Toxoplasma Gondii Rhoptry Protein 16 (ROP16) Modifies Apoptosis in Human 293T Cells.

Toxoplasma Gondii is an obligate intracellular protozoan. T. gondii tachyzoites can invade nucleated host cells and inhibit their apoptosis. Therefore, the goal of the present study was to determine whether rhoptry protein 16 (ROP16) secreted by the invading T. gondii can reduce the apoptotic response of the host cell. For this purpose, a vector for in vitro overexpression of T. gondii ROP16 was constructed and used to transfect human 293T cells. Cells transfected with the vector robustly expressed ROP16, as evidenced by Western blotting. Apoptosis of 293T cells was induced by incubation with 0.5 μg/mL actinomycin D (ActD) for 24 h, and its magnitude was measured using Annexin V-FITC/PI and TUNEL assays. Cells transfected by ROP16-expressing vector were characterized by a significantly lower level of apoptosis measured by both techniques.Moreover, caspase-3 activity was also reduced. Thus, ROP16 inhibited ActD-induced apoptosis of human 293T cells, documenting the ability of this rhoptry protein to modulate apoptosis of host cells infected by T. gondii.