title: Glycogen synthase kinase-3 beta activity is critical for neuronal death caused by inhibiting phosphatidylinositol 3-kinase or Akt but not for death caused by nerve growth factor withdrawal.
abstract: Numerous studies reveal that phosphatidylinositol (PI) 3-kinase and Akt protein kinase are important mediators of cell survival. However, the survival-promoting mechanisms downstream of these enzymes remain uncharacterized. Glycogen synthase kinase-3 beta (GSK-3 beta), which is inhibited upon phosphorylation by Akt, was recently shown to function during cell death induced by PI 3-kinase inhibitors. In this study, we tested whether GSK-3 beta is critical for the death of sympathetic neurons caused by the withdrawal of their physiological survival factor, the nerve growth factor (NGF). Stimulation with NGF resulted in PI 3-kinase-dependent phosphorylation of GSK-3 beta and inhibition of its protein kinase activity, indicating that GSK-3 beta is targeted by PI 3-kinase/Akt in these neurons. Expression of the GSK-3 beta inhibitor Frat1, but not a mutant Frat1 protein that does not bind GSK-3 beta, rescued neurons from death caused by inhibiting PI 3-kinase. Similarly, expression of Frat1 or kinase-deficient GSK-3 beta reduced death caused by inhibiting Akt. In NGF-maintained neurons, overexpression of GSK-3 beta caused a small but significant decrease in survival. However, expression of neither Frat1, kinase-deficient GSK-3 beta, nor GSK-3-binding protein inhibited NGF withdrawal-induced death. Thus, although GSK-3 beta function is required for death caused by inactivation of PI 3-kinase and Akt, neuronal death caused by NGF withdrawal can proceed through GSK-3 beta-independent pathways.
authors.affiliation: Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
authors.forename: R J
authors.initials: RJ
authors.lastname: Crowder
authors.forename: R S
authors.initials: RS
authors.lastname: Freeman
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D002478:Cells, Cultured; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D020932:Nerve Growth Factor / Q000378:metabolism* / Q000502:physiology; D009474:Neurons / Q000166:cytology / Q000201:enzymology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors*; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats
chemical_list: D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D020932:Nerve Growth Factor; D038341:Glycogen Synthase Kinases; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3