Host Cell Vimentin Restrains Toxoplasma gondii Invasion and Phosphorylation of Vimentin is Partially Regulated by Interaction with TgROP18

He, Cheng; Kong, Ling; Zhou, Lijuan; Xia, Jing; Wei, Haixia; Liu, Min; Peng, Hongjuan

TgROP18 is a key serine/threonine kinase that phosphorylates host proteins to modulate the acute virulence of T. gondii [25, 26, 27, 38] , regulates host cell signaling pathways [39, 40] , prevents host cell apoptosis [41] , and alters host cell gene expression [42] . TgROP18 can interact with, and phosphorylate host cell proteins, such as ATF6β and Irga6, to facilitate parasite infection [23, 25, 27] . Interestingly, host cell vimentin was found to interact with TgROP18 in our previous protein interaction screening based on BiFC, and the results of this study verified those findings further using FRET and Co-IP experiments ( Figure 6 ). In our previous phosphoproteinomics assays of T. gondii infected HFF cells, host cell vimentin exhibited a complex phosphorylation pattern at different infection times [34] . In this study, a dynamic phosphorylation pattern of vimentin was identified in host cells infected with T. gondii RH and RH Δrop18 strains using phos-Tag assays, and the results indicated that the phosphorylation pattern of vimentin was partly affected by T. gondii ROP18; moreover, vimentin phosphorylated by TgROP18 was also demonstrated by our kinase assay in vitro (Figure 7) .