A-Kinase Anchoring Protein AKAP220 Binds to Glycogen Synthase Kinase-3β (GSK-3β) and Mediates Protein Kinase A-dependent Inhibition of GSK-3β*

Glycogen synthase kinase-3 (GSK-3) is regulated by various extracellular ligands and phosphorylates many substrates, thereby regulating cellular functions. Using yeast two-hybrid screening, we found that GSK-3β binds to AKAP220, which is known to act as an A-kinase anchoring protein. GSK-3β formed a complex with AKAP220 in intact cells at the endogenous level. Cyclic AMP-dependent protein kinase (PKA) and type 1 protein phosphatase (PP1) were also detected in this complex, suggesting that AKAP220, GSK-3β, PKA, and PP1 form a quaternary complex. It has been reported that PKA phosphorylates GSK-3β, thereby decreasing its activity. When COS cells were treated with dibutyryl cyclic AMP to activate PKA, the activity of GSK-3β bound to AKAP220 decreased more markedly than the total GSK-3β activity. Calyculin A, a protein phosphatase inhibitor, also inhibited the activity of GSK-3β bound to AKAP220 more strongly than the total GSK-3β activity. These results suggest that PKA and PP1 regulate the activity of GSK-3β efficiently by forming a complex with AKAP220.