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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 ( Eh eIF2α) with a conserved phosphorylatable serine at position 59 (Ser 59 ). 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- Eh eIF2α. Long-term serum starvation, long-term heat shock, and oxidative stress induced an increase in the level of phospho- Eh eIF2α, 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  Eh eIF2α. We generated transgenic cells that overexpress wildtype  Eh eIF2α, a non-phosphorylatable variant of eIF2α in which Ser 59  was mutated to alanine ( Eh eIF2α-S59A), or a phosphomimetic variant of eIF2α in which Ser 59  was mutated to aspartic acid ( Eh eIF2α-S59D). Consistent with the known functions of eIF2α, cells expressing wildtype or  Eh eIF2α-S59D exhibited increased or decreased translation, respectively. Surprisingly, cells expressing  Eh eIF2α-S59A also exhibited reduced translation. Cells expressing  Eh eIF2α-S59D were more resistant to long-term serum starvation underscoring the significance of  Eh eIF2α 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.

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