Autophagy protein 16-mediated autophagy is required for the encystation of Acanthamoeba castellanii

Autophagy, an evolutionarily conserved protein degradation pathway in eukaryotes, plays essential roles during starvation and cellular differentiation by eliminating unwanted and/or unnecessary cell material including organelles. Autophagy protein 16 (Atg16) is an essential component of the autophagic machinery. The present study identified and characterized an Atg16 homologue (AcAtg16) in Acanthamoeba, an opportunistic pathogen responsible for several distinct diseases in humans. AcAtg16 was highly expressed during encystation and was found to be associated with small or large vesicular structures that partially colocalized with autophagolysosomes. Small interfering RNA against AcAtg16 inhibited autophagosome formation and reduced the encystation efficiency of Acanthamoeba. Moreover, most mitochondria remained undigested in these knockdown cells. Taken together, these results indicate that AcAtg16 is involved in autophagosome formation and plays an essential role in the encystation of Acanthamoeba.