title: Glut4 Is Sorted from a Rab10 GTPase-independent Constitutive Recycling Pathway into a Highly Insulin-responsive Rab10 GTPase-dependent Sequestration Pathway after Adipocyte Differentiation.
abstract: The RabGAP AS160/TBC1D4 controls exocytosis of the insulin-sensitive glucose transporter Glut4 in adipocytes. Glut4 is internalized and recycled through a highly regulated secretory pathway in these cells. Glut4 also cycles through a slow constitutive endosomal pathway distinct from the fast transferrin (Tf) receptor recycling pathway. This slow constitutive pathway is the only Glut4 cycling pathway in undifferentiated fibroblasts. The α2-macroglobulin receptor LRP1 cycles with Glut4 and the Tf receptor through all three exocytic pathways. To further characterize these pathways, the effects of knockdown of AS160 substrates on the trafficking kinetics of Glut4, LRP1, and the Tf receptor were measured in adipocytes and fibroblasts. Rab10 knockdown decreased cell surface Glut4 in insulin-stimulated adipocytes by 65%, but not in basal adipocytes or in fibroblasts. This decrease was due primarily to a 62% decrease in the rate constant of Glut4 exocytosis (kex), although Rab10 knockdown also caused a 1.4-fold increase in the rate constant of Glut4 endocytosis (ken). Rab10 knockdown in adipocytes also decreased cell surface LRP1 by 30% by decreasing kex 30-40%. There was no effect on LRP1 trafficking in fibroblasts or on Tf receptor trafficking in either cell type. These data confirm that Rab10 is an AS160 substrate that limits exocytosis through the highly insulin-responsive specialized secretory pathway in adipocytes. They further show that the slow constitutive endosomal (fibroblast) recycling pathway is Rab10-independent. Thus, Rab10 is a marker for the specialized pathway in adipocytes. Interestingly, mathematical modeling shows that Glut4 traffics predominantly through the specialized Rab10-dependent pathway both before and after insulin stimulation.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Nevada 89557.
authors.forename: Paul Duffield
authors.initials: PD
authors.lastname: Brewer
authors.affiliation: the Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut 06520, and.
authors.forename: Estifanos N
authors.initials: EN
authors.lastname: Habtemichael
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Nevada 89557.
authors.forename: Irina
authors.initials: I
authors.lastname: Romenskaia
authors.affiliation: From the Department of Biochemistry and Molecular Biology, University of Nevada, Reno, Nevada 89557, cmastick@unr.edu.
authors.forename: Cynthia Corley
authors.identifier: http://orcid.org/0000-0003-4769-5412
authors.initials: CC
authors.lastname: Mastick
authors.affiliation: the Department of Applied Mathematics, School of Mathematics and Statistics, University of New South Wales, Sydney, New South Wales 2052, Australia.
authors.forename: Adelle C F
authors.initials: AC
authors.lastname: Coster
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003198:Computer Simulation; D004705:Endocytosis / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D055785:Gene Knockdown Techniques; D051275:Glucose Transporter Type 4 / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D051379:Mice; D008954:Models, Biological; D011973:Receptors, LDL / Q000378:metabolism; D011990:Receptors, Transferrin / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C486645:Lrp1 protein, mouse; D011973:Receptors, LDL; D011990:Receptors, Transferrin; D025521:Tumor Suppressor Proteins; C520736:Rab10 protein, mouse; D020691:rab GTP-Binding Proteins
keywords: LRP1; Rab10; adipocyte; as160/TBC1D4; endocytosis; exocytosis; glucose; glucose transporter type 4 (GLUT4); insulin