Toxoplasma gondii Mechanisms of Entry Into Host Cells.

Juliana Portes,Márcia Attias,Emile Barrias,Renata Travassos,Wanderley De Souza

doi:10.3389/fcimb.2020.00294

Abstract

Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan parasite. Toxoplasma can invade and multiply inside any nucleated cell of a wide range of homeothermic hosts. The canonical process of internalization involves several steps: an initial recognition of the host cell surface and a sequential secretion of proteins from micronemes followed by rhoptries that assemble a macromolecular complex constituting a specialized and transient moving junction. The parasite is then internalized via an endocytic process with the establishment of a parasitophorous vacuole (PV), that does not fuse with lysosomes, where the parasites survive and multiply. This process of host cell invasion is usually referred to active penetration. Using different cell types and inhibitors of distinct endocytic pathways, we show that treatment of host cells with compounds that interfere with clathrin-mediated endocytosis (hypertonic sucrose medium, chlorpromazine hydrochloride, and pitstop 2 inhibited the internalization of tachyzoites). In addition, treatments that interfere with macropinocytosis, such as incubation with amiloride or IPA-3, increased parasite attachment to the host cell surface but significantly blocked parasite internalization. Immunofluorescence microscopy showed that markers of macropinocytosis, such as the Rab5 effector rabankyrin 5 and Pak1, are associated with parasite-containing cytoplasmic vacuoles. These results indicate that entrance of T. gondii into mammalian cells can take place both by the well-characterized interaction of parasite and host cell endocytic machinery and other processes, such as the clathrin-mediated endocytosis, and macropinocytosis.

Highlights

Intracellular parasitism is a strategy adopted by several eukaryotic microorganisms that developed the ability to penetrate and divide inside cells of vertebrate hosts
Proteins secreted by the neck of the rhoptries, Rhoptry proteins (RONs) 2, RON 4 and RON 5 form a complex on the host cell membrane and RON2 has a domain that serves as a receptor for the parasite. The binding of this receptor to AMA1, a protein secreted by micronemes, anchored to the parasite membrane is the basic mechanism by which T. gondii recognizes any type of cell (Tonkin et al, 2011)
Three classical inhibitors of clathrin-mediated endocytic processes—chlorpromazine, sucrose hypertonic medium, and pitstop 2- were used to analyze the participation of clathrincoated pits in T. gondii entry into host cells

Summary

Introduction

Intracellular parasitism is a strategy adopted by several eukaryotic microorganisms that developed the ability to penetrate and divide inside cells of vertebrate hosts. Some have a narrow choice of specific cell types in which they can penetrate, as is the case for Plasmodium and Leishmania, that infect reticulocytes-erythrocytes and macrophages, respectively (Podinovskaia and Descoteaux, 2015; Kanjee et al, 2018). Other parasites, such as Trypanosoma cruzi and Toxoplasma gondii, can invade almost all cell types (Zhu et al, 2019; Breyner et al, 2020). Toxoplasma gondii Entry Host Cell process that results in a membrane-bound vacuole inside the host cell, the parasitophorous vacuole (PV). Previous studies shown that T. gondii has an active participation in the penetration into the host cell, even interfering with the composition of the PV membrane to prevent its fusion with host cell lysosomes (Morisaki et al, 1995; Coppens et al, 2006; Frénal et al, 2017) Organelles from the apical complex of the parasite, as micronemes and rhoptries, release their contents during the interaction process (Dubremetz et al, 1993; Carruthers and Sibley, 1997; Carruthers et al, 1999)

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Conclusion