The Apicomplexa comprise a medically important phylum of obligate intracellular parasites, including Plasmodium falciparum, the causative agent of malaria, Cryptosporidium, which causes gastrointestinal disease, and the category B agent Toxoplasma gondii, which can be pathogenic in immunocompromised hosts and the developing fetus. Drug therapies that effectively treat all stages of some of these parasites are currently lacking and in many cases existing drugs are quickly becoming ineffective due to the emergence of drug-resistant parasite strains. Thus, the discovery of new targets for drug design and the understanding of resistance mechanisms are high priorities in the studies of apicomplexan parasites. Our approach to this challenge has been to isolate and characterize T. gondii mutants that are resistant to specific anti- parasitic drugs. We have recently discovered that disruption of a mitochondrial MutS homologue (MSH), TgMSH-1, directly confers multi-drug resistance in T. gondii. MSHs are critical components of the eukaryotic DNA mismatch repair machinery and are also involved in signaling cell cycle arrest and apoptosis in response to DNA damaging agents. Interestingly, we have observed that certain anti-parasitic drugs cause disruption in the expression of cell cycle markers in a TgMSH1 dependent manner. Thus, we have identified a novel pathway in T. gondii, that when induced by certain drugs leads to parasite death. It is our hypothesis that that certain drugs affect the mitochondrion of the parasite directly or indirectly and that this effect results in the activation of a signaling pathway, which includes TgMSH1 and results in parasite death. It is our goal to dissect this TgMSH1 dependent death mechanism as to characterize a novel mode of killing apicomplexan parasites. Using a combination of cell biology, biochemistry and genomic approaches we will determine the effect of TgMSH1-dependent drugs on mitochondrial function, identify signaling partners of TgMHS1 and determine the effect of TgMSH1 dependent drugs on cell cycle. The completion of these aims will elucidate the details and mechanisms of an inducible death pathway. This constitutes an innovative approach to the discovery of drug targets in this important pathogen.

Public Health Relevance

Toxoplasma gondii is a common parasitic infection in humans. Drugs against this parasite are limited and can often cause severe side effects. Thus, new drugs against Toxoplasma are critically needed. We have discovered a mechanism by which the parasite can be induced to die. It is our goal to understand all the players and events involved in this inducible death pathway as a means to discover novel targets for drug development.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Drug Discovery and Mechanisms of Antimicrobial Resistance Study Section (DDR)
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Rogers, Martin J
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Indiana University-Purdue University at Indianapolis
Schools of Medicine
United States
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Padgett, Leah R; Arrizabalaga, Gustavo; Sullivan Jr, William J (2017) Targeting of tail-anchored membrane proteins to subcellular organelles in Toxoplasma gondii. Traffic 18:149-158
Garbuz, Tamila; Arrizabalaga, Gustavo (2017) Lack of mitochondrial MutS homolog 1 in Toxoplasma gondii disrupts maintenance and fidelity of mitochondrial DNA and reveals metabolic plasticity. PLoS One 12:e0188040
Charvat, Robert A; Arrizabalaga, Gustavo (2016) Oxidative stress generated during monensin treatment contributes to altered Toxoplasma gondii mitochondrial function. Sci Rep 6:22997
Varberg, Joseph M; Padgett, Leah R; Arrizabalaga, Gustavo et al. (2016) TgATAT-Mediated ?-Tubulin Acetylation Is Required for Division of the Protozoan Parasite Toxoplasma gondii. mSphere 1:
Gaji, Rajshekhar Y; Johnson, Derrick E; Treeck, Moritz et al. (2015) Phosphorylation of a Myosin Motor by TgCDPK3 Facilitates Rapid Initiation of Motility during Toxoplasma gondii egress. PLoS Pathog 11:e1005268
Garrison, Erin; Treeck, Moritz; Ehret, Emma et al. (2012) A forward genetic screen reveals that calcium-dependent protein kinase 3 regulates egress in Toxoplasma. PLoS Pathog 8:e1003049
Lavine, Mark D; Arrizabalaga, Gustavo (2012) Analysis of monensin sensitivity in Toxoplasma gondii reveals autophagy as a mechanism for drug induced death. PLoS One 7:e42107
Hass, Jamie L; Garrison, Erin M; Wicher, Sarah A et al. (2012) Synthetic osteogenic extracellular matrix formed by coated silicon dioxide nanosprings. J Nanobiotechnology 10:6
Lavine, Mark D; Arrizabalaga, Gustavo (2011) The antibiotic monensin causes cell cycle disruption of Toxoplasma gondii mediated through the DNA repair enzyme TgMSH-1. Antimicrob Agents Chemother 55:745-55
Francia, Maria E; Wicher, Sarah; Pace, Douglas A et al. (2011) A Toxoplasma gondii protein with homology to intracellular type Na?/H? exchangers is important for osmoregulation and invasion. Exp Cell Res 317:1382-96

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