title: Interplay between Rab27a effectors in pancreatic β-cells.
abstract: The small GTPase Rab27a is a member of the Rab family that is involved in membrane trafficking in various kinds of cells. Rab27a has GTP- and GDP-bound forms, and their interconversion regulates intracellular signaling pathways. Typically, only a GTP-bound GTPase binds its specific effectors with the resulting downstream signals controlling specific cellular functions. We previously identified novel Rab27a-interacting proteins. Surprisingly, some of these proteins interacted with GDP-bound Rab27a. The present study reviews recent progress in our understanding of the roles of Rab27a and its effectors in the secretory process. In pancreatic β-cells, GTP-bound Rab27a regulates insulin secretion at the pre-exocytotic stages via its GTP-specific effectors such as Exophilin8/Slac2-c/MyRIP and Slp4/Granuphilin. Glucose stimulation causes insulin exocytosis. Glucose stimulation also converts Rab27a from its GTP- to its GDP-bound form. GDP-bound Rab27a interacts with GDP-specific effectors and controls endocytosis of the secretory membrane. Thus, Rab27a cycling between GTP- and GDP-bound forms synchronizes with the recycling of secretory membrane to re-use the membrane and keep the β-cell volume constant.
authors.affiliation: Mami Yamaoka, Toshimasa Ishizaki, Toshihide Kimura, Department of Pharmacology, Oita University Faculty of Medicine, Oita 879-5593, Japan.
authors.forename: Mami
authors.initials: M
authors.lastname: Yamaoka
authors.affiliation: Mami Yamaoka, Toshimasa Ishizaki, Toshihide Kimura, Department of Pharmacology, Oita University Faculty of Medicine, Oita 879-5593, Japan.
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Ishizaki
authors.affiliation: Mami Yamaoka, Toshimasa Ishizaki, Toshihide Kimura, Department of Pharmacology, Oita University Faculty of Medicine, Oita 879-5593, Japan.
authors.forename: Toshihide
authors.initials: T
authors.lastname: Kimura
keywords: Coronin 3; Endocytosis; Exocytosis; Glucose; IQGAP1; Insulin; Rab27a; Small GTPase