Egress from host cells is a crucial step in the life cycle of intracellular pathogens including the parasitic protozoan Toxoplasma gondii. T. gondii can cause severe disease during pregnancy or immune dysfunction, and debilitating ocular pathology in otherwise healthy people. After intracellular replication, the parasite ruptures from host cells in a manner shared by other parasites including Plasmodium. Lytic egress frees the parasite to infect new host cells but the ensuing damage also fuels inflammation and fever, hallmarks of toxoplasmosis and malaria. We recently showed that T. gondii rapid egress and fatal acute disease both depend on the timely secretion of a pore-forming protein, TgPLP1. Our finding that TgPLP1 is released from apical micronemes exposed a novel role for these regulated secretory organelles. How TgPLP1 lyses host membranes during egress is not known. The absence of such knowledge precludes strategic efforts to extinguish its activity and alter the course of infection. Our long-term goal is to understand the roles of key microneme proteins in T. gondii infection. The objective for this funding period is to determine how TgPLP1 selectively and rapidly lyses host cell membranes during egress without causing parasite self-damage. We hypothesize that TgPLP1 pore formation is dictated by the lipid composition of its target membranes, environmental factors, and specific structural features of the protein. This assertion is based on preliminary data identifying host lipid receptors targeted for selective lysis, potential roles for pH and proteolysis in regulating pore formation, and conserved structural features of TgPLP1 predicted to drive membrane binding and oligomerization.
The specific aims are: (1) Reveal the mechanism for selective cytolysis of host but not parasite membranes;(2) Uncover how TgPLP1 is active during egress but not during invasion;and (3) Identify the molecular basis for rapid pore formation. By providing a deeper mechanistic understanding of an essential step in the T. gondii life cycle, we expect the proposed work will create novel opportunities to interrupt infection and potentially ameliorate disease.

Public Health Relevance

We seek to understand how a putative pore forming protein called TgPLP1 facilitates cell egress by the human parasite Toxoplasma gondii. TgPLP1 belongs to a family of pore forming proteins are used for both for microbial aggression and host defense. Our work will reveal mechanistic and regulatory features of pore formation that are relevant to a broad range of microbial infections and immune-related diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI046675-14
Application #
8451408
Study Section
Pathogenic Eukaryotes Study Section (PTHE)
Program Officer
Mcgugan, Glen C
Project Start
1999-12-01
Project End
2016-04-30
Budget Start
2013-05-01
Budget End
2014-04-30
Support Year
14
Fiscal Year
2013
Total Cost
$321,981
Indirect Cost
$110,481
Name
University of Michigan Ann Arbor
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
073133571
City
Ann Arbor
State
MI
Country
United States
Zip Code
48109
Huynh, My-Hang; Carruthers, Vern B (2016) A Toxoplasma gondii Ortholog of Plasmodium GAMA Contributes to Parasite Attachment and Cell Invasion. mSphere 1:
Pszenny, Viviana; Ehrenman, Karen; Romano, Julia D et al. (2016) A Lipolytic Lecithin:Cholesterol Acyltransferase Secreted by Toxoplasma Facilitates Parasite Replication and Egress. J Biol Chem 291:3725-46
Lunghi, Matteo; Spano, Furio; Magini, Alessandro et al. (2016) Alternative splicing mechanisms orchestrating post-transcriptional gene expression: intron retention and the intron-rich genome of apicomplexan parasites. Curr Genet 62:31-8
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Bullen, Hayley E; Jia, Yonggen; Yamaryo-Botté, Yoshiki et al. (2016) Phosphatidic Acid-Mediated Signaling Regulates Microneme Secretion in Toxoplasma. Cell Host Microbe 19:349-60
Carruthers, Vern B (2015) Parasites and their heterophagic appetite for disease. PLoS Pathog 11:e1004803
Huynh, My-Hang; Boulanger, Martin J; Carruthers, Vern B (2014) A conserved apicomplexan microneme protein contributes to Toxoplasma gondii invasion and virulence. Infect Immun 82:4358-68
Kremer, Katrin; Kamin, Dirk; Rittweger, Eva et al. (2013) An overexpression screen of Toxoplasma gondii Rab-GTPases reveals distinct transport routes to the micronemes. PLoS Pathog 9:e1003213
Gaji, Rajshekhar Y; Huynh, My-Hang; Carruthers, Vern B (2013) A novel high throughput invasion screen identifies host actin regulators required for efficient cell entry by Toxoplasma gondii. PLoS One 8:e64693
Tomavo, Stanislas; Slomianny, Christian; Meissner, Markus et al. (2013) Protein trafficking through the endosomal system prepares intracellular parasites for a home invasion. PLoS Pathog 9:e1003629

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