A large form of secretogranin III functions as a sorting receptor for chromogranin A aggregates in PC12 cells.
Granin-family proteins, including chromogranin A and secretogranin III, are sorted to the secretory granules in neuroendocrine cells. We previously demonstrated that secretogranin III binds chromogranin A and targets it to the secretory granules in pituitary corticotrope-derived AtT-20 cells. However, secretogranin III has not been identified in adrenal chromaffin and PC12 cells, where chromogranin A is correctly sorted to the secretory granules. In this study, low levels of a large and noncleaved secretogranin III have been identified in PC12 cells and rat adrenal glands. Although the secretogranin III expression was limited in PC12 cells, when the FLAG-tagged secretogranin III lacking the secretory granule membrane-binding domain was expressed excessively, hemagglutinin-tagged chromogranin A was unable to target to the secretory granules at the tips and shifted to the constitutive secretory pathway. Secretogranin III was able to bind the aggregated form of chromogranin A, suggesting that a small quantity of secretogranin III is enough to carry a large quantity of chromogranin A. Furthermore, secretogranin III bound adrenomedullin, a major peptide hormone in chromaffin cells. Indeed, small interfering RNA-directed secretogranin III depletion impaired intracellular retention of chromogranin A and adrenomedullin, suggesting that they are constitutively released to the medium. We suggest that the sorting function of secretogranin III for chromogranin A is common in PC12 and chromaffin cells as well as in other endocrine cells, and a small amount of secretogranin III is able to sort chromogranin A aggregates together with adrenomedullin to secretory granules.
Han
Lu
L
Department of Molecular Medicine, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi 371-8512, Japan.
Suda
Masayuki
M
Tsuzuki
Keisuke
K
Wang
Rong
R
Ohe
Yoshihide
Y
Hirai
Hirokazu
H
Watanabe
Tsuyoshi
T
Takeuchi
Toshiyuki
T
Hosaka
Masahiro
M
D053607:Adrenomedullin / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D022081:Cell Surface Extensions / Q000378:metabolism; D053379:Chromogranin A / Q000737:chemistry* / Q000378:metabolism*; D002864:Chromogranins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D042541:Intracellular Space / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D016716:PC12 Cells; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism
D053379:Chromogranin A; D002864:Chromogranins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; C506167:secretogranin III; D053607:Adrenomedullin