Wednesday, August 28, 2013

CD4+ T cells are trigger and target of the glucocorticoid response that prevents lethal immunopathology in toxoplasma infection

2013 Aug 26. [Epub ahead of print]

CD4+ T cells are trigger and target of the glucocorticoid response that prevents lethal immunopathology in toxoplasma infection

Source

Immunobiology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases; 2 Laboratory of Immune Cell Biology, Center for Cancer Research, National Cancer Institute; and 3 The Johns Hopkins University/National Institutes of Health Graduate Partnership Program; National Institutes of Health, Bethesda, MD 20892.

Abstract

Synthetic glucocorticoids (GCs) are commonly used in the treatment of inflammatory diseases, but the role of endogenous GCs in the regulation of host-protective immune responses is poorly understood. Here we show that GCs are induced during acute Toxoplasma gondii infection and directly control the T cell response to the parasite. When infected with toxoplasma, mice that selectively lack GC receptor (GR) expression in T cells (GRlck-Cre) rapidly succumb to infection despite displaying parasite burdens indistinguishable from control animals and unaltered levels of the innate cytokines IL-12 and IL-27. Mortality in the GRlck-Cre mice was associated with immunopathology and hyperactive Th1 cell function as revealed by enhanced IFN-γ and TNF production in vivo. Unexpectedly, these CD4+ T lymphocytes also overexpressed IL-10. Importantly, CD4+ T cell depletion in wild-type or GRlck-Cre mice led to ablation of the GC response to infection. Moreover, in toxoplasma-infected RAG-/- animals, adoptive transfer of CD4+ T lymphocytes was required for GC induction. These findings establish a novel IL-10-independent immunomodulatory circuit in which CD4+ T cells trigger a GC response that in turn dampens their own effector function. In the case of T. gondii infection, this self-regulatory pathway is critical for preventing collateral tissue damage and promoting host survival.
PMID:
23980098
[PubMed - as supplied by publisher]

In vitro effects of novel ruthenium complexes in Neospora caninum and Toxoplasma gondii tachyzoites

2013 Aug 26. [Epub ahead of print]

In vitro effects of novel ruthenium complexes in Neospora caninum and Toxoplasma gondii tachyzoites

Source

Institute of Parasitology, Vetsuisse Faculty, University of Berne, Länggass-Strasse 122, CH-3012 Berne, Switzerland.

Abstract

Upon screening of 16 anti-proliferative compounds against Toxoplasma gondii and Neospora caninum, two hydrolytically stable ruthenium complexes (16, 18) exhibited IC50 values of 18.7 and 41.1 nM (T.gondii) and 6.7 and 11.3nM (N.caninum). To achieve parasiticidal activity for compound 16, long-term treatments (22-27 days at 80-160nM) were required. TEM demonstrated the rapid impact and ultrastructural alterations in both parasites. The potential of ruthenium-based compounds should thus be further exploited.
PMID:
23979747
[PubMed - as supplied by publisher]

Monday, August 26, 2013

A nucleolar AAA-NTPase is required for parasite division

2013 Aug 22. doi: 10.1111/mmi.12367. [Epub ahead of print]

A nucleolar AAA-NTPase is required for parasite division

Source

Departments of Molecular Medicine & Global Health, University of South Florida, Tampa, FL 33612.

Abstract

Apicomplexa division involves several distinct phases shared with other eukaryote cell cycles including a gap period (G1) prior to chromosome synthesis, although how progression through the parasite cell cycle is controlled is not understood. Here we describe a cell cycle mutant that reversibly arrests in the G1 phase. The defect in this mutant was mapped by genetic complementation to a gene encoding a novel AAA-ATPase/CDC48 family member called TgNoAP1. TgNoAP1 is tightly regulated and expressed in the nucleolus during the G1/S phases. A tyrosine to a cysteine change upstream of the second AAA+ domain in the temperature sensitive TgNoAP1 allele leads to conditional protein instability, which is responsible for rapid cell cycle arrest and a primary defect in 28S rRNA processing as confirmed by knock-in of the mutation back into the parent genome. The interaction of TgNoAP1 with factors of the snoRNP and R2TP complexes indicates this protein has a role in pre-rRNA processing. This is a novel role for a cdc48-related chaperone protein and indicates that TgNoAP1 may be part of a dynamic mechanism that senses the health of the parasite protein machinery at the initial steps of ribosome biogenesis and conveys that information to the parasite cell cycle checkpoint controls.
This article is protected by copyright. All rights reserved.

KEYWORDS:

AAA-ATPase, Apicomplexa, G1 phase, Toxoplasma gondii, cell cycle, nucleolus, replication
PMID:
23964771
[PubMed - as supplied by publisher]

MAP Kinase Phosphatase-2 Plays a Key Role in the Control of Infection with Toxoplasma gondii by Modulating iNOS and Arginase-1 Activities in Mice

2013 Aug;9(8):e1003535. doi: 10.1371/journal.ppat.1003535. Epub 2013 Aug 15.

MAP Kinase Phosphatase-2 Plays a Key Role in the Control of Infection with Toxoplasma gondii by Modulating iNOS and Arginase-1 Activities in Mice

Source

Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, United Kingdom.

Abstract

The dual specific phosphatase, MAP kinase phosphatase-2 (MKP-2) has recently been demonstrated to negatively regulate macrophage arginase-1 expression, while at the same time to positively regulate iNOS expression. Consequently, MKP-2 is likely to play a significant role in the host interplay with intracellular pathogens. Here we demonstrate that MKP-2(-/-) mice on the C57BL/6 background have enhanced susceptibility compared with wild-type counterparts following infection with type-2 strains of Toxoplasma gondii as measured by increased parasite multiplication during acute infection, increased mortality from day 12 post-infection onwards and increased parasite burdens in the brain, day 30 post-infection. MKP-2(-/-) mice did not, however, demonstrate defective type-1 responses compared with MKP-2(+/+) mice following infection although they did display significantly reduced serum nitrite levels and enhanced tissue arginase-1 expression. Early resistance to T. gondii in MKP-2(+/+), but not MKP-2(-/-), mice was nitric oxide (NO) dependent as infected MKP-2(+/+), but not MKP-2(-/-) mice succumbed within 10 days post-infection with increased parasite burdens following treatment with the iNOS inhibitor L-NAME. Conversely, treatment of infected MKP-2(-/-) but not MKP-2(+/+) mice with nor-NOHA increased parasite burdens indicating a protective role for arginase-1 in MKP-2(-/-) mice. In vitro studies using tachyzoite-infected bone marrow derived macrophages and selective inhibition of arginase-1 and iNOS activities confirmed that both iNOS and arginase-1 contributed to inhibiting parasite replication. However, the effects of arginase-1 were transient and ultimately the role of iNOS was paramount in facilitating long-term inhibition of parasite multiplication within macrophages.
PMID:
23966857
[PubMed - in process]

Saturday, August 24, 2013

Fusidic acid is an effective treatment against Toxoplasma gondii and Listeria monocytogenes in vitro, but not in mice



 2013 Aug 16. [Epub ahead of print]

Fusidic acid is an effective treatment against Toxoplasma gondii and Listeria monocytogenes in vitro, but not in mice

Source

Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, 1550 Linden Drive, Madison, WI, 53706, USA.
Abstract
Fusidic acid is a bacteriostatic antibiotic that inhibits the growth of bacteria by preventing the release of translation elongation factor G (EF-G) from the ribosome. The apicomplexan parasite Toxoplasma gondii has an orthologue of bacterial EF-G that can complement bacteria and is necessary for parasite virulence. Fusidic acid has been shown to be effective in tissue culture against the related pathogen Plasmodium falciparum, and current drug treatments against T. gondii are limited. We therefore investigated the therapeutic value of fusidic acid for T. gondii and found that the drug was effective in tissue culture, but not in a mouse model of infection. To determine whether this trend would occur in another intracellular pathogen that elicits a T helper 1-type immune response, we tested the efficacy of fusidic acid for the bacterium Listeria monocytogenes. Similar to its effects on T. gondii, fusidic acid inhibits the growth of L. monocytogenes in vitro, but not in mice. These findings highlight the necessity of in vivo follow-up studies to validate in vitro drug investigations.
PMID: 
23949312 
[PubMed - as supplied by publisher]

Toxoplasma gondii exposure affects neural processing speed as measured by acoustic startle latency in schizophrenia and controls


 2013 Aug 13. pii: S0920-9964(13)00372-1. doi: 10.1016/j.schres.2013.07.028. [Epub ahead of print]

Toxoplasma gondii exposure affects neural processing speed as measured by acoustic startle latency in schizophrenia and controls

Source

Department of Epidemiology, Rollins School of Public Health, Emory University, 1518 Clifton Rd NE, Atlanta, GA 30329, USA. Electronic address:bpearce@emory.edu.

Abstract

The prevalence of Toxoplasma gondii (TOXO) infection in schizophrenia (SCZ) is elevated compared to controls (odds ratio=2.73). TOXO infection is associated with psychomotor slowing in rodents and non-psychiatric humans. Latency of the acoustic startle response, an index of neural processing speed, is the time it takes for a startling stimulus to elicit the reflexive response through a three-synapse subcortical circuit. We report a significant slowing of latency in TOXO seropositive SCZ vs. seronegative SCZ, and in TOXO seropositive controls vs. seronegative controls. Latency was likewise slower in SCZ subjects than in controls. These findings indicate a slowing of neural processing speed with chronic TOXO infection; the slowest startle latency was seen in the TOXO seropositive SCZ group.
Published by Elsevier B.V.

KEYWORDS:

Acoustic startle, Latency, Schizophrenia, Toxoplasma gondii
PMID: 
23953218 
[PubMed - as supplied by publisher]

Toxoplasma gondii: Ultrastructure study of the entry of tachyzoites into mammalian cells


 2011 Apr;18(2):151-6. doi: 10.1016/j.sjbs.2010.12.005. Epub 2010 Dec 15.

Toxoplasma gondii: Ultrastructure study of the entry of tachyzoites into mammalian cells

Source

Department of Zoology, Girls' College of Education, King Abdel Aziz University, Departments of Parasitology and Histology, Faculty of Medicine for Girls, Al-Azhar University and Department of Pathology, Animal Health Research Institute, Cairo, Egypt.
Abstract
Toxoplama gondii (Apicomplexa: Coccidia), an obligatory intracellular parasite with a unique capacity to invade virtually all nucleated cell type from warm-blooded vertebrate hosts. Despite the efficiency with which Toxoplasma enters its host cell, it remains unresolved if invasion occurs by direct penetration of the parasite or through phagocytosis. In the present work, electron microscopic study was designed to examine the entry process of Toxoplasma (RH strain) into macrophages and non phagocytic-host cells (Hela cells) and to observe the ultrastructure changes associated with intracellular parasitism. The results showed that both active invasion and phagocytosis were occurred and revealed that invasion is an ordered process that initiates with binding of the parasite at its apical end followed by tight-fitting invagination of the host cell membrane and a prominent constriction in the parasite at the site of penetration. The process ended by the professional parasitophorous vacuole that is distinct at the outset from those formed by phagocytosis in which once Toxoplasma triggered, phagocytic uptake can proceed by capture of the parasite within a loose fitting vacuole formed by localized membrane ruffling. The cytopathic effects of the parasite on macrophages and Hela cells were demonstrated within 5-15 h post-inoculation in the form of degenerative mitochondria, swelling Golgi apparatus and widening of endoplasmic reticulum indicating intracellular oedema. These changes were exaggerated and several cells were found dead after 48-72 h.

KEYWORDS:

Mammalian cells, Tachyzoites, Toxoplasma gondii, Ultrastructure
PMID: 
23961118 
[PubMed]

Toxoplasma gondii Syntaxin 6 is required for vesicular transport between endosomal-like compartments and the Golgi


 2013 Aug 20. doi: 10.1111/tra.12102. [Epub ahead of print]

Toxoplasma gondii Syntaxin 6 is required for vesicular transport between endosomal-like compartments and the Golgi

Source

Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity and Inflammation, College of Medical, Veterinary and Life Sciences, The University of Glasgow, Glasgow, G12 8TA, United Kingdom.

Abstract

Apicomplexans are obligate intracellular parasites that invade the host cell in an active process that relies on unique secretory organelles (micronemes, rhoptries, and dense granules) localised at the apical tip of these highly polarised eukaryotes. In order for the contents of these specialised organelles to reach their final destination, these proteins are sorted post-Golgi and it has been speculated that they pass through endosomal-like compartments, where they undergo maturation. Here we characterise a Toxoplasma gondii homolog of Syntaxin 6 (TgStx6), a well-established marker for the early endosomes and trans-Golgi network (TGN) in diverse eukaryotes. Indeed TgStx6 appears to have a role in the retrograde transport between endosomal-like compartments, the TGN and the Golgi, since overexpression of TgStx6 results in the development of abnormally shaped parasites with expanded endosomal-like compartments, a fragmented Golgi and a defect in inner membrane complex maturation. Interestingly, other organelles, such as the micronemes, rhoptries and the apicoplast are not affected, establishing the TGN as a major sorting compartment where several transport pathways intersect. It therefore appears that Toxoplasma has retained a plant-like secretory pathway.
This article is protected by copyright. All rights reserved.

KEYWORDS:

Golgi, Syntaxin, TGN, Toxoplasma gondii, conditional mutant, endosomes, vesicular traffic
PMID: 
23962112 
[PubMed - as supplied by publisher]

Monday, August 19, 2013

POSTDOCTORAL POSITION available


POSTDOCTORAL POSITION

Biochemistry, Microbiology, Drug development
 

Indiana University School of Medicine


POSTDOCTORAL POSITION available to investigate the efficacy and mechanism of experimental drugs to treat infection caused by the protozoan parasite Toxoplasma gondii. Related to the malaria parasite, Toxoplasma causes birth defects and life-threatening infection in immunocompromised AIDS or heart transplant patients. The successful candidate will continue the study of small molecules that interfere with stress responses and differentiation as a means to subvert acute and chronic parasite infection using in vivo and in vitro models (see Konrad et al., Antimicrob Agents Chemother. 2013, 57(4):1815-22). The candidate is also expected to employ state of the art genetic and biochemical approaches to determine the detailed mechanism of action for these compounds.

Position requires a Ph.D., expertise in animal (mouse) handling, biochemistry & cell biology,  and excellent communication skills (speaking and writing English). Submit CV and contact information for three references to Dr. Bill Sullivan (wjsulliv@iu.edu).

Located in downtown Indianapolis, Indiana University School of Medicine (IUSM) is the second largest medical school in the US and boasts an outstanding intellectual atmosphere and core facilities. IUSM was nationally ranked in the Top 30 Best Places to Work for Postdocs. Our lab is part of a larger intracellular parasitism group at IU that fosters innovation and collaboration. IUSM is an equal opportunity employer. Visit www.sullivanlab.com for more information.

Thursday, August 15, 2013

Chromera velia: The Missing Link in the Evolution of Parasitism

2013;85:119-44. doi: 10.1016/B978-0-12-407672-3.00004-6.

Chromera velia: The Missing Link in the Evolution of Parasitism

Source

School of Molecular Bioscience, University of Sydney, Sydney, New South Wales, Australia.

Abstract

Since the pivotal publication announcing the discovery of Chromera velia in 2008, there has been a flurry of interest and research into this novel alga. Found by chance while studying the symbionts of corals in Australian reefs, C. velia has turned out to be a very important organism. It holds a unique position as the evolutionary intermediate between photosynthetic dinoflagellate algae and parasitic apicomplexans. Biological characterization has revealed similarities to both dinoflagellates and apicomplexans. Of particular interest is the photosynthetic plastid that is closely related to the apicomplexan apicoplast. This plastid in C. velia has a highly effective photosynthetic system with photoprotective properties such as nonphotochemical quenching. The apicoplast is essential for cell health and is therefore a potential drug target for the apicomplexans that cause malaria and other diseases. The tetrapyrrole, sterol, and galactolipid pathways have been explored in C. velia to find parallels with apicomplexans that could lead to new insights to fight these parasites. Ecologically, C. velia is very similar to dinoflagellates, reflecting their common ancestry and revealing how the ancestors of apicomplexans may have lived before they evolved to become parasitic.
© 2013 Elsevier Inc. All rights reserved.

KEYWORDS:

Apicomplexa, Apicoplast, Biosynthesis, Chromera velia, Dinoflagellate, Photosynthesis, Plastid, Vitrella brassicaformis
PMID:
23942150
[PubMed - in process]

Toxoplasma gondii Sporozoites Invade Host Cells Using Two Novel Paralogues of RON2 and AMA1

2013 Aug 5;8(8):e70637. doi: 10.1371/journal.pone.0070637. Print 2013.

Toxoplasma gondii Sporozoites Invade Host Cells Using Two Novel Paralogues of RON2 and AMA1

Source

Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, United States of America.

Abstract

Toxoplasma gondii is an obligate intracellular parasite of the phylum Apicomplexa. The interaction of two well-studied proteins, Apical Membrane Antigen 1 (AMA1) and Rhoptry Neck protein 2 (RON2), has been shown to be critical for invasion by the asexual tachyzoite stage. Recently, two paralogues of these proteins, dubbed sporoAMA1 and sporoRON2 (or RON2L2), respectively, have been identified but not further characterized in proteomic and transcriptomic analyses of Toxoplasma sporozoites. Here, we show that sporoAMA1 and sporoRON2 localize to the apical region of sporozoites and that, in vitro, they interact specifically and exclusively, with no detectable interaction of sporoAMA1 with generic RON2 or sporoRON2 with generic AMA1. Structural studies of the interacting domains of sporoRON2 and sporoAMA1 indicate a novel pairing that is similar in overall form but distinct in detail from the previously described interaction of the generic pairing. Most notably, binding of sporoRON2 domain 3 to domains I/II of sporoAMA1 results in major alterations in the latter protein at the site of binding and allosterically in the membrane-proximal domain III of sporoAMA1 suggesting a possible role in signaling. Lastly, pretreatment of sporozoites with domain 3 of sporoRON2 substantially impedes their invasion into host cells while having no effect on tachyzoites, and vice versa for domain 3 of generic RON2 (which inhibits tachyzoite but not sporozoite invasion). These data indicate that sporozoites and tachyzoites each use a distinct pair of paralogous AMA1 and RON2 proteins for invasion into host cells, possibly due to the very different environment in which they each must function.
PMID:
23940612
[PubMed - in process]

New details on the fine structure of the rhoptry of Toxoplasma gondii

2011 Sep;74(9):812-8. doi: 10.1002/jemt.20960. Epub 2010 Nov 17.

New details on the fine structure of the rhoptry of Toxoplasma gondii

Source

Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brazil; Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagens, Rio de Janeiro, Brazil.

Abstract

Rhoptries are organelles that have important, complex roles in Apicomplexa biology. During Toxoplasma gondii infection, these organelles take part in several essential and complex processes that include host cell entry and parasite development. Using different electron microscopy techniques, we characterized the fine morphology of the rhoptries of two of the most important life stages of T. gondii: the tachyzoite and the bradyzoite forms. The observed tachyzoite and bradyzoite rhoptries had delimited regions characterized by a dark and electron-dense neck, an amorphous and less electron-dense bulb, and a region of intermediate electron density, which connects the bulb to the neck. Metal replicas of frozen-fractured tachyzoites showed intramembranous particles of different densities and sizes on the fractured faces of rhoptry membranes. Both in tachyzoites and bradyzoites, the intramembranous particles were arranged in distinctive parallel arrays that decorated most part of these organelles. Tubulo-vesicular subcompartments and free particles within the rhoptry lumen were observed on freeze-fractured replicas. Cryo-fixed, deep-etched samples showed several pore-like structures localized in the bulb portion. No obvious evidence was found of a possible connection between rhoptries and micronemes. Microsc. Res. Tech., 2011. © 2010 Wiley-Liss, Inc.
Copyright © 2010 Wiley-Liss, Inc.

KEYWORDS:

Toxoplasma, cryo-techniques, freeze-fracture, quick-freeze/deep-etching, rhoptry
PMID:
23939668
[PubMed - in process]

Mortality in Schizophrenia: Clinical and Serological Predictors

2013 Aug 13. [Epub ahead of print]

Mortality in Schizophrenia: Clinical and Serological Predictors

Source

Stanley Research Program, Sheppard Pratt Health System, Baltimore, MD;

Abstract

Persons with schizophrenia have a reduced life expectancy largely due to death from natural causes. Factors that have been previously associated with excess mortality include cigarette smoking and antipsychotic medication. The role of other environmental factors such as exposure to infectious agents has been the subject of only limited investigation. We prospectively assessed a cohort of persons with schizophrenia with a clinical evaluation and a blood sample from which antibodies to human herpes viruses and Toxoplasma gondii were measured. Mortality was determined with data from the National Death Index following a period of up to 11 years. We examined the role of demographic, serological, and clinical factors on mortality. A total of 25 (5%) of 517 persons died of natural causes. The standardized mortality ratio was 2.80 (95% CI 0.89, 6.38). After adjusting for age and gender, mortality from natural causes was predicted in separate models by cigarette smoking (relative risk [RR] = 4.66, P = .0029); lower cognitive score (RR = 0.96, P = .013); level of antibodies to Epstein-Barr virus (RR = 1.22, P = .0041) and to Herpes Simplex virus type 1 (RR = 1.19, P = .030); immunologic disease (RR = 3.14, P = .044); and genitourinary disease (RR = 2.70; P = .035). Because cigarette smoking confers an almost 5-fold risk of mortality, smoking cessation is an urgent priority. Having an elevated level of antibodies to Epstein-Barr virus and to Herpes Simplex virus type 1 are also significant predictors of death from natural causes.

KEYWORDS:

Epstein–Barr virus, cigarette smoking, premature death
PMID:
23943410
[PubMed - as supplied by publisher]

Tuesday, August 13, 2013

Small-molecule inhibition of a depalmitoylase enhances Toxoplasma host-cell invasion


 2013 Aug 11. doi: 10.1038/nchembio.1315. [Epub ahead of print]

Small-molecule inhibition of a depalmitoylase enhances Toxoplasma host-cell invasion

Source

Department of Pathology, Stanford University School of Medicine, Stanford, California, USA.

Abstract

Although there have been numerous advances in our understanding of how apicomplexan parasites such as Toxoplasma gondii enter host cells, many of the signaling pathways and enzymes involved in the organization of invasion mediators remain poorly defined. We recently performed a forward chemical-genetic screen in T. gondii and identified compounds that markedly enhanced infectivity. Although molecular dissection of invasion has benefited from the use of small-molecule inhibitors, the mechanisms underlying induction of invasion by small-molecule enhancers have never been described. Here we identify the Toxoplasma ortholog of human APT1, palmitoyl protein thioesterase-1 (TgPPT1), as the target of one class of small-molecule enhancers. Inhibition of this uncharacterized thioesterase triggered secretion of invasion-associated organelles, increased motility and enhanced the invasive capacity of tachyzoites. We demonstrate that TgPPT1 is a bona fide depalmitoylase, thereby establishing an important role for dynamic and reversible palmitoylation in host-cell invasion by T. gondii.
PMID:
 
23934245
 
[PubMed - as supplied by publisher]

Monday, August 12, 2013

The metabolic roles of the endosymbiotic organelles of Toxoplasma and Plasmodium spp

2013 Aug 5. pii: S1369-5274(13)00091-X. doi: 10.1016/j.mib.2013.07.003. [Epub ahead of print]

The metabolic roles of the endosymbiotic organelles of Toxoplasma and Plasmodium spp

Source

Center for Tropical and Emerging Global Diseases & Department of Cellular Biology, University of Georgia, 500 D.W. Brooks Drive, Athens, GA 30602, USA; Wellcome Trust Centre for Molecular Parasitology, Institute of Infection, Immunity & Inflammation, College of Medical, Veterinary & Life Sciences, Sir Graeme Davies Building, University of Glasgow, 120 University Place, Glasgow G12 8TA, United Kingdom. Electronic address: lilash@uga.edu.

Abstract

The apicoplast and the mitochondrion of Apicomplexa cooperate in providing essential metabolites. Their co-evolution during the ancestral acquisition of a plastid and subsequent loss of photosynthesis resulted in divergent metabolic pathways compared with mammals and plants. This is most evident in their chimerical haem synthesis pathway. Toxoplasma and Plasmodium mitochondria operate canonical tricarboxylic acid (TCA) cycles and electron transport chains, although the roles differ between Toxoplasma tachyzoites and Plasmodium erythrocytic stages. Glutamine catabolism provides TCA intermediates in both parasites. Isoprenoid precursor synthesis is the only essential role of the apicoplast in Plasmodium erythrocytic stages. An apicoplast-located fatty acid synthesis is dispensable in these stages, which instead predominantly salvage fatty acids, while in Plasmodium liver stages and in Toxoplasma tachyzoites fatty acid synthesis is an essential role of the plastid.
Published by Elsevier Ltd.
PMID:
23927894
[PubMed - as supplied by publisher]

Targeting tumors with nonreplicating Toxoplasma gondii uracil auxotroph vaccines

2013 Aug 5. pii: S1471-4922(13)00106-2. doi: 10.1016/j.pt.2013.07.001. [Epub ahead of print]

Targeting tumors with nonreplicating Toxoplasma gondii uracil auxotroph vaccines

Source

Department of Microbiology and Immunology, Geisel School of Medicine at Dartmouth, 1 Medical Center Drive, Lebanon, NH 03756, USA.

Abstract

Toxoplasma gondii is an intracellular parasite that has evolved to actively control its invaded host cells. Toxoplasma triggers then actively regulates host innate interleukin-12 (IL-12) and interferon-γ (IFN-γ) responses that elicit T cell control of infection. A live, nonreplicating avirulent uracil auxotroph vaccine strain (cps) of Toxoplasma triggers novel innate immune responses that stimulate amplified CD8+ T cell responses and life-long immunity in vaccinated mice. Here, we review recent reports showing that intratumoral treatment with cps activated immune-mediated regression of established solid tumors in mice. We speculate that a better understanding of host-parasite interaction at the molecular level and applying improved genetic models based on Δku80 Toxoplasma strains will stimulate development of highly effective immunotherapeutic cancer vaccine strategies using engineered uracil auxotrophs.
Copyright © 2013 Elsevier Ltd. All rights reserved.

KEYWORDS:

CD8(+) T cells, IL-12p70, Toxoplasma gondii, avirulent uracil auxotrophs, immunotherapy, tumor regression
PMID:
23928100
[PubMed - as supplied by publisher]

Thursday, August 08, 2013

The unusual dynamics of parasite actin result from isodesmic polymerization


 2013 Aug 7;4:2285. doi: 10.1038/ncomms3285.

The unusual dynamics of parasite actin result from isodesmic polymerization

Source

1] Department of Molecular Microbiology, Washington University School of Medicine, 660 South Euclid Avenue, St Louis, Missouri 63110-1093, USA [2].

Abstract

Previous reports have indicated that parasite actins are short and inherently unstable, despite being required for motility. Here we re-examine the polymerization properties of actin in Toxoplasma gondii, unexpectedly finding that it exhibits isodesmic polymerization in contrast to the conventional nucleation-elongation process of all previously studied actins from both eukaryotes and bacteria. Polymerization kinetics of actin in T. gondii lacks both a lag phase and critical concentration, normally characteristic of actins. Unique among actins, the kinetics of assembly can be fit with a single set of rate constants for all subunit interactions, without need for separate nucleation and elongation rates. This isodesmic model accurately predicts the assembly, disassembly and the size distribution of actin filaments in T. gondii in vitro, providing a mechanistic explanation for actin dynamics in vivo. Our findings expand the repertoire of mechanisms by which actin polymerization is governed and offer clues about the evolution of self-assembling, stabilized protein polymers.
PMID:
 
23921463
 
[PubMed - in process]

Wednesday, August 07, 2013

Characterisation of a serine hydrolase targeted by acyl protein thioesterase inhibitors in Toxoplasma gondii


 2013 Aug 2. [Epub ahead of print]

Characterisation of a serine hydrolase targeted by acyl protein thioesterase inhibitors in Toxoplasma gondii

Source

University of Geneva, Switzerland;

Abstract

In eukaryotic organisms, cysteine palmitoylation is an important reversible modification impacting on protein targeting, folding, stability and interactions with partners. Evidence suggests that protein palmitoylation contributes to key biological processes in Apicomplexa with the recent palmitome of the malaria parasite, Plasmodium falciparum, reporting over 400 substrates that are modified with palmitate by a broad range of Palmitoyl Acyl Transferases (PATs). Dynamic palmitoylation cycles require the action of an Acyl Protein Thioesterase (APT) that cleaves palmitate from substrates and conveys reversibility to this post-translational modification. In this work, we identified candidates for APT activity in Toxoplasma gondii. Treatment of parasites with low micromolar concentrations of beta-lactone or triazole urea-based inhibitors that target human APT1 show varied detrimental effects at multiple steps of the parasite lytic cycle. The use of an activity-based probe in combination with these inhibitors revealed the existence of several serine hydrolases that are targeted by APT1 inhibitors. The active serine hydrolase, TgASH1, was identified as the closest homologue to human APT1 and APT2 and characterized further. Biochemical analysis of TgASH1 indicated that this enzyme cleaves substrates with a similar specificity to APTs and homology modelling points toward an APT-like enzyme. TgASH1 is dispensable for parasite survival, which indicates that the severe effects observed with the beta-lactone inhibitors are caused by the inhibition of non-TgASH1 targets. Other ASH candidates for APT activity were functionally characterized and one of them was found resistant to gene disruption due either to an experimental failure or to the essential nature of the protein.

KEYWORDS:

Acyl protein thioesterase, Enzyme inhibitors, Hydrolases, Parasitology, Plasmodium falcuparum, Post translational modification, Protein palmitoylation, Serine hydrolase, Toxoplasma gondii, inhibitor
PMID:
 
23913689
 
[PubMed - as supplied by publisher]