Ehrlichia secretes Etf-1 to induce autophagy and capture nutrients for its growth through RAB5 and class III phosphatidylinositol 3-kinase

Lin, Mingqun; Liu, Hongyan; Xiong, Qingming; Niu, Hua; Cheng, Zhihui; Yamamoto, Akitsugu; Rikihisa, Yasuko

Eukaryotic proteasomes can cleave only very poorly (if at all) within polyglutamine sequences such as polyglutamine tracts in HTT (huntingtin) protein. 88 Expansions of polyglutamine tracts in HTT causes aggregation of polyglutamine peptides, leading to a neurodegenerative genetic disorder, Huntington disease. 89 NPEPPS/PSA (aminopeptidase, puromycin sensitive; EC 3.4.11.14) is a mammalian cytosolic Zn 2C metallopeptidase that can digest aggregationprone proteins including polyglutamine-containing peptides such as HTT via autophagy, thereby reducing cellular toxicity. 90 NPEPPS overexpression can enhance macroautophagy. 91 In the yeast cytoplasm-to-vacuole targeting pathway, the precursor form of aminopeptidase I is sequestered in phagophores in an Atg5-dependent manner 67 and is targeted to the vacuole (the yeast equivalent of mammalian lysosomes). 92 We found that ectopically expressed NPEPPS-GFP colocalized with Etf-1 puncta (Fig. 8A ) and, at 1 d p.i., encased E. chaffeensis inclusions (Fig. 8B ). PAQ-22 is a synthetic, noncompetitive NPEPPS inhibitor that does not act as a substrate mimic and thus binds to NPEPPS at a site distinct from the catalytic site. 93, 94 Compared with the DMSO-treated control cells, E. chaffeensis infection was significantly decreased in PAQ-22-treated cells at 2 d p.i. based on qPCR (Fig. 8C) . PAQ-22 was not toxic to the host cells at 100 mM (data not shown).