cyclin D1, survivin and VEGF, thereby contributing to tumour growth, metastasis and therapy resistance. As an essential regulatory hub in cancer signalling network, many oncogenic signalling pathways appear to converge on eIF4E. Therefore, targeting eIF4E-mediated cap-dependent translation is considered a promising anticancer strategy. This paper reviews the strategies that can be used to target eIF4E, highlighting agents that target eIF4E activity at each distinct level.

Genistein exerts anti-leukemic effects on genetically different acute myeloid leukemia cell lines by inhibiting protein synthesis and cell proliferation while inducing apoptosis - molecular insights from an iTRAQ™ quantitative proteomics study

Acute myeloid leukemia (AML) is a form of cancer that affects the hematopoietic precursor cells with lethal effects. We investigated the prospect of using genistein as an effective alternate therapy for AML. A two-cell line model, one possessing the FLT3 gene with the ITD mutation (MV4−11) and the other with the wildtype FLT3 gene (HL−60) has been employed. Our 8−plexed iTRAQ™−based quantitative proteomics analysis together with various functional studies demonstrated that genistein exerts anti-leukemic effects on both the AML cell lines. Genistein treatment on the AML cells showed that the drug arrested the mTOR pathway leading to down−regulation of protein synthesis. Additionally, genistein treatment is found to induce cell death via apoptosis. Contrasting regulatory effects of genistein on the cell cycle of the two cell lines were also identified, with the induction of G2/M phase arrest in HL-60 cells but not in MV4−11 cells. Hence, our study highlights the potent anti-leukemic effect of genistein on AML cells irrespective of their genetic status. This suggests the potential use of genistein as an effective general drug therapy for AML patients.

Plant-derived immunomodulators: an insight on their preclinical evaluation and clinical trials

The phagocyte-microbe interactions in the immune system is a defense mechanism but when excessively or inappropriately deployed can harm host tissues and participate in the development of different non-immune and immune chronic inflammatory diseases such as autoimmune problems, allergies, some rheumatoid disorders, cancers and others. Immunodrugs include organic synthetics, biological agents such as cytokines and antibodies acting on single targets or pathways have been used to treat immune-related diseases but with limited success. Most of immunostimulants and immunosuppressants in clinical use are the cytotoxic drugs which possess serious side effects. There is a growing interest to use herbal medicines as multi-component agents to modulate the complex immune system in the prevention of infections rather than treating the immune-related diseases. Many therapeutic effects of plant extracts have been suggested to be due to their wide array of immunomodulatory effects and influence on the immune system of the human body. Phytochemicals such as flavonoids, polysaccharides, lactones, alkaloids, diterpenoids and glycosides, present in several plants, have been reported to be responsible for the plants immunomodulating properties. Thus the search for natural products of plant origin as new leads for development of potent and safe immunosuppressant and immunostimulant agents is gaining much major research interest. The present review will give an overview of widely investigated plant-derived compounds (curcumin, resveratrol, epigallocatechol-3-gallate, quercetin, colchicine, capsaicin, andrographolide, and genistein) which have exhibited potent effects on cellular and humoral immune functions in pre-clinical investigations and will highlight their clinical potential.

Phytochemicals and their impact on adipose tissue inflammation and diabetes

Type 2 diabetes mellitus is an inflammatory disease and the mechanisms that underlie this disease, although still incompletely understood, take place in the adipose tissue of obese subjects. Concurrently, the prevalence of obesity caused by Western diet's excessive energy intake and the lack of exercise escalates, and is believed to be causative for the chronic inflammatory state in adipose tissue. Overnutrition itself as an overload of energy may induce the adipocytes to secrete chemokines activating and attracting immune cells to adipose tissue. But also inflammation-mediating food ingredients like saturated fatty acids are believed to directly initiate the inflammatory cascade. In addition, hypoxia in adipose tissue as a direct consequence of obesity, and its effect on gene expression in adipocytes and surrounding cells in fat tissue of obese subjects appears to play a central role in this inflammatory response too. In contrast, revisiting diet all over the world, there are also some natural food products and beverages which are associated with curative effects on human health. Several natural compounds known as spices such as curcumin, capsaicin, and gingerol, or secondary plant metabolites catechin, resveratrol, genistein, and quercetin have been reported to provide an improved health status to their consumers, especially with regard to diabetes, and therefore have been investigated for their anti-inflammatory effect. In this review, we will give an overview about these phytochemicals and their role to interfere with inflammatory cascades in adipose tissue and their potential for fighting against inflammatory diseases like diabetes as investigated in vivo.

HDAC pharmacological inhibition promotes cell death through the eIF2α kinases PKR and GCN2

Histone deacetylase inhibitors (HDACi) comprise a family of chemotherapeutic agents used in the clinic to treat cutaneous T-cell lymphoma and tested for the therapy of other malignancies. Previous reports have shown that eIF2α phosphorylation is induced upon treatment with HDACi. However the kinase responsible for this phosphorylation or the biological significance of this finding is not yet established. Herein, we show that eIF2α phosphorylation is not attributed to a specific eIF2α kinase, but rather different eIF2α kinases contribute to its upregulation in response to the HDACi, vorinostat. More importantly our data indicate that eIF2α phosphorylation acts in a cytoprotective manner, whereas the eIF2α kinases PKR and GCN2 promote vorinostat-induced apoptosis. These results reveal a dual nature for eIF2α kinases with potential implications in the treatment with histone deacetylase inhibitors.

Hormesis and synergy: pathways and mechanisms of quercetin in cancer prevention and management

Quercetin is a unique dietary polyphenol because it can exert biphasic dose-responses on cells depending on its concentration. Cancer preventative effects of quercetin are observed at concentrations of approximately 1-40 microM and are likely mediated by quercetin's antioxidant properties. Pro-oxidant effects are present at cellular concentrations of 40-100 microM. However, at higher concentrations, many novel pathways in addition to ROS contribute to its effects. The potent bioactivity of quercetin has led to vigorous study of this compound and revealed numerous pathways that could interact synergistically to prevent or treat cancer. The effect of intake and concentration on emerging pathways and how they may interact are discussed in this review.

Flavonol activation defines an unanticipated ligand-binding site in the kinase-RNase domain of IRE1

Signaling in the most conserved branch of the endoplasmic reticulum (ER) unfolded protein response (UPR) is initiated by sequence-specific cleavage of the HAC1/XBP1 mRNA by the ER stress-induced kinase-endonuclease IRE1. We have discovered that the flavonol quercetin activates yeast IRE1's RNase and potentiates activation by ADP, a natural activating ligand that engages the IRE1 nucleotide-binding cleft. Enzyme kinetics and the structure of a cocrystal of IRE1 complexed with ADP and quercetin reveal engagement by quercetin of an unanticipated ligand-binding pocket at the dimer interface of IRE1's kinase extension nuclease (KEN) domain. Analytical ultracentrifugation and crosslinking studies support the preeminence of enhanced dimer formation in quercetin's mechanism of action. These findings hint at the existence of endogenous cytoplasmic ligands that may function alongside stress signals from the ER lumen to modulate IRE1 activity and at the potential for the development of drugs that modify UPR signaling from this unanticipated site.

A role for PKR in hematologic malignancies

The double-stranded RNA-dependent kinase PKR has been described for many years as strictly a pro-apoptotic kinase. Recent data suggest that the main purpose of this kinase is damage control and repair following stress and, if all else fails, apoptosis. Aberrant activation of PKR has been reported in numerous neurodegenerative diseases and cancer. Although a subset of myelodysplastic syndromes (MDS) and chronic lymphocytic leukemia contain low levels of PKR expression and activity, elevated PKR activity and/or expression have been detected in a wide range of hematologic malignancies, from bone marrow failure disorders to acute leukemia. With the recent findings that cancers containing elevated PKR activity are highly sensitive to PKR inhibition, we explore the role of PKR in hematologic malignancies, signal transduction pathways affected by PKR, and how PKR may contribute to leukemic transformation.

Natural compounds and the hypoxia-inducible factor (HIF) signalling pathway

A decline in the tissue oxygen level below normal leads to cellular hypoxia. This situation is very frequently encountered in solid tumors as existing blood vessels cannot satisfy the requirements in oxygen of the rapidly growing tumor. Like hyperoxia, hypoxia is a stress factor for cells and tissues. Adapting to this stressful situation leads to activation of the dimeric transcription factor hypoxia-inducible factor-1 (HIF-1) that induces gene expression in promoting tumor cell survival. In addition, hypoxia acts as a selection factor for radio- and chemotherapy resistant tumor cells with a high potential of malignancy. Consequently, over expression of the HIF-1alpha subunit is associated with an advanced disease stage and poor prognosis of cancer patients. During the last few years intense effort has been made in investigating natural compounds that can be used as HIF-1 inhibitors. These compounds aim to suppress tumor hypoxia and to increase the susceptibility of tumor cells to radio- and chemo-therapy. In this review we summarize recent findings concerning HIF-1 regulation and present a survey of HIF-1 inhibiting natural compounds that have been discovered in the last few years.

RAX is required for fly neuronal development and mouse embryogenesis

RAX was originally discovered as the unique cellular activator for the dsRNA-dependent, interferon-inducible protein kinase PKR. Recent findings indicate that RAX is also a critical component of the RNA-induced silencing complex and a regulator of transcription. Here we report novel phenotypes for both fruit flies carrying a transposon insertion in the 5' UTR of dRax (independently identified as loqs/R3D1) and mice with a deletion of the entire Rax gene. In Drosophila we observe a high level of dRax expression in the developing nerve cord. Mutant fly embryos homozygous for the insertion dRax[f00791] display highly abnormal commissural axon structure of the CNS and 70% of the flies homozygous for the mutant allele die prior to adulthood. Surviving male flies have reduced fertility and female flies are sterile. Furthermore, these flies appear to have a severe defect in nervous system coordination or neuromuscular function resulting in significantly reduced locomotion. Mice were also generated that are heterozygous for a deletion of the entire Rax gene (exons 1-8). While mice that are heterozygous for the mutant allele are viable and appear normal, we are unable to obtain mice homozygous for this mutant allele. Furthermore, we have not observed any embryo obtained by mating heterozygous mice at either E3.5, 7, or 14 that is nullizygous for the Rax gene. Since Rax is expressed in preimplantation blastocysts, these data indicate that deletion of the entire Rax gene is embryonic lethal in mice at a preimplantation stage of development. Collectively, these findings in two different species illustrate the importance of RAX for embryonic development.

Involvement of ERKs, RSK2 and PKR in UVA-induced signal transduction toward phosphorylation of eIF2alpha (Ser(51))

Double-stranded RNA-dependent protein kinase R (PKR) has been implicated in anti-viral (antitumor) and apoptotic responses. PKR is activated by extracellular stresses and phosphorylates the alpha subunit of protein synthesis initiation factor eIF2, thereby inhibiting protein synthesis and impeding virus multiplication. Phosphorylation of eIF2alpha in mammalian cells has been shown to be increased after ultraviolet (UV) stress and to be required for UV-induced repression of protein translation. UVA is an important etiological factor in skin carcinogenesis and we observed that UVA induced phosphorylation of PKR (Thr(451)) and eIF2alpha (Ser(51)) in mouse skin epidermal JB6 Cl41 cells. The induction was suppressed by the MEK1 inhibitor, PD 98059. UVA stimulation of PKR and eIF2alpha phosphorylation was also inhibited by a dominant-negative mutant (DNM) of ERK2- or RSK2-deficient cells (RSK2(-)). An inhibitor of p38, SB 202190 or a DNM of p38alpha kinase (DNM-p38alpha) suppressed UVA-induced phosphorylation of eIF2alpha (Ser(51)) but had no effect on phosphorylation of PKR (Thr(451)). Our data indicated that phosphorylation of PKR at Thr(451) is mediated through ERK2 and RSK2, but not through p38 kinase, and is involved in the regulation of Ser(51) phosphorylation of eIF2alpha in UVA-irradiated JB6 cells. In vitro and in vivo kinase assays indicated that phosphorylation of eIF2alpha at Ser(51) occurred indirectly through ERK2, RSK2 or p38 kinase in the cellular response to UVA. These data may lead to the use of these signaling molecules as targets to develop more effective chemopreventive agents with fewer side effects to control UV-induced skin cancer.

Protein synthesis inhibition as a potential strategy for metabolic down-regulation

OBJECTIVE

This pilot study tested the potential of puromycin (PUR) to inhibit protein synthesis and reduce oxygen utilization in a non-hibernating, whole animal preparation.

METHODS

After anesthesia and instrumentation, male rats received a single dose of PUR or 0.9% saline (control), followed 60 min later with [(35)S] methionine/cysteine radiolabeling. Thirty minutes after isotope injection, organ biopsies were taken for quantification of de novo protein synthesis. Arterial and central venous blood gases were obtained at baseline and 60 min after injection of PUR or 0.9% saline. Temperature, mean arterial pressure (MAP), and heart rate were recorded continuously.

RESULTS

Animals receiving PUR demonstrated significant reductions in protein synthesis in all organ systems sampled (p<0.05). The overall reduction averaged 67.8%. Central venous oxygen saturations (S(cv)O(2)) were higher in the PUR group than the controls at 60 min (90+/-2% versus 80+/-4%, p<0.05). The oxygen extraction ratio (O(2)ER) decreased from 16.1+/-1.7% to 6.8+/-1.2% in the PUR group (p<0.05) and increased from 12.5+/-3.2% to 16.0+/-4.2% in the controls (p=0.44). There was no difference in temperature, MAP, heart rate or blood gas variables, other than S(cv)O(2), at baseline or 60 min between groups.

CONCLUSIONS

These results demonstrate that PUR is capable of reducing whole body protein synthesis significantly within a relatively short duration of time. This appears to decrease whole body oxygen utilization as evidenced by an increase in S(cv)O(2) and a decrease in O(2)ER. Protein synthesis inhibition may reduce metabolic demands and should be tested for its potential to improve outcomes where oxygen demands exceed oxygen delivery.

Methoxyflavones protect cells against endoplasmic reticulum stress and neurotoxin

Enhanced endoplasmic reticulum (ER) stress leads to cell death in various pathophysiological situations. During a search for compounds that regulate ER stress, we identified methoxyflavones, a group of flavonoids, as strong protective agents against ER stress. Analysis in mouse insulinoma MIN6 cells revealed that methoxyflavones mildly activated the eukaryotic initiation factor 2alpha and nuclear factor erythroid 2-related factor pathways, but not the XBP1 pathway, and induced downstream genes, including glucose-regulated protein (GRP) 78, a molecular chaperone in the ER. The protective effect of methoxyflavones was enhanced by agents that increase intracellular cAMP levels such as forskolin, dibutyryl-cAMP and IBMX, but suppressed by the protein kinase A (PKA) inhibitor H-89, suggesting involvement of the PKA pathway in the regulation of ER stress by methoxyflavones. Consistent with the results in cultured cells, pretreatment of mice with tangeretin, a methoxyflavone, enhanced expression of GRP78 and HO-1 without causing ER stress in renal tubular epithelium and prevented tunicamycin-induced cell death. Furthermore, preadministration of tangeretin in mice enhanced expression of GRP78 in the substantia nigra pars compacta and protected dopaminergic neurons against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, a neurotoxin that induces both oxidative and ER stress. These results suggest that methoxyflavones play an important role in the regulation of ER stress and could be a therapeutic target for the ER stress-related diseases.

Quercetin blocks airway epithelial cell chemokine expression

Quercetin (3,3',4',5,7-pentahydroxyflavone), a dietary flavonoid, is an inhibitor of phosphatidylinositol (PI) 3-kinase and potent antioxidant. We hypothesized that quercetin blocks airway epithelial cell chemokine expression via PI 3-kinase-dependent mechanisms. Pretreatment with quercetin and the PI 3-kinase inhibitor LY294002 each reduced TNF-alpha-induced IL-8 and monocyte chemoattractant protein (MCP)-1 (also called CCL2) expression in cultured human airway epithelial cells. Quercetin also inhibited TNF-alpha-induced PI 3-kinase activity, Akt phosphorylation, intracellular H(2)O(2) production, NF-kappaB transactivation, IL-8 promoter activity, and steady-state mRNA levels, consistent with the notion that quercetin inhibits chemokine expression by attenuating NF-kappaB transactivation via a PI 3-kinase/Akt-dependent pathway. Quercetin also reduced TNF-alpha-induced chemokine secretion in the presence of the transcriptional inhibitor actinomycin D, while inducing phosphorylation of eukaryotic translation initiation factor (eIF)-2alpha, suggesting that quercetin attenuates chemokine expression by post-transcriptional as well as transcriptional mechanisms. Finally, we tested the effects of quercetin in cockroach antigen-sensitized and -challenged mice. These mice show MCP-1-dependent airways hyperresponsiveness and inflammation. Quercetin significantly reduced lung MCP-1 and methacholine responsiveness. We conclude that quercetin blocks airway cell chemokine expression via transcriptional and post-transcriptional pathways.

PERK is responsible for the increased phosphorylation of eIF2alpha and the severe inhibition of protein synthesis after transient global brain ischemia

Reperfusion after global brain ischemia results initially in a widespread suppression of protein synthesis in neurons that is due to inhibition of translation initiation as a result of the phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 (eIF2). To address the role of the eIF2alpha kinase RNA-dependent protein kinase-like endoplasmic reticulum kinase (PERK) in the reperfused brain, transgenic mice with a targeted disruption of the Perk gene were subjected to 20 min of forebrain ischemia followed by 10 min of reperfusion. In wild-type mice, phosphorylated eIF2alpha was detected in the non-ischemic brain and its levels were elevated threefold after 10 min of reperfusion. Conversely, there was no phosphorylated eIF2alpha detected in the non-ischemic transgenic mice and there was no sizeable rise in phosphorylated eIF2alpha levels in the forebrain after ischemia and reperfusion. Moreover, there was a substantial rescue of protein translation in the reperfused transgenic mice. Neither group showed any change in total eIF2alpha, phosphorylated eukaryotic elongation factor 2 or total eukaryotic elongation factor 2 levels. These data demonstrate that PERK is responsible for the large increase in phosphorylated eIF2alpha and the suppression of translation early in reperfusion after transient global brain ischemia.

Flavonoid effects on normal and leukemic cells

Quercetin and flavopiridol, both flavonoids which influence oxidative milieu, proliferation, and apoptosis of various cell types, were examined for their effects on acute myelogenous leukemic cells and normal progenitors. Both quercetin and flavopiridol inhibited the growth and viability of various acute myelogenous leukemia (AML) cell lines and AML blasts isolated afresh from patients with AML of various subtypes. The effects on inhibition of proliferation and decreased viability were also significant in normal CD34+ cells isolated from normal marrow donors. In certain AML cases, the effects of flavopiridol appeared to be mediated through activation of caspase 3, offering one possible mechanism for the apoptosis evident after exposure to flavopiridol as measured by annexin V expression. These flavonoid compounds might find use in various therapeutic settings in AML.

Phosphorylation of eukaryotic initiation factor-2alpha (eIF2alpha) is associated with neuronal degeneration in Alzheimer's disease

Inhibition of protein translation is a mode of inducing neuronal apoptosis and neurodegeneration in Alzheimer's disease (AD). Phosphorylation of eukaryotic initiation factor-2alpha (eIF2alpha) terminates global protein translation and induces apoptosis. We examined whether this signaling pathway occurs in degenerating neurons of AD. Brain sections from young individuals, age-matched control individuals and AD patients were examined for immunoreactivity of phosphorylated eIF2alpha by immunohistochemical analysis. While young brain sections did not display and age-matched brain sections have mild immunoreactive positive cells, AD brain sections revealed intense immunoreactivity for phosphorylated eIF2alpha. Most of the phosphorylated eIF2alpha immunoreactive positive neurons have high immunoreactivity for phosphorylated tau using AT8 antibody. Also, intense staining of phosphorylated eIF2alpha is associated vacuoles in degenerating neurons. This phenomenon was also observed for the immunohistochemical staining of phosphorylated PKR (double-stranded RNA-dependent protein kinase), the upstream kinase for eIF2alpha. Activation of PKR-eIF2alpha pathway is considered to be pro-apoptotic. In addition, formation of autophagy is regulated by eIF2alpha kinase. Therefore, it is concluded that phosphorylation of eIF2alpha is associated with the degeneration of neurons in AD.

Involvement of double-stranded RNA-dependent protein kinase and phosphorylation of eukaryotic initiation factor-2alpha in neuronal degeneration

Inhibition of protein translation plays an important role in apoptosis. While double-stranded RNA-dependent protein kinase (PKR) is named as it is activated by double-stranded RNA produced by virus, its activation induces an inhibition of protein translation and apoptosis via the phosphorylation of the eukaryotic initiation factor 2alpha (eIF2alpha). PKR is also a stress kinase and its levels increase during ageing. Here we show that PKR activation and eIF2alpha phosphorylation play a significant role in apoptosis of neuroblastoma cells and primary neuronal cultures induced by the beta-amyloid (Abeta) peptides, the calcium ionophore A23187 and flavonoids. The phosphorylation of eIF2alpha and the number of apoptotic cells were enhanced in over-expressed wild-type PKR neuroblastoma cells exposed to Abeta peptide, while dominant-negative PKR reduced eIF2alpha phosphorylation and apoptosis induced by Abeta peptide. Primary cultured neurons from PKR knockout mice were also less sensitive to Abeta peptide toxicity. Activation of PKR and eIF2alpha pathway by Abeta peptide are triggered by an increase in intracellular calcium because the intracellular calcium chelator BAPTA-AM significantly reduced PKR phosphorylation. Taken together, these results reveal that PKR and eIF2alpha phosphorylation could be involved in the molecular signalling events leading to neuronal apoptosis and death and could be a new target in neuroprotection.

Translation initiation and its deregulation during tumorigenesis

Regulation of protein synthesis at the level of translation initiation is fundamentally important for the control of cell proliferation under normal physiological conditions. Conversely, misregulation of protein synthesis is emerging as a major contributory factor in cancer development. Most bulk protein synthesis is initiated via recognition of the mRNA 5' cap and subsequent recognition of the initiator AUG codon by a directional scanning mechanism. However, several key regulators of tumour development are translated by a cap-independent pathway. Here we review eukaryotic translation initiation, its regulation and the ways in which this regulation can break down during tumorigenesis.

Initiation factor eIF2 alpha phosphorylation in stress responses and apoptosis

The alpha subunit of polypeptide chain initiation factor eIF2 can be phosphorylated by a number of related protein kinases which are activated in response to cellular stresses. Physiological conditions which result in eIF2 alpha phosphorylation include virus infection, heat shock, iron deficiency, nutrient deprivation, changes in intracellular calcium, accumulation of unfolded or denatured proteins and the induction of apoptosis. Phosphorylated eIF2 acts as a dominant inhibitor of the guanine nucleotide exchange factor eIF2B and prevents the recycling of eIF2 between successive rounds of protein synthesis. Extensive phosphorylation of eIF2 alpha and strong inhibition of eIF2B activity can result in the downregulation of the overall rate of protein synthesis; less marked changes may lead to alterations in the selective translation of alternative open reading frames in polycistronic mRNAs, as demonstrated in yeast. These mechanisms can provide a signal transduction pathway linking eukaryotic cellular stress responses to alterations in the control of gene expression at the translational level.