IfkA, a presumptive eIF2α kinase of Dictyostelium, is required for proper timing of aggregation and regulation of mound size

Entamoeba histolytica is an enteric pathogen responsible for amoebic dysentery and liver abscess. It alternates between the host-restricted trophozoite form and the infective environmentally-stable cyst stage. Throughout its lifecycle E. histolytica experiences stress, in part, from host immune pressure. Conversion to cysts is presumed to be a stress-response. In other systems, stress induces phosphorylation of a serine residue on eukaryotic translation initiation factor-2α (eIF2α). This inhibits eIF2α activity resulting in a general decline in protein synthesis. Genomic data reveal that E. histolytica possesses eIF2α (EheIF2α) with a conserved phosphorylatable serine at position 59 (Ser59). Thus, this pathogen may have the machinery for stress-induced translational control. To test this, we exposed cells to different stress conditions and measured the level of total and phospho-EheIF2α. Long-term serum starvation, long-term heat shock, and oxidative stress induced an increase in the level of phospho-EheIF2α, while short-term serum starvation, short-term heat shock, or glucose deprivation did not. Long-term serum starvation also caused a decrease in polyribosome abundance, which is in accordance with the observation that this condition induces phosphorylation of EheIF2α. We generated transgenic cells that overexpress wildtype EheIF2α, a non-phosphorylatable variant of eIF2α in which Ser59 was mutated to alanine (EheIF2α-S59A), or a phosphomimetic variant of eIF2α in which Ser59 was mutated to aspartic acid (EheIF2α-S59D). Consistent with the known functions of eIF2α, cells expressing wildtype or EheIF2α-S59D exhibited increased or decreased translation, respectively. Surprisingly, cells expressing EheIF2α-S59A also exhibited reduced translation. Cells expressing EheIF2α-S59D were more resistant to long-term serum starvation underscoring the significance of EheIF2α phosphorylation in managing stress. Finally, phospho-eIF2α accumulated during encystation in E. invadens, a model encystation system. Together, these data demonstrate that the eIF2α-dependent stress response system is operational in Entamoeba species.

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“…[9] Leishmania spp. [45], yeast [11], and Dictyostelium discoideum [12]. The accumulation of phospho- Ei eIF2α during encystation of E .…”

Section: Discussionmentioning

confidence: 99%

“…[9] and the transition of promastigotes to amastigotes in Leishmania [10]. In non-parasitic organisms, such as yeast [11] and Dictyostelium [12], phosphorylation of eIF2α stimulates the formation of latent spores. Genomic data suggest that E .…”

Section: Introductionmentioning

confidence: 99%

Phosphorylation of Eukaryotic Initiation Factor-2α during Stress and Encystation in Entamoeba Species

et al. 2016

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“…In agreement with our proposal, independent studies have revealed that BDNF treatment (Takei et al 2001), fibroblast adhesion (Gorrini et al 2005), and L-LTP-inducing protocol (Costa-Mattioli et al 2005 enhance translation by reducing P-eIF2␣. The regulation of P-eIF2␣ also has physiological roles in various developmental events (Harding et al 2001;Shen et al 2001;Fang et al 2003), which indicates the involvement of signals unrelated to stress in multiple aspects of eIF2␣-mediated biological processes. Suppression of the ray defect in plx-1/smp-1 smp-2 mutants by gcn-1; pek-1 mutation was highly but not fully penetrant (Fig.…”

Section: Discussionmentioning

confidence: 99%

Semaphorin controls epidermal morphogenesis by stimulating mRNA translation via eIF2α in Caenorhabditis elegans

Nukazuka¹,

Fujisawa²,

Inada³

et al. 2008

Genes Dev.

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Conserved semaphorin-plexin signaling systems govern various aspects of animal development, including axonal guidance in vertebrates and epidermal morphogenesis in Caenorhabditis elegans. Here we provide in vivo evidence that stimulation of mRNA translation via eukaryotic initiation factor 2␣ (eIF2␣) is an essential downstream event of semaphorin signaling in C. elegans. In semaphorin/plexin mutants, a marked elevation in the phosphorylation of eIF2␣ is observed, which causes translation repression and is causally related to the morphological epidermal phenotype in the mutants. Conversely, removal of constraints on translation by genetically reducing the eIF2␣ phosphorylation largely bypasses requirement for the semaphorin signal in epidermal morphogenesis. We also identify an actin-depolymerizing factor/cofilin, whose expression in the mutants is predominantly repressed, as a major translational target of semaphorin signaling. Thus, our results reveal a physiological significance for translation of mRNAs for cytoskeletal regulators, linking environmental cues to cytoskeletal rearrangement during cellular morphogenesis in vivo.[Keywords: C. elegans; cofilin; eIF2; epidermal morphogenesis; mRNA translation; semaphorin] Supplemental material is available at http://www.genesdev.org.

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“…For example, when the fungi Candida albicans is subjected to nutrient limitation, the target of GCN2 eIF2 kinase, GCN4, is required to trigger filamentous growth (37). Furthermore, deletion of eIF2 kinases related to GCN2 in the slime mold Dictyostelium results in significant morphological and patterning defects triggered during stressed-induced differentiation from growing amoebae to fruiting bodies (38,39). Together with our results, these studies point to eIF2 kinasemediated translation control as having a key role in development and progression through the life cycle in response to changes in the environment of the organism.…”

Section: Development and Differentiation Involves Eif2␣ Phosphorylation-mentioning

confidence: 99%

Translation Regulation by Eukaryotic Initiation Factor-2 Kinases in the Development of Latent Cysts in Toxoplasma gondii

Narasimhan

Joyce

Naguleswaran³

et al. 2008

Journal of Biological Chemistry

117

203

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A key problem in the treatment of numerous pathogenic eukaryotes centers on their development into latent forms during stress. For example, the opportunistic protist Toxoplasma gondii converts to latent cysts (bradyzoites) responsible for recrudescence of disease. We report that Toxoplasma eukaryotic initiation factor-2␣ (TgIF2␣) is phosphorylated during stress and establish that protozoan parasites utilize translation control to modulate gene expression during development. Importantly, TgIF2␣ remains phosphorylated in bradyzoites, explaining how these cells maintain their quiescent state. Furthermore, we have characterized novel eIF2 kinases; one in the endoplasmic reticulum and a likely regulator of the unfolded protein response (TgIF2K-A) and another that is a probable responder to cytoplasmic stresses (TgIF2K-B). Significantly, our data suggest that 1) the regulation of protein translation through eIF2 kinases is associated with development, 2) eIF2␣ phosphorylation is employed by cells to maintain a latent state, and 3) endoplasmic reticulum and cytoplasmic stress responses evolved in eukaryotic cells before the early diverging Apicomplexa. Given its importance to pathogenesis, eIF2 kinase-mediated stress responses may provide opportunities for novel therapeutics.A well characterized mechanism by which eukaryotic cells respond to environmental stress involves phosphorylation of eukaryotic initiation factor-2 (eIF2) 3 (1-3). The eIF2 combined with GTP delivers Met-tRNA i Met to the translational machinery during initiation of protein synthesis. In mammalian cells, four eIF2 kinases have been described that are each activated by unique stress arrangements. For example, in response to accumulation of malfolded protein in the lumen of the endoplasmic reticulum (so-called ER stress), PEK/Perk (EIF2KA3) phosphorylates the ␣ subunit of eIF2 at serine 51, causing this translation factor to become an inhibitor of its own guanine nucleotide exchange factor, eIF2B. The resulting repression in general translation prevents further synthesis of secretory proteins that would further overload the ER and allows cells sufficient time to trigger the unfolded protein response (UPR) (2). The UPR is a program of mRNA expression involving genes that function in the assembly and transport of secretory proteins (4). In addition to ER stress, three other eIF2 kinases have been described that recognize different forms of cytoplasmic stress in mammalian cells. These include: GCN2 (EIF2KA4), which responds to nutrient deprivation and is well conserved among eukaryotes (3, 5), HRI (EIF2KA1), which is reported to be activated by heme deficiency, oxidative stress induced by arsenite treatment, and heat shock (6, 7), and PKR (EIF2KA2), which is involved in the antiviral defenses (8, 9).Very little research has been performed on eIF2 kinase and related stress response pathways in early-diverging eukaryotes, including pathogenic eukaryotes. However, viability, pathogenesis, and transmission of many parasites hinges on their ability to recogn...

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IfkA, a presumptive eIF2α kinase of Dictyostelium, is required for proper timing of aggregation and regulation of mound size

Cited by 14 publications

References 53 publications

Phosphorylation of Eukaryotic Initiation Factor-2α during Stress and Encystation in Entamoeba Species

Phosphorylation of Eukaryotic Initiation Factor-2α during Stress and Encystation in Entamoeba Species

Semaphorin controls epidermal morphogenesis by stimulating mRNA translation via eIF2α in Caenorhabditis elegans

Translation Regulation by Eukaryotic Initiation Factor-2 Kinases in the Development of Latent Cysts in Toxoplasma gondii

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