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

Toxoplasma gondii is an intracellular parasite that reconfigures its host cell to promote pathogenesis. One consequence of Toxoplasma parasitism is increased migratory activity of host cells, which facilitates dissemination. Here, we show that Toxo-plasma triggers the unfolded protein response (UPR) in host cells through calcium release from the endoplasmic reticulum (ER). We further identify a novel role for the host ER stress sensor protein IRE1 in Toxoplasma pathogenesis. Upon infection, Toxoplasma activates IRE1, engaging its noncanonical role in actin remodeling through the binding of filamin A. By inducing cytoskeletal remodeling via IRE1 oligomerization in host cells, Toxoplasma enhances host cell migration in vitro and dissemination of the parasite to host organs in vivo. Our study has identified novel mechanisms used by Toxoplasma to induce dissemination of infected cells, providing new insights into strategies for treatment of toxoplasmosis. IMPORTANCE Cells that are infected with the parasite Toxoplasma gondii exhibit heightened migratory activity, which facilitates dissemination of the infection throughout the body. In this report, we identify a new mechanism used by Toxo-plasma to hijack its host cell and increase its mobility. We further show that the ability of Toxoplasma to increase host cell migration involves not the enzymatic activity of IRE1 but rather IRE1 engagement with actin cytoskeletal remodeling. Depletion of IRE1 from infected host cells reduces their migration in vitro and significantly hinders dissemination of Toxoplasma in vivo. Our findings reveal a new mechanism underly-ing host-pathogen interactions, demonstrating how host cells are co-opted to spread a persistent infection around the body.