Abstract
Toxoplasma gondii and members of the genus Plasmodium are obligate intracellular parasites that leave their infected host cell upon a tightly controlled process of egress. Intracellular replication of the parasites occurs within a parasitophorous vacuole, and its membrane as well as the host plasma membrane need to be disrupted during egress, leading to host cell lysis. While several parasite-derived factors governing egress have been identified, much less is known about host cell factors involved in this process. Previously, RNA interference (RNAi)-based knockdown and antibody-mediated depletion identified a host signaling cascade dependent on guanine nucleotide-binding protein subunit alpha q (GNAQ) to be required for the egress of Toxoplasma tachyzoites and Plasmodium blood stage merozoites. Here, we used CRISPR/Cas9 technology to generate HeLa cells deficient in GNAQ and tested their capacity to support the egress of T. gondii tachyzoites and Plasmodium berghei liver stage parasites. While we were able to confirm the importance of GNAQ for the egress of T. gondii, we found that the egress of P. berghei liver stages was unaffected in the absence of GNAQ. These results may reflect differences between the lytic egress process in apicomplexans and the formation of host cell-derived vesicles termed merosomes by P. berghei liver stages.IMPORTANCE The coordinated release of apicomplexan parasites from infected host cells prior to reinvasion is a critical process for parasite survival and the spread of infection. While Toxoplasma tachyzoites and Plasmodium blood stages induce a fast disruption of their surrounding membranes during their egress from host cells, Plasmodium liver stages keep the host cell membrane intact and leave their host cell in host cell-derived vesicles called merosomes. The knockout of GNAQ, a protein involved in G-protein-coupled receptor signaling, demonstrates the importance of this host factor for the lytic egress of T. gondii tachyzoites. Contrastingly, the egress of P. berghei is independent of GNAQ at the liver stage, indicating the existence of a mechanistically distinct strategy to exit the host cell.
Highlights
Toxoplasma gondii and members of the genus Plasmodium are obligate intracellular parasites that leave their infected host cell upon a tightly controlled process of egress
After the rupture of the PV membrane (PVM), liver stage-derived Plasmodium merozoites leave the infected host cells packed in merosomes
Merozoites are released to infect erythrocytes, thereby initiating the pathogenic blood phase of infection [4, 5]. This strategy contrasts with the lytic egress of T. gondii tachyzoites and Plasmodium blood stage merozoites, whereby the PVM and host cell plasma membrane (HCM) are disrupted in quick succession, leading to fast parasite exit and reinvasion of neighboring cells [1,2,3]
Summary
Toxoplasma gondii and members of the genus Plasmodium are obligate intracellular parasites that leave their infected host cell upon a tightly controlled process of egress. RNA interference (RNAi)-based knockdown and antibody-mediated depletion previously showed that a host signaling cascade dependent on guanine nucleotidebinding protein subunit alpha q (GNAQ) is necessary for the egress of T. gondii tachyzoites and P. falciparum blood stage parasites from host cells. We aimed at testing whether GNAQmediated host cell signaling contributes to Plasmodium liver stage egress and used CRISPR/Cas9 technology to generate GNAQ-deficient knockout (KO) cells.
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