title: Thioredoxin reductase is required for growth and regulates entry into culmination of Dictyostelium discoideum.
abstract: The thioredoxin system, consisting of thioredoxin, thioredoxin reductase and NADPH, has been well established to be critical for the redox regulation of protein function and signalling. To investigate the role of thioredoxin reductase (Trr) in Dictyostelium discoideum, we generated mutant cells that underexpress or overexpress Trr. Trr-underexpressing cells exhibited severe defects in axenic growth and development. Trr-overexpressing (TrrOE) cells formed very tiny plaques on a bacterial lawn and had a lower rate of bacterial uptake. When developed in the dark, TrrOE cells exhibited a slugger phenotype, defined by a prolonged migrating slug stage. Like other slugger mutants, they were hypersensitive to ammonia, which has been known to inhibit culmination by raising the pH of intracellular acidic compartments. Interestingly, TrrOE cells showed defective acidification of intracellular compartments and decreased activity of vacuolar H+-ATPase which functions in the acidification of intracellular compartments. Moreover, biochemical studies revealed that the thioredoxin system can directly reduce the catalytic subunit of vacuolar H+-ATPase whose activity is regulated by reversible disulphide bond formation. Taken together, these results suggest that Dictyostelium Trr may be essential for growth and play a role in regulation of phagocytosis and culmination, possibly through the modulation of vacuolar H+-ATPase activity.
authors.affiliation: Laboratory of Biophysics, School of Biological Sciences, and Institute of Microbiology, Seoul National University, Seoul 151-742, Korea.
authors.forename: Sun-Young
authors.initials: SY
authors.lastname: Jeong
authors.forename: Chang-Hoon
authors.initials: CH
authors.lastname: Choi
authors.forename: Ji-Sun
authors.initials: JS
authors.lastname: Kim
authors.forename: Seong-Jun
authors.initials: SJ
authors.lastname: Park
authors.forename: Sa-Ouk
authors.initials: SO
authors.lastname: Kang
mesh_terms: D000595:Amino Acid Sequence; D000641:Ammonia / Q000494:pharmacology; D000818:Animals; D002384:Catalysis; D004023:Dictyostelium / Q000201:enzymology* / Q000254:growth & development* / Q000648:ultrastructure; D020043:Genes, Essential; D008969:Molecular Sequence Data; D009154:Mutation; D010084:Oxidation-Reduction; D010587:Phagocytosis / Q000235:genetics*; D006180:Proton-Translocating ATPases / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000502:physiology*; D016372:RNA, Antisense / Q000494:pharmacology; D013880:Thioredoxin-Disulfide Reductase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D014617:Vacuoles / Q000201:enzymology
chemical_list: D015800:Protozoan Proteins; D016372:RNA, Antisense; D000641:Ammonia; D013880:Thioredoxin-Disulfide Reductase; D006180:Proton-Translocating ATPases