title: Distinct subcellular localization of three isoforms of insulinoma-associated protein 2β in neuroendocrine tissues.
abstract: OBJECTIVE
  Insulinoma-associated protein 2β (IA-2β) is considered to play a significant role in regulated secretion. Recent studies have shown that the mouse brain expresses three major isoforms of IA-2β, named IA-2β60, IA-2β64, and IA-2β71. In this study, we analyzed the tissue-, cell- and organelle-specific distributions of IA-2β isoforms in mice.
  
  
  METHODS
  To localize IA-2β expression in mouse tissues and cells, western blot and immunohistochemical analyses were carried out. The subcellular distribution of IA-2β isoforms was assessed by sedimentation of mouse brain homogenates in a discontinuous sucrose density gradient.
  
  
  RESULTS
  IA-2β60 was abundant in the cerebrum, cerebellum, medulla oblongata, pancreas, adrenal gland, and pituitary, and in the muscular and mucosal layers of the digestive organs. In contrast, the expression of IA-2β64 and IA-2β71 was restricted to the cerebrum, cerebellum, medulla oblongata, and pituitary, and the muscular layers of the digestive organs. Immunohistochemical analysis of mouse pancreatic islets revealed that pancreatic beta cells expressed IA-2β60 exclusively, whereas alpha and delta cells expressed all three isoforms. By the sedimentation of mouse brain homogenates, it was shown that IA-2β64 and IA-2β71 were co-localized with IA-2 on secretory granules, but were absent from synaptic vesicles (SVs). On the other hand, IA-2β60 was co-localized with synaptophisin on SVs, but was absent from secretory granules.
  
  
  CONCLUSIONS
  The tissue-, cell- and organelle-specific distributions of IA-2β isoforms suggest that IA-2β60 has a role in secretion from SVs, whereas IA-2β64 and IA-2β71 are involved in secretion from secretory granules.
authors.affiliation: Department of Molecular Immunology, School of Agricultural and Life Sciences, University of Tokyo, Bunkyo-ku, Tokyo, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Nakajima
authors.forename: Guoying
authors.initials: G
authors.lastname: Wu
authors.forename: Akikazu
authors.initials: A
authors.lastname: Sakudo
authors.forename: Takashi
authors.initials: T
authors.lastname: Onodera
authors.forename: Natsumi
authors.initials: N
authors.lastname: Takeyama
mesh_terms: D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002531:Cerebellum / Q000378:metabolism; D054022:Cerebrum / Q000378:metabolism; D008526:Medulla Oblongata / Q000378:metabolism; D051379:Mice; D009130:Muscle, Smooth / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism; D020033:Protein Isoforms / Q000378:metabolism; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8 / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D054635:Receptor-Like Protein Tyrosine Phosphatases, Class 8