scholarly journals Toxoplasma gondii secreted effectors co-opt host repressor complexes to inhibit necroptosis

2020 ◽  
Author(s):  
Alex Rosenberg ◽  
L. David Sibley
Keyword(s):  
Cell Death ◽  
Toxoplasma Gondii ◽  
Host Cell ◽  
Kinase Domain ◽  
Effector Proteins ◽  
Type I ◽  
Immune Functions ◽  
Protein Kinase R ◽  
Repressor Complex

SummaryDuring infection, Toxoplasma gondii translocates effector proteins directly into its host cell to subvert various signaling pathways. Here we characterize a novel secreted effector that localizes to the host cell nucleus where it modulates NCoR/SMRT repressor complex levels to repress interferon regulated genes involved in cell death. Type I and type II interferons upregulate many genes including protein kinase R (PKR), inducing formation of the necrosome complex that activates Mixed Lineage Kinase Domain Like Pseudokinase (MLKL) to execute necrotic cell death. Toxoplasma NCoR/SMRT modulator (TgNSM) acts together with another secreted effector TgIST, previously shown to down-modulate IFN-γ signaling to block immune functions. Together TgNSM and TgIST block IFN driven expression of PKR and MLKL, thus preventing host cell necroptotic death. The mechanism of action of TgNSM highlights a previously unappreciated role of NCoR/SMRT in regulation of necroptosis, assuring survival of intracellular cysts, and maintenance of chronic infection.

scholarly journals Role of Hypoxia-Mediated Autophagy in Tumor Cell Death and Survival

Cancers ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 533
Author(s):  
Rania F. Zaarour ◽  
Bilal Azakir ◽  
Edries Y. Hajam ◽  
Husam Nawafleh ◽  
Nagwa A. Zeinelabdin ◽  
...  
Keyword(s):  
Cell Death ◽  
Type I ◽  
Dependent Manner ◽  
Destruction Process ◽  
Tumor Cell Death ◽  
Complex Regulation ◽  
Cancer Immunotherapies ◽  
The Relationship ◽  
Shed Light

Programmed cell death or type I apoptosis has been extensively studied and its contribution to the pathogenesis of disease is well established. However, autophagy functions together with apoptosis to determine the overall fate of the cell. The cross talk between this active self-destruction process and apoptosis is quite complex and contradictory as well, but it is unquestionably decisive for cell survival or cell death. Autophagy can promote tumor suppression but also tumor growth by inducing cancer-cell development and proliferation. In this review, we will discuss how autophagy reprograms tumor cells in the context of tumor hypoxic stress. We will illustrate how autophagy acts as both a suppressor and a driver of tumorigenesis through tuning survival in a context dependent manner. We also shed light on the relationship between autophagy and immune response in this complex regulation. A better understanding of the autophagy mechanisms and pathways will undoubtedly ameliorate the design of therapeutics aimed at targeting autophagy for future cancer immunotherapies.

scholarly journals TolC-Dependent Modulation of Host Cell Death by the Francisella tularensis Live Vaccine Strain

2014 ◽  
Vol 82 (5) ◽  
pp. 2068-2078 ◽  
Author(s):  
Christopher R. Doyle ◽  
Ji-An Pan ◽  
Patricio Mena ◽  
Wei-Xing Zong ◽  
David G. Thanassi
Keyword(s):  
Cell Death ◽  
Immune Responses ◽  
Host Cell ◽  
Francisella Tularensis ◽  
Vaccine Strain ◽  
Live Vaccine ◽  
Live Vaccine Strain ◽  
Type I ◽  
Content Type ◽  
Host Cell Death

ABSTRACTFrancisella tularensisis a facultative intracellular, Gram-negative pathogen and the causative agent of tularemia. We previously identified TolC as a virulence factor of theF. tularensislive vaccine strain (LVS) and demonstrated that a ΔtolCmutant exhibits increased cytotoxicity toward host cells and elicits increased proinflammatory responses compared to those of the wild-type (WT) strain. TolC is the outer membrane channel component used by the type I secretion pathway to export toxins and other bacterial virulence factors. Here, we show that the LVS delays activation of the intrinsic apoptotic pathway in a TolC-dependent manner, both during infection of primary macrophages and during organ colonization in mice. The TolC-dependent delay in host cell death is required forF. tularensisto preserve its intracellular replicative niche. We demonstrate that TolC-mediated inhibition of apoptosis is an active process and not due to defects in the structural integrity of the ΔtolCmutant. These findings support a model wherein the immunomodulatory capacity ofF. tularensisrelies, at least in part, on TolC-secreted effectors. Finally, mice vaccinated with the ΔtolCLVS are protected from lethal challenge and clear challenge doses faster than WT-vaccinated mice, demonstrating that the altered host responses to primary infection with the ΔtolCmutant led to altered adaptive immune responses. Taken together, our data demonstrate that TolC is required for temporal modulation of host cell death during infection byF. tularensisand highlight how shifts in the magnitude and timing of host innate immune responses may lead to dramatic changes in the outcome of infection.

scholarly journals Death-domain dimerization-mediated activation of RIPK1 controls necroptosis and RIPK1-dependent apoptosis

2018 ◽  
Vol 115 (9) ◽  
pp. E2001-E2009 ◽  
Author(s):  
Huyan Meng ◽  
Zhen Liu ◽  
Xingyan Li ◽  
Huibing Wang ◽  
Taijie Jin ◽  
...  
Keyword(s):  
Cell Death ◽  
Proinflammatory Cytokine ◽  
Kinase Activity ◽  
Kinase Domain ◽  
Death Domain ◽  
Degenerative Diseases ◽  
Intermediate Domain ◽  
A Charge ◽  
Mutant Cells

RIPK1 is a critical mediator of cell death and inflammation downstream of TNFR1 upon stimulation by TNFα, a potent proinflammatory cytokine involved in a multitude of human inflammatory and degenerative diseases. RIPK1 contains an N-terminal kinase domain, an intermediate domain, and a C-terminal death domain (DD). The kinase activity of RIPK1 promotes cell death and inflammation. Here, we investigated the involvement of RIPK1-DD in the regulation of RIPK1 kinase activity. We show that a charge-conserved mutation of a lysine located on the surface of DD (K599R in human RIPK1 or K584R in murine RIPK1) blocks RIPK1 activation in necroptosis and RIPK1-dependent apoptosis and the formation of complex II. Ripk1K584R/K584R knockin mutant cells are resistant to RIPK1 kinase-dependent apoptosis and necroptosis. The resistance of K584R cells, however, can be overcome by forced dimerization of RIPK1. Finally, we show that the K584R RIPK1 knockin mutation protects mice against TNFα-induced systematic inflammatory response syndrome. Our study demonstrates the role of RIPK1-DD in mediating RIPK1 dimerization and activation of its kinase activity during necroptosis and RIPK1-dependent apoptosis.

scholarly journals ROP18-Mediated Transcriptional Reprogramming of HEK293T Cell Reveals New Roles of ROP18 in the Interplay Between Toxoplasma gondii and the Host Cell

2020 ◽  
Vol 10 ◽  
Author(s):  
Jie-Xi Li ◽  
Jun-Jun He ◽  
Hany M. Elsheikha ◽  
Jun Ma ◽  
Xiao-Pei Xu ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Hek293t Cell ◽  
Effector Proteins ◽  
Host Cells ◽  
Pathway Enrichment Analysis ◽  
Type I ◽  
Human Embryonic Kidney Cells ◽  
Pathway Enrichment

Toxoplasma gondii secretes a number of virulence-related effector proteins, such as the rhoptry protein 18 (ROP18). To further broaden our understanding of the molecular functions of ROP18, we examined the transcriptional response of human embryonic kidney cells (HEK293T) to ROP18 of type I T. gondii RH strain. Using RNA-sequencing, we compared the transcriptome of ROP18-expressing HEK293T cells to control HEK293T cells. Our analysis revealed that ROP18 altered the expression of 750 genes (467 upregulated genes and 283 downregulated genes) in HEK293T cells. Gene ontology (GO) and pathway enrichment analyses showed that differentially expressed genes (DEGs) were significantly enriched in extracellular matrix– and immune–related GO terms and pathways. KEGG pathway enrichment analysis revealed that DEGs were involved in several disease-related pathways, such as nervous system diseases and eye disease. ROP18 significantly increased the alternative splicing pattern “retained intron” and altered the expression of 144 transcription factors (TFs). These results provide new insight into how ROP18 may influence biological processes in the host cells via altering the expression of genes, TFs, and pathways. More in vitro and in vivo studies are required to substantiate these findings.

scholarly journals The Protozoan Parasite Toxoplasma gondii Selectively Reprograms the Host Cell Translatome

2018 ◽  
Vol 86 (9) ◽  
Author(s):  
Louis-Philippe Leroux ◽  
Julie Lorent ◽  
Tyson E. Graber ◽  
Visnu Chaparro ◽  
Laia Masvidal ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Cell Activation ◽  
Immune Cell ◽  
Mrna Translation ◽  
Protozoan Parasite ◽  
Translational Efficiency ◽  
Type I ◽  
Content Type ◽  
Infection Inhibition

ABSTRACT The intracellular parasite Toxoplasma gondii promotes infection by targeting multiple host cell processes; however, whether it modulates mRNA translation is currently unknown. Here, we show that infection of primary murine macrophages with type I or II T. gondii strains causes a profound perturbation of the host cell translatome. Notably, translation of transcripts encoding proteins involved in metabolic activity and components of the translation machinery was activated upon infection. In contrast, the translational efficiency of mRNAs related to immune cell activation and cytoskeleton/cytoplasm organization was largely suppressed. Mechanistically, T. gondii bolstered mechanistic target of rapamycin (mTOR) signaling to selectively activate the translation of mTOR-sensitive mRNAs, including those with a 5′-terminal oligopyrimidine (5′ TOP) motif and those encoding mitochondrion-related proteins. Consistent with parasite modulation of host mTOR-sensitive translation to promote infection, inhibition of mTOR activity suppressed T. gondii replication. Thus, selective reprogramming of host mRNA translation represents an important subversion strategy during T. gondii infection.

scholarly journals Migratory Activation of Primary Cortical Microglia upon Infection with Toxoplasma gondii

2011 ◽  
Vol 79 (8) ◽  
pp. 3046-3052 ◽  
Author(s):  
Isabel Dellacasa-Lindberg ◽  
Jonas M. Fuks ◽  
Romanico B. G. Arrighi ◽  
Henrik Lambert ◽  
Robert P. A. Wallin ◽  
...  
Keyword(s):  
T Cells ◽  
Toxoplasma Gondii ◽  
Mhc Class Ii ◽  
Glial Cells ◽  
Costimulatory Molecule ◽  
Toxoplasmic Encephalitis ◽  
Immune Functions ◽  
Content Type

ABSTRACTDisseminated toxoplasmosis in the central nervous system (CNS) is often accompanied by a lethal outcome. Studies with murine models of infection have focused on the role of systemic immunity in control of toxoplasmic encephalitis, while knowledge remains limited on the contributions of resident cells with immune functions in the CNS. In this study, the role of glial cells was addressed in the setting of recrudescentToxoplasmainfection in mice. Activated astrocytes and microglia were observed in the close vicinity of foci with replicating parasitesin situin the brain parenchyma.Toxoplasma gondiitachyzoites were allowed to infect primary microglia and astrocytesin vitro. Microglia were permissive to parasite replication, and infected microglia readily transmigrated across transwell membranes and cell monolayers. Thus, infected microglia, but not astrocytes, exhibited a hypermotility phenotype reminiscent of that recently described for infected dendritic cells. In contrast to gamma interferon-activated microglia,Toxoplasma-infected microglia did not upregulate major histocompatibility complex (MHC) class II molecules and the costimulatory molecule CD86. YetToxoplasma-infected microglia and astrocytes exhibited increased sensitivity to T cell-mediated killing, leading to rapid parasite transfer to effector T cellsin vitro. We hypothesize that glial cells and T cells, besides their role in triggering antiparasite immunity, may also act as “Trojan horses,” paradoxically facilitating dissemination ofToxoplasmawithin the CNS. To our knowledge, this constitutes the first report of migratory activation of a resident CNS cell by an intracellular parasite.

scholarly journals Plant mixed lineage kinase domain-like proteins limit biotrophic pathogen growth

2019 ◽  
Author(s):  
Lisa Mahdi ◽  
Menghang Huang ◽  
Xiaoxiao Zhang ◽  
Ryohei Thomas Nakano ◽  
Leïla Brulé Kopp ◽  
...  
Keyword(s):  
Cell Death ◽  
Host Cell ◽  
Kinase Domain ◽  
Protein Family ◽  
Mixed Lineage Kinase ◽  
Helical Bundles ◽  
Cryo Electron Microscopy ◽  
Host Cell Death ◽  
A Cell ◽  
Immunity Mechanism

AbstractMixed lineage kinase domain-like (MLKL) protein mediates necroptotic cell death in vertebrates. We report here the discovery of a conserved protein family across seed plants that is structurally homologous to vertebrate MLKL. TheArabidopsis thalianagenome encodes three MLKLs with overlapping functions in limiting growth of obligate biotrophic fungal and oomycete pathogens. Although displaying a cell death activity mediated by N-terminal helical bundles, termed HeLo domain,AtMLKL-dependent immunity can be separated from host cell death. Cryo-electron microscopy structures ofAtMLKLs reveal a tetrameric configuration, in which the pseudokinase domain and brace region bury the HeLo-domains, indicative of an auto-repressed complex. We also show the association of twoAtMLKLs with microtubules. These findings, coupled with resistance-enhancing activity and altered microtubule association of a phosphomimetic mutation in the pseudokinase domain ofAtMLKL1, point to a cell death-independent immunity mechanism.One Sentence SummaryPlants have a protein family that is structurally homologous to vertebrate mixed lineage kinase domain-like protein, which induces necroptotic cell death, but these plant proteins can confer immunity without host cell death.

scholarly journals NleB2 from enteropathogenic Escherichia coli is a novel arginine-glucose transferase effector

2021 ◽  
Vol 17 (6) ◽  
pp. e1009658
Author(s):  
Cristina Giogha ◽  
Nichollas E. Scott ◽  
Tania Wong Fok Lung ◽  
Georgina L. Pollock ◽  
Marina Harper ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Death ◽  
Host Cell ◽  
Peptide Sequencing ◽  
Effector Proteins ◽  
Host Protein ◽  
Death Domain ◽  
T3ss Effector ◽  
Arginine Residues

During infection, enteropathogenic Escherichia coli (EPEC) and enterohaemorrhagic E. coli (EHEC) directly manipulate various aspects of host cell function through the translocation of type III secretion system (T3SS) effector proteins directly into the host cell. Many T3SS effector proteins are enzymes that mediate post-translational modifications of host proteins, such as the glycosyltransferase NleB1, which transfers a single N-acetylglucosamine (GlcNAc) to arginine residues, creating an Arg-GlcNAc linkage. NleB1 glycosylates death-domain containing proteins including FADD, TRADD and RIPK1 to block host cell death. The NleB1 paralogue, NleB2, is found in many EPEC and EHEC strains but to date its enzymatic activity has not been described. Using in vitro glycosylation assays combined with mass spectrometry, we found that NleB2 can utilize multiple sugar donors including UDP-glucose, UDP-GlcNAc and UDP-galactose during glycosylation of the death domain protein, RIPK1. Sugar donor competition assays demonstrated that UDP-glucose was the preferred substrate of NleB2 and peptide sequencing identified the glycosylation site within RIPK1 as Arg603, indicating that NleB2 catalyses arginine glucosylation. We also confirmed that NleB2 catalysed arginine-hexose modification of Flag-RIPK1 during infection of HEK293T cells with EPEC E2348/69. Using site-directed mutagenesis and in vitro glycosylation assays, we identified that residue Ser252 in NleB2 contributes to the specificity of this distinct catalytic activity. Substitution of Ser252 in NleB2 to Gly, or substitution of the corresponding Gly255 in NleB1 to Ser switches sugar donor preference between UDP-GlcNAc and UDP-glucose. However, this switch did not affect the ability of the NleB variants to inhibit inflammatory or cell death signalling during HeLa cell transfection or EPEC infection. NleB2 is thus the first identified bacterial Arg-glucose transferase that, similar to the NleB1 Arg-GlcNAc transferase, inhibits host protein function by arginine glycosylation.

scholarly journals ROP16-Mediated Activation of STAT6 Suppresses Host Cell Reactive Oxygen Species Production, Facilitating Type III Toxoplasma gondii Growth and Survival

mBio ◽  
2021 ◽  
Vol 12 (2) ◽  
Author(s):  
Joshua A. Kochanowsky ◽  
Kaitlin K. Thomas ◽  
Anita A. Koshy
Keyword(s):  
Reactive Oxygen Species ◽  
Toxoplasma Gondii ◽  
Host Cell ◽  
Parasite Growth ◽  
Effector Proteins ◽  
Oxygen Species ◽  
Content Type ◽  
Growth And Survival ◽  
Type Iii ◽  
Ifn Γ

ABSTRACT Polymorphic effector proteins determine the susceptibility of Toxoplasma gondii strains to IFN-γ-mediated clearance mechanisms deployed by murine host cells. However, less is known about the influence of these polymorphic effector proteins on IFN-γ-independent clearance mechanisms. Here, we show that deletion of one such polymorphic effector protein, ROP16, from a type III background leads to a defect in parasite growth and survival in unstimulated human fibroblasts and murine macrophages. Rescue of these defects requires a ROP16 with a functional kinase domain and the ability to activate a specific family of host cell transcription factors (STAT3, 5a, and 6). The growth and survival defects correlate with an accumulation of host cell reactive oxygen species (ROS) and are prevented by treatment with an ROS inhibitor. Exogenous activation of STAT3 and 6 suppresses host cell ROS production during infection with ROP16-deficient parasites and depletion of STAT6, but not STAT3 or 5a, causes an accumulation of ROS in cells infected with wild-type parasites. Pharmacological inhibition of NOX2 and mitochondrially derived ROS also rescues growth and survival of ROP16-deficient parasites. Collectively, these findings reveal an IFN-γ-independent mechanism of parasite restriction in human cells that is subverted by injection of ROP16 by type III parasites. IMPORTANCE Toxoplasma gondii is an obligate intracellular parasite that infects up to one-third of the world’s population. Control of the parasite is largely accomplished by IFN-γ-dependent mechanisms that stimulate innate and adaptive immune responses. Parasite suppression of IFN-γ-stimulated responses has been linked to proteins that the parasite secretes into its host cell. These secreted proteins vary by T. gondii strain and determine strain-specific lethality in mice. How these strain-specific polymorphic effector proteins affect IFN-γ-independent parasite control mechanisms in human and murine cells is not well known. This study shows that one such secreted protein, ROP16, enables efficient parasite growth and survival by suppressing IFN-γ-independent production of ROS by human and mouse cells.

Sign in / Sign up

Export Citation Format

Share Document