Increased flux through the hexosamine biosynthesis pathway inhibits glucose transport acutely by activation of protein kinase C.
The hexosamine biosynthesis pathway and protein kinase C (PKC) activation mediate hyperglycaemia-induced impaired glucose transport, but the relative role of each pathway is unknown. Following a 2 h preincubation of rat adipocytes in the presence of either high glucose (30 mM) plus insulin (0.7 nM) or glucosamine (3 mM), both high glucose and glucosamine inhibited subsequent basal and insulin-stimulated glucose transport, measured at 5.0 mM glucose. Azaserine, an inhibitor of the enzyme glutamine:fructose-6-phosphate aminotransferase, abolished the effect of high glucose, but not that of glucosamine. Ro-31-8220, an inhibitor of PKC, reversed the effects of both high glucose and glucosamine, suggesting that flux through the hexosamine biosynthesis pathway impaired glucose transport acutely by activating PKC. Both high glucose and glucosamine caused a 3-fold increase in PKC activity; this effect of high glucose, but not that of glucosamine, was partially decreased by azaserine. Neither high glucose nor glucosamine altered basal or insulin-stimulated plasma membrane GLUT1 levels, whereas both treatments decreased basal, but not insulin-stimulated, GLUT4 levels. Azaserine abolished the effect of high glucose, but not that of glucosamine, on basal plasma membrane GLUT4 levels. Ro-31-8220, which returned glucose transport to control values, caused a further decrease in plasma membrane GLUT4 levels. It is concluded that, in rat adipocytes, an acute increase in flux through the hexosamine biosynthesis pathway inhibits glucose transport by activation of PKC.
Filippis
A
A
The University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville 3050, Victoria, Australia.
Clark
S
S
Proietto
J
J
D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D004789:Enzyme Activation; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D006595:Hexosamines / Q000096:biosynthesis / Q000378:metabolism*; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D006595:Hexosamines; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495679:Slc2a1 protein, rat; C495694:Slc2a4 protein, rat; D011493:Protein Kinase C; D005947:Glucose