title: Stability of proICA512/IA-2 and its targeting to insulin secretory granules require β4-sheet-mediated dimerization of its ectodomain in the endoplasmic reticulum.
abstract: The type 1 diabetes autoantigen ICA512/IA-2/RPTPN is a receptor protein tyrosine phosphatase of the insulin secretory granules (SGs) which regulates the size of granule stores, possibly via cleavage/signaling of its cytosolic tail. The role of its extracellular region remains unknown. Structural studies indicated that β2- or β4-strands in the mature ectodomain (ME ICA512) form dimers in vitro. Here we show that ME ICA512 prompts proICA512 dimerization in the endoplasmic reticulum. Perturbation of ME ICA512 β2-strand N-glycosylation upon S508A replacement allows for proICA512 dimerization, O-glycosylation, targeting to granules, and conversion, which are instead precluded upon G553D replacement in the ME ICA512 β4-strand. S508A/G553D and N506A/G553D double mutants dimerize but remain in the endoplasmic reticulum. Removal of the N-terminal fragment (ICA512-NTF) preceding ME ICA512 allows an ICA512-ΔNTF G553D mutant to exit the endoplasmic reticulum, and ICA512-ΔNTF is constitutively delivered to the cell surface. The signal for SG sorting is located within the NTF RESP18 homology domain (RESP18-HD), whereas soluble NTF is retained in the endoplasmic reticulum. Hence, we propose that the ME ICA512 β2-strand fosters proICA512 dimerization until NTF prevents N506 glycosylation. Removal of this constraint allows for proICA512 β4-strand-induced dimerization, exit from the endoplasmic reticulum, O-glycosylation, and RESP18-HD-mediated targeting to granules.
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Juha M
authors.initials: JM
authors.lastname: Torkko
authors.affiliation: University of Buenos Aires, Buenos Aires, Argentina Instituto Multidisciplinario de Biología Celular, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina.
authors.forename: M Evangelina
authors.initials: ME
authors.lastname: Primo
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Ronald
authors.initials: R
authors.lastname: Dirkx
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Friedrich
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Antje
authors.initials: A
authors.lastname: Viehrig
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Elisa
authors.initials: E
authors.lastname: Vergari
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany.
authors.forename: Barbara
authors.initials: B
authors.lastname: Borgonovo
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Anke
authors.initials: A
authors.lastname: Sönmez
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Carolin
authors.initials: C
authors.lastname: Wegbrod
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Lachnit
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany.
authors.forename: Carla
authors.initials: C
authors.lastname: Münster
authors.affiliation: Instituto Multidisciplinario de Biología Celular, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal, Buenos Aires, Argentina.
authors.forename: Mauricio P
authors.initials: MP
authors.lastname: Sica
authors.affiliation: Instituto Multidisciplinario de Biología Celular, Consejo Nacional de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Bernal, Buenos Aires, Argentina.
authors.forename: Mario R
authors.initials: MR
authors.lastname: Ermácora
authors.affiliation: Paul Langerhans Institute Dresden, Uniklinikum Carl Gustav Carus, TU Dresden, Germany German Center for Diabetes Research (DZD e.V.), Neuherberg, Germany Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Germany michele.solimena@tu-dresden.de.
authors.forename: Michele
authors.initials: M
authors.lastname: Solimena
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006031:Glycosylation; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D051381:Rats; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8 / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*
chemical_list: D007328:Insulin; C516864:Ptprn protein, rat; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8