title: Toxoplasma gondii Cyclic AMP-Dependent Protein Kinase Subunit 3 Is Involved in the Switch from Tachyzoite to Bradyzoite Development.
abstract: Toxoplasma gondii is an obligate intracellular apicomplexan parasite that infects warm-blooded vertebrates, including humans. Asexual reproduction in T. gondii allows it to switch between the rapidly replicating tachyzoite and quiescent bradyzoite life cycle stages. A transient cyclic AMP (cAMP) pulse promotes bradyzoite differentiation, whereas a prolonged elevation of cAMP inhibits this process. We investigated the mechanism(s) by which differential modulation of cAMP exerts a bidirectional effect on parasite differentiation. There are three protein kinase A (PKA) catalytic subunits (TgPKAc1 to -3) expressed in T. gondii Unlike TgPKAc1 and TgPKAc2, which are conserved in the phylum Apicomplexa, TgPKAc3 appears evolutionarily divergent and specific to coccidian parasites. TgPKAc1 and TgPKAc2 are distributed in the cytomembranes, whereas TgPKAc3 resides in the cytosol. TgPKAc3 was genetically ablated in a type II cyst-forming strain of T. gondii (PruΔku80Δhxgprt) and in a type I strain (RHΔku80Δhxgprt), which typically does not form cysts. The Δpkac3 mutant exhibited slower growth than the parental and complemented strains, which correlated with a higher basal rate of tachyzoite-to-bradyzoite differentiation. 3-Isobutyl-1-methylxanthine (IBMX) treatment, which elevates cAMP levels, maintained wild-type parasites as tachyzoites under bradyzoite induction culture conditions (pH 8.2/low CO2), whereas the Δpkac3 mutant failed to respond to the treatment. This suggests that TgPKAc3 is the factor responsible for the cAMP-dependent tachyzoite maintenance. In addition, the Δpkac3 mutant had a defect in the production of brain cysts in vivo, suggesting that a substrate of TgPKAc3 is probably involved in the persistence of this parasite in the intermediate host animals.
  
  
  
  Toxoplasma gondii is one of the most prevalent eukaryotic parasites in mammals, including humans. Parasites can switch from rapidly replicating tachyzoites responsible for acute infection to slowly replicating bradyzoites that persist as a latent infection. Previous studies have demonstrated that T. gondii cAMP signaling can induce or suppress bradyzoite differentiation, depending on the strength and duration of cAMP signal. Here, we report that TgPKAc3 is responsible for cAMP-dependent tachyzoite maintenance while suppressing differentiation into bradyzoites, revealing one mechanism underlying how this parasite transduces cAMP signals during differentiation.
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
authors.forename: Tatsuki
authors.initials: T
authors.lastname: Sugi
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Yan Fen
authors.initials: YF
authors.lastname: Ma
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Tadakimi
authors.initials: T
authors.lastname: Tomita
authors.affiliation: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
authors.forename: Fumi
authors.initials: F
authors.lastname: Murakoshi
authors.affiliation: Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Eaton
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Rama
authors.initials: R
authors.lastname: Yakubu
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Han
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Vincent
authors.initials: V
authors.lastname: Tu
authors.affiliation: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Kato
authors.affiliation: National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido, Japan.
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Kawazu
authors.affiliation: Department of Molecular Parasitology, Humboldt University, Berlin, Germany.
authors.forename: Nishith
authors.initials: N
authors.lastname: Gupta
authors.affiliation: Departments of Molecular Medicine and Global Health, University of South Florida, Tampa, Florida, USA.
authors.forename: Elena S
authors.initials: ES
authors.lastname: Suvorova
authors.affiliation: Departments of Molecular Medicine and Global Health, University of South Florida, Tampa, Florida, USA.
authors.forename: Michael W
authors.initials: MW
authors.lastname: White
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, New York, USA Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA.
authors.forename: Kami
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York, USA Department of Medicine, Albert Einstein College of Medicine, Bronx, New York, USA louis.weiss@einstein.yu.edu.
authors.forename: Louis M
authors.initials: LM
authors.lastname: Weiss
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000469:parasitology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D005816:Genetic Complementation Test; D006790:Host-Parasite Interactions; D008018:Life Cycle Stages / Q000235:genetics* / Q000502:physiology; D051379:Mice; D009154:Mutation; D015398:Signal Transduction; D014122:Toxoplasma / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development*
chemical_list: D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D015056:1-Methyl-3-isobutylxanthine