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

ABSTRACT: 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-2? (eIF2?). This inhibits eIF2? activity resulting in a general decline in protein synthesis. Genomic data reveal that E. histolytica possesses eIF2? (EheIF2?) 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-EheIF2?. Long-term serum starvation, long-term heat shock, and oxidative stress induced an increase in the level of phospho-EheIF2?, 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 EheIF2?. We generated transgenic cells that overexpress wildtype EheIF2?, a non-phosphorylatable variant of eIF2? in which Ser59 was mutated to alanine (EheIF2?-S59A), or a phosphomimetic variant of eIF2? in which Ser59 was mutated to aspartic acid (EheIF2?-S59D). Consistent with the known functions of eIF2?, cells expressing wildtype or EheIF2?-S59D exhibited increased or decreased translation, respectively. Surprisingly, cells expressing EheIF2?-S59A also exhibited reduced translation. Cells expressing EheIF2?-S59D were more resistant to long-term serum starvation underscoring the significance of EheIF2? phosphorylation in managing stress. Finally, phospho-eIF2? accumulated during encystation in E. invadens, a model encystation system. Together, these data demonstrate that the eIF2?-dependent stress response system is operational in Entamoeba species.

SUBMITTER: Hendrick HM 

PROVIDER: S-EPMC5179133 | biostudies-literature | 2016 Dec

REPOSITORIES: biostudies-literature