Toxoplasma gondii co-opts the unfolded protein response to enhance migration and dissemination of infected host cells

Abstract

26Toxoplasma gondii is an intracellular parasite that reconfigures its host cell to promote 27 pathogenesis. One consequence of Toxoplasma parasitism is increased migratory activity of host 28 cells, which facilitates dissemination. Here we show that Toxoplasma triggers the unfolded 29 protein response (UPR) in host cells through calcium release from the endoplasmic reticulum 30 (ER). We further found that host IRE1, an ER stress sensor protein activated during Toxoplasma 31 infection, also plays a noncanonical role in actin remodeling by binding filamin A in infected 32 cells. By inducing cytoskeletal remodeling via IRE1 oligomerization in host cells, Toxoplasma 33 enhances host cell migration in vitro and dissemination of the parasite to host organs in vivo. Our 34 study identifies novel mechanisms used by Toxoplasma to induce dissemination of infected cells, 35 providing new insights into strategies for treatment of toxoplasmosis. 36 37 interactions 39 3 Importance 40Cells that are infected with the parasite Toxoplasma gondii exhibit heightened migratory 41 activity, which facilitates dissemination of the infection throughout the body. In this study, we 42 identify a new mechanism used by Toxoplasma to hijack its host cell and increase its mobility. 43 We further show that the ability of Toxoplasma to increase host cell migration does not involve 44 the enzymatic activity of IRE1, but rather IRE1 engagement with actin cytoskeletal remodeling. 45 Depletion of IRE1 from infected host cells reduces their migration in vitro and significantly 46 hinders dissemination of Toxoplasma in vivo. Our findings reveal a new mechanism underlying 47 host-pathogen interactions, demonstrating how host cells are co-opted to spread a persistent 48 infection around the body. 49 50 93 leading to IRE1 oligomerization, association with filamin A, and enhanced cell migration.94 Importantly, the IRE1-associated migration is a crucial determinant for successful dissemination 95 of toxoplasmosis in a mouse model of infection. 96 6 Results 97 Induction of the UPR in Toxoplasma-infected host cells 98 It is currently unclear why intracellular tachyzoites recruit host ER to the parasite PV. To 99 address whether Toxoplasma perturbs host ER homeostasis, we infected mouse embryonic 100 fibroblast (MEF) cells with RH strain parasites and measured three primary markers of the host 101 UPR over a 36-hour time course. Within 12 h of infection, Toxoplasma increased activation of 102 PERK as measured by its self-phosphorylation (PERK-P), induced expression of ATF6 and 103 formation of its cleavage product ATF6-N, and increased levels of the IRE1-derived spliced 104 variant of XBP1 (XBP1s) ( Fig. 1A). It is noteworthy that whereas expression of ATF6-N and 105 XBP1s were transient, with increased amounts of the proteins appearing between 12 to 20 h post-106 infection (hpi), PERK-P increased throughout the 36 h of infection (Fig. 1A). These results 107 indicate that Toxoplasma infection causes ER stress that activates each of the sensory prote...

The UPR sensor IRE1α promotes dendritic cell responses to control Toxoplasma gondii infection

“…Along these lines, a recent study demonstrated that T. gondii infection activates IRE1a through calcium release from the ER. As described previously (Urra et al, 2018), IRE1a oligomerization and recruitment of filamin A promoted migration of T. gondii-infected MEF and BMDCs (Augusto et al, 2020). While this study did not investigate activation of additional UPR branches in T. gondii-infected BMDCs, these findings are consistent with our results showing a sustained activation of IRE1a in infected BMDCs (Augusto et al, 2020).…”

Host sensing and signal transduction during Toxoplasma stage conversion

“…We have recently shown that intracellular tachyzoites also alter stress response pathways in the host as a means to initiate hypermigration. Toxoplasma infection activates the host cell's unfolded protein response (UPR), prompting the ER stress sensor, IRE1, to interact with the actin‐binding protein filamin A, which remodels the cytoskeleton to produce hypermigration (Augusto et al, 2020a). Depletion of IRE1 from infected host cells reduced their migration in vitro and significantly hindered parasite dissemination in a mouse model of acute toxoplasmosis.…”