title: A Novel Secreted Protein, MYR1, Is Central to Toxoplasma's Manipulation of Host Cells.
abstract: The intracellular protozoan Toxoplasma gondii dramatically reprograms the transcriptome of host cells it infects, including substantially up-regulating the host oncogene c-myc. By applying a flow cytometry-based selection to infected mouse cells expressing green fluorescent protein fused to c-Myc (c-Myc-GFP), we isolated mutant tachyzoites defective in this host c-Myc up-regulation. Whole-genome sequencing of three such mutants led to the identification of MYR1 (Myc regulation 1; TGGT1_254470) as essential for c-Myc induction. MYR1 is a secreted protein that requires TgASP5 to be cleaved into two stable portions, both of which are ultimately found within the parasitophorous vacuole and at the parasitophorous vacuole membrane. Deletion of MYR1 revealed that in addition to its requirement for c-Myc up-regulation, the MYR1 protein is needed for the ability of Toxoplasma tachyzoites to modulate several other important host pathways, including those mediated by the dense granule effectors GRA16 and GRA24. This result, combined with its location at the parasitophorous vacuole membrane, suggested that MYR1 might be a component of the machinery that translocates Toxoplasma effectors from the parasitophorous vacuole into the host cytosol. Support for this possibility was obtained by showing that transit of GRA24 to the host nucleus is indeed MYR1-dependent. As predicted by this pleiotropic phenotype, parasites deficient in MYR1 were found to be severely attenuated in a mouse model of infection. We conclude, therefore, that MYR1 is a novel protein that plays a critical role in how Toxoplasma delivers effector proteins to the infected host cell and that this is crucial to virulence.
  
  
  OBJECTIVE
  Toxoplasma gondii is an important human pathogen and a model for the study of intracellular parasitism. Infection of the host cell with Toxoplasma tachyzoites involves the introduction of protein effectors, including many that are initially secreted into the parasitophorous vacuole but must ultimately translocate to the host cell cytosol to function. The work reported here identified a novel protein that is required for this translocation. These results give new insight into a very unusual cell biology process as well as providing a potential handle on a pathway that is necessary for virulence and, therefore, a new potential target for chemotherapy.
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, USA Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, California, USA.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Franco
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Panas
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Nicole D
authors.initials: ND
authors.lastname: Marino
authors.affiliation: Department of Biomolecular Engineering, University of California, Santa Cruz, California, USA.
authors.forename: Mei-Chong Wendy
authors.initials: MC
authors.lastname: Lee
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Kerry R
authors.initials: KR
authors.lastname: Buchholz
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, USA.
authors.forename: Felice D
authors.initials: FD
authors.lastname: Kelly
authors.affiliation: Department of Pediatrics, Washington University in St. Louis, St. Louis, Missouri, USA.
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Bednarski
authors.affiliation: Department of Pathology and Immunology, Washington University in St. Louis, St. Louis, Missouri, USA.
authors.forename: Barry P
authors.initials: BP
authors.lastname: Sleckman
authors.affiliation: Department of Biomolecular Engineering, University of California, Santa Cruz, California, USA.
authors.forename: Nader
authors.initials: N
authors.lastname: Pourmand
authors.affiliation: Department of Microbiology and Immunology, Stanford University School of Medicine, Stanford, California, USA jboothr@stanford.edu.
authors.forename: John C
authors.initials: JC
authors.lastname: Boothroyd
mesh_terms: D000818:Animals; D017353:Gene Deletion; D054884:Host-Pathogen Interactions; D008264:Macrophages / Q000469:parasitology; D051379:Mice; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D014122:Toxoplasma / Q000502:physiology*; D014124:Toxoplasmosis, Animal / Q000469:parasitology / Q000473:pathology; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D015800:Protozoan Proteins; D037521:Virulence Factors
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