Tyrosine dephosphorylation of glycogen synthase kinase-3 is involved in its extracellular signal-dependent inactivation.
We examined whether extracellular signals regulate glycogen synthase kinase-3 (GSK-3) activity through tyrosine dephosphorylation of GSK-3. In resting Chinese hamster ovary cells overexpressing the human insulin receptor (CHO-IR cells), GSK-3 was tyrosine-phosphorylated and active. Insulin and 12-0-tetradecanoylphorbol 13-acetate (TPA) induced inactivation and tyrosine dephosphorylation of GSK-3. It is known that Ser-9 of GSK-3beta is phosphorylated in response to insulin and that the phosphorylation of this amino acid residue causes inactivation of GSK-3beta. However, the ectopically expressed GSK-3beta(delta9), in which the N-terminal nine amino acids of GSK-3beta were deleted, was still inactivated and tyrosine-dephosphorylated in response to insulin. Protein phosphatase 2A treatment partially reversed insulin-induced GSK-3beta inactivation, but did not change GSK-3beta(delta9) inactivation. In CHO-IR cells where protein kinase C was down-regulated, TPA neither inactivated nor tyrosine-dephosphorylated GSK-3. However, insulin inactivated and tyrosine-dephosphorylated GSK-3, although to a lesser degree than in the control cells. These results suggest that in addition to serine phosphorylation, tyrosine dephosphorylation of GSK-3 is also important for the regulation of GSK-3 activity in response to extracellular signals and that insulin regulates GSK-3 activity through both protein kinase C-dependent as well as protein kinase C-independent pathways.
Murai
H
H
Department of Biochemistry, Hiroshima University School of Medicine, Japan.
Okazaki
M
M
Kikuchi
A
A
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D008969:Molecular Sequence Data; D010766:Phosphorylation; D012694:Serine / Q000378:metabolism; D015398:Signal Transduction; D014443:Tyrosine / Q000378:metabolism*
D007328:Insulin; D014443:Tyrosine; D012694:Serine; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3