The role of glucose metabolites in the activation and translocation of glycogen synthase by insulin in 3T3-L1 adipocytes.
The role of increased glucose transport in the hormonal regulation of glycogen synthase by insulin was investigated in 3T3-L1 adipocytes. Insulin treatment stimulated glycogen synthase activity 4-5-fold in these cells. Cytosolic glycogen synthase levels decreased by 75% in response to insulin, whereas, conversely, the glycogenolytic agent isoproterenol increased cytosolic enzyme levels by 200%. Removal of extracellular glucose reduced glycogen synthase activation by 40% and completely blocked enzymatic translocation. Addition of 5 mM 2-deoxyglucose did not restore glycogen synthase translocation but did augment dephosphorylation of the protein by insulin. The translocation event could be reconstituted in vitro only by the addition of UDP-glucose to basal cell lysates. Amylase pretreatment of the extracts suppressed glycogen synthase translocation, indicating that the enzyme was binding to glycogen. Incubation of 3T3-L1 adipocytes with 10 mM glucosamine induced a state of insulin resistance, blocked the translocation of glycogen synthase, and inhibited insulin-stimulated glycogen synthesis by 50%. Surprisingly, glycogen synthase activation by insulin was enhanced 4-fold, in part due to allosteric activation by a glucosamine metabolite. In vitro, glucosamine 6-phosphate and glucose 6-phosphate stimulated glycogen synthase activity with similar concentration curves. These results indicate that glucose metabolites have an impact on the regulation of glycogen synthase activation and localization by insulin.
Brady
M J
MJ
Department of Cell Biology, Parke-Davis Pharmaceutical Research Division, Ann Arbor, Michigan 48105, USA.
Kartha
P M
PM
Aysola
A A
AA
Saltiel
A R
AR
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000681:Amylases / Q000494:pharmacology; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D005944:Glucosamine / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology* / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D015398:Signal Transduction / Q000502:physiology; D014532:Uridine Diphosphate Glucose / Q000378:metabolism
D007328:Insulin; D006003:Glycogen; D006006:Glycogen Synthase; D000681:Amylases; D005947:Glucose; D007545:Isoproterenol; D005944:Glucosamine; D014532:Uridine Diphosphate Glucose