Two isotypes of phosphatidylinositol 3‐phosphate‐binding sorting nexins play distinct roles in trogocytosis in Entamoeba histolytica. (1st December 2019) - Watanabe, Natsuki
Abstract: Phosphatidylinositol phosphates (PIPs) function as important second messengers in many cellular events. In the human intestinal protist Entamoeba histolytica, where phagocytosis/trogocytosis plays an indispensable role in proliferation and pathophysiology during infection, various PIPs are involved in multiple steps of phago/trogocytosis. PI3‐phosphate (PI3P) plays a pivotal role in the biogenesis of phagosome/trogosomes via recruitment of PI3P effectors. Because no known PI3P downstream effectors are conserved in E. histolytica, we exploited a unique method to identify the proteins PI3P dependently recruited to phagosomes. We rationalised that overexpression of PI3P‐binding GFP‐HrsFYVE competes for PI3P on phagosomal membranes and results in dissociation of PI3P effectors from phagosomes. EhVps26 and EhVps35, but not sorting nexins (SNXs), of the retromer complex were detected from phagosomes only without GFP‐HrsFYVE overexpression. Two potential SNXs, EhSNX1 and EhSNX2, identified in the genome, possess only phox homology domain and specifically bound to PI3P, but retromer components, EhVps26 and EhVps35, did not bind to PI3P. Live and immunofluorescence imaging showed that EhSNX1 was recruited to the trogocytic cup and tunnel‐like structures, and subsequently, EhSNX2 was recruited to trogosomes. Furthermore, EhSNX1, but not EhSNX2, specifically bound to Arp2/3 and EhVps26, which were localised to the tunnel‐like structures and the trogosomes, respectively. EhSNX2 gene silencing increased trogocytosis, suggesting that EhSNX2 plays an inhibitory role in trogocytosis. Abstract : Phosphatidylinositol (PI) phosphates function as important second messengers in many cellular events. PI3‐phosphate plays a pivotal role in phagosome/trogosome biogenesis, which is essential for pathogenesis of Entamoeba histolytica, causing amebiasis. We report novel PI3‐phosphate‐mediated regulation of phagocytosis/trogocytosis via two isotypes of sorting nexins (SNXs) that function as PI3‐phosphate effectors, which play distinct and tempo‐spatial regulatory roles. SNX1 is involved in the recruitment of the retromer complex to the ingestion site, while SNX2 functions as a negative regulator of phagocytosis/trogocytosis.