title: Carboxyl-Terminal SSLKG Motif of the Human Cystinosin-LKG Plays an Important Role in Plasma Membrane Sorting.
abstract: Cystinosin mediates an ATP-dependent cystine efflux from lysosomes and causes, if mutated, nephropathic cystinosis, a rare inherited lysosomal storage disease. Alternative splicing of the last exon of the cystinosin sequence produces the cystinosin-LKG isoform that is characterized by a different C-terminal region causing changes in the subcellular distribution of the protein. We have constructed RFP-tagged proteins and demonstrated by site-directed mutagenesis that the carboxyl-terminal SSLKG sequence of cystinosin-LKG is an important sorting motif that is required for efficient targeting the protein to the plasma membrane, where it can mediate H+ coupled cystine transport. Deletion of the SSLKG sequence reduced cystinosin-LKG expression in the plasma membrane and cystine transport by approximately 30%, and induced significant accumulation of the protein in the Golgi apparatus and in lysosomes. Cystinosin-LKG, unlike the canonical isoform, also moves to the lysosomes by the indirect pathway, after endocytic retrieval from the plasma membrane, mainly by a clathrin-mediated endocytosis. Nevertheless, silencing of AP-2 triggers the clathrin-independent endocytosis, showing the complex adaptability of cystinosin-LKG trafficking.
authors.affiliation: Department of Nephrology-Urology, Division of Nephrology and Dialysis, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.
authors.forename: Francesco
authors.identifier: 0000-0003-2912-8764
authors.initials: F
authors.lastname: Bellomo
authors.affiliation: Department of Nephrology-Urology, Division of Nephrology and Dialysis, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Taranta
authors.affiliation: Confocal Microscopy Core Facility, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Petrini
authors.affiliation: Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli (NA), Italy.
authors.forename: Rossella
authors.initials: R
authors.lastname: Venditti
authors.affiliation: Department of Emergency and Organ Transplantation (DETO), Nephrology, Dialysis and Transplantation Unit, University of Bari Aldo Moro, Bari, Italy.
authors.forename: Maria Teresa
authors.initials: MT
authors.lastname: Rocchetti
authors.affiliation: Department of Nephrology-Urology, Division of Nephrology and Dialysis, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.
authors.forename: Laura Rita
authors.initials: LR
authors.lastname: Rega
authors.affiliation: Department of Nephrology-Urology, Division of Nephrology and Dialysis, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Corallini
authors.affiliation: Department of Emergency and Organ Transplantation (DETO), Nephrology, Dialysis and Transplantation Unit, University of Bari Aldo Moro, Bari, Italy.
authors.forename: Loreto
authors.initials: L
authors.lastname: Gesualdo
authors.affiliation: Telethon Institute of Genetics and Medicine (TIGEM), Pozzuoli (NA), Italy.
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: De Matteis
authors.affiliation: Department of Nephrology-Urology, Division of Nephrology and Dialysis, Bambino Gesù Children's Hospital and Research Institute, Rome, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Emma
mesh_terms: D020816:Amino Acid Motifs; D026921:Amino Acid Transport Systems, Neutral / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism*
chemical_list: D026921:Amino Acid Transport Systems, Neutral; C111445:CTNS protein, human; D020033:Protein Isoforms