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Infect. Immun. doi:10.1128/IAI.00636-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Autophagy during proliferation and encystation in the protozoan parasite Entamoeba invadens

Department of Parasitology, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-851, Japan

^* To whom correspondence should be addressed. Email: nozaki{at}med.gunma-u.ac.jp.

	Abstract

Autophagy is one of the three systems responsible for degradation of cytosolic proteins and organelles. Autophagy has been implicated in the stress response to starvation, antigen cross presentation, defense against invading bacteria and viruses, differentiation, and development. Yeast Atg8 and its mammalian ortholog LC3 play an essential role in autophagy. The intestinal protozoan parasite Entamoeba histolytica and a related reptilian species E. invadens possess the Atg8 conjugation system, consisting of Atg8, Atg4, Atg3, and Atg7, but lack the Atg5-Atg12 conjugation system. Immunofluorescence imaging revealed that polymorphic Atg8-associated structures emerged in the logarithmic growth phase, and decreased in the stationary phase, as well as in the early phase of encystation in E. invadens. Immunoblot analysis showed that increase of phosphatidylethanolamine-conjugated membrane-associated Atg8 was also accompanied with the emergence of Atg8-associated structures during the proliferation and differentiation above mentioned. Specific inhibitors of class I and III phosphatidylinositol 3 kinases simultaneously inhibited both growth of trophozoites and autophagy, and also both encystation and autophagy in E. invadens. These results suggest that core machinery for autophagy is conserved and plays an important role during proliferation and differentiation in Entamoeba.