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

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 ser59was mutated to alanine (eheif2α-s59a),or a phosphomimetic variant of eif2α in which ser59was 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. © 2016 hendrick et al.