title: EPI64B acts as a GTPase-activating protein for Rab27B in pancreatic acinar cells.
abstract: The small GTPase Rab27B localizes to the zymogen granule membranes and plays an important role in regulating protein secretion by pancreatic acinar cells, as does Rab3D. A common guanine nucleotide exchange factor (GEF) for Rab3 and Rab27 has been reported; however, the GTPase-activating protein (GAP) specific for Rab27B has not been identified. In this study, the expression in mouse pancreatic acini of two candidate Tre-2/Bub2/Cdc16 (TBC) domain-containing proteins, EPI64 (TBC1D10A) and EPI64B (TBC1D10B), was first demonstrated. Their GAP activity on digestive enzyme secretion was examined by adenovirus-mediated overexpression of EPI64 and EPI64B in isolated pancreatic acini. EPI64B almost completely abolished the GTP-bound form of Rab27B, without affecting GTP-Rab3D. Overexpression of EPI64B also enhanced amylase release. This enhanced release was independent of Rab27A, but dependent on Rab27B, as shown using acini from genetically modified mice. EPI64 had a mild effect on both GTP-Rab27B and amylase release. Co-overexpression of EPI64B with Rab27B can reverse the inhibitory effect of Rab27B on amylase release. Mutations that block the GAP activity decreased the inhibitory effect of EPI64B on the GTP-bound state of Rab27B and abolished the enhancing effect of EPI64B on the amylase release. These data suggest that EPI64B can serve as a potential physiological GAP for Rab27B and thereby participate in the regulation of exocytosis in pancreatic acinar cells.
authors.affiliation: Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Yanan
authors.initials: Y
authors.lastname: Hou
authors.forename: Xuequn
authors.initials: X
authors.lastname: Chen
authors.forename: Tatyana
authors.initials: T
authors.lastname: Tolmachova
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Ernst
authors.forename: John A
authors.initials: JA
authors.lastname: Williams
mesh_terms: D061354:Acinar Cells / Q000166:cytology / Q000378:metabolism*; D000681:Amylases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D064194:Apc6 Subunit, Anaphase-Promoting Complex-Cyclosome; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology*; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009154:Mutation; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000075745:rab27 GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D064194:Apc6 Subunit, Anaphase-Promoting Complex-Cyclosome; C577396:Cdc16 protein, mouse; D018797:Cell Cycle Proteins; C515119:EPI64 protein, mouse; D020690:GTPase-Activating Proteins; D000075745:rab27 GTP-Binding Proteins; D000681:Amylases; C512958:Rab27b protein, mouse; C116711:Rab3d protein, mouse; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins; D020692:rab3 GTP-Binding Proteins
keywords: Adenovirus; EPI64B; GTPase-activating protein; Pancreas; Rab Proteins; Rab27B; Secretion; Small GTPases