Abstract
Toxoplasma gondii critically relies on cell invasion as a survival strategy to evade immune clearance during infection. Although it was widely thought that Toxoplasma entry is parasite directed and that the host cell is largely a passive victim, recent studies have suggested that host components such as microfilaments and microtubules indeed contribute to entry. Hence to identify additional host factors, we performed a high-throughput siRNA screen of a human siRNA library targeting druggable proteins using a novel inducible luciferase based invasion assay. The top 100 hits from the primary screen that showed the strongest decreases in invasion were subjected to confirmation by secondary screening, revealing 24 proteins that are potentially involved in Toxoplasma entry into host cells. Interestingly, 6 of the hits appear to affect parasite invasion by modifying host cell actin dynamics, resulting in increased deposition of F-actin at the periphery of the cell. These findings support the emerging notion that host actin dynamics are important for Toxoplasma invasion along with identifying several novel host factors that potentially participate in parasite entry.
Highlights
Toxoplasma gondii is an obligatory intracellular parasite classified in the phylum Apicomplexa with other notable pathogens including Plasmodium, Cryptosporidium, Eimeria and Neospora spp
Whereas parasite factors involved in cell invasion have been extensively identified and characterized, little attention has been focused on the roles of host components in Toxoplasma cell invasion
The prevailing view based on a series of elegant studies is that Toxoplasma invasion is an active process that is driven by the parasite whereas the host cell is a largely passive entity [30]
Summary
Toxoplasma gondii is an obligatory intracellular parasite classified in the phylum Apicomplexa with other notable pathogens including Plasmodium, Cryptosporidium, Eimeria and Neospora spp. Two recent studies have shown that the host cell is not entirely passive during Toxoplasma invasion and that host actin and microtubules contribute to entry [12,13]. RNA interference (RNAi) mediated gene knockdown is one of the most powerful biological tools available to define protein function [14] This approach has been successfully used to identify and characterize many novel proteins involved in various aspects of cell biology. Six of identified host proteins showed a nearly identical phenotype of enhanced formation of cortical Factin upon silencing Three of these hits were previously implicated in the regulation of actin and cell motility, while the other three have not been linked to actin dynamics and are putative novel regulators of F-actin. Our findings underscore the importance of host actin dynamics in Toxoplasma invasion and reveal novel host-derived potential contributors to parasite entry
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