Dataset Information

RabGDI? is a negative regulator of interferon-?-inducible GTPase-dependent cell-autonomous immunity to Toxoplasma gondii.

ABSTRACT: IFN-? orchestrates cell-autonomous host defense against various intracellular vacuolar pathogens. IFN-?-inducible GTPases, such as p47 immunity-related GTPases (IRGs) and p65 guanylate-binding proteins (GBPs), are recruited to pathogen-containing vacuoles, which is important for disruption of the vacuoles, culminating in the cell-autonomous clearance. Although the positive regulation for the proper recruitment of IRGs and GBPs to the vacuoles has been elucidated, the suppressive mechanism is unclear. Here, we show that Rab GDP dissociation inhibitor ? (RabGDI?), originally identified as a Rab small GTPase inhibitor, is a negative regulator of IFN-?-inducible GTPases in cell-autonomous immunity to the intracellular pathogen Toxoplasma gondii. Overexpression of RabGDI?, but not of RabGDI?, impaired IFN-?-dependent reduction of T. gondii numbers. Conversely, RabGDI? deletion in macrophages and fibroblasts enhanced the IFN-?-induced clearance of T. gondii. Furthermore, upon a high dose of infection by T. gondii, RabGDI?-deficient mice exhibited a decreased parasite burden in the brain and increased resistance in the chronic phase than did control mice. Among members of IRGs and GBPs important for the parasite clearance, Irga6 and Gbp2 alone were more frequently recruited to T. gondii-forming parasitophorous vacuoles in RabGDI?-deficient cells. Notably, Gbp2 positively controlled Irga6 recruitment that was inhibited by direct and specific interactions of RabGDI? with Gbp2 through the lipid-binding pocket. Taken together, our results suggest that RabGDI? inhibits host defense against T. gondii by negatively regulating the Gbp2-Irga6 axis of IFN-?-dependent cell-autonomous immunity.

SUBMITTER: Ohshima J

PROVIDER: S-EPMC4547277 | biostudies-literature | 2015 Aug

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

RabGDIα is a negative regulator of interferon-γ-inducible GTPase-dependent cell-autonomous immunity to Toxoplasma gondii.

Ohshima Jun J Sasai Miwa M Liu Jianfa J Yamashita Kazuo K Ma Ji Su JS Lee Youngae Y Bando Hironori H Howard Jonathan C JC Ebisu Shigeyuki S Hayashi Mikako M Takeda Kiyoshi K Standley Daron M DM Frickel Eva-Maria EM Yamamoto Masahiro M

Proceedings of the National Academy of Sciences of the United States of America 20150803 33

IFN-γ orchestrates cell-autonomous host defense against various intracellular vacuolar pathogens. IFN-γ-inducible GTPases, such as p47 immunity-related GTPases (IRGs) and p65 guanylate-binding proteins (GBPs), are recruited to pathogen-containing vacuoles, which is important for disruption of the vacuoles, culminating in the cell-autonomous clearance. Although the positive regulation for the proper recruitment of IRGs and GBPs to the vacuoles has been elucidated, the suppressive mechanism is unc ...[more]

PMID: 26240314

Similar Datasets

Project description:BackgroundThe interferon-inducible immunity-related GTPases (IRG proteins/p47 GTPases) are a distinctive family of GTPases that function as powerful cell-autonomous resistance factors. The IRG protein, Irga6 (IIGP1), participates in the disruption of the vacuolar membrane surrounding the intracellular parasite, Toxoplasma gondii, through which it communicates with its cellular hosts. Some aspects of the protein's behaviour have suggested a dynamin-like molecular mode of action, in that the energy released by GTP hydrolysis is transduced into mechanical work that results in deformation and ultimately rupture of the vacuolar membrane.ResultsIrga6 forms GTP-dependent oligomers in vitro and thereby activates hydrolysis of the GTP substrate. In this study we define the catalytic G-domain interface by mutagenesis and present a structural model, of how GTP hydrolysis is activated in Irga6 complexes, based on the substrate-twinning reaction mechanism of the signal recognition particle (SRP) and its receptor (SRα). In conformity with this model, we show that the bound nucleotide is part of the catalytic interface and that the 3'hydroxyl of the GTP ribose bound to each subunit is essential for trans-activation of hydrolysis of the GTP bound to the other subunit. We show that both positive and negative regulatory interactions between IRG proteins occur via the catalytic interface. Furthermore, mutations that disrupt the catalytic interface also prevent Irga6 from accumulating on the parasitophorous vacuole membrane of T. gondii, showing that GTP-dependent Irga6 activation is an essential component of the resistance mechanism.ConclusionsThe catalytic interface of Irga6 defined in the present experiments can probably be used as a paradigm for the nucleotide-dependent interactions of all members of the large family of IRG GTPases, both activating and regulatory. Understanding the activation mechanism of Irga6 will help to explain the mechanism by which IRG proteins exercise their resistance function. We find no support from sequence or G-domain structure for the idea that IRG proteins and the SRP GTPases have a common phylogenetic origin. It therefore seems probable, if surprising, that the substrate-assisted catalytic mechanism has been independently evolved in the two protein families.

Project description:Virulence of complex pathogens in mammals is generally determined by multiple components of the pathogen interacting with the functional complexity and multiple layering of the mammalian immune system. It is most unusual for the resistance of a mammalian host to be overcome by the defeat of a single defence mechanism. In this study we uncover and analyse just such a case at the molecular level, involving the widespread intracellular protozoan pathogen Toxoplasma gondii and one of its most important natural hosts, the house mouse (Mus musculus). Natural polymorphism in virulence of Eurasian T. gondii strains for mice has been correlated in genetic screens with the expression of polymorphic rhoptry kinases (ROP kinases) secreted into the host cell during infection. We show that the molecular targets of the virulent allelic form of ROP18 kinase are members of a family of cellular GTPases, the interferon-inducible IRG (immunity-related GTPase) proteins, known from earlier work to be essential resistance factors in mice against avirulent strains of T. gondii. Virulent T. gondii strain ROP18 kinase phosphorylates several mouse IRG proteins. We show that the parasite kinase phosphorylates host Irga6 at two threonines in the nucleotide-binding domain, biochemically inactivating the GTPase and inhibiting its accumulation and action at the T. gondii parasitophorous vacuole membrane. Our analysis identifies the conformationally active switch I region of the GTP-binding site as an Achilles' heel of the IRG protein pathogen-resistance mechanism. The polymorphism of ROP18 in natural T. gondii populations indicates the existence of a dynamic, rapidly evolving ecological relationship between parasite virulence factors and host resistance factors. This system should be unusually fruitful for analysis at both ecological and molecular levels since both T. gondii and the mouse are widespread and abundant in the wild and are well-established model species with excellent analytical tools available.

Dataset Information

RabGDI? is a negative regulator of interferon-?-inducible GTPase-dependent cell-autonomous immunity to Toxoplasma gondii.

Publications

RabGDIα is a negative regulator of interferon-γ-inducible GTPase-dependent cell-autonomous immunity to Toxoplasma gondii.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets