Lithium chloride and staurosporine potentiate the accumulation of phosphorylated glycogen synthase kinase 3beta/Tyr216, resulting in glycogen synthase kinase 3beta activation in SH-SY5Y human neuroblastoma cell lines.

摘要

Glycogen synthase kinase 3beta (GSK3beta) activity is regulated by phosphorylation processes and regulates in turn through phosphorylation several proteins, including eukaryotic initiation factor 2B (eIF2B). Serine 9 phosphorylation of GSK3beta (pGSK3betaSer9), usually promoted by activation of the PI3K/Akt survival pathway, triggers GSK3beta inhibition. By contrast, tyrosine 216 phosphorylation of GSK3beta (pGSK3betaTyr216) increases under apoptotic conditions, leading to GSK3beta activation. Lithium chloride (LiCl) is usually described to increase pGSK3betaSer9 through the PI3K/Akt pathway, resulting in GSK3beta inhibition. The purpose of this study is to demonstrate that in some cases LiCl is also able to increase pGSK3betaTyr216, resulting in GSK3beta activation. For this, we used SH-SY5Y cells and primary neuronal cultures and investigated the effects of LiCl on the two phosphorylated forms of GSK3beta under staurosporine (STS)-intoxicated conditions. The ratios between the phosphorylated and total forms of GSK3beta and eIF2B were determined by Western blotting. Our results revealed that, besides its ability to increase pGSK3betaSer9, LiCl is also able to increase pGSK3betaTyr216 greatly in STS-intoxicated SH-SY5Y cells but not in STS-intoxicated primary neuronal cultures. This accumulation of both Ser9 and Tyr216 phosphorylation results in GSK3beta activation in STS-intoxicated SH-SY5Y cells in spite of the presence of LiCl. These findings indicate that LiCl treatment is not necessarily correlated with GSK3beta inhibition even though it generates Ser9 phosphorylation. Consequently, the ratio pGSK3betaSer9/pGSK3betaTyr216, which takes into account the balance between the two inactive (Ser9) and active (Tyr216) forms of GSK3beta, could be more useful for predicting GSK3beta inhibition.