Toxoplasma gondii exploits the host ESCRT machinery for parasite uptake of host cytosolic proteins.

Yolanda Rivera-Cuevas,Benjamin S Waldman,Anna-Lisa E Lawrence,Akira Ono,Romir K Patel,Jonathan Z Sexton,Joshua Mayoral,Vern B Carruthers,Louis M Weiss,Sebastian Lourido,Dishari Thornhill,Manlio Di Cristina,Einar B Olafsson

doi:10.1371/journal.ppat.1010138

Abstract

Toxoplasma gondii is a master manipulator capable of effectively siphoning the resources from the host cell for its intracellular subsistence. However, the molecular underpinnings of how the parasite gains resources from its host remain largely unknown. Residing within a non-fusogenic parasitophorous vacuole (PV), the parasite must acquire resources across the limiting membrane of its replicative niche, which is decorated with parasite proteins including those secreted from dense granules. We discovered a role for the host Endosomal Sorting Complex Required for Transport (ESCRT) machinery in host cytosolic protein uptake by T. gondii by disrupting host ESCRT function. We identified the transmembrane dense granule protein TgGRA14, which contains motifs homologous to the late domain motifs of HIV-1 Gag, as a candidate for the recruitment of the host ESCRT machinery to the PV membrane. Using an HIV-1 virus-like particle (VLP) release assay, we found that the motif-containing portion of TgGRA14 is sufficient to substitute for HIV-1 Gag late domain to mediate ESCRT-dependent VLP budding. We also show that TgGRA14 is proximal to and interacts with host ESCRT components and other dense granule proteins during infection. Furthermore, analysis of TgGRA14-deficient parasites revealed a marked reduction in ingestion of a host cytosolic protein compared to WT parasites. Thus, we propose a model in which T. gondii recruits the host ESCRT machinery to the PV where it can interact with TgGRA14 for the internalization of host cytosolic proteins across the PV membrane (PVM). These findings provide new insight into how T. gondii accesses contents of the host cytosol by exploiting a key pathway for vesicular budding and membrane scission.

Highlights

Intracellular pathogens have evolved diverse strategies that rely on the exploitation of host factors to ensure intracellular subsistence, replication, and immune evasion
We report a role for the parasite effector protein TgGRA14 in the recruitment of the host Endosomal Sorting Complex Required for Transport (ESCRT) machinery and in the uptake of host cytosolic proteins
Disrupting the host ESCRT machinery impairs uptake of host cytosolic proteins The ESCRT machinery is composed of five complexes (ESCRT-0 –ESCRT-III and VPS4) that subsequently interact with one another to form vesicles that bud away from the cytosol (Fig 1A)

Summary

Introduction

Intracellular pathogens have evolved diverse strategies that rely on the exploitation of host factors to ensure intracellular subsistence, replication, and immune evasion. The protozoan parasite Toxoplasma gondii is a successful intracellular pathogen that can infect a wide range of nucleated cells while residing in a classical non-fusogenic replicative vacuole that helps protect it from host intrinsic defenses. This replicative vacuole, known as the parasitophorous vacuole (PV), is remodeled by a subset of specialized secretory proteins called dense granules proteins (GRAs) [1]. This compartment segregates the parasite from the nutrient-rich environment of the host cytosol, T. gondii has developed multiple mechanisms for acquiring the resources it needs to sustain infection [2]. The molecular mechanisms by which this material is trafficked across the PV membrane (PVM) and is further endocytosed by the parasite remained poorly understood

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Conclusion