title: Intracellular delivery of phosphatidylinositol (3,4,5)-trisphosphate causes incorporation of glucose transporter 4 into the plasma membrane of muscle and fat cells without increasing glucose uptake.
abstract: Insulin stimulates glucose uptake into muscle and fat cells by translocating glucose transporter 4 (GLUT4) to the cell surface, with input from phosphatidylinositol (PI) 3-kinase and its downstream effector Akt/protein kinase B. Whether PI 3,4,5-trisphosphate (PI(3,4,5)P(3)) suffices to produce GLUT4 translocation is unknown. We used two strategies to deliver PI(3,4,5)P(3) intracellularly and two insulin-sensitive cell lines to examine Akt activation and GLUT4 translocation. In 3T3-L1 adipocytes, the acetoxymethyl ester of PI(3,4,5)P(3) caused GLUT4 migration to the cell periphery and increased the amount of plasma membrane-associated phospho-Akt and GLUT4. Intracellular delivery of PI(3,4,5)P(3) using polyamine carriers also induced translocation of myc-tagged GLUT4 to the surface of intact L6 myoblasts, demonstrating membrane insertion of the transporter. GLUT4 translocation caused by carrier-delivered PI(3,4,5)P(3) was not reproduced by carrier-PI 4,5-bisphosphate or carrier alone. Like insulin, carrier-mediated delivery of PI(3,4,5)P(3) elicited redistribution of perinuclear GLUT4 and Akt phosphorylation at the cell periphery. In contrast to its effect on GLUT4 mobilization, delivered PI(3,4,5)P(3) did not increase 2-deoxyglucose uptake in either L6GLUT4myc myoblasts or 3T3-L1 adipocytes. The ability of exogenously delivered PI(3,4,5)P(3) to augment plasma membrane GLUT4 content without increasing glucose uptake suggests that input at the level of PI 3-kinase suffices for GLUT4 translocation but is insufficient to stimulate glucose transport.
authors.affiliation: Programme in Cell Biology, Hospital for Sick Children, and Department of Biology, York University, Toronto, Ontario, Canada.
authors.forename: Gary
authors.initials: G
authors.lastname: Sweeney
authors.forename: Rami R
authors.initials: RR
authors.lastname: Garg
authors.forename: Rolando B
authors.initials: RB
authors.lastname: Ceddia
authors.forename: Dailin
authors.initials: D
authors.lastname: Li
authors.forename: Manabu
authors.initials: M
authors.lastname: Ishiki
authors.forename: Romel
authors.initials: R
authors.lastname: Somwar
authors.forename: Leonard J
authors.initials: LJ
authors.lastname: Foster
authors.forename: Paul O
authors.initials: PO
authors.lastname: Neilsen
authors.forename: Glenn D
authors.initials: GD
authors.lastname: Prestwich
authors.forename: Assaf
authors.initials: A
authors.lastname: Rudich
authors.forename: Amira
authors.initials: A
authors.lastname: Klip
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003847:Deoxyglucose / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005452:Fluoresceins / Q000494:pharmacology; D019084:Fluorescent Antibody Technique, Indirect; D005947:Glucose / Q000493:pharmacokinetics*; D051275:Glucose Transporter Type 4; D051379:Mice; D008856:Microscopy, Fluorescence; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D009132:Muscles / Q000378:metabolism*; D032446:Myoblasts / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry*; D010766:Phosphorylation; D020033:Protein Isoforms; D021381:Protein Transport
chemical_list: D005452:Fluoresceins; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D018129:Phosphatidylinositol Phosphates; D020033:Protein Isoforms; C495693:Slc2a4 protein, mouse; C060974:phosphatidylinositol 3,4,5-triphosphate; C057433:2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D003847:Deoxyglucose; D005947:Glucose