Intersection of endocytic and exocytic systems in Toxoplasma gondii

Abstract

Host cytosolic proteins are endocytosed by Toxoplasma gondii and degraded in its lysosome-like compartment, the vacuolar compartment (VAC), but the dynamics and route of endocytic trafficking remain undefined. Conserved endocytic components and plant-like features suggest T. gondii endocytic trafficking involves transit through early and late endosome-like compartments (ELCs) and potentially the trans-Golgi network (TGN) as in plants. However, exocytic trafficking to regulated secretory organelles, micronemes and rhoptries, also proceeds through ELCs and requires classical endocytic components, including a dynamin-related protein, DrpB. Here, we show that host cytosolic proteins are endocytosed within 7 minutes post-invasion, trafficked through ELCs en route to the VAC, and degraded within 30 minutes. We could not definitively interpret if ingested protein is trafficked through the TGN. We also found that parasites ingest material from the host cytosol throughout the parasite cell cycle. Ingested host proteins colocalize with immature microneme proteins, proM2AP and proMIC5, in transit to the micronemes, but not with the immature rhoptry protein proRON4, indicating that endocytic trafficking of ingested protein intersects with exocytic trafficking of microneme proteins. Finally, we show that conditional expression of a DrpB dominant negative mutant increases T. gondii ingestion of host-derived proteins, suggesting that DrpB is not required for parasite endocytosis.

Differential protein phosphorylation affects the localisation of two secretedToxoplasmaproteins and is widespread during stage conversion

“…Cells were fixed in 3% 557 FA, quenched in 50mM ammonium chloride and permeabilised in 0.2% triton, 0.1% glycine 558 0.2% BSA in PBS for 20 mins on ice. 559 560 Intracellular fluorescent protein ingestion assay 561 Intracellular fluorescent protein ingestion was assessed as described in McGovern et al (42). 562…”

Apicomplexan motility depends on the operation of an endocytic-secretory cycle

“…Uptake of host cell material from intracellular parasites has recently been demonstrated and it appears that this material is taken up by an endocytic route that merges with the secretory pathway of the parasite (15). This endocytic process appears to occur rapidly, with endocytosed proteins eventually reaching the vacuolar-like compartment (26,27) of the parasite, in which they are digested (16).…”

“…Here we set out to determine if extracellular parasites are capable of efficiently recycling membrane and taking up exogenous material via endocytosis. To date, uptake of exogenous material has been demonstrated during the intracellular stages of the parasite (15,16). In other eukaryotes, endocytic processes play key roles in membrane dynamics, making it an important participant in cell motility (17,18).…”

A proteomic analysis unravels novel CORVET and HOPS proteins involved in Toxoplasma gondii secretory organelles biogenesis

“…These vesicles proceed through the trans‐Golgi network, endosome‐like compartments marked by Rab5 and Rab7, the lysosome‐like vacuolar compartment (VAC), and immature secretory organelles (pro‐rhoptries and pro‐micronemes) (Jimenez‐Ruiz, Morlon‐Guyot, Daher, & Meissner, ). Interestingly, in T. gondii , proteins acquired from the host cell cytosol are degraded in the VAC during or immediately following invasion and intersect with exocytic trafficking of microneme proteins (Dou, McGovern, Di Cristina, & Carruthers, ; McGovern, Rivera‐Cuevas, Kannan, Narwold Jr., & Carruthers, ). This process is important for both acute and chronic stages of the infection (Di Cristina et al, ).…”