scholarly journals Ionophore-resistant mutant of Toxoplasma gondii reveals involvement of a sodium/hydrogen exchanger in calcium regulation

2004 ◽  
Vol 165 (5) ◽  
pp. 653-662 ◽  
Author(s):  
Gustavo Arrizabalaga ◽  
Felix Ruiz ◽  
Silvia Moreno ◽  
John C. Boothroyd
Keyword(s):  
Toxoplasma Gondii ◽  
Morphological Changes ◽  
Resistant Mutant ◽  
Host Cells ◽  
Ionophore A23187 ◽  
Obligate Intracellular ◽  
Sodium Hydrogen ◽  
Sodium Hydrogen Exchanger ◽  
Direct Genetic Evidence ◽  
Insight Into

Calcium is a critical mediator of many intracellular processes in eukaryotic cells. In the obligate intracellular parasite Toxoplasma gondii, for example, a rise in [Ca2+] is associated with significant morphological changes and rapid egress from host cells. To understand the mechanisms behind such dramatic effects, we isolated a mutant that is altered in its responses to the Ca2+ ionophore A23187 and found the affected gene encodes a homologue of Na+/H+ exchangers (NHEs) located on the parasite's plasma membrane. We show that in the absence of TgNHE1, Toxoplasma is resistant to ionophore-induced egress and extracellular death and amiloride-induced proton efflux inhibition. In addition, the mutant has increased levels of intracellular Ca2+, which explains its decreased sensitivity to A23187. These results provide direct genetic evidence of a role for NHE1 in Ca2+ homeostasis and important insight into how this ubiquitous pathogen senses and responds to changes in its environment.

scholarly journals Toxoplasma gondii Development of Its Replicative Niche: in Its Host Cell and Beyond

2014 ◽  
Vol 13 (8) ◽  
pp. 965-976 ◽  
Author(s):  
Ira J. Blader ◽  
Anita A. Koshy
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Host Cells ◽  
Content Type ◽  
Obligate Intracellular ◽  
Cellular Processes ◽  
High Prevalence ◽  
Life Threatening ◽  
Cell Processes ◽  
Cellular Pathways

ABSTRACTIntracellular pathogens can replicate efficiently only after they manipulate and modify their host cells to create an environment conducive to replication. While diverse cellular pathways are targeted by different pathogens, metabolism, membrane and cytoskeletal architecture formation, and cell death are the three primary cellular processes that are modified by infections.Toxoplasma gondiiis an obligate intracellular protozoan that infects ∼30% of the world's population and causes severe and life-threatening disease in developing fetuses, in immune-comprised patients, and in certain otherwise healthy individuals who are primarily found in South America. The high prevalence ofToxoplasmain humans is in large part a result of its ability to modulate these three host cell processes. Here, we highlight recent work defining the mechanisms by whichToxoplasmainteracts with these processes. In addition, we hypothesize why some processes are modified not only in the infected host cell but also in neighboring uninfected cells.

Invasion of Toxoplasma gondii occurs by active penetration of the host cell

1995 ◽  
Vol 108 (6) ◽  
pp. 2457-2464 ◽  
Author(s):  
J.H. Morisaki ◽  
J.E. Heuser ◽  
L.D. Sibley
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Tyrosine Phosphorylation ◽  
Host Cells ◽  
The Novel ◽  
Host Proteins ◽  
Host Cell Membrane ◽  
Membrane Ruffling ◽  
Obligate Intracellular ◽  
Obligate Intracellular Parasite

Toxoplasma gondii is an obligate intracellular parasite that infects a wide variety of vertebrate cells including macrophages. We have used a combination of video microscopy and fluorescence localization to examine the entry of Toxoplasma into macrophages and nonphagocytic host cells. Toxoplasma actively invaded host cells without inducing host cell membrane ruffling, actin microfilament reorganization, or tyrosine phosphorylation of host proteins. Invasion occurred rapidly and within 25–40 seconds the parasite penetrated into a tight-fitting vacuole formed by invagination of the plasma membrane. In contrast, during phagocytosis of Toxoplasma, extensive membrane ruffling captured the parasite in a loose-fitting phagosome that formed over a period of 2–4 minutes. Phagocytosis involved both reorganization of the host cytoskeleton and tyrosine phosphorylation of host proteins. In some cases, parasites that were first internalized by phagocytosis, were able to escape from the phagosome by a process analogous to invasion. These studies reveal that active penetration of the host cell by Toxoplasma is fundamentally different from phagocytosis or induced endocytic uptake. The novel ability to penetrate the host cell likely contributes to the capability of Toxoplasma-containing vacuoles to avoid endocytic processing.

scholarly journals Insight Into Inflammasome Signaling: Implications for Toxoplasma gondii Infection

2020 ◽  
Vol 11 ◽  
Author(s):  
Yang Wang ◽  
Jinjin Zhu ◽  
Yuanyuan Cao ◽  
Jilong Shen ◽  
Li Yu
Keyword(s):  
Toxoplasma Gondii ◽  
Protein Complexes ◽  
Innate Immune ◽  
Leucine Rich Repeat ◽  
Proteolytic Activation ◽  
Obligate Intracellular ◽  
Obligate Intracellular Parasite ◽  
Multimeric Protein ◽  
Toxoplasma Gondii Infection ◽  
Insight Into

Inflammasomes are multimeric protein complexes regulating the innate immune response to invading pathogens or stress stimuli. Recent studies have reported that nucleotide-binding leucine-rich repeat-containing (NLRs) proteins and DNA sensor absent in melanoma 2 (AIM2) serve as inflammasome sentinels, whose stimulation leads to the proteolytic activation of caspase-1, proinflammatory cytokine secretion, and pyroptotic cell death. Toxoplasma gondii, an obligate intracellular parasite of phylum Apicomplexans, is reportedly involved in NLRP1, NLRP3 and AIM2 inflammasomes activation; however, mechanistic evidence regarding the activation of these complexes is preliminary. This review describes the current understanding of inflammasome signaling in rodent and human models of T. gondii infection.

scholarly journals A Novel Polyclonal Antiserum against Toxoplasma gondii Sodium Hydrogen Exchanger 1

2016 ◽  
Vol 54 (1) ◽  
pp. 21-29 ◽  
Author(s):  
Bin Xiao ◽  
Zhenzhan Kuang ◽  
Yanli Zhan ◽  
Daxiang Chen ◽  
Yang Gao ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Polyclonal Antiserum ◽  
Sodium Hydrogen ◽  
Sodium Hydrogen Exchanger

scholarly journals The Toxoplasma gondii Active Serine Hydrolase 4 Regulates Parasite Division and Intravacuolar Parasite Architecture

mSphere ◽  
2018 ◽  
Vol 3 (5) ◽  
Author(s):  
Ian T. Foe ◽  
Ouma Onguka ◽  
Katherine Amberg-Johnson ◽  
Rikki M. Garner ◽  
Neri Amara ◽  
...  
Keyword(s):  
Cell Division ◽  
Toxoplasma Gondii ◽  
Low Frequency ◽  
Host Cells ◽  
Serine Hydrolase ◽  
Cellular Division ◽  
Content Type ◽  
Obligate Intracellular ◽  
Radial Dispersion ◽  
Residual Bodies

ABSTRACT Hydrolase are enzymes that regulate diverse biological processes, including posttranslational protein modifications. Recent work identified four active serine hydrolases (ASHs) in Toxoplasma gondii as candidate depalmitoylases. However, only TgPPT1 (ASH1) has been confirmed to remove palmitate from proteins. ASH4 (TgME49_264290) was reported to be refractory to genetic disruption. We demonstrate that recombinant ASH4 is an esterase that processes short acyl esters but not palmitoyl thioesters. Genetic disruption of ASH4 causes defects in cell division and premature scission of parasites from residual bodies. These defects lead to the presence of vacuoles with a disordered intravacuolar architecture, with parasites arranged in pairs around multiple residual bodies. Importantly, we found that the deletion of ASH4 correlates with a defect in radial dispersion from host cells after egress. This defect in dispersion of parasites is a general phenomenon that is observed for disordered vacuoles that occur at low frequency in wild-type parasites, suggesting a possible general link between intravacuolar organization and dispersion after egress. IMPORTANCE This work defines the function of an enzyme in the obligate intracellular parasite Toxoplasma gondii. We show that this previously uncharacterized enzyme is critical for aspects of cellular division by the parasite and that loss of this enzyme leads to parasites with cell division defects and which also are disorganized inside their vacuoles. This leads to defects in the ability of the parasite to disseminate from the site of an infection and may have a significant impact on the parasite's overall infectivity of a host organism.

scholarly journals Signaling Cascades Governing Entry into and Exit from Host Cells by Toxoplasma gondii

2019 ◽  
Vol 73 (1) ◽  
pp. 579-599 ◽  
Author(s):  
Hugo Bisio ◽  
Dominique Soldati-Favre
Keyword(s):  
Toxoplasma Gondii ◽  
Conceptual Framework ◽  
Lytic Cycle ◽  
Host Cells ◽  
Current Understanding ◽  
Signaling Cascades ◽  
Protozoan Parasites ◽  
Obligate Intracellular ◽  
Warm Blooded Animal ◽  
Infected Cells

The Apicomplexa phylum includes a large group of obligate intracellular protozoan parasites responsible for important diseases in humans and animals. Toxoplasma gondii is a widespread parasite with considerable versatility, and it is capable of infecting virtually any warm-blooded animal, including humans. This outstanding success can be attributed at least in part to an efficient and continuous sensing of the environment, with a ready-to-adapt strategy. This review updates the current understanding of the signals governing the lytic cycle of T. gondii, with particular focus on egress from infected cells, a key step for balancing survival, multiplication, and spreading in the host. We cover the recent advances in the conceptual framework of regulation of microneme exocytosis that ensures egress, motility, and invasion. Particular emphasis is given to the trigger molecules and signaling cascades regulating exit from host cells.

scholarly journals The Toxoplasma gondii Dense Granule Protein GRA7 Is Phosphorylated upon Invasion and Forms an Unexpected Association with the Rhoptry Proteins ROP2 and ROP4

2008 ◽  
Vol 76 (12) ◽  
pp. 5853-5861 ◽  
Author(s):  
Joe Dan Dunn ◽  
Sandeep Ravindran ◽  
Seon-Kyeong Kim ◽  
John C. Boothroyd
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Parasitophorous Vacuole ◽  
Opportunistic Pathogen ◽  
Dense Granule ◽  
Host Cells ◽  
Obligate Intracellular ◽  
Dense Granules ◽  
Obligate Intracellular Parasite ◽  
Granule Protein

ABSTRACT The obligate intracellular parasite Toxoplasma gondii infects warm-blooded animals throughout the world and is an opportunistic pathogen of humans. As it invades a host cell, Toxoplasma forms a novel organelle, the parasitophorous vacuole, in which it resides during its intracellular development. The parasite modifies the parasitophorous vacuole and its host cell with numerous proteins delivered from rhoptries and dense granules, which are secretory organelles unique to the phylum Apicomplexa. For the majority of these proteins, little is known other than their localization. Here we show that the dense granule protein GRA7 is phosphorylated but only in the presence of host cells. Within 10 min of invasion, GRA7 is present in strand-like structures in the host cytosol that contain rhoptry proteins. GRA7 strands also contain GRA1 and GRA3. Independently of its phosphorylation state, GRA7 associates with the rhoptry proteins ROP2 and ROP4 in infected host cells. This is the first report of interactions between proteins secreted from rhoptries and dense granules.

scholarly journals Receptor for Retrograde Transport in the Apicomplexan Parasite Toxoplasma gondii

2005 ◽  
Vol 4 (2) ◽  
pp. 432-442 ◽  
Author(s):  
Stacy L. Pfluger ◽  
Holly V. Goodson ◽  
Jennifer M. Moran ◽  
Christine J. Ruggiero ◽  
Xin Ye ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Membrane Trafficking ◽  
Cell Biology ◽  
Retrograde Transport ◽  
Stable Expression ◽  
Host Cells ◽  
Functional Assay ◽  
Obligate Intracellular ◽  
Intracellular Parasites ◽  
A Subunit

ABSTRACT Toxoplasma gondii and its apicomplexan relatives (such as Plasmodium falciparum, which causes malaria) are obligate intracellular parasites that rely on sequential protein release from specialized secretory organelles for invasion and multiplication within host cells. Because of the importance of these unusual membrane trafficking pathways for drug development and comparative cell biology, characterizing them is essential. In particular, it is unclear what role retrieval mechanisms play in parasite membrane trafficking or where they operate. Previously, we showed that T. gondii’s beta-COP (TgΒCOP; a subunit of coatomer protein complex I, COPI) and retrieval reporters localize exclusively to the zone between the parasite endoplasmic reticulum (ER) and Golgi apparatus. This suggested the existence of an HDEL receptor in T. gondii. We have now identified, cloned, and sequenced this receptor, TgERD2. TgERD2 localizes in a Golgi or ER pattern suggestive of the HDEL retrieval reporter (K. M. Hager, B. Striepen, L. G. Tilney, and D. S. Roos, J. Cell Sci. 112 :2631-2638, 1999). A functional assay reveals that TgERD2 is able to complement the Saccharomyces cerevisiae ERD2 null mutant. Retrieval studies reveal that stable expression of a fluorescent exogenous retrieval ligand results in a dispersal of βCOP signal throughout the cytoplasm and, surprisingly, results in βCOP staining of the vacuolar space of the parasite. In contrast, stable expression of TgERD2GFP does not appear to disturb βCOP staining. In addition to TgERD2, Toxoplasma contains two more divergent ERD2 relatives. Phylogenetic analysis reveals that these proteins belong to a previously unrecognized ERD2 subfamily common to plants and alveolate organisms and as such could represent mediators of parasite-specific retrieval functions. No evidence of class 2 ERD2 proteins was found in metazoan organisms or fungi.

scholarly journals Ionophore-Resistant Mutants of Toxoplasma gondii Reveal Host Cell Permeabilization as an Early Event in Egress

2000 ◽  
Vol 20 (24) ◽  
pp. 9399-9408 ◽  
Author(s):  
Michael W. Black ◽  
Gustavo Arrizabalaga ◽  
John C. Boothroyd
Keyword(s):  
Toxoplasma Gondii ◽  
Host Cell ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Lytic Cycle ◽  
Host Cells ◽  
Infected Host ◽  
Early Event ◽  
Ionophore A23187 ◽  
Cell Permeabilization

ABSTRACT Toxoplasma gondii is an obligate intracellular pathogen within the phylum Apicomplexa. Invasion and egress by this protozoan parasite are rapid events that are dependent upon parasite motility and appear to be directed by fluctuations in intracellular [Ca2+]. Treatment of infected host cells with the calcium ionophore A23187 causes the parasites to undergo rapid egress in a process termed ionophore-induced egress (IIE). In contrast, when extracellular parasites are exposed to this ionophore, they quickly lose infectivity (termed ionophore-induced death [IID]). From among several Iie− mutants described here, two were identified that differ in several attributes, most notably in their resistance to IID. The association between the Iie− and Iid− phenotypes is supported by the observation that two-thirds of mutants selected as Iid− are also Iie−. Characterization of three distinct classes of IIE and IID mutants revealed that the Iie− phenotype is due to a defect in a parasite-dependent activity that normally causes infected host cells to be permeabilized just prior to egress. Iie−parasites underwent rapid egress when infected cells were artificially permeabilized by a mild saponin treatment, confirming that this step is deficient in the Iie− mutants. A model is proposed that includes host cell permeabilization as a critical part of the signaling pathway leading to parasite egress. The fact that Iie−mutants are also defective in early stages of the lytic cycle indicates some commonality between these normal processes and IIE.

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