Role of the parafusin orthologue, PRP1, in microneme exocytosis and cell invasion in Toxoplasma gondii

Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.
Cellular Microbiology (Impact Factor: 4.92). 10/2003; 5(9):613-24. DOI: 10.1046/j.1462-5822.2003.00305.x
Source: PubMed


The association of PRP1, a Paramecium parafusin orthologue, with Toxoplasma gondii micronemes, now confirmed by immunoelectron microscopy, has here been studied in relation to exocytosis and cell invasion. PRP1 becomes labelled in vivo by inorganic 32P and is dephosphorylated when ethanol is used to stimulate Ca2+-dependent exocytosis of the micronemes. The ethanol Ca2+-stimulated exocytosis is accompanied by translocation of PRP1 and microneme content protein (MIC3) from the apical end of the parasite. Immunoblotting showed that PRP1 is redistributed inside the parasite, while microneme content is secreted. To study whether similar changes occur during cell invasion, quantitative microscopy was performed during secretion, invasion and exit (egress) from the host cell. Time-course experiments showed that fluorescence intensities of PRP1 and MIC3 immediately after invasion were reduced 10-fold compared to preinvasion levels, indicating that PRP1 translocation and microneme secretion accompanies invasion. MIC3 regained fluorescence intensity and apical distribution after 15 min, while PRP1 recovered after 1 h. Intensity of both proteins then increased throughout the parasite division period until host cell lysis, suggesting the need to secrete microneme proteins to egress. These studies suggest that PRP1 associated with the secretory vesicle scaffold serves an important role in Ca2+-regulated exocytosis and cell invasion.

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Available from: Kami Kim, Mar 06, 2014
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    • "This, however, does not preclude a role in some other phenomena accompanying exocytosis, assuming that a Paramecium cell does not de-and re-phosphorylate an important protein without any need. In fact, a role for pp63/pf in Toxoplasma gondii is reported in host cell penetration [34]. In sum, its role remained open and will be discussed here in the context of present knowledge. "
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    ABSTRACT: Trichocyst discharge in Paramecium is associated with a calcium-dependent dephosphoglucosylation of the protein parafusin (PFUS), which is believed to be a critical step in the exocytosis cascade. After trichocyst release PFUS dissociates from the empty trichocyst capsule and remains in the cytosol until a new trichocyst develops.The minute tachyzoite of the apicomplexan parasite Toxoplasma contains three types of secretory organelle, the exocytoses of two of which, the micronemes and rhoptries, are essential for invasion of host cells. The discharge of micronemes is a calcium-dependent event, and an ortholog of PFUS, named parafusin-related protein (PRP1), has been found to co-localize with antibodies to microneme contents. The distribution of PRP1 changes upon discharge of micronemes, and localized staining of PRP1 disappeared only to reappear as new micronemes were formed.These results suggest that PFUS, PRP1 and probably other PFUS orthologs have a conserved role in calcium-dependent exocytosis in alveolates.
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