Exophilin-8 assembles secretory granules for exocytosis in the actin cortex via interaction with RIM-BP2 and myosin-VIIa (Prof. Tetsuro Izumi’s group)
Hormones and other chemical messengers released from cells into the blood or tissues are stored in containers called secretory granules, which are held just under the surface of the cell by a web of fibres made from a protein called actin. When a message needs to be sent, the granules fuse with the membrane that surrounds the cell, releasing their contents into the space outside. Prof. Tetsuro Izumi’s group shows that a protein called exophilin-8 associates with a group of other proteins that work together to catch the secretory granules and anchor them to the actin bundles near to the inner edge of the cell, thereby promoting granules to fuse with the membrane. Furthermore, mutant mice that cannot make exophilin-8 fail to build up granules at the edges of cells and reveals a decrease in the amount of insulin –a hormone that regulates blood sugar levels – released by cells in the pancreas. As a result, the mutant mice had higher levels of blood sugar than normal mice.
Fan F, Matsunaga K, Wang H, Ishizaki R, Kobayashi E, Kiyonari H, Mukumoto Y, Okunishi K, and Izumi T (2017). Exophilin-8 assembles secretory granules for exocytosis in the actin cortex via interaction with RIM-BP2 and myosin-VIIa. eLife, 6, e26174 doi: 10.7554/eLife.26174. PMID: 28673385