オクニシ　カツヒデ   Okunishi Katsuhide   奥西　勝秀    所属   東邦大学  医学部 医学科    職種   教授
論文種別	原著
言語種別	英語
査読の有無	査読あり
表題	Melanophilin Accelerates Insulin Granule Fusion without Predocking to the Plasma Membrane.
掲載誌名	正式名：Diabetes
掲載区分	国外
巻・号・頁	69(12),pp.2655-2666
著者・共著者	Hao Wang,Kouichi Mizuno,Noriko Takahashi,Eri Kobayashi,Jun Shirakawa,Yasuo Terauchi,Haruo Kasai,Katsuhide Okunishi,Tetsuro Izumi
発行年月	2020/12
概要	Direct observation of fluorescence-labeled secretory granule exocytosis in living pancreatic β-cells has revealed heterogeneous prefusion behaviors: some granules dwell beneath the plasma membrane before fusion, while others fuse immediately once they are recruited to the plasma membrane. Although the former mode seems to follow sequential docking-priming-fusion steps as found in synaptic vesicle exocytosis, the latter mode, which is unique to secretory granule exocytosis, has not been explored well. Here, we show that melanophilin, one of the effectors of the monomeric guanosine-5'-triphosphatase Rab27 on the granule membrane, is involved in such an accelerated mode of exocytosis. Melanophilin-mutated leaden mouse and melanophilin-downregulated human pancreatic β-cells both exhibit impaired glucose-stimulated insulin secretion, with a specific reduction in fusion events that bypass stable docking to the plasma membrane. Upon stimulus-induced [Ca2+]i rise, melanophilin mediates this type of fusion by dissociating granules from myosin-Va and actin in the actin cortex and by associating them with a fusion-competent, open form of syntaxin-4 on the plasma membrane. These findings provide the hitherto unknown mechanism to support sustainable exocytosis by which granules are recruited from the cell interior and fuse promptly without stable predocking to the plasma membrane.
DOI	10.2337/db20-0069
PMID	32994278