title: The GDP-dependent Rab27a effector coronin 3 controls endocytosis of secretory membrane in insulin-secreting cell lines.
abstract: Rab27a is involved in the control of membrane traffic, a crucial step in the regulated secretion. Typically, the guanosine triphosphate (GTP)-bound form has been considered to be active and, therefore, searching for proteins binding to the GTP-form has been attempted to look for their effectors. Here, we have identified the actin-bundling protein coronin 3 as a novel Rab27a effector that paradoxically bound guanosine diphosphate (GDP)-Rab27a in the pancreatic beta-cell line MIN6. Coronin 3 directly bound GDP-Rab27a through its beta-propeller structure. The most important insulin secretagogue glucose promptly shifted Rab27a from the GTP- to GDP-bound form. Knockdown of coronin 3 by RNAi resulted in the inhibition of phogrin (an insulin-granule-associated protein) internalization and the uptake of FM4-64 (a marker of endocytosis). Similar results were reproduced by disruption of the coronin-3-GDP-Rab27a interaction with the dominant-negative coronin 3, and coexpression of the GDP-Rab27a mutant rescued these changes. Taken together, our results indicate that interaction of GDP-Rab27a and coronin 3 is important in stimulus-endocytosis coupling, and that GTP- and GDP-Rab27a regulates insulin membrane recycling at the distinct stages.
authors.affiliation: Department of Pharmacology, Oita University Faculty of Medicine, Hasama, Yufu, Oita 879-5593, Japan.
authors.forename: Toshihide
authors.initials: T
authors.lastname: Kimura
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Shogo
authors.initials: S
authors.lastname: Yamada
authors.forename: Hisamitsu
authors.initials: H
authors.lastname: Ishihara
authors.forename: Takao
authors.initials: T
authors.lastname: Senda
authors.forename: Akihiro
authors.initials: A
authors.lastname: Iwamatsu
authors.forename: Ichiro
authors.initials: I
authors.lastname: Niki