Molecular mechanism of exocytosis from secretory granules that have been trapped into the cortical actin network

• Project/Area Number: 18K14647
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 43030:Functional biochemistry-related
• Research Institution: Gunma University
• Principal Investigator: Wang Hao 群馬大学, 生体調節研究所, 助教 (70775874)
• Project Period (FY): 2018-04-01 – 2020-03-31
• Project Status: Completed (Fiscal Year 2019)
• Budget Amount: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000); Fiscal Year 2019: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000); Fiscal Year 2018: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000)
• Keywords: インスリン分泌 / Rabエフェクター / 全反射顕微鏡 / Rabタンパク質 / インスリン / 分泌顆粒 / 開口放出 / 細胞内膜輸送 / 糖尿病

Outline of Final Research Achievements

Direct observation of fluorescence-labeled secretory granule exocytosis in living pancreatic β cells has revealed that some granules fuse immediately once they are recruited to the plasma membrane. We show that melanophilin, one of the effectors of the monomeric GTPase Rab27 on the granule membrane, is involved in such an accelerated mode of exocytosis. Both melanophilin-mutated leaden mouse and melanophilin-downregulated human pancreatic β cells exhibit impaired glucose-stimulated insulin secretion, with a specific reduction in fusion events that bypass stable docking to the plasma membrane. Melanophilin mediates this type of fusion by dissociates granules from myosin-5a and actin in the actin cortex and associates them with a fusion-competent, open form of syntaxin-4 on the plasma membrane in stimulus-induced [Ca2+]i rise-dependent manners, which provides the hitherto unknown mechanism to support sustainable exocytosis from granules in the cell interior.

Academic Significance and Societal Importance of the Research Achievements

安定的な細胞膜ドッキングを介さずに、細胞内部から動員される顆粒からの開口放出は、特にグルコース刺激後期に多く認められ、持続的なインスリン分泌に重要な機構と考えられるが、その分子機序はわかっていなかった。本研究は、その分子機序を明らかにし、今後、刺激依存性に開口放出可能な機能的顆粒プール形成を促進するという、糖尿病の新たな治療戦略とその分子標的を創出・提示する可能性がある。

Research Products

• [Journal Article] Exophilin-5 regulates allergic airway inflammation by controlling IL-33-mediated Th2 responses. (2020)
  • Author(s): Okunishi K, Wang H, Suzukawa M, Ishizaki R, Kobayashi E, Kihara M, Abe T, Miyazaki J, Horie M, Saito A, Saito H, Nakae S, and Izumi T
  • Journal Title: J. Clin. Invest. Volume: in press
  • Peer Reviewed
• [Journal Article] Coixol amplifies glucose-stimulated insulin secretion via cAMP mediated signaling pathway. (2019)
  • Author(s): Hameed A, Hafizur RM, Kahn MI, Jawed A, Wang H, Zhao M, Matsunaga K, Izumi T, Siddiqui S, Khan F, Adhikari A, and Sharma KR.
  • Journal Title: Eur. J. Pharmacol. Volume: 858 Pages: 172514-172514
  • DOI: 10.1016/j.ejphar.2019.172514
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] メラノフィリンは開放型シンタキシン-4との結合を介して細胞膜ドッキングを迂回するインスリン開口放出を制御する。 (2020)
  • Author(s): 水野 広一、王 昊、奥西 勝秀、泉 哲郎
  • Organizer: 第34回日本糖尿病・肥満動物学会年次学術集会
• [Presentation] Rab27エフェクターexophilin-5のアレルギー性気道炎症における新奇の役割の解明 (2019)
  • Author(s): 奥西 勝秀、王 昊、泉 哲郎
  • Organizer: 第56回日本臨床分子医学会
• [Presentation] Coixol amplifies glucose stimulated insulin secretion through cAMP-PKA signaling cascade-independent of K-ATP Channels. (2019)
  • Author(s): Abdul Hameed, Rahman M Hafizur, M Israr Khan, Hao Wang, Miaomiao Zhao, Kohichi Matsunaga, Tetsuro Izumi, Sonia Siddiqui, Faisal Khan, Achyut Adhikari, and Khaga Raj Sharma.
  • Organizer: The 11th Scientific Meeting of the Asian Association for the Study of Diabetes.
  • Int'l Joint Research
• [Presentation] Hymecromone potentiates glucose-stimulated insulin secretion through cAMP-PKA signaling pathway. (2019)
  • Author(s): Rahman M Hafizur, M Israr Khan, Abdul Hameed, Kiran Maryam, Huma Aslam Bhatti, Munneb Ali, Zaheer-UI, Faisal Khan, Ghulam Abbas, Hao Wang, Kohichi Matsunaga, and Tetsuro Izumi.
  • Organizer: 第62回日本糖尿病学会年次学術集会
• [Presentation] Rab27エフェクターexophilin-5のアレルギー反応における役割 (2019)
  • Author(s): 奥西 勝秀、王 昊、泉 哲郎
  • Organizer: 第68回日本アレルギー学会学術大会
• [Presentation] Melanophilin accelerates insulin granule fusion without stable docking to the plasma membrane via interaction with myosin-Va and syntaxin-4. (2019)
  • Author(s): Tetsuro Izumi, Kouichi Mizuno, Katsuhide Okunishi, and Hao Wang.
  • Organizer: The 55th Annual Meeting of the EASD
  • Int'l Joint Research
• [Presentation] Exploring the insulin secretory mechanisms of hymecromone and eupatorin in mice islets. (2019)
  • Author(s): Rahman M Hafizur, Abdul Hameed, M Israr Khan, Kiran Maryam, Muneeb Ali, Za-heer Ul-Haq, Hao Wang, Miaomiao Zhao, Kohichi Matsunaga, Tetsuro Izumi, Achyut Adhi-kari, Huma Aslam Bhatti.
  • Organizer: The 7th International Symposium-cum-Training Course on Molecular Medicine and Drug Research, Karachi, Pakistan
  • Int'l Joint Research
• [Presentation] A novel regulatory role of the Rab27 effector exophilin5 in allergic airway inflammation. (2019)
  • Author(s): Katsuhide Okunishi, Hao Wang, Maho Suzukawa, Susumu Nakae, and Tetsuro Izumi.
  • Organizer: 第48回日本免疫学会
• [Presentation] Exophilin-8/MyRIP/Slac2C assembles secretory granules for exocytosis in the actin cortex via interaction with RIM-BP2 and myosin-VIIa. (2018)
  • Author(s): Kohichi Matsunaga, Fushun Fan, Hao Wang, Ray Ishizaki, Eri Kobayashi, Hiroshi Kiyonari, Yoshiko Mukumoto, Katsuhide Okunishi, and Tetsuro Izumi
  • Organizer: Joint Annual Meeting of JSDB 51st and JSCB 70th
  • Int'l Joint Research
• [Presentation] Roles of Eupatorin and Hymecromone as Potent Insulin Secretagogues and their Mechanisms. (2018)
  • Author(s): M. Hafizur Rahman, Abdul Hameed, M. Israr Khan, Kiran Maryam, Hao Wang, Miaomiao Zhao, Kohichi Matsunaga, Tetsuro Izumi, Achyut Adhikari, Huma Aslam Bhatti
  • Organizer: 14th Biennial Conference of Pakistan Society for Biochemistry and Molecular Biology
  • Int'l Joint Research
• [Remarks] 群馬大学生体調節研究所遺伝生化学分野
  • URL: http://molend.showa.gunma-u.ac.jp/
• [Remarks] 喘息重症化の抑制機構の解明 ～エキソフィリン5が喘息の重症化を防ぐ
  • URL: https://www.imcr.gunma-u.ac.jp/?p=7861