title: TSSC1 is novel component of the endosomal retrieval machinery.
abstract: Endosomes function as a hub for multiple protein-sorting events, including retrograde transport to the trans-Golgi network (TGN) and recycling to the plasma membrane. These processes are mediated by tubular-vesicular carriers that bud from early endosomes and fuse with a corresponding acceptor compartment. Two tethering complexes named GARP (composed of ANG2, VPS52, VPS53, and VPS54 subunits) and EARP (composed of ANG2, VPS52, VPS53, and Syndetin subunits) were previously shown to participate in SNARE-dependent fusion of endosome-derived carriers with the TGN and recycling endosomes, respectively. Little is known, however, about other proteins that function with GARP and EARP in these processes. Here we identify a protein named TSSC1 as a specific interactor of both GARP and EARP and as a novel component of the endosomal retrieval machinery. TSSC1 is a predicted WD40/β-propeller protein that coisolates with both GARP and EARP in affinity purification, immunoprecipitation, and gel filtration analyses. Confocal fluorescence microscopy shows colocalization of TSSC1 with both GARP and EARP. Silencing of TSSC1 impairs transport of internalized Shiga toxin B subunit to the TGN, as well as recycling of internalized transferrin to the plasma membrane. Fluorescence recovery after photobleaching shows that TSSC1 is required for efficient recruitment of GARP to the TGN. These studies thus demonstrate that TSSC1 plays a critical role in endosomal retrieval pathways as a regulator of both GARP and EARP function.
authors.affiliation: Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors.forename: David C
authors.initials: DC
authors.lastname: Gershlick
authors.affiliation: Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Christina
authors.initials: C
authors.lastname: Schindler
authors.affiliation: Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Yu
authors.initials: Y
authors.lastname: Chen
authors.affiliation: Cell Biology and Neurobiology Branch, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892 bonifacinoj@helix.nih.gov.
authors.forename: Juan S
authors.initials: JS
authors.lastname: Bonifacino
mesh_terms: D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology; D011992:Endosomes / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport / Q000502:physiology; D050600:SNARE Proteins / Q000378:metabolism; D022621:Shiga Toxin / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: C109558:EIPR1 protein, human; D009687:Nuclear Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins; D022621:Shiga Toxin