scholarly journals eIF2α Kinases Control Chalone Production in Dictyostelium discoideum

2011 ◽  
Vol 10 (4) ◽  
pp. 494-501 ◽  
Author(s):  
Robert L. Bowman ◽  
Yanhua Xiong ◽  
Janet H. Kirsten ◽  
Charles K. Singleton
Keyword(s):  
Cell Proliferation ◽  
Kinase Domain ◽  
Initiation Factor ◽  
High Molecular Weight Complex ◽  
Α Subunit ◽  
Inhibition Of Proliferation ◽  
Translational Initiation ◽  
Content Type ◽  
Enhanced Production ◽  
In Cells

ABSTRACT Growing Dictyostelium cells secrete CfaD and AprA, two proteins that have been characterized as chalones. They exist within a high-molecular-weight complex that reversibly inhibits cell proliferation, but not growth, via cell surface receptors and a signaling pathway that includes G proteins. How the production of these two proteins is regulated is unknown. Dictyostelium cells possess three GCN2-type eukaryotic initiation factor 2 α subunit (eIF2α) kinases, proteins that phosphorylate the translational initiation factor eIF2α and possess a tRNA binding domain involved in their regulation. The Dictyostelium kinases have been shown to function during development in regulating several processes. We show here that expression of an unregulated, activated kinase domain greatly inhibits cell proliferation. The inhibitory effect on proliferation is not due to a general inhibition of translation. Instead, it is due to enhanced production of a secreted factor(s). Indeed, extracellular CfaD and AprA proteins, but not their mRNAs, are overproduced in cells expressing the activated kinase domain. The inhibition of proliferation is not seen when the activated kinase domain is expressed in cells lacking CfaD or AprA or in cells that contain a nonphosphorylatable eIF2α. We conclude that production of the chalones CfaD and AprA is translationally regulated by eIF2α phosphorylation. Both proteins are upregulated at the culmination of development, and this enhanced production is lacking in a strain that possesses a nonphosphorylatable eIF2α.

scholarly journals Varicella-Zoster Virus IE63, a Major Viral Latency Protein, Is Required To Inhibit the Alpha Interferon-Induced Antiviral Response

2007 ◽  
Vol 81 (15) ◽  
pp. 7844-7851 ◽  
Author(s):  
Aruna P. N. Ambagala ◽  
Jeffrey I. Cohen
Keyword(s):  
Varicella Zoster Virus ◽  
Melanoma Cells ◽  
Alpha Interferon ◽  
Parental Virus ◽  
Initiation Factor ◽  
Viral Gene ◽  
Α Subunit ◽  
Varicella Zoster ◽  
In Cells ◽  
Hsv 1

ABSTRACT Varicella-zoster virus (VZV) open reading frame 63 (ORF63) is the most abundant transcript expressed during latency in human sensory ganglia. VZV with ORF63 deleted is impaired for replication in melanoma cells and fibroblasts and for latency in rodents. We found that replication of the ORF63 deletion mutant is fully complemented in U2OS cells, which have been shown to complement the growth of herpes simplex virus type 1 (HSV-1) ICP0 mutants. Since HSV-1 ICP0 mutants are hypersensitive to alpha interferon (IFN-α), we examined the effect of IFN-α on VZV replication. Replication of the ORF63 mutant in melanoma cells was severely inhibited in the presence of IFN-α, in contrast to other VZV mutants that were similarly impaired for replication or to parental virus. The VZV ORF63 mutant was not hypersensitive to IFN-γ. IFN-α inhibited viral-gene expression in cells infected with the ORF63 mutant at a posttranscriptional level. Since IFN-α stimulates gene products that can phosphorylate the α subunit of eukaryotic initiation factor 2 (eIF-2α) and inhibit translation, we determined whether cells infected with the ORF63 mutant had increased phosphorylation of eIF-2α compared with cells infected with parental virus. While phosphorylated eIF-2α was undetectable in uninfected cells or cells infected with parental virus, it was present in cells infected with the ORF63 mutant. Conversely, expression of IE63 (encoded by ORF63) in the absence of other viral proteins inhibited phosphorylation of eIF-2α. Since IFN-α has been shown to limit VZV replication in human skin xenografts, the ability of VZV IE63 to block the effects of the cytokine may play a critical role in VZV pathogenesis.

scholarly journals Cell proliferation, apoptosis and accumulation of lipid droplets in U937-1 cells incubated with eicosapentaenoic acid

1998 ◽  
Vol 336 (2) ◽  
pp. 451-459 ◽  
Author(s):  
Hanne S. FINSTAD ◽  
Christian A. DREVON ◽  
Mari Ann KULSETH ◽  
Anne V. SYNSTAD ◽  
Eirunn KNUDSEN ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
Eicosapentaenoic Acid ◽  
Lipid Droplets ◽  
Lipid Peroxide ◽  
Cell Cycle Distribution ◽  
Monocytic Differentiation ◽  
Monocytic Cell ◽  
Monocytic Cell Line ◽  
Inhibition Of Proliferation ◽  
In Cells

The monocytic cell line U937-1 was cultured in the presence of eicosapentaenoic acid (20:5, n-3) (EPA) or oleic acid (18:1, n-9) (OA). EPA caused a dose-dependent inhibition of cell proliferation, whereas OA had no effect. At the highest EPA concentrations, 120 and 240 µM, inhibition of cell proliferation was accompanied by initiation of apoptosis. A concentration of 60 µM EPA caused a 35% reduction in cell proliferation without inducing apoptosis, and was therefore used for further studies. Addition of antioxidants or inhibitors of eicosanoid synthesis had no influence on the reduced cell proliferation after EPA treatment. The inhibition required continuous presence of EPA in the incubation medium as the cells resumed a normal proliferation rate when they were placed in EPA-free medium. The inhibition of proliferation was not accompanied by differentiation into macrophage-like cells, as expression of serglycin and the ability to perform respiratory burst was unaffected by EPA. Expression of CD23 mRNA increased when the cells were incubated with EPA, but to a smaller extent than after retinoic acid (RA) or PMA treatment. Furthermore, expression of the monocytic differentiation markers CD36 and CD68 was lower in cells treated with EPA or OA when compared with untreated cells. The cell cycle distribution of U937-1 cells was similar in cells incubated with EPA or PMA, whereas RA-treated cells accumulated in the G1 phase. Side scatter increased in cells incubated with EPA and OA, which was ascribed to an accumulation of lipid droplets after examination of the cells by electron microscopy. The number of droplets per cell was higher in cells exposed to EPA than OA. The cellular triacylglycerol (TAG) increased 5.5- and 15.5-fold after incubation with OA and EPA respectively. No difference in the cellular content of cholesterol compared with untreated cells was observed. The TAG fraction in EPA-treated cells contained high amounts of EPA and docosapentaenoic acid and minor amounts of docosahexaenoic acid, whereas OA-treated cells had high levels of OA in the TAG. In cells incubated with a sulphur-substituted EPA, only minor effects on cell proliferation and no accumulation of cellular TAG were observed. These findings may indicate the existence of other mechanisms for regulation of cell behaviour by very-long-chain polyunsaturated n-3 fatty acids than the well established lipid peroxide and eicosanoid pathways.

scholarly journals Regulation of protein synthesis by the heme-regulated eIF2α kinase: relevance to anemias

Blood ◽  
2006 ◽  
Vol 109 (7) ◽  
pp. 2693-2699 ◽  
Author(s):  
Jane-Jane Chen
Keyword(s):  
Protein Synthesis ◽  
Translational Regulation ◽  
Erythroid Differentiation ◽  
Protective Role ◽  
Initiation Factor ◽  
Protective Function ◽  
Α Subunit ◽  
Translational Initiation ◽  
Major Mechanism ◽  
Binding Domains

Abstract During erythroid differentiation and maturation, it is critical that the 3 components of hemoglobin, α-globin, β-globin, and heme, are made in proper stoichiometry to form stable hemoglobin. Heme-regulated translation mediated by the heme-regulated inhibitor kinase (HRI) provides one major mechanism that ensures balanced synthesis of globins and heme. HRI phosphorylates the α-subunit of eukaryotic translational initiation factor 2 (eIF2α) in heme deficiency, thereby inhibiting protein synthesis globally. In this manner, HRI serves as a feedback inhibitor of globin synthesis by sensing the intracellular concentration of heme through its heme-binding domains. HRI is essential not only for the translational regulation of globins, but also for the survival of erythroid precursors in iron deficiency. Recently, the protective function of HRI has also been demonstrated in murine models of erythropoietic protoporphyria and β-thalassemia. In these 3 anemias, HRI is essential in determining red blood cell size, number, and hemoglobin content per cell. Translational regulation by HRI is critical to reduce excess synthesis of globin proteins or heme under nonoptimal disease states, and thus reduces the severity of these diseases. The protective role of HRI may be more common among red cell disorders.

scholarly journals DAP1, a Negative Regulator of Autophagy, Controls SubAB-Mediated Apoptosis and Autophagy

2014 ◽  
Vol 82 (11) ◽  
pp. 4899-4908 ◽  
Author(s):  
Kinnosuke Yahiro ◽  
Hiroyasu Tsutsuki ◽  
Kohei Ogura ◽  
Sayaka Nagasawa ◽  
Joel Moss ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Hela Cells ◽  
Mammalian Target Of Rapamycin ◽  
Negative Regulator ◽  
Initiation Factor ◽  
Parp Cleavage ◽  
Apoptotic Pathway ◽  
Α Subunit ◽  
Content Type ◽  
Initiation Factor 2

ABSTRACTAutophagy and apoptosis play critical roles in cellular homeostasis and survival. Subtilase cytotoxin (SubAB), produced by non-O157 type Shiga-toxigenicEscherichia coli(STEC), is an important virulence factor in disease. SubAB, a protease, cleaves a specific site on the endoplasmic reticulum (ER) chaperone protein BiP/GRP78, leading to ER stress, and induces apoptosis. Here we report that in HeLa cells, activation of a PERK (RNA-dependent protein kinase [PKR]-like ER kinase)-eIF2α (α subunit of eukaryotic initiation factor 2)-dependent pathway by SubAB-mediated BiP cleavage negatively regulates autophagy and induces apoptosis through death-associated protein 1 (DAP1). We found that SubAB treatment decreased the amounts of autophagy markers LC3-II and p62 as well as those of mTOR (mammalian target of rapamycin) signaling proteins ULK1 and S6K. These proteins showed increased expression levels in PERK knockdown or DAP1 knockdown cells. In addition, depletion of DAP1 in HeLa cells dramatically inhibited the SubAB-stimulated apoptotic pathway: SubAB-induced Bax/Bak conformational changes, Bax/Bak oligomerization, cytochromecrelease, activation of caspases, and poly(ADP-ribose) polymerase (PARP) cleavage. These results show that DAP1 is a key regulator, through PERK-eIF2α-dependent pathways, of the induction of apoptosis and reduction of autophagy by SubAB.

scholarly journals Effects of PERK eIF2α Kinase Inhibitor against Toxoplasma gondii

2018 ◽  
Vol 62 (11) ◽  
Author(s):  
Leonardo Augusto ◽  
Jennifer Martynowicz ◽  
Kirk A. Staschke ◽  
Ronald C. Wek ◽  
William J. Sullivan
Keyword(s):  
Endoplasmic Reticulum ◽  
Toxoplasma Gondii ◽  
Er Stress ◽  
Lethal Dose ◽  
Lytic Cycle ◽  
Host Cells ◽  
Initiation Factor ◽  
Α Subunit ◽  
Content Type ◽  
Eif2α Kinase

ABSTRACT Toxoplasma gondii is an obligate intracellular parasite that has infected one-third of the population. Upon infection of warm-blooded vertebrates, the replicating form of the parasite (tachyzoite) converts into a latent form (bradyzoite) present in tissue cysts. During immune deficiency, bradyzoites can reconvert into tachyzoites and cause life-threatening toxoplasmosis. We previously reported that translational control through phosphorylation of the α subunit of T. gondii eukaryotic initiation factor 2 (eIF2α) (TgIF2α) is a critical component of the parasite stress response. Diverse stresses can induce the conversion of tachyzoites to bradyzoites, including those disrupting the parasite's endoplasmic reticulum (ER) (ER stress). Toxoplasma possesses four eIF2α kinases, one of which (TgIF2K-A) localizes to the parasite ER analogously to protein kinase R-like endoplasmic reticulum kinase (PERK), the eIF2α kinase that responds to ER stress in mammalian cells. Here, we investigated the effects of a PERK inhibitor (PERKi) on Toxoplasma. Our results show that the PERKi GSK2606414 blocks the enzymatic activity of TgIF2K-A and reduces TgIF2α phosphorylation specifically in response to ER stress. PERKi also significantly impeded multiple steps of the tachyzoite lytic cycle and sharply lowered the frequency of bradyzoite differentiation in vitro. Pretreatment of host cells with PERKi prior to infection did not affect parasite infectivity, and PERKi still impaired parasite replication in host cells lacking PERK. In mice, PERKi conferred modest protection from a lethal dose of Toxoplasma. Our findings represent the first pharmacological evidence supporting TgIF2K-A as an attractive new target for the treatment of toxoplasmosis.

scholarly journals eIF4GI links nutrient sensing by mTOR to cell proliferation and inhibition of autophagy

2008 ◽  
Vol 181 (2) ◽  
pp. 293-307 ◽  
Author(s):  
Francisco Ramírez-Valle ◽  
Steve Braunstein ◽  
Jiri Zavadil ◽  
Silvia C. Formenti ◽  
Robert J. Schneider
Keyword(s):  
Cell Proliferation ◽  
Nutrient Sensing ◽  
Open Reading Frames ◽  
Initiation Factor ◽  
Mitochondrial Activity ◽  
Breast Cancers ◽  
Initiation Factors ◽  
Translation Initiation Factors ◽  
Upstream Open Reading Frames ◽  
In Cells

Translation initiation factors have complex functions in cells that are not yet understood. We show that depletion of initiation factor eIF4GI only modestly reduces overall protein synthesis in cells, but phenocopies nutrient starvation or inhibition of protein kinase mTOR, a key nutrient sensor. eIF4GI depletion impairs cell proliferation, bioenergetics, and mitochondrial activity, thereby promoting autophagy. Translation of mRNAs involved in cell growth, proliferation, and bioenergetics were selectively inhibited by reduction of eIF4GI, as was the mRNA encoding Skp2 that inhibits p27, whereas catabolic pathway factors were increased. Depletion or overexpression of other eIF4G family members did not recapitulate these results. The majority of mRNAs that were translationally impaired with eIF4GI depletion were excluded from polyribosomes due to the presence of multiple upstream open reading frames and low mRNA abundance. These results suggest that the high levels of eIF4GI observed in many breast cancers might act to specifically increase proliferation, prevent autophagy, and release tumor cells from control by nutrient sensing.

scholarly journals Translational Control in Plasmodium and Toxoplasma Parasites

2012 ◽  
Vol 12 (2) ◽  
pp. 161-167 ◽  
Author(s):  
Min Zhang ◽  
Bradley R. Joyce ◽  
William J. Sullivan ◽  
Victor Nussenzweig
Keyword(s):  
Translational Control ◽  
Life Cycles ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Control Of Gene Expression ◽  
Α Subunit ◽  
Content Type ◽  
Eukaryotic Translation ◽  
Precise Control ◽  
Eif2α Phosphorylation

ABSTRACT The life cycles of apicomplexan parasites such as Plasmodium spp. and Toxoplasma gondii are complex, consisting of proliferative and latent stages within multiple hosts. Dramatic transformations take place during the cycles, and they demand precise control of gene expression at all levels, including translation. This review focuses on the mechanisms that regulate translational control in Plasmodium and Toxoplasma , with a particular emphasis on the phosphorylation of the α subunit of eukaryotic translation initiation factor 2 (eIF2α). Phosphorylation of eIF2α (eIF2α∼P) is a conserved mechanism that eukaryotic cells use to repress global protein synthesis while enhancing gene-specific translation of a subset of mRNAs. Elevated levels of eIF2α∼P have been observed during latent stages in both Toxoplasma and Plasmodium , indicating that translational control plays a role in maintaining dormancy. Parasite-specific eIF2α kinases and phosphatases are also required for proper developmental transitions and adaptation to cellular stresses encountered during the life cycle. Identification of small-molecule inhibitors of apicomplexan eIF2α kinases may selectively interfere with parasite translational control and lead to the development of new therapies to treat malaria and toxoplasmosis.

Proapoptotic protein PACT is expressed at high levels in colonic epithelial cells in mice

2002 ◽  
Vol 283 (3) ◽  
pp. G801-G808 ◽  
Author(s):  
Vishal Gupta ◽  
Rekha C. Patel
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Epithelial Cell ◽  
Epithelial Cells ◽  
Initiation Factor ◽  
Colonic Epithelial Cells ◽  
Α Subunit ◽  
Proapoptotic Protein ◽  
Mouse Tissues ◽  
In Cells

The protein activator of RNA-activated protein kinase (PKR) is a proapoptotic protein called PACT. PKR is an interferon (IFN)-induced serine-threonine protein kinase that plays a central role in IFN's antiviral and antiproliferative activities. PKR activation in cells leads to phosphorylation of the α-subunit of the eukaryotic protein synthesis initiation factor (eIF)2α, inhibition of protein synthesis, and apoptosis. In the absence of viral infections, PKR is activated by its activator PACT, especially in response to diverse stress signals. Overexpression of PACT in cells causes enhanced sensitivity to stress-induced apoptosis. We examined PACT expression in different mouse tissues and evaluated its possible role in regulating apoptosis. PACT is expressed at high levels in colonic epithelial cells, especially as they exit the cell cycle and enter an apoptotic program. PACT expression also coincides with the presence of active PKR and phosphorylated eIF2α. These results suggest a possible role of PACT-mediated PKR activation in the regulation of epithelial cell apoptosis in mouse colon. In addition, transient overexpression of PACT in a nontransformed intestinal epithelial cell line leads to induction of apoptosis, further supporting PACT's role in inducing apoptosis.

scholarly journals Translational Regulation Promotes Oxidative Stress Resistance in the Human Fungal Pathogen Cryptococcus neoformans

mBio ◽  
2019 ◽  
Vol 10 (6) ◽  
Author(s):  
Jay Leipheimer ◽  
Amanda L. M. Bloom ◽  
Christopher S. Campomizzi ◽  
Yana Salei ◽  
John C. Panepinto
Keyword(s):  
Oxidative Stress ◽  
Cryptococcus Neoformans ◽  
Initiation Factor ◽  
Mammalian Host ◽  
Response Factors ◽  
Critical Determinant ◽  
Α Subunit ◽  
Content Type ◽  
Cellular Stresses ◽  
Translational Suppression

ABSTRACT Cryptococcus neoformans is one of the few environmental fungi that can survive within a mammalian host and cause disease. Although many of the factors responsible for establishing virulence have been recognized, how they are expressed in response to certain host-derived cellular stresses is rarely addressed. Here, we characterize the temporal translational response of C. neoformans to oxidative stress. We find that translation is largely inhibited through the phosphorylation of the critical initiation factor eIF2α (α subunit of eukaryotic initiation factor 2) by a sole kinase. Preventing eIF2α-mediated translational suppression resulted in growth sensitivity to hydrogen peroxide (H2O2). Our work suggests that translational repression in response to H2O2 partly facilitates oxidative stress adaptation by accelerating the decay of abundant non-stress-related transcripts while facilitating the proper expression levels of select oxidative stress response factors. Our results illustrate translational suppression as a critical determinant of select mRNA decay, gene expression, and subsequent survival in response to oxidative stress. IMPORTANCE Fungal survival in a mammalian host requires the coordinated expression and downregulation of a large cohort of genes in response to cellular stresses. Initial infection with C. neoformans occurs in the lungs, where it interacts with host macrophages. Surviving macrophage-derived cellular stresses, such as the production of reactive oxygen and nitrogen species, is believed to promote dissemination into the central nervous system. Therefore, investigating how an oxidative stress-resistant phenotype is brought about in C. neoformans not only furthers our understanding of fungal pathogenesis but also unveils mechanisms of stress-induced gene reprogramming. We discovered that H2O2-derived oxidative stress resulted in severe translational suppression and that this suppression was necessary for the accelerated decay and expression of tested transcripts.

scholarly journals The Herpes Simplex Virus US11 Protein Effectively Compensates for the γ134.5 Gene if Present before Activation of Protein Kinase R by Precluding Its Phosphorylation and That of the α Subunit of Eukaryotic Translation Initiation Factor 2

1998 ◽  
Vol 72 (11) ◽  
pp. 8620-8626 ◽  
Author(s):  
Kevin A. Cassady ◽  
Martin Gross ◽  
Bernard Roizman
Keyword(s):  
Herpes Simplex Virus ◽  
Herpes Simplex ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Protein Kinase R ◽  
Α Subunit ◽  
Eukaryotic Translation ◽  
Initiation Factor 2 ◽  
Simplex Virus ◽  
In Cells

ABSTRACT In herpes simplex virus-infected cells, viral γ134.5 protein blocks the shutoff of protein synthesis by activated protein kinase R (PKR) by directing the protein phosphatase 1α to dephosphorylate the α subunit of eukaryotic translation initiation factor 2 (eIF-2α). The amino acid sequence of the γ134.5 protein which interacts with the phosphatase has high homology to a domain of the eukaryotic protein GADD34. A class of compensatory mutants characterized by a deletion which results in the juxtaposition of the α47 promoter next to US11, a γ2 (late) gene in wild-type virus-infected cells, has been described. In cells infected with these mutants, protein synthesis continues even in the absence of the γ134.5 gene. In these cells, PKR is activated but eIF-2α is not phosphorylated, and the phosphatase is not redirected to dephosphorylate eIF-2α. We report the following: (i) in cells infected with these mutants, US11 protein was made early in infection; (ii) US11 protein bound PKR and was phosphorylated; (iii) in in vitro assays, US11 blocked the phosphorylation of eIF-2α by PKR activated by poly(I-C); and (iv) US11 was more effective if present in the reaction mixture during the activation of PKR than if added after PKR had been activated by poly(I-C). We conclude the following: (i) in cells infected with the compensatory mutants, US11 made early in infection binds to PKR and precludes the phosphorylation of eIF-2α, whereas US11 driven by its natural promoter and expressed late in infection is ineffective; and (ii) activation of PKR by double-stranded RNA is a common impediment countered by most viruses by different mechanisms. The γ134.5 gene is not highly conserved among herpesviruses. A likely scenario is that acquisition by a progenitor of herpes simplex virus of a portion of the cellular GADD34 gene resulted in a more potent and reliable means of curbing the effects of activated PKR. US11 was retained as a γ2 gene because, like many viral proteins, it has multiple functions.

Sign in / Sign up

Export Citation Format

Share Document