title: Role for RalA downstream of Rac1 in skeletal muscle insulin signalling.
abstract: Insulin-stimulated glucose uptake in skeletal muscle is mediated by the translocation of the glucose transporter GLUT4 from intracellular storage sites to the plasma membrane. The small GTPase Rac1 has been implicated in this insulin signalling, but the mechanism whereby Rac1 stimulates GLUT4 translocation remains obscure. In the present study, we examined the role of the small GTPase RalA downstream of Rac1 in skeletal muscle fibres isolated from genetically modified mice. A dominant-negative mutant of RalA, when ectopically overexpressed, significantly reduced GLUT4 translocation in response to insulin or either one of constitutively activated mutants of Rac1 and its upstream regulators, including the guanine-nucleotide-exchange factor FLJ00068, the protein kinase Akt2 and phosphoinositide 3-kinase. Constitutively activated Rac1 also failed to induce GLUT4 translocation in mouse skeletal muscle fibres in which the expression of RalA was abrogated by specific siRNA molecules. Furthermore, we applied a novel approach to detect the activated form of RalA in situ by immunofluorescence microscopy of mouse skeletal muscle fibres, demonstrating that constitutively activated mutants of Rac1 and its upstream regulators as well as insulin indeed cause the activation of RalA. Notably, this RalA activation was remarkably impaired in rac1-deficient skeletal muscle fibres. Taken together, these results provide evidence that RalA is indeed activated and involved in the regulation of GLUT4 translocation in response to insulin downstream of Rac1 in mouse skeletal muscle.
authors.affiliation: Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Takenaka
authors.affiliation: Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan.
authors.forename: Yukio
authors.initials: Y
authors.lastname: Sumi
authors.affiliation: Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Matsuda
authors.affiliation: Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan.
authors.forename: Junko
authors.initials: J
authors.lastname: Fujita
authors.affiliation: Division of Diabetes and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hosooka
authors.affiliation: Division of Diabetes and Endocrinology, Department of Internal Medicine, Kobe University Graduate School of Medicine, 7-5-1 Kusunoki-cho, Chuo-ku, Kobe 650-0017, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Noguchi
authors.affiliation: Laboratory of Animal Resources, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
authors.forename: Atsu
authors.initials: A
authors.lastname: Aiba
authors.affiliation: Laboratory of Cell Biology, Department of Biological Science, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai 599-8531, Japan tkysato@b.s.osakafu-u.ac.jp.
authors.forename: Takaya
authors.initials: T
authors.lastname: Satoh
mesh_terms: D000818:Animals; D004789:Enzyme Activation; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018485:Muscle Fibers, Skeletal / Q000201:enzymology / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D020725:ral GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D009479:Neuropeptides; C107953:RAC1 protein, human; C484602:Rac1 protein, mouse; C492198:RALA protein, human; C118120:Rala protein, mouse; D020830:rac1 GTP-Binding Protein; D020725:ral GTP-Binding Proteins
keywords: GLUT4; Rac1; RalA; glucose uptake; insulin; skeletal muscle; small GTPase