title: Dephosphorylation of beta2-syntrophin and Ca2+/mu-calpain-mediated cleavage of ICA512 upon stimulation of insulin secretion.
abstract: Islet cell autoantigen (ICA) 512 is a receptor-tyrosine phosphatase-like protein associated with the secretory granules of neuroendocrine cells, including pancreatic beta-cells. Binding of its cytoplasmic tail to beta2-syntrophin suggests that ICA512 connects secretory granules to the utrophin complex and the actin cytoskeleton. Here we show that stimulation of insulin secretion from INS-1 cells triggers the biosynthesis of pro-ICA512 and the degradation of its mature form. Inhibition of calpain, which is activated upon stimulation of insulin secretion, prevents the Ca2+-dependent proteolysis of ICA512. In vitro mu-calpain cleaves ICA512 between a putative PEST domain and the beta2-syntrophin binding site, whereas binding of ICA512 to beta2-syntrophin protects the former from cleavage. beta2-syntrophin and its F-actin-binding protein utrophin are enriched in subcellular fractions containing secretory granules. ICA512 preferentially binds phospho-beta2-syntrophin and stimulation of insulin secretion induces the Ca2+-dependent, okadaic acid-sensitive dephosphorylation of beta2-syntrophin. Similarly to calpeptin, okadaic acid inhibits ICA512 proteolysis and insulin secretion. Thus, stimulation of insulin secretion might promote the mobilization of secretory granules by inducing the dissociation of ICA512 from beta2-syntrophin-utrophin complexes and the cleavage of the ICA512 cytoplasmic tail by mu-calpain.
authors.affiliation: Department of Internal Medicine, Section of Endocrinology, School of Nursing, Yale University School of Medicine, New Haven, CT 06520-8020, USA.
authors.forename: T
authors.initials: T
authors.lastname: Ort
authors.forename: S
authors.initials: S
authors.lastname: Voronov
authors.forename: J
authors.initials: J
authors.lastname: Guo
authors.forename: K
authors.initials: K
authors.lastname: Zawalich
authors.forename: S C
authors.initials: SC
authors.lastname: Froehner
authors.forename: W
authors.initials: W
authors.lastname: Zawalich
authors.forename: M
authors.initials: M
authors.lastname: Solimena
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000096:biosynthesis / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004151:Dipeptides / Q000494:pharmacology; D049029:Dystrophin-Associated Proteins; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000378:metabolism*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000378:metabolism*; D008969:Molecular Sequence Data; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011485:Protein Binding; D011498:Protein Precursors / Q000096:biosynthesis / Q000378:metabolism*; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis / Q000378:metabolism; D051381:Rats; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D022142:Secretory Vesicles / Q000378:metabolism; D014407:Tumor Cells, Cultured; D049411:Utrophin
chemical_list: D001324:Autoantigens; D015853:Cysteine Proteinase Inhibitors; D003598:Cytoskeletal Proteins; D004151:Dipeptides; D049029:Dystrophin-Associated Proteins; D004791:Enzyme Inhibitors; D007328:Insulin; D008565:Membrane Proteins; D011498:Protein Precursors; D049411:Utrophin; C091824:syntrophin; C071482:calpeptin; D019319:Okadaic Acid; C516862:PTPRN protein, human; D017027:Protein Tyrosine Phosphatases; C516864:Ptprn protein, rat; D054623:Receptor-Like Protein Tyrosine Phosphatases, Class 2; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8; D002154:Calpain