Insulin-regulated Glut4 Translocation: MEMBRANE PROTEIN TRAFFICKING WITH SIX DISTINCTIVE STEPS*
| Autor: | Brewer, Paul Duffield, Habtemichael, Estifanos N., Romenskaia, Irina, Mastick, Cynthia Corley, Coster, Adelle C. F. |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2014 |
| Předmět: |
Glucose Transporter Type 4
endocrine system diseases Tumor Suppressor Proteins Cell Membrane GTPase-Activating Proteins nutritional and metabolic diseases Cell Differentiation Endosomes Fibroblasts musculoskeletal system Exocytosis Mice Protein Transport Metabolism Receptors LDL 3T3-L1 Cells Gene Knockdown Techniques Receptors Transferrin Adipocytes Animals Hypoglycemic Agents Insulin hormones hormone substitutes and hormone antagonists Low Density Lipoprotein Receptor-Related Protein-1 |
| Popis: | The trafficking kinetics of Glut4, the transferrin (Tf) receptor, and LRP1 were quantified in adipocytes and undifferentiated fibroblasts. Six steps were identified that determine steady state cell surface Glut4: (i) endocytosis, (ii) degradation, (iii) sorting, (iv) sequestration, (v) release, and (vi) tethering/docking/fusion. Endocytosis of Glut4 is 3 times slower than the Tf receptor in fibroblasts (ken = 0.2 min(-1) versus 0.6 min(-1)). Differentiation decreases Glut4 ken 40% (ken = 0.12 min(-1)). Differentiation also decreases Glut4 degradation, increasing total and cell surface Glut4 3-fold. In fibroblasts, Glut4 is recycled from endosomes through a slow constitutive pathway (kex = 0.025-0.038 min(-1)), not through the fast Tf receptor pathway (kex = 0.2 min(-1)). The kex measured in adipocytes after insulin stimulation is similar (kex = 0.027 min(-1)). Differentiation decreases the rate constant for sorting into the Glut4 recycling pathway (ksort) 3-fold. In adipocytes, Glut4 is also sorted from endosomes into a second exocytic pathway through Glut4 storage vesicles (GSVs). Surprisingly, transfer from endosomes into GSVs is highly regulated; insulin increases the rate constant for sequestration (kseq) 8-fold. Release from sequestration in GSVs is rate-limiting for Glut4 exocytosis in basal adipocytes. AS160 regulates this step. Tethering/docking/fusion of GSVs to the plasma membrane is regulated through an AS160-independent process. Insulin increases the rate of release and fusion of GSVs (kfuseG) 40-fold. LRP1 cycles with the Tf receptor and Glut4 in fibroblasts but predominantly with Glut4 after differentiation. Surprisingly, AS160 knockdown accelerated LRP1 exocytosis in basal and insulin-stimulated adipocytes. These data indicate that AS160 may regulate trafficking into as well as release from GSVs. |
| Databáze: | OpenAIRE |
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