Toxoplasma GRA15 limits parasite growth in IFNγ‐activated fibroblasts through TRAF ubiquitin ligases

• Published in: The EMBO journal Vol. 39; no. 10; pp. e103758 - n/a
• Main Authors: Mukhopadhyay, Debanjan, Sangaré, Lamba Omar, Braun, Laurence, Hakimi, Mohamed‐Ali, Saeij, Jeroen PJ
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.05.2020; Blackwell Publishing Ltd; John Wiley and Sons Inc
• Subjects: Animals; Cells, Cultured; Cytosol; EMBO19; EMBO23; Fibroblasts; Fibroblasts - cytology; Fibroblasts - metabolism; Fibroblasts - parasitology; Foreskin - cytology; Foreskin - metabolism; Foreskin - parasitology; GABARAP protein; Gene Expression Regulation - drug effects; GRA15; Humans; IFNγ; Immune response; Immunity; Innate immunity; Interferon-gamma - drug effects; Interferon-gamma - pharmacology; Intracellular Signaling Peptides and Proteins - metabolism; Lysosomes; Male; Mice; p62; Parasites; Parasitophorous vacuole; Protozoa; Protozoan Proteins - metabolism; Receptors; Recruitment; Signal Transduction; Toxoplasma; Toxoplasma - growth & development; Toxoplasma - metabolism; TRAF2 protein; TRAF6; TRAF6 protein; Ubiquitin; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases - metabolism; Vacuoles - metabolism; γ-Interferon; IFNγ; GRA15; p62; TRAF6; Toxoplasma
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2019103758

The protozoan parasite Toxoplasma gondii lives inside a vacuole in the host cytosol where it is protected from host cytoplasmic innate immune responses. However, IFNγ‐dependent cell‐autonomous immunity can destroy the vacuole and the parasite inside. Toxoplasma strain differences in susceptibility to human IFNγ exist, but the Toxoplasma effector(s) that determine these differences are unknown. We show that in human primary fibroblasts, the polymorphic Toxoplasma ‐secreted effector GRA15 mediates the recruitment of ubiquitin ligases, including TRAF2 and TRAF6, to the vacuole membrane, which enhances recruitment of ubiquitin receptors (p62/NDP52) and ubiquitin‐like molecules (LC3B, GABARAP). This ultimately leads to lysosomal degradation of the vacuole. In murine fibroblasts, GRA15‐mediated TRAF6 recruitment mediates the recruitment of immunity‐related GTPases and destruction of the vacuole. Thus, we have identified how the Toxoplasma effector GRA15 affects cell‐autonomous immunity in human and murine cells. Synopsis The polymorphic Toxoplasma effector GRA15 determines parasite strain differences in susceptibility to IFNγ by recruiting TRAF ubiquitin ligases that mediate the recruitment of p62, LC3B and LAMP1 to the parasitophorous vacuole in IFNγ‐stimulated human fibroblasts and the recruitment of IRGs/GBPs in IFNγ‐stimulated murine fibroblasts. The polymorphic effector GRA15 enhances Toxoplasma susceptibility to IFNγ‐mediated growth inhibition in HFFs and MEFs and determines parasite strain differences in susceptibility to IFNγ in HFFs and MEFs. In IFNγ‐stimulated HFFs parasites are eliminated through endolysosomal fusion with the parasitophorous vacuole, which is mediated by GRA15 recruitment of TRAF ubiquitin ligases and ubiquitin‐like molecules and receptors to the parasitophorous vacuole. In IFNγ‐stimulated MEFs parasites are eliminated through recruitment of IRGs/GBPs to parasitophorous vacuole, which is mediated by GRA15 recruitment of the TRAF6 ubiquitin ligase to the parasitophorous vacuole. Graphical Abstract Inter‐strain differences in susceptibility to interferon‐induced lysosomal degradation of parasite‐containing vacuoles is determined by secretion of a protozoan effector interfering with host ubiquitin signaling.