scholarly journals Translation Initiation Control by Heme-Regulated Eukaryotic Initiation Factor 2α Kinase in Erythroid Cells under Cytoplasmic Stresses

2001 ◽  
Vol 21 (23) ◽  
pp. 7971-7980 ◽  
Author(s):  
Linrong Lu ◽  
An-Ping Han ◽  
Jane-Jane Chen
Keyword(s):  
Oxidative Stress ◽  
Heat Shock ◽  
Stress Responses ◽  
Fetal Liver ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Erythroid Cells ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase ◽  
In Erythroid Cells

ABSTRACT Cytoplasmic stresses, including heat shock, osmotic stress, and oxidative stress, cause rapid inhibition of protein synthesis in cells through phosphorylation of eukaryotic initiation factor 2α (eIF2α) by eIF2α kinases. We have investigated the role of heme-regulated inhibitor (HRI), a heme-regulated eIF2α kinase, in stress responses of erythroid cells. We have demonstrated that HRI in reticulocytes and fetal liver nucleated erythroid progenitors is activated by oxidative stress induced by arsenite, heat shock, and osmotic stress but not by endoplasmic reticulum stress or nutrient starvation. While autophosphorylation is essential for the activation of HRI, the phosphorylation status of HRI activated by different stresses is different. The contributions of HRI in various stress responses were assessed with the aid of HRI-null reticulocytes and fetal liver erythroid cells. HRI is the only eIF2α kinase activated by arsenite in erythroid cells, since HRI-null cells do not induce eIF2α phosphorylation upon arsenite treatment. HRI is also the major eIF2α kinase responsible for the increased eIF2α phosphorylation upon heat shock in erythroid cells. Activation of HRI by these stresses is independent of heme and requires the presence of intact cells. Both hsp90 and hsc70 are necessary for all stress-induced HRI activation. However, reactive oxygen species are involved only in HRI activation by arsenite. Our results provide evidence for a novel function of HRI in stress responses other than heme deficiency.

scholarly journals Heme-regulated eIF2α kinase in erythropoiesis and hemoglobinopathies

Blood ◽  
2019 ◽  
Vol 134 (20) ◽  
pp. 1697-1707 ◽  
Author(s):  
Jane-Jane Chen ◽  
Shuping Zhang
Keyword(s):  
Protein Synthesis ◽  
Stress Response ◽  
Initiation Factor ◽  
Integrated Stress Response ◽  
Iron Availability ◽  
Eukaryotic Initiation Factor ◽  
Erythroid Cells ◽  
Eif2α Kinase ◽  
In Erythroid Cells

Chen and Zhang review the role of eukaryotic initiation factor 2α (eIF2α) in regulating the balance between protein synthesis and iron availability as part of the integrated stress response in erythroid cells.

scholarly journals Role of Mitogen-Activated Protein Kinase Sty1 in Regulation of Eukaryotic Initiation Factor 2α Kinases in Response to Environmental Stress in Schizosaccharomyces pombe

2009 ◽  
Vol 9 (1) ◽  
pp. 194-207 ◽  
Author(s):  
Juan José Berlanga ◽  
Damariz Rivero ◽  
Ruth Martín ◽  
Saturnino Herrero ◽  
Sergio Moreno ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Heat Shock ◽  
Protein Kinase ◽  
Schizosaccharomyces Pombe ◽  
Mitogen Activated Protein Kinase ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Transcriptional Responses ◽  
Mitogen Activated Protein ◽  
Eif2α Kinase

ABSTRACT The mitogen-activated protein kinase (MAPK) Sty1 is essential for the regulation of transcriptional responses that promote cell survival in response to different types of environmental stimuli in Schizosaccharomyces pombe. In fission yeast, three distinct eukaryotic initiation factor 2α (eIF2α) kinases, two mammalian HRI-related protein kinases (Hri1 and Hri2) and the Gcn2 ortholog, regulate protein synthesis in response to cellular stress conditions. In this study, we demonstrate that both Hri1 and Hri2 exhibited an autokinase activity, specifically phosphorylated eIF2α, and functionally replaced the endogenous Saccharomyces cerevisiae Gcn2. We further show that Gcn2, but not Hri1 or Hri2, is activated early after exposure to hydrogen peroxide and methyl methanesulfonate (MMS). Cells lacking Gcn2 exhibit a later activation of Hri2. The activated MAPK Sty1 negatively regulates Gcn2 and Hri2 activities under oxidative stress but not in response to MMS. In contrast, Hri2 is the primary activated eIF2α kinase in response to heat shock. In this case, the activation of Sty1 appears to be transitory and does not contribute to the modulation of the eIF2α kinase stress pathway. In strains lacking Hri2, a type 2A protein phosphatase is activated soon after heat shock to reduce eIF2α phosphorylation. Finally, the MAPK Sty1, but not the eIF2α kinases, is essential for survival upon oxidative stress or heat shock, but not upon MMS treatment. These findings point to a regulatory coordination between the Sty1 MAPK and eIF2α kinase pathways for a particular range of stress responses.

scholarly journals Inactivation of eukaryotic initiation factor 2B in vitro by heat shock

1998 ◽  
Vol 334 (2) ◽  
pp. 463-467 ◽  
Author(s):  
Gert C. SCHEPER ◽  
Adri A. M. THOMAS ◽  
van Roel WIJK
Keyword(s):  
Heat Shock ◽  
Thermal Inactivation ◽  
Ribosomal Subunit ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Nucleotide Exchange ◽  
Mild Heat ◽  
Eif2α Phosphorylation ◽  
Cell Extracts

Protein synthesis in rat H35 Reuber hepatoma cells is rapidly inhibited on heat shock. At mild heat-shock temperatures the main cause for inhibition is the inactivation of the guanine nucleotide exchange factor eukaryotic initiation factor 2B (eIF2B); under more severe heat-shock conditions the activity of several initiation factors is compromised. eIF2B is required for GDP/GTP exchange on eIF2, which delivers methionyl-tRNA to the 40 S ribosomal subunit. We have tried to elucidate the mechanism underlying the inactivation of eIF2B by assays in vitro. Incubation of cell extracts at 41 °C or higher led to the inactivation of eIF2B. In agreement with observations in cells exposed to mild heat shocks, the thermal inactivation of eIF2B could be ascribed to neither eIF2α phosphorylation nor the induction of another inhibitor. With the use of glycerol gradients we show that eIF2B forms aggregates in heat-treated extracts. Furthermore eIF2B activity is protected against heat shock in thermotolerant cells. Taken together, these results suggest a role for chaperones in the control of eIF2B activity.

scholarly journals Heme-regulated eIF2α kinase activated Atf4 signaling pathway in oxidative stress and erythropoiesis

Blood ◽  
2012 ◽  
Vol 119 (22) ◽  
pp. 5276-5284 ◽  
Author(s):  
Rajasekhar N. V. S. Suragani ◽  
Roshini S. Zachariah ◽  
Jason G. Velazquez ◽  
Sijin Liu ◽  
Chiao-Wang Sun ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Iron Deficiency ◽  
Signaling Pathway ◽  
Ex Vivo ◽  
Fetal Liver ◽  
Erythroid Differentiation ◽  
Erythroid Progenitors ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase

Heme-regulated eIF2α kinase (Hri) is necessary for balanced synthesis of heme and globin. In addition, Hri deficiency exacerbates the phenotypic severity of β-thalassemia intermedia in mice. Activation of Hri during heme deficiency and in β-thalassemia increases eIF2α phosphorylation and inhibits globin translation. Under endoplasmic reticulum stress and nutrient starvation, eIF2α phosphorylation also induces the Atf4 signaling pathway to mitigate stress. Although the function of Hri in regulating globin translation is well established, its role in Atf4 signaling in erythroid precursors is not known. Here, we report the role of the Hri-activated Atf4 signaling pathway in reducing oxidative stress and in promoting erythroid differentiation during erythropoiesis. On acute oxidative stress, Hri−/− erythroblasts suffered from increased levels of reactive oxygen species (ROS) and apoptosis. During chronic iron deficiency in vivo, Hri is necessary both to reduce oxidative stress and to promote erythroid differentiation. Hri−/− mice developed ineffective erythropoiesis during iron deficiency with inhibition of differentiation at the basophilic erythroblast stage. This inhibition is recapitulated during ex vivo differentiation of Hri−/− fetal liver erythroid progenitors. Importantly, the Hri-eIF2αP-Atf4 pathway was activated and required for erythroid differentiation. We further demonstrate the potential of modulating Hri-eIF2αP-Atf4 signaling with chemical compounds as pharmaceutical therapies for β-thalassemia.

scholarly journals The Plasmodium eukaryotic initiation factor-2α kinase IK2 controls the latency of sporozoites in the mosquito salivary glands

2010 ◽  
Vol 207 (7) ◽  
pp. 1465-1474 ◽  
Author(s):  
Min Zhang ◽  
Clare Fennell ◽  
Lisa Ranford-Cartwright ◽  
Ramanavelan Sakthivel ◽  
Pascale Gueirard ◽  
...  
Keyword(s):  
Salivary Gland ◽  
Life Cycle ◽  
Salivary Glands ◽  
Stress Responses ◽  
Initiation Factor ◽  
Eukaryotic Cells ◽  
Mammalian Host ◽  
Eukaryotic Initiation Factor ◽  
Active Process ◽  
Eif2α Kinase

Sporozoites, the invasive form of malaria parasites transmitted by mosquitoes, are quiescent while in the insect salivary glands. Sporozoites only differentiate inside of the hepatocytes of the mammalian host. We show that sporozoite latency is an active process controlled by a eukaryotic initiation factor-2α (eIF2α) kinase (IK2) and a phosphatase. IK2 activity is dominant in salivary gland sporozoites, leading to an inhibition of translation and accumulation of stalled mRNAs into granules. When sporozoites are injected into the mammalian host, an eIF2α phosphatase removes the PO4 from eIF2α-P, and the repression of translation is alleviated to permit their transformation into liver stages. In IK2 knockout sporozoites, eIF2α is not phosphorylated and the parasites transform prematurely into liver stages and lose their infectivity. Thus, to complete their life cycle, Plasmodium sporozoites exploit the mechanism that regulates stress responses in eukaryotic cells.

scholarly journals Circadian clock control of eIF2α phosphorylation is necessary for rhythmic translation initiation

2020 ◽  
Vol 117 (20) ◽  
pp. 10935-10945 ◽  
Author(s):  
Shanta Karki ◽  
Kathrina Castillo ◽  
Zhaolan Ding ◽  
Olivia Kerr ◽  
Teresa M. Lamb ◽  
...  
Keyword(s):  
Circadian Clock ◽  
Translation Initiation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Nutrient Metabolism ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase ◽  
The Impact

The circadian clock in eukaryotes controls transcriptional and posttranscriptional events, including regulation of the levels and phosphorylation state of translation factors. However, the mechanisms underlying clock control of translation initiation, and the impact of this potential regulation on rhythmic protein synthesis, were not known. We show that inhibitory phosphorylation of eIF2α (P-eIF2α), a conserved translation initiation factor, is clock controlled in Neurospora crassa, peaking during the subjective day. Cycling P-eIF2α levels required rhythmic activation of the eIF2α kinase CPC-3 (the homolog of yeast and mammalian GCN2), and rhythmic activation of CPC-3 was abolished under conditions in which the levels of charged tRNAs were altered. Clock-controlled accumulation of P-eIF2α led to reduced translation during the day in vitro and was necessary for the rhythmic synthesis of select proteins in vivo. Finally, loss of rhythmic P-eIF2α levels led to reduced linear growth rates, supporting the idea that partitioning translation to specific times of day provides a growth advantage to the organism. Together, these results reveal a fundamental mechanism by which the clock regulates rhythmic protein production, and provide key insights into how rhythmic translation, cellular energy, stress, and nutrient metabolism are linked through the levels of charged versus uncharged tRNAs.

scholarly journals Developmental Expression of Mouse Erythrocyte Protein 4.2 mRNA: Evidence for Specific Expression in Erythroid Cells

Blood ◽  
1998 ◽  
Vol 91 (2) ◽  
pp. 695-705 ◽  
Author(s):  
Lingyun Zhu ◽  
Samir B. Kahwash ◽  
Long-Sheng Chang
Keyword(s):  
Mrna Expression ◽  
Fetal Liver ◽  
Late Gestation ◽  
Developmental Expression ◽  
Erythroid Cells ◽  
Mouse Development ◽  
Specific Expression ◽  
Protein 4.2 ◽  
Specific Regulation ◽  
In Erythroid Cells

Abstract Erythrocyte protein 4.2 (P4.2) is an important component of the erythrocyte membrane skeletal network with an undefined biologic function. Presently, very little is known about the expression of the P4.2 gene during mouse embryonic development and in adult animals. By using the Northern blot and in situ hybridization techniques, we have examined the spatial and temporal expression of the P4.2 gene during mouse development. We show that expression of the mouse P4.2 gene is temporally regulated during embryogenesis and that the P4.2 mRNA expression pattern coincides with the timing of erythropoietic activity in hematopoietic organs. P4.2 transcripts are first detected in embryos on day 7.5 of gestation and are localized exclusively in primitive erythroid cells of yolk sac origin. These erythroid cells remain to be the only source for P4.2 expression until the switch of the hematopoietic producing site to fetal liver. In mid- and late-gestation periods, P4.2 mRNA expression is restricted to the erythroid cells in fetal liver and to circulating erythrocytes. Around and after birth, the site for P4.2 expression is switched from liver to spleen and bone marrow, and P4.2 transcripts are only detected in cells of the erythroid lineage. These results provide the evidence for specific P4.2 expression in erythroid cells. In addition, the timing and pattern of expression of the P4.2 gene suggest the specific regulation of the P4.2 gene.

scholarly journals GCN2 phosphorylation of eIF2α activates NF-κB in response to UV irradiation

2005 ◽  
Vol 385 (2) ◽  
pp. 371-380 ◽  
Author(s):  
Hao-Yuan JIANG ◽  
Ronald C. WEK
Keyword(s):  
Uv Irradiation ◽  
Mammalian Cells ◽  
Transcriptional Control ◽  
Control Cell ◽  
Nuclear Factor Κb ◽  
Initiation Factor ◽  
Α Subunit ◽  
Eif2α Phosphorylation ◽  
Eif2α Kinase ◽  
Secondary Function

In response to UV irradiation, mammalian cells elicit a gene expression programme designed to repair damage and control cell proliferation and apoptosis. Important members of this stress response include the NF-κB (nuclear factor-κB) family. However, the mechanisms by which UV irradiation activates NF-κB are not well understood. In eukaryotes, a variety of environmental stresses are recognized and remediated by a family of protein kinases that phosphorylate the α subunit of eIF2 (eukaryotic initiation factor-2). In the present study we show that NF-κB in MEF (murine embryo fibroblast) cells is activated by UV-C and UV-B irradiation through a mechanism requiring eIF2α phosphorylation. The primary eIF2α kinase in response to UV is GCN2 (general control non-derepressible-2), with PEK/PERK (pancreatic eIF2α kinase/RNA-dependent-protein-kinase-like endoplasmic-reticulum kinase) carrying out a secondary function. Our studies indicate that lowered protein synthesis accompanying eIF2α phosphorylation, combined with eIF2α kinase-independent turnover of IκBα (inhibitor of κBα), reduces the levels of IκBα in response to UV irradiation. Release of NF-κB from the inhibitory IκBα would facilitate NF-κB entry into the nucleus and targeted transcriptional control. We also find that loss of GCN2 in MEF cells significantly enhances apoptosis in response to UV exposure similar to that measured in cells deleted for the RelA/p65 subunit of NF-κB. These results demonstrate that GCN2 is central to recognition of UV stress, and that eIF2α phosphorylation provides resistance to apoptosis in response to this environmental insult.

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