title: GCN2-like eIF2α kinase manages the amino acid starvation response in Toxoplasma gondii.
abstract: The apicomplexan protozoan Toxoplasma gondii is a significant human and veterinary pathogen. As an obligate intracellular parasite, Toxoplasma depends on nutrients provided by the host cell and needs to adapt to limitations in available resources. In mammalian cells, translational regulation via GCN2 phosphorylation of the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α) is a key mechanism for adapting to nutrient stress. Toxoplasma encodes two GCN2-like protein kinases, TgIF2K-C and TgIF2K-D. We previously showed that TgIF2K-D phosphorylates T. gondii eIF2α (TgIF2α) upon egress from the host cell, which enables the parasite to overcome exposure to the extracellular environment. However, the function of TgIF2K-C remained unresolved. To determine the functions of TgIF2K-C in the parasite, we cloned the cDNA encoding TgIF2K-C and generated knockout parasites of this TgIF2α kinase to study its function during the lytic cycle. The TgIF2K-C knockout did not exhibit a fitness defect compared with parental parasites. However, upon infection of human fibroblasts that were subsequently cultured in glutamine-free medium, the intracellular TgIF2K-C knockout parasites were impeded for induced phosphorylation of TgIF2α and showed a 50% reduction in the number of plaques formed compared with parental parasites. Furthermore, we found that this growth defect in glutamine-free media was phenocopied in parasites expressing only a non-phosphorylatable TgIF2α (TgIF2α-S71A), but not in a TgIF2K-D knockout. These studies suggest that Toxoplasma GCN2-like kinases TgIF2K-C and TgIF2K-D evolved to have distinct roles in adapting to changes in the parasite's environment.
authors.affiliation: Department of Biochemistry & Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; Department of Pharmacology & Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: Konrad
authors.affiliation: Department of Biochemistry & Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Ronald C
authors.initials: RC
authors.lastname: Wek
authors.affiliation: Department of Pharmacology & Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; Department of Microbiology & Immunology, Indiana University School of Medicine, Indianapolis, IN 46202, USA. Electronic address: wjsulliv@iu.edu.
authors.forename: William J
authors.initials: WJ
authors.lastname: Sullivan
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D003600:Cytosol; D015852:Eukaryotic Initiation Factor-2 / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D005786:Gene Expression Regulation / Q000502:physiology*; D055786:Gene Knockout Techniques; D010766:Phosphorylation; D014122:Toxoplasma / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D015852:Eukaryotic Initiation Factor-2; C492453:eukaryotic initiation factor-2 alpha, Toxoplasma gondii; D019892:eIF-2 Kinase
keywords: Apicomplexa; Glutamine; Parasite; Stress; Translational control; eIF2α kinase