Role of autophagy in stress and drug-responsive cell death in Entamoeba histolytica and its cross-talk with apoptosis-inducing factor.

Cell death in unicellular protozoan parasite Entamoeba histolytica is not yet reported though it displays several features of autophagic cell death. Autophagic cell death was reported to take place in ancient protozoans under several stresses. Here we report the occurrence of autophagic cell death in the Entamoeba histolytica trophozoites under oxidative stress as well as by the treatment with metronidazole, the most-widely-used drug for amoebiasis treatment and was shown to generate oxidative stress in the trophozoites. The autophagic flux increases during nutrient deprivation and metronidazole treatment and decreases upon oxidative stress. During oxidative stress the autophagy leads to nucleophagy that is ultimately destined to be digested within the lysosomal chamber. The formation of nucleophagosome depends on the apoptosis-inducing factor (AIF) that translocates to the nucleus from cytoplasm upon oxidative stress. It was experimentally proved that ATG8 (Autophagy-related protein 8) binds with the AIF in the nucleus of the trophozoites and helps in ATG8 recruitment and autophagy initiation overall suggesting that oxidative stress-driven AIF translocation to nucleus results in binding with ATG8 and initiates nucleophagy leading to cell death.

Apoptosis-inducing factor-like protein-mediated stress and metronidazole-responsive programmed cell death pathway in Entamoeba histolytica.

Apoptosis-inducing factor (AIF) is the major component of the caspase-independent cell death pathway that is considered to be evolutionarily ancient. Apoptosis is generally evolved with multicellularity as a prerequisite for the elimination of aged, stressed, or infected cells promoting the survival of the organism. Our study reports the presence of a putative AIF-like protein in Entamoeba histolytica, a caspase-deficient primitive protozoan, strengthening the concept of occurrence of apoptosis in unicellular organisms as well. The putative cytoplasmic EhAIF migrates to the nucleus on receiving stresses that precede its binding with DNA, following chromatin degradation and chromatin condensation as evident from both in vitro and in vivo experiments. Down-regulating the EhAIF expression attenuates the apoptotic features of insulted cells and increases the survival potency in terms of cell viability and vitality of the trophozoites, whereas over-expression of the EhAIF effectively enhances the phenomena. Interestingly, metronidazole, the most widely used drug for amoebiasis treatment, is also potent to elicit similar AIF-mediated cell death responses like other stresses indicating the AIF-mediated cell death could be the probable mechanism of trophozoite-death by metronidazole treatment. The occurrence of apoptosis in a unicellular organism is an interesting phenomenon that might signify the altruistic death that overall improves the population health.