Atg8 is involved in endosomal and phagosomal acidification in the parasitic protist Entamoeba histolytica.
Autophagy is one of two major bulk protein degradation systems and is conserved throughout eukaryotes. The protozoan Entamoeba histolytica, which is a human intestinal parasite, possesses a restricted set of autophagy-related (Atg) proteins compared with other eukaryotes and thus represents a suitable model organism for studying the minimal essential components and ancestral functions of autophagy. E. histolytica possesses two conjugation systems: Atg8 and Atg5/12, although a gene encoding Atg12 is missing in the genome. Atg8 is considered to be the central and authentic marker of autophagosomes, but recent studies have demonstrated that Atg8 is not exclusively involved in autophagy per se, but other fundamental mechanisms of vesicular traffic. To investigate this question in E. histolytica, we studied on Atg8 during the proliferative stage. Atg8 was constitutively expressed in both laboratory-maintained and recently established clinical isolates and appeared to be lipid-modified in logarithmic growth phase, suggesting a role of Atg8 in non-stress and proliferative conditions. These findings are in contrast to those for Entamoeba invadens, in which autophagy is markedly induced during an early phase of differentiation from the trophozoite into the cyst. The repression of Atg8 gene expression in En. histolytica by antisense small RNA-mediated transcriptional gene silencing resulted in growth retardation, delayed endocytosis and reduced acidification of endosomes and phagosomes. Taken together, these results suggest that Atg8 and the Atg8 conjugation pathway have some roles in the biogenesis of endosomes and phagosomes in this primitive eukaryote.
Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan.
Karina
K
Picazarri
Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan.
Kumiko
K
Nakada-Tsukui
Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan.
Kumiko
K
Tsuboi
Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan.|Department of Biomolecular Science, Faculty of Science, Toho University, Chiba, Japan.
Eri
E
Miyamoto
Department of Biomolecular Science, Faculty of Science, Toho University, Chiba, Japan.
Naoko
N
Watanabe
Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan.|Laboratory for Disease Systems Modeling, RIKEN Center for integrative Medical Sciences, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa, Japan.
Eiryo
E
Kawakami
Department of Parasitology, National Institute of Infectious Diseases, Tokyo, Japan.|Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
Tomoyoshi
T
Nozaki
D011992:Endosomes / Q000378:metabolism*; D004748:Entamoeba histolytica / Q000235:genetics / Q000502:physiology*; D020869:Gene Expression Profiling; D001678:Organelle Biogenesis; D010588:Phagosomes / Q000378:metabolism*; D015800:Protozoan Proteins / Q000378:metabolism*
D015800:Protozoan Proteins