title: Cystinosin is a Component of the Vacuolar H+-ATPase-Ragulator-Rag Complex Controlling Mammalian Target of Rapamycin Complex 1 Signaling.
abstract: Cystinosis is a rare autosomal recessive storage disorder characterized by defective lysosomal efflux of cystine due to mutations in the CTNS gene encoding the lysosomal cystine transporter, cystinosin. Lysosomal cystine accumulation leads to crystal formation and functional impairment of multiple organs. Moreover, cystinosis is the most common inherited cause of renal Fanconi syndrome in children. Oral cysteamine therapy delays disease progression by reducing intracellular cystine levels. However, because cysteamine does not correct all complications of cystinosis, including Fanconi syndrome, we hypothesized that cystinosin could have novel roles in addition to transporting cystine out of the lysosome. By coimmunoprecipitation experiments and mass spectrometry, we found cystinosin interacts with almost all components of vacuolar H(+)-ATPase and the Ragulator complex and with the small GTPases Ras-related GTP-binding protein A (RagA) and RagC. Furthermore, the mammalian target of rapamycin complex 1 (mTORC1) pathway was downregulated in proximal tubular cell lines derived from Ctns(-/-) mice. Decrease of lysosomal cystine levels by cysteamine did not rescue mTORC1 activation in these cells, suggesting that the downregulation of mTORC1 is due to the absence of cystinosin rather than to the accumulation of cystine. Our results show a dual role for cystinosin as a cystine transporter and as a component of the mTORC1 pathway, and provide an explanation for the appearance of Fanconi syndrome in cystinosis. Furthermore, this study highlights the need to develop new treatments not dependent on lysosomal cystine depletion alone for this devastating disease.
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France; corinne.antignac@inserm.fr.
authors.forename: Zuzanna
authors.initials: Z
authors.lastname: Andrzejewska
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France;
authors.forename: Nathalie
authors.initials: N
authors.lastname: Nevo
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France;
authors.forename: Lucie
authors.initials: L
authors.lastname: Thomas
authors.affiliation: Proteomic Platform Necker (PPN), 3P5, SFR, Paris Descartes University, Faculty of Medicine, Paris, France;
authors.forename: Cerina
authors.initials: C
authors.lastname: Chhuon
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France;
authors.forename: Anne
authors.initials: A
authors.lastname: Bailleux
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France;
authors.forename: Véronique
authors.initials: V
authors.lastname: Chauvet
authors.affiliation: Cell Biology Unit, de Duve Institute, Université Catholique de Louvain, Brussels, Belgium; and.
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Courtoy
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France;
authors.forename: Marie
authors.initials: M
authors.lastname: Chol
authors.affiliation: Proteomic Platform Necker (PPN), 3P5, SFR, Paris Descartes University, Faculty of Medicine, Paris, France;
authors.forename: Ida Chiara
authors.initials: IC
authors.lastname: Guerrera
authors.affiliation: French Institute of Health and Medical Research (INSERM) U1163, Laboratory of Hereditary Kidney Diseases, Paris, France; Paris Descartes-Sorbonne Paris Cité University, Imagine Institute, Paris, France; Department of Genetics, Necker Hospital, Assistance Publique-Hôpitaux de Paris, Paris, France.
authors.forename: Corinne
authors.initials: C
authors.lastname: Antignac
mesh_terms: D026921:Amino Acid Transport Systems, Neutral / Q000502:physiology*; D000818:Animals; D003554:Cystinosis / Q000209:etiology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D046912:Multiprotein Complexes / Q000502:physiology*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000502:physiology*; D025262:Vacuolar Proton-Translocating ATPases / Q000502:physiology*
chemical_list: D026921:Amino Acid Transport Systems, Neutral; C111445:CTNS protein, human; D046912:Multiprotein Complexes; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D025262:Vacuolar Proton-Translocating ATPases
keywords: Fanconi syndrome; cystinosin; cystinosis; mTORC1