title: Ca²⁺ signals promote GLUT4 exocytosis and reduce its endocytosis in muscle cells.
abstract: Elevating cytosolic Ca(2+) stimulates glucose uptake in skeletal muscle, but how Ca(2+) affects intracellular traffic of GLUT4 is unknown. In tissue, changes in Ca(2+) leading to contraction preclude analysis of the impact of individual, Ca(2+)-derived signals. In L6 muscle cells stably expressing GLUT4myc, the Ca(2+) ionophore ionomycin raised cytosolic Ca(2+) and caused a gain in cell surface GLUT4myc. Extra- and intracellular Ca(2+) chelators (EGTA, BAPTA-AM) reversed this response. Ionomycin activated calcium calmodulin kinase II (CaMKII), AMPK, and PKCs, but not Akt. Silencing CaMKIIδ or AMPKα1/α2 partly reduced the ionomycin-induced gain in surface GLUT4myc, as did peptidic or small molecule inhibitors of CaMKII (CN21) and AMPK (Compound C). Compared with the conventional isoenzyme PKC inhibitor Gö6976, the conventional plus novel PKC inhibitor Gö6983 lowered the ionomycin-induced gain in cell surface GLUT4myc. Ionomycin stimulated GLUT4myc exocytosis and inhibited its endocytosis in live cells. siRNA-mediated knockdown of CaMKIIδ or AMPKα1/α2 partly reversed ionomycin-induced GLUT4myc exocytosis but did not prevent its reduced endocytosis. Compared with Gö6976, Gö6983 markedly reversed the slowing of GLUT4myc endocytosis triggered by ionomycin. In summary, rapid Ca(2+) influx into muscle cells accelerates GLUT4myc exocytosis while slowing GLUT4myc endocytosis. CaMKIIδ and AMPK stimulate GLUT4myc exocytosis, whereas novel PKCs reduce endocytosis. These results identify how Ca(2+)-activated signals selectively regulate GLUT4 exocytosis and endocytosis in muscle cells.
authors.affiliation: Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Key Laboratory of Hormones and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China;
authors.forename: Q
authors.initials: Q
authors.lastname: Li
authors.affiliation: Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Key Laboratory of Hormones and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China;
authors.forename: X
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada;
authors.forename: S
authors.initials: S
authors.lastname: Ishikura
authors.affiliation: Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Key Laboratory of Hormones and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China;
authors.forename: D
authors.initials: D
authors.lastname: Zhang
authors.affiliation: Clinical Laboratory, First Teaching Hospital of Tianjin University of TCM, Tianjin, China; and.
authors.forename: J
authors.initials: J
authors.lastname: Gao
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada;
authors.forename: Y
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Advanced Center for Chronic Diseases and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas/Facultad Medicina; Universidad de Chile; Santiago, Chile.
authors.forename: A
authors.initials: A
authors.lastname: Contreras-Ferrat
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada;
authors.forename: K P
authors.initials: KP
authors.lastname: Foley
authors.affiliation: Advanced Center for Chronic Diseases and Center for Molecular Studies of the Cell, Facultad de Ciencias Quimicas y Farmaceuticas/Facultad Medicina; Universidad de Chile; Santiago, Chile.
authors.forename: S
authors.initials: S
authors.lastname: Lavandero
authors.affiliation: Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Key Laboratory of Hormones and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China;
authors.forename: Z
authors.initials: Z
authors.lastname: Yao
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada;
authors.forename: P J
authors.initials: PJ
authors.lastname: Bilan
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, Canada;
authors.forename: A
authors.initials: A
authors.lastname: Klip
authors.affiliation: Department of Immunology, Key Laboratory of Immuno Microenvironment and Disease of the Educational Ministry of China, Key Laboratory of Hormones and Development (Ministry of Health), Metabolic Diseases Hospital and Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China; wniu@tijmu.edu.cn.
authors.forename: W
authors.initials: W
authors.lastname: Niu
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D000818:Animals; D020013:Calcium Signaling / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002478:Cells, Cultured; D004705:Endocytosis / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D015759:Ionomycin / Q000494:pharmacology; D051379:Mice; D032342:Muscle Cells / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects
chemical_list: D051275:Glucose Transporter Type 4; C495693:Slc2a4 protein, mouse; D015759:Ionomycin; D011493:Protein Kinase C; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D000263:Adenylate Kinase
keywords: AMPK; CAMKII; GLUT4; PKC; cytosolic Ca2+, endocytosis; exocytosis