title: A subset of p23 localized on secretory granules in pancreatic beta-cells.
abstract: Proteins on the membrane of secretory granules (SGs) involved in their biogenesis and exocytosis are poorly characterized compared with those of synaptic vesicle in neurons. Thus the secretory granule membrane was prepared from a mouse pancreatic beta-cell line MIN6 by subcellular fractionation, and protein constituents were analyzed by microscale two-dimensional liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Using this proteomics approach, one of the p24 family proteins, p23, was unexpectedly found in the granule fraction, although p24 proteins are generally regarded as functioning in the early secretory pathways between the endoplasmic reticulum and the Golgi apparatus. We further showed that p23 is expressed at high levels in endocrine cells. Furthermore, immunocytochemical analyses of pancreatic beta-cells at the light and electron microscopic levels demonstrated that a significant amount of p23 is localized on the insulin granule membrane, although it is most intensely concentrated at the cis-Golgi compartment as previously shown in non-endocrine cells. These findings suggest that a fraction of p23 enters post-Golgi compartments and may function in the biogenesis and/or quality control of SGs.
authors.affiliation: Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, 3-39-15 Showa-machi, Maebashi 371-8512, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hosaka
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Yamauchi
authors.forename: Yuko
authors.initials: Y
authors.lastname: Sakai
authors.forename: Masayuki
authors.initials: M
authors.lastname: Suda
authors.forename: Shin
authors.initials: S
authors.lastname: Mizutani
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takeuchi
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Isobe
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Izumi
mesh_terms: D000818:Animals; D002460:Cell Line; D002522:Chlorocebus aethiops; D002853:Chromatography, Liquid; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D040901:Proteomics; D051381:Rats; D017208:Rats, Wistar; D022142:Secretory Vesicles / Q000378:metabolism*; D053719:Tandem Mass Spectrometry
chemical_list: D007328:Insulin; D008565:Membrane Proteins; C100672:Tmed10 protein, rat