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Molecular and Cellular Biology, March 2008, p. 1515-1527, Vol. 28, No. 5
0270-7306/08/$08.00+0 doi:10.1128/MCB.02227-06
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Turku Centre for Biotechnology, Turku University and Åbo Akademi University, Turku, Finland,1 A. I. Virtanen Institute, University of Kuopio, Kuopio, Finland2
Received 28 November 2006/ Returned for modification 3 January 2007/ Accepted 10 December 2007
Glycogen synthase kinase 3 (GSK-3) is implicated in neuronal death through a causal role, and precise mechanisms have not been unambiguously defined. We show that short hairpin RNA (shRNA) knockdown of GSK-3β, but not GSK-3
, protects cerebellar granule neurons from trophic-deprivation-induced death. Using compartment-targeted inhibitors of the Wnt-regulated GSK-3 pool, NLS-FRAT1, NES-FRAT1, and axin-GSK-3-interacting domain (axin-GID), we locate proapoptotic GSK-3 action to the cytosol and regulation of Bim protein turnover despite constitutive cycling of GSK-3 between the cytosol and nucleus, revealed by leptomycin B. We examine the importance of Ser21/9 (GSK-3
/β) phosphorylation on proapoptotic GSK-3 function. Neurons isolated from GSK-3
/βS21A/S9A knock-in mice survive normally and are fully sensitive to trophic-deprivation-induced death. Nonetheless, inhibition of GSK-3 catalytic activity with lithium or SB216763 protects GSK-3
/βS21A/S9A neurons from death. This indicates that dephosphorylation of GSK-3β/Ser9 and GSK-3
/Ser21 is insufficient for GSK-3 proapoptotic function and that another level of regulation is required. Gel filtration reveals a stress-induced loss of neuronal GSK-3β from a high-molecular-mass complex with a concomitant decrease in axin-bound GSK-3β. These data imply that Wnt-regulated GSK-3β plays a nonredundant role in trophic-deprivation-induced death of neurons.
Published ahead of print on 14 January 2008.
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