title: Endoproteolytic cleavage of TUG protein regulates GLUT4 glucose transporter translocation.
abstract: To promote glucose uptake into fat and muscle cells, insulin causes the translocation of GLUT4 glucose transporters from intracellular vesicles to the cell surface. Previous data support a model in which TUG traps GLUT4-containing vesicles and tethers them intracellularly in unstimulated cells and in which insulin mobilizes this pool of vesicles by releasing this tether. Here we show that TUG undergoes site-specific endoproteolytic cleavage, which separates a GLUT4-binding, N-terminal region of TUG from a C-terminal region previously suggested to bind an intracellular anchor. Cleavage is accelerated by insulin stimulation in 3T3-L1 adipocytes and is highly dependent upon adipocyte differentiation. The N-terminal TUG cleavage product has properties of a novel 18-kDa ubiquitin-like modifier, which we call TUGUL. The C-terminal product is observed at the expected size of 42 kDa and also as a 54-kDa form that is released from membranes into the cytosol. In transfected cells, intact TUG links GLUT4 to PIST and also binds Golgin-160 through its C-terminal region. PIST is an effector of TC10α, a GTPase previously shown to transmit an insulin signal required for GLUT4 translocation, and we show using RNAi that TC10α is required for TUG proteolytic processing. Finally, we demonstrate that a cleavage-resistant form of TUG does not support highly insulin-responsive GLUT4 translocation or glucose uptake in 3T3-L1 adipocytes. Together with previous results, these data support a model whereby insulin stimulates TUG cleavage to liberate GLUT4 storage vesicles from the Golgi matrix, which promotes GLUT4 translocation to the cell surface and enhances glucose uptake.
authors.affiliation: Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520-8020, USA. jonathan.bogan@yale.edu
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Bogan
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Rubin
authors.forename: Chenfei
authors.initials: C
authors.lastname: Yu
authors.forename: Michael G
authors.initials: MG
authors.lastname: Löffler
authors.forename: Charisse M
authors.initials: CM
authors.lastname: Orme
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Belman
authors.forename: Leah J
authors.initials: LJ
authors.lastname: McNally
authors.forename: Mingming
authors.initials: M
authors.lastname: Hao
authors.forename: James A
authors.initials: JA
authors.lastname: Cresswell
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism* / Q000493:pharmacokinetics; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D007328:Insulin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D021381:Protein Transport / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D034622:RNA Interference; D017386:Sequence Homology, Amino Acid
chemical_list: C478539:Aspscr1 protein, mouse; D002352:Carrier Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D049452:Green Fluorescent Proteins; D005947:Glucose