Regulation and function of glycogen synthase kinase-3 isoforms in neuronal survival.
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase consisting of two isoforms, alpha and beta. The activities of GSK-3 are regulated negatively by serine phosphorylation but positively by tyrosine phosphorylation. GSK-3 inactivation has been proposed as a mechanism to promote neuronal survival. We used GSK-3 isoform-specific small interfering RNAs, dominant-negative mutants, or pharmacological inhibitors to search for functions of the two GSK-3 isoforms in regulating neuronal survival in cultured cortical neurons in response to glutamate insult or during neuronal maturation/aging. Surprisingly, RNA interference-induced depletion of either isoform was sufficient to block glutamate-induced excitotoxicity, and the resulting neuroprotection was associated with enhanced N-terminal serine phosphorylation in both GSK-3 isoforms. However, GSK-3beta depletion was more effective than GSK-3alpha depletion in suppressing spontaneous neuronal death in extended culture. This phenomenon is likely due to selective and robust inhibition of GSK-3beta activation resulting from GSK-3beta Ser9 dephosphorylation during the course of spontaneous neuronal death. GSK-3alpha silencing resulted in reduced tyrosine phosphorylation of GSK-3beta, suggesting that tyrosine phosphorylation is also a critical autoregulatory event. Interestingly, GSK-3 inhibitors caused a rapid and long-lasting increase in GSK-3alpha Ser21 phosphorylation levels, followed by a delayed increase in GSK-3beta Ser9 phosphorylation and a decrease in GSK-3alpha Tyr279 and GSK-3beta Tyr216 phosphorylation, thus implying additional levels of GSK-3 autoregulation. Taken together, our results underscore important similarities and dissimilarities of GSK-3alpha and GSK-3beta in the roles of cell survival as well as their distinct modes of regulation. The development of GSK-3 isoform-specific inhibitors seems to be warranted for treating GSK-3-mediated pathology.
Liang
Min-Huei
MH
Molecular Neurobiology Section, National Institute of Mental Health, Bethesda, Maryland 20892-1363, USA.
Chuang
De-Maw
DM
D000818:Animals; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000187:drug effects / Q000201:enzymology; D020868:Gene Silencing; D018698:Glutamic Acid / Q000633:toxicity; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000071679:Glycogen Synthase Kinase 3 beta; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D009154:Mutation; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D009924:Organ Culture Techniques; D010766:Phosphorylation / Q000187:drug effects; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D014162:Transfection
D007527:Isoenzymes; D034741:RNA, Small Interfering; D018698:Glutamic Acid; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3; C448021:glycogen synthase kinase 3 alpha