It is known that Toxoplasma gondii infection both initiates and inhibits host cell apoptosis through different proapoptotic signaling cascades, but the parasitic factors involved in these processes remain unclear. T. gondii virulence factor ROP18 has been reported to regulate host cell apoptosis, but the results of this regulation are few reported and contradictory. In this study, we found that immune or neuro cells infected by any one of the T. gondii strains (RH-type I, ME49-type II, and VEG-type III) showed a significantly lower apoptosis index than their uninfected controls when apoptosis was induced by staurosporine (STS). We further found that ROP18 of RH strain inhibited ATP induced apoptosis in human glioblastoma cells (SF268) with endogenous expression of human proapoptotic protein purinergic receptor 1 (P2X1), but had no effects on the immune cells of RAW264.7 and THP-1 without detectable P2X1 expression, which may indicate that ROP18’s inhibition of host cell apoptosis is related to P2X1. Interestingly, we further identified that ROP18 (RH strain) interacted with P2X1, and over-expression of ROP18 in COS-7 cells inhibited the cell apoptosis mediated by P2X1. We also found that ROP18 of RH strain inhibited P2X1-mediated Ca2+ influx, translocation of cytochrome C from mitochondria to cytoplasm, and 1 ATP-triggered caspases activation. Collectively, these findings supported that ROP18 inhibited the host cell apoptosis through the intrinsic mitochondria pathway by targeting host cell P2X1, thereby suggesting a sensor role of the host proapoptotic protein P2X1 in this processAuthor summary
The obligate intracellular protozoan Toxoplasma gondii has been shown to modulate cell apoptosis through different apoptotic pathways. However, the consequences are various and even contradictory, and the parasite effectors and the precise biological mechanisms remain unclear. Herein we showed that T. gondii of type I, II, and III strains could inhibit the apoptosis of neuro cells and immune cells. Toxoplasma gondii ROP18 (RH strain) inhibited apoptosis of human glioblastoma cell SF268 by targeting C terminal of host cell P2X1 protein, but not through proteasome-dependent degradation of P2X1.