In vivo regulation of protein-serine kinases by insulin in skeletal muscle of fructose-hypertensive rats.
The effects of tail-vein insulin injection (2 U/kg) on the regulation of protein-serine kinases in hindlimb skeletal muscle were investigated in hyperinsulinemic hypertensive fructose-fed (FF) animals that had been fasted overnight. Basal protein kinase B (PKB) activity was elevated about twofold in FF rats and was not further stimulated by insulin. Phosphatidylinositol 3-kinase (PI3K), which lies upstream of PKB, was increased approximately 3.5-fold within 2-5 min by insulin in control rats. Basal and insulin-activated PI3K activities were further enhanced up to 2-fold and 1.3-fold, respectively, in FF rats. The 70-kDa S6 kinase (S6K) was stimulated about twofold by insulin in control rats. Both basal and insulin-stimulated S6K activity was further enhanced up to 1.5-fold and 3.5-fold, respectively, in FF rats. In control rats, insulin caused a 40-50% reduction of the phosphotransferase activity of the beta-isoform of glycogen synthase kinase 3 (GSK-3beta), which is a PKB target in vitro. Basal GSK-3beta activity was decreased by approximately 40% in FF rats and remained unchanged after insulin treatment. In summary, 1) the PI3K --> PKB --> S6K pathway was upregulated under basal conditions, and 2) insulin stimulation of PI3K and S6K activities was enhanced, but both PKB and GSK-3 were refractory to the effects of insulin in FF rats.
Bhanot
S
S
Department of Medicine, Faculty of Medicine, The University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3.
Salh
B S
BS
Verma
S
S
McNeill
J H
JH
Pelech
S L
SL
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D005632:Fructose; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006946:Hyperinsulinism / Q000201:enzymology; D006973:Hypertension / Q000139:chemically induced* / Q000201:enzymology* / Q000378:metabolism; D007328:Insulin / Q000502:physiology*; D018482:Muscle, Skeletal / Q000201:enzymology*; D004676:Myelin Basic Protein / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism
D017871:Calcium-Calmodulin-Dependent Protein Kinases; D005632:Fructose; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D007328:Insulin; D004676:Myelin Basic Protein; D019869:Phosphatidylinositol 3-Kinases; D010770:Phosphotransferases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019893:Ribosomal Protein S6 Kinases