title: RalA and RalB function as the critical GTP sensors for GTP-dependent exocytosis.
abstract: Although it has been established that the activation of GTPases by non-hydrolyzable GTP stimulates neurotransmitter release from many different secretory cell types, the underlying mechanisms remain unclear. In the present study we aimed to elucidate the functional role(s) for endogenous Ras-like protein A (RalA) and RalB GTPases in GTP-dependent exocytosis. For this purpose stable neuroendocrine pheochromocytoma 12 (PC12) cell lines were generated in which the expressions of both RalA and RalB were strongly downregulated. In these double knock-down cells GTP-dependent exocytosis was reduced severely and was restored after the expression of RalA or RalB was reintroduced by transfection. In contrast, Ca2+-dependent exocytosis and the docking of dense core vesicles analyzed by electron microscopy remained unchanged in the double knock-down cells. Furthermore, the transfected RalA and RalB appeared to be localized primarily on the dense core vesicles in undifferentiated and nerve growth factor-differentiated PC12 cells. Our results indicate that endogenous RalA and RalB function specifically as GTP sensors for the GTP-dependent exocytosis of dense core vesicles, but they are not required for the general secretory pathways, including tethering of vesicles to the plasma membrane and Ca2+-dependent exocytosis.
authors.affiliation: Division of Cellular and Molecular Biology, Toronto Western Research Institute, University Health Network, Toronto, Ontario, Canada M5T 2S8.
authors.forename: Gang
authors.initials: G
authors.lastname: Li
authors.forename: Liping
authors.initials: L
authors.lastname: Han
authors.forename: Ting-Chieh
authors.initials: TC
authors.lastname: Chou
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Fujita
authors.forename: Lakshmanan
authors.initials: L
authors.lastname: Arunachalam
authors.forename: Ainan
authors.initials: A
authors.lastname: Xu
authors.forename: Aaron
authors.initials: A
authors.lastname: Wong
authors.forename: Soon-Kwang
authors.initials: SK
authors.lastname: Chiew
authors.forename: Qi
authors.initials: Q
authors.lastname: Wan
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Shuzo
authors.initials: S
authors.lastname: Sugita
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D016716:PC12 Cells; D051381:Rats; D020725:ral GTP-Binding Proteins / Q000378:metabolism*
chemical_list: C082190:Ralb protein, rat; D006160:Guanosine Triphosphate; C492197:Rala protein, rat; D020725:ral GTP-Binding Proteins; D002118:Calcium