Toxoplasma gondii MAF1b Binds the Host Cell MIB Complex To Mediate Mitochondrial Association

ABSTRACT Parasites interact intimately with their hosts, and the interactions shape both parties. The common human parasite Toxoplasma gondii replicates exclusively in a vacuole in a host cell and alters its host cell’s environment through secreted proteins. One of these secreted proteins, MAF1b, acts to concentrate mitochondria around the parasite’s vacuole, and this relocalization alters the host immune response. Many other intracellular pathogens also recruit host mitochondria, but the identities of the partners that mediate this interaction have not previously been described in any infection. Here, we show that Toxoplasma MAF1b binds to the multifunctional MIB protein complex on the host mitochondria. Reducing the levels of the proteins in this mitochondrial complex reduces the close association of host cell mitochondria and the parasite’s vacuole. This work provides new insight into a key host-pathogen interaction and identifies possible targets for future therapeutic intervention as well as a more molecular understanding of important biology. Many diverse intracellular pathogens, such as Legionella pneumophila, Chlamydia psittaci, Encephalitozoon sp., and Toxoplasma gondii, manipulate and relocate host cell organelles, including mitochondria. Toxoplasma tachyzoites use a secreted protein, mitochondrial association factor 1b (MAF1b), to drive the association between the host mitochondria and the membrane of the parasitophorous vacuole, in which the parasites grow. The identity of the host partner in this interaction, however, has not previously been identified. By exogenously expressing tagged MAF1b in mouse embryonic fibroblasts, we were able to isolate host cell proteins that specifically interact with MAF1b. We then verified these interactions in the MAF1b-expressing fibroblasts, as well as in the context of parasite infection in human fibroblasts and HeLa cells. The results show that a host cell mitochondrial complex, the mitochondrial intermembrane space bridging (MIB) complex, specifically interacts with MAF1b. We further demonstrate that a version of MAF1b that is deficient in host-mitochondrial association does not efficiently coprecipitate the MIB complex. Validation of the importance of the MAF1b-MIB interaction came from showing that knockdown of two MIB complex components, MIC60 and SAM50, substantially reduces mitochondrial association with the parasitophorous vacuole membrane. This interaction between a secreted membrane-integral parasite protein and a membrane-bound complex of a host organelle represents the first instance of organelle relocalization in which both the host and pathogen molecules are known and provides the foundation for more detailed biochemical studies. IMPORTANCE Parasites interact intimately with their hosts, and the interactions shape both parties. The common human parasite Toxoplasma gondii replicates exclusively in a vacuole in a host cell and alters its host cell’s environment through secreted proteins. One of these secreted proteins, MAF1b, acts to concentrate mitochondria around the parasite’s vacuole, and this relocalization alters the host immune response. Many other intracellular pathogens also recruit host mitochondria, but the identities of the partners that mediate this interaction have not previously been described in any infection. Here, we show that Toxoplasma MAF1b binds to the multifunctional MIB protein complex on the host mitochondria. Reducing the levels of the proteins in this mitochondrial complex reduces the close association of host cell mitochondria and the parasite’s vacuole. This work provides new insight into a key host-pathogen interaction and identifies possible targets for future therapeutic intervention as well as a more molecular understanding of important biology.

Download Full-text

Targeted Disruption of Toxoplasma gondii Serine Protease Inhibitor 1 Increases Bradyzoite Cyst FormationIn Vitroand Parasite Tissue Burden in Mice

Infection and Immunity ◽

10.1128/iai.06167-11 ◽

2011 ◽

Vol 80 (3) ◽

pp. 1156-1165 ◽

Cited By ~ 22

Author(s):

Viviana Pszenny ◽

Paul H. Davis ◽

Xing W. Zhou ◽

Christopher A. Hunter ◽

Vern B. Carruthers ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Protease Inhibitor ◽

Host Cell ◽

Serine Protease ◽

Parasitophorous Vacuole ◽

Parasite Burden ◽

Serine Protease Inhibitor ◽

Genomic Locus ◽

Content Type

As an intracellular protozoan parasite,Toxoplasma gondiiis likely to exploit proteases for host cell invasion, acquisition of nutrients, avoidance of host protective responses, escape from the parasitophorous vacuole, differentiation, and other activities.T. gondiiserine protease inhibitor 1 (TgPI1) is the most abundantly expressed protease inhibitor in parasite tachyzoites. We show here that alternative splicing produces twoTgPI1 isoforms, both of which are secreted via dense granules into the parasitophorous vacuole shortly after invasion, become progressively more abundant over the course of the infectious cycle, and can be detected in the infected host cell cytoplasm. To investigateTgPI1 function, the endogenous genomic locus was disrupted in the RH strain background. ΔTgPI1 parasites replicate normally as tachyzoites but exhibit increased bradyzoite gene transcription and labeling of vacuoles withDolichos bifloruslectin under conditions promotingin vitrodifferentiation. The differentiation phenotype can be partially complemented by eitherTgPI1 isoform. Mice infected with the ΔTgPI1 mutant display ∼3-fold-increased parasite burden in the spleen and liver, and thisin vivophenotype is also complemented by eitherTgPI1 isoform. These results demonstrate thatTgPI1 influences both parasite virulence and bradyzoite differentiation, presumably by inhibiting parasite and/or host serine proteases.

Download Full-text

The Secreted Acid Phosphatase Domain-Containing GRA44 from Toxoplasma gondii Is Required for c-Myc Induction in Infected Cells

mSphere ◽

10.1128/msphere.00877-19 ◽

2020 ◽

Vol 5 (1) ◽

Cited By ~ 6

Author(s):

William J. Blakely ◽

Michael J. Holmes ◽

Gustavo Arrizabalaga

Keyword(s):

Acid Phosphatase ◽

Toxoplasma Gondii ◽

Host Cell ◽

Secretory Pathway ◽

Parasitophorous Vacuole ◽

Severe Disease ◽

Immune Recognition ◽

Phosphatase Domain ◽

Content Type ◽

Cell Defense

ABSTRACT During host cell invasion, the eukaryotic pathogen Toxoplasma gondii forms a parasitophorous vacuole to safely reside within the cell, while it is partitioned from host cell defense mechanisms. From within this safe niche, parasites sabotage multiple host cell systems, including gene expression, apoptosis, and intracellular immune recognition, by secreting a large arsenal of effector proteins. Many parasite proteins studied for active host cell manipulative interactions have been kinases. The translocation of effectors from the parasitophorous vacuole into the host cell is mediated by a putative translocon complex, which includes the proteins MYR1, MYR2, and MYR3. Whether other proteins are involved in the structure or regulation of this putative translocon is not known. We have discovered that the secreted protein GRA44, which contains a putative acid phosphatase domain, interacts with members of this complex and is required for host cell effects downstream of effector secretion. We have determined that GRA44 is processed in a region with homology to sequences targeted by protozoan proteases of the secretory pathway and that both major cleavage fragments are secreted into the parasitophorous vacuole. Immunoprecipitation experiments showed that GRA44 interacts with a large number of secreted proteins, including MYR1. Importantly, conditional knockdown of GRA44 resulted in a lack of host cell c-Myc upregulation, which mimics the phenotype seen when members of the translocon complex are genetically disrupted. Thus, the putative acid phosphatase GRA44 is crucial for host cell alterations during Toxoplasma infection and is associated with the translocon complex which Toxoplasma relies upon for success as an intracellular pathogen. IMPORTANCE Approximately one-third of humans are infected with the parasite Toxoplasma gondii. Toxoplasma infections can lead to severe disease in those with a compromised or suppressed immune system. Additionally, infections during pregnancy present a significant health risk to the developing fetus. Drugs that target this parasite are limited, have significant side effects, and do not target all disease stages. Thus, a thorough understanding of how the parasite propagates within a host is critical in the discovery of novel therapeutic targets. Toxoplasma replication requires that it enter the cells of the infected organism. In order to survive the environment inside a cell, Toxoplasma secretes a large repertoire of proteins, which hijack a number of important cellular functions. How these Toxoplasma proteins move from the parasite into the host cell is not well understood. Our work shows that the putative phosphatase GRA44 is part of a protein complex responsible for this process.

Download Full-text

A Glycosylphosphatidylinositol-Anchored Carbonic Anhydrase-Related Protein of Toxoplasma gondii Is Important for Rhoptry Biogenesis and Virulence

mSphere ◽

10.1128/msphere.00027-17 ◽

2017 ◽

Vol 2 (3) ◽

Cited By ~ 13

Author(s):

Nathan M. Chasen ◽

Beejan Asady ◽

Leandro Lemgruber ◽

Rossiane C. Vommaro ◽

Jessica C. Kissinger ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Carbonic Anhydrase ◽

Host Cell ◽

Parasitophorous Vacuole ◽

Lytic Cycle ◽

Host Cells ◽

Intracellular Pathogen ◽

Related Protein ◽

Content Type ◽

Initial Interaction

ABSTRACT Toxoplasma gondii is an intracellular pathogen that infects humans and animals. The pathogenesis of T. gondii is linked to its lytic cycle, which starts when tachyzoites invade host cells and secrete proteins from specialized organelles. Once inside the host cell, the parasite creates a parasitophorous vacuole (PV) where it divides. Rhoptries are specialized secretory organelles that contain proteins, many of which are secreted during invasion. These proteins have important roles not only during the initial interaction between parasite and host but also in the formation of the PV and in the modification of the host cell. We report here the identification of a new T. gondii carbonic anhydrase-related protein (TgCA_RP), which localizes to rhoptries of mature tachyzoites. TgCA_RP is important for the morphology of rhoptries and for invasion and growth of parasites. TgCA_RP is also critical for parasite virulence. We propose that TgCA_RP plays a role in the biogenesis of rhoptries. Carbonic anhydrase-related proteins (CARPs) have previously been described as catalytically inactive proteins closely related to α-carbonic anhydrases (α-CAs). These CARPs are found in animals (both vertebrates and invertebrates) and viruses as either independent proteins or domains of other proteins. We report here the identification of a new CARP (TgCA_RP) in the unicellular organism Toxoplasma gondii that is related to the recently described η-class CA found in Plasmodium falciparum. TgCA_RP is posttranslationally modified at its C terminus with a glycosylphosphatidylinositol anchor that is important for its localization in intracellular tachyzoites. The protein localizes throughout the rhoptry bulbs of mature tachyzoites and to the outer membrane of nascent rhoptries in dividing tachyzoites, as demonstrated by immunofluorescence and immunoelectron microscopy using specific antibodies. T. gondii mutant tachyzoites lacking TgCA_RP display a growth and invasion phenotype in vitro and have atypical rhoptry morphology. The mutants also exhibit reduced virulence in a mouse model. Our results show that TgCA_RP plays an important role in the biogenesis of rhoptries. IMPORTANCE Toxoplasma gondii is an intracellular pathogen that infects humans and animals. The pathogenesis of T. gondii is linked to its lytic cycle, which starts when tachyzoites invade host cells and secrete proteins from specialized organelles. Once inside the host cell, the parasite creates a parasitophorous vacuole (PV) where it divides. Rhoptries are specialized secretory organelles that contain proteins, many of which are secreted during invasion. These proteins have important roles not only during the initial interaction between parasite and host but also in the formation of the PV and in the modification of the host cell. We report here the identification of a new T. gondii carbonic anhydrase-related protein (TgCA_RP), which localizes to rhoptries of mature tachyzoites. TgCA_RP is important for the morphology of rhoptries and for invasion and growth of parasites. TgCA_RP is also critical for parasite virulence. We propose that TgCA_RP plays a role in the biogenesis of rhoptries.

Download Full-text

Differential Impacts on Host Transcription by ROP and GRA Effectors from the Intracellular Parasite Toxoplasma gondii

mBio ◽

10.1128/mbio.00182-20 ◽

2020 ◽

Vol 11 (3) ◽

Cited By ~ 2

Author(s):

Suchita Rastogi ◽

Yuan Xue ◽

Stephen R. Quake ◽

John C. Boothroyd

Keyword(s):

Toxoplasma Gondii ◽

Host Cell ◽

Cell Biology ◽

Parasitophorous Vacuole ◽

Effector Proteins ◽

Transcriptomic Analysis ◽

Host Cells ◽

Intracellular Parasite ◽

Content Type ◽

I Cells

ABSTRACT The intracellular parasite Toxoplasma gondii employs a vast array of effector proteins from the rhoptry and dense granule organelles to modulate host cell biology; these effectors are known as ROPs and GRAs, respectively. To examine the individual impacts of ROPs and GRAs on host gene expression, we developed a robust, novel protocol to enrich for ultrapure populations of a naturally occurring and reproducible population of host cells called uninfected-injected (U-I) cells, which Toxoplasma injects with ROPs but subsequently fails to invade. We then performed single-cell transcriptomic analysis at 1 to 3 h postinfection on U-I cells (as well as on uninfected and infected controls) arising from infection with either wild-type parasites or parasites lacking the MYR1 protein, which is required for soluble GRAs to cross the parasitophorous vacuole membrane (PVM) and reach the host cell cytosol. Based on comparisons of infected and U-I cells, the host’s earliest response to infection appears to be driven primarily by the injected ROPs, which appear to induce immune and cellular stress pathways. These ROP-dependent proinflammatory signatures appear to be counteracted by at least some of the MYR1-dependent GRAs and may be enhanced by the MYR-independent GRAs (which are found embedded within the PVM). Finally, signatures detected in uninfected bystander cells from the infected monolayers suggest that MYR1-dependent paracrine effects also counteract inflammatory ROP-dependent processes. IMPORTANCE This work performs transcriptomic analysis of U-I cells, captures the earliest stage of a host cell’s interaction with Toxoplasma gondii, and dissects the effects of individual classes of parasite effectors on host cell biology.

Download Full-text

Phosphorylation of Toxoplasma gondii Secreted Proteins during Acute and Chronic Stages of Infection

mSphere ◽

10.1128/msphere.00792-20 ◽

2020 ◽

Vol 5 (5) ◽

Cited By ~ 1

Author(s):

Joanna C. Young ◽

Malgorzata Broncel ◽

Helena Teague ◽

Matt R. G. Russell ◽

Olivia L. McGovern ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Cyst Wall ◽

Dominant Role ◽

Parasitophorous Vacuole ◽

Cyst Formation ◽

Secreted Proteins ◽

New Host ◽

Content Type ◽

Chronic Stage ◽

Membrane Bound

ABSTRACT The intracellular parasite Toxoplasma gondii resides within a membrane-bound parasitophorous vacuole (PV) and secretes an array of proteins to establish this replicative niche. It has been shown previously that Toxoplasma secretes kinases and that numerous proteins are phosphorylated after secretion. Here, we assess the role of the phosphorylation of strand-forming protein 1 (SFP1) and the related protein GRA29, two secreted proteins with unknown function. We show that both proteins form stranded structures in the PV that are independent of the previously described intravacuolar network or actin. SFP1 and GRA29 can each form these structures independently of other Toxoplasma secreted proteins, although GRA29 appears to regulate SFP1 strands. We show that an unstructured region at the C termini of SFP1 and GRA29 is required for the formation of strands and that mimicking the phosphorylation of this domain of SFP1 negatively regulates strand development. When tachyzoites convert to chronic-stage bradyzoites, both proteins show a dispersed localization throughout the cyst matrix. Many secreted proteins are reported to dynamically redistribute as the cyst forms, and secreted kinases are known to play a role in cyst formation. Using quantitative phosphoproteome and proteome analyses comparing tachyzoite and early bradyzoite stages, we reveal widespread differential phosphorylation of secreted proteins. While we found no direct evidence for phosphorylation playing a dominant role for SFP1/GRA29 redistribution in the cyst, these data support a model in which secreted kinases and phosphatases contribute to the regulation of secreted proteins during stage conversion. IMPORTANCE Toxoplasma gondii is a common parasite that infects up to one-third of the human population. Initially, the parasite grows rapidly, infecting and destroying cells of the host, but subsequently switches to a slow-growing form and establishes chronic infection. In both stages, the parasite lives within a membrane-bound vacuole within the host cell, but in the chronic stage, a durable cyst wall is synthesized, which provides protection to the parasite during transmission to a new host. Toxoplasma secretes proteins into the vacuole to build its replicative niche, and previous studies identified many of these proteins as phosphorylated. We investigate two secreted proteins and show that a phosphorylated region plays an important role in their regulation in acute stages. We also observed widespread phosphorylation of secreted proteins when parasites convert from acute to chronic stages, providing new insight into how the cyst wall may be dynamically regulated.

Download Full-text

ISG15 Connects Autophagy and IFN-γ-Dependent Control of Toxoplasma gondii Infection in Human Cells

mBio ◽

10.1128/mbio.00852-20 ◽

2020 ◽

Vol 11 (5) ◽

Author(s):

Jaya Bhushan ◽

Joshua B. Radke ◽

Yi-Chieh Perng ◽

Michael Mcallaster ◽

Deborah J. Lenschow ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Parasitophorous Vacuole ◽

Interferon Γ ◽

Parasite Growth ◽

Human Cells ◽

Growth Restriction ◽

Intracellular Pathogens ◽

Functional Link ◽

Content Type ◽

Ifn Γ

ABSTRACT The intracellular protozoan parasite Toxoplasma gondii is capable of infecting most nucleated cells, where it survives in a specially modified compartment called the parasitophorous vacuole (PV). Interferon gamma (IFN-γ) is the major cytokine involved in activating cell-autonomous immune responses to inhibit parasite growth within this intracellular niche. In HeLa cells, IFN-γ treatment leads to ubiquitination of susceptible parasite strains, recruitment of the adaptors p62 and NDP52, and engulfment in microtubule-associated protein 1 light chain 3 (LC3)-positive membranes that restrict parasite growth. IFN-γ-mediated growth restriction depends on core members of the autophagy (ATG) pathway but not the initiation or degradative steps in the process. To explore the connection between these different pathways, we used permissive biotin ligation to identify proteins that interact with ATG5 in an IFN-γ-dependent fashion. Network analysis of the ATG5 interactome identified interferon-stimulated gene 15 (ISG15), which is highly upregulated by IFN treatment, as a hub connecting the ATG complex with other IFN-γ-induced genes, suggesting that it forms a functional link between the pathways. Deletion of ISG15 resulted in impaired recruitment of p62, NDP52, and LC3 to the PV and loss of IFN-γ-restricted parasite growth. The function of ISG15 required conjugation, and a number of ISGylated targets overlapped with the IFN-γ-dependent ATG5 interactome, including the adapter p62. Collectively, our findings establish a role for ISG15 in connecting the ATG pathway with IFN-γ-dependent restriction of T. gondii in human cells. IMPORTANCE Interferon(s) provide the primary defense against intracellular pathogens, a property ascribed to their ability to upregulate interferon-stimulated genes. Due to the sequestered niche occupied by Toxoplasma gondii, the host has elaborated intricate ways to target the parasite within its vacuole. One such mechanism is the recognition by a noncanonical autophagy pathway that envelops the parasite-containing vacuole and stunts growth in human cells. Remarkably, autophagy-dependent growth restriction requires interferon-γ, yet none of the classical components of autophagy are induced by interferon. Our studies draw a connection between these pathways by demonstrating that the antiviral protein ISG15, which is normally upregulated by interferons, links the autophagy-mediated control to ubiquitination of the vacuole. These findings suggest a similar link between interferon-γ signaling and autophagy that may underlie defense against other intracellular pathogens.

Download Full-text

MYR1-Dependent Effectors Are the Major Drivers of a Host Cell’s Early Response to Toxoplasma , Including Counteracting MYR1-Independent Effects

mBio ◽

10.1128/mbio.02401-17 ◽

2018 ◽

Vol 9 (2) ◽

Cited By ~ 27

Author(s):

Adit Naor ◽

Michael W. Panas ◽

Nicole Marino ◽

Michael J. Coffey ◽

Christopher J. Tonkin ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Host Cell ◽

Expression Profiles ◽

Parasitophorous Vacuole ◽

Effector Proteins ◽

Gene Set Enrichment Analysis ◽

Host Cells ◽

Content Type ◽

Cell Functions ◽

The Impact

ABSTRACT The obligate intracellular parasite Toxoplasma gondii controls its host cell from within the parasitophorous vacuole (PV) by using a number of diverse effector proteins, a subset of which require the aspartyl protease 5 enzyme (ASP5) and/or the recently discovered MYR1 protein to cross the PV membrane. To examine the impact these effectors have in the context of the entirety of the host response to Toxoplasma , we used RNA-Seq to analyze the transcriptome expression profiles of human foreskin fibroblasts infected with wild-type RH (RH-WT), RHΔ myr1 , and RHΔ asp5 tachyzoites. Interestingly, the majority of the differentially regulated genes responding to Toxoplasma infection are MYR1 dependent. A subset of MYR1 responses were ASP5 independent, and MYR1 function did not require ASP5 cleavage, suggesting the export of some effectors requires only MYR1. Gene set enrichment analysis of MYR1-dependent host responses suggests an upregulation of E2F transcription factors and the cell cycle and a downregulation related to interferon signaling, among numerous others. Most surprisingly, “hidden” responses arising in RHΔ myr1 - but not RH-WT-infected host cells indicate counterbalancing actions of MYR1-dependent and -independent activities. The host genes and gene sets revealed here to be MYR1 dependent provide new insight into the parasite’s ability to co-opt host cell functions. IMPORTANCE Toxoplasma gondii is unique in its ability to successfully invade and replicate in a broad range of host species and cells within those hosts. The complex interplay of effector proteins exported by Toxoplasma is key to its success in co-opting the host cell to create a favorable replicative niche. Here we show that a majority of the transcriptomic effects in tachyzoite-infected cells depend on the activity of a novel translocation system involving MYR1 and that the effectors delivered by this system are part of an intricate interplay of activators and suppressors. Removal of all MYR1-dependent effectors reveals previously unknown activities that are masked or hidden by the action of these proteins.

Download Full-text

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

Eukaryotic Cell ◽

10.1128/ec.00081-14 ◽

2014 ◽

Vol 13 (8) ◽

pp. 965-976 ◽

Cited By ~ 32

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.

Download Full-text

Association of host cell endoplasmic reticulum and mitochondria with the Toxoplasma gondii parasitophorous vacuole membrane: a high affinity interaction

Journal of Cell Science ◽

10.1242/jcs.110.17.2117 ◽

1997 ◽

Vol 110 (17) ◽

pp. 2117-2128 ◽

Cited By ~ 8

Author(s):

A.P. Sinai ◽

P. Webster ◽

K.A. Joiner

Keyword(s):

Endoplasmic Reticulum ◽

Toxoplasma Gondii ◽

Host Cell ◽

Parasitophorous Vacuole ◽

Protozoan Parasite ◽

Host Cells ◽

Parasitophorous Vacuole Membrane ◽

Vacuole Membrane ◽

Protein Protein Interaction ◽

High Affinity

The parasitophorous vacuole membrane (PVM) of the obligate intracellular protozoan parasite Toxoplasma gondii forms tight associations with host mitochondria and the endoplasmic reticulum (ER). We have used a combination of morphometric and biochemical approaches to characterize this unique phenomenon, which we term PVM-organelle association. The PVM is separated from associated mitochondria and ER by a mean distance of 12 and 18 nm, respectively. The establishment of PVM-organelle association is dependent on active parasite entry, but does not require parasite viability for its maintenance. Association is not a consequence of spatial constraints imposed on the growing vacuole. Morphometric analysis indicates that the extent of mitochondrial association with the PVM stays constant as the vacuole enlarges, whereas the extent of ER association decreases. Disruption of host cell microtubules partially blocks the establishment but not the maintenance of PVM-mitochondrial association, and has no significant effect on PVM-ER association. PVM-organelle association is maintained following disruption of infected host cells, as assessed by electron microscopy and by sub-cellular fractionation showing co-migration of fixed PVM and organelle markers. Taken together, the data suggest that a high affinity, potentially protein-protein interaction between parasite and organelle components is responsible for PVM-organelle association.

Download Full-text

Fierce Competition between Toxoplasma and Chlamydia for Host Cell Structures in Dually Infected Cells

Eukaryotic Cell ◽

10.1128/ec.00313-12 ◽

2012 ◽

Vol 12 (2) ◽

pp. 265-277 ◽

Cited By ~ 11

Author(s):

Julia D. Romano ◽

Catherine de Beaumont ◽

Jose A. Carrasco ◽

Karen Ehrenman ◽

Patrik M. Bavoil ◽

...

Keyword(s):

Host Cell ◽

Parasitophorous Vacuole ◽

Productive Infection ◽

Microtubule Organizing Center ◽

Nutrient Pools ◽

Content Type ◽

Cell Structures ◽

Organizing Center ◽

A Cell ◽

Fierce Competition

ABSTRACTThe prokaryoteChlamydia trachomatisand the protozoanToxoplasma gondii, two obligate intracellular pathogens of humans, have evolved a similarmodus operandito colonize their host cell and salvage nutrients from organelles. In order to gain fundamental knowledge on the pathogenicity of these microorganisms, we have established a cell culture model whereby single fibroblasts are coinfected byC. trachomatisandT. gondii. We previously reported that the two pathogens compete for the same nutrient pools in coinfected cells and thatToxoplasmaholds a significant competitive advantage overChlamydia. Here we have expanded our coinfection studies by examining the respective abilities ofChlamydiaandToxoplasmato co-opt the host cytoskeleton and recruit organelles. We demonstrate that the two pathogen-containing vacuoles migrate independently to the host perinuclear region and rearrange the host microtubular network around each vacuole. However,ToxoplasmaoutcompetesChlamydiato the host microtubule-organizing center to the detriment of the bacterium, which then shifts to a stress-induced persistent state. Solely in cells preinfected withChlamydia, the centrosomes become associated with the chlamydial inclusion, while theToxoplasmaparasitophorous vacuole displays growth defects. Both pathogens fragment the host Golgi apparatus and recruit Golgi elements to retrieve sphingolipids. This study demonstrates that the productive infection by bothChlamydiaandToxoplasmadepends on the capability of each pathogen to successfully adhere to a finely tuned developmental program that aims to remodel the host cell for the pathogen's benefit. In particular, this investigation emphasizes the essentiality of host organelle interception by intravacuolar pathogens to facilitate access to nutrients.

Download Full-text