title: Identification of a chromogranin A domain that mediates binding to secretogranin III and targeting to secretory granules in pituitary cells and pancreatic beta-cells.
abstract: Chromogranin A (CgA) is transported restrictedly to secretory granules in neuroendocrine cells. In addition to pH- and Ca(2+)-dependent aggregation, CgA is known to bind to a number of vesicle matrix proteins. Because the binding-prone property of CgA with secretory proteins may be essential for its targeting to secretory granules, we screened its binding partner proteins using a yeast two-hybrid system. We found that CgA bound to secretogranin III (SgIII) by specific interaction both in vitro and in endocrine cells. Localization analysis showed that CgA and SgIII were coexpressed in pituitary and pancreatic endocrine cell lines, whereas SgIII was not expressed in the adrenal glands and PC12 cells. Immunoelectron microscopy demonstrated that CgA and SgIII were specifically colocalized in large secretory granules in male rat gonadotropes, which possess large-type and small-type granules. An immunocytochemical analysis revealed that deletion of the binding domain (CgA 48-111) for SgIII missorted CgA to the constitutive pathway, whereas deletion of the binding domain (SgIII 214-373) for CgA did not affect the sorting of SgIII to the secretory granules in AtT-20 cells. These findings suggest that CgA localizes with SgIII by specific binding in secretory granules in SgIII-expressing pituitary and pancreatic endocrine cells, whereas other mechanisms are likely to be responsible for CgA localization in secretory granules of SgIII-lacking adrenal chromaffin cells and PC12 cells.
authors.affiliation: Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, 371-8512, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hosaka
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Yuko
authors.initials: Y
authors.lastname: Sakai
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Uchiyama
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takeuchi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D053379:Chromogranin A; D002864:Chromogranins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000378:metabolism; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology*; D011506:Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D022142:Secretory Vesicles / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
chemical_list: C506150:CHGA protein, human; D053379:Chromogranin A; D002864:Chromogranins; D009479:Neuropeptides; D011506:Proteins; C506153:chromogranin A, rat