GSK3β inhibition is involved in the neuroprotective effects of cyclin-dependent kinase inhibitors in neurons

In the present study, we evaluated the effects of roscovitine (Rosco) and flavopiridol (Flavo), both of which are classified as cyclin-dependent kinase (CDK) inhibitors, on apoptosis induced by the inhibition of PI3K/AKT pathway in cerebellar granule neurons (CGNs). Our results demonstrate that both CDK inhibitors prevented apoptosis induced by LY294002 (LY), as also occurs with SB415286 (SB4), a selective GSK3 beta inhibitor. Our findings also indicate that these CDK inhibitors inhibit GSK3 beta, representing a potential pharmacological mechanism involved in their neuroprotective properties. Thus, the increased activity of GSK3 beta induced by LY294002 and detected by dephosphorylation at Ser9 was prevented by both compounds. Likewise, GSK3 beta activity was measured by a radioactivity assay, revealing that CDK inhibitors and SB415286 prevented the increase in GSK3 beta activity induced by PI3K inhibition. In addition, we analysed c-Jun, which is also a mediator of PI3K inhibition-induced apoptosis. However, neither of the CDK inhibitors nor 513415286 prevented the increase in c-Jun phosphorylation induced by PI3K inhibition. Therefore, our data identify GSK3 beta as a crucial mediator of CGN apoptosis induced by PI3K inhibition and indicate that the antiapoptotic effects of CDKs are mediated by the inhibition of this pharmacological target. (C) 2011 Elsevier Ltd. All rights reserved.