title: ATG24 Represses Autophagy and Differentiation and Is Essential for Homeostasy of the Flagellar Pocket in Trypanosoma brucei.
abstract: We have previously identified homologs for nearly half of the approximately 30 known yeast Atg's in the genome database of the human sleeping sickness parasite Trypanosoma brucei. So far, only a few of these homologs have their role in autophagy experimentally confirmed. Among the candidates was the ortholog of Atg24 that is involved in pexophagy in yeast. In T. brucei, the peroxisome-like organelles named glycosomes harbor core metabolic processes, especially glycolysis. In the autotrophic yeast, autophagy is essential for adaptation to different nutritional environments by participating in the renewal of the peroxisome population. We hypothesized that autophagic turnover of the parasite's glycosomes plays a role in differentiation during its life cycle, which demands adaptation to different host environments and associated dramatic changes in nutritional conditions. We therefore characterized T. brucei ATG24, the T. brucei ortholog of yeast Atg24 and mammalian SNX4, and found it to have a regulatory role in autophagy and differentiation as well as endocytic trafficking. ATG24 partially localized on endocytic membranes where it was recruited via PI3-kinase III/VPS34. ATG24 silencing severely impaired receptor-mediated endocytosis of transferrin, but not adsorptive uptake of a lectin, and caused a major enlargement of the flagellar pocket. ATG24 silencing approximately doubled the number of autophagosomes, suggesting a role in repressing autophagy, and strongly accelerated differentiation, in accordance with a role of autophagy in parasite differentiation. Overexpression of the two isoforms of T. brucei ATG8 fused to GFP slowed down differentiation, possibly by a dominant-negative effect. This was overcome by ATG24 depletion, further supporting its regulatory role.
authors.affiliation: Research Unit for Tropical Diseases, de Duve Institute, and Laboratory of Biochemistry, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Ana
authors.initials: A
authors.lastname: Brennand
authors.affiliation: Research Unit for Tropical Diseases, de Duve Institute, and Laboratory of Biochemistry, Université catholique de Louvain, Brussels, Belgium; Departamento de Bioquímica y Biología Molecular, Campus Universitario, Universidad de Alcalá, 28871 Alcalá de Henares, Madrid, Spain.
authors.forename: Eva
authors.initials: E
authors.lastname: Rico
authors.affiliation: Institute of Integrative Biology, Biosciences Building, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Rigden
authors.affiliation: Cell Biology Unit, de Duve Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Patrick
authors.initials: P
authors.lastname: Van Der Smissen
authors.affiliation: Cell Biology Unit, de Duve Institute, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Courtoy
authors.affiliation: Research Unit for Tropical Diseases, de Duve Institute, and Laboratory of Biochemistry, Université catholique de Louvain, Brussels, Belgium.
authors.forename: Paul A M
authors.initials: PA
authors.lastname: Michels
mesh_terms: D000595:Amino Acid Sequence; D001343:Autophagy; D058546:Class III Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017124:Conserved Sequence; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D005407:Flagella / Q000378:metabolism*; D006706:Homeostasis; D008969:Molecular Sequence Data; D021381:Protein Transport; D015800:Protozoan Proteins / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D014346:Trypanosoma brucei brucei / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D015800:Protozoan Proteins; D058546:Class III Phosphatidylinositol 3-Kinases