Insulin stimulation of glutamine: fructose-6-phosphate amidotransferase occurs via an insulin-like growth factor-1 pathway in rat fibroblasts.
The biosynthetic pathway for hexosamine mediates some of the adverse effects of high glucose. The rate limiting enzyme in this pathway is glutamine:fructose-6-phosphate amidotransferase (GFA). Using HPLC, the regulation of GFA activity by glucose and insulin was studied in wild type and rat-1 fibroblasts overexpressing human insulin receptors (HIRcB cells). In wild type cells only maximal doses of insulin (580 ng/ml) resulted in an increase in GFA activity (51.0 +/- 40.6%). In HIRcB cells insulin led to a dose dependent increase in GFA activity that was enhanced when compared to wild type (89 +/- 5% (p<0.001) increase at 580 ng/ml). Insulin's action was glucose dependent and required prolonged serum deprivation. HIRcB's cultured in 0 mM glucose had a 58.2% (p<0.001) decrease in insulin stimulation. However, when present the concentration of glucose (2-20 mM) did not affect insulin stimulation of GFA activity. Most of insulin's effects occur by way of the IGF-1 receptor as a two-fold stimulation of GFA activity was seen with significantly lower doses (10 ng/ml) of IGF-1. We conclude that GFA enzyme activity is upregulated by insulin and this may occur via a IGF-1 receptor mediated pathway.
Simmons
S T
ST
Department of Medicine, University of Mississippi Medical Center, Jackson 39216, USA.
Daniels
M C
MC
Huddleston
E
E
Hebert
L F
LF
McClain
D A
DA
Crook
E D
ED
D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D051381:Rats; D017451:Receptors, Somatomedin / Q000378:metabolism
D007328:Insulin; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing)