title: Insulin regulates Glut4 confinement in plasma membrane clusters in adipose cells.
abstract: Insulin-stimulated delivery of glucose transporter-4 (GLUT4) to the plasma membrane (PM) is the hallmark of glucose metabolism. In this study we examined insulin's effects on GLUT4 organization in PM of adipose cells by direct microscopic observation of single monomers tagged with photoswitchable fluorescent protein. In the basal state, after exocytotic delivery only a fraction of GLUT4 is dispersed into the PM as monomers, while most of the GLUT4 stays at the site of fusion and forms elongated clusters (60-240 nm). GLUT4 monomers outside clusters diffuse freely and do not aggregate with other monomers. In contrast, GLUT4 molecule collision with an existing cluster can lead to immediate confinement and association with that cluster. Insulin has three effects: it shifts the fraction of dispersed GLUT4 upon delivery, it augments the dissociation of GLUT4 monomers from clusters ∼3-fold and it decreases the rate of endocytic uptake. All together these three effects of insulin shift most of the PM GLUT4 from clustered to dispersed states. GLUT4 confinement in clusters represents a novel kinetic mechanism for insulin regulation of glucose homeostasis.
authors.affiliation: Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Lizunov
authors.forename: Karin
authors.initials: K
authors.lastname: Stenkula
authors.forename: Aaron
authors.initials: A
authors.lastname: Troy
authors.forename: Samuel W
authors.initials: SW
authors.lastname: Cushman
authors.forename: Joshua
authors.initials: J
authors.lastname: Zimmerberg
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D021961:Cell Membrane Structures / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000235:genetics / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism*; D006706:Homeostasis / Q000502:physiology*; D007328:Insulin / Q000378:metabolism*; D008297:Male; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; C495694:Slc2a4 protein, rat; D005947:Glucose