Lytic Cycle of<i>Toxoplasma gondii</i>

Black, Michael W.; Boothroyd, John C.

doi:10.1128/mmbr.64.3.607-623.2000

Cited by 438 publications

(378 citation statements)

References 170 publications

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“…gondii is a member of the Apicomplexa, a phylum of parasites that includes several medically and agriculturally significant pathogens (Black and Boothroyd, 2000). Apicomplexans are obligate intracellular parasites; these protozoa only grow and replicate within host cells.…”

Section: Introductionmentioning

confidence: 99%

Dinitroanilines Bind α-Tubulin to Disrupt Microtubules

Morrissette

Mitra

Sept

et al. 2004

MBoC

135

153

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Protozoan parasites are remarkably sensitive to dinitroanilines such as oryzalin, which disrupt plant but not animal microtubules. To explore the basis of dinitroaniline action, we isolated 49 independent resistant Toxoplasma gondii lines after chemical mutagenesis. All 23 of the lines that we examined harbored single point mutations in ␣-tubulin. These point mutations were sufficient to confer resistance when transfected into wild-type parasites. Several mutations were in the M or N loops, which coordinate protofilament interactions in the microtubule, but most of the mutations were in the core of ␣-tubulin. Docking studies predict that oryzalin binds with an average affinity of 23 nM to a site located beneath the N loop of Toxoplasma ␣-tubulin. This binding site included residues that were mutated in several resistant lines. Moreover, parallel analysis of Bos taurus ␣-tubulin indicated that oryzalin did not interact with this site and had a significantly decreased, nonspecific affinity for vertebrate ␣-tubulin. We propose that the dinitroanilines act through a novel mechanism, by disrupting M-N loop contacts. These compounds also represent the first class of drugs that act on ␣-tubulin function. INTRODUCTIONMicrotubules are polymers constructed from ␣-␤-tubulin heterodimers (Downing and Nogales, 1998a,b). These structures are rapidly assembled and disassembled to create essential components of eukaryotic cells, such as spindles and flagella. The dynamic nature of microtubules makes them susceptible to pharmacological agents. Microtubule-disrupting and microtubule-stabilizing drugs have provided great insight into tubulin and microtubule function; they also have tremendous practical use. Compounds that perturb microtubule dynamics are currently some of the most effective drugs to treat medical conditions, including cancer, gout, and helminth infection (Jordan et al., 1998). Dinitroanilines (oryzalin, ethafluralin, and trifluralin) disrupt the microtubules of plants, ranging from the single-celled alga Chlamydomonas reinhardtii to higher plants such as the monocot Eleusine indica (James et al., 1993;Anthony et al., 1998;Zeng and Baird, 1999). Dinitroanilines also disrupt the microtubules of protozoa, including both free-living species such as Tetrahymena and protozoan parasites such as Trypanosoma spp., Leishmania spp., Entamoeba spp., Plasmodium falciparum, Cryptosporidium parvum, and Toxoplasma gondii (Chan and Fong, 1990;Chan et al., 1991;Gu et al., 1995;Edlind et al., 1996;Stokkermans et al., 1996;Armson et al., 1999; Makioka et al., 2000a,b;Traub-Cseko et al., 2001). Remarkably, the activity of dinitroanilines is restricted to plants and protozoa; these compounds are ineffective against vertebrate or fungal microtubules (Chan and Fong, 1990;Hugdahl and Morejohn, 1993;Murthy et al., 1994;Edlind et al., 1996).T. gondii is a member of the Apicomplexa, a phylum of parasites that includes several medically and agriculturally significant pathogens (Black and Boothroyd, 2000). Apicomplexans are obligate intracell...

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Section: Introductionmentioning

confidence: 99%

Dinitroanilines Bind α-Tubulin to Disrupt Microtubules

Morrissette

Mitra

Sept

et al. 2004

MBoC

135

153

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Section: Introductionmentioning

confidence: 99%

“…Host cell invasion by apicomplexan parasites is a complex, multistep process (reviewed in Black and Boothroyd, 2000;Chitnis and Blackman, 2000). In T. gondii, the asexual stage tachyzoites move over solid surfaces, including cells, by an unusual form of substrate-dependent gliding motility (Sibley et al, 1998;Hakansson et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

“…Host cell invasion is a critical step in the pathogenesis of the diseases caused by apicomplexan parasites, including toxoplasmosis. T. gondii represents an excellent model system for studying the relatively conserved process of apicomplexan invasion, because of the ease with which this parasite can be cultured and genetically manipulated (Roos et al, 1994;Black and Boothroyd, 2000;Kim and Weiss, 2004).Host cell invasion by apicomplexan parasites is a complex, multistep process (reviewed in Black and Boothroyd, 2000;Chitnis and Blackman, 2000). In T. gondii, the asexual stage tachyzoites move over solid surfaces, including cells, by an unusual form of substrate-dependent gliding motility (Sibley et al, 1998;Hakansson et al, 1999).…”

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confidence: 99%

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Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Mital

Meissner

Soldati

et al. 2005

MBoC

229

250

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Toxoplasma gondii is an obligate intracellular parasite and an important human pathogen. Relatively little is known about the proteins that orchestrate host cell invasion by T. gondii or related apicomplexan parasites (including Plasmodium spp., which cause malaria), due to the difficulty of studying essential genes in these organisms. We have used a recently developed regulatable promoter to create a conditional knockout of T. gondii apical membrane antigen-1 (TgAMA1). TgAMA1 is a transmembrane protein that localizes to the parasite's micronemes, secretory organelles that discharge during invasion. AMA1 proteins are conserved among apicomplexan parasites and are of intense interest as malaria vaccine candidates. We show here that T. gondii tachyzoites depleted of TgAMA1 are severely compromised in their ability to invade host cells, providing direct genetic evidence that AMA1 functions during invasion. The TgAMA1 deficiency has no effect on microneme secretion or initial attachment of the parasite to the host cell, but it does inhibit secretion of the rhoptries, organelles whose discharge is coupled to active host cell penetration. The data suggest a model in which attachment of the parasite to the host cell occurs in two distinct stages, the second of which requires TgAMA1 and is involved in regulating rhoptry secretion. INTRODUCTIONToxoplasma gondii is one of the one most common protozoan parasites of humans, infecting approximately one-third of the world's population. The disease caused by an acute T. gondii infection, toxoplasmosis, can be life threatening in the congenitally infected fetus and immunocompromised hosts. Like all members of the Phylum Apicomplexa, including Plasmodium spp. (the causative agents of malaria) and Cryptosporidium parvum (a significant worldwide cause of waterborne illness), T. gondii is an obligate intracellular parasite. Host cell invasion is a critical step in the pathogenesis of the diseases caused by apicomplexan parasites, including toxoplasmosis. T. gondii represents an excellent model system for studying the relatively conserved process of apicomplexan invasion, because of the ease with which this parasite can be cultured and genetically manipulated (Roos et al., 1994;Black and Boothroyd, 2000;Kim and Weiss, 2004).Host cell invasion by apicomplexan parasites is a complex, multistep process (reviewed in Black and Boothroyd, 2000;Chitnis and Blackman, 2000). In T. gondii, the asexual stage tachyzoites move over solid surfaces, including cells, by an unusual form of substrate-dependent gliding motility (Sibley et al., 1998;Hakansson et al., 1999). After the apical end of a parasite comes in contact with the host cell membrane, apical secretory organelles (micronemes and rhoptries) sequentially discharge their contents (Dubremetz et al., 1993;Carruthers and Sibley, 1997) and a zone of tight interaction forms between the two cells (Nichols and O'Connor, 1981;Dubremetz et al., 1985;Grimwood and Smith, 1995). An invagination in the host cell plasma membrane develops at the point ...

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“…A second way of transmission of T. gondii to humans is by the consumption of undercooked meat containing tissue cysts from a variety of animals that are susceptible to infection, including sheep, pigs, and poultry. Finally, T. gondii tachyzoites can also be transmitted from mother to developing fetus, leading to congenital disease (Black & Boothroyd, 2000). Toxoplasmosis in humans is commonly asymptomatic, but the symptoms can vary depending on the immune status of the patient and the clinical setting, that is, ocular or congenital toxoplasmosis (Montoya & Liesenfeld, 2004;Sharif et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Bothrops pirajai snake venom L-amino acid oxidase: in vitro effects on infection of Toxoplasma gondii in human foreskin fibroblasts

Izidoro¹,

Alves²,

Rodrigues³

et al. 2011

Rev. bras. farmacogn.

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Abstract:The effect of an L-amino acid oxidase isolated from Bothrops pirajai snake venom (BpirLAAO-I) was investigated on infection of Toxoplasma gondii in human foreskin fibroblasts (HFF). The cytotoxic activity of BpirLAAO-I on HFF cells showed a dose-dependent toxicity with median cytotoxic dose (TD50) of 11.8 µg/mL. BpirLAAO-I induced considerable dose-dependent decrease in the T. gondii infection index under two different conditions, treatment of tachyzoites before infection or treatment of HFF cells after infection. A maximal inhibition of infection (56%) was found for treatment before infection, with a median inhibitory dose (ID50) at 1.83 µg/mL and selectivity index (SI) at 6.45. For treatment after infection, it was observed a maximal inhibition of infection at 65%, ID50 of 1.20 µg/mL and SI of 9.83. The treatment before infection was also effective to reduce intracellular parasitism up to 62%, although presenting higher values of ID50 (3.14 µg/mL) and lower values of SI (3.76). However, treatment after infection was not effective, suggesting that the enzyme seems to have no effect on the parasite intracellular replication for this condition. In conclusion, BpirLAAO-I was more effective to inhibit the infection of neighboring cells and consequently parasite dissemination than primary infection and parasite replication. Thus, the effect of BpirLAAO-I described herein could be taken into account for the development of new synthetic anti-parasite therapeutic agents.

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Lytic Cycle ofToxoplasma gondii

Cited by 438 publications

References 170 publications

Dinitroanilines Bind α-Tubulin to Disrupt Microtubules

Dinitroanilines Bind α-Tubulin to Disrupt Microtubules

Conditional Expression ofToxoplasma gondiiApical Membrane Antigen-1 (TgAMA1) Demonstrates That TgAMA1 Plays a Critical Role in Host Cell Invasion

Bothrops pirajai snake venom L-amino acid oxidase: in vitro effects on infection of Toxoplasma gondii in human foreskin fibroblasts

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