Insulin promotes the cell surface recruitment of the SAT2/ATA2 system A amino acid transporter from an endosomal compartment in skeletal muscle cells.
SAT1-3 comprise members of the recently cloned family of System A transporters that mediate the sodium-coupled uptake of short chain neutral amino acids, and their activity is regulated extensively by stimuli such as insulin, growth factors, and amino acid availability. In skeletal muscle, insulin stimulates System A activity rapidly by a presently ill-defined mechanism. Here we demonstrate that insulin induces an increase in the plasma membrane abundance of SAT2 in a phosphatidylinositol 3-kinase-dependent manner and that this increase is derived from an endosomal compartment that is required for the hormonal activation of System A. Chloroquine, an acidotropic weak base that impairs endosomal recycling of membrane proteins, induced a complete inhibition in the insulin-mediated stimulation of System A, which was associated with a loss in SAT2 recruitment to the plasma membrane. The failure to stimulate System A and recruit SAT2 to the cell surface could not be attributed to a block in insulin signaling, as chloroquine had no effect on the insulin-mediated phosphorylation of protein kinase B or glycogen synthase kinase 3 or upon insulin-stimulated GLUT4 translocation and glucose transport. Our data indicate strongly that insulin increases System A transport in L6 cells by stimulating the exocytosis of SAT2 carriers from a chloroquine-sensitive endosomal compartment.
Hyde
Russell
R
Division of Molecular Physiology, Medical Sciences Institute/Wellcome Trust Biocentre Complex, Dow Street, University of Dundee, Dundee DD1 5EH, United Kingdom.
Peyrollier
Karine
K
Hundal
Harinder S
HS
D026924:Amino Acid Transport System A / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002738:Chloroquine / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D011992:Endosomes / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D007328:Insulin / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D051379:Mice; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D021381:Protein Transport; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014168:Transferrin / Q000378:metabolism
D026924:Amino Acid Transport System A; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002738:Chloroquine; D004791:Enzyme Inhibitors; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D014168:Transferrin; C498798:Slc38a2 protein, mouse; C412568:Slc38a2 protein, rat