Glycogen synthase kinase-3 (GSK-3) is a protein serine kinase that phosphorylates glycogen synthase and thereby inactivates it. Insulin stimulates the dephosphorylation of glycogen synthase at the sites phosphorylated by GSK-3 and subsequently inhibits GSK-3 acutely leading to the stimulation of glycogen synthesis. GSK-3 signaling is performed by two isoforms, GSK-3alpha and GSK-3beta. The two isoforms share 97% sequence similarity within their catalytic domains. GSK-3 has also been shown to play a role in protein synthesis, cell adhesion, cell proliferation, cell differentiation, microtubule dynamics and cell motility.