title: Muscle cells engage Rab8A and myosin Vb in insulin-dependent GLUT4 translocation.
abstract: Insulin causes translocation of glucose transporter 4 (GLUT4) to the membrane of muscle and fat cells, a process requiring Akt activation. Two Rab-GTPase-activating proteins (Rab-GAP), AS160 and TBC1D1, were identified as Akt substrates. AS160 phosphorylation is required for insulin-stimulated GLUT4 translocation, but the participation of TBC1D1 on muscle cell GLUT4 is unknown. Moreover, there is controversy as to the AS160/TBC1D1 target Rabs in fat and muscle cells, and Rab effectors are unknown. Here we examined the effect of knockdown of AS160, TBC1D1, and Rabs 8A, 8B, 10, and 14 (in vitro substrates of AS160 and TBC1D1 Rab-GAP activities) on insulin-induced GLUT4 translocation in L6 muscle cells. Silencing AS160 or TBC1D1 increased surface GLUT4 in unstimulated cells but did not prevent insulin-induced GLUT4 translocation. Knockdown of Rab8A and Rab14, but not of Rab8B or Rab10, inhibited insulin-induced GLUT4 translocation. Furthermore, silencing Rab8A or Rab14 but not Rab8B or Rab10 restored the basal-state intracellular retention of GLUT4 impaired by AS160 or TBC1D1 knockdown. Lastly, overexpression of a fragment of myosin Vb, a recently identified Rab8A-interacting protein, inhibited insulin-induced GLUT4 translocation and altered the subcellular distribution of GTP-loaded Rab8A. These results support a model whereby AS160, Rab8A, and myosin Vb are required for insulin-induced GLUT4 translocation in muscle cells, potentially as part of a linear signaling cascade.
authors.affiliation: Cell Biology Program, The Hospital for Sick Children, Toronto, Ontario, M5G 1X8, Canada.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Ishikura
authors.forename: Amira
authors.initials: A
authors.lastname: Klip
mesh_terms: D000818:Animals; D002460:Cell Line; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D032342:Muscle Cells / Q000378:metabolism*; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism*; D009218:Myosins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D020690:GTPase-Activating Proteins; D051275:Glucose Transporter Type 4; D007328:Insulin; C101826:Myo5b protein, rat; D009687:Nuclear Proteins; C082378:Rab10 protein, rat; C495694:Slc2a4 protein, rat; C533101:TBC1D4 protein, rat; D006160:Guanosine Triphosphate; D024701:Myosin Type V; C494592:Rab14 protein, rat; C530052:Rab8a protein, rat; D009218:Myosins; D020691:rab GTP-Binding Proteins