title: Rab14 limits the sorting of Glut4 from endosomes into insulin-sensitive regulated secretory compartments in adipocytes.
abstract: Insulin increases glucose uptake by increasing the rate of exocytosis of the facilitative glucose transporter isoform 4 (Glut4) relative to its endocytosis. Insulin also releases Glut4 from highly insulin-regulated secretory compartments (GSVs or Glut4 storage vesicles) into constitutively cycling endosomes. Previously it was shown that both overexpression and knockdown of the small GTP-binding protein Rab14 decreased Glut4 translocation to the plasma membrane (PM). To determine the mechanism of this perturbation, we measured the effects of Rab14 knockdown on the trafficking kinetics of Glut4 relative to two proteins that partially co-localize with Glut4, the transferrin (Tf) receptor and low-density-lipoprotein-receptor-related protein 1 (LRP1). Our data support the hypothesis that Rab14 limits sorting of proteins from sorting (or 'early') endosomes into the specialized GSV pathway, possibly through regulation of endosomal maturation. This hypothesis is consistent with known Rab14 effectors. Interestingly, the insulin-sensitive Rab GTPase-activating protein Akt substrate of 160 kDa (AS160) affects both sorting into and exocytosis from GSVs. It has previously been shown that exocytosis of GSVs is rate-limited by Rab10, and both Rab10 and Rab14 are in vitro substrates of AS160. Regulation of both entry into and exit from GSVs by AS160 through sequential Rab substrates would provide a mechanism for the finely tuned 'quantal' increases in cycling Glut4 observed in response to increasing concentrations of insulin.
authors.affiliation: Department of Biochemistry and Molecular Biology, and Department of Pharmacology, University of Nevada, Reno, NV 89557, U.S.A.
authors.forename: Paul Duffield
authors.initials: PD
authors.lastname: Brewer
authors.affiliation: Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT 06520, U.S.A.
authors.forename: Estifanos N
authors.initials: EN
authors.lastname: Habtemichael
authors.affiliation: Department of Biochemistry and Molecular Biology, and Department of Pharmacology, University of Nevada, Reno, NV 89557, U.S.A.
authors.forename: Irina
authors.initials: I
authors.lastname: Romenskaia
authors.affiliation: Department of Applied Mathematics, School of Mathematics and Statistics, University of New South Wales, Sydney 2052, Australia.
authors.forename: Adelle C F
authors.initials: AC
authors.lastname: Coster
authors.affiliation: Department of Biochemistry and Molecular Biology, and Department of Pharmacology, University of Nevada, Reno, NV 89557, U.S.A. cmastick@unr.edu.
authors.forename: Cynthia Corley
authors.initials: CC
authors.lastname: Mastick
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D004705:Endocytosis / Q000235:genetics / Q000502:physiology; D011992:Endosomes / Q000378:metabolism*; D005434:Flow Cytometry; D007328:Insulin / Q000494:pharmacology; D008259:Macroglobulins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D021381:Protein Transport / Q000502:physiology; D014168:Transferrin / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D007328:Insulin; D008259:Macroglobulins; D014168:Transferrin; C555882:Rab14 protein, mouse; D020691:rab GTP-Binding Proteins
keywords: LRP1; Rab14; adipocyte; glucose transporter isoform 4 (Glut4); insulin; transferrin