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 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 eIF2B as a Target for Viral Evasion of PKR-Mediated Translation Inhibition

mBio ◽  
2020 ◽  
Vol 11 (4) ◽  
Author(s):  
Jennifer Deborah Wuerth ◽  
Matthias Habjan ◽  
Markus Kainulainen ◽  
Besim Berisha ◽  
Damien Bertheloot ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Protein Kinase ◽  
Nonstructural Protein ◽  
Mrna Translation ◽  
Translation Initiation Factor ◽  
Initiation Factor ◽  
Mammalian Host ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Immune Factor

ABSTRACT RNA-activated protein kinase (PKR) is a major innate immune factor that senses viral double-stranded RNA (dsRNA) and phosphorylates eukaryotic initiation factor (eIF) 2α. Phosphorylation of the α subunit converts the eIF2αβγ complex into a stoichiometric inhibitor of eukaryotic initiation factor eIF2B, thus halting mRNA translation. To escape this protein synthesis shutoff, viruses have evolved countermechanisms such as dsRNA sequestration, eIF-independent translation by an internal ribosome binding site, degradation of PKR, or dephosphorylation of PKR or of phospho-eIF2α. Here, we report that sandfly fever Sicilian phlebovirus (SFSV) confers such a resistance without interfering with PKR activation or eIF2α phosphorylation. Rather, SFSV expresses a nonstructural protein termed NSs that strongly binds to eIF2B. Although NSs still allows phospho-eIF2α binding to eIF2B, protein synthesis and virus replication are unhindered. Hence, SFSV encodes a unique PKR antagonist that acts by rendering eIF2B resistant to the inhibitory action of bound phospho-eIF2α. IMPORTANCE RNA-activated protein kinase (PKR) is one of the most powerful antiviral defense factors of the mammalian host. PKR acts by phosphorylating mRNA translation initiation factor eIF2α, thereby converting it from a cofactor to an inhibitor of mRNA translation that strongly binds to initiation factor eIF2B. To sustain synthesis of their proteins, viruses are known to counteract this on the level of PKR or eIF2α or by circumventing initiation factor-dependent translation altogether. Here, we report a different PKR escape strategy executed by sandfly fever Sicilian virus (SFSV), a member of the increasingly important group of phleboviruses. We found that the nonstructural protein NSs of SFSV binds to eIF2B and protects it from inactivation by PKR-generated phospho-eIF2α. Protein synthesis is hence maintained and the virus can replicate despite ongoing full-fledged PKR signaling in the infected cells. Thus, SFSV has evolved a unique strategy to escape the powerful antiviral PKR.

scholarly journals Phosphorylation of Eukaryotic Initiation Factor 2 by Heme-Regulated Inhibitor Kinase-Related Protein Kinases in Schizosaccharomyces pombe Is Important for Resistance to Environmental Stresses

2002 ◽  
Vol 22 (20) ◽  
pp. 7134-7146 ◽  
Author(s):  
Ke Zhan ◽  
Krishna M. Vattem ◽  
Bettina N. Bauer ◽  
Thomas E. Dever ◽  
Jane-Jane Chen ◽  
...  
Keyword(s):  
Protein Synthesis ◽  
Schizosaccharomyces Pombe ◽  
Environmental Stresses ◽  
Initiation Factor ◽  
Eukaryotic Initiation Factor ◽  
Α Subunit ◽  
Eukaryotic Initiation Factor 2 ◽  
Initiation Factor 2 ◽  
Eif2α Kinase

ABSTRACT Protein synthesis is regulated by the phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) in response to different environmental stresses. One member of the eIF2α kinase family, heme-regulated inhibitor kinase (HRI), is activated under heme-deficient conditions and blocks protein synthesis, principally globin, in mammalian erythroid cells. We identified two HRI-related kinases from Schizosaccharomyces pombe which have full-length homology with mammalian HRI. The two HRI-related kinases, named Hri1p and Hri2p, exhibit autokinase and kinase activity specific for Ser-51 of eIF2α, and both activities were inhibited in vitro by hemin, as previously described for mammalian HRI. Overexpression of Hri1p, Hri2p, or the human eIF2α kinase, double-stranded-RNA-dependent protein kinase (PKR), impeded growth of S. pombe due to elevated phosphorylation of eIF2α. Cells from strains with deletions of the hri1+ and hri2+ genes, individually or in combination, exhibited a reduced growth rate when exposed to heat shock or to arsenic compounds. Measurements of in vivo phosphorylation of eIF2α suggest that Hri1p and Hri2p differentially phosphorylate eIF2α in response to these stress conditions. These results demonstrate that HRI-related enzymes are not unique to vertebrates and suggest that these eIF2α kinases are important participants in diverse stress response pathways in some lower eukaryotes.

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 Antibodies against MAEBL Ligand Domains M1 and M2 Inhibit Sporozoite Development In Vitro

2004 ◽  
Vol 72 (6) ◽  
pp. 3604-3608 ◽  
Author(s):  
Peter Preiser ◽  
Laurent Rénia ◽  
Naresh Singh ◽  
Bharath Balu ◽  
William Jarra ◽  
...  
Keyword(s):  
Salivary Gland ◽  
Salivary Glands ◽  
Vaccine Development ◽  
Molecular Form ◽  
Mammalian Host ◽  
Phenotypic Differences ◽  
Apical Membrane Antigen 1 ◽  
Erythrocyte Binding ◽  
Development In Vitro

ABSTRACT MAEBL is a type 1 membrane protein that is implicated in the merozoite invasion of erythrocytes and sporozoite invasion of mosquito salivary glands. This apical organelle protein is structurally similar to the ebl erythrocyte binding proteins, such as EBA-175, except that the tandem ligand domains of MAEBL are similar to part of the extracellular domain of apical membrane antigen 1 and not the Duffy binding-like domain. Although midgut and salivary gland sporozoites are morphologically similar, salivary gland sporozoites undergo a period of new gene expression after infecting the salivary glands, display distinct phenotypic differences, and are more infectious for the mammalian host. The objectives of this project were to determine the molecular form of MAEBL in the infectious salivary gland sporozoites and whether the ligand has a role in the sporozoite development to exoerythrocytic stages in hepatocytes. We determined that MAEBL is newly expressed in salivary gland sporozoites and in a form distinct from what is present in the midgut sporozoites or present in erythrocytic stages. Both ligand domains (M1 and M2) were expressed as part of a full-length membrane form of MAEBL in the salivary gland sporozoites in contrast to the other stages that retain only the M2 ligand domain as part of the membrane form of the protein. Antisera developed against the cysteine-rich regions of the extracellular portion of MAEBL inhibited sporozoite development to exoerythrocytic forms in vitro. Together these data indicate that MAEBL has a role in this third developmental stage in the life cycle of the malaria parasite. Thus, MAEBL is another target for pre-erythrocytic-stage vaccine development against malaria parasites.

scholarly journals Specific Expression of Anaplasma marginale Major Surface Protein 2 Salivary Gland Variants Occurs in the Midgut and Is an Early Event during Tick Transmission

2002 ◽  
Vol 70 (1) ◽  
pp. 114-120 ◽  
Author(s):  
Christiane V. Löhr ◽  
Fred R. Rurangirwa ◽  
Terry F. McElwain ◽  
David Stiller ◽  
Guy H. Palmer
Keyword(s):  
Salivary Gland ◽  
Salivary Glands ◽  
Surface Protein ◽  
Anaplasma Marginale ◽  
Mammalian Host ◽  
Early Event ◽  
Variant Selection ◽  
Specific Expression ◽  
Major Surface Protein ◽  
Major Surface

ABSTRACT Infectivity of Anaplasma spp. develops when infected ticks feed on a mammalian host (transmission feed). Specific Anaplasma marginale major surface protein 2 (MSP2) variants are selected for within the tick and are expressed within the salivary glands. The aims of this study were to determine when and where MSP2 variant selection occurs in the tick, how MSP2 expression is regulated in salivary glands of transmission-feeding ticks, and whether the number of A. marginale organisms per salivary gland is significantly increased during transmission feeding. The South Idaho strain of A. marginale was used, as MSP2 expression is restricted to two variants, SGV1 and SGV2, in Dermacentor andersoni. Using Western blot, real-time PCR, and DNA sequencing analyses it was shown that restriction and expression of MSP2 occurs early in the midgut within the first 48 h of the blood meal, when ticks acquire infection. A. marginale is present in the tick salivary glands before transmission feeding is initiated, but the msp2 mRNA and MSP2 protein levels per A. marginale organism increase only minimally and transiently in salivary glands of transmission-feeding ticks compared to that of unfed ticks. A. marginale numbers per tick increase gradually in salivary glands of both transmission-fed and unfed ticks. It is concluded that MSP2 variant selection is an early event in the tick and that MSP2 variants SGV1 and SGV2 are expressed both in the midgut and salivary glands. While MSP2 may be required for infectivity, there is no strict temporal correlation between MSP2 expression and the development of infectivity.

Differential development and emission ofTheileria parvasporozoites from the salivary gland ofRhipicephalus appendiculatus

Parasitology ◽  
1995 ◽  
Vol 111 (2) ◽  
pp. 153-160 ◽  
Author(s):  
M. K. Shaw ◽  
A. S. Young
Keyword(s):  
Salivary Gland ◽  
Salivary Glands ◽  
Rapid Development ◽  
Secretory Activity ◽  
Rhipicephalus Appendiculatus ◽  
Parasite Development ◽  
Mammalian Host ◽  
Free Access ◽  
Collecting Ducts ◽  
The Individual

SUMMARYThe initiation of feeding of infectedRhipicephalus appendiculatusadults induces the rapid development ofTheileria parvasporoblasts within the salivary gland acini leading to the production of numerous sporozoites which are inoculated into the mammalian host initiating infection. In this study the pattern of development, host cell specificity and emission ofT. parvasporozoites within the salivary glands of heavily infected, 4-day fed adultR. appendiculatusticks was examined. Infected acini were randomly distributed throughout the salivary gland. Sporozoite development within each gland was not synchronized and wide variation in the rate of parasite development, which correlated with the secretory activity of the individual acinus, was observed in all glands examined. Previous studies had shown thatT. parvadeveloped primarily in Type III ‘e’ cells. However, in heavily infected salivary glands sporogony and the emission of mature sporozoites also occurred in ‘c’ cells of Type II acini. Sporozoite emission from infected cells occurred by a process similar to apocrine secretion. The loss of the apical membrane of the infected cell allowed sporozoites free access to the lumen of the acinus and into the collecting ducts of the salivary gland. Sporozoite discharge was gradual since few parasites were found in the acinus valve or in the collecting ducts. Furthermore, the small size of the acinar valve aperature ensures that only small numbers of sporozoites can be released at any one time from an infected acinus.

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 Inhibitor of Cysteine Proteases Is Critical for Motility and Infectivity of Plasmodium Sporozoites

mBio ◽  
2013 ◽  
Vol 4 (6) ◽  
Author(s):  
Katja E. Boysen ◽  
Kai Matuschewski
Keyword(s):  
Life Cycle ◽  
Salivary Glands ◽  
Cysteine Proteases ◽  
Gliding Motility ◽  
Parasitic Infections ◽  
Mammalian Host ◽  
Insect Vector ◽  
Mosquito Vector ◽  
Infected Female ◽  
Wide Range

ABSTRACT Malaria is transmitted when motile sporozoites are injected into the dermis by an infected female Anopheles mosquito. Inside the mosquito vector, sporozoites egress from midgut-associated oocysts and eventually penetrate the acinar cells of salivary glands. Parasite-encoded factors with exclusive vital roles in the insect vector can be studied by classical reverse genetics. Here, we characterized the in vivo roles of Plasmodium berghei falstatin/ICP (inhibitor of cysteine proteases). This protein was previously suggested to act as a protease inhibitor during erythrocyte invasion. We show by targeted gene disruption that loss of ICP function does not affect growth inside the mammalian host but causes a complete defect in sporozoite transmission. Sporogony occurred normally in icp(−) parasites, but hemocoel sporozoites showed a defect in continuous gliding motility and infectivity for salivary glands, which are prerequisites for sporozoite transmission to the mammalian host. Absence of ICP correlates with enhanced cleavage of circumsporozoite protein, in agreement with a role as a protease regulator. We conclude that ICP is essential for only the final stages of sporozoite maturation inside the mosquito vector. This study is the first genetic evidence that an ICP is necessary for the productive motility of a eukaryotic parasitic cell. IMPORTANCE Cysteine proteases and their inhibitors are considered ideal drug targets for the treatment of a wide range of diseases, including cancer and parasitic infections. In protozoan parasites, including Leishmania, Trypanosoma, and Plasmodium, cysteine proteases play important roles in life cycle progression. A mouse malaria model provides an unprecedented opportunity to study the roles of a parasite-encoded inhibitor of cysteine proteases (ICP) over the entire parasite life cycle. By precise gene deletion, we found no evidence that ICP influences disease progression or parasite virulence. Instead, we discovered that this factor is necessary for parasite movement and malaria transmission from mosquitoes to mammals. This finding in a fast-moving unicellular protozoan has important implications for malaria intervention strategies and the roles of ICPs in the regulation of eukaryotic cell migration.

scholarly journals Association of Pathogen Strain-Specific Gene Transcription and Transmission Efficiency Phenotype of Anaplasma marginale

2010 ◽  
Vol 78 (6) ◽  
pp. 2446-2453 ◽  
Author(s):  
Joseph T. Agnes ◽  
David Herndon ◽  
Massaro W. Ueti ◽  
Solomon S. Ramabu ◽  
Marc Evans ◽  
...  
Keyword(s):  
Salivary Gland ◽  
Life Cycle ◽  
High Titer ◽  
Anaplasma Marginale ◽  
Transmission Efficiency ◽  
Mammalian Host ◽  
Specific Gene ◽  
Arthropod Vector ◽  
Expression Levels ◽  
Efficient Transmission

ABSTRACT Efficient transmission of pathogens by an arthropod vector is influenced by the ability of the pathogen to replicate and develop infectiousness within the arthropod host. While the basic life cycle of development within and transmission from the arthropod vector are known for many bacterial and protozoan pathogens, the determinants of transmission efficiency are largely unknown and represent a significant gap in our knowledge. The St. Maries strain of Anaplasma marginale is a high-transmission-efficiency strain that replicates to a high titer in the tick salivary gland and can be transmitted by <10 ticks. In contrast, A. marginale subsp. centrale (Israel vaccine strain) has an identical life cycle but replicates to a significantly lower level in the salivary gland, with transmission requiring >30-fold more ticks. We hypothesized that strain-specific genes expressed in the tick salivary gland at the time of transmission are linked to the differences in the transmission efficiency phenotype. Using both annotation-dependent and -independent analyses of the complete genome sequences, we identified 58 strain-specific genes. These genes most likely represent divergence from common ancestral genes in one or both strains based on analysis of synteny and lack of statistical support for acquisition as islands by lateral gene transfer. Twenty of the St. Maries strain-specific genes and 16 of the strain-specific genes in the Israel strain were transcribed in the tick salivary gland at the time of transmission. Although associated with the transmission phenotype, the expression levels of strain-specific genes were equal to or less than the expression levels in infected erythrocytes in the mammalian host, suggesting that function is not limited to salivary gland colonization.

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