title: The translocation of the glucose transporter sub-types GLUT1 and GLUT4 in isolated fat cells is differently regulated by phorbol esters.
abstract: Insulin stimulates glucose transport in isolated fat cells by activation of glucose transporters in the plasma membranes and through translocation of the glucose transporter sub-types GLUT4 (insulin-regulatable) and GLUT1 (HepG2 transporter). The protein kinase C-stimulating phorbol ester phorbol 12-myristate 13-acetate (PMA) is able to mimic partially the effect of insulin on glucose transport, apparently through stimulation of carrier translocation. In order to ascertain whether protein kinase C is involved in the translocation signal to both carrier sub-types, we determined the effect of PMA on the subcellular distribution of GLUT1 and GLUT4 by immunoblotting with specific antibodies directed against these transporters. Isolated rat fat cells (4 x 10(6) cells/ml) were stimulated for 20 min with insulin (6 nM) or PMA (1 nM). 3-O-Methylglucose transport was determined and plasma membranes and low-density microsomes were prepared for Western blotting. 3-O-Methylglucose transport was stimulated 8-9-fold by insulin, and 3-4-fold by PMA (basal, 5.6 +/- 2.3%; insulin, 43.6 +/- 7.3%; PMA, 18.4 +/- 4.9%, n = 9). PMA was able to increase the amount of GLUT4 in the plasma membrane fraction by 2.5(+/- 0.9)-fold (n = 6) whereas insulin stimulation was 4.4(+/- 1.7)-fold (n = 6), paralleled by a corresponding decrease of transport in the low-density microsomes (insulin, 50 +/- 5% of basal; PMA, 63 +/- 11% of basal, n = 6). Although PMA regulates the translocation of GLUT4, it has no effect on GLUT1 in the same cell fractions (increase in plasma membranes: insulin, 1.7 +/- 0.5-fold; PMA, 0.91 +/- 0.1-fold, n = 4; decrease in low-density microsomes: insulin, 53 +/- 11% of basal; PMA, 101 +/- 5% of basal, n = 4). These data are in favour of a role for protein kinase C in signal transduction to GLUT4 but not to GLUT1 in fat cells.
authors.affiliation: Institut für Diabetesforschung, München, Federal Republic of Germany.
authors.forename: B
authors.initials: B
authors.lastname: Vogt
authors.forename: J
authors.initials: J
authors.lastname: Mushack
authors.forename: E
authors.initials: E
authors.lastname: Seffer
authors.forename: H U
authors.initials: HU
authors.lastname: Häring
mesh_terms: D019325:3-O-Methylglucose; D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D008297:Male; D008757:Methylglucosides / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D007328:Insulin; D008757:Methylglucosides; D009004:Monosaccharide Transport Proteins; D019325:3-O-Methylglucose; D013755:Tetradecanoylphorbol Acetate