Wednesday, July 23, 2014

Pantothenic acid biosynthesis in the parasite Toxoplasma gondii: a target for chemotherapy

2014 Jul 21. pii: AAC.02640-14. [Epub ahead of print
Toxoplasma gondii is a major food pathogen and neglected parasitic infection that causes eye disease, birth defects, and fetal abortion and plays a role as an opportunistic infection in AIDS. In this study, we investigated pantothenic acid (vitamin B5) biosynthesis in T. gondii. Genes encoding the full repertoire of enzymes for pantothenate synthesis and subsequent metabolism to Coenzyme A were identified and are expressed in T. gondii. A panel of inhibitors developed to target Mycobacterium tuberculosis pantothenate synthetase were tested and found to exhibit a range of inhibitions of growth of T. gondii. Two inhibitors exhibited lower effective concentrations than the current toxoplasmosis drug pyrimethamine. The inhibition was specific for the pantothenate pathway as the effect of the pantothenate synthetase inhibitors was abrogated by supplementation with pantothenate. Hence, T. gondii encodes and expresses the enzymes for pantothenate synthesis and this pathway is essential for parasite growth. These promising findings increase our understanding of growth and metabolism in this important parasite and highlight pantothenate synthetase as a new drug target.
Copyright © 2014, American Society for Microbiology. All Rights Reserved.
[PubMed - as supplied by publisher]

Repurposing the Open Access Malaria Box to discover potent inhibitors of Toxoplasma gondii and Entamoeba histolytica

2014 Jul 21. pii: AAC.02541-14. [Epub ahead of print]
Toxoplasmosis and amoebiasis are important public health concerns worldwide. Currently available drugs to control these diseases have proven their limitations. Therefore, innovative approaches should be adopted to identify and develop new leads from novel scaffolds exhibiting novel modes of actions. This paper describes results from the screening of Medicines for Malaria Venture's Open Access Malaria Box compounds in a search for new anti-Toxoplasma and anti-Entamoeba agents. Standard in vitro phenotypic screening procedures were adopted to assess the biological activities. Seven anti-Toxoplasma hits with IC50 < 5μM and selectivity indexes (SI) greater than 6 were identified. The most interesting hit compound was MMV007791, a piperazinacetamide, with an IC50 of 0.19 μM and a Selectivity Index greater than 157. Also, two compounds MMV666600 and MMV006861 were identified with modest activity against E. histolytica with IC50 values of 10.66 μM and 15.58 μM respectively. The anti-Toxoplasma hits identified in this study belong to different scaffold types than currently used drugs, underscoring their novelty and potential as starting points for the development of new anti-toxoplasmosis drugs with novel modes of action.
Copyright © 2014, American Society for Microbiology. All Rights Reserved.
[PubMed - as supplied by publisher]

Friday, July 18, 2014

BCKDH: The Missing Link in Apicomplexan Mitochondrial Metabolism Is Required for Full Virulence of Toxoplasma gondii and Plasmodium berghei

2014 Jul 17;10(7):e1004263. doi: 10.1371/journal.ppat.1004263. eCollection 2014.
While the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii are thought to primarily depend on glycolysis for ATP synthesis, recent studies have shown that they can fully catabolize glucose in a canonical TCA cycle. However, these parasites lack a mitochondrial isoform of pyruvate dehydrogenase and the identity of the enzyme that catalyses the conversion of pyruvate to acetyl-CoA remains enigmatic. Here we demonstrate that the mitochondrial branched chain ketoacid dehydrogenase (BCKDH) complex is the missing link, functionally replacing mitochondrial PDH in both T. gondii and P. berghei. Deletion of the E1a subunit of T. gondii and P. berghei BCKDH significantly impacted on intracellular growth and virulence of both parasites. Interestingly, disruption of the P. berghei E1a restricted parasite development to reticulocytes only and completely prevented maturation of oocysts during mosquito transmission. Overall this study highlights the importance of the molecular adaptation of BCKDH in this important class of pathogens.
[PubMed - as supplied by publisher]

Thursday, July 17, 2014

Toxoplasma gondii Ingests and Digests Host Cytosolic Proteins

2014 Jul 15;5(4). pii: e01188-14. doi: 10.1128/mBio.01188-14.
The protozoan parasite Toxoplasma gondii resides within a nonfusogenic vacuole during intracellular replication. Although the limiting membrane of this vacuole provides a protective barrier to acidification and degradation by lysosomal hydrolases, it also physically segregates the parasite from the host cytosol. Accordingly, it has been suggested that T. gondii acquires material from the host via membrane channels or transporters. The ability of the parasite to internalize macromolecules via endocytosis during intracellular replication has not been tested. Here, we show that Toxoplasma ingests host cytosolic proteins and digests them using cathepsin L and other proteases within its endolysosomal system. Ingestion was reduced in mutant parasites lacking an intravacuolar network of tubular membranes, implicating this apparatus as a possible conduit for trafficking to the parasite. Genetic ablation of proteins involved in the pathway is associated with diminished parasite replication and virulence attenuation. We show that both virulent type I and avirulent type II strain parasites ingest and digest host-derived protein, indicating that the pathway is not restricted to highly virulent strains. The findings provide the first definitive evidence that T. gondii internalizes proteins from the host during intracellular residence and suggest that protein digestion within the endolysosomal system of the parasite contributes to toxoplasmosis.


Toxoplasma gondii causes significant disease in individuals with weak immune systems. Treatment options for this infection have drawbacks, creating a need to understand how this parasite survives within the cells it infects as a prelude to interrupting its survival strategies. This study reveals that T. gondii internalizes proteins from the cytoplasm of the cells it infects and degrades such proteins within a digestive compartment within the parasite. Disruption of proteins involved in the pathway reduced parasite replication and lessened disease severity. The identification of a novel parasite ingestion pathway opens opportunities to interfere with this process and improve the outcome of infection.
Copyright © 2014 Dou et al.
[PubMed - in process]

Type II Toxoplasma gondii induction of CD40 on infected macrophages enhances IL-12 responses

2014 Jul 14. pii: IAI.01615-14. [Epub ahead of print]
Toxoplasma gondii is an obligate intracellular parasite that can cause severe neurological disease in infected humans. CD40 is a receptor on macrophages that plays a critical role in controlling T. gondii infection. We examined the regulation of CD40 on the surface of T. gondii-infected bone marrow-derived macrophages (BMdM). T. gondii induced CD40 expression at both the transcript level and on the cell surface, and interestingly, the effect was parasite strain-specific: CD40 levels were dramatically increased in type II T. gondii-infected BMdM compared to type I- or type III-infected cells. Type II induction of CD40 was specific to cells harboring intracellular parasites and detectable as early as 6 hours post-infection (hpi) at the transcript level. CD40 protein expression peaked at 18 hpi. Using forward genetics with progeny from a type II x type III cross, we found that CD40 induction mapped to a region of chromosome X that included the gene encoding the dense granule protein 15 (GRA15). Using type I parasites stably expressing the type II allele of GRA15 (GRA15II), we found that GRA15II induced the expression of CD40 on infected cells in an NF-κB-dependent manner. In addition, stable expression of HA-tagged GRA15II in THP-1 cells resulted in CD40 up-regulation in the absence of infection. Since CD40 signaling contributes to IL-12 production, we examined IL-12 from infected macrophages and found that CD40L engagement of CD40 amplified the IL-12 response in type II-infected cells. These data indicate that GRA15II induction of CD40 promotes parasite immunity through the production of IL-12.
Copyright © 2014, American Society for Microbiology. All Rights Reserved.
[PubMed - as supplied by publisher]

The use of transgenic parasites and host reporters to dissect the events that promote IL-12 production during toxoplasmosis

2014 Jul 14. pii: IAI.01643-14. [Epub ahead of print]
The intracellular parasite Toxoplasma gondii has multiple strategies to alter host cell function, including the injection of rhoptry proteins into the cytosol of host cells as well as bystander populations, but the consequence of these latter events is unclear. Here, a reporter system using fluorescent parasite strains that inject Cre recombinase with their rhoptry proteins (Toxoplasma-Cre) were combined with Ai6 Cre reporter mice to identify cells that have been productively infected, rhoptry-injected but lack the parasite, or that have phagocytosed T.gondii. The ability to distinguish these host-parasite interactions was then utilized to dissect the events that lead to the production of IL-12p40 that is required for resistance to T. gondii. In vivo, the use of invasion-competent or invasion-inhibited (phagocytosed) parasites with IL-12p40 (YET40) reporter mice revealed that DC and macrophage populations that phagocytose the parasite or are infected can express IL-12p40 but are not the major source as larger numbers of uninfected cells secrete this cytokine. Similarly, the use of Toxoplasma-Cre parasite strains indicated that dendritic cells and inflammatory monocytes untouched by the parasite and not cells injected by the parasite are the primary source of IL-12p40. These results imply that a soluble host or parasite factor are responsible for the bulk of IL-12p40 production in vivo rather than cellular interactions with T. gondii that result in infection, infection and clearance, injection of rhoptry proteins, or phagocytosis of the parasite.
Copyright © 2014, American Society for Microbiology. All Rights Reserved.
[PubMed - as supplied by publisher]

Wednesday, July 16, 2014

Does Toxoplasma play a role in curing cancer?

From the litter box to the laboratory, a microscopic organism native to cats shows promise in treating cancer. Researchers’ mutated strain of T. gondii has been found to reprogram the natural power of the immune system to kill cells. Found worldwide, T. gondii affects about one-third of the world's population, 60 million of which are Americans.

Toxoplasma gondii (T. gondii) is a single-celled parasite that is happiest in a cat's intestines, but it can live in any warm blooded animal. Found worldwide, T. gondii affects about one-third of the world's population, 60 million of which are Americans.
Credit: © Africa Studio / Fotolia
Toxoplasma gondii (T. gondii) is a single-celled parasite that is happiest in a cat's intestines, but it can live in any warm blooded animal. Found worldwide, T. gondii affects about one-third of the world's population, 60 million of which are Americans. Most people have no symptoms, but some experience a flu-like illness. Those with suppressed immune systems, however, can develop a serious infection if they are unable to fend off T. gondii.

An Anti-Cancer Agent in Nature?
A healthy immune system responds vigorously to T. gondii in a manner that parallels how the immune system attacks a tumor.
"We know biologically this parasite has figured out how to stimulate the exact immune responses you want to fight cancer," said David J. Bzik, PhD, professor of Microbiology and Immunology, Geisel School of Medicine at Dartmouth.
In response to T. gondii, the body produces natural killer cells and cytotoxic T cells. These cell types wage war against cancer cells. Cancer can shut down the body's defensive mechanisms, but introducing T. gondii into a tumor environment can jump start the immune system.
"The biology of this organism is inherently different from other microbe-based immunotherapeutic strategies that typically just tickle immune cells from the outside," said Barbara Fox, senior research associate of Microbiology and Immunology. "By gaining preferential access to the inside of powerful innate immune cell types, our mutated strain of T. gondii reprograms the natural power of the immune system to clear tumor cells and cancer."
Engineering T. gondii as a Cancer Vaccine
Since it isn't safe to inject a cancer patient with live replicating strains of T. gondii, Bzik and Fox created "cps," an immunotherapeutic vaccine. Based on the parasite's biochemical pathways, they delete a Toxoplasma gene needed to make a building block of its genome and create a mutant parasite that can be grown in the laboratory but is unable to reproduce in animals or people. Cps is both nonreplicating and safe. Even when the host is immune deficient, cps still retains that unique biology that stimulates the ideal vaccine responses.
"Aggressive cancers too often seem like fast moving train wrecks. Cps is the microscopic, but super strong, hero that catches the wayward trains, halts their progression, and shrinks them until they disappear," said Bzik.
Laboratory Success in Melanoma and Ovarian Cancers
Published laboratory studies from the Geisel School of Medicine at Dartmouth labs have tested the cps vaccine in extremely aggressive lethal mouse models of melanoma or ovarian cancer and found unprecedented high rates of cancer survival.
"Cps stimulates amazingly effective immunotherapy against cancers, superior to anything seen before," said Bzik. "The ability of cps to communicate in different and unique ways with the cancer and special cells of the immune system breaks the control that cancer has leveraged over the immune system."
A Promising Future for a Personalized Cancer Vaccine
This new weapon against cancer could even be tailored to the individual patient. "In translating cps therapy to the clinic, we imagine cps will be introduced into cells isolated from the patient. Then Trojan Horse cells harboring cps will be given back to the patient as an immunotherapeutic cancer vaccine to generate the ideal immune responses necessary to eradicate their cancer cells and to also provide life-long immunity against any future recurrence of that cancer," said Bzik.
Fox and Bzik say a lot more study is needed before cps leaves the laboratory. They are trying to understand how and why it works so well by examining its molecular targets and mechanisms.
"Cancer immunotherapy using cps holds incredible promise for creating beneficial new cancer treatments and cancer vaccines," said Bzik.

Story Source:
The above story is based on materials provided by Norris Cotton Cancer CenterDartmouth-Hitchcock Medical CenterNote: Materials may be edited for content and length.

Cite This Page:
Norris Cotton Cancer CenterDartmouth-Hitchcock Medical Center. "Does cat poop parasite play a role in curing cancer?." ScienceDaily. ScienceDaily, 15 July 2014. .

Saturday, July 12, 2014

Antibodies to Toxoplasma gondii and Cognitive Functioning in Schizophrenia, Bipolar Disorder, and Nonpsychiatric Controls

 2014 Jul 9. [Epub ahead of print]


Increased rates of exposure to Toxoplasma gondii have been found in individuals with schizophrenia and bipolar disorder, but the association between Toxoplasma and cognitive functioning has not previously been examined. We measured IgG and IgM class antibodies to Toxoplasma in 408 nonelderly individuals with schizophrenia, 347 with bipolar disorder, and 352 nonpsychiatric controls. Cognitive functioning was measured with the Repeatable Battery for the Assessment of Neuropsychological Status. Multivariate linear and regression analyses showed significant associations between Toxoplasma IgM antibody level and cognitive scores within the control group and the bipolar disorder group but not the schizophrenia group. Within the control group, having an elevated Toxoplasma IgM antibody level, greater than or equal to the 50th and 75th levels of the control group, was associated with significantly elevated odds of a low total cognitive score. Exposure to Toxoplasma may confer risk for lower cognitive functioning in persons without a psychiatric disorder and those with bipolar disorder.
[PubMed - as supplied by publisher]

1,4-Disubstituted Thiosemicarbazide Derivatives are Potent Inhibitors of Toxoplasma gondii Proliferation

 2014 Jul 9;19(7):9926-43. doi: 10.3390/molecules19079926.


A series of 4-arylthiosemicarbazides substituted at the N1 position with a 5-membered heteroaryl ring was synthesized and evaluated in vitro for T. gondii inhibition proliferation and host cell cytotoxicity. At non-toxic concentrations for the host cells all studied compounds displayed excellent anti-parasitic effects when compared to sulfadiazine, indicating a high selectivity of their anti-T. gondii activity. The differences in bioactivity investigated by DFT calculations suggest that the inhibitory activity of 4-aryl-thiosemicarbazides towards T. gondii proliferation is connected with the electronic structure of the molecule. Further, these compounds were tested as potential antibacterial agents. No growth-inhibiting effect on any of the test microorganisms was observed for all the compounds, even at high concentrations.
[PubMed - in process]

Monday, July 07, 2014

Calcium-dependent phosphorylation alters Class XIVa myosin function in the protozoan parasite Toxoplasma gondii

2014 Jul 2. pii: mbc.E13-11-0648. [Epub ahead of print]
Class XIVa myosins are a unique group of myosin motor proteins found in apicomplexan parasites, including those that cause malaria and toxoplasmosis. The founding member of the class XIVa family, Toxoplasma gondii myosin A (TgMyoA), is a monomeric unconventional myosin that functions at the parasite periphery to control gliding motility, host cell invasion and host cell egress. How the motor activity of TgMyoA is regulated during these critical steps in the parasite's lytic cycle is unknown. We show here that a small-molecule enhancer of T. gondii motility and invasion (compound 130038) causes an increase parasite intracellular calcium levels leading to a calcium-dependent increase in TgMyoA phosphorylation. Mutation of the major sites of phosphorylation altered parasite motile behavior upon compound 130038 treatment, and parasites expressing a non-phosphorylatable mutant myosin egressed from host cells more slowly in response to treatment with calcium ionophore. These data demonstrate that TgMyoA undergoes calcium-dependent phosphorylation, which modulates myosin-driven processes in this important human pathogen.
© 2014 by The American Society for Cell Biology.
[PubMed - as supplied by publisher]

Toxoplasmosis can be a sexually transmitted infection with serious clinical consequences

2014 Jun 14. pii: S0306-9877(14)00223-0. doi: 10.1016/j.mehy.2014.05.019. [Epub ahead of print]
Toxoplasma gondii infects about 30% of the human population. Common sources of infection are oocysts in cat faeces contaminating drinking water or unwashed vegetables, undercooked meat containing tissue cysts, and organ transplants from infected donors containing tissue cysts. However, very often, it is not possible to identify any potential source of infection in mothers of children with congenital toxoplasmosis. Here we present a hypothesis suggesting that toxoplasmosis is transmitted from infected men to noninfected women during unprotected sexual intercourse, which can result in the most serious form of disease, congenital toxoplasmosis. Arguments for the hypothesis: (1) Toxoplasma tachyzoites are present in the seminal fluid and tissue of the testes of various animals including humans. In some species infection of females by artificial insemination with semen from infected males has been observed. (2) Up to two thirds of Toxoplasma infections in pregnant women cannot be explained by the known risk factors. (3) Prevalence of toxoplasmosis in women in child-bearing age covaries with the incidence of sexually transmitted diseases in particular countries. (4) In some countries, an increased incidence of toxoplasmosis has been reported in women (but not men) aged 25-35years. This second peak of infection could be associated with women having regular unprotected sex after marriage. (5) Toxoplasmosis triggers schizophrenia in predisposed subjects. Onset of schizophrenia is about 2-3years earlier in men than in women. However, this difference in the onset can be found only between Toxoplasma-infected patients. The increased onset of schizophrenia in infected women could be associated with the already mentioned second peak of toxoplasmosis incidence. (6) The prevalence of toxoplasmosis decreases in developed countries in last 20years. This trend could be a result of decrease in promiscuity and increase in safe sex practices, both associated with the AIDS pandemics. (7) In women, probability of being Toxoplasma-infected correlates positively with the amount of unprotected sex with the child's father before the conception. Evidence against the hypothesis: Questionnaire study showed negative association between Toxoplasma infection and the number of earlier partners with whom the woman had unprotected sex. If our hypothesis turns out to be true, then sexual route of transmission, even if rare, could be responsible for a large part of cases of congenital toxoplasmosis. Women should be warned that having unprotected sex with men of positive or unknown toxoplasmosis status should be avoided during pregnancy.
Copyright © 2014 Elsevier Ltd. All rights reserved.
[PubMed - as supplied by publisher]

Rhoptry protein 6 from Toxoplasma gondii is an intrinsically disordered protein

2014 Jun 30. pii: S1046-5928(14)00155-7. doi: 10.1016/j.pep.2014.06.011. [Epub ahead of print]
Rhoptry protein 6 (ROP6) from Toxoplasma gondii is a 480-amino acid protein with no homology to any reported excretory or secretory protein. Especially, unlike the many other rhoptry protein types, ROP6 does not have a kinase domain. The biochemical and biophysical properties of ROP6 are unknown. Here, we investigated its structure using an in silico analysis method and overexpression and purification using an Escherichia coli system. The protein was purified to more than 85% homogeneity using immobilized metal affinity chromatography in denaturing conditions. After purification, ROP6 showed slow migration in SDS-PAGE, including fast proteolysis. This implies that ROP6 has a high percentage of flexible regions or extended loop structures. Secondary structure prediction and prediction of intrinsically disordered regions by using various bioinformatics tools, indicated that approximately 60% of ROP6 is predicted to be intrinsically disordered or random coil regions. These observations indicate that ROP6 is an intrinsically disordered protein.
[PubMed - as supplied by publisher]

NLR proteins and parasitic disease

2014 Jul 3. [Epub ahead of print]
Parasitic diseases are a serious global health concern. Many of the most common and most severe parasitic diseases, including Chagas' disease, leishmaniasis, and schistosomiasis, are also classified as neglected tropical diseases and are comparatively less studied than infectious diseases prevalent in high income nations. The NLRs (nucleotide-binding domain leucine-rich-repeat-containing proteins) are cytosolic proteins known to be involved in pathogen detection and host response. The role of NLRs in the host response to parasitic infection is just beginning to be understood. The NLR proteins NOD1 and NOD2 have been shown to contribute to immune responses during Trypanosoma cruzi infection, Toxoplasma gondii infection, and murine cerebral malaria. The NLRP3 inflammasome is activated by T. cruzi and Leishmania amazonensis but also induces pathology during infection with schistosomes or malaria. Both the NLRP1 and NLRP3 inflammasomes respond to T. gondii infection. The NLRs may play crucial roles in human immune responses during parasitic infection, usually acting as innate immune sensors and driving the inflammatory response against invading parasites. However, this inflammatory response can either kill the invading parasite or be responsible for destructive pathology. Therefore, understanding the role of the NLR proteins will be critical to understanding the host defense against parasites as well as the fine balance between homeostasis and parasitic disease.
[PubMed - as supplied by publisher]

Microplate assay for screening Toxoplasma gondii bradyzoite differentiation with DUAL luciferase assay

2014 Jun 30. pii: S0003-2697(14)00277-2. doi: 10.1016/j.ab.2014.06.018. [Epub ahead of print]
Toxoplasma gondii can differentiate into tachyzoites or bradyzoites. To accelerate the investigation of bradyzoite differentiation mechanisms, we constructed a reporter parasite, PLK/DLUC_1C9, for a high-throughput assay. PLK/DLUC_1C9 expressed firefly luciferase under the bradyzoite-specific BAG1 promoter. Firefly luciferase activity was detected with a minimum of 102 parasites induced by pH 8.1. To normalize bradyzoite differentiation, PLK/DLUC_1C9 expressed Renilla luciferase under the parasite's alpha-tubulin promoter. Renilla luciferase activity was detected with at least 102 parasites. By using PLK/DLUC_1C9 with this 96-well format screening system, we found that the protein kinase inhibitor analogs "bumped kinase inhibitors 1NM-PP1, 3MB-PP1, and 3BrB-PP1, had bradyzoite-inducing effects.
PMID: 24991689

Midichlorians - the biomeme hypothesis: is there a microbial component to religious rituals?

2014 Jul 2;9(1):14. [Epub ahead of print]


Cutting edge research of human microbiome diversity has led to the development of the microbiome-gut-brain axis concept, based on the idea that gut microbes may have an impact on the behavior of their human hosts. Many examples of behavior-altering parasites are known to affect members of the animal kingdom. Some prominent examples include Ophiocordyceps unilateralis (fungi), Toxoplasma gondii (protista), Wolbachia (bacteria), Glyptapanteles sp. (arthropoda), Spinochordodes tellinii (nematomorpha) and Dicrocoelium dendriticum (flat worm). These organisms belong to a very diverse set of taxonomic groups suggesting that the phenomena of parasitic host control might be more common in nature than currently established and possibly overlooked in humans.


Some microorganisms would gain an evolutionary advantage by encouraging human hosts to perform certain rituals that favor microbial transmission. We hypothesize that certain aspects of religious behavior observed in the human society could be influenced by microbial host control and that the transmission of some religious rituals could be regarded as the simultaneous transmission of both ideas (memes) and parasitic organisms.


We predict that next-generation microbiome sequencing of samples obtained from gut or brain tissues of control subjects and subjects with a history of voluntary active participation in certain religious rituals that promote microbial transmission will lead to the discovery of microbes, whose presence has a consistent and positive association with religious behavior. Our hypothesis also predicts a decline of participation in religious rituals in societies with improved sanitation.


If proven true, our hypothesis may provide insights on the origin and pervasiveness of certain religious practices and provide an alternative explanation for recently published positive associations between parasite-stress and religiosity. The discovery of novel microorganisms that affect host behavior may improve our understanding of neurobiology and neurochemistry, while the diversity of such organisms may be of interest to evolutionary biologists and religious scholars.Reviewers: This article was reviewed by Prof. Dan Graur, Dr. Rob Knight and Dr. Eugene Koonin.
[PubMed - as supplied by publisher]

Tuesday, July 01, 2014

Vacuolar-H+ -Pyrophosphatase (TgVP1) is Required for Microneme Secretion, Host Cell Invasion, and Extracellular Survival of Toxoplasma gondii

2014 Jun 26. doi: 10.1111/mmi.12685. [Epub ahead of print]
The vacuolar proton pyrophosphatase (H+ -PPase) of Toxoplasma gondii (TgVP1), a membrane proton pump, localizes to acidocalcisomes and a novel lysosome-like compartment termed plant-like vacuole (PLV) or vacuolar compartment (VAC). We report the characterization of a T. gondii null mutant for the TgVP1 gene. Propagation of these mutants decreased significantly because of deficient attachment and invasion of host cells, which correlated with deficient microneme secretion. Processing of cathepsin L (CPL) in these mutants was deficient only when the parasites were incubated in the presence of low concentrations of the vacuolar H+ -ATPase (V-H+ -ATPase) inhibitor bafilomycin A1 , suggesting that either TgVP1 or the T. gondii V-H+ -ATPase (TgVATPase) are sufficient to support CPL processing. The lack of TgVP1 did not affect processing of micronemal proteins, indicating that it does not contribute to proMIC maturations. The TgVP1 null mutants were more sensitive to extracellular conditions and were less virulent in mice. We demonstrate that T. gondii tachyzoites possess regulatory volume decrease capability during hypo-osmotic stress and this ability is impaired in TgVP1 null mutants implicating TgVP1 in osmoregulation. We hypothesize that osmoregulation is needed for host cell invasion and that TgVP1 plays a role during the normal lytic cycle of T. gondii.
PMID: 24975633