Calcineurin dephosphorylates glycogen synthase kinase-3 beta at serine-9 in neuroblast-derived cells

This study examined the role of calcineurin, a major calcium-dependent protein phosphatase, in dephosphorylating Ser-9 and activating glycogen synthase kinase-3 beta (GSK-3 beta). Treatment with calcineurin inhibitors increased phosphorylation of GSK-3 beta at Ser-9 in SH-SY5Y human neuroblastoma cells. The over-expression of a constitutively active calcineurin mutant, calcineurin A beta (1-401), led to a significant decrease in phosphorylation at Ser-9, an increase in the activity of GSK-3 beta, and an increase in the phosphorylation of tau. K-m of calcineurin for a GSK-3 beta phosphopeptide was 469.3 mu M, and specific activity of calcineurin was 15.2 nmol/min/mg. In addition, calcineurin and GSK-3 beta were co-immunoprecipitated in neuron-derived cells and brain tissues, and calcineurin formed a complex only with dephosphorylated GSK-3 beta. We conclude that in vitro, calcineurin can dephosphorylate GSK-3 beta at Ser-9 and form a stable complex with GSK-3 beta, suggesting the possibility that calcineurin regulates the dephosphorylation and activation of GSK-3 beta in vivo.