title: Phosphorylation of the adipose/muscle-type glucose transporter (GLUT4) and its relationship to glucose transport activity.
abstract: The effects of protein phosphorylation and dephosphorylation on glucose transport activity reconstituted from adipocyte membrane fractions and its relationship to the phosphorylation state of the adipose/muscle-type glucose transporter (GLUT4) were studied. In vitro phosphorylation of membranes in the presence of ATP and protein kinase A produced a stimulation of the reconstituted glucose transport activity in plasma membranes and low-density microsomes (51% and 65% stimulation respectively), provided that the cells had been treated with insulin prior to isolation of the membranes. Conversely, treatment of membrane fractions with alkaline phosphatase produced an inhibition of reconstituted transport activity. However, in vitro phosphorylation catalysed by protein kinase C failed to alter reconstituted glucose transport activity in membrane fractions from both basal and insulin-treated cells. In experiments run under identical conditions, the phosphorylation state of GLUT4 was investigated by immunoprecipitation of glucose transporters from membrane fractions incubated with [32P]ATP and protein kinases A and C. Protein kinase C stimulated a marked phosphate incorporation into GLUT4 in both plasma membranes and low-density microsomes. Protein kinase A, in contrast to its effect on reconstituted glucose transport activity, produced a much smaller phosphorylation of the GLUT4 in plasma membranes than in low-density microsomes. The present data suggest that glucose transport activity can be modified by protein phosphorylation via an insulin-dependent mechanism. However, the phosphorylation of the GLUT4 itself was not correlated with changes in its reconstituted transport activity.
authors.affiliation: Institut für Pharmakologie und Toxikologie, RWTH Aachen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schürmann
authors.forename: G
authors.initials: G
authors.lastname: Mieskes
authors.forename: H G
authors.initials: HG
authors.lastname: Joost
mesh_terms: D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D009132:Muscles / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology; D010766:Phosphorylation; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010703:Phorbol Esters; C495694:Slc2a4 protein, rat; D011494:Protein Kinases; D011493:Protein Kinase C; D000469:Alkaline Phosphatase; D005947:Glucose; D007545:Isoproterenol