Toxoplasma gondii Microneme Secretion Involves Intracellular Ca2+ Release from Inositol 1,4,5-Triphosphate (IP3)/Ryanodine-sensitive Stores

Lovett, Jennie L.; Marchesini, Norma; Moreno, Silvia N.J.; Sibley, L. David

doi:10.1074/jbc.m202553200

Cited by 161 publications

(175 citation statements)

References 46 publications

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“…Recent findings have established that host cell Ca 2C is not essential but that intracellular stores of Ca 2C in T. gondii are both necessary and sufficient to support microneme secretion and to initiate motility and host cell entry [32]. [33]. Collectively, these data suggest that an unknown receptor senses host cell stimuli and activates PLC to produce Ins(1,4,5)P 3 , which then operates as a second messenger and mediates intracellular Ca 2C release by opening a specific Ca 2C channel of the Ins(1,4,5)P 3 /ryanodine receptor superfamily.…”

Section: Host Cell Invasion Parasitophorous Vacuole Formation and Egmentioning

confidence: 99%

Molecular and functional aspects of parasite invasion

Soldati

Foth

Cowman

2004

Trends in Parasitology

109

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Apicomplexan parasites have evolved an efficient mechanism to gain entry into non-phagocytic cells, hence challenging their hosts by the establishment of infection in immuno-privileged tissues. Gliding motility is a prerequisite for the invasive stage of most apicomplexans, allowing them to migrate across tissues, and actively invade and egress host cells. In the late 1960s, detailed morphological studies revealed that motile apicomplexans share an elaborate architecture comprising a subpellicular cytoskeleton and apical organelles. Since 1993, the development of technologies for transient and stable transfection have provided powerful tools with which to identify gene products associated with these structures and organelles, as well as to understand their functions. In combination with access to several parasite genomes, it is now possible to compare and contrast the strategies and molecular machines that have been selectively designed by distinct life stages within a species, or by different apicomplexan species, to optimize infection

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Section: Host Cell Invasion Parasitophorous Vacuole Formation and Egmentioning

confidence: 99%

Molecular and functional aspects of parasite invasion

Soldati

Foth

Cowman

2004

Trends in Parasitology

109

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“…The amount of MIC5 secreted into the culture supernatant by ⌬ama1/ AMA1-myc parasites was analyzed by Western blotting. There was no observable difference in the amount of MIC5 secreted, either constitutively or in response to calcium ionophore Lovett et al, 2002), by parasites grown with or without Atc ( Figure 5). Similar results were seen with a second microneme protein, MIC10, and when AMA1/AMA1-myc and ⌬ama1/AMA1-myc parasites were compared (unpublished data).…”

Section: A Tgama1 Deficiency Does Not Affect the Early Steps Of Invasionmentioning

confidence: 99%

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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“…In studies first performed in Toxoplasma, equalizing Ca 2ϩ gradients across membranes with A23187, or liberating Ca 2ϩ from intracellular stores with ethanol, stimulated microneme secretion, whereas chelating intracellular Ca 2ϩ with BAPTA-AM blocked it (5,6). Ethanol is thought to act by activating phospholipase C and inducing production of inositol trisphosphate (IP 3 ) production followed by release of intracellular Ca 2ϩ (7). A variety of alcohols in addition to acetaldehyde show this activity in T. gondii, although we have chosen to use ethanol here as it is the most potent secretagogue (7).…”

mentioning

confidence: 99%

“…Ethanol is thought to act by activating phospholipase C and inducing production of inositol trisphosphate (IP 3 ) production followed by release of intracellular Ca 2ϩ (7). A variety of alcohols in addition to acetaldehyde show this activity in T. gondii, although we have chosen to use ethanol here as it is the most potent secretagogue (7). The downstream effectors that regulate Ca 2ϩ -dependent microneme secretion include the kinases TgCDPK1 (8) and TgCDPK3 (9 -11) as well as other downstream Ca 2ϩ effectors including TgPRP1 (12), TgDJ-1 (13), and TgDOC2.1 (14).…”

mentioning

confidence: 99%

Serum Albumin Stimulates Protein Kinase G-dependent Microneme Secretion in Toxoplasma gondii

Brown

Lourido

Sibley

2016

Journal of Biological Chemistry

Self Cite

103

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Microneme secretion is essential for motility, invasion, and egress in apicomplexan parasites. Although previous studies indicate that Ca 2؉ and cGMP control microneme secretion, little is known about how these pathways are naturally activated. Here we have developed genetically encoded indicators for Ca 2؉ and microneme secretion to better define the signaling pathways that regulate these processes in Toxoplasma gondii. We found that microneme secretion was triggered in vitro by exposure to a single host protein, serum albumin. The natural agonist serum albumin induced microneme secretion in a protein kinase G-dependent manner that correlated with increased cGMP levels. Surprisingly, serum albumin acted independently of elevated Ca 2؉ and yet it was augmented by artificial agonists that raise Ca 2؉ , such as ethanol. Furthermore, although ethanol elevated intracellular Ca 2؉ , it alone was unable to trigger secretion without the presence of serum or serum albumin. This dichotomy was recapitulated by zaprinast, a phosphodiesterase inhibitor that elevated cGMP and separately increased Ca 2؉ in a protein kinase G-independent manner leading to microneme secretion. Taken together, these findings reveal that microneme secretion is centrally controlled by protein kinase G and that this pathway is further augmented by elevation of intracellular Ca 2؉ .Toxoplasma gondii is an important opportunistic pathogen and model organism for studying the biology of members of the phylum Apicomplexa (1). Micronemes are specialized secretory vesicles present in all motile stages of apicomplexan parasites (reviewed in Ref. 2). The majority of internal microneme (MIC) 3 proteins (i.e. cargo) consist of adhesive proteins that translocate to the surface of the parasite following the regulated fusion of the organelle with the apical plasma membrane.

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Toxoplasma gondii Microneme Secretion Involves Intracellular Ca2+ Release from Inositol 1,4,5-Triphosphate (IP3)/Ryanodine-sensitive Stores

Cited by 161 publications

References 46 publications

Molecular and functional aspects of parasite invasion

Molecular and functional aspects of parasite invasion

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

Serum Albumin Stimulates Protein Kinase G-dependent Microneme Secretion in Toxoplasma gondii

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